Proteins in electric fields and pressure fields: basic aspects

This paper emphasizes the basic aspects of the interactions of chromoproteins at low temperatures with external pressure fields and electric fields. We discuss how the respective spectral properties can be modified and what we can learn from the spectral changes about the thermodynamic, electrostatic, functional and structural properties of proteins. A few examples are discussed in more detail.     

Biochemical and structural approach to collagen synthesis under electric fields

The effects of electric fields of different intensities and directions on the collagen synthesis of guinea pigs was studied. The effects of vertical and horizontal electric fields of 1.9 kV/m and 0.9 kV/m, generated with voltages of 300 V and 150 V DC, respectively, on collagen synthesis, was evaluated by assessing the amount of hydroxyproline in the liver tissue, and by histological examination of tissue samples. The Stegemann-Stalder method was used to determine hydroxyproline content of the tissues. While the 0.9 kV/m vertical and horizontal electric fields substantially decreased the amount of hydroxyproline in the liver, the 1.9 kV/m electric fields in both directions increased the hydroxyproline content. The vertical electric field was more effective than the horizontal one both in the increases and the decreases. These findings were verified histologically.     

Influence of human model resolution on computed currents induced in organs by 60-Hz magnetic fields

The effects of human body model resolution on computed electric fields induced by 60 Hz uniform magnetic fields are investigated. A recently-developed scalar potential finite difference code for low-frequency electromagnetic computations is used to model induction in two anatomically realistic human body models. The first model consists of 204290 cubic voxels with 7.2-mm edges, while the second comprises 1639146 cubic voxels with 3.6-mm edges. Calculations on the lower-resolution model using, for example, the finite difference time domain or impedance methods, push the capabilities of workstations. The scalar method, in contrast, can handle the higher-resolution model using comparable resources. The results are given in terms of average and maximum electric field intensities and current density magnitudes in selected tissues and organs. Although the lower-resolution model provides generally acceptable results, there are important differences that make the added computational burden of the higher-resolution calculations worthwhile. In particular, the higher-resolution modelling generally predicts peak electric fields intensities and current density magnitudes that are slightly higher than those computed using the lower-resolution modelling. The differences can be quite large for small organs such as glands.     

Migration of human keratinocytes in electric fields requires growth factors and extracellular calcium

Currents that leak out of wounds generate electric fields lateral to the wound. These fields induce directional locomotion of human keratinocytes in vitro and may promote wound healing in vivo. We have examined the effects of growth factors and calcium, normally present in culture medium and the wound fluid, on the directional migration of human keratinocytes in culture. In electric fields of physiologic strength (100 mV per mm), keratinocytes migrated directionally towards the cathode at a rate of about 1 microm per min. This directional migration requires several growth factors. In the absence of these growth factors, the cell migration rate decreased but directionality was maintained. Epidermal growth factor alone restored cell migration rates at concentrations as low as 0.2 ng per ml. Insulin at 5-100 microg per ml or bovine pituitary extract at 0.2%-2% vol/vol also stimulated keratinocyte motility but was not sufficient to fully restore the migration rate. Keratinocyte migration in electric fields requires extracellular calcium. Changes in calcium concentrations from 3 microM to 3.3 mM did not significantly change keratinocyte migration rate nor directionality in electric fields; however, addition of the chelator ethyleneglycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid to migration medium reduced, and eventually abolished, keratinocyte motility. Our results show that (i) growth factors and extracellular calcium are required for electric field-induced directional migration of human keratinocytes, and (ii) keratinocytes migrate equally well in low and high calcium media.     

Deformation anisotropy induced by presence of physical fields

An attempt is made to develop an internally consistent theory of plastic flow with anisotropic hardening induced by physical fields of arbitrary structure. Standard theories of plastic flow based on the assumption that the deformation anisotropy is induced by presence of plastic strain, strain rate and temperature. It is worth to be noted that the presence of plastic anisotropy may be induced by influence of another physical fields, like radiation, magnetic fields and so on.     

A review of in vitro studies: low-frequency electromagnetic fields

In vitro studies of effects of low-frequency (LF) electromagnetic (EM) fields have revealed a variety of sensitive cell-physiologic end-points. Effects have been reported on (1) DNA, RNA, and protein synthesis; (2) cell proliferation; (3) cation fluxes and binding; (4) immune responses; and (5) membrane signal transduction (i.e., hormones, enzymes, and neuro-transmitters). Typically such effects occurred as a result of short-term exposure of cells to EM at frequencies of 100 Hz or less and at low field intensities. The dependency on frequency or modulation, as well as the apparent weak cellular interaction of these LF EM fields, lacks theoretic explanation. It has not been determined whether effects are induced by electric or magnetic fields. Confounding interpretation of the results are phenomena such as (1) transient or time-delayed responses; (2) modulation- and intensity-specific effects, referred to as modulation or intensity "windows;" and (3) general lack of dose- (or dose-rate) response data or EM field thresholds. Consequently, although it is well-established that LF EM fields affect biological systems in vitro, use of these data to assess human health effects is limited. This paper reviews selected published reports of LF EM fields on in vitro systems. Where possible, relevance of the findings to occupational exposures will be assessed, principally by considering the consistency of in vitro and in vivo EM exposure effects and comparison of EM field intensities that affect in vitro systems with occupational EM exposure intensities. Finally, suggestions will be made for the direction of future in vitro research of direct pertinence to potential occupational exposure problems.     

Biological responses to electromagnetic fields

Electrification in developed countries has progressively increased the mean level of extremely low-frequency electromagnetic fields (ELF-EMFs) to which populations are exposed; these humanmade fields are substantially above the naturally occurring ambient electric and magnetic fields of approximately 10(-4) Vm(-1) and approximately 10(-13) T, respectively. Several epidemiological studies have concluded that ELF-EMFs may be linked to an increased risk of cancer, particularly childhood leukemia. These observations have been reinforced by cellular studies reporting EMF-induced effects on biological systems, most notably on the activity of components of the pathways that regulate cell proliferation. However, the limited number of attempts to directly replicate these experimental findings have been almost uniformly unsuccessful, and no EMF-induced biological response has yet been replicated in independent laboratories. Many of the most well-defined effects have come from gene expression studies; several attempts have been made recently to repeat these key findings. This review analyses these studies and summarizes other reports of major cellular responses to EMFs and the published attempts at replication. The opening sections discuss quantitative aspects of exposure to EMFs and the incidence of cancers that have been correlated with such fields. The concluding section considers the problems that confront research in this area and suggests feasible strategies.     

场活化烧结中场特点、影响和作用

场活化烧结技术是一种在电场、应力场和温度场作用下实现快速致密化的粉末活化烧结技术.场活化烧结的特殊致密化过程和活化机理,源自于其特有的电场、应力场以及温度场作用.本文就各种场在场活化烧结过程中的特点、作用和影响的研究进展进行介绍.对于各种场在场活化烧结中的特点、作用和影响的认识,仍存在较多问题和分歧.各场间交互作用显著.从多场耦合的角度研究场活化烧结过程,有助于更准确、全面掌握各种场的特点、作用和影响,深入揭示场活化烧结的特殊致密化过程和活化机理.通过外加磁场提高场活化烧结的均匀性,进一步赋予材料特殊性能,具有良好的研究开发前景.     

Sudden, unexpected death of infants and electromagnetic fields (author's transl)

The examination of 337 cases of Sudden Infant Death Syndorme (SIDS) ro Crib Deaths in Philadelphia, Penn., USA, and 294 cases in Hamburg, Federal Republic of Germany, shows regional concentrations which are close to uncommon magnetic fields or stray electric currents in the ground. The risk in the cellar and first floor of houses is higher than in the other floors. Therefore a possible causal relationship between electromagnetic fields and SIDS cases must be considered and checked by on-site measurements, animal experiments, and by more research on magnetic fields as stressor for infants.     

Determination of exposure to electric fields in extra high voltage substations

Electrophysical effects related to extra high voltage are surveyed for the determination of the exposure of personnel to electric fields in substations. It is concluded that the electric field strengths and the electrical discharges to the personnel are the important electrophysical factors. Instruments for measuring the field strength at grounded surfaces and at nonzero potentials were constructed. Results are presented of measurements with these instruments in substations. A dummy was used for the measurement of the distribution of capacitive currents to a man. The dummy can also be used for measuring the effectiveness of special shielding clothes.     

Calculation of electric fields induced near metal implants by magnetic resonance imaging switched-gradient magnetic fields

Electric (E) fields induced near metal implants by MRI switched-gradient magnetic fields are calculated by a new equivalent-circuit numerical technique. Induced E-field results are found for a metallic spinal-fusion implant consisting of two thin wires connected to the metallic case of a current generator as well as for its subsections: a bare U-shaped wire, an insulated U-shaped wire, a cut insulated wire, and a generator. The presence of the metallic implants perturbs the E field significantly. Near the ends of the bare U-shaped wire, the E field is 89.7 times larger than in the absence of the wire. The greatest E field concentration occurs near the ends of the cut insulated wire, where the E field is 196.7 times greater than in the absence of the wire. In all cases, the perturbation of the induced E field by the implanted wire is highly localized within a few diameters of the wire.     

The ecological-hygienic aspects of the study of industrial-frequency magnetic fields

Magnetic fields of industrial frequency with magnetic flux density of 10 mkTl were studied for their effects on the morbidity pattern in the population of the settlement located in the vicinity of a high-voltage electric power line of 750 kV. A trend was noted towards increase in the incidence of nervous and endocrine diseases as well as metabolic disturbances and disorders of the immune system.     

Effects of electromagnetic fields on the levels of biogenic amine metabolites, quinolinic acid, and beta-endorphin in the cerebrospinal fluid of dairy cows

Eight multiparous non-lactating pregnant Holstein cows at 198 +/- 35 d of gestation, weighing 608 +/- 24 kg, were confined to wooden metabolic cages in an electric and magnetic field chamber with a 12:12 h light:dark cycle. Subarachnoidal catheters were installed 5 d before the activation of the electric and magnetic fields. The cows were exposed to electric and magnetic fields (60 Hz, 10 kV/m and 30 microT) continuously except for the feeding and cleaning time for an average of 21.44 +/- 1.4 h per day for a period of 30 d. Cerebrospinal fluid samples were collected on three consecutive days before an exposure period of 30 d, on the last 3 d of the exposure period, and for 3 d starting 5 d after the exposure period. The concentrations of beta-endorphin, tryptophan, 5-hydroxyindoleacetic acid, homovanillic acid, 3-methoxy-4-hydroxyphenylethyleneglycol and quinolinic acid in cerebrospinal fluid were determined. There was a significant increase in quinolinic acid, and a trend towards an increase in tryptophan, findings consistent with a weakening of the blood-brain barrier due to exposure to the electric and magnetic fields.     

Toughening and weakening in ferroelectric ceramics by domain-switching process under mixed electric and mechanical loading

The structural reliability of ferroelectric ceramics calls for a better understanding of the mechanism of fracture. For a ferroelectric ceramic under mechanical and electric loadings, the intensified stress and electric fields in the vicinity of a crack tip lead to polarization switching. The switched zone induces an incompatible strain and, consequently, changes the stress intensities and the apparent fracture toughness. This article investigates the effects on fracture parameters of an initially poled ferroelectric ceramic induced by polarization switching in the case of small-scale switching. The changes of stress intensities and energy release rate at the crack tip induced by the switched zone are calculated when the specimen is under both electric and mechanical loadings. Our results show that a switched zone usually produces both mode I and mode II stress intensities at the crack tip, and the increments are strongly dependent on the initial poling direction and electric-field strength. With certain initial poling directions, the material could be toughened, whereas, with other directions, be weakened. Generally, high-magnitude electric fields (both positive and negative) decrease the material toughness when both the mechanical and electric fields at the crack tip are singular.     

Neuropsychological testing

According to task by Environmental Protection Department of St. Petersburg Municipal Administration, levels of electromagnetic fields induced by high-voltage electric power lines were measured in development lands of St. Petersburg. The authors present hygienic evaluation of electromagnetic fields intensity, match calculated and actual values of magnetic induction of occupational magnetic fields.     

Dielectric increment of low molecular weight RNA in dioxane after application of static electric fields

A soluble RNA with a molecular weight between 15 000 and 23 000 was extracted from calf thymus and chromatographically purified. The RNA was slightly soluble in doxane (approx. 2.5 mug/ml) and RNA-dioxane solutions were used to fill a cell (452.02 pF capacitance) to which static electric fields of variable strength were applied. The dielectric permittivity of the solutions was measured at a fixed time interval after the application of the electric field. The RNA solutions showed a dielectric increment proportional to the strength of the applied field and to the RNA concentration. The existence of a hystersis effect was proven and the effect of the electric field on the RNA molecule might be related to a dielectric saturation phenomenon parallel to long-term changes of the molecule.     

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.     

Effects of coil orientation and magnetic field shield on transcranial magnetic stimulation in cats

To obtain suitable stimulus conditions for transcranial magnetic stimulation, the evoked compound muscle action potential (ECMAP), evoked spinal cord potential (ESCP), and magnetic and electric fields were analyzed in cats with and without the use of a magnetic field shield. Cats were stimulated using a figure 8 magnetic coil placed on the cranium above the motor cortex. The maximum ECMAP amplitude was recorded when the electric current in the coil was in the mediolateral direction, regardless of whether a magnetic shield with a 5 x 5 cm window was used. ECMAP and ESCP thresholds were reduced when magnetic shielding was in place. Due to the edge effect, the strengths of the magnetic and electric fields were highest in the brainstem area, which is an inhomogeneous volume conductor of the cat's cranium. A large induced electric field directed caudally elicited ECMAP and ESCP responses effectively when a magnetic shield with a 5 x 5 cm window was in place.     

Diphtheria and poliomyelitis incidence in Europe

Measurements are presented of angular velocities of rotation of mammalian cells of K562 (human) and SP2 (mouse) in external alternating electric fields over a frequency range of 0.5 kHz to 12 MHz. Electro-rotation of the cells was observed for the case of "two cells in contact' using two parallel, cylindrical electrodes; only one cell was located on the electrode. A theoretical analysis is also presented which shows that the cell rotation arises from a torque produced by the interaction between the primary electric dipole moment induced in the spinning cell and the secondary electric fields, generated by the primary dipole induced in the adjacent cell. These secondary fields are out of phase with the applied electric field. The results show that (a) only the cell not located on the electrode rotates, (b) maximal electro-rotation occurs at two different excitation field frequency domains for the frequency range employed here, (c) the spin speed of the rotating cell at each frequency domain is much less than the excitation frequency, (d) the rotation direction of the cell depends on the angle (theta) between the external electric field and the line joining the centres of the two cells and (e) for a given angle theta, the rotation direction is the same for both excitation frequency domains. The experimental measurements allowed us to estimate the conductivities of the cytoplasms and membrane capacitances of the cells of K562 and SP2. The conductivities of the cytoplasms of the cells of K562 and SP2 were estimated to be 0.2 and 0.3 Sm-(1), respectively, whereas the membrane capacitances of these cells were found to be 2.7 +/- 0.8 and 9.8 +/- 0.6 mFm-(2), respectively.