A Comparison of Mammalian Cell-killing by Incorporated3H-thymidine and3H-uridine

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Abstract
The fact that the β-radiation from 3H atoms incorporated into cellular DNA is absorbed largely in the nucleus, while more of that from 3H incorporated into RNA is absorbed in the cytoplasm than in the nucleus, provides a means of determining the relative importance of nuclear and cytoplasmic damage in radiation-induced mammalian cell-death. Synchronously-dividing populations of Chinese hamster fibroblasts were pulse-labelled with variosu doses of either 3H-thymidine or 3H-uridine. The labelled cells were plated, and survival-curves obtained. Autoradiographic silver grain-counts and liquid scintillation counting were used to measure the nuclear β-radiation doses. It was found that the slope of the 3H-uridine survival-curve was somewhat greater than that of the 3H-thymidine curve. Since the β-radiation dose to the cytoplasm was larger than that to the nucleus, however, it is concluded that the contribution of cytoplasmic damage to radiation-induced reproductive death of mammalian cells is very small.