The Relation Between Mitochondrial Membrane Potential and Reactive Oxygen Species Formation

Mitochondria are considered one of the main sites of reactive oxygen species (ROS) production in the eukaryotic cells. For this reason, mitochondrial dysfunction associated with increased ROS production underlies various pathological conditions as well as promotes aging. Chronically increased rates of ROS production contribute to oxidative damage to macromolecules, i.e., DNA, proteins, and lipids. Accumulation of unrepaired oxidative damage may result in progressive cell dysfunction, which can finally trigger cell death. The main by-product of mitochondrial oxidative phosphorylation is superoxide, which is generated by the leak of electrons from the mitochondrial respiratory chain complexes leading to one-electron reduction of oxygen. Mitochondrial superoxide dismutase (MnSOD, SOD2) as well as cytosolic superoxide dismutase (Cu/ZnSOD, SOD1), whose smaller pool is localized in the mitochondrial intermembrane space, converts superoxide to H₂O₂, which can be then degraded by the catalase to harmless H₂O.In this chapter, we focus on the relationship between one of the bioenergetic parameters, which is mitochondrial membrane potential, and the rate of ROS formation. We present a set of various methods enabling the characterization of these parameters applicable to isolated mitochondria or intact cells. We also present examples of experimental data demonstrating that the magnitude and direction (increase or decrease) of a change in mitochondrial ROS production depend on the mitochondrial metabolic state.