Thermodynamics of the charge recombination in photosystem II

The temperature dependence of the electric field-induced chlorophyll luminescence in photosystem II was studied in Tris-washed, osmotically swollen spinach chloroplasts (blebs). The system II reaction centers were brought in the state Z⁺P⁺-Q_A ^-Q_B ^- by preillumination and the charge recombination to the state Z⁺PQ_AQ_B ^- was measured at various temperatures and electrical field strengths. It was found that the activation enthalpy of this back reaction was 0.16 eV in the absence of an electrical field and diminished with increasing field strength. It is argued that this energy is the enthalpy difference between the states IQ_A ^- and I^-Q_A and accounts for about half of the free energy difference between these states. The redox state of Q_B does not influence this free energy difference within 150 s after the photoreduction of Q_A. The consequences for the interpretation of thermodynamic properties of Q_A are discussed.Abbreviations DCMU 3(3,4-dichlorophenyl)-1,1-dimethylurea - I intermediary electron acceptor - Mops 3-(N-morpholino)propanesulphonic acid - P (P₆₈₀) primary electron donor - PS II photosystem II - Q_A and Q_B first and second quinone electron acceptors - Tricine N-tris(hydroxymethyl)methylglycine - Tris tris-(hydroxymethyl)aminomethane - Z secondary electron donor Dedicated to Professor L.N.M. Duysens on the occasion of his retirement     

Kinetics of sterilization of Lactobacillus brevis cells by the application of high voltage pulses

The technique of irreversible electroporation has been successfully applied to cause a lethal effect on Lactobacillus brevis cells suspended in phosphate buffer solution, Na(2)HPO(4)/NaH(2)PO(4) . H(2)O (0.845/0.186 mM) between parallel plane electrodes. Tests were carried out at different temperatures (24,45,60, and 80 degrees C) to determine if there was a synergistic effect of temperature and electric pulse treatment on the destruction of L. brevis. Experimental results indicate that the viability (log N/N(0); where N(0) and N are the number of cells survived per milliliter before and after pulse voltage application, respectively) of L. brevis decreased with electric field strength E and temperature T and treatment time t(t). The relations between log(N/N(0)) and t(t) and log(N/N(0)) and E indicate that higher field strengths are more effective than higher treatment times in causing destruction of L. brevis cells. It was also found that as the temperature of the liquid medium containing L. brevis cells increased from 24 to 60 degrees C, the death rate of L. brevis cells increased with a decrease in the total treatment time t(t) (pulse width x number of pulses applied). The application of an electric field strength E = 25 kV/cm at 60 degrees C and treatment time t(t) = 10 ms resulted in very high destruction levels of L. brevis cells (N/N(0) = 10(-9)). In comparison with existing steam sterilization technology, this new method of sterilization using relatively low temperature and short treatment time could prove to be an excellent method to minimize thermal denaturation of important nutrient components in liquid media. (c) John Wiley & Sons, Inc.     

Echinocyte formation induced by potential changes of human red blood cells

Summary In isotonic 30mm NaCl-saccharose solution, human red blood cells with intact membrane and normal inside ionic content (C-state) indicate a transmembrane potential between +30 mV (at pH 7.4) and +46 mV (at pH 5.1). After treatment with amphotericin B or nystatin as ionophores, a Donnan equilibrium (D-state) will be reached with the same potential at pH 5.1 but a sharp drop down to –20 mV will occur at pH 7.4. Concerning the erythrocyte shape at these states, a stomatocyteechinocyte transformation takes place, in correlation with the potential shift. Stomatocytes formed at >+25 mV, echinocytes at <+25 mV. At potentials lower than +5 mV, no further effect can be observed. This process is reversible. Neuraminidase treatment as well as outside EDTA do not influence this process significantly. Human serum albumin in concentrations of 2% stabilizes the stomatocytes.     

脉冲电场下肿瘤细胞的窗口效应

基于多层电介质模型,对于适应于球形生物细胞的脉冲电场,提出了一种等效电路模型,在相同频域下,内膜和外膜的变化趋势相同,频域分析表明,不同频谱场将引起不同的生物医学效应．我们针对癌症细胞计算了跨膜电压,并讨论了脉冲和跨膜电压以及阻抗的关系．结果表明不同的频域和不同的持续时间对细胞的内膜和外膜有选择性的影响,时域和频域的分析显示,在细胞上有一个窗口,当持续时间在10^-8～10^-6 s之间,细胞内膜的电压将高于细胞外膜的电压．窗口效应为解释生物细胞的脉冲电学效应提供了一种参考思路．     

Nanosecond electric pulses cause mitochondrial membrane permeabilization in Jurkat cells

Nanosecond, high‐voltage electric pulses (nsEP) induce permeabilization of the plasma membrane and the membranes of cell organelles, leading to various responses in cells including cytochrome c release from mitochondria and caspase activation associated with apoptosis. We report here evidence for nsEP‐induced permeabilization of mitochondrial membranes in living cells. Using three different methods with fluorescence indicators—rhodamine 123 (R123), tetramethyl rhodamine ethyl ester (TMRE), and cobalt‐quenched calcein—we have shown that multiple nsEP (five pulses or more, 4 ns duration, 10 MV/m, 1 kHz repetition rate) cause an increase of the inner mitochondrial membrane permeability and an associated loss of mitochondrial membrane potential. These effects could be a consequence of nsEP permeabilization of the inner mitochondrial membrane or the activation of mitochondrial membrane permeability transition pores. Plasma membrane permeabilization (YO‐PRO‐1 influx) was detected in addition to mitochondrial membrane permeabilization. Bioelectromagnetics 33:257–264, 2012. © 2011 Wiley Periodicals, Inc.     

Effects of static magnetic field on specific adenosine-5′-triphosphatase activities and bioelectrical and biomechanical properties in the rat diaphragm muscle

In this study, we aimed to clarify the effects of chronically applied static magnetic field (200 Gauss) on specific ATPase activities and bioelectrical and biomechanical responses in the isolated rat diaphragm muscle. The mean activities of Na⁺-K⁺ ATPase and Ca²⁺ ATPase determined from the diaphragm homogenates were significantly higher in the magnetic field exposed group (n = 20), but that of Mg²⁺ ATPase was nonsignificantly lower compared to the control group (n = 13). Resting membrane potential, amplitude of muscle action potential, and overshoot values (mean ± SE) in the control group were found to be ?76.5 ± 0.6, 100 ± 0.8, and 23.5 ± 0.6 mV, respectively; these values were determined to be ?72.8 ± 0.4, 90.3 ± 0.5, and 17.2 ± 0.4 mV in the magnetic field-exposed group, respectively. The latency was determined to increase in the experimental group, and all the above-mentioned bioelectrical differences between the groups were significant statistically. Force of muscle twitch was found to decrease significantly in the magnetic field-exposed group, and this finding was attributed to the augmenting effect of magnetic field on Ca²⁺ ATPase activity. These results suggest that magnetic field exposure changes specific ATPase activities and, thence, bioelectrical and biomechanical properties in the rat diaphragm muscle. © 1995 Wiley-Liss, Inc.     

A cytohistological analysis of roots whose growth is affected by a 60-Hz electric field

Roots of Pisum sativum were exposed for 48 h to 60-Hz electric fields of 430 V/m in an aqueous inorganic growth medium. The growth in length of the exposed roots was 44% of that for control roots. Root tips were analyzed for mitotic index and cell cycle duration. Mature, differentiated root sections from tissue produced after electrode energization were analyzed for cell lengths and number of files. The major reason for the observation that exposed roots are shorter than control roots is that cell elongation in the former is greatly diminished relative to controls.     

Use of Ψ<Superscript>α</Superscript>-ETOs in the unified treatment of electronic attraction,electric field and electric field gradient multicenter integrals of screened Coulomb potentials over Slater orbitals

In this study, using complete orthonormal sets of -ETOs (where =1, 0, –1, –2, ...)introduced by the author, a large number of series expansion formulae for the multicenter electronic attraction (EA), electric field (EF) and electric field gradient (EFG) integrals of the Yukawa-like screened Coulomb potentials (SCPs) is presented through the new central and noncentral potentials and the overlap integrals with the same screening constants. The final results obtained are valid for arbitrary locations of STOs and their parameters.An erratum to this article can be found at     

Threshold for inhibition of Na, K-ATPase by ELF alternating currents.

Alternating currents can increase or decrease the ATP-splitting activity of the membrane enzyme Na,K-ATPase. Either change depends on the AC frequency, and the greatest effect appears to be in the ELF range at about 100 Hz. The threshold for enzyme inhibition by AC was determined, and it is estimated to be an internal electric field circa 5 microV/cm. The corresponding current-density threshold approximates 8 nA/cm2.     

The dependence of the antibacterial effect of the polycationic peptide warnerin on the energy state of target cells

The bactericidal effect of the polycationic peptide warnerin, produced by Staphylococcus warneri IEGM KL-1, was found to depend on the energy state of susceptible Staphylococcus epidermidis cells. The pretreatment of these cells with compounds that diminish the proton-motive force of plasma membranes enhanced cell tolerance to warnerin. The components and pH of the membrane proton potential influenced the antibacterial activity of warnerin in different ways. In particular, the antibacterial activity of warnerin decreased when the electric component of the proton-motive force of target membranes declined.__________Translated from Mikrobiologiya, Vol. 74, No. 2, 2005, pp. 166–171.Original Russian Text Copyright © 2005 by Korobov, Titova, Lemkina, Polyudova, Pankova.     

Cation transport in nanopores

Using periodic boundary conditions and external electric potential field, we have simulated an ion current flow through a flexible nanopore using cations and an explicit extended simple point charge (SPC/E) water with molecular dynamics simulation. The simulation voltages range goes beyond the usual ionic channel measurements ( ± 1 V) and yields useful information about density profiles, current density distribution and current–voltage (I–V) characteristics.     

Induced fluctuations of electric potentials in the apoplast of leaves

Extracellular recordings of electrical potential in leaves of different species by means of band-pass amplifiers showed the occurrence of fast, small changes (spikes) with an amplitude below 1 mV. Local illumination of leaves induced temporal patterns of spikes outside the illuminated region. The light-induced patterns recorded by a given electrode in a particular experimental setup were similar for successive illuminations. The patterns recorded at different sites on the same leaf were different. Locally repetitive patterns of spikes at the electrode outside the illuminated region indicate the occurrence of some signals transmitted from this region to the cells in the neighborhood of the electrode.     

Active electric properties of cardiac muscle

A model of electrical activity in the heart has been developed that treats the intracellular domain and the extracellular domain as electrical syncytia with anisotropic resistivities (bi-syncytial model). At the microscopic level, propagation is assumed to proceed primarily along the axes of individual cells. Considerations at the macroscopic level relate the transmembrane current to the intracellular and extracellular resistivity and the transmembrane potential. The result is a relationship between instantaneous extracellular potentials and cardiac action potentials.     

土壤表面电场对黑土团聚体破碎和侵蚀的影响

通过定量调控土粒表面电场强度,采用湿筛法和模拟降雨试验,研究了土壤表面电场对东北黑土团聚体稳定性和土壤侵蚀的影响。结果表明: 1)随着土壤本体溶液电解质浓度的降低,土壤颗粒表面电位绝对值和电场强度均不断增加,宾县黑土和克山黑土表面电场强度均可达10⁸ V·m^-1数量级;2)随着土粒表面电场增强,土壤团聚体的破碎程度增大,平均重量直径表现为先急剧减小而后保持不变;3)通过人工模拟降雨试验可知,随本体溶液电解质浓度降低,颗粒表面电场增强,土壤流失强度增大。当电解质浓度＜0.01 mol·L^-1,对应宾县黑土和克山黑土的表面电位绝对值分别大于210和209 mV时,土壤累积流失量随时间的分布曲线较为接近,表明0.01 mol·L^-1是影响土壤侵蚀强度的电解质临界浓度值;4)土壤累积流失量与团聚体平均重量直径之间表现出良好的线性关系。综上,当雨水进入土壤,土粒表面电场增强,引发土壤团聚体破碎并释放大量细颗粒,最后在雨水冲刷作用下发生侵蚀。该研究结果可为深入理解东北黑土区土壤水蚀机理提供新的思路。     

Distribution of AC Electric Field-Induced Transmembrane Voltage in Escherichia coli Cell Wall Layers

On the basis of Gram-negative bacterium Escherichia coli models previously published in the literature, the transmembrane voltage induced by the application of an alternating current (AC) electric field on a bacterial suspension is calculated using COMSOL Multiphysics software, in the range 1–20 MHz, for longitudinal and transverse field orientations. The voltages developed on each of the three layers of the cell wall are then calculated using an electrical equivalent circuit. This study shows that the overall voltage on the cell wall, whose order of magnitude is a few tens of µV, is mainly distributed on inner and outer layers, while a near-zero voltage is found on the periplasm, due to its much higher electrical conductivity compared with the other layers. Although the outer membrane electrical conductivity taken in the model is a thousand times higher than that of the inner membrane, the voltage there is about half of that on the inner membrane, due to capacitive effects. It follows that the expression of protein complexes anchored in the inner membrane could potentially be disrupted, inducing in particular a possible perturbation of biological processes related to cellular respiration and proton cycle, and leading to growth inhibition as a consequence. Protein complexes anchored in the outer membrane or constituting a bridge between the three layers of the cell wall, such as some porins, may also undergo the same action, which would add another growth inhibition factor, as a result of deficiency in porin filtration function when the external environment contains biocides. Bioelectromagnetics. 2020;41:279–288 © 2020 Bioelectromagnetics Society.     

Development of dielectrophoresis separator with an insulating porous membrane using DC‐Offset AC Electric Fields

Our previous studies revealed that the dielectrophoresis method is effective for separating cells having different dielectric properties. The purpose of this study was to evaluate the separation characteristics of two kinds of cells by direct current (DC) voltage offset/alternating current (AC) voltage using an insulating porous membrane dielectrophoretic separator. The separation device gives dielectrophoretic (DEP) force and electrophoretic (EP) force to dispersed particles by applying the DC‐offset AC voltage. This device separates cells of different DEP properties by adopting a structure in which only the parallel plate electrodes and the insulating porous membrane are disposed in the flow path through which the cell‐suspension flows. The difference in the retention ratios of electrically homogeneous 4.5 μm or 20.0 μm diameter standard particles was a maximum of 82 points. Furthermore, the influences of the AC voltage or offset voltage on the retention ratios of mouse hybridoma 3‐2H3 cells and horse red blood cells (HRBC) were investigated. The difference in the retention ratio of the two kinds of cells was a maximum of 56 points. The separation efficiency of this device is expected to be improved by changing the device shape, number of pores, and pore placement. © 2016 American Institute of Chemical Engineers Biotechnol. Prog., 32:1292–1300, 2016     

Depolarization of the membrane potential by hyaluronan

The membrane potential is mainly maintained by the K⁺ concentration gradient across the cell membrane between the cytosol and the extracellular matrix. Here, we show that extracellular addition of high‐molecular weight hyaluronan depolarized the membrane potential of human fibroblasts, human embryonic kidney cells (HEK), and central nervous system neurons in a concentration‐dependent manner, whereas digestion of cell surface hyaluronan by hyaluronidase caused hyperpolarization. This effect could not be achieved by other glycosaminoglycans or hyaluronan oligosaccharides, chondroitin sulfate, and heparin which did not affect the membrane potential. Mixtures of high‐molecular weight hyaluronan and bovine serum albumin had a larger depolarization effect than expected as the sum of both individual components. The different behavior of high‐molecular weight hyaluronan versus hyaluronan oligosaccharides and other glycosaminoglycans can be explained by a Donnan effect combined with a steric exclusion of other molecules from the water solvated chains of high‐molecular weight hyaluronan. Depolarization of the plasma membrane by hyaluronan represents an additional pathway of signal transduction to the classical CD44 signal transduction pathway, which links the extracellular matrix to intracellular metabolism. J. Cell. Biochem. 111: 858–864, 2010. © 2010 Wiley‐Liss, Inc.     

Ion channel enzyme in an oscillating electric field

To explain the electrical activation of several membrane ATPases, an electroconformational coupling (ECC) model has previously been proposed. The model explained many features of experimental data but failed to reproduce a window of the field intensity for the stimulated activity. It is shown here that if the affinities of the ion for the two conformational states of the transporter (one with binding site on the left side and the other on the right side of the membrane) are dependent on the electric field, the field-dependent transport can exhibit the observed window. The transporter may be described as a channel enzyme which opens to one side of the membrane at a time. It retains the energy-transducing ability of the earlier ECC models. Analysis of the channel enzyme in terms of the Michaelis-Menten kinetics has been done. The model reproduced the amplitude window for the electric field-induced cation pumping by (Na,K)-ATPase.