Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Membrane Potentials”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 451 records · Page 25Linked to original sources
PubMed1989

[Dependence of the character of EPSP summation in mollusk neurons on the level of the membrane potential].

The dependence of monosynaptic EPSP summation properties on the membrane potential level was studied in the experiments on identified neurons of mollusc Planorbis corneus. Summation functions were obtained by means of randomized paired stimuli technique. It was shown that the value of the interstimulus++ interval corresponding to the most marked EPSP interactions depended, mainly, on the postsynaptic mechanism. Really, selective changes in postsynaptic neuron parameters produced by changes in hyperpolarizing current led to a shift of the appropriate position of the summation function extremum. The results obtained made it possible to put forward the suggestion of selective (for every input or groups of inputs) "settlement" of neurons to specific intervals (frequencies); such "settlement" may be modulated by changes in the membrane potential in the corresponding part of a neuron. Possible functional role of this mechanism is discussed.

Animals↗
PubMed2006

Influence of the membrane potential on the protonation of bacteriorhodopsin: insights from electrostatic calculations into the regulation of proton pumping.

Proton binding and release are elementary steps for the transfer of protons within proteins, which is a process that is crucial in biochemical catalysis and biological energy transduction. Local electric fields in proteins affect the proton binding energy compared to aqueous solution. In membrane proteins, also the membrane potential affects the local electrostatics and can thus be crucial for protein function. In this paper, we introduce a procedure to calculate the protonation probability of titratable sites of a membrane protein in the presence of a membrane potential. In the framework of continuum electrostatics, we use a modified Poisson-Boltzmann equation to include the influence of the membrane potential. Our method considers that in a transmembrane protein each titratable site is accessible for protons from only one side of the membrane depending on the hydrogen bond pattern of the protein. We show that the protonation of sites receiving their protons from different sides of the membrane is differently influenced by the membrane potential. In addition, the effect of the membrane potential is combined with the effect of the pH gradient resulting from proton pumping. Our method is applied to bacteriorhodopsin, a light-activated proton pump. We find that the proton pumping of this protein might be regulated by Asp115, a conserved residue for which no function has been identified yet. According to our calculations, the interaction of Asp115 with Asp85 leads to the protonation of the latter if the pH gradient or the membrane potential becomes too large. Since Asp85 is the primary proton acceptor in the photocycle, bacteriorhodopsin molecules in which Asp85 is protonated cannot pump protons. Furthermore, we estimate how the membrane potential affects the energetics of the individual proton-transfer reactions of the photocycle. Most reactions, except the initial proton transfer from the Schiff base to Asp85, are influenced. Our calculations give new insights into the mechanism with which bacteriorhodopsin senses the membrane potential and the pH gradient and how the proton pumping is regulated by these parameters.

Animals↗
PubMed2004

tRNA-triggered ATP hydrolysis and generation of membrane potential by the leishmania mitochondrial tRNA import complex.

Translocation of tRNAs across mitochondrial membranes is a receptor-mediated active transport process requiring ATP. A large tRNA import complex from the inner membrane of Leishmania mitochondria catalyzes translocation into phospholipid vesicles. In this reconstituted system, the import substrate tRNA(Tyr)(GUA) specifically stimulated hydrolysis of ATP within the vesicles, with the subsequent generation of a membrane potential by pumping out of protons, as shown by the protonophore-sensitive uptake of the potential-sensitive dye rhodamine 123. Generation of membrane potential was dependent on ATP hydrolysis, and inhibited by oligomycin, recalling the proton-translocation mechanism of the respiratory F(1)-F(0)-ATPase. For translocation of tRNA, ATP could be replaced by low pH of the medium, but proton-dependent import was resistant to oligomycin. Moreover, ATP hydrolysis, generation of membrane potential and tRNA uptake were inhibited by carboxyatractyloside, a specific inhibitor of mitochondrial ATP-ADP translocase, implying an ATP requirement within the vesicles. These observations imply a gating mechanism in which tRNA, on binding to its receptor, triggers the energetic activation of the complex, leading to the opening of import channels.

Adenosine Triphosphatases↗
PubMed2003

Voltage-dependent membrane potential oscillations of rat striatal fast-spiking interneurons.

We used whole-cell recordings to investigate subthreshold membrane potential oscillations and their relationship with intermittent firing in striatal fast-spiking interneurons. During current injections (100-500 pA, 1 s), these cells displayed a highly variable pattern of spike bursts (comprising 1-30 action potentials) interspersed with membrane potential oscillations. The oscillation threshold was -42 +/- 10 mV, and coincided with that for action potentials. The oscillation frequency was voltage dependent and ranged between 20 and 100 Hz. Oscillations were unaffected by the calcium channel blockers cadmium and nickel and by blockers of ionotropic glutamate and GABA receptors. Conversely, the sodium channel blocker tetrodotoxin fully abolished the oscillations and the spike bursts. The first spike of a burst appeared to be triggered by an oscillation, since the timing and rate of rise of the membrane potential in the subthreshold voltage region was similar for the two events. Conversely, the second spike (and the subsequent ones) displayed much faster depolarisations in the subthreshold voltage range, indicating that they were generated by a different mechanism. Consistent with these notions, a small pulse of intracellular current delivered during the oscillation was effective in triggering a burst of action potentials that largely outlasted the pulse. We conclude that fast-spiking interneuron oscillations are generated by an intrinsic membrane mechanism that does not require fast synaptic transmission, and which depends on sodium conductance but not calcium conductance, and that such oscillations are responsible for triggering the intermittent spike bursts that are typical of these neurons.

Action Potentials↗
PubMed1999

Factors and processes involved in membrane potential build-up in yeast: diS-C3(3) assay.

No methods are currently available for fully reliable monitoring of membrane potential changes in suspensions of walled cells such as yeast. Our method using the Nernstian cyanine probe diS-C3(3) monitors even relatively fast changes in membrane potential delta psi by recording the shifts of probe fluorescence maximum lambda max consequent on delta psi-dependent probe uptake into, or exit from, the cells. Both increased [K+]out and decreased pHout, but not external NaCl or choline chloride depolarise the membrane. The major ion species contributing to the diS-C3(3)-reported membrane potential in S. cerevisiae are thus K+ and H+, whereas Na+ and Cl- do not perceptibly contribute to measured delta psi. The strongly pHout-dependent depolarisation caused by the protonophores CCCP and FCCP, lack of effect of the respiratory chain inhibitors rotenone and HQNO on the delta psi, as well as results obtained with a respiration-deficient rho- mutant show that the major component of the diS-C3(3)-reported membrane potential is the delta psi formed on the plasma membrane while mitochondrial potential forms a minor part of the delta psi. Its role may be reflected in the slight depolarisation caused by the F1F0-ATPase inhibitor azide in both rho- mutant and wildtype cells. Blocking the plasma membrane H(+)-ATPase with the DMM-11 inhibitor showed that the enzyme participates in delta psi build-up both in the absence and in the presence of added glucose. Pore-forming agents such as nystatin cause a fast probe entry into the cells signifying membrane damage and extensive binding of the probe to cell constituents reflecting obviously disruption of ionic balance in permeabilised cells. In damaged cells the probe therefore no longer reports on membrane potential but on loss of membrane integrity. The delta psi-independent probe entry signalling membrane damage can be distinguished from the potential-dependent diS-C3(3) uptake into intact cells by being insensitive to the depolarising action of CCCP.

Carbonyl Cyanide m-Chlorophenyl Hydrazone↗
PubMed1993

The inward rectifier and two levels of the membrane potential in human term placental cells.

Whole-cell variations of patch-clamp techniques were applied to human term placental cells. The inward rectifier K currents were recorded. The current-voltage relationship in some cells crossed the voltage axis at two different potentials. Such cells showed two stable levels of the membrane potential. The current-clamp method could switch the membrane potentials between those two levels. The present results provide evidence that the inward rectifier K conductance could set two changeable levels of the membrane potential in some human term placental cells.

Cell Membrane↗
PubMed1984

Glucagon effects on the membrane potential and calcium uptake rate of rat liver mitochondria.

It has been widely reported that the in vivo administration of glucagon to rats results in the stimulation of calcium influx in subsequently isolated liver mitochondria. The mechanism of this effect is investigated through simultaneous measurements of calcium uptake rate and mitochondrial membrane potential. This allows the measurement of the calcium uniporter conductance independent of hormonal effects on electron transport or respiration. Two experimental approaches are used. The first involves measuring the uptake of 40-50 nmol of Ca2+/mg of mitochondrial protein with the calcium dye antipyrylazo III; the second uses 45Ca2+ to follow uptake in the presence of 0.5 to 1.5 microM free calcium, buffered with HEDTA. In both cases a tetraphenyl phosphonium electrode is used to follow membrane potential, and membrane potential is varied using either malonate or butylmalonate in the presence of rotenone. The relative merits of these two approaches are discussed. The conductance of the calcium uniporter is found not to be stimulated by glucagon pretreatment. Also, the relative glucagon stimulation of both calcium influx and membrane potential is found to increase with increasing malonate concentration. These results imply that there is no direct stimulation of calcium uptake into liver mitochondria following glucagon treatment. The results are consistent with a glucagon stimulation of substrate transport, substrate oxidation, or a stimulation of electron transport resulting in an increased membrane potential and secondary stimulation of calcium uptake.

Animals↗
PubMed1979

Requirement for membrane potential in active transport of glutamine by Escherichia coli.

The effect of reducing the membrane potential on glutamine transport in cells of Escherichia coli has been investigated. Addition of valinomycin to tris(hydroxymethyl)aminomethane-ethylenediaminetetraacetic acid-treated E. coli cells in the presence of 20 mM exogenous potassium reduced the membrane potential, as measured by the uptake of the lipophilic cation triphenylmethylphosphonium, and caused a complete inhibition of glutamine transport. Valinomycin plus potassium also caused a rapid decrease in the intracellular levels of ATP of normal E. coli cells, but had little if any effect on the ATP levels of two mutants of E. coli carrying lesions in the energy-transducing ATP complex (unc mutants). Yet both the membrane potential and the capacity to transport glutamine were depressed in the unc mutants by valinomycin and potassium. These findings are consistent with the hypothesis that both ATP and a membrane potential are essential to the active transport of glutamine by E. coli cells.

Adenosine Triphosphatases↗
PubMed1984

Reduction in the mitochondrial membrane potential of Toxoplasma gondii after invasion of host cells.

The membrane potential of Toxoplasma gondii, an obligatory intracellular protozoan parasite, was monitored with the cationic permeant fluorescent dye rhodamine 123 (R123). Fluorescence microscopy revealed R123 to be partitioned predominantly in a restricted part of the parasite, which consisted of twisted or branched tubules, or of granular bodies. These structures were frequently connected to each other. The dye retention by these structures was markedly reduced by treating R123-labelled parasites with the proton ionophore, carbonylcyanide m-chlorophenylhydrazone, the potassium ionophore, valinomycin and the inhibitor of electron transport, antimycin A. Thus, these structures are regarded as the parasite mitochondria. Another cationic fluorescent dye, rhodamine 6G, stained the parasite mitochondria, whereas a negatively charged fluorescent dye, fluorescein, and the neutral compounds, rhodamine 110 and rhodamine B, did not. This fact indicates that R123 monitored the parasite mitochondrial membrane potential. T. gondii-infected 3T3 cells were also stained with R123. In contrast to the mitochondria of extracellular parasites, those of intracellular parasites failed to take up the dye. The absence of fluorescence in intracellular parasites persisted until the infected host cells ruptured and liberated daughter parasites 1 day after infection. Parasites, liberated from the host cells, either spontaneously or artificially by passing the infected cells through a 27G needle, regained the ability to take up the dye. After direct microinjection of R123 into the vacuole in which the parasite grows and multiples, the dye appeared in the host-cell mitochondria but not in the parasite's mitochondria. Thus, we conclude that the mitochondrial membrane potential of T. gondii was reduced after invasion of host cells by the parasite.

Animals↗
PubMed1984

Dependence of the activity of colicin E1 in artificial membrane vesicles on pH, membrane potential, and vesicle size.

The dependence on pH and membrane potential of the ability of colicin E1 and a COOH-terminal tryptic fragment of the colicin to form membrane channels has been measured using a chloride-sensitive electrode to measure colicin-induced ion efflux from asolectin vesicles of two different size classes. This method allows measurement of ion efflux on a faster time scale, with half-times for efflux less than or equal to 3 s, than previously possible using labeled solutes. Activity measurements were also made through the use of potential-indicating fluorescence probes. The activities of both colicin E1 and the fragment increased with decreasing pH. The activity of the colicin was maximum at pH values near 4.0, with an apparent pK of 4.5-4.6, whereas that of the COOH-terminal fragment continued to increase to the lowest pH value, 3.4, that could be used, showing an apparent pK less than or equal to 3.8. Using relatively small vesicles (average diameter approximately equal to 0.1 micron) made by a freeze-thaw procedure, chloride efflux caused by addition of fragment or colicin was independent of the initial transmembrane K+-diffusion potential imposed upon the system. However, with larger (0.5-micron diameter) vesicles prepared by a fusion method, the chloride efflux showed a dependence upon membrane potential, with the activity decreasing as the membrane potential was made more positive. The average size of the different vesicle populations was determined by electron microscopy. It is proposed that the lack of potential dependence observed in the freeze-thaw vesicles and the small voltage dependence, relative to planar membranes, seen in the larger fused vesicles, results from rapid discharge of the membrane potential and internal ion content of the vesicles.

Amino Acid Sequence↗
PubMed1994

The effect of bicarbonate-free artificial cerebrospinal fluid on spontaneous oscillations of the membrane potential in inferior olivary neurons of the rat.

The membrane potential of mature inferior olivary (IO) neurons oscillates spontaneously at frequencies up to about 10 Hz. This behavior has been attributed to the complement of membrane conductances in these cells and electronic coupling of the neurons via dendro-dendritic gap junctions. In this study intracellular recordings of transmembrane potentials were made in 52 neurons in brainstem slices from rats aged 8-23 days postnatal. During the recordings in 31 neurons the extracellular solution was exchanged from a bicarbonate- to a tris-buffered solution with constant pH. In all cells the spontaneous oscillations of the membrane potential ceased within a few minutes and in 14 of these cells the oscillations resumed with re-exposure to bicarbonate-buffered solution. The spontaneous oscillations in another 6 neurons also ceased when they were exposed to bicarbonate-buffered solution containing 10 mmol NH4Cl. These experimental manipulations produce a rise in intracellular pH despite constant extracellular pH. The low- and high-threshold potentials associated with voltage-sensitive calcium conductances in these neurons and the large hyperpolarization that follows these potentials were unaffected by substitution of the extracellular solution. However, the anomalous rectification of the membrane potential in these neurons (which could be abolished by exposure of the neurons to 2 mM CsCl) was significantly increased by 12.6% in the tris-buffered solution. The data are consistent with the hypothesis that the continuity of oscillations of the membrane potential in IO neurons depends on the transfer of current between the dendro-dendritic junctions and the soma of each neuron. This transfer is reduced when rectifying K+ conductances in the neurons are increased and the ensemble properties of the group of neurons, and the membrane potential oscillations, are lost.

Ammonium Chloride↗
PubMed1995

Membrane potential of rat hepatoma cells in culture: influence of factors affecting amino acid transport.

The effect has been studied of various media, hormones and of amino acids on the membrane potential of rat hepatoma cells in culture measured by microelectrode impalement. Cells in Eagle's minimal essential medium plus 5% serum had a value which varied daily from about 5-8 mV, inside negative. The membrane potential of rat hepatocytes was measured to be 8.7 +/- 0.2 mV, inside negative. The membrane potential of the hepatoma cells was decreased by insulin and increased by glucagon. Membrane potential was unaffected by change of medium to Hanks' or Earle's balanced salt solutions or deprivation of serum. It was, however, reduced in cells in phosphate-buffered saline and by reduction of pH. The former effect was shown to be due to the higher [Na+] of phosphate-buffered saline as opposed to the other media. Addition of alanine, glycine, serine, proline and methylaminoisobutyrate all reduced membrane potential by 2-3 mV. Smaller decreases were seen with methionine, leucine and phenylalanine, but none with glutamine, threonine, BCH (2-aminonorborane-2-carboxylic acid) and D-alanine. The results are compared with the effects of similar conditions on aminoisobutyrate uptake. Whilst there was a correlation under some conditions there was not under others. It is concluded that for the hepatoma cells factors additional to the membrane potential must exert some influence on the capacity for amino acid transport.

Amino Acids↗
PubMed1967

Membrane potential measurement in cells of the adrenal gland.

1. Recordings of transmembrane potentials have been made in vitro from the cells of the adrenal gland using glass micro-electrodes.2. There was only a small species variation in the mean membrane potential of the cortical cells of the rabbit, rat and kitten; 66.2, 70.5, and 71.4 mV respectively.3. The membrane potential of cortical cells was dependent upon the external potassium concentration, [K](o). Raising [K](o) above the normal concentration of 4.7 mM by addition of KCl decreased the membrane potential; lowering [K](o) from normal increased it. The decrease in membrane potential was still evident when chloride was replaced by sulphate. Increasing [K](o) 10-fold decreased the membrane potential of rabbit cortical cells by 44 mV and of kitten cortical cells by 50 mV.4. The mean membrane potential measured in medullary chromaffin cells was for the rabbit 24.2 mV, rat 20 mV, and kitten 31.7 mV. The potentials of medullary cells were much less affected by changes in [K](o) than were cortical cell potentials.5. Age had little influence upon either cortical or medullary membrane potentials of adrenal glands, at least in early life.

Journal Article↗
PubMed1989

Mechanisms of Aluminum Tolerance in Wheat : An Investigation of Genotypic Differences in Rhizosphere pH, K, and H Transport, and Root-Cell Membrane Potentials.

Control of rhizosphere pH and exclusion of Al by the plasma membrane have been hypothesized as possible mechanisms for Al tolerance. To test primarily the rhizosphere pH hypothesis, wheat cultivars (Triticum aestivum L. ;Atlas 66' and ;Scout'), which differ in Al tolerance, were grown in either complete nutrient solution, or 0.6 millimolar CaSO(4), with and without Al at pH 4.50. A microelectrode system was used to simultaneously measure rhizosphere pH, K(+), and H(+) fluxes, and membrane potentials (E(m)) along the root at various distances from the root apex. In complete nutrient solution, the rhizosphere pH associated with mature root cells (measured 10-40 millimeters from the root apex) of Al-tolerant ;Atlas 66' was slightly higher than that of the bulk solution, whereas roots of Al-sensitive ;Scout' caused a very small decrease in the rhizosphere pH. In CaSO(4) solution, no significant differences in rhizosphere pH were found between wheat cultivars, while differential Al tolerance was still observed, indicating that the rhizosphere pH associated with mature root tissue is not directly involved in the mechanism(s) of differential Al tolerance. In Al-tolerant ;Atlas 66', growth in a CaSO(4) solution with 5 micromolar Al (pH 4.50) had little effect on net K(+) influx, H(+) efflux, and root-cell membrane potential measured in cells of mature root tissue (from 10-40 mm back from apex). However, in Al-sensitive ;Scout', Al treatment caused a dramatic inhibition of K(+) influx and both a moderate reduction of H(+) efflux and depolarization of the membrane potential. These results demonstrate that increased Al tolerance in wheat is associated with the increased ability of the tolerant plant to maintain normal ion fluxes and membrane potentials across the plasmalemma of root cells in the presence of Al.

Journal Article↗
PubMed1981

Effect of membrane potential on the passive transport of Tl+ in human red blood cells.

It was earlier found that Tl+ can easily penetrate the red cell membrane. The main finding of this work is that Tl+ can be used for studying alterations in the membrane potential of human red blood cells exposed to various experimental conditions. It was shown that after inhibiting active transport by ouabain, both the rate of trans-membrane movement and the cell/medium distribution of Tl+ were in a good agreement with the expected changes in membrane potential. Alterations in membrane potential were induced by modifying the cation permeability of the red cell membrane and by varying the cation concentration gradient across the membrane, which were achieved: 1) by incubation in an electrolyte-free sucrose solution. 2) by addition of valinomycin or 3) by addition of propranolol. Changes in cation permeability were followed by means of 86Rb tracer. Hyperpolarization of the red cell membrane led to accelerated influx and retarded efflux of Tl+. The opposite effect was obtained by depolarization. Quantification of the results was made using the Nernst equation and the cell/medium concentration ratio of Tl+ at equilibrium. The calculations show that the membrane potential of the propranolol-treated cells increased to about -20 mV, negative inside. The mechanism of the propranolol effect is briefly discussed.

Biological Transport↗
PubMed1997

Assessment of amphotericin B susceptibility in Leishmania infantum promastigotes by flow cytometric membrane potential assay.

Flow cytometry was used for measuring the effects of amphotericin B on the membrane of Leishmania infantum strains. The technique was adapted from the rapid flow cytometric membrane potential assay developed by Ordonez and Wehman (Cytometry 22:154-157, 1995) for evaluating antibiotic-susceptibility of Candida species. The study consisted of measuring membrane potential changes induced by amphotericin B in 3 initial strains and 12 laboratory-generated variants adapted to grow with amphotericin B. Results showed that, after 3 h of incubation, amphotericin B induced a dose-related decrease of membrane potential that reached its maximal level at the same concentrations that inhibited parasite growth. These results suggest that the flow cytometric membrane potential assay could be used to assess the susceptibility of Leishmania promastigotes to amphotericin B.

Amphotericin B↗
PubMed1994

The effects of altering extracellular potassium ion concentration on the membrane potential and circadian clock of Paramecium bursaria.

In some neural models of circadian rhythmicity, membrane potential and transmembrane flux of potassium and calcium ions appear to play important roles in the entrainment and central mechanisms of the biological clock. We wondered whether these cellular variables might be generally involved in circadian clocks, even non-neural clocks. Therefore, we tested the impact of changing extracellular potassium level on the circadian rhythm of photoaccumulation of Paramecium cells, whose membrane potential responds to changes of extracellular potassium in a manner similar to that of neurones. We found that pulse or step changes of extracellular potassium concentration did not phase-shift the circadian clock of P. bursaria cells in a phase-specific manner. Furthermore, modifying the extracellular concentration of calcium did not affect the magnitude of light-induced phase resetting. Therefore, while membrane potential and calcium fluxes may be crucial components of the circadian clock system in some organisms, especially in neural systems that involve intercellular communication, the P. bursaria data indicate that membrane potential changes are not necessarily an intrinsic component of circadian organization at the cellular level.

Animals↗
PubMed1995

Effect of ionic strength on membrane potential generation in reconstituted cytochrome c oxidase.

In this study we applied the potential-sensitive fluorescent dye indocyanine to measure the initial rate of membrane potential development in liposomes containing reconstituted cytochrome c oxidase from bovine heart. A linear relationship was found between the initial rate of membrane potential development, related to the H+/e(-)-stoichiometry, and the rate of electron flow at various substrate concentrations. By increasing the salt concentration a decrease of the initial rate of membrane potential development was found. A similar dependence on the salt concentration was also found for the membrane potential under steady state conditions. The data further demonstrate variation of the H+/e(-)-stoichiometry in cytochrome c oxidase depending on the salt concentration in the buffer.

Animals↗