1. From the Cardiovascular Research Institute and Department of Medical Physiology, Texas A&M University System Health Science Center (J.A.F., M.L.M., J.L.P.), and Department of Health and Kinesiology (J.M.M.-D., M.D.D.), Texas A&M University, College Station, Tex, and Dalton Cardiovascular Research Center and Departments of Physiology and Biomedical Sciences, University of Missouri, Columbia (M.H.L.).