Intracellular membrane junctions during the exocytosis of insulin

In the process of insulin release by exocytosis, a fusion between the membranes of secretory vesicles and the plasma membrane occurs which is followed by the rupture of these membranes and the formation of an exocytotic stoma. As revealed by freeze-fracturing, the membrane structure is altered in the region of membrane interaction. An accumulation of membrane-associated particles can be observed in membranes of secretory vesicles contacting the plasma membrane. At the exocytotic stoma the boundary between granule limiting membrane and plasma membrane is occasionally outlined by a ring-like aggregation of membrane-associated particles. The effects of hypertonic solutions on tissue structure indicate that the membrane junctions during exocytosis are permeable to ions and small molecules, forming a communication between the interior of the secretory vesicle and the extracellular space.