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Single Channel Conductance (single + channel_conductance)
Selected AbstractsDiversity of GABAA receptor synaptic currents on individual pyramidal cortical neuronsEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 3 2007Timothy Ing Abstract Miniature GABAA receptor-mediated inhibitory postsynaptic currents (mIPSCs) in cortical pyramidal neurons have previously been categorized into two types: small amplitude mIPSCs with a mono-exponential deactivation (mono-mIPSCs) and relatively larger mIPSCs with bi-exponential deactivation (bi-mIPSCs). The aim of this study was to determine if the GABAA channels that underlie these mIPSCSs are molecularly distinct. We found, using non-stationary noise analysis, that the difference in their amplitude could be not accounted for by their single channel conductance (both were 40 pS). Next, using , subunit selective GABAA receptor modulators, we examined the identity of the , subunits that may be expressed in the synapses that give rise to these mIPSCs. Zolpidem (100 and 500 nm, ,1 selective) affected the deactivation of a subset of the mono-mIPSCs, indicating that ,1 subunits are not highly expressed in these synapses. However, zolpidem (100 nm) prolonged the deactivation of all bi-mIPSCs, indicating a high abundance of ,1 subunits in these synapses. SB-205384 (,3 selective) had no effect on the mono-mIPSCs but the bi-mIPSCs were prolonged. Furosemide (,4 selective) reduced the amplitude of only the mono-mIPSCs. L655,708 (,5 selective) reduced the amplitude of both populations and shortened the duration of the mono-mIPSCs. Finally, we found that the neuroactive steroid pregesterone sulphate reduced the amplitude of both mIPSC types. These results provide pharmacological evidence that synapses on cortical pyramidal neurons are molecularly distinct. The purpose of these different types of synapses may be to provide different inhibitory timing patterns on these cells. [source] Properties of ion channels in the protoplasts of the Mediterranean seagrass Posidonia oceanicaPLANT CELL & ENVIRONMENT, Issue 3 2004A. CARPANETO ABSTRACT Posidonia oceanica (L) Delile, a seagrass endemic of the Mediterranean sea, provides food and shelter to marine organisms. As environment contamination and variation in physico-chemical parameters may compromise the survival of the few Posidonia genotypes living in the Mediterranean, comprehending the molecular mechanisms controlling Posidonia growth and development is increasingly important. In the present study the properties of ion channels in P. oceanica plasma membranes studied by the patch-clamp technique in protoplasts obtained from the young non-photosynthetic leaves were investigated. In protoplasts that were presumably originated from sheath cells surrounding the vascular bundles of the leaves, an outward-rectifying time-dependent channel with a single channel conductance of 58 ± 2 pS which did not inactivate, was selective for potassium and impermeable to monovalent cations such as Na+, Li+ and Cs+ was identified. In the same protoplasts, an inward-rectifying channel that has a time-dependent component with single channel conductance of the order of 10 pS, a marked selectivity for potassium and no permeation to sodium was also identified, as was a third type of channel that did not display any ionic selectivity and was reversibly inhibited by tetraethylammonium and lanthanum. A comparison of Posidonia channel characteristics with channels identified in terrestrial plants and other halophytic plants is included. [source] Control of the single channel conductance of K2P10.1 (TREK-2) by the amino-terminus: role of alternative translation initiationTHE JOURNAL OF PHYSIOLOGY, Issue 23 2008Dina Simkin TREK-2 expressed in mammalian cells exhibits small (,52 pS) and large (,220 pS) unitary conductance levels. Here we tested the role of the N-terminus (69 amino acids long) in the control of the unitary conductance, and role of the alternative translation initiation as a mechanism that produces isoforms of TREK-2 that show different conductance levels. Deletion of the first half (,1,36) of the N-terminus had no effect. However, deletion of most of the N-terminus (,1,66) resulted in the appearance of only the large-conductance channel (,220 pS). In support of the critical function of the distal half of the N-terminus, the deletion mutants ,1,44 and ,1,54 produced ,90 pS and 188 pS channels, respectively. In Western blot analysis, TREK-2 antibody detected two immunoreactive bands at ,54 kDa and ,60 kDa from cells expressing wild-type TREK-2 that has three potential translation initiation sites (designated M1M2M3) within the N-terminus. Mutation of the second and third initiation sites from Met to Leu (M1L2L3) produced only the ,60 kDa isoform and the small-conductance channel (,52 pS). Mutants designed to produce translation from the second (M2L3) or third (M3) initiation site produced the ,54 kDa isoform, and the large conductance channel (,185,224 pS). M1L2L3, M2L3 and M3 were relatively selectively permeable to K+, as judged by the 51,55 mV shifts in reversal potential following a 10-fold change in [K+]o. PNa/PK values were also similar for M1L2L3 (,0.02), M2L3 (,0.02) and M3 (,0.03). Arachidonic acid, proton and membrane stretch activated, whereas dibutyryl-cAMP inhibited all three isoforms of TREK-2, indicating that deletion of the N-terminus does not abolish modulation. These results show that the small and large conductance TREK-2 channels are produced as a result of alternative translation initiation, producing isoforms with long and short N-termini, and that the distal half of the N-terminus controls the unitary conductance. [source] The peptaibol antiamoebin as a model ion channel: similarities to bacterial potassium channels,JOURNAL OF PEPTIDE SCIENCE, Issue 11-12 2003Andrias O. O'Reilly Abstract Antiamoebin (AAM) is a polypeptide antibiotic that is capable of forming ion channels in phospholipid membranes; planar bilayer studies have suggested the channels are octamers. The crystal structure of a monomeric form of AAM has provided the basis for molecular modelling of an octameric helical bundle channel. The channel model is funnel-shaped due to a substantial bend in the middle of the polypeptide chain caused by the presence of several imino acids. Inter-monomer hydrogen bonds orientate a ring of glutamine side chains to form a constriction in the pore lumen. The channel lumen is lined both by side chains of Gln11 and by polypeptide backbone carbonyl groups. Electrostatic calculations on the model are compatible with a channel that transports cations across membranes. The AAM channel model is compared with the crystal structures of two bacterial (KcsA and MthK) potassium channels. AAM and the potassium channels exhibit common functional features, such as cation-selectivity and similar single channel conductances. Common structural features include being multimers, each formed from a bundle of eight transmembrane helices, with lengths roughly comparable to the thickness of lipid bilayers. In addition, they all have aromatic amino acids that lie at the bilayer interfaces and which may aid in the stabilization of the transmembrane helices, as well as narrower constrictions that define the ion binding sites or selectivity filters in the pore lumen. The commonality of structural and functional features in these channels thus suggests that antiamoebin is a good, simple model for more complex bacterial and eukaryotic ion channels, capable of providing insight into details of the mechanisms of ion transport and multimeric channel stability. Copyright © 2003 European Peptide Society and John Wiley & Sons, Ltd. [source] | ||||||||||