Susceptibility of L5178Y-R and L5178Y-S cells to HTO, 3H-lysine and 3H-thymidine exposure.

Two strains of murine leukaemic lymphoblasts: L5178Y-R and L5178Y-S differing in the X-ray sensitivity by a factor of ca. 2 and showing X-ray-UV-light cross-sensitivity were exposed to: (a) 104 muCi/ml of HTO for time intervals from 25 to 600 h, (b) 10 muCi/ml of L-[4,5(n)-3H]lysine for 25 to 600 h, and (c) 0.05 muCi/ml of [methyl-3H] thymidine for 4 to 600 h. After completion of the exposure, survival was determined by cloning or by backward extrapolation of growth curves. In the case of HTO and 3H-thymidine exposure time the survival relationship passed through broad minima (75--200 and 50--400 h for (a) and (c), respectively). After longer exposures, higher survivals were observed reaching values close to 1 in the extreme cases. The results of shorter exposures indicate that L5178Y-R and L5178Y-S cells considerably differ in their susceptibilities to the tritiated compounds and that this difference increases with the shift of 3H localization towards DNA.