Cytochrome C as an amplifier of ROS release in mitochondria.

The influence of exogenous cytochrome c on reactive oxygen species (ROS) formation and its dependence on mitochondrial permeability transition pore (MPTP) opening is studied in rat liver mitochondria. Fluorescent probe dichlorofluorescein (DCF) was used. It was shown that MPTP activation by increasing concentrations of Ca2+ in the medium results in the increase in mitochondrial ROS production and oxygen consumption, but the decrease in matrix calcium retention, dependent on the amount of added Ca2+. Cytochrome c in the incubation medium does not much influence ROS formation when MPTP opening is blocked by cyclosporine A. However, in the presence of cytochrome c MPTP opening is accompanied by dramatic increase in ROS production. Steep rise in DCF fluorescence because of matrix ROS formation is sensitive to MPTP opening and is not resulted from the direct interaction between the probe and cytochrome c outside the mitochondria. To explain obtained data the hypothesis is put forward that MPTP could serve for ROS exchange between the matrix and the medium where heme iron of cytochrome c would act as a catalytic center to enhance ROS production. We suppose that apart of its conventional function, cytochrome c which is not involved in electron transport, could serve in such way as the amplifier of ROS production which in turn would provide a background for the development of apoptosis due to MPTP opening.