SYNAPTOTAGMIN-I-DEFICIENT AND SYNAPTOTAGMIN-II-DEFICIENT PC12 CELLS EXHIBIT CALCIUM-INDEPENDENT, DEPOLARIZATION-INDUCED NEUROTRANSMITTER RELEASE FROM SYNAPTIC-LIKE MICROVESICLES

Synaptotagmin I- and Il-deficient PC12 cells (Shoji-Kasai et al. [1]) were used to compare the role of this protein in the calcium-dependent exocytosis of secretory granules and synaptic-like microvesicles (SLM Vs), While neither catecholamine nor protein secretion from secretory granules were altered, the depolarization-induced acetylcholine releas e from SLMVs was no longer calcium-dependent. We propose that within t he exocytotic process of SLMVs, there exist two depolarization-induced steps, One is calcium-dependent and no longer present in synaptotagmi n I- and II-deficient cells. The other is induced by depolarization, d oes not require calcium, and suffices to trigger neurotransmitter rele ase from SLMVs in synaptotagmin I- and II-deficient PC12 cells.