1. From the Departments of Molecular Physiology and Biophysics (M.S.M., P.V.B., M.M.L., B.M.P., D.W.M., M.J.T.) and Medicine (P.V.B., M.M.L., D.E.S., P.A.A., M.J.T.), University of Vermont, College of Medicine, Burlington, Vt; and Renal Division (S.H.L.), Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, Mass.