X-Ray Survival Response of the Mouse L Cells

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By the use of synchronous mouse L cells, survival response to X-rays was determined throughout the cell cycle. The pattern of a single dose survival was essentially the same as found for HeLa cells previously, i. e. , most sensitive at mitosis and the G1-S transition phase; most resistant at the early G1 and intermediately resistant at the late S phase. The survival parameters, extrapolation number (n) and mean lethal dose (Do), underwent the similar change during the cell cycle. Difference in sensitivity between early G1 and G1-S transition phase was a factor of 3 in terms of n value, roughly 1.4 in Do value. The development of resistance during the S phase was suppressed, although not entirely, by the introduction of hydroxyurea, an inhibitor of DNA synthesis. The finding suggests that the sensitivity during the S phase is strongly related to the DNA synthesis. The survival curve of L cells, either randomly or synchronously growing, exhibited an increasing curvature with radiation dose. however, the frequent renewals of growth medium improved only survivals to more than 900 rads. Several possibilities for such anomalous inactivation were discussed on the basis of medium renewal experiments.
日本放射線影響学会の論文