Alcohol inhibits the depolarization-induced stimulation of oxidative phosphorylation in synaptosomes

The effects of alcohol and Ca2+ transport inhibitors on depolarization-induced stimulation of oxidative phosphorylation and free-Ca2+ concentrations in rat synaptosomes were investigated. Glucose oxidation was stimulated by depolarization with K+ or veratridine and by the Ca2+ ionophore ionomycin. The stimulation by K+, veratridine, and ionomycin was correlated with elevation of synaptosomal free Ca2+. Depolarization-stimulated respiration was inhibited by verapamil, Cd2+, and ruthenium red but not by diltiazem. Synaptosomal Ca2+ elevation was inhibited by verapamil but not by ruthenium red. These results indicate that the stimulation depends on elevation of mitochondrial free Ca2+. Ethanol, at pharmacological concentrations (50-200 mM), inhibited the Ca2+-dependent stimulation of oxidative phosphorylation. This inhibition resulted, in part, from the inhibition of voltage-gated Ca2+ channels, which inhibited the elevation of synaptosomal free Ca2+, and, in part, from the stimulation of the mitochondrial Ca2+/Na+ antiporter, which inhibited the elevation of the mitochondrial matrix free Ca2+. The inhibition by ethanol of the excitation-induced stimulation of oxidative phosphorylation in the synapse may contribute to the depressant and narcotic effects of alcohol and enhance excitotoxicity.