TIME-COURSE OF RELEASE OF CONTENT OF SINGLE VESICLES IN BOVINE CHROMAFFIN CELLS

The time course of the spontaneous current spikes produced by release of the catecholamine contents of individual vesicles was examined in b ovine chromaffin cells using carbon filament electrodes. The rate of s pontaneous release was enhanced by adding either LaCl3 (0.01-0.5 mM) o r BaCl2 (2 mM) to the extracellular solution. A paucity of events of v ery short duration was evident from the frequency histograms of the ri se and the decay times. In the scatterograms of the rise and of the de cay times the regression lines are invariably positive (i.e. the longe r the duration of the rise times the longer the duration of the decay times). However, the regression lines never go through the origin but intercept the ordinate (the axis of the decay times) at (+/- SD) 16.1 +/- 6.4 ms (n = 11). On the other hand, the regression lines of paired rise and decay times for the time courses of diffusion are both linea r and go through the origin. This relationship holds irrespective of w hether the diffusion from an instantaneous point source was assumed to occur in an infinite plane or in an infinite volume. Therefore our ex perimental findings are incompatible with the model(s) assuming that d iffusional broadening determines entirely the time course of current s pikes. However, they can be explained, although only partially by the possible slow speed of the electrode. They thus suggest that in chroma ffin cells the duration of exocytosis of individual vesicles is much l onger than in synapses.