[Resistance to ethidium bromide in L929 cells is accompanied by regular changes in karyotypic structure]

The method of differential staining of chromosomes (G- and C-banding) has been used for comparative karyological analysis of mouse fibroblasts of L929 cells selected for resistance to ethidium bromide (EB) at concentrations 1, 10, 25, 50 mkg/ml. All variants have been shown to maintain resistance to EB for a long period of cultivation in nonselective conditions. Only 13 of 36 marker chromosomes of the initial EB-sensitive cells persist, 16 markers being specific for resistant variants. The karyotype changes found occur as early as at the first step of selection and are maintained in variants resistant to the higher drug concentrations. Detection of similar karyotypic changes in clones of independent origin, resistant to EB at concentrations 3 and 25 mkg/ml, allows to conclude that they are quite uniform for L929 cells selected for resistance to EB.