Physical, chemical, and biological factors affecting sister-chromatid exchange induction in human lymphocytes exposed to mitomycin C prior to culture.

In experiments to assess the effects of several biological, chemical, and physical variables on sister-chromatid exchange (SCE) induction in cultured lymphocytes exposed to mitomycin C (MMC) before PHA stimulation we observed: (1) high SCE frequencies in female cells, and normal SCE frequencies in Y-bearing metaphases in mixed cultures containing equal numbers of MMC-treated female lymphocytes and untreated male lymphocytes; (2) small, but statistically significant, decreases in SCEs with increasing pH after G0 exposure in the pH range 6.6-7.6; (3) pronounced reductions in MMC-induced SCEs in lymphocytes exposed at 4 degrees C vs. 37 degrees C. In other studies, SCE induction was evaluated in cultures exposed during G0 to MMC concentrations ranging from 0.25 to 2.5 microgram/ml for varying time intervals ranging from 5 min to 24 h. For all concentrations tested SCE induction varied as a linear function of G0 exposure time. To compare SCE induction between cultures, we calculated the mean frequencies of SCEs induced per metaphase/unit dose MMC/unit G0 exposure time (SCE/microgram/h). A mean frequency of 20.7 +/- 4.8 SCE/microgram/h was observed for 41 lymphocyte cultures suggesting that a single term adequately describes the rate of SCE induction following G0 exposure to a 10-fold range in concentration of MMC for time intervals of 30 min to 24 h.