Effect of ionizing radiation on liver mitochondrial respiratory functions in mice.
To investigate the radiation effect on mitochondria of the mouse liver in vivo. Livers of BALB/c mice were squeezed out through openings cut on the upper abdomen and radiation doses were delivered only to the livers. Radiation effects on the structure and function of liver mitochondria were evaluated from both respiratory control ratio (RCR) and ADP/O (adenosine 5'-diphosphate/oxygen) ratio supported by two substrates, succinate and glutamate/malate mixtures. The data showed that both state 3 and state 4 respiratory rates were significantly decreased concomitantly with the increase of radiation dose up to 20 Gy. Succinate-supported, but not glutamate/malate-supported, respiratory control ratio, was also decreased with the increase of radiation dose. ADP/O ratios measured from the support of both succinate and glutamate/malate were not changed by gamma-radiation. This differential radiation damage indicated that respiratory control ratio was more vulnerable to radiation than oxidative phosphorylation. Although the functional integrity of ATP synthetic machinery of the mitochondria was not perturbed by ionizing radiation under 20 Gy, the structural integrity of mitochondrial membrane might be affected by ionizing radiation at a dose-dependent manner.