1. L. B. MacMillan and L. E. Limbird, Department of Pharmacology, Vanderbilt University, Nashville, TN 37232, USA.
2. L. Hein, Departments of Medicine, and Molecular and Cellular Physiology, Stanford University, Stanford, CA 94305, USA.
3. M. S. Smith and M. T. Piascik, Department of Pharmacology, University of Kentucky, Lexington, KY 40536, USA.