Evidence for the role of calcium in the hydrosmotic response to antidiuretic hormone in frog skin.

Treatment with the calcium ionophore A23187 on either the serosal or mucosal sides of frog skin, strongly inhibits the hydrosmotic response to vasopressin. On the contrary, the hydrosmotic response to 8-br-cAMP is not affected by treatment with the A23187. Trifluoperazine, a drug which inhibits the Ca2+-calmodulin complex, selectively inhibits vasopressin-induced water transport. Collectively, our results suggest that an increase in the intracellular concentration of Ca2+, obtained by treatment with the ionophore A23187, interferes with a pre-cAMP step of the hydrosmotic response to the antidiuretic hormone. Calcium ions could regulate adenyl-cyclase activity and consequently intracellular levels of cAMP. This effect may probably involve calmodulin.