1. From the Cardiovascular Medicine Section, Department of Medicine, Boston Medical Center and Myocardial Biology Unit, Boston University School of Medicine, Boston, Mass (D.B.S., T.A.M.), and the Institute of Cell Biology, Swiss Federal Institute of Technology, Zurich, and Swiss Cardiovascular Center Bern, Inselspital, Bern, Switzerland (C.Z., H.M.E., T.M.S.).