Effects of various modifiers of insulin release on the lanthanum-nondisplaceable45ca2+ uptake by isolated pancreatic islets

Abstract

The uptake of⁴⁵Ca²⁺ by a lanthanum-nondisplaceable pool in pancreatic islets was studied. Raising the extracellular D-glucose concentration from 3 to 20 mM stimulated the⁴⁵Ca²⁺ uptake in hand-dissected islets of ob/ob-mice as well as in collagenase-isolated islets of ob/ob or normal mice. The effect was dose-dependent in the range of 0–20 mM D-glucose and was seen throughout a wide range of extracellular calcium concentrations (16 μmol — 2.56 mmol of Ca²⁺ added per litre of medium). The⁴⁵Ca²⁺ uptake was also enhanced by other known insulin secretagogues (D-mannose, L-leucine, tolbutamide) and was uninfluenced by compounds lacking insulinreleasing capacity (3-O-methyl-D-glucose, L-glucose, D-galactose, D-leucine). The stimulatory effect of D-glucose was blocked by inhibitors of glucoseinduced insulin release (D-mannoheptulose, diazoxide, L-adrenaline). The results support the view that the lanthanum-nondisplaceable calcium pool is related to the insulin-releasing mechanism, although the exact nature of this relationship is still unclear.