Showing papers on "Conductance published in 1979"
TL;DR: The acetylcholine‐sensitive ionic channels at the neuromuscular junction were studied in voltage‐clamped single muscle fibres from a monolayer preparation of the cutaneous pectoris muscle from Rana pipiens to argue that ion interactions must occur at e.p.c. channels because ion flux independence is the only asumption in the derivation of the Takeuchi approach.
Abstract: 1. The acetylcholine-sensitive ionic channels at the neuromuscular junction were studied in voltage-clamped single muscle fibres from a monolayer preparation of the cutaneous pectoris muscle from Rana pipiens. The experimental observations were of three types: (a) reversal potential as a function of external Na and Ca concentrations, (b) the single channel conductance (gamma) from noise analysis as a function of these same concentrations, and (c) gamma as a function of membrane potential. 2. The reversal potential in normal Na Ringer was -3.8 +/- 0.5 mV (+/- S.E. of mean, n = 22) and decreased approximately linearly as the logarithm of the outside Na activity as this activity decreased to 10% of normal. 3. The single channel conductance in normal Na Ringer was 27.5 +/- 0.7 pS (n = 28) and reached a limiting value close to 10 pS as Na was replaced with sucrose. 4. Increasing [Ca]o from 2 to 10 mM made the reversal potential more positive and decreased the single channel conductance. Mg caused similar effects. 5. Various theories that have been used to describe the mechanism of ion permeation through e.p.c. channels were tested. Constant field theory (eqns. (3), (4) and (5)), a modified Takeuchi approach (eqn. (6)), and a single barrier theory (eqns. (8), (9) and (10)) could not account for all of the experimental observations. 6. In particular, constant field theory, with no surface charge density, could account for the following: (a) the reversal potential measurements for solutions containing 2 mM-Ca (with PK/PNa = 1.2 and PCa/PNa = 1.02), (b) the single channel conductance values for solutions containing 2 mM-Ca and Na concentrations down to 20% of normal, (c) that gamma has little voltage dependence. 7. However, constant field theory, with no assumed surface charge density, could not account for the following: (a) the reversal potential observed for Ringer containing 80 mM-Ca, (b) the gamma values observed for very low Na concentrations, (c) the observation that increasing Ca from 2 to 10 mM in a solution containing 75% normal Na results in a decrease in gamma. 8. From the failure of the Takeuchi approach (eqn. (6)), it is argued that ion interactions must occur at e.p.c. channels because ion flux independence is the only asumption in the derivation of eqn. (6) without experimental verification. 9. The ion interactions at e.p.c. channels probably include both surface charge effects and competition for a binding site.
366 citations
TL;DR: In this paper, the fabrication and operation of a thin-film conductance modulation sensor is described and a microscopic model for its operation is developed, which accounts for the dependence of the sensor conductance on the square root of the partial pressure, the requirement of oxygen as a constituent of the background gas, and the existence of a temperature window outside which the sensor does not function.
Abstract: The fabrication and operation of a thin‐film conductance modulation sensor is described and a microscopic model for its operation is developed The physical basis of the model comprises the oxidation of on the sensor surface by chemisorbed oxygen and the subsequent emission of an electron from the chemisorbed species into the conduction band of the sensor The model accounts for the following experimental observations: (i) the dependence of the sensor conductance on the square root of the partial pressure; (ii) the requirement of oxygen as a constituent of the background gas; and (iii) the existence of a temperature window outside of which the sensor does not function The model also touches on the selectivity of the sensor for in the 1–100 ppm range in a background gas containing oxidizing and reducing constituents
361 citations
TL;DR: Isotonic suspensions of erythrocytes exposed to intense electric fields for a duration in microseconds showed time-dependent increase in the conductivity, indicating that the induced membrane conductance is strongly dependent on the membrane potential.
239 citations
TL;DR: The anion channel, but not the background conductance, is inhibited by submillimolar concentrations of SITS and DIDS, two well known anion transport inhibitors.
194 citations
TL;DR: Intracellular Na+ ions are necessary for the activation of inward rectification; the K conductance increases sharply with internal Na+ concentration, reaching saturation at 200 mM, and a similar potentiating effect is found for Li+, although it is weaker.
Abstract: 1. The effects of alterations of the intracellular ionic composition on the properties of anomalous (or inward) rectification of the egg membrane of the starfish, Mediaster aequalis, were studied by using an intracellular perfusion technique. The following results were obtained, analysing the membrane current with the voltage-clamp technique. 2. The inward rectification of the K conductance depends only on the membrane potential, V, when the K equilibrium potential, VK, is altered by changing the internal K+ concentration at a fixed external K+ concentration, while it depends on V-VK when VK is altered by changing the external K+ at a fixed internal K+ concentration. 3. From the above the conclusion is reached that the gating of the K channel of the inward rectification depends on V and external but not internal K+ concentration. 4. The conductance of the K channel at a given voltage is roughly proportional to the square root of [K+]i when the latter is altered at a fixed external K+ concentration. 5. Since the conductance is proportional to the square root of [K+]o when this is altered at a fixed internal K+ concentration, the final conclusion is that this conductance is proportional to the geometric mean of the external and internal K+ concentrations. 6. Intracellular Na+ ions are necessary for the activation of inward rectification; the K conductance increases sharply with internal Na+ concentration, reaching saturation at 200 mM. 7. A similar potentiating effect is found for Li+, although it is weaker. Rb+, Cs+ and organic cations such as arginine+ do not have this effect.
150 citations
TL;DR: It is found that the electrostatic effect on the conductance is much larger for a neutral channel embedded in a negatively charged lipid than for the negatively charged O-pyromellityl analog (with three charges at the channel mouth) embedded inA neutral lipid.
110 citations
TL;DR: Osteoblasts were investigated by two methods, electrical conductance and dye injection, indicating high conductance pathways between the two cells.
Abstract: Osteoblasts were investigated by two methods, electrical conductance and dye injection. Current injection into one cell caused a change in the recorded transmembrane potential of a second cell, indicating high conductance pathways between the two cells. Dyes injected into a single osteoblast were transmitted to numerous surrounding cells.
101 citations
TL;DR: Cs+ ions block the K+ conductance of a voltage-gated ionic channel derived from fragmented sarcoplasmic reticulum and incorporated into an artificial phospholipid bilayer.
Abstract: Cs+ ions block the K+ conductance of a voltage-gated ionic channel derived from fragmented sarcoplasmic reticulum (SR) and incorporated into an artificial phospholipid bilayer. The block follows a single-site titration curve with a voltage-dependent dissociation constant of 18 mM at +50 mV. Blockade observed with the macroscopic conductance can be fully accounted for by the reduction of the apparent single-channel conductance in the presence of Cs+. The voltage dependence is explained by assuming that Cs+ binds to the open state of a single channel on a site located about 40% of the way through the membrane from the cis side (the side to which the SR vesicles are added). The blocking site is accessible only from the cis side.
100 citations
TL;DR: In this article, a conductance equation based on a new model for ions in solution was derived, which described charge transport in solutions containing any number of ionic species of any valency type.
Abstract: In the first two papers of this series a conductance equation, based on a new model for ions in solution, was derived. The equation described charge transport in solutions containing any number of ionic species of any valency type.In this paper the model upon which the new equation is based is discussed in greater detail and the equation is used to analyse conductance data for a number of symmetrical electrolyte solutions. Excellent agreement is found between experimental results and theoretical predictions and the distance parameter values obtained show clearly the existence of solvent-separated ion-pairs (SSIP's) in many systems.
98 citations
TL;DR: In the range of pH examined (5.2-10), variations of internal pH from high to low values result in a reversible decrease of the conductance of the open K channels, without significantly affecting the kinetics parameters.
93 citations
TL;DR: The pH insensitivity of this low basal H+ conductance supports the idea that a circulation of protons can mediate highly efficiency engery transductions across the membranes of bacteria.
Abstract: Membrane conductance to H+ was measured in the anaerobic bacterium Streptoccus lactis by a pulse technique employing a low driving force (0.1 pH unit; 6 mV). Over the pH range of 3.7 to 8.5, a constant value for passive H+ conductance was observed, corresponding to 0.2 mumol of H+/s per p/ unit per g, dry weight (1.6 microS/cm2 of surface area). The pH insensitivity of this low basal H+ conductance supports the idea that a circulation of protons can mediate highly efficiency engery transductions across the membranes of bacteria.
TL;DR: A kinetic scheme is developed to describe single-file transport through pores containing up to two ions which may be of different species and the solution for the fluxes in terms of rate constants for entry, exit, and transfer is derived without specific assumptions about symmetry or the voltage and activity dependence of the constants.
01 Jan 1979
TL;DR: All equations in this chapter can be used either with SI or cgs units, and appropriate physical constants and conversion factors are summarized in Table 1.
Abstract: All equations in this chapter can be used either with SI or cgs units.1 For this purpose, appropriate physical constants and conversion factors are summarized in Table 1. Concentration c is used throughout at mol liter−1. This requires a conversion factor 10 n with n(SI)=+3; n(cgs)=−3.
TL;DR: Water-soluble Folch-Lees proteolipid apoprotein from bovine CNS white matter induces a voltage-dependent conductance in black lipid membranes, suggesting that the apop protein is at least partially imbedded in the membrane interior.
Abstract: Water-soluble Folch-Lees proteolipid apoprotein from bovine CNS white matter induces a voltage-dependent conductance in black lipid membranes. Na+ is required for the induced conductance change but the established conductance has very low ionic selectivity. The induced conductance fluctuates with a minimum amplitude of 10−11–10−10 mho. The magnitude of the conductivity change is dependent on protein concentration and on the composition of lipid bilayers. At a fixed voltage the induced conductance of a phosphatidylcholine-cholesterol membrane is proportional to the sixth power of the protein concentration and the first power of Na+ concentration. The interactions between the apoprotein and the lipids are both electrostatic and hydrophobic, but the interaction leading to the conductance increase appears to be mainly hydrophobic. Both the increase in conductance and the current fluctuations remain after extensive washing of the chambers to remove the protein. Furthermore, pronase or glutaraldehyde added to either the cis or trans side of the membrane does not affect the apoprotein-established conductance. However, if the bilayer is formed in the presence of both the apoprotein and pronase or if the apoprotein is treated with pronase prior to its addition to the chamber, no conductance change is observed. The association of the apoprotein with the membrane thus appears to render the protein inaccessible to proteolytic digestion, suggesting that the apoprotein is at least partially imbedded in the membrane interior.
TL;DR: The differential sensitivity of peak and residual conductance to alkanol treatment was eliminated after internal pronase treatment, suggesting that n-octanol and n-decanol enhance the normal inactivation mechanism rather than directly blocking channels in a time-dependent manner.
01 Mar 1979-Journal of Comparative Physiology A-neuroethology Sensory Neural and Behavioral Physiology
TL;DR: Evidence is obtained that in the visual sense cells of Calliphora the light-independent conductance increase is mediated by the influx of Ca2+-ions, and the increase of the intracellular Ca2-ion concentration not only decreases theLight-induced conductance, but also increases the light, independent conductance.
Abstract: Simultaneous membrane potential and membrane resistance measurements and current clamp experiments were performed on the visual sense cells ofCalliphora. The results suggest that the receptor potential is due to two different conductance variations: (i) a conductance increase for both Na+- and K+-ions upon illumination, and (ii) a light-independent conductance increase for K+-ions. Evidence is obtained that in the visual sense cells ofCalliphora the light-independent conductance increase is mediated by the influx of Ca2+-ions.
Patent•
15 May 1979
TL;DR: An instrument for computing resistivity based upon measurements of thickness and conductance is described in this article. But this instrument is not suitable for the measurement of pressure wave and does not have the ability to measure the thickness of an article.
Abstract: An instrument for computing resistivity based upon measurements of thickness and conductance. A conductance transducer is a solenoid in an annular ferrite cup connected to a tank circuit for an eddy current measurement of conductance. Within the center of the annular ferrite cup concentric acoustic wave sending and receiving channels are disposed for making an acoustic pressure wave measurement which is used for a thickness measurement using two gauge heads, spaced on opposite sides of an article to be measured. Each gauge head contains identical conductance and thickness transducers. The thickness measurement is divided by the conductance measurement to derive resistivity.
TL;DR: The experiments reported here show that alamethicin channels have similar conductances in the sarcolemmal membrane of frog and rat muscle and in lipid bilayers formed from synthetic lecithin, which is one order of magnitude larger in the biological membranes.
Abstract: Alamethicin, a polypeptide of molecular weight ∼2,000, induces voltage-dependent conductance phenomena in artificial lipid bilayer membranes that are in some ways similar to those found in excitable membranes1. Alamethicin-indueed conductance is probably a consequence of the formation of predominantly cation-selective channels which span the bilayer, and single open channels fluctuate at random between several well defined conductance states2–5. Statistical analysis of single channel conductance fluctuations in planar lipid bilayers of various compositions has revealed that, whereas the conductance values are relatively constant in a variety of membranes, the average lifetime of the individual conductance states depends strongly on the lipid used to form the bilayer. This variability has tentatively been attributed to differences in lipid fluidity6,7. Alamethicin is therefore a probe of some aspects of membrane composition. The study of single alamethicin channels in various natural membranes would allow comparison with the well defined bilayer systems and might yield information on lipid properties of natural membranes that could be important for the functioning of natural membrane channels and receptors. The experiments reported here show that alamethicin channels have similar conductances in the sarcolemmal (surface) membrane of frog and rat muscle and in lipid bilayers formed from synthetic lecithin. The average lifetime of the conductance states is, however, one order of magnitude larger in the biological membranes.
TL;DR: In the presence of the plant hormone 2-cis,4-trans abscisic acid, bimolecular lipid membranes exhibited conductance fluctuations of the type associated with channels as discussed by the authors.
Abstract: Summary
In the presence of the plant hormone 2-cis,4-trans abscisic acid, bimolecular lipid membranes exhibited conductance fluctuations of the type associated with channels. Under a voltage clamp of 100 mV, channels were observed of mean conductance 0-4 × 10−10 S and mean lifetime 0·2 msec.
Membrane conductance was measured as a function of concentration of abscisic acid and a log-log plot of the data revealed a linear relationship. The slope of the regression line was 0·52 ± 0·08 with Pearson's product moment 0·85.
An analysis of current fluctuations is presented.
The results are discussed in terms of a process in which multimeric channels are generated from abscisic acid monomers and in which channels are destroyed by collision.
TL;DR: The complex admittance,Y(p), of squid axon was measured during step voltage clamp to obtain linear data on Na+ conduction and a measurement of dielectric capacitance at low frequency suggests that the capacitance is ideal.
Abstract: The complex admittance,Y(p), of squid axon was measured (4-1000 Hz) during step voltage clamp to obtain linear data on Na+ conduction.Y(p) is used as a spectroscopic tool to identify Na+ and K+ conduction, which dominateY(p) at low frequencies and can be separated from each other and from the static capacitance. Na+ conduction is readily distinguishable from K+ conduction in that it produces a steady-state negative conductance. The admittance of the Na+ system can show an anomalous resonance or an antiresonance depending on whether the net shunt conductance is negative or positive. Use of the Na+ negative conductance to neutralize leakage yields a measurement of dielectric capacitance at low frequency. A 90o phase angle suggests that the capacitance is ideal.
TL;DR: The results imply that the AK+ -selective membrane conductance channel from rabbit sarcoplasmic reticulum contains a highly charged polypeptide region which moves in the direction perpendicular to the membrane plane when transitions between the open and closed states occur.
Abstract: AK+ -selective membrane conductance channel from rabbit sarcoplasmic reticulum (SR) is studied in an artificial planar phospholipid bilayer. Membranes containing many such channels display voltage-dependent conductance, which is well described by a two-state conformational equilibrium with a free energy term linearly dependent on applied voltage. Pronase-derived alkaline proteinase b (APb), when added to the side of the membrane opposite to the SR vesicles (trans side), reduces the voltage dependence of the K+ conductance. Single-channel fluctuation experiments show that after APb treatment, the channel is still able to undergo transitions between its open and closed states, but that the probability of forming the open state is only slightly voltage-dependent. In terms of the conformational model, the enzyme's primary effect is to reduce the effective gating charge of the opening process by over 80%; a second effect of APb is to reduce the internal free energy of opening from +1.2 to +0.4 kcal/mol. The kinetics of APb action are strongly voltage-dependent, so as to indicate that the enzyme can react only with the channel's open state. The results imply that the channel contains a highly charged polypeptide region which moves in the direction perpendicular to the membrane plane when transitions between the open and closed states occur. A lysine or arginine residue in this region becomes exposed to the trans aqueous solution when the channel is in its open conformation.
TL;DR: In this article, the degradation mechanism of X-band low-noise GaAs MESFETs is examined to obtain meaningful information on a common mode of failure, which is an increase in series resistance of the ohmic contacts.
Abstract: The degradation mechanism of X-band low-noise GaAs MESFET's is examined to obtain meaningful information on a common mode of failure. The devices tested have a half-micrometer gate (Au/ Mo) and source and drain ohmic contacts (Au/Ni/Au-Ge). Zero bias drain conductance g_{D0} is considered as a representative parameter for degradation during aging. The major failure mode is an increase in series resistance of the ohmic contacts. The amount of degradation, decrease in g_{D0} , is proportional to the square root of aging time, and accompanied by an increase in minimum noise figure F_{\min} . A degradation model based on the formation of a high-resistance layer between the ohmic metals and GaAs crystal by a diffusion reaction mechanism is proposed, resulting in excellent agreement between calculated and experimental results. Using ion-microspectroscopy analysis (IMA), diffusion of Ni into GaAs crystal is revealed. Mean time to failure (MTTF) is estimated to be 107-108h at channel temperature of 80°C with an increase in F_{\min} of 0.5 dB as failure criterion.
TL;DR: In this article, a new effect has been observed at low temperatures when conduction is restricted to two dimensions in an n-type GaAs impurity band, where the conductance is found to oscillate as a function of carrier concentration.
Abstract: A new effect has been observed at low temperatures when conduction is restricted to two dimensions in an n-type GaAs impurity band. When the carrier concentration is less than 1011 cm-2 the conductance is found to oscillate as a function of carrier concentration. The oscillations can be resolved into simple series with the minima periodic functions of the mean electron separation. Suppression of the main series and enhancement of a subsidiary series is achieved by increasing the electric field responsible for transport; this results in differential negative resistance at certain carrier concentrations. The effect may possibly arise from an ordering of the electrons by Coulomb repulsion, although it is difficult to envisage how this can happen in a random array of donors and there is at present no model to explain the effect.
TL;DR: The data available suggests that permeation is through “long” neutral channels, lined with high field-strength negative polar groups and including one or possibly more high resistance barriers for anions.
Abstract: Measurements of acetylcholine-induced single-channel conductance and null potentials at the amphibian motor end-plate in solutions containing Na, K, Li and Cs ions (Gage & Van Helden, 1979;J. Physiol. (London) (in press) were analyzed in terms of three models. Two of these models, the “neutral” site channel model and the “charged” site channel model were developed to cater for three cations. Both were shown to be able to explain the dependence of single-channel conductance on membrane potential and gave the following sequences of equilibrium constants and mobilities.KLi/KNa/KK/KCs=7∶1.7∶1∶0.9 anduCs/uK/uNa/uLi=1.4∶1∶0.58∶0.13 at 8 °C. Similar sequences were obtained at 20 °C. Although the neutral model fitted the data for relative conductances in Li-, Cs-and Na-solutions slightly better than the charged model, experiments done in normal [NaCl] and [NaCl]/2 solutions could only be fitted by the neutral model. In contrast, the third model, the Constant Field Equation, was unable to fit the conductance data in any of the above situations. The data available suggests that permeation is through “long” neutral channels, lined with high field-strength negative polar groups and including one or possibly more high resistance barriers for anions.
TL;DR: This single site conductance value of 7 pS is in close agreement with estimates of the conductance of one open sodium channel from measurements of gating currents and of noise on squid giant axons, and is consistent with the hypothesis that one saxitoxin molecule binds to one sodium channel.
Abstract: The binding of saxitoxin, a specific inhibitor of the sodium conductance in excitable membranes, has been measured in giant axons from the squid,Loligo pealei. Binding was studied by labeling saxitoxin with tritium, using a solvent-exchange technique, and measuring the toxin uptake by liquid scintillation counting. Total toxin binding is the sum of a saturable, hyperbolic binding component, with a dissociation constant at 2–4°C of 4.3±1.7nm (meanse), and a linear, nonsaturable component. The density of saturable binding sites is 166±20.4 μm−2. From this density and published values of the maximum sodium conductance, the conductance per toxin site is estimated to be about 7 pS, assuming sequential activation and inactivation processes (F. Bezanilla & C.M. Armstrong, 1977,J. Gen. Physiol.
70: 549). This single site conductance value of 7 pS is in close agreement with estimates of the conductance of one open sodium channel from measurements of gating currents and of noise on squid giant axons, and is consistent with the hypothesis that one saxitoxin molecule binds to one sodium channel.
TL;DR: Evaluation of the relevant parameters for cardiac Purkinje fibres, from published experimental data, suggests that concentration changes in the extracellular space may play a significant role in determining when an action potential is initiated.
Abstract: For an isolated membrane, the resting (zero current) potential is stable if the slope conductance is positive, and is unstable if the slope conductance is negative. Recent work suggests that the properties of many preparations are influenced by the presence of an extracellular space that is not in good diffusive contact with the bulk extracellular fluid. Ionic current flow across the membrane changes the ion concentrations in this space. These concentration changes affect the stability of the membrane potential. Even if the slope conductance is negative, the presence of the extracellular space can confer stability on the resting potential. Conversely, even if the slope conductance is positive, the extracellular space can produce instability of the resting potential. Evaluation of the relevant parameters for cardiac Purkinje fibres, from published experimental data, suggests that concentration changes in the extracellular space may play a significant role in determining when an action potential is initiated.
TL;DR: Analysis of the biphasic time course of the conductance changes, as determined under controlled voltage conditions, suggests that treatment with formaldehyde alters simultaneously, but in opposite ways, two factors that determine the Conductance of the inward rectifier.
Abstract: 1. The inwardly rectifying potassium conductance of the membrane of frog sartorius muscle fibres is greatly reduced by treatment of muscles for 30 min with a solution containing formaldehyde (10 mM). 2. A transient increase in the conductance of the inward rectifier is observed early during formaldehyde action. 3. Analysis of the biphasic time course of the conductance changes, as determined under controlled voltage conditions, suggests that treatment with formaldehyde alters simultaneously, but in opposite ways, two factors that determine the conductance of the inward rectifier. 4. The linear component of the current-voltage relation, which dominates the relation at strongly positive potentials, is not affected while the above changes occur. But on prolonged exposure to formaldehyde the leak conductance increases. 5. The effects of formaldehyde on the inward rectifier are reversible on prolonged superfusion with normal Ringer solution. 6. The slight inward rectification remaining after most of the extracellular K is replaced by Rb, is similarly reduced by treatment with formaldehyde. 7. The results are interpreted in terms of the chemical properties of formaldehyde and present views of the mechanisms of inward rectification.
TL;DR: In this paper, the authors investigated electrical conduction processes in a Ti-Si-Ti sandwich structure following a switching sequence and showed a Poole-Frenkel-type conduction above 104 V cm−1 but the ratio, βPF/βm(βm= measured coefficient), varied from 0.63 to 1.89 within the samples investigated and temperature range.
Abstract: Electrical conduction processes in a‐Si films prepared by electron‐beam evaporation in a Ti–Si–Ti sandwich structure are investigated following a switching sequence. The results show a Poole–Frenkel‐type conduction above 104 V cm−1 but the ratio, βPF/βm(βm= measured coefficient), varied from 0.63 to 1.89 within the samples investigated and temperature range. A discrete activation energy of 0.21 eV was obtained in the region −75°C to +25°C. However, at very low temperature a T−1/4 dependence appropriate to the hopping conductance was obtained. Further support to the above was derived from the observed power‐law dependence of ac conductivity on frequency and very low activation energy. The σαωs graph gave a value of s=2.28 which was unaffected by temperature. The higher than quadratic frequency dependence together with other few departures from theories prove that although the amorphous nature of the film is retained after ’’forming’’ the structure is significantly disturbed and both material and phase chan...
TL;DR: In this article, a frequency dispersion of conductance has been observed in a heterogeneous multilayer system of Cd•behenate and Cd−stearate in accordance with the hopping theory of the multi-layer assemblies.
Abstract: A frequency dispersion of conductance has been observed in a heterogeneous multilayer system of Cd‐behenate and Cd‐stearate in accordance with the hopping theory of the multilayer assemblies. The values of the single‐layer dc conductance evaluated for Cd‐behenate are consistent with those for palmitate, stearate, and arachidate, suggesting the availability of the heterogeneous multilayer system for the evaluation of the bulk conductivity of a single monolayer.