Deficiency in fast repair process of potentially lethal damage induced by X-irradiation in fibroblasts derived from LEC strain rats

The time course for the repair of PLD in LEC and WKAH rat cells irradiated at 5 Gy was examined. In the case of WKAH rat cells, the surviving fraction increased with increasing incubation times after X-irradiation. When hyper tonic treatment was performed at each incubation time with 0.5 M NaCl for 2 0 min, increase in the surviving fractions was not shown. In contrast, no s ignificant recovery of the surviving fraction in LEC rat cells was observed after incubation of irradiated cells with or without 0.5 M NaCl for 20 min . On dose-survival curves, hypertonic treatment with 0.5 M NaCl enhanced ra diosensitivity of WKAH rat cells, but not LEC rat cells. Although the survi ving fraction of the cells from backcross mice with normal radiosensitivity reduced by treatment with 0.5 M NaCl, the survival fraction was not affect ed in the cells from backcross mice with higher radiosensitivity by treatme nt with 0.5 M NaCl. When the cells were X-irradiated and incubated with or without 0.225 M NaCl, the radiosensitivities of LEC and WKAH rat cells trea ted with 0.225 M NaCl for 4 h were approximately two-fold higher than those of untreated cells. Treatment with caffeine also reduced the surviving fra ctions of both X-irradiated LEC and WKAH rat cells, compared with those of untreated cells. These results indicated that the slow repair of PLD occurr ed in LEC rat cells but not the fast repair of PLD. (C) 1999 Elsevier Scien ce B.V. All rights reserved.