Involvement of calcium ion in elevation of mRNA for gamma-glutamylcysteinesynthetase (gamma-GCS) induced by low-dose gamma-rays

Purpose. To investigate the mechanism of the intracellular glutathione elev ation induced by low-dose gamma -radiation. Materials and methods: RAW 264.7 cells were irradiated with 1-400 cGy gamma -rays. Intracellular total glutathione content was determined by DTNB-recy cling assay. Expression of mRNA for intracellular glutathione synthesis-rel ated enzymes with or without treatment with Various inhibitors of second me ssengers of gene expression were examined by Northern blot analysis. Results: Expression of mRNA for gamma -glutamylcysteine synthetase (gamma - GCS), a race-limiting enzyme of the de novo glutathione synthesis pathway, was elevated much more than that of glutathione reductase (GR) mRNA after e xposure to 50 cGy gamma -rays. The low-dose gamma -ray-induced gamma -GCS m RNA elevation was abolished by inhibitors of protein kinase C and protein t yrosine kinase, as well as by the calcium ion channel blocker, nifedipine. Calcium-related reagents, such BAPTA/AM and EGTA, chelators of intra- and e xtracellular Ca2+ respectively, and a Ca2+ ionophore (A23187), also strongl y blocked the elevation of gamma -GCS mRNA expression induced by gamma -ray s. Conclusions: The increase of intracellular glutathione in RAW 264.7 soon af ter low-dose gamma -ray exposure mainly occurs through the operation of the de novo pathway, following by the induction of gamma -GCS mRNA, for which elevation of intracellular calcium is required.