INTERACTIONS OF ETHANOL AND QUINIDINE ON CONTRACTILITY AND MYOCYTE ACTION-POTENTIAL IN THE RAT VENTRICLE

The combined effects of ethanol and quinidine on cardiac electromechan ical coupling are unknown, but both drugs affect cardiac conduction an d can cause myocardial depression. Isolated left ventricular papillary and ventricular myocytes were used to assess the combined effects of quinidine and ethanol on the electrophysiologic and mechanical propert ies of rat myocardium. The combination of quinidine (1-300 muM) and et hanol (120-240 mg/dL) depressed active papillary muscle tension within the clinically useful concentration range. In electrophysiologic stud ies of isolated ventricular myocytes, quinidine prolonged the action p otential duration at 50% (APD50) and 90% (APD90) repolarization, the a bsolute refractory period, and the relative refractory period, but dec rease the maximum rate of change of depolarization in phase 0 (V(max). When cells were exposed to ethanol (240 mg/dL) and quinidine (1.5 muM ) together, a significant decrease in the quinidine-induced prolongati on of the absolute refractory and relative refractory periods was seen . Additional changes in action potential parameters from the quinidine values included slight reductions in V(max) and in APD50 and APD90, b ut these reductions were not consistently displayed, nor were they sta tistically significant.