Adrenaline Release by Chromaffin Cells: Constrained Swelling of the Vesicle Matrix Leads to Full Fusion

The vesicle size determines whether or not the vesicle and cell membranes fully fuse during the exocytosis of neurotransmitters (see picture). Based upon both theoretical and experimental results presented herein, a vesicle of diameter <20–30 nm should always release its load through its nanometer-sized fusion pore.