Vesicular fusion modes in neurons and neuroendocrine cells are associated to different recovery paths of new vesicles. While kiss-and-run implies fast membrane retrieval and “in situ” replenishment of intact vesicles, total collapse is followed by slower clathrin mediated endocytosis, and “de novo” generation, transport and maturation of vesicles. The first event that initiates fusion of vesicles to plasma membrane is the formation of a small fusion pore. Recent publications suggest that the fusion pore is finely regulated by a variety of proteins, which may modulate positively or negatively the opening of the pore, favoring the total collapse of the vesicle in the membrane or the closure of the pore (kiss-and-run). The main goal of this project is to study the relationship between fusion pore stability and the associated processes of endocytosis and secretory vesicles replenishment, after the exocytosis of the immediately releasable pool in mouse chromaffin cells. To reach this goal, we are going to express diverse proteins in primary chromaffin cell cultures, which alternatively promote pore stability (and closure) or pore opening. Variations in pore stability are going to be evaluated by amperometry, and endocytosis and IRP replenishment by cell capacitance measurements. We hypothesize that factors promoting pore closure will favor fast endocytosis and replenishment, while factors promoting pore opening are going to be associated to slow endocytosis and replenishment.