A Surprise from Spatiotemporal Analysis of Exocytic Events in Chromaffin Cells

Exocytosis of individual secretory vesicles is mostly being studied by fluorescence imaging of vesicles loaded with a fluorescent marker, by amperometric detection of release of oxidizable transmitters such as catecholamines, or by measurements of membrane capacitance steps resulting from the increase in membrane area upon vesicle fusion. The relation between amperometric detection of catecholamine release and membrane capacitance changes has been characterized directly by patch amperometry and revealed that the amperometric pre spike foot signal (PSF) preceding the amperometric spike reflects release through a narrow fusion pore with fluctuations in catecholamine flux reflecting directly fluctuations of fusion pore conductance.