Figure 3.

Proton leak kinetics in thymocytes from WT and UCP2-deficient mice. Titrations were performed as described in Materials and Methods. State 4 respiration (i.e., the cells do not synthesize ATP) was induced by incubation with 160 ng/ml oligomycin (top right-hand points of each curve). ΔΨ_m was altered by titrations with different concentrations of myxothiazol (40, 80, and 480 nM). Data are means ± SEM (n = 6 and n = 5 cell preparations for WT and UCP2-deficient thymocytes, respectively). At steady state, the number of protons pumped by the complexes of the electron-transport chain equals the number of protons that leak back into the mitochondrial matrix. Because proton pumping and oxygen consumption are stoichiometrically linked, the oxygen consumption rates at any given potential reflect proton leak across the inner mitochondrial membrane.