Comparison of apex and bottom secretion efficiency at chromaffin cells as measured by amperometry.

In chromaffin cells, the exocytosis of neuromediators involves the fusion between a secretory vesicle and the cell membrane. Many techniques based on electrophysiology, electrochemistry and fluorescence microscopy allow the study of such a complex process at active zones of single immobilized cells. These techniques can provide an effective analysis either at the apex, either at the base of the cell adhering onto a substrate. For instance, patch-clamp (electrophysiology) and amperometry (electrochemistry) deal with detection at the exposed top of the cell, whereas evanescent field microscopy concerns mainly its bottom, i.e., the zone on which the cell rests onto the surface. However, in chromaffin cells, comparison between the two sets of methods remains to be established and whether apex fusion events are comparable or not to those observed at the base of the cell is an open question. In this work, we compare both active zones upon using the same measurement method, viz., by performing electrochemical detection at these both poles (top and bottom) of bovine chromaffin cells. This is performed upon using carbon fiber microelectrodes (apical analysis) and planar ITO transparent (basal analysis) electrodes, respectively. Our results indicate that the processes monitored at each pole differ though the same technique is used.