Calcium Antagonists and Islet Function. VIII. The Effect of Magnesium

Mg2+ in high concentration (10 to 20 mEq/l) caused a dose-related inhibition of glucose-induced 45calcium net uptake and subsequent insulin release in isolated islets. Experiments performed with the isolated perfused pancreas indicated that the inhibitory effect of Mg2+ upon insulin secretion was rapid and reversible. Although excess Mg2+ reduced lactate production by the islets, the process of glucose recognition by the B-cell was apparently unaltered as judged by the inhibitory effect of the hexose upon 45calcium efflux from perifused islets and the resultant accumulation of 45calcium in the islets. Mg2+ in high concentration failed to facilitate 45calcium efflux from the islets, whether in the presence or absence of glucose. These data suggest that the major effect of Mg2+ upon islet function is to inhibit Ca2+ entry in the B-cell.