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PubMed2001

Ionic Environmental Effect on the Time-Dependent Characteristics of Membrane Potential in a Bipolar Membrane.

The membrane potential characteristics of a bipolar membrane are discussed in an examination of the contribution of an intermediate phase to time-dependent behavior. Bipolar membranes, which consist of a poly(sulfone) base polymer with a quaternary amino group and a poly(styrene-co-divinylbenzene) cation-exchange membrane, were prepared in this study. The membrane potentials in various external concentration differences, the facing directions of the membrane, and the external electrolyte solutions were measured as a function of time. In this study, the time course of the membrane potential was simulated by using the equation based on the Teorell-Meyer-Sievers theory and by assuming the concentration in the intermediate phase, which is much higher or lower than that in the external solution. The membrane facing direction and the intermediate phase condition will alter the direction of the membrane potential change. The intermediate phase in a bipolar membrane seems to act as an alteration barrier for the membrane potential according to the membrane facing direction. Copyright 2001 Academic Press.

Journal Article↗
PubMed1988

Oxygen radicals and plasma membrane potential.

Plasma membrane potential is an important physiologic parameter dependent both upon cellular metabolism and upon the integrity of the cell membrane. Oxygen radicals have been shown to produce significant and early changes in the membrane potential. This data is reviewed along with the physico-chemical origins of the membrane potential and methods of its measurement.

Animals↗
PubMed1978

Developmental changes in rat adrenocortical cell membrane potential.

Resting membrane potentials of zona fasciculata-reticularis cells of the rat adrenal gland varied with age. The mean membrane potentials of newborn rat adrenal cells was -56.4 +/- 0.7 mV in the first week of life. The mean potential increased slightly to -61.9 +/- 0.8 mV in the second week and then decreased with age to a mean of -38.5 +/- 0.8 mV in 25--50 week old rats and of -25.9 +/- 1.9 mV in 100 week old rats. The changes in membrane potential may correlate with the indices of adrenocortical growth and activity.

Adrenal Cortex↗
PubMed1974

Influence of Phenolic Acids on Ion Uptake: IV. Depolarization of Membrane Potentials.

The membrane potentials of aged, excised barley (Hordeum vulgare L.) root cells were rapidly depolarized by the addition of salicylic acid (o-hydroxybenzoic acid) to the buffered medium bathing root segments. Initial values for membrane potentials were restored very slowly (within 100 minutes) by replacing the phenolic solution by phenolic-free buffer. Several other naturally occurring benzoic and cinnamic acids depolarized cell membrane potentials. The cinnamic acids consistently caused a greater depolarization than the correspondingly substituted benzoic acids. A strong positive correlation was found between the depolarization values (DeltaE) for the benzoic acids and their lipid solubilities. This study supports the hypothesis that the inhibition of ion uptake brought about by naturally occurring phenolic acids is caused by a generalized increase in membrane permeability to inorganic ions.

Journal Article↗
PubMed1992

The fertilization potential and associated membrane potential oscillations during the resumption of meiosis in the egg of the ascidian Phallusia mammillata.

The fertilization potential in Phallusia mammillata consisted of an initial rapid depolarization. This initial sperm-triggered depolarization was followed by a phase of membrane depolarization which was of either long or short duration, depending on the eggs. When of long duration, the phase of membrane depolarization was divided into two periods: the first one began with a plateau (Em = +20.2 +/- 1.1 mV; duration = 1.7 +/- 0.14 min) which was followed by a series of membrane potential oscillations (n = 3.1 +/- 0.25) lasting 2.4 +/- 0.2 min. The second period also began as a plateau (Em = approximately 0 mV; duration = 3.40 +/- 0.20 min) which was followed by a series of oscillations (n = 11.5 +/- 0.5) lasting 11.8 +/- 0.6 min, followed by a membrane repolarization. The second series of oscillations often continued rising from the resting potential value. In the eggs displaying a short duration of membrane depolarization, the second period of depolarization was shortened (lasting only 3.5 +/- 0.5 min) since it lacked the second plateau. In addition it displayed a smaller number of oscillations (n = 4.7 +/- 0.6). As a consequence of this shortening, the membrane repolarized sooner. After repolarization, the membrane displayed several potential oscillations that started from the repolarization level. Regardless of the length of the depolarized plateau phases, the total number of membrane oscillations and the time period during which they occurred were constant. Eggs displaying a long depolarization phase had 15.9 +/- 0.6 oscillations in a 19.5 +/- 0.6 min interval, while eggs having a short depolarization phase had 16.0 +/- 0.8 oscillations in a 18.1 +/- 0.3 min interval. The time period during which the potential oscillations occurred corresponded remarkably well with the time of the meiotic divisions: the formation of the first polar body was detected about 80 sec after the end of the first series of oscillations; the second polar body was extruded about 85 sec after the last membrane oscillation occurred.

Animals↗
PubMed1985

Oxonol dyes as monitors of membrane potential: the effect of viruses and toxins on the plasma membrane potential of animal cells in monolayer culture and in suspension.

Optical indicators of the cationic, cyanine and anionic oxonol classes were used to evaluate the plasma membrane potential of animal cells in suspension and in monolayer culture. The optical signals were calibrated by using diffusion potentials either of K+ (in the presence of valinomycin) or of H+ (in the presence of carbonyl cyanide p-trifluoromethoxyphenylhydrazone; FCCP); both classes of dye gave similar values of plasma membrane potential, in the range -40 to -90 mV for different cell types. Addition of haemolytic Sendai virus or Staphylococcus aureus alpha-toxin depolarizes cells and causes them to leak monovalent cations; these effects are antagonized by extracellular Ca2+. Cells infected with vesicular stomatitis or Semliki Forest virus become depolarized during an infectious cycle; infection with other viruses was without affect on plasma membrane potential.

Animals↗
PubMed2006

Measurements of plasma membrane potential changes in Saccharomyces cerevisiae cells reveal the importance of the Tok1 channel in membrane potential maintenance.

K+ is one of the cations (besides protons) whose transport across the plasma membrane is believed to contribute to the maintenance of membrane potential. To ensure K+ transport, Saccharomyces cerevisiae cells possess several types of active and passive transporters mediating the K+ influx and efflux, respectively. A diS-C3(3) assay was used to compare the contributions of various potassium transporters to the membrane potential changes of S. cerevisiae cells in the exponential growth phase. Altogether, the contributions of six K+ transporters to the maintenance of a stable membrane potential were tested. As confirmed by the observed hyperpolarization of trk1 trk2 deletion strains, the diS-C3(3) assay is a suitable method for comparative studies of the membrane potential of yeast strains differing in the presence/absence of one or more cation transporters. We have shown that the presence of the Tok1 channel strongly influences membrane potential: deletion of the TOK1 gene results in significant plasma membrane depolarization, whereas strains overexpressing the TOK1 gene are hyperpolarized. We have also proved that plasma membrane potential is not the only parameter determining the hygromycin B sensitivity of yeast cells, and that the role of intracellular transporters in protecting against its toxic effects must also be considered.

Cell Membrane↗
PubMed1979

Inhibition of the respiratory-linked membrane potential in E. coli membrane vesicles by octapeptin.

Octapeptin is a peptide antibiotic which affects bacterial membrane structure and selective membrane permeability for protons and potassium. The influence of octapeptin on the formation of a membrane potential generated across bacterial vesicles was monitored using the Rb+-valinomycin transport system. Octapeptin inhibited the respiratory-linked generation of membrane potentials formed in the presence of succinate or Asc/PMS. In addition, the antibiotic inhibited [3H]-leucine transport driven either by succinate or Asc/PMS. These studies support the proposal that the antimicrobial activity of octapeptin is due to inhibition of the formation of a membrane potential generated in the presence of appropriate respiratory substrates.

Anti-Bacterial Agents↗
PubMed1990

Chloride current in mammalian cardiac myocytes. Novel mechanism for autonomic regulation of action potential duration and resting membrane potential.

The properties of the autonomically regulated chloride current (ICl) were studied in isolated guinea pig ventricular myocytes. This current was elicited upon exposure to isoproterenol (ISO) and reversed upon concurrent exposure to acetylcholine (ACh). ICl was time independent and exhibited outward rectification. The responses to ISO and ACh could be blocked by propranolol and atropine, respectively, and ICl was also elicited by forskolin, 8-bromoadenosine 3',5'-cyclic monophosphate, and 3-isobutyl-l-methylxanthine, indicating that the current is regulated through a cAMP-dependent pathway. The reversal potential of the ISO-induced current followed the predicted chloride equilibrium potential, consistent with it being carried predominantly by Cl-. Activation of ICl produced changes in the resting membrane potential and action potential duration, which were Cl- gradient dependent. These results indicate that under physiological conditions ICl may play an important role in regulating action potential duration and resting membrane potential in mammalian cardiac myocytes.

Acetylcholine↗
PubMed1998

The calculation of intracellular ion concentrations and membrane potential from cell-attached and excised patch measurements. Cytosolic K+ concentration and membrane potential in Vicia faba guard cells.

Ion channel activity in cell-attached patch recordings shows channel behavior under more physiological conditions than whole-cell and excised patch measurements. Yet the analysis of cell-attached patch measurements is complicated by the fact that the system is ill defined with respect to the intracellular ion activities and the electrical potential actually experienced by the membrane patch. Therefore, of the several patch-clamp configurations, the information that is obtained from cell-attached patch measurements is the most ambiguous. The present study aims to achieve a better understanding of cell-attached patch measurements. Here we describe a method to calculate the intracellular ion concentration and membrane potential prevailing during cell-attached patch recording. The first step is an analysis of the importance of the input resistance of the intact cell on the cell-attached patch measurement. The second step, and actual calculation, is based on comparison of the single channel conductance and reversal potential in the cell-attached patch and excised patch configurations. The method is demonstrated with measurements of membrane potential and cytosolic K+ concentrations in Vicia faba guard cells. The approach described here provides an attractive alternative to the measurement of cytosolic ion concentrations with fluorescent probes or microelectrodes.

Cell Adhesion↗
PubMed1985

Monitoring human neutrophil granule secretion by flow cytometry: secretion and membrane potential changes assessed by light scatter and a fluorescent probe of membrane potential.

Purified human peripheral blood polymorphonuclear neutrophils (PMN) were incubated at 37 degrees C with the fluorescent membrane potential sensitive cyanine dye di-O-C(5)(3) and exposed to a number of stimulatory agents (N-formylmethionylleucylphenylalanine (FMLP), cytochalasin B (cyto B) + FMLP, phorbol myristate acetate (PMA). Flow cytometry was utilized to measure changes in forward light scatter (FS), orthogonal light scatter (90 degrees-SC), and fluorescence intensity of individual cells over time. A saturating (10(-6) M) dose of FMLP lead to a significant increase in the cells' FS without a change in 90 degrees-SC as well as a heterogeneous loss of di-O-C(5)(3) fluorescence. PMA (100 ng/ml) also caused an increase in FS but a uniform loss of dye fluorescence by all cells (apparent depolarization). Cyto B + FMLP produced an increase in FS, a marked loss of 90 degrees-SC, and a uniform loss of fluorescence. Secretion experiments under identical incubation conditions indicated a significantly positive relationship between loss of enzyme markers or cell granularity and orthogonal light scatter (r = 0.959, 0.998, and 0.989 for loss of 90 degrees-SC vs lysozyme, beta-glucuronidase, and granularity index, respectively). Sequential exposure of PMN to PMA and then cyto B + FMLP produced a stepwise shift in scatter parameters (increased FS then loss of 90 degrees-SC). Normalization of membrane potential dye fluorescence changes for the changes in light scatter did not abrogate the heterogeneous fluorescence response of cells to stimulus, indicating that stimulus-induced scatter changes were not responsible for such fluorescence shifts. The data demonstrate that loss of 90 degrees-SC relates closely to secretion of primary granules while changes in FS reflect alterations in cell shape and/or surface/volume ratios that accompany cell activation. Flow cytometric light scatter measurements may yield important information on the extent of prior cell degranulation or activation.

Cytochalasin B↗
PubMed1998

Cyclosporin A increases resting mitochondrial membrane potential in SY5Y cells and reverses the depressed mitochondrial membrane potential of Alzheimer's disease cybrids.

Alzheimer's disease (AD) brains exhibit oxidative stress and a biochemical defect of complex IV (cytochrome oxidase, COX) of the mitochondrial electron transport chain (ETC). This defect can be transferred through mitochondrial DNA (mtDNA) into clonal SY5Y cells depleted of their mtDNA. The resulting cytoplasmic hybrids or "cybrids" retain the complex IV defect and exhibit oxidative stress. We measured the mitochondrial membrane potential (delta psi m) in AD and control cybrids via H3-tetraphenylphosphonium ion (H3-TPP+) accumulation. AD cybrids exhibited a significant (about 30%) decrease in H3-TPP+ accumulation relative to controls. Acute treatment of normal SY5Ys with azide, a COX inhibitor, moderately decreased H3-TPP+ retention and strongly inhibited COX activity in a dose-dependent manner. As the mitochondrial transition pore (MTP) can be activated by reactive oxygen species and ETC inhibitors, and its opening causes delta psi m dissipation, we tested the effects of the MTP inhibitor cyclosporin A (CsA) on TPP+ accumulation. 5mM CsA increased basal H3-TPP+ accumulation in SY5Y cells about 10-fold, corresponding to about a 2-fold increase in delta psi m. In the AD cybrids, CsA increased the apparent delta psi m to the same final levels as it did in controls. These results indicate that low-conductance MTP activity contributes significantly to resting delta psi m in SY5Y cells. We propose the novel hypothesis that the COX defect and resulting oxidative stress in AD may pathologically activate the MTP, resulting in lower delta psi m and the release of mitochondrial factors involved in apoptosis.

Alzheimer Disease↗
PubMed1999

Membrane Potential of Composite Bipolar Membrane in Ethanol-Water Solutions: The Role of the Membrane Interface.

The membrane potential across a composite bipolar membrane (CBM) composed of a cation-exchange membrane with an anion-exchange membrane is theoretically and experimentally analyzed for LiCl ethanol-water solutions. The theoretical approach is based on an extension of the Donnan equilibrium and the Nernst-Planck equation of monopolar charged membranes for the case of two ion-exchange layers by considering the effect of electrolyte ion pairing in the external solution. The experimental results show that the effective membrane charge densities of the two ion-exchange layers will become smaller than those which are separately estimated for each layer. We have introduced a contact factor, zeta, into the theoretical approach to clarify this phenomenon in this study, and the theoretical predictions were in good agreement with the experimental data. The membrane potential measurements show that CBM has the characteristics of a bipolar membrane and can significantly contribute to a better electrochemical characterization of the CBMs. Copyright 1999 Academic Press.

Journal Article↗
PubMed1991

[Effects of isoflurane on membrane potentials, refractory periods and membrane ionic currents in rabbit single ventricular myocytes].

In order to analyze direct action of isoflurane on myocardium, we studied effects of isoflurane on membrane potentials and transmembrane ionic currents in single ventricular myocytes isolated enzymatically from rabbit hearts. Membrane potentials were recorded with a suction microelectrode technique, and an action potential was elicited by a brief intracellular stimulus. Isoflurane 3% depressed the action potential overshoot, plateau phase and duration without changing resting potential. Isoflurane decreased the refractory period of the action potential and prolonged the time-constant (tau) of the recovery process. In corresponding voltage clamp experiments, isoflurane significantly depressed the Ca2+ current (ICa), which generates the plateau phase. However, isoflurane had no effect on the transient outward current (I(t)), which triggers repolarization of the action potential. In rabbit ventricular cells, the time- and voltage-dependent outward K+ current (IK) was nearly absent. In conclusion, the depression of the action potential plateau by isoflurane is due to the decrease of ICa. Since isoflurane has no effect on It, the depression of the plateau phase by isoflurane may explain the shortening in the duration and the refractory period of the action potential.

Action Potentials↗
PubMed1979

Ion Transport in Isolated Protoplasts from Tobacco Suspension Cells: III. Membrane Potential.

The membrane electrical potential difference was measured in cultured cells and isolated protoplasts of tobacco (Nicotiana glutinosa L.) by inserting a microelectrode into cells held fast by a suction micropipette. The potential difference (+/- standard deviation) for unplasmolyzed tobacco cells was -52 +/- 12 millivolts, for cells in 0.3 molar mannitol, -50 +/- 11 millivolts; and for cells plasmolyzed in 0.7 molar mannitol, -49 +/- 12 millivolts all inside negative. The potential difference for isolated protoplasts in 0.7 molar mannitol was -49 +/- 16 millivolts, inside negative. In both cultured cells and protoplasts, the addition of 0.1 millimolar KCN caused a depolarization of the membrane potential. It was concluded that plasmolysis and enzymic release of the protoplast had no significant effect on the membrane potential of cultured tobacco cells.

Journal Article↗
PubMed2001

Mitochondrial K(ATP) channel activation reduces anoxic injury by restoring mitochondrial membrane potential.

Mitochondrial membrane potential (DeltaPsi(m)) is severely compromised in the myocardium after ischemia-reperfusion and triggers apoptotic events leading to cell demise. This study tests the hypothesis that mitochondrial ATP-sensitive K(+) (mitoK(ATP)) channel activation prevents the collapse of DeltaPsi(m) in myocytes during anoxia-reoxygenation (A-R) and is responsible for cell protection via inhibition of apoptosis. After 3-h anoxia and 2-h reoxygenation, the cultured myocytes underwent extensive damage, as evidenced by decreased cell viability, compromised membrane permeability, increased apoptosis, and decreased ATP concentration. Mitochondria in A-R myocytes were swollen and fuzzy as shown after staining with Mito Tracker Orange CMTMRos and in an electron microscope and exhibited a collapsed DeltaPsi(m), as monitored by 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazolcarbocyanine iodide (JC-1). Cytochrome c was released from mitochondria into the cytosol as demonstrated by cytochrome c immunostaining. Activation of mitoK(ATP) channel with diazoxide (100 micromol/l) resulted in a significant protection against mitochondrial damage, ATP depletion, cytochrome c loss, and stabilized DeltaPsi(m). This protection was blocked by 5-hydroxydecanoate (500 micromol/l), a mitoK(ATP) channel-selective inhibitor, but not by HMR-1098 (30 micromol/l), a putative sarcolemmal K(ATP) channel-selective inhibitor. Dissipation of DeltaPsi(m) also leads to opening of mitochondrial permeability transition pore, which was prevented by cyclosporin A. The data support the hypothesis that A-R disrupts DeltaPsi(m) and induces apoptosis, which are prevented by the activation of the mitoK(ATP) channel. This further emphasizes the therapeutic significance of mitoK(ATP) channel agonists in the prevention of ischemia-reperfusion cell injury.

Animals↗
PubMed1990

Maturation of pig oocytes: observations on membrane potential.

The membrane-potential changes of pig oocytes during maturation are described. Cumulus-enclosed oocytes have a resting potential of -41.81 +/- 0.60 mV; the removal of cumulus cells caused this potential to drop to -30.95 +/- 0.43 mV. Adding LH to the culture medium did not influence the potential of denuded oocytes but depolarized the potential of cumulus-enclosed oocytes to -32.90 +/- 0.43 mV. FSH did not affect the membrane potential of denuded or cumulus-enclosed oocytes, but significantly reduced the amplitude of the depolarization induced by LH. The effect of gonadotropins on cultured granulosa cells was also investigated. Plated granulosa cells have a resting potential of -45.21 +/- 0.72 mV, similar to that of cumulus-enclosed oocytes. As recorded in cumulus-enclosed oocytes, LH depolarized granulosa cell membrane potential (-30.33 +/- 0.69 mV) and FSH reduced this effect. To evaluate if oocyte maturation in vivo is accompanied by membrane-potential depolarization, follicular growth and oocyte maturation were induced in 6 prepubertal gilts by using an eCG-hCG treatment. Twenty hours after the beginning of oocyte maturation in vivo (induced by hCG), the membrane potential of the oocyte was depolarized to -28.84 +/- 1.01 mV, a value similar to that observed in vitro. These data indicate that both LH and FSH can influence the membrane potential of follicular somatic cells and, consequently, that of the oocyte. The electrical coupling between somatic cell and oocyte may represent a means by which the gonadotropin message is passed to the germinal cell by the somatic compartment.

Animals↗