DNA damage measured using the alkaline elution assay depends on time between subculturing of cells and irradiation

In experiments utilizing the alkaline filter elution assay for radiation-induced DNA damage we observed an unexpected dependence of hypoxic dose-response curves on the length of time V79 cells were in exponential growth between subculturing and irradiation. Dose-response curves for DNA from cells irradiated in air were identical regardless of whether the exponential-phase cells had been subcultured 24 or 48 h prior to irradiation, but cells irradiated in hypoxia 24 h after subculture displayed a dose-response curve for DNA damage which was two times steeper than that obtained for cells irradiated in hypoxia 48 h after subculture. Possible mechanisms for this effect are discussed.