Figure 1. Schematic of the major players involved in cellular respiration and the effect of FCCP and sodium azide.
Transfer of electrons from NADH to the ETC complex I results in the generation of an electrochemical gradient across the inner mitochondrial membrane as protons get pumped across it. Protons flowing back into the mitochondrial matrix from the intermembrane space via complex V results in ATP synthesis. Addition of FCCP results in the uncoupling of this process by disrupting the mitochondrial membrane potential and thereby ATP synthesis, while oxygen consumption continues, allowing for the measurement of maximal OCR. Sodium azide (NaN3) is an inhibitor of complexes IV and V, thereby allowing for the measurement of non-mitochondrial respiration.