Development of tolerance in brain mitochondria for calcium uptake following chronic ethanol ingestion

Cytotoxicity of short-chain alcohols

Ethanol and other short-chain alcohols elicit a number of cellular responses that are potentially cytotoxic and, to some extent, independent of cell type. Aberrations in phospholipid and fatty acid metabolism, changes in the cellular redox state, disruptions of the energy state, and increased production of reactive oxygen metabolites have been implicated in cellular damage resulting from acute or chronic exposure to short-chain alcohols. Resulting disruptions of intracellular signaling cascades through interference with the synthesis of phosphatidic acid, decreases in phosphorylation potential and lipid peroxidation are mechanisms by which solvent alcohols can affect the rate of cell proliferation and, consequently, cell number. Nonoxidative metabolism of short-chain alcohols, including phospholipase D-mediated synthesis of alcohol phospholipids, and the synthesis of fatty acid alcohol esters are additional mechanisms by which alcohols can affect membrane structure and compromise cell function.

Mitochondrial respiratory activity and superoxide radical generation in the liver, brain and heart after chronic ethanol intake

Functional characteristics of mitochondria isolated from liver, brain and heart were studied in ethanol-fed rats using ethanol administration in drinking water as a model of moderate alcohol intoxication. Our results show a slight decrease in liver cytochrome aa3 content, the mitochondrial alteration which is most consistently observed during chronic ethanol feeding. In liver and heart mitochondria, ethanol consumption led to an increase in state 3 respiration with NAD(+)-linked substrates, whereas no changes were apparent in respiration rates with succinate as substrate. However a decrease was found in state 3 respiration with succinate in brain mitochondria isolated from ethanol-fed rats. Submitochondrial particles (SMP) were used to study the superoxide radical (O2-.) production at the level of antimycin-inhibited regions of the respiratory chain. It appears that there is no clear correlation between ethanol effects on respiration and O2-. production. Whereas O2-. generation remained unchanged in heart mitochondria, an elevation of O2-. generation was observed in brain mitochondria, and in contrast, the rate of O2-. production was decreased in liver mitochondria of the ethanol-group in comparison to the control-group. Our findings support a tissue specificity for the toxic effects of ethanol towards the mitochondria and indicate that mitochondrial free radical mechanisms are involved in ethanol-induced toxicity in the brain.

Effects of flunarizine and diltiazem on physical dependence on barbital in rats

The effects of flunarizine and diltiazem both on development of physical dependence on barbital and on barbital withdrawal signs in rats were examined using the drug-admixed food (DAF) method. Rats were chronically treated with barbital or barbital in combination with flunarizine (fixed at 1.5 mg/g of food) or diltiazem (fixed at 0.75 mg/g of food)-admixed food on the schedule of gradually increasing doses of barbital. Motor incoordination during the treatment was potentiated by coadministration of flunarizine, but not by coadministration of diltiazem. After the termination of drug treatment, the body weight loss and withdrawal scores were significantly suppressed in the group coadministered flunarizine, but not in that coadministered diltiazem. There were no significant differences in plasma barbital levels after the withdrawal between groups. In the substitution test, flunarizine (20 and 40 mg/kg, IP) significantly suppressed the body weight loss and withdrawal scores after the withdrawal, but diltiazem (20 mg/kg, IP) did not. These results indicated that flunarizine suppressed both the development of physical dependence on barbital and barbital withdrawal signs, mainly according to the suppression of convulsions, but not diltiazem, which is known to poorly penetrate into the brain. Therefore, the present findings suggest that central calcium channels may be involved in both the development of physical dependence on barbital and the appearance of barbital withdrawal signs.

Comparative effects of chronic ethanol consumption on the properties of mitochondria from rat brain and liver

The effects of chronic alcohol consumption on biochemical properties of mitochondria isolated from liver and brain were compared in rats. As has been found in previous studies (reviewed in Thayer WS: Ann NY Acad Sci 492: 193-206, 1987) in liver, ethanol consumption led to a 41% decrease in active phosphorylating (state 3) respiration and a 25% decrease in resting (state 4) respiration. These changes resulted in a 23% decrease in the respiratory control ratio (ratio of respiration rate in state 3 to that in state 4). These effects were associated with a 40% decrease in functional cytochrome oxidase content, determined spectrophotometrically as heme aa3. By contrast, in brain mitochondria isolated from the same rats, ethanol consumption did not result in any significant changes in respiration rates, respiratory control ratio, or cytochrome contents. The findings demonstrate a differential pathobiologic response of brain and liver mitochondria to chronic ethanol consumption. Since the liver is predominant in metabolism of ingested ethanol, the findings of this study suggest that the deleterious effects of chronic alcohol consumption on the structure and function of liver mitochondria may be related to ethanol metabolism.

Maintenance of structural and functional characteristics of skeletal-muscle mitochondria and sarcoplasmic-reticular membranes after chronic ethanol treatment

The effect of long-term ethanol intake on the structural and functional characteristics of rat skeletal-muscle mitochondria and sarcoplasmic reticulum was investigated. Functionally, skeletal-muscle mitochondria were characterized by a high respiratory control index and ADP/O ratio and a high State-3 respiration rate with different substrates. These parameters were not significantly different in preparations from control and ethanol-fed rats, except for a small increase in the rate of oxidation of alpha-oxoglutarate/malate in the latter. In submitochondrial particles from the two groups of animals there was no significant difference in cytochrome content, ATPase activity or the activity of respiratory-chain complexes. Mitochondrial membranes from untreated and ethanol-fed rats showed no difference in the baseline e.s.r. order parameter, and both preparations were equally sensitive to disordering by ethanol in vitro. Similarly, sarcoplasmic-reticulum preparations were not significantly affected by long-term ethanol feeding with respect to Ca2(+)-ATPase activity or in baseline order parameter and susceptibility to membrane disordering by ethanol in vitro. These membranes were also equally sensitive to degradation by exogenous phospholipase A2. Ethanol feeding did not alter the class composition of mitochondrial or sarcoplasmic-reticulum membrane phospholipids, nor the acyl composition of individual phospholipid classes. Specifically, the changes in acyl composition that characteristically occur in liver microsomal phosphatidylinositol and liver mitochondrial cardiolipin were not observed in the corresponding phospholipids from skeletal-muscle membranes. In experiments where membrane preparations from liver and skeletal muscle from the same ethanol-fed animals were compared, the liver membranes developed membrane tolerance, with the muscle membranes retaining normal sensitivity to disordering effects by ethanol. It is concluded that: (a) different tissues from the same animals differ in their susceptibility to ethanol; (b) the tissue-specific lack of development of membrane tolerance correlates with a lack of chemical changes in the phospholipids and with a retention of normal function of mitochondria and sarcoplasmic reticulum; (c) effects of chronic ethanol intake on muscle function are not due to a defect in the mitochondrial energy supply.

Alcohol stimulates Na+/Ca2+ exchange in brain mitochondria

Ethanol, at low concentrations, specifically stimulates the Na(+)-dependent Ca2(+)-efflux in brain mitochondria. In addition, at higher concentrations, ethanol inhibits the Na(+)-independent Ca2(+)-efflux. The electrogenic Ca(+)-uptake system is not affected by ethanol. The specific stimulation of Na+/Ca2+ exchange reaches a maximum of 60% stimulation, with half-maximal stimulation at 130 mM ethanol. The inhibition of the Na(+)-independent efflux is proportional to the ethanol concentration, becoming significant only above 200 mM, with 50% inhibition at 0.5 M. The inhibition of the Na(+)-independent efflux is, in large part, due to an inhibition of the activation of the Cyclosporin-sensitive pore. Long-term ethanol-feeding had no effect on the Ca2+ transport systems and their sensitivity to acute ethanol treatment. It is suggested that the stimulation of the Na(+)-dependent Ca2(+)-efflux, which is the dominant Ca2+ efflux pathway in brain mitochondria, contributes to the intoxicating effects of ethanol.