RADIOADAPTIVE RESPONSE - EFFICIENT REPAIR OF RADIATION-INDUCED DNA-DAMAGE IN ADAPTED CELLS

To verify the hypothesis that the induction of a novel, efficient repa ir mechanism for chromosomal DNA breaks may be involved in the radioad aptive response, the repair kinetics of DNA damage has been studied in cultured Chinese hamster V79 cells with single-cell gel electrophores is. The cells were adapted by priming exposure with 5 cGy of gamma-ray s and 4-h incubation at 37 degrees C. There were no indication of any difference in the initial yields of DNA double-strand breaks induced b y challenging doses from non-adapted cells and from adapted cells. The rejoining of DNA double-strand breaks was monitored over 120 min afte r the adapted cells were challenged with 5 or 1.5 Gy, doses at the sam e level to those used in the cytogenetical adaptive response. The rate of DNA damage repair in adapted cells was higher than that in non-ada pted cells, and the residual damage was less in adapted cells than in non-adapted cells. These results indicate that the radioadaptive respo nse may result from the induction of a novel, efficient DNA repair mec hanism which leads to less residual damage, but not from the induction of protective functions that reduce the initial DNA damage.