Loss of voltage-gated proton channel Hv1 decreases insulin secretion and leads to hyperglycemia and glucose intolerance in mice

Insulin secretion by pancreatic islet beta-cells is regulated by glucose levels and is accompanied by proton generation. The voltage-gated proton channel Hv1 is present in pancreatic beta-cells and extremely selective for protons. However, whether Hv1 is involved in insulin secretion is unclear. Here we demonstrate that Hv1 promotes insulin secretion of pancreatic beta-cells and glucose homeostasis. Hv1-deficient mice displayed hyperglycemia and glucose intolerance because of reduced insulin secretion but retained normal peripheral insulin sensitivity. Moreover, Hv1 loss contributed much more to severe glucose intolerance as the mice got older. Islets of Hv1-deficient and heterozygous mice were markedly deficient in glucose- and K(+)-induced insulin secretion. In perifusion assays, Hv1 deletion dramatically reduced the first and second phase of glucose-stimulated insulin secretion. Islet insulin and proinsulin content was reduced, and histological analysis of pancreas slices revealed an accompanying modest reduction of beta-cell mass in Hv1 knockout mice. EM observations also indicated a reduction in insulin granule size, but not granule number or granule docking, in Hv1-deficient mice. Mechanistically, Hv1 loss limited the capacity for glucose-induced membrane depolarization, accompanied by a reduced ability of glucose to raise Ca(2+) levels in islets, as evidenced by decreased durations of individual calcium oscillations. Moreover, Hv1 expression was significantly reduced in pancreatic beta-cells from streptozotocin-induced diabetic mice, indicating that Hv1 deficiency is associated with beta-cell dysfunction and diabetes. We conclude that Hv1 regulates insulin secretion and glucose homeostasis through a mechanism that depends on intracellular Ca(2+) levels and membrane depolarization.