Probing endogenous coenzyme Q10 (CoQ10) redox status in intact pulmonary arterial endothelial cells using the CoQ10 homolog, coenzyme Q1 (CoQ1)

The exogenous quinone, CoQ 1 , is reduced predominately via mitochondrial complex I (CI) in intact, cultured bovine pulmonary arterial endothelial cells (PAECs), wherein the hydroquinone (CoQ 1 H 2 ) product can be oxidized at complex III or appear in the extracellular medium. We hypothesized that insofar as CoQ 1 is a homolog of the endogenous CI electron acceptor, CoQ 10 , CoQ 1 reduction kinetics might reflect competition with oxidized CoQ 10 for reduction at CI and provide information regarding CoQ 10 redox status. Cell‐mediated CoQ 1 reduction rates vs CoQ 1 concentration (1–50 μM) were obtained in the presence of cyanide to eliminate CoQ 10 as a CoQ 1 competitor. A CoQ 10 competition model was fit to cell‐mediated CoQ 1 H 2 oxidation and CoQ 1 reduction vs time and CoQ 1 reduction rates vs CoQ 1 concentration curves in the absence of cyanide. The model fit was consistent with CoQ 10 competing with CoQ 1 for reducing equivalents at CI. The 95% nonlinear confidence region for CoQ 10 participating in competition for reducing equivalents at CI was 7–31 mM. The nonlinear confidence region provides an estimate of CoQ 10 redox poise, % CoQ 10 H 2 / (CoQ 10 H 2 + CoQ 10 ) of 57–64%, which is consistent with values reported for total tissue CoQ 10 in various organs. The study reveals the potential utility of CoQ 1 as a probe of CoQ 10 redox status, which may be altered in oxidative stress and lung disease, in PAECs. Funding: HL‐65537,‐24349 and Dept of Veterans Affairs.