Low extracellular magnesium does not impair glucose-stimulated insulin secretion

There is an increasing amount of clinical evidence that hypomagnesemia (serum Mg(2+) levels < 0.7 mmol/l) contributes to type 2 diabetes mellitus pathogenesis. Amongst other hypotheses, it has been suggested that Mg(2+) deficiency affects insulin secretion. The aim of this study was, therefore, to investigate the acute effects of extracellular Mg(2+) on glucose-stimulated insulin secretion in primary mouse islets of Langerhans and the rat insulinoma INS-1 cell line. Here we show that acute lowering of extracellular Mg(2+) concentrations from 1.0 mM to 0.5 mM did not affect glucose-stimulated insulin secretion in islets or in insulin-secreting INS-1 cells. The expression of key genes in the insulin secretory pathway (e.g. Gck, Abcc8) was also unchanged in both experimental models. Knockdown of the most abundant Mg(2+) channel Trpm7 by siRNAs in INS-1 cells resulted in a 3-fold increase in insulin secretion at stimulatory glucose conditions compared to mock-transfected cells. Our data suggest that insulin secretion is not affected by acute lowering of extracellular Mg(2+) concentrations.