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

Effects of electromagnetic fields on cells: physiological and therapeutical approaches and molecular mechanisms of interaction. A review

This review concentrates on findings described in the recent literature on the response of cells and tissues to electromagnetic fields (EMF). Models of the causal interaction between different forms of EMF and ions or biomolecules of the cell will be presented together with our own results in cell surface recognition. Naturally occurring electric fields are not only important for cell-surface interactions but are also pivotal for the normal development of the organism and its physiological functions. A further goal of this review is to bridge the gap between recent cell biological studies (which, indeed, show new data of EMF actions) and aspects of EMF-based therapy, e.g., in wounds and bone fractures.

Incubation temperature and hemoglobin dielectric of chicken embryos incubated under the influence of electric field

Eggs from a layer-type breeder flock (Baladi, King Saud University) between 61 and 63 weeks of age were used in 3 trials to study the effects of electric field (EF) during incubation on the internal temperature of incubation, and eggs and hemoglobin (Hb) dielectric of chicken embryos at 18 days of age. Dielectric relative permittivity (epsilon') and conductivity (sigma) of Hb were examined in the range of frequency from 20 to 100 kHz. The values of dielectric increment (Deltaepsilon') and the relaxation times (tau) of Hb molecules were calculated. The internal temperature of eggs was measured in empty (following the removal of egg contents) and fertilized eggs in trials 1 and 2, respectively. The level of the EF was 30 kV/m, 60 Hz. EF incubation of embryos influenced the temperature of incubation and electrical properties of Hb molecules and did not influence the temperature of incubation and internal environment of eggs when empty eggs were incubated. EF incubation of fertilized eggs significantly raised the temperature of incubation, egg air cell, and at the surface of the egg yolk by approximately 0.09, 0.60, and 0.61 degrees F, respectively and Hb epsilon', sigma, Deltaepsilon', and tau as a function of the range of frequency of 20 to 100 kHz when compared with their counterparts of the control group. It was concluded that the exposure of fertilized chicken eggs to EF of 30 kV/m, 60 Hz, during incubation altered dielectric properties of Hb and that probably affected cell to cell communication and created the right environment for enhancing the growing process and heat production of embryos consequently increasing the temperature of the internal environment of the egg, and incubation.

Macroscopic and histological effects of magnetic field exposition in the process of tissue reparation in Wistar rats

Exposing body tissue, in vivo, to a magnetic field promotes metabolic alterations in the cell membrane's permeability and in the apoptosis phenomenon. This aim of the study was to investigate magnetic field interactions in the process of tissue repair in rats. Twenty-four male Wistar rats, weighing 200-350 g, were assigned to one of the three different groups: Control (without exposure to the magnetic field), South Pole (with exposure to the South magnetic field), and North Pole (with exposure to the north magnetic field). The intensity of the magnetic field used was 1,600 G. All the animals were anesthetized and immobilized on a surgical board in order to receive circular wounds. The size of the wounds was measured by a milimetric paquimeter. For the histological study, the tissues were fixed in paraffin and colored with hematoxylin and eosin. Wound size data were submitted to one-way analysis of variance (ANOVA) and to the test of Student-Newman-Keuls when appropriated. The results of day 5 (F (2,23):F (3,84); P < 0.05), day 10 (F (2,23):F (8,89); P < 0.05), and day 15 (F (2,23):F (7,88); P < 0.05) revealed a significant reduction between the size of the wounds of both North and South groups when compared to Control group. Our data suggest that chronic exposure to a magnetic field of 1,600 G can accelerate the speed of tissue repair in rats.

Electromagnetic fields affect transcript levels of apoptosis-related genes in embryonic stem cell-derived neural progenitor cells

Mouse embryonic stem (ES) cells were used as an experimental model to study the effects of electromagnetic fields (EMF). ES-derived nestin-positive neural progenitor cells were exposed to extremely low frequency EMF simulating power line magnetic fields at 50 Hz (ELF-EMF) and to radiofrequency EMF simulating the Global System for Mobile Communication (GSM) signals at 1.71 GHz (RF-EMF). Following EMF exposure, cells were analyzed for transcript levels of cell cycle regulatory, apoptosis-related, and neural-specific genes and proteins; changes in proliferation; apoptosis; and cytogenetic effects. Quantitative RT-PCR analysis revealed that ELF-EMF exposure to ES-derived neural cells significantly affected transcript levels of the apoptosis-related bcl-2, bax, and cell cycle regulatory "growth arrest DNA damage inducible" GADD45 genes, whereas mRNA levels of neural-specific genes were not affected. RF-EMF exposure of neural progenitor cells resulted in down-regulation of neural-specific Nurr1 and in up-regulation of bax and GADD45 mRNA levels. Short-term RF-EMF exposure for 6 h, but not for 48 h, resulted in a low and transient increase of DNA double-strand breaks. No effects of ELF- and RF-EMF on mitochondrial function, nuclear apoptosis, cell proliferation, and chromosomal alterations were observed. We may conclude that EMF exposure of ES-derived neural progenitor cells transiently affects the transcript level of genes related to apoptosis and cell cycle control. However, these responses are not associated with detectable changes of cell physiology, suggesting compensatory mechanisms at the translational and posttranslational level.

Effects of 2450 MHz electromagnetic fields with a wide range of SARs on methylcholanthrene-induced transformation in C3H10T1/2 cells

This study examined whether 2450 MHz continuous wave high frequency electromagnetic fields (HFEMF) could induce cancer-like changes in mouse C3H10T1/2 cells, and whether HFEMF could initiate malignant or synergistic transformation. Transformed foci, Type II and Type III, were independently counted as the experiment endpoint. The cells were exposed to HFEMF alone at a wide range of specific absorption rates (SARs) of 5 to 200 W/kg for 2 h and/or were treated with a known initiating chemical, methylcholanthrene (MC) (2.5 microg/ml). No significant differences were observed in the malignant transformation (Type II + Type III) frequency between the controls and HFEMF with or without 12-O-tetradecanoylphorbol-13-acetate (TPA) (0.5 ng/ml), a tumor promoter that could enhance transformation frequency initiated by MC in multistage carcinogenesis. However, the transformation frequency for HFEMF at SAR of more than 100 W/kg with MC or MC plus TPA was increased compared with MC alone or MC plus TPA. On the other hand, the corresponding heat groups (heat alone, heat + MC, and heat + MC + TPA) did not increase transformation compared with each control level in C3H10T1/2 cells. This result suggests that 2450 MHz HFEMF could not contribute to the initiation stage of tumor formation, but it may contribute to the promotion stage at the extremely high SAR (100 W/kg).

Effects of a time-varying strong magnetic field on transient increase in Ca2+ release induced by cytosolic Ca2+ in cultured pheochromocytoma cells

Exposure of pheochromocytoma (PC 12) cells to a time-varying 1.51 T magnetic field inhibited an increase in the intracellular Ca2+ concentration ([Ca2+]i) induced by addition of caffeine to Ca(2+)-free medium. This inhibition occurred after a 15-min exposure and was maintained for at least 2 h. [Ca2+]i sharply increased in cells loaded with cyclic ADP-ribose, and 2-h exposure significantly suppressed the increase. Addition of ATP induced a transient increase in intracellular Ca2+ release mediated by IP3 receptor, and this increase was strongly inhibited by the exposure. Results indicated that the magnetic field exposure strongly inhibited Ca2+ release mediated by both IP3 and ryanodine receptors in PC 12 cells. However, thapsigargin-induced Ca2+ influx (capacitative Ca2+ entry) across the cell membrane was unaffected. The ATP content was maintained at the normal level during the 2-h exposure, suggesting that ATP hydrolysis was unchanged. Therefore, Mg2+ which is known to be released by ATP hydrolysis and inhibit intracellular Ca2+ release may not relate the exposure-caused inhibition. Eddy currents induced in culture medium appear to change cell membrane properties and indirectly inhibit Ca2+ release from endoplasmic reticulum and other Ca2+ stores in PC 12 cells.

Magnetic field inhibits isolated lymphocytes' proliferative response to mitogen stimulation

We aimed to find out how the exposure of isolated lymphocytes to a pulsed magnetic field (MF) affected their in vitro proliferative response to mitogenic stimulation. Cells were exposed to MF of various intensities (0.3, 0.6, and 1.2 T) at a constant frequency of 30 Hz, for a period of 60, 180, and 330 s. Then, the proliferative response of splenocytes was induced by optimal concentrations of concanavalin A (Con A; mitogenic toward T cells), bacterial lipopolysaccharide (LPS; mitogenic toward B cells), or pokeweed mitogen (PWM; mitogenic toward both populations). We found that the exposure of lymphocytes to the MF profoundly inhibited their proliferative response to mitogens. The suppressive action of the MF on B and T cell proliferation was intensified when a cooperative response of those two lymphocyte populations was simultaneously induced by PWM. The inhibitory effect of MF depended on the exposure time and MF intensity. Prolonged exposure and/or a stronger intensity of the MF weakened its inhibitory influence on the response of lymphocyte to mitogenic stimulation. The data show that an exposure to MF may influence the activity of lymphocytes in their response to mitogenic stimuli.

Exposure to 50 Hz electromagnetic radiation promote early maturation and differentiation in newborn rat cerebellar granule neurons

The wish of this work is the study of the effect of electromagnetic (EMF) radiations at a frequency of 50 Hz on the development of cerebellar granule neurons (CGN). Granule neurons, prepared from newborn rat cerebellum (8 days after birth), were cultured after plate-seeding in the presence of EMF radiations, with the plan of characterizing their cellular and molecular biochemistry, after exposure to the electromagnetic stimulus. Five days challenge to EMF radiations showed, by the cytotoxic glutamate (Glu) pulse test, a 30% decrease of cells survival, while only 5% of mortality was reported for unexposed sample. Moreover, blocking the glutamate receptor (GluR) with the Glu competitor MK-801, no toxicity effect after CGN challenge to EMF radiations and Glu was detected. By patch-clamp recording technique, the Kainate-induced currents from 6 days old exposed CGN exhibited a significant increase with respect to control cells. Western blot and reverse transcription-polymerase chain reaction (RT-PCR) analyses show that EMF exposure of rats CGN, induces a change in both GluRs proteins and mRNAs expression with respect to control. In addition, the use of monoclonal antibody raised against neurofilament protein (NF-200) reveals an increase in NF-200 synthesis in the exposed CGN. All these results indicate that exposure to non-ionizing radiations contribute to a premature expression of GluRs reducing the life span of CGN, leading to a more rapid cell maturation.

Effects of 50Hz electromagnetic fields on voltage-gated Ca2+ channels and their role in modulation of neuroendocrine cell proliferation and death

Possible correlation between the effects of electromagnetic fields (EFs) on voltage-gated Ca(2+) channels, cell proliferation and apoptosis was investigated in neural and neuroendocrine cells. Exposure to 50 Hz EFs significantly enhanced proliferation in human neuroblastoma IMR32 (+40%) and rat pituitary GH3 cells (+38%). In IMR32 cells EF stimulation also inhibited puromycin- and H(2)O(2)-induced apoptosis (-22 and -33%, respectively). EF effects on proliferation and apoptosis were counteracted by Ca(2+) channel blockade. In whole-cell patch-clamp experiments 24-72 h exposure to EFs increased macroscopic Ba(2+)-current density in both GH3 (+67%) and IMR32 cells (+40%). Single-channel recordings showed that gating of L and N channels was instead unaffected, thus suggesting that the observed enhancement of current density was due to increased number of voltage-gated Ca(2+) channels. Western blot analysis of plasma membrane-enriched microsomal fractions of GH3 and IMR32 cells confirmed enhanced expression of Ca(2+) channel subunit alpha(1) following exposure to EFs. These data provide the first direct evidence that EFs enhance the expression of voltage-gated Ca(2+) channels on plasma membrane of the exposed cells. The consequent increase in Ca(2+) influx is likely responsible for the EF-induced modulation of neuronal cell proliferation and apoptosis.

Expression levels of heat shock protein 60 in human endothelial cells in vitro are unaffected by exposure to 50 Hz magnetic fields

Magnetic fields (MFs) from domestic power sources have been implicated as being a potential risk to human health. A number of epidemiological studies have found a significant link between exposure to MFs and increased rates of cancers. There have also been a number of in vivo and in vitro studies reporting effects of MFs in animal disease models and on the expression or activity of a range of proteins. In the past decade, our group proposed that atherosclerosis may have an autoimmune component, with heat shock protein 60 (Hsp60) expressed in endothelial cells as the dominant autoantigen. A number of stressors have been shown to induce the expression of Hsp60, including the classical risk factors for atherosclerosis. We were interested to see if the exposure of endothelial cells to an MF elicited increased expression of Hsp60, as has been reported previously for Hsp70. The present work describes the exposure of endothelial cells to domestic power supply (50 Hz) MFs at an intensity of 700 microT. The results from our system indicate that cultured endothelial cells exposed to a high intensity of MF either alone or in combination with classical heat stress show no effects on the expression of Hsp60 at either the messenger ribonucleic acid or the protein level. As such, there is no evidence that exposure to extremely low-frequency MF would be expected to increase the expression of Hsp60 and therefore the initiation or progression of atherosclerosis.

Non-thermal effects of power-line magnetic fields (50Hz) on gene expression levels of pluripotent embryonic stem cells—the role of tumour suppressor p53

The diffusion of extremely low-frequency (50 Hz) electromagnetic fields (ELF-EMF) in the human environment raises the question of the induction of biological effects of EMF on mammalian cells. We used the model of mouse pluripotent embryonic stem (ES) cells, which have the capacity to develop in vitro into cells of all lineages, to analyse non-thermal effects of ELF-EMF. Wild type (wt) and p53-deficient ES cells were exposed under controlled conditions to ELF-EMF signals simulating power-line (50 Hz) magnetic field (PL-MF) exposure. Different flux densities of 0.1 mT, 1.0 mT or 2.3 mT and intermittency schemes with various ON/OFF cycles were applied for 6 h or 48 h during the first stages of cell differentiation. Transcript levels of regulatory genes, such as egr-1, p21, c-jun, c-myc, hsp70 and bcl-2, were analysed by semi-quantitative RT-PCR immediately after exposure or after a recovery time of 18 h. Intermittent PL-MF exposure to 5 min ON/30 min OFF cycles at a flux density of 2.3 mT for 6 h resulted in a significant up-regulation of c-jun, p21 and egr-1 mRNA levels in p53-deficient, but not in wild-type cells. No significant effects were observed in both cell systems by PL-MF at lower flux densities, longer exposure time or after 18 h recovery time. Our data indicate that 5 min ON/30 min OFF intermittent PL-MF exposure is capable of evoking non-thermal responses in ES cells, dependent on the cellular p53 function. The nature of the biological responses triggered by PL-MF is discussed.

Low electromagnetic field (50 Hz) induces differentiation on primary human oral keratinocytes (HOK)

This work concerns the effect of low frequency electromagnetic fields (ELF) on biochemical properties of human oral keratinocytes (HOK). Cells exposed to a 2 mT, 50 Hz, magnetic field, showed by scanning electron microscopy (SEM) modification in shape and morphology; these modifications were also associated with different actin distribution, revealed by phalloidin fluorescence analysis. Moreover, exposed cells had a smaller clonogenic capacity, and decreased cellular growth. Indirect immunofluorescence with fluorescent antibodies against involucrin and beta-catenin, both differentiation and adhesion markers, revealed an increase in involucrin and beta-catenin expression. The advance in differentiation was confirmed by a decrease of expression of epidermal growth factor (EGF) receptor in exposed cells, supporting the idea that exposure to electromagnetic field carries keratinocytes to higher differentiation level. These observations support the hypothesis that 50 Hz electromagnetic fields may modify cell morphology and interfere in differentiation and cellular adhesion of normal keratinocytes.

60 Hz electric field upregulates cytosolic Ca2+ level in mouse splenocytes stimulated by lectin

The effect of a 60 Hz electric field (EF) on alteration of cytosolic free Ca2+ level ([Ca2+]c) was examined in mouse splenocytes stimulated by lectins, namely concanavalin A (ConA) or phytohemagglutinin. In order to understand the role of EF on alterations in [Ca2+]c and to determine whether EF exposure increased cell mortality the splenocytes were cultured under the 60 Hz EFs producing current densities of 6 or 60 microA/cm2 for 30 min or 24 h. Cell mortality was less than 2% in experimental all conditions. [Ca2+]c in the splenocyte was not changed by the 6 microA/cm2 exposure alone, while a lectin-induced [Ca2+]c elevation in the EF exposed cells was significantly higher than that of the sham exposed cells (P <.05: ANOVA, P <.05: paired t-test). Moreover, the enhanced increase of [Ca2+]c in the EF exposed, lectin stimulated cells was only observed in the presence of extracellular Ca2+. The EF dependent upregulation of [Ca2+]c persisted after EF exposure (P <.05: paired t-test). The results clearly indicate that Ca2+ influx across the plasma membrane is responsible for the enhanced increase of [Ca2+]c in the EF exposed, lectin stimulated cells and that EF has persistent effect on the cells. Although the precise mechanisms of the EF dependent upregulation of [Ca2+]c is not fully elucidated, the present results demonstrate that the 60 Hz EF (6 microA/cm2) affects [Ca2+]c during cell activation via a Ca2+ influx pathway induced by lectin stimulation.

Effects of ELF magnetic field on membrane protein structure of living HeLa cells studied by Fourier transform infrared spectroscopy

The effects of exposure to a 50 Hz magnetic field (maximum of 41.7 to 43.6 mT) on the membrane protein structures of living HeLa cells were studied using attenuated total reflection infrared spectroscopy. One min of such exposure shifted peak absorbance of the amide I band to a smaller wave number, reduced peak absorbance of the amide II band, and increased absorbance at around 1600 cm(-1). These results suggest that exposure to the ELF magnetic field has reversible effects on the N-H inplane bending and C-N stretching vibrations of peptide linkages, and changes the secondary structures of alpha-helix and beta-sheet in cell membrane proteins.

Power line frequency electromagnetic fields do not increase the rate of protein synthesis in human skin fibroblasts as previously reported

Rodemann et al. [Rodemann et al. (1987): Biochem Biophys Res Commun 145:1-9] reported that human skin fibroblasts increase their rate of protein synthesis by as much as over ninefold in response to long term exposure to 20 Hz, 8.4 mT (84 G) magnetic fields. Here we report studies of protein synthesis using an identical cell type, exposure conditions, and the same means of measuring protein synthetic rates. Our initial goal was to determine if the earlier results could be replicated, but we found an inconsistency in the earlier protocol. It exposed cells to [(3)H]leucine for 6 h prior to measuring incorporation into protein. We found, however, that 24 h is required for [(3)H]leucine to reach a steady state distribution across the cells' plasma membranes. In addition, we typically measured 100-200 cpm/thousand cells. This is four- to eightfold higher than the 19-28 cpm/1000 cells previously reported. Using these conditions, we could find no significant difference in protein synthesis rates between control cells and cells exposed for up to three weeks in an identical electromagnetic field. In addition, we investigated the effects of a 60 Hz field since that is the frequency used for electric power distribution in the United States. Again, we could find no significant effect of this field on rates of protein synthesis, even after 21 days of exposure.

Interactions of zero-frequency and oscillating magnetic fields with biostructures and biosystems

This review points to the investigations concerning the effects of zero-frequency (DC) and oscillating (AC) magnetic fields (MFs) on living matter, and especially those exerted by weak DC and low-frequency/low-intensity AC MFs. Starting from the analysis of observations on the action of natural magnetic storms (MSs) or periodic geomagnetic field (GMF) variations on bacteria, plants and animals, which led to an increasing interest in MFs in general, this survey pays particular attention to the background knowledge regarding the action of artificial MFs not only at the ionic, molecular or macromolecular levels, but also at the levels of subcellular regions, in vitro cycling cells, in situ functioning tissues or organs and total bodies or entire populations. The significance of some crucial findings concerning, for instance, the MF-dependence of the nuclear or cellular volumes, rate of cell proliferation vs. that of cell death, extent of necrosis vs. that of apoptosis and cell membrane fluidity, is judged by comparing the results obtained in a solenoid (SLD), where an MF can be added to a GMF, with those obtained in a magnetically shielded room (MSR), where the MFs can be partially attenuated or null. This comparative criterion is required because the differences detected in the behaviour of the experimental samples against that of the controls are rather small per se and also because the evaluation of the data often depends upon the peculiarity of the methodologies used. Therefore, only very small differences are observed in estimating the MF-dependence of the expression of a single gene or of the rates of total DNA replication, RNA transcription and protein translation. The review considers the MF-dependence of the interactions between host eukaryotic cells and infecting bacteria, while documentation of the harmful effects of the MFs on specific life processes is reported; cases of favourable action of the MFs on a number of biological functions are also evidenced. In the framework of studies on the origin and adaptation of life on Earth or in the Universe, theoretical insights paving the way to elucidate the mechanisms of the MF interactions with biostructures and biosystems are considered.

Teratogenic effect of broad-band electromagnetic field on neonatal mice (Mus musculus)

Pregnant mice (Mus musculus), strain Swiss Webster, were exposed to a continuous electromagnetic field (12.8V/m) beginning in the third week of pregnancy. Histological and hematological analysis showed gender specific responses in 21 day-old mice after in-utero and post-natal continuous exposure. Automated lymphocyte percentage and total white blood cell counts were significantly elevated in exposed 21 day-old female mice compared to control mice. Lymphoma-like cells were seen in higher numbers in exposed 21 day-old male mice. Megaloblastic changes, such as hypersegmented neutrophils, were observed in exposed mice. The blood from control neonatal mice was more viscous than that of exposed mice, enough to interfere with making a blood smear. The adult female mice showed no significant differences in the above hematologic parameters between exposed and control groups. Histological study showed the following pathological changes in the adrenal cortex: degeneration/necrosis in the zona glomerulosa; hypertrophy in zona reticularis; degeneration/necrosis, intracytoplasmic inclusions and inflammation in the zona fasciculata/reticularis, more prominent in exposed female neonates; and lipidosis in the zona fasciculata. In the adrenal medulla: atrophy was more common in exposed female neonates; and intracytoplasmic inclusions and vacuolation were more common in exposed male neonates. Cystic proliferations were found in the cortical area of the thymus. In the medulla of the thymus, there was vacuolation, inflammation, or eosinophilic intracytoplasmic inclusions in exposed adults. Behavioral differences occurred in both neonates and adult females. Control neonates were able to manipulate through a maze more quickly than exposed neonates; and control adult females displayed more thorough grooming behavior than exposed mothers, and maintained more distance between the nest and dropping location than did the exposed group.

Static magnetic fields affect calcium fluxes and inhibit stress-induced apoptosis in human glioblastoma cells

BACKGROUND

Epidemiologic data revealed increased brain tumor incidence in workers exposed to magnetic fields (MFs), raising concerns about the possible link between MF exposure and cancer. However, MFs seem to be neither mutagenic nor tumorigenic. The mechanism of their tumorigenic effect has not been elucidated.

METHODS

To evaluate the interference of MFs with physical (heat shock, HS) and chemical (etoposide, VP16) induced apoptoses, respectively, we exposed a human glioblastoma primary culture to 6 mT static MF. We investigated cytosolic Ca(2+) ([Ca(2+)](i)) fluxes and extent of apoptosis as key endpoints. The effect of MFs on HS- and VP16-induced apoptoses in primary glioblastoma cultures from four patients was also tested.

RESULTS

Static MFs increased the [Ca(2+)](i) from a basal value of 124 +/- 4 nM to 233 +/- 43 nM (P < 0.05). MF exposure dramatically reduced the extent of HS- and VP16-induced apoptoses in all four glioblastoma primary cultures analyzed by 56% (range, 28-87%) and 44% (range, 38-48%), respectively. However, MF alone did not exert any apoptogenic activity. Differences were observed across the four cultures with regard to apoptotic induction by HS and VP16 and to MF apoptotic reduction, with an individual variability with regard to apoptotic sensitivity.

CONCLUSION

The ability of static MFs to reduce the extent of damage-induced apoptosis in glioblastoma cells might allow the survival of damaged and possibly mutated cells.

Cellular target of weak magnetic fields: ionic conduction along actin filaments of microvilli

The interaction of weak electromagnetic fields (EMF) with living cells is a most important but still unresolved biophysical problem. For this interaction, thermal and other types of noise appear to cause severe restrictions in the action of weak signals on relevant components of the cell. A recently presented general concept of regulation of ion and substrate pathways through microvilli provides a possible theoretical basis for the comprehension of physiological effects of even extremely low magnetic fields. The actin-based core of microfilaments in microvilli is proposed to represent a cellular interaction site for magnetic fields. Both the central role of F-actin in Ca2+ signaling and its polyelectrolyte nature eliciting specific ion conduction properties render the microvillar actin filament bundle an ideal interaction site for magnetic and electric fields. Ion channels at the tip of microvilli are connected with the cytoplasm by a bundle of microfilaments forming a diffusion barrier system. Because of its polyelectrolyte nature, the microfilament core of microvilli allows Ca2+ entry into the cytoplasm via nonlinear cable-like cation conduction through arrays of condensed ion clouds. The interaction of ion clouds with periodically applied EMFs and field-induced cation pumping through the cascade of potential barriers on the F-actin polyelectrolyte follows well-known physical principles of ion-magnetic field (MF) interaction and signal discrimination as described by the stochastic resonance and Brownian motor hypotheses. The proposed interaction mechanism is in accord with our present knowledge about Ca2+ signaling as the biological main target of MFs and the postulated extreme sensitivity for coherent excitation by very low field energies within specific amplitude and frequency windows. Microvillar F-actin bundles shielded by a lipid membrane appear to function like electronic integration devices for signal-to-noise enhancement; the influence of coherent signals on cation transduction is amplified, whereas that of random noise is reduced.

Effect of microwave electromagnetic field on skeletal muscle fibre activity

The aim of the present study was to investigate the influence of microwave irradiation on fatiguing activity of isolated frog skeletal muscle fibres. The changes in the electrical and mechanical activity were used as criteria for the exposure effects. Repetitive suprathreshold stimulation with interstimulus interval of 200 ms for 3 min was applied. Intracellular (ICAP) and extracellular (ECAP) action potentials and twitch contractions (Tw) of muscle fibres after 1 hour microwave exposure (2.45 GHz, 20 mW/cm( 2) power density) were compared with those recorded after one hour sham exposure (control). The duration of uninterrupted activity in the trial (endurance time; ET) was not significantly affected by microwave field exposure. After microwave irradiation, the ICAP amplitude was higher, the rising time was shorter, and the resting membrane potential was more negative compared to controls. There was a slower rate of parameters changes during ET in potentials obtained from irradiated fibres. Microwave exposure increased the propagation velocity of excitation, the ECAP and Tw amplitudes, as well as shortened their time parameters. We concluded that a 2.45 GHz microwave field possesses a stimulating effect on muscle fibre activity, which is in part due to its specific, non-thermal properties. The microwave induced-changes in muscle fibre activity may reduce development of skeletal muscle fatigue.

Insights into electromagnetic interaction mechanisms

Low frequency (< 300 Hz) electromagnetic (EM) fields induce biological changes that include effects ranging from increased enzyme reaction rates to increased transcript levels for specific genes. The induction of stress gene HSP70 expression by exposure to EM fields provides insight into how EM fields interact with cells and tissues. Insights into the mechanism(s) are also provided by examination of the interaction of EM fields with moving charges and their influence on enzyme reaction rates in cell-free systems. Biological studies with in vitro model systems have focused, in general, on the nature of the signal transduction pathways involved in response to EM fields. It is likely, however, that EM fields also interact directly with electrons in DNA to stimulate biosynthesis. Identification of an EM field-sensitive DNA sequence in the heat shock 70 (HSP70) promoter, points to the application of EM fields in two biomedical applications: cytoprotection and gene therapy. EM field induction of the stress protein hsp70 may also provide a useful biomarker for establishing a science-based safety standard for the design of cell phones and their transmission towers.

Effects of extremely low frequency (50 Hz) magnetic field on morphological and biochemical properties of human keratinocytes

We investigated the effects on human keratinocytes (HaCaT) of exposure to a sinusoidal magnetic field of 2 mT (50 Hz). These cells are a good model for studying interaction of nonionising radiation, because they are not shielded from fields in vivo and also because they are resistant to both mechanical and thermal stimuli. We performed scanning microscopy which showed modification in shape and morphology in exposed cells. This modification is related to differential actin distribution as revealed by phalloidin fluorescence analysis. Moreover, the exposed cells show increased clonogenic capacity, as well as increased cellular growth as showed by clonogenicity assays and growth curves. Indirect immunofluorescence analysis using a fluorescent antibody against involucrin and beta4 integrin, which are respectively differentiation and adhesion markers, revealed an increase of involucrin expression and segregation of beta4 integrin in the cell membrane in cells exposed to 50 Hz; a higher percentage of the exposed cells shows a modified pattern of adhesion and differentiation markers. We also present evidence that exposure of HaCaT cells can interfere with protein kinase activity. Our observations confirm the hypothesis that electromagnetic fields at 50 Hz may modify cell membrane morphology and interfere with initiation of the signal cascade pathway and cellular adhesion.

Calcium protects differentiating neuroblastoma cells during 50 Hz electromagnetic radiation

Despite growing concern about electromagnetic radiation, the interaction between 50- to 60-Hz fields and biological structures remains obscure. Epidemiological studies have failed to prove a significantly correlation between exposure to radiation fields and particular pathologies. We demonstrate that a 50- to 60-Hz magnetic field interacts with cell differentiation through two opposing mechanisms: it antagonizes the shift in cell membrane surface charges that occur during the early phases of differentiation and it modulates hyperpolarizing K channels by increasing intracellular Ca. The simultaneous onset of both mechanisms prevents alterations in cell differentiation. We propose that cells are normally protected against electromagnetic insult. Pathologies may arise, however, if intracellular Ca regulation or K channel activation malfunctions.

Magnetic fields (MF) of 50 Hz at 1.2 microT as well as 100 microT cause uncoupling of inhibitory pathways of adenylyl cyclase mediated by melatonin 1a receptor in MF-sensitive MCF-7 cells

Magnetic fields (MF) of 60 Hz at 1.2 microT were previously shown to inhibit the antiproliferative effect of melatonin on MCF-7 cells (Liburdy,R.P., 1993, J. Pimeal Res. 14, 89-97). In addition, three laboratories (Blackman,C.F. and Benane,S.G., 1998; Luben,R.A. and Morgan,A.P., 1998; Morris,J.E., Chrisler,W.B., Miller,D.L., Sasser,L.B. and Anderson,L.E., 1998; 20th Annual Meeting of the Bioelectromagnetics Society, At. Pete Beach, FL) independently reported results consistent with this finding. In this study, we investigated the molecular basis of the biological effects of MF using MCF-7 cells. Only 1a melatonin receptors were identified by the [125I]melatonin binding assay and RT-PCR analysis. Moreover, preceding exposures to MF of 100 microT for 3, 5 and 7 days blocked the melatonin-induced inhibition of cAMP accumulation in a time-dependent manner, while none of the melatonin receptor functions or GTPase and adenylyl cyclase activities were affected. Estrogen-evoked cell proliferation was not altered by MF either. Exposure to 1.2 microT MF exerted the same effects on the melatonin-signaling pathway as that to 100 microT. Thus, this is the first study to provide evidence that MF may cause uncoupling of signal transduction from melatonin receptors to adenylyl cyclase.

Effects of magnetic fields on the accumulation of thiobarbituric acid reactive substances induced by iron salt and H(2)O(2) in mouse brain homogenates or phosphotidylcholine

In this study, we examined the effects of magnetic fields (MFs) on the generation of thiobarbituric acid reactive substances (TBARS) in the mouse brain homogenates or phosphotidylcholine (PC) solution, incubated with FeCl(3) and/or H(2)O(2). Active oxygen species were generated and lipid peroxidation was induced in mouse brain homogenates by incubation with iron ions, resulting in the accumulation of TBARS. Lipid peroxidation was induced in PC by incubation with iron ions and H(2)O(2). Exposure to sinusoidal MFs (60 Hz, 0.2-1.2 mT), symmetric sawtooth-waveform MFs (50 Hz, 25-600 mT/s), rectangular MFs (1/0.4-1/16 Hz, 3.3 mT) and static MFs (1, 5-300 mT) had no effect on the accumulation of TBARS in brain homogenates induced by FeCl(3). In contrast, when the homogenates were incubated with FeCl(3) in static MFs (2-4 mT), the accumulation of TBARS was decreased. However, this inhibitory effect disappeared when EDTA was added to the homogenate and incubated with H(2)O(2). The accumulation of TBARS in PC solution incubated with FeCl(3) and H(2)O(2) was also inhibited by the static MF. These results indicate that only static MFs had an inhibitory effect on iron-induced lipid peroxidation and the effectiveness of this magnetic field on iron ion-induced active oxygen species generation is restricted to a so called 'window' of field intensity of 2-4 mT.

Microvillar ion channels: cytoskeletal modulation of ion fluxes

The recently presented theory of microvillar Ca(2+)signaling [Lange, K. (1999) J. Cell. Physiol.180, 19-35], combined with Manning's theory of "condensed counterions" in linear polyelectrolytes [Manning, G. S. (1969). J. Chem. Phys.51, 924-931] and the finding of cable-like ion conductance in actin filaments [Lin, E. C. & Cantiello, H. F. (1993). Biophys. J.65, 1371-1378], allows a systematic interpretation of the role of the actin cytoskeleton in ion channel regulation. Ion conduction through actin filament bundles of microvilli exhibits unique nonlinear transmission properties some of which closely resemble that of electronic semiconductors: (1) bundles of microfilaments display significant resistance to cation conduction and (2) this resistance is decreased by supply of additional energy either as thermal, mechanical or electromagnetic field energy. Other transmission properties, however, are unique for ionic conduction in polyelectrolytes. (1) Current pulses injected into the filaments were transformed into oscillating currents or even into several discrete charge pulses closely resembling that of single-channel recordings. Discontinuous transmission is due to the existence of counterion clouds along the fixed anionic charge centers of the polymer, each acting as an "ionic capacitor". (2) The conductivity of linear polyelectrolytes strongly decreases with the charge number of the counterions; thus, Ca(2+)and Mg(2+)are effective modulator of charge transfer through linear polyelectrolytes. Field-dependent formation of divalent cation plugs on either side of the microvillar conduction line may generate the characteristic gating behavior of cation channels. (3) Mechanical movement of actin filament bundles, e.g. bending of hair cell microvilli, generates charge translocations along the filament structure (mechano-electrical coupling). (4) Energy of external fields, by inducing molecular dipoles within the polyelectrolyte matrix, can be transformed into mechanical movement of the system (electro-mechanical coupling). Because ionic transmission through linear polyelectrolytes is very slow compared with electronic conduction, only low-frequency electromagnetic fields can interact with the condensed counterion systems of linear polyelectrolytes. The delineated characteristics of microvillar ion conduction are strongly supported by the phenomenon of electro-mechanical coupling (reverse transduction) in microvilli of the audioreceptor (hair) cells and the recently reported dynamics of Ca(2+)signaling in microvilli of audio- and photoreceptor cells. Due to the cell-specific expression of different types and combinations of ion channels and transporters in the microvillar tip membrane of differentiated cells, the functional properties of this cell surface organelle are highly variable serving a multitude of different cellular functions including receptor-mediated effects such as Ca(2+)signaling, regulation of glucose and amino acid transport, as well as modulation of membrane potential. Even mechanical channel activation involved in cell volume regulation can be deduced from the systematic properties of the microvillar channel concept. In addition, the specific ion conduction properties of microfilaments combined with their proposed role in Ca(2+)signaling make microvilli the most likely cellular site for the interaction with external electric and magnetic fields.

In vitro evaluation of teratogenic effects by time-varying MR gradient fields on fetal human fibroblasts

The purpose of this study was to evaluate the influence on fetal cell growth in vitro of rapidly changing magnetic gradient fields such as those produced by the gradient coils of a typical magnetic resonance (MR) imager. The static magnetic field and the radiofrequency pulses were disabled during all measurements. Human fetal fibroblasts were placed within a specially designed MR-compatible incubation system inside the magnet. Trapezoid-shaped waveforms of 500 and 75 Hz base frequency and an amplitude of 2 mT were applied for 2-24 hours. Proliferation of the cells was monitored for 3 weeks after exposure. Cell cycle analysis was performed until 24 hours after exposure to detect alterations in cell division. Tests were performed under two different conditions of growth to detect increased as well as decreased proliferation effects. None of these tests showed differences in proliferation and cell cycle distribution between exposed and nonexposed cells.

Pulsed magnetic fields enhance nitric oxide synthase activity in rat cerebellum

The effect of pulsed magnetic fields on nitric oxide synthase (NOS) activity in the rat brain was investigated. Sprague-Dawley rats (male, 200-250 g body weight) brain were dissected regionally, and the crude enzyme solutions were treated with pulsed DC, AC or static DC magnetic fields at 0 degrees C for 1 h. After exposure, NOS activity was measured as nitrite and nitrate levels generated from incubation with arginine, CaCl(2) and beta-nicotinamide adenine dinucleotide phosphate. Under these experimental conditions, neither AC nor static DC field treatment showed any significant change in NOS activity. A significant increase in NOS activity was observed in the cerebellum (111.2+/-2.0%, P<0.05, five separate experiments) for a 1 Gauss (0.1 mT) pulsed DC field. Under the same experimental condition, only a slight change or no effect was observed in the hippocampus, cortex, medulla oblongata, hypothalamus, striatum and midbrain. These studies suggest that pulsed magnetic fields result in a different effect on NOS activity in the cerebellum of the rats.

Effects of an in vivo 60 Hz magnetic field on monoamine levels in mouse brain

We studied the effects of electromagnetic fields (EMF) on mouse brain monoamine levels in models of (1) chronic exposure (7 days) of EMF (60 Hz, 10 Gauss) to mice in a vertical orientation, (2) prolonged chronic exposure (84 days) of EMF (60 Hz, 10 Gauss) to mice in a horizontal mode, (3) acute exposure (6 h) of EMF (60 Hz, 10 Gauss) to senescence accelerated mice (SAM-P8) at ages 1, 3, 6, 9 and 12 months in the horizontal mode, and (4) acute exposure (1 h) of EMF (60 Hz, 1, 3.3 and 10 Gauss) to restrained mice in the horizontal mode. No model except the restrained one changed their monoamine or metabolite levels by exposure to EMF. In the restrained group, dihydroxyphenylacetic acid (DOPAC) was significantly increased in the hippocampus (HP) and hypothalamus (HY), homovanillic acid (HVA) was significantly increased in HY, and 5-hydroxyindolacetic acid (5-HIAA) was significantly increased in HP and thalamus-midbrain (TM). None of these monoamine metabolite levels were changed when the mouse was restrained without EMF exposure. These results suggest that monoamine metabolism is influenced by EMF only when the exposure is in the same direction as the mouse position. Another possibility is that EMF enhances the restraint stress since stress is known to increase monoamine metabolism.

Electric field-induced changes in agonist-stimulated calcium fluxes of human HL-60 leukemia cells

The mechanism of biological effects of extremely-low-frequency electric and magnetic fields may involve induced changes of Ca2+ transport through plasma membrane ion channels. In this study we investigated the effects of externally applied, low-intensity 60 Hz electric (E) fields (0.5 V/m, current density 0.8 A/m2) on the agonist-induced Ca2+ fluxes of HL-60 leukemia cells. The suspensions of HL-60 cells received E-field or sham exposure for 60 min and were simultaneously stimulated either by 1 microM ATP or by 100 microM histamine or were not stimulated at all. After E-field or sham exposure, the responses of the intracellular calcium levels of the cells to different concentrations of ATP (0.2-100 microM) were assessed. Compared with control cells, exposure of ATP-activated cells to an E-field resulted in a 20-30% decrease in the magnitude of [Ca2+]i elevation induced by a low concentration of ATP (<1 microM). In contrast, exposure of histamine-activated HL-60 cells resulted in a 20-40% increase of ATP-induced elevation of [Ca2+]i. E-field exposure had no effect on non-activated cells. Kinetic analysis of concentration-response plots also showed that compared with control cells, exposure to the E-field resulted in increases of the Michaelis constant, Km, value in ATP-treated cells and of the maximal [Ca2+]i peak rise in histamine-treated HL-60 cells. The observed effects were reversible, indicating the absence of permanent structural damages induced by acute 60 min exposure to electric fields. These results demonstrate that low-intensity electric fields can alter calcium distribution in cells, most probably due to the effect on receptor-operated Ca2+ and/or ion channels.

Circadian locomotor activity of Musca flies: recording method and effects of 10 Hz square-wave electric fields

Musca domestica flies that were exposed to a uniform vertical 10 Hz electric square-wave field of 1 kVm(-1) changed the period length of their circadian locomotor activity rhythm. Under constant conditions, the clock of short-period flies was slowed down by the field, whereas the clock of long-period flies either was affected only scarcely (experiments at about 19 degrees C) or ran faster (experiments at 25 degrees C). If the field was applied for only 12 h daily, then 30-40 percent of the flies were synchronized. Thus, the field could function as a weak "Zeitgeber" (synchronizer). If the field was increased to 10 kVm(-1), then 50-70 percent of the flies were synchronized. Flies avoided becoming active around the onset of the 12 h period of exposure to a 10 Hz field. The results of these experiments are discussed with respect to similar experiments by Wever on the effects of exposure to a 10 Hz field on the circadian system of man.

Action of extremely low frequency electric fields on the cytosolic calcium concentration of differentiated HL-60 cells: nonactivated cells

The effect of sinusoidal electric fields on the cytosolic free [Ca2+]i concentration in differentiated HL-60 cells was measured. The calcium concentration was measured in a fluorescence spectrometer using the fluorescence sample fluo-3. In the fluorescence spectrometer two samples can be measured simultaneously, one as the sham-exposed control and the other as the field-exposed sample. The effects of an external field, applied using two capacitor plates outside the cuvettes, and a field applied directly to the medium, using two platinum electrodes inside the cuvettes, were measured at selected frequencies between 0 and 100 Hz and field strengths from 1 to 2000 Vpp/m (external field) and from 0.1 to 1000 Vpp/m (in medium). No significant effects of the fields on the cytosolic free [Ca2+]i concentration in HL-60 cells have been observed at the measured frequencies and field strengths.

Effects of low-level 50 Hz magnetic fields on the level of host defense and on spleen colony formation

The results of 3 sets of experiments on the effects of 22 microT sinusoidal 50 Hz magnetic fields (MF), applied for 1 h on 5 successive days (1 h/5 days), on the level of host defense and on spleen colony formation are reported. The first set of experiments shows the effects on the number of colony-forming units (CFUs) on the spleen and on the cellularity of the thymus in mice. The MF exposures resulted in an increase in CFUs which was statistically significant with respect to the controls, but not with respect to the shams. Statistically significant changes in the thymic weight and thymic index with respect to both the controls and the shams were measured 1 h after the last MF exposure. In the second set of experiments, the mice were given a sublethal dose of X-rays (6 Gy), which was followed by exposure 2 h later to the MF. The MF exposure was repeated at the same time of day for 5 days. The number of colonies per spleen showed a consistent, statistically significant increase with MF exposure and the number of CFUs per femur was decreased. In the third set of experiments, bone marrow was taken from mice which had been exposed to 22 microT fields and injected into mice which had been exposed to a lethal dose of X-rays (9 Gy). The number of CFUs per femur in the recipient mice was shown to be reduced by a statistically significant amount at 1 and 4 days after injection.

Environmental magnetic fields inhibit the antiproliferative action of tamoxifen and melatonin in a human breast cancer cell line

We have previously reported that environmental-level magnetic fields (1.2 microT [12 milligauss], 60 Hz) block the growth inhibition of the hormone melatonin (10(-9) M) on MCF-7 human breast cancer cells in vitro. We now report that the same 1.2 microT, 60 Hz magnetic fields significantly block the growth inhibitory action of pharmacological levels of tamoxifen (10(-7) M). In biophysical studies we have taken advantage of Faraday's Law of Current Induction and tested whether the 1.2 microT magnetic field or the associated induced electric field is responsible for this field effect on melatonin and tamoxifen. We observe that the magnetic field component is associated with the field blocking effect on melatonin and tamoxifen function. To our knowledge the tamoxifen studies represent the first experimental evidence for an environmental-level magnetic field modification of drug interaction with human breast cancer cells. Together, these findings provide support to the theory that environmental-level magnetic fields can act to modify the action of a drug or hormone on regulation of cell proliferation. Melatonin and tamoxifen may act through different biological pathways to down-regulate cell growth, and further studies are required to identify a specific biological site of interaction for the 1.2 microT magnetic field.

Ion-protein dissociation predicts 'windows' in electric field-induced wound-cell proliferation

There are many experiments showing that weak, non-thermal electric fields influence living tissues. In many cases, biological effects display 'windows' in biologically effective parameters of electric fields: most dramatic is the fact that relatively intense electric fields sometimes do not cause appreciable effect, while smaller fields do. Linear resonant physical processes do not explain frequency windows in this case. Both frequency and amplitude windows are evident from experiments on human dermal fibroblasts in a collagen matrix. For this in vitro model of skin, exposure to extremely low frequency (ELF) electric fields in the frequency range 10-100 Hz and the amplitude range of 0-130 microA/cm(2) macroscopic current density demonstrates such unusual 'window' behavior. Amplitude window phenomena suggest a non-linear physical mechanism. We consider non-linear quantum-interference effects on protein-bound substrate ions: These ions experience, due to electric fields in the media or biological tissue as small as 1 mV/m, electric gradients produced by polarized binding ligand atomic shells. The electric gradients cause an interference of ion quantum states. This ion-interference mechanism predicts specific electric-field frequency and amplitude windows within which fibroblast proliferation occurs.

Effects on Rb(+)(K+) uptake of HeLa cells in a high K(+) medium of exposure to a switched 1.7 Tesla magnetic field

Effects of a switched, time-varying 1.7 T magnetic field on Rb(+)(K+) uptake by HeLa S3 cells incubated in an isosmotic high K(+) medium were examined. The magnetic flux density was varied intermittently from 0.07-1.7 T at an interval of 3 s. K(+) uptake was activated by replacement of normal medium by high K(+) medium. A membrane-permeable Ca(2+) chelating agent (BAPTA-AM) and Ca(2+)-dependent K(+) channel inhibitors (quinine, charibdotoxin, and iberiotoxin) were found to reduce the Rb(+)(K+) uptake by about 30-40%. Uptake of K(+) that is sensitive to these drugs is possibly mediated by Ca(2+)-dependent K(+) channels. The intermittent magnetic field partly suppress ed the drug-sensitive K(+) uptake by about 30-40% (P < 0.05). To test the mechanism of inhibition by the magnetic fields, intracellular Ca(2+) concentration ([Ca(2+)]c) was measured using Fura 2-AM. When cells were placed in the high K(&plus;) medium, [Ca(2+)]c increased to about 1.4 times the original level, but exposure to the magnetic fields completely suppressed the increase (P < 0.01). Addition of a Ca(2+) ionophore (ionomycin) to the high K(+) medium increased [Ca(2+)]c to the level of control cells, regardless of exposure to the magnetic field. But the inhibition of K(+) uptake by the magnetic fields was not restored by addition of ionomycin. Based on our previous results on magnetic field-induced changes in properties of the cell membrane, these results indicate that exposure to the magnetic fields partly suppresses K(+) influx, which may be mediated by Ca(2+)-dependent K(+) channels. The suppress ion of K(+) fluxes could relate to a change in electric properties of cell surface and an inhibition of Ca(2+) influx mediated by Ca(2+) channels of either the cell plasma membrane or the inner vesicular membrane of intracellular Ca(2+) stores.

Three dimensional (3D) analysis of the morphological changes induced by 50 Hz magnetic field exposure on human lymphoblastoid cells (Raji)

Human Raji B lymphoid cells after exposure for 64 h to a 1 mT (rms) 50 Hz sinusoidal magnetic field showed a reorganization of membrane and cytoskeletal components. Atomic force microscopy in air revealed several modifications in 80% of the exposed cells, such as loss of microvilli-like structures followed by progressive appearance of membrane introflections. This change in plasma membrane morphology was also accompanied by a different actin distribution, as detected by phalloidin fluorescence. These observations support our previous hypothesis that electric and magnetic fields may modify the plasma membrane structure.

Effects of 60 Hz magnetic field exposure on polymorphonuclear leukocyte activation

We have investigated the effects of a sinusoidal 60 Hz magnetic field on free radical (superoxide anion) production, degranulation (beta-glucuronidase and lysozyme release) and viability in human neutrophils (PMNs). Experiments were performed blindly in very controlled conditions to examine the effects of a magnetic field in resting PMNs and in PMNs stimulated with a tumor promoter: phorbol 12-myristate 13-acetate (PMA). Exposure of unstimulated human PMNs to a 60 Hz magnetic field did not affect the functions examined. In contrast, exposure of PMNs to a 22 milliTesla (mT), 60 Hz magnetic field induced significant increases in superoxide anion (O2-) production (26.5%) and in beta-glucuronidase release (53%) when the cells were incubated with a suboptimal stimulating dose of PMA. Release of lysozyme and lactate dehydrogenase was unchanged by the magnetic field, whether the cells were stimulated or not. A 60 Hz magnetic field did not have any effect on O2- generation by a cell-free system xanthine/xanthine oxidase, suggesting that a magnetic field could upregulate common cellular events (signal transduction) leading to O2- generation and beta-glucuronidase release. In conclusion, exposure of PMNs to a 22 mT, 60 Hz magnetic field potentiates the effect of PMA on O2- generation and beta-glucuronidase release. This effect could be the result of an alteration in the intracellular signaling.

Five hypotheses to examine the nature of magnetic field transduction in biological systems

This paper postulates five experiments that may be used to characterize the nature of the transduction step in which a magnetic or electric field is converted into a biological signal. Each of the five experiments is formulated as a refutable hypothesis in such a manner that rejection of the hypothesis will provide information about the transduction process and an associated confidence level for evaluating each experiment. The proposed hypotheses are formulated to provide inferences about the mode of interaction (magnetic field or induced electric field transduction), spatial distribution of the detector elements in the biological system, and the timescale of the transductive step.

Problems of weak electromagnetic field effects in cell biology

Electrostimulations of cells by weak electric or electromagnetic LF and HF-fields are applied widely today; capacitively or inductively coupled, however, they are seldom applied for cell-free and membrane-free solutions of enzymes. First, the detection of a response of the cells ('electrical window') is a prerequisite for testing at least three parameters: frequency, amplitude and treatment time, besides reproducible biological conditions. The 'state-of-the-art' of this fast developing direction of bioelectrochemistry can be characterized in the following way: the results from several laboratories of (a) cell proliferation, (b) ion transport, (c) activation of several enzymes (Na,K-ATPase), (d) increase of certain protein concentrations (heat-shock protein hsp70) are more or less in agreement. Unfortunately, there are discrepancies between no less than 7 labs in the gene expression of c-myc, c-fos histone 2B, -actin, URA-3 and others, especially for low fields (< 0.05 mT), e.g., in HL60 cells! The reason why seems to be: (1) differences in the most suitable isolation procedure, (2) interferences in the case of too low magnetic flux and (3) too small ranges of parameters have been measured. Today, three open problems must be pointed out: (A) What is the physiological causality for specific 'electrical windows' and their positive or negative efficacy? (B) What are the biochemical targets for either magnetic or electric fields or both? (C) What is the influence of electrical and (or) thermal noise on field efficiency?