Effect of magnetic field exposure on anchorage-independent growth of a promoter-sensitive mouse epidermal cell line (JB6).

The anchorage-independent growth of mouse epidermal cells (JB6) exposed to 60-Hz magnetic fields (MF) was investigated. Promotion-responsive JB6 cells were suspended in agar (10(4)cells/plate) and exposed continuously to 0.10 or 0.96 mT, 60-Hz magnetic fields for 10-14 days, with or without concurrent treatment with the tumor promoter tetradecanoylphorbol acetate (TPA). Exposures to MF were conducted in a manner such that the experimenter was blind to the treatment group of the cells. At the end of the exposure period, the anchorage-independent growth of JB6 cells on soft agar was examined by counting the number of colonies larger than 60 microm (minimum of 60 cells). The use of a combined treatment of the cells with both MF and TPA was to provide an internal positive control to estimate the success of the assay and to allow evaluation of co-promotion. Statistical analysis was performed by a randomized block design analysis of variance to examine both the effect of TPA treatment (alone and in combination with MF exposure) and the effect of intra-assay variability. Transformation frequency of JB6 cells displayed a dose-dependent response to increasing concentrations of TPA. Coexposure of cells to both TPA and 0.10 or 0.96 mT, 60-Hz MF did not result in any differences in transformation frequency for any TPA concentrations tested (0-1 ng/ml). These data indicate that exposure to a 0.10 or 0.96 mT, 60-Hz MF does not act as a promoter or co-promoter in promotion-sensitive JB6 cell anchorage-independent growth.