1. Departments of Pharmacology and Medicine, The University of Tennessee Health Science Center, 874 Union Avenue, Memphis, TN 38163, U.S.A.
2. Department of Veterans Affairs Medical Center, 1030 Jefferson Avenue, Memphis, TN 38104, U.S.A.
3. Division of Clinical Pharmacology, The University of Tennessee Health Science Center, 874 Union Avenue, Memphis, TN 38163, U.S.A.