Influence of 50-Hz magnetic fields and ionizing radiation on c-jun and c-fos oncoproteins

The effect of magnetic fields (50 Hz, 100 μT_rms sinusoidal magnetic field combined with a 55 μT geomagnetic-like field) and/or gamma rays of 60 Cobalt on the expression of the c-jun and c-fos proteins was investigated in primary rat tracheal epithelial cells and two related immortalized cell lines. Quite similar patterns and amplitudes of induction of these proteins were evidenced after either ionizing radiation or magnetic field exposure. No synergism after both treatments was observed. These findings suggest that magnetic fields explored in the present study may be considered as an insult at the cellular level. Bioelectromagnetics 19: 112–116, 1998. © 1998 Wiley-Liss, Inc.     

The effects of 50 Hz magnetic field exposure on dimethylbenz(α)anthracene induced thymic lymphoma/leukemia in mice

Several epidemiological investigations have suggested an increased incidence of lymphoma, leukemia, and brain tumor in residents living near power transmission lines. However, some observers failed to confirm such a positive correlation. To evaluate the effects of extremely low frequency (ELF) magnetic fields on leukemogenesis, an experimental animal model was used, in which thymic lymphoma/leukemia was induced by dimethylbenz(α)anthracene (DMBA) injected subcutaneously into the interscapular region of newborn mice within 24 h after birth. Beginning at the second week of age, 165 mice were exposed to 50 Hz magnetic field at 1 mT, 3 h/day, 6 days/week for 16 weeks, and 155 animals exposed to sham conditions. All surviving animals were killed by cervical dislocation at the age of 32 weeks and were examined pathologically. The results showed that the incidences of advanced thymic lymphoma, complicated with lymphomatous leukemia, were 21.8 and 23.9% in the two groups, respectively, without statistically significant differences. But dense metastatic infiltration by lymphoma cells into liver in the field exposure group greater (50%) than that in the sham-exposure group (16.2%) was observed (χ² = 9.847, P < 0.01). To determine whether ELF acts as a tumor promoter, further experiments are required. Bioelectromagnetics 18:360–364, 1997. © 1997 Wiley-Liss, Inc.     

Shedding light on a Group IV (ECF11) alternative σ factor

This year marks the 50^th anniversary of the discovery of σ⁷⁰ as a protein factor that was needed for bacterial RNA polymerase to accurately transcribe a promoter in vitro. It was 25 years later that the Group IV alternative σs were described as a distinct family of proteins related to σ⁷⁰. In the intervening time, there has been an ever‐growing list of Group IV σs, numbers of genes they transcribe, insight into the diverse suite of processes they control, and appreciation for their impact on bacterial lifestyles. This work summarizes knowledge of the Rhodobacter sphaeroides σ^E‐ChrR pair, a member of the ECF11 subfamily of Group IV alternative σs, in protecting cells from the reactive oxygen species, singlet oxygen. It describes lessons learned from analyzing ChrR, a zinc‐dependent anti‐σ factor, that are generally applicable to Group IV σs and relevant to the response to single oxygen. This MicroReview also illustrates insights into stress responses in this and other bacteria that have been acquired by analyzing or modeling the activity of the σ^E‐ChrR across the bacterial phylogeny.     

Sinusoidal 60 Hz electromagnetic fields failed to induce changes in protein synthesis in Escherichia coli

Escherichia coli JM83 {F^? ara Δ(lac-proAB) rpsL [?80dΔ(lacZ)M15]} in midlog growth phase at 30 °C were exposed to 60 Hz sinusoidal magnetic field of 3 mT of nonuniform diverging flux, inducing a nonuniform electric field with a maximum intensity of 32 μV/cm using an inductor coil. Exposed and unexposed control cells were maintained at 30.8 ± 0.1 °C and 30.5 ± 0.1 °C, respectively. Quadruplicate samples of exposed and unexposed E. coli cells were simultaneously radiolabeled with ³⁵S-L-methionine at 10 min intervals over 2 hr. Radiochemical incorporation into proteins was analyzed via liquid scintillation counting and by denaturing 12.5% polyacrylamide gel electrophoresis. The results showed that E. coli exposed to a 60 Hz magnetic field of 3 mT exhibited no qualitative or quantitative changes in protein synthesis compared to unexposed cells. Thus small prokaryotic cells (less than 2 μm × 0.5 μm) under constant-temperature conditions do not alter their protein synthesis following exposure to 60 Hz magnetic fields at levels at 3 mT. © 1994 Wiley-Liss, Inc.     

Effects of Extremely Low-Frequency Magnetic Field on Growth and Differentiation of Human Mesenchymal Stem Cells

Human Mesenchymal Stem Cells (hMSCs) were exposed to a developed extremely low-frequency (ELF) magnetic fields (50?Hz ,20?mT ELF) system to evaluate whether exposure to (ELF) magnetic fields affects growth, metabolism, and differentiation of hMSCs. MTT method was used to determine the growth and metabolism of hMSCs following exposure to ELF magnetic fields. Na⁺/K⁺ concentration and osmolality of extracelluar were measured after exposured culture. Alkaline phosphatase (ALP) assay and Calcium assay, ALP staining, and Alizarin red staining were performed to evaluate the osteogenic differentiation of hMSCs under the ELF magnetic field exposure. In these experiments, the cells were exposed to ELF for up to 23 days. The results showed that exposure to ELF magnetic field could inhibit the growth and metabolism of hMSC, but have no significant effect on differentiation of hMSCs. These results suggested that ELF magnetic field may influence the early development of hMSCs related adult cells.     

ENHANCEMENT OF INVERTASE PRODUCTION BY Aspergillus niger OZ-3 USING LOW-INTENSITY STATIC MAGNETIC FIELDS

The aim of this study is to investigate the effect of low-intensity static magnetic fields (SMFs) on invertase activity and growth on different newly identified molds. The most positive effect of SMFs on invertase activity and growth was observed for Aspergillus niger OZ-3. The submerged production of invertase was performed with the spores obtained at the different exposure times (120, 144, 168, and 196 hr) and magnetic field intensities (0.45, 3, 5, 7, and 9 mT). The normal magnetic field of the laboratory was assayed as 0.45 mT (control). Optimization of magnetic field intensity and exposure time significantly increased biomass production and invertase activity compared to 0.45 mT. The maximum invertase activity (51.14 U/mL) and biomass concentration (4.36 g/L) were achieved with the spores obtained at the 144 hr exposure time and 5 mT magnetic field intensity. The effect of low-intensity static magnetic fields (SMFs) on invertase activities of molds was investigated for the first time in the present study. As an additional contribution, a new hyper-invertase-producing mold strain was isolated.

Supplemental materials are available for this article. Go to the publisher's online edition of Preparative Biochemistry and Biotechnology to view the supplemental file.     

Electromagnetic field effects on <Emphasis Type="Italic">Artemia</Emphasis> hatching and chromatin state

The influence of magnetic fields on hatching and chromatin state of brine shrimp, Artemia sp., was investigated. Dry Artemia cysts were exposed to a magnetic field of intensity 25 mT for 10 min. The magnetic field was applied in different variants: constant field, rotating field of different directions (right-handed and left-handed) and different magnet polarization. The effect of ultra wideband pulse radiation and microwave radiation was also investigated. The energy density on the surface of object exposed to ultra wideband pulse radiation was 10⁻², 10⁻³, 10⁻⁴, 10⁻⁵ and 10⁻⁶ W/cm², the power of microwave radiation was 10⁻⁴ and 10⁻⁵ W/cm², exposure time - 10 s. After incubation of the cysts for 48 hours in sea water the hatching percentage of Artemia from exposed cysts was higher than in controls. The number of heterochromatin granules was significantly higher in the nauplia (newborn larvae of Artemia) developed from cysts that had been exposed to magnetic and electromagnetic fields. The data obtained demonstrate an increase in percentage hatching of Artemia cysts after treatment with magnetic and electromagnetic fields and chromatin condensation in nauplia. We have also shown different effects of right-handed and left-handed rotating magnetic fields on these processes.     

Effect of weak combined magnetic fields on the metamorphosis of the mealworm beetle Tenebrio molitor

The effects of weak combined magnetic fields adjusted to the parametric resonance for Ca²⁺ and K⁺ and extremely weak alternating magnetic field on the metamorphosis of the mealworm beetle Tenebrio molitor have been studied. It was shown that the exposure of pupas of insects to all above-indicated types of fields stimulates the metamorphosis. However, after the exposure to weak combined magnetic fields adjusted to the parametric resonance for Ca²⁺ and K⁺, the number of insects with anomalies increases, which is not observed by the action of the weak alternating magnetic field.     

Effects of Weak Environmental Magnetic Fields on the Spontaneous Bioelectrical Activity of Snail Neurons

We examined the effects of 50-Hz magnetic fields in the range of flux densities relevant to our current environmental exposures on action potential (AP), after-hyperpolarization potential (AHP) and neuronal excitability in neurons of land snails, Helix aspersa. It was shown that when the neurons were exposed to magnetic field at the various flux densities, marked changes in neuronal excitability, AP firing frequency and AHP amplitude were seen. These effects seemed to be related to the intensity, type (single and continuous or repeated and cumulative) and length of exposure (18 or 20 min). The extremely low-frequency (ELF) magnetic field exposures affect the excitability of F1 neuronal cells in a nonmonotonic manner, disrupting their normal characteristic and synchronized firing patterns by interfering with the cell membrane electrophysiological properties. Our results could explain one of the mechanisms and sites of action of ELF magnetic fields. A possible explanation of the inhibitory effects of magnetic fields could be a decrease in Ca²⁺ influx through inhibition of voltage-gated Ca²⁺ channels. The detailed mechanism of effect, however, needs to be further studied under voltage-clamp conditions.     

Effect of static magnetic fields on the budding of yeast cells

The effect of static magnetic fields on the budding of single yeast cells was investigated using a magnetic circuit that was capable of generating a strong magnetic field (2.93 T) and gradient (6100 T² m^?1). Saccharomyces cerevisiae yeast cells were grown in an aqueous YPD agar in a silica capillary under either a homogeneous or inhomogeneous static magnetic field. Although the size of budding yeast cells was only slightly affected by the magnetic fields after 4 h, the budding angle was clearly affected by the direction of the homogeneous and inhomogeneous magnetic fields. In the homogeneous magnetic field, the budding direction of daughter yeast cells was mainly oriented in the direction of magnetic field B. However, when subjected to the inhomogeneous magnetic field, the daughter yeast cells tended to bud along the axis of capillary flow in regions where the magnetic gradient, estimated by B(dB/dx), were high. Based on the present experimental results, the possible mechanism for the magnetic effect on the budding direction of daughter yeast cells is theoretically discussed. Bioelectromagnetics 31:622–629, 2010. © 2010 Wiley‐Liss, Inc.     

Intracellular Ca2+ levels in rat ventricle cells exposed to extremely low frequency magnetic field

Objective: Electromagnetic fields can affect intracellular Ca²⁺ levels. The aim of this study was to determine the changes intracellular Ca²⁺ concentration in cardiac ventricle cells of rats exposed to 0.25 mT (2.5 Gauss) magnetic field.

Methods: Forty-five male rats were introduced to this study. The rats were divided into three groups: control, sham, and experiment. The experimental group was exposed to 0.25 mT extremely low frequency (ELF) magnetic field for 14 days, 3 h/day. The sham group was treated like the experimental group, except for elf-magnetic field exposure. The control group was not subjected to anything and differed from the experimental group and sham group. In the end of experiment, rats were sacrificed, cardiac tissue was removed, and these were fixed in 10% neutral formalin. Then, ventricular cells were stained by Alizarin red staining method.

Results: In the light microscopic examinations of control groups, in myofibril structures between groups, changes were not observed. In myofibril regions of the experimental group compared to other groups, increased heterogen Ca²⁺ accumulations were found.

Conclusion: ELF magnetic fields are used in daily life. The results of this study show that intracellular Ca²⁺ accumulation in cardiac ventricles can increase in rats exposed to ELF magnetic field.     

Potassium ion influx measurements on cultured Chinese hamster cells exposed to 60-Hertz electromagnetic fields

Potassium ion influx was measured by monitoring ⁴²KCI uptake by Chinese hamster ovary (CHO) cells grown in suspension culture and exposed in the culture medium to 60–Hz electromagnetic fields up to 2.85 V/m. In the presence of the field CHO cells exhibited two components of uptake, the same as previously observed for those grown under normal conditions; both these components of influx were decreased when compared to sham-exposed cells. Although decreases were consistently observed in exposed cells when plotted as log_c of uptake, the differences between the means of the calculated fluxes of exposed and sham-exposed cells were quite small (on the order of 4–7%). When standard deviations were calculated, there was no significant difference between these means; however, when time-paired uptake data were analyzed, the differences were found to be statistically significant. Cells exposed only to the magnetic field exhibited similar small decreases in influx rates when compared to sham-exposed cells, suggesting that the reduction in K⁺ uptake could be attributed to the magnetic field. Additionally, intracellular K⁺ levels were measured over a prolonged exposure period (96 h), and no apparent differences in intracellular K⁺ levels were observed between field-exposed and shamexposed cultures. These results indicate that high-strength electric fields have a small effect on the rate of transport of potassium ions but no effect on long-term maintenance of intracellular K⁺.     

Influence of low-intensity magnetic fields on the development of satellite muscle cells of a newborn rat in primary culture

The influence of Earth magnetic field shielded down to 0.3 μT and static magnetic field (60–160 μT) on the proliferation and differentiation of satellite muscle cells in primary culture has been investigated. A stimulatory effect of static magnetic fields on the rate of the formation of massive multinucleate myotubes and an increase in the intracellular calcium concentration ([Ca²⁺] _i ) have been detected for magnetic fields of the microtesla range. On the other hand, it was shown that the reduction of earth magnetic fields to 0.3 μT leads to inhibition of proliferation and differentiation of skeletal muscle cells in primary culture. Since the formation of contractile myotubes during in vitro experiments is similar to the regeneration of skeletal muscle fibers under muscle damage in vivo, it may be concluded that weak magnetic fields have a strong effect on intracellular processes by influencing all phases of muscle fiber formation. It is necessary to take this fact into consideration when forecasting probable complications of skeletal muscle regeneration during long-term exposure of man to low-intensity magnetic fields and also for the potential use of low static magnetic fields as a tool to recover the affected myogenesis.     

Nocturnal exposure to intermittent 60 Hz magnetic fields alters human cardiac rhythm

Heart rate variability (HRV) results from the action of neuronal and cardiovascular reflexes, including those involved in the control of temperature, blood pressure and respiration. Quantitative spectral analyses of alterations in HRV using the digital Fourier transform technique provide useful in vivo indicators of beat-to-beat variations in sympathetic and parasympathetic nerve activity. Recently, decreases in HRV have been shown to have clinical value in the prediction of cardiovascular morbidity and mortality. While previous studies have shown that exposure to power-frequency electric and magnetic fields alters mean heart rate, the studies reported here are the first to examine effects of exposure on HRV. This report describes three double-blind studies involving a total of 77 human volunteers. In the first two studies, nocturnal exposure to an intermittent, circularly polarized magnetic field at 200 mG significantly reduced HRV in the spectral band associated with temperature and blood pressure control mechanisms (P = 0.035 and P = 0.02), and increased variability in the spectral band associated with respiration (P = 0.06 and P = 0.008). In the third study the field was presented continuously rather than intermittently, and no significant effects on HRV were found. The changes seen as a function of intermittent magnetic field exposure are similar, but not identical, to those reported as predictive of cardiovascular morbidity and mortality. Furthermore, the changes resemble those reported during stage II sleep. Further research will be required to determine whether exposure to magnetic fields alters stage II sleep and to define further the anatomical structures where field-related interactions between magnetic fields and human physiology should be sought. Bioelectromagnetics 19: 98–106, 1998. © 1998 Wiley-Liss, Inc.     

Serum plays a critical role in modulating [Ca2+]c of primary culture bone cells exposed to weak ion-resonance magnetic fields

Primary-culture bone cells were exposed to ion-resonance (IR) magnetic fields tuned to Ca²⁺. Cytosolic calcium concentration, [Ca²⁺]_c, was measured by using fura-2 during field exposure. The fields investigated were 20 μT static + 40 μT p-p at either 15.3 or 76.6 Hz, and 0.13 mT static + either 0.5 or 1.0 mT p-p at 100 Hz. Other parameters included field orientation, culture age (2 or 5 days after plating), and the presence of serum (0 or 2%) during exposure. Total experiment time was 29.5 min: The field was applied after 2 min, and bradykinin was added as an agonist control after 22 min. The data were quantified on a single-cell basis during the 2–22 min exposure period in terms of the magnitude of the largest occurring [Ca²⁺]_c spike normalized to local baseline. Field-exposed and control groups were characterized in terms of the percent of cells exhibiting spike magnitudes above thresholds of 100 or 66% over baseline and were compared by using Fisher's exact test. Without serum, there was little evidence that IR magnetic fields altered [Ca²⁺]_c. However, in the presence of 2% serum, 3 of the 16 experiments exhibited significant effects at the 100% threshold. Reducing this threshold to 66% resulted in five experiments exhibiting significant effects. Most strikingly, in all of these cases, the field acted to enhance [Ca²⁺]_c activity as opposed to suppressing [Ca²⁺]_c activity. These findings suggest a role for serum or for constituents within serum in mediating the effects of IR magnetic fields on cells and may provide a resolution pathway to the dilemma imposed by theoretical arguments regarding the possibility of such phenomena. Possible roles of serum and future studies are discussed. Bioelectromagnetics 18:203–214, 1997. © 1997 Wiley-Liss, Inc.     

The σE stress response is required for stress‐induced mutation and amplification in Escherichia coli

Pathways of mutagenesis are induced in microbes under adverse conditions controlled by stress responses. Control of mutagenesis by stress responses may accelerate evolution specifically when cells are maladapted to their environments, i.e. are stressed. Stress‐induced mutagenesis in the Escherichia coli Lac assay occurs either by ‘point’ mutation or gene amplification. Point mutagenesis is associated with DNA double‐strand‐break (DSB) repair and requires DinB error‐prone DNA polymerase and the SOS DNA‐damage‐ and RpoS general‐stress responses. We report that the RpoE envelope‐protein‐stress response is also required. In a screen for mutagenesis‐defective mutants, we isolated a transposon insertion in the rpoE P2 promoter. The insertion prevents rpoE induction during stress, but leaves constitutive expression intact, and allows cell viability. rpoE insertion and suppressed null mutants display reduced point mutagenesis and maintenance of amplified DNA. Furthermore, σ^E acts independently of stress responses previously implicated: SOS/DinB and RpoS, and of σ³², which was postulated to affect mutagenesis. I‐SceI‐induced DSBs alleviated much of the rpoE phenotype, implying that σ^E promoted DSB formation. Thus, a third stress response and stress input regulate DSB‐repair‐associated stress‐induced mutagenesis. This provides the first report of mutagenesis promoted by σ^E, and implies that extracytoplasmic stressors may affect genome integrity and, potentially, the ability to evolve.