Potentiation of the negative chronotropic action of verapamil by ethanol.

Ethanol and verapamil are both known to affect the transmembrane movement of Ca2+ in several biological systems. Both ethanol and verapamil have negative chronotropic actions on the isolated sinus node. The following study was designed to determine if these actions were synergistic. Studies on sinoatrial (SA) node-atrial preparations from rats pair-fed either sucrose or ethanol liquid diets showed that the preparations from the ethanol rats were more sensitive to verapamil. Studies on SA node-atrial preparations from control rats showed that acutely administered ethanol (20 mg/dl, 40 mg/dl) reduced spontaneous beating. In addition, verapamil had a greater negative chronotropic effect in the presence of ethanol (20 mg/dl, 40 mg/dl) than it did alone. It is hypothesized that the ethanol-verapamil interaction is mediated through a reduction in transmembrane Ca2+ movement.