Stability of membrane potential in heart mitochondria: Single mitochondrion imaging

Mitochondrial membrane potential (ΔΨm) plays an important role in cellular activity. Although ΔΨm of intracellular mitochondria are relatively stable, the recent experiments with isolated mitochondria demonstrate that individual mitochondria show frequent fluctuations of ΔΨm. The current study is performed to investigate the factors that stabilize ΔΨm in cells by observing ΔΨm of individual isolated mitochondria with fluorescence microscopy. Here, we report that (1) the transient depolarizations are also induced for mitochondria in plasma membrane permeabilized cells, (2) almost all mitochondria isolated from porcine hearts show the transient depolarizations that is enhanced with the net efflux of protons from the matrix to the intermembrane space, and (3) ATP and ADP significantly inhibit the transient depolarizations by plural mechanisms. These results suggest that the suppression of acute alkalinization of the matrix together with the presence of ATP and ADP contributes to the stabilization of ΔΨm in cells.