Comparison of exocytotic mechanisms between acetylcholine- and catecholamine-containing vesicles in rat pheochromocytoma cells

The molecular mechanisms of exocytosis from two types of secretory organelles, synaptic-like microvesicles and secretory vesicles, were compared by measuring acetylcholine (ACh) and catecholamine (CA) release from a newly isolated PC12 subclone, PC12-C3 which contains a high level of Ach. Digitonin-permeabilized PC12-C3 cells released both transmitters with similar Ca²⁺ dependency. Ca²⁺-evoked ACh and CA release from permeabilized cells were increased in the presence of MgATP, suggesting the existence of a MgATP-dependent priming step prior to the Ca²⁺-triggered fusion step in both ACh release and CA release. The non-hydrolyzable analogue of GTP, guanosine 5'(γ- thio)triphosphate (GTPγS), produced both ACh and CA release from permeabilized cells in the absence of Ca²⁺. Pretreatment with a phorbol ester which activates protein kinase C, potentiated depolarization-induced ACh and CA release from unpermeabilized cells. These results indicate that exocytosis from two distinct vesicle populations are mediated by the same basic molecular mechanisms.