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Artykuły w czasopismach na temat „Open channel”

Autor: Grafiati

Data publikacji: 4 czerwca 2021

Data aktualizacji: 1 czerwca 2024

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1

Barnes, S., i B. Hille. "Veratridine modifies open sodium channels." Journal of General Physiology 91, nr 3 (1.03.1988): 421–43. http://dx.doi.org/10.1085/jgp.91.3.421.

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The state dependence of Na channel modification by the alkaloid neurotoxin veratridine was investigated with single-channel and whole-cell voltage-clamp recording in neuroblastoma cells. Several tests of whole-cell Na current behavior in the presence of veratridine supported the hypothesis that Na channels must be open in order to undergo modification by the neurotoxin. Modification was use dependent and required depolarizing pulses, the voltage dependence of production of modified channels was similar to that of normal current activation, and prepulses that caused inactivation of normal current had a parallel effect on the generation of modified current. This hypothesis was then examined directly at the single-channel level. Modified channel openings were easily distinguished from normal openings by their smaller current amplitude and longer burst times. The modification event was often seen as a sudden, dramatic reduction of current through an open Na channel and produced a somewhat flickery channel event having a mean lifetime of 1.6 s at an estimated absolute membrane potential of -45 mV (23 degrees C). The modified channel had a slope conductance of 4 pS, which was 20-25% the size of the slope conductance of normal channels with the 300 mM NaCl pipette solution used. Most modified channel openings were initiated by depolarizing pulses, began within the first 10 ms of the depolarizing step, and were closely associated with the prior opening of single normal Na channels, which supports the hypothesis that modification occurs from the normal open state.

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2

Pandey, Bharat Raj. "Open Channel Surges". Journal of Advanced College of Engineering and Management 1 (13.05.2016): 35. http://dx.doi.org/10.3126/jacem.v1i0.14919.

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<p>The open channel Surges due to sudden changes of flow depth creates Celerity (Wave Velocity) in the flow in addition to the normal water velocity of the channels. These waves travel in the downstream and sometimes upstream of the channels depending on the various situations. The propagation of the Surges becomes positives or negatives depending on its crest and the trough of the waves. Therefore, on this topic, these principals are presented in the analytical methods<strong><em>.</em></strong></p><p><em>Journal of Advanced College of Engineering and Management, Vol. 1, 2015</em>, pp. 35-43</p>

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3

Undrovinas, A. I., i J. C. Makielski. "Blockade of lysophosphatidylcholine-modified cardiac Na channels by a lidocaine derivative QX-222". American Journal of Physiology-Heart and Circulatory Physiology 271, nr 2 (1.08.1996): H790—H797. http://dx.doi.org/10.1152/ajpheart.1996.271.2.h790.

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Single Na channels from rat and rabbit ventricular cells were studied with use of the excised inside-out patch-clamp technique. To investigate local anesthetic interactions with Na channels modified by the ischemic metabolite lysophosphatidylcholine (LPC), the quaternary ammonium lidocaine derivative QX-222 [2-(trimethylamino)-N-(2,6-dimethylphenyl)acetamide] was applied to the cytoplasmic side of patches from untreated cells and from those treated with LPC for approximately 1 h. Single-channel amplitudes and kinetics for unmodified channels were similar to those reported previously for cardiac cells with a single-component, mean-channel open time. LPC-modified channels showed prolonged open channel bursting with a two-component, mean open time, suggesting two open states. Conductance sublevels to the 60-70% level of the main conductance were found in both unmodified and LPC-modified channels and also with and without QX-222 present. QX-222 reversibly shortened the open time of the unmodified channel and for both open times of the LPC-modified channel without decreasing single-channel amplitude. Calculated association rates for QX-222 with the channel were found to be greater for the open states of the modified channel than those for the unmodified channel. Thus the lidocaine analogue QX-222 interacts with and blocks the open state of both unmodified and LPC-modified, cardiac Na channels. The blocking effect on LPC-modified channels would be predicted to be greater both because of the longer dwell time in the high-affinity open states for modified channels and also because of an intrinsically greater association rate in the modified channels.

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4

Marabelli, Alessandro, Remigijus Lape i Lucia Sivilotti. "Mechanism of activation of the prokaryotic channel ELIC by propylamine: A single-channel study". Journal of General Physiology 145, nr 1 (29.12.2014): 23–45. http://dx.doi.org/10.1085/jgp.201411234.

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Prokaryotic channels, such as Erwinia chrysanthemi ligand-gated ion channel (ELIC) and Gloeobacter violaceus ligand-gated ion channel, give key structural information for the pentameric ligand-gated ion channel family, which includes nicotinic acetylcholine receptors. ELIC, a cationic channel from E. chrysanthemi, is particularly suitable for single-channel recording because of its high conductance. Here, we report on the kinetic properties of ELIC channels expressed in human embryonic kidney 293 cells. Single-channel currents elicited by the full agonist propylamine (0.5–50 mM) in outside-out patches at −60 mV were analyzed by direct maximum likelihood fitting of kinetic schemes to the idealized data. Several mechanisms were tested, and their adequacy was judged by comparing the predictions of the best fit obtained with the observable features of the experimental data. These included open-/shut-time distributions and the time course of macroscopic propylamine-activated currents elicited by fast theta-tube applications (50–600 ms, 1–50 mM, −100 mV). Related eukaryotic channels, such as glycine and nicotinic receptors, when fully liganded open with high efficacy to a single open state, reached via a preopening intermediate. The simplest adequate description of their activation, the “Flip” model, assumes a concerted transition to a single intermediate state at high agonist concentration. In contrast, ELIC open-time distributions at saturating propylamine showed multiple components. Thus, more than one open state must be accessible to the fully liganded channel. The “Primed” model allows opening from multiple fully liganded intermediates. The best fits of this type of model showed that ELIC maximum open probability (99%) is reached when at least two and probably three molecules of agonist have bound to the channel. The overall efficacy with which the fully liganded channel opens was ∼102 (∼20 for α1β glycine channels). The microscopic affinity for the agonist increased as the channel activated, from 7 mM for the resting state to 0.15 mM for the partially activated intermediate state.

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5

Liin, Sara I., Per-Eric Lund, Johan E. Larsson, Johan Brask, Björn Wallner i Fredrik Elinder. "Biaryl sulfonamide motifs up- or down-regulate ion channel activity by activating voltage sensors". Journal of General Physiology 150, nr 8 (12.07.2018): 1215–30. http://dx.doi.org/10.1085/jgp.201711942.

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Voltage-gated ion channels are key molecules for the generation of cellular electrical excitability. Many pharmaceutical drugs target these channels by blocking their ion-conducting pore, but in many cases, channel-opening compounds would be more beneficial. Here, to search for new channel-opening compounds, we screen 18,000 compounds with high-throughput patch-clamp technology and find several potassium-channel openers that share a distinct biaryl-sulfonamide motif. Our data suggest that the negatively charged variants of these compounds bind to the top of the voltage-sensor domain, between transmembrane segments 3 and 4, to open the channel. Although we show here that biaryl-sulfonamide compounds open a potassium channel, they have also been reported to block sodium and calcium channels. However, because they inactivate voltage-gated sodium channels by promoting activation of one voltage sensor, we suggest that, despite different effects on the channel gates, the biaryl-sulfonamide motif is a general ion-channel activator motif. Because these compounds block action potential–generating sodium and calcium channels and open an action potential–dampening potassium channel, they should have a high propensity to reduce excitability. This opens up the possibility to build new excitability-reducing pharmaceutical drugs from the biaryl-sulfonamide scaffold.

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6

Hu, S. L., Y. Yamamoto i C. Y. Kao. "The Ca2+-activated K+ channel and its functional roles in smooth muscle cells of guinea pig taenia coli." Journal of General Physiology 94, nr 5 (1.11.1989): 833–47. http://dx.doi.org/10.1085/jgp.94.5.833.

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Currents through single potassium channels were studied in cell-attached or inside-out patches from collagenase-dispersed smooth muscle cells of the guinea pig taenia coli. Under conditions mimicking the physiological state with [K+]i = 135 mM: [K+]o = 5.4 mM, three distinct types of K+ channel were identified with conductances around 0 mV of 147, 94, and 63 pS. The activities of the 94- and 63-pS channel were observed infrequently. The 147-pS channel was most abundant. It has a reversal potential of approximately -75 mV. It is sensitive to [Ca2+]i and to membrane potential. At -30 mV, the probability of a channel being open is at a minimum. At more positive voltages, the probability follows Boltzman distribution. A 10-fold change in [Ca2+]i causes a 25-mV negative shift of the voltage where half of the channels are open; an 11.3-mV change in membrane potential produces an e-fold increase in the probability of the channel being open when P is low. At voltages between -30 and -50 mV, the open probability increases in an anomalous manner because of a large decrease of the channel closed time without much change in the channel open time. This anomalous activity may play a regulatory role in maintaining the resting potential. The histograms of channel open and closed time fit well, respectively, with single and double exponential distributions. Upon step depolarizations by 100-ms pulses, the 147-pS channel opens with a brief delay. The delay shortens and both the number of open channels and the open time increase with increasing positivity of the potential. The averaged currents during the step depolarizations closely resemble the delayed rectifying outward K+ currents in whole-cell recordings.

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7

Silverå Ejneby, Malin, Björn Wallner i Fredrik Elinder. "Coupling stabilizers open KV1-type potassium channels". Proceedings of the National Academy of Sciences 117, nr 43 (13.10.2020): 27016–21. http://dx.doi.org/10.1073/pnas.2007965117.

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The opening and closing of voltage-gated ion channels are regulated by voltage sensors coupled to a gate that controls the ion flux across the cellular membrane. Modulation of any part of gating constitutes an entry point for pharmacologically regulating channel function. Here, we report on the discovery of a large family of warfarin-like compounds that open the two voltage-gated type 1 potassium (KV1) channels KV1.5 and Shaker, but not the related KV2-, KV4-, or KV7-type channels. These negatively charged compounds bind in the open state to positively charged arginines and lysines between the intracellular ends of the voltage-sensor domains and the pore domain. This mechanism of action resembles that of endogenous channel-opening lipids and opens up an avenue for the development of ion-channel modulators.

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8

Khan, S., i M. K. Khan. "Entanglement of Open Quantum Systems in Noninertial Frames". Open Systems & Information Dynamics 19, nr 02 (czerwiec 2012): 1250013. http://dx.doi.org/10.1142/s1230161212500138.

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We study the effects of decoherence on the entanglement generated by Unruh effect in accelerated frames by using various combinations of an amplitude damping channel, a phase damping channel and a depolarizing channel in the form of multilocal and collective environments. Using concurrence as entanglement quantifier, we show that the occurrence of entanglement sudden death (ESD) depends on different combinations of the channels. The ESD can be avoided under a particular configuration of the channels. We show that the channels can be used to distinguish between a moving and a stationary frame.

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9

Miller, C., R. Latorre i I. Reisin. "Coupling of voltage-dependent gating and Ba++ block in the high-conductance, Ca++-activated K+ channel." Journal of General Physiology 90, nr 3 (1.09.1987): 427–49. http://dx.doi.org/10.1085/jgp.90.3.427.

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Voltage-dependent Ca++-activated K+ channels from rat skeletal muscle were reconstituted into planar lipid bilayers, and the kinetics of block of single channels by Ba++ were studied. The Ba++ association rate varies linearly with the probability of the channel being open, while the dissociation rate follows a rectangular hyperbolic relationship with open-state probability. Ba ions can be occluded within the channel by closing the channel with a strongly hyperpolarizing voltage applied during a Ba++-blocked interval. Occluded Ba ions cannot dissociate from the blocking site until after the channel opens. The ability of the closed channel to occlude Ba++ is used as an assay to study the channel's gating equilibrium in the blocked state. The blocked channel opens and closes in a voltage-dependent process similar to that of the unblocked channel. The presence of a Ba ion destabilizes the closed state of the blocked channel, however, by 1.5 kcal/mol. The results confirm that Ba ions block this channel by binding in the K+-conduction pathway. They further show that the blocking site is inaccessible to Ba++ from both the cytoplasmic and external solutions when the channel is closed.

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10

Nielsen. "The Open Channel". Computer 18, nr 1 (styczeń 1985): 88. http://dx.doi.org/10.1109/mc.1985.1662689.

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11

Patterson i Hennessy. "The Open Channel". Computer 18, nr 11 (listopad 1985): 142–43. http://dx.doi.org/10.1109/mc.1985.1662752.

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12

Colwell, Hitchcock, Jensen, Brinkley Sprunt i Becker. "The Open Channel". Computer 18, nr 12 (grudzień 1985): 93–99. http://dx.doi.org/10.1109/mc.1985.1662784.

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13

Fenwick, Wellck, Lipp i Laws. "The Open Channel". Computer 18, nr 3 (marzec 1985): 112–14. http://dx.doi.org/10.1109/mc.1985.1662837.

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14

Andrews i Feinberg. "The Open Channel". Computer 18, nr 4 (kwiecień 1985): 94–96. http://dx.doi.org/10.1109/mc.1985.1662871.

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15

Nichols. "The Open Channel". Computer 18, nr 5 (maj 1985): 114–15. http://dx.doi.org/10.1109/mc.1985.1662900.

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16

Botting, Siddappa i McClintock. "The Open Channel". Computer 18, nr 8 (sierpień 1985): 95. http://dx.doi.org/10.1109/mc.1985.1662981.

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17

Yellayi, Mohan, Bill Janssen, Daryoush Morshedian i Gilman D. Chesley. "The Open Channel". Computer 19, nr 1 (styczeń 1986): 104–5. http://dx.doi.org/10.1109/mc.1986.1663042.

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18

Horning i Tabak. "The Open Channel". Computer 19, nr 10 (październik 1986): 85–86. http://dx.doi.org/10.1109/mc.1986.1663077.

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19

Jacobs. "The Open Channel". Computer 19, nr 12 (grudzień 1986): 61. http://dx.doi.org/10.1109/mc.1986.1663129.

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20

Almanack. "The Open Channel". Computer 19, nr 3 (marzec 1986): 94–95. http://dx.doi.org/10.1109/mc.1986.1663183.

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21

Sen, Nelson, Kirchner, Tracz i Ludewig. "The Open Channel". Computer 19, nr 6 (czerwiec 1986): 90–91. http://dx.doi.org/10.1109/mc.1986.1663262.

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22

Valentine, Eric M. "Open-Channel Flow". Journal of Hydraulic Engineering 127, nr 9 (wrzesień 2001): 788. http://dx.doi.org/10.1061/(asce)0733-9429(2001)127:9(788).

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23

Sturm,, TW, i J. Tuzson,. "Open Channel Hydraulics". Applied Mechanics Reviews 54, nr 6 (1.11.2001): B107—B108. http://dx.doi.org/10.1115/1.1421122.

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24

Rabbat, G., B. Furht i R. Kibler. "The Open Channel". Computer 21, nr 7 (lipiec 1988): 59–60. http://dx.doi.org/10.1109/2.69.

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25

Guthery. "The Open Channel". Computer 20, nr 1 (styczeń 1987): 115. http://dx.doi.org/10.1109/mc.1987.1663368.

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26

Estell. "The Open Channel". Computer 20, nr 11 (listopad 1987): 90–91. http://dx.doi.org/10.1109/mc.1987.1663419.

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27

Freeman i Drissel. "The Open Channel". Computer 20, nr 2 (luty 1987): 104–5. http://dx.doi.org/10.1109/mc.1987.1663487.

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28

Jordan i Chesley. "The Open Channel". Computer 20, nr 3 (marzec 1987): 80. http://dx.doi.org/10.1109/mc.1987.1663513.

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29

Milutinovic, Milutinovic, Soucek i Estell. "The Open Channel". Computer 20, nr 4 (kwiecień 1987): 81–83. http://dx.doi.org/10.1109/mc.1987.1663541.

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30

Harper i Estell. "The Open Channel". Computer 20, nr 5 (maj 1987): 107–9. http://dx.doi.org/10.1109/mc.1987.1663569.

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31

Tracz i Feinberg. "The Open Channel". Computer 20, nr 6 (czerwiec 1987): 76–77. http://dx.doi.org/10.1109/mc.1987.1663595.

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32

Shaw i Tracz. "The Open Channel". Computer 20, nr 7 (lipiec 1987): 104–5. http://dx.doi.org/10.1109/mc.1987.1663632.

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33

Lansdowne, Cousins i Wilkinson. "The Open Channel". Computer 20, nr 8 (sierpień 1987): 90–91. http://dx.doi.org/10.1109/mc.1987.1663668.

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34

Holmes, N. "The Open Channel". Computer 31, nr 11 (listopad 1998): 121–22. http://dx.doi.org/10.1109/mc.1998.730742.

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35

Fyfe, Gregor K., i Cecilia M. Canessa. "Subunit Composition Determines the Single Channel Kinetics of the Epithelial Sodium Channel". Journal of General Physiology 112, nr 4 (1.10.1998): 423–32. http://dx.doi.org/10.1085/jgp.112.4.423.

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We have further characterized at the single channel level the properties of epithelial sodium channels formed by coexpression of α with either wild-type β or γ subunits and α with carboxy-terminal truncated β (βT) or γ (γT) subunits in Xenopus laevis oocytes. αβ and αβT channels (9.6 and 8.7 pS, respectively, with 150 mM Li+) were found to be constitutively open. Only upon inclusion of 1 μM amiloride in the pipette solution could channel activity be resolved; both channel types had short open and closed times. Mean channel open probability (Po) for αβ was 0.54 and for αβT was 0.50. In comparison, αγ and αγT channels exhibited different kinetics: αγ channels (6.7 pS in Li+) had either long open times with short closings, resulting in a high Po (0.78), or short openings with long closed times, resulting in a low Po (0.16). The mean Po for all αγ channels was 0.48. αγT (6.6 pS in Li+) behaved as a single population of channels with distinct kinetics: mean open time of 1.2 s and closed time of 0.4 s, with a mean Po of 0.6, similar to that of αγ. Inclusion of 0.1 μM amiloride in the pipette solution reduced the mean open time of αγT to 151 ms without significantly altering the closed time. We also examined the kinetics of amiloride block of αβ, αβT (1 μM amiloride), and αγT (0.1 μM amiloride) channels. αβ and αβT had similar blocking and unblocking rate constants, whereas the unblocking rate constant for αγT was 10-fold slower than αβT. Our results indicate that subunit composition of ENaC is a main determinant of Po. In addition, channel kinetics and Po are not altered by carboxy-terminal deletion in the β subunit, whereas a similar deletion in the γ subunit affects channel kinetics but not Po.

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36

Pradhan, Siprarani, Lokesh Dash i Kishanjit Kumar Khatua. "A Critical Review of Turbulence Characteristics in Open Channel Flow". International Journal for Research in Applied Science and Engineering Technology 11, nr 10 (31.10.2023): 441–50. http://dx.doi.org/10.22214/ijraset.2023.56011.

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Abstract: This study subject encompasses a comprehensive evaluation of the available literature on turbulence in open channel flows. Open channel flows are characterized by intricate fluid dynamics, including the production of turbulent eddies and vortices that can profoundly alter transport processes and mixing of diverse fluids. The paper addresses the numerous forms of turbulence that can occur in open channels, such as coherent structures, secondary currents, and bed-generated turbulence. We investigate the elements that determine the intensity and features of these turbulent flows, including channel geometry, flow velocity, fluid properties, and roughness of the channel substrate. The paper also assesses the current theoretical models used to characterise open channel turbulence and the experimental techniques used to quantify and demonstrate turbulent flows in open channels. By critically scrutinising the strengths and limits of the current literature, this review outlines the essential research gaps that need to be addressed to expand our understanding of turbulent open channel flows. This study contributes to the development of enhanced models and techniques for managing and modulating open channel flows in diverse applications.

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37

Sackin, H., i L. G. Palmer. "Basolateral potassium channels in renal proximal tubule". American Journal of Physiology-Renal Physiology 253, nr 3 (1.09.1987): F476—F487. http://dx.doi.org/10.1152/ajprenal.1987.253.3.f476.

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Potassium (K+) channels in the basolateral membrane of unperfused Necturus proximal tubules were studied in both cell-attached and excised patches, after removal of the tubule basement membrane by manual dissection without collagenase. Two different K+ channels were identified on the basis of their kinetics: a short open-time K+ channel, with a mean open time less than 1 ms, and a long open-time K+ channel with a mean open time greater than 20 ms. The short open-time channel occurred more frequently than the longer channel, especially in excised patches. For inside-out excised patches with Cl- replaced by gluconate, the current-voltage relation of the short open-time K+ channel was linear over +/- 60 mV, with a K+-Na+ selectivity of 12 +/- 2 (n = 12), as calculated from the reversal potential with oppositely directed Na+ and K+ gradients. With K-Ringer in the patch pipette and Na-Ringer in the bath, the conductance of the short open-time channel was 47 +/- 2 pS (n = 15) for cell-attached patches, 26 +/- 2 pS (n = 15) for patches excised (inside out) into Na-Ringer, and 36 +/- 6 pS (n = 3) for excised patches with K-Ringer on both sides. These different conductances can be partially explained by a dependence of single-channel conductance on the K+ concentration on the interior side of the membrane. In experiments with a constant K+ gradient across excised patches, large changes in Na+ at the interior side of the membrane produced no change in single-channel conductance, arguing against a direct block of the K+ channel by Na+. Finally, the activity of the short open-time channel was voltage gated, where the mean number of open channels decreased as a linear function of basolateral membrane depolarization for potentials between -60 and 0 mV. Depolarization from -60 to -40 mV decreased the mean number of open K+ channels by 28 +/- 8% (n = 6).

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38

Waldeck, Clemens, Kerstin Vocke, Nicole Ungerer, Stephan Frings i Frank Möhrlen. "Activation and desensitization of the olfactory cAMP-gated transduction channel: identification of functional modules". Journal of General Physiology 134, nr 5 (12.10.2009): 397–408. http://dx.doi.org/10.1085/jgp.200910296.

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Olfactory receptor neurons respond to odor stimulation with a receptor potential that results from the successive activation of cyclic AMP (cAMP)-gated, Ca2+-permeable channels and Ca2+-activated chloride channels. The cAMP-gated channels open at micromolar concentrations of their ligand and are subject to a Ca2+-dependent feedback inhibition by calmodulin. Attempts to understand the operation of these channels have been hampered by the fact that the channel protein is composed of three different subunits, CNGA2, CNGA4, and CNGB1b. Here, we explore the individual role that each subunit plays in the gating process. Using site-directed mutagenesis and patch clamp analysis, we identify three functional modules that govern channel operation: a module that opens the channel, a module that stabilizes the open state at low cAMP concentrations, and a module that mediates rapid Ca2+-dependent feedback inhibition. Each subunit could be assigned to one of these functions that, together, define the gating logic of the olfactory transduction channel.

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39

Trapani, Josef G., Payam Andalib, Joseph F. Consiglio i Stephen J. Korn. "Control of Single Channel Conductance in the Outer Vestibule of the Kv2.1 Potassium Channel". Journal of General Physiology 128, nr 2 (31.07.2006): 231–46. http://dx.doi.org/10.1085/jgp.200509465.

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Current magnitude in Kv2.1 potassium channels is modulated by external [K+]. In contrast to behavior expected from the change in electrochemical driving force, outward current through Kv2.1 channels becomes larger when extracellular [K+] is increased within the physiological range. The mechanism that underlies this unusual property involves the opening of Kv2.1 channels into one of two different outer vestibule conformations, which are defined by their sensitivity to TEA. Channels that open into a TEA-sensitive conformation generate larger macroscopic currents, whereas channels that open into a TEA-insensitive conformation generate smaller macroscopic currents. At higher [K+], more channels open into the TEA-sensitive conformation. In this manuscript, we examined the mechanism by which the conformational change produced a change in current magnitude. We started by testing the simplest hypothesis: that each pharmacologically defined channel conformation produces a different single channel conductance, one smaller and one larger, and that the [K+]-dependent change in current magnitude reflects the [K+]-dependent change in the percentage of channels that open into each of the two conformations. Using single channel and macroscopic recordings, as well as hidden Markov modeling, we were able to quantitatively account for [K+]-dependent regulation of macroscopic current with this model. Combined with previously published work, these results support a model whereby an outer vestibule lysine interferes with K+ flux through the channel, and that the [K+]-dependent change in orientation of this lysine alters single channel conductance by changing the level of this interference. Moreover, these results provide an experimental example of single channel conductance being modulated at the outer end of the conduction pathway by a mechanism that involves channel activation into open states with different outer vestibule conformations.

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40

Weiss, D. S. "Membrane potential modulates the activation of GABA-gated channels". Journal of Neurophysiology 59, nr 2 (1.02.1988): 514–27. http://dx.doi.org/10.1152/jn.1988.59.2.514.

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1. The activity of single gamma-aminobutyric acid (GABA)-gated Cl- channels (GABA = 0.5-2.0 microM) was recorded in inside-out patches of membrane from cultured chick cerebral neurons. 2. The distribution of open intervals of the GABA channel was described by the sum of two exponentials, which suggests the presence of at least two open states of the channel. The time constants of these two components were 0.39 +/- 0.1 and 2.1 +/- 0.9 ms (+/- SD, n = 9). 3. The distribution of shut intervals was described by the sum of either three (n = 5) or four (n = 3) exponentials. This suggests the presence of at least three or four shut states. 4. At all GABA concentrations examined, the activity of the GABA channel decreased over time. This decline in activity was most likely the result of desensitization of the GABA channels. 5. The distribution of open intervals was unchanged during desensitization of the GABA channel. Thus desensitization is not associated with an alteration in either the mean lifetime of the two open states or the relative number of transitions to these two states. Rather, desensitization results from a decrease in the probability of channel opening. 6. There was an e-fold increase in the probability of finding a GABA channel open for every 80 +/- 43 mV (n = 4) of depolarization. The degree of voltage dependence decreased as the GABA channels desensitized. 7. The depolarization-induced increase in open channel probability was not associated with any change in the distribution of open intervals. Thus depolarization does not affect the mean open time of the channel but rather increases the likelihood that it will open. 8. A simple model with three or four shut and two open states is considered for the gating of the GABA channel by the agonist. Possible sites for the voltage dependence within this proposed model are discussed.

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41

Sumiadi, Sumiadi, Bambang Kironoto, Djoko Legono i Istiarto Istiarto. "Bed-Shear Velocity Measurement in Curved Open Channel". Civil and Environmental Science 004, nr 01 (1.04.2021): 093–105. http://dx.doi.org/10.21776/ub.civense.2021.00401.9.

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Generally, the condition of the rivers in Indonesia are alluvial rivers which had meanders, where the change in the river bed topography often occur. One of the parameters associated with changes in the river bed topography is bed-shear velocity, or Reynolds stress. The bed-shear velocity can be calculated by the Reynolds stress distribution method and the Clauser method which commonly used in straight channels. In fact, on natural channel there is a curve and even a meandering channel. With more complex flow conditions, the use of the Clauser method in curved channels can be questioned, is it still accurate or not. In this paper, both methods will be discussed by comparing the measurement data in the laboratory using 180 curved channel with flat bed. The results of data analysis show that the use of these two methods in curved channels produces an average difference of around 19.81%, where the Clauser method gives greater results and better tendencies. Apart from the differences in the results given, it can be said that the Clauser method as well as the Reynolds stress distribution method can still be used to calculate the bed-shear velocity in the curved channel

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42

Latorre, Ramon, Riccardo Olcese, Claudia Basso, Carlos Gonzalez, Fabian Muñoz, Diego Cosmelli i Osvaldo Alvarez. "Molecular Coupling between Voltage Sensor and Pore Opening in the Arabidopsis Inward Rectifier K+ Channel KAT1". Journal of General Physiology 122, nr 4 (29.09.2003): 459–69. http://dx.doi.org/10.1085/jgp.200308818.

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Animal and plant voltage-gated ion channels share a common architecture. They are made up of four subunits and the positive charges on helical S4 segments of the protein in animal K+ channels are the main voltage-sensing elements. The KAT1 channel cloned from Arabidopsis thaliana, despite its structural similarity to animal outward rectifier K+ channels is, however, an inward rectifier. Here we detected KAT1-gating currents due to the existence of an intrinsic voltage sensor in this channel. The measured gating currents evoked in response to hyperpolarizing voltage steps consist of a very fast (τ = 318 ± 34 μs at −180 mV) and a slower component (4.5 ± 0.5 ms at −180 mV) representing charge moved when most channels are closed. The observed gating currents precede in time the ionic currents and they are measurable at voltages (less than or equal to −60) at which the channel open probability is negligible (≈10−4). These two observations, together with the fact that there is a delay in the onset of the ionic currents, indicate that gating charge transits between several closed states before the KAT1 channel opens. To gain insight into the molecular mechanisms that give rise to the gating currents and lead to channel opening, we probed external accessibility of S4 domain residues to methanethiosulfonate-ethyltrimethylammonium (MTSET) in both closed and open cysteine-substituted KAT1 channels. The results demonstrate that the putative voltage–sensing charges of S4 move inward when the KAT1 channels open.

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Alvarez, Osvaldo, Carlos Gonzalez i Ramon Latorre. "COUNTING CHANNELS: A TUTORIAL GUIDE ON ION CHANNEL FLUCTUATION ANALYSIS". Advances in Physiology Education 26, nr 4 (grudzień 2002): 327–41. http://dx.doi.org/10.1152/advan.00006.2002.

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Ion channels open and close in a stochastic fashion, following the laws of probability. However, distinct from tossing a coin or a die, the probability of finding the channel closed or open is not a fixed number but can be modified (i.e., we can cheat) by some external stimulus, such as the voltage. Single-channel records can be obtained using the appropriate electrophysiological technique (e.g., patch clamp), and from these records the open probability and the channel conductance can be calculated. Gathering these parameters from a membrane containing many channels is not straightforward, as the macroscopic current I = iNPo, where i is the single-channel current, N the number of channels, and Po the probability of finding the channel open, cannot be split into its individual components. In this tutorial, using the probabilistic nature of ion channels, we discuss in detail how i, N, and Po max (the maximum open probability) can be obtained using fluctuation (nonstationary noise) analysis (Sigworth FJ. G Gen Physiol 307: 97–129, 1980). We also analyze the sources of possible artifacts in the determination of i and N, such as channel rundown, inadequate filtering, and limited resolution of digital data acquisition by use of a simulation computer program (available at www.cecs.cl ).

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Oh, Y., i D. J. Benos. "Single-channel characteristics of a purified bovine renal amiloride-sensitive Na+ channel in planar lipid bilayers". American Journal of Physiology-Cell Physiology 264, nr 6 (1.06.1993): C1489—C1499. http://dx.doi.org/10.1152/ajpcell.1993.264.6.c1489.

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We have purified an amiloride-inhibitable Na+ channel protein from bovine renal papillae using ion-exchange and immunoaffinity chromatography. In the present study, these purified Na+ channels were reconstituted into planar lipid bilayers, and their single-channel characteristics were studied. We observed both large- and small-conductance Na(+)-selective ion channels in planar lipid bilayers. Single-channel conductance for the large- and small-conductance channels saturated as a function of Na+ concentration. These relations could be fitted by a simple Langmuir isotherm with a Michaelis constant of 55 and 45 mM and a maximum open-state conductance of 56 or 8.4 pS, respectively. Both channels were perfectly cation selective, with a Na(+)-to-K+ permeability ratio of 6.7:1 for the large channel and 7.8:1 for the small channel, and their open single-channel current-voltage relations were linear when bathed with symmetrical Na+ solutions. The percent open time of the reconstituted large or small channels varied between 10 and 50% or 1 and 20%, respectively. After application of amiloride, both the large- and small-conductance Na+ channels were inhibited in a dose-dependent manner.

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45

Setiyadi, S. "Flow velocity behavior programming on open channel bends". IOP Conference Series: Earth and Environmental Science 878, nr 1 (1.10.2021): 012049. http://dx.doi.org/10.1088/1755-1315/878/1/012049.

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Abstract Flow velocity on open channel bends generally experiences additional velocity which is called secondary velocity. This paper aims to analyse and calculate the velocity that occurs in an open channel bend in general. The calculation that the writer uses is the calculation with fortran programming, in a case study of a river that bends, where the variables that must be present are given. The results of calculations and measurements of Secondary Speeds that occur at channel bends in this Open Channel will be very useful for river channel improvement or flood prevention in river channels, especially on existing bends. The conclusion is that at the bend of an open channel or river, there will be an increase in flow velocity in the transverse direction. This additional velocity is caused by the additional secondary velocity, namely the transverse velocity.

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46

Kleyman, Thomas R., i Douglas C. Eaton. "Regulating ENaC’s gate". American Journal of Physiology-Cell Physiology 318, nr 1 (1.01.2020): C150—C162. http://dx.doi.org/10.1152/ajpcell.00418.2019.

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Epithelial Na+ channels (ENaCs) are members of a family of cation channels that function as sensors of the extracellular environment. ENaCs are activated by specific proteases in the biosynthetic pathway and at the cell surface and remove embedded inhibitory tracts, which allows channels to transition to higher open-probability states. Resolved structures of ENaC and an acid-sensing ion channel revealed highly organized extracellular regions. Within the periphery of ENaC subunits are unique domains formed by antiparallel β-strands containing the inhibitory tracts and protease cleavage sites. ENaCs are inhibited by Na+ binding to specific extracellular site(s), which promotes channel transition to a lower open-probability state. Specific inositol phospholipids and channel modification by Cys-palmitoylation enhance channel open probability. How these regulatory factors interact in a concerted manner to influence channel open probability is an important question that has not been resolved. These various factors are reviewed, and the impact of specific factors on human disorders is discussed.

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47

Sayed, Tarek. "An experimental study of branching flow in open channels". Limnological Review 19, nr 2 (1.06.2019): 93–101. http://dx.doi.org/10.2478/limre-2019-0008.

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Abstract Branching channel flow describes any side water withdrawals from rivers or main channels. Branching channels have widespread application in many practical projects, such as irrigation and drainage network systems, water and waste-water treatment plants, and many water resources projects. Therefore, in this research, a comprehensive analysis of laboratory data has been carried out to discover the best angle of branching. The study also aims to introduce simple, practical equations to help engineers of water resources to fix the percentage of discharge diverted to the branch channel. The study was carried out in the Irrigation and hydraulics laboratory of the civil department, Faculty of Engineering, Assiut University. The laboratory channel consisted of two parts, the main channel, and a branch channel. The main channel was 8.0 m in length, 20 cm wide, and 20 cm in depth. The division corner to the branch channel was sharp edged and located 5.0 m downstream of the main channel inlet. The branch channel was 3.0 m long, 20 cm in depth and its width was changed three times (10, 15, and 20 cm) respectively. A total of 84 runs were carried out. Investigations of the flow into the branching channel show that the branching discharge depends on many interlinked parameters. It increases with a decrease of the main channel flow velocity and the Froude number upstream of the branch channel junction. It also increases with an increase in the Yb / Yu ratio. In subcritical flow, water depth in the branch channel is always lower than the main channel water depth. The flow diversion to the branch channel leads to a decrease in water depth downstream of the main channel. In addition, the study showed that the highest discharge rate was obtained when the angle of branching was equal to 45° and then an angle of 60o. While the lowest discharge rate was obtained at an angle of 90°. Furthermore, at Br = 1.0, using a branching angle equal to 45° the discharge ratio (Qr) increases from about 4.42 to 19.01%, more than that obtained with using the branching angle equal 90°, while the discharge ratio (Qr) increases from about 0.52 to 49.18% and 1.51 to 24.79%, at Br = 0.75, and Br = 0.5 respectively.

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48

Hoshi, T., i R. W. Aldrich. "Gating kinetics of four classes of voltage-dependent K+ channels in pheochromocytoma cells." Journal of General Physiology 91, nr 1 (1.01.1988): 107–31. http://dx.doi.org/10.1085/jgp.91.1.107.

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Clonal pheochromocytoma (PC-12) cells have four different types of voltage-dependent K+ channels whose activation does not require high concentrations of Ca++ on the cytoplasmic side of the membrane (Hoshi, T., and R. W. Aldrich, 1988, Journal of General Physiology, 91:73-106). The durations of open and closed events of these four different types of voltage-dependent K+ channels were measured using the excised configuration of the patch-clamp method. The open durations of a class of K+ channels termed the Kz channel, which activates rapidly and inactivates slowly in response to depolarizing pulses, had two exponential components. The closed durations of the Kz channel had at least four exponential components. The time constants of the fastest of the two exponential components in the closed durations were very similar to those of the two exponential components present in the first-latency distribution. The first latencies of the Kz channel decreased steeply with depolarization, contributing to the increased probability of the channel being open with depolarization. The Kz channel also had a very slow gating process that resulted in a clustering of blank sweeps. A gating scheme containing two open states and five closed states is consistent with the observations. The Ky channel had one exponential component in the open durations and three exponential components in the closed durations. The first latencies varied greatly depending on the prepulse voltage and duration. The results were consistent with a sequential model with a large number of closed states and one open state. The Kx channel, which required large hyperpolarizing prepulses to remove steady state inactivation and did not show inactivation with maintained depolarization, had two exponential components in the open durations and three exponential components in the closed durations. The burst behavior of the Kx channel involved many more than two states. The transient Kw channel had one exponential component in the open durations and the mean open time increased with depolarization. The first latencies of the Kw channel were steeply dependent on the voltage, decreasing with depolarization.

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Bao, Hongxia, Atiya Hakeem, Mark Henteleff, John G. Starkus i Martin D. Rayner. "Voltage-insensitive Gating after Charge-neutralizing Mutations in the S4 Segment of Shaker Channels". Journal of General Physiology 113, nr 1 (1.01.1999): 139–51. http://dx.doi.org/10.1085/jgp.113.1.139.

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Shaker channel mutants, in which the first (R362), second (R365), and fourth (R371) basic residues in the S4 segment have been neutralized, are found to pass potassium currents with voltage-insensitive kinetics when expressed in Xenopus oocytes. Single channel recordings clarify that these channels continue to open and close from −160 to +80 mV with a constant opening probability (Po). Although Po is low (∼0.15) in these mutants, mean open time is voltage independent and similar to that of control Shaker channels. Additionally, these mutant channels retain characteristic Shaker channel selectivity, sensitivity to block by 4-aminopyridine, and are partially blocked by external Ca2+ ions at very negative potentials. Furthermore, mean open time is approximately doubled, in both mutant channels and control Shaker channels, when Rb+ is substituted for K+ as the permeant ion species. Such strong similarities between mutant channels and control Shaker channels suggests that the pore region has not been substantially altered by the S4 charge neutralizations. We conclude that single channel kinetics in these mutants may indicate how Shaker channels would behave in the absence of voltage sensor input. Thus, mean open times appear primarily determined by voltage-insensitive transitions close to the open state rather than by voltage sensor movement, even in control, voltage-sensitive Shaker channels. By contrast, the low and voltage-insensitive Po seen in these mutant channels suggests that important determinants of normal channel opening derive from electrostatic coupling between S4 charges and the pore domain.

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Li, Chunyan, i James O’Donnell. "The Effect of Channel Length on the Residual Circulation in Tidally Dominated Channels". Journal of Physical Oceanography 35, nr 10 (1.10.2005): 1826–40. http://dx.doi.org/10.1175/jpo2804.1.

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Abstract With an analytic model, this paper describes the subtidal circulation in tidally dominated channels of different lengths, with arbitrary lateral depth variations. The focus is on an important parameter associated with the reversal of the exchange flows. This parameter (δ) is defined as the ratio between the channel length and one-quarter of the tidal wavelength, which is determined by water depth and tidal frequency. In this study, a standard bottom drag coefficient, CD = 0.0025, is used. For a channel with δ smaller than 0.6–0.7 (short channels), the exchange flow at the open end has an inward transport in deep water and an outward transport in shallow water. This situation is just the opposite of channels with a δ value larger than 0.6–0.7 (long channels). For a channel with a δ value of about 0.35–0.5, the exchange flow at the open end reaches the maximum of a short channel. For a channel with a δ value of about 0.85–1.0, the exchange flow at the open end reaches the maximum of a long channel, with the inward flux of water occurring over the shoal area and the outward flow in the deep-water area. However, near the closed end of a long channel, the exchange flow appears as that in a short channel—that is, the exchange flow changes direction along the channel from the head to the open end of the channel. For a channel with a δ value of about 0.6–0.7, the tidally induced subtidal exchange flow at the open end reaches its minimum when there is little flow across the open end and the water residence time reaches its maximum. The mean sea level increases toward the closed end for all δ values. However, the spatial gradient of the mean sea level in a short channel is much smaller than that of a long channel. The differences between short and long channels are caused by a shift in dynamical balance of momentum or, equivalently, a change in tidal wave characteristics from a progressive wave to a standing wave.

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