TRPV2 channels mediate insulin secretion induced by cell swelling in mouse pancreatic β-cells.

β-Cell swelling induces membrane depolarization, which has been suggested to be caused at least partly by the activation of cation channels. Here, we show the identification of the cation channels. In isolated mouse pancreatic β-cells, the exposure to 30% hypotonic solution elicited an increase in cytosolic Ca2+ concentration ([Ca2+ ]c ). The [Ca2+ ]c elevation was partially inhibited by ruthenium red, a blocker of several Ca2+ -permeable channels including transient receptor potential vanilloid receptors (TRPV), and by nicardipine, but not by the depletion of intracellular Ca2+ stores with thapsigargin and caffeine. The hypotonic stimulation also increased insulin secretion from isolated mouse islets, which was significantly suppressed by ruthenium red. Expression of TRPV2 and V4 was confirmed in mouse pancreatic islets and the MIN6 β-cell line by RT-PCR, western blotting, and immunohistochemical analyses. However, 4α-phorbol-12,13 didecanoate or GSK1016790A, TRPV4 activators, showed no apparent effect on [Ca2+ ]c in isolated mouse β-cells as well as in MIN6 cells. In contrast, probenecid, a TRPV2 activator, induced an increase in [Ca2+ ]c in MIN6 cells, which was attenuated by ruthenium red. Moreover, the [Ca2+ ]c elevation induced by 30% hypotonic stimulation was significantly reduced by knockdown of TRPV2 with siRNA and by tranilast, a TRPV2 inhibitor. The knockdown of TRPV2 also decreased insulin secretion induced by the hypotonic stimulation. In addition, glucose-stimulated insulin secretion was also significantly reduced in the TRPV2-knockdown MIN6 cells. These results suggest that osmotic cell swelling activates TRPV2 in mouse β-cells, thereby causing membrane depolarization and subsequent activation of voltage-dependent Ca2+ channels and insulin secretion.