Potentiometric dyes: Imaging electrical activity of cell membranes

Voltage sensitive dyes offer the opportunity to monitor neuronal electrical activity where microelectrode measurements are unsuitable or inadequate. This technology is especially powerful for the study of patterns of activity in complex multicellular preparations. It also makes possible the measurement of spatial and temporal variations in membrane potential along the surface of single cells. The fast dyes which have been developed in this laboratory are in the structural class called styryl or naphthylstyryl. These are amphiphilic membrane staining dyes which usually have a pair of hydrocarbon chains acting as membrane anchors and a hydrophilic group which aligns the chromophore perpendicular to the membrane/aqueous interface. The chromophore is believed to undergo a large electronic charge shift as a result of excitation from the ground to the excited state and this underlies the putative electrochromic mechanism for the sensitivity of these dyes to membrane potential. We have used these dyes to map the membrane potential along the surface of single cells with high resolution digital imaging microscopy techniques. These compounds also display remarkable efficiencies for second harmonic generation. Further, the second harmonic signal can be generated from a dye-stained membrane and is modulatable by changing the membrane voltage.