Underestimation of the Maximal Capacity of the Mitochondrial Electron Transport System in Oligomycin-Treated Cells

Abstract

The maximal capacity of the mitochondrial electron transport system (ETS) in intact cells is frequently estimated by promoting protonophore-induced maximal oxygen consumption preceded by inhibition of oxidative phosphorylation by oligomycin. In the present study, human glioma (T98G and U-87MG) and prostate cancer (PC-3) cells were titrated with different concentrations of the protonophore CCCP to induce maximal oxygen consumption rate (OCR) within respirometers in a conventional growth medium. The results demonstrate that the presence of oligomycin or its A-isomer leads to underestimation of maximal ETS capacity. In the presence of oligomycin, the spare respiratory capacity (SRC), i.e., the difference between the maximal and basal cellular OCR, was underestimated by 25 to 45%. The inhibitory effect of oligomycin on SRC was more pronounced in T98G cells and was observed in both suspended and attached cells. Underestimation of SRC also occurred when oxidative phosphorylation was fully inhibited by the ATP synthase inhibitor citreoviridin. Further experiments indicated that oligomycin cannot be replaced by the adenine nucleotide translocase inhibitors bongkrekic acid or carboxyatractyloside because, although these compounds have effects in permeabilized cells, they do not inhibit oxidative phosphorylation in intact cells. We replaced CCCP by FCCP, another potent protonophore and similar results were observed. Lower maximal OCR and SRC values were obtained with the weaker protonophore 2,4-dinitrophenol, and these parameters were not affected by the presence of oligomycin. In permeabilized cells or isolated brain mitochondria incubated with respiratory substrates, only a minor inhibitory effect of oligomycin on CCCP-induced maximal OCR was observed. We conclude that unless a previously validated protocol is employed, maximal ETS capacity in intact cells should be estimated without oligomycin. The inhibitory effect of an ATP synthase blocker on potent protonophore-induced maximal OCR may be associated with impaired metabolism of mitochondrial respiratory substrates.

Pravastatin Chronic Treatment Sensitizes Hypercholesterolemic Mice Muscle to Mitochondrial Permeability Transition: Protection by Creatine or Coenzyme Q10

“…The inhibitions were 14, 24, and 40% for ADP-, oligomycin- and FCCP- stimulated respiration, respectively [ n = 8; P = 0.0103; P = 0.0442; P = 0.0004]. The lower rate of FCCP-induced respiration compared to ADP-induced respiration is in agreement with recent data (Ruas et al, 2016) showing that oligomycin treatment previous to FCCP addition leads to an underestimation of maximal respiratory capacity induced by FCCP. In contrast to plantaris, no significant alterations of oxygen consumption rates were observed in soleus muscle ( Figure 1C ).…”

A spontaneous mitonuclear epistasis converging on Rieske Fe-S protein exacerbates complex III deficiency in mice

“…Different oligomycin preparations and concentrations (0.5 µg/ml, sc-201551, Santa Cruz vs 0.4 µg/ml, Sigma, O4876) were used for the F1 and later respirometric panels, respectively. The change in oligomycin preparation, a problem discussed by Ruas et al 46 , may explain why we did not observe decreased leak respiration in the liver of mt-Cyb p.D242N mice in the F1 data. To normalize any difference in mitochondria mass, we set the maximal capacity of the terminal oxidase, CIV, as the reference state (polarographic CIV activity assay).…”

Positive Feedback Amplifies the Response of Mitochondrial Membrane Potential to Glucose Concentration in Clonal Pancreatic Beta Cells

“…Cell respiration in oligomycin-inhibited INS-1E (but not HEK293) cells gradually declined due to unidentified effects on substrate supply to the respiratory chain [49]. ATP synthase inhibition was also found to reduce maximal uncoupled respiration in certain tumor cell lines, but negligibly when these cells were permeabilized, and it was ascribed similarly to impaired metabolism [50]. …”