1. From the Department of Integrative Physiology (A.J.C., S.A.M., C.A.E., G.C.S., M.L.R., D.A.B., K.D.M., R.L.M.), University of Colorado Cardiovascular Research Institute, University of Colorado, Boulder; and the Department of Pharmacology (R.C.M.), University of Colorado at Denver and Health Sciences Center, Aurora. Current address: Department of Health and Exercise Science (A.J.C.), Colorado State University, Fort Collins.