Charles Polk

“Power frequency fields promote cell differentiation coincident with an increase in transforming growth factor-b1 expression”

Recent information from several laboratories suggest that power frequency fields may stimulate cell differentiation in a number of model systems. In this way, they may be similar to pulsed electromagnetic fields, which have been used therapeutically. However, the effects of power frequency fields on phenotypic or genotypic expression have not been explained. This study describes the ability of power frequency fields to accelerate cell differentiation in vivo and describes dose relationships in terms of both amplitude and exposure duration. No change in proliferation or cell content were observed. A clear dose relationship, in terms of both amplitude and duration of exposure, was determined with the maximal biological response occurring at 0.1 mT and 7–9 h/day. Because this study was designed to explore biological activity at environmental exposure levels, this exposure range does not necessarily define optimal dosing conditions from the therapeutic point of view. This study reports the stimulation by power frequency fields of transforming growth factor-β, an important signalling cytokine known to regulate cell differentiation. The hypothesis is raised that the stimulation of regulatory cytokines by electromagnetic fields may be an intermediary mechanism by which these fields have their biological activity. Bioelectromagnetics 20:453–458, 1999.

Biological effects of low-level low-frequency electric and magnetic fields

The extent of penetration into tissue of extremely low frequency (ELF) and very low frequency (VLF) electric and magnetic fields is discussed. Experimental results on the biological effects of such fields of low amplitude are reviewed. The author concludes that while numerous effects have been reported, it is not possible at the present time to decide whether they constitute a health hazard. Information is insufficient for establishing firm exposure guidelines. Nevertheless, prudence would suggest, particularly on the basis of epidemiological evidence, that long-period human exposure above relatively low-field intensity levels should be avoided. >

Transient Behavior of Aperture Antennas

The transient behavior of aperture antennas is analyzed. For an antenna which is illuminated by a field of uniform phase and either uniform or cosine tapered amplitude, it is shown that the steady-state main lobe is established within (τ/,sub>2</sub>+R/c) seconds after the aperture is energized. τ is the period of the carrier frequency, R is the distance from the center of the aperture to the point where the field is evaluated, and c is the velocity of light. The time required for the establishment of the steady-state pattern at all angles between 0° and 90° is (τ/2θ₀+R/c) where 2θ₀ radians is the beamwidth between first nulls of the steady-state pattern (θ₀<_l). An antenna may be useful, however, before (τ/2θ₀+R/c) seconds, because the maxima of the transient sidelobes are not higher than the maxima of the steady-state sidelobes. The requirement that the steady-state pattern be established at all angles between 0° and 90° leads to a limitation on range discrimination ΔR and angular discrimination Δθ for a pulse radar ΔRΔθ=λ, where λ is the wavelength of the carrier frequency. For a scanning antenna employing linear phase variation over the aperture, it is shown that the main lobe, located at an angle θ_max, is established within a time (τ/₂+ R/c + a sin θ_max/₂c) measured from the instant at which one edge of the aperture is first energized. The quantity a is the dimension of the aperture in the plane in which the field is evaluated.

Physical mechanisms by which low-frequency magnetic fields can affect the distribution of counterions on cylindrical biological cell surfaces

Effects of dc and low-frequency ac magnetic fields on the motion and distribution of counterions on surfaces of cylindrical biological cells are examined. Magnetic fields along the cell axis as well as perpendicular to it are considered. When a dc magnetic field of any physically realizable magnitude is parallel to the cell axis it has no effect on ion motion, since the resulting Lorentz force is much smaller than the counterion-to-ion attractive force. However a dc magnetic field perpendicular to the cell surface will distort any preexisting ion motion and the resulting current (i⊥) perpendicular to the original motion will be much larger than any current induced by a low-frequency ac magnetic field of the same magnitude as the dc field and parallel to it. Nevertheless i⊥ will still be much smaller than the current io constituting the original ion motion since (i⊥/io)=Ω/ν, where Ω is the ion cyclotron frequency and ν the effective counterion collision frequency. With no preexisting coherent ion motion (io=0) the circulating current induced by a sinusoidally time-varying magnetic field parallel to the cell axis will be well below thermal fluctuation noise as long as only a single cell is considered; however when even an infinitesimal exchange of ions between adjacent cells is assumed the magnetic field will cause a redistribution of counterions on the cell surface. The resulting steady-state distribution becomes independent of the frequency of the applied magnetic field (ω) when ω≫α, where α is 1/2 of the relaxation frequency for counterion diffusion. On the basis of these results it is suggested that whenever modification of cell behavior in response to application of a low-frequency magnetic field is established, measurements of dielectric permittivity versus frequency of the cell preparation be performed. Redistribution of counterions on the cell surface would be a likely cause if the noted effect becomes independent of the frequency of the applied magnetic field above the counterion dielectric relaxation frequency. It is also suggested that in magnetic field exposure of cell preparations the size of the sample (e.g. diameter of Petri dish) and direction of the magnetic field relative to average cell orientation can critically affect experimental results.

Therapeutic Applications of Low Frequency Electric and Magnetic Fields

As early as 1962 in the US and even earlier in Japan [Fukada and Yasuda, 1957], it was shown that electric potential differences appear across both living and dead bone subjected to mechanical stress. C.A.L. Bassett and R.O. Becker (1962) observed that these stress generated electrical signals decayed very slowly in comparison with similarly initiated signals in piezo-electric crystals and concluded that piezo-electric phenomena “while probably present, were not the sole cause of these potentials”. Later analysis and experiments established that the observed signals were primarily due to ion displacement within the porous regions and multiple fluid filled channels present in all bone [Anderson and Erikson, 1970; Erikson, 1976; Piekarski and Muro, 1977; Guzelsu and Demiray, 1979; Chakkalakal et al., 1980; Gross and Williams, 1982; Pienkowski and Pollack, 1983; Grodzinsky, 1983; Pollack et al. 1984]. The early observations already suggested that direct application of an externally generated voltage might have an effect on bone development. This was shown to be the case by Bassett, Pawluk and Becker (1964) who found that a DC current of the order of 1 µA (corresponding to a current density of approximately 0.01 A/m2) produced massive osteogenesis near the cathode when electrodes were implanted into the femur of living dogs.

Measurement of ELF field strength

This article reviews the measurement of the absolute magnitude of electric and magnetic fields at extremely low frequencies (ELF), 3 Hz to 3 KHz, when the dimensions ( L ) of any practical receiving antenna are an infinitesimal fraction of the wavelength ( L ) and the incident electric and magnetic fields are, in general, not related to each other by the wave impedance of free space. Various sensor systems and techniques for their calibration are discussed.

Physical Mechanisms for Biological Effects of Low Field Intensity ELF Magnetic Fields

Biological effects of high intensity ELF electric fields, such as muscle stimulation and - at still higher intensities - cell damage by electroporation and heating, are reasonably well (although not completely) understood. However power frequency effects of magnetically induced electric fields of less than 10 -3 V/m or alternating magnetic fields of less than about 100 μT cannot be explained very well at the present time. The biological processes involved, notably signal transduction at the cell membrane and subsequent biochemical processes involving “second messengers” are beginning to be identified (Adcy, 1990; Luben, 1993). These processes involve vast amplification of the incident “signal” with metabolically supplied energy. The physical mechanisms of conversion from an electric or magnetic field to biochemical process are however unknown at the present time. As a consequence we do not know which aspect of the applied or environment field is important. Properties such as polarization, duration and/or intermittency of the signal, frequency and harmonic content may turn out to be as important as amplitude. The biological, chemical and mechanical condition of the organism (e.g. stage in cell cycle, stimulation by a mitogen or cell density) will also influence the effectiveness of the applied field. A key question, which is still only resolved for a few experimentally observed effects, is whether specific biological results arc caused directly by the magnetic field or by the electric field that is induced in tissue by a time varying magnetic field. Particularly for fields larger than about 100 μT direct “magne-tochemical” effects have been suggested and the presence of magnetite particles in some tissues may also play a biological role. Experimental findings suggest that effects of induced electric fields are particularly likely when their magnitudes at the tissue or cell level are relatively “large”, of the order of 10-3 V/m or larger, (McLeod et al., 1993b; Liburdy, 1992; Lyle et al., 1988), and when multiple cells are connected by gap junctions. Induced electric fields may also affect the motion of “counterions” on the cell surface and possibly the structural fluctuations of nucleic acid molecules. While most proteins have a small net electrostatic charge, nucleic acids are polyelectrolytes with large net charge and are surrounded by counterions (McCammon and Harvey, 1987). However in view of the inefficiency of electric field induction by an ELF magnetic field, illustrated by equation (25). The mechanisms for “direct” interaction of time varying magnetic fields with biological processes need serious consideration. This is particularly necessary when the applied ELF magnetic fields that produce unambiguous biological effects are of such amplitude and orientation (in relation to the culture medium or animal) as to produce very small induced electric fields. Experimental results have suggested that the relative magnitude and direction of a static magnetic field (such as that of the earth) can determine the biological effectiveness of a simultaneously present alternating field in some biological systems under controlled laboratory conditions.

Modification of Charge Distribution at Boundaries Between Electrically Dissimilar Media

This chapter is primarily concerned with effects of low intensity and low frequency electric and magnetic fields on spherical or cylindrical cells. Low intensity is understood to mean field amplitudes insufficient to produce measurable thermal effects. Low frequency will mean here that the frequencies contained in the externally applied field are sufficiently low for wavelengths to be much larger than the dimensions of the structures with which the field interacts. Thus we will not consider primary fields in the microwave region, although we will indicate that pulsed signals can generate at boundaries between electrically dissimilar media “secondary” electrical transients that contain very high frequency components, even if the initiating “primary” pulse has a long rise or decay time and only a low frequency repetition rate. Low frequency of the primary signal will also imply that the externally applied electric and magnetic fields are not simply related by a constant wave impedance as they are in the “far field” region of a microwave source.

Environmental Impact of Magnetic Fields Generated by A Large Superconductive Magnetic Energy Storage (SMES) System

Consideration of the environmental impact of SMES systems includes possible biological effects on humans as well as on other vertebrates, plants and bacteria; effects on the operation of essential life support systems such as cardiac pace makers; and effects on such equipment as watches, microprocessors, automobile and aircraft ignition systems and magnetic credit cards. Present knowledge of the biological effects of steady (DC) high and low intensity magnetic fields is reviewed, including synergetic effects of such fields in the presence of 60 Hz electric and magnetic fields; effects on cell growth, DNA synthesis, endocrine system rhythms, Ca++ efflux, bacterial motion and bird migration are considered briefly. If the environment outside the fenced-in SMES area is to be accessible to persons with cardiac pace makers the safe field level will have to be below 1.7 mT. Selecting an arbitrary safety factor of 1.7 giving a field of 1.0 mT one obtains an exclusion radius of 2.0 km for a presently considered 5500 MWh solenoidal storage system and 255 m for a proposed 20 MWh device.

When is a field initiated bioeffect thermal

Physics and biology concepts important for understanding interaction of electric fields with biological systems are discussed with emphasis on how heating effects may be separated from non-thermal mechanisms. Electric fields from DC to millimeter waves are considered. Average amplitudes inside tissue important for eliciting different phenomena are indicated.