Electrical Properties Of Cell Membrane Research Articles

Synthesis, characterization and anticonvulsant activity of new azobenzene-containing VV-hemorphin-5 bio photoswitch.

A novel analog of VV-hemorphin-5 containing azobenzene moiety has been synthesized and investigated for anticonvulsant activity in relation to its E → Z photophysical properties activated by long wavelength light at 365nm. The synthesis was achieved by a modified SPPS by Fmoc-dimerization strategy. The electrochemical behavior before and after UV illumination was investigated using different voltammetric modes. The number of electrons transferred, heterogenic rate constant and diffusion coefficient for E- and Z-isomers were also evaluated. Revealing the governing principles involved in signaling and nerve pulse propagation requires the detailed characterization of the electrical properties of cell membranes. For probing the effect of synthesized azo-peptide on the membrane electrical properties, we measured the specific capacitance of lipid bilayers, representing a basic physical model of biomembranes with their simple reproducibility in laboratory conditions at controlled membrane composition and physicochemical parameters of the surrounding aqueous medium. Our results have shown reduced membrane capacitance in the presence of the azo-peptide, thus providing evidences for possible alterations in the dielectric permittivity of the bilayer. The (Val-Val-Tyr-Pro-Trp-Thr-Gln)2Azo peptide was explored also in vivo for preliminary anticonvulsant activity by using the 6-Hz seizure test and pentylenetetrazol (PTZ) seizure test in mice. The Z-isomer has exhibited higher potency compared to E-isomer most pronouncedly in the 6Hz test for psychomotor seizures where the compound had activity at all three tested doses. It was found that the Z-isomer decrease the latency for onset of clonic seizures induced by PTZ. These results demonstrate that the Z-isomer deserves further evaluation in other screening tests for anticonvulsant activity.

Development of an adaptive electroporation system for intratumoral plasmid DNA delivery

Intratumoral electroporation of plasmid DNA encoding the proinflammatory cytokine interleukin 12 promotes innate and adaptive immune responses correlating with anti-tumor effects. Clinical electroporation conditions are fixed parameters optimized in preclinical tumors, which consist of cells implanted into skin. These conditions have little translatability to clinically relevant tumors, as implanted models cannot capture the heterogeneity encountered in genetically engineered mouse models or clinical tumors. Variables affecting treatment outcome include tumor size, degree of vascularization, fibrosis, and necrosis, which can result in suboptimal gene transfer and variable therapeutic outcomes. To address this, a feedback controlled electroporation generator was developed, which is capable of assessing the electrochemical properties of tissue in real time. Determination of these properties is accomplished by impedance spectroscopy and equivalent circuit model parameter estimation. Model parameters that estimate electrical properties of cell membranes are used to adjust electroporation parameters for each applied pulse. Studies performed in syngeneic colon carcinoma tumors (MC38) and spontaneous mammary tumors (MMTV-PyVT) demonstrated feedback-based electroporation is capable of achieving maximum expression of reporter genes with significantly less variability and applied energy. These findings represent an advancement to the practice of gene electro-transfer, as reducing variability and retaining transfected cell viability is paramount to treatment success.

Identification of Capacitance Distribution in Neuronal Membranes from a Fractional-Order Electrical Circuit and Whole-Cell Patch-Clamped Cells

Passive electrical membrane properties are key determinants of signaling processes in brain cells, influencing input-output responses as well as action potential firing. We propose a novel interpretation of patch-clamp recordings that brings out the fractional dynamic of the electrical properties of cell membranes and provides a better knowledge of their microscopic behavior. The passive electrical properties of the cell membrane were modeled using an electrical equivalent circuit (EEC) consisting of a constant phase element (CPE) in parallel with a resistor. The Mittag-Leffler function was used to describe the non-exponential behavior of the voltage transients that are attributable to the processes of charging and discharging the membrane capacitance. The procedure proposed, based on circuit theory and fractional calculus, was used to study the voltage transients obtained in response to low-amplitude hyperpolarizing current pulses applied to cultured mice dorsal root ganglion (DRG) neurons under whole-cell current-clamp configuration. To further validate the method, we also analyzed the voltage transients obtained from hippocampal pyramidal neurons and glial cells recorded in mice brain slices in vitro using the short-time behavior of the resulting membrane voltages.

Cell Membrane Transport Mechanisms: Ion Channels and Electrical Properties of Cell Membranes.

Cellular life strongly depends on the membrane ability to precisely control exchange of solutes between the internal and external (environmental) compartments. This barrier regulates which types of solutes can enter and leave the cell. Transmembrane transport involves complex mechanisms responsible for passive and active carriage of ions and small- and medium-size molecules. Transport mechanisms existing in the biological membranes highly determine proper cellular functions and contribute to drug transport. The present chapter deals with features and electrical properties of the cell membrane and addresses the questions how the cell membrane accomplishes transport functions and how transmembrane transport can be affected. Since dysfunctions of plasma membrane transporters very often are the cause of human diseases, we also report how specific transport mechanisms can be modulated or inhibited in order to enhance the therapeutic effect.

The Nonlinear Response of Lipid Membranes to Voltage Perturbations as an Alternative Explanation of Electrophysiological Data

The electrical properties of cell membranes are typically investigated in experiments where a time dependent voltage or current perturbation is applied to the membrane and its electrical response is measured. The relevant informations are derived from the measured output by finding an electronic equivalent which would show the same or a similar response as the biological system. In electronics, complementary information about the structure of the system investigated are necessary in order to choose between the equivalent electric configurations which can explain a specific electrical recording. The same applies in electrophysiology. The traditional electrical model of cell membranes, for instance, represents the lipid matrix as an inert capacitor and the interpretation of electrical data addresses primary the functional role of protein channels. However, It has been shown both in theory and experiments that lipid bilayers are not inert insulators and especially close to their melting transition their capacitance and conductance are nonlinear functions of the voltage, area and volume density. As a result, strong similarities exist between the response of biological and artificial membranes. Since biological membranes display phase transitions close to physiological temperature, this has to be included in the electrical models of the cell membrane when interpreting electrophysiological data. Here we show how electric data commonly interpreted as gating currents of proteins and inductance can be explained by the nonlinear dynamics of the lipid matrix itself.

The Effect of the Nonlinearity of the Response of Lipid Membranes to Voltage Perturbations on the Interpretation of Their Electrical Properties. A New Theoretical Description.

Our understanding of the electrical properties of cell membranes is derived from experiments where the membrane is exposed to a perturbation (in the form of a time-dependent voltage or current change) and information is extracted from the measured output. The interpretation of such electrical recordings consists in finding an electronic equivalent that would show the same or similar response as the biological system. In general, however, there is no unique circuit configuration, which can explain a single electrical recording and the choice of an electric model for a biological system is based on complementary information (most commonly structural information) of the system investigated. Most of the electrophysiological data on cell membranes address the functional role of protein channels while assuming that the lipid matrix is an insulator with constant capacitance. However, close to their melting transition the lipid bilayers are no inert insulators. Their conductivity and their capacitance are nonlinear functions of both voltage, area and volume density. This has to be considered when interpreting electrical data. Here we show how electric data commonly interpreted as gating currents of proteins and inductance can be explained by the nonlinear dynamics of the lipid matrix itself.

The extracellular calcium-sensing receptor increases the number of calcium steps and action currents in pituitary melanotrope cells

Secretion of α-melanophore-stimulating hormone (α-MSH) from the neuroendocrine melanotrope cells in the intermediate lobe of the pituitary gland of the clawed frog Xenopus laevis is regulated by various inhibitory, stimulatory and autocrine factors. The neuropeptide sauvagine stimulates α-MSH secretion by changing the pattern of intracellular Ca 2+ oscillations and the electrical properties of the cell membrane. In the present study we investigated whether another secreto-stimulator, the extracellular Ca 2+-sensing receptor (CaR), also affects the Ca 2+ oscillatory pattern and electrical membrane properties. Using high-speed dynamic video-imaging we show that activation of the CaR with the specific agonist l-phenylalanine ( l-Phe) changes the Ca 2+ oscillatory pattern by increasing the number of Ca 2+ steps, which are the “building blocks” of the oscillations. Moreover, using patch-clamp electrophysiology it is demonstrated that l-Phe affects membrane properties by increasing frequency and duration of action currents. Compared to sauvagine, the CaR has different effects on the action current parameters, suggesting that multiple mechanisms regulate the electrical properties of the melanotrope cell membrane and, thereby, the Ca 2+ oscillation-dependent level of α-MSH secretion.

Instantaneous, quantitative single-cell viability assessment by electrical evaluation of cell membrane integrity with microfabricated devices

Abstract Cell viability determination is an important process in life science. The loss of physical integrity in the plasma membrane is one of the major indications of cell death. Cell viability is thus usually determined through examination of membrane integrity with colorometric or fluorescent dyes. It occurred to us that when cell membrane loses the ability to exclude macromolecule dyes, its permeability to ions should also change, which could result in change in the electrical properties of the cell membrane. Therefore, evaluating the electrical properties of cell membrane should provide an indication on membrane integrity. We have designed and fabricated a chip to measure electrical currents that flow through single cells. For the purpose of detecting cell viability, the electrical measurements were correlated with conventional fluorescent dye assays that are typically used to distinguish between dead and live cells. Our experiments on human prostate carcinoma cells demonstrated that the electrical currents flow through live cells and membrane-impaired cells were substantially different. The dynamic processes of cell damage induced by various concentrations of Triton X100™, a cell lysing compound, have also been investigated. Our experimental results suggest that evaluation of cell membrane integrity by electrical measurements provides a simple, quantitative and instantaneous method for cell viability determination, which could be very useful in fundamental cell death study as well as cell-based biosensors for toxic-detection.

Electrical properties of cell pellets and cell electrofusion in a centrifuge

A new approach is proposed for studying cell deformability by centrifugal force, electrical properties of cell membranes in a high electric field, and for performing efficient cell electrofusion. Suspensions of cells (L929 and four other cell types examined) are centrifuged in special chambers, thus forming compact cell pellets in the gap between the electrodes. The setup allows measurement of the pellet resistance and also the high-voltage pulse application during centrifugation. The pellet resistance increases sharply with the centripetal acceleration, which correlates with reduction of the cell pellet porosity due to cell compression and deformation. Experiments with cells pretreated with cytochalasin B or colcemid showed that cell deformability depends significantly on the state of cytoskeleton. When the voltage applied to the cell pellet exceeds a ‘critical’ value, electrical breakdown (poration) of cell membranes occurs. This is seen as a deflection in the I(V) curve for the cell pellet. The electropores formed during the breakdown reseal in several stages: the fastest takes 0.5–1 ms while the whole process completes in minutes. A novel effect of colloid-osmotic compression of cell pellets after electric cell permeabilization is described. Supercritical pulse application to the cell pellet during intensive centrifugation leads to massive cell fusion. The fusion index grows with the increase of centripetal acceleration, and drops drastically when the pulse is applied after the centrifuge is stopped. The colloid-osmotic pellet compression enhances the fusion efficiency. No fusion occurs when cells are brought in contact after the pulse treatment. The data suggest that tight intermembrane contact formed prior to pulse application is a prerequisite condition for efficient cell electrofusion. The capacities of the technique proposed and the mechanism of membrane electrofusion are discussed.

Voltage modulation of membrane permeability and energy utilization in cells

Cell membranes are inherently electrical in nature. Charge movements across, and electric potentials experienced by membranes are used to process and transmit information, transduce energy, and perform other essential functions of a cell. Thus, the electrical properties of cell membranes are topics of study in nearly every branch of the biological sciences (1-6). This article will limit its scope to two recent developments using electric pulses, namely, (1) to implant pores of controlled size in cell membranes, and hence, to modify the permeability of the membrane; (2) to activate membranebound ATPases, and hence, to study the energy utilization process in cells. The use of electric pulses to induce cell alignments and fusions will also be briefly mentioned. It will focus on some basic findings and how this newly acquired knowledge may be further developed into useful tools for biological research. As such, a large portion of the material covered will be selected from our own experience. Readers interested in a broader aspect of the electrical properties of membranes, or in a survey of the literature in specific areas of research, should consult regular and more complete reviews (1-6). When a ceil in suspension is exposed to a voltage pulse, it experiences effects of an electric field and 3oule heating (7; Table 1). Electric field effects, such as electrophoresis of charged molecules or membrane proteins (8,9), orientation of ceils (10-12), and dissociation of molecules or complexes (13), are common to all chemical systems. However, because o5 the specific architecture of cells and membrane vesicles, all of these eifects may be amplified. This occurs when a spherical cell (radius a), made of membrane material much less conductive compared to the medium on both sides of the membrane, is exposed to an electric field, inducing a transmembrane potential, AO.

Hormonal regulation of electrical properties of cell membrane.

1. Many hormones (insulin, hydrocortisone, adrenalin, somatotropin, EDDP, and DOCA) cause an increase in the membrane potential of cells, changes their excitability, the resistance of the membrane, and the content of intracellular potassium and sodium. 2. The changes in the electrical properties of the cell membrane caused by hormones correlate with an increase in the synthesis of fractions of RNA, with the transcribing capacity of the chromatin. 3. Inhibitors of protein synthesis (actinomycin D, olivomycin, x-irradiation) prevent the development of the hyperpolarization, ionic shifts, and activation of the genetic apparatus caused by hormones. 4. Inhibitors of energy metabolism (sodium fluoride, monoiodoacetate, 2,4-dinitro-phenol) do not have an effect on the increase in the membrane potential caused by hormones. 5. Changes in the electrical properties of the cell membrane connected with their primary effect on the genetic apparatus of the cells are of great importance in the mechanism of action of a number of hormones.

Electrical Properties of Egg Cell Membranes

The scope of this review is the electrical properties of the cell membrane. The first section concerns the resting potential, action potential, and K permeabilities of the cell membrane; these properties are compared with those of the maturing oocyte and early embryo. The second section concerns electrical phenomena associated with fertilization, in particular, the activation potential or fertilization potential and its function in prevent­ ing polyspermy and possibly in initiating development. Certain related topics have been reviewed elsewhere and are not discussed here: electrical phenomena associated with the establishment of pattern in the embryo (73); electrical coupling between blastomeres ( 124); and the development of membrane channels at later embryonic stages ( 139). Other reviews about the electrical properties of the cell membrane have been written (44, 58). One confusing issue in describing properties of eggs is the definitions of egg and oocyte. Two different definitions are commonly used. Some­ times the term oocyte is used to refer to stages not yet ready to be fertilized, whereas other authors distinguish oocytes and eggs according to the stage of meiosis, i.e. oocyte is used to refer to any stage before meiosis is complete and is used to refer to subsequent stages. This is confusing since in different species fertilization occurs at different stages of meiosis of the female gamete ( 13 1). (The male gamete has always completed meiosis at the time of fertilization.) Rather than attempt to reform this ambiguous usage, in general we have used the terminology used in the papers under discussion. 385

The Electrical Properties of Cell Membranes in Granular or Agranular Anterior Pituitary Clonal Cells

SummaryThe electrical properties of the membrane of granular and agranular growth hormone-secreting clonal cells derived from the same parent clone of rat anterior pituitary cells were studied by the intracellular micro-electrode technique. An evoked spike potential was generated by a depolarizing current in the granular (SR7E8) but not in the agranular (SR7F2) clonal cells. The potential was not suppressed by tetrodotoxin (TTX), but could be abolished by somatostatin, verapamil and D-600. It, therefore, seems likely that it is a Ca-potential, rather than a Na-potential.

Electrical and Mechanical Responses to Diltiazem in Potassium Depolarized Myocardium of the Guinea Pig

Effects of diltiazem on the electrical and mechanical activities of guinea pig papillary muscle were investigated in K-rich Tyrode’s solution (KCl 12.7 mM). The electrical properties of cell membrane in K-rich solution were also examined in the ventricular muscle fibers. It was found that the overshoot as well as the maximum rate of rise (V˙max) of the action potential were highly sensitive to the extracellular concentration of CaCl2 in K-rich solution. V˙max was also affected by NaCl. Diltiazem at a lower concentration (1.1×10−7 M) caused a reduction in the contractile force of K-depolarized papillary muscle without producing significant changes in the resting and action potentials. In the presence of a higher concentration of diltiazem (1.1×10−5 M), the contractile force decreased concurrently with the change in the action potential. Addition of CaCl2 restored the original strength of contraction in parallel to the recovery of the action potential, especially in its overshoot and V˙max. From these results, it is inferred that diltiazem may decrease the contractile force of guinea pig papillary muscle either by interfering with the transmembrane calcium influx or by intracellularly reducing the free calcium ion concentration in the myoplasm.