The action of ethanol upon the action potential and contraction of ventricular muscle

Isolated isometric ventricular muscle of frogs and cats was studied. Perfusing solutions were played directly on the muscle to permit rapid exchange of the extracellular space. Developed force and maximal rate of rise of force were measured in all studies and action potentials (AP) were recorded in some. For both species low concentrations of ethanol (75 degrees mg/l) potentiate contraction. Higher concentrations ( greater than or equal to 750 mg/l) depress contraction progressively with increasing concentration. Concentrations which depress contraction, e.g., 3-4.5 gm/l, usually shorten AP duration. The shortening of AP duration can occur even though contractile force does not fall and, conversely, force may fall while AP duration is unaffected. When 10 mM caffeine is added to the perfusate of either species, AP duration is prolonged and contraction is potentiated. If both ethanol (4.5 gm/l) and 10 mM caffeine are added simultaneously to the perfusate, there is a rapid (within 4 beats) increase in AP duration and an initial depression of contraction, followed by a further increase in AP duration and a significant potentiation of contraction. The steady state contraction is less than with caffeine alone. These preliminary studies suggest that ethanol may depress contraction both by shortening AP duration and by a direct effect upon the contractile apparatus.