Ethanol inhibits electrically-induced calcium transients in isolated rat cardiac myocytes

The fluorescent Ca²⁺ indicator fura-2 was used to follow cytosolic Ca²⁺ transients during excitation-contraction coupling in suspensions of isolated rat heart cells induced to beat synchronously by electrical field stimulation. The Ca²⁺ transient reached a maximum at about 30 ms after application of the electrical stimulus and then relaxed to the basal level over the following 200 ms. Treatment of the myocytes with 0.25 to 2.0% ethanol (40 to 340 mm) caused a decrease in the peak of the Ca²⁺ transient, with no apparent change in the time to peak. This effect of ethanol occurred progressively over a period of about 1 min before a new stable state was achieved. At 1% ethanol the peak Ca²⁺ level was reduced by 50%. Ethanol reversed the stimulatory effect of isoproterenol on peak Ca²⁺ and at high levels of ethanol the β-adrenergic agonist no longer caused any enhancement of the Ca²⁺ transient. Ethanol did not cause any marked change in the basal Ca²⁺ level between beats. The effects of ethanol were readily reversible. These results suggest that the negative inotropic effect of ethanol observed in intact cardiac muscle preparations may result in part from interference with the Ca²⁺ fluxes responsible for excitation-contraction coupling in ventricular myocytes.