Influence of vasopressin and calcium on electrolyte transport across isolated colonic mucosa of the rat.

Vasopressin enhanced the absorption of water and Na+ across everted sacs of rat colon descendens but had no effect on absorption across the colon ascendens. The short-circuit current (Isc) and open-circuit potential difference (p.d.) across the colon descendens were dose-dependently decreased by vasopressin. Isc and p.d. across the colon ascendens were not altered by vasopressin. In the colon descendens the decrease in Isc and p.d. was significant at 1 microu. vasopressin/ml and reached a maximum at 1 mu./ml. Propranolol and phentolamine or naloxone did not alter the decrease in Isc and p.d. to a submaximal dose of vasopressin. Vasopressin increased the mucosal to serosal flux of Na+ and Cl- and decreased the serosal to mucosal flux of Cl- across short-circuited colon descendens. Consequently these changes increased the net flux of Na+ and Cl-. Adenylate cyclase activity in homogenates of the colon descendens was not altered by vasopressin. Omission of Ca2+ from the serosal bathing solution reversibly decreased Isc and p.d. and increased Na+ and Cl- absorption across the colon descendens in a similar way as did vasopressin. The results suggest that the effect of vasopressin on the colon descendens may be due to a decrease in intracellular Ca2+ activity.