Ethanol actions on the mechanisms of Ca 2+ mobilization in rat hippocampal cells are mediated by protein kinase C

Abstract

The effects of ethanol on intracellular free Ca 2+ concentration, [Ca] i, were studied in cultured rat hippocampal neurons using fluo-3 and confocal microscopy. Ethanol application transiently elevated [Ca] i due to Ca 2+-induced Ca 2+ release from internal stores since the effect was observed also in solutions containing zero Ca 2+ or 0.3 mM La 3+ and restoration of external Ca 2+ content led to secondary response in presense of ethanol. The sites of highest [Ca] i increases correlated well with those obtained after Ca 2+ release from caffeineand IP 3-sensitive internal stores. After single ethanol exposure the caffeine-evoked [Ca] i transients were potentiated whereas Ca 2+ release induced by IP 3-mobilizing agonists was suppressed. Similar effects were observed by activation of protein kinase C (PKC) by phorbol esters which also occluded ethanol actions. Ethanol increased fluorescence of Rim-1, a PKC indicator dye. The data obtained are consistent with ethanol activation of PKC whereby Ca 2+ release via ryanodine receptors is potentiated and IP 3 receptors are down-modulated. Since the effects of both ethanol and phorbol esters were mimicked by cytochalasins B and D, PKC-induced cytoskeleton phosphorylation and its subsequent rearrangements can be responsible for observed effects.