Common mechanisms for regulated exocytosis in the chromaffin cell and the synapse

Chromaffin granule exocytosis differs in many physiological respects from neuronal synaptic vesicle exocytosis, which has led to the assumption that the two processes occur by distinct mechanisms. While different mechanisms are certainly in operation for the biogenesis of granules and synaptic vesicles, it is now becoming clear that similar mechanisms are used by both beyond this stage. The similarities extend to various aspects of regulated exocytosis, including regulation of the number of vesicles released in response to cell stimulation. Most strikingly, it now appears that the same proteins mediate the docking and fusion of both chromaffin granules and synaptic vesicles, and that homologues of these proteins act similarly in constitutive membrane traffic throughout evolution.