1. Institut für Herz- und Kreislaufphysiologie, Heinrich-Heine-Universität Düsseldorf, Universitätsklinikum, Düsseldorf, Germany.
2. Department of Medicine-Cardiovascular Medicine, University of Virginia, Charlottesville, Virginia.
3. Center for Skeletal Muscle Research at Robert Berne Cardiovascular Research Center, University of Virginia, Charlottesville, Virginia.