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8/3/2019 Chapter 7 Interaction of Emf With Cells
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Chapter 7 Interaction of Electromagnetic Field With Cells
In this section we shall discuss have electromagnetic field interacts with cell and sub cellular organ cell,
in this section most of the studies done are from invitro studies done one individual cells as it is not
possible monitor all the cells in a living organism at a same time. Now we shall split the electromagneticelectromagnetic field into two components i.e. (a) electric field, (b) Magnetic field. The cell membrane
blocks the electric component from penetrating the cytoplasma. But magnetic component pass through the
cells without any resistance. Before we understand the mechanism by which EMF interacts with cells lets
first study the normal structure and function of the cell.
Normal cell structure
An adult human being is made up of approximately 100,000 billion cells. A cell contains many
different compartments, organelles, each surrounded by a membrane. The organelles are
specialized to carry out different tasks. A large number of proteins carrying out essential
functions are constantly being made
within our cells. These proteins have to be
transported either out of the cell, or to the
different compartments - the organelles -
within the cell, newly synthesized
proteins have an intrinsic signal that is
essential for governing them to and across
the membrane of the endoplasmic
reticulum,. The cell nucleus contains the
genetic material (DNA) and thus governs
all functions of the cell. The mitochondria
are the "power plants" producing energy
needed by the cell, and the endoplasmic
reticulum is, together with the ribosomes, responsible for synthesizing proteins, every cell
contains approximately one billion protein molecules. The different proteins have a large number
of important functions. Some constitute the building blocks for constructing the cell while others
function as enzymes catalyzing thousands of specific chemical reactions. The proteins within a
cell are constantly degraded and resynthesized.
Figure 1.1 structure of atypical cell
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Structure of cell membrane
Membrane Structure,
Structurally, cell membranes are thought to be field mosaic composed of large proteins
embedded in a thin planar bilayer of aliphatic phospholipids molecules, as indicated in Figure 1.2
A pure phospholipid bilayer arrangement is one of the strongest electric insulators known and is
therefore quite suitable for maintaining large electrochemical potential gradients at minimal
energy expense,. In cell membranes, most ionic current permeates through channels formed by
large transmembrane proteins. Some cells have specialized protein channels thatallow regulation
and selective permeation of ions.
Many membrane proteins serve as receptors for external ligands that cannot penetrate to the
interior of the cell. The attachment of a ligand, such as a hormone, to a receptor protein in the
membrane forms a complex that activates a secondary messenger within the cell to affect a
cellular response. Generally, three different schemes of ligand-mediated signal transduction have
been described. The first involves activation of cyclic adensosine monophosphate (cAMP) as the
secondary messenger. Including inositol triphosphate (IP3), diacylglycerol, and calcium ions. The
third involves ligand-mediated opening (gating) of ion channels in membrane receptors. Here I
have described these signal mechanisms and the ways in which electric fields may perturb them.
Figure 1.2 structure of atypical cell membrane showing (from left to right) c AMP pathway,voltage gated ion channels, inositol phosphate pathway. (Courtesy by lee. Doong et al)
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The cAMP Pathweay.
Signal transduction through the cAMP pathway begins with the arrival of an external signal at
either a stimulatory or an inhibitory membrane receptor. Activation of the stimulatory receptor
molecule signals G3 proteins within the membrane to react with guanine triphosphate (GTP).
The G3 protein then activates another membrane-bound enzyme, adenylate cyclase, to form
cAMP. CcAMP molecules bind to the regulatory sub-unit of protein kinases within the cell,
allowing these enzymes to activated latent proteins by phosphorylation to perform a genetically
programmed fundion. cAMP molecules also work by modulating the flow of other secondary
messengers such as calcium ions. In contrast, activation of the inhibitory receptor provokes a
similar mechanism that results in the inhibition of adenylate cyclase, thereby slowing the
production of cAMP. Although these schemes are similar across a wide range of cell types, the
responses to activation of this pathway vary tremendously.
The Inositol-Membrane Lipid Pathway.
In the inositol-membrane lipid pathway, a phospholipid constituent of the inner membrane,
phosphatidylinositol4.5
biphosphate, is used as the precursor of the second messengers.
Activation begins when ligand interaction with a receptor protein signals a G protein to react
with GTP. This causes activation of phosphatdylinositol biphosphate on the inner membrane and
its hydrolyzation into the secondary messengers IP3 and diacylglycerol. IP3 is water-soluble and
dissolves into the cytosol. It is thought that IP3 acts by stimulating the release of calcium ions
from intracellular organelles such as the endoplasmic reticulum. Like other cellular organelles,
IP3 released from the plasma membrane causes the organelles to rapidly release calcium back
into the cytosol. Increased cytoplasmic free calcium has many known effects, including the
activation of calmodulin, a molecule that regulates many transport and metabolic processes.
Diacylglycerol molecules diffuse laterally with the membrane, activating the membrane-bound
enzyme protein kinase C. Protein kinase C, in turn, activates additional latent proteins to regulate
cellular metabolic function.
Ligand Gated Channels.
Both the cAMP and inositollipid pathways use calcium ions as secondary messengers within the
cell. Besides being released from internal stores such as the endoplasmic reticulum, the internal
calcium concentration can also be raised in response to an external ligand by an increase in flux
across the cell membrane. The external concentration of calcium ion is four times greater than
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internal levels, and the regulation of specific ion channels permits the careful control of calcium
influx. As an example, the binding of parathyroid hormone (PTH) is accompanied by an increase
in calcium influx. In addition to ligand-gates channels, many ion channels are sensitive to the
strength of the transmembrane potential changes in the voltage across the membrane. Changes in
the voltage across the membrane directly turn the channel on and off. Compared with electrically
excitable cells like nerve and muscle, relatively few calcium channels exist in non excitable cells
such as blood cells and bone cells. However, two distinct voltage-gated calcium ion channels in
non excitable cells have been discovered. One type is activated by a change in transmembrane
potential from -30 mV to 20 mV. Relatively large changes in transmembrane potential (i.e., 40
mV to 50 mV) are required to significantly alter calcium ion flux. These channels are the most
direct membrane-bound electrochemical transducers.
Important Note:-
Cell membrane does not permit the electric field to enter into the cytoplasm hence the electric
field acts on the cell via membrane channels and proteins to bring changes inside the cell. The
magnetic field can pass through the cell without any resistance it directly acts on the intra
cellular molecules and organellae to bring about the changes. Hence in following section we will
discuss the effects of electric field and magnetic field differently even though they are two sides
of a same coin.
Mechanismofelectric field interaction with cell membrane,Cell membrane is considered to be the main site where the electric field interacts with the cell.
There are four reasons for this notion.
a) An applied electric field is amplified within the cell membrane.
b) The cell membrane is major transduction pathway as many ligand gated channels and
voltage gated channels are located in it.
c) Changes in the ion flow across the membrane especially calcium ion have been reported
in many EMF studies.
d) Membrane itself is involved in controlling the electrical aspects of the cell, maintaining a
potential gradient of almost 100 mV across the membrane through ion pumps.
Dose ofelectric field
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Cell membrane has a high dielectric constant it behaves as a good insulator for electric field.
Only less than 1% electric field penetrates anterior of the cell i.e if 1 Volt is applied only 1mV
enters the cytoplasma1,2
.
The conductivity of cell membrane is 10-6
times lesser than the conductivity of the plasma. In
cell cultures it is observed that cell which are placed parallel to the electric field are more
sensitive to applied electric field than cells which are perpendicular to the electric field, this is
because when the cells are placed parallel to the electric field the electric fiels is distributed
equallt around the cell as shown in the figure 1.3 below.
figure 1.3 schematic diagram showing distribution of electric field around the cell placed parallel
to the electric field (Eo) (Courtesy by lee. Doong et al).
As we know there is lot of electrochemical activity is going on in a cell, the applied field must
overcome this background noise i.e. signal to noise ratio should be greater then (one) 1, in a
typical mammalian cell a electric field signal of 20-5-mV/cm2
is must to stimulate cell
membrane3-5
Field Interaction Mechanisms
One possible method of electrochemical transduction involves the ability of applied fields to
alter the density and distribution of charged cell-surface proteins6. Several binding interactions
between physiologic ligands and cell-surface receptors have been shown to obey second-order
reversible binding kinetics. Because of this, it is likely that ligand-receptor binding can be
regulated by redistribution and local concentration of surface receptors. This receptor
redistribution would directlyperturb the cAMP and IP3 mechanisms described above by acting
on the ligand-receptor bidning kinetics7.
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In an oscillating electrical field of 1 V/cm and a frequency of 1 Hz, the expected distance
traveled in half a cycle by a single-membrane-imbedded concanavalin A receptor with
effective electrophoretic mobility of ~2x10-7 cm2/V-sec is less than 1 A0
Although this
distance is negligible compared with Brownian motion, if resistance-to-receptor movement in the
plane of the cell membrane is anisotropic, mechanical rectification of electrophoretic movement
may result. Rectification would lead to a net lateral displacement of the receptor over many
cycles. Receptor crowding toward one part of the cell may occur and may change the probability
of ligand binding or dissociation. Because hormone-receptor binding also regulates Trans
membrane ion fluxes, electric fields could in theory indirectly regulate intracellular calcium
transport68,9.
Established evidence exists for anisotropic resistance to movement along certain cells, including
fibroblasts. In 1978 Smith et al. demonstrated that succinyl concanavalinA receptors diffuse
anisotropically on murine fibroblasts10
, with the most rapid diffusion occurring in the direction
parallel to the underlying actin stress fibers. Controversy still exists regarding the existence of
this mechanism in different cell types. Kaptza et al., using a video-FRAP (Fluorescent
Recovery After Photo bleaching) technique, observed that concanavalinA receptor diffusion on
human foreskin fibroblasts is independent of direction11
. Recently, Stolpen et al., using a new
technique called line FRAP,: observed that human dermal fibroblasts exhibit anisotropic
diffusion of fluorescence recovery in class I major histocompatibility complex proteins but that
human vascular endothelial cells do not exhibit this diffusion12
.
Calcium Modulated Effects.
Many studies implicate intracellular calcium fluxes as an intermediate in EMF stimulation of
cellular response. This has been most clearly shown to occur in calcium-dependent
galvanotaxis13
. Calcium ions mediate the action of many other epigenetic regulatory signals and
are known as one of the universal second messengers14
. The complexity of the calcium
messenger system varies from one cell to another. In some cells the magnitude of the response is
related to the magnitude of the change in cytoplasmic calcium (eg, skeletal muscle contraction).
Cells in which the response to calcium is prolonged (e.g., smooth-muscle constriction, insulin
secretion) exhibit no simple corleation, however, between the magnitude or duration of calcium
change and the magnitude or duration of the cellular response15
.
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Recent work by Grazians et al., has demonstrated the influence of electric fields on the
membrane bound calcium ATPase pumps that maintain the large calcium gradient inside the cell.
Grazana et al., found that 20 V/cm electric field exposure increases Na+
Ca2+
transport activity in
plant protoplasts in a frequency-dependent manner. They attribute this change to an indirect
mechanism in which electric field stimulation of membrane-bound ATPsynthase and increases
the intracellular concentration of ATP, which then increases Na+
Ca2+
membrane transport16
.
Changing intracellular calcium concentration has profound effects on cell migration,
proliferation, and the synthesis of tissue components. The migration of fibroblasts into the
wound during the healing process is probably related to a 90 Kd protein, geloslin. When gelsolin
is activated by the binding of calcium ions, it breaks up the cross-linked network of actin
filaments within the cell and makes the cell more fluid and mobile. By alternately breaking and
reassembling the filaments of cytoskeleton, gelsolin may help the overall migration of
fibroblasts17
.
One role of calcium in biosynthesis involves exocytosis of procollagen into the extracellular
matrix. Experiments by Kelly and others have shown that exocytosis is a calcium-dependent
process. Blocking calcium ion flow into the cell may interrupt the secretion of cell matrix
constituents and may therefore inhibit the formation of tissue collagen. The modulation of
calcium concentration may therefore provide the mechanisms by which electric fields effect the
synthesis of extracellular tissue products18
.
Because IP3 release can be triggered by elevated free calcium in the cytoplasm a feedback loop
may exist that can drive large oscillations in cytoplasmic free calcium ion concentration.
Berridge and Galione recently reported that the oscillation frequency appears to be cell-type
specific and seems to vary with the presence of external ligands, indicating that the oscillation
frequency itself may act as a secondary signal for mediating cellular activity20
.
These calcium oscillations may contain a transmembrane ion flux component sensitive to electric
field changes in ion transport. Because variations in oscillation frequency have been linked to
ligand in terection at the membrane, field-imposed variations might similarly modulte cellular
behavior . Imposed transmembrane potentials are small, yet any alteration in the transport of
calcium ion channels might shift the frequency of these oscillations and provide a signal to the
cell.
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Metaphore illustration
Compare the lipid bilayer if the csll
membrane with butter, compare the
transmembrane receptors to emall iron pins
with cap, now place butter in a jar and
place the iron pins above its surface this is
analogous to the cellmembrane with
receptosa, now place a strong magnet near
the jar after some time the iron pins will be
collected towards the side of magnet, this
is what exactly happens to receptors and
this is called anisotropic property, due to
this movement channels open and ions
flow across the membrane.
Figure 1.5 shows displacement of membrane proteins
along the direction of the electric field, note that with
each pule or wave of electric field more number of
transmembrane proteins displaced increases. (Courtesy
by lee. Doong et al).
Figure 1.4 schematic diagram of effect of electric field on
the membrane receptors, arrows show the direction of
electric field (Courtesy by lee. Doong et al).
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Other Mechanisms
Some other less accepted theories are available which attempts to explain effect of electric field
on the cell membrane. A new theory proposed by Blank and Goodman suggests that counter ion
migration away from the equilibrium position around charged intracellular proteins may result
from applied electrical fields. The exposed fixed charges on the protein could alter protein
conformation and result in altered mRNA transcription or translation. This theory predicts the
frequency dependence of biosynthetic response that has been reported21,22.
Mechanismofmagnetic field interaction with cell
Cellular responses to magnetic fields are even more complex and difficult to understand because
the field penetrates the cell uniformly. Cyclotron resonance is one mechanism proposed toexplain the experimentally observed interaction of electric and magnetic fields are applied that
corresponds to the natural resonant frequency of the ion. This energetic response includes
absorbing sufficient velocity to traverse a membrane channel more easily. As evidence, the
authors cite changes in applied magnetic fields that have been observed to shift the frequency
window of cell sensitivity to applied electric fields23,24.
Magnetic field in living tissues effects directly and/or induces electrical currents that interacts
with the cell and its organellae to bring about the biological response, it is beyond the scope of
this book to explain all the effects, in the following section we have covered only those
phenomenon which are supported by a good amount of scientific evidence, the major
phenomenon are;
1. Stabilize cytosolic Calcium
2. Restore equilibrium in ROS (free radical)/antioxidant chemistry
3. Upregulate classes of protective and restorative gene loci
4. Downregulate dysregulatory and apoptotic gene loci.
1, Cytosolic Calcium
The magnetic field increases the free energy or entropy of the intracellular organellae cells
preview this as homeostatic challenge and cellular response to homeostatic challenge is the
release of calcium from intracellular stores that prompts mitochondria to produce free radicals
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(in physiological limit) and heightens DNA response which eventually leads to protein
synthesis25,26
.
2, Stabilized free radical chemistry.
Free radicals of oxygen are paramagnetic in nature and they exhibit dipole alignment when
exposed to a magnetic field, due to this when a magnetic field is applied to the cell as the free
radicals carry a negative charge they exhibit dipole alignment and become stabilized in one
position, this makes the anti oxidant machinery to detect the free radical very easy, thus
antioxidation process is facilitated27,28
.
3, Upregulation ofcytoprotective and restoration genes.
Cytoprotective genes come in to play when there is challenge to the survival of the cell, for
example reperfusion injury, transplant survival, bone graft survival, ischemic injury and so on
whenever such threat is detected the cytoprotective genes are activated, one of the most
important cytoprotective gene is HSP 70, application of magnetic field of 8 micro T, 60 Hz
frequency for 20 minutes (in invitro setting) upregulates HSP70 gene and decreases cell
mortality by 80%, which is of great therapeutic significance29-32
.
Downregulate dysregulatory genes.
In the NASA study some 13,000 gene loci responses to square wave with rapid dB/dt pulse
characteristics were studied with two software programs at an n96. It found that 3,000 loci
were upregulated that represented classes of restorative genes, 2,000 were down regulated
representing dysregulatory loci, and 8,000 loci were unaffected. The latter were reported as
house-keeping loci and other closely conserved sites. This also seems a logical
phenomenology among living systems to achieve homeostasis; this knowledge may pose
interesting possibilities when cancer mitigation becomes part of this technology33
.
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