The latency of exocytosis varies with the mechanism of stimulated release in PC12 cells

To compare the time course of different mechanisms of chemically stimulated release, amperometric detection of dopamine was carried out at single PC12 cells. The rapid response of carbon fiber microelectrodes allowed the detection of single exocytotic events, thus providing time-resolved information about the dynamics of stimulated release, in particular the latency between the stimulation of a cell and the secretion of catecholamines. On rapid depolarization of the cell membrane caused by application of 105 mM K⁺, almost immediate (6 ± 1 s) release of dopamine was observed. Stimulation with 1 mM nicotine, involving the stimulant binding to a ligand-gated ion channel, resulted in a short (37 ± 5 s) delay between stimulation and secretion. Application of 1 mM muscarine to the cells caused a long (103 ± 11 s) latency before exocytosis was detected. A biphasic response that appeared to be similar to a combination of nicotine- and muscarine-stimulated release was observed when cells were stimulated with 10 mM acetylcholine. Thus, it appears that the dynamics of stimulated release at single PC12 cells is significantly affected by the mechanism leading to exocytosis.