[1] MICHAEL REESE HOSP & MED CTR, DEPT MED, DIV GASTROENTEROL, CHICAGO, IL 60616 USA
[2] UNIV CHICAGO, DEPT MED, CHICAGO, IL 60637 USA
[3] UNIV CHICAGO, DEPT PHARMACOL & PHYSIOL SCI, CHICAGO, IL 60637 USA
[4] COLUMBIA UNIV COLL PHYS & SURG, DEPT MED, NEW YORK, NY 10032 USA
[5] COLUMBIA UNIV COLL PHYS & SURG, DEPT PHYSIOL, NEW YORK, NY 10032 USA