Combined action of static and alternating magnetic fields on ion motion in a macromolecule: Theoretical aspects

This is an attempt to solve the energetic problem of the primary detection of weak parallel static (DC) and alternating (AC) extremely low frequency (ELF) magnetic fields. We studied the equations of motion for an ion situated inside a macromolecule under the influence of these fields. The main concern is with the magnetic field influence on thermal motion of the ion in the macromolecule. The resonance effects are revealed at discrete frequencies of the ion thermal oscillations determined by the DC field magnitude and the AC field frequency. These phenomena result from the Larmor precession of the ion thermal motion. When the DC field or, to a greater extent, the combined DC and AC fields with the specific frequencies are turned on or cut off, changes occur in the energy of the ion thermal motion. If, inside the macromolecule, the ion is sufficiently protected against immediate impacts of particles of the medium surrounding the macromolecule, these changes may be enough to trigger alteration in the quantum state of the macromolecule. Bioelectromagnetics 19:279–292, 1998. © 1998 Wiley-Liss, Inc.     

Mechanisms of the Effect of Dimephosphone on Synaptic Transmission in the Frog Neuromuscular Junction

We studied the influence of dimephosphone, an organophosphorus drug with a broad spectrum of therapeutic effects on the peripheral and central nervous systems, on postsynaptic end-plate currents (EPC) in the frog neuromuscular junction. Dimephosphone was demonstrated to decrease in a voltage-independent manner the EPC amplitude and to prolong the EPC decay. These effects are not related to inhibition of acetylcholinesterase. We propose a theoretical interpretation of the observed phenomena based on the model of blockade of an open ion channel of the acetylcholine receptor and conclude that postsynaptic receptors are one of the most probable targets for the action of dimephosphone.     

离子束生物效应及应用中值得研究的几个问题

重离子束生物效应及重离子束在生命科学中的应用研究,在国内外物理学与生命科学领域中得到了广泛的开展,但对出现的一些现象还没有深刻地揭露其本质,作出机理性解释。为了深入研究,本文提出一些值得研究的问题供参考,如:重离子径迹结构及能量沉积分布模型,DNA辐射敏感位点,质量沉积-分子改造,直接作用与间接作用,放射性核束的应用等。     

G蛋白对神经细胞电压依赖性离子通道的直接调制作用

神经递质对神经细胞电压依赖性离子通道具有调制作用。近年来观察到,神经递质可通过Ｇ蛋白介导对神经细胞电压依赖性离子通道直接发挥调制作用,而不经过目前已知的多种第二信使的介导,使人们对递质,Ｇ蛋白与电压依赖性离子通道间的相互关系有了新的认识。     

A few remarks on 'combined action of DC and AC magnetic fields on ion motion in a macromolecule'

Zhadin and Barnes [2005:26:323-330] concluded that they solved the differential equation describing combined action of DC and AC magnetic fields on thermal motion of ions in a biological macromolecule and, as a result, a diversity of biological phenomena could be explained. It is shown here that biological phenomena cannot be explained based on this model. Adair [2006:27:332-334] gave several arguments for the statement that the interaction of weak magnetic fields with ions trapped in protein cavities cannot produce detectable biological effects through changing the character of the ion orbits. The arguments are analyzed here and some are shown to be questionable or unjustified. We stress the difference between the conclusion made by Adair and that stated in this article.     

The transport of hydrophobic ions across lipid bilayers

The three-capacitor model for hydrophobic ion adsorption in lipid membranes (Andersen, O.S., Feldberg, S., Nakadomari, H., Levy, S. and McLaughlin, S. (1978) Biophys. J. 21, 35-70) is extended to ion transport whereby electrostatic effects from the interfacially adsorbed hydrophobic space charge have been encountered. The phenomena of current saturation with increasing concentrations of hydrophobic ions in the bulk electrolyte and the associated increase of the time constant of current relaxation can be quantitatively understood on the basis of space charge-limited currents as well as the nonexponential current decay.     

Role of osmoregulation in the actions of taurine

Summary. Taurine regulates an unusual number of biological phenomena, including heart rhythm, contractile function, blood pressure, platelet aggregation, neuronal excitability, body temperature, learning, motor behavior, food consumption, eye sight, sperm motility, cell proliferation and viability, energy metabolism and bile acid synthesis. Many of these actions are associated with alterations in either ion transport or protein phosphorylation. Although the effects on ion transport have been attributed to changes in membrane structure, they could be equally affected by a change in the activity of the affected transporters. Three common ways of altering transporter activity is enhanced expression, changes in the phosphorylation status of the protein and cytoskeletal changes. Interestingly, all three events are altered by osmotic stress. Since taurine is a key organic osmolyte in most cells, the possibility that the effects of taurine on ion transport could be related to its osmoregulatory activity was considered. This was accomplished by comparing the effects of taurine, cell swelling and cell shrinkage on the activities of key ion channels and ion transporters. The review also compares the phosphorylation cascades initiated by osmotic stress with some of the phosphorylation events triggered by taurine depletion or treatment. The data reveal that certain actions of taurine are probably caused by the activation of osmotic-linked signaling pathways. Nonetheless, some of the actions of taurine are unique and appear to be correlated with its membrane modulating and phosphorylation regulating activities. Received January 25, 2000/Accepted January 31, 2000     

Effects of Exogenous Electromagnetic Fields on a Simplified Ion Channel Model

In this paper, we calculate the effect of an exogenous perturbation (an electromagnetic field [EMF] oscillating in the range of microwave frequencies in the range of 1 GHz) on the flux of two ion species through a cylindrical ion channel, implementing a continuous model, the Poisson–Smoluchowski system of equations, to study the dynamics of charged particle density inside the channel. The method was validated through comparison with Brownian dynamics simulations, supposed to be more accurate but computationally more demanding, obtaining a very good agreement. No EMF effects were observed for low field intensities below the level for thermal effects, as the highly viscous regime and the simplicity of the channel do not exhibit resonance phenomena. For high intensities of the external field (>10⁵ V/m), we observed slightly different behavior of ion concentration oscillations and ion currents as a function of EMF orientation with respect to the channel axis.     

Ion-responsive supramolecular fluorescent systems based on multichromophoric calixarenes: A review

Calixarenes are useful building platforms in the design of multichromophoric systems in which photoinduced phenomena (electron, charge and proton transfers, excimer formation and resonance energy transfer) are controlled by ions. The applications mainly concern ion sensing with high selectivity.     

SENSORY TRANSDUCTION AS A PROPOSED MODEL FOR BIOLOGICAL DETECTION OF ELECTROMAGNETIC FIELDS

Laboratory studies of the biological effects of low-frequency electromagnetic fields (EMFs) have demonstrated that the fields can produce or alter a wide range of phenomena. Explaining the diversity of the reported effects is a central problem. Our basic hypothesis is that the effects are generally indirect, and arise as a consequence of sensory transduction of the fields. In this view, EMF detection and its biological consequences occur in different types of cells. Experimental verification of the hypothesis will ultimately require data showing that the interaction of EMFs with tissue results in biological changes that are the same as or similar to changes that occur during sensory transduction. The goal was to identify the specific phenomena that would be expected to occur if the hypothesis were true. We therefore analyzed the presently accepted models of sensory transduction in the somatic and special senses. Many kinds of processes were identified in connection with transduction of different kinds of stimuli, but we found that a change in the conductance of a membrane ion channel in a neuron or a neuroepithelial cell was the earliest process that occurred in all forms of sensory transduction. Evidence from an appropriate model excitable cell or tissue that EMFs affect membrane currents or membrane potential would therefore support the hypothesis that EMF transduction is a species of sensory transduction.     

Non-proton ion release in purple membrane.

Large conductivity changes have been measured during the photocycle of bacteriorhodopsin in purple membrane. These phenomena were explained as being due to the occurrence of large-scale non-proton ion release. Here we show that these conductivity changes do not appear if the purple membrane is immobilized. We propose an alternative hypothesis that explains the presence of conductivity change in suspensions and their absence in gels, as well as several related effects suggesting that the observed conductivity changes are due to alteration of the polarizability of purple membrane during the photocycle.     

Frequency and amplitude windows in the combined action of DC and low frequency AC magnetic fields on ion thermal motion in a macromolecule: theoretical analysis

We solved the differential equation describing combined action of DC and AC magnetic fields on thermal motion of ions in a biological macromolecule. The solution showed the occurrence of a new set of resonant peaks for ion oscillations under the influence of magnetic fields. After establishment of steady ion oscillations in the macromolecule interior that is well shielded from the action of small particles of the medium surrounding this molecule, the change in energy of ion thermal motion could be sufficient to alter the conformation state of the macromolecule. On this basis, a diversity of biological phenomena can be explained, including the appearance of the known "frequency" and "amplitude" windows, without any resort to the ideas of participation of cyclotron or parametric resonances in these effects.     

Electrophoresis in nanochannels: brief review and speculation

The relevant physical phenomena that dominate electrophoretic transport of ions and macromolecules within long, thin nanochannels are reviewed, and a few papers relevant to the discussion are cited. Sample ion transport through nanochannels is largely a function of their interaction with electric double layer. For small ions, this coupling includes the net effect of the external applied field, the internal field of the double layer, and the non-uniform velocity of the liquid. Adsorption/desorption kinetics and the effects of surface roughness may also be important in nanochannel electrophoresis. For macromolecules, the resulting motion is more complex as there is further coupling via steric interactions and perhaps polarization effects. These complex interactions and coupled physics represent a valuable opportunity for novel electrophoretic and chromatographic separations.     

Self-organization effects induced by ion-conformational interaction in biomembrane channels

It is shown that phenomena of molecular self-organization can take place in biomembrane channels. A strong interaction between charged groups of channel-forming protein and ion flux passing through the channel causes bistable or steady limit cycle regimes. These regimes are possible only far from the equilibrium state when the ion flux exceeds a certain threshold value. A number of such synergetic models is reviewed. Each time, only the simplest (monostable) regime takes place near the zero value of the ion flux. Some experimental data may be explained by this approach.     

Velocity auto-correlation function of ions and water molecules in different concentrations,anions and ion clusters

The characteristics of ion solvation are important for electrochemical and biophysical phenomena because all such phenomena occur under the presence of solvated ions. In this study, we performed an all-atom molecular dynamics simulation of aqueous NaCl ranging from 0.5 to 3.0 M, and aqueous NaF, NaBr and NaI in 2.0 M, to investigate the time-averaged velocity auto-correlation function (TAVAF) of ions and water molecules. By comparing the concentrations and ion pairs, we observed three behaviours: (i) in the case of NaCl, the velocity auto-correlation of Cl^?  becomes weaker as the concentration increases, whereas those of Na⁺ are not clearly different, (ii) the intensity of fluctuations of the TAVAF gradually decreases following the decrease in ionic radius and (iii) every TAVAF of water molecules in ionic solutions is clearly lower than that of bulk because of the cage effect. Furthermore, we observed that the first minimum of the TAVAF in the cluster is smaller than that of the isolated ions. These results indicate that the diffusion of ions and water molecules is affected by cage effect, and that the generation of ion cluster affects the diffusion of ions.     

The different sources of variation in inbreeding depression, heterosis and outbreeding depression in a metapopulation of Physa acuta

Understanding how parental distance affects offspring fitness, i.e., the effects of inbreeding and outbreeding in natural populations, is a major goal in evolutionary biology. While inbreeding is often associated with fitness reduction (inbreeding depression), interpopulation outcrossing may have either positive (heterosis) or negative (outbreeding depression) effects. Within a metapopulation, all phenomena may occur with various intensities depending on the focal population (especially its effective size) and the trait studied. However, little is known about interpopulation variation at this scale. We here examine variation in inbreeding depression, heterosis, and outbreeding depression on life-history traits across a full-life cycle, within a metapopulation of the hermaphroditic snail Physa acuta. We show that all three phenomena can co-occur at this scale, although they are not always expressed on the same traits. A large variation in inbreeding depression, heterosis, and outbreeding depression is observed among local populations. We provide evidence that, as expected from theory, small and isolated populations enjoy higher heterosis upon outcrossing than do large, open populations. These results emphasize the need for an integrated theory accounting for the effects of both deleterious mutations and genetic incompatibilities within metapopulations and to take into account the variability of the focal population to understand the genetic consequences of inbreeding and outbreeding at this scale.     

Charge pulse studies of transport phenomena in bilayer membranes. I. Steady-state measurements of actin- and valinomycin-mediated transport in glycerol monooleate bilayers.

A charge pulse technique has been applied to studies of transport phenomena in bilayer membranes. The membrane capacitance can be rapidly charged (in less than a microsecond). The charge then decays through the membrane's conductive mechanism-no current flows through the solution or external circuitry. The resulting voltage decay is thus a manifestation of membrane and boundary layer phenomena only. There are a number of advantages to this approach over conventional voltage or current-clamp techniques: the rise-time of the voltage perturbation is not limited by the time constant deriving from the membrane capacitance and solution resistance, thus permitting study of extremely rapid rate processes; the membrane is exposed to high voltage for relatively short times and thus can be subjected to higher voltages without breakdown; the steady-state current-voltage behavior of the membrane can be deduced from a single charge pulse experiment; the charge (and therefore the integral of the ion flux through the membrane) is monitored allowing detection of rate processes too rapid to follow directly. In this paper we present what is primarily a steady-state analysis of actin (non-, mon-, din-, trin-)-mediated transport of ammonium ion and valinomycin-mediated transport of cesium and potassium ions through glycerol monooleate bilayers. We introduce the concept of the "intercept discrepancy", a method for measuring charge lost through extremely rapid rate processes. Directly observable pre-steady-state phenomena are also discussed but will be the main subject of part II.     

Alloy Anode Materials for Rechargeable Mg Ion Batteries

Rechargeable magnesium ion batteries are interesting as one of the alternative metal ion battery systems to lithium ion batteries due to the wide availability and accessibility of magnesium in the earth's crust. On the one hand, electrolyte solutions in which Mg metal anodes are fully reversible are not suitable for the use of high voltage/high capacity transition metal oxide cathodes due to complex surface phenomena. On the other hand, Mg metal anodes cannot work reversibly in conventional electrolyte solutions in which high voltage/high capacity Mg insertion cathodes can work because of passivation phenomena that fully block them. Replacing Mg metal with alternative anodes that can work reversibly in conventional electrolyte solutions could provide a promising route to elaborate high voltage and high capacity rechargeable Mg battery systems. Herein, the recent progress in alloy anodes based on group IIIA, IVA, VA elements is summarized. The theoretical evaluations, achievable capacities, synthetic strategies, battery test configurations, electrochemical properties, and underlying reaction mechanisms are systematically summarized and discussed. The key issues and challenges impeding their current use are identified and some valuable suggestions for their future development as practical reversible anodes for Mg batteries are provided.     

The protein component of bacterial ribonuclease P flickers the metal ion response to the substrate shape preference of the ribozyme

The substrate shape specificity of the Escherichia coli ribonuclease P (RNase P) ribozyme depends on the concentration of magnesium ion. At 10 mM or more, it can cleave a hairpin substrate as well as a cloverleaf pre-transfer RNA (tRNA). The results showed, however, that the holo enzyme cleaved the hairpin substrate at low concentrations of magnesium ion. Considering that the homologous E. coli tRNAs are resistant to internal cleavage by the RNase P, the phenomena suggest that this catalytic activity might take part in the removing the mis-folded RNAs in the cell.