Membrane Fusion during Mast Cell Secretion

Much evidence has been adduced to support exocytosis as the mechanism utilized by a variety of cells to secrete substances stored in intracellular vesicles or granules. Since in all instances the vesicle or granule is bounded or surrounded by a membrane which in turn is separated from the external milieu by the plasma membrane, exocytosis must involve an interaction between two membranes leading to the formation of a channel through which the secretory product leaves the cell . Secretion of histamine and other secretory granule components by mast cells probably occurs not only at the cell surface but also deep in the cell (24) . The extent of membrane interaction required during secretion might be expected to make the mast cell an auspicious object for the investigation of membrane interactions. An ultrastructural search for examples of membrane interaction during mast cell secretion yielded the preliminary results reported here .