Characterization of the effect of quinidine on Na transport by the toad and turtle bladders.

Quinidine inhibits Na transport by the toad and turtle bladder. This effect of quinidine is thought to be mediated by an increase in cytosolic calcium. In the present study, we characterized the effect of quinidine on Na transport by the toad and turtle bladders. Quinidine induced a release of calcium by turtle liver mitochondria. Quinidine inhibited Na transport by increasing the resistance of the active pathway to Na transport without affecting the electromotive force. Amphotericin B addition to the mucosal solution partially reversed the inhibitory effect of quinidine on Na transport, thus suggesting that quinidine decreases Na transport by decreasing the permeability of luminal membrane to Na. The effect of amiloride was unaltered in the presence of quinidine. Vasopressin failed to stimulate Na transport in the presence of quinidine, suggesting that the drug interferes with the natriferetic effect in addition to interfering with the hydrosmotic effect. The effect of quinidine was not prevented by inhibition of cyclooxygenase system or mitochondrial inhibition, thus suggesting that alterations in prostaglandin release or mitochondrial function are not involved in the inhibition of Na transport by quinidine.