ESTIMATION OF MEAN EXOCYTIC VESICLE CAPACITANCE IN MOUSE ADRENAL CHROMAFFIN CELLS

Whole-cell membrane capacitance measurements are frequently used to mo nitor neuronal and nonneuronal secretory activity, However, unless ind ividual fusion events can be resolved, the type of the fusing vesicles cannot be identified in these experiments. Here we apply statistical analysis of trial-to-trial variations between depolarization-induced c apacitance increases of mouse adrenal chromaffin cells and obtain esti mates for the capacitance contribution of individual exocytic vesicles between 0.6 and 2 fF, For com parison, measurements of membrane capac itance were combined with amperometric recordings of catecholamine rel ease during intracellular perfusion of chromaffin cells with high [Ca2 +], Crosscorrelation of both signals yielded a mean capacitance contri bution of individual catecholaminergic vesicles of 1.3 fF. We suggest that depolarization-induced capacitance increases in mouse adrenal chr omaffin cells mainly represent fusion of chromaffin granules.