CALMODULIN INCREASES THE INITIAL RATE OF EXOCYTOSIS IN ADRENAL CHROMAFFIN CELLS

The effect of calmodulin on exocytosis in bovine adrenal medullary chr omaffin cells was examined by the use of patch-clamp capacitance recor ding. Calmodulin was dialysed into cells via the patch-pipette and cel ls stimulated by depolarisation. Following a test stimulation, cells w ere dialysed with a control or with a calmodulin containing buffer for 10mins and then were stimulated at 2min intervals thereafter. The inc lusion of calmodulin in the pipette did not increase Ca2+ currents whi ch instead decreased during dialysis. The presence of calmodulin, howe ver, resulted in a 2-fold increase in the initial rate of exocytosis d uring the 10min depolarisation step. These results demonstrate the uti lity of the patch-clamp capacitance technique for the examination of t he effect of soluble proteins on exocytosis and in conjunction with pr evious work on permeabilised chromaffin cells suggest that calmodulin regulates late steps in Ca2+-dependent exocytosis.