Na+−K+ pump activity and the glucose-stimulated Ca2+-sensitive K+ permeability in the pancreatic B-cell

Abstract

A rise in the extracellular concentration of glucose from an intermediate to a high value changes the burst pattern of electrical activity of the pancreatic B-cell into a continuous firing, and yet activates the B-cell Ca²⁺-sensitive K⁺ permeability. The hypothesis that glucose exerts such effects by inhibiting the Na⁺, K⁺-ATPase was investigated. Ouabain (1 mM) mimicked the effect of 16.7mm glucose in stimulating⁸⁶Rb,⁴⁵Ca outflow and insulin release from perifused rat pancreatic islets first exposed to 8.3mm glucose. The stimulation by ouabain of⁸⁶Rb outflow was reduced in the absence of extracellular Ca²⁺ and almost completely abolished in the presence of quinine, and inhibitor of the Ca²⁺-sensitive K⁺ permeability. In the presence of ouabain, a rise in the glucose concentration from 8.3 to 16.7mm failed to stimulate⁸⁶Rb outflow. However, the rise in the glucose concentration failed to inhibit⁸⁶Rb influx in islet cells, while ouabain dramatically reduced⁸⁶Rb influx whether in the presence of 8.3 or 16.7mm glucose. These findings do not suggest that inhibition of the B-cell Na⁺, K⁺-ATPase represents the mechanism by which glucose in high concentration stimulates⁸⁶Rb outflow and induces continous electrical activity in the B-cell.