1. Division of Clinical Cell Biology, University of Bergen, Medical Department A, Haukeland Sykehus, N-5021 Bergen, Norway
2. Department of Cell Biology, Institute of Anatomy, University of Aarhus, DK-8000 Aarhus C, Denmark
3. Medical Department, NYCOMED AS, P.O. Box 4220 Torshov, N-0401 Oslo, Norway