THE LATENCY OF EXOCYTOSIS VARIES WITH THE MECHANISM OF STIMULATED RELEASE IN PC12 CELLS

To compare the time course of different mechanisms of chemically stimu lated release, amperometric detection of dopamine was carried out at s ingle PC12 cells. The rapid response of carbon fiber microelectrodes a llowed the detection of single exocytotic events, thus providing time- resolved information about the dynamics of stimulated release, in part icular the latency between the stimulation of a cell and the secretion of catecholamines, On rapid depolarization of the cell membrane cause d 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 simil ar 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.