X-ray induced DNA strand break induction and rejoining in cultured bovine lens epithelial cells

DNA strand break induction and rejoining in cultured bovine lens epithelial cells were measured by the alkaline unwinding technique followed by hydroxyapatite chromatography. DNA damage is described in terms of dose effect curves for unwinding immediately after irradiation (0 min) and for unwinding after a recovery period (30 min). The dose effect curves obtained are purely exponential with D0 values of 29.3 Gy (0 min) and 138 Gy (30 min), respectively. Rejoining data are given in terms of rejoining enhancement curves with half-times for overall rejoining being in the range from 4 to 10 min, independent of the dose. Kinetics of strand breaks are also presented in terms of decay curves, which are best described by the sum of three exponential components. The half-times of these components have been determined as tau(I) approximately 2 min, tau(II) approximately 15 min and tau(III) approximately 500 min. These components of damage decay curves are discussed in relation to cell killing.