The role of calcium in glucagon release. Studies with verapamil

The role of calcium transport into the pancreatic A2-cell in release of glucagon was studied in the perfused in vitro rat pancreas exposed to the organic calcium-antagonist verapamil (10 and 20 microns). As judged by the inhibitory effect of verapamil, a sufficient influx of calcium was required for glucagon release to be stimulated by either arginine (10 mM) or a lowering of the glucose concentration from 16.6 to 3.3 mM. However, such was not the case for glucose to inhibit the release of glucagon or when the A-2-cell was established in a stimulated state during prolonged exposure to a low, 3.3 mM, glucose concentration. These findings suggest that the role of inwardly directed transport of calcium in the secretory process of the A2-cell is of a complex nature, being dependent on the type of stimulus employed (arginine or glucose) and, in the case of glucose, on the static or dynamic state of the cell. The intimate mechanisms by which calcium exerts such complex effects on the secretory process in the A2-cell remain to be elucidated.