The Kinetics of Chromatid Aberrations Induced in Chinese Hamster Cells by Tritium-Labeled Thymidine

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Abstract
Dose curves were obtained for the induction of the various types of chromatid aberrations by tritiated thymidine. When the yields of aberrations were plotted against the number of grains in the autoradiograms, terminal deletions and chromatid exchanges exhibited 1-hit and 2-hit components in their dose curves, and isochromatid deletions exhibited linear kinetics. Since the numbers of Ag grains obtained for a given film exposure time were measures of relative dose rates, it was assumed that they were also an accurate estimation of the total relative doses. The great majority of the data available on the induction of aberrations by chronic ionizing radiations indicate that when both a 1-hit and a 2-hit component are present in an acute radiation dose curve, the 2-hit component is severely reduced when chronic radiation is employed and the dose curve approaches linearity. The present data are not in agreement with these findings. If stage sensitivity and mitotic delay are taken into consideration, however, an equation can be constructed which satisfactorily explains the shapes of the dose curves obtained and shows that linear kinetics hold for all classes of aberrations. The nonlinear portions of the dose curves apparently arise from variation, with dose, in the time spent in cell stages of different sensitivity.