Key result
In platelets, the reduction state of cytochrome c, NADH concentration, and glycolytic output did not change as oxygen concentration declined from 40 to 5 microM.
Contrary to previous hypotheses, platelet mitochondria do not sense oxygen concentrations above 5 microM via changes in cytochrome c reduction state.
Challenges prior platelet oxygen-sensing models; leaves open mechanisms below 5 microM and human relevance.
The range over which cells are sensitive to changes in oxygen concentration remains uncertain. Wilson and colleagues [Wilson, D.F. (1994) Med. Sci. Sports Exerc. 26, 37-43] have suggested that cytochrome oxidase is sensitive to oxygen concentrations below about 40 microM, but proposed that this sensitivity is obscured in intact cells because an increase in reduction state of cytochrome c acts to maintain oxygen consumption. We have tested this hypothesis in platelets, which are small cells (2-4 micrometer diameter, < 0.5 micrometer thick) that do not decrease their rate of oxygen consumption until oxygen concentrations fall below 2.5 microM. Contrary to the expectations of the hypothesis, the reduction state of cytochrome c, the concentration of NADH and the rate of glycolytic output are not changed as oxygen concentration declines from 40 microM down to 5 microM. Therefore, we conclude that at least some cell types contain mitochondria that are not capable of sensing oxygen above 5 microM by the mechanism proposed by Wilson and colleagues.
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Arthur et al. (1999) studied this question. Decreasing oxygen concentration was evaluated on Reduction state of cytochrome c, concentration of NADH, and rate of glycolytic output. In platelets, the reduction state of cytochrome c, NADH concentration, and glycolytic output did not change as oxygen concentration declined from 40 to 5 microM.
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