1. Departments of Anesthesia, Pharmacology, and Pediatrics, UMDNJ−Robert Wood Johnson Medical School, New Brunswick, New Jersey 08901, Department of Chemistry, Rutgers University, Piscataway, New Jersey 08855, National Tritium Labelling Facility and Physical Biosciences Division, E. O. Lawrence Berkeley National Laboratory, One Cyclotron Road, Berkeley, California 94720, and Department of Pharmaceutical Chemistry, School of Pharmacy, University of California, San Francisco, California 94143