of Work:
AIMS : Biological and epidemiological studies have suggested that low frequency EMFs may adversely affect human health. However, the mode of action of EMFs on cells is largely unknown. On the other hand, DC electric fields have long been known to be an effective stimulus for cell activation. For example, it causes polarized cell movement, neurite outgrowth and clustering of integral membrane proteins. Some of these effects may be mediated by the activation of receptor tyrosine kinases. The main purpose of this project was to examine the possibility that low frequency EMFs may affect cell activity by activation of receptor tyrosine kinases in cell cultures. ACCOMPLISHMENTS: We have employed cultured human epidermoid carinoma A 431 cells as a model to examine the effects of 60 Hz EMFs on receptor tyrosine kinases. These cells have an abundance of receptors for epidermal growth factor (EGF) on their surface. Upon ligand binding, these receptors dimerize and autophosphorylate tyrosines. By probing Western blots of the lysates of A 431 cells with an antibody to phosphotyrosine, we were able to demonstrate the tyrosine phosphorylation of the EGF receptor with an apparent molecular weight around 170 kDa. Two series of experiments were conducted to examine the effects of 60 Hz EMFs on EGF receptor tyrosine phosphorylation in A 431 cells. Initially, cells were exposed to a field strength of 1 gauss (using the EMF generator in Dr. C. Rinehart's laboratory at UNC) for 30, 60, 90, and 120 minutes with corresponding controls which were placed in the incubator with no field strength. Results indicated that the phosphorylation patterns were the same between the EMF exposed and the control groups. This experiment was repeated twice with similar results. The second series of experiments was to extend the EMFs exposure to longer periods of 2, 4, 6, and 8 hours. Results from two independent experiments showed no effect of EMFs exposure. To further confirm these negative results, we have conducted the same exposure using the setup in Dr. C. Blackman's laboratory at EPA, and the results were similar to those obtained at UNC. Thus, we conclude that unlike DC electrical fields, EMFs fail to affect receptor tyrosine kinases in A 431 cells. Currently, we are studying the effects of EMFs exposure on the phosphorylation of NGF receptors in PC12 cells since it was reported that EMFs exposure prevents NGF-induced neurite outgrowth in this cell line.
