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PubMed1994

Ion dependence of resting membrane potential of rat spermatids.

The membrane potential of rat spermatids was estimated as -22 +/- 2 mV (mean +/- SEM) using three independent methods: using oxonol as a fluorescent membrane potential sensitive probe, from the passive distribution of hydrogen ions and from whole-cell patch-clamp records. The estimated permeability ratios PK+:PCl- and PNa+:PCl- of the plasma membrane of rat spermatids were 1.0 and 0.3, respectively. These data indicate that the high luminal K+ concentration found in seminiferous tubules could partially close voltage-sensitive calcium channels in these cells.

Animals↗

PubMedDate not supplied

[Effect of ionizing radiation on the membrane potential and electrical input resistance of Chinese hamster fibroblast membranes].

X-irradiation with a dose of 8 Gy leads to a sharp decrease in membrane potential of cultured Chinese hamster cells followed by restoration thereof. Changes in the membrane potential are accompanied by a monotonous increase of mean values of input cell resistance. It is assumed that radiation elicits a decrease in the resistance of a plasma membrane and a concurrent increase in the resistance of intercellular gap contacts which lead to impairment of cell interaction.

Animals↗

PubMed2000

Effect of combined treatment with perindoprilat and low-power red light laser irradiation on human erythrocyte membrane fluidity, membrane potential and acetylcholinesterase activity.

Erythrocyte membrane fluidity, membrane potential and acetylcholinesterase activity were estimated after in vitro combined treatment of human erythrocytes with perindoprilat and low-power red light irradiation. Membrane fluidity was determined using fluorescent labels spectroscopy; membrane potential was evaluated by means of potential-sensitive fluorescent dyes; and acetylcholinesterase activity was estimated using the Ellman method. Both perindoprilat and laser irradiation, when used separately, increase microviscosity in the polar region and hyperpolarize the membranes in comparison with control erythrocytes. The combined action of these agents does not cause any further change in these parameters. Perindoprilat has an additional inhibitory effect on the activity of acetylcholinesterase, whereas laser irradiation causes an increase in the activity of the enzyme. Their combined action restores the initial activity of the enzyme independently of the sequence of treatment with both agents.

Acetylcholinesterase↗

PubMed1983

Sodium-channels in non-excitable glioma cells, shown by the influence of veratridine, scorpion toxin, and tetrodotoxin on membrane potential and on ion transport.

Veratridine induces membrane potential oscillations in non-excitable glioma cells, which are not affected by ouabain (2 mM) or by D600 (0.1 mM). In the presence of veratridine, scorpion toxin causes depolarization of the glioma cells to a positive value of the membrane potential. These effects of veratridine and of scorpion toxin are observed in Na+ but not in choline medium and are inhibited by tetrodotoxin. The response of the glioma cells to bradykinin has also been studied during these experiments. Previously bradykinin has been shown in these cells to induce a hyperpolarizing response caused by an increase in K+ conductance. This response to bradykinin can still be seen during the veratridine-induced oscillations of the membrane potential. In the glioma cells the uptake of guanidinium, a substitute for Na+, is enhanced by veratridine plus scorpion toxin. This stimulation is tetrodotoxin-sensitive. However, in the excitable neuroblastoma X glioma hybrid cells studied for comparison, veratridine causes membrane potential oscillations accompanied at the rising phase by one action potential or a train of action potentials. The results demonstrate that in non-excitable glioma cells tetrodotoxin-sensitive Na+ channels can be activated by veratridine and by scorpion toxin.

Animals↗

PubMed1991

J-aggregate formation of a carbocyanine as a quantitative fluorescent indicator of membrane potential.

The spectral properties of a novel membrane potential sensitive probe (JC-1) were characterized in aqueous buffers and in isolated cardiac mitochondria. JC-1 is a carbocyanine with a delocalized positive charge. It formed under favorable conditions a concentration-dependent fluorescent nematic phase consisting of J-aggregates. When excited at 490 nm, the monomers exhibited an emission maximum at 527 nm and J-aggregates at 590 nm. Increasing concentrations of JC-1 above a certain concentration caused a linear rise in the J-aggregate fluorescence, while the monomer fluorescence remained constant. The membrane potential of energized mitochondria (negative inside) promoted a directional uptake of JC-1 into the matrix, also with subsequent formation of J-aggregates. The J-aggregate fluorescence was sensitive to transient membrane potential changes induced by ADP and to metabolic inhibitors of oxidative phosphorylation. The J-aggregate fluorescence was found to be pH independent within the physiological pH range of 7.15-8.0 and could be linearly calibrated with valinomycin-induced K+ diffusion potentials. The advantage of JC-1 over rhodamines and other carbocyanines is that its color altered reversibly from green to red with increasing membrane potentials. This can be exploited for imaging live mitochondria on the stage of a microscope.

Animals↗

PubMed1979

The resting membrane potential of frog sartorius muscle.

1. The absolute resting membrane potential of the frog sartorius muscle was determined in Ringer solution at 20 degrees C. 2. Membrane potentials were measured with 0.03, 0.1, 0.3, 1.0 and 3.0 M-KCl electrodes; potentials, including the micro-electrode-tip potentials, were -62.4, -75.7, -83.0, -87.7 and -90.7 mV respectively. 3. Membrane potentials were corrected for the liquid junction potentials between the Ringer and KCl solutions, and the myoplasm and the KCl solutions of the micro-electrodes, using the Henderson's liquid junction equation. 4. The cation (U) and anion (V) conductances of the myoplasm were adjusted to give a constant membrane potential after correction for liquid junction potentials. The final values for U and V were 5.6 and 1.3 mmho/cm respectively, resulting in a membrane potential of -93.0 mV. 5. The correction for the liquid junction potential was -2.6 mV when a 3 M-KCl micro-electrode was used.

Animals↗

PubMed1994

Calcium ion and the membrane potential of tumor cells.

Calcium ion affects ion permeability and membrane potential among many other aspects of cell function. Initial effects of increasing extracellular calcium upon membrane potential were studied in a quail fibrosarcoma (QT35) where calcium had a dose dependent effect, and normal quail fibroblasts, where there was little effect. Comparisons were then made in six different human hepatocellular carcinomas (Tong, HepG2, Hep3B, PLC/PRF/5, Mahlavu, and HA22T) in response to smaller changes in concentration. There were insignificant changes in membrane potential in two cell lines and significant elevations in four. Cytolysis by natural killer cells also declined in rough proportion to the increase in membrane potential. The less differentiated hepatocellular carcinoma cells have both higher baseline membrane potentials and a greater potential increase to increased calcium. By contrast, more highly differentiated tumor cells had paradoxically smaller membrane potentials and along with normal cells had small potential responses to calcium increases.

Animals↗

PubMed1963

THE INFLUENCE OF SODIUM-FREE SOLUTIONS ON THE MEMBRANE POTENTIAL OF FROG MUSCLE FIBERS.

The membrane potential of frog sartorius muscle fibers in a Cl- and Na-free Ringer's solution when sucrose replaces NaCl is about the same as that in normal Ringer's solution. The K(+) efflux is also about the same in the two solutions but muscles lose K and PO(4) in sucrose Ringer's solutions. The membrane potential in sucrose Ringer's solution is equal to that given by the Nernst equation for a K(+) electrode, when corrections are made for the activity coefficients for K(+) inside and outside the fiber. For a muscle in normal Ringer's solution, the measured membrane potential is within a few millivolts of E(K). This finding is incompatible with a 1:1 coupled Na-K pump. It is consistent with either no coupling of Na efflux to K influx, or a coupling ratio of 3 or greater.

Animals↗

PubMed1979

Membrane potential of mitochondria measured with an electrode sensitive to tetraphenyl phosphonium and relationship between proton electrochemical potential and phosphorylation potential in steady state.

The membrane potential of mitochondria was estimated from the accumulation of tetraphenyl phosphonium (TPP+), which was determined with the TPP+-selective electrode developed in the present study. The preparation and some operational parameters of the electrode were described. The kinetics for uptake by mitochondria of TPP+ and DDA+ (dibenzyldimethyl ammonium) were analyzed, and it was found that TPP+ permeated the mitochondrial membrane about 15 times faster than DDA+. The final amounts of accumulation of TPP+ and DDA+ by mitochondria were approximately equal. For the state-4 mitochondria, the membrane potential was about 180 mV (interior negative). Simultaneous measurements of TPP+-uptake and oxygen consumption showed that the transition between states 3 and 4 was detectable by use of the TPP+-electrode. After the TPP+-electrode showed that state-4 was reached, the extra-mitochondrial phosphorylation potential was measured. The difference in pH across the membrane was measured from the distribution of permeant anion, acetate, so as to calculate the proton electrochemical potential. The ratio of extra-mitochondrial phosphorylation potential to proton electro-chemical potential, n was close to 3. This value of n was also found to be 3 when ATP was hydrolyzed under the condition that the respiratory chain was arrested. The implication that n = 3 was discussed.

Adenosine Diphosphate↗

PubMed2005

Intrinsic subthreshold oscillations of the membrane potential in pyramidal neurons of the olfactory amygdala.

The amygdala complex is a heterogeneous group of temporal lobe brain structures involved in the processing of biologically significant sensory stimuli and in the generation of appropriate responses to them. The amygdala has also been implicated in certain forms of emotional learning and memory. While much progress has been made in understanding neural processing in the basolateral subgroup of the amygdala, physiological studies in the cortical regions of the complex, also known as olfactory amygdala, are missing. Using a rat brain slice preparation, we conducted whole-cell recordings on pyramidal neurons of the periamygdaloid cortex and the anterior cortical nucleus, two structures receiving direct connections from the olfactory bulb. Upon depolarization by current injection through the recording electrode, a fraction of periamygdaloid cortex and most anterior cortical nucleus layer II pyramidal neurons displayed an intermittent discharge pattern, where clusters of action potentials were interspersed by periods of membrane potential subthreshold oscillations. Oscillations frequency increased with membrane potential and correlated linearly with the cluster spiking frequency. Frequency ranged from 3 to 20 Hz, considering different cells and membrane potential values (up to approximately 30 mV above resting potentials of typically approximately -70 mV). Subthreshold oscillations were preserved after pharmacological inhibition of fast excitatory and inhibitory synaptic transmission, but were abolished by application of the sodium channel blocker tetrodotoxin. We conclude that pyramidal neurons of the olfactory cortical amygdala display intrinsically generated voltage-dependent membrane potential rhythmic fluctuations in the theta-low beta range, requiring the activation of a sodium conductance.

2-Amino-5-phosphonovalerate↗

PubMed1989

[The effect of limiting neuronal energy metabolism on the level of impulse activity and membrane potentials].

The changes of the membrane potential and the frequency of impulse activity of the crayfish stretch receptor neuron have been studied under condition of energy supply deficiency. The energetic metabolism inhibitors have been found not to exert a significant effect on the membrane potential. The activity of the glycolysis process and the Krebs cycle have different effect on the sensitivity of the generating mechanism.

Animals↗

PubMed1985

In vivo membrane potentials of smooth muscle cells in the caudal artery of the rat.

Membrane potentials measured in vivo may differ significantly from those measured in vitro in part due to humoral factors, innervation, and wall tension. These studies were initiated to determine whether it is feasible to record membrane potentials from vascular smooth muscle cells in vivo in the caudal artery of the pentobarbital-anesthetized male Wistar rat. Membrane potentials were measured using glass microelectrodes and correlated with systolic, diastolic, and mean blood pressures. For systolic blood pressures between 100 and 140 mmHg the average resting membrane potential was -38.4 +/- 0.48 mV. There was good correlation of systolic, diastolic, and mean blood pressures with membrane potential between 100 and 140 mmHg (r = 0.89, 0.75, and 0.89, respectively). Below 80 mmHg the arterial muscle cells became more depolarized than would be expected if the membrane potential were determined solely by transmural pressure. The depolarized membrane potential at low arterial pressures may be due to enhanced neural input. Spontaneous electrical activity was observed in some of the in vivo cells. When action potentials were present, they were generated at rates between 1-2/s and 6-7/min. These studies indicate that it is feasible to measure membrane potentials from arterial smooth muscle cells in vivo in the caudal artery of the rat.

Action Potentials↗

PubMed2001

A high-throughput assay for mitochondrial membrane potential in permeabilized yeast cells.

A fluorometric assay for mitochondrial membrane potential in permeabilized yeast cells has been developed. This method involves permeabilizing the plasma membrane and measuring the distribution of a mitochondrial membrane potential sensitive probe 3,3'-dipropylthiadicarbocyanine iodide (DiSC(3)(5); DiSC(3)). In permeabilized cells, DiSC(3) fluorescence decreased when introduced into energized mitochondria and increased three- to sixfold when the mitochondrial membrane potential was dissipated by the chemical uncoupler carbonylcyanide m-chlorophenyl hydrazone. Plasma membrane potential was abolished by permeabilization, as shown by a lack of polarization of the plasma membrane induced by K(+) and glucose. Uncoupling protein 1 (UCP1), a mitochondrial H(+) transporter, was used as a model for method validation. The fluorescence intensity responded vigorously to specific modulators in UCP1-expressing cells. This method has been adapted as a high-throughput assay to screen for modulators of mitochondrial membrane potential.

Benzothiazoles↗

PubMed1989

Calculation of membrane potential in synaptosomes with use of a lipophilic cation (tetraphenylphosphonium).

To estimate membrane potential in synaptosomes with the use of tetraphenylphosphonium (TPP+), an equation relating the amount of TPP+ accumulated in synaptosomes with membrane potential was derived from the following two assumptions. (1) TPP+ molecules were distributed into plasma membranes, mitochondria and cytosol of synaptosomes. (2) TPP+ achieves a Nernst equilibrium across both the synaptosomal and inner mitochondrial membranes. We propose three methods for calculation of membrane potential using this equation. The concentration of TPP+ was measured under various controlled conditions with an electrode selective for TPP+. The amount of TPP+ accumulated in synaptosomes was determined by measuring the difference between its initial concentration and the concentration after addition of synaptosomes, and membrane potential was estimated by the three methods. The resting potential of synaptosomes was estimated to be -75 to -90 mV by all of these methods. Membrane potentials under various controlled conditions were calculated, and the characteristics of the methods for estimation of membrane potential and those of membrane potential obtained by the methods are discussed.

Animals↗

PubMed2000

Membrane potential estimation by flow cytometry.

Membrane potential (delta psi) is generated and maintained by concentration gradients of ions such as sodium, potassium, chloride, and hydrogen. Changes in cytoplasmic delta psi in the course of surface-receptor-mediated processes related to the development, function, and pathology of many cell types often play a role in transmembrane signaling. Cytoplasmic delta psi is also reduced to zero when the membrane is ruptured by chemical or physical agents. Mitochondrial delta psi is reduced when energy metabolism is disrupted, notably in apoptosis. In bacteria, which lack mitochondria, delta psi reflects both the state of energy metabolism and the physical integrity of the cytoplasmic membrane. Flow cytometry can be used to estimate membrane potential in eukaryotic cells, mitochondria in situ, isolated mitochondria, and bacteria. Older methods, using lipophilic cationic dyes such as the cyanines and rhodamine 123 or lipophilic anionic dyes such as the oxonols can detect relatively large changes in delta psi and identify heterogeneity of response in subpopulations comprising substantial fractions of a cell population. Newer ratiometric techniques allow precise measurement of delta psi to within 10 mV or less. Among other factors, action of efflux pumps, changes in membrane structure, and changes in protein or lipid concentration in the medium in which cells are suspended can produce changes in cellular fluorescence which may be misinterpreted as changes in delta psi. Techniques for estimation and measurement of Delta Psi therefore typically require careful control of cell and reagent concentrations and incubation times and selection of appropriate controls if they are to provide accurate information.

Bacteria↗

PubMed2003

Membrane potential of CA3 hippocampal pyramidal cells during postnatal development.

A depolarized resting membrane potential has long been considered to be a universal feature of immature neurons. Despite the physiological importance, the underlying mechanisms of this developmental phenomenon are poorly understood. Using perforated-patch, whole cell, and cell-attached recordings, we measured the membrane potential in CA3 pyramidal cells in hippocampal slices from postnatal rats. With gramicidin perforated-patch recordings, membrane potential was -44 +/- 4 (SE) mV at postnatal days P0-P2, and it progressively shifted to -67 +/- 2 mV at P13-15. A similar developmental change of the membrane potential has been also observed with conventional whole cell recordings. However, the value of the membrane potential deduced from the reversal potential of N-methyl-d-aspartate channels in cell-attached recordings did not change with age and was -77 +/- 2 mV at P2 and -77 +/- 2 mV at P13-14. The membrane potential measured using whole cell recordings correlated with seal and input resistance, being most depolarized in neurons with high, several gigaohms, input resistance and low seal resistance. Simulations revealed that depolarized values of the membrane potential in whole cell and perforated-patch recordings could be explained by a shunt through the seal contact between the pipette and membrane. Thus the membrane potential of CA3 pyramidal cells appears to be strongly negative at birth and does not change during postnatal development.

Animals↗

PubMed1981

Oscillation of membrane potential in syncytiotrophoblast of human term placenta in culture.

The membrane potentials and resistances of the cultured syncytiotrophoblast of human chorionic villi obtained from normal term placentas were measured using a standard electrophysiological technique. The mean value of membrane potentials and resistances for 156 cells in the control tris-buffered saline at 37 degrees C were -40.0 +/- 1.2 mV and 8.6 +/- 0.7 M omega (mean +/- S.E.), respectively. The membrane potential was markedly affected by the change of external concentration of Ca++ or K+. In 32 cells among 156 cells examined, spontaneous oscillations of membrane potentials were observed. They oscillated between around -38 mV and -57 mV with the average frequency of 2.4 +/- 0.2 times per minute, accompanied by decrease in membrane resistance on each hyperpolarization. Although oscillations of membrane potentials have been observed in other cultured cells, this is the first report on the oscillation of membrane potential in the human trophoblast.

Cells, Cultured↗

PubMed1997

Interactions between neuropeptide Y and the adenylate cyclase pathway in rat mesenteric small arteries: role of membrane potential.

1. Simultaneous measurements of membrane potential and tension were performed to investigate the intracellular mechanisms of neuropeptide Y (NPY) in rat mesenteric small arteries. 2. NPY (0.1 microM) depolarized arterial smooth muscle cells from -55 to -47 mV and increased wall tension by 0.22 N m-1, representing 11% of the contraction elicited by a high-potassium solution. Isoprenaline (1 microM) and acetylcholine (1 microM) evoked hyperpolarizations of 11 and 17 mV, respectively. NPY inhibited the isoprenaline-induced effects on membrane potential without affecting those of acetylcholine. 3. Forskolin evoked sustained concentration-dependent hyperpolarizations of small mesenteric arteries. NPY (0.1 microM) inhibited the responses to 1 microM forskolin, but did not alter the stable hyperpolarization elicited by the specific activator of protein kinase A (PKA) SP-5,6-DCl-cBIMPS (0.1 mM). Forskolin increased the cyclic AMP (cAMP) content of the arteries 21-fold, and NPY inhibited the forskolin-evoked increase in cAMP levels by 91%. 4. The hyperpolarization produced by 1 microM forskolin was not affected by either charybdotoxin (0.1 microM) or 4-aminopyridine (0.5 mM), but glibenclamide (5 microM) inhibited the hyperpolarization by 70%. Glibenclamide also inhibited the hyperpolarization evoked by SP-5,6-DCl-cBIMPS by 59%. 5. Neither depolarization nor contraction caused by NPY were significantly affected by either glibenclamide (5 microM) or nifedipine (1 microM), but they were reduced by gadolinium (10 microM). However, the blocking effect of NPY on forskolin-elicited hyperpolarization was not affected by gadolinium. 6. Charybdotoxin (0.1 microM) and 4-aminopyridine (0.5 mM) strongly enhanced the depolarization and contraction caused by NPY (0.1 microM), and nifedipine (1 microM) prevented the enhanced responses to NPY in the presence of charybdotoxin. 7. These findings suggest that NPY acts through at least two different intracellular mechanisms in mesenteric small arteries: a depolarization of arterial smooth muscle which is probably due to activation of non-selective cation channels, and a marked inhibition of adenylate cyclase activity, which in turn inhibits the hyperpolarization produced by cAMP accumulation in these arteries.

4-Aminopyridine↗