1. Institute of Organic and Pharmaceutical Chemistry, National Hellenic Research Foundation, 48 Vas. Constantinou Avenue, 116 35 Athens, Greece, Department of Animal and Human Physiology, School of Biology, University of Athens, Panepistimiopolis, 15784 Athens, Greece, Department of Pharmacology and Pharmacotherapy, University of Szeged, Szeged Dom ter 12 H-6720, Hungary, Research Unit for Cardiovascular Pharmacology, Hungarian Academy of Sciences, Szeged Hungary