Membrane potentials spatial imaging

The dominant technologies (outlined above) utilised to determine biological membrane potentials are optically based and particularly involve fluorescence. Thus spatial imaging is a logical extension of these spectroscopic applications. The use of a modified electrode technology has also been utilized to acquire imaging data in which the electrode is rastered over a cell surface to identify localization of ion transport behaviour and by implication spatial variations of the transmembrane potential... 

A more direct optical method has been introduced whereby a membrane-permeant, charged dye equilibrates across the membrane of interest. Ideally the dye will equilibrate rapidly and show minimal binding to materials on either side of the membrane (34). Using quantitative confocal fluorescence microscopy, the fluorescence of the dye on either side of the membrane is measured as fluorescence intensity is linearly proportional to fluorophore concentration, the measured intensities can be substituted for the ion concentrations ([M" ] and [M ]o) in equation 1 and the potential obtained (34). This technique is ultimately limited by the spatial resolution of the confocal microscope—it works well for large compartments in whole cells. Recent computational approaches to image analysis have allowed the spatial resolution to be increased to the level where mitochondrial membrane potential can be monitored by such means in individual cells (35). 

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