Analysis of submembrane insulin granule number and behavior during the initial phase of secretion – dynamic measurements using TIRF microscopy

Background and aims: The release of a pool of membrane-adjacent secretory granules which are in a primed and docked state and await one final trigger, a depolarization-induced influx of Ca2+, is held responsible for the first phase of glucose-induced insulin secretion. Recently, we observed that 15 mM K+ led to a 20 mV depolarization and to a lasting increase of the cytosolic Ca2+ concentration ([Ca2+]i), but only to a modest transient increase in secretion, suggesting that the effect of depolarization on insulin secretion is only incompletely understood. Methods: Insulin secretion was measured by perifusion of…