Electrochemistry at the cell membrane-solution interface

The initiation of this process is triggered by a cascade of biochemical processes, which are being studied extensively by numerous research groups (1 ). Depolarization of the plasma membrane and a rise in intracellular calcium levels are hallmarks of the initiation of the exocytotic process. 

The bovine adrenal chromaffin cells used by Wightman et al. typically release roughly 5 attomoles of detectable epinephrine and norepinephrine. Efforts have been made to detect smaller numbers of molecules released via exocytosis to the point where it has been reported that the release of 4700 and 6000 molecules can be detected per event from release of a small portion of transmitter in a vesicle (28, 29). 

Spatially persistent on the minute time scale. Also, there are zones where no release occurs and these do not change position on the scale of minutes. 

Certain cell types, in particular chromaffin and mast cells, are known to synthesize and release more than one messenger molecule. Chromaffin cells synthesize, store, and release epinephrine and norepinephrine, while mast cells synthesize and release serotonin and histamine. In an attempt to determine if corelease of these molecules takes place in chromaffin cells, Pihel et al. used fast scan cyclic voltammetry with a scan rate of 800 V/sec repeated every 16.7 msec at a S-pm diameter carbon fiber UME (6). Expanded potential scan limits were employed to distinguish epinephrine from norepinephrine, because a second oxidation wave is present at large positive potentials for the oxidation of epinephrine o-quinone, an amine, to the imine form of the molecule. The second oxidation wave made it possible to determine whether an individual release event was attributable to epinephrine or norepinephrine. The results from this smdy suggest that the majority of chromaffin cells release either norepinephrine or epinephrine. However, 17% of the cells observed released both epinephrine and norepinephrine, and each secretory vesicle contained either epinephrine or norepinephrine, but in general not both. 

3 Combined electrochemical/electrophysiological measurements patch amperometry 

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