CULTURED-CELLS FROM A SEVERE COMBINED IMMUNODEFICIENT MOUSE HAVE A SLOWER THAN NORMAL RATE OF REPAIR OF POTENTIALLY LETHAL DAMAGE SENSITIVETO HYPERTONIC TREATMENT

The effects of hypertonic 0.5 M NaCl treatment after irradiation on th e repair of DNA damage were examined in fibroblasts of the severe comb ined immunodeficient (scid) mouse, These cells are hypersensitive to i onizing radiation because of a deficiency in the repair of double-stra nd breaks. Hypertonic treatment caused radiosensitization due to a fix ation of potentially lethal damage (PLD) in scid cells, demonstrating that scid cells normally repair PLD, To assess the kinetics of the rep air of PLD, hypertonic treatment was delayed for various times after i rradiation, Potentially lethal damage was repaired during these times in isotonic medium at 37 degrees C. It was found that the rate of repa ir of PLD was much slower in scid cells than in BALB/c 3T3 cells, whic h have a ''wild-type'' level of radiosensitivity. This fact indicates that the scid mutation affects the type of repair of PLD that is sensi tive to 0.5 hi NaCl treatment, In scid hybrid cells containing fragmen ts of human chromosome 8, which complements the radiosensitivity of th e scid cells, the rate of repair was restored to a normal level, An en zyme encoded by a gene on chromosome 8 may also be connected with PLD which is sensitive to hypertonic treatment. (C) 1995 by Radiation Rese arch Society