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

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.