1. From the Department of Medical Physics (E.N.T.P.B., J.A.E.S., J.P., A.G., T.M.R., O.S., E.V.B.) and Cardiovascular Research Institute Amsterdam, Academic Medical Center, Amsterdam, the Netherlands; and the Department of Pharmacology (C.L.B., L.H.B., M.J.M.), University of Aarhus, Aarhus, Denmark.