1. Department of Cardiovascular Physiology, Ruhr University Bochum, Universitätsstr. 150, D-44780 Bochum, Germany.
2. Department of Pharmaceutical Chemistry, Philipps University Marburg, Marbacher Weg 6, D-35032 Marburg, Germany.
3. Department of Cell Physiology and Pharmacology, University of Leicester, University Road, P. O. Box 138, Leicester LE1 9HN, UK.
4. Department of Pharmacology and Clinical Pharmacy, Philipps University Marburg, Karl-von-Frisch-Str. 1, D-35043 Marburg, Germany.