The association of vesicular contents and its effects on release.

The oxidation of catecholamines with a carbon-fiber electrode can be used to monitor exocytosis at the single cell level at a variety of different types of cells. These measurements allow release to be followed from individual vesicles and have revealed several unique aspects concerning the coupling between release and storage. The strong association of the vesicular components in chromaffin cells dictates the time course of extrusion of the vesicle contents. Furthermore, liberation of the Ca(2+) normally stored within the vesicles can promote exocytosis without an external Ca(2+) source.