Conductance

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

Conductive Gold Nanoparticle Mirrors at Liquid/Liquid Interfaces

Abstract: Gold nanoparticle (Au NP) mirrors, which exhibit both high reflectance and electrical conductance, were self-assembled at a [heptane + 1,2-dichloroethane]/water liquid/liquid interface. The highest reflectance, as observed experimentally and confirmed by finite difference time domain calculations, occurred for Au NP films consisting of 60 nm diameter NPs and approximate monolayer surface coverage. Scanning electrochemical microscopy approach curves over the interfacial metallic NP films revealed a transition from an insulating to a conducting electrical material on reaching a surface coverage at least equivalent to the formation of a single monolayer. Reflectance and conductance transitions were interpreted as critical junctures corresponding to a surface coverage that exceeded the percolation threshold of the Au NP films at the [heptane + 1,2-dichloroethane]/water interface.

Ionic selectivity, saturation and block in gramicidin A channels:

Abstract: A model for the gramicidin A channel is proposed which extends existing models by adding a specific cationic binding site at each entrance to the channel. The binding of ions to these outer channel sites is assumed to shift the energy levels of the inner sites and barriers and thereby alter the channel conductance. The resulting properties are analyzed theoretically for the simplest case of two inner sites and a single energy barrier. This four-site model (two outer and two inner) predicts that the membrane potential at zero current (U0) should be described by a Goldman-Hodgkin-Katz equation with concentration-dependent permeability ratios. The coefficients of the concentration-dependent terms are shown to be related to the peak energy shifts of the barrier and to the binding constants of the outer sites. The theory also predicts the channel conductance in symmetrical solutions to exhibit three limiting behaviors, from which the properties of the outer and inner sites can be characterized. In two-cation symmetrical mixtures the conductance as a function of mole fraction is shown to have a minimum, and the related phenomenon of inhibition and block exerted by one ion on the other is explained explicitly by the theory. These various phenomena, having ion interactions in a multiply occupied channel as a common physical basis, are all related (by the theory) through a set of measurable parameters describing the properties of the system.

Proton currents in human granulocytes: regulation by membrane potential and intracellular pH.

Abstract: 1. To determine whether conductive pathways contribute to the H+ efflux from granulocytes, we used the whole-cell patch-clamp technique combined with microfluorimetric determinations of cytosolic pH (pHi) in single, dimethylsulphoxide-differentiated HL-60 cells. 2. In voltage-clamp mode, depolarization of the cell from the resting potential (around -60 mV) to +60 mV caused an increase in pHi that was accompanied by a sizeable outward current. 3. Ion substitution experiments and analysis of the reversal potential of tail currents indicated that the outward current is carried largely by H+ ions. 4. Full activation of the H+ current occurred within 1-2s after depolarization and deactivation within 100-200 ms upon repolarization. 5. This H+ conductance was strongly dependent on pHi, being larger at acidic pH. In addition, at low pHi the threshold for voltage activation of the H+ conductance was shifted to more negative values. 6. Addition of millimolar concentrations of Cd2+ and Zn2+ to the bath solution reduced the maximum H+ conductance and shifted the voltage dependence of the H+ conductance to more positive potentials. The effects were reversible. 7. In conclusion, our results demonstrate that granulocytic HL-60 cells possess a voltage-gated and pHi-sensitive H+ conductance. Because both a depolarization and a cytosolic acidification occur during the activation of granulocytes, this conductance may play a role in pHi homeostasis of granulocytes during microbial killing.