Clustering Of Membrane Surface EGF Receptors Induced By GSM 1800 MHz Radiofrequency Electromagnetic Fields And Interference By Noise Magnetic Fields

Recent advances in wireless technology have resulted in the exponential rising use of mobile telecommunications around the world. So the increasing exposure to radiofrequency electromagnetic fields (RF EMF) emitted from mobile phone has raised wide concerns for the possible adverse effects of RF fields on human health. Epidemiological studies have indicated a relationship between cell phone use and the risk of human diseases, but conclusive correlation has not been well established. ICNIRP set up the RF exposure limits for whole body with 10-50 safety factors on the basis of the SAR threshold of 4 W/kg in which adverse heating effects may occur. However, whether low intensity electromagnetic waves may cause health effects is controversial and its mechanism is unclear, which led to remarkable differences in the EMF hygienic standards in different countries for over 10 years.Generally, the potential adverse effects induced by RF EMF are weak,especially short term exposure, while the effects and its mechanism of long term exposure remains vague. Individual differences of EMF-induced effects appear obviously in different levels of human, animal and cell. Researches on mechanisms of RF EMF become essential under the condition that no definite conclusion has been drawn on RF-induced biological effects and health influence. Reports suggested that cell signal transduction pathways could participate in biological effects of EMF, but it is not clear how EMF activates those pathways.Cell membrane receptor is the action site of the ligand. The special binding of receptor to its relevant ligand usually induces receptor clustering, which initiates signal transduction pathways. Previously, we have reported that 0.4 mT 50 Hz magnetic fields could induce the clustering of membrane EGFR, a 170-kD transmembrane glycoprotein of ErbB family of receptor tyrosine kinases (RTKs), which plays a crucial role in cell proliferation, differentiation and survival. In the present study, EGFR clustering was investigated to explore the initiative action induced by GSM 1800 MHz RF EMF.Litovitz put forward the temporally and spatially coherent theory that external MF only with both temporal coherence and spatial coherence may induce biological effects. Noise MF is an incoherent field and has no biological effects. Superposition of a noise MF (incoherent fields) can inhibit the response of biological systems to a coherent MF when the intensity of noise MF is similar to or bigger than the coherent fields. Litovitz has also shown that ornithine decarboxylase (ODC) activity enhancement in Mouse Fibroblast (L929) cells induced by exposure to 60 Hz magnetic fields can be inhibited completely by superposition of noise MF.In the present study, we investigated the possible effects of exposure to GSM 1800 MHz RF EMF on EGFR and its possible interference by noise MF. Chinese hamster Lung fibroblasts (CHL) cells were exposed to 1800 MHz RF EMF at different intensities with different modulation modes and sham exposure, including:1) continuous RF exposure modulated by 217 Hz for 15 minutes at average specific absorption rates (SARs) of 0.1, 0.5, 1, 2, and 4 W/kg, respectively;2) continuous RF exposure at SAR of 0.5 W/kg modulated by different frequencies including 217, 50 and 0 Hz for 15 minutes, respectively;3) continuous RF exposure modulated by 0 Hz at SARs of 1, 2, and 4 W/kg for 15 minutes, respectively;4) exposure to 2 uT noise MF for 15 minutes;5) exposure to RF modulated by 217 and 50 Hz at SAR of 0.5 W/kg combined with 2 uT noise MF for 15 minutes, respectively. Immediately after exposure, the cells were fixed with paraformaldehyde (PFA), blocked with goat serum, incubated with rabbit anti mouse EGFR antibody followed by goat anti rabbit IgG-FITC, stained with propidium iodide (PI), and observed with laser cofocal scanning microscope (LCSM). It showed that EGFR clustering was induced after exposure to GSM 1800 MHz RF EMF modulated by 217 Hz at SARs of 0.5, 1, 2, and 4 W/kg for 15 min as induced by 1 ng/ml EGF, but not at SAR of 0.1 W/kg. GSM 1800 MHz RF EMF modulated by 217 and 50 Hz at SAR of 0.5 W/kg for 15 min both induced EGFR clustering, while no EGF receptor clustering was found in cells after exposure to unmodulated RF EMF or 2 uT noise MF. In addition, superposition of 2 uT noise MF could inhibit the EGFR clustering induced by GSM 1800 MHz RF EMF.In conclusion, EGFR clustering in CHL cells could be induced by GSM 1800 MHz RF EMF at the SAR down to 0.5 W/kg, which could be inhibited by 2 uT noise MF. The modulation of wave may play an important role in the inducement of receptor clustering after RF exposure.