The effects of moderate-intensity gradient static magnetic fields on nerve conduction

Whether exposure to static magnetic fields (SMF) for medical applications poses a therapeutic benefit or a health hazard is at the focus of current debate. As a peripheral nerve model for studies of the SMF effects, we have investigated whether exposure of in vitro frog sciatic nerve fibers to moderate-intensity gradient SMF up to 0.7 T modulates membrane excitation and refractory processes. We measured the changes in the amplitudes of the electrically evoked compound action potentials for three groups: a control group without SMF exposure and two exposed groups with continuous inhomogeneous exposure to maximum flux densities (B(max)) of 0.21 and 0.7 T SMF for 6 h. The values of the nerve conduction velocity of C fibers were significantly reduced by B(max) of 0.7 T SMF during the 4- to 6-h exposure period but not by B(max) of 0.21 T SMF during the entire exposure period of 6 h, relative to the unexposed control. From these findings, we speculate that exposure to moderate-intensity gradient SMF may attenuate pain perception because the C fibers are responsible for pain transmission. Although the mechanistic reasons for this decrease have yet to be clarified, SMF could affect the behavior of some types of ion channels associated with C fibers.     

Mechanobiology of MG63 osteoblast-like cells adaptation to static magnetic forces

The aim of this study was to explore the biophysical effects of static magnetic field on osteoblastic cells. MG63 cells were exposed to 0.25 and 0.4-T static magnetic fields (SMF). The cell cycle effects were tested by flow cytometry. The differentiation of the cells was assessed by detecting the changes in prostaglandin E2, osteocalcin, and extracellular matrix expression. Membrane fluidity was used to evaluate the alterations in the biophysical properties of cellular membranes after the SMF simulations. Our results show that SMF exposure increases prostaglandin E2 level and extracellular matrix express in MG63 cells. On the other hand, MG63 cells exposed to 0.4-T SMF exhibited a significant decrease in membrane fluidity at 8 h. Based on these findings, it appears reasonable to suggest that SMF affect osteoblastic maturation by increasing membrane rigidity and then inducing differentiation pathway.     

Effects of static magnetic fields on bone microstructure and mechanical properties in mice

All the living organisms originate, evolve and live under geomagnetic field (GMF, 20–70 µT). With rapid development in science and technology, exposure to various static magnetic fields (SMFs) from natural and man-made sources remains a public environmental topic in consideration of its probable health risk for humans. Many animal studies related to health effect have demonstrated that SMF could improve bone formation and enhance bone healing. Moreover, most of the studies focused on local SMF generated by rod-type magnet. It was difficult to come to a conclusion that how SMF affected bone metabolism in mice. The present study employed hypomagnetic field (HyMF, 500 nT), and moderate SMF (MMF, 0.2 T) to systematically investigate the effects of SMF with continuous exposure on microstructure and mechanical properties of bone. Our results clearly indicated that 4-week MMF exposure did not affect bone biomechanical properties or bone microarchitecture, while HyMF significantly inhibited the growth of mice and elasticity of bone. Furthermore, mineral elements might mediate the biological effect of SMF.     

Increase of seed germination,growth and membrane integrity of wheat seedlings by exposure to static and a 10-KHz electromagnetic field

There is a large body of experimental data demonstrating various effects of magnetic field (MF) on plants growth and development. Although the mechanism(s) of perception of MF by plants is not yet elucidated, there is a possibility that like other stimuli, MF exerts its effects on plants by changing membrane integrity and conductance of its water channels, thereby influencing growth characteristics. In this study, the seeds of wheat (Triticum aestivum L. cv. Kavir) were imbibed in water overnight and then treated with or without a 30-mT static magnetic field (SMF) and a 10-kHz electromagnetic field (EMF) for 4 days, each 5 h. Water uptake of seeds reduced 5 h of the treatment with EMF but did not show changes in SMF treatment. Exposure to both magnetic fields did not affect germination percent of the seeds but increased the speed of germination, compared to the control group. Treatment with EMF significantly reduced seedling length and subsequently vigor index I, while SMF had no effects on these parameters. Both treatments significantly increased vigor index II, compared to the control group. These treatments also remarkably increased catalase activity and proline contents of seedlings but reduced the activity of peroxidase, the rate of lipid peroxidation and electrolyte leakages of membranes. The results suggest promotional effects of EMFs on membrane integrity and growth characteristics of wheat seedlings.     

稳恒磁场抑制肿瘤增殖的实验研究与理论探讨

作为模型处理最简单的稳恒磁场,其与肿瘤作用的研究是最具理论和实际意义的。分别介绍了稳恒磁场作用于微循环系统、免疫系统对肿瘤的间接抑制和杀伤作用,磁场影响自由基代谢和细胞膜及细胞内结构对肿瘤的抑制作用;回顾了磁场干扰细胞周期、诱导细胞凋亡对肿瘤的影响,并介绍了稳恒磁场联合抗癌药物在治癌中的应用现状;最后结合实验的进展情况,分析探讨了稳恒磁场抑制肿瘤细胞增殖的物理机理,对肿瘤磁疗的发展前景进行了展望。     

Magnetostatic Field System for Uniform Cell Cultures Exposure

The aim of the present work has been the design and the realization of a Magnetostatic Field System for Exposure of Cell cultures (MaFiSEC) for the uniform and the reproducible exposure of cell cultures to static magnetic fields (SMFs) of moderate magnetic induction. Experimental and computer-simulated physical measurements show that MaFiSEC: i) generates a SMF with magnetic induction that can be chosen in the range of 3 to 20 mT; ii) allows the uniform SMF exposure of cells growing in adhesion and in suspension; iii) is cheap and easy to use. The efficacy and reproducibility of MaFiSEC has been tested by comparing the biological effects exerted on isolated human lymphocytes by 72 h of exposure to a magnet (i.e. Neodymium Magnetic Disk, NMD) placed under the culture Petri dish. Lymphocytes morphology, viability, cell death, oxidative stress and lysosomes activity were the parameters chosen to evaluate the SMF biological effects. The continuous exposure of cells to a uniform SMF, achieved with MaFiSEC, allows highly reproducible biochemical and morphological data.     

Statistical mechanical equilibrium theory of selective ion channels.

A rigorous statistical mechanical formulation of the equilibrium properties of selective ion channels is developed, incorporating the influence of the membrane potential, multiple occupancy, and saturation effects. The theory provides a framework for discussing familiar quantities and concepts in the context of detailed microscopic models. Statistical mechanical expressions for the free energy profile along the channel axis, the cross-sectional area of the pore, and probability of occupancy are given and discussed. In particular, the influence of the membrane voltage, the significance of the electric distance, and traditional assumptions concerning the linearity of the membrane electric field along the channel axis are examined. Important findings are: 1) the equilibrium probabilities of occupancy of multiply occupied channels have the familiar algebraic form of saturation properties which is obtained from kinetic models with discrete states of denumerable ion occupancy (although this does not prove the existence of specific binding sites; 2) the total free energy profile of an ion along the channel axis can be separated into an intrinsic ion-pore free energy potential of mean force, independent of the transmembrane potential, and other contributions that arise from the interfacial polarization; 3) the transmembrane potential calculated numerically for a detailed atomic configuration of the gramicidin A channel embedded in a bilayer membrane with explicit lipid molecules is shown to be closely linear over a distance of 25 A along the channel axis. Therefore, the present analysis provides some support for the constant membrane potential field approximation, a concept that has played a central role in the interpretation of flux data based on traditional models of ion permeation. It is hoped that this formulation will provide a sound physical basis for developing nonequilibrium theories of ion transport in selective biological channels.     

Comparison between low-level 50 Hz and 900 MHz electromagnetic stimulation on single channel ionic currents and on firing frequency in dorsal root ganglion isolated neurons

Alteration of membrane surface charges represents one of the most interesting effects of the electromagnetic exposure on biological structures. Some evidence exists in the case of extremely low frequency whereas the same effect in the radiofrequency range has not been detected. Changes in transmembrane voltages are probably responsible for the mobilization of intracellular calcium described in some previous studies but not confirmed in others. These controversial results may be due to the cell type under examination and/or to the permeability properties of the membranes. According to such a hypothesis, calcium oscillations would be a secondary effect due to the induced change in the membrane voltage and thus dependent on the characteristics of ionic channels present in a particular preparation. Calcium increases could suggest more than one mechanism to explain the biological effects of exposure due to the fact that all the cellular pathways using calcium ions as a second messenger could be, in theory, disturbed by the electromagnetic field exposure. In the present work, we investigate the early phase of the signal transmission in the peripheral nervous system. We present evidence that the firing rate of rat sensory neurons can be modified by 50/60 Hz magnetic field but not by low level 900 MHz fields. The action of the 50/60 Hz magnetic field is biphasic. At first, the number of action potentials increases in time. Following this early phase, the firing rate decreases more rapidly than in control conditions. The explanation can be found at the single-channel level. Dynamic action current recordings in dorsal root ganglion neurons acutely exposed to the electromagnetic field show increased functionality of calcium channels. In parallel, a calcium-activated potassium channel is able to increase its mean open time.     

Comparison between low-level 50 Hz and 900 MHz electromagnetic stimulation on single channel ionic currents and on firing frequency in dorsal root ganglion isolated neurons

Alteration of membrane surface charges represents one of the most interesting effects of the electromagnetic exposure on biological structures. Some evidence exists in the case of extremely low frequency whereas the same effect in the radiofrequency range has not been detected. Changes in transmembrane voltages are probably responsible for the mobilization of intracellular calcium described in some previous studies but not confirmed in others. These controversial results may be due to the cell type under examination and/or to the permeability properties of the membranes. According to such a hypothesis, calcium oscillations would be a secondary effect due to the induced change in the membrane voltage and thus dependent on the characteristics of ionic channels present in a particular preparation. Calcium increases could suggest more than one mechanism to explain the biological effects of exposure due to the fact that all the cellular pathways using calcium ions as a second messenger could be, in theory, disturbed by the electromagnetic field exposure. In the present work, we investigate the early phase of the signal transmission in the peripheral nervous system. We present evidence that the firing rate of rat sensory neurons can be modified by 50/60 Hz magnetic field but not by low level 900 MHz fields. The action of the 50/60 Hz magnetic field is biphasic. At first, the number of action potentials increases in time. Following this early phase, the firing rate decreases more rapidly than in control conditions. The explanation can be found at the single-channel level. Dynamic action current recordings in dorsal root ganglion neurons acutely exposed to the electromagnetic field show increased functionality of calcium channels. In parallel, a calcium-activated potassium channel is able to increase its mean open time.     

Action of calcium ions on channels of inward and outward currents in the molluscan neuron membrane

Changes in the characteristics of activity of sodium, calcium, and potassium channels in the surface membrane during variation of the calcium ion concentration in the extracellular and intracellular medium were investigated by the voltage clamp method during intracellular dialysis of isolated neurons of the mollusksLimnea stagnalis andHelix pomatia. Besides their direct role in passage of the current through the membrane, calcium ions were shown to have two actions, differing in their mechanism, on the functional properties of this membrane. The first was caused by the electrostatic action of calcium ions on the outer surface of the membrane and was manifested as a shift of the potential-dependent characteristics of the ion transport channels along the potential axis; the second is determined by closer interaction of calcium ions with the specific structures of the channels. During the action of calcium-chelating agents EGTA and EDTA on the inner side of the membrane the conductivity of the potassium channels is substantially reduced. With an increase in the intracellular free calcium concentration the conductivity is partially restored. The action of EGTA and EDTA on the outer side of the membrane causes a substantial decrease in the ion selectivity of the calcium channels and changes the kinetics of the portal mechanism. These changes are easily abolished by rinsing off the chelating agents or by returning calcium ions to the external medium. A specific blocking action of an increase in the intracellular free calcium concentration on conductivity of the calcium channels was found.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 9, No. 1, pp. 69–77, January–February, 1977.     

Zipper transition in an alpha-helix: a mechanism for gating of voltage-sensitive ion channels in a biological membrane

It is suggested that the gating currents which control the ion channels in a biological membrane are comprised of positive charges crossing the membrane along chains of hydrogen bonds. These chains are the sets of hydrogen bonds which hold alpha-helical protein segments in their rigid conformations. The passage of a positive charge in one direction along such a chain will convert hydrogen bonds from the usual rigid N--C = O...H--N form to a flaccid N = C--O--H...N form. This "zipper" transition can be reversed by the passage of the positive charge along the return route. A flaccid protein rod can clog an ion channel and thereby close it. When all of the protein rods framing an ion channel are in the rigid conformation, the channel is open. This mechanism is used to explain some of the observed characteristics of calcium ion channels and sodium ion channels.     

Modeling of mechanosensitive channel gating in response to wall shear stress

The accurate biological function of mechanosensitive (MS) channels is crucial for maintaining the viability of living cells. For instance, in vascular endothelial cells, calcium influx from the extracellular environment into cytoplasm is regulated by stretch-activated channels. However, the mechanism by which cells sense force remains unclear. For this study, we hypothesized that gating of ion channels is simply regulated by the direct mechanical stress induced in a membrane. We modeled a membrane channel using crystallographic data of the bacteria Mycobacterium tuberculosis (Tb-MscL) because MscL homologs are integral membrane proteins with sequence similarity to most known ion channels. Molecular dynamics (MD) simulations were performed to elucidate the gating mechanism of the channel protein in response to the fluid shear stress. Results suggest that the stretched membrane drives the interfacial part of the protein–membrane complex to expand and maintains the stability of the constricted part of the transmembrane pore. Moreover, structural similarities between Tb-MscL and the family of ligand-gated ion channels suggest that the conformational change of this model in response to fluid shear stress is useful for modeling the gating mechanism in a broad class of gated channels.     

Importance of Cationic Channels for Functioning of the Nuclear Envelope of Neurons as a Calcium Store

The membrane of the endoplasmic reticulum is, in fact, an extension of the nuclear envelope of eukaryotic cells; both these compartments can fulfill the function of intracellular calcium stores. Using a patch-clamp technique, we studied the biophysical properties of the channels expressed in the inner nuclear membrane of pyramidal neurons of the rat hippocampal CA1 area, in particular of large-conductance cationic channels and calcium channels of inositol trisphosphate receptors (the main channels in membranes of this type). As the results of the measurements showed, the activity of channels of both types demonstrates clearly pronounced voltage dependences. The probability of their open state (P _o) depends on the voltage inside the nuclear envelope lumen. At positive potentials, the activity of these channels is significantly more intense than at negative potentials. Moreover, channels of both types are reversibly blocked at considerable negative potentials. We believe that this property of ion channels in the nuclear envelope is an important factor responsible for the control of calcium signals in the cell nucleus. We propose a hypothesis on the mechanism underlying termination of Ca²⁺ release from such intracellular stores, which is based on the specificity of the voltage dependence of ion channels of the above-mentioned types.     

Effects of a Static Magnetic Field on Hemodynamics During Administration of a Cell Membrane Calcium Channel Blocking Agent

We investigated the influence of a 0.2 T static magnetic field (SMF) on the carotid sinus region in rabbits during infusion of a cell membrane calcium channel blocking agent (verapamil). The experiments were carried out under pentobarbital anesthesia. Blood pressure, heart rate, and respiration were also monitored. Contrary to our earlier studies without verapamil (1–4), the SMF had no significant effect on blood pressure and heart rate during verapamil infusion. Changes in calcium membrane channel transport might be participants in SMF effects on sinocarotid baro-receptors.     

Resolving the spatial kinetics of electric pulse-induced ion release

Exposure of cells to nanosecond pulsed electric fields (nsPEF) causes a rapid increase in intracellular calcium. The mechanism(s) responsible for this calcium burst remains unknown, but is hypothesized to be from direct influx through nanopores, the activation of specific ion channels, or direct disruption of organelles. It is likely, however, that several mechanisms are involved/activated, thereby resulting in a complex chain of events that are difficult to separate by slow imaging methods. In this letter, we describe a novel high-speed imaging system capable of determining the spatial location of calcium bursts within a single cell following nsPEF exposure. Preliminary data in rodent neuroblastoma cells are presented, demonstrating the ability of this system to track the location of calcium bursts in vitro within milliseconds of exposure. These data reveal that calcium ions enter the cell from the plasma membrane regions closest to the electrodes (poles), and that intracellular calcium release occurs in the absence of extracellular calcium. We believe that this novel technique will allow us to temporally and spatially separate various nsPEF-induced effects, leading to powerful insights into the mechanism(s) of interaction between electric fields and cellular membranes.     

Amphotericin B channels in the bacterial membrane: role of sterol and temperature

Amphotericin B is an antibiotic that forms ion channels in the membrane of a host cell. The change in permeability produced by these channels is greatly improved by sterols; nevertheless, the single channel conductivity remains invariant. Hence, it is proposed that sterols do not act directly, but rather through the modulation of the membrane phase. We look at the formation of these channels in the bacterial membrane to determine the mechanism of its known antibiotic resistance. We found that channels can indeed be formed in this membrane, but a substantial amount of amphotericin B is required. We also study the effects of the antibiotic concentration needed for channel expression as well as the dynamics of channels affected by both sterol and temperature in phosphatidylcholine membranes. The results support the idea that membrane structure is a determining factor in the action of the antibiotic.     

Predicting ion channels and their types by the dipeptide mode of pseudo amino acid composition

Ion channels are integral membrane proteins that control movement of ions into or out of cells. They are key components in a wide range of biological processes. Different types of ion channels have different biological functions. With the appearance of vast proteomic data, it is highly desirable for both basic research and drug-target discovery to develop a computational method for the reliable prediction of ion channels and their types. In this study, we developed a support vector machine-based method to predict ion channels and their types using primary sequence information. A feature selection technique, analysis of variance (ANOVA), was introduced to remove feature redundancy and find out an optimized feature set for improving predictive performance. Jackknife cross-validated results show that the proposed method can discriminate ion channels from non-ion channels with an overall accuracy of 86.6%, classify voltage-gated ion channels and ligand-gated ion channels with an overall accuracy of 92.6% and predict four types (potassium, sodium, calcium and anion) of voltage-gated ion channels with an overall accuracy of 87.8%, respectively. These results indicate that the proposed method can correctly identify ion channels and provide important instructions for drug-target discovery. The predictor can be freely downloaded from http://cobi.uestc.edu.cn/people/hlin/tools/IonchanPred/.     

Stretch-activated chloride,potassium, and calcium channels coexisting in plasma membranes of guard cells of Vicia faba L.

Mechanosensitive ion channels in the plasma membrane of Vicia faba guard cell protoplasts were studied by use of the patch clamp technique. Stretch-activated (SA) channels in outside-out patches were analyzed for channel conductance, kinetics and ion selectivity. We found three distinct SA channels, permeable to Cl^–, K⁺ and Ca²⁺ and distinguishable from spontaneous (non-SA) channels for these ions on the basis of conductance, kinetics, and voltage-dependence, as well as sensitivity to membrane stretch. In the attached patch configuration, light suction (2 to 10 kPa) reversibly induced channel opening with multiple amplitudes and complex kinetics. The open probability for SA channels increased nonlinearly with pipette suction. In guard cells in situ, these SA channels may mediate ion transport across the plasma membrane directly, as well as influence the activity of non-SA channels via effects on membrane voltage and cytoplasmic calcium. Through such effects, SA channels likely influence volume and turgor regulation of guard cells, and thereby control of leaf gas exchange.Abbreviations EK equilibrium potential for potassium transport - E_Cl equilibrium potential for chloride transport - SA stretchactivated Dedicated to the 80. birthday of Franz HedrichSupported by a grant from the Deutsche Forschungsgemeinschaft to R.H. and a Department of Energy grant to D.J.C. gratefully acknowledges a John S. Guggenheim Fellowship and Fulbright Kommission Senior Professor Award. We thank Ingrid Baumann and Angela Schön for technical assistance, and Klaus Raschke and Heiner Busch for spirited discussions and support.     

Modulation of channel activity and gadolinium block of MscL by static magnetic fields

The magnetic field of the Earth has for long been known to influence the behaviour and orientation of a variety of living organisms. Experimental studies of the magnetic sense have, however, been impaired by the lack of a plausible cellular and/or molecular mechanism providing meaningful explanation for detection of magnetic fields by these organisms. Recently, mechanosensitive (MS) ion channels have been implied to play a role in magnetoreception. In this study we have investigated the effect of static magnetic fields (SMFs) of moderate intensity on the activity and gadolinium block of MscL, the bacterial MS channel of large conductance, which has served as a model channel to study the basic physical principles of mechanosensory transduction in living cells. In addition to showing that direct application of the magnetic field decreased the activity of the MscL channel, our study demonstrates for the first time that SMFs can reverse the effect of gadolinium, a well-known blocker of MS channels. The results of our study are consistent with a notion that (1) the effects of SMFs on the MscL channels may result from changes in physical properties of the lipid bilayer due to diamagnetic anisotropy of phospholipid molecules and consequently (2) cooperative superdiamagnetism of phospholipid molecules under influence of SMFs could cause displacement of Gd³⁺ ions from the membrane bilayer and thus remove the MscL channel block.     

Biologic effects of SMF and paclitaxel on K562 human leukemia cells

In this study, we evaluated the ability of 8.8 mT static magnetic fields (SMF) to enhance the in vitro action of a chemotherapeutic agent, paclitaxel, against K562 human leukemia cells. We analyzed the cell proliferation, cell cycle distribution, DNA damage and alteration of cell surface and cell organelle ultrastructure after K562 cells were exposed to paclitaxel in the presence or absence of 8.8 mT SMF. The results showed that in the presence of SMF, the efficient concentration of paclitaxel on K562 cells was decreased from 50 to 10 ng/ml. Cell cycle analysis indicated that K562 cells treated with SMF plus paclitaxel were arrested at the G2 phase, which was mainly induced by paclitaxel. Through comet assay, we found that the cell cycle arrest effect of paclitaxel with or without SMF on K562 cells was correlated with DNA damage. The results of atomic force microscopy and transmission electron microscopy observation showed that the cell ultrastructure was altered in the group treated with the combination of SMF and paclitaxel, holes and protuberances were observed, and vacuoles in cytoplasm were augmented. Our data indicated that the potency of the combination of SMF and paclitaxel was greater than that of SMF or paclitaxel alone on K562 cells, and these effects were correlated with DNA damage induced by SMF and paclitaxel. Therefore, the alteration of cell membrane permeability may be one important mechanism underlying the effects of SMF and paclitaxel on K562 cells.