vH + -ATPase-induced intracellular acidification is critical to glucose-stimulated insulin secretion

ABSTRACT Swelling of secretory vesicles is critical for the regulated expulsion of intra-vesicular contents from cells during secretion. At the secretory vesicle membrane of the exocrine pancreas and neurons, GTP-binding G proteins, vH+-ATPase, potassium channels and AQP water channels, are among the players implicated in vesicle volume regulation. Here we report in insulin secreting MIN6 cells, the requirement of vH+-ATPase-mediated intracellular acidification, on glucose-stimulated insulin release. MIN6 cells exposed to the vH+-ATPase inhibitor Bafilomycin A show decreased acidification of the cytosolic compartment that include insulin-carrying granules. Additionally, a loss of insulin granule association with the cell plasma membrane is demonstrated and results in a decrease in glucose-stimulated insulin secretion and accumulation of intracellular insulin. These results suggest that vH+-ATPase-mediated intracellular acidification is required both at the level of secretory vesicles and the cell plasma membrane for cell secretion.