1. Department of Physiology and Pharmacology and Calvin, Phoebe and Joan Snyder Institute for Chronic Diseases, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada;
2. Département de Pharmacologie-Physiologie, Université de Sherbrooke, Sherbrooke, Quebec, Canada; and
3. Departments of Pathology and Medicine (GI), Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts