1. 1Department of Biochemical and Experimental Pharmacology, St. Mary's Hospital Medical School, London W2 1PG, U.K.; Department of Clinical Pharmacology, St. Mary's Hospital Medical School, London W2 1PG, U.K.
2. 2Department of Biochemical and Experimental Pharmacology, St. Mary's Hospital Medical School, London W2 1PG, U.K.; Department of Clinical Pharmacology, St. Mary's Hospital Medical School, London W2 1PG, U.K.
3. 3Department of Biochemical and Experimental Pharmacology, St. Mary's Hospital Medical School, London W2 1PG, U.K.; Department of Clinical Pharmacology, St. Mary's Hospital Medical School, London W2 1PG, U.K.
4. 4Department of Biochemical and Experimental Pharmacology, St. Mary's Hospital Medical School, London W2 1PG, U.K.; Department of Clinical Pharmacology, St. Mary's Hospital Medical School, London W2 1PG, U.K.