Contribution of Diffusion to the Oxygen Dependence of Energy Metabolism in Human Neuroblastoma Cells

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Abstract
The oxygen dependence of cellular energy metabolism is normally expressed as a function of the extracellular oxygen pressure. This means it is a function not only of the oxygen dependence of mitochondrial oxidative phosphorylation, but also of the diffusion induced oxygen pressure differences which develop between the extracellular medium and the mitochondria. Evaluation of the relative contributions of the oxygen dependence of mitochondrial oxidative phosphorylation and diffusion has proven difficult due to technical limitations in the methods available for measuring oxygen in biological samples. In general, workers have chosen to continuously add oxygen to the the suspensions of mitochondria and cells in order to generate “steady states” in which the oxygen pressure was essentially unchanging and the oxygen measurements could be made over longer times. Unfortunately, in this approach the oxygen pressure is higher at the site of addition than in the rest of the suspension and regional differences in oxygen pressure in the medium were present and not adequately evaluated. An optical method for measuring oxygen has been recently developed which has both high sensitivity (10−3 M to 10−8 M) and rapid response (< 1 msec) (Vanderkooi and Wilson, 1986; Vanderkooi et al, 1987; Wilson et al, 1987; 1988). This method permits accurate measurements under conditions without continuous addition of oxygen and thereby without differences in the oxygen pressure in the extracellular medium.

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