Severe chromosomal damage in mammalian cells induced by pulse labeling with small amounts of [3H]thymidine

Pulse labeling of cultured mammalian cells with tritiated thymidine ([3H]TdR; different specific activities, 2-47 Ci/mmole) for 30 min at low concentrations of radioactivity (0.2-2 microCi/ml) causes an unusually high degree of chromosomal aberrations which becomes fully evident in the cohort of cells analyzed 8 h later. The effect depends on the total amount of radioactivity. In HeLa cells up to 93% aberrant metaphases with up to 3.6 aberrations per metaphase were observed; in CHO cells the corresponding figures are 62% aberrant metaphases with 1 aberration per metaphase. The results may be valuable (i) for users of the pulse-labeling technique for analysis of cell-cycle kinetics, as this shows the technique as such may delay the labeled cohort of cells and therefore interferes with the matter under study and (ii) for risk assessment.