60 Hz magnetic field acts as co-promoter in focus formation of C3H/10T1/2 cells.

Disruption of communication between transformed cells and normal cells is involved in tumor promotion. We have tested the hypothesis that 60 Hz electromagnetic (EM) field exposures and a chemical tumor promoter, 12-O-tetradecanoylphorbol-13-acetate (TPA) are co-promoters that enhance focus formation of transformed cells in co-culture with normal cells. EM field exposures alone did not affect the growth curves of parental C3H/10T1/2 fibroblasts or daughter mutant cells, UV-TDTx10e. Furthermore, EM field exposures alone did not promote focus formation of mutant cells in co-culture with parental cells under the conditions tested. However, EM field exposures co-promoted with TPA by increasing focus formation in co-culture. Cell cultures were exposed to an EM field in custom-built solenoidal incubators. The field exposures were 1.0 Gauss in a schedule of 1 h epochs four times daily for 28 days. Video image analysis of three independent experiments showed that field-exposed cultures produced 1.9-fold more foci than sham-exposed cultures when treated with TPA. The total area of foci per dish increased 2.2-fold and the number of cells in stained foci increased 2.3-fold. In a TPA dose-response, focus formation began at 3 ng/ml with no difference between field-exposed and sham-exposed co-cultures. However, at the TPA concentrations of 10, 20, 40, 50 and 100 ng/ml EM field exposures enhanced focus formation by an average of 150%. This study suggests that chronic intermittent exposures to a 60 Hz EM field and a chemical tumor promoter influenced membrane-related events by co-promoting focus formation.