Characterization of the glucose-induced lowering of sodium in mouse pancreatic beta-cells.

The mechanisms for glucose regulation of the sodium content of the pancreatic beta-cells were examined using aggregates of cells prepared from ob/ob-mice of a local colony. Exposure to glucose rapidly resulted in a protracted lowering of the sodium content as estimated with integrating flame photometry. Sodium became decreased after addition of 1 mmol l-1 glucose, and this effect was maximal with 5 mmol l-1 of the sugar. The effects of low glucose concentrations on the sodium content could not be mimicked by the poorly metabolized 3-o-methyl-D-glucose, and it disappeared in the presence of the metabolic inhibitor antimycin A. The significance of the Na/K pump for maintaining low sodium was illustrated by a substantial increase of the element in the presence of ouabain. However, there was no indication that glucose-induced lowering of sodium reflected activation of this pump when measuring the ouabain-sensitive uptake of 86Rb+. Neither bumetanide nor the bromo derivatives of cyclic AMP or cyclic GMP modified the glucose action on the sodium content. In evaluating whether the effect of glucose was mimicked by other inhibitors of the K+ permeability it was observed that 100 mumol l-1 quinine, but not tolbutamide, decreased sodium. It is concluded that the beta-cell is exceptional among excitable cells in responding to its natural physiological stimulant (glucose) by reduction of sodium. Acting in this way glucose facilitates the removal of Ca2+ from the cytoplasm.