1. Department of Surgery, Faculty of Medicine, University of Debrecen P.O. Box 400, Debrecen H-4002, Hungary
2. Department of Physiology, McGill University, 3655 Promenade Sir William Osler, Montreal H3G1Y6, Canada
3. Department of Biophysics and Cell Biology, Faculty of Medicine, University of Debrecen, P.O. Box 400, Debrecen H-4002, Hungary