Effects of isothermal 2.45 GHz microwave radiation on the mammalian cell cycle: Comparison with effects of isothermal 27 MHz radiofrequency radiation exposure

Synchronized Chinese hamster ovary (CHO) cells were exposed to continuous wave (CW) 2.45 GHz microwave radiation (MWR) or CW 27 MHz radiofrequency radiation (RFR) under isothermal conditions (37 +/- 0.2 degrees) to test the following hypotheses: (1) high frequency electromagnetic radiation exposure directly affects the mammalian cell cycle in the absence of radiation-induced heating; and (2) the magnitude of the cell cycle alteration is frequency dependent. CHO cells in either G(0)/G(1)-, S-, or G(2)/M-phase of the cell cycle were simultaneously exposed to CW 27 MHz RFR or CW 2.45 GHz MWR at specific absorption rates (SARs) of 5 or 25 W kg(-1), or sham exposed, at 37 +/- 0.2 degrees C. Cell cycle alterations were determined by flow cytofluorometry over a 4 d period after exposure. The DNA distributions of RFR, MWR, and sham exposed cells were compared to detect qualitative effects on the cell cycle. Quantitative measures of the effects of isothermal radiation exposure were determined from differences in the number of exposed and sham exposed cells in various cell cycle phases as well as comparison of the mean DNA content of exposed and sham exposed cell samples. Flow cytofluorometric assay precision and accuracy were determined by comparison of DNA distributions of replicate CHO control cell samples and by the use of internal DNA standards. Exposure to 27 MHz RFR or 2.45 GHz MWR altered the CHO cell cycle for periods of up to 4 d following exposure at SARs of 5 or 25 W kg(-1). There were significant differences in temporal responses, cell cycle phase sensitivity, and overall degree of cell cycle alteration for 27 MHz compared with 2.45 GHz radiation exposure, In contrast to the effect of 27 MHz RFR, which did not affect G(2)/M-phase CHO cells, 2.45 GHz MWR altered all cell cycle phases to varying degrees. Exposure to 2.45 GHz MWR at 5 or 25 W kg(-1) was twice as effective as 27 MHz RFR in inducing cell cycle alterations as determined by differences in the number of exposed versus sham-exposed cells in various cell cycle phases.