Effects of [3H]Udr On the Cell-Cycle Progression of L1210 Cells

Tritium-labelled uridine (³H]UdR) perturbs progression of L1210 cells through the mitotic cycle. the main effect manifests as a slowdown or arrest of a portion of cells in G₂ and is already observed 2 hr after addition of 0.5–5.0 μCi/ml of ³H]UdR into cultures. At 2.5–5.0 μCi/ml of ³H]UdR a slowdown of cell progression through S is also apparent. Additionally, there is an increase in the number of cells with DNA values higher than 4C in cultures growing in the presence of ³H]UdR for 8–24 hr. A pulse of ³H]UdR of 2 hr duration labels predominantly (95%) cellular RNA. the first cell-cycle effects (G₂ slowdown) are observed when the amount of the incorporated ³H]UdR is such that, on average there are fewer than thirty-six ³H] decays per cell which corresponds to approximately 12–19 rads of radiation. the S-phase slowdown is seen at a dose of incorporated ³H]UdR twice as high as that inducing G₂ effects. the specific localization of ³H]UdR in nucleoli, peripheral nucleoplasm and in cytoplasm, as well as differences in the kinetics of the incorporation in relation to phases of the cell cycle are discussed in the light of the differences between the effects of ³H]UdR and ³H]thymidine. Mathematical modelling of the cell-cycle effects of ³H]UdR is provided.