1. From the Departments of Physiology (S.P.H., C.R.B., P.A.P., R.L.M.) and Medicine (T.A.H., P.S.D.), Section of Cardiovascular Medicine, University of Wisconsin Medical School, Madison, Wis; the Biotechnology Center (C.R.B., P.A.P.) and Muscle Biology Laboratory (M.L.G.), University of Wisconsin-Madison, Madison, Wis; and the Department of Physiology (K.S.M.), University of Missouri School of Medicine, Columbia, Mo.