To define further the influence of ethanol on membranes, its effects on Na+ pump function were studied in monolayer cultures of fetal rat hepatocytes. The effects of ethanol (2 and 4 mg/ml) on total K+ influx, ouabain-sensitive K+ influx, Na+ pump density (from specific [3H]ouabain binding), pump turnover rates and intracellular Na+ were measured following exposure of the cells to ethanol for 1-24 hr. In parallel studies, the effects of ethanol (2 mg/ml) on cell water content and membrane fluidity were measured. Ethanol had no immediate effect on K+ influx, but after 1 hr ethanol in concentrations of 2 and 4 mg/ml decreased the total K+ influx (μmol/1011 cells/sec) from a control of 8.5 ± 0.64 to 4.46 ± 0.50 and 4.09 ± 0.26 respectively (N = 6 for each experiment; P < 0.001). This represented the maximum effect of ethanol since after 6 and 24 hr of ethanol treatment the K+ influx had increased towards control levels but remained significantly (P < 0.01 for 2 mg/ml and P < 0.001 for 4 mg/ml) below that in control cells even at 24 hr. The decrease in K+ influx reflected a decrease in mean ouabain sensitive K+ influx from a control of 5.87 to 3.24 and 2.70 (μmol/1011 cells/sec) after a 1-hr treatment with 2 and 4 mg ethanol/ml medium respectively. Ethanol (2 mg/ml) treatment for 1 hr decreased Na+ pump density (× 105 molecules ouabain per cell) from a control of 2.80 ± 0.30 to 1.70 ± 0.11 (P < 0.001). At 6 and 24 hr [3H]ouabain binding showed a pattern similar to that seen with the K+ influx, tending to return to pretreatment levels. There was no change in individual pump turnover rates in the presence of ethanol. Following exposure to ethanol, cellular Na+ content steadily increased over the first 6 hr and then returned to control levels. When corrected for parallel changes in cell volume, however, intracellular Na+ concentration increased by 17% (P < 0.01) after 1 hr and thereafter remained at this higher level throughout the 24-hr period. Measurements of membrane fluidity showed that it was increased markedly by ethanol at a concentration of 2 mg/ml and that the effect bore a close temporal relationship to the changes in active K+ influx and Na+ pump density. We conclude that ethanol has a depressant effect on hepatic Na+ pump function, resulting in an increase in intracellular Na+ and an eventual gain in cell water. The results suggest that this is due to a decrease in the number of functional Na+ pumps, possibly resulting from the solubilizing effect of ethanol on the plasma membrane.
ASJC Scopus subject areas