1. From the Department of Physiology and Biophysics (E.B.T., M.J.R.) and Department of Pharmacology & Toxicology (H.R.T.), University of Mississippi Medical Center, Jackson; Department of Medicine, University of Louisville School of Medicine, KY (M.T.B., D.W.P.); and G.V. (Sonny) Montgomery Veterans Affairs Medical Center, Jackson, MS (M.J.R.).