D-glucose Stimulates the Na+/K+ Pump in Mouse Pancreatic Islet Cells

To determine the effect of D-glucose on the β-cellNa⁺/K⁺ pump, ⁸⁶Rb⁺ influx was studied in isolated,-cell-rich islets of Umeå-ob/ob mice in the absenceor presence of lmM ouabain. D-glucose (20 mM)stimulated the ouabain-sensitive portion of ⁸⁶Rb⁺influx by 65%, whereas the ouabain-resistantportion was inhibited by 48%. The Na⁺/K⁺ ATPaseactivity in homogenates of islets of Umeå-ob/obmice or normal mice was determined to search fordirect effects of D-glucose. Thus, ouabain-sensitiveATP hydrolysis in islet homogenates was measuredin the presence of different D-glucose concentrations.No effect of D-glucose (3–20 mM)was observed in either ob/ob or normal islets atthe optimal Na⁺/K⁺ ratio for the enzyme (135 mMNa⁺ and 20 mM K⁺). Neither D-glucose (3–20 mM)nor L-glucose or 3-O-methyl-D-glucose (20 mM)affected the enzyme activity at a high Na⁺/K⁺ratio (175 mM Na⁺ and 0.7mM K⁺). Diphenylhydantoin(150 μM) decreased the enzyme activity atoptimal Na⁺/K⁺ ratio, whereas 50 μM of the drughad no effect. The results suggest that D-glucoseinduces a net stimulation the Na⁺/K⁺ pump of β-cells in intact islets and that D-glucose doesnot exert any direct effect on the Na⁺/K⁺ ATPase activity.