Fig. 2. Effect of hypoxia (1% O₂ for 10 minutes) on the inhibition of cellular respiration by exogenous CO in HEK293 cells. (i) Tracing of O₂ consumption of control cells incubated in hypoxia. (ii) Tracing of O₂ consumption of cells treated with 20 µM CO under ambient O₂ concentrations. (iii) Tracing of O₂ consumption of cells treated with 20 µM CO in hypoxia. No difference was observed between untreated control cells kept under ambient O₂ concentrations and those incubated in hypoxia. The K_i of CO for cells in hypoxia was calculated to be 0.35 µM. Tracings are representative of at least three independent experiments.