1. Department of Medical Physiology and Internal Medicine, Scott & White Hospital and Texas A&M University Health Science Center College of Medicine and Central Texas Veterans Health Care System, Temple, Texas 76504; and
2. Center for Basic Research in Digestive Diseases, Division of Gastroenterology and Hepatology, Departments of Internal Medicine and of Biochemistry and Molecular Biology, Mayo Medical School, Clinic, and Foundation, Rochester, Minnesota 55905