1. Department of Pharmacology, University of California, San Diego, La Jolla, CA 92093-0636, U.S.A.
2. Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, CA 92093-0636, U.S.A.
3. Department of Cellular and Molecular Medicine, University of California, San Diego, La Jolla, CA 92093-0636, U.S.A.