COMMON MECHANISMS FOR REGULATED EXOCYTOSIS IN THE CHROMAFFIN CELL ANDTHE SYNAPSE

Chromaffin granule exocytosis differs in many physiological respects f rom neuronal synaptic vesicle exocytosis, which has led to the assumpt ion that the two processes occur by distinct mechanisms. While differe nt mechanisms are certainly in operation for the biogenesis of granule s and synaptic vesicles, it is now becoming clear that similar mechani sms are used by both beyond this stage. The similarities extend to var ious aspects of regulated exocytosis, including regulation of the numb er of vesicles released in response to cell stimulation. Most striking ly, it now appears that the same proteins mediate the docking and fusi on of both chromaffin granules and synaptic vesicles, and that homolog ues of these proteins act similarly in constitutive membrane traffic t hroughout evolution.