Effect of chronic ethanol treatment on specific [3H]ouabain binding to (Na+ + K+)-ATPase in different areas of cat brain

Ethanol-induced changes in membrane ATPases: inhibition by iron chelation

The effect of chronic ethanol intake, with and without an iron chelator, on the activity of rat membrane ATPases was investigated. Using the intragastric feeding model, male Wistar rats (250 g) were fed a liquid diet and ethanol for 1 month. In control pair-fed animals, ethanol was isocalorically replaced by dextrose. In addition to the above groups, two groups of animals (dextrose or ethanol-fed) also received an oral iron chelator (1,2-dimethyl-3-hydroxypyrid-4-one, L1) (25 mg/kg/day for 30 days). The blood ethanol levels were maintained between 150 and 300 mg/dL. Red cells were washed immediately with ice-cold saline, membranes were prepared, and ATPases were measured. The mean Ca2+ pump ATPase in animals fed ethanol was lower than in dextrose-fed controls. In contrast, Na+/K+ pump ATPase was enhanced following chronic ethanol treatment. The addition of L1 to the diet prevented the changes in both the Ca(2+)-ATPase and Na+/K(+)-ATPase in ethanol-fed rats. Although the exact mechanism for the prevention of changes in ATPase activity by L1 is unknown, it is not a result of non-specific interaction between the chelator and membranes. Incubation of purified membranes with different concentrations of L1 for 60 min at 37 degrees had no effect on the activity of the ATPase. In conclusion, chronic intake of ethanol specifically inhibited Ca2+ pump ATPase and enhanced Na+/K(+)-ATPase in rat red blood cell membranes. The iron chelator, L1, corrected both of these ethanol-induced changes.

Regulation of Na+, K(+)-ATPase by chronic ethanol exposure of PC 12 cells

The effects of chronic ethanol exposure on Na+, K(+)-ATPase were investigated in PC 12 cells. Inclusion of ethanol in the Na+, K(+)-ATPase assay (i.e. in vitro addition of ethanol) inhibited enzyme activity. Conversely, intrinsic Na+, K(+)-ATPase activity was increased after chronic ethanol exposure of the cells. This increase in Na+, K+ pumps occurred without any alteration in the inhibitory effects of in vitro ethanol. A similar response was observed when the chronic treatments were carried out using serum-free defined medium. The effects of other agents, which like ethanol decrease membrane order, were investigated. The addition of ketamine and tert-butanol in vitro caused a concentration-dependent inhibition of Na+, K(+)-ATPase activity. However, chronic exposure of the PC 12 cells to tert-butanol or ketamine did not alter either intrinsic Na+, K(+)-ATPase activity or the inhibitory effects of ethanol in vitro. Maintenance of PC 12 cells in medium containing ethanol resulted in an increase in the intracellular content of Na+ without any change in the K+ levels. In contrast, maintenance of the cells in medium containing tert-butanol did not alter intracellular levels of Na+ or K+. The present study shows that the ethanol-induced increase in Na+, K+ pumps involved an increase in the intracellular content of Na+. This increase in Na+ content did not appear to be secondary to an inhibition of Na+, K(+)-ATPase activity.

Increases in Na+,K+-ATPase activity of erythrocytes and skeletal muscle after chronic ethanol consumption: evidence for reduced efficiency of the enzyme

Increased Na+,K+-ATPase activity observed after chronic ethanol consumption has been examined to determine whether the increase is due to changes in the kinetic properties of the enzyme or increases in the amount of enzyme in the membranes examined. In skeletal muscle and erythrocyte ghosts from rat, as well as from humans, increased Na+,K+-ATPase activity in ethanol-consuming individuals was not accompanied by an increase in the number of ouabain binding sites. In studies with intact human erythrocytes, similar ouabain-sensitive 22Na+ and 86Rb+ pumping rates were observed between normal and ethanol-consuming individuals and the Na+ to Rb+ pumping ratio was found to be 1.5 in all cases. However, ouabain-sensitive lactate plus Pi formation was increased in cells from alcoholic individuals. Thus these data suggest that increased enzyme activity may be due to a kinetic alteration of the Na+,K+-ATPase and that the enzyme may be less efficient in coupling ion pumping to ATP hydrolysis than the enzyme in normal cells.

Erythrocyte 3H-ouabain binding and digitalis treatment in ethanol addicted patients

The binding of 3H-ouabain to human erythrocytes was analyzed in a population of hospitalized male ethanol addicted patients under long term digitalis treatment. In the non-alcoholic patient group the long term digitalis treatment induced an increase in Bmax and Kd values; such modification was not observed in the alcoholic patients. Chronic alcohol intake itself induced an increase in 3H-ouabain kinetic parameters. These observations confirm that ouabain binding to human erythrocytes is subject to pharmacological and toxicological regulation and that adaptive changes in peripheral tissues can be useful in predicting possible parallel modifications in other less accessible tissues.

Quantitative autoradiography of [3H]ouabain binding sites in rat brain

In vitro quantitative autoradiography was used to localize in rat brain binding sites for [3H]ouabain, an inhibitor of the Na+,K+-ATP-ase. High levels of [3H]ouabain binding sites were found in the superior and inferior colliculi, the mammillary nucleus, the interpeduncular nucleus, and in various divisions of the olfactory, auditory and somatomotor systems. The heterogeneous distribution of [3H]ouabain binding closely parallels the regional brain glucose consumption as determined by the [14C]deoxyglucose method. Lesion studies of the rat hippocampus using the excitotoxin, ibotenic acid, showed both a marked decrease of neuronal cell types on the injected side and a corresponding decrease in [3H]ouabain binding, indicating that some of the [3H]ouabain binding sites are localized to neurons. The close correlation between [3H]-ouabain binding and regional glucose utilization provides further evidence for a linkage between glucose utilization and the neuronal Na+,K+-ATPase.