Estimation of mean exocytic vesicle capacitance in mouse adrenal chromaffin cells.

Whole-cell membrane capacitance measurements are frequently used to monitor neuronal and nonneuronal secretory activity. However, unless individual 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 capacitance increases of mouse adrenal chromaffin cells and obtain estimates for the capacitance contribution of individual exocytic vesicles between 0.6 and 2 fF. For comparison, measurements of membrane capacitance were combined with amperometric recordings of catecholamine release during intracellular perfusion of chromaffin cells with high [Ca2+]. Crosscorrelation of both signals yielded a mean capacitance contribution of individual catecholaminergic vesicles of 1.3 fF. We suggest that depolarization-induced capacitance increases in mouse adrenal chromaffin cells mainly represent fusion of chromaffin granules.