Non-linear Dose—effect Curve for DNA Double-strand Breaks by Low LET Radiation: The Effect of Eluting Buffer Composition on the Measurement of Breaks by the Filter Elution Technique

Chinese hamster V79 cells were irradiated with 250 kVp X-rays and analysed for the presence of DNA double-strand breaks using filter elution. Changing the pH of the elution and lysis buffers from pH 9.6 to 7.2 leads to a decreased rate of elution of the DNA from the filters and a small difference in the dose-effect relationship obtained. In both cases the dose-effect curves were non-linear. When cells are irradiated with 238Pu alpha-particles a difference in the rate of elution of the DNA is also observed between the two pH values, although the dose-effect curves are linear. These findings suggest that there may be qualitative differences in the types of lesions being induced by low-LET radiation and being scored as dsb in the filter elution assay at pH 9.6. However, carrying out elution at pH 7.2 does not eliminate the nonlinear response measured after X-irradiation.