1. From the School of Physiology and Pharmacology, Bristol Heart Institute, Medical Sciences Building, University of Bristol, Bristol, BS8 1TD, England (D.J.A.M., J.F.R.P.); and Department of Physiology, School of Medicine of Ribeirão Preto, University of São Paulo, Ribeirão Preto, 14049–900, SP, Brazil (D.J.A.M., B.H.M.).