Control of Exocytosis in Secretory Cells: the Adrenal Chromaffin Cell

Abstract

Exocytosis of secretory vesicles may occur from cells along one of two pathways: the constitutive pathway or the regulated pathway. In neurons and specialized secretory cells these two pathways co-exist (Burgess and Kelly, 1987). Constitutive secretion involves the exocytosis of vesicles within a short time of their formation and is the mechanism by which membrane components and certain soluble proteins are released. In contrast, in the regulated secretory pathway, the vesicles are stored in the cytoplasm until exocytosis is triggered by a intracellular signal, and is the pathway for secretion of neurotransmitters and many hormones. The regulated secretory pathway in neurons and secretory cells has a number of aspects in common (Cheek and Burgoyne, 1990) and we and many others have chosen to study the bovine adrenal chromaffin cell as a convenient model system for the investigation of regulated exocytosis (Burgoyne, 1984a; Rink and Knight, 1988; Winkler, 1988). The adrenal chromaffin cell is derived, during embryogenesis, from precursors that also give rise to sympathetic neurons and has many neuronlike properties. This review will concentrate on information from work on adrenal chromaffin cells with some reference to work on exocytosis in other secretory cells.