A comparative study of assay systems for drug-resistant mutation in cultured mammalian cells.

Three assay methods which have been reported previously for the detection of drug-resistant mutation in mammalian cells were compared using V79 cells growing monolayer and FM3A cells growing in suspension. 8-Azaguanine and ouabain were used for the selection. A method in which mutagen-treated cells were replated and cultured in the control medium during expression period, followed by the incubation in a selection medium (we named immediate replating method), was more efficient for demonstrating mutated cells than other replating methods in every occasions examined. Further, the optimum expression periods by this method were shown to be 3 to 4 cell divisions after the replating on cells treated with different concentrations of a mutagen.