Ž . Bioelectrochemistry and Bioenergetics 48 1999 177–180 The effects of radiofrequency fields on cell proliferation are non-thermal S. Velizarov a , P. Raskmark b , S. Kwee c, ) a Institute of Chemical Engineering, Bulgarian Academy of Sciences, Bl. 103, 1113 Sofia, Bulgaria b Institute of Communication Technology, Aalborg UniÕersity, DK-9220 Aalborg Ø, Denmark c Department of Medical Biochemistry, UniÕersity of Aarhus, Build. 170, DK-8000 Aarhus C, Denmark Received 30 November 1998; revised 14 December 1998; accepted 14 December 1998 Abstract Ž . Ž . The number of reports on the effects induced by radiofrequency RF electromagnetic fields and microwave MW radiation in various cellular systems is still increasing. Until now no satisfactory mechanism has been proposed to explain the biological effects of these fields. One of the current theories is that heat generation by RFrMW is the cause, in spite of the fact that a great number of studies under isothermal conditions have reported significant cellular changes after exposure to RFrMW. Therefore, this study was undertaken to investigate which effect MW radiation from these fields in combination with a significant change of temperature could have on cell w proliferation. The experiments were performed on the same cell line, and with the same exposure system as in a previous work S. Kwee, P. Raskmark, Changes in cell proliferation due to environmental non-ionizing radiation: 2. Microwave radiation, Bioelectrochem. Ž . x Bioenerg., 44 1998 , pp. 251–255 . The field was generated by signal simulation of the Global System for Mobile communications Ž . GSM of 960 MHz. Cell cultures, growing in microtiter plates, were exposed in a specially constructed chamber, a Transverse Ž . Ž . Electromagnetic TEM cell. The Specific Absorption Rate SAR value for each cell well was calculated for this exposure system. However, in this study the cells were exposed to the field at a higher or lower temperature than the temperature in the field-free incubator i.e., the temperature in the TEM cell was either 39 or 35 "0.18C. The corresponding sham experiments were performed under exactly the same experimental conditions. The results showed that there was a significant change in cell proliferation in the exposed cells in Ž . comparison to the non-exposed control cells at both temperatures. On the other hand, no significant change in proliferation rate was found in the sham-exposed cells at both temperatures. This shows that biological effects due to RFrMW cannot be attributed only to a change of temperature. Since the RFrMW induced changes were of the same order of magnitude at both temperatures and also comparable to our previous results under isothermal conditions at 378C, cellular stress caused by electromagnetic fields could initiate the changes in cell cycle reaction rates. It is widely accepted that certain classes of heat-shock proteins are involved in these stress reactions. q 1999 Elsevier Science S.A. All rights reserved. Keywords: Radiofrequency electromagnetic fields; Microwave radiation; Athermal effects; Cell proliferation; Microtiter plate culture 1. Introduction The expansive growth in mobile communication in recent years has resulted in an increased exposure of the Ž . environment to weak radiofrequency RF electromagnetic fields. This has aroused a general interest in the possible Ž . effects of radiofrequency and microwave MW radiation on human health. Consequently, the number of reports on RF and MW induced effects on various cellular processes is increasing rapidly. However, a satisfactory explanation by what bio- physical and biological mechanisms these fields exert their biological effects has not yet been offered. ) Corresponding author. Tel.: q45-8942-2869; Fax: q45-8613-1160 Unfortunately, the misconception still persists that RF and MW effects are solely the result of heat generation, contrary to the fact that a number of reported studies showed significant effects on various cellular activities in w x experimental systems under isothermal conditions 1–3 . However, if RF and MW effects were only due to increased temperatures, then it should be possible to detect changes in cellular activities depending only on tempera- ture changes in the experimental system. And conse- quently, there should be no difference between the cellular activities of field exposed and non-exposed cells. In a previous study, we showed that exposure of trans- Ž . formed human epithelial amnion cells AMA to a modu- lated RF field at 960 MHz at different power levels and exposure times, resulted in significant changes in cell 0302-4598r99r$ - see front matter q 1999 Elsevier Science S.A. All rights reserved. Ž . PII: S0302-4598 98 00238-4