Suppression of Na+ influx in ATP-depleted hepatocytes.

The change of cytosolic Na+ concentration was examined in ATP-depleted cultured rat hepatocytes. Cytosolic Na+ concentration was increased in the hepatocytes where ATP was more than 95% depleted by chemical hypoxia with 2.5 mM KCN and 0.5 mM iodoacetate as reported in J. Biol. Chem. 266 20062-20069 (1991). However, the effect was due to the iodoacetate-treatment rather than the ATP-depletion, because the Na+ concentration was increased not by KCN but by iodoacetate, while KCN decreased ATP more than iodoacetate. Although oligomycin (10 micrograms/ml) decreased ATP to less than 5%, it did not increase cytosolic Na+ concentration much within 50 min. Ouabain (1.0 mM), an inhibitor of Na(+)-K+ pump, increased the Na+ concentration, and the increase was suppressed by oligomycin These results suggest that Na+ influx was suppressed in ATP-depleted hepatocytes.