Ruas 2016 PLOS ONE

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Ruas JS, Siqueira-Santos ES, Amigo I, Rodrigues-Silva E, Kowaltowski AJ, Castilho RF (2016) Underestimation of the maximal capacity of the mitochondrial electron transport system in oligomycin-treated cells. PLOS ONE 11:e0150967.

» PMID: 26950698 Open Access

Ruas JS, Siqueira-Santos ES, Amigo I, Rodrigues-Silva E, Kowaltowski AJ, Castilho RF (2016) PLoS One

Abstract: The maximal capacity of the mitochondrial electron transport system (ET-pathway) 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 ET 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 ET 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.

Keywords: Human glioma T98G cells, Human glioma U-87MG cells, Human prostate cancer PC-3 cells

O2k-Network Lab: BR Sao Paulo Kowaltowski AJ

Labels: MiParea: Respiration, Instruments;methods, Comparative MiP;environmental MiP  Pathology: Cancer 

Organism: Human, Rat  Tissue;cell: Nervous system, Genital, Other cell lines  Preparation: Intact cells, Permeabilized cells, Isolated mitochondria 

Regulation: Inhibitor, Substrate  Coupling state: LEAK, OXPHOS, ET  Pathway:HRR: Oxygraph-2k