BIOCHEMICAL-CHARACTERIZATION OF ETHANOL ACTIONS ON DIHYDROPYRIDINE-SENSITIVE CALCIUM CHANNELS IN BRAIN SYNAPTOSOMES

This study was undertaken to investigate the biochemical events underl ying the inhibitory action of ethanol on dihydropyridine-sensitive vol tage-dependent Ca2+ channels in brain synaptosomes. The binding of rad iolabeled dihydropyridine was used to determine functional Ca2+ channe ls in synaptosomes following exposure to ethanol. No effect on [H-3]PN 200-110 binding was found when disrupted synaptosomal membranes were incubated with ethanol concentrations as high as 300 mM, suggesting th at ethanol did not interact directly with sites on or near the Ca2+ ch annels. However, when intact synaptosomes were first incubated with et hanol (100 mM) at 37 degrees and then disrupted, a significant reducti on in membrane binding of [H-3]PN 200-110 was found. Ethanol incubatio n of synaptosomes at 0 degrees was ineffective. It appears that metabo lic processes involving intracellular factors were required in the eth anol action. In examining this possibility, [H-3]PN 200-110 binding wa s activated by incubation of disrupted membranes with MgATP and Ca2+-c almodulin, and ethanol was found to inhibit the activation in a concen tration-dependent manner (50-200 mM). [H-3]PN 200-110 binding to membr anes was also activated by incubation with MgATP and cyclic AMP-depend ent protein kinase, but this activation was not inhibited by ethanol. These findings are consistent with the interpretation that ethanol act s on Ca2+ channels by inhibiting calmodulin-dependent activation of th e channels.