Insight in the exocytotic process in chromaffin cells: Regulation by trimeric and monomeric G proteins

Catecholamine secretion from chromaffin cells has been used for a long time as a general model to study exocytosis of large dense core secretory granu les. Permeabilization and microinjection techniques have brought the possib ility to dissect at the molecular level the multi-protein machinery involve d in this complex physiological process. Regulated exocytosis comprises dis tinct and sequential steps including the priming of secretory granules, the formation of a docking complex between granules and the plasma membrane an d the subsequent fusion of the granule with the plasma membrane. Key protei ns involved in the exocytotic machinery have been identified. For instance, SNAREs which participate in the docking events in most intracellular trans port steps along the secretory pathway, play a role in exocytosis in both n euronal and endocrine cells. However, in contrast to intracellular transpor t processes for which the highest fusion efficiency is required after corre ct targeting of the vesicles, the number of exocytotic events in activated secretory cells needs to be tightly controlled. We describe here the multis tep control exerted by heterotrimeric and monomeric G proteins on the progr ession of secretory granules from docking to fusion and the molecular natur e of some of their downstream effectors in neuroendocrine chromaffin cells. (C) 2000 societe francaise de biochimie et biologic moleculaire / Editions scientifiques et medicales Elsevier SAS.