Exposure of human cells to low-frequency electromagnetic fields results in quantitative changes in transcripts

Effects of electromagnetic fields on molecules and cells

Evidence suggests that cell processes can be influenced by weak electromagnetic fields (EMFs). EMFs appear to represent a global interference or stress to which a cell can adapt without catastrophic consequences. There may be exceptions to this observation, however, such as the putative role of EMFs as promoters in the presence of a primary tumor initiator. The nature of the response suggests that the cell is viewing EMFs as it would another subtle environmental change. The age and state of the cell can profoundly affect the EMF bioresponse. There is no evidence that direct posttranscription effects occur as a result of EMF exposure. Although transcription alterations occur, no apparent disruption in routine physiological processes such as growth and division is immediately evident. What is usually observed is a transient perturbation followed by an adjustment by the normal homeostatic machinery of the cells. DNA does not appear to be significantly altered by EMF. If EMF exposure is associated with an increased risk of cancer, the paucity of genotoxic effects would support the suggestion that the fields act in tumor promotion rather than initiation. The site(s) and mechanisms of interaction remain to be elaborated. Although there are numerous studies and hypotheses that suggest the membrane represents the primary site of interaction, there are also several different studies showing that in vitro systems, including cell-free systems, are responsive to EMFs. The debate about potential hazards or therapeutic value of weak electromagnetic fields will continue until the mechanism of interaction has been clarified.

Neurochemical effects of a 20 kHz magnetic field on the central nervous system in prenatally exposed mice

C57/B1 mice were exposed during pregnancy (gestation days 0-19) to a 20 kHz magnetic field (MF). The asymmetric sawtooth-waveform magnetic field in the exposed racks had a flux density of 15 microT (peak to peak). After 19 days, the exposure was terminated, and the mice were housed individually under normal laboratory conditions. On postnatal day (PD) 1, PD21, and PD308, various neurochemical markers in the brains of the offspring were investigated and the brains weighed. No significant difference was found in the whole brain weight at PD1 or PD21 between exposed offspring and control animals. However, on PD308, a significant decrease in weight of the whole brain was detected in exposed animals. No significant differences were found in the weight of cortex, hippocampus, septum, or cerebellum on any of the sampling occasions, nor were any significant differences detected in protein-, DNA-level, nerve growth factor (NGF), acetylcholine esterase- (AChE), or 2',3'-cyclic nucleotide 3'-phosphodiesterase- (CNP; marker for oligodendrocytes) activities on PD21 in cerebellum. Cortex showed a more complex pattern of response to MF: MF treatment resulted in a decrease in DNA level and increases in the activities of CNP, AChE, and NGF protein. On PD308, the amount of DNA was significantly reduced in MF-treated cerebellum and CNP activity was still enhanced in MF-treated cortex compared to controls. Most of the effects of MF treatment during the embryonic period were similar to those induced by ionizing radiation but much weaker. However, the duration of the exposure required to elucidate the response of different markers to MF seems to be greater and effects appear later during development compared to responses to ionizing radiation.

Effects of 50 Hz magnetic fields on C-myc transcript levels in nonsynchronized and synchronized human cells

The effects of 50 Hz electromagnetic fields (EMFs) on the expression of the c-myc oncogene, known to be involved in normal cell proliferation and possibly also in tumor processes, were investigated in nonsynchronized human lymphoid cells immortalized by Epstein-Barr virus. Viral injury to such cells makes them a good model for exploring the possible cancer-promoting effects of 50 Hz magnetic fields. Parallel experiments were conducted on human HL60 leukemic cells. Cells were exposed to sinusoidal 50 Hz EMFs at 10 microT or 1 mT for 20 min, 1 h, 24 h, or 72 h. Exposure was performed either immediately after refeeding or 1.5 h after refeeding. C-myc transcript values were assessed by Northern blot analysis and normalized to those of the noninducible gene GaPDH. No statistically significant difference between the c-myc transcript levels of control and exposed cells was found in lymphoid or leukemic cells under our experimental conditions, either after short exposures of 20 min and 1 h or after longer exposures of 24 and 72 h. Other experiments were carried out with pseudosynchronized cells in an attempt to establish whether cells were especially sensitive to 50 Hz magnetic field exposure in any particular phase of the cell cycle. Accordingly, cells were pseudosynchronized in G0/G1 by serum deprivation and exposed for 20 min to a 50 Hz magnetic field, at 10 microT for lymphoid cells and 1 mT for HL60 cells. No significant difference was observed between the c-myc transcript levels of control and exposed cells for either of the synchronized cell types. These results for synchronized cells correlated with those for nonsynchronized cells.

Low-power electromagnetic stimulation of osteotomized rabbit fibulae. A randomized, blinded study

The purpose of this study was to determine whether low-power-consuming symmetrical-waveform electromagnetic stimuli could increase the stiffness of fracture sites in a rabbit fibular-osteotomy model. Both active and placebo devices were used in a blinded study protocol. Dose-response studies of pulse amplitude and pulse width were performed by continuous application (twenty-four hours a day) of repetitive (fifteen-hertz), bursted (five-millisecond-long) symmetrical, rectangular electromagnetic stimulus waveforms. The power consumed by these stimuli is approximately one-fifth that consumed by the pulsing electromagnetic field devices that are in current clinical use. Significant increase of callus bending stiffness was produced by pulse widths of five to seven microseconds and pulse amplitudes of fifty to 100 millivolts.

Animal studies on the role of 50/60-Hertz magnetic fields in carcinogenesis

A number of epidemiological studies have suggested that exposure to 50/60-Hz magnetic fields (MF) from power lines and electrical equipment may be associated with a modestly increased incidence of various types of cancer. Laboratory studies have indicated that nonionizing radiation has no mutagenic effect, i.e. does not initiate cancer. Thus, if 50/60-Hz MF are truly associated with an increased risk of cancer, then these fields must act as a promoter or co-promoter of cancer in cells that have already been initiated. This paper reviews the evidence produced by animal studies. As shown in this review, the available animal data on 50/60-Hz MF exposures seem to indicate that intermediate MF exposure exerts co-promoting effects in different tumor models, particularly cocarcinogenesis models of breast cancer, while chronic (up to life-time) exposure may exert promoting effects on "spontaneous" development of certain tumors. The tumor promoting or co-promoting effects of 50/60-Hz MF exposure found in several animal studies could relate to actions of MF on gene expression, immune surveillance, and Ca2+ homeostasis as demonstrated by in vitro experiments in cell cultures. However, the most plausible evidence for an in vivo effect of MF exposure which could be related to tumor promotion is reduction of circulating levels of melatonin, i.e. a hormone which is inhibitory to the growth of a wide range of cancers, particularly breast cancer. Animal studies have shown that 50-Hz MF exposure at flux densities as low as 0.3-1 mu Tesla significantly reduces nocturnal melatonin levels in plasma. While decrease of melatonin levels alone could explain tumor promoting or co-promoting effects of MF exposure, recent data indicate that MF exposure also impairs the effects of melatonin at the cellular level. Thus, the oncostatic effect of melatonin on cell proliferation of a human breast cancer cell line was antagonized by 60-Hz MF exposure at a flux density of about 1 mu Tesla. All these data indicate that interactions between 50/60-HZ MF exposure and melatonin may be the key mechanism of any carcinogenic effects. Although the existing experimental evidence is still insufficient for discerning a cause-effect relationship for MF exposure and human disease or injury, it does suggest the need for further laboratory research under well-defined laboratory exposure conditions to allow for a realistic assessment of the possible health risks and their magnitude.

Magnetic fields after translation in Escherichia coli

Quantitative two-dimensional gel electrophoresis of proteins in E. coli exposed for 60 min to weak, pulsed magnetic fields (1.5 mT peak) show that numerous proteins are both increased and decreased by a factor of 2 or more. An increase in the levels of two proteins, the a subunit of DNA-dependent RNA polymerase and NusA, was confirmed by Western blot analysis.

Experimental evidence for 60 Hz magnetic fields operating through the signal transduction cascade. Effects on calcium influx and c-MYC mRNA induction

We tested the hypothesis that early alterations in calcium influx induced by an imposed 60 Hz magnetic field are propagated down the signal transduction (ST) cascade to alter c-MYC mRNa induction. To test this we measured both ST parameters in the same cells following 60 Hz magnetic field exposures in a specialized annular ring device (220 G (22 mT), 1.7 mV/cm maximal E(induced), 37 degrees C, 60 min). Ca2+ influx is a very early ST marker that precedes the specific induction of mRNA transcripts for the proto-oncogene c-MYC, an immediate early response gene. In three experiments influx of 45Ca2+ in the absence of mitogen was similar to that in cells treated with suboptimal levels of Con-A (1 micrograms/ml). However, calcium influx was elevated 1.5-fold when lymphocytes were exposed to Con-A plus magnetic fields; this co-stimulatory effect is consistent with previous reports from our laboratory [FEBS Lett. 301 (1992) 53-59; FEBS Lett. 271 (1990) 157-160; Ann. N.Y. Acad. Sci. 649 (1992) 74-95]. The level of c-MYC mRNA transcript copies in non-activated cells and in suboptimally-activated cells was also similar, which is consistent with the above calcium influx findings. Significantly, lymphocytes exposed to the combination of magnetic fields plus suboptimal Con-A responded with an approximate 3.0-fold increase in band intensity of c-MYC mRNA transcripts. Importantly, transcripts for the housekeeping gene GAPDH were not influenced by mitogen or magnetic fields. We also observed that lymphocytes that failed to exhibit increased calcium influx in response to magnetic fields plus Con-A, also failed to exhibit an increase in total copies of c-MYC mRNA. Thus, calcium influx and c-MYC mRNA expression, which are sequentially linked via the signal transduction cascade in contrast to GAPDH, were both increased by magnetic fields. These findings support the above ST hypothesis and provide experimental evidence for a general biological framework for understanding magnetic field interactions with the cell through signal transduction. In addition, these findings indicate that magnetic fields can act as a co-stimulus at suboptimal levels of mitogen; pronounced physiological changes in lymphocytes such as calcium influx and c-MYC mRNA induction were not triggered by a weak mitogenic signal unless accompanied by a magnetic field. Magnetic fields, thus, have the ability to potentiate or amplify cell signaling.

Altered protein synthesis in a cell-free system exposed to a sinusoidal magnetic field

This report describes a new approach for examining weak extremely low frequency (ELF) electric and magnetic field interactions with living systems that exploits a cell-free transcription/translation system derived from Escherichia coli. Using two-dimensional polyacrylamide gel electrophoresis we previously had determined that the level of the alpha subunit of RNA polymerase in intact E. coli was elevated by exposure to weak ELF magnetic fields. In this paper, plasmids containing the alpha, or both the beta,beta' subunits of the RNA polymerase from E. coli were placed into a cell-free expression system. When this transcription/translation system was exposed to a 72-Hz sinusoidal magnetic field in the range 0.07 to 1.1 mT (rms) for periods of 5 min to 1 h, expression was enhanced. Weaker fields must be applied longer to produce an effect. For 10 min of field exposure, the threshold for an effect is 0.1 mT. These experiments demonstrate that an intact membrane is not an absolute requirement for transducing magnetic bio-effects.

Environmental magnetic fields: influences on early embryogenesis

A 10-mG, 50 to 60-Hz magnetic field is in the intensity and frequency range that people worldwide are often exposed to in homes and in the workplace. Studies about the effects of 50- to 100-Hz electromagnetic fields on various species of animal embryos (fish, chick, fly, sea urchin, rat, and mouse) indicate that early stages of embryonic development are responsive to fluctuating magnetic fields. Chick, sea urchin, and mouse embryos are responsive to magnetic field intensities of 10-100 mG. Results from studies on sea urchin embryos indicate that exposure to conditions of rotating 60-Hz magnetic fields, e.g., similar to those in our environment, interferes with cell proliferation at the morula stage in a manner dependent on field intensity. The cleavage stages, prior to the 64-cell stage, were not delayed by this rotating 60-Hz magnetic field suggesting that the ionic surges, DNA replication, and translational events essential for early cleavage stages were not significantly altered. Studies of histone synthesis in early sea urchin embryos indicated that the rotating 60-Hz magnetic field decreased zygotic expression of "early" histone genes at the morula stage and suggests that this decrease in early histone production was limiting to cell proliferation. Whether these comparative observations from animal development studies will be paralleled by results from studies of human embryogenesis, as suggested by some epidemiology studies, has yet to be established.

Effects of electromagnetic field exposure on gene transcription

Exposure of whole animals, isolated tissues, and cells to electromagnetic fields of various characteristics has resulted in a substantial literature detailing a wide range of effects at the morphological, physiological, biochemical, and molecular levels. In recent years, considerable effort has been devoted to defining a mechanism by which electromagnetic fields can couple to biological systems and generate this plethora of effects. As a consequence, there has been a growing interest in electromagnetic field-induced alterations in gene expression. Key studies are discussed which indicate that exposure of several cell types to electromagnetic fields that differ in waveform, amplitude, and frequency induced general changes in gene transcription. Moreover, exposure of T-lymphoblastoid cells to a 60 Hz sinusoidal magnetic field altered the transcription of genes encoding c-fos, c-jun, c-myc, and protein kinase C. Future studies in this area should focus on independent replication of key studies and identification of which events in the signal transduction pathways leading to gene transcription are altered by electromagnetic field exposure.

Rat liver foci study on coexposure with 50 Hz magnetic fields and known carcinogens

A study was performed to investigate possible interactions by magnetic fields (MF) with the processes of initiation and promotion of chemically induced preneoplastic lesions in rat liver. Male Sprague-Dawley rats were subjected to a 70% partial hepatectomy followed after 24 h by i.p. injection of diethylnitrosamine (DENA) as a tumour initiator. Starting one week after the DENA-treatment phenobarbital (PB) was given to promote growth of enzymatically altered foci of liver cells. MF was applied immediately after the partial hepatectomy and continued until sacrifice after 12 weeks of PB exposure. Homogenous horizontal AC magnetic fields with a frequency of 50 Hz and flux densities of 0.5 mu T or 0.5 mT were used. The rats coexposed with MF and DENA plus PB did not gain weight as much as the rats exposed to the chemical agents only. The MF-exposure also resulted in a slight reduction in size and numbers of the focal lesions. The results suggest an interaction of MF with the processes of chemical carcinogenesis either as a result of stress or depending on effects on the proliferation of preneoplastic cells.

The role of coherence time in the effect of microwaves on ornithine decarboxylase activity

Previously, we demonstrated the requirements for a minimum coherence time of an applied, small amplitude (10 microT) ELF magnetic field if the field were to produce an enhancement of ornithine decarboxylase activity in L929 fibroblasts. Further investigation has revealed a remarkably similar coherence time phenomenon for enhancement of ornithine decarboxylase activity by amplitude-modulated 915 MHz microwaves of large amplitude (SAR 2.5 W/kg). Microwave fields modulated at 55, 60, or 65 Hz approximately doubled ornithine decarboxylase activity after 8 h. Switching modulation frequencies from 55 to 65 Hz at coherence times of 1.0 s or less abolished enhancement, while times of 10 s or longer provided full enhancement. Our results show that the microwave coherence effects are remarkably similar to those observed with ELF fields.

Mechanisms of electromagnetic interaction with cellular systems

The question of how electromagnetic fields--static or low to high frequency--interact with biological systems is of great interest. The current discussion among biologists, chemists, and physicists emphasizes aspects of experimental verification and of defining microscopic and macroscopic mechanisms. Both aspects are reviewed here. We emphasize that in certain situations nonthermal interactions of electromagnetic fields occur with cellular systems.

Pulsed electric current enhances the phorbol ester induced oxidative burst in human neutrophils

Oxidative burst (OB) response in human neutrophils, measured with chemiluminescence (CL), has been used to determine whether pulsed electric current (PEC) might induce a functional response in these electrically nonexcitable cells, and also whether it might modify cellular response to tumor-promoting phorbol ester (PMA). Five minutes of PEC treatment caused no significant changes in neutrophil CL levels in HBSS (1.2 mM Ca2+ concentration) as well as in HBSS-EGTA, where the extracellular Ca2+ concentration was reduced to less than 30 nM. The CL level of PMA-activated neutrophils in HBSS was 52% higher than in HBSS-EGTA. In HBSS the CL level, after the combined PMA and PEC treatment, was 53% higher than in PMA-alone-treated neutrophils. Activation of the OB in HBSS-EGTA with PMA and PEC was 13% higher than in solely PMA treated neutrophils. The results suggest that in neutrophil OB response, the PEC effect is closely related with cellular calcium mobilization, since depletion of extracellular Ca2+ decreased the PEC effect.

Magnetic field-induced changes in specific gene transcription

Magnetic fields are physical, environmental agents that have been shown to produce a variety of responses in cellular and animal studies, including general changes in gene transcription. In this study, the nuclear run-off assay has been employed to assess alterations in specific gene transcription in CEM-CM3 T-lymphoblastoid cells exposed for 15-120 min to a 1 gauss sinusoidal magnetic field at 60 Hz. Time-dependent and cell density-dependent changes in the transcription of c-fos, c-jun, c-myc and protein kinase C (beta-form) have been observed and quantitated. Additionally, changes in transcript levels, assessed by slot-blot analysis, have been found to parallel the changes in gene transcription. These data suggest an important role for magnetic field exposure in altering cellular processes.

A portable pulsed electromagnetic field (PEMF) device to enhance healing of recalcitrant venous ulcers: a double-blind, placebo-controlled clinical trial

A prospective, randomized, double-blind, placebo-controlled multicentre study assessed the clinical efficacy and safety of pulsed electromagnetic limb ulcer therapy (PELUT) in the healing of recalcitrant, predominantly venous leg ulcers. The portable device was used at home for 3 h daily during this 8-week clinical trial as an adjunct to a wound dressing. Wound surface area, ulcer depth and pain intensity were assessed at weeks 0, 4 and 8. At week 8 the active group had a 47.7% decrease in wound surface area vs. a 42.3% increase for placebo (P < 0.0002). Investigators' global evaluations indicated that 50% of the ulcers in the active group healed or markedly improved vs. 0% in the placebo group, and 0% of the active group worsened vs. 54% of the placebo group (P < 0.001). Significant decreases in wound depth (P < 0.04) and pain intensity (P < 0.04) favouring the active group were seen. Patients whose ulcers improved significantly after 8 weeks were permitted to continue double-blind therapy for an additional 4 weeks. Eleven active and one placebo patient continued therapy until week 12, with the active treatment group continuing to show improvement. There were no reports of adverse events attributable to this device. We conclude that the PELUT device is a safe and effective adjunct to non-surgical therapy for recalcitrant venous leg ulcers.

Calcium signaling in lymphocytes and ELF fields. Evidence for an electric field metric and a site of interaction involving the calcium ion channel

Calcium influx increased during mitogen-activated signal transduction in thymic lymphocytes exposed to a 22 mT, 60 Hz magnetic field (E induced = 1.7 mV/cm, 37 degrees C, 60 min). To distinguish between an electric or a magnetic field dependence a special multi-ring annular cell culture plate based on Faraday's Law of Induction was employed. Studies show a dependence on the strength of the induced electric field at constant magnetic flux density. Moreover, exposure to a pure 60 Hz electric field or to a magnetically-induced electric field of identical strength resulted in similar changes in calcium transport. The first real-time monitoring of [Ca2+]i during application of a 60 Hz electric field revealed an increase in [Ca2+]i observed 100 s after mitogen stimulation; this suggests that the plateau phase rather than the early phase of calcium signaling was influenced. The hypothesis was tested by separating, in time, the early release of calcium from intracellular stores from the influx of extracellular calcium. In calcium-free buffer, 60 Hz field exerted little influence on the early release of calcium from intracellular stores. In contrast, addition of extracellular calcium during exposure enhanced calcium influx through the plasma membrane. Alteration of the plateau phase of calcium signaling implicates the calcium channel as a site of field interaction. In addition, an electric field exposure metric is mechanistically consistent with a cell-surface interaction site.

Time-varying and static magnetic fields act in combination to alter calcium signal transduction in the lymphocyte

We have tested the hypothesis that extremely low frequency (ELF) time-varying magnetic fields act in combination with static magnetic fields to alter calcium signalling in the lymphocyte. Results indicate that a 60-min exposure of thymic lymphocytes at 37 +/- 0.05 degrees C to a 16 Hz, 421 mG (42.1 microT) magnetic field simultaneously with a colinear static magnetic field of 234 mG (23.4 microT) (a.c./d.c. field intensity ratio = 1.8) inhibits calcium influx triggered by the mitogen Concanavalin A. Significantly, resting lymphocytes do not respond to the fields, thus, only mitogen-activated cells undergoing calcium signalling exhibit a field response. These results indicate that signal transduction involving calcium is an important biological constraint which operates to mediate this field interaction. Additional split field exposures show that the presence of the a.c. field or the d.c. field alone does not produce an effect. This is consistent with a proposed parametric resonance theory of interaction of low intensity magnetic fields with biological systems (L.L. Lednev (1991) Bioelectromagnetics 12, 71-75), which predicts the occurrence of biological effects at specific values for the frequency and field intensity of the ELF and static magnetic fields.

Transcription in Drosophila melanogaster salivary gland cells is altered following exposure to low-frequency electromagnetic fields: analysis of chromosome 3R

The use of the transcription autoradiographic method permits identification of nascent RNA chains directly on identifiable regions of Drosophila salivary gland chromosomes. Changes in transcriptional activity at 13 defined regions of the right arm of chromosome 3 (3R) were observed following 20-min exposures of salivary glands to five different extremely low frequency (ELF) electromagnetic (EM) fields. Changes in translational patterns were also induced by the ELF EM fields in exposed cells. Differences included an increase in over-all polypeptide synthesis as well as in the number of polypeptides resolved in cells exposed to EM fields.

Regulation of cell cycle and growth control

The potential biological effects of electric and/or magnetic fields on cells and tissues must be addressed systematically within a context of perturbations in cell cycle control. Such studies should not be pursued in an isolated manner but as a component of the fundamental relationship between proliferation and differentiation, the multi-step process by which structural and functional properties of specialized cells, tissues, and organs progressively develop. It is necessary to quantitatively establish the influence of electric and magnetic fields on the integrated signalling mechanisms which transduce regulatory information for 1) control of the proliferative process and 2) down-regulation of proliferation associated with the initiation of gene expression that mediates the development and maintenance of phenotypic properties characteristic of differentiated cells. We will present an overview of our current understanding of regulatory mechanisms that control proliferation and cell specialization in normal diploid cells with emphasis on rate limiting steps that may be the basis for biological perturbations by electric and magnetic fields. Addressing such questions in normal diploid cells is essential since the loss of growth control in transformed and tumor cells is accompanied by an abrogation of developmental regulatory mechanisms that are functionally coupled to proliferation.

Development of chicken embryos following exposure to 60-Hz magnetic fields with differing waveforms

Previous studies in my laboratory have revealed a reproducible and statistically significant increase in the number of malformations in live chicken embryos that had been exposed during the first 48 h of incubation to a pulsed magnetic field (unipolar pulses, 100-pps, 1-microT peak density). In marked contrast, no adverse effect was seen following similar exposure to 60-Hz, bipolar, unipolar, or split-sine waves at 3-microT peak-to-peak. In the four experiments comprising the present study, differences in the numbers of malformations between control and experimental groups were not statistically significant. Field-free incubation for an additional 72 h after exposure to a bipolar sine wave for 48 h resulted in an increase in normal live embryos in both control and treated groups.

Voltage-sensitive dyes: measurement of membrane potentials induced by DC and AC electric fields

Dye indicators of membrane potential have been available for the past 15 years and have been employed in numerous studies of cell physiology. Since the cell membrane is a likely primary site for the cascade of events resulting in a biological response to electromagnetic fields, methodologies for monitoring the membrane voltage will be critical. This laboratory has developed a series of dyes by using theoretical molecular orbital calculations to predict electrochromic structures. The spectra of electrochromic dyes are altered via a direct coupling of the molecular electronic states with an electric field. This mechanism has the advantage of providing both high temporal and high spatial resolution because the effect is instantaneous and is localized to the level of individual indicator molecules. It therefore can have significant advantages over traditional microelectrode techniques because fast changes in potential can be monitored simultaneously over many different regions of a biological preparation. We have used these dyes to monitor membrane potentials induced by both DC and AC electric fields. In a series of studies with a model membrane system, a spherical lipid bilayer, we showed that the potential develops on the membrane in good agreement with a time-dependent solution to Laplace's equation. Cell membranes can also be stained with voltage sensitive dyes. In experiments with dc fields, we are able to map the variation of the induced membrane potential along the surface of the cell by employing digital video fluorescence microscopy. We can also use the fluorescence microscope to detect membrane potential induced by ac fields by using a phase-sensitive detection scheme to extract the corresponding change in the light intensity from the fluorescent indicator. The technology can be extended to more complex biological preparations and can be used in conjunction with other optical techniques such as those which monitor intracellular ion concentrations. It may, therefore, prove highly valuable for the elucidation of biological responses to electromagnetic fields.

Alternative functional relationships between ELF field exposure and possible health effects: report on an expert workshop

If exposure to 60 Hz fields poses risks to public health, the relationship between exposure and risk may involve something other than the product of field strength and time. Such alternative possible relations, or "effects functions," are of great interest to epidemiologists, engineers, risk analysts, and regulators. A structured survey and workshop were used to explore whether leading researchers in bioelectromagnetics share similar views about alternative possible effects functions. Substantial agreement was found about several effects functions in a few specific contexts such as calcium-ion efflux and cell signalling, and biosynthesis pathways. No significant agreement emerged in many other contexts. No effects function possibilities were ruled out. Further effort of this sort was judged unlikely to yield greater consensus until more complete scientific understanding becomes available. However, a series of structured workshops on research planning and priority setting were judged to hold great potential for useful results.

Dose-response implications of the transient nature of electromagnetic-field-induced bioeffects: theoretical hypotheses and predictions

Data in the literature imply that the relationship between exposure and bio-effect involves more than a simple time integral of the field strength to which the living system has been subjected. Windows--ranges in which the system exhibits enhanced sensitivity--have been reported for power (or field strength), frequency, and the duration of the exposure. In this paper we show that such isolated window effects can be accounted for by recognizing the transient character of the response of the biological system. The principal assumption here is that the direct effect of the field is to increase the rates of production and degradation of mRNA or proteins. In this paper we review and extend the mathematical model that quantifies this. The model predicts that, for a given field strength, certain optimum relatively short duration exposures cause significantly larger bio-effects than exposure for much longer or much shorter times. The thinking embodied in the model should provide a framework for obtaining a meaningful working definition of "effective dose" and for predicting the response of subjects to environmental electromagnetic fields. It should help in deciding the relevant variables in the design and analysis of epidemiological studies.

Low-amplitude, low-frequency electric field-stimulated bone cell proliferation may in part be mediated by increased IGF-II release

We have developed an in vitro model incorporating a low-amplitude (10(-7) V/cm), low frequency (f less than 100 Hz), capacitively coupled electric field in order to study the mechanism through which an electric field may increase bone cell proliferation. Utilizing this model we have previously shown that electric field-stimulated bone cell proliferation was dependent on release of mitogen activity into the culture medium from exposed cells. The current studies were intended to characterize this mitogen activity. In these studies we found that electric field-stimulated human bone cell proliferation was associated with increased IGF-II mRNA accumulation and IGF-II secretion suggesting that IGF-II may in part mediate the increase in bone cell proliferation following electric field exposure.

An increase in the negative surface charge of U937 cells exposed to a pulsed magnetic field

Pulsed magnetic fields have been used to enhance healing of bone fractures and purportedly of lesions in soft tissue. However, their mechanism of action is poorly understood. We report changes in the plasma membrane of a nonadherent mammalian cell line, U937, which was exposed to a 25-pps magnetic field for 48 hours. Aqueous polymer two-phase partition studies showed that magnetic-field-exposed cells exhibited an increased negative surface charge but membrane hydrophobicity was not significantly altered. The observed increase in membrane electronegativity of exposed cells did not reflect a significant change in growth rate.