Quantitative analysis of mitochondrial membrane potential heterogeneity in unsynchronized and synchronized cancer cells

Mitochondrial membrane potential (Delta psi m) is a global indicator of mitochondrial function. Previous reports on heterogeneity of Delta psi m were qualitative or semiquantitative. Here, we quantified intercellular differences in Delta psi m in unsynchronized human cancer cells, cells synchronized in G1, S, and G2, and human fibroblasts. We assessed Delta psi m using a two-pronged microscopy approach to measure relative fluorescence of tetramethylrhodamine methyl ester (TMRM) and absolute values of Delta psi m. We showed that Delta psi m is more heterogeneous in cancer cells compared to fibroblasts, and it is maintained throughout the cell cycle. The effect of chemical inhibition of the respiratory chain and ATP synthesis differed between basal, low and high Delta psi m cells. Overall, our results showed that intercellular heterogeneity of Delta psi m is mainly modulated by intramitochondrial factors, it is independent of the Delta psi m indicator and it is not correlated with intercellular heterogeneity of plasma membrane potential or the phases of the cell cycle.