HYDROGEN-PEROXIDE CYTOTOXICITY UNDER CONDITIONS OF NORMAL OR REDUCED CATALASE ACTIVITY IN H2O2-SENSITIVE AND H2O2-RESISTANT CHINESE-HAMSTEROVARY (CHO) CELL VARIANTS

H2O2-sensitive and -resistant sublines of Chinese Hamster Ovary (CHO) cells were tested for their sensitivity to the growth inhibitory effec t elicited by increasing concentrations of the oxidant under condition s of normal or reduced catalase activity. Experimental results have de monstrated that, under conditions of reduced catalase activity, the cy totoxic action of H2O2 was differentially regulated in resistant and s ensitive cells. Indeed, the parental cell line and cells resistant to low concentrations of H2O2 (V 250 cells) depended on catalase to a low er extent than did highly resistant cells (V 850 cells). It is interes ting to note that V 250 cells had more catalase, on a per million cell basis, than V 850 cells. We conclude that acquired resistance to oxid ative stress is not entirely dependent on catalase and that the contri bution of catalase depends on the degree of resistance to the oxidant.