‘Full fusion’ is not ineluctable during vesicular exocytosis of neurotransmitters by endocrine cells

International audienceVesicular exocytosis is an essential and ubiquitous process in neurons and endocrine cells by which neurotransmitters are released in synaptic clefts or extracellular fluids. It involves the fusion of a vesicle loaded with chemical messengers with the cell membrane through a nanometric fusion pore. In endocrine cells, unless it closes after some flickering (" Kiss-and-Run " events), this initial pore is supposed to expand exponentially leading to a full integration of the vesicle membrane into the cell one, a stage called " full fusion ". We report hereafter a compact analytical formulation that allows extracting precise measurements of the fusion pore expansion extent and rate from individual amperometric spikes time-courses. These data definitively establish that during release of catecholamines fusion pores enlarge at most to ca. one fifth of the radius of their parent vesicle, hence ruling out the ineluctability of " full fusion "