Relation Between Mitochondrial Membrane Potential and ROS Formation

Mitochondria are considered the main source of reactive oxygen species (ROS) in the cell. For this reason they have been recognized as a source of various pathological conditions as well as aging. Chronic increase in the rate of ROS production is responsible for the accumulation of ROS-associated damages in DNA, proteins, and lipids and may result in progressive cell dysfunctions and, in a consequence, apoptosis, increasing the overall probability of an organism's pathological conditions. The superoxide anion is the main undesired by-product of mitochondrial oxidative phosphorylation. Its production is triggered by a leak of electrons from the mitochondrial respiratory chain and the reaction of these electrons with O2. Superoxide dismutase (MnSOD, SOD2) from the mitochondrial matrix, as well as superoxide dismutase (Cu/ZnSOD, SOD1) present in small amounts in the mitochondrial intramembrane space, converts superoxide anion to hydrogen peroxide, which can be then converted by catalase to harmless H2O.In the chapter we describe a relation between mitochondrial membrane potential and the rate of ROS formation. We present different methods applicable for isolated mitochondria or intact cells. We also present experiments demonstrating that a magnitude and a direction (increase or decrease) of a change in mitochondrial ROS production depend on the metabolic state of this organelle.