Effects of arsenite, hydrogen peroxide, and NONOate on PARP-1 activity in HaCat (A, B, C) and HEKn (D, E, F) cells. Cells were treated with sodium arsenite (A, D), hydrogen peroxide (B, E), or NONOate (C, F) separately for 48hours, and then PARP-1 protein was isolated by immunoprecipitation. PARP-1 activity was determined using a HT Colorimetric PARP/Apoptosis Assay kit. Data are presented as means ± S.D., * P<0.05 vs. 0 group, n=6 for HaCat (A, B, C), n=3 for HEKn (D, E, F).