Monitoring of relative mitochondrial membrane potential in living cells by fluorescence microscopy.

Permeant cationic fluorescent probes are shown to be selectively accumulated by the mitochondria of living cells. Mitochondria-specific interaction of such molecules is apparently dependent on the high trans-membrane potential (inside negative) maintained by functional mitochondria. Dissipation of the mitochondrial trans-membrane and potential by ionophores or inhibitors of electron transport eliminates the selective mitochondrial association of these compounds. The application of such potential-dependent probes in conjunction with fluorescence microscopy allows the monitoring of mitochondrial membrane potential in individual living cells. Marked elevations in mitochondria-associated probe fluorescence have been observed in cells engaged in active movement. This approach to the analysis of mitochondrial membrane potential should be of value in future investigations of the control of energy metabolism and energy requirements of specific biological functions at the cellular level.