Добірка наукової літератури з теми "Current-voltage locus"
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Статті в журналах з теми "Current-voltage locus"
1
Cibulsky, Susan M., and William A. Sather. "The Eeee Locus Is the Sole High-Affinity Ca2+ Binding Structure in the Pore of a Voltage-Gated Ca2+ Channel." Journal of General Physiology 116, no. 3 (August 14, 2000): 349–62. http://dx.doi.org/10.1085/jgp.116.3.349.
Повний текст джерелаАнотація:
Selective permeability in voltage-gated Ca2+ channels is dependent upon a quartet of pore-localized glutamate residues (EEEE locus). The EEEE locus is widely believed to comprise the sole high-affinity Ca2+ binding site in the pore, which represents an overturning of earlier models that had postulated two high-affinity Ca2+ binding sites. The current view is based on site-directed mutagenesis work in which Ca2+ binding affinity was attenuated by single and double substitutions in the EEEE locus, and eliminated by quadruple alanine (AAAA), glutamine (QQQQ), or aspartate (DDDD) substitutions. However, interpretation of the mutagenesis work can be criticized on the grounds that EEEE locus mutations may have additionally disrupted the integrity of a second, non-EEEE locus high-affinity site, and that such a second site may have remained undetected because the mutated pore was probed only from the extracellular pore entrance. Here, we describe the results of experiments designed to test the strength of these criticisms of the single high-affinity locus model of selective permeability in Ca2+ channels. First, substituted-cysteine accessibility experiments indicate that pore structure in the vicinity of the EEEE locus is not extensively disrupted as a consequence of the quadruple AAAA mutations, suggesting in turn that the quadruple mutations do not distort pore structure to such an extent that a second high affinity site would likely be destroyed. Second, the postulated second high-affinity site was not detected by probing from the intracellularly oriented pore entrance of AAAA and QQQQ mutants. Using inside-out patches, we found that, whereas micromolar Ca2+ produced substantial block of outward Li+ current in wild-type channels, internal Ca2+ concentrations up to 1 mM did not produce detectable block of outward Li+ current in the AAAA or QQQQ mutants. These results indicate that the EEEE locus is indeed the sole high-affinity Ca2+ binding locus in the pore of voltage-gated Ca2+ channels.
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Cloues, Robin K., Susan M. Cibulsky, and William A. Sather. "Ion Interactions in the High-Affinity Binding Locus of a Voltage-Gated Ca2+ Channel." Journal of General Physiology 116, no. 4 (September 25, 2000): 569–86. http://dx.doi.org/10.1085/jgp.116.4.569.
Повний текст джерелаАнотація:
The selectivity filter of voltage-gated Ca2+ channels is in part composed of four Glu residues, termed the EEEE locus. Ion selectivity in Ca2+ channels is based on interactions between permeant ions and the EEEE locus: in a mixture of ions, all of which can pass through the pore when present alone, those ions that bind weakly are impermeant, those that bind more strongly are permeant, and those that bind more strongly yet act as pore blockers as a consequence of their low rate of unbinding from the EEEE locus. Thus, competition among ion species is a determining feature of selectivity filter function in Ca2+ channels. Previous work has shown that Asp and Ala substitutions in the EEEE locus reduce ion selectivity by weakening ion binding affinity. Here we describe for wild-type and EEEE locus mutants an analysis at the single channel level of competition between Cd2+, which binds very tightly within the EEEE locus, and Ba2+ or Li+, which bind less tightly and hence exhibit high flux rates: Cd2+ binds to the EEEE locus ∼104× more tightly than does Ba2+, and ∼108× more tightly than does Li+. For wild-type channels, Cd2+ entry into the EEEE locus was 400× faster when Li+ rather than Ba2+ was the current carrier, reflecting the large difference between Ba2+ and Li+ in affinity for the EEEE locus. For the substitution mutants, analysis of Cd2+ block kinetics shows that their weakened ion binding affinity can result from either a reduction in blocker on rate or an enhancement of blocker off rate. Which of these rate effects underlay weakened binding was not specified by the nature of the mutation (Asp vs. Ala), but was instead determined by the valence and affinity of the current-carrying ion (Ba2+ vs. Li+). The dependence of Cd2+ block kinetics upon properties of the current-carrying ion can be understood by considering the number of EEEE locus oxygen atoms available to interact with the different ion pairs.
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Huang, Chien-Jung, Isabelle Favre, and Edward Moczydlowski. "Permeation of Large Tetra-Alkylammonium Cations through Mutant and Wild-Type Voltage-Gated Sodium Channels as Revealed by Relief of Block at High Voltage." Journal of General Physiology 115, no. 4 (April 1, 2000): 435–54. http://dx.doi.org/10.1085/jgp.115.4.435.
Повний текст джерелаАнотація:
Many large organic cations are potent blockers of K+ channels and other cation-selective channels belonging to the P-region superfamily. However, the mechanism by which large hydrophobic cations enter and exit the narrow pores of these proteins is obscure. Previous work has shown that a conserved Lys residue in the DEKA locus of voltage-gated Na+ channels is an important determinant of Na+/K+ discrimination, exclusion of Ca2+, and molecular sieving of organic cations. In this study, we sought to determine whether the Lys(III) residue of the DEKA locus interacts with internal tetra-alkylammonium cations (TAA+) that block Na+ channels in a voltage-dependent fashion. We investigated block by a series of TAA+ cations of the wild-type rat muscle Na+ channel (DEKA) and two different mutants of the DEKA locus, DEAA and DERA, using whole-cell recording. TEA+ and larger TAA+ cations block both wild-type and DEAA channels. However, DEAA exhibits dramatic relief of block by large TAA+ cations as revealed by a positive inflection in the macroscopic I–V curve at voltages greater than +140 mV. Paradoxically, relief of block at high positive voltage is observed for large (e.g., tetrapentylammonium) but not small (e.g., TEA+) symmetrical TAA+ cations. The DEKA wild-type channel and the DERA mutant exhibit a similar relief-of-block phenomenon superimposed on background current rectification. The results indicate: (a) hydrophobic TAA+ cations with a molecular diameter as large as 15 Å can permeate Na+ channels from inside to outside when driven by high positive voltage, and (b) the Lys(III) residue of the DEKA locus is an important determinant of inward rectification and internal block in Na+ channels. From these observations, we suggest that hydrophobic interfaces between subunits, pseudosubunits, or packed helices of P-region channel proteins may function in facilitating blocker access to the pore, and may thus play an important role in the blocking and permeation behavior of large TAA+ cations and potentially other kinds of local anesthetic molecules.
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Puil, E., B. Gimbarzevsky, and R. M. Miura. "Quantification of membrane properties of trigeminal root ganglion neurons in guinea pigs." Journal of Neurophysiology 55, no. 5 (May 1, 1986): 995–1016. http://dx.doi.org/10.1152/jn.1986.55.5.995.
Повний текст джерелаАнотація:
Passive and active (voltage- and time-dependent) membrane properties of trigeminal root ganglion neurons of decerebrate guinea pigs have been determined using frequency-domain analyses of small-amplitude perturbations of membrane voltage. The complex impedance functions of trigeminal ganglion neurons were computed from the ratios of the fast Fourier transforms of the intracellularly recorded voltage response from the neuron and of the input current, which had a defined oscillatory waveform. The impedance magnitude functions and corresponding impedance locus diagrams were fitted with various membrane models such that the passive and active properties were quantified. The complex impedances of less than one-quarter of the 105 neurons which were investigated extensively could be described by the complex impedance function for a simple RC-electrical circuit. In such neurons, the voltage responses to constant-current pulses, using conventional bridge-balance techniques, could be fitted with single exponential curves, also suggesting passive membrane behavior. A nonlinear least-squares fit of the complex impedance function for the simple model to the experimentally observed complex impedance yielded estimates of the resistance of the electrode, and of input capacitance (range, 56 to 490 pF) and input resistance (range, 0.8 to 30 M omega) of the neurons. The majority of trigeminal ganglion neurons were characterized by a resonance in the 50- to 250-Hz bandwidth of their impedance magnitude functions. Such neurons when injected with "large" hyperpolarizing current pulses using bridge-balance techniques showed membrane voltage responses that "sagged" (time-dependent rectification). Also, repetitive firing commonly occurred with depolarizing current pulses; this characteristic of neurons with resonance in their impedance magnitude functions was not observed in neurons with "purely" passive membrane behavior. A nonlinear least-squares fit of a five-parameter impedance fitting function based on a membrane model to the impedance locus diagram of a neuron with resonance yielded estimates of its membrane properties: input capacitance, the time-invariant part of the conductance, the conductance activated by the small oscillatory input current, and the relaxation time constant for this conductance. The ranges of the estimates for input capacitance and input resistance were comparable to the ranges of corresponding properties derived for neurons exhibiting "purely" passive behavior.(ABSTRACT TRUNCATED AT 400 WORDS)
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Sun, Ye-Ming, Isabelle Favre, Laurent Schild, and Edward Moczydlowski. "On the Structural Basis for Size-selective Permeation of Organic Cations through the Voltage-gated Sodium Channel." Journal of General Physiology 110, no. 6 (December 1, 1997): 693–715. http://dx.doi.org/10.1085/jgp.110.6.693.
Повний текст джерелаАнотація:
Recent evidence indicates that ionic selectivity in voltage-gated Na+ channels is mediated by a small number of residues in P-region segments that link transmembrane elements S5 and S6 in each of four homologous domains denoted I, II, III, and IV. Important determinants for this function appear to be a set of conserved charged residues in the first three homologous domains, Asp(I), Glu(II), and Lys(III), located in a region of the pore called the DEKA locus. In this study, we examined several Ala-substitution mutations of these residues for alterations in ionic selectivity, inhibition of macroscopic current by external Ca2+ and H+, and molecular sieving behavior using a series of organic cations ranging in size from ammonium to tetraethylammonium. Whole-cell recording of wild-type and mutant channels of the rat muscle μ1 Na+ channel stably expressed in HEK293 cells was used to compare macroscopic current–voltage behavior in the presence of various external cations and an intracellular reference solution containing Cs+ and very low Ca2+. In particular, we tested the hypothesis that the Lys residue in domain III of the DEKA locus is responsible for restricting the permeation of large organic cations. Mutation of Lys(III) to Ala largely eliminated selectivity among the group IA monovalent alkali cations (Li+, Na+, K+, Rb+, Cs+) and permitted inward current of group IIA divalent cations (Mg2+, Ca2+, Sr2+, Ba2+). This same mutation also resulted in the acquisition of permeability to many large organic cations such as methylammonium, tetramethylammonium, and tetraethylammonium, all of which are impermeant in the native channel. The results lead to the conclusion that charged residues of the DEKA locus play an important role in molecular sieving behavior of the Na+ channel pore, a function that has been previously attributed to a hypothetical region of the channel called the “selectivity filter.” A detailed examination of individual contributions of the Asp(I), Glu(II), and Lys(III) residues and the dependence on molecular size suggests that relative permeability of organic cations is a complex function of the size, charge, and polarity of these residues and cation substrates. As judged by effects on macroscopic conductance, charged residues of the DEKA locus also appear to play a role in the mechanisms of block by external Ca2+ and H+, but are not essential for the positive shift in activation voltage that is produced by these ions.
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Wüstenberg, Daniel G., Milena Boytcheva, Bernd Grünewald, John H. Byrne, Randolf Menzel, and Douglas A. Baxter. "Current- and Voltage-Clamp Recordings and Computer Simulations of Kenyon Cells in the Honeybee." Journal of Neurophysiology 92, no. 4 (October 2004): 2589–603. http://dx.doi.org/10.1152/jn.01259.2003.
Повний текст джерелаАнотація:
The mushroom body of the insect brain is an important locus for olfactory information processing and associative learning. The present study investigated the biophysical properties of Kenyon cells, which form the mushroom body. Current- and voltage-clamp analyses were performed on cultured Kenyon cells from honeybees. Current-clamp analyses indicated that Kenyon cells did not spike spontaneously in vitro. However, spikes could be elicited by current injection in approximately 85% of the cells. Of the cells that produced spikes during a 1-s depolarizing current pulse, approximately 60% exhibited repetitive spiking, whereas the remaining approximately 40% fired a single spike. Cells that spiked repetitively showed little frequency adaptation. However, spikes consistently became broader and smaller during repetitive activity. Voltage-clamp analyses characterized a fast transient Na+ current ( INa), a delayed rectifier K+ current ( IK,V), and a fast transient K+ current ( IK,A). Using the neurosimulator SNNAP, a Hodgkin–Huxley-type model was developed and used to investigate the roles of the different currents during spiking. The model led to the prediction of a slow transient outward current ( IK,ST) that was subsequently identified by reevaluating the voltage-clamp data. Simulations indicated that the primary currents that underlie spiking are INa and IK,V, whereas IK,A and IK,ST primarily determined the responsiveness of the model to stimuli such as constant or oscillatory injections of current.
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Modabbernia, Mohammad Reza, Alireza Akoushideh, and Seyed Yaser Fakhrmoosavi. "Design and Analysis of the Voltage Controller for the Non Isolated Boost DC-DC Convertor." EMITTER International Journal of Engineering Technology 7, no. 1 (June 15, 2019): 14–33. http://dx.doi.org/10.24003/emitter.v7i1.312.
Повний текст джерелаАнотація:
In this paper, a controller has been presented by the root locus method based on the state space average model of the boost switching regulator with all of the converter’s parameters and uncertainties. In this model, the load current is unknown and the inductor, capacitor, diode and active switch are non ideal and have an on-state resistance. Furthermore, an on-state voltage drop has been considered for diode and active switch. By neglecting the load current and assuming the ideal elements the simplified model of the regulator has been caddied out. By these complete and simplified models, a step by step method has been proposed to design a single input single output (SISO), second order controller based on roots locus method. In this regard the controller's electronic circuit has been introduced by operational amplifiers. At the end, by simulation of the complete closed-loop system in MATLAB Simulink environment and comparing its results by the results of the regulator and controller circuits in PLECS, the accuracy of the designed controller performance has been shown.
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Osmanović, S. S., and S. A. Shefner. "gamma-Aminobutyric acid responses in rat locus coeruleus neurones in vitro: a current-clamp and voltage-clamp study." Journal of Physiology 421, no. 1 (February 1, 1990): 151–70. http://dx.doi.org/10.1113/jphysiol.1990.sp017938.
Повний текст джерела
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Mulolani, Francis, Francis Kafata, and Esau Zulu. "Design and Control of a Grid-connected Seven Level Inverter for Photovoltaic Applications." Zambia ICT Journal 3, no. 1 (March 7, 2019): 21–27. http://dx.doi.org/10.33260/zictjournal.v3i1.72.
Повний текст джерелаАнотація:
This paper presents the design and closed-loop current control of a grid connected seven-level, 3-phase diode-clamped multilevel inverter for Photovoltaic (PV) applications. The proposed closed loop current control technique is based on the voltage-oriented proportional integral (PI) controller theory. The modulation technique used is level-shifted-carrier sinusoidal pulse width modulation (SPWM). The gain values of PI controller were selected to achieve good current quality and dynamic response. Grid synchronization was achieved by using a synchronous-reference frame phase-locked loop (SRF-PLL). Matlab/Simulink was used for the control system design and simulation. The simulation results show that a 1.34% total harmonic distortion (THD) of the output current was achieved which is within the allowable current distortion limits by international standards. The stability of the system was analyzed using pole-zero mapping and root locus.
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Zhang, Xiaoli, Ningren Cui, Zhongying Wu, Junda Su, Jyothirmayee S. Tadepalli, Sowmya Sekizar, and Chun Jiang. "Intrinsic membrane properties of locus coeruleus neurons in Mecp2-null mice." American Journal of Physiology-Cell Physiology 298, no. 3 (March 2010): C635—C646. http://dx.doi.org/10.1152/ajpcell.00442.2009.
Повний текст джерелаАнотація:
Rett syndrome caused by mutations in methyl-CpG-binding protein 2 ( Mecp2) gene shows abnormalities in autonomic functions in which brain stem norepinephrinergic systems play an important role. Here we present systematic comparisons of intrinsic membrane properties of locus coeruleus (LC) neurons between Mecp2−/Y and wild-type (WT) mice. Whole cell current clamp was performed in brain slices of 3- to 4-wk-old mice. Mecp2−/Y neurons showed stronger inward rectification and had shorter time constant than WT cells. The former was likely due to overexpression of inward rectifier K+ (Kir)4.1 channel, and the latter was attributable to the smaller cell surface area. The action potential duration was prolonged in Mecp2−/Y cells with an extended rise time. This was associated with a significant reduction in the voltage-activated Na+ current density. After action potentials, >60% Mecp2−/Y neurons displayed fast and medium afterhyperpolarizations (fAHP and mAHP), while nearly 90% WT neurons showed only mAHP. The mAHP amplitude was smaller in Mecp2−/Y neurons. The firing frequency was higher in neurons with mAHP, and the frequency variation was greater in cells with both fAHP and mAHP in Mecp2−/Y mice. Small but significant differences in spike frequency adaptation and delayed excitation were found in Mecp2−/Y neurons. These results indicate that there are several electrophysiological abnormalities in LC neurons of Mecp2−/Y mice, which may contribute to the dysfunction of the norepinephrine system in Rett syndrome.
Дисертації з теми "Current-voltage locus"
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Liaw, Chong-Zhi. "A high power interior permanent magnet alternator for automotive applications." Thesis, 2013. http://hdl.handle.net/2440/83587.
Повний текст джерелаАнотація:
This thesis examines the operation of a 6 kW interior permanent magnet machine as a generator and its use in conjunction with a switched-mode rectifier as a controllable current source. The interior permanent magnet machine was designed for optimum field-weakening performance which allows it to achieve a wide constant-power speed range. This configuration has possible applications in power generation, e.g. as an alternator in automotive electrical systems and in renewable energy systems such as small-scale wind turbines. The thesis starts from a study of the behaviour of the interior PM machine while generating into a three-phase resistive load and also through a rectifier into a voltage source load. Steady-state and dynamic d-q models are developed which describe the machine generation characteristics. The concept of the VI locus is introduced which provides insights into the generating performance of interior PM machines. In particular, the phenomenon of hysteresis in the current versus speed characteristic of highly salient interior PM machines is explained using the VI locus and for the first time is experimentally demonstrated. The steady-state and transient response of the 6 kW interior PM machine while operating with a switched-mode rectifier is modeled and experimentally measured, forming the basis for the design of a closed-loop controller to regulate the output voltage. The experimental performance and stability of the closed-loop system is examined and evaluated. Further improvements to the output power of the system at low speed using a switched-mode rectifier modulation scheme are investigated and a 66% improvement in output power from 2.8 kW to 4.7 kW is experimentally demonstrated.Thesis (Ph.D.) -- University of Adelaide, School of Electrical and Electronic Engineering, 2013
Тези доповідей конференцій з теми "Current-voltage locus"
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Berto, Matteo, Paolo Gherardo Carlet, Virginia Manzolini, and Luigi Alberti. "An Effective Ellipse Fitting Technique of the Current Response Locus to Rotating HF Voltage Injection in IPMSM for Sensorless Rotor Position Estimation." In IECON 2018 - 44th Annual Conference of the IEEE Industrial Electronics Society. IEEE, 2018. http://dx.doi.org/10.1109/iecon.2018.8591855.
Повний текст джерела
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Mastud, Sachin, Mayank Garg, Ramesh Singh, Johnson Samuel, and Suhas Joshi. "Experimental Characterization of Vibration-Assisted Reverse Micro Electrical Discharge Machining (EDM) for Surface Texturing." In ASME 2012 International Manufacturing Science and Engineering Conference collocated with the 40th North American Manufacturing Research Conference and in participation with the International Conference on Tribology Materials and Processing. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/msec2012-7314.
Повний текст джерелаАнотація:
There are several examples in nature where the biological surfaces exhibit unique functional response, such as velcro, fish scale and lotus leaves. The texture on lotus leaf exhibits super-hydrophobicity and self cleaning properties. Lotus leaf has hemispherical protrusions of 20–30 μm in diameters which are randomly distributed over the surface. This work is focused on creating similar textured surfaces on Ti6Al4V rods via a vibration assisted reverse micro Electrical Discharge Machining (R-MEDM) process. Textured surfaces containing micropillars of 40–50 μm in diameter spaced at 35 μm have been created during the process. These textured surfaces are expected to exhibit hydrophobicity and hemocompatibility. To experimentally characterize the process, a full factorial design of experiments has been conducted to analyze the effects of voltage, capacitance, amplitude and frequency of the anode (plate electrode) vibrations on the erosion rate and process stability. The process stability is expressed in terms of the percentages of the normal, open circuit and the short circuit durations in the voltage-current (VI) signature obtained during the process. It has been observed that the normal discharge durations increase with an increase in the amplitude and the frequency of the vibrations. Fabricated texture exhibits hydrophobicity and the measured contact angles in a sessile drop test with water varied between 110 and 115°. Also, the textured surface was subjected to hemotoxicity tests which yielded positive results. Based on these results, it can be seen that the machined textured surface are hydrophobic and biocompatible in nature which could potentially find applications in cardiovascular biomedical implants. In addition, this process has been used to create hierarchical structures comprising of primary and a secondary structure over it to mimic the hierarchical structures found on lotus leaves.