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Single Channel (single + channel)

Distribution by Scientific Domains
Life Sciences60%
Medical Sciences30%

Terms modified by Single Channel

  • single channel conductance
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    Selected Abstracts

    Octanol Modulation of Neuronal Nicotinic Acetylcholine Receptor Single Channels

    ALCOHOLISM, Issue 11 2004
    Yi Zuo
    Background: We have previously shown that alcohols exert a dual action on neuronal nicotinic acetylcholine receptors (AChRs), with short-chain alcohols potentiating and long-chain alcohols inhibiting acetylcholine (ACh)-induced whole-cell currents. At the single-channel level, ethanol increased the channel open probability and prolonged the channel open time and burst duration. In this study, we examined the detailed mechanism of the inhibitory action of the long-chain alcohol n -octanol on the neuronal nicotinic AChR. Methods: Single-channel currents induced by application of 30 nm ACh were recorded with the patch-clamp technique from human embryonic kidney cells stably expressing the human ,4,2 AChR. Results: Several single-channel parameters were markedly changed by octanol. At least two conductance-state currents were induced by low concentrations of ACh, and octanol increased the proportion of the low-conductance-state current relative to the high-conductance-state current without changing the current amplitude. Major analyses of temporal properties of single-channel currents were performed on the high-conductance-state currents. Octanol decreased the burst duration and duration of openings within burst and prolonged the mean closed time. All of these changes contributed to the decrease in the open probability in a concentration-dependent manner. Conclusions: Several aspects of octanol action on neuronal AChRs at the single-channel level are compatible with an atypical open channel block model reported with muscle nicotinic AChRs. The potentiating action of short-chain alcohols and the inhibitory action of long-chain alcohols on the neuronal nicotinic AChR are mediated through different mechanisms. [source]

    Understanding the temporal dynamics of the wandering Renous River, New Brunswick, Canada

    EARTH SURFACE PROCESSES AND LANDFORMS, Issue 10 2005
    Leif M. Burge
    Abstract Wandering rivers are composed of individual anabranches surrounding semi-permanent islands, linked by single channel reaches. Wandering rivers are important because they provide habitat complexity for aquatic organisms, including salmonids. An anabranch cycle model was developed from previous literature and field observations to illustrate how anabranches within the wandering pattern change from single to multiple channels and vice versa over a number of decades. The model was used to investigate the temporal dynamics of a wandering river through historical case studies and channel characteristics from field data. The wandering Renous River, New Brunswick, was mapped from aerial photographs (1945, 1965, 1983 and 1999) to determine river pattern statistics and for historical analysis of case studies. Five case studies consisting of a stable single channel, newly formed anabranches, anabranches gaining stability following creation, stable anabranches, and an abandoning anabranch were investigated in detail. Long profiles, hydraulic geometry, channel energy, grain size and sediment mobility variables were calculated for each channel. Within the Renous study area, the frequency of channel formation and abandonment were similar over the 54 years of analysis, indicating that the wandering pattern is being maintained. Eight anabranches were formed through avulsions, five were formed through the emergence of islands from channel bars and 11 anabranches were abandoned. The stable anabranch pair displayed similar hydraulic geometry and channel energy characteristics, while unstable anabranch pairs did not. The anabranch pair that gained stability displayed more similar channel energy characteristics than the anabranch pair that was losing stability (abandoning). It appears that anabranch pairs with similar energy characteristics are more stable than anabranches where these characteristics are out of balance. This is consistent with the hypothesis that anabranch pairs of similar length will be more stable than those with dissimilar lengths. Copyright © 2005 John Wiley & Sons, Ltd. [source]

    Microfluidic devices for electrokinetic sample fractionation

    ELECTROPHORESIS, Issue 15 2010
    Zhen Wang
    Abstract We present three generations of microchip-based "in-space" sample fractionators and collectors for use in proteomics. The basic chip design consisted of a single channel for CE separation of analytes that then intersects a fractionation zone feed into multiple high aspect ratio microchannels for fractionation of separated components. Achievements of each generation are discussed in relation to important design criteria. CE-separated samples were electrokinetically driven to multiple collection channels in sequence without cross-contamination under the protection of sheath streams. A 36-channel fractionator demonstrated the efficacy of a high-throughput fractionator with no observed cross-contamination. A mixture of IgG and BSA was used to test the efficiency of the fractionator and collector. CE of the fractionated samples was performed on the same device to verify their purity. Our demonstration proved to be efficient and reproducible in obtaining non-contaminated samples over 15 sample injections. Experimental results were found to be in close agreement with PSpice simulation in terms of flow behavior, contamination control and device performance. The design presented here has a great potential to be integrated in proteomic platforms. [source]

    Involvement of Calmodulin in Glucagon-Like Peptide 1(7-36) Amide-Induced Inhibition of the ATP-Sensitive K+ Channel in Mouse Pancreatic ,-Cells

    EXPERIMENTAL PHYSIOLOGY, Issue 3 2001
    W. G. Ding
    The present investigation was designed to examine whether calmodulin is involved in the inhibition of the ATP-sensitive K+ (KATP) channel by glucagon-like peptide 1(7-36) amide (GLP-1) in mouse pancreatic ,-cells. Membrane potential, single channel and whole-cell currents through the KATP channels, and intracellular free Ca2+ concentration ([Ca2+]i) were measured in single mouse pancreatic ,-cells. Whole-cell patch-clamp experiments with amphotericin-perforated patches revealed that membrane conductance at around the resting potential is predominantly supplied by the KATP channels in mouse pancreatic ,-cells. The addition of 20 nM GLP-1 in the presence of 5 mM glucose significantly reduced the membrane KATP conductance, accompanied by membrane depolarization and the generation of electrical activity. A calmodulin inhibitor N -(6-aminohexyl)-5-chloro-1-naphthalenesulphonamide (W-7, 20 ,M) completely reversed the inhibitory actions of GLP-1 on the membrane KATP conductance and resultant membrane depolarization. Cell-attached patch recordings confirmed the inhibition of the KATP channel activity by 20 nM GLP-1 and its restoration by 20 ,M W-7 or 10 ,M calmidazolium at the single channel level. Bath application of 20 ,M W-7 also consistently abolished the GLP-1-evoked increase in [Ca2+]i in the presence of 5 mM glucose. These results strongly suggest that the mechanisms by which GLP-1 inhibits the KATP channel activity accompanied by the initiation of electrical activity in mouse pancreatic ,-cells include a calmodulin-dependent mechanism in addition to the well-documented activation of the cyclic AMP-protein kinase A system. [source]

    Static single channel and multichannel water perfusion pressure profilometry in a bench model of a urethra,,

    NEUROUROLOGY AND URODYNAMICS, Issue 7 2010
    G.R. Hirst
    Abstract Aims To determine the catheter perfusion and withdrawal rate which generate the most repeatable single (SCPP) and multichannel pressure profilometry (MCPP) profiles in a bench model. Methods A bench model using a urethral substitute was developed in which SCPP and MCPP were performed using the Brown,Wickham method. One single channel and four multichannel catheters were tested using seven withdrawal rates and three perfusion rates. Repeatability was determined using spread of mean profile pressure, cross-correlation, Bland,Altman statistic, and a one-tailed Student's t -statistic. An artificial urinary sphincter (AUS) model was constructed to create a predictable intraluminal profile. MCPP data were used to generate three-dimensional (3D) images of the pressures exerted by the AUS model. Results A withdrawal rate of 0.5,mm/sec and perfusion rate 1,ml/min produced the most repeatable SCPP profiles with a spread of mean profile pressure ,7,cmH2O. For MCPP, a 10,F 6-channel catheter using a withdrawal rate of 1,mm/sec and perfusion rate of 1,ml/min produced the most similar profiles (cross-correlation,=,0.99). However, the spread of MCPP was large (spread ,44,cmH2O per channel). Nevertheless MCPP was able to consistently demonstrate areas of high pressure as predicted by the AUS model. Conclusions MCPP was not repeatable and is an unreliable measure of urethral pressure. MCPP and 3D images do demonstrate directional differences predicted from the AUS model. These may be of use for qualitative understanding and appreciation of relative relationships if not actual forces within the urethra and have application in understanding urethral function in vivo. Neurourol. Urodynam. 29:1312,1319, 2010. © 2010 Wiley-Liss, Inc. [source]

    The ,1 and ,6 subunit subtypes of the mammalian GABAA receptor confer distinct channel gating kinetics

    THE JOURNAL OF PHYSIOLOGY, Issue 2 2004
    Janet L. Fisher
    The GABAA receptors show a large degree of structural heterogeneity, with seven different subunit families, and 16 different subtypes in mammalian species. The , family is the largest, with six different subtypes. The ,1 and ,6 subtypes are among the most diverse within this family and confer distinct pharmacological properties to recombinant and neuronal receptors. To determine whether different single channel and macroscopic kinetic properties were also associated with these subtypes, the ,1 or ,6 subunit was expressed in mammalian cells along with ,3 and ,2L subunits and the kinetic properties examined with outside-out patch recordings. The ,1,3,2L receptors responded to GABA with long-duration openings organized into multi-opening bursts. In contrast, channel openings of the ,6,3,2L receptors were predominately short in duration and occurred as isolated, single openings. The subunit subtype also affected the deactivation rate of the receptor, which was almost 2-fold slower for ,6,3,2L, compared with the ,1,3,2L isoform. Onset of fast desensitization did not differ between the isoforms. To determine the structural domains responsible for these differences in kinetic properties, we constructed six chimeric subunits, combining different regions of the ,1 and ,6 subunits. The properties of the chimeric subunits indicated that structures within the third transmembrane domain (TM3) and the TM3,TM4 intracellular loop conferred differences in single channel gating kinetics that subsequently affected the deactivation rate and GABA EC50. The effect of agonist concentration on the rise time of the current showed that the extracellular N-terminal domain was largely responsible for binding characteristics, while the transmembrane domains determined the activation rate at saturating GABA concentrations. This suggests that subunit structures outside of the agonist binding and pore-lining domains are responsible for the kinetic differences conferred by the ,1 and ,6 subtypes. Structural heterogeneity within these transmembrane and intracellular regions can therefore influence the characteristics of the postsynaptic response of GABAA receptors with different subunit composition. [source]

    Continuous scalable blood filtration device using inertial microfluidics

    BIOTECHNOLOGY & BIOENGINEERING, Issue 2 2010
    Albert J. Mach
    Abstract Cell separation is broadly useful for applications in clinical diagnostics, biological research, and potentially regenerative medicine. Recent attention has been paid to label-free size-based techniques that may avoid the costs or clogging issues associated with centrifugation and mechanical filtration. We present for the first time a massively parallel microfluidic device that passively separates pathogenic bacteria cells from diluted blood with macroscale performance. The device was designed to process large sample volumes in a high-throughput, continuous manner using 40 single microchannels placed in a radial array with one inlet and two rings of outlets. Each single channel consists of a short focusing, gradual expansion and collection region and uses unique differential transit times due to size-dependent inertial lift forces as a method of cell separation. The gradual channel expansion region is shown to manipulate cell equilibrium positions close to the microchannel walls, critical for higher efficiency collection. We demonstrate >80% removal of pathogenic bacteria from blood after two passes of the single channel system. The massively parallel device can process 240,mL/h with a throughput of 400 million cells/min. We expect that this parallelizable, robust, and label-free approach would be useful for filtration of blood as well as for other cell separation and concentration applications from large volume samples. Biotechnol. Bioeng. 2010;107: 302,311. © 2010 Wiley Periodicals, Inc. [source]

    Single mechano-gated channels activated by mechanical deformation of acutely isolated cardiac fibroblasts from rats

    ACTA PHYSIOLOGICA, Issue 3 2010
    A. Kamkin
    Abstract Aim:, Mechanosensitive conductances were reported in cardiac fibroblasts, but the properties of single channels mediating their mechanosensitivity remain uncharacterized. The aim of this work was to investigate single mechano-gated channels (MGCs) activated by mechanical deformations of cardiac fibroblasts. Methods:, Currents through single MGCs and mechanosensitive whole-cell currents were recorded from isolated rat atrial fibroblasts using the cell-attached and whole-cell patch-clamp configurations respectively. Defined mechanical stress was applied via the patch pipette used for the whole-cell recordings. Results:, Under resting conditions occasional short openings of two types of single MGCs with conductances of 43 and 87 pS were observed. Both types of channels displayed a linear current,voltage relationship with the reversal potential around 0 mV. Small (1 ,m) mechanical deformations affected neither single nor whole-cell mechano-gated currents. Cell compressions (2, 3 and 4 ,m) augmented the whole-cell currents and increased the frequency and duration of single channel openings. Cell stretches (2, 3 and 4 ,m) inactivated the whole-cell currents and abolished the activity of single MGCs. Gd3+ (8 ,m) blocked the whole-cell currents within 5 min. No single channel activity was observed in the cell-attached mode when Gd3+ was added to the intrapipette solution. Cytochalasin D and colchicine (100 ,m each) completely blocked both the whole-cell and single channel currents. Conclusions:, These findings show that rat atrial fibroblasts express two types of MGCs whose activity is governed by cell deformation. We conclude that fibroblasts can sense the direction of applied stress and contribute to mechano-electrical coupling in the heart. [source]

    Sodium channel distribution on uninnervated and innervated embryonic skeletal myotubes

    DEVELOPMENTAL NEUROBIOLOGY, Issue 1 2001
    Blake D. Anson
    Abstract Acetylcholine receptor (AChR) and sodium (Na+) channel distributions within the membrane of mature vertebrate skeletal muscle fibers maximize the probability of successful neuromuscular transmission and subsequent action potential propagation. AChRs have been studied intensively as a model for understanding the development and regulation of ion channel distribution within the postsynaptic membrane. Na+ channel distributions have received less attention, although there is evidence that the temporal accumulation of Na+ channels at developing neuromuscular junctions (NMJs) may differ between species. Even less is known about the development of extrajunctional Na+ channel distributions. To further our understanding of Na+ channel distributions within junctional and extrajunctional membranes, we used a novel voltage-clamp method and fluorescent probes to map Na+ channels on embryonic chick muscle fibers as they developed in vitro and in vivo. Na+ current densities on uninnervated myotubes were approximately one-tenth the density found within extrajunctional regions of mature fibers, and showed several-fold variations that could not be explained by a random scattering of single channels. Regions of high current density were not correlated with cellular landmarks such as AChR clusters or myonuclei. Under coculture conditions, AChRs rapidly concentrated at developing synapses, while Na+ channels did not show a significant increase over the 7 day coculture period. In vivo investigations supported a significant temporal separation between Na+ channel and AChR aggregation at the developing NMJ. These data suggest that extrajunctional Na+ channels cluster together in a neuronally independent manner and concentrate at the developing avian NMJ much later than AChRs. © 2001 John Wiley & Sons, Inc. J Neurobiol 48: 42,57, 2001 [source]