1. Katholieke Universiteit Leuven, Campus Gasthuisberg (O/N), Departement Moleculaire Celbiologie, Afdeling Farmacologie, Herestraat 49, B-3000 Leuven, Belgium
2. Banyu Tsukuba Research Institute in Collaboration with Merck Research Laboratories, Okubo 3, Tsukuba 300-26, Japan
3. Faculty of Science, University of Waterloo, Waterloo, Ontario, Canada NSL 3G1