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Showing papers on "Conductance published in 1975"


Journal ArticleDOI
TL;DR: In this article, the mean magnetizations of the two ferromagnetic film are parrallel or antiparallel and conductance measurement is related to the spin polarizations of conduction electrons.

3,365 citations



Journal ArticleDOI
TL;DR: Membrane currents from voltage-clamped frog muscle fibers were recorded during iontophoretic application of steady doses of carbachol, acetylcholine, and suberyldicholine to the endplate region and the time constant of relaxation was found to be voltage-dependent.
Abstract: Membrane currents from voltage-clamped frog muscle fibers were recorded during iontophoretic application of steady doses of carbachol, acetylcholine, and suberyldicholine to the endplate region. In the presence of these drugs, an exponentially relaxing current was observed after step changes of membrane potential. The time constant of relaxation was found to be voltage-dependent. It was equal to the time constant obtained from the autocorrelation function of drug-induced conductance fluctuations measured under similar conditions. Analysis of instantaneous current at the on- and offsets of voltageclamp pulses showed that there is no shift in equilibrium potential during the pulses.

141 citations


Journal ArticleDOI
TL;DR: The results support the hypothesis that the decay (but not the onset) of acetylcholine‐induced conductance changes is rate‐limited by a first‐order reaction which involves dipoles and occurs in the lipid environment of the post‐synaptic membrane.
Abstract: 1. The post-synaptic effects of the aliphatic alcohols, ethanol to hexanol, were investigated at the neuromuscular junctions of toads, with particular emphasis on the effects of ethanol. 2. The alcohols increased the amplitude and duration of miniature end-plate potentials. It is shown that this effect was due to the prolongation of the decay phase of miniature end-plate currents (m.e.p.c.s). There was no effect of alcohols on the growth phase of m.e.p.c.s. 3. The prolonged decay of m.e.p.c.s in ethanol remained exponential and was normally sensitive to membrane potential. Prolonged m.e.p.c.s were associated with an equivalent prolongation of the mean duration of elementary events, as determined from power spectra of acetylcholine noise in 0-5 M ethanol. 4. The relationship betweeen the time constant of decay of m.e.p.c.s (tau) and the concentration of an alcohol of carbon chain length N (C-N) was exponential, conforming to the equation tau equals tau-s exp (B-N-C-N), in which tau-s is the decay time constant in standard solution and B-N is a constant, different for each alcohol. 5. There was also an exponential relationship between B-N and N, which closely followed the relationship between membrane-buffer partition coefficient and carbon chain length for the different alcohols, indicating that the alcohols are active in the lipid phase of the post-synaptic membrane. 6. It is suggested that the alcohols act by causing a change in the dielectric constant of the post-synaptic membrane which forms the environment of the rate-limiting reaction responsible for the decay of the end-plate conductance. On the assumption that this reaction involves dipoles, it is shown that the small changes in dielectric constant, calculated from the partition coefficients of the alcohols and by assuming an initial lipid dielectric constant of 3, would give an exponential relationship between the time constant of decay of m.e.p.c.s and alcohol concentration. 7. The results support the hypothesis that the decay (but not the onset) of acetylcholine-induced conductance changes is rate-limited by a first-order reaction which involves dipoles and occurs in the lipid environment of the post-synaptic membrane.

128 citations


Journal ArticleDOI
TL;DR: The values obtained from the noise analysis of the kinetics of channel formation and the conductance of the single channel agreed closely with the values determined by relaxation measurments and single-channel experiments.
Abstract: If a membrane contains ion-conducting channels which form and disappear in a random fashion, an electric current which is passed through the membrane under constant voltage shows statistical fluctuations. Information on the kinetics of channel formation and on the conductance of the single channel may be obtained by analyzing the electrical noise generated in a membrane containing a great number of channels. For this purpose the autocorrelation function of the current noise is measured at different concentrations of the channel-forming substance. As a test system for the application of this technique we have used lipid bilayer membranes doped with gramicidin A. From the correlation time of the current noise generated by the membrane, the rate constants of formation (kR) and dissociation (kD) of the channels could be determined. In addition, the mean square of the current fluctuations yielded the single-channel conductance Λ. The values ofkR,kD, and Λ obtained from the noise analysis agreed closely with the values determined by relaxation measurments and single-channel experiments.

98 citations


Journal ArticleDOI
TL;DR: When solutions containing agonists are applied to the innervated face of an Electrophorus electroplaque, the membrane's conductance increases, and the agonist-induced conductance is increased at more negative membrane potentials.
Abstract: When solutions containing agonists are applied to the innervated face of an Electrophorus electroplaque, the membrane's conductance increases. The agonist-induced conductance is increased at more negative membrane po- tentials. The "instantaneous" current-voltage curve for agonist-induced cur- rents is linear and shows a reversal potential near zero mV; chord conductances, calculated on the basis of this reversal potential, change e-fold for every 62-mV change in potential when the conductance is small. Conductance depends non- linearly on small agonist concentrations; at all potentials, the dose-response curve has a Hill coefficient of 1.45 for decamethonium (Deca) and 1.90 for carbamylcholine (Carb). With agonist concentrations greater than 10 -'a M Carb or 10 -5 M Deca, the conductance rises to a peak 0.5-1.5 rain after in- troduction of agonist, then declines with time; this effect resembles the "de- sensitization" reported for myoneural junctions. Elapid a-toxin, tubocurarine, and desensitization reduce the conductance without changing the effects of potential; the apparent dissociation constant for tubocurarine is 2 X 10 -7 M. By contrast, procaine effects a greater fractional inhibition of the conductance at high negative potentials.

87 citations


Journal ArticleDOI
TL;DR: The kinetic data explain several aspects of the steady-state conductance induced by agonists, but shed no light on apparent cooperative effects.
Abstract: In Electrophorus electroplaques, the agonist-induced postsynaptic conductance depends on membrane potential. During steady exposure to agonists, after a voltage step the conductance relaxes on a millisecond time scale, exponentially approaching a new equilibrium value. The relaxation rate constant k is an instantaneous function of voltage, insensitive to the past or present conductance. Two components sum to form k. A concentration-sensitive component increases linearly with agonist concentration and decreases during desensitization or exposure to curare. Thus this component reflects the average frequency at which acetylcholine receptors are opening. The voltage-sensitive component, obtained by extrapolating k to zero agonist concentration, increases at more positive potentials. For acetylcholine, the voltage-sensitive component equals the rate constant for the exponential decay of postsynaptic currents; it thus seems to be the closing rate for active receptors. The voltage-sensitive component has the relative amplitudes acetylcholine less than carbamoylcholine less than decamethonium, and for each agonist equals the closing rate determined from "noise" measurements at neuromuscular junctions. The kinetic data explain several aspects of the steady-state conductance induced by agonists, but shed no light on apparent cooperative effects.

77 citations



Journal ArticleDOI
TL;DR: In this paper, a four-electrode cell was used to measure the contplex dielectric constant of polyelectrolytes including biopolymers, and the effect of frequency-independent d.c. conductance was eliminated.
Abstract: Difficulties in measuring the contplex dielectric constant of a highly conductive material such as aqueous polyelectrolytes including biopolymers arise from (l) electrode polarization effect and (2) d.c. conductance of the specimen which is very much higher than the conductance due to dielectric loss and drifts with time. A new method has been developed in which the first difficulty is avoided by employing a four-electrode cell and the second orue is overcome by direct measurement of the frequency difference spectrum of specimen impedance, ΔZ(ω)=Z(ω)-Z(ω0), between the measuring frequency ω and the reference ω0. By this procedure, the effect of frequency-independent d.c. conductance is eliminated. With the new method, the frequency range of dielectric measurement is extended from 0.2 Hz to 30 kHz.

44 citations


Journal ArticleDOI
TL;DR: In this paper, the dc conductance of Langmuir films of the Cd salts of fatty acids CH3• (CH2)n•2•COOH, with various n, has been measured at liquid-nitrogen temperature.
Abstract: The dc conductance of Langmuir films of the Cd salts of fatty acids CH3‐ (CH2)n‐2‐COOH, with various n, has been measured at liquid‐nitrogen temperature. The conductivity decreases exponentially with increasing chain length of the fatty acid molecules. This agrees well with the theoretical prediction for hopping conduction in a multilayer system associated with interface states.

36 citations


Journal ArticleDOI
TL;DR: In this article, an increase in membrane conductance in crayfish muscle produced by γ-aminobutyric acid (GABA) was measured and compared with the effect of various structurally related compounds.

Journal ArticleDOI
TL;DR: Data suggest that, in lipid membranes, hemocyanin conducts ions through discrete channels, and the voltage-dependent conductance observed at high levels of conductance seems to be a consequence of the properties of the conductance of the single channel.

Journal ArticleDOI
TL;DR: A charge pulse technique applied to the study of charge transfer at metal-solution interfaces has been used to determine the capacity and the conductance of a membrane bilayer at both zero time and zero voltage.

Journal ArticleDOI
TL;DR: In this paper, the dc conductance of thin Pt films has been measured with respect to film thickness and to the surface effects as a function of the electrode potential in the "ideal" double layer, platinum "oxygen" and adsorbed hydrogen regions.

Journal ArticleDOI
TL;DR: An analysis of the ultraviolet light-induced changes in ionic conductances of lobster giant axon membranes has been carried out using the double sucrose gap voltage-clamp technique, suggesting that individual sodium channels are closed upon absorption of single photons by aromatic amino acid residues in membrane proteins.
Abstract: An analysis of the ultraviolet light-induced changes in ionic conductances of lobster giant axon membranes has been carried out using the double sucrose gap voltage-clamp technique. The predominant effect of monochromatic light from a xenon arc source in the 255 to 305 nm region is an irreversible reduction in the magnitude of sodium conductance, without change in sodium channel activation or inactivation kinetics. A considerably smaller reduction in the magnitude of potassium conductance occurs, with some slowing of potassium channel activation kinetics. Leakage conductance is essentially not altered. The fall in sodium conductance follows an exponential time course toward a zero asymptote. The rate constant for conductance decrease was used as an assay for the wavelength dependence. The sodium conductance was maximally sensitive at 290 nm. It is suggested that individual sodium channels are closed upon absorption of single photons by aromatic amino acid residues in membrane proteins.

Journal ArticleDOI
TL;DR: The characteristics of the saturation curves suggest that the continuous conductance changes occur at the edges of the channel and that the mean time an ion spends in the channel is 4 nanoseconds, which indicates that the voltage-dependent conductance of many-channel membranes arises from two different mechanisms.
Abstract: The electrical responses of individual hemocyanin channels in oxidized cholesterol membranes demonstrate that the voltage-dependent conductance of many-channel membranes arises from two different mechanisms These are the voltage-dependent redistribution of channels among several discrete single-channel conductance states and the continuously voltage-dependent conductance of the single-channel states themselves The relaxation time for the discrete conductance changes is of the order of seconds and the relaxation time of the continuous conductance changes is of the order 10−4 seconds As salt concentration in the bathing medium is increased, the single-channel conductance first increases linearly and then saturates The characteristics of the saturation curves suggest that the continuous conductance changes occur at the edges of the channel and that the mean time an ion spends in the channel is 4 nanoseconds

Journal ArticleDOI
TL;DR: In this paper, a study was made of the conductivity of a range of concentrations from 0.01 M to 5 M to temperatures >500°C and to pressures of 2000bar.
Abstract: Concentrated sodium chloride solutions are commonly used in electrochemical machining and a knowledge of their conductance is important. A study was made of the conductivity of a range of concentrations from 0.01 M to 5 M to temperatures >500°C and to pressures of 2000bar. The conductances were found to go through maxima at 250–300°C after increasing in magnitude by a factor of >4.

Journal ArticleDOI
TL;DR: In this paper, the conductance behavior of tetrahydrofuran was studied over a temperature range of −70 to +20°C, where the authors interpreted the physical meaning of the distance parameter in agreement with Bjerrum's concept for the distinction between short and long-range electrostatic interactions.
Abstract: The conductance behavior of potassium tetraphenylboride and of sodium and potassium tetraphenylborides complexed by macroheterobicycles was studied in tetrahydrofuran over a temperature range of −70 to +20°C. Stokes' radii of potassium and of alkaline cryptates were compared with ionic radii. The conductance data were analyzed by a more careful method than that usually used for this solvent. This leads to an interpretation of the physical meaning of the distance parameter in agreement with Bjerrum's concept for the distinction between short- and long-range electrostatic interactions.

Journal ArticleDOI
TL;DR: The experimental results support the generally accepted view that complexation between ions and the macrocyclic antibiotics occurs at the membrane surface and show that for a different mechanism, such as that by which the complexes would form in the aqueous solutions and cross the interfaces as lipid-soluble ions, the same type of saturation would be expected to be observable only for unrealistically high values of the rate constants of the ion-carrier association.
Abstract: Some effects of diffusion polarization and chemical reactions on the steady-state zero-current conductance of lipid bilayers mediated by neutral carriers of ions have been studied theoretically and experimentally Assuming that ion permeation across the interfaces occurs via a heterogeneous reaction between ions in the solution and carriers in the membrane, the relationship between the conductance and the aqueous concentration of carriers is shown to be linear only in a limited range of sufficiently low concentrations At higher carrier concentrations, which for the most strongly bound cations are within the range of the experimentally accessible values, the conductance is expected to become limited by diffusion of the carried ion in the unstirred layers and therefore reach an upper limiting value independent of the membrane properties This expectation has been successfully verified for glyceryl-monooleate membranes in the presence of the ionsK +, Rb+ and NH 4 + and carriers such as valinomycin and trinactin The experimental results support, at least for the present system, the generally accepted view that complexation between ions and the macrocyclic antibiotics occurs at the membrane surface; it is shown, in fact, that for a different mechanism, such as that by which the complexes would form in the aqueous solutions and cross the interfaces as lipid-soluble ions, the same type of saturation would be expected to be observable only for unrealistically high values of the rate constants of the ion-carrier association A previously proposed criterion to distinguish between these two mechanisms, based on the dependence of the conductance on the ion concentration, is discussed from the viewpoint of this more comprehensive model

Journal ArticleDOI
TL;DR: Voltage fluctuations associated with the sodium system were measured upon elimination of the potassium current in the nodal membrane by internal application of cesium-ions and the sodium-channel conductance was calculated to be 2 to 5·10−12S.
Abstract: Voltage fluctuations associated with the sodium system were measured upon elimination of the potassium current in the nodal membrane by internal application of cesium-ions. The intensity of this noise reaches a maximal value at a membrane potential in the vicinity of −40 mV. Here the power spectrum consists of two additive components: a 1/f component and a Lorentzian. The Lorentzian is associated with h-gate kinetics and is consistent with the binary state conduction model. On the basis of this model the sodium-channel conductance is calculated to be2 to 5·10 −12 S. The analysis is complicated by the existence of an incomplete slow sodium inactivation process.

Journal ArticleDOI
TL;DR: In this article, the electrical conductivity of Na-montmorillonite suspensions in various salt and clay con- centrations was measured, and two resistors in series model was proposed to predict the observed weight conductance changes of the suspen- sions, while the mobility of the adsorbed ions remains constant.
Abstract: The electrical conductivity of Na-montmorillonite suspensions in various salt and clay con- centrations was measured. The weight conductance of the clay suspension was found to decrease with increase in clay concentration between 0 and approximately 0.5 g clay/100 ml, then rose to a plateau at 6-10 g clay/100 ml. The weight conductance of the clay suspensions also increased with an increase in the salt solution concentration. If the model of two resistors in parallel is used in interpreting the experimental data, these changes can be attributed to an increase in the mobility of the adsorbed Na ions. It is proposed that the two resistors in series model is more realistic in describing the conducti- vity of the suspensions. This model predicts the observed weight conductance changes of the suspen- sions, while the mobility of the adsorbed ions remains constant. A constant mobility of the adsorbed Na ions in clay-water systems of low to medium salt and clay concentrations also is predicted by the diffuse double layer.

Journal ArticleDOI
TL;DR: In this paper, conductance measurements of dilute solutions of methanesulphonic, sulphuric, nitric, perchloric and trifluoromethane-lphonic acids in anhydrous DMSO were analyzed in terms of the Fuoss Hsia conductance equation.

Journal ArticleDOI
TL;DR: It is concluded that the K+ conductance is at least a second-order system whose relaxation spectrum is composed of two exponential terms the magnitudes of which are markedly dependent on the initial conditions.

Journal ArticleDOI
TL;DR: In this paper, an investigation is reported in which ion-pair formation is sensed quantitatively by the laser-Raman technique using as the model electrolyte system solutions of AgNO3 in acetonitrile.
Abstract: In this communication an investigation is reported in which ion-pair formation is sensed quantitatively by the laser-Raman technique using as the model electrolyte system solutions of AgNO3 in acetonitrile. The measurements were extended to the dilute-solution range in an attempt to intercompare the results forKa with those calculated from conductance studies and the Fuoss-Onsager theory of conductance. The highest dilution attained in the spectroscopic studies was in the region of 10⩼−3M. In the region of concentration overlap, it is found that the values forKa from the present laser-Raman studies and from the Fuoss-Onsager theory of conductance are, respectively, 84±14 and 70.3±1.2; corresponding values for the ion-size parameteraj fall in the range of 3.1–4.0 A. The latter are examined relative to the predictions spectroscopically for contact-ion pair formation at these high dilutions.


Journal ArticleDOI
TL;DR: It is suggested that the inhibitory membrane activated by β-guanidinopropionic acid does not increase the Cl− conductance, but permits the permeation of foreign anions such as I−.

Journal ArticleDOI
TL;DR: In this paper, the on-state conductance and radiative emission properties of an amorphous semiconductor threshold switch have been investigated for time intervals τ of up to 120 nsec during which the voltage is below the low-frequency holding voltage but above the knee voltage.
Abstract: The on−state conductance and radiative emission properties of an amorphous semiconductor threshold switch have been investigated. The transient on−state conductance GT and differential conductance GT are found to be constant for time intervals τ of up to 120 nsec during which the voltage is below the low−frequency holding voltage but above the knee voltage. The knee voltage is the voltage at which the transient on−state current−voltage curve coalesces into the transient off−state curve in the down−voltage direction. For τ≳120 nsec, GT and GT vary asymptotically with time. As ambient temperature is increased from 300 to 400 °K, GT is observed to remain constant or increase slightly as would be expected in dGT/dT for a metal. If the on−state is assumed to have a band gap, conductance vs temperature measurements indicate that the gap would have a value less than 1.2×10−4 eV, and thus for practical purposes the gap could be considered to be essentially zero. The intensity of the nonthermal radiative emissi...


Journal ArticleDOI
TL;DR: In this article, the effect of the silicon content of the glass has been found to have a large effect on the activation energy and conductivity parameters of formed STAG threshold switches of changing both the composition of the virgin films and the ON time of the switching pulse during the forming process.
Abstract: The effect on the conductance of formed STAG threshold switches of changing both the composition of the virgin films and the ON time of the switching pulse during the forming process has been studied. It was found that the silicon content of the glass has a large effect on the activation energy and conductivity parameters of virgin devices. After forming, the conductance of the device is much higher than in the unformed state; however, silicon no longer controls the conductivity parameters. When switching STAG threshold switches it was found that increasing the ON time of each switching cycle causes a decrease in the conductance of the formed device from its value when formed with very short ON times. For low pulse repetition frequencies the conductance saturates for ON times typically greater than 100 μs. The rate at which the conductance decreases is dependent upon the silicon content of the virgin glass. For high pulse repetition frequencies the conductance initially falls, following the low pulse repetition frequency case, and then rises, finally locking on to a memory state. The observations have been explained in terms of an initial large structural change of the glass, caused through adiabatic heating during switching. Relaxation of this structure back to more stable glass phases is possible during the ON time if the ON state temperature is sufficiently high. For high pulse repetition frequencies the temperature of the device is much higher, allowing for the possibility of crystalline growth. This leads to an increase in conductance and eventual lock on.

Journal ArticleDOI
TL;DR: In this article, conductance measurements at 25°C were obtained for dilute solutions of hydrochloric acid in dimethylsulphoxide and dimethyl sulfoxide in water mixtures containing up to 15% by weight of water.