Mechanisms involved in the elevation of glutathione in RAW 264.7 cells exposed to low doses of gamma-rays.
We examined the mechanisms of the elevation of glutathione level induced in macrophage-like RAW 264.7 cells by low doses of gamma-rays. The level increased soon after exposure of the cells to 50 cGy of gamma-rays, peaked between 3 hours and 6 hours and returned almost to the time 0 value by 24 hours post-irradiation. Doses between 25 and 100 cGy significantly increased the glutathione level at 4 hours post-irradiation. However, there was no significant elevation at doses of more than 100 cGy or less than 25 cGy. When the effect of dose rate was examined at a constant absorbed dose of 50 cGy, dose rates of more than 50 cGy/minute significantly increased the GSH level at 4 hours post-irradiation. It was also shown that the elevation of glutathione level in cells irradiated with low doses of gamma-rays followed the induction of mRNA coding for gamma-glutamylcysteine synthetase (gamma-GCS), a rate-limiting enzyme of the de novo glutathione synthesis pathway. When the cells were exposed to the radiation in the presence of genistein, calphostin C or nifedipine, the elevations of glutathione and gamma-GCS mRNA expression were both mostly blocked. EGTA also strongly inhibited these elevations. These results suggest that the tyrosine kinase, calcium channel and protein kinase C activities play an essential role in the low-dose-radiation-induced elevation of cellular glutathione.
Research Institute for Biological Sciences, Science University of Tokyo, Chiba, Japan. kjma@rs.noda.sut.ac.jp
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Kojima
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Teshima
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Yamaoka
D000818:Animals; D002478:Cells, Cultured; D004307:Dose-Response Relationship, Radiation; D004790:Enzyme Induction / Q000528:radiation effects; D005720:Gamma Rays; D005721:Glutamate-Cysteine Ligase / Q000096:biosynthesis; D005978:Glutathione / Q000378:metabolism*; D051379:Mice; D012333:RNA, Messenger / Q000096:biosynthesis / Q000528:radiation effects; D011829:Radiation Dosage; D013997:Time Factors
D012333:RNA, Messenger; D005721:Glutamate-Cysteine Ligase; D005978:Glutathione