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

The purpose of this study was to test the hypothesis that 27 MHz continuous-wave radio-frequency radiation can alter the mammalian cell cycle in the absence of radiation-induced heating. Relative effects of r.f. radiation on specific phases of the cell cycle were determined by exposing 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 determinations conducted over a period of 4 days after exposure. The DNA distributions of r.f.- or sham-exposed CHO cell samples were compared qualitatively by direct comparison of overlaid and difference distribution. A quantitative measure of the magnitude of the r.f.-induced CHO cell-cycle alterations was obtained by summation of the absolute value of the difference in the number of cells in all regions of the DNA distribution. 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 alterations. Maximum responses occurred 3 days after exposure at a specific absorption 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 of r.f. exposure intensity with cell cycle phase. In contrast to r.f.-radiation-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 CHO cells at either SAR, indicating lessened sensitivity of this cell cycle phase. Whereas G(0)/G(1)- or S-phase cells exposed to either SAR approached baseline levels of alteration by 4 days after exposure, there was a statistically significant increased alteration in cells exposed at 25 W kg(-1) relative to cells exposed at 5 W kg(-1). This indicated an r.f.-dose-rate-dependent effect on the duration of cell cycle alterations.