Response of X-ray-sensitive CHO mutant cells to gamma radiation. I. Effects of low dose rates and the process of repair of potentially lethal damage in G1 phase.
X-ray-sensitive CHO mutants (xrs-5 and xrs-6) were exposed to isoleucine-deficient (IL-) medium for 24-36 h to accumulate G1-phase cells. Cells exposed to IL- medium for up to 5 days did not show significant changes in plating efficiency when returned to normal medium. Nearly confluent cultures of IL- -treated cells were irradiated with either 60Co gamma rays (75 cGy/min) or 137Cs gamma rays (2.7, 6.0, or 15.3 cGy/h). A significant reduction (approximately 2.5-fold) in the radiation sensitivity of the parental CHO K-1 cells was observed for chronic low-dose-rate radiation exposure compared to the results obtained for acute high-dose-rate exposure. However, no noticeable differences were observed in the survival curves of either xrs-5 or xrs-6 cells when low-dose-rate and acute exposures were compared. CHO K-1 cells exhibited potentially lethal damage repair while held in IL- medium after gamma irradiation, whereas no repair was observed in either of the radiation-sensitive mutant lines examined at similar survival levels.
Nagasawa
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H
Laboratory of Radiobiology, Harvard School of Public Health, Boston, Massachusetts 02115.
Chen
D J
DJ
Strniste
G F
GF
D000818:Animals; D002460:Cell Line; D003037:Cobalt Radioisotopes; D006224:Cricetinae; D004247:DNA / Q000528:radiation effects*; D004249:DNA Damage; D004260:DNA Repair; D004307:Dose-Response Relationship, Radiation; D005720:Gamma Rays; D066298:In Vitro Techniques; D007399:Interphase / Q000528:radiation effects*; D009154:Mutation; D011836:Radiation Tolerance
D003037:Cobalt Radioisotopes; D004247:DNA