Mitochondrial NADH redox potential impacts the reactive oxygen species production of reverse Electron transfer through complex I.

There is substantial evidence that Reactive Oxygen Species (ROS) play a major part in cell functioning. Although their harmfulness through oxidative stress is well documented, their role in signaling and sensing as an oxidative signal still needs to be investigated. In most cells, the mitochondrial Electron Transport Chain (ETC) is the primary source of ROS. The production of ROS by reverse electron transfer through complex I has been demonstrated both in an experimental context but also in many pathophysiological situations. Therefore, understanding the mechanisms that regulate this ROS production is of great interest to control its harmful effects. We used nigericin, Pi and valinomycin as tools to modulate the pH gradient (∆pH) and the membrane potential (∆Ψ) of the protonmotive force (∆p) in liver and muscle mitochondria to accurately determine how these parameters control the ROS production. We show that a high ∆Ψ is the "sine qua none" condition for ROS production from the reverse electron transfer (RET) through the complex I. However, a high ∆Ψ is not the only condition governing ROS production. Indeed, using tools that modulate the mitochondrial NADH level, we also demonstrate that ROS production is directly related to the mitochondrial redox potential when the membrane potential is almost stable.