1. From the Division of Cardiovascular Medicine (C.C.H., T.K.), Department of Medicine; and Departments of Pharmacology (C.C.H.) and Cell and Developmental Biology (T.K.), Vanderbilt University School of Medicine, Nashville, Tenn; and Cardiovascular Research Center and Division of Cardiology (R.T.P.), Department of Medicine, Massachusetts General Hospital, Harvard Medical School, Charlestown, Mass.