1. M. T. Nelson, A. D. Bonev, H. J. Knot, Department of Pharmacology, 55A South Park Drive, University of Vermont, Colchester, Vermont 05446, USA.
2. H. Cheng, L. F. Santana, W. J. Lederer, Department of Physiology and The Medical Biotechnology Center, University of Maryland School of Medicine, 660 West Redwood Street, Baltimore, MD 21201, USA.
3. M. Rubart, Krannert Institute of Cardiology, Indiana University School of Medicine, Indianapolis, IN 46202-4800, USA.