Reflectance spectrophotometry of cytochrome aa3 in vivo

Abstract

Measurements of changes in the oxidation-reduction level of cytochrome aa3, in the oxygenation state of Hb and in the local volume of blood were made in approximately 3 mm diameter fields on the surface of the intact cerebral cortex of cats (cerveau isole preparations) by differential reflectance spectrophotometry. Standard transillumination spectrophotometry in the split-beam mode was used to assess the contribution of Hb in solution and in red blood cells at the cytochrome wavelengths in the steady state. Reflectance split-beam spectrophotometry established that cytochrome aa3 absorption changes could be recorded from the normally perfused tissue. Dual-wavelength reflectance spectrophotometry during anoxic and ischemic episodes confirmed that the reduction level of cytochrome aa3 could be monitored in spite of large changes in blood volume or Hb oxygenation state. Reaction spectra identified the cytochrome aa3 absorption peak. When the cortex was stimulated to activity, cytochrome aa3 became more oxidized. Provision of increased CO2 or O2 in the inspired gas mixture produced an oxidation of cytochrome aa3. It became reduced during periods of hypoxia, anoxia or ischemia. The high resting reduction level of cytochrome aa3, its O2 sensitivity and the oxidative responses to increased activity differ markedly from those of isolated mitochondria and may relate to ion transport activity of the cerebral cortex. Apparently this reaction complex is lost in the in vitro preparation.