PATCH-CLAMP CAPACITANCE ANALYSIS OF THE EFFECTS OF ALPHA-SNAP ON EXOCYTOSIS IN ADRENAL CHROMAFFIN CELLS

We have examined the effect of alpha-SNAP on exocytosis in adrenal chr omaffin cells by direct assay of exocytosis using patch-clamp capacita nce analysis. Cells were recorded using the whole cell patch-clamp con figuration and the cells dialysed with control pipette solution or wit h a pipette solution containing alpha-SNAP or the deletion mutant alph a-SNAP(41-295). The deletion mutant was found to be unable to bind to syntaxin allowing a test of the requirement for syntaxin-binding for a ny effect of alpha-SNAP on exocytosis. Following cell dialysis for 10 minutes, cells were depolarised five times at 2 minute intervals. At e ach depolarisation step cells dialysed with alpha-SNAP showed a signif icant increase in both the initial rate and extent of exocytosis which was seen as a rise in membrane capacitance. This increase in exocytos is was not observed with alpha-SNAP(41-295) which instead produced som e inhibition of the extent but had no effect on the initial rate of ex ocytosis. These results show directly that alpha-SNAP has a specific a nd marked stimulatory effect on exocytosis in chromaffin cells.