Quinidine and quinine effects on the slow wave activity of colonic circular muscle

The slow wave plateau phase has an important role in the regulation of contractile activity in the canine colon. Quinidine (EC50 approximately 5 microM) and quinine (EC50 approximately 13 microM) inhibited in a concentration dependent manner the plateau phase. Quinidine and quinine decreased the plateau amplitude, and increased the plateau potential; whereas, they did not affect the upstroke amplitude, and the average rate of rise of the slow waves. Their specific effect on the slow wave plateau suggests that the plateau phase depolarization is mediated by a quinidine- and quinine-sensitive inward current. Quinidine and quinine will be useful experimental tools to further characterize the ionic conductances responsible for the plateau depolarization.