1. Department of Pharmacology and Physiology, UMDNJ-New Jersey Medical School, Newark, New Jersey 07101
2. Instituto de Química y Fisicoquímica Biológicas y Departamento de Química Biológica, Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires, C1113AAD Buenos Aires, Argentina
3. Department of Microbiology and Immunology, Drexel University School of Medicine, Philadelphia, Pennsylvania 19129
4. Schering-Plough Research Institute, Summit, New Jersey 07901