Dynamin 1 (dyn1) is required for clathrin-mediated endocytosis in most secretory (neuronal and neuroendocrine) cells. There are two modes of Ca 2ϩ -dependent catecholamine release from single dense-core vesicles: full-quantal (quantal) and subquantal in adrenal chromaffin cells, but their relative occurrences and impacts on total secretion remain unclear. To address this fundamental question in neurotransmission area using both sexes of animals, here we report the following: (1) dyn1-KO increased quantal size (QS, but not vesicle size/content) by Ն250% in dyn1-KO mice; (2) the KO-increased QS was rescued by dyn1 (but not its deficient mutant or dyn2); (3) the ratio of quantal versus subquantal events was increased by KO; (4) following a release event, more protein contents were retained in WT versus KO vesicles; and (5) the fusion pore size (d p ) was increased from Յ9 to Ն9 nm by KO. Therefore, Ca 2ϩ -induced exocytosis is generally a subquantal release in sympathetic adrenal chromaffin cells, implying that neurotransmitter release is generally regulated by dynamin in neuronal cells. Ca 2ϩ -dependent neurotransmitter release from a single vesicle is the primary event in all neurotransmission, including synaptic/ neuroendocrine forms. To determine whether Ca 2ϩ -dependent vesicular neurotransmitter release is "all-or-none" (quantal), we provide compelling evidence that most Ca 2ϩ -induced secretory events occur via the subquantal mode in native adrenal chromaffin cells. This subquantal release mode is promoted by dynamin 1, which is universally required for most secretory cells, including neurons and neuroendocrine cells. The present work with dyn1-KO mice further confirms that Ca 2ϩ -dependent transmitter release is mainly via subquantal mode, suggesting that subquantal release could be also important in other types of cells.

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Our findings suggest that depolarisation-induced Ca(2+) influx plays dual roles in regulating exocytosis in rat pancreatic beta cells by triggering vesicle fusion and replenishing the vesicle pool to support sustained insulin release. Therefore, Ca(2+) influx may be important for glucose-stimulated insulin secretion.