Exponentially growing Chinese hamster V79 cells were delayed in G2 very efficiently by 3.4-MeV a particles. In comparison with the effect caused by sparsely ionizing 60Co y rays, G2 delay after a irradiation was greater by a factor of 6.7 and 4.2 for doses 0.5 Gy, respectively, if the slopes of the dose-effect curves are compared. While at low doses (0.03-0.5 Gy) G2 arrest was reversible within 10 hr, increasing doses (0.5-4.38 Gy) of a irradiation blocked increasing fractions of cells for more than 16 hr, as determined by flow cytometry, and only some of these were able to complete mitosis. Addition of caffeine, however, reduced G2 arrest considerably if given directly after irradiation and reversed G2 arrest if added 8 hr after 4.38 Gy of a particles, a time when most of the cells already had accumulated in G2. Caffeine treatment during G2 decreased survival after a irradiation by factors of 1.3 and 1.7 for 1 and 2 mM caffeine, respectively.
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Lücke‐Huhle et al. (1982) studied this question.