Conductance

About: Conductance is a research topic. Over the lifetime, 8088 publications have been published within this topic receiving 235961 citations.

A p- to n-transition on α-Fe2O3-based thick film sensors studied by conductance and work function change measurements

Abstract: Transition from p- to n-type response, induced by the change in the gas concentration and the operating temperature, was observed for α-Fe 2 O 3 -based semiconducting sensors. This phenomenon is due to the formation of an inversion layer at the surface and therefore to the inversion of the type of mobile carrier at the surface. Different gas atmospheres leads to the different contribution of surface electrons and holes in the overall conductivity, which leads for the predominating either p- or n-type response.

Conduction switching of photochromic molecules.

Abstract: We report a theoretical study of single molecule conduction switching of photochromic dithienylethene molecules. The light-induced intramolecular transformation drives a swapping of the highest occupied molecular orbital and lowest unoccupied molecular orbital between two distinct conjugated paths. The shuffling of single and double bonds produces a significant conductance change when the molecule is sandwiched between metal electrodes. We model the switching event using quantum molecular dynamics and the conductance changes using Green's function electronic transport theory. We find large on-off conductance ratios (between 10 and over 100) depending on the side group outside the switching core.

Effects of some aliphatic alcohols on the conductance change caused by a quantum of acetylcholine at the toad end‐plate.

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.

Monovalent Ion Selectivity Sequences of the Rat Connexin43 Gap Junction Channel

Abstract: The relative permeability sequences of the rat connexin 43 (rCx43) gap junction channel to seven cations and chloride were examined by double whole cell patch clamp recording of single gap junction channel currents in rCx43 transfected neuroblastoma 2A (N2A) cell pairs. The measured maximal single channel slope conductances (gammaj, in pS) of the junctional current-voltage relationships in 115 mM XCI were RbC1 (103) > or = CsC1 (102) > KC1 (97) > NaC1 (79) > or = LiC1 (78) > TMAC1 (65) > TEAC1 (53) and for 115 mM KY were KBr (105) > KC1 (97) > Kacetate (77) > Kglutamate (61). The single channel conductance- aqueous mobility relationships for the test cations and anions were linear. However, the predicted minimum anionic and cationic conductances of these plots did not accurately predict the rCx43 channel conductance in 115 mM KC1. Instead, the conductance of the rCx43 channel in 115 mM KC1 was accurately predicted from cationic and anionic conductance-mobility plots by applying a mobility scaling factor Dx/Do, which depends upon the relative radii of the permeant ions to an estimated pore radius. Relative permeabilities were determined for all of the monovalent catious and anions tested from asymmetric salt reversal potential measurements and the Goldman-Hodgkin-Katz voltage equation. These experiments estimate the relative chloride to potassium permeability to be 0.13. The relationship between the relative cation permeability and hydrated radius was modeled using the hydrodynamic equation assuming a pore radius of 6.3 +/- 0.4 A. Our data quantitatively demonstrate that the rCx43 gap junction channel is permeable to monovalent atomic and organic cations and anions and the relative permeability sequences are consistent with an Eisenman sequence II or I, respectively. These predictions about the rCx43 channel pore provide a useful basis for future investigations into the structural determinants of the conductance and permeability properties of the connexin channel pore.

Batrachotoxin-modified sodium channels in planar lipid bilayers. Ion permeation and block.

Abstract: Batrachotoxin-modified, voltage-dependent sodium channels from canine forebrain were incorporated into planar lipid bilayers. Single-channel conductances were studied for [Na+] ranging between 0.02 and 3.5 M. Typically, the single-channel currents exhibited a simple two-state behavior, with transitions between closed and fully open states. Two other conductance states were observed: a subconductance state, usually seen at [NaCl] greater than or equal to 0.5 M, and a flickery state, usually seen at [NaCl] less than or equal to 0.5 M. The flickery state became more frequent as [NaCl] was decreased below 0.5 M. The K+/Na+ permeability ratio was approximately 0.16 in 0.5 and 2.5 M salt, independent of the Na+ mole fraction, which indicates that there are no interactions among permeant ions in the channels. Impermeant and permeant blocking ions (tetraethylammonium, Ca++, Zn++, and K+) have different effects when added to the extracellular and intracellular solutions, which indicates that the channel is asymmetrical and has at least two cation-binding sites. The conductance vs. [Na+] relation saturated at high concentrations, but could not be described by a Langmuir isotherm, as the conductance at low [NaCl] is higher than predicted from the data at [NaCl] greater than or equal to 1.0 M. At low [NaCl] (less than or equal to 0.1 M), increasing the ionic strength by additions of impermeant monovalent and divalent cations reduced the conductance, as if the magnitude of negative electrostatic potentials at the channel entrances were reduced. The conductances were comparable for channels in bilayers that carry a net negative charge and bilayers that carry no net charge. Together, these results lead to the conclusion that negative charges on the channel protein near the channel entrances increase the conductance, while lipid surface charges are less important.