DEFINITION OF ELF FIELDS
Extremely low frequency electromagnetic fields (ELF- EMF) are fields with frequencies up to 300 Hz. Electromagnetic fields are the combination of an electric field (arising from the presence of static electric charges) and a magnetic field (arising from the motion of electric charges) in phase. The frequency simply describes the number of field's oscillations or cycles per second.
ELF fields are generated by natural sources as lightning and natural disturbances in Earth's magnetic field, and especially by human-made sources. All appliances using electricity are sources of ELF fields:
1. Power distribution systems
3. Vacuum cleaners
4. shavers and hair dryers
5. electric can-openers
6. microwave ovens
7. Induction heating
The frequency of alternating current flowing in this appliances, 50 or 60 Hz, falls within ELF frequency band.
Electric and magnetic fields are strongest close to a charge or charged conductor, and their strength rapidly diminishes with distance from it. In particular, close to certain appliances, magnetic field intensity (or flux density) can be of the order of a few hundred microtesla, but rapidly diminish with distance.
WHO – What are electromagnetic fields? 2010
Fields of different frequencies interact with matter and biological systems in different ways. ELF fields quantum energy is too low to cause ionization of molecules (to break chemical bonds), so ELF radiations are called 'non-ionizing radiations'. Non-ionizing radiations effects are thermal and non-thermal effects. Thermal effects are mediated by temperature changes induced by the fields. ELF fields arising from common devices are also unable to give thermal effects: frequency and intensity exposure is too weak. Non thermal effects are mechanisms that do not involved any macroscopic heating. These are related to direct effects of electric or magnetic fields (particularly magnetic) on bodies.
Figure 1. Electromagnetic fields spectrum and effects
Non thermal effects are not well understood in mechanisms. Concerning non-thermal based negative health effects, there are no conclusive scientific evidence. However, many in vitro, in vivo and epidemiological studies has highlighted that significant biological effects may occur from non-thermal fields exposure to ELF fields or other low frequency fields. Genetic damage, cancer, reproductive defects, immune system dysfunctions, neurological disfunctions, protein and peptide damage, kidney damage, and developmental effects are reported in the reviewed scientific literature.
ELF-EMF are categorized by International Agency for Research on Cancer (AIRC) as possibly carcinogenic to humans with regard to childhood leukemia. Epidemiological research also reported weak association between occupational elf exposure and chronic lymphocyte leukemia.
Accordingly to cellular studies, ELF fields may not be genotoxic but may be responsible for aggravation of the cancer state (tumor promotion). Little evidence was found demonstrating the direct damaging ELF effects on DNA: these fields can cause DNA damage only at very high density, in range of mTesla.
In contrast, important alterations induced by these fields on the synthesis of bio-molecules, enzymes, secondary messengers, and cellular surviving have been reported. Early studies by Lin et al show increasing expression of the oncogenes MYC, JUN and FOS and HSP-70 stress protein and it has been demonstrated that ELF fields are capable of increasing the activity of enzymes such as cytochrome oxidase and Na,K-ATPase. This suggest that cells respond to field as an environmental stress (Magnetic field stress induces expression of hsp70. 1998).
Some study seems to demonstrate that magnetic fields induce changes in apoptosis in cultured cells exposed to different experimental protocols. If low intensity induces cancer cells development, high intensity (in order of mT) seems to inhibit cancer cells proliferation and induce apoptosis, and this may be related to experimental model and experimental conditions (Extremely low frequency (ELF) magnetic fields and apoptosis: a review. 2005).
There is no compelling evidence of causal relationship between prenatal development and ELF-EMF exposure. However there is increasing evidence that ELF fields exposure is involved with germ cell apoptosis in testes in animal study.
Results that emerged from in vitro studies of immune cells exposed to ELF fields during these years are deregulation in calcium metabolism and in cell division, including changes in RNA transcription and RNA and DNA synthesis.
Exposure to ELF fields may exert various biological effects on the nervous system. It should be recalled that charged species, particularly calcium ions, are essential in the regulation of the resting membrane potential and in the sequence of events in synaptic excitation. Consequently, it can be speculated that the application of an external magnetic field can influence the behavior of nerve cells through calcium ion dysregulation. Investigations on the effects of electromagnetic fields on human EEG patterns are still conducted today and results stimulate researchers to develop many theories to explain this observation. We will see this theories later. Numerous studies have reported that ELF fields may influence central nervous system function in vivo, for example alteration of plasma and pineal melatonin levels in animal models.
Effects of ELF fields on bone cells represent a scenario quite different from those on other cell types. In fact, since antiquity, electric and magnetic forces have been used to treat numerous diseases, although in a very empirical manner. It is clearly that ELF stimulus promote osteoblast differentiation and bone remodeling.
Cellular effects of extremely low frequency (ELF) electromagnetic fields. 2009
MECHANISMS OF INTERACTION WITH CELLS
Numerous mechanisms by which weak electric or magnetic fields (environmental fields) might produce biological non thermal-effects are being proposed. Even if strong intensity fields have effects based on physical principle as field-charge interactions, field induced dipole, electrical breakdown of cell membranes (electroporation), weak field effects are major concern and have been much debated in the literature.
Mechanisms are related to chemical kinetic effects or physics phenomenons. Several authors have speculated in the bioeffects literature that alternating magnetic fields may interact with biological systems by affecting chemical reactions involving free radical mechanisms. Many others have proposed mechanisms for biological effects of ELF fields based on resonance response in biological systems.
Physical fields may have effect on behavior of all cells’ structures. As the majority of biological molecules and structures are electrically polar an electromagnetic mechanism in participating in their organization cannot be neglected. Endogenous fields can exert forces on charges and dipoles and may be important for transport of molecules in cytoplasm between different reaction compartments, for active transport of molecules across plasma membrane, and for transfer of electrons. External fields can interact with endogenous fields. In particular, membrane electrical properties such as membrane surface charge and membrane potential may be directly influenced by eddy current induced by changing the flux density of magnetic field on membrane through external field.
Non-Thermal Effects and Mechanisms of Interaction Between Electromagnetic Fields and Living Matter. 2011
CALCIUM HOMEOSTASIS AS A POSSIBLE TARGET
ELF fields may in some way increase intracellular calcium concentration.
For example, Lisi et al. provide evidence that ELF electromagnetic fields may induce on AtT20 pituitari cells membrane depolarization followed by an increase in [Ca2+]. Intracellular calcium ([Ca2+]i) was monitored in single exposed cells using fluorophores Indo-1 for [Ca2+]i. Fluorescence microscopy showed a statistically significant increase in [Ca2+]i in exposed cells (Extremely Low Frequency Electromagnetic Field Exposure Promotes Differentiation of Pituitary Corticotrope-Derived AtT20 D16V Cells. 2006.).
Figure 2. Steady state (A) and statistical analysis (B) on fluorometric determination of ELF-EMF effect on AtT20 D16V cells [Ca2+]i
Immunological effects on lymphocyte activation and proliferation, such as effects on bone proliferation and differentiation seems to be mediated by calcium flux interaction. Ca2+ influx is essential for regulating processes involving enzyme control, gene regulation, exocytosis, electric signal transmission in excitable cells. Excessive calcium concentration is a cell stress factor and induces an alteration in intracellular signaling pathway, enzyme control, reduces ATP concentration, alters cellular cytoscheleton, activates calcium- dependent idrolazing enzyme inducing apoptosis.
Electromagnetic field effects on cells of the immune system: the role of calcium signaling. 1992.
SUPPOSED LINK BETWEEN ALTHERATION IN CALCIUM HOMEOSTASIS AND EFFECTS ON METABOLISM
When calcium levels increases in cells, activity of sodium-calcium exchanger and other specific ATP-dependent transporters increases to extrude calcium ions. So cells under ELF fields exposure require more energy as ATP for maintaining calcium homeostasis. In this way, not only intracellular calcium signaling is affected, but cellular metabolism may be directly altered.
To supply for ATP requirements, oxidative phosphorilation increases, and changes in all mitochondrial metabolism is involved. Increasing mitochondrial electron chain transporters expression and activity disturbs oxidative balance and this is a cell stress factor. TCA Cycle increase activity and intermediates diversion to biosintetic pathways decreases. Oxidative metabolism increase at the expense of anabolic process required for cell proliferation.
According to this suppositions, ELF fields may increase apoptosis and inhibit proliferation in cells. This is a possible explanation of a series of studies in which ELF has an antiproliferative, apoptotic or differentiating role.
Figure 3. Calcium channel (in skeletal muscle excitation-contraction coupling) and sodium-calcium exchanger activity.
THREE PROPOSED MECHANISM FOR ALTERED CALCIUM HOMEOSTASIS
Mechanism of increasing intracellular calcium concentration by ELF-EMF are only supposed and remain uncertain. Many theories are proposed and everyone is supported by experimental evidence. Here I report three mechanism related to action of fields on ion transporters across membrane or on the same ions.
1) DIRECT EFFECT ON CALCIUM CHANNELS
Membrane calcium signaling is mediated by calcium channel. One of the first proposed and validated mechanism to explain effetcs on calcium intracellular levels was interaction of external field with transmembrane calcium channels.
This channels are classified by trigger of activation in ligand-gated or voltage-gated calcium channels (VGCCs). The latter seem the main target of ELF fields, in particular L-type (long lasting, referring to the length of activation) calcium channel.
ELF exposure can act to produce excessive activity of the VGCCs in cellular culture suggesting that these may be direct targets. Many of these study implicate specifically the L-type VGCCs such that various L-type calcium channel blockers (dihydropyridine) can block responses to EMF exposure. Study on AtT20 cells showed that L-type voltage gated channel blocker verapamil prevents ELF-EMF (50 Hz) induced differentiation (Stimulation of Ca2+ influx in rat pituitary cells under exposure to a 50 Hz magnetic field. 1998.(SICI)1521-186X(1996)17:4%3C303::AID-BEM6%3E3.0.CO;2-7/abstract). Other calcium type blockers produce also weak response. In another study, the L-type calcium channel inhibitor nifedipine inhibits ELF-EMF (60 Hz) induced neurite-like growth of rat chromaffin cells, and an agonist of L-type calcium channels promotes ELF-EMF induced neurite-like growth in chromaffin cells (The role of voltage-gated Ca2+ channels in neurite growth of cultured chromaffin cells induced by extremely low frequency (ELF) magnetic field stimulation. 1998.). New experiments on vescicles confirm calcium interaction with channel proteins in membrane (Interaction between weak low frequency magnetic fields and cell membranes.).
VGCCs are formed as a complex of several different subunits but the α1 subunit forms the ion conducting pore and contains 4 homologous domains (labeled I–IV), each containing 6 transmembrane helices (S1–S6). S1–4 helices have roles in gating and voltage sensing (S4 helix in particular). S4 has many positive charges such that a high positive charge outside the cell repels the helix, keeping the channel in its closed state. Depolarization of the cell interior causes the helix to move, inducing a conformational change such that ions may flow through the channel (the open state). L-type VGCCs are expressed in neurons, smoot, skeletal and cardiac muscle and endocrine glands. They are responsible for excitation-contraction coupling of muscle and hormone secretion in endocrine cells.
Figura 4. L-type calcium channel subunits and α1 subunit domains
Exposure to electric component of ELF fields can act to change the electrical voltage-gradient across the plasma membrane and may be expected to stimulate VGCCs acting on the electric dipole voltage sensor within the ion channel. Magnetic component of fields, that do not induce electrical changes on static objects, may be involved because cell are not static and cytoplasmic sheets bonded on both side of membrane move rapidly and may influence electrical charge across plasma membrane.
Direct stimulation by partial depolarization across plasma membrane is suggest by observations that the response is rapid and most effects are blocked by VGCC blockers. However, other studies sustain other mechanisms (discussed below) involving other calcium channels.
Electromagnetic fields act via activation of voltage-gated calcium channels to produce beneficial or adverse effects. 2013.:
International Union of Pharmacology. XLVIII. Nomenclature and structure–function relationships of voltage-gated calcium channels. 2005.: http://pharmrev.aspetjournals.org.offcampus.dam.unito.it/content/57/4/411.long
2) INCREASE PLASMA MEMBRANE PERMEABILITY
The cell surface has been suggested as a likely site of interaction for electromagnetic fields. If ELF can act on calcium channel, they can also directly alter membrane permeability. About this hypothesis, only in vitro study were performed. For example, Ramundo A. et al report steady state kinetic studies on carbonic anhidrase entrapped in cationic liposome exposed to ELF-EMFs. A significant increase of enzymatic activity, as a function of increase in the diffusion rate of substrate across the lipid bilayer, was observed in the exposed samples. Authors suppose a direct involvement of charges of stearylamine on the lipid membrane surface and exclude direct effects on carbonic anhidrase (enzyme catalizyng reversible hydration of CO2) as conformational changes. The deprotonation of SA, induced by increasing the pH of the reaction medium to 8.95, nullified the magnetic field effect. Authors sustain that SA has dipolar structure such as NH3+ or CH2 that interact with exogenous magnetic fields and alter motion of SA in lipid bilayer.
In the same way, alteration in membrane fluidity can change membrane permeability to ions, in particular calcium ion.
Effect of low frequency, low amplitude magnetic fields on the permeability of cationic liposomes entrapping carbonic anhydrase: II. No evidence for surface enzyme involvement. 2000.
3) ION CYCLOTRON RESONANCE
The middle of the 1980s was marked with the discovery that a low-frequency alternating magnetic field (ELF) is capable of changing free calcium concentrations in nervous tissue only in the presence of a simultaneously acting static magnetic field (as earth field) having the same direction. The most prominent effect was observed at ELF field frequency close to the cyclotron frequency of a calcium ion (Ca2+-ICR).
Various studies show that ELF at cyclotrone frequency interfere with cellular growth, proliferation, and differentiation and other various biological processes. One of the first work measured the intracellular calcium concentration, by means of a sensitive fluorescent probe, during a 60 min exposure of mouse lymphocytes to 'cyclotron resonance' conditions for calcium ions. Resonance' conditions at two frequencies (16 Hz and 50 Hz) were tested and intracellular calcium concentration increase only when lymphocytes were exposed to 'cyclotron resonance' conditions and not to the other magnetic field combinations used (Magnetic fields and intracellular calcium: effects on lymphocytes exposed to conditions for 'cyclotron resonance').
Study on pituitary AtT20 cell line differentiation give a combination of static and alternate EMFs, tuned to Ca2+ion cyclotron energy resonance. Since the geomagnetic component parallel to the applied ELF field is 9.2 μT, the calculated frequency for calcium is 7.0 Hz. Exposed samples showed by contrast Microscopy modification in shape and morphology; these modifications were associated to an increase amount of neurite-like formations (Calcium Ion Cyclotron Resonance, 7.0 Hz, 9.2 μT Magnetic Field Exposure Initiates Differentiation of Pituitary Corticotrope-Derived AtT20 D16V Cells. 2002.). The same authors recently demonstrated differentiation in human cardiac stem cell, murine and rat neuronal cells, and interference in endorphinergic and cholinergic systems.
The effects of ion cyclotron resonance were investigated also on rat pineal glands. Both the synthesis and the release of pineal melatonin, the gland's major hormone, were significantly reduced by Ca2+ion cyclotron energy resonance exposure, presumably caused by a reduced activity of the enzyme N-acetyltransferase (Evidence that extremely low frequency Ca(2+)-cyclotron resonance depresses pineal melatonin synthesis in vitro).
Ion cyclotron resonance (ICR) is a phenomenon related to the movement of ions in a magnetic field. Liboff was the first scientists who developed a model based on this phenomenon. An ion (that is charged) in a static and uniform magnetic field will move in a circle due to the Lorentz force. An electric excitation signal having the same frequency as rotation will therefore resonate with ions. In this case, the circular motion may be superimposed with a uniform axial motion, resulting in a helix, or with a uniform motion perpendicular to the field. Frequency is related to specific ion mass and charge and only at particular frequency ion absorbe energy and has a motion. Accordingly to Liboff, ions can pass trough channel on membrane and accumulate in cells. But at body temperature this idea can be realized only in very large systems capable of including the large radius of ion rotation, measured by meters.
Figure 5. Ion cyclotron resonance model.
This model is not working but serves as the basis for the next experiment and theories. None of the reported efforts have been entirely successful in accounting for the observed experimental results. Thereafter, Liboff support the idea that the inside shape of the channel plus the ELF magnetic fields at specific frequencies and amplitudes could act as a gate to control the movement of the ion across the cell membrane. Another ICR sustainer, Lednev, explaining the results in terms of magnetically induced changes in the transition probability of calcium binding states in calcium channel.
The last Liboff model hypothesize that the selectively enhanced drift velocity predicted in this model can explain ICR-like phenomena as resulting from increased interaction probabilities in the vicinity of ion channel gates.
Even if complex mathematical model are developed, to date there is no reasonable theoretical explanation for ICR phenomenon, and this remain a debate mechanism of action of ELF.
Possible mechanism for the influence of weak magnetic fields on biological systems. 1991
New theoretical treatment of ion resonance phenomena. 2008
Extremely-low-frequency electromagnetic fields, such as other electromagnetic fields, are very diffuse and this is a concern about public health. Research on the biological effects of ELF fields has been extensive, such as developed models and theories. It is clear that ELF fields may have some effects and one of this is the alteration of calcium concentration in cells. However, no conclusive results have been achieved. Concerning to effects on calcium homeostasis, major evidence result from study on calcium channel. Some problem in reach a definitive evidence is related to non homogenous esperimentally conditions (intensity and frequency in fields exposure, incubation time etc). Moreover, different cellular models could respond in different way to the same field. However, in future new improvement in research may provide proven models of ELF fields action on biological matter.