Radiosensitivity of parenchymal hepatocytes as a function of oxygen concentration.
To investigate the mechanism(s) of hepatocyte radioresistance (D0 2.7 Gy), the radiosensitivities of respiring (37 degrees C) and nonrespiring (0 degrees C) hepatocytes were determined as a function of oxygen concentration. Fischer 344 female rat hepatocytes were isolated by liver perfusion, equilibrated in Leibowitz-15 media with different oxygen tensions, and exposed to 60Co radiation at either 37 or 0 degrees C. Cell survival and DNA single-strand breaks were used as the biological end points of radiosensitivity. The K value for respiring hepatocytes (37 degrees C) was 14.3 +/- 0.5 mm Hg O2 (18.8 +/- 0.7 mumol O2/liter), demonstrating that the K value for freshly isolated parenchymal hepatocytes is significantly greater than those previously obtained for cultured cells. In contrast, the K value for nonrespiring hepatocytes (0 degree C) is 1.4 +/- 0.4 mm Hg O2 (3.7 +/- 1.0 mumol O2/liter) indicating that hepatocyte respiration results in a plasma membrane-to-nucleus oxygen gradient of approximately 12.9 +/- 0.6 mm Hg (15.1 +/- 1.2 microns O2/liter). The hypothesis that the hepatic nucleus typically resides in a hypoxic condition, although the liver is uniformly perfused with well-oxygenated blood, is supported by (1) the nonradom perinuclear distribution of the mitochondria, (2) the high cellular respiration rate, and (3) the large intracellular oxygen diffusion distance in hepatocytes (25 microns diameter).
Alati
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Laboratory of Pathology, ENEA Centro Richerche Energia, Casaccia, Rome, Italy.
Van Cleeff
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Jirtle
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RL
D000818:Animals; D002470:Cell Survival / Q000528:radiation effects; D003037:Cobalt Radioisotopes; D005260:Female; D066298:In Vitro Techniques; D008099:Liver / Q000166:cytology / Q000528:radiation effects*; D010100:Oxygen / Q000502:physiology*; D010313:Partial Pressure; D011836:Radiation Tolerance; D051381:Rats; D011916:Rats, Inbred F344
D003037:Cobalt Radioisotopes; D010100:Oxygen