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Mechanism of action of moderate-intensity static magnetic fields on biological systems.
Rosen AD.
Department of Biological Sciences, Purdue University, West Lafayette, IN 47907, USA. arosen@bilbo.bio.purdue.edu
There is substantial evidence indicating that moderate-intensity
static magnetic fields (SMF) are capable of influencing a number of
biological systems, particularly those whose function is closely linked
to the properties of membrane channels. Most of the reported moderate
SMF effects may be explained on the basis of alterations in membrane
calcium ion flux. The mechanism suggested to explain these effects is
based on the diamagnetic anisitropic properties of membrane
phospholipids. It is proposed that reorientation of these molecules
during moderate SMF exposure will result in the deformation of imbedded
ion channels, thereby altering their activation kinetics. Channel
inactivation would not be expected to be influenced by these fields
because this mechanism is not located within the intramembraneous
portion of the channel. Patch-clamp studies of calcium channels have
provided support for this hypothesis, as well as demonstrating a
temperature dependency that is understandable on the basis of the
membrane thermotropic phase transition. Additional studies have
demonstrated that sodium channels are similarly affected by SMFs,
although to a lesser degree. These findings support the view that
moderate SMF effects on biological membranes represent a general
phenomenon, with some channels being more susceptible than others to
membrane deformation.
Cell Biochem Biophys. 2003;39(2):163-73.
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Neuronal ion channels and their sensitivity to extremely low frequency weak electric field effects.
Mathie A, Kennard LE, Veale EL.
Biophysics Section, Department of Biological Sciences, Imperial College London, London SW7 2AZ, UK. a.mathie@imperial.ac.uk
Neuronal ion channels are gated pores whose opening and closing is
usually regulated by factors such as voltage or ligands. They are often
selectively permeable to ions such as sodium, potassium or calcium.
Rapid signalling in neurons requires fast voltage sensitive mechanisms
for closing and opening the pore. Anything that interferes with the
membrane voltage can alter channel gating and comparatively small
changes in the gating properties of a channel can have profound effects.
Extremely low frequency electrical or magnetic fields are thought to
produce, at most, microvolt changes in neuronal membrane potential. At
first sight, such changes in membrane potential seem orders of magnitude
too small to significantly influence neuronal signalling. However, in
the central nervous system, a number of mechanisms exist which amplify
signals. This may allow such small changes in membrane potential to
induce significant physiological effects.
Radiat Prot Dosimetry. 2003; 106(4): 311-6.
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The microscopic nature of localization in the quantum Hall effect.
Ilani S, Martin J, Teitelbaum E, Smet JH, Mahalu D, Umansky V, Yacoby A.
[1] Department of Condensed Matter Physics, Weizmann Institute of
Science, Rehovot 76100, Israel [2] Present address: Laboratory of Atomic
and Solid State Physics, Cornell University, Ithaca, New York 14853,
USA.
The quantum Hall effect arises from the interplay between localized
and extended states that form when electrons, confined to two
dimensions, are subject to a perpendicular magnetic field. The effect
involves exact quantization of all the electronic transport properties
owing to particle localization. In the conventional theory of the
quantum Hall effect, strong-field localization is associated with a
single-particle drift motion of electrons along contours of constant
disorder potential. Transport experiments that probe the extended states
in the transition regions between quantum Hall phases have been used to
test both the theory and its implications for quantum Hall phase
transitions. Although several experiments on highly disordered samples
have affirmed the validity of the single-particle picture, other
experiments and some recent theories have found deviations from the
predicted universal behaviour. Here we use a scanning single-electron
transistor to probe the individual localized states, which we find to be
strikingly different from the predictions of single-particle theory.
The states are mainly determined by Coulomb interactions, and appear
only when quantization of kinetic energy limits the screening ability of
electrons. We conclude that the quantum Hall effect has a greater
diversity of regimes and phase transitions than predicted by the
single-particle framework. Our experiments suggest a unified picture of
localization in which the single-particle model is valid only in the
limit of strong disorder.
Nature. 2004 Jan 22; 427(6972): 328-332.
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Abnormal shift of connexin 43 gap-junction protein induced by 50 Hz electromagnetic fields in Chinese hamster lung cells.
Zeng Q, Hu G, Chiang H, Fu Y, Mao G, Lu D.
Microwave Lab., Zhejiang University School of Medicine, Hangzhou 310031, China.
OBJECTIVE: To study the effects of extremely low frequency magnetic
fields(ELF MF) on the amount and localization of connexin 43(Cx43)
gap-junction protein in the Chinese hamster lung(CHL) cells, and to
explore the mechanism of ELF MF suppression on gap-junctional
intercellular communication(GJIC).
METHODS: The cells were irradiated for 24 h with 50 Hz sinusoidal
magnetic field at 0.8 mT without or with
12-O-tetrade-canoylphorbol-3-acetate(TPA), 5 ng/ml for 1 h. The
localization of Cx43 proteins were performed by indirect
immunofluorescence histochemical analysis and detected by confocal
microscopy. The second experiment was conducted to examine the quantity
of Cx43 proteins level in nuclei or cytoplasm and detected by Western
blotting analysis.
RESULTS: The cells exposed to TPA for 1 h displayed less bright
labelled spots in the regions of intercellular junction than the normal
cells. Most of Cx43 labelled spots occurred in the cytoplasm and
aggregated near the nuclei. At the same time, the amount of Cx43 protein
in cytoplasm were increased[(2.03 +/- 0.89) in ELF group, (2.43 +/-
0.82) in TPA group] as compared to normal control(1.04 +/- 0.17) (P <
0.01).
CONCLUSION: Inhibition on GJIC function by ELF MF alone or combined
with TPA may be related with the shift of Cx43 from the regions of
intercellular junction to the cytoplasm.
Zhonghua Lao Dong Wei Sheng Zhi Ye Bing Za Zhi. 2002 Aug; 20(4): 260-2.
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Physical mechanisms in neuroelectromagnetic therapies.
Liboff AR, Jenrow KA.
Department of Physics, Oakland University, Rochester, MI 48309, USA. liboff@oakland.edu
Physical parameters that are used to characterize different types of
electromagnetic devices used in neurotherapy can include power,
frequency, carrier frequency, current, magnetic field intensity, and
whether an application is primarily electric or primarily magnetic.
Currents can range from tens of microamperes to hundreds of
milliamperes, magnetic fields from tens of microtesla to more than one
tesla, and frequencies from a few Hz to more than 50 GHz. A division
into three device categories is proposed, based on the current applied
and the specificity of the therapeutic signal. Two research areas have
great potential for new neuroelectromagnetic strategies. Studies of
endogenous neural oscillatory states suggest using external fields to
reinforce or inhibit such states. Also, various independent groups have
reported that weak magnetic fields, in particular ion cyclotron
resonance fields, are capable of sharply altering behavior in rats.
NeuroRehabilitation. 2002;17(1):9-22.
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A mechanism for action of extremely low frequency electromagnetic fields on biological systems.
Balcavage WX, Alvager T, Swez J, Goff CW, Fox MT, Abdullyava S, King MW.
Indiana University School of Medicine, Indiana State University, Terre Haute 47809, USA.
This report outlines a simple mechanism, based on the Hall Effect, by
which static and low frequency (50-60 Hz) pulsed electromagnetic fields
(PEMFs) can modify cation flow across biological membranes and alter
cell metabolism. We show that magnetic fields commonly found in the
environment can be expected to cause biologically significant
interactions between transported cations and basic domains of cation
channel proteins. We calculate that these interactions generate forces
of a magnitude similar to those created by normal transmembrane voltage
changes known to gate cation channels. Thus PEMFs are shown to have the
potential of regulating flow through cation channels, changing the
steady state concentrations of cellular cations and thus the metabolic
processes dependent on cation concentrations.
Biochem Biophys Res Commun. 1996 May 15;222(2):374-8.
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A proposed mechanism for the action of strong static magnetic fields on biomembranes.
Rosen AD.
Department of Neurology, School of Medicine, State University of New York at Stony Brook 11794-8121.
Experimental studies have demonstrated a temperature dependent effect
by strong static magnetic fields on synaptic function. It is proposed
that these findings may be explained by the diamagnetic properties of
membrane phospholipids. The change in diamagnetic anisotropy
coincidental with membrane thermotropic phase transition is responsible
for the temperature dependence of this phenomenon and provides insight
into the mechanism of action of these fields. At the prephase transition
temperature highly diamagnetic anisotropic gel phase domains exist
within a more fluid liquid-crystal phase. The partial magnetic
reorientation of these domains results in membrane distortion and,
thereby, functional impairment of contiguous ion specific channels. This
mechanism adequately explains observations of the effects of static
magnetic fields both on the central nervous system and at the
neuromuscular junction. It is suggested that the same mechanism may be
operative in other biosystems.
Int J Neurosci. 1993 Nov;73(1-2):115-9.
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