[Genotypic and phenotypic characteristics of L-line cells resistant to ethidium bromide].

Stable mutants resistant to ethidium bromide in concentrations of 1 and 3 micrograms/ml have been selected in a single step in L cells. The frequency of spontaneously occurring ethidium bromide resistant clones after the exposure to 1 microgram/ml of the drug has been established as 5.10(-5). Resistant variants were induced following treatment with mutagen N-methyl-N-nitro-N-nitrosoguanidine. The resistant clones were shown to be resistant to higher concentration of the agent then which was used for selection. In multistep selection, a number of clones resistant to ethidium bromide in concentration up to 50 micrograms/ml was obtained. The alteration in the permeability of plasma membrane to the drug is the clue mechanism of the resistance.