D-glucose Stimulates theNa+/k+Pump in Mouse Pancreatic Islet Cells

Abstract

To determine the effect of D-glucose on the β-cellNa+/k+pump,R86b+influx was studied in isolated, -cell-rich islets of Umeå-ob/obmice in the absence or presence of lmM ouabain. D-glucose (20 mM) stimulated the ouabain-sensitive portion ofR86b+influx by 65%, whereas the ouabain-resistant portion was inhibited by 48%. TheNa+/k+ATPase activity in homogenates of islets of Umeå-ob/obmice or normal mice was determined to search for direct effects of D-glucose. Thus, ouabain-sensitive ATP hydrolysis in islet homogenates was measured in the presence of different D-glucose concentrations. No effect of D-glucose (3–20 mM) was observed in eitherob/obor normal islets at the optimalNa+/k+ratio for the enzyme (135 mMNa+and 20 mMK+). Neither D-glucose (3–20 mM) nor L-glucose or 3-O-methyl-D-glucose (20 mM) affected the enzyme activity at a highNa+/k+ratio (175 mMNa+and 0.7mMk+). Diphenylhydantoin (150 μM) decreased the enzyme activity at optimalNa+/k+ratio, whereas 50 μM of the drug had no effect. The results suggest that D-glucose induces a net stimulation theNa+/k+pump of β-cells in intact islets and that D-glucose does not exert any direct effect on theNa+/k+ATPase activity.