Plasma membrane Ca2+-ATPase overexpression reduces Ca2+ oscillations and increases insulin release induced by glucose in insulin-secreting BRIN-BD11 cells

In the mouse beta-cell, glucose generates large amplitude oscillations of the cytosolic-free Ca2+ concentration ([Ca2+](i)) that are synchronous to insulin release oscillations. To examine the role played by [Ca2+](i) oscillations in the process of insulin release, we examined the effect of plasma membrane Ca2+-ATPase (PMCA) overexpression on glucose-induced Ca2+ oscillations and insulin release in BRIN-BD11 cells. BRIN-BD11 cells were stably transfected with PMCA2wb. Overexpression could be assessed at the mRNA and protein level, with appropriate targeting to the plasma membrane assessed by immunofluorescence and the increase in PMCA activity. In response to K+, overexpressing cells showed a markedly reduced rise in [Ca2+](i). In response to glucose, control cells showed large amplitude [Ca2+](i) oscillations, whereas overexpressing cells showed markedly reduced increases in [Ca2+](i) without such large oscillations. Suppression of [Ca2+](i) oscillations was accompanied by an increase in glucose metabolism and insulin release that remained oscillatory despite having a lower periodicity. Hence, [Ca2+](i) oscillations appear unnecessary for glucose-induced insulin release and may even be less favorable than a stable increase in [Ca2+](i) for optimal hormone secretion. [Ca2+](i) oscillations do not directly drive insulin release oscillations but may nevertheless intervene in the fine regulation of such oscillations.