1. From the Robert M. Berne Cardiovascular Research Center (K.H., E.L.C., L.J.D., C.M., B.E.I., S.K.S.), Department of Molecular Physiology and Biological Physics (C.M., B.E.I., S.K.S.), and Department of Pharmacology (L.J.D., S.K.S), University of Virginia-School of Medicine, Charlottesville.