Kinetics of the effect of ara C on chromosome aberration yield in irradiated human lymphocytes.

In unstimulated lymphocytes the enhancing effect of ara C on the yield of X-ray-induced dicentric aberrations was maximal if ara C was added immediately or up to 2 h after irradiation. When ara C was added later the enhancing effect decreased and practically vanished by 5 h. In stimulated lymphocytes the ara C effect declined faster and practically vanished by 3 h. If ara C was added for 1 h immediately after irradiation, then the aberration yield observed in G0, early G1 and late G1 cells was similar whereas it increased significantly from G0 to late G1 cells without ara C post-treatment. The results are discussed in relation to the classical model of aberration formation.