Federal immigration authorities have freed a Palestinian woman and her 18-year-old son to return to their Alabama home.
Sana Alsayed and her son, Imad Mohammad, had been in custody since Jan. 12 when they were arrested by immigration agents at their home near Birmingham. They were released from a Louisiana lockup late Wednesday after an inquiry by Republican Congressman Spencer …
Georgia Sen. Sam Nunn announced Thursday he won't be a candidatefor the 1988 Democratic presidential nomination.
Ending months of speculation about a White House bid, Nunnlisted his family and legislative responsibilities as major reasonshe would not launch a campaign.
Strategists in both major political parties had rated Nunn asthe most formidable potential Democratic nominee in a generalelection because of his popularity in the vote-rich Sun Belt. "Nunnwould have been hell on wheels," said Lee Atwater, Vice PresidentGeorge Bush's national campaign manager.
Nunn's decision revived the hopes of Sen. Albert Gore Jr. ofTennessee, now the only Democratic …
BAGHDAD, Iraq - Eleven more U.S. troops were slain in combat, the military said Wednesday, putting October on track to be the deadliest month for U.S. forces since the siege of Fallujah nearly two years ago.
The military says the sharp increase in U.S. casualties - 70 so far this month - is tied to Ramadan and a security crackdown that has left American forces more vulnerable to attack in Baghdad and its suburbs. Muslim tenets hold that fighting a foreign occupation force during Islam's holy month puts a believer especially close to God.
As the death toll climbed for both U.S. forces and Iraqi civilians, who are being killed at a rate of 43 a day, the country's …
First lady Michelle Obama is taking on a new role as international hostess when she welcomes the spouses of world leaders headed to this U.S. river city for a two-day economic summit.
While the presidents and prime ministers spend Thursday evening and Friday chewing over the world's problems, Mrs. Obama will entertain their spouses by introducing them to Pittsburgh as well as to some of her own interests, including art and architecture, arts education, and sustainable farming and eating locally grown food.
Mrs. Obama and President Barack Obama will welcome world leaders and their spouses at a reception Thursday at the Phipps Conservatory and Botanical …
It's almost April 18 - tax day! It's the day when Americans will queue at post offices to ensure a pre-midnight postmark on their federal income tax returns.
For American corporations, every day is a battle with taxes, and every day we're losing the battle.
At 39.2 percent - inclusive of federal and average state taxes - the corporate tax rate in the United States is second only to Japan's among the developed nations of the world. American corporations face taxes nearly 14 percent higher than the average of the 34 member nations of the Organization for Economic Co-operation and Development. The OECD members are mostly western European democracies, Japan and emerging …
Leading season scorers in the Bundesliga after Saturday's final round:
Luca Toni, Bayern Munich, 24 goals.
Mario Gomez, VfB Stuttgart, 19.
Kevin Kuranyi, Schalke, 15.
Ivica Olic, Hamburger SV, 14.
Markus Rosenberg, Werder Bremen, 14.
Mladen Petric, Borussia Dortmund), 13.
Marko Pantelic, Hertha …
We admit to being at times conflicted about the Billy Goat Tavern,and we don't just mean whether to stop in or head home. On one hand,it was the backdrop of so many journalistic memories, of Mike Roykoand the days when there were typewriters to throw and men to throwthem. On the other, all those tourist buses, all those pink-facedIowa ladies in their cat sweaters nursing a light beer for an hour,then giddily hurrying to the Hard Rock Cafe.
The answer, of course, is that the Goat is all those things andmore. A Chicago icon, now with several locations. We can't help butroot for the Goat because it's close, it's cheap, and mostimportantly, it's home, at times. So we …
The mistakes of the Bush administration to go into war with Iraq will only escalate because the United States is creating a "giant magnet" in Iraq that will attract more home-grown terrorists, warned prominent University of Chicago Professor John Mearsheimer.
Reacting to the latest bombing of the Iraqi U.N. headquarters by extremists, Mearsheimer told the Chicago Defender the United States must get out of Iraq. At least 20 people were killed in last Tuesday's bombing of the United Nations headquarters in Iraq, including U.N. envoy, Sergio Vieira de Mello, who was rescued from the demolished building but died later.
"I thought it was a major mistake to go into Iraq. The idea …
Iraq wants a security agreement with the U.S. to include a clear ban on U.S. troops using Iraqi territory to attack Iraq's neighbors, the government spokesman said Wednesday, three days after a dramatic U.S. raid on Syria.
Also Wednesday, the country's most influential Shiite cleric expressed concern that Iraqi sovereignty be protected in the pact. Grand Ayatollah Ali al-Sistani wields vast influence among the Shiite majority and his explicit opposition could scuttle the deal.
Government spokesman Ali al-Dabbagh said the ban was among four proposed amendments to the draft agreement approved by the Cabinet this week and forwarded to the U.S.
…
ROYAL CRESCENT Agents Savills Contact 01225 474550 Price Pounds425,000 This stylish and well presented one-bedroom apartment is inthe highly desirable Royal Crescent. A delightful lower ground-floor apartment, the property offers a unique opportunity to live inone of Bath's premier addresses. It also benefits from the ease andup-keep that goes with owning a one-bedroom apartment.
The home has its own dining hall, a sitting room over-looking thesouth-facing courtyard, a stylish fitted kitchen with …
A Northlake woman is suing the fast-food titan, claiming her daughter suffered a bad burn in April 2009 when hot chocolate from a Schiller Park drive-through spilled.
"The mother isn't loving it either," said Chicago lawyer Eric Krumdick, referring to his client, Vicki LaRocco. "Her 10-year-old daughter now has a serious scar resulting from a second- and third-degree burn."
LaRocco is seeking compensation in excess of $50,000 to cover daughter Mykael Vasquez's medical bills and pain and suffering associated with scarring that Krumdick described as "ribbed" from the sock she was wearing.
In the suit filed Wednesday in Cook County Circuit Court, LaRocco claims the McDonald's at 9449 Irving Park served hot chocolate "too hot for consumption," particularly for children. It also charges that McDonald's failed to adequately secure the cup's lid.
But Juan Mendez, owner of the franchise, said, "At this time, these are just allegations. I would strongly caution . . . jumping to conclusions without the facts. Beyond that, it would be inappropriate for me to further comment or speculate on these claims."
The case mirrors a 1994 suit against McDonald's by an elderly customer burned by hot coffee in New Mexico. She was awarded more than $2 million, but the judge later reduced the amount.
Photo: (See microfilm for photo description).
China Eastern Airlines Corp.'s deal to sell a 24 percent stake to Singapore Airlines Ltd. and its parent company, Temasek Holdings Pte., has been ratified, Singapore Airlines said Friday.
Singapore Airlines agreed in September to buy a 15.7 percent stake in the Chinese carrier, while Temasek Holdings agreed to simultaneously buy another 8.3 percent of China Eastern.
The combined offer of 7.2 billion Hong Kong dollars (US$927 million; euro639 million), or 3.80 Hong Kong dollars a share, had already been approved by the Chinese government and China Eastern's board.
The statement said the three sides signed four agreements that ratified the purchase terms and strategic partnership.
It said that SIA will be entitled to buy a further stake in China Eastern if Beijing relaxes its foreign ownership rules in the future.
The deal is still subject to approval by CEA shareholders who are expected to vote on the deal in December.
China Eastern suspended trading in its yuan-denominated A shares on Monday and said trading will resume after the agreement is signed.
If it is true that champions show their real colors underpressure, this was Black Monday for the Cubs.
After the 11-0 squishing at the hands of the Expos, the pennantpicture is anything but rosy at Wrigley.
It appears to be time for long-suffering Cubs fans to dream of awhite Christmas and sing "Wait Till Next Year."
Next year is certainly a more pleasant picture than tomorrow.There is always a next year, but there are very few tomorrows at thistime of the season.
In truth, this three-game series against the Expos was onefilled with todays. Each day was - and is - the most important in amust-win series.
If these were to be contending Cubs, they needed to sweep theseries. And you can't sweep the series without winning the firstgame.
The Cubs were anything but colorful in the series debut. Infact, they laid an egg Monday - one of those rotten, stinky eggs.
A blown rundown play, a wild pitch on an intentional walk, adropped easy out and a dropped pickoff play. All in one inning fromhell.
In the course of a baseball season, one inning of one gamedoesn't seem like much.
But the game Monday cost the Cubs two games in the standings.Instead of closing to within three games of the second-place Expos,they fell five behind.
The best they can hope for now are victories today and tomorrow- a total of one game gained on second place.
Make no mistake, second place is what the Cubs need to focus on.First place is out of sight when you are in third.
What the Cubs need now is help from someone else. Serious help in beating the Expos, which noteam has done in the 10 series since they were last in last placeJune 23.
"But," ever-optimistic Cubs manager Jim Lefebvre said, "we aredone with Atlanta and Cincinnati. Montreal's got some tough games infront of them."
The Expos have six games left against the West-leading Bravesand six left against the Reds. Both teams have better records thanthe East-leading Pirates.
But baseball helps those who help themselves. And the Cubs didthemselves no favors in a big game. The Expos did, no matter howmanager Felipe Alou tries to cover it up.
"Our club, the way we think is that every game is big," saidAlou, who took over the team after Tom Runnells was fired May 22."Every game that keeps us out of last place because we know we werenot given any chance of getting out of last place."
But this was a bigger game than other big games.
"We were swept here the last time," Alou said. "We didn't talkabout it, but we knew it. We had to win."
The Cubs knew it, too. But now they are forced to talk aboutit. Forced to say the game Monday wasn't bigger than other biggames, that the series isn't any bigger than other big series, thatthe smell is just one rotten egg in a big basket. And that the smellwill go away once the bad egg is discarded.
"Personally, I think it's way too early to start saying thatnow," Lefebvre said. "That's the importance of playing 162ballgames. You can't put all your eggs into one basket in oneseries. If you did that in the Mets series (a Cubs sweep), we wouldlook great."
But in reality, all that did was keep the Cubs out of fourthplace and prove how bad the Mets are.
What Monday did was keep the Cubs solidly in third place andprove the Expos might be a better team.
If the Cubs are to win 90 games, they must go 35-16 in theirfinal 51 games. Color that almost impossible. The game Monday doesnot paint a pretty picture because next year is getting closer thantomorrow.
Humanitarian aid is getting in to the beleaguered Georgian city of Gori, but Russia needs to open corridors to allow assessment teams and more supplies to get through, the head of USAID said Friday.
Henrietta Holsman Fore, administrator of the U.S. Agency for International Development, said NGOs had managed to get into the city Thursday to hand out supplies that had been brought in to the country by her agency and the U.S. military.
"The distribution of food and hygiene kits went well _ that is just one day, but it's a step in the right direction," she said.
Still, she said USAID's own people needed to be allowed into the Russian-held area to increase the supplies, and also get their own picture of what the people need.
"We've been calling on the Russians for access," she said, adding that they had not yet received a reply.
"It is extremely important for humanitarian assistance and assessment teams to be able to get through _ if they can get through, they can save lives."
The United Nations says 158,000 Georgians have been displaced since fighting with Russia began Aug. 7 over Georgia's separatist province of South Ossetia.
About 80,000 displaced people are being housed in more than 600 centers in and around the capital, Tbilisi.
To date, more than US$11 million in aid has been flown in to Georgia, Fore said. Supplies include prepared meals, blankets, cots, mattresses and even portable showers.
Fore said the focus right now is on bringing in the supplies needed for the short-term, but that later the U.S. would be focusing on reconstruction and helping rebuild the damaged Georgian infrastructure.
"We intend to be here by your side for many years to come," she told a Georgian reporter.
Fore was on a two-day trip to Georgia with the head of U.S. European Command, U.S. Gen. John Craddock, who is also NATO's supreme allied commander for Europe.
The general talked with American flight crews and USAID workers at the Tbilisi airport, where the aid has been coming in on regular flights.
One issue brought up by USAID personnel on the ground was that they did not know exactly what supplies were being brought in on which plane _ making distribution more difficult to coordinate.
Craddock said he would make sure the problem was sorted out.
BASKETBALL
National Basketball Association
CONFERENCE SEMIFINALS
(Best-of-7)
Sunday
Denver 109, Dallas 95, Denver leads 1-0
Today
Orlando at Boston, 8 p.m.
Houston at L.A. Lakers, 10:30 p.m.
Tuesday
Atlanta at Cleveland, 8 p.m.
Dallas at Denver, 10:30 p.m.
Wednesday
Orlando at Boston, 8 p.m.
Houston at L.A. Lakers, 10:30 p.m.
Thursday
Atlanta at Cleveland, 8 p.m.
Friday
Boston at Orlando, 7 p.m.
L.A. Lakers at Houston, 9:30 p.m.
Saturday
Denver at Dallas, 5 p.m.
Cleveland at Atlanta, 8 p.m.
May 10
L.A. Lakers at Houston, 3:30 p.m.
Boston at Orlando, 8 p.m.
May 11
Cleveland at Atlanta, 7 p.m.
Denver at Dallas, 9:30 p.m.
May 12
Orlando at Boston, TBA, if necessary
Houston at L.A. Lakers, TBA, if necessary
May 13
Atlanta at Cleveland, TBA, if necessary
Dallas at Denver, TBA, if necessary
May 14
Boston at Orlando, TBA, if necessary
L.A. Lakers at Houston, TBA, if necessary
May 15
Cleveland at Atlanta, TBA, if necessary
Denver at Dallas, TBA, if necessary
May 17
Orlando at Boston, TBA, if necessary
Houston at L.A. Lakers, TBA, if necessary
Dallas at Denver, TBA, if necessary
May 18
Atlanta at Cleveland, 8 p.m., if necessary
GOLF
PGA Tour-Quail Hollow Championship Scores
By The Associated Press
Sunday
At Quail Hollow Club
Charlotte, N.C.
Purse: $1.17 million
Yardage: 7,442; Par: 72
Final
(FedExCup points in parentheses)
Sean O'Hair (500), $1,170,000 69-72-67-69-277
Bubba Watson (245), $572,000 71-65-72-70-278
Lucas Glover (245), $572,000 68-71-68-71-278
Tiger Woods (135), $312,000 65-72-70-72-279
Jonathan Byrd (90), $212,875 72-72-70-66-280
Phil Mickelson (90), $212,875 67-71-75-67-280
Tim Petrovic (90), $212,875 71-70-71-68-280
Ted Purdy (90), $212,875 70-69-72-69-280
Ian Poulter (90), $212,875 71-70-70-69-280
Jason Dufner (90), $212,875 67-71-71-71-280
Boo Weekley (60), $129,071 71-70-72-68-281
Fredrik Jacobson (60), $129,071 71-70-70-70-281
Jim Furyk (60), $129,071 71-66-73-71-281
Martin Kaymer (0), $129,071 71-70-69-71-281
Y.E. Yang (60), $129,071 72-71-66-72-281
Retief Goosen (60), $129,071 68-68-72-73-281
Zach Johnson (60), $129,071 70-67-68-76-281
Shaun Micheel (52), $87,750 74-69-73-66-282
Charles Warren (52), $87,750 69-71-71-71-282
David Toms (52), $87,750 71-71-67-73-282
George McNeill (52), $87,750 69-68-70-75-282
Hunter Mahan (46), $58,593 68-72-75-68-283
Matt Bettencourt (46), $58,593 72-71-71-69-283
Rocco Mediate (46), $58,593 72-70-72-69-283
Camilo Villegas (46), $58,593 71-67-74-71-283
Bill Haas (46), $58,593 69-71-71-72-283
Nick Watney (46), $58,593 71-71-69-72-283
Davis Love III (46), $58,593 70-69-70-74-283
Cameron Beckman (41), $44,200 73-71-72-68-284
Bo Van Pelt (41), $44,200 69-71-71-73-284
Ross Fisher (0), $44,200 73-67-69-75-284
John Senden (37), $35,967 71-72-73-69-285
Ben Curtis (37), $35,967 74-70-71-70-285
Cliff Kresge (37), $35,967 69-72-72-72-285
Geoff Ogilvy (37), $35,967 71-73-68-73-285
Joe Ogilvie (37), $35,967 71-72-69-73-285
Jeff Klauk (37), $35,967 69-71-70-75-285
Tom Pernice, Jr. (31), $27,300 72-69-77-68-286
Ken Duke (31), $27,300 70-72-73-71-286
Brian Davis (31), $27,300 72-71-72-71-286
Michael Allen (31), $27,300 70-73-72-71-286
Steve Marino (31), $27,300 67-72-74-73-286
Danny Lee (0), $27,300 71-69-70-76-286
Mathew Goggin (26), $21,450 71-71-74-71-287
John Huston (26), $21,450 73-71-69-74-287
Brendon de Jonge (26), $21,450 72-69-67-79-287
Robert Allenby (22), $16,922 67-74-77-70-288
Kevin Sutherland (22), $16,922 71-72-75-70-288
Anthony Kim (22), $16,922 70-69-78-71-288
Will MacKenzie (22), $16,922 70-74-71-73-288
Martin Laird (22), $16,922 74-70-70-74-288
Brendon Todd (22), $16,922 70-70-72-76-288
Chris Stroud (16), $14,907 73-69-78-69-289
Steve Wheatcroft (0), $14,907 70-73-77-69-289
Robert Karlsson (0), $14,907 70-69-78-72-289
Jonathan Kaye (16), $14,907 70-72-74-73-289
Jeff Overton (16), $14,907 70-71-73-75-289
Kent Jones (16), $14,907 72-70-71-76-289
Steve Lowery (11), $14,300 73-71-73-73-290
Peter Tomasulo (11), $14,300 74-69-73-74-290
Jeff Maggert (11), $14,300 68-70-75-77-290
John Rollins (8), $13,910 70-74-76-71-291
Chad Campbell (8), $13,910 72-70-73-76-291
David Mathis (8), $13,910 70-73-72-76-291
Aron Price (5), $13,520 71-73-78-71-293
Pat Perez (5), $13,520 74-70-76-73-293
Trevor Immelman (5), $13,520 73-70-76-74-293
Brad Faxon (3), $13,195 74-69-80-71-294
Parker McLachlin (3), $13,195 73-71-74-76-294
Steve Flesch (1), $12,870 69-74-78-74-295
Bill Lunde (1), $12,870 72-72-74-77-295
Mark Calcavecchia (1), $12,870 69-74-74-78-295
Gary Woodland (1), $12,610 70-74-76-76-296
Rich Beem (1), $12,480 71-73-76-82-302
BASEBALL
Major League leaders
National League
BATTING-Beltran, New York, .391; Votto, Cincinnati, .363; Ibanez,Philadelphia, .360; Pujols, St. Louis, .356; MRamirez, Los Angeles,.349; Utley, Philadelphia, .342; NJohnson, Washington, .341.
RBI-Pujols, St. Louis, 29; Cantu, Florida, 25; Ethier, LosAngeles, 23; Votto, Cincinnati, 22; Ibanez, Philadelphia, 21;Ludwick, St. Louis, 21; Utley, Philadelphia, 21.
HITS-Beltran, New York, 34; Hudson, Los Angeles, 34; Votto,Cincinnati, 33; FLopez, Arizona, 32; FSanchez, Pittsburgh, 32; 4tied at 31.
DOUBLES-Cameron, Milwaukee, 10; FSanchez, Pittsburgh, 10; Votto,Cincinnati, 10; Kotchman, Atlanta, 9; CYoung, Arizona, 9; Zimmerman,Washington, 9; 5 tied at 8.
TRIPLES-Bourn, Houston, 3; Kemp, Los Angeles, 3; Victorino,Philadelphia, 3; 13 tied at 2.
HOME RUNS-AdGonzalez, San Diego, 9; Pujols, St. Louis, 9; Ibanez,Philadelphia, 8; Utley, Philadelphia, 8; Cantu, Florida, 7; Dunn,Washington, 7; ASoriano, Chicago, 7.
STOLEN BASES-Fowler, Colorado, 9; Bourn, Houston, 8; Bonifacio,Florida, 6; Burriss, San Francisco, 6; Morgan, Pittsburgh, 6; 3 tiedat 5.
PITCHING (3 Decisions)-Billingsley, Los Angeles, 4-0, 1.000;Maholm, Pittsburgh, 3-0, 1.000; Wainwright, St. Louis, 3-0, 1.000;Condrey, Philadelphia, 3-0, 1.000; Martis, Washington, 3-0, 1.000;Broxton, Los Angeles, 3-0, 1.000.
SAVES-Bell, San Diego, 8; Franklin, St. Louis, 7; Broxton, LosAngeles, 7; Cordero, Cincinnati, 7; BWilson, San Francisco, 6;Qualls, Arizona, 6; 3 tied at 5.
American League
BATTING-Youkilis, Boston, .407; MiCabrera, Detroit, .393;VMartinez, Cleveland, .388; Callaspo, Kansas City, .380; Bartlett,Tampa Bay, .368; Longoria, Tampa Bay, .365; Cano, New York, .363.
RBI-Longoria, Tampa Bay, 30; CPena, Tampa Bay, 28; Lowell,Boston, 24; Markakis, Baltimore, 24; Kinsler, Texas, 23; Lind,Toronto, 23; 2 tied at 22.
HITS-AHill, Toronto, 43; VMartinez, Cleveland, 38; Cano, NewYork, 37; MiCabrera, Detroit, 35; Longoria, Tampa Bay, 35; Youkilis,Boston, 35; Markakis, Baltimore, 34.
DOUBLES-Callaspo, Kansas City, 12; Longoria, Tampa Bay, 12;Youkilis, Boston, 11; Iwamura, Tampa Bay, 10; Polanco, Detroit, 10;3 tied at 9.
TRIPLES-Crisp, Kansas City, 4; Andrus, Texas, 2; Bloomquist,Kansas City, 2; JBuck, Kansas City, 2; Crosby, Oakland, 2; Fields,Chicago, 2; 41 tied at 1.
HOME RUNS-CPena, Tampa Bay, 11; Granderson, Detroit, 8; Hunter,Los Angeles, 8; Inge, Detroit, 8; Kinsler, Texas, 8; Quentin,Chicago, 8; 3 tied at 7.
STOLEN BASES-Crawford, Tampa Bay, 17; Ellsbury, Boston, 13;Abreu, Los Angeles, 11; Figgins, Los Angeles, 9; Kinsler, Texas, 7;Span, Minnesota, 7; 3 tied at 6.
PITCHING (3 Decisions)-Greinke, Kansas City, 5-0, 1.000;Richmond, Toronto, 4-0, 1.000; Frasor, Toronto, 4-0, 1.000; Slowey,Minnesota, 4-0, 1.000; FHernandez, Seattle, 4-0, 1.000; Buehrle,Chicago, 4-0, 1.000.
SAVES-FFrancisco, Texas, 7; Jenks, Chicago, 6; Rodney, Detroit,6; Papelbon, Boston, 6; Soria, Kansas City, 6; 4 tied at 5.
AUTO RACING
NASCAR Sprint Cup
Russ Friedman 400 results
Saturday night
At Richmond (Va.) International Raceway
Lap length: .75 mile
(Start position in parentheses)
1. (14) Kyle Busch, Toyota, 400 laps, 129.4 rating, 190 points,$257,248.
2. (16) Tony Stewart, Chevrolet, 400, 107.1, 170, $172,773.
3. (5) Jeff Burton, Chevrolet, 400, 96.5, 165, $177,906.
4. (10) Ryan Newman, Chevrolet, 400, 113.6, 165, $142,829.
5. (7) Mark Martin, Chevrolet, 400, 114.4, 155, $112,350.
6. (28) Sam Hornish Jr., Dodge, 400, 90.3, 150, $121,035.
7. (27) Jamie McMurray, Ford, 400, 88.2, 146, $102,425.
8. (2) Jeff Gordon, Chevrolet, 400, 117.5, 147, $127,001.
9. (41) Casey Mears, Chevrolet, 400, 71.5, 138, $97,125.
10. (29) Juan Pablo Montoya, Chevrolet, 400, 81, 134, $118,448.
11. (21) Marcos Ambrose, Toyota, 400, 79.8, 130, $96,798.
12. (17) Kurt Busch, Dodge, 400, 108.4, 132, $93,475.
13. (35) Matt Kenseth, Ford, 400, 65.7, 124, $121,390.
14. (3) Denny Hamlin, Toyota, 400, 126.5, 131, $101,050.
15. (1) Brian Vickers, Toyota, 400, 85.4, 123, $109,498.
16. (36) Robby Gordon, Toyota, 400, 66.6, 115, $95,060.
17. (20) Greg Biffle, Ford, 400, 68.9, 112, $90,525.
18. (12) Clint Bowyer, Chevrolet, 400, 86.2, 114, $82,100.
19. (13) Joey Logano, Toyota, 400, 63, 106, $119,126.
20. (23) Reed Sorenson, Dodge, 400, 63.9, 103, $112,851.
21. (31) AJ Allmendinger, Dodge, 400, 60.2, 100, $73,475.
22. (4) Martin Truex Jr., Chevrolet, 400, 89.9, 102, $113,815.
23. (22) David Ragan, Ford, 400, 64.8, 94, $82,225.
24. (30) Michael Waltrip, Toyota, 400, 52.7, 91, $80,675.
25. (32) Elliott Sadler, Dodge, 400, 51.4, 88, $80,925.
26. (37) Carl Edwards, Ford, 400, 63.2, 85, $118,056.
27. (25) Dale Earnhardt Jr., Chevrolet, 399, 60.3, 82, $87,050.
28. (9) David Reutimann, Toyota, 399, 66.9, 79, $94,498.
29. (18) Kasey Kahne, Dodge, 399, 51.7, 76, $111,248.
30. (33) Paul Menard, Ford, 398, 43, 73, $102,531.
31. (40) Bobby Labonte, Ford, 398, 46.2, 70, $98,629.
32. (42) John Andretti, Chevrolet, 397, 33, 67, $77,350.
33. (8) Scott Speed, Toyota, 396, 46.2, 64, $80,298.
34. (19) Kevin Harvick, Chevrolet, 394, 81.6, 61, $106,403.
35. (38) Jeremy Mayfield, Toyota, 371, 34.9, 58, $67,975.
36. (15) Jimmie Johnson, Chevrolet, 368, 62.4, 55, $121,976.
37. (6) Mike Bliss, Dodge, 368, 60, 52, $67,700.
38. (11) David Stremme, Dodge, accident, 324, 68.4, 49, $100,065.
39. (34) David Gilliland, Chevrolet, electrical, 92, 32.4, 46,$67,450.
40. (24) Joe Nemechek, Toyota, brakes, 90, 34, 43, $67,325.
41. (43) Tony Raines, Chevrolet, brakes, 74, 24.4, 0, $67,175.
42. (39) Scott Riggs, Toyota, electrical, 54, 30, 37, $67,050.
43. (26) Dave Blaney, Toyota, accident, 8, 25.8, 34, $67,424.
Race Statistics
Average Speed of Race Winner: 90.627 mph.
Time of Race: 3 hours, 18 minutes, 37 seconds.
Margin of Victory: 2.751 seconds.
Caution Flags: 15 for 79 laps.
Lead Changes: 21 among 8 drivers.
Lap Leaders: B.Vickers 1-6; J.Gordon 7; B.Vickers 8-22; J.Gordon23-72; D.Hamlin 73-95; Ku.Busch 96; J.Gordon 97-98; R.Newman 99-100; D.Hamlin 101-116; C.Bowyer 117-123; D.Hamlin 124-144; Ku.Busch145-151; D.Hamlin 152-213; M.Truex Jr. 214-235; R.Newman 236-248;D.Hamlin 249-274; R.Newman 275-299; Ky.Busch 300-302; R.Newman 303-307; Ky.Busch 308; J.Gordon 309-351; Ky.Busch 352-400.
Leaders Summary (Driver, Times Led, Laps Led): D.Hamlin, 5 timesfor 148 laps; J.Gordon, 4 times for 96 laps; Ky.Busch, 3 times for53 laps; R.Newman, 4 times for 45 laps; M.Truex Jr., 1 time for 22laps; B.Vickers, 2 times for 21 laps; Ku.Busch, 2 times for 8 laps;C.Bowyer, 1 time for 7 laps.
Top 12 in Points: 1. J.Gordon, 1,441; 2. Ku.Busch, 1,431; 3.T.Stewart, 1,402; 4. D.Hamlin, 1,321; 5. Ky.Busch, 1,314; 6.J.Johnson, 1,290; 7. J.Burton, 1,257; 8. C.Bowyer, 1,212; 9.C.Edwards, 1,204; 10. R.Newman, 1,198; 11. G.Biffle, 1,193; 12.M.Kenseth, 1,187.
HOCKEY
National Hockey League
Playoffs
CONFERENCE SEMIFINALS
(Best-of-7)
Sunday
Anaheim at Detroit, 2 p.m., Detroit leads 1-0
Carolina at Boston, 7:30 p.m., Boston leads 1-0
Today
Pittsburgh at Washington, 7 p.m., Washington leads 1-0
Tuesday
Vancouver at Chicago, 8 p.m.
Detroit at Anaheim, 10:30 p.m.
Wednesday
Washington at Pittsburgh, 7 p.m.
Boston at Carolina, 7:30 p.m.
Thursday
Vancouver at Chicago, 8 p.m.
Detroit at Anaheim, 10:30 p.m.
Friday
Washington at Pittsburgh, 7 p.m.
Boston at Carolina, 7:30 p.m.
Saturday
Pittsburgh at Washington, 7 p.m., if necessary
Chicago at Vancouver, 10:30 p.m.
TRANSACTIONS
Baseball
American League
BALTIMORE ORIOLES-Placed RHP Dennis Sarfate on the 15-day DL,retroactive to May 2. Recalled RHP Bob McCrory from Norfolk (IL).
KANSAS CITY ROYALS-Placed INF Tony Pena Jr. on the 15-day DL.Purchased the contract of INF Luis Hernandez from Omaha (PCL).
LOS ANGELES ANGELS-Optioned RHP Fernando Rodriguez to Salt Lake(PCL).
NEW YORK YANKEES-Placed LHP Damaso Marte on the 15-day DL.Recalled RHP Anthony Claggett from Scranton/Wilkes Barre (IL).
National League
WASHINGTON NATIONALS-Agreed to terms with RHP Mike MacDougal on aminor league contract.
Football
National Football League
MIAMI DOLPHINS-Named Michael Dee chief executive officer.
North Korea reportedly test-fired several short-range missiles off its western coast Friday, the communist nation's latest apparent angry response to the new South Korean government's tougher stance on Pyongyang.
The launches came as the North issued a stern rebuke to Washington over an impasse at nuclear disarmament talks, warning that the Americans' attitude could "gravely" affect the continuing disablement of Pyongyang's atomic facilities.
The firing of three ship-to-ship missiles happened at around 10:30 a.m. (0130 GMT), South Korea's Yonhap news agency reported, citing unidentified government officials.
South Korea's Joint Chiefs of Staff and the Defense Ministry said they were checking on the report, which came one day after South Korea withdrew officials from a joint industrial zone with North Korea at Pyongyang's request.
That move was prompted by the North's anger over South Korean statements that any expansion of the project in the border city of Kaesong would only happen if the North resolved the international standoff over its nuclear weapons.
The North showed signs earlier this week it was preparing to test short-range missiles as part of routine training, Yonhap reported. The country declared a no-sailing zone off the coastal city of Nampo and placed a military boat equipped with anti-ship missiles on standby, according to the news agency.
But the North appeared to have dropped the plan, after it did not fire a missile at that time, Yonhap said.
The North regularly test fires missiles, and its long-range models are believed able to possibly reach as far as the western coast of the United States. The country conducted its first-and-only nuclear bomb test in October 2006, but it is not known to have a weapon design able to fit inside a missile warhead.
North Korea shut down its sole operating nuclear reactor and has taken steps to disable its main atomic facilities under a landmark disarmament-for-aid deal reached last year with the United States and other regional powers.
However, negotiations on further disarmament have hit an impasse over the North's pledge to give a full declaration of its nuclear programs.
North Korea has claimed it gave the U.S. a nuclear list in November, but Washington said the North never produced a "complete and correct" declaration that would address all its past atomic activity.
On Friday, the North blamed Washington for the deadlocked talks and warned it would slow ongoing disablement of its atomic facilities.
The North's Foreign Ministry said the country has done its best to clear U.S. suspicions that it pursued a uranium-based atomic bomb program and also transferred nuclear technology to Syria, but Washington has been sticking to its "wrong" claims.
Pyongyang has "never dreamed" of doing either, it said in a statement carried by the North's official Korean Central News Agency, "and these things will not happen in the future too."
"The United States is clinging to shabby magic to make us a criminal in order to save face," the ministry said. "If the United States keeps delaying the resolution of the nuclear issue ... it could gravely affect disablement of nuclear facilities."
___
Associated Press writer Jae-soon Chang contributed to this report.
CARACAS, Venezuela (AP) — Elections chief says Chavez's allies win majority in Venezuelan congressional vote.
Denmark has evacuated staff from its embassies in Algeria and Afghanistan because of terror threats following the reprint in Danish newspapers of a caricature depicting the Prophet Muhammad, officials said Wednesday.
Embassy employees in the Algerian capital, Algiers, and the Afghan capital, Kabul, would continue to work out of "secret locations" in those cities, and would be reachable by phone and e-mail, Foreign Ministry spokesman Erik Laursen said.
The threat "is so concrete that we had to take this decision," Laursen told The Associated Press. "The decision is based on intelligence," he added, declining to elaborate.
The Netherlands took similar precautions, announcing Wednesday that it had closed its embassy's offices in Kabul two days earlier after reassessing the security situation in the Afghan capital.
Last week, Dutch Embassy personnel in Pakistan shifted to a luxury hotel in Islamabad due to heightened security concerns following the release of a film critical of the Quran, the Islamic holy book, by Dutch parliament member Geert Wilders.
The Netherlands has stationed 1,600 combat troops with the NATO-led security force in southern Afghanistan.
In Copenhagen, Foreign Minister Per Stig Moeller suggested Danish embassies in other locations also could be forced to relocate their staff following a warning last month by al-Qaida leader Osama bin Laden.
"There has been a general threat from al-Qaida which means that their cells or people who sympathize with them around the world will try to see where they can fulfill al-Qaida's desires," Moeller said in a TV interview. "Therefore I can certainly not say that they are the last two embassies (to be evacuated)."
In an audio recording posted on a militant Web site on March 19, bin Laden warned of a "severe" reaction against Europe over the republishing of the cartoon.
Danish intelligence officials have warned of an "aggravated" terror threat against Denmark because of the Feb. 13 reprinting of the drawing, which showed Muhammad wearing a bomb-shaped turban. It was one of the 12 Danish prophet cartoons that sparked riots in the Muslim world in 2006.
More than a dozen newspapers reprinted the cartoon, saying they wanted to support free speech after police revealed a plot to kill the creator of the caricature.
Islamic law generally opposes any depiction of the prophet, even favorable, for fear it could lead to idolatry.
The Foreign Ministry said in a statement Wednesday that employees had been moved from the Danish embassies in Algiers and Kabul "because of terror threats."
Laursen said the employees in Algiers were relocated "some days ago," while the staff in Kabul was moved Wednesday.
"Right now, we are in places that we consider safe," he said.
Scores of people have applied to work at a Rhode Island strip club _ but the vast majority don't need to show any leg to get the job.
Providence's Foxy Lady held a job fair Saturday, seeking to fill about 35 positions for dancers, masseuses, bartenders and bouncers.
But The Providence Journal reports the vast majority of the more than 150 job seekers were men looking to work at the door _ and most of the women said they were looking for work that didn't involve taking their clothes off.
Foxy Lady co-owner Tom Tsoumas (SOO'-muhs) says a recent promotion to cut prices has helped the club regain business lost due to the bad economy, forcing it to hire more employees.
___
Information from: The Providence Journal, http://www.projo.com/
President Barack Obama says Africa facing 'new moment of promise'
AMERICAN LEAGUE
East Division
W L Pct GB WCGB L10 Str Home Away
x-Tampa Bay 96 66 .593 - - 5-5 W-2 49-32 47-34
y-New York 95 67 .586 1 - 3-7 L-2 52-29 43-38
Boston 89 73 .549 7 6 5-5 W-2 46-35 43-38
Toronto 85 77 .525 11 10 8-2 W-1 46-35 39-42
Baltimore 66 96 .407 30 29 5-5 L-1 37-44 29-52
Central Division
W L Pct GB WCGB L10 Str Home Away
x-Minnesota 94 68 .580 - - 2-8 L-1 53-28 41-40
Chicago 88 74 .543 6 7 8-2 W-2 45-36 43-38
Detroit 81 81 .500 13 14 4-6 W-1 52-29 29-52
Cleveland 69 93 .426 25 26 7-3 L-2 38-43 31-50
Kansas City 67 95 .414 27 28 4-6 L-2 38-43 29-52
West Division
W L Pct GB WCGB L10 Str Home Away
x-Texas 90 72 .556 - - 6-4 L-1 51-30 39-42
Oakland 81 81 .500 9 14 4-6 W-4 47-34 34-47
Los Angeles 80 82 .494 10 15 5-5 W-1 43-38 37-44
Seattle 61 101 .377 29 34 3-7 L-5 35-46 26-55
NATIONAL LEAGUE
East Division
W L Pct GB WCGB L10 Str Home Away
x-Philadelphia 97 65 .599 - - 6-4 L-1 52-29 45-36
y-Atlanta 91 71 .562 6 - 5-5 W-1 56-25 35-46
Florida 80 82 .494 17 11 4-6 W-2 41-40 39-42
New York 79 83 .488 18 12 5-5 L-1 47-34 32-49
Washington 69 93 .426 28 22 5-5 W-1 41-40 28-53
Central Division
W L Pct GB WCGB L10 Str Home Away
x-Cincinnati 91 71 .562 - - 5-5 W-2 49-32 42-39
St. Louis 86 76 .531 5 5 8-2 W-5 52-29 34-47
Milwaukee 77 85 .475 14 14 6-4 L-2 40-41 37-44
Houston 76 86 .469 15 15 3-7 W-1 42-39 34-47
Chicago 75 87 .463 16 16 6-4 L-1 35-46 40-41
Pittsburgh 57 105 .352 34 34 4-6 L-2 40-41 17-64
West Division
W L Pct GB WCGB L10 Str Home Away
x-San Francisco 92 70 .568 - - 7-3 W-1 49-32 43-38
San Diego 90 72 .556 2 1 5-5 L-1 45-36 45-36
Colorado 83 79 .512 9 8 1-9 L-8 52-29 31-50
Los Angeles 80 82 .494 12 11 7-3 W-2 45-36 35-46
Arizona 65 97 .401 27 26 4-6 L-2 40-41 25-56
x-clinched division; y-clinched wild card
Saturday
Minnesota 5, Toronto 4
Yankees 6, Boston 5, 10 innings, 1st game
White Sox 6, Cleveland 2, 6 innings
Baltimore 2, Detroit 1
Tampa Bay 4, Kansas City 0
Texas 6, L.A. Angels 2
Boston 7, Yankees 6, 10 innings, 2nd game
Oakland 5, Seattle 3
Sunday
Detroit 4, Baltimore 2
Boston 8, N.Y. Yankees 4
Chicago White Sox 6, Cleveland 5
Tampa Bay 3, Kansas City 2, 12 innings
Toronto 2, Minnesota 1
L.A. Angels 6, Texas 2
Oakland 4, Seattle 3
Saturday
St. Louis 1, Colorado 0, 11 innings
Cincinnati 7, Milwaukee 4
N.Y. Mets 7, Washington 2
Philadelphia 7, Atlanta 0
San Diego 4, San Francisco 2
Chicago Cubs 8, Houston 3
Florida 2, Pittsburgh 0
L.A. Dodgers 3, Arizona 2
Sunday
Cincinnati 3, Milwaukee 2
Florida 5, Pittsburgh 2
Washington 2, N.Y. Mets 1, 14 innings
Atlanta 8, Philadelphia 7
Houston 4, Chicago Cubs 0
St. Louis 6, Colorado 1
San Francisco 3, San Diego 0
L.A. Dodgers 3, Arizona 1
Public comment is requested by the federal bank and thrift regulatory agencies on a notice of proposed rulemaking that would implement new risk-based capital requirements in the United States for large, internationally active banking organizations. The NPR details the agencies' plans for implementing the Basel Committee on Banking Supervision's new capital accord issued in 2004. The agencies also will request comment on proposed Basel II supervisory reporting templates.
The Federal Reserve Board, the FDIC, the Office of the Comptroller of the Currency and the Office of Thrift Supervision first adopted risk-based capital standards in 1989. Those standards were based on the Basel Capital Accord that the BCBS originally issued in 1988, Basel I. For banking organizations that meet qualifying criteria, the Basel II NPR would replace U.S. rules implementing Basel I. The proposed framework would be mandatory for large, internationally active banking organizations and optional for others.
In March, the Fed released a preliminary draft of the Basel II NPR. The version being made available now differs in some respects from the March draft. For example, the agencies have responded to certain requests from the industry to seek comment on alternative risk-based capital approaches and have clarified that in evaluating credit risk, banking organizations should not rely on the possibility of U.S. government financial assistance, except for the financial assistance that the government has legally committed to provide. The final document, which will be published in the Federal Register, should be used as the basis for comments, the agencies said.
Separately, the agencies announced that they will request comment on proposed revisions to the market risk capital rules that the OCC, Fed and FDIC have used since 1997 for banking organizations with significant exposure to market risk. Under the market risk capital rule, certain banking organizations are required to calculate a capital requirement for the general market risk of their covered positions and the specific risk of their covered debt and equity positions. The proposed revisions would enhance the rule's risk sensitivity and would require public disclosures of certain qualitative and quantitative market risk information.
The NPR on the market risk capital rule would implement changes the BCBS approved in 2005 and also would apply to certain savings associations, which currently are not covered under the rule.
The agencies will also seek comment on proposed supervisory reporting templates related to the market risk capital rule. The agencies said they remain committed to issuing in the near future additional proposed revisions to their existing risk-based capital rules, known as Basel IA, in a timeframe that will allow for overlapping comment periods for both the Basel II NPR and the NPR for the proposed Basel IA revisions.
ABSTRACT
Certain signaling events that promote L-type Ca^sup 2+^ channel (LCC) phosphorylation, such as β-adrenergic stimulation or an increased expression of Ca^sup 2+^/calmodulin-dependent protein kinase II, promote mode 2 gating of LCCs. Experimental data suggest the hypothesis that these events increase the likelihood of early after-depolarizations (EADs). We test this hypothesis using an ionic model of the canine ventricular myocyte incorporating stochastic gating of LCCs and ryanodine-sensitive calcium release channels. The model is extended to describe myocyte responses to the β-adrenergic agonist isoproterenol. Results demonstrate that in the presence of isoproterenol the random opening of a small number of LCCs gating in mode 2 during the plateau phase of the action potential (AP) can trigger EADs. EADs occur randomly, where the likelihood of these events increases as a function of the fraction of LCCs gating in mode 2. Fluctuations of the L-type Ca^sup 2+^ current during the AP plateau lead to variability in AP duration. Consequently, prolonged APs are occasionally observed and exhibit an increased likelihood of EAD formation. These results suggest a novel stochastic mechanism, whereby phosphorylation-induced changes in LCC gating properties contribute to EAD generation.
INTRODUCTION
Single cardiac L-Type Ca^sup 2+^ channels (LCCs) exhibit four distinct gating modes (Hess et al., 1984; Tsien et al., 1986; Yue et al., 1990). Mode 0 is a silent mode. Mode 0^sub a^, is a low-activity mode characterized by sparse, brief openings. Modes 1 and 2 are high-activity modes displaying bursts of brief or long-lasting openings, respectively. Although first identified in experiments using barium (Ba^sup 2+^) as the charge carrier (Hess et al., 1984; Yue et al., 1990), mode 2 gating of LCCs has been demonstrated recently to occur at physiological concentrations of extracellular calcium (Ca^sup 2+^) (Josephson et al., 2002a).
Several phosphorylation-related events regulate the fraction of LCCs gating in each mode. β-adrenergic receptor (β-AR) agonists induce protein kinase A (PKA)-mediated phosphorylation of the LCC α^sub 1c^ subunit at the Ser1928 residue (Gao et al., 1997; De Jongh et al., 1996; Yoshida et al., 1992). This phosphorylation increases both the fraction of LCCs available for gating as well as the fraction gating in mode 2 (Chen-Izu et al., 2000; Yue et al., 1990). The signaling molecule Ca^sup 2+^/calmodulin-dependent protein kinase II (CaMKII), through phosphorylation of an as yet unidentified cell membrane protein(s), increases the fraction of LCCs gating in mode 2 relative to other modes (Dzhura et al., 2000). LCC agonists such as BayK8644 also increase mode 2 activity (Hess et al., 1984), potentially by inhibiting channel dephosphorylation or through allosteric interactions that mimic the effects of phosphorylation (Erxleben et al., 2003).
Early after-depolarizations (EADs) are depolarizations of membrane potential occurring during phases 2 or 3 of the cardiac action potential (AP). They are thought to be a possible trigger for development of polymorphic ventricular tachycardia (Roden, 1993; Zhou et al., 1992). Occurrence of EADs is often associated with prolongation of AP duration (APD, at 90% repolarization) produced, for example, by the action of LCC agonists (January and Riddle, 1989; January et al., 1988; Marb�n et al., 1986) or by block of repolarizing potassium currents (Marb�n et al., 1986). Cardiac myocytes can also exhibit EADs in response to β-adrenergic agonists such as isoproterenol (ISO) (De Ferrari et al., 1995; Volders et al., 1997), even at ISO concentrations producing shortening of APD (Priori and Corr, 1990). Recently, Wu et al. (2002) investigated AP properties in cardiac ventricular myocytes isolated from transgenic mice expressing a constitutively active form of CaMKII, which would be expected to induce an increase in the number of LCCs gating in mode 2 (Dzhura et al., 2000). These mice exhibited APD prolongation accompanied by frequent EADs. A CaMKII inhibitory peptide AC3-I eliminated EADs with little APD shortening (Wu et al., 2002). In addition, blockers of PKA and CaMKII have been shown to eliminate EADs and torsade de pointes in ventricular myocytes isolated from rabbits (Mazur et al., 1999).
These data suggest the hypothesis that factors which promote mode 2 gating of LCCs may be linked with the generation of EADs. We test this hypothesis using an ionic model of the canine ventricular myocyte incorporating stochastic gating of LCCs and ryanodine-sensitive Ca^sup 2+^ release channels (RyRs) (Greenstein and Winslow, 2002). The model is extended to describe mode 2 gating of LCCs, and is then used to simulate myocyte responses to 1 �M ISO.
Results demonstrate that random fluctuations in the number of open LCCs during the plateau phase of the AP can generate EADs. The most important fluctuations are those of LCCs gating in mode 2 and exhibiting long open times, which drive the slow-timescale fluctuations of L-type Ca^sup 2+^ current (I^sub CaL^). EADs occur randomly, and the likelihood of occurrence is an increasing function of the fraction of LCCs gating in mode 2. These results suggest a novel mechanism whereby phosphorylation-induced changes in LCC gating properties contribute to EAD generation.
METHODS
Simulations are performed using a recently developed canine ventricular myocyte model which incorporates stochastic gating of LCCs and RyRs within a large number of Ca^sup 2+^ release units (Greenstein and Winslow, 2002). This model is able to reproduce experimentally measured properties of Ca^sup 2+^ -induced Ca^sup 2+^ release such as graded release, voltage dependence of excitation-contraction coupling gain, stable release termination, and the relative magnitude of voltage- versus Ca^sup 2+^ -dependent inactivation of LCCs. The model has been extended to describe the action of 1 �M ISO on both Ca^sup 2+^ regulatory proteins and ion channels of the cardiac ventricular myocyte (Greenstein et al., 2004). Details of model development, as well as a comparison of model Ca^sup 2+^ transients and APs with and without ISO to those measured experimentally are provided in the following.
The local-control myocyte model
Simulations are performed using a canine ventricular myocyte model incorporating stochastic gating of LCCs and RyRs (Greenstein and Winslow, 2002). The model incorporates 1), sarcolemmal ion currents of the Winslow et al. (1999) canine ventricular cell model; 2), continuous-time Markov chain models of the rapidly activating delayed rectifier potassium (K+) current I^sub Kr^ (Mazhari et al., 2001), the Ca^sup 2+^-independent transient outward K+ current I^sub to1^ (Greenstein et al., 2000), and the Ca^sup 2+^-dependent transient outward chloride (Cl-) current I^sub to2^; 3), a continuous-time Markov chain model of I^sub CaL^ in which Ca^sup 2+^-mediated inactivation occurs via the mechanism of mode-switching (Imredy and Yue, 1994; Jafri et al., 1998); 4), an RyR channel model adapted from that of Keizer and Smith (Jafri et al., 1998; Keizer et al., 1998); and 5), locally controlled Ca^sup 2+^-induced Ca^sup 2+^ release from junctional sarcoplasmic reticulum (JSR) via inclusion of LCCs, RyRs, Cl- channels, and local JSR and diadic subspace compartments within Ca^sup 2+^ release units (CaRUs).
The L-type Ca^sup 2+^ channel gating scheme
The gating scheme of the LCC model is shown in Fig. 1 and has been described previously (Greenstein and Winslow, 2002; Jafri et al., 1998; Rice et al., 1999). Briefly, upper-row states encompass Mode Normal and lower-row states encompass Mode Ca. Each mode contains an open state (denoted O and O^sub Ca^). Depolarization promotes transitions from left to right toward the open states. Elevation of subspace Ca^sup 2+^ promotes transitions from Mode Normal to Mode Ca. When LCCs gate in Mode Ca, transitions into state O^sub Ca^ are infrequent. Mode Ca therefore corresponds to Ca^sup 2+^-inactivated states. Transition rates from Mode Ca to Mode Normal (i.e., recovery from Ca^sup 2+^-mediated inactivation) are Ca^sup 2+^-independent. The LCC also contains a separate voltage-dependent inactivation gate (not shown in Fig. 1) whose open probability decreases with membrane depolarization.
In this cell model, I^sub CaL^ is a function of the total number of channels (N^sub LCC^), single-channel current magnitude (i), open probability (p^sub o^), and the fraction of channels that are available for activation (f^sub active^), where I^sub CaL^ = N^sub LCC^ � f^sub active^ � i 7times; p^sub o^, (Handrock et al., 1998). The product N^sub LCC^ � f^sub active^ is chosen such that the amplitude of the whole-cell current agrees with that measured experimentally in canine myocytes (Hobai and O'Rourke, 2001). This approach yields a value of 50,000 for N^sub LCC^ � f^sub active^, consistent with experimental estimates of active LCC density (McDonald et al., 1986; Rose et al., 1992) and corresponding to 12,500 active CaRUs.
The number of CaRUs simulated explicitly need not be equal to the actual number of CaRUs in a cell. In simulations including a reduced number of CaRUs, total fluxes between the cytosol and the population of simulated CaRUs are scaled by the ratio N^sub actual^/N^sub simulated^ to maintain an average flux independent of the number of CaRUs simulated. No variance-reduction methods were used, hence use of reduced numbers of CaRUs increases the standard deviation of the scaled currents/fluxes by a factor of ~(N^sub actual^/ N^sub simulated^)1/2. Unless stated otherwise, all simulations in this study are performed using a minimum of 10,000 simulated CaRUs, which results in no greater than an ~2.2-fold increase in standard deviation of I^sub CaL^ compared to the full 50,000-CaRU model. This approach was a necessary compromise between model accuracy and tractability.
Stochastic simulation
The algorithm for solving the stochastic ordinary differential equations defining the model has been described previously (Greenstein and Winslow, 2002). Briefly, transition rates for each channel are determined by their gating schemes and their dependence on local Ca^sup 2+^ level. Stochastic simulation of CaRU dynamics is used to determine all Ca^sup 2+^ flux into and out of each local subspace. The summation of all Ca fluxes crossing the CaRU boundaries is taken as inputs to the global model, which is defined by a system of coupled ordinary differential equations. The dynamical equations defining the global model are solved using the Prince-Dormand algorithm (Engeln-M�llges and Uhlig, 1996) which has been modified to embed the stochastic CaRU simulations within each time step. The Mersenne Twister (Matsumoto and Nishimura, 1998) random number generator algorithm (period = 2^sup 19,937^ - 1) is used in stochastic computations.
This model provides the ability to investigate the ways in which LCC, RyR, and subspace properties impact on Ca^sup 2+^-induced Ca^sup 2+^ release and the integrative behavior of the myocyte. However, this ability is achieved at a high computational cost: up to 1 s of model activity was simulated in 3 min of simulation time with 1,250 CaRUs, and in 22 min with 12,500 CaRUs when running on 20 IBM Power4 processors configured with 4 gigabytes memory each.
Model of β-AR responses
β-AR agonists increase LCC availability (f^sub active^; Chen-Izu et al., 2000; Herzig et al., 1993; Yue et al., 1990). In guinea pig and human ventricular myocytes, baseline values of f^sub active^ are relatively low and are increased by 2- to 2.5-fold in response to β-AR stimulation (or in heart failure, in which there may be hyperphosphorylation of LCCs; Chen et al., 2002; Handrock et al., 1998; Herzig et al., 1993; Schr�der et al., 1998; Yue et al., 1990). These data differ from those in rat, which show considerably higher baseline availability and a smaller change in f^sub active^ in response to β-AR stimulation (Chen-Izu et al., 2000). We have therefore elected to develop a "baseline" model of β-AR action using data primarily from guinea pig, canine, and human ventricular myocytes (Greenstein et al., 2004). β-AR-induced phosphorylation of LCCs is modeled by including populations of both active (phosphorylated) and inactive (unphosphorylated) LCCs. Model parameters are adjusted based on analyses of slow cycling between active and inactive modes in the presence of ISO, indicating that at 1 �M concentration, ~25% of LCCs are available under control conditions, and that this increases to ~60% in the presence of ISO (Herzig et al., 1993), which corresponds to 30,000 active CaRUs out of a total of 50,000 simulated CaRUs. The fraction of active CaRUs is set equal to the fraction of active LCCs (i.e., active CaRUs contain active LCCs).
Increased PKA-mediated phosphorylation of LCCs in response to β-AR agonists has also been shown to shift the distribution of LCCs into high-activity gating modes (Chen-Izu et al., 2000; Herzig et al., 1993; Yue et al., 1990). In this study it has been assumed that mode 0^sub a^ openings do not significantly contribute to whole-cell I^sub CaL^ (see Herzig et al., 1993) and are therefore lumped into the inactive population of LCCs. Mode 1 gating of the LCC corresponds to the LCC model control parameter set. Mode 2 gating is defined as a modification of mode 1 parameters based on the data of Yue et al. (1990) in which mean LCC open time is increased from 0.5 ms to 5 ms. This is implemented by reducing the exit rate from the open state (g) (Fig. 1) by a factor of 10. LCC activation and inactivation is shifted by 2 mV in the hyperpolarizing direction in response to ISO consistent with experiments (Chen et al., 2002; K��b et al., 1996). Under control conditions, all active LCCs are assumed to operate in mode 1, whereas in response to 1 �M ISO, 15% of the active population of LCCs are assumed to operate in mode 2, with 85% remaining in mode 1 (Yue et al., 1990).
β-AR Stimulation has also been shown to enhance SERCA2a function (Simmerman and Jones, 1998), reduce inactivation/rectification of I^sub Kr^ (Heath and Terrar, 2000), and increase amplitude of I^sub Ks^ (Kathofer et al., 2000). Functional increase in SERCA2a availability is modeled by simultaneous scaling of both the forward and reverse maximum pump rates V^sub maxf^ and V^sub maxr^ (Shannon et al., 2000) by a factor of 3.3. Reduction in the degree of steady-state inactivation of I^sub Kr^ is modeled by reducing rates entering the inactivation state (α^sub i^ and α^sub i3^) by a factor of 4, and increasing the rates exiting the inactivation state (β^sub i^ and ψ) by this same factor (Mazhari et al., 2001). Functional upregulation of I^sub Ks^ is modeled by scaling maximal conductance by a factor of 2.
Fig. 2 shows the ability of the baseline model to reproduce experimentally measured β-AR responses to 1 �M ISO. Simultaneous measurements of APs and Ca^sup 2+^ transients are shown in Fig. 2, A and B, respectively, for control (black lines) and after application of ISO (shaded lines). APD in response to ISO (Fig. 2 A) is shortened by ~30%, plateau potential becomes ~10-15 mV more depolarized, and phase I notch depth and duration are reduced. In addition, ISO produces an ~3-fold increase in Ca^sup 2+^ transient amplitude and speeds the relaxation rate of the Ca^sup 2+^ transient ~3-fold (Fig. 2 B). The AP generated by the baseline β-AR model (Fig. 2 C) exhibits shortening of duration, depolarization of AP plateau, and reduction in phase 1 notch depth and duration similar to that seen experimentally (Fig. 2A). Peak amplitude of the model Ca^sup 2+^ transient (Fig. 2D) is increased ~3-fold and the rate of decay of the transient is increased (shortening its overall duration), as seen in experiments (Fig. 2 B).
RESULTS
The shape and duration of the cardiac AP are directly influenced by the dynamical properties of the underlying L-type Ca^sup 2+^ current. Fig. 3 demonstrates that the occurrence and frequency of EAD events are influenced by the modal gating properties of EAD. A representative train of 20 action potentials, simulated using the full 50,000-CaRU model and paced at 1 Hz with 25% LCCs gating in mode 2, yields a total of three EADs occurring within two of the APs (Fig. 3 A). The timing of EADs appears to be random, i.e., they do not occur at regular time intervals. To better understand the role of modal LCC gating on the frequency dependence of EAD events, long-term simulations were performed. Panels B, C, and D of Fig. 3 show APD distributions measured from a series of 150 APs simulated with 0%, 15%, and 25%, respectively, of LCCs gating in mode 2. In the absence of mode 2 LCCs (Fig. 3 B), nearly all APs exhibit a duration in the range of 190-200 ms and no EADs are observed. With 15% of LCCs gating in mode 2 (Fig. 3 C), average APD increases to 240 ms, APD variability increases, and two EADs occur (Fig. 3 C, inset). Further increasing the ratio of mode 2 LCCs to 25% yields an average APD of 263 ms and the rate of EAD occurrence increases dramatically (Fig. 3 D, inset). These simulation results demonstrate that 1), the rate of EAD occurrence is a monotonic increasing function of the fraction of LCCs gating in mode 2, such that no EADs occur when the fraction is zero; and 2), the average APD increases with increased ratio of LCCs gating in mode 2.
Fig. 4 compares I^sub CaL^ underlying APs simulated with 0% (black line), 15% (light shaded line), and 25% (dark shaded line) of LCCs operating in mode 2. The shift in composition of I^sub CaL^ from pure mode 1 to mixed mode 1 and 2 currents has little effect on the peak current magnitude (Fig. 4 A). However, the late component of current corresponding to the plateau phase of the AP is enhanced as the ratio of LCCs in mode 2 is increased (Fig. 4 B). To clarify this effect, the stochastic gating noise in the L-type current signal has been reduced by averaging I^sub CaL^ over 10 APs (Fig. 4 C), demonstrating that an increased occupancy of mode 2 results in an increased mean I^sub CaL^ during the plateau. This increase in sustained inward I^sub CaL^ underlies the observed relationship between APD prolongation and mode 2 occupancy (Fig. 3).
Stochastic nature of EADs
The occurrence of EADs in this model is stochastic in nature due to the gating noise inherent in I^sub CaL^. Fig. 5 A demonstrates two model APs simulated during β-adrenergic stimulation using the full 50,000-CaRU model. Model parameters and initial conditions are identical for both APs shown. However, different seeds are used to initialize the pseudorandom number generator, thus yielding different realizations of LCC and RyR gating during each of the two APs. One of the APs exhibits an EAD, whereas the other does not. This behavior demonstrates that in the presence of LCC mode 2 gating, purely stochastic gating events (i.e., different realizations of the same gating scheme) can determine whether or not an EAD is triggered, in contrast to earlier models in which EADs occur deterministically (Zeng and Rudy, 1995). Stochastic events during the plateau and "second plateau" following an EAD can trigger additional EADs. A non-EAD, a single-EAD, and a double-EAD AP are shown in Fig. 5 B. Using the single-EAD AP as a test case, the random number generator seed was reset at 150 ms and 180 ms (Fig. 5 B, arrows), leading to the elimination of the EAD and to the appearance of a second EAD, respectively. These results show that there appears to be a critical time during the late plateau of the AP, where the cell may either repolarize or depolarize (into an EAD), and that the outcome as to which of these events occurs is a random event determined by the stochastic gating of LCCs. Fig. 5 C shows I^sub CaL^ associated with each of the three APs shown in Fig. 5 B. A large rapid increase of I^sub CaL^ coincides with EAD onset. The time course of I^sub CaL^ inactivation mechanisms corresponding to the single-EAD AP of Fig. 5 B is shown in Fig. 5 D. The ratio of LCCs that are not in an inactivated state (solid black line) reaches a minimum at ~120 ms (corresponding to maximal LCC inactivation), and then proceeds to gradually increase. Both voltage- and Ca^sup 2+^-dependent inactivation (dashed and dash-dotted lines, respectively) of the LCCs have partially recovered at the time of onset of the EAD (~260 ms). The results of Fig. 5 D show that 10.2% of the LCC population recover from inactivation by the time of EAD onset. Of these, 9.5% recover from Ca^sup 2+^-dependent inactivation, whereas only 1.4% recover from V-dependent inactivation. The overlap of these population subsets represents 0.7% of LCCs which recover from both Ca^sup 2+^- and V-dependent inactivation. This demonstrates that preceding the EAD, LCC recovery from inactivation is due primarily to recovery from the Ca^sup 2+^-mediated inactivation state (i.e., transitions from Mode Ca to Mode Normal in the model). This recovery from inactivation is necessary to provide a sufficient number of available LCCs, and hence a sufficient amount of inward current for an EAD to be triggered successfully.
The nature of the current fluctuations in I^sub CaL^ differ for mode 1 and mode 2 LCC populations. To elucidate how channels in each mode contribute to the mechanism of EAD generation, the model currents are separated in the following analyses. Fig. 6, A-C, shows total I^sub CaL^, mode 1 I^sub CaL^, and mode 2 I^sub CaL^, respectively, corresponding to APs both with (black line) and without (shaded line) an EAD. The timescale is chosen to show the detail at the time of onset of the EAD. These two AP simulations differ only by a change in the random number generator seed at 160 ms. There is little difference between non-EAD and EAD currents preceding 235 ms, at which time the two currents begin to diverge, where the non-EAD current begins to decrease in amplitude, whereas the other grows in amplitude indicating the start of the EAD. A small spike in inward mode 2 current (Fig. 6 C, arrow) occurs at 232 ms and may be an EAD triggering event. Immediately after this event, an inward current deflection is observed in both mode 1 (Fig. 6 B, arrow) and total I^sub CaL^ (Fig. 6 A, arrow) at 235 ms. This inward deflection in I^sub CaL^ may be sufficient to trigger an EAD; however, events such as these are generally difficult to identify because the magnitude of inward LCC current deflection preceding an EAD is comparable to the range in which deflections occur at other time points during the plateau of the AP. For this reason, it cannot be determined whether these brief events are in fact playing a role in the trigger mechanism of EADs.
Power spectral analysis can be performed on I^sub CaL^ to better understand the relationship between mode 2 occupancy fraction and frequency content of the gating noise. Power spectra of I^sub CaL^ are calculated using Burg's method (Percival and Walden, 1993) for simulations with 0% (solid black line), 15% (dark shaded dashed line), and 25% (light shaded dashed line) of LCCs in mode 2. Currents are recorded during a voltage-clamp simulation, in which the cell is first held at -90 mV for 3 s, stepped to 40 mV for 10 ms, and then stepped to 5 mV for 7 s. Spectral analysis is performed on currents obtained during the final 5 s of this protocol and the results are shown in Fig. 7 A. The results indicate that the amplitude of slow-timescale (low-frequency) fluctuations of I^sub CaL^ does not depend upon frequency and increases as the fraction of LCCs gating in mode 2 increases. There is an ~7-dB/Hz, or fivefold, difference in power between I^sub CaL^ composed purely of mode 1 channels and that containing 50% mode 2 channels. This corresponds to a 2.2-fold difference in current amplitude in the low-frequency range. At high frequencies, the power drops off as 1/f^sup a^ where a is ~2. These results agree with theoretical calculations, which predict that the power spectral density for a collection of ion channels with exponentially distributed open times is flat at low frequencies (i.e., white noise) and is decreasing at high frequencies with slope proportional to 1/f^sup 2^. The boundary between these regions is expected to occur at a frequency which corresponds to the timescale of channel gating, and occurs in the range of 0.5-1.5 ms in this model. These results indicate that the presence of mode 2 channels significantly increases the amplitude of I^sub CaL^ fluctuations at a timescale slower than 1 ms.
The properties of fluctuations in membrane potential during an AP are determined by both the noise in I^sub CaL^ as well as overall membrane impedance. Fig. 7 B shows the power spectrum of voltage noise for APs simulated with 0% (solid black line) and 25% (dark shaded line) of LCCs gating in mode 2. Only membrane potential during the AP plateau is analyzed. This is accomplished using a window of 250 ms duration starting at the time when membrane potential crosses + 15 mV. Each signal is detrended by subtraction of the mean AP profile. Spectra are calculated for the plateau of each AP in a series of 10 beats and averaged. The results indicate that an increase in the fraction of channels gating in mode 2 from 0% to 25% leads to a substantial increase in the amplitude of slow-timescale (low-frequency) fluctuations in voltage. These results indicate that the presence of LCCs gating in mode 2 significantly increases the amplitude of voltage fluctuations at a timescale slower than 40 ms, which results in increased APD variation, and hence leads to an enhanced propensity for EAD formation.
DISCUSSION
Experimental data indicate that LCC phosphorylation events which promote mode 2 gating of LCCs, such as β-AR stimulation and increased expression of CaMKII (Chen-Izu et al., 2000; Dzhura et al., 2000; Yue et al., 1990), contribute to the generation of EADs (De Ferrari et al., 1995; Priori and Corr, 1990; Volders et al., 1997; Wu et al., 2002). We have tested the hypothesis that increased mode 2 gating induces EADs. Modeling results demonstrate that an increase in the ratio of LCCs gating in mode 2 favors the occurrence of EADs via a mechanism whereby the likelihood of such events is raised by stochastic prolongation of APD and subsequent reactivation of LCCs. Results of this study demonstrate that 1), the rate of EAD occurrence in response to long-term (150-s) 1-Hz pacing is a monotonic increasing function of the fraction of LCCs gating in mode 2, where no EADs occur if that fraction is zero (Fig. 2 A); 2), when the fraction of LCCs gating in mode 2 is >0, EAD occurrence is a stochastic event; and 3), the random opening of a sufficient number of LCCs gating in mode 2 can initiate an EAD (Figs. 3 and 7).
Mechanism of EAD formation
Generation of an EAD requires an inward current that is sufficiently large that total membrane current becomes inward. The main ionic current candidates that may be responsible for inducing EADs are therefore I^sub CaL^ and I^sub NCX^ (Na+-Ca^sup 2+^ exchanger). I^sub NCX^ did not play a significant role in EAD generation in this model (data not shown), whereas the role of I^sub CaL^ is evident from Fig. 5, B and C, where the increase in magnitude of I^sub CaL^ coincides with the onset of each EAD.
In the β-AR stimulated model of the canine cardiac myocyte, EADs have been shown to be stochastic events (Fig. 3). Variation in I^sub CaL^ due to stochastic gating of LCCs leads to variation in APD, and hence some APs are prolonged. These prolonged APs exhibit an increased likelihood of EAD occurrence since the time available for LCC to recover from Ca^sup 2+^-mediated inactivation is extended during the AP plateau and recovered channels are likely to reopen, possibly triggering an EAD. Even when these conditions are present, however, an EAD is not guaranteed to occur because it is an inherently stochastic event that depends upon the number and duration of LCC openings during the late plateau of the AP. This is demonstrated in Fig. 5 B, where changes in the random number generator seeds late in the plateau of a single EAD-AP can either eliminate the EAD or produce an additional EAD within the same AP. This behavior demonstrates that the trajectory of an AP is bistable, as small changes in I^sub CaL^ (of a magnitude comparable to the noise in this current) can dramatically alter the morphology of the AP. This behavior is a form of stochastic resonance (see, e.g., White et al., 2000) which relies upon intrinsic noise levels in I^sub CaL^ and the fact that net membrane current is small during the plateau.
The effect of increasing the ratio of mode 2 LCCs can be separated into two components: 1), an increase in the mean amplitude of the sustained inward Ca^sup 2+^ current during plateau, which prolongs AP in a deterministic manner (Fig. 4); and 2), an increase in slow-timescale fluctuations of total I^sub CaL^ (Fig. 7 A), which enhances the likelihood of EAD triggering due to increased variation in APD (Figs. 3, B-D, and 7). Interestingly, the balance between mode 1 and mode 2 LCCs does not significantly influence the peak amplitude of I^sub CaL^.
The relationship between noise in I^sub CaL^ and noise in membrane potential can be deduced from Fig. 7. The addition of mode 2 channels to I^sub CaL^ enhances the amplitude of current fluctuations at timescales slower than 1 ms, whereas the enhancement of fluctuation in membrane potential is limited to timescales slower than 40 ms. This is a theoretically expected feature of this relationship since membrane impedance is low-pass in nature. In addition, the power spectrum of membrane potential may be influenced by time-dependent changes in membrane impedance during the AP. However, calculation of instantaneous I-V curves during the AP plateau time interval that was used to calculate power spectra indicates that membrane conductance does not change significantly over this interval (data not shown). The spectral properties of voltage noise are therefore largely determined by fluctuations of I^sub CaL^ during the AP plateau, rather than fluctuation of membrane impedance.
Injection of an external current during the late plateau of an AP during β-adrenergic stimulation can induce an EAD. The strength-duration relationship for an EAD-inducing square current pulse is quasihyperbolic, such that the current amplitude required to induce an EAD is quite small for a long duration pulse (data not shown). This system property suggests that modest amplification of slow-timescale fluctuations could effectively increase the likelihood of triggering EADs, and this is precisely what occurs as a fraction of the LCCs transition to mode 2 activity (Fig. 7). This result demonstrates that the appearance of LCCs with a long mean open time can have a profound impact on AP profile, even if only a small fraction of channels exhibit these high-activity gating dynamics.
To reduce computational load, not all simulations were run with the full 50,000-CaRU model. Reduction of the number of simulated CaRUs increases the variance of I^sub CaL^, which may in turn produce an increased frequency of EADs in the simulations presented in Fig. 3, B-D (compared to the full model). This increase in I^sub CaL^ noise, however, does not influence the interpretation of the results regarding the mechanism of EAD generation. Both the full 50,000-CaRU model (Fig. 3 A) and the reduced 10,000-CaRU model (Fig. 3, B-D) exhibit EADs only in the presence of LCCs gating in mode 2. In the absence of mode 2 gating of LCCs both the full and the reduced models fail to exhibit EADs in runs as long as 400 s at 1 Hz (data not shown). Regardless of the number of CaRUs simulated, the mechanism of EAD generation was consistently observed to be dependent on stochastic gating of LCCs (Fig. 5, A and B).
Comparison with previous studies
In traditional approaches to myocyte modeling, it has often been assumed that it is sufficient to simulate the behavior of a large number (10^sup 5^-10^sup 7^) of ion channels using equations that describe the expected (average) behavior of the channel population. In this approach, fluctuations about the average behavior are assumed to be insignificant with respect to whole-cell dynamics.
Previous studies in the neuron (Chow and White, 1996; White et al., 1998, 2000) have shown that in the presence of a small number of stochastically gating ion channels, spontaneous action potentials can be triggered in a random pattern. For a population of independent identical channels, the central limit theorem states that as the number of channels (N) increases, the standard deviation in the signal will scale as N^sup -1/2^ (Feller, 1970), indicating that the amplitude of the gating noise may not be so small as to be considered inconsequential. This property coupled with the nonlinear bistability exhibited by the myocyte late in the AP plateau, results in a system where gating noise can contribute to the triggering of EADs in the presence of a physiological number of channels (40,000-200,000 LCCs).
Experimental measurements have demonstrated that gating noise may be the primary source of APD variability (Zaniboni et al., 2000). The coefficient of variation of APD in guinea pig ventricular myocytes (without β-AR stimulation) has been measured to be 2.3 � 0.9%, and 1.3 � 0.4% in the absence of the late Na+ current (Zaniboni et al., 2000). In the baseline canine myocyte model (which does not include a late Na+ current), in the absence of β-AR stimulation, coefficient of variation of APD is 1.4% with all 12,500 CaRUs included in the simulation, which agrees well with the experimental value.
Electrotonic coupling effects have been shown to have a major influence on the generation and propagation of EADs in myocardial tissue. A recent study by Zaniboni et al. (2000) demonstrated that EADs in single isolated myocytes were suppressed when the EAD-producing myocyte was electrically coupled to a normal myocyte. It is likely that in the presence of electrotonic loading, there must be a critical mass of cells that generate near simultaneous EADs for propagation to occur. This is an important consideration with respect to any mechanism of generation of EADs at the cellular level, including the mechanism considered here. However, it is important to understand all possible mechanisms by which EADs may be generated at the cellular level. It is known that EAD frequency is increased in ventricular myocytes isolated from the failing heart (Nuss et al., 1999), likely due to hyperphosphorylation of LCCs (Chen et al., 2002). Overexpression of CaMKII in isolated murine myocytes, which increases mode 2 gating of LCCs, leads to increased EAD frequency (Wu et al., 2002). Our results provide a possible explanation for these experimental data. Overexpression of CaMKII is also shown to produce EADs in murine ventricular tissue and these EADs are eliminated with application of CaMKII inhibitors, with little or no accompanying APD shortening (Wu et al., 2002). These data demonstrate that under these particular experimental conditions, EADs produced by increased mode 2 gating of LCCs may occur in tissue. The precise mechanism(s) by which EAD generation is supported at the tissue level remains an important issue that is central to the interpretation of our results. We are currently working on methods to further optimize simulation runtime, and plan to address this issue once more efficient algorithms have been developed.
In the LCC model used in this study, mode 2 activity differs from that of mode 1 only in channel mean open time. Recently, Josephson et al. (2002a,b) have found that mode 2 LCCs exhibit a 70% increase in unitary current amplitude compared to mode 1 channels, as well as a shift in the voltage dependence of channel opening. Mean open time was also observed to be 10-100 times greater for mode 2 channels than for mode 1 channels. Inclusion of these experimental findings would likely enhance the contribution of mode 2 LCC fluctuations to total I^sub CaL^, further supporting the idea that modal gating of LCCs is an important component of the mechanism of EAD generation.
Calmodulin kinase II and EADs
The effects of CaMKII on cardiac myocytes are under intensive investigation (reviewed in Anderson, 2004). Recent evidence obtained in the presence of constitutively active CaMKII indicate that 1), there is a significant shift in LCC gating from mode 1 to mode 2 (Dzhura et al., 2000); and 2), myocytes isolated from transgenic mice exhibit both EADs and enhanced LCC activity (open probability) (Wu et al., 2002). Both of these effects are eliminated by the CaMKII-inhibiting peptide AC3-I. The agreement of our simulation results with these experiments suggests that phosphorylation targets of CaMKII are likely similar to those of PKA as implemented in this study. Wu et al. (2002) also observed that the decrease in EAD frequency with CaMKII inhibition was not associated with a decrease in APD, suggesting that AP prolongation alone does not cause EADs. The modeling results presented here suggest that an altered distribution of LCCs among modes, combined with altered channel availability, can influence the frequency of EADs in the absence of a change in APD, and therefore may be an important mechanism underlying these experimental observations.
CONCLUSIONS
The results presented here suggest that the traditional approach to building models of excitable cells by implementing descriptions of the expected (average) behavior for each population of ion channels may in some instances fail to capture important cellular phenomena. Fluctuations in cell signals about their average value can induce dramatic qualitative changes in cell behavior as a result of stochastic resonance. In the cardiac myocyte model used here, the rate of EAD occurrence was shown to be enhanced by mode 2 L-type channel gating via a mechanism that depends upon an increase in both the average current level and the amplitude of low-frequency fluctuations in the current.
Recent evidence indicates that in human heart failure, the number of LCCs expressed is reduced and the fraction of LCCs available for gating is increased (Schr�der et al, 1998). It has been suggested that the phosphorylation of protein targets within the cellular microdomain between the t-tubule and the JSR may be regulated locally, and that the phosphorylation state of these molecules is increased in failing human ventricular myocytes, potentially as a result of decreased activity of phosphatases in the microdomain (Chen et al., 2002). We therefore speculate that the stochastic mechanism of EAD generation investigated in this simulation study may also be of importance in explaining the increased rate of EAD occurrence in failing ventricular myocytes (Nuss et al., 1999). There is as yet no evidence of any shift in the relative distribution of LCC gating modes in human heart failure. Experimental studies directed at understanding details of LCC modal gating in both normal and diseased human myocytes would be an important direction for future investigation.
The model presented here can be found on the Center for Cardiovascular Bioinformatics and Modeling web site (http://www.ccbm.jhu.edu/).
This work was supported by National Institutes of Health grants RO1 HL60133, RO1 HL61711, and P50 HL52307, the Falk Medical Trust, the Whitaker Foundation, and IBM.
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doi: 10.1529/biophysj.104.051508
[Reference]
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[Author Affiliation]
Antti J. Tanskanen,*[dagger] Joseph L. Greenstein,*[dagger] Brian O'Rourke,[double dagger]� and Raimond L. Winslow*[dagger]�
* Center for Cardiovascular Bioinformatics and Modeling, [dagger] The Whitaker Biomedical Engineering Institute, [double dagger] Department of Medicine Division of Cardiology, and � The Institute for Molecular Cardiobiology, The Johns Hopkins University School of Medicine and Whiting School of Engineering, Baltimore, Maryland
[Author Affiliation]
Submitted August 17, 2004, and accepted for publication October 5, 2004.
Address reprint requests to Antti Tanskanen, The Johns Hopkins University, Clark Hall, Rm. 204, 3400 N. Charles St., Baltimore, MD 21218. E-mail: atanskan@bme.jhu.edu.
� 2005 by the Biophysical Society
0006-3495/05/01/85/11 $2.00
