Altered calcium signal transduction after chronic ethanol consumption

Chronic ethanol consumption decreases the phorbol ester binding to membranal but not cytosolic protein kinase C in rat brain

We examined the effect of 60 days of ethanol treatment on protein kinase C (PKC) in membrane and cytosolic fractions of the rat cerebral cortex. Membranal and cytosolic PKC were determined by binding technique using [3H]-phorbol 12,13 dibutyrate (PDBU) as radioligand and phorbol 12-myristate 13-acetate (PMA) as displacer. Chronic ethanol consumption resulted in a decrease in the maximum number of binding sites (Bmax) of [3H]-PDBU binding to membranal PKC without significant change in the apparent dissociation constant (KD) in the rat cortex. We also observed that chronic ethanol consumption had no significant effect on Bmax or KD of [3H]-PDBU binding to cytosolic PKC in the rat cerebral cortex. These results suggest that chronic ethanol consumption leads to the down-regulation of brain PKC associated with membrane but not with cytosol.

Influence of ethanol on calcium, inositol phospholipids and intracellular signalling mechanisms

Studies have implicated Ca++ in the actions of ethanol at many biochemical levels. Calcium as a major intracellular messenger in the central nervous system is involved in many processes, including protein phosphorylation enzyme activation and secretion of hormones and neurotransmitters. The control of intracellular calcium, therefore, represents a major step by which neuronal cells regulate their activities. The present review focuses on three primary areas which influence intracellular calcium levels; voltage-dependent Ca++ channels, receptor-mediated inositol phospholipid hydrolysis, and Ca++/Mg++-ATPase, the high affinity membrane Ca++ pump. Current research suggests that a subtype of the voltage-dependent Ca++ channel, the dihydropyridine-sensitive Ca++ channel, is uniquely sensitive to acute and chronic ethanol treatment. Acute exposure inhibits, while chronic ethanol exposure increases 45Ca++-influx and [3H]dihydropyridine receptor binding sites. In addition, acute and chronic exposure to ethanol inhibits, then increases Ca++/Mg++-ATPase activity in neuronal membranes. Changes in Ca++ channel and Ca++/Mg++-ATPase activity following chronic ethanol may occur as an adaptation process to increase Ca++ availability for intracellular processes. Since receptor-dependent inositol phospholipid hydrolysis is enhanced after chronic ethanol treatment, subsequent activation of protein kinase-C may also be involved in the adaptation process and may indicate increased coupling for receptor-dependent changes in Ca++/Mg++-ATPase activity. The increased sensitivity of three Ca++-dependent processes suggest that adaptation to chronic ethanol exposure may involve coupling of one or more of these processes to receptor-mediated events.

Chronic alcohol intake modifies phorbol ester binding in selected rat brain areas

3H-Phorbol 12,13 dibutyrate binding to rat brain was modified by chronic ethanol treatment. Among the areas examined hippocampus and cortex showed a decrease in Bmax values of 32 and 24% respectively. No significant effect was observed in hypothalamus and cerebellum. In vitro ethanol did not modify the binding in all the areas except at molar concentrations. In hippocampus and cortex the direct measurement of protein kinase C activity indicated that the decrease in phorbol ester binding was accompanied with a concomitant decrease in kinase activity. The results indicate that chronic ethanol treatment leads to an inhibition of brain protein kinase C function.