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PubMed1985

Effects of ELF (1-120 Hz) and modulated (50 Hz) RF fields on the efflux of calcium ions from brain tissue in vitro.

We have previously shown that 16-Hz, sinusoidal electromagnetic fields can cause enhanced efflux of calcium ions from chick brain tissue, in vitro, in two intensity regions centered on 6 and 40 Vp-p/m. Alternatively, 1-Hz and 30-Hz fields at 40 Vp-p/m did not cause enhanced efflux. We now demonstrate that although there is no enhanced efflux associated with a 42-Hz field at 30, 40, 50, or 60 Vp-p/m, a 45-Hz field causes enhanced efflux in an intensity range around 40 Vp-p/m that is essentially identical to the response observed for 16-Hz fields. Fields at 50 Hz induce enhanced efflux in a narrower intensity region between 45 and 50 Vp-p/m, while radiofrequency carrier waves, amplitude modulated at 50 Hz, also display enhanced efflux over a narrow power density range. Electromagnetic fields at 60 Hz cause enhanced efflux only at 35 and 40 Vp-p/m, intensities slightly lower than those that are effective at 50 Hz. Finally, exposures over a series of frequencies at 42.5 Vp-p/m reveal two frequency regions that elicit enhanced efflux--one centered on 15 Hz, the other extending from 45 to 105 Hz.

Animals↗
PubMed1985

Low-voltage ELF electric field measurements in ionic media.

Low-voltage electric fields were measured in conductive tissue culture media using three techniques: voltage slope, current density-conductivity, and dipole methods. All three methods tested yielded comparable results. However, all three techniques have associated errors. These errors fall into three major categories: those associated with the measurement equipment, those associated with electrodes, and errors in cross-sectional area measurements. Each source of error is discussed so that all can be taken into account during construction and/or testing of exposure equipment.

Culture Media↗
PubMed1989

ELF electromagnetic environment in power substations.

This paper presents a theoretical analysis of electromagnetic environments in power substations in service. A new analytical method is developed and applied to magnetic field calculations in 187-kV and 66-kV substations. Experimental results verify that the method offers a good prediction of the magnetic field profiles in the substations except for the areas where localized field sources exist. The analytical results show that the magnetic field strength depends to a great extent on how the load powers distribute on individual lines and buses, that the magnetic fields in substations have a three-dimensional characteristic, and that the predominant field component depends on the position of interest. Moreover, it is suggested that objects placed in substations are exposed not only to magnetic fields of high strength in comparison to those in houses or near the distribution networks but also to fields with several percent of harmonic distortion.

Electromagnetic Fields↗
PubMed1992

ELF exposure facility for human testing.

A laboratory facility specifically designed for controlled human exposure to 60-Hz electric (0 to 16 kV/m) and magnetic (0 to 32 A/m, B = 0 to 40 microT) fields has been constructed. The facility presents uniform fields under controlled temperature and humidity. Special control systems allow collection of physiological data during, as well as before and after, exposure to electric fields at strengths to 16 kV/m under verified double-blind control. Exposure to continuous or intermittent fields is possible in the facility. The capability of obtaining physiological data during actual exposure to constant or intermittent, 60-Hz fields, and of doing so without either the subject or the experimenter being aware of actual field conditions, is a critical factor in valid experimentation.

Electromagnetic Fields↗
PubMed1992

An integrated ELF magnetic-field generator and incubator for long-term in vitro studies.

Long-term studies of the effects of low-frequency magnetic fields on cells in culture require an incubator that is free of contaminating magnetic fields and that provides automatic control of exposure duration, uniform applied fields, a uniform and well-controlled environmental temperature, and high reliability of the total system. We describe a dual-incubator system in which the enclosed solenoid of either unit can provide a sham exposure while the other generates a magnetic induction of up to 500 microT. Each solenoid-incubator unit contains an enclosed rack that can hold as many as 140 petri dishes for culturing cells; each unit is heated radiantly by circulating warm water. Field-exposure conditions and temperatures are continuously monitored and controlled by a microcomputer.

Cells, Cultured↗
PubMed1992

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.

Animals↗
PubMed1992

Estimates for ELF effects: noise-based thresholds and the number of experimental conditions required for empirical searches.

Interactions between physical fields and biological systems present difficult conceptual problems. Complete biological systems, even isolated cells, are exceedingly complex. This argues against the pursuit of theoretical models, with the possible consequence that only experimental studies should be considered. In contrast, electromagnetic fields are well understood. Further, some subsystems of cells (viz. cell membranes) can be reasonably represented by physical models. This argues for the pursuit of theoretical models which quantitatively describe interactions of electromagnetic fields with that subsystem. Here we consider the hypothesis that electric fields, not magnetic fields, are the source of interactions, From this it follows that the cell membrane is a relevant subsystem, as the membrane is much more resistive than the intra- or extracellular regions. A general class of interactions is considered: electroconformational changes associated with the membrane. Expected results of such as approach include the dependence of the interaction on key parameters (e.g., cell size, field magnitude, frequency, and exposure time), constraints on threshold exposure conditions, and insight into how experiments might be designed. Further, because it is well established that strong and moderate electric fields interact significantly with cells, estimates of the extrapolated interaction for weaker fields can be sought. By employing signal-to-noise (S/N) ratio criteria, theoretical models can also be used to estimate threshold magnitudes. These estimates are particularly relevant to in vitro conditions, for which most biologically generated background fields are absent. Finally, we argue that if theoretical model predictions are unavailable to guide the selection of experimental conditions, an overwhelmingly large number of different conditions will be needed to find, establish, and characterize bioelectromagnetic effects in an empirical search. This is contrasted with well-established chemical dosimetry, which is much simpler. Because of the large number of possible electromagnetic field conditions, we also conclude that in vitro studies, rather than in vivo studies, should be emphasized in studies aimed at discovering and characterizing mechanisms for bioelectromagnetic effects.

Cell Membrane↗
PubMed1993

Determination of the induced ELF electric field distribution in a two layer in vitro system simulating biological cells in nutrient solution.

In-vitro studies of biological effects of electromagnetic fields are often conducted with cultured cells either in suspension or grown in a monolayer. In the former case, the exposed medium can be assumed to be homogeneous; however, eventually the cells settle to the bottom of the container forming a two layer system with different dielectric and conductive properties. In the present work the effect of this separation on the electric field distribution is calculated and experimentally measured at selected positions for a commonly used exposure configuration. The settled cell suspension is modeled by a well-defined two layer system placed in a rectangular container with the base of the container parallel to the direction of the magnetic field. Theoretical calculations based on numerical techniques are done for various two layer systems with different conductivities in each layer. The agreement between the theoretical calculations and the experimental measurements is within +/- 1.5 mV/m, or 10% of the maximum induced field when the conductivity of the lower layer is ten times that of the upper layer. This result is well within experimental error. When the thickness of one of the layers is small compared to the thickness of the other layer, it is found that the electric field distribution is essentially that of the homogeneous case. The latter situation corresponds to a typical cell exposure condition.

Cells, Cultured↗
PubMed1993

Biologic effects of prolonged exposure to ELF electromagnetic fields in rats. I. 50 Hz electric fields.

A three-year investigation was conducted on the biological effects of high-intensity electric field exposures of rats for up to 18% of their life span. Two hundred and forty adult male rats, divided into groups of 20 animals each, were exposed at ground potential for 8 h/day at 25-kV/m and 100-kV/m 50-Hz electric fields or were sham exposed for 280, 440, and 1240 h. The corresponding ages at sacrifice were 140, 164, and 315 days. An additional group of 40 rats was investigated under similar experimental conditions after 440 h of exposure at floating potential. Independent of exposure duration, mode of grounding, and field strength, no statistical differences in body weight, morphology, and histology of the liver, heart, mesenteric lymph nodes, and blood variables (hematology and serum chemistry) were found in comparison with sham-exposed animals. Plasma levels of luteinizing hormone (LH), follicle-stimulating hormone (FSH), and testosterone (TS) at sacrifice varied widely among experimental animals in the same group but did not differ in exposed compared with sham-exposed rats. A nonsignificant tendency toward a decrease in the testes/body weight ratio was found after 1240 h of exposure. Microscopic examination of a large number of specimens showed no quantitative or qualitative statistical differences in testes alterations either among exposed animals or between exposed and their corresponding sham-exposed groups. We conclude that 50-Hz electric field exposure, even of long duration at very high field strengths, does not induce harmful effects on tissues with high cellular turnover rates and does not impair the reproductive function of rats. Moreover, after exposure, all variables investigated were well within the normal physiological range.

Animals↗
PubMed1993

Facility for chronic exposure of rats to ELF magnetic fields.

The facility consists of a 12 x 11.5 x 2.4 m high room containing six sets of exposure apparatus and the other equipment necessary to maintain a pathogen-free system. The apparatus sets produced 5 mT (rms), 0.5 mT, or a sham exposure. The apparatus was arranged in the room to minimize the fringing field of the 5 mT set at the sham position. Each set was 3.85 x 1.80 x 0.66 m in outside dimension, containing 24 cages in the magnetically homogeneous region. The apparatus was designed using Harvey's figure-eight-configuration and generated a horizontal sinusoidal alternating field. In order to save electric power, the coil of the apparatus constituted a 50 Hz LC resonance circuit with a condensor bank to which electric power was supplied to compensate losses. Magnetic flux density was kept constant by controlling the coil current. Although mild steel was used in the skeleton of the building, the fringing flux at the sham was as low as 0.1 to 1 microT. Stainless steel was used for ventilating ducts, racks for the cages, cage covers, feeder baskets, and watering nozzles. The homogeneity of the field was measured to be +/- 10% in the animal residence area, and food and water consumption was found to be unaffected by the field. At 5 mT, the coil current was 370 A, and the hollow coil was cooled by a stream of 20 degrees C water to prevent both heat and dew on the coil surface. Vibration and acoustic noise was prevented by fiber reinforced plastic framework of the coil. High harmonic distortion was not observed at the output terminal of the coil driver. The facility has operated without trouble for 2 years.

Animals↗
PubMed1995

Biologic effects of prolonged exposure to ELF electromagnetic fields in rats: II. 50 Hz magnetic fields.

To provide possible laboratory support to health risk evaluation associated with long-term, low-intensity magnetic field exposure, 256 male albino rats and an equal number of control animals (initial age 12 weeks) were exposed 22 h/day to a 50 Hz magnetic flux density of 5 microT for 32 weeks (a total of about 5000 h). Hematology was studied from blood samples before exposure to the field and at 12 week intervals. Morphology and histology of liver, heart, mesenteric lymph nodes, and testes as well as brain neurotransmitters were assessed at the end of the exposure period. In two identical sets of experiments, no significant differences in the investigated variables were found between exposed and sham-exposed animals. It is concluded that continuous exposure to a 50 Hz magnetic field of 5 microT from week 12 to week 44, which makes up approximately 70% of the life span of the rat before sacrifice, does not cause changes in growth rate, in the morphology and histology of liver, heart, mesenteric lymph nodes, testes, and bone marrow, in hematology and hematochemistry, or in the neurotransmitters dopamine and serotonin.

Animals↗
PubMed2002

Influence of alternating extremely low frequency ELF magnetic field on structure and function of pancreas in rats.

The aim of this study was to estimate the influence on ultrastructure and function of endocrine and excretoric part of pancreas in rats of extremely low frequency alternating magnetic fields with parameters used in therapy in humans. The animals from the two experimental groups were exposed to a rectangular magnetic field waveform at a frequency of 10 Hz and induction of 1.8-3.8 mT--(group P) or a sinusoidal magnetic field at a frequency of 40 Hz and induction of 1.3-2.7 mT--(group S), respectively. The control rats were subjected to sham exposure. The cycle of 1, 3, 6, 9, and 14 daily exposure sessions lasting 30 min was made in all groups. Some of rats after finishing the cycle of 14 exposures were left in the same conditions except for the magnetic field for 3 or 10 days. In both groups of rats exposed to magnetic field, a distinct tendency to decrease glucose concentration, compared to control group, was observed during the exposure cycle. Serum glucose became normal after the end of exposure sessions. The concentrations of insulin in both groups of rats exposed to magnetic field were significantly higher, compared to the controls, during the exposure cycle. After the end of exposure cycle the concentration of insulin in group S became normal. In contrast, in group P the concentration of insulin decreased significantly on the last day of exposure, with a subsequent increase in the following days. The activity of alpha-amylase and lipase in the serum of experimental and control rats was not affected. In both groups of exposed rats, reversible changes of ultrastructure of the pancreatic islets, including expansion of the Golgi apparatus, extension of rough endoplasmatic reticulum, mitochondrial swelling, expansion of beta-granules and increase in number of empty vesicles in beta cells, occurred during the exposure. In acinar cells of exposed animals, a slight extension of rough endoplasmatic reticulum and mitochondrial swelling as transitory changes were observed. The structural and functional changes in pancreas are probably adaptative ones.

Animals↗
PubMed1996

A test of the hypothesis that ELF magnetic fields affect calcium uptake in rat thymocytes in vitro.

The experiment's objective was to test the statistical hypothesis that a 60-min exposure of rat thymocytes in vitro to a unique combination of static and a.c. magnetic fields results in suppression of calcium influx triggered by concanavalin A (Con A). Con A (10 micrograms/ml) induced about a 50% increase in 45Ca2+ uptake relative to no Con A (control). Magnetic field exposures had no statistically significant effect on Con A-stimulated calcium uptake. The data did not support the hypothesis.

Animals↗
PubMed1990

Proportionality of ELF electric field-induced growth inhibition to induced membrane potential in Zea mays and Vicia faba roots.

The postulate that 60-Hz electric field-induced bioeffect severity is proportional to induced transmembrane potential [Vmi] magnitude was tested and supported using a plant root model cell system. Statistically significant correlations were obtained upon regression of the relative rates of exposed Vicia faba and Zea mays root segment growth on the average Vmi (calculated) arising in those segments under specified 60 Hz field exposure conditions. The Vmi associated with the apparent threshold for growth inhibition was similar in Zea and Vicia roots (2.5 vs 2.4 mV, respectively). At Vmi greater than this threshold, Zea root growth declined by about 9% per mV, and Vicia root growth by about 19% per mV induced potential.

Electricity↗