CELL-CYCLE ALTERATIONS INDUCED BY ISOTHERMAL 27-MHZ RADIOFREQUENCY RADIATION EXPOSURE

The purpose of this study was to test the hypothesis that 27 MHz conti nuous-wave radio-frequency radiation can alter the mammalian cell cycl e in the absence of radiation-induced heating. Relative effects of r.f . radiation on specific phases of the cell cycle were determined by ex posing synchronized Chinese hamster ovary (CHO) cells in G(0)/G(1)-, S - or G(2)/ M-phase. The dose-rate dependence of r.f. radiation-induced direct cell-cycle alterations was investigated by exposing CHO cells for 2 h to 5 or 25 W kg(-1) under isothermal conditions in vitro. Cell cycle alterations were determined by flow cytofluorometric DNA determ inations conducted over a period of 4 days after exposure. The DNA dis tributions of r.f.- or sham-exposed CHO cell samples were compared qua litatively by direct comparison of overlaid and difference distributio n. A quantitative measure of the magnitude of the r.f.-induced CHO cel l-cycle alterations was obtained by summation of the absolute value of the difference in the number of cells in all regions of the DNA distr ibution. The precision of the cytoflorometric assay was determined by comparison of DNA distributions of replicate CHO cell samples. The r.f . exposure induced time- and dose-rate-dependent cell cycle alteration s. Maximum responses occurred 3 days after exposure at a specific abso rption rate (SAR) of 25 W kg(-1). Comparison of temporal responses of cells exposed to 5 W kg(-1) vs. 25 W kg(-1) indicated an interaction o f r.f. exposure intensity with cell cycle phase. In contrast to r.f.-r adiation-induced alterations in the cycles of CHO cells exposed during G(0)/G(1)- or S-phase, there were minimal effects on G(2)/ M-phase CH O cells at either SAR, indicating lessened sensitivity of this cell cy cle phase. Whereas G(0)/G(1)- or S-phase cells exposed to either SAR a pproached baseline levels of alteration by 4 days after exposure, ther e was a statistically significant increased alteration in cells expose d at 25 W kg(-1) relative to cells exposed at 5 W kg(-1). This indicat ed an r.f.-dose-rate-dependent effect on the duration of cell cycle al terations.