The role of Ca2+ as a trigger for membrane fusion.

As revealed by freeze-fracturing, secretory vesicles isolated from pancreatic islet cells fuse when incubated with low concentration of Ca2+. The properties of this process are described and were found to be similar to those investigated with isolated secretory vesicles from different tissue origin. Secretory vesicle fusion is compared mainly with the ionic requirements of insulin secretion by the pancreatic B-cells and exocytosis by other secretory cells.