AGI October 40/4

Sato, Yoshihiko, Hiroyuki Hanai, Atsuhiro Nogaki, Koki Hirasawa, Eizo Kaneko, Hisayoshi Hayashi, and Yuichi Suzuki. Role of the vasopressin V1 receptor in regulating the epithelial functions of the guinea pig distal colon. Am. J. Physiol. 277 (Gastrointest. Liver Physiol. 40): G819–G828, 1999.—Vasopressin has a wide spectrum of biological action. In this study, the role of vasopressin in regulating electrolyte transport in the colon was elucidated by measuring the short-circuit current (Isc) as well as the Na1, K1, and Cl2 flux in a chamber-mounted mucosal sheet. The cytosolic Ca21 concentration ([Ca]i) was also measured in fura 2-loaded cells by fluorescence imaging. Serosal vasopressin decreased Isc at 1029 M and increased Isc at 1027–1026 M. The decrease in Isc was accompanied by two effects: one was a decrease in the amiloride-sensitive Na1 absorption, whereas the other was an increase in the bumetanidesensitive K1 secretion. The increase in Isc was accompanied by an increase in the Cl2 secretion that can be inhibited by serosal bumetanide or mucosal diphenylamine-2-carboxylate. Vasopressin caused an increase in [Ca]i in crypt cells. These responses of Isc and the [Ca]i increase in crypt cells were all more potently inhibited by the vasopressin V1 receptor antagonist than by the V2 receptor antagonist. These results suggest that vasopressin inhibits electrogenic Na1 absorption and stimulates electrogenic K1 and Cl2 secretion. In all of these responses, the V1 receptor is involved, and the [Ca]i increase may play an important role.