Negative pion irradiation of mammalian cells. II. A comparative analysis of cell-cycle progression after exposure to pi-mesons and cobalt gamma-rays.

The effect of negative pi-mesons on cell-cycle progression of exponentially-growing V 79 monolayer cultures was examined by flow-microfluorometric analysis. Comparison with proliferative changes of the same cell-line after cobalt gamma-irradiation yielded r.b.e. values (relative biological effectiveness) of 2.2 for both, G2+M accumulation and division delay after irradiation at the pion peak. A dose-dependent prolongation of S-phase was found after Co gamma-irradiation which, however, was not detectable after pi-exposure. This observation is so far the only qualitative difference demonstrated in the effects of the two types of radiation.