Damien Roussel, Melanie Boël, Mathieu Mortz, Caroline Romestaing, Claude Duchamp, and Yann Voituron

Under nutritional deprivation, the energetic benefits of reducing mitochondrial metabolism are often associated with enhanced harmful pro-oxidant effects and a subsequent long-term negative impact on cellular integrity. However, the flexibility of mitochondrial functioning under stress has rarely been explored during the transition from basal non-phosphorylating to maximal phosphorylating oxygen consumption. Here, we experimentally tested whether ducklings (Cairina moschata) fasted for 6 days and thereafter refed for 3 days, exhibited modifications to their mitochondrial fluxes, i.e. oxygen consumption, ATP synthesis, reactive oxygen species generation (ROS) and associated ratios, such as the electron leak (% ROS/O) and the oxidative cost of ATP production (% ROS/ATP). This was done at different steady state rate of oxidative phosphorylation in both pectoralis (glycolytic) and gastrocnemius (oxidative) muscles. Fasting induced a decrease in the rates of oxidative phosphorylation and maximal ROS release. All these changes were completely reversed by 3 days of refeeding. Yet, the fundamental finding of the present study is the existence of a clear threshold in ROS release and associated ratios, which remained low until a low level of mitochondrial activity is reached (30-40% of maximal oxidative phosphorylation activity).

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