Inhibition of ATP levels by quinidine in a human colonic epithelial cell line.

The influence of quinidine, a putative K+ channel blocker, on Cl- secretion induced by vasoactive intestinal polypeptide (VIP) was investigated. Quinidine inhibited Cl- secretion induced by VIP in T84 cell monolayers. A similar inhibitory effect of quinidine on Cl- secretion was observed in an isolated human colon. However, in the isolated human colon, which absorbs Na+ avidly, inhibition of Na+ absorption predominated. In the T84 cell, the half-maximal inhibition by quinidine occurred at 60 microM, while 300 microM almost completely inhibited the VIP-induced Cl- secretion. Mucosal addition of quinidine was at least equally effective compared with serosal addition, suggesting that quinidine acts on the apical membrane or intracellularly. Quinidine had little or no effect on VIP-stimulated Cl- efflux in the first 15 min after its addition, suggesting that blockage of the Cl- exit pathway on the apical membrane is an unlikely mechanism. Similarly, quinidine did not inhibit the K+-recycling mechanism on the basolateral membrane in the first 15 min after its addition. The initial inhibitory action of quinidine corresponded better with its ability to decrease cellular ATP levels. Our study suggests that the depletion of cellular ATP levels may explain the initial inhibitory action of quinidine on electrolyte transport in the intestine, while the late effect is multifactorial.