Abstract
Purpose : To investigate the mechanism of the intracellular glutathione elevation induced by low-dose gamma-radiation. Materials and methods : RAW 264.7 cells were irradiated with 1-400 cGy γ-rays. Intracellular total glutathione content was determined by DTNB-recycling assay. Expression of mRNA for intracellular glutathione synthesis-related enzymes with or without treatment with various inhibitors of second messengers of gene expression were examined by Northern blot analysis. Results : Expression of mRNA for γ-glutamylcysteine synthetase (γ-GCS), a rate-limiting enzyme of the de novo glutathione synthesis pathway, was elevated much more than that of glutathione reductase (GR) mRNA after exposure to 50 cGy γ-rays. The low-dose γ-ray-induced γ-GCS mRNA elevation was abolished by inhibitors of protein kinase C and protein tyrosine kinase, as well as by the calcium ion channel blocker, nifedipine. Calcium-related reagents, such BAPTA/AM and EGTA, chelators of intra- and extracellular Ca 2+ respectively, and a Ca 2+ ionophore (A23187), also strongly blocked the elevation of γ-GCS mRNA expression induced by γ-rays. Conclusions : The increase of intracellular glutathione in RAW 264.7 soon after low-dose gamma-ray exposure mainly occurs through the operation of the de novo pathway, following by the induction of γ-GCS mRNA, for which elevation of intracellular calcium is required.
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