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At least 19 recordsLinked to original sources
PubMed1980

[The influence of 2,4-dichlorphenoxyacetate (2,4-D) on the membrane potential, membrane resistance and electromyogram of the frog skeletal muscle before and after stimulation (author's transl)].

The influence of 2,5-Dichlorphenoxyacetate (2,4-D) on the membrane potential, membrane resistance and electromyogram of the isolated frog skeletal muscle was studied. The membrane potential and membrane resistance were measured in the rest and after an impulse series of 10 impulses which was applicated with 1 impulse/s. The membrane resistance was not significantly variable. The membrane potential decreased about 30 mV when the muscle was 4 hours in 2,4-D (Fig. 1). At rest the membrane potential as well as the muscle in a solution with and without 2,4-D had constant values when the muscle was only a short time in 2,4-D. But when the muscle was stimulated several times with 1 impulse/s the membrane potential decreased about 20 mV. After a time of 30 s the normal value of the rest-potential was reached again. The effects induced by 2,4-D were reversible in Ringer-solution (Fig. 2). These findings are discussed and beside changes in conductances the role of the Ca-ions is also mentioned as a possible cause. An anomalous temporary binding of ions on the membranes of the muscle is assumed.

2,4-Dichlorophenoxyacetic Acid↗
PubMed1980

A single-cell technique for the measurement of membrane potential, membrane conductance, and the efflux of rapidly penetrating solutes in Amphiuma erythrocytes.

We describe a single-cell technique for measuring membrane potential, membrane resistance, and the efflux of rapidly penetrating solutes such as Cl and H2O. Erythrocytes from Amphiuma means were aspirated into a Sylgard (Dow Corning Corp.)-coated capillary. The aspirated cell separated a solution within the capillary from a solution in the bath. Each of these two solutions was contiguous with approximately 5% of the total membrane surface. Microelectrodes placed concentrically within the capillary permit the measurement of intracellular voltage, specific membrane resistance, and the electrical seal between the two solutions. The intracellular voltage averaged -17.7 mV (pH 7.6) and changed as either intra- or extracellular chloride was varied. The average specific membrane resistance measured by passing current across the exposed membrane surface was 110 ohm-cm2. 36Cl and tritiated H2O fluxes (0.84 +/- 0.05 x 10(-6) M . cm-2 . min-1 and 6.4 +/- 1.5 x 10(-3) M . cm-2 . min-1, respectively) were determined by noting the rate at which isotope leaves the cell and crosses the membrane exposed to the bath. Our measured values for the flux of 36Cl and tritiated H2O approximate reported values for free-floating cells. 36Cl efflux, in addition, is inhibited by 4-acetamido-4'-isothiocyano-stilbene 2,2'-disulfonic acid (SITS) and furosemide, known inhibitors of the anion exchange mechanism responsible for the rapid anion fluxes of red blood cells. One can also demonstrate directly that > 89% of 36Cl efflux is "electrically silent" by analyzing the flux in the presence of an imposed transcellular voltage.

Animals↗
PubMed1980

Sampling membrane potential, membrane resistance and electrode resistance with a glass electrode impaled into a single cell.

A method is demonstrated to measure membrane resistances and membrane potentials of single cells during impalement by a single glass microelectrode. The intention was to develop a procedure which would provide data almost continuously. Therefore, a frequency-dependent voltage divider network has been chosen to represent the basic electrical properties of the electrode and cell membrane, and used to explore its voltage response to a current stimulus, consisting of two rectangular pulses of different widths. It can be shown that the resolution of the method can be improved by inverting this stimulus so that each polarization becomes a relaxation and vice versa. In order to generate, analyze and display this signal continuously, a device has been designed which has been called 'Electrophysiological Monitor, (E1M2)'. E1M2 provides a current stimulus as input into a standard bridge network and can analyze the summed response of the electrode and cell by a set of sample-hold amplifiers. It then decodes and displays the data continuously, as membrane potential (Em), input resistance of the cell (Rinp) and the electrode resistance (Re) respectively. From Rinp the membrane resistance (Rm) can be deduced. The validity of the method has been examined by measuring these parameters in frog muscle cells. Technical design considerations, the accuracy and possible pitfalls with the suggested procedure are discussed.

Animals↗
PubMed2000

Multiparameter flow cytometric analysis of antibiotic effects on membrane potential, membrane permeability, and bacterial counts of Staphylococcus aureus and Micrococcus luteus.

Although flow cytometry has been used to study antibiotic effects on bacterial membrane potential (MP) and membrane permeability, flow cytometric results are not always well correlated to changes in bacterial counts. Using new, precise techniques, we simultaneously measured MP, membrane permeability, and particle counts of antibiotic-treated and untreated Staphylococcus aureus and Micrococcus luteus cells. MP was calculated from the ratio of red and green fluorescence of diethyloxacarbocyanine [DiOC(2)(3)]. A normalized permeability parameter was calculated from the ratio of far red fluorescence of the nucleic acid dye TO-PRO-3 and green DiOC(2)(3) fluorescence. Bacterial counts were calculated by the addition of polystyrene beads to the sample at a known concentration. Amoxicillin increased permeability within 45 min. At concentrations of <1 microg/ml, some organisms showed increased permeability but normal MP; this population disappeared after 4 h, while bacterial counts increased. At amoxicillin concentrations above 1 microg/ml, MP decreased irreversibly and the particle counts did not increase. Tetracycline and erythromycin caused smaller, dose- and time-dependent decreases in MP. Tetracycline concentrations of <1 microg/ml did not change permeability, while a tetracycline concentration of 4 microg/ml permeabilized 50% of the bacteria; 4 microg of erythromycin per ml permeabilized 20% of the bacteria. Streptomycin decreased MP substantially, with no effect on permeability; chloramphenicol did not change either permeability or MP. Erythromycin pretreatment of bacteria prevented streptomycin and amoxicillin effects. Flow cytometry provides a sensitive means of monitoring the dynamic cellular events that occur in bacteria exposed to antibacterial agents; however, it is probably simplistic to expect that changes in a single cellular parameter will suffice to determine the sensitivities of all species to all drugs.

Anti-Bacterial Agents↗
PubMed1979

Hysteresis in the responses of membrane potential, membrane resistance, and growth rate to cyclic temperature change.

Measurements of electrical potential, membrane resistance, and elongation rate have been carried out on the developing pollen tube of Oenothera drummondii.The plasmalemma potential was observed to be -138 millivolts +/- 19 (sd). Approximately 70% of this potential was apparently due to the operation of an electrogenic pump(s). KCN rapidly and reversibly depolarized the potential to about -40 millivolts. Lowering the temperature from 20 to 4 C brought about similar rapid depolarization. The effects of KCN and of temperature were in no degree additive. KCN had only a small effect on membrane resistance. In contrast, the latter was markedly increased by lowering the temperature.When the pollen tubes were submitted to cyclic temperature changes striking hysteresis effects were observed in the response of all three parameters, membrane potential, resistance, and growth rate. The hysteresis pattern for potential differed from that for resistance but resembled that for growth rate (measured simultaneously on the same pollen tube). The correlation coefficient between potential and growth rate was very high.The probable relevance to our results of the hysteresis phenomena associated with "clustering" and phase transition in lipids is pointed out. Attention is also drawn to the possible significance of the large difference between the electric potentials at the start of the cooling and heating paths, respectively.

Journal Article↗
PubMed1970

The relation between membrane potential, membrane currents and activation of contraction in ventricular myocardial fibres.

1. Membrane currents and contractile responses have been measured in ventricular myocardial preparations under voltage clamp conditions.2. In Tyrode solution, steady-state contraction was obtained only after 5-8 depolarizations to a given potential level. The threshold of steady-state tension was identical to the potential where the calcium inward current, I(Ca), was activated (about -35 mV). Both thresholds were shifted in the same direction along the voltage axis and by the same amount by changing [Ca](o) or [Na](o). Maximum tension was obtained at inside positive potentials.3. The time courses of steady-state tension and of activation of I(Ca) were different by more than one order of magnitude in Tyrode solution. But in order to achieve any appreciable steady-state tension, I(Ca) had to flow during several identical depolarizations. Tension decreased again at potentials above E(Ca). This suggests that calcium inward current must flow in order to fill intracellular calcium stores from which calcium can be released by an unknown mechanism.4. The ability of a fibre bundle to contract again after a preceding twitch is greatly dependent on the membrane potential between two equal depolarizations. In Tyrode solutions with 1.8 and 7.2 mM-CaCl(2) half restoration of this ability occurred at -45 +/- 3 mV (+/- S.E. of mean) and -23 +/- 4 mV, respectively.5. In sodium-free bathing solutions, steady-state tension was attained upon the first depolarization provided I(Ca) was activated. Furthermore, at different potentials, the time courses of activation of tension and of activation of I(Ca) were identical, i.e. tension reached its maximum when I(Ca) was fully activated. This suggests that in sodium-free solutions the flow of calcium ions into the fibre directly activates contraction.

Animals↗
PubMed1968

Direct measurements of membrane potential and membrane resistance of human red cells.

1. In order to evaluate the membrane potentials calculated from the distribution of chloride ions in human red cells and plasma, it is desirable to have a direct measurement of the transmembrane potential of these cells.2. A method has been devised for introducing a capillary micro-electrode into human red cells. The method allows simultaneous measurements of potential and membrane resistance with only one micro-electrode located in the cell.3. Upon impalement of single cells in plasma, a scatter of membrane potentials and of resistance values was obtained. The potential drop never exceeded -14 mV and the maximum resistances were about 7 Omega. cm(2). Positive potentials were obtained on impalement of red cell aggregates.4. Arguments are given to support the view that it is in these cells which suffer least damage from the impalement that maximum values of membrane potentials and resistances are observed. The errors caused by the change in the liquid junction during the impalement have been estimated.5. As judged from this study, it seems permissible under normal conditions to calculate the membrane potential of the red cell from the chloride concentrations in plasma and in intracellular water.

Body Fluids↗
PubMedDate not supplied

The effect of reactive oxygen species on equine sperm motility, viability, acrosomal integrity, mitochondrial membrane potential, and membrane lipid peroxidation.

The objective of this study was to examine the influence of reactive oxygen species (ROS), generated through the use of the xanthine (X)-xanthine oxidase (XO) system, on equine sperm motility, viability, acrosomal integrity, mitochondrial membrane potential, and membrane lipid peroxidation. Equine spermatozoa were separated from seminal plasma on a discontinuous Percoll gradient, and spermatozoa were incubated with 0.6 mM X and 0.05 U/mL XO for 30 minutes. Catalase (150 U/mL), superoxide dismutase (SOD, 150 U/mL), or glutathione (GSH, 1.5 mM) were evaluated for their ability to preserve sperm function in the presence of the induced oxidative stress. At the end of the 30-minute incubation, sperm motility was determined by computer-assisted semen analysis. Viability and acrosomal integrity were determined by Hoechst-Pisum sativum staining, and mitochondrial membrane potential was determined by staining with JC-1. Incubation with the X-XO system led to a significant (P < .01) increase in hydrogen peroxide production and an associated decrease (P < .01) in motility parameters. Total motility was significantly (P < .01) lower in the presence of X-XO compared with the case of the control (29%+/-9% vs 73%+/-1%, respectively). Catalase, but not SOD, prevented a decline in motility secondary to oxidative stress (71%+/-4% vs 30%+/-3%, respectively). The addition of glutathione had an intermediate effect in preserving sperm motility at the end of the 30-minute incubation (53%+/-3%). No influence of X-XO could be determined on viability, acrosomal integrity, or mitochondrial membrane potential. In order to promote lipid peroxidation, samples were incubated with ferrous sulfate (0.64 mM) and sodium ascorbate (20 mM) for 2 hours after the X-XO incubation. No increase in membrane lipid peroxidation was detected. This study indicates that hydrogen peroxide is the major ROS responsible for damage to equine spermatozoa. The decrease in sperm motility associated with ROS occurs in the absence of any detectable decrease in viability, acrosomal integrity, or mitochondrial membrane potential or of any detectable increase in lipid peroxidation.

Acrosome↗
PubMed1973

Adaptation in the ventral eye of Limulus is functionally independent of the photochemical cycle, membrane potential, and membrane resistance.

The early receptor potential (ERP), membrane potential, membrane resistance, and sensitivity were measured during light and/or dark adaptation in the ventral eye of Limulus. After a bright flash, the ERP amplitude recovered with a time constant of 100 ms, whereas the sensitivity recovered with an initial time constant of 20 s. When a strong adapting light was turned off, the recovery of membrane potential and of membrane resistance had time-courses similar to each other, and both recovered more rapidly than the sensitivity. The receptor depolarization was compared during dark adaptation after strong illumination and during light adaptation with weaker illumination; at equal sensitivities the cell was more depolarized during light adaptation than during dark adaptation. Finally, the waveforms of responses to flashes were compared during dark adaptation after strong illumination and during light adaptation with weaker illumination. At equal sensitivities (equal amplitude responses for identical flashes), the responses during light adaptation had faster time-courses than the responses during dark adaptation. Thus neither the photochemical cycle nor the membrane potential nor the membrane resistance is related to sensitivity changes during dark adaptation in the photoreceptors of the ventral eye. By elimination, these results imply that there are (unknown) intermediate process(es) responsible for adaptation interposed between the photochemical cycle and the electrical properties of the photoreceptor.

Action Potentials↗
PubMed1993

Rabbit corneal endothelial cell membrane potential.

Membrane potential of rabbit corneal endothelial cells measured using microelectrodes was -29.3 +/- 0.8 mV, n = 45, (mean +/- SEM). Histological location of Lucifer Yellow dye iontophoresed out of the microelectrode confirmed that the microelectrode was located intracellularly. The Lucifer Yellow diffused five to six cell diameters away from the impaled cell indicating endothelial cell coupling. Depolarization by ouabain (10(-4) M) and high extracellular potassium (potassium for sodium substitution) showed the cells to be responsive to changes in the bathing solution whilst impaled, that the cell membrane is more permeable to potassium than sodium and that membrane bound Na(+)-K(+)-ATPase activity generates the transmembrane electrolyte gradients.

Animals↗
PubMed1976

Change in zeta potential and membrane potential of slime mold Physarum polycephalum in response to chemical stimuli.

Electrophoretic study of microplasmodia of the true slime mold Physarum polycephalum was carried out in the presence of various concentrations of inorganic salts, nucleotides and sugars, and the zeta potential at the surface of the plasmodia was determined from the electrophoretic mobilities. The membrane potential of the plasmodia was also measured under the same external conditions. It was shown that changes in the membrane potential induced by the chemical stimuli agreed approximately with those induced in the zeta potential in all cases examined. These results suggested that the phase boundary potential at the membrane-solution interface is mainly responsible for the membrane potential in the chemoreception of the slime mold.

Adenosine Triphosphate↗
PubMed1993

The effect of cocaine on membrane potential, on membrane depolarization by veratridine or elevated [K]o and on sodium/potassium permeability ratios in synaptosomes from the limbic cortex of the rat.

Effects of cocaine on the synaptosomal membrane potential (Em), on membrane depolarization induced by veratridine or elevated [K]o and on sodium/potassium permeability ratios (pNa/pK), have been measured in buffer containing either low or high [Na]. Fluorescence of the dye rhodamine 6G was used to measure the membrane potential. Cocaine began to reduce the Em (depolarized) at concentrations between 10(-6) and 10(-5) M in low [Na] buffer and between 10(-5) and 10(-4) M in high [Na] buffer. Maximum depolarization (with 10(-3) M cocaine) was 21 mV in low [Na] buffer and 11 mV in high [Na] buffer. Cocaine also reduced the depolarization caused by veratridine or elevated [K]o; the effective concentration of cocaine in reducing the response to veratridine was one-tenth that necessary to reduce the response to elevated [K]o. The antagonism by cocaine of the response to veratridine was similar to that found by other investigators; however, this action would tend to oppose depolarization and thus cannot explain the depolarizing effect of cocaine alone. The antagonism by cocaine of the depolarization caused by elevated [K] was consistent with a reduction in pK; such a change in pK could explain the observed reduction in Em caused by cocaine alone. The effect of cocaine (10(-3) M) on the Em was also measured as a function of [K]o at low and high [Na]o. Cocaine caused membrane depolarization at all [K]o's (3.9-19.2 mV), an effect that was somewhat greater in the low [Na] medium. These measurements of Em were fitted to the Goldman equation and the ratio of pNa/pK estimated. The presence of cocaine increased the estimate of pNa/pK by 45.7%, presumably by reducing pK.

Animals↗
PubMed1981

Calcium transport by intact synaptosomes. Influence of ionophore A23187 on plasma-membrane potential, plasma-membrane calcium transport, mitochondrial membrane potential, respiration, cytosolic free-calcium concentration and noradrenaline release.

Ionophore A23187, a Ca2+/2H+ exchanger, has multiple effects on the function of isolated nerve endings (synaptosomes). (a) There is a net uptake of Ca2+, the rate of which increases with ionophore concentration. (b) When Ca2+ uptake is terminated by EGTA, the ionophore induces an apparent efflux of Ca2+. (c) The plasma-membrane potential, calculated from the 86Rb+ distribution, decreases slowly upon addition of the ionophore. (d) Release of [3H]noradrenaline induced by the ionophore consists of a rapid phase followed by a subsequent slower phase, which coincides with the fall in plasma-membrane potential. (e) Ouabain depolarizes the plasma membrane without inducing the rapid phase of transmitter release. (f) The membrane potential of intrasynaptosomal mitochondria determined in situ falls rapidly upon addition of A23187, and there is a synchronous increase in synaptosomal respiration. (g) All these effects require external Ca2+ and the same range of ionophore concentrations. (h) Using the respiratory stimulation induced by the ionophore in isolated mitochondria to calibrate the cytosolic concentration of free Ca2+ in intact synaptosomes it is concluded that the cytosolic Ca2+ required for release of [3H]noradrenaline is in the range 1-10 microM.

Animals↗
PubMed2001

[Effect of dingxin recipe on intracellular free calcium, membrane potential and mitochondria membrane potential in normal and hypoxia myocytes of rats].

OBJECTIVE: To elucidate the molecular mechanism on anti-arrhythmic function of Dingxin Recipe (DXR). METHODS: Cardial myocytes isolated by trypsin method were cultured and labelled with various fluorescence stains. DXR contained serum induced changes of cytolic calcium concentration [Ca2+]i, cell membrane potential (MP) and mitochondria membrane potential (MMP) were determined with laser confocal microscopy. RESULTS: Hypoxia caused increase of [Ca2+]i and MMP, and decrease of MP, while DXR contained serum lowered the [Ca2+]i in normal or hypoxian myocytes, improved hypoxia induced MP reduction and maintain MMP at baseline level under hypoxia circumstances. CONCLUSION: Through inhibiting the hypoxia caused [Ca2+]i and MMP elevation and MP lowering, DXR displays its action in protecting myocardial cells to prevent and treat arrhythmia.

Animals↗