DIFFERENTIAL EFFECTS OF QUINIDINE AND DIPHENYLHYDATOIN ON MONOPHASIC ACTION POTENTIAL OF ISOLATED RABBIT HEART

Experiments were performed on isolated, perfused rabbit hearts which were electrically paced. Monophasic action potentials were recorded from the left ventricle by means of a suction electrode. Quinidine, diphenylhydantoin, SC-7031 and SC-12757 were added to the perfusate (5 experiments each) to produce cumulative concentrations of 5, 10 and 20 mg/1. Measurements of diastolic threshold, total monophasic action potential duration (MAPDt) and functional refractory period (FRP) were made 10 minutes after each drug addition. Quinidine and SC-7031, antiarrhythmic agents, caused an elevation of thershold, prolongation of MAPDt. This latter effect is related to an increase in the upstroke velocity of the cellular action potential and/or shortening of the duration of the cellular action potential, and is evidence for improved ventricular conduction. The technique presented is useful for differentiating quinidine from diphenylhydantion-type antiarrhythmic agents. © 1969.