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Channel Conductance (channel + conductance)
Kinds of 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] Calcium and Fos Involvement in Brain-Derived Ca2+ -Binding Protein (S100)-Dependent Apoptosis in Rat Phaeochromocytoma CellsEXPERIMENTAL PHYSIOLOGY, Issue 3 2000Stefania Fulle Brain-derived calcium-binding protein S100 induces apoptosis in a significant fraction of rat phaeochromocytoma (PC12) cells. We used single cell techniques (patch clamp, videomicroscopy and immunocytochemistry) to clarify some of the specific aspects of S100-induced apoptosis, the modality(ies) of early intracellular Ca2+ concentration increase and the expression of some classes of genes (c-fos, c-jun, bax, bcl-x, p-15, p-21) known to be implicated in apoptosis of different cells. The results show that S100: (1) causes an increase of [Ca2+]i due to an increased conductance of L-type Ca2+ channels; (2) induces a sustained increase of the Fos levels which is evident since the first time point tested (3 h) and remains elevated until to the last time point (72 h). All these data suggest that S100-derived apoptosis in PC12 cells may be the consequence of a system involving an increase in L-type Ca2+ channel conductance with consequent [Ca2+]i increase which up-regulates, directly or indirectly, the expression of Fos. [source] Molecular cloning, genomic organization and functional characterization of a new short-chain potassium channel toxin-like peptide BmTxKS4 from Buthus martensii Karsch(BmK)JOURNAL OF BIOCHEMICAL AND MOLECULAR TOXICOLOGY, Issue 4 2004Sheng Jiqun Abstract Scorpion venom contains many small polypeptide toxins, which can modulate Na+, K+, Cl,, and Ca2+ ion,channel conductance in the cell membrane. A full-length cDNA sequence encoding a novel type of K+ -channel toxin (named BmTxKS4) was first isolated and identified from a venom gland cDNA library of Buthus martensii Karsch (BmK). The encoded precursor contains 78 amino acid residues including a putative signal peptide of 21 residues, propeptide of 11 residues, and a mature peptide of 43 residues with three disulfide bridges. BmTxKS4 shares the identical organization of disulfide bridges with all the other short-chain K+ -channel scorpion toxins. By PCR amplification of the genomic region encoding BmTxKS4, it was shown that BmTxKS4 composed of two exons is disrupted by an intron of 87 bp inserted between the first and the second codes of Phe (F) in the encoding signal peptide region, which is completely identical with that of the characterized scorpion K+ -channel ligands in the size, position, consensus junctions, putative branch point, and A+T content. The GST-BmTxKS4 fusion protein was successfully expressed in BL21 (DE3) and purified with affinity chromatography. About 2.5 mg purified recombinant BmTxKS4 (rBmTxKS4) protein was obtained by treating GST-BmTxKS4 with enterokinase and sephadex chromatography from 1 L bacterial culture. The electrophysiological activity of 1.0,M rBmTxKS4 was measured and compared by whole cell patch-clamp technique. The results indicated that rBmTxKS4 reversibly inhibited the transient outward K+ current (Ito), delayed inward rectifier K+ current (Ik1), and prolonged the action potential duration of ventricular myocyte, but it has no effect on the action potential amplitude. Taken together, BmTxKS4 is a novel subfamily member of short-strain K+ -channel scorpion toxin. © 2004 Wiley Periodicals, Inc. J Biochem Mol Toxicol 18:187,195, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/jbt.20026 [source] Identification of hyperpolarization-activated calcium channels in apical pollen tubes of Pyrus pyrifoliaNEW PHYTOLOGIST, Issue 3 2007Hai-Yong Qu Summary ,,The pollen tube has been widely used to study the mechanisms underlying polarized tip growth in plants. A steep tip-to-base gradient of free cytosolic calcium ([Ca2+]cyt) is essential for pollen-tube growth. Local Ca2+ influx mediated by Ca2+ -permeable channels plays a key role in maintaining this [Ca2+]cyt gradient. ,,Here, we developed a protocol for successful isolation of spheroplasts from pollen tubes of Pyrus pyrifolia and identified a hyperpolarization-activated cation channel using the patch-clamp technique. ,,We showed that the cation channel conductance displayed a strong selectivity for divalent cations, with a relative permeability sequence of barium (Ba2+) , Ca2+ > magnesium (Mg2+) > strontium (Sr2+) > manganese (Mn2+). This channel conductance was selective for Ca2+ over chlorine (Cl,) (relative permeability PCa/PCl = 14 in 10 mm extracellular Ca2+). We also showed that the channel was inhibited by the Ca2+ channel blockers lanthanum (La3+) and gadolinium (Gd3+). Furthermore, channel activity depended on extracellular pH and pollen viability. ,,We propose that the Ca2+ -permeable channel is likely to play a role in mediating Ca2+ influx into the growing pollen tubes to maintain the [Ca2+]cyt gradient. [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] Bicuculline, pentobarbital and diazepam modulate spontaneous GABAA channels in rat hippocampal neuronsBRITISH JOURNAL OF PHARMACOLOGY, Issue 4 2000Bryndis Birnir Spontaneously opening, chloride-selective channels that showed outward rectification were recorded in ripped-off patches from rat cultured hippocampal neurons and in cell-attached patches from rat hippocampal CA1 pyramidal neurons in slices. In both preparations, channels had multiple conductance states and the most common single-channel conductance varied. In the outside-out patches it ranged from 12 to 70 pS (Vp=40 mV) whereas in the cell-attached patches it ranged from 56 to 85 pS (,Vp=80 mV). Application of GABA to a patch showing spontaneous channel activity evoked a rapid, synchronous activation of channels. During prolonged exposure to either 5 or 100 ,M GABA, the open probability of channels decreased. Application of GABA appeared to have no immediate effect on single-channel conductance. Exposure of the patches to 100 ,M bicuculline caused a gradual decrease on the single-channel conductance of the spontaneous channels. The time for complete inhibition to take place was slower in the outside-out than in the cell-attached patches. Application of 100 ,M pentobarbital or 1 ,M diazepam caused 2,4 fold increase in the maximum channel conductance of low conductance (<40 pS) spontaneously active channels. The observation of spontaneously opening GABAA channels in cell-attached patches on neurons in slices suggests that they may have a role in neurons in vivo and could be an important site of action for some drugs such as benzodiazepines, barbiturates and general anaesthetics. British Journal of Pharmacology (2000) 131, 695,704; doi:10.1038/sj.bjp.0703621 [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] | |||||||||||||||||||||||||