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.