Pre-exocytotic mobility of insulin granules in the submembrane space

Background and aims: Current hypotheses of insulin exocytosis provide that a pool of membrane-adjacent secretory granules exists which are in a primed and docked state and await one final trigger, a depolarization-induced influx of Ca2+. This pool is held responsible for the first phase of glucose-induced insulin secretion. A number of recent observations have put this hypothesis into question. Methods: Submembrane granules were visualized by transient transfection of insulin-secreting MIN6 cells with an insulin-EGFP fusion protein and imaged by TIRF microscopy. The cells were perifused with HEPES-buffered Krebs…