Sensitivity of Neutral Filter Elution but Not PFGE Can Be Modified by Non-dsb Chromatin Damage

Hamster V79 fibroblast cells and human squamous carcinoma cells (Caski) were exposed to 60Co radiation and DNA double-strand break (dsb) induction was analysed by DNA elution at neutral pH from polycarbonate filter or out of an agarose matrix in pulsed-field electrophoresis (PFGE). While dsb yields were equal for the two cell lines (using 125-iodine calibration) a reduced responsiveness of filter elution was found for V79 versus Caski cells. This difference could be abolished when additional single-strand breaks (ssb) were introduced by an incubation at 10−4m H2O2 for up to 40 min that itself did not give a response in neutral elution. No such lack of specificity for the detection of dsb was seen in electrophoretic elution where also the influence of peroxide incubation was absent. The presumed potential of ssb to modify dsb detection was paralleled by the kinetics of dsb rejoining: a pronounced transient increase of DNA elution from filters was observed for V79 cells (less prominent with Caski cells) at ...