Lack of oxygen sensing by mitochondria in platelets

The range over which cells are sensitive to changes in oxygen concentration remains uncertain. Wilson and colleagues [Wilson, D.F. (1994) Med. Sci. Sp orts Exerc. 26, 37-43] have suggested that cytochrome oxidase is sensitive to oxygen concentrations below about 40 mu M, but proposed that this sensit ivity is obscured in intact cells because an increase in reduction state of cytochrome c acts to maintain oxygen consumption. We have tested this hypo thesis in platelets, which are small cells (2-4 mu m diameter, < 0.5 mu m t hick) that do not decrease their rate of oxygen consumption until oxygen co ncentrations fall below 2.5 mu M Contrary to the expectations of the hypoth esis, the reduction state of cytochrome c, the concentration of NADH and th e rate of glycolytic output are not changed as oxygen concentration decline s from 40 mu M down to 5 mu M. Therefore, we conclude that at least some ce ll types contain mitochondria that are not capable of sensing oxygen above 5 mu M by the mechanism proposed by Wilson and colleagues.