Requirement for calcium ion in insulin secretion by the perfused rat pancreas

Abstract

Following a standard glucose stimulus, insulin secretion (determined by immunochemical assay of the total portal vein effluent) was directly dependent or perfusate Ca ion concentrations up to 4 mEq/liter. At C levels greater than this, the total insulin release exhibited a plateau which was independent of C ion concentration. Following a standard 2-min. tolbutamide stimulus, insulin release was directly dependent on the perfusate C concentration throughout the whole spectrum of C concentrations studied (0.59-10.9 mEq/liter). At high Ca levels, insulin secretion was prolonged throughout a 6-min. period of tolbutamide stimulation. Preparations which were perfused with solutions containing glucose, but to which no Ca had been added, failed to have a significant release of insulin. When Ca was added to the perfusates of these preparations, a marked increase in insulin secretion was observed (provided that the Ca deprivation lasted no longer than 20 min.). Ca ion itself will not produce a relaease of insulin, but it is necessary for normal insulin secretion in response to glucose or tolbutamide.