Fig. 4.
Correlation between membrane potential and changes in fluorescence. The fluorescent dye partitions across the intracellular and extracellular compartments in a voltage-dependent manner. Upon depolarization of the cells, the dye movement into the cell and subsequent binding to intracellular hydrophobic sites results in enhanced quantum yield of the dye and an increase in fluorescence intensity. Conversely, membrane hyperpolarization triggers dye extrusion from the cells and consequently decreases in fluorescence, because the quantum yield of the dye is low in an aqueous environment.