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