1. J. R. Henley, H. Cao, M. A. McNiven, Center for Basic Research in Digestive Diseases, Mayo Clinic and Foundation, Rochester, MN 55905, USA.
2. S. M. Jones, K. E. Howell, Department of Cellular & Structural Biology, University of Colorado School of Medicine, 4200 East 9th Avenue, Denver, CO 80262, USA.