Spectrophotometric monitoring of O2 delivery to the exposed rat kidney

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Abstract
Optical spectrophotometry was used to measure changes in the oxidation-reduction state of cytochrome c oxidase in the in situ rat kidney. Alterations in the redox state of cytochrome c oxidase were monitored during variations in the amount of oxygen being delivered to the animal. Spectral analyses were performed on whole kidney, cortical tubule suspensions, and blood (the latter flowing freely through surgically implanted femoral arteriovenous shunts). Reaction spectra identified the location of the absorption maxima for reduced cytochrome c oxidase to be at approx. 605 nm. Additional spectral analysis indicated that hemoglobin oxygenation-deoxygenation changes had minimal artifactual interference on the cytochrome redox signals. The present results indicate that mitochondrial cytochrome c oxidase is not maximally oxidized in the in situ kidney of anesthetized rats at arterial oxygen in the in situ kidney of anesthetized rats at arterial oxygen tensions within the normal physiological range. The redox state of the enzyme in vivo is altered by changes in the level of inspired oxygen over a wide range. The current data are consistent with the existence of nonuniform regions of aerobic respiration occurring in the in situ kidney.