Effect of ethanol on guinea pig ventricular action potentials

The effects of low concentrations of ethanol on transmembrane potentials of guinea pig ventricular muscle were analyzed. Papillary muscles were superfused with Tyrode solution in vitro at 30°C while driven at 60 min.⁻¹ Transmembrane potentials were recorded by means of intracellular microelectrodes before, during and after a 15 min exposure to ethanol. Ethanol 2.5 mg/100 ml (0.55mM) did not affect transmembrane potentials. Ethanol 5 mg/100 ml enhanced the amplitude of the action potential (AAP) without affecting the membrane resting potential (MRP) and the maximum velocity of the upstroke (dV/dt). Ethanol 40 mg/100 ml also enhanced AAP without modifying MRP and dV/dt. Verapamil and propranolol blocked the augmenting effect of ethanol on AAP. Ethanol 40 mg/100 ml also enhanced the amplitude of responses restored by norepinephrine in fibers depolarized by high [K]₀ to a level of resting potential at which the fast component of the upstroke was abolished. The enhancement of AAP was accompanied by a shift of the plateau to more positive values, but the duration of the action potential measured at 50% of repolarization was not affected. The results indicate that ethanol in low concentrations augments, through a catechol-mediated effect, the slow component of the upstroke of ventricular action potentials.