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 signfiicant changes in plating efficiency when returned to normal medium. Nearly confluent cultures of IL--treated cells were irradiated with either 60Co γ rays (75 cGy/min) or 137Cs γ rays (2.7, 6.0, or 15.3 cGy/h). A significant reduction (~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 γ irradiation, whereas no repair was observed in either of the radiation-sensitive mutant lines examined at similar survival levels.
ASJC Scopus subject areas
- Radiology Nuclear Medicine and imaging