DNA STRAND BREAKAGE, CYTOTOXICITY AND MUTAGENICITY OF HYDROGEN-PEROXIDE TREATMENT AT 4-DEGREES-C AND 37-DEGREES-C IN L5178Y SUBLINES

Cells from the L5178Y murine lymphoma subline LY-R are twofold more re sistant to killing by ionizing radiation than the subline LY-S. In con trast, LY-R cells are more sensitive to killing by hydrogen peroxide. Cells of the two sublines in logarithmic growth phase were treated wit h hydrogen peroxide in phosphate-buffered saline for 1 h at 4 degrees C or 37 degrees C. From the comparison of D-o values it followed that at 37 degrees C LY-R were 3.6 times more sensitive to the killing effe ct of H2O2 than LY-S cells; at 4 degrees C they were 11 times more sen sitive. Treatment with hydrogen peroxide at 4 degrees C gave a conside rable sparing effect, which was substantially greater for the LY-S sub line; for LY-S cells D, was 5.7 times lower at 37 degrees C than at 4 degrees C, for LY-R cells only 1.9 times. The mutation frequency (HGPR T) in LY-R cells was increased in proportion to H2O2 concentration and was the same at both treatment temperatures. In contrast, mutation fr equencies initially increased, then decreased with increasing H2O2 con centration in LY-S cells treated at 4 or 37 degrees C. The concentrati on at which the decline was initiated was higher at 4 than at 37 degre es C. DNA damage after H2O2 treatment (both temperatures, 5 min) was e stimated from the 'comet' assay (single-cell gel electrophoresis). The initial damage, but not the residual damage, differed significantly i n LY sublines. A period of slower repair (between 3 and 10 min) was fo und in LY-R cells.