Voltage-Dependent Gating of hERG Potassium Channels

PubMed Central

Cheng, Yen May; Claydon, Tom W.

2012-01-01

The mechanisms by which voltage-gated channels sense changes in membrane voltage and energetically couple this with opening of the ion conducting pore has been the source of significant interest. In voltage-gated potassium (Kv) channels, much of our knowledge in this area comes from Shaker-type channels, for which voltage-dependent gating is quite rapid. In these channels, activation and deactivation are associated with rapid reconfiguration of the voltage-sensing domain unit that is electromechanically coupled, via the S4–S5 linker helix, to the rate-limiting opening of an intracellular pore gate. However, fast voltage-dependent gating kinetics are not typical of all Kv channels, such as Kv11.1 (human ether-à-go-go related gene, hERG), which activates and deactivates very slowly. Compared to Shaker channels, our understanding of the mechanisms underlying slow hERG gating is much poorer. Here, we present a comparative review of the structure–function relationships underlying activation and deactivation gating in Shaker and hERG channels, with a focus on the roles of the voltage-sensing domain and the S4–S5 linker that couples voltage sensor movements to the pore. Measurements of gating current kinetics and fluorimetric analysis of voltage sensor movement are consistent with models suggesting that the hERG activation pathway contains a voltage independent step, which limits voltage sensor transitions. Constraints upon hERG voltage sensor movement may result from loose packing of the S4 helices and additional intra-voltage sensor counter-charge interactions. More recent data suggest that key amino acid differences in the hERG voltage-sensing unit and S4–S5 linker, relative to fast activating Shaker-type Kv channels, may also contribute to the increased stability of the resting state of the voltage sensor. PMID:22586397

The tarantula toxins ProTx-II and huwentoxin-IV differentially interact with human Nav1.7 voltage sensors to inhibit channel activation and inactivation.

PubMed

Xiao, Yucheng; Blumenthal, Kenneth; Jackson, James O; Liang, Songping; Cummins, Theodore R

2010-12-01

The voltage-gated sodium channel Na(v)1.7 plays a crucial role in pain, and drugs that inhibit hNa(v)1.7 may have tremendous therapeutic potential. ProTx-II and huwentoxin-IV (HWTX-IV), cystine knot peptides from tarantula venoms, preferentially block hNa(v)1.7. Understanding the interactions of these toxins with sodium channels could aid the development of novel pain therapeutics. Whereas both ProTx-II and HWTX-IV have been proposed to preferentially block hNa(v)1.7 activation by trapping the domain II voltage-sensor in the resting configuration, we show that specific residues in the voltage-sensor paddle of domain II play substantially different roles in determining the affinities of these toxins to hNa(v)1.7. The mutation E818C increases ProTx-II's and HWTX-IV's IC(50) for block of hNa(v)1.7 currents by 4- and 400-fold, respectively. In contrast, the mutation F813G decreases ProTx-II affinity by 9-fold but has no effect on HWTX-IV affinity. It is noteworthy that we also show that ProTx-II, but not HWTX-IV, preferentially interacts with hNa(v)1.7 to impede fast inactivation by trapping the domain IV voltage-sensor in the resting configuration. Mutations E1589Q and T1590K in domain IV each decreased ProTx-II's IC(50) for impairment of fast inactivation by ~6-fold. In contrast mutations D1586A and F1592A in domain-IV increased ProTx-II's IC(50) for impairment of fast inactivation by ~4-fold. Our results show that whereas ProTx-II and HWTX-IV binding determinants on domain-II may overlap, domain II plays a much more crucial role for HWTX-IV, and contrary to what has been proposed to be a guiding principle of sodium channel pharmacology, molecules do not have to exclusively target the domain IV voltage-sensor to influence sodium channel inactivation.

Potential role of voltage-sensing phosphatases in regulation of cell structure through the production of PI(3,4)P2.

PubMed

Yamaguchi, Shinji; Kurokawa, Tatsuki; Taira, Ikuko; Aoki, Naoya; Sakata, Souhei; Okamura, Yasushi; Homma, Koichi J

2014-04-01

Voltage-sensing phosphatase, VSP, consists of the transmembrane domain, operating as the voltage sensor, and the cytoplasmic domain with phosphoinositide-phosphatase activities. The voltage sensor tightly couples with the cytoplasmic phosphatase and membrane depolarization induces dephosphorylation of several species of phosphoinositides. VSP gene is conserved from urochordate to human. There are some diversities among VSP ortholog proteins; range of voltage of voltage sensor motions as well as substrate selectivity. In contrast with recent understandings of biophysical mechanisms of VSPs, little is known about its physiological roles. Here we report that chick ortholog of VSP (designated as Gg-VSP) induces morphological feature of cell process outgrowths with round cell body in DF-1 fibroblasts upon its forced expression. Expression of the voltage sensor mutant, Gg-VSPR153Q with shifted voltage dependence to a lower voltage led to more frequent changes of cell morphology than the wild-type protein. Coexpression of PTEN that dephosphorylates PI(3,4)P2 suppressed this effect by Gg-VSP, indicating that the increase of PI(3,4)P2 leads to changes of cell shape. In addition, visualization of PI(3,4)P2 with the fluorescent protein fused with the TAPP1-derived pleckstrin homology (PH) domain suggested that Gg-VSP influenced the distribution of PI(3,4)P2 . These findings raise a possibility that one of the VSP's functions could be to regulate cell morphology through voltage-sensitive tuning of phosphoinositide profile. © 2013 Wiley Periodicals, Inc.

Gating mechanism of Kv11.1 (hERG) K+ channels without covalent connection between voltage sensor and pore domains.

PubMed

de la Peña, Pilar; Domínguez, Pedro; Barros, Francisco

2018-03-01

Kv11.1 (hERG, KCNH2) is a voltage-gated potassium channel crucial in setting the cardiac rhythm and the electrical behaviour of several non-cardiac cell types. Voltage-dependent gating of Kv11.1 can be reconstructed from non-covalently linked voltage sensing and pore modules (split channels), challenging classical views of voltage-dependent channel activation based on a S4-S5 linker acting as a rigid mechanical lever to open the gate. Progressive displacement of the split position from the end to the beginning of the S4-S5 linker induces an increasing negative shift in activation voltage dependence, a reduced z g value and a more negative ΔG 0 for current activation, an almost complete abolition of the activation time course sigmoid shape and a slowing of the voltage-dependent deactivation. Channels disconnected at the S4-S5 linker near the S4 helix show a destabilization of the closed state(s). Furthermore, the isochronal ion current mode shift magnitude is clearly reduced in the different splits. Interestingly, the progressive modifications of voltage dependence activation gating by changing the split position are accompanied by a shift in the voltage-dependent availability to a methanethiosulfonate reagent of a Cys introduced at the upper S4 helix. Our data demonstrate for the first time that alterations in the covalent connection between the voltage sensor and the pore domains impact on the structural reorganizations of the voltage sensor domain. Also, they support the hypothesis that the S4-S5 linker integrates signals coming from other cytoplasmic domains that constitute either an important component or a crucial regulator of the gating machinery in Kv11.1 and other KCNH channels.

Reciprocal voltage sensor-to-pore coupling leads to potassium channel C-type inactivation

PubMed Central

Conti, Luca; Renhorn, Jakob; Gabrielsson, Anders; Turesson, Fredrik; Liin, Sara I; Lindahl, Erik; Elinder, Fredrik

2016-01-01

Voltage-gated potassium channels open at depolarized membrane voltages. A prolonged depolarization causes a rearrangement of the selectivity filter which terminates the conduction of ions – a process called slow or C-type inactivation. How structural rearrangements in the voltage-sensor domain (VSD) cause alteration in the selectivity filter, and vice versa, are not fully understood. We show that pulling the pore domain of the Shaker potassium channel towards the VSD by a Cd2+ bridge accelerates C-type inactivation. Molecular dynamics simulations show that such pulling widens the selectivity filter and disrupts the K+ coordination, a hallmark for C-type inactivation. An engineered Cd2+ bridge within the VSD also affect C-type inactivation. Conversely, a pore domain mutation affects VSD gating-charge movement. Finally, C-type inactivation is caused by the concerted action of distant amino acid residues in the pore domain. All together, these data suggest a reciprocal communication between the pore domain and the VSD in the extracellular portion of the channel. PMID:27278891

Reciprocal voltage sensor-to-pore coupling leads to potassium channel C-type inactivation

NASA Astrophysics Data System (ADS)

Conti, Luca; Renhorn, Jakob; Gabrielsson, Anders; Turesson, Fredrik; Liin, Sara I.; Lindahl, Erik; Elinder, Fredrik

2016-06-01

Voltage-gated potassium channels open at depolarized membrane voltages. A prolonged depolarization causes a rearrangement of the selectivity filter which terminates the conduction of ions - a process called slow or C-type inactivation. How structural rearrangements in the voltage-sensor domain (VSD) cause alteration in the selectivity filter, and vice versa, are not fully understood. We show that pulling the pore domain of the Shaker potassium channel towards the VSD by a Cd2+ bridge accelerates C-type inactivation. Molecular dynamics simulations show that such pulling widens the selectivity filter and disrupts the K+ coordination, a hallmark for C-type inactivation. An engineered Cd2+ bridge within the VSD also affect C-type inactivation. Conversely, a pore domain mutation affects VSD gating-charge movement. Finally, C-type inactivation is caused by the concerted action of distant amino acid residues in the pore domain. All together, these data suggest a reciprocal communication between the pore domain and the VSD in the extracellular portion of the channel.

Local anesthetics disrupt energetic coupling between the voltage-sensing segments of a sodium channel.

PubMed

Muroi, Yukiko; Chanda, Baron

2009-01-01

Local anesthetics block sodium channels in a state-dependent fashion, binding with higher affinity to open and/or inactivated states. Gating current measurements show that local anesthetics immobilize a fraction of the gating charge, suggesting that the movement of voltage sensors is modified when a local anesthetic binds to the pore of the sodium channel. Here, using voltage clamp fluorescence measurements, we provide a quantitative description of the effect of local anesthetics on the steady-state behavior of the voltage-sensing segments of a sodium channel. Lidocaine and QX-314 shifted the midpoints of the fluorescence-voltage (F-V) curves of S4 domain III in the hyperpolarizing direction by 57 and 65 mV, respectively. A single mutation in the S6 of domain IV (F1579A), a site critical for local anesthetic block, abolished the effect of QX-314 on the voltage sensor of domain III. Both local anesthetics modestly shifted the F-V relationships of S4 domain IV toward hyperpolarized potentials. In contrast, the F-V curve of the S4 domain I was shifted by 11 mV in the depolarizing direction upon QX-314 binding. These antagonistic effects of the local anesthetic indicate that the drug modifies the coupling between the voltage-sensing domains of the sodium channel. Our findings suggest a novel role of local anesthetics in modulating the gating apparatus of the sodium channel.

Induction of divalent cation permeability by heterologous expression of a voltage sensor domain.

PubMed

Arima, Hiroki; Tsutsui, Hidekazu; Sakamoto, Ayako; Yoshida, Manabu; Okamura, Yasushi

2018-01-06

The voltage sensor domain (VSD) is a protein domain that confers sensitivity to membrane potential in voltage-gated ion channels as well as the voltage-sensing phosphatase. Although VSDs have long been considered to function as regulatory units acting on adjacent effectors, recent studies have revealed the existence of direct ion permeation paths in some mutated VSDs and in the voltage-gated proton channel. In this study, we show that calcium currents are evoked upon membrane hyperpolarization in cells expressing a VSD derived from an ascidian voltage-gated ion channel superfamily. Unlike the previously reported omega-pore in the Shaker K + channel and rNav1.4, mutations are not required. From electrophysiological experiments in heterologous expression systems, we found that the conductance is directly mediated by the VSD itself and is carried by both monovalent and divalent cations. This is the first report of divalent cation permeation through a VSD-like structure. Copyright © 2018 Elsevier B.V. All rights reserved.

Structure and hydration of membranes embedded with voltage-sensing domains.

PubMed

Krepkiy, Dmitriy; Mihailescu, Mihaela; Freites, J Alfredo; Schow, Eric V; Worcester, David L; Gawrisch, Klaus; Tobias, Douglas J; White, Stephen H; Swartz, Kenton J

2009-11-26

Despite the growing number of atomic-resolution membrane protein structures, direct structural information about proteins in their native membrane environment is scarce. This problem is particularly relevant in the case of the highly charged S1-S4 voltage-sensing domains responsible for nerve impulses, where interactions with the lipid bilayer are critical for the function of voltage-activated ion channels. Here we use neutron diffraction, solid-state nuclear magnetic resonance (NMR) spectroscopy and molecular dynamics simulations to investigate the structure and hydration of bilayer membranes containing S1-S4 voltage-sensing domains. Our results show that voltage sensors adopt transmembrane orientations and cause a modest reshaping of the surrounding lipid bilayer, and that water molecules intimately interact with the protein within the membrane. These structural findings indicate that voltage sensors have evolved to interact with the lipid membrane while keeping energetic and structural perturbations to a minimum, and that water penetrates the membrane, to hydrate charged residues and shape the transmembrane electric field.

Structure and hydration of membranes embedded with voltage-sensing domains

PubMed Central

Krepkiy, Dmitriy; Mihailescu, Mihaela; Freites, J. Alfredo; Schow, Eric V.; Worcester, David L.; Gawrisch, Klaus; Tobias, Douglas; White, Stephen H.; Swartz, Kenton J.

2009-01-01

Despite the growing number of atomic-resolution membrane protein structures, direct structural information about proteins in their native membrane environment is scarce. This problem is particularly relevant in the case of the highly-charged S1–S4 voltage-sensing domains responsible for nerve impulses, where interactions with the lipid bilayer are critical for the function of voltage-activated potassium channels. Here we use neutron diffraction, solid-state nuclear magnetic resonance spectroscopy, and molecular dynamics simulations to investigate the structure and hydration of bilayer membranes containing S1–S4 voltage-sensing domains. Our results show that voltage sensors adopt transmembrane orientations, cause a modest reshaping of the surrounding lipid bilayer, and that water molecules intimately interact with the protein within the membrane. These structural findings reveal that voltage sensors have evolved to interact with the lipid membrane while keeping the energetic and structural perturbations to a minimum, and that water penetrates into the membrane to hydrate charged residues and shape the transmembrane electric field. PMID:19940918

Temporal Dynamics of Microbial Rhodopsin Fluorescence Reports Absolute Membrane Voltage

PubMed Central

Hou, Jennifer H.; Venkatachalam, Veena; Cohen, Adam E.

2014-01-01

Plasma membrane voltage is a fundamentally important property of a living cell; its value is tightly coupled to membrane transport, the dynamics of transmembrane proteins, and to intercellular communication. Accurate measurement of the membrane voltage could elucidate subtle changes in cellular physiology, but existing genetically encoded fluorescent voltage reporters are better at reporting relative changes than absolute numbers. We developed an Archaerhodopsin-based fluorescent voltage sensor whose time-domain response to a stepwise change in illumination encodes the absolute membrane voltage. We validated this sensor in human embryonic kidney cells. Measurements were robust to variation in imaging parameters and in gene expression levels, and reported voltage with an absolute accuracy of 10 mV. With further improvements in membrane trafficking and signal amplitude, time-domain encoding of absolute voltage could be applied to investigate many important and previously intractable bioelectric phenomena. PMID:24507604

Functional diversity of voltage-sensing phosphatases in two urodele amphibians.

PubMed

Mutua, Joshua; Jinno, Yuka; Sakata, Souhei; Okochi, Yoshifumi; Ueno, Shuichi; Tsutsui, Hidekazu; Kawai, Takafumi; Iwao, Yasuhiro; Okamura, Yasushi

2014-07-16

Voltage-sensing phosphatases (VSPs) share the molecular architecture of the voltage sensor domain (VSD) with voltage-gated ion channels and the phosphoinositide phosphatase region with the phosphatase and tensin homolog (PTEN), respectively. VSPs enzymatic activities are regulated by the motions of VSD upon depolarization. The physiological role of these proteins has remained elusive, and insights may be gained by investigating biological variations in different animal species. Urodele amphibians are vertebrates with potent activities of regeneration and also show diverse mechanisms of polyspermy prevention. We cloned cDNAs of VSPs from the testes of two urodeles; Hynobius nebulosus and Cynops pyrrhogaster, and compared their expression and voltage-dependent activation. Their molecular architecture is highly conserved in both Hynobius VSP (Hn-VSP) and Cynops VSP (Cp-VSP), including the positively-charged arginine residues in the S4 segment of the VSD and the enzymatic active site for substrate binding, yet the C-terminal C2 domain of Hn-VSP is significantly shorter than that of Cp-VSP and other VSP orthologs. RT-PCR analysis showed that gene expression pattern was distinct between two VSPs. The voltage sensor motions and voltage-dependent phosphatase activities were investigated electrophysiologically by expression in Xenopus oocytes. Both VSPs showed "sensing" currents, indicating that their voltage sensor domains are functional. The phosphatase activity of Cp-VSP was found to be voltage dependent, as shown by its ability to regulate the conductance of coexpressed GIRK2 channels, but Hn-VSP lacked such phosphatase activity due to the truncation of its C2 domain. © 2014 The Authors. Physiological Reports published by Wiley Periodicals, Inc. on behalf of the American Physiological Society and The Physiological Society.

Sensing voltage across lipid membranes

PubMed Central

Swartz, Kenton J.

2009-01-01

The detection of electrical potentials across lipid bilayers by specialized membrane proteins is required for many fundamental cellular processes such as the generation and propagation of nerve impulses. These membrane proteins possess modular voltage-sensing domains, a notable example being the S1-S4 domains of voltage-activated ion channels. Ground-breaking structural studies on these domains explain how voltage sensors are designed and reveal important interactions with the surrounding lipid membrane. Although further structures are needed to fully understand the conformational changes that occur during voltage sensing, the available data help to frame several key concepts that are fundamental to the mechanism of voltage sensing. PMID:19092925

Voltage-dependent motion of the catalytic region of voltage-sensing phosphatase monitored by a fluorescent amino acid

PubMed Central

Sakata, Souhei; Jinno, Yuka; Kawanabe, Akira; Okamura, Yasushi

2016-01-01

The cytoplasmic region of voltage-sensing phosphatase (VSP) derives the voltage dependence of its catalytic activity from coupling to a voltage sensor homologous to that of voltage-gated ion channels. To assess the conformational changes in the cytoplasmic region upon activation of the voltage sensor, we genetically incorporated a fluorescent unnatural amino acid, 3-(6-acetylnaphthalen-2-ylamino)-2-aminopropanoic acid (Anap), into the catalytic region of Ciona intestinalis VSP (Ci-VSP). Measurements of Anap fluorescence under voltage clamp in Xenopus oocytes revealed that the catalytic region assumes distinct conformations dependent on the degree of voltage-sensor activation. FRET analysis showed that the catalytic region remains situated beneath the plasma membrane, irrespective of the voltage level. Moreover, Anap fluorescence from a membrane-facing loop in the C2 domain showed a pattern reflecting substrate turnover. These results indicate that the voltage sensor regulates Ci-VSP catalytic activity by causing conformational changes in the entire catalytic region, without changing their distance from the plasma membrane. PMID:27330112

Voltage-dependent motion of the catalytic region of voltage-sensing phosphatase monitored by a fluorescent amino acid.

PubMed

Sakata, Souhei; Jinno, Yuka; Kawanabe, Akira; Okamura, Yasushi

2016-07-05

The cytoplasmic region of voltage-sensing phosphatase (VSP) derives the voltage dependence of its catalytic activity from coupling to a voltage sensor homologous to that of voltage-gated ion channels. To assess the conformational changes in the cytoplasmic region upon activation of the voltage sensor, we genetically incorporated a fluorescent unnatural amino acid, 3-(6-acetylnaphthalen-2-ylamino)-2-aminopropanoic acid (Anap), into the catalytic region of Ciona intestinalis VSP (Ci-VSP). Measurements of Anap fluorescence under voltage clamp in Xenopus oocytes revealed that the catalytic region assumes distinct conformations dependent on the degree of voltage-sensor activation. FRET analysis showed that the catalytic region remains situated beneath the plasma membrane, irrespective of the voltage level. Moreover, Anap fluorescence from a membrane-facing loop in the C2 domain showed a pattern reflecting substrate turnover. These results indicate that the voltage sensor regulates Ci-VSP catalytic activity by causing conformational changes in the entire catalytic region, without changing their distance from the plasma membrane.

Deletion of cytosolic gating ring decreases gate and voltage sensor coupling in BK channels.

PubMed

Zhang, Guohui; Geng, Yanyan; Jin, Yakang; Shi, Jingyi; McFarland, Kelli; Magleby, Karl L; Salkoff, Lawrence; Cui, Jianmin

2017-03-06

Large conductance Ca 2+ -activated K + channels (BK channels) gate open in response to both membrane voltage and intracellular Ca 2+ The channel is formed by a central pore-gate domain (PGD), which spans the membrane, plus transmembrane voltage sensors and a cytoplasmic gating ring that acts as a Ca 2+ sensor. How these voltage and Ca 2+ sensors influence the common activation gate, and interact with each other, is unclear. A previous study showed that a BK channel core lacking the entire cytoplasmic gating ring (Core-MT) was devoid of Ca 2+ activation but retained voltage sensitivity (Budelli et al. 2013. Proc. Natl. Acad. Sci. USA http://dx.doi.org/10.1073/pnas.1313433110). In this study, we measure voltage sensor activation and pore opening in this Core-MT channel over a wide range of voltages. We record gating currents and find that voltage sensor activation in this truncated channel is similar to WT but that the coupling between voltage sensor activation and gating of the pore is reduced. These results suggest that the gating ring, in addition to being the Ca 2+ sensor, enhances the effective coupling between voltage sensors and the PGD. We also find that removal of the gating ring alters modulation of the channels by the BK channel's β1 and β2 subunits. © 2017 Zhang et al.

Deletion of cytosolic gating ring decreases gate and voltage sensor coupling in BK channels

PubMed Central

Zhang, Guohui; Shi, Jingyi; McFarland, Kelli; Magleby, Karl L.; Salkoff, Lawrence

2017-01-01

Large conductance Ca2+-activated K+ channels (BK channels) gate open in response to both membrane voltage and intracellular Ca2+. The channel is formed by a central pore-gate domain (PGD), which spans the membrane, plus transmembrane voltage sensors and a cytoplasmic gating ring that acts as a Ca2+ sensor. How these voltage and Ca2+ sensors influence the common activation gate, and interact with each other, is unclear. A previous study showed that a BK channel core lacking the entire cytoplasmic gating ring (Core-MT) was devoid of Ca2+ activation but retained voltage sensitivity (Budelli et al. 2013. Proc. Natl. Acad. Sci. USA. http://dx.doi.org/10.1073/pnas.1313433110). In this study, we measure voltage sensor activation and pore opening in this Core-MT channel over a wide range of voltages. We record gating currents and find that voltage sensor activation in this truncated channel is similar to WT but that the coupling between voltage sensor activation and gating of the pore is reduced. These results suggest that the gating ring, in addition to being the Ca2+ sensor, enhances the effective coupling between voltage sensors and the PGD. We also find that removal of the gating ring alters modulation of the channels by the BK channel’s β1 and β2 subunits. PMID:28196879

Inter-subunit interactions across the upper voltage sensing-pore domain interface contribute to the concerted pore opening transition of Kv channels.

PubMed

Shem-Ad, Tzilhav; Irit, Orr; Yifrach, Ofer

2013-01-01

The tight electro-mechanical coupling between the voltage-sensing and pore domains of Kv channels lies at the heart of their fundamental roles in electrical signaling. Structural data have identified two voltage sensor pore inter-domain interaction surfaces, thus providing a framework to explain the molecular basis for the tight coupling of these domains. While the contribution of the intra-subunit lower domain interface to the electro-mechanical coupling that underlies channel opening is relatively well understood, the contribution of the inter-subunit upper interface to channel gating is not yet clear. Relying on energy perturbation and thermodynamic coupling analyses of tandem-dimeric Shaker Kv channels, we show that mutation of upper interface residues from both sides of the voltage sensor-pore domain interface stabilizes the closed channel state. These mutations, however, do not affect slow inactivation gating. We, moreover, find that upper interface residues form a network of state-dependent interactions that stabilize the open channel state. Finally, we note that the observed residue interaction network does not change during slow inactivation gating. The upper voltage sensing-pore interaction surface thus only undergoes conformational rearrangements during channel activation gating. We suggest that inter-subunit interactions across the upper domain interface mediate allosteric communication between channel subunits that contributes to the concerted nature of the late pore opening transition of Kv channels.

Coupling interactions between voltage sensors of the sodium channel as revealed by site-specific measurements.

PubMed

Chanda, Baron; Asamoah, Osei Kwame; Bezanilla, Francisco

2004-03-01

The voltage-sensing S4 segments in the sodium channel undergo conformational rearrangements in response to changes in the electric field. However, it remains unclear whether these structures move independently or in a coordinated manner. Previously, site-directed fluorescence measurements were shown to track S4 transitions in each of the four domains. Here, using a similar technique, we provide direct evidence of coupling interactions between voltage sensors in the sodium channel. Pairwise interactions between S4s were evaluated by comparing site-specific conformational changes in the presence and absence of a gating perturbation in a distal domain. Reciprocity of effect, a fundamental property of thermodynamically coupled systems, was measured by generating converse mutants. The magnitude of a local gating perturbation induced by a remote S4 mutation depends on the coupling strength and the relative equilibrium positions of the two voltage sensors. In general, our data indicates that the movement of all four voltage sensors in the sodium channel are coupled to a varying extent. Moreover, a gating perturbation in S4-DI has the largest effect on the activation of S4-DIV and vice versa, demonstrating an energetic linkage between S4-DI and S4-DIV. This result suggests a physical mechanism by which the activation and inactivation process may be coupled in voltage-gated sodium channels. In addition, we propose that cooperative interactions between voltage sensors may be the mechanistic basis for the fast activation kinetics of the sodium channel.

Multiple pore conformations driven by asynchronous movements of voltage sensors in a eukaryotic sodium channel

PubMed Central

Goldschen-Ohm, Marcel P.; Capes, Deborah L.; Oelstrom, Kevin M.; Chanda, Baron

2013-01-01

Voltage-dependent Na+ channels are crucial for electrical signalling in excitable cells. Membrane depolarization initiates asynchronous movements in four non-identical voltage-sensing domains of the Na+ channel. It remains unclear to what extent this structural asymmetry influences pore gating as compared with outwardly rectifying K+ channels, where channel opening results from a final concerted transition of symmetric pore gates. Here we combine single channel recordings, cysteine accessibility and voltage clamp fluorimetry to probe the relationships between voltage sensors and pore conformations in an inactivation deficient Nav1.4 channel. We observe three distinct conductance levels such that DI-III voltage sensor activation is kinetically correlated with formation of a fully open pore, whereas DIV voltage sensor movement underlies formation of a distinct subconducting pore conformation preceding inactivation in wild-type channels. Our experiments reveal that pore gating in sodium channels involves multiple transitions driven by asynchronous movements of voltage sensors. These findings shed new light on the mechanism of coupling between activation and fast inactivation in voltage-gated sodium channels. PMID:23322038

Two separate interfaces between the voltage sensor and pore are required for the function of voltage-dependent K(+) channels.

PubMed

Lee, Seok-Yong; Banerjee, Anirban; MacKinnon, Roderick

2009-03-03

Voltage-dependent K(+) (Kv) channels gate open in response to the membrane voltage. To further our understanding of how cell membrane voltage regulates the opening of a Kv channel, we have studied the protein interfaces that attach the voltage-sensor domains to the pore. In the crystal structure, three physical interfaces exist. Only two of these consist of amino acids that are co-evolved across the interface between voltage sensor and pore according to statistical coupling analysis of 360 Kv channel sequences. A first co-evolved interface is formed by the S4-S5 linkers (one from each of four voltage sensors), which form a cuff surrounding the S6-lined pore opening at the intracellular surface. The crystal structure and published mutational studies support the hypothesis that the S4-S5 linkers convert voltage-sensor motions directly into gate opening and closing. A second co-evolved interface forms a small contact surface between S1 of the voltage sensor and the pore helix near the extracellular surface. We demonstrate through mutagenesis that this interface is necessary for the function and/or structure of two different Kv channels. This second interface is well positioned to act as a second anchor point between the voltage sensor and the pore, thus allowing efficient transmission of conformational changes to the pore's gate.

A distinct sodium channel voltage-sensor locus determines insect selectivity of the spider toxin Dc1a.

PubMed

Bende, Niraj S; Dziemborowicz, Sławomir; Mobli, Mehdi; Herzig, Volker; Gilchrist, John; Wagner, Jordan; Nicholson, Graham M; King, Glenn F; Bosmans, Frank

2014-07-11

β-Diguetoxin-Dc1a (Dc1a) is a toxin from the desert bush spider Diguetia canities that incapacitates insects at concentrations that are non-toxic to mammals. Dc1a promotes opening of German cockroach voltage-gated sodium (Nav) channels (BgNav1), whereas human Nav channels are insensitive. Here, by transplanting commonly targeted S3b-S4 paddle motifs within BgNav1 voltage sensors into Kv2.1, we find that Dc1a interacts with the domain II voltage sensor. In contrast, Dc1a has little effect on sodium currents mediated by PaNav1 channels from the American cockroach even though their domain II paddle motifs are identical. When exploring regions responsible for PaNav1 resistance to Dc1a, we identified two residues within the BgNav1 domain II S1-S2 loop that when mutated to their PaNav1 counterparts drastically reduce toxin susceptibility. Overall, our results reveal a distinct region within insect Nav channels that helps determine Dc1a sensitivity, a concept that will be valuable for the design of insect-selective insecticides.

Substitutions in the domain III voltage-sensing module enhance the sensitivity of an insect sodium channel to a scorpion beta-toxin.

PubMed

Song, Weizhong; Du, Yuzhe; Liu, Zhiqi; Luo, Ningguang; Turkov, Michael; Gordon, Dalia; Gurevitz, Michael; Goldin, Alan L; Dong, Ke

2011-05-06

Scorpion β-toxins bind to the extracellular regions of the voltage-sensing module of domain II and to the pore module of domain III in voltage-gated sodium channels and enhance channel activation by trapping and stabilizing the voltage sensor of domain II in its activated state. We investigated the interaction of a highly potent insect-selective scorpion depressant β-toxin, Lqh-dprIT(3), from Leiurus quinquestriatus hebraeus with insect sodium channels from Blattella germanica (BgNa(v)). Like other scorpion β-toxins, Lqh-dprIT(3) shifts the voltage dependence of activation of BgNa(v) channels expressed in Xenopus oocytes to more negative membrane potentials but only after strong depolarizing prepulses. Notably, among 10 BgNa(v) splice variants tested for their sensitivity to the toxin, only BgNa(v)1-1 was hypersensitive due to an L1285P substitution in IIIS1 resulting from a U-to-C RNA-editing event. Furthermore, charge reversal of a negatively charged residue (E1290K) at the extracellular end of IIIS1 and the two innermost positively charged residues (R4E and R5E) in IIIS4 also increased the channel sensitivity to Lqh-dprIT(3). Besides enhancement of toxin sensitivity, the R4E substitution caused an additional 20-mV negative shift in the voltage dependence of activation of toxin-modified channels, inducing a unique toxin-modified state. Our findings provide the first direct evidence for the involvement of the domain III voltage-sensing module in the action of scorpion β-toxins. This hypersensitivity most likely reflects an increase in IIS4 trapping via allosteric mechanisms, suggesting coupling between the voltage sensors in neighboring domains during channel activation.

Global versus local mechanisms of temperature sensing in ion channels.

PubMed

Arrigoni, Cristina; Minor, Daniel L

2018-05-01

Ion channels turn diverse types of inputs, ranging from neurotransmitters to physical forces, into electrical signals. Channel responses to ligands generally rely on binding to discrete sensor domains that are coupled to the portion of the channel responsible for ion permeation. By contrast, sensing physical cues such as voltage, pressure, and temperature arises from more varied mechanisms. Voltage is commonly sensed by a local, domain-based strategy, whereas the predominant paradigm for pressure sensing employs a global response in channel structure to membrane tension changes. Temperature sensing has been the most challenging response to understand and whether discrete sensor domains exist for pressure and temperature has been the subject of much investigation and debate. Recent exciting advances have uncovered discrete sensor modules for pressure and temperature in force-sensitive and thermal-sensitive ion channels, respectively. In particular, characterization of bacterial voltage-gated sodium channel (BacNa V ) thermal responses has identified a coiled-coil thermosensor that controls channel function through a temperature-dependent unfolding event. This coiled-coil thermosensor blueprint recurs in other temperature sensitive ion channels and thermosensitive proteins. Together with the identification of ion channel pressure sensing domains, these examples demonstrate that "local" domain-based solutions for sensing force and temperature exist and highlight the diversity of both global and local strategies that channels use to sense physical inputs. The modular nature of these newly discovered physical signal sensors provides opportunities to engineer novel pressure-sensitive and thermosensitive proteins and raises new questions about how such modular sensors may have evolved and empowered ion channel pores with new sensibilities.

Mapping the receptor site for alpha-scorpion toxins on a Na+ channel voltage sensor.

PubMed

Wang, Jinti; Yarov-Yarovoy, Vladimir; Kahn, Roy; Gordon, Dalia; Gurevitz, Michael; Scheuer, Todd; Catterall, William A

2011-09-13

The α-scorpions toxins bind to the resting state of Na(+) channels and inhibit fast inactivation by interaction with a receptor site formed by domains I and IV. Mutants T1560A, F1610A, and E1613A in domain IV had lower affinities for Leiurus quinquestriatus hebraeus toxin II (LqhII), and mutant E1613R had ~73-fold lower affinity. Toxin dissociation was accelerated by depolarization and increased by these mutations, whereas association rates at negative membrane potentials were not changed. These results indicate that Thr1560 in the S1-S2 loop, Phe1610 in the S3 segment, and Glu1613 in the S3-S4 loop in domain IV participate in toxin binding. T393A in the SS2-S6 loop in domain I also had lower affinity for LqhII, indicating that this extracellular loop may form a secondary component of the receptor site. Analysis with the Rosetta-Membrane algorithm resulted in a model of LqhII binding to the voltage sensor in a resting state, in which amino acid residues in an extracellular cleft formed by the S1-S2 and S3-S4 loops in domain IV interact with two faces of the wedge-shaped LqhII molecule. The conserved gating charges in the S4 segment are in an inward position and form ion pairs with negatively charged amino acid residues in the S2 and S3 segments of the voltage sensor. This model defines the structure of the resting state of a voltage sensor of Na(+) channels and reveals its mode of interaction with a gating modifier toxin.

Expression of the voltage-sensing phosphatase gene in the chick embryonic tissues and in the adult cerebellum.

PubMed

Yamaguchi, Shinji; Aoki, Naoya; Kitajima, Takaaki; Okamura, Yasushi; Homma, Koichi J

2014-10-01

Voltage-sensing phosphatase (VSP) consists of a transmembrane voltage sensor domain (VSD) and the cytoplasmic domain with phosphoinositide-phosphatase activities. It operates as the voltage sensor and directly translates membrane potential into phosphoinositide turnover by coupling VSD to the cytoplasmic domain. VSPs are evolutionarily conserved from marine invertebrate up to humans. Recently, we demonstrated that ectopic expression of the chick ortholog of VSP, Gg-VSP, in a fibroblast cell line caused characteristic cell process outgrowths. Co-expression of chick PTEN suppressed such morphological change, suggesting that VSP regulates cell shape by increasing PI(3,4)P2. However, the in vivo function of Gg-VSP remains unclear. Here, we showed that in chick embryos Gg-VSP is expressed in the stomach, mesonephros, pharyngeal arch, limb bud, somites, floor plate of neural tube, and notochord. In addition, both Gg-VSP transcripts and the protein were found in the cerebellar Purkinje neurons. These findings provide an insight into the physiological functions of VSP.

Analysis of the transfer function for layered piezoelectric ultrasonic sensors

NASA Astrophysics Data System (ADS)

Gutiérrrez-Reyes, E.; García-Segundo, C.; García-Valenzuela, A.; Reyes-Ramírez, B.; Gutiérrez-Juárez, G.; Guadarrama-Santana, A.

2017-06-01

We model theoretically the voltage response to an acoustic pulse of a multilayer system forming a low noise capacitive sensor including a Polyvinylidene Fluoride piezoelectric film. First we model a generic piezoelectric detector consisting of a piezoelectric film between two metallic electrodes that are the responsible to convert the acoustic signal into a voltage signal. Then we calculate the pressure-to-voltage transfer function for a N-layer piezo-electric capacitor detector, allowing to study the effects of the electrode and protective layers thickness in typical layered piezoelectric sensors. The derived transfer function, when multiplied by the Fourier transform of the incident acoustic pulse, gives the voltage electric response in the frequency domain. An important concern regarding the transfer function is that it may have zeros at specific frequencies, and thus inverting the voltage Fourier transform of the pulse to recover the pressure signal in the time domain is not always, in principle, possible. Our formulas can be used to predict the existence and locations of such zeroes. We illustrate the use of the transfer function by predicting the electric signal generated at a multilayer piezoelectric sensor to an ultrasonic pulse generated photoacoustically by a laser pulse at a three media system with impedance mismatch. This theoretical calculations are compared with our own experimental measurements.

Structure of the voltage-gated K⁺ channel Eag1 reveals an alternative voltage sensing mechanism.

PubMed

Whicher, Jonathan R; MacKinnon, Roderick

2016-08-12

Voltage-gated potassium (K(v)) channels are gated by the movement of the transmembrane voltage sensor, which is coupled, through the helical S4-S5 linker, to the potassium pore. We determined the single-particle cryo-electron microscopy structure of mammalian K(v)10.1, or Eag1, bound to the channel inhibitor calmodulin, at 3.78 angstrom resolution. Unlike previous K(v) structures, the S4-S5 linker of Eag1 is a five-residue loop and the transmembrane segments are not domain swapped, which suggest an alternative mechanism of voltage-dependent gating. Additionally, the structure and position of the S4-S5 linker allow calmodulin to bind to the intracellular domains and to close the potassium pore, independent of voltage-sensor position. The structure reveals an alternative gating mechanism for K(v) channels and provides a template to further understand the gating properties of Eag1 and related channels. Copyright © 2016, American Association for the Advancement of Science.

C-terminal modulatory domain controls coupling of voltage-sensing to pore opening in Cav1.3 L-type Ca(2+) channels.

PubMed

Lieb, Andreas; Ortner, Nadine; Striessnig, Jörg

2014-04-01

Activity of voltage-gated Cav1.3 L-type Ca(2+) channels is required for proper hearing as well as sinoatrial node and brain function. This critically depends on their negative activation voltage range, which is further fine-tuned by alternative splicing. Shorter variants miss a C-terminal regulatory domain (CTM), which allows them to activate at even more negative potentials than C-terminally long-splice variants. It is at present unclear whether this is due to an increased voltage sensitivity of the Cav1.3 voltage-sensing domain, or an enhanced coupling of voltage-sensor conformational changes to the subsequent opening of the activation gate. We studied the voltage-dependence of voltage-sensor charge movement (QON-V) and of current activation (ICa-V) of the long (Cav1.3L) and a short Cav1.3 splice variant (Cav1.342A) expressed in tsA-201 cells using whole cell patch-clamp. Charge movement (QON) of Cav1.3L displayed a much steeper voltage-dependence and a more negative half-maximal activation voltage than Cav1.2 and Cav3.1. However, a significantly higher fraction of the total charge had to move for activation of Cav1.3 half-maximal conductance (Cav1.3: 68%; Cav1.2: 52%; Cav3.1: 22%). This indicated a weaker coupling of Cav1.3 voltage-sensor charge movement to pore opening. However, the coupling efficiency was strengthened in the absence of the CTM in Cav1.342A, thereby shifting ICa-V by 7.2 mV to potentials that were more negative without changing QON-V. We independently show that the presence of intracellular organic cations (such as n-methyl-D-glucamine) induces a pronounced negative shift of QON-V and a more negative activation of ICa-V of all three channels. These findings illustrate that the voltage sensors of Cav1.3 channels respond more sensitively to depolarization than those of Cav1.2 or Cav3.1. Weak coupling of voltage sensing to pore opening is enhanced in the absence of the CTM, allowing short Cav1.342A splice variants to activate at lower voltages without affecting QON-V. Copyright © 2014 The Authors. Published by Elsevier Inc. All rights reserved.

Mapping of voltage sensor positions in resting and inactivated mammalian sodium channels by LRET

PubMed Central

Kubota, Tomoya; Durek, Thomas; Dang, Bobo; Finol-Urdaneta, Rocio K.; Craik, David J.; Kent, Stephen B. H.; French, Robert J.; Bezanilla, Francisco; Correa, Ana M.

2017-01-01

Voltage-gated sodium channels (Navs) play crucial roles in excitable cells. Although vertebrate Nav function has been extensively studied, the detailed structural basis for voltage-dependent gating mechanisms remain obscure. We have assessed the structural changes of the Nav voltage sensor domain using lanthanide-based resonance energy transfer (LRET) between the rat skeletal muscle voltage-gated sodium channel (Nav1.4) and fluorescently labeled Nav1.4-targeting toxins. We generated donor constructs with genetically encoded lanthanide-binding tags (LBTs) inserted at the extracellular end of the S4 segment of each domain (with a single LBT per construct). Three different Bodipy-labeled, Nav1.4-targeting toxins were synthesized as acceptors: β-scorpion toxin (Ts1)-Bodipy, KIIIA-Bodipy, and GIIIA-Bodipy analogs. Functional Nav-LBT channels expressed in Xenopus oocytes were voltage-clamped, and distinct LRET signals were obtained in the resting and slow inactivated states. Intramolecular distances computed from the LRET signals define a geometrical map of Nav1.4 with the bound toxins, and reveal voltage-dependent structural changes related to channel gating. PMID:28202723

Mapping of voltage sensor positions in resting and inactivated mammalian sodium channels by LRET.

PubMed

Kubota, Tomoya; Durek, Thomas; Dang, Bobo; Finol-Urdaneta, Rocio K; Craik, David J; Kent, Stephen B H; French, Robert J; Bezanilla, Francisco; Correa, Ana M

2017-03-07

Voltage-gated sodium channels (Navs) play crucial roles in excitable cells. Although vertebrate Nav function has been extensively studied, the detailed structural basis for voltage-dependent gating mechanisms remain obscure. We have assessed the structural changes of the Nav voltage sensor domain using lanthanide-based resonance energy transfer (LRET) between the rat skeletal muscle voltage-gated sodium channel (Nav1.4) and fluorescently labeled Nav1.4-targeting toxins. We generated donor constructs with genetically encoded lanthanide-binding tags (LBTs) inserted at the extracellular end of the S4 segment of each domain (with a single LBT per construct). Three different Bodipy-labeled, Nav1.4-targeting toxins were synthesized as acceptors: β-scorpion toxin (Ts1)-Bodipy, KIIIA-Bodipy, and GIIIA-Bodipy analogs. Functional Nav-LBT channels expressed in Xenopus oocytes were voltage-clamped, and distinct LRET signals were obtained in the resting and slow inactivated states. Intramolecular distances computed from the LRET signals define a geometrical map of Nav1.4 with the bound toxins, and reveal voltage-dependent structural changes related to channel gating.

Contribution of S4 segments and S4-S5 linkers to the low-voltage activation properties of T-type CaV3.3 channels.

PubMed

Sanchez-Sandoval, Ana Laura; Herrera Carrillo, Zazil; Díaz Velásquez, Clara Estela; Delgadillo, Dulce María; Rivera, Heriberto Manuel; Gomora, Juan Carlos

2018-01-01

Voltage-gated calcium channels contain four highly conserved transmembrane helices known as S4 segments that exhibit a positively charged residue every third position, and play the role of voltage sensing. Nonetheless, the activation range between high-voltage (HVA) and low-voltage (LVA) activated calcium channels is around 30-40 mV apart, despite the high level of amino acid similarity within their S4 segments. To investigate the contribution of S4 voltage sensors for the low-voltage activation characteristics of CaV3.3 channels we constructed chimeras by swapping S4 segments between this LVA channel and the HVA CaV1.2 channel. The substitution of S4 segment of Domain II in CaV3.3 by that of CaV1.2 (chimera IIS4C) induced a ~35 mV shift in the voltage-dependence of activation towards positive potentials, showing an I-V curve that almost overlaps with that of CaV1.2 channel. This HVA behavior induced by IIS4C chimera was accompanied by a 2-fold decrease in the voltage-dependence of channel gating. The IVS4 segment had also a strong effect in the voltage sensing of activation, while substitution of segments IS4 and IIIS4 moved the activation curve of CaV3.3 to more negative potentials. Swapping of IIS4 voltage sensor influenced additional properties of this channel such as steady-state inactivation, current decay, and deactivation. Notably, Domain I voltage sensor played a major role in preventing CaV3.3 channels to inactivate from closed states at extreme hyperpolarized potentials. Finally, site-directed mutagenesis in the CaV3.3 channel revealed a partial contribution of the S4-S5 linker of Domain II to LVA behavior, with synergic effects observed in double and triple mutations. These findings indicate that IIS4 and, to a lesser degree IVS4, voltage sensors are crucial in determining the LVA properties of CaV3.3 channels, although the accomplishment of this function involves the participation of other structural elements like S4-S5 linkers.

Contribution of S4 segments and S4-S5 linkers to the low-voltage activation properties of T-type CaV3.3 channels

PubMed Central

Sanchez-Sandoval, Ana Laura; Herrera Carrillo, Zazil; Díaz Velásquez, Clara Estela; Delgadillo, Dulce María; Rivera, Heriberto Manuel

2018-01-01

Voltage-gated calcium channels contain four highly conserved transmembrane helices known as S4 segments that exhibit a positively charged residue every third position, and play the role of voltage sensing. Nonetheless, the activation range between high-voltage (HVA) and low-voltage (LVA) activated calcium channels is around 30–40 mV apart, despite the high level of amino acid similarity within their S4 segments. To investigate the contribution of S4 voltage sensors for the low-voltage activation characteristics of CaV3.3 channels we constructed chimeras by swapping S4 segments between this LVA channel and the HVA CaV1.2 channel. The substitution of S4 segment of Domain II in CaV3.3 by that of CaV1.2 (chimera IIS4C) induced a ~35 mV shift in the voltage-dependence of activation towards positive potentials, showing an I-V curve that almost overlaps with that of CaV1.2 channel. This HVA behavior induced by IIS4C chimera was accompanied by a 2-fold decrease in the voltage-dependence of channel gating. The IVS4 segment had also a strong effect in the voltage sensing of activation, while substitution of segments IS4 and IIIS4 moved the activation curve of CaV3.3 to more negative potentials. Swapping of IIS4 voltage sensor influenced additional properties of this channel such as steady-state inactivation, current decay, and deactivation. Notably, Domain I voltage sensor played a major role in preventing CaV3.3 channels to inactivate from closed states at extreme hyperpolarized potentials. Finally, site-directed mutagenesis in the CaV3.3 channel revealed a partial contribution of the S4-S5 linker of Domain II to LVA behavior, with synergic effects observed in double and triple mutations. These findings indicate that IIS4 and, to a lesser degree IVS4, voltage sensors are crucial in determining the LVA properties of CaV3.3 channels, although the accomplishment of this function involves the participation of other structural elements like S4-S5 linkers. PMID:29474447

Functional interactions at the interface between voltage-sensing and pore domains in the Shaker K(v) channel.

PubMed

Soler-Llavina, Gilberto J; Chang, Tsg-Hui; Swartz, Kenton J

2006-11-22

Voltage-activated potassium (K(v)) channels contain a central pore domain that is partially surrounded by four voltage-sensing domains. Recent X-ray structures suggest that the two domains lack extensive protein-protein contacts within presumed transmembrane regions, but whether this is the case for functional channels embedded in lipid membranes remains to be tested. We investigated domain interactions in the Shaker K(v) channel by systematically mutating the pore domain and assessing tolerance by examining channel maturation, S4 gating charge movement, and channel opening. When mapped onto the X-ray structure of the K(v)1.2 channel the large number of permissive mutations support the notion of relatively independent domains, consistent with crystallographic studies. Inspection of the maps also identifies portions of the interface where residues are sensitive to mutation, an external cluster where mutations hinder voltage sensor activation, and an internal cluster where domain interactions between S4 and S5 helices from adjacent subunits appear crucial for the concerted opening transition.

A Neutron View of Proteins in Lipid Bilayers

NASA Astrophysics Data System (ADS)

White, Stephen

2012-02-01

Despite the growing number of atomic-resolution membrane protein structures, direct structural information about proteins in their native membrane environment is scarce. This problem is particularly relevant in the case of the highly-charged S1-S4 voltage- sensing domains responsible for nerve impulses, where interactions with the lipid bilayer are critical for the function of voltage-activated potassium channels. We have used neutron diffraction, solid-state nuclear magnetic resonance spectroscopy, and molecular dynamics simulations to investigate the structure and hydration of bilayer membranes containing S1-S4 voltage-sensing domains. Our results show that voltage sensors adopt transmembrane orientations, cause a modest reshaping of the surrounding lipid bilayer, and that water molecules intimately interact with the protein within the membrane. These structural findings reveal that voltage sensors have evolved to interact with the lipid membrane while keeping the energetic and structural perturbations to a minimum, and that water penetrates into the membrane to hydrate charged residues and shape the transmembrane electric field.

Developing Fast Fluorescent Protein Voltage Sensors by Optimizing FRET Interactions

PubMed Central

Sung, Uhna; Sepehri-Rad, Masoud; Piao, Hong Hua; Jin, Lei; Hughes, Thomas; Cohen, Lawrence B.; Baker, Bradley J.

2015-01-01

FRET (Förster Resonance Energy Transfer)-based protein voltage sensors can be useful for monitoring neuronal activity in vivo because the ratio of signals between the donor and acceptor pair reduces common sources of noise such as heart beat artifacts. We improved the performance of FRET based genetically encoded Fluorescent Protein (FP) voltage sensors by optimizing the location of donor and acceptor FPs flanking the voltage sensitive domain of the Ciona intestinalis voltage sensitive phosphatase. First, we created 39 different “Nabi1” constructs by positioning the donor FP, UKG, at 8 different locations downstream of the voltage-sensing domain and the acceptor FP, mKO, at 6 positions upstream. Several of these combinations resulted in large voltage dependent signals and relatively fast kinetics. Nabi1 probes responded with signal size up to 11% ΔF/F for a 100 mV depolarization and fast response time constants both for signal activation (~2 ms) and signal decay (~3 ms). We improved expression in neuronal cells by replacing the mKO and UKG FRET pair with Clover (donor FP) and mRuby2 (acceptor FP) to create Nabi2 probes. Nabi2 probes also had large signals and relatively fast time constants in HEK293 cells. In primary neuronal culture, a Nabi2 probe was able to differentiate individual action potentials at 45 Hz. PMID:26587834

Direct Interaction between the Voltage Sensors Produces Cooperative Sustained Deactivation in Voltage-gated H+ Channel Dimers*

PubMed Central

Okuda, Hiroko; Yonezawa, Yasushige; Takano, Yu; Okamura, Yasushi; Fujiwara, Yuichiro

2016-01-01

The voltage-gated H+ channel (Hv) is a voltage sensor domain-like protein consisting of four transmembrane segments (S1–S4). The native Hv structure is a homodimer, with the two channel subunits functioning cooperatively. Here we show that the two voltage sensor S4 helices within the dimer directly cooperate via a π-stacking interaction between Trp residues at the middle of each segment. Scanning mutagenesis showed that Trp situated around the original position provides the slow gating kinetics characteristic of the dimer's cooperativity. Analyses of the Trp mutation on the dimeric and monomeric channel backgrounds and analyses with tandem channel constructs suggested that the two Trp residues within the dimer are functionally coupled during Hv deactivation but are less so during activation. Molecular dynamics simulation also showed direct π-stacking of the two Trp residues. These results provide new insight into the cooperative function of voltage-gated channels, where adjacent voltage sensor helices make direct physical contact and work as a single unit according to the gating process. PMID:26755722

Actions and Mechanisms of Polyunsaturated Fatty Acids on Voltage-Gated Ion Channels.

PubMed

Elinder, Fredrik; Liin, Sara I

2017-01-01

Polyunsaturated fatty acids (PUFAs) act on most ion channels, thereby having significant physiological and pharmacological effects. In this review we summarize data from numerous PUFAs on voltage-gated ion channels containing one or several voltage-sensor domains, such as voltage-gated sodium (Na V ), potassium (K V ), calcium (Ca V ), and proton (H V ) channels, as well as calcium-activated potassium (K Ca ), and transient receptor potential (TRP) channels. Some effects of fatty acids appear to be channel specific, whereas others seem to be more general. Common features for the fatty acids to act on the ion channels are at least two double bonds in cis geometry and a charged carboxyl group. In total we identify and label five different sites for the PUFAs. PUFA site 1 : The intracellular cavity. Binding of PUFA reduces the current, sometimes as a time-dependent block, inducing an apparent inactivation. PUFA site 2 : The extracellular entrance to the pore. Binding leads to a block of the channel. PUFA site 3 : The intracellular gate. Binding to this site can bend the gate open and increase the current. PUFA site 4 : The interface between the extracellular leaflet of the lipid bilayer and the voltage-sensor domain. Binding to this site leads to an opening of the channel via an electrostatic attraction between the negatively charged PUFA and the positively charged voltage sensor. PUFA site 5 : The interface between the extracellular leaflet of the lipid bilayer and the pore domain. Binding to this site affects slow inactivation. This mapping of functional PUFA sites can form the basis for physiological and pharmacological modifications of voltage-gated ion channels.

Actions and Mechanisms of Polyunsaturated Fatty Acids on Voltage-Gated Ion Channels

PubMed Central

Elinder, Fredrik; Liin, Sara I.

2017-01-01

Polyunsaturated fatty acids (PUFAs) act on most ion channels, thereby having significant physiological and pharmacological effects. In this review we summarize data from numerous PUFAs on voltage-gated ion channels containing one or several voltage-sensor domains, such as voltage-gated sodium (NaV), potassium (KV), calcium (CaV), and proton (HV) channels, as well as calcium-activated potassium (KCa), and transient receptor potential (TRP) channels. Some effects of fatty acids appear to be channel specific, whereas others seem to be more general. Common features for the fatty acids to act on the ion channels are at least two double bonds in cis geometry and a charged carboxyl group. In total we identify and label five different sites for the PUFAs. PUFA site 1: The intracellular cavity. Binding of PUFA reduces the current, sometimes as a time-dependent block, inducing an apparent inactivation. PUFA site 2: The extracellular entrance to the pore. Binding leads to a block of the channel. PUFA site 3: The intracellular gate. Binding to this site can bend the gate open and increase the current. PUFA site 4: The interface between the extracellular leaflet of the lipid bilayer and the voltage-sensor domain. Binding to this site leads to an opening of the channel via an electrostatic attraction between the negatively charged PUFA and the positively charged voltage sensor. PUFA site 5: The interface between the extracellular leaflet of the lipid bilayer and the pore domain. Binding to this site affects slow inactivation. This mapping of functional PUFA sites can form the basis for physiological and pharmacological modifications of voltage-gated ion channels. PMID:28220076

Structure of Voltage-gated Two-pore Channel TPC1 from Arabidopsis thaliana

PubMed Central

Guo, Jiangtao; Zeng, Weizhong; Chen, Qingfeng; Lee, Changkeun; Chen, Liping; Yang, Yi; Cang, Chunlei; Ren, Dejian; Jiang, Youxing

2015-01-01

Two-pore channels (TPCs) contain two copies of a Shaker-like six-transmembrane (6-TM) domain in each subunit and are ubiquitously expressed in both animals and plants as organellar cation channels. Here, we present the first crystal structure of a vacuolar two-pore channel from Arabidopsis thaliana, AtTPC1, which functions as a homodimer. AtTPC1 activation requires both voltage and cytosolic Ca2+. Ca2+ binding to the cytosolic EF-hand domain triggers conformational changes coupled to the pair of pore-lining inner helices (IS6 helices) from the first 6-TM domains, whereas membrane potential only activates the second voltage-sensing domain (VSD2) whose conformational changes are coupled to the pair of inner helices (IIS6 helices) from the second 6-TM domains. Luminal Ca2+ or Ba2+ can modulate voltage activation by stabilizing VSD2 in the resting state and shifts voltage activation towards more positive potentials. Our Ba2+ bound AtTPC1 structure reveals a voltage sensor in the resting state, providing hitherto unseen structural insight into the general voltage-gating mechanism among voltage-gated channels. PMID:26689363

Beyond voltage-gated ion channels: Voltage-operated membrane proteins and cellular processes.

PubMed

Zhang, Jianping; Chen, Xingjuan; Xue, Yucong; Gamper, Nikita; Zhang, Xuan

2018-04-18

Voltage-gated ion channels were believed to be the only voltage-sensitive proteins in excitable (and some non-excitable) cells for a long time. Emerging evidence indicates that the voltage-operated model is shared by some other transmembrane proteins expressed in both excitable and non-excitable cells. In this review, we summarize current knowledge about voltage-operated proteins, which are not classic voltage-gated ion channels as well as the voltage-dependent processes in cells for which single voltage-sensitive proteins have yet to be identified. Particularly, we will focus on the following. (1) Voltage-sensitive phosphoinositide phosphatases (VSP) with four transmembrane segments homologous to the voltage sensor domain (VSD) of voltage-gated ion channels; VSPs are the first family of proteins, other than the voltage-gated ion channels, for which there is sufficient evidence for the existence of the VSD domain; (2) Voltage-gated proton channels comprising of a single voltage-sensing domain and lacking an identified pore domain; (3) G protein coupled receptors (GPCRs) that mediate the depolarization-evoked potentiation of Ca 2+ mobilization; (4) Plasma membrane (PM) depolarization-induced but Ca 2+ -independent exocytosis in neurons. (5) Voltage-dependent metabolism of phosphatidylinositol 4,5-bisphosphate (PtdIns[4,5]P 2 , PIP 2 ) in the PM. These recent discoveries expand our understanding of voltage-operated processes within cellular membranes. © 2018 Wiley Periodicals, Inc.

Molecular basis of the interaction between gating modifier spider toxins and the voltage sensor of voltage-gated ion channels

NASA Astrophysics Data System (ADS)

Lau, Carus H. Y.; King, Glenn F.; Mobli, Mehdi

2016-09-01

Voltage-sensor domains (VSDs) are modular transmembrane domains of voltage-gated ion channels that respond to changes in membrane potential by undergoing conformational changes that are coupled to gating of the ion-conducting pore. Most spider-venom peptides function as gating modifiers by binding to the VSDs of voltage-gated channels and trapping them in a closed or open state. To understand the molecular basis underlying this mode of action, we used nuclear magnetic resonance to delineate the atomic details of the interaction between the VSD of the voltage-gated potassium channel KvAP and the spider-venom peptide VSTx1. Our data reveal that the toxin interacts with residues in an aqueous cleft formed between the extracellular S1-S2 and S3-S4 loops of the VSD whilst maintaining lipid interactions in the gaps formed between the S1-S4 and S2-S3 helices. The resulting network of interactions increases the energetic barrier to the conformational changes required for channel gating, and we propose that this is the mechanism by which gating modifier toxins inhibit voltage-gated ion channels.

Direct Evidence of Conformational Changes Associated with Voltage Gating in a Voltage Sensor Protein by Time-Resolved X-ray/Neutron Interferometry

PubMed Central

2015-01-01

The voltage sensor domain (VSD) of voltage-gated cation (e.g., Na+, K+) channels central to neurological signal transmission can function as a distinct module. When linked to an otherwise voltage-insensitive, ion-selective membrane pore, the VSD imparts voltage sensitivity to the channel. Proteins homologous with the VSD have recently been found to function themselves as voltage-gated proton channels or to impart voltage sensitivity to enzymes. Determining the conformational changes associated with voltage gating in the VSD itself in the absence of a pore domain thereby gains importance. We report the direct measurement of changes in the scattering-length density (SLD) profile of the VSD protein, vectorially oriented within a reconstituted phospholipid bilayer membrane, as a function of the transmembrane electric potential by time-resolved X-ray and neutron interferometry. The changes in the experimental SLD profiles for both polarizing and depolarizing potentials with respect to zero potential were found to extend over the entire length of the isolated VSD’s profile structure. The characteristics of the changes observed were in qualitative agreement with molecular dynamics simulations of a related membrane system, suggesting an initial interpretation of these changes in terms of the VSD’s atomic-level 3-D structure. PMID:24697545

Binding site in eag voltage sensor accommodates a variety of ions and is accessible in closed channel.

PubMed

Silverman, William R; Bannister, John P A; Papazian, Diane M

2004-11-01

In ether-a-go-go K+ channels, voltage-dependent activation is modulated by ion binding to a site located in an extracellular-facing crevice between transmembrane segments S2 and S3 in the voltage sensor. We find that acidic residues D278 in S2 and D327 in S3 are able to coordinate a variety of divalent cations, including Mg2+, Mn2+, and Ni2+, which have qualitatively similar functional effects, but different half-maximal effective concentrations. Our data indicate that ions binding to individual voltage sensors in the tetrameric channel act without cooperativity to modulate activation gating. We have taken advantage of the unique phenotype of Ni2+ in the D274A channel, which contains a mutation of a nonbinding site residue, to demonstrate that ions can access the binding site from the extracellular solution when the voltage sensor is in the resting conformation. Our results are difficult to reconcile with the x-ray structure of the KvAP K+ channel, in which the binding site residues are widely separated, and with the hydrophobic paddle model for voltage-dependent activation, in which the voltage sensor domain, including the S3-S4 loop, is near the cytoplasmic side of the membrane in the closed channel.

A limited 4 Å radial displacement of the S4-S5 linker is sufficient for internal gate closing in Kv channels.

PubMed

Faure, Élise; Starek, Greg; McGuire, Hugo; Bernèche, Simon; Blunck, Rikard

2012-11-16

Voltage-gated ion channels are responsible for the generation of action potentials in our nervous system. Conformational rearrangements in their voltage sensor domains in response to changes of the membrane potential control pore opening and thus ion conduction. Crystal structures of the open channel in combination with a wealth of biophysical data and molecular dynamics simulations led to a consensus on the voltage sensor movement. However, the coupling between voltage sensor movement and pore opening, the electromechanical coupling, occurs at the cytosolic face of the channel, from where no structural information is available yet. In particular, the question how far the cytosolic pore gate has to close to prevent ion conduction remains controversial. In cells, spectroscopic methods are hindered because labeling of internal sites remains difficult, whereas liposomes or detergent solutions containing purified ion channels lack voltage control. Here, to overcome these problems, we controlled the state of the channel by varying the lipid environment. This way, we directly measured the position of the S4-S5 linker in both the open and the closed state of a prokaryotic Kv channel (KvAP) in a lipid environment using Lanthanide-based resonance energy transfer. We were able to reconstruct the movement of the covalent link between the voltage sensor and the pore domain and used this information as restraints for molecular dynamics simulations of the closed state structure. We found that a small decrease of the pore radius of about 3-4 Å is sufficient to prevent ion permeation through the pore.

The sliding-helix voltage sensor

PubMed Central

Peyser, Alexander; Nonner, Wolfgang

2012-01-01

The voltage sensor (VS) domain of voltage-gated ion channels underlies electrical excitability of living cells. We simulate a mesoscale model of the VS domain to determine the functional consequences of some of its physical elements. Our mesoscale model is based on VS charges, linear dielectrics and whole-body motion, applied to an S4 ‘sliding helix’. The electrostatics under voltage-clamped boundary conditions are solved consistently using a boundary element method. Based on electrostatic configurational energy, statistical-mechanical expectations of the experimentally observable relation between displaced charge and membrane voltage are predicted. Consequences of the model are investigated for variations of: S4 configuration (α- and 310-helical), countercharge alignment with S4 charges, protein polarizability, geometry of the gating canal, screening of S4 charges by the baths, and fixed charges located at the bath interfaces. The sliding helix VS domain has an inherent electrostatic stability in the explored parameter space: countercharges present in the region of weak dielectric always retain an equivalent S4 charge in that region but allow sliding movements displacing 3 to 4 e0. That movement is sensitive to small energy variations (< 2kT) along the path dependent on a number of electrostatic parameters tested in our simulations. These simulations show how the slope of the relation between displaced charge and voltage could be tuned in a channel. PMID:22907204

Hydrophobic interaction between contiguous residues in the S6 transmembrane segment acts as a stimuli integration node in the BK channel

PubMed Central

Carrasquel-Ursulaez, Willy; Contreras, Gustavo F.; Sepúlveda, Romina V.; Aguayo, Daniel; González-Nilo, Fernando

2015-01-01

Large-conductance Ca2+- and voltage-activated K+ channel (BK) open probability is enhanced by depolarization, increasing Ca2+ concentration, or both. These stimuli activate modular voltage and Ca2+ sensors that are allosterically coupled to channel gating. Here, we report a point mutation of a phenylalanine (F380A) in the S6 transmembrane helix that, in the absence of internal Ca2+, profoundly hinders channel opening while showing only minor effects on the voltage sensor active–resting equilibrium. Interpretation of these results using an allosteric model suggests that the F380A mutation greatly increases the free energy difference between open and closed states and uncouples Ca2+ binding from voltage sensor activation and voltage sensor activation from channel opening. However, the presence of a bulky and more hydrophobic amino acid in the F380 position (F380W) increases the intrinsic open–closed equilibrium, weakening the coupling between both sensors with the pore domain. Based on these functional experiments and molecular dynamics simulations, we propose that F380 interacts with another S6 hydrophobic residue (L377) in contiguous subunits. This pair forms a hydrophobic ring important in determining the open–closed equilibrium and, like an integration node, participates in the communication between sensors and between the sensors and pore. Moreover, because of its effects on open probabilities, the F380A mutant can be used for detailed voltage sensor experiments in the presence of permeant cations. PMID:25548136

The voltage-sensing domain of a phosphatase gates the pore of a potassium channel.

PubMed

Arrigoni, Cristina; Schroeder, Indra; Romani, Giulia; Van Etten, James L; Thiel, Gerhard; Moroni, Anna

2013-03-01

The modular architecture of voltage-gated K(+) (Kv) channels suggests that they resulted from the fusion of a voltage-sensing domain (VSD) to a pore module. Here, we show that the VSD of Ciona intestinalis phosphatase (Ci-VSP) fused to the viral channel Kcv creates Kv(Synth1), a functional voltage-gated, outwardly rectifying K(+) channel. Kv(Synth1) displays the summed features of its individual components: pore properties of Kcv (selectivity and filter gating) and voltage dependence of Ci-VSP (V(1/2) = +56 mV; z of ~1), including the depolarization-induced mode shift. The degree of outward rectification of the channel is critically dependent on the length of the linker more than on its amino acid composition. This highlights a mechanistic role of the linker in transmitting the movement of the sensor to the pore and shows that electromechanical coupling can occur without coevolution of the two domains.

Enzyme domain affects the movement of the voltage sensor in ascidian and zebrafish voltage-sensing phosphatases.

PubMed

Hossain, Md Israil; Iwasaki, Hirohide; Okochi, Yoshifumi; Chahine, Mohamed; Higashijima, Shinichi; Nagayama, Kuniaki; Okamura, Yasushi

2008-06-27

The ascidian voltage-sensing phosphatase (Ci-VSP) consists of the voltage sensor domain (VSD) and a cytoplasmic phosphatase region that has significant homology to the phosphatase and tensin homolog deleted on chromosome TEN (PTEN). The phosphatase activity of Ci-VSP is modified by the conformational change of the VSD. In many proteins, two protein modules are bidirectionally coupled, but it is unknown whether the phosphatase domain could affect the movement of the VSD in VSP. We addressed this issue by whole-cell patch recording of gating currents from a teleost VSP (Dr-VSP) cloned from Danio rerio expressed in tsA201 cells. Replacement of a critical cysteine residue, in the phosphatase active center of Dr-VSP, by serine sharpened both ON- and OFF-gating currents. Similar changes were produced by treatment with phosphatase inhibitors, pervanadate and orthovanadate, that constitutively bind to cysteine in the active catalytic center of phosphatases. The distinct kinetics of gating currents dependent on enzyme activity were not because of altered phosphatidylinositol 4,5-bisphosphate levels, because the kinetics of gating current did not change by depletion of phosphatidylinositol 4,5-bisphosphate, as reported by coexpressed KCNQ2/3 channels. These results indicate that the movement of the VSD is influenced by the enzymatic state of the cytoplasmic domain, providing an important clue for understanding mechanisms of coupling between the VSD and its effector.

Design and Experimental Verification of a 0.19 V 53 μW 65 nm CMOS Integrated Supply-Sensing Sensor With a Supply-Insensitive Temperature Sensor and an Inductive-Coupling Transmitter for a Self-Powered Bio-sensing System Using a Biofuel Cell.

PubMed

Kobayashi, Atsuki; Ikeda, Kei; Ogawa, Yudai; Kai, Hiroyuki; Nishizawa, Matsuhiko; Nakazato, Kazuo; Niitsu, Kiichi

2017-12-01

In this paper, we present a self-powered bio-sensing system with the capability of proximity inductive-coupling communication for supply sensing and temperature monitoring. The proposed bio-sensing system includes a biofuel cell as a power source and a sensing frontend that is associated with the CMOS integrated supply-sensing sensor. The sensor consists of a digital-based gate leakage timer, a supply-insensitive time-domain temperature sensor, and a current-driven inductive-coupling transmitter and achieves low-voltage operation. The timer converts the output voltage from a biofuel cell to frequency. The temperature sensor provides a pulse width modulation (PWM) output that is not dependent on the supply voltage, and the associated inductive-coupling transmitter enables proximity communication. A test chip was fabricated in 65 nm CMOS technology and consumed 53 μW with a supply voltage of 190 mV. The low-voltage-friendly design satisfied the performance targets of each integrated sensor without any trimming. The chips allowed us to successfully demonstrate proximity communication with an asynchronous receiver, and the measurement results show the potential for self-powered operation using biofuel cells. The analysis and experimental verification of the system confirmed their robustness.

Voltage dependence of a stochastic model of activation of an alpha helical S4 sensor in a K channel membrane

NASA Astrophysics Data System (ADS)

Vaccaro, S. R.

2011-09-01

The voltage dependence of the ionic and gating currents of a K channel is dependent on the activation barriers of a voltage sensor with a potential function which may be derived from the principal electrostatic forces on an S4 segment in an inhomogeneous dielectric medium. By variation of the parameters of a voltage-sensing domain model, consistent with x-ray structures and biophysical data, the lowest frequency of the survival probability of each stationary state derived from a solution of the Smoluchowski equation provides a good fit to the voltage dependence of the slowest time constant of the ionic current in a depolarized membrane, and the gating current exhibits a rising phase that precedes an exponential relaxation. For each depolarizing potential, the calculated time dependence of the survival probabilities of the closed states of an alpha helical S4 sensor are in accord with an empirical model of the ionic and gating currents recorded during the activation process.

A new mechanism of voltage-dependent gating exposed by KV10.1 channels interrupted between voltage sensor and pore.

PubMed

Tomczak, Adam P; Fernández-Trillo, Jorge; Bharill, Shashank; Papp, Ferenc; Panyi, Gyorgy; Stühmer, Walter; Isacoff, Ehud Y; Pardo, Luis A

2017-05-01

Voltage-gated ion channels couple transmembrane potential changes to ion flow. Conformational changes in the voltage-sensing domain (VSD) of the channel are thought to be transmitted to the pore domain (PD) through an α-helical linker between them (S4-S5 linker). However, our recent work on channels disrupted in the S4-S5 linker has challenged this interpretation for the KCNH family. Furthermore, a recent single-particle cryo-electron microscopy structure of K V 10.1 revealed that the S4-S5 linker is a short loop in this KCNH family member, confirming the need for an alternative gating model. Here we use "split" channels made by expression of VSD and PD as separate fragments to investigate the mechanism of gating in K V 10.1. We find that disruption of the covalent connection within the S4 helix compromises the ability of channels to close at negative voltage, whereas disconnecting the S4-S5 linker from S5 slows down activation and deactivation kinetics. Surprisingly, voltage-clamp fluorometry and MTS accessibility assays show that the motion of the S4 voltage sensor is virtually unaffected when VSD and PD are not covalently bound. Finally, experiments using constitutively open PD mutants suggest that the presence of the VSD is structurally important for the conducting conformation of the pore. Collectively, our observations offer partial support to the gating model that assumes that an inward motion of the C-terminal S4 helix, rather than the S4-S5 linker, closes the channel gate, while also suggesting that control of the pore by the voltage sensor involves more than one mechanism. © 2017 Tomczak et al.

A new mechanism of voltage-dependent gating exposed by KV10.1 channels interrupted between voltage sensor and pore

PubMed Central

Fernández-Trillo, Jorge; Bharill, Shashank; Panyi, Gyorgy; Stühmer, Walter; Isacoff, Ehud Y.

2017-01-01

Voltage-gated ion channels couple transmembrane potential changes to ion flow. Conformational changes in the voltage-sensing domain (VSD) of the channel are thought to be transmitted to the pore domain (PD) through an α-helical linker between them (S4–S5 linker). However, our recent work on channels disrupted in the S4–S5 linker has challenged this interpretation for the KCNH family. Furthermore, a recent single-particle cryo-electron microscopy structure of KV10.1 revealed that the S4–S5 linker is a short loop in this KCNH family member, confirming the need for an alternative gating model. Here we use “split” channels made by expression of VSD and PD as separate fragments to investigate the mechanism of gating in KV10.1. We find that disruption of the covalent connection within the S4 helix compromises the ability of channels to close at negative voltage, whereas disconnecting the S4–S5 linker from S5 slows down activation and deactivation kinetics. Surprisingly, voltage-clamp fluorometry and MTS accessibility assays show that the motion of the S4 voltage sensor is virtually unaffected when VSD and PD are not covalently bound. Finally, experiments using constitutively open PD mutants suggest that the presence of the VSD is structurally important for the conducting conformation of the pore. Collectively, our observations offer partial support to the gating model that assumes that an inward motion of the C-terminal S4 helix, rather than the S4–S5 linker, closes the channel gate, while also suggesting that control of the pore by the voltage sensor involves more than one mechanism. PMID:28360219

The topogenic function of S4 promotes membrane insertion of the voltage-sensor domain in the KvAP channel.

PubMed

Mishima, Eriko; Sato, Yoko; Nanatani, Kei; Hoshi, Naomi; Lee, Jong-Kook; Schiller, Nina; von Heijne, Gunnar; Sakaguchi, Masao; Uozumi, Nobuyuki

2016-12-01

Voltage-dependent K + (K V ) channels control K + permeability in response to shifts in the membrane potential. Voltage sensing in K V channels is mediated by the positively charged transmembrane domain S4. The best-characterized K V channel, KvAP, lacks the distinct hydrophilic region corresponding to the S3-S4 extracellular loop that is found in other K + channels. In the present study, we evaluated the topogenic properties of the transmembrane regions within the voltage-sensing domain in KvAP. S3 had low membrane insertion activity, whereas S4 possessed a unique type-I signal anchor (SA-I) function, which enabled it to insert into the membrane by itself. S4 was also found to function as a stop-transfer signal for retention in the membrane. The length and structural nature of the extracellular S3-S4 loop affected the membrane insertion of S3 and S4, suggesting that S3 membrane insertion was dependent on S4. Replacement of charged residues within the transmembrane regions with residues of opposite charge revealed that Asp 72 in S2 and Glu 93 in S3 contributed to membrane insertion of S3 and S4, and increased the stability of S4 in the membrane. These results indicate that the SA-I function of S4, unique among K + channels studied to date, promotes the insertion of S3 into the membrane, and that the charged residues essential for voltage sensing contribute to the membrane-insertion of the voltage sensor domain in KvAP. © 2016 The Author(s); published by Portland Press Limited on behalf of the Biochemical Society.

High-fidelity optical reporting of neuronal electrical activity with an ultrafast fluorescent voltage sensor

PubMed Central

St-Pierre, François; Marshall, Jesse D; Yang, Ying; Gong, Yiyang; Schnitzer, Mark J; Lin, Michael Z

2015-01-01

Accurate optical reporting of electrical activity in genetically defined neuronal populations is a long-standing goal in neuroscience. Here we describe Accelerated Sensor of Action Potentials 1 (ASAP1), a novel voltage sensor design in which a circularly permuted green fluorescent protein is inserted within an extracellular loop of a voltage-sensing domain, rendering fluorescence responsive to membrane potential. ASAP1 demonstrates on- and off- kinetics of 2.1 and 2.0 ms, reliably detects single action potentials and subthreshold potential changes, and tracks trains of action potential waveforms up to 200 Hz in single trials. With a favorable combination of brightness, dynamic range, and speed, ASAP1 enables continuous monitoring of membrane potential in neurons at KHz frame rates using standard epifluorescence microscopy. PMID:24755780

Molecular Dynamics Simulations of Voltage-Gated Cation Channels: Insights on Voltage-Sensor Domain Function and Modulation

PubMed Central

Delemotte, Lucie; Klein, Michael L.; Tarek, Mounir

2012-01-01

Since their discovery in the 1950s, the structure and function of voltage-gated cation channels (VGCC) has been largely understood thanks to results stemming from electrophysiology, pharmacology, spectroscopy, and structural biology. Over the past decade, computational methods such as molecular dynamics (MD) simulations have also contributed, providing molecular level information that can be tested against experimental results, thereby allowing the validation of the models and protocols. Importantly, MD can shed light on elements of VGCC function that cannot be easily accessed through “classical” experiments. Here, we review the results of recent MD simulations addressing key questions that pertain to the function and modulation of the VGCC’s voltage-sensor domain (VSD) highlighting: (1) the movement of the S4-helix basic residues during channel activation, articulating how the electrical driving force acts upon them; (2) the nature of the VSD intermediate states on transitioning between open and closed states of the VGCC; and (3) the molecular level effects on the VSD arising from mutations of specific S4 positively charged residues involved in certain genetic diseases. PMID:22654756

The voltage-sensing domain of a phosphatase gates the pore of a potassium channel

PubMed Central

Arrigoni, Cristina; Schroeder, Indra; Romani, Giulia; Van Etten, James L.; Thiel, Gerhard

2013-01-01

The modular architecture of voltage-gated K+ (Kv) channels suggests that they resulted from the fusion of a voltage-sensing domain (VSD) to a pore module. Here, we show that the VSD of Ciona intestinalis phosphatase (Ci-VSP) fused to the viral channel Kcv creates KvSynth1, a functional voltage-gated, outwardly rectifying K+ channel. KvSynth1 displays the summed features of its individual components: pore properties of Kcv (selectivity and filter gating) and voltage dependence of Ci-VSP (V1/2 = +56 mV; z of ∼1), including the depolarization-induced mode shift. The degree of outward rectification of the channel is critically dependent on the length of the linker more than on its amino acid composition. This highlights a mechanistic role of the linker in transmitting the movement of the sensor to the pore and shows that electromechanical coupling can occur without coevolution of the two domains. PMID:23440279

Coupling of the phosphatase activity of Ci-VSP to its voltage sensor activity over the entire range of voltage sensitivity

PubMed Central

Sakata, Souhei; Hossain, Md. Israil; Okamura, Yasushi

2011-01-01

Abstract The voltage sensing phosphatase Ci-VSP is composed of a voltage sensor domain (VSD) and a cytoplasmic phosphatase domain. Upon membrane depolarization, movement of the VSD triggers the enzyme's phosphatase activity. To gain further insight into its operating mechanism, we studied the PI(4,5)P2 phosphatase activity of Ci-VSP expressed in Xenopus oocytes over the entire range of VSD motion by assessing the activity of coexpressed Kir2.1 channels or the fluorescence signal from a pleckstrin homology domain fused with green fluorescent protein (GFP) (PHPLC-GFP). Both assays showed greater phosphatase activity at 125 mV than at 75 mV, which corresponds to ‘sensing’ charges that were 90% and 75% of maximum, respectively. On the other hand, the activity at 160 mV (corresponding to 98% of the maximum ‘sensing’ charge) was indistinguishable from that at 125 mV. Modelling the kinetics of the PHPLC-GFP fluorescence revealed that its time course was dependent on both the level of Ci-VSP expression and the diffusion of PHPLC-GFP beneath the plasma membrane. Enzyme activity was calculated by fitting the time course of PHPLC-GFP fluorescence into the model. The voltage dependence of the enzyme activity was superimposable on the Q–V curve, which is consistent with the idea that the enzyme activity is tightly coupled to VSD movement over the entire range of membrane potentials that elicit VSD movement. PMID:21486809

Coupling between the voltage-sensing and phosphatase domains of Ci-VSP.

PubMed

Villalba-Galea, Carlos A; Miceli, Francesco; Taglialatela, Maurizio; Bezanilla, Francisco

2009-07-01

The Ciona intestinalis voltage sensor-containing phosphatase (Ci-VSP) shares high homology with the phosphatidylinositol phosphatase enzyme known as PTEN (phosphatase and tensin homologue deleted on chromosome 10). We have taken advantage of the similarity between these proteins to inquire about the coupling between the voltage sensing and the phosphatase domains in Ci-VSP. Recently, it was shown that four basic residues (R11, K13, R14, and R15) in PTEN are critical for its binding onto the membrane, required for its catalytic activity. Ci-VSP has three of the basic residues of PTEN. Here, we show that when R253 and R254 (which are the homologues of R14 and R15 in PTEN) are mutated to alanines in Ci-VSP, phosphatase activity is disrupted, as revealed by a lack of effect on the ionic currents of KCNQ2/3, where current decrease is a measure of phosphatase activity. The enzymatic activity was not rescued by the introduction of lysines, indicating that the binding is an arginine-specific interaction between the phosphatase binding domain and the membrane, presumably through the phosphate groups of the phospholipids. We also found that the kinetics and steady-state voltage dependence of the S4 segment movement are affected when the arginines are not present, indicating that the interaction of R253 and R254 with the membrane, required for the catalytic action of the phosphatase, restricts the movement of the voltage sensor.

Structural refinement of the hERG1 pore and voltage-sensing domains with ROSETTA-membrane and molecular dynamics simulations.

PubMed

Subbotina, Julia; Yarov-Yarovoy, Vladimir; Lees-Miller, James; Durdagi, Serdar; Guo, Jiqing; Duff, Henry J; Noskov, Sergei Yu

2010-11-01

The hERG1 gene (Kv11.1) encodes a voltage-gated potassium channel. Mutations in this gene lead to one form of the Long QT Syndrome (LQTS) in humans. Promiscuous binding of drugs to hERG1 is known to alter the structure/function of the channel leading to an acquired form of the LQTS. Expectably, creation and validation of reliable 3D model of the channel have been a key target in molecular cardiology and pharmacology for the last decade. Although many models were built, they all were limited to pore domain. In this work, a full model of the hERG1 channel is developed which includes all transmembrane segments. We tested a template-driven de-novo design with ROSETTA-membrane modeling using side-chain placements optimized by subsequent molecular dynamics (MD) simulations. Although backbone templates for the homology modeled parts of the pore and voltage sensors were based on the available structures of KvAP, Kv1.2 and Kv1.2-Kv2.1 chimera channels, the missing parts are modeled de-novo. The impact of several alignments on the structure of the S4 helix in the voltage-sensing domain was also tested. Herein, final models are evaluated for consistency to the reported structural elements discovered mainly on the basis of mutagenesis and electrophysiology. These structural elements include salt bridges and close contacts in the voltage-sensor domain; and the topology of the extracellular S5-pore linker compared with that established by toxin foot-printing and nuclear magnetic resonance studies. Implications of the refined hERG1 model to binding of blockers and channels activators (potent new ligands for channel activations) are discussed. © 2010 Wiley-Liss, Inc.

Calibration of ultra-high frequency (UHF) partial discharge sensors using FDTD method

NASA Astrophysics Data System (ADS)

Ishak, Asnor Mazuan; Ishak, Mohd Taufiq

2018-02-01

Ultra-high frequency (UHF) partial discharge sensors are widely used for conditioning monitoring and defect location in insulation system of high voltage equipment. Designing sensors for specific applications often requires an iterative process of manufacturing, testing and mechanical modifications. This paper demonstrates the use of finite-difference time-domain (FDTD) technique as a tool to predict the frequency response of UHF PD sensors. Using this approach, the design process can be simplified and parametric studies can be conducted in order to assess the influence of component dimensions and material properties on the sensor response. The modelling approach is validated using gigahertz transverse electromagnetic (GTEM) calibration system. The use of a transient excitation source is particularly suitable for modeling using FDTD, which is able to simulate the step response output voltage of the sensor from which the frequency response is obtained using the same post-processing applied to the physical measurement.

A Novel Passive Wireless Sensor for Concrete Humidity Monitoring.

PubMed

Zhou, Shuangxi; Deng, Fangming; Yu, Lehua; Li, Bing; Wu, Xiang; Yin, Baiqiang

2016-09-20

This paper presents a passive wireless humidity sensor for concrete monitoring. After discussing the transmission of electromagnetic wave in concrete, a novel architecture of wireless humidity sensor, based on Ultra-High Frequency (UHF) Radio Frequency Identification (RFID) technology, is proposed for low-power application. The humidity sensor utilizes the top metal layer to form the interdigitated electrodes, which were then filled with polyimide as the humidity sensing layer. The sensor interface converts the humidity capacitance into a digital signal in the frequency domain. A two-stage rectifier adopts a dynamic bias-voltage generator to boost the effective gate-source voltage of the switches in differential-drive architecture. The clock generator employs a novel structure to reduce the internal voltage swing. The measurement results show that our proposed wireless humidity can achieve a high linearity with a normalized sensitivity of 0.55% %RH at 20 °C. Despite the high losses of concrete, the proposed wireless humidity sensor achieves reliable communication performances in passive mode. The maximum operating distance is 0.52 m when the proposed wireless sensor is embedded into the concrete at the depth of 8 cm. The measured results are highly consistent with the results measured by traditional methods.

A Novel Passive Wireless Sensor for Concrete Humidity Monitoring

PubMed Central

Zhou, Shuangxi; Deng, Fangming; Yu, Lehua; Li, Bing; Wu, Xiang; Yin, Baiqiang

2016-01-01

This paper presents a passive wireless humidity sensor for concrete monitoring. After discussing the transmission of electromagnetic wave in concrete, a novel architecture of wireless humidity sensor, based on Ultra-High Frequency (UHF) Radio Frequency Identification (RFID) technology, is proposed for low-power application. The humidity sensor utilizes the top metal layer to form the interdigitated electrodes, which were then filled with polyimide as the humidity sensing layer. The sensor interface converts the humidity capacitance into a digital signal in the frequency domain. A two-stage rectifier adopts a dynamic bias-voltage generator to boost the effective gate-source voltage of the switches in differential-drive architecture. The clock generator employs a novel structure to reduce the internal voltage swing. The measurement results show that our proposed wireless humidity can achieve a high linearity with a normalized sensitivity of 0.55% %RH at 20 °C. Despite the high losses of concrete, the proposed wireless humidity sensor achieves reliable communication performances in passive mode. The maximum operating distance is 0.52 m when the proposed wireless sensor is embedded into the concrete at the depth of 8 cm. The measured results are highly consistent with the results measured by traditional methods. PMID:27657070

Transfer of Kv3.1 voltage sensor features to the isolated Ci-VSP voltage-sensing domain.

PubMed

Mishina, Yukiko; Mutoh, Hiroki; Knöpfel, Thomas

2012-08-22

Membrane proteins that respond to changes in transmembrane voltage are critical in regulating the function of living cells. The voltage-sensing domains (VSDs) of voltage-gated ion channels are extensively studied to elucidate voltage-sensing mechanisms, and yet many aspects of their structure-function relationship remain elusive. Here, we transplanted homologous amino acid motifs from the tetrameric voltage-activated potassium channel Kv3.1 to the monomeric VSD of Ciona intestinalis voltage-sensitive phosphatase (Ci-VSP) to explore which portions of Kv3.1 subunits depend on the tetrameric structure of Kv channels and which properties of Kv3.1 can be transferred to the monomeric Ci-VSP scaffold. By attaching fluorescent proteins to these chimeric VSDs, we obtained an optical readout to establish membrane trafficking and kinetics of voltage-dependent structural rearrangements. We found that motifs extending from 10 to roughly 100 amino acids can be readily transplanted from Kv3.1 into Ci-VSP to form engineered VSDs that efficiently incorporate into the plasma membrane and sense voltage. Some of the functional features of these engineered VSDs are reminiscent of Kv3.1 channels, indicating that these properties do not require interactions between Kv subunits or between the voltage sensing and the pore domains of Kv channels. Copyright © 2012 Biophysical Society. Published by Elsevier Inc. All rights reserved.

Development of a low noise induction magnetic sensor using magnetic flux negative feedback in the time domain.

PubMed

Wang, X G; Shang, X L; Lin, J

2016-05-01

Time-domain electromagnetic system can implement great depth detection. As for the electromagnetic system, the receiver utilized an air coil sensor, and the matching mode of the sensor employed the resistance matching method. By using the resistance matching method, the vibration of the coil in the time domain can be effectively controlled. However, the noise of the sensor, especially the noise at the resonance frequency, will be increased as well. In this paper, a novel design of a low noise induction coil sensor is proposed, and the experimental data and noise characteristics are provided. The sensor is designed based on the principle that the amplified voltage will be converted to current under the influence of the feedback resistance of the coil. The feedback loop around the induction coil exerts a magnetic field and sends the negative feedback signal to the sensor. The paper analyses the influence of the closed magnetic feedback loop on both the bandwidth and the noise of the sensor. The signal-to-noise ratio is improved dramatically.

Structure of a eukaryotic cyclic nucleotide-gated channel

PubMed Central

Li, Minghui; Zhou, Xiaoyuan; Wang, Shu; Michailidis, Ioannis; Gong, Ye; Su, Deyuan; Li, Huan; Li, Xueming; Yang, Jian

2018-01-01

Summary Cyclic nucleotide-gated (CNG) channels are essential for vision and olfaction. They belong to the voltage-gated ion channel superfamily but their activities are controlled by intracellular cyclic nucleotides instead of transmembrane voltage. Here we report a 3.5 Å-resolution single-particle electron cryomicroscopy structure of a CNG channel from C. elegans in the cGMP-bound open state. The channel has an unusual voltage-sensor-like domain (VSLD), accounting for its deficient voltage dependence. A C-terminal linker connecting S6 and the cyclic nucleotide-binding domain interacts directly with both the VSLD and pore domain, forming a gating ring that couples conformational changes triggered by cyclic nucleotide binding to the gate. The selectivity filter is lined by the carboxylate side chains of a functionally important glutamate and three rings of backbone carbonyls. This structure provides a new framework for understanding mechanisms of ion permeation, gating and channelopathy of CNG channels and cyclic nucleotide modulation of related channels. PMID:28099415

High temperature sensitivity is intrinsic to voltage-gated potassium channels

PubMed Central

Yang, Fan; Zheng, Jie

2014-01-01

Temperature-sensitive transient receptor potential (TRP) ion channels are members of the large tetrameric cation channels superfamily but are considered to be uniquely sensitive to heat, which has been presumed to be due to the existence of an unidentified temperature-sensing domain. Here we report that the homologous voltage-gated potassium (Kv) channels also exhibit high temperature sensitivity comparable to that of TRPV1, which is detectable under specific conditions when the voltage sensor is functionally decoupled from the activation gate through either intrinsic mechanisms or mutations. Interestingly, mutations could tune Shaker channel to be either heat-activated or heat-deactivated. Therefore, high temperature sensitivity is intrinsic to both TRP and Kv channels. Our findings suggest important physiological roles of heat-induced variation in Kv channel activities. Mechanistically our findings indicate that temperature-sensing TRP channels may not contain a specialized heat-sensor domain; instead, non-obligatory allosteric gating permits the intrinsic heat sensitivity to drive channel activation, allowing temperature-sensitive TRP channels to function as polymodal nociceptors. DOI: http://dx.doi.org/10.7554/eLife.03255.001 PMID:25030910

Mutations in the voltage-sensing domain affect the alternative ion permeation pathway in the TRPM3 channel.

PubMed

Held, Katharina; Gruss, Fabian; Aloi, Vincenzo Davide; Janssens, Annelies; Ulens, Chris; Voets, Thomas; Vriens, Joris

2018-03-31

Mutagenesis at positively charged amino acids (arginines and lysines) (R1-R4) in the voltage-sensor domain (transmembrane segment (S) 4) of voltage-gated Na + , K + and Ca 2+ channels can lead to an alternative ion permeation pathway distinct from the central pore. Recently, a non-canonical ion permeation pathway was described in TRPM3, a member of the transient receptor potential (TRP) superfamily. The non-canonical pore exists in the native TRPM3 channel and can be activated by co-stimulation of the endogenous agonist pregnenolone sulphate and the antifungal drug clotrimazole or by stimulation of the synthetic agonist CIM0216. Alignment of the voltage sensor of Shaker K + channels with the entire TRPM3 sequence revealed the highest degree of similarity in the putative S4 region of TRPM3, and suggested that only one single gating charge arginine (R2) in the putative S4 region is conserved. Mutagenesis studies in the voltage-sensing domain of TRPM3 revealed several residues in the voltage sensor (S4) as well as in S1 and S3 that are crucial for the occurrence of the non-canonical inward currents. In conclusion, this study provides evidence for the involvement of the voltage-sensing domain of TRPM3 in the formation of an alternative ion permeation pathway. Transient receptor potential (TRP) channels are cationic channels involved in a broad array of functions, including homeostasis, motility and sensory functions. TRP channel subunits consist of six transmembrane segments (S1-S6), and form tetrameric channels with a central pore formed by the region encompassing S5 and S6. Recently, evidence was provided for the existence of an alternative ion permeation pathway in TRPM3, which allows large inward currents upon hyperpolarization independently of the central pore. However, very little knowledge is available concerning the localization of this alternative pathway in the native TRPM3 channel protein. Guided by sequence homology with Shaker K + channels, in which mutations in S4 can create an analogous 'omega' pore, we performed site-directed mutagenesis studies and patch clamp experiments to identify amino acid residues involved in the formation of the non-canonical pore in TRPM3. Based on our results, we pinpoint four residues in S4 (W982, R985, D988 and G991) as crucial determinants of the properties of the alternative ion permeation pathway. © 2018 KU Leuven The Journal of Physiology published by John Wiley & Sons Ltd on behalf of The Physiological Society.

Using lidocaine and benzocaine to link sodium channel molecular conformations to state-dependent antiarrhythmic drug affinity.

PubMed

Hanck, Dorothy A; Nikitina, Elena; McNulty, Megan M; Fozzard, Harry A; Lipkind, Gregory M; Sheets, Michael F

2009-08-28

Lidocaine and other antiarrhythmic drugs bind in the inner pore of voltage-gated Na channels and affect gating use-dependently. A phenylalanine in domain IV, S6 (Phe1759 in Na(V)1.5), modeled to face the inner pore just below the selectivity filter, is critical in use-dependent drug block. Measurement of gating currents and concentration-dependent availability curves to determine the role of Phe1759 in coupling of drug binding to the gating changes. The measurements showed that replacement of Phe1759 with a nonaromatic residue permits clear separation of action of lidocaine and benzocaine into 2 components that can be related to channel conformations. One component represents the drug acting as a voltage-independent, low-affinity blocker of closed channels (designated as lipophilic block), and the second represents high-affinity, voltage-dependent block of open/inactivated channels linked to stabilization of the S4s in domains III and IV (designated as voltage-sensor inhibition) by Phe1759. A homology model for how lidocaine and benzocaine bind in the closed and open/inactivated channel conformation is proposed. These 2 components, lipophilic block and voltage-sensor inhibition, can explain the differences in estimates between tonic and open-state/inactivated-state affinities, and they identify how differences in affinity for the 2 binding conformations can control use-dependence, the hallmark of successful antiarrhythmic drugs.

Design and Characterization of a High Resolution Microfluidic Heat Flux Sensor with Thermal Modulation

PubMed Central

Nam, Sung-Ki; Kim, Jung-Kyun; Cho, Sung-Cheon; Lee, Sun-Kyu

2010-01-01

A complementary metal-oxide semiconductor-compatible process was used in the design and fabrication of a suspended membrane microfluidic heat flux sensor with a thermopile for the purpose of measuring the heat flow rate. The combination of a thirty-junction gold and nickel thermoelectric sensor with an ultralow noise preamplifier, a low pass filter, and a lock-in amplifier can yield a resolution 20 nW with a sensitivity of 461 V/W. The thermal modulation method is used to eliminate low-frequency noise from the sensor output, and various amounts of fluidic heat were applied to the sensor to investigate its suitability for microfluidic applications. For sensor design and analysis of signal output, a method of modeling and simulating electro-thermal behavior in a microfluidic heat flux sensor with an integrated electronic circuit is presented and validated. The electro-thermal domain model was constructed by using system dynamics, particularly the bond graph. The electro-thermal domain system model in which the thermal and the electrical domains are coupled expresses the heat generation of samples and converts thermal input to electrical output. The proposed electro-thermal domain system model is in good agreement with the measured output voltage response in both the transient and the steady state. PMID:22163568

Chloride Anions Regulate Kinetics but Not Voltage-Sensor Qmax of the Solute Carrier SLC26a5.

PubMed

Santos-Sacchi, Joseph; Song, Lei

2016-06-07

In general, SLC26 solute carriers serve to transport a variety of anions across biological membranes. However, prestin (SLC26a5) has evolved, now serving as a motor protein in outer hair cells (OHCs) of the mammalian inner ear and is required for cochlear amplification, a mechanical feedback mechanism to boost auditory performance. The mechanical activity of the OHC imparted by prestin is driven by voltage and controlled by anions, chiefly intracellular chloride. Current opinion is that chloride anions control the Boltzmann characteristics of the voltage sensor responsible for prestin activity, including Qmax, the total sensor charge moved within the membrane, and Vh, a measure of prestin's operating voltage range. Here, we show that standard narrow-band, high-frequency admittance measures of nonlinear capacitance (NLC), an alternate representation of the sensor's charge-voltage (Q-V) relationship, is inadequate for assessment of Qmax, an estimate of the sum of unitary charges contributed by all voltage sensors within the membrane. Prestin's slow transition rates and chloride-binding kinetics adversely influence these estimates, contributing to the prevalent concept that intracellular chloride level controls the quantity of sensor charge moved. By monitoring charge movement across frequency, using measures of multifrequency admittance, expanded displacement current integration, and OHC electromotility, we find that chloride influences prestin kinetics, thereby controlling charge magnitude at any particular frequency of interrogation. Importantly, however, this chloride dependence vanishes as frequency decreases, with Qmax asymptoting at a level irrespective of the chloride level. These data indicate that prestin activity is significantly low-pass in the frequency domain, with important implications for cochlear amplification. We also note that the occurrence of voltage-dependent charge movements in other SLC26 family members may be hidden by inadequate interrogation timescales, and that revelation of such activity could highlight an evolutionary means for kinetic modifications within the family to address hearing requirements in mammals. Copyright © 2016 Biophysical Society. Published by Elsevier Inc. All rights reserved.

Full-length structure of a monomeric histidine kinase reveals basis for sensory regulation

DOE PAGES

Rivera-Cancel, Giomar; Ko, Wen-huang; Tomchick, Diana R.; ...

2014-12-02

Although histidine kinases (HKs) are critical sensors of external stimuli in prokaryotes, the mechanisms by which their sensor domains control enzymatic activity remain unclear. In this paper, we report the full-length structure of a blue light-activated HK from Erythrobacter litoralis HTCC2594 (EL346) and the results of biochemical and biophysical studies that explain how it is activated by light. Contrary to the standard view that signaling occurs within HK dimers, EL346 functions as a monomer. Its structure reveals that the light–oxygen–voltage (LOV) sensor domain both controls kinase activity and prevents dimerization by binding one side of a dimerization/histidine phosphotransfer-like (DHpL) domain.more » The DHpL domain also contacts the catalytic/ATP-binding (CA) domain, keeping EL346 in an inhibited conformation in the dark. Upon light stimulation, interdomain interactions weaken to facilitate activation. Our data suggest that the LOV domain controls kinase activity by affecting the stability of the DHpL/CA interface, releasing the CA domain from an inhibited conformation upon photoactivation. Finally, we suggest parallels between EL346 and dimeric HKs, with sensor-induced movements in the DHp similarly remodeling the DHp/CA interface as part of activation.« less

Structure of the TRPV1 ion channel determined by electron cryo-microscopy.

PubMed

Liao, Maofu; Cao, Erhu; Julius, David; Cheng, Yifan

2013-12-05

Transient receptor potential (TRP) channels are sensors for a wide range of cellular and environmental signals, but elucidating how these channels respond to physical and chemical stimuli has been hampered by a lack of detailed structural information. Here we exploit advances in electron cryo-microscopy to determine the structure of a mammalian TRP channel, TRPV1, at 3.4 Å resolution, breaking the side-chain resolution barrier for membrane proteins without crystallization. Like voltage-gated channels, TRPV1 exhibits four-fold symmetry around a central ion pathway formed by transmembrane segments 5-6 (S5-S6) and the intervening pore loop, which is flanked by S1-S4 voltage-sensor-like domains. TRPV1 has a wide extracellular 'mouth' with a short selectivity filter. The conserved 'TRP domain' interacts with the S4-S5 linker, consistent with its contribution to allosteric modulation. Subunit organization is facilitated by interactions among cytoplasmic domains, including amino-terminal ankyrin repeats. These observations provide a structural blueprint for understanding unique aspects of TRP channel function.

NaV1.4 mutations cause hypokalaemic periodic paralysis by disrupting IIIS4 movement during recovery

PubMed Central

Lehmann-Horn, Frank; Fan, Chunxiang; Wolf, Markus; Winston, Vern; Merlini, Luciano

2014-01-01

Hypokalaemic periodic paralysis is typically associated with mutations of voltage sensor residues in calcium or sodium channels of skeletal muscle. To date, causative sodium channel mutations have been studied only for the two outermost arginine residues in S4 voltage sensor segments of domains I to III. These mutations produce depolarization of skeletal muscle fibres in response to reduced extracellular potassium, owing to an inward cation-selective gating pore current activated by hyperpolarization. Here, we describe mutations of the third arginine, R3, in the domain III voltage sensor i.e. an R1135H mutation which was found in two patients in separate families and a novel R1135C mutation identified in a third patient in another family. Muscle fibres from a patient harbouring the R1135H mutation showed increased depolarization tendency at normal and reduced extracellular potassium compatible with the diagnosis. Additionally, amplitude and rise time of action potentials were reduced compared with controls, even for holding potentials at which all NaV1.4 are fully recovered from inactivation. These findings may be because of an outward omega current activated at positive potentials. Expression of R1135H/C in mammalian cells indicates further gating defects that include significantly enhanced entry into inactivation and prolonged recovery that may additionally contribute to action potential inhibition at the physiological resting potential. After S4 immobilization in the outward position, mutant channels produce an inward omega current that most likely depolarizes the resting potential and produces the hypokalaemia-induced weakness. Gating current recordings reveal that mutations at R3 inhibit S4 deactivation before recovery, and molecular dynamics simulations suggest that this defect is caused by disrupted interactions of domain III S2 countercharges with S4 arginines R2 to R4 during repolarization of the membrane. This work reveals a novel mechanism of disrupted S4 translocation for hypokalaemic periodic paralysis mutations at arginine residues located below the gating pore constriction of the voltage sensor module. PMID:24549961

Tryptophan scanning mutagenesis of the HERG K+ channel: the S4 domain is loosely packed and likely to be lipid exposed

PubMed Central

Subbiah, Rajesh N; Kondo, Mari; Campbell, Terence J; Vandenberg, Jamie I

2005-01-01

Inherited mutations or drug-induced block of voltage-gated ion channels, including the human ether-à-go-go-related gene (HERG) K+ channel, are significant causes of malignant arrhythmias and sudden death. The fourth transmembrane domain (S4) of these channels contains multiple positive charges that move across the membrane electric field in response to changes in transmembrane voltage. In HERG K+ channels, the movement of the S4 domain across the transmembrane electric field is particularly slow. To examine the basis of the slow movement of the HERG S4 domain and specifically to probe the relationship between the S4 domain with the lipid bilayer and rest of the channel protein, we individually mutated each of the S4 amino acids in HERG (L524–L539) to tryptophan, and characterized the activation and deactivation properties of the mutant channels in Xenopus oocytes, using two-electrode voltage-clamp methods. Tryptophan has a large bulky hydrophobic sidechain and so should be tolerated at positions that interact with lipid, but not at positions involved in close protein–protein interactions. Significantly, we found that all S4 tryptophan mutants were functional. These data indicate that the S4 domain is loosely packed within the rest of the voltage sensor domain and is likely to be lipid exposed. Further, we identified residues K525, R528 and K538 as being the most important for slow activation of the channels. PMID:16166152

Molecular Interactions between Tarantula Toxins and Low-Voltage-Activated Calcium Channels

PubMed Central

Salari, Autoosa; Vega, Benjamin S.; Milescu, Lorin S.; Milescu, Mirela

2016-01-01

Few gating-modifier toxins have been reported to target low-voltage-activated (LVA) calcium channels, and the structural basis of toxin sensitivity remains incompletely understood. Studies of voltage-gated potassium (Kv) channels have identified the S3b–S4 “paddle motif,” which moves at the protein-lipid interface to drive channel opening, as the target for these amphipathic neurotoxins. Voltage-gated calcium (Cav) channels contain four homologous voltage sensor domains, suggesting multiple toxin binding sites. We show here that the S3–S4 segments within Cav3.1 can be transplanted into Kv2.1 to examine their individual contributions to voltage sensing and pharmacology. With these results, we now have a more complete picture of the conserved nature of the paddle motif in all three major voltage-gated ion channel types (Kv, Nav, and Cav). When screened with tarantula toxins, the four paddle sequences display distinct toxin binding properties, demonstrating that gating-modifier toxins can bind to Cav channels in a domain specific fashion. Domain III was the most commonly and strongly targeted, and mutagenesis revealed an acidic residue that is important for toxin binding. We also measured the lipid partitioning strength of all toxins tested and observed a positive correlation with their inhibition of Cav3.1, suggesting a key role for membrane partitioning. PMID:27045173

Tarantula huwentoxin-IV inhibits neuronal sodium channels by binding to receptor site 4 and trapping the domain ii voltage sensor in the closed configuration.

PubMed

Xiao, Yucheng; Bingham, Jon-Paul; Zhu, Weiguo; Moczydlowski, Edward; Liang, Songping; Cummins, Theodore R

2008-10-03

Peptide toxins with high affinity, divergent pharmacological functions, and isoform-specific selectivity are powerful tools for investigating the structure-function relationships of voltage-gated sodium channels (VGSCs). Although a number of interesting inhibitors have been reported from tarantula venoms, little is known about the mechanism for their interaction with VGSCs. We show that huwentoxin-IV (HWTX-IV), a 35-residue peptide from tarantula Ornithoctonus huwena venom, preferentially inhibits neuronal VGSC subtypes rNav1.2, rNav1.3, and hNav1.7 compared with muscle subtypes rNav1.4 and hNav1.5. Of the five VGSCs examined, hNav1.7 was most sensitive to HWTX-IV (IC(50) approximately 26 nM). Following application of 1 microm HWTX-IV, hNav1.7 currents could only be elicited with extreme depolarizations (>+100 mV). Recovery of hNav1.7 channels from HWTX-IV inhibition could be induced by extreme depolarizations or moderate depolarizations lasting several minutes. Site-directed mutagenesis analysis indicated that the toxin docked at neurotoxin receptor site 4 located at the extracellular S3-S4 linker of domain II. Mutations E818Q and D816N in hNav1.7 decreased toxin affinity for hNav1.7 by approximately 300-fold, whereas the reverse mutations in rNav1.4 (N655D/Q657E) and the corresponding mutations in hNav1.5 (R812D/S814E) greatly increased the sensitivity of the muscle VGSCs to HWTX-IV. Our data identify a novel mechanism for sodium channel inhibition by tarantula toxins involving binding to neurotoxin receptor site 4. In contrast to scorpion beta-toxins that trap the IIS4 voltage sensor in an outward configuration, we propose that HWTX-IV traps the voltage sensor of domain II in the inward, closed configuration.

Outward stabilization of the voltage sensor in domain II but not domain I speeds inactivation of voltage-gated sodium channels.

PubMed

Sheets, Michael F; Chen, Tiehua; Hanck, Dorothy A

2013-10-15

To determine the roles of the individual S4 segments in domains I and II to activation and inactivation kinetics of sodium current (INa) in NaV1.5, we used a tethered biotin and avidin approach after a site-directed cysteine substitution was made in the second outermost Arg in each S4 (DI-R2C and DII-R2C). We first determined the fraction of gating charge contributed by the individual S4's to maximal gating current (Qmax), and found that the outermost Arg residue in each S4 contributed ∼19% to Qmax with minimal contributions by other arginines. Stabilization of the S4's in DI-R2C and DII-R2C was confirmed by measuring the expected reduction in Qmax. In DI-R2C, stabilization resulted in a decrease in peak INa of ∼45%, while its peak current-voltage (I-V) and voltage-dependent Na channel availability (SSI) curves were nearly unchanged from wild type (WT). In contrast, stabilization of the DII-R2C enhanced activation with a negative shift in the peak I-V relationship by -7 mV and a larger -17 mV shift in the voltage-dependent SSI curve. Furthermore, its INa decay time constants and time-to-peak INa became more rapid than WT. An explanation for these results is that the depolarized conformation of DII-S4, but not DI-S4, affects the receptor for the inactivation particle formed by the interdomain linker between DIII and IV. In addition, the leftward shifts of both activation and inactivation and the decrease in Gmax after stabilization of the DII-S4 support previous studies that showed β-scorpion toxins trap the voltage sensor of DII in an activated conformation.

Mapping of Residues Forming the Voltage Sensor of the Voltage-Dependent Anion-Selective Channel

NASA Astrophysics Data System (ADS)

Thomas, Lorie; Blachly-Dyson, Elizabeth; Colombini, Marco; Forte, Michael

1993-06-01

Voltage-gated ion-channel proteins contain "voltage-sensing" domains that drive the conformational transitions between open and closed states in response to changes in transmembrane voltage. We have used site-directed mutagenesis to identify residues affecting the voltage sensitivity of a mitochondrial channel, the voltage-dependent anion-selective channel (VDAC). Although charge changes at many sites had no effect, at other sites substitutions that increased positive charge also increased the steepness of voltage dependance and substitutions that decreased positive charge decreased voltage dependance by an appropriate amount. In contrast to the plasma membrane K^+ and Na^+ channels, these residues are distributed over large parts of the VDAC protein. These results have been used to define the conformational transitions that accompany voltage gating of an ion channel. This gating mechanism requires the movement of large portions of the VDAC protein through the membrane.

Using Lidocaine and Benzocaine to Link Sodium Channel Molecular Conformations to State-Dependent Antiarrhythmic Drug Affinity

PubMed Central

Hanck, Dorothy A.; Nikitina, Elena; McNulty, Megan M.; Fozzard, Harry A.; Lipkind, Gregory M.; Sheets, Michael F.

2009-01-01

Rationale Lidocaine and other antiarrhythmic drugs bind in the inner pore of voltage-gated Na channels and affect gating use-dependently. A phenylalanine in domain IV, S6 (Phe1759 in NaV1.5), modeled to face the inner pore just below the selectivity filter, is critical in use-dependent drug block. Objective Measurement of gating currents and concentration-dependent availability curves to determine the role of Phe1759 in coupling of drug binding to the gating changes. Methods & Results The measurements showed that replacement of Phe1759 with a non-aromatic residue permits clear separation of action of lidocaine and benzocaine into two components that can be related to channel conformations. One component represents the drug acting as a voltage-independent, low-affinity blocker of closed channels (designated as lipophilic block), and the second represents high-affinity, voltage-dependent block of open/inactivated channels linked to stabilization of the S4's in domains III and IV (designated as voltage-sensor inhibition) by Phe1759. A homology model for how lidocaine and benzocaine bind in the closed and open/inactivated channel conformation is proposed. Conclusions These two components, lipophilic block and voltage-sensor inhibition, can explain the differences in estimates between tonic and open-state/inactivated-state affinities, and they identify how differences in affinity for the two binding conformations can control use-dependence, the hallmark of successful antiarrhythmic drugs. PMID:19661462

Gating currents from Kv7 channels carrying neuronal hyperexcitability mutations in the voltage-sensing domain.

PubMed

Miceli, Francesco; Vargas, Ernesto; Bezanilla, Francisco; Taglialatela, Maurizio

2012-03-21

Changes in voltage-dependent gating represent a common pathogenetic mechanism for genetically inherited channelopathies, such as benign familial neonatal seizures or peripheral nerve hyperexcitability caused by mutations in neuronal K(v)7.2 channels. Mutation-induced changes in channel voltage dependence are most often inferred from macroscopic current measurements, a technique unable to provide a detailed assessment of the structural rearrangements underlying channel gating behavior; by contrast, gating currents directly measure voltage-sensor displacement during voltage-dependent gating. In this work, we describe macroscopic and gating current measurements, together with molecular modeling and molecular-dynamics simulations, from channels carrying mutations responsible for benign familial neonatal seizures and/or peripheral nerve hyperexcitability; K(v)7.4 channels, highly related to K(v)7.2 channels both functionally and structurally, were used for these experiments. The data obtained showed that mutations affecting charged residues located in the more distal portion of S(4) decrease the stability of the open state and the active voltage-sensing domain configuration but do not directly participate in voltage sensing, whereas mutations affecting a residue (R4) located more proximally in S(4) caused activation of gating-pore currents at depolarized potentials. These results reveal that distinct molecular mechanisms underlie the altered gating behavior of channels carrying disease-causing mutations at different voltage-sensing domain locations, thereby expanding our current view of the pathogenesis of neuronal hyperexcitability diseases. Copyright © 2012 Biophysical Society. Published by Elsevier Inc. All rights reserved.

S1-S3 counter charges in the voltage sensor module of a mammalian sodium channel regulate fast inactivation.

PubMed

Groome, James R; Winston, Vern

2013-05-01

The movement of positively charged S4 segments through the electric field drives the voltage-dependent gating of ion channels. Studies of prokaryotic sodium channels provide a mechanistic view of activation facilitated by electrostatic interactions of negatively charged residues in S1 and S2 segments, with positive counterparts in the S4 segment. In mammalian sodium channels, S4 segments promote domain-specific functions that include activation and several forms of inactivation. We tested the idea that S1-S3 countercharges regulate eukaryotic sodium channel functions, including fast inactivation. Using structural data provided by bacterial channels, we constructed homology models of the S1-S4 voltage sensor module (VSM) for each domain of the mammalian skeletal muscle sodium channel hNaV1.4. These show that side chains of putative countercharges in hNaV1.4 are oriented toward the positive charge complement of S4. We used mutagenesis to define the roles of conserved residues in the extracellular negative charge cluster (ENC), hydrophobic charge region (HCR), and intracellular negative charge cluster (INC). Activation was inhibited with charge-reversing VSM mutations in domains I-III. Charge reversal of ENC residues in domains III (E1051R, D1069K) and IV (E1373K, N1389K) destabilized fast inactivation by decreasing its probability, slowing entry, and accelerating recovery. Several INC mutations increased inactivation from closed states and slowed recovery. Our results extend the functional characterization of VSM countercharges to fast inactivation, and support the premise that these residues play a critical role in domain-specific gating transitions for a mammalian sodium channel.

Threading the biophysics of mammalian Slo1 channels onto structures of an invertebrate Slo1 channel

PubMed Central

2017-01-01

For those interested in the machinery of ion channel gating, the Ca2+ and voltage-activated BK K+ channel provides a compelling topic for investigation, by virtue of its dual allosteric regulation by both voltage and intracellular Ca2+ and because its large-single channel conductance facilitates detailed kinetic analysis. Over the years, biophysical analyses have illuminated details of the allosteric regulation of BK channels and revealed insights into the mechanism of BK gating, e.g., inner cavity size and accessibility and voltage sensor-pore coupling. Now the publication of two structures of an Aplysia californica BK channel—one liganded and one metal free—promises to reinvigorate functional studies and interpretation of biophysical results. The new structures confirm some of the previous functional inferences but also suggest new perspectives regarding cooperativity between Ca2+-binding sites and the relationship between voltage- and Ca2+-dependent gating. Here we consider the extent to which the two structures explain previous functional data on pore-domain properties, voltage-sensor motions, and divalent cation binding and activation of the channel. PMID:29025867

Neutralisation of a single voltage sensor affects gating determinants in all four pore-forming S6 segments of Ca(V)1.2: a cooperative gating model.

PubMed

Beyl, Stanislav; Depil, Katrin; Hohaus, Annette; Stary-Weinzinger, Anna; Linder, Tobias; Timin, Eugen; Hering, Steffen

2012-10-01

Voltage sensors trigger the closed-open transitions in the pore of voltage-gated ion channels. To probe the transmission of voltage sensor signalling to the channel pore of Ca(V)1.2, we investigated how elimination of positive charges in the S4 segments (charged residues were replaced by neutral glutamine) modulates gating perturbations induced by mutations in pore-lining S6 segments. Neutralisation of all positively charged residues in IIS4 produced a functional channel (IIS4(N)), while replacement of the charged residues in IS4, IIIS4 and IVS4 segments resulted in nonfunctional channels. The IIS4(N) channel displayed activation kinetics similar to wild type. Mutations in a highly conserved structure motif on S6 segments ("GAGA ring": G432W in IS6, A780T in IIS6, G1193T in IIIS6 and A1503G in IVS6) induce strong left-shifted activation curves and decelerated channel deactivation kinetics. When IIS4(N) was combined with these mutations, the activation curves were shifted back towards wild type and current kinetics were accelerated. In contrast, 12 other mutations adjacent to the GAGA ring in IS6-IVS6, which also affect activation gating, were not rescued by IIS4(N). Thus, the rescue of gating distortions in segments IS6-IVS6 by IIS4(N) is highly position-specific. Thermodynamic cycle analysis supports the hypothesis that IIS4 is energetically coupled with the distantly located GAGA residues. We speculate that conformational changes caused by neutralisation of IIS4 are not restricted to domain II (IIS6) but are transmitted to gating structures in domains I, III and IV via the GAGA ring.

An Analog Circuit Approximation of the Discrete Wavelet Transform for Ultra Low Power Signal Processing in Wearable Sensor Nodes

PubMed Central

Casson, Alexander J.

2015-01-01

Ultra low power signal processing is an essential part of all sensor nodes, and particularly so in emerging wearable sensors for biomedical applications. Analog signal processing has an important role in these low power, low voltage, low frequency applications, and there is a key drive to decrease the power consumption of existing analog domain signal processing and to map more signal processing approaches into the analog domain. This paper presents an analog domain signal processing circuit which approximates the output of the Discrete Wavelet Transform (DWT) for use in ultra low power wearable sensors. Analog filters are used for the DWT filters and it is demonstrated how these generate analog domain DWT-like information that embeds information from Butterworth and Daubechies maximally flat mother wavelet responses. The Analog DWT is realised in hardware via gmC circuits, designed to operate from a 1.3 V coin cell battery, and provide DWT-like signal processing using under 115 nW of power when implemented in a 0.18 μm CMOS process. Practical examples demonstrate the effective use of the new Analog DWT on ECG (electrocardiogram) and EEG (electroencephalogram) signals recorded from humans. PMID:26694414

An Analog Circuit Approximation of the Discrete Wavelet Transform for Ultra Low Power Signal Processing in Wearable Sensor Nodes.

PubMed

Casson, Alexander J

2015-12-17

Ultra low power signal processing is an essential part of all sensor nodes, and particularly so in emerging wearable sensors for biomedical applications. Analog signal processing has an important role in these low power, low voltage, low frequency applications, and there is a key drive to decrease the power consumption of existing analog domain signal processing and to map more signal processing approaches into the analog domain. This paper presents an analog domain signal processing circuit which approximates the output of the Discrete Wavelet Transform (DWT) for use in ultra low power wearable sensors. Analog filters are used for the DWT filters and it is demonstrated how these generate analog domain DWT-like information that embeds information from Butterworth and Daubechies maximally flat mother wavelet responses. The Analog DWT is realised in hardware via g(m)C circuits, designed to operate from a 1.3 V coin cell battery, and provide DWT-like signal processing using under 115 nW of power when implemented in a 0.18 μm CMOS process. Practical examples demonstrate the effective use of the new Analog DWT on ECG (electrocardiogram) and EEG (electroencephalogram) signals recorded from humans.

Outward Rectification of Voltage-Gated K+ Channels Evolved at Least Twice in Life History

PubMed Central

Riedelsberger, Janin; Dreyer, Ingo; Gonzalez, Wendy

2015-01-01

Voltage-gated potassium (K+) channels are present in all living systems. Despite high structural similarities in the transmembrane domains (TMD), this K+ channel type segregates into at least two main functional categories—hyperpolarization-activated, inward-rectifying (Kin) and depolarization-activated, outward-rectifying (Kout) channels. Voltage-gated K+ channels sense the membrane voltage via a voltage-sensing domain that is connected to the conduction pathway of the channel. It has been shown that the voltage-sensing mechanism is the same in Kin and Kout channels, but its performance results in opposite pore conformations. It is not known how the different coupling of voltage-sensor and pore is implemented. Here, we studied sequence and structural data of voltage-gated K+ channels from animals and plants with emphasis on the property of opposite rectification. We identified structural hotspots that alone allow already the distinction between Kin and Kout channels. Among them is a loop between TMD S5 and the pore that is very short in animal Kout, longer in plant and animal Kin and the longest in plant Kout channels. In combination with further structural and phylogenetic analyses this finding suggests that outward-rectification evolved twice and independently in the animal and plant kingdom. PMID:26356684

Outward Rectification of Voltage-Gated K+ Channels Evolved at Least Twice in Life History.

PubMed

Riedelsberger, Janin; Dreyer, Ingo; Gonzalez, Wendy

2015-01-01

Voltage-gated potassium (K+) channels are present in all living systems. Despite high structural similarities in the transmembrane domains (TMD), this K+ channel type segregates into at least two main functional categories-hyperpolarization-activated, inward-rectifying (Kin) and depolarization-activated, outward-rectifying (Kout) channels. Voltage-gated K+ channels sense the membrane voltage via a voltage-sensing domain that is connected to the conduction pathway of the channel. It has been shown that the voltage-sensing mechanism is the same in Kin and Kout channels, but its performance results in opposite pore conformations. It is not known how the different coupling of voltage-sensor and pore is implemented. Here, we studied sequence and structural data of voltage-gated K+ channels from animals and plants with emphasis on the property of opposite rectification. We identified structural hotspots that alone allow already the distinction between Kin and Kout channels. Among them is a loop between TMD S5 and the pore that is very short in animal Kout, longer in plant and animal Kin and the longest in plant Kout channels. In combination with further structural and phylogenetic analyses this finding suggests that outward-rectification evolved twice and independently in the animal and plant kingdom.

Roderick MacKinnon - Patents

Science.gov Websites

CHANNEL PROTEINS, MUTANT PROKARYOTIC CATION CHANNEL PROTEINS, AND USES THEREOF - MacKinnon, Roderick cation channel proteins, and potentially have uses in treating conditions related to the function of SENSOR DOMAINS OF VOLTAGE-DEPENDENT ION CHANNEL PROTEINS AND USES THEREOF - MacKinnon, Roderick; et. al

Optimized expression and purification of NavAb provide the structural insight into the voltage dependence.

PubMed

Irie, Katsumasa; Haga, Yukari; Shimomura, Takushi; Fujiyoshi, Yoshinori

2018-01-01

Voltage-gated sodium channels are crucial for electro-signalling in living systems. Analysis of the molecular mechanism requires both fine electrophysiological evaluation and high-resolution channel structures. Here, we optimized a dual expression system of NavAb, which is a well-established standard of prokaryotic voltage-gated sodium channels, for E. coli and insect cells using a single plasmid vector to analyse high-resolution protein structures and measure large ionic currents. Using this expression system, we evaluated the voltage dependence and determined the crystal structures of NavAb wild-type and two mutants, E32Q and N49K, whose voltage dependence were positively shifted and essential interactions were lost in voltage sensor domain. The structural and functional comparison elucidated the molecular mechanisms of the voltage dependence of prokaryotic voltage-gated sodium channels. © 2017 Federation of European Biochemical Societies.

S3b amino acid residues do not shuttle across the bilayer in voltage-dependent Shaker K+ channels

PubMed Central

Gonzalez, Carlos; Morera, Francisco J.; Rosenmann, Eduardo; Alvarez, Osvaldo; Latorre, Ramon

2005-01-01

In voltage-dependent channels, positive charges contained within the S4 domain are the voltage-sensing elements. The “voltage-sensor paddle” gating mechanism proposed for the KvAP K+ channel has been the subject of intense discussion regarding its general applicability to the family of voltage-gated channels. In this model, the voltage sensor composed of the S3b and the S4 segment shuttles across the lipid bilayer during channel activation. Guided by this mechanism, we assessed here the accessibility of residues in the S3 segment of the Shaker K+ channel by using cysteine-scanning mutagenesis. Mutants expressed robust K+ currents in Xenopus oocytes and reacted with methanethiosulfonate ethyltrimethylammonium in both closed and open conformations of the channel. Because Shaker has a long S3–S4 linker segment, we generated a deletion mutant with only three residues to emulate the KvAP structure. In this short linker mutant, all of the tested residues in the S3b were accessible to methanethiosulfonate ethyltrimethylammonium in both closed and open conformations. Because the S3b moves together with the S4 domain in the paddle model, we tested the effects of deleting two negative charges or adding a positive charge to this region of the channel. We found that altering the S3b net charge does not modify the total gating charge involved in channel activation. We conclude that the S3b segment is always exposed to the external milieu of the Shaker K+ channel. Our results are incompatible with any model involving a large membrane displacement of segment S3b. PMID:15774578

A novel tarantula toxin stabilizes the deactivated voltage sensor of bacterial sodium channel.

PubMed

Tang, Cheng; Zhou, Xi; Nguyen, Phuong Tran; Zhang, Yunxiao; Hu, Zhaotun; Zhang, Changxin; Yarov-Yarovoy, Vladimir; DeCaen, Paul G; Liang, Songping; Liu, Zhonghua

2017-07-01

Voltage-gated sodium channels (Na V s) are activated by transiting the voltage sensor from the deactivated to the activated state. The crystal structures of several bacterial Na V s have captured the voltage sensor module (VSM) in an activated state, but structure of the deactivated voltage sensor remains elusive. In this study, we sought to identify peptide toxins stabilizing the deactivated VSM of bacterial Na V s. We screened fractions from several venoms and characterized a cystine knot toxin called JZTx-27 from the venom of tarantula Chilobrachys jingzhao as a high-affinity antagonist of the prokaryotic Na V s Ns V Ba (nonselective voltage-gated Bacillus alcalophilus ) and NaChBac (bacterial sodium channel from Bacillus halodurans ) (IC 50 = 112 nM and 30 nM, respectively). JZTx-27 was more efficacious at weaker depolarizing voltages and significantly slowed the activation but accelerated the deactivation of Ns V Ba, whereas the local anesthetic drug lidocaine was shown to antagonize Ns V Ba without affecting channel gating. Mutation analysis confirmed that JZTx-27 bound to S3-4 linker of Ns V Ba, with F98 being the critical residue in determining toxin affinity. All electrophysiological data and in silico analysis suggested that JZTx-27 trapped VSM of Ns V Ba in one of the deactivated states. In mammalian Na V s, JZTx-27 preferably inhibited the inactivation of Na V 1.5 by targeting the fourth transmembrane domain. To our knowledge, this is the first report of peptide antagonist for prokaryotic Na V s. More important, we proposed that JZTx-27 stabilized the Ns V Ba VSM in the deactivated state and may be used as a probe to determine the structure of the deactivated VSM of Na V s.-Tang, C., Zhou, X., Nguyen, P. T., Zhang, Y., Hu, Z., Zhang, C., Yarov-Yarovoy, V., DeCaen, P. G., Liang, S., Liu, Z. A novel tarantula toxin stabilizes the deactivated voltage sensor of bacterial sodium channel. © FASEB.

Phosphatase activity of the voltage-sensing phosphatase, VSP, shows graded dependence on the extent of activation of the voltage sensor

PubMed Central

Sakata, Souhei; Okamura, Yasushi

2014-01-01

The voltage-sensing phosphatase (VSP) consists of a voltage sensor and a cytoplasmic phosphatase region, and the movement of the voltage sensor is coupled to the phosphatase activity. However, its coupling mechanisms still remain unclear. One possible scenario is that the phosphatase is activated only when the voltage sensor is in a fully activated state. Alternatively, the enzymatic activity of single VSP proteins could be graded in distinct activated states of the voltage sensor, and partial activation of the voltage sensor could lead to partial activation of the phosphatase. To distinguish between these two possibilities, we studied a voltage sensor mutant of zebrafish VSP, where the voltage sensor moves in two steps as evidenced by analyses of charge movements of the voltage sensor and voltage clamp fluorometry. Measurements of the phosphatase activity toward phosphatidylinositol 4,5-bisphosphate revealed that both steps of voltage sensor activation are coupled to the tuning of phosphatase activities, consistent with the idea that the phosphatase activity is graded by the magnitude of the movement of the voltage sensor. PMID:24277865

Phosphatase activity of the voltage-sensing phosphatase, VSP, shows graded dependence on the extent of activation of the voltage sensor.

PubMed

Sakata, Souhei; Okamura, Yasushi

2014-03-01

The voltage-sensing phosphatase (VSP) consists of a voltage sensor and a cytoplasmic phosphatase region, and the movement of the voltage sensor is coupled to the phosphatase activity. However, its coupling mechanisms still remain unclear. One possible scenario is that the phosphatase is activated only when the voltage sensor is in a fully activated state. Alternatively, the enzymatic activity of single VSP proteins could be graded in distinct activated states of the voltage sensor, and partial activation of the voltage sensor could lead to partial activation of the phosphatase. To distinguish between these two possibilities, we studied a voltage sensor mutant of zebrafish VSP, where the voltage sensor moves in two steps as evidenced by analyses of charge movements of the voltage sensor and voltage clamp fluorometry. Measurements of the phosphatase activity toward phosphatidylinositol 4,5-bisphosphate revealed that both steps of voltage sensor activation are coupled to the tuning of phosphatase activities, consistent with the idea that the phosphatase activity is graded by the magnitude of the movement of the voltage sensor.

Mapping the interaction site for the tarantula toxin hainantoxin-IV (β-TRTX-Hn2a) in the voltage sensor module of domain II of voltage-gated sodium channels.

PubMed

Cai, Tianfu; Luo, Ji; Meng, Er; Ding, Jiuping; Liang, Songping; Wang, Sheng; Liu, Zhonghua

2015-06-01

Peptide toxins often have pharmacological applications and are powerful tools for investigating the structure-function relationships of voltage-gated sodium channels (VGSCs). Although a group of potential VGSC inhibitors have been reported from tarantula venoms, little is known about the mechanism of their interaction with VGSCs. In this study, we showed that hainantoxin-IV (β-TRTX-Hn2a, HNTX-IV in brief), a 35-residue peptide from Ornithoctonus hainana venom, preferentially inhibited rNav1.2, rNav1.3 and hNav1.7 compared with rNav1.4 and hNav1.5. hNav1.7 was the most sensitive to HNTX-IV (IC50∼21nM). In contrast to many other tarantula toxins that affect VGSCs, HNTX-IV at subsaturating concentrations did not alter activation and inactivation kinetics in the physiological range of voltages, while very large depolarization above +70mV could partially activate toxin-bound hNav1.7 channel, indicating that HNTX-IV acts as a gating modifier rather than a pore blocker. Site-directed mutagenesis indicated that the toxin bound to site 4, which was located on the extracellular S3-S4 linker of hNav1.7 domain II. Mutants E753Q, D816N and E818Q of hNav1.7 decreased toxin affinity for hNav1.7 by 2.0-, 3.3- and 130-fold, respectively. In silico docking indicated that a three-toed claw substructure formed by residues with close contacts in the interface between HNTX-IV and hNav1.7 domain II stabilized the toxin-channel complex, impeding movement of the domain II voltage sensor and inhibiting hNav1.7 activation. Our data provide structural details for structure-based drug design and a useful template for the design of highly selective inhibitors of a specific subtype of VGSCs. Copyright © 2014 Elsevier Inc. All rights reserved.

Pharmacology of the Nav1.1 domain IV voltage sensor reveals coupling between inactivation gating processes.

PubMed

Osteen, Jeremiah D; Sampson, Kevin; Iyer, Vivek; Julius, David; Bosmans, Frank

2017-06-27

The Na v 1.1 voltage-gated sodium channel is a critical contributor to excitability in the brain, where pathological loss of function leads to such disorders as epilepsy, Alzheimer's disease, and autism. This voltage-gated sodium (Na v ) channel subtype also plays an important role in mechanical pain signaling by primary afferent somatosensory neurons. Therefore, pharmacologic modulation of Na v 1.1 represents a potential strategy for treating excitability disorders of the brain and periphery. Inactivation is a complex aspect of Na v channel gating and consists of fast and slow components, each of which may involve a contribution from one or more voltage-sensing domains. Here, we exploit the Hm1a spider toxin, a Na v 1.1-selective modulator, to better understand the relationship between these temporally distinct modes of inactivation and ask whether they can be distinguished pharmacologically. We show that Hm1a inhibits the gating movement of the domain IV voltage sensor (VSDIV), hindering both fast and slow inactivation and leading to an increase in Na v 1.1 availability during high-frequency stimulation. In contrast, ICA-121431, a small-molecule Na v 1.1 inhibitor, accelerates a subsequent VSDIV gating transition to accelerate entry into the slow inactivated state, resulting in use-dependent block. Further evidence for functional coupling between fast and slow inactivation is provided by a Na v 1.1 mutant in which fast inactivation removal has complex effects on slow inactivation. Taken together, our data substantiate the key role of VSDIV in Na v channel fast and slow inactivation and demonstrate that these gating processes are sequential and coupled through VSDIV. These findings provide insight into a pharmacophore on VSDIV through which modulation of inactivation gating can inhibit or facilitate Na v 1.1 function.

Voltage-dependent gating of KCNH potassium channels lacking a covalent link between voltage-sensing and pore domains

PubMed Central

Lörinczi, Éva; Gómez-Posada, Juan Camilo; de la Peña, Pilar; Tomczak, Adam P.; Fernández-Trillo, Jorge; Leipscher, Ulrike; Stühmer, Walter; Barros, Francisco; Pardo, Luis A.

2015-01-01

Voltage-gated channels open paths for ion permeation upon changes in membrane potential, but how voltage changes are coupled to gating is not entirely understood. Two modules can be recognized in voltage-gated potassium channels, one responsible for voltage sensing (transmembrane segments S1 to S4), the other for permeation (S5 and S6). It is generally assumed that the conversion of a conformational change in the voltage sensor into channel gating occurs through the intracellular S4–S5 linker that provides physical continuity between the two regions. Using the pathophysiologically relevant KCNH family, we show that truncated proteins interrupted at, or lacking the S4–S5 linker produce voltage-gated channels in a heterologous model that recapitulate both the voltage-sensing and permeation properties of the complete protein. These observations indicate that voltage sensing by the S4 segment is transduced to the channel gate in the absence of physical continuity between the modules. PMID:25818916

Voltage-dependent gating of KCNH potassium channels lacking a covalent link between voltage-sensing and pore domains.

PubMed

Lörinczi, Éva; Gómez-Posada, Juan Camilo; de la Peña, Pilar; Tomczak, Adam P; Fernández-Trillo, Jorge; Leipscher, Ulrike; Stühmer, Walter; Barros, Francisco; Pardo, Luis A

2015-03-30

Voltage-gated channels open paths for ion permeation upon changes in membrane potential, but how voltage changes are coupled to gating is not entirely understood. Two modules can be recognized in voltage-gated potassium channels, one responsible for voltage sensing (transmembrane segments S1 to S4), the other for permeation (S5 and S6). It is generally assumed that the conversion of a conformational change in the voltage sensor into channel gating occurs through the intracellular S4-S5 linker that provides physical continuity between the two regions. Using the pathophysiologically relevant KCNH family, we show that truncated proteins interrupted at, or lacking the S4-S5 linker produce voltage-gated channels in a heterologous model that recapitulate both the voltage-sensing and permeation properties of the complete protein. These observations indicate that voltage sensing by the S4 segment is transduced to the channel gate in the absence of physical continuity between the modules.

Voltage-dependent gating of KCNH potassium channels lacking a covalent link between voltage-sensing and pore domains

NASA Astrophysics Data System (ADS)

Lörinczi, Éva; Gómez-Posada, Juan Camilo; de La Peña, Pilar; Tomczak, Adam P.; Fernández-Trillo, Jorge; Leipscher, Ulrike; Stühmer, Walter; Barros, Francisco; Pardo, Luis A.

2015-03-01

Voltage-gated channels open paths for ion permeation upon changes in membrane potential, but how voltage changes are coupled to gating is not entirely understood. Two modules can be recognized in voltage-gated potassium channels, one responsible for voltage sensing (transmembrane segments S1 to S4), the other for permeation (S5 and S6). It is generally assumed that the conversion of a conformational change in the voltage sensor into channel gating occurs through the intracellular S4-S5 linker that provides physical continuity between the two regions. Using the pathophysiologically relevant KCNH family, we show that truncated proteins interrupted at, or lacking the S4-S5 linker produce voltage-gated channels in a heterologous model that recapitulate both the voltage-sensing and permeation properties of the complete protein. These observations indicate that voltage sensing by the S4 segment is transduced to the channel gate in the absence of physical continuity between the modules.

NMR structural and dynamical investigation of the isolated voltage-sensing domain of the potassium channel KvAP: implications for voltage gating.

PubMed

Shenkarev, Zakhar O; Paramonov, Alexander S; Lyukmanova, Ekaterina N; Shingarova, Lyudmila N; Yakimov, Sergei A; Dubinnyi, Maxim A; Chupin, Vladimir V; Kirpichnikov, Mikhail P; Blommers, Marcel J J; Arseniev, Alexander S

2010-04-28

The structure and dynamics of the isolated voltage-sensing domain (VSD) of the archaeal potassium channel KvAP was studied by high-resolution NMR. The almost complete backbone resonance assignment and partial side-chain assignment of the (2)H,(13)C,(15)N-labeled VSD were obtained for the protein domain solubilized in DPC/LDAO (2:1) mixed micelles. Secondary and tertiary structures of the VSD were characterized using secondary chemical shifts and NOE contacts. These data indicate that the spatial structure of the VSD solubilized in micelles corresponds to the structure of the domain in an open state of the channel. NOE contacts and secondary chemical shifts of amide protons indicate the presence of tightly bound water molecule as well as hydrogen bond formation involving an interhelical salt bridge (Asp62-R133) that stabilizes the overall structure of the domain. The backbone dynamics of the VSD was studied using (15)N relaxation measurements. The loop regions S1-S2 and S2-S3 were found mobile, while the S3-S4 loop (voltage-sensor paddle) was found stable at the ps-ns time scale. The moieties of S1, S2, S3, and S4 helices sharing interhelical contacts (at the level of the Asp62-R133 salt bridge) were observed in conformational exchange on the micros-ms time scale. Similar exchange-induced broadening of characteristic resonances was observed for the VSD solubilized in the membrane of lipid-protein nanodiscs composed of DMPC, DMPG, and POPC/DOPG lipids. Apparently, the observed interhelical motions represent an inherent property of the VSD of the KvAP channel and can play an important role in the voltage gating.

Voltage-gated calcium flux mediates Escherichia coli mechanosensation.

PubMed

Bruni, Giancarlo N; Weekley, R Andrew; Dodd, Benjamin J T; Kralj, Joel M

2017-08-29

Electrically excitable cells harness voltage-coupled calcium influx to transmit intracellular signals, typically studied in neurons and cardiomyocytes. Despite intense study in higher organisms, investigations of voltage and calcium signaling in bacteria have lagged due to their small size and a lack of sensitive tools. Only recently were bacteria shown to modulate their membrane potential on the timescale of seconds, and little is known about the downstream effects from this modulation. In this paper, we report on the effects of electrophysiology in individual bacteria. A genetically encoded calcium sensor expressed in Escherichia coli revealed calcium transients in single cells. A fusion sensor that simultaneously reports voltage and calcium indicated that calcium influx is induced by voltage depolarizations, similar to metazoan action potentials. Cytoplasmic calcium levels and transients increased upon mechanical stimulation with a hydrogel, and single cells altered protein concentrations dependent on the mechanical environment. Blocking voltage and calcium flux altered mechanically induced changes in protein concentration, while inducing calcium flux reproduced these changes. Thus, voltage and calcium relay a bacterial sense of touch and alter cellular lifestyle. Although the calcium effectors remain unknown, these data open a host of new questions about E. coli , including the identity of the underlying molecular players, as well as other signals conveyed by voltage and calcium. These data also provide evidence that dynamic voltage and calcium exists as a signaling modality in the oldest domain of life, and therefore studying electrophysiology beyond canonical electrically excitable cells could yield exciting new findings.

Voltage-gated calcium flux mediates Escherichia coli mechanosensation

PubMed Central

Weekley, R. Andrew; Dodd, Benjamin J. T.

2017-01-01

Electrically excitable cells harness voltage-coupled calcium influx to transmit intracellular signals, typically studied in neurons and cardiomyocytes. Despite intense study in higher organisms, investigations of voltage and calcium signaling in bacteria have lagged due to their small size and a lack of sensitive tools. Only recently were bacteria shown to modulate their membrane potential on the timescale of seconds, and little is known about the downstream effects from this modulation. In this paper, we report on the effects of electrophysiology in individual bacteria. A genetically encoded calcium sensor expressed in Escherichia coli revealed calcium transients in single cells. A fusion sensor that simultaneously reports voltage and calcium indicated that calcium influx is induced by voltage depolarizations, similar to metazoan action potentials. Cytoplasmic calcium levels and transients increased upon mechanical stimulation with a hydrogel, and single cells altered protein concentrations dependent on the mechanical environment. Blocking voltage and calcium flux altered mechanically induced changes in protein concentration, while inducing calcium flux reproduced these changes. Thus, voltage and calcium relay a bacterial sense of touch and alter cellular lifestyle. Although the calcium effectors remain unknown, these data open a host of new questions about E. coli, including the identity of the underlying molecular players, as well as other signals conveyed by voltage and calcium. These data also provide evidence that dynamic voltage and calcium exists as a signaling modality in the oldest domain of life, and therefore studying electrophysiology beyond canonical electrically excitable cells could yield exciting new findings. PMID:28808010

Tyrosine Residues from the S4-S5 Linker of Kv11.1 Channels Are Critical for Slow Deactivation.

PubMed

Ng, Chai-Ann; Gravel, Andrée E; Perry, Matthew D; Arnold, Alexandre A; Marcotte, Isabelle; Vandenberg, Jamie I

2016-08-12

Slow deactivation of Kv11.1 channels is critical for its function in the heart. The S4-S5 linker, which joins the voltage sensor and pore domains, plays a critical role in this slow deactivation gating. Here, we use NMR spectroscopy to identify the membrane-bound surface of the S4S5 linker, and we show that two highly conserved tyrosine residues within the KCNH subfamily of channels are membrane-associated. Site-directed mutagenesis and electrophysiological analysis indicates that Tyr-542 interacts with both the pore domain and voltage sensor residues to stabilize activated conformations of the channel, whereas Tyr-545 contributes to the slow kinetics of deactivation by primarily stabilizing the transition state between the activated and closed states. Thus, the two tyrosine residues in the Kv11.1 S4S5 linker play critical but distinct roles in the slow deactivation phenotype, which is a hallmark of Kv11.1 channels. © 2016 by The American Society for Biochemistry and Molecular Biology, Inc.

Structure of the TRPV1 ion channel determined by electron cryo-microscopy

PubMed Central

Liao, Maofu; Cao, Erhu; Julius, David; Cheng, Yifan

2014-01-01

Transient receptor potential (TRP) channels are sensors for a wide range of cellular and environmental signals, but elucidating how these channels respond to physical and chemical stimuli has been hampered by a lack of detailed structural information. Here, we exploit advances in electron cryo-microscopy to determine the structure of a mammalian TRP channel, TRPV1, at 3.4Å resolution, breaking the side-chain resolution barrier for membrane proteins without crystallization. Like voltage-gated channels, TRPV1 exhibits four-fold symmetry around a central ion pathway formed by transmembrane helices S5–S6 and the intervening pore loop, which is flanked by S1–S4 voltage sensor-like domains. TRPV1 has a wide extracellular ‘mouth’ with short selectivity filter. The conserved ‘TRP domain’ interacts with the S4–S5 linker, consistent with its contribution to allosteric modulation. Subunit organization is facilitated by interactions among cytoplasmic domains, including N-terminal ankyrin repeats. These observations provide a structural blueprint for understanding unique aspects of TRP channel function. PMID:24305160

Large scale rearrangement of protein domains is associated with voltage gating of the VDAC channel.

PubMed Central

Peng, S; Blachly-Dyson, E; Forte, M; Colombini, M

1992-01-01

The VDAC channel of the mitochondrial outer membrane is voltage-gated like the larger, more complex voltage-gated channels of the plasma membrane. However, VDAC is a low molecular weight (30 kDa), abundant protein, which is readily purified and reconstituted, making it an ideal system for analyzing the molecular basis for ion selectivity and voltage-gating. We have probed the VDAC channel by subjecting the cloned yeast (S. cerevisiae) VDAC gene to site-directed mutagenesis and introducing the resulting mutant channels into planar bilayers to detect the effects of specific sequence changes on channel properties. This approach has allowed us to formulate and test a model of the open state structure of the VDAC channel. Now we have applied the same approach to analyzing the structure of the channel's low-conducting "closed state" (essentially closed to important metabolites). We have identified protein domains forming the wall of the closed conformation and domains that seem to be removed from the wall of the pore during channel closure. The latter can explain the reduction in pore diameter and volume and the dramatically altered channel selectivity resulting from the channel closure. This process would make a natural coupling between motion of the sensor and channel gating. PMID:1376163

A BK (Slo1) channel journey from molecule to physiology

PubMed Central

Contreras, Gustavo F; Castillo, Karen; Enrique, Nicolás; Carrasquel-Ursulaez, Willy; Castillo, Juan Pablo; Milesi, Verónica; Neely, Alan; Alvarez, Osvaldo; Ferreira, Gonzalo; González, Carlos; Latorre, Ramón

2013-01-01

Calcium and voltage-activated potassium (BK) channels are key actors in cell physiology, both in neuronal and non-neuronal cells and tissues. Through negative feedback between intracellular Ca2+ and membrane voltage, BK channels provide a damping mechanism for excitatory signals. Molecular modulation of these channels by alternative splicing, auxiliary subunits and post-translational modifications showed that these channels are subjected to many mechanisms that add diversity to the BK channel α subunit gene. This complexity of interactions modulates BK channel gating, modifying the energetic barrier of voltage sensor domain activation and channel opening. Regions for voltage as well as Ca2+ sensitivity have been identified, and the crystal structure generated by the 2 RCK domains contained in the C-terminal of the channel has been described. The linkage of these channels to many intracellular metabolites and pathways, as well as their modulation by extracellular natural agents, has been found to be relevant in many physiological processes. This review includes the hallmarks of BK channel biophysics and its physiological impact on specific cells and tissues, highlighting its relationship with auxiliary subunit expression. PMID:24025517

Giant piezoelectric voltage coefficient in grain-oriented modified PbTiO 3 material

DOE PAGES

Yan, Yongke; Zhou, Jie E.; Maurya, Deepam; ...

2016-10-11

A rapid surge in the research on piezoelectric sensors is occurring with the arrival of the Internet of Things. Single-phase oxide piezoelectric materials with giant piezoelectric voltage coefficient (g, induced voltage under applied stress) and high Curie temperature (T c) are crucial towards providing desired performance for sensing, especially under harsh environmental conditions. Here, we report a grain-oriented (with 95% <001> texture) modified PbTiO 3 ceramic that has a high T c (364°C) and an extremely large g 33 (115 × 10 -3 Vm N -1) in comparison with other known single-phase oxide materials. Our results reveal that self-polarization duemore » to grain orientation along the spontaneous polarization direction plays an important role in achieving large piezoelectric response in a domain motion-confined material. Finally, the phase field simulations confirm that the large piezoelectric voltage coefficient g 33 originates from maximized piezoelectric strain coefficient d 33 and minimized dielectric permittivity ε 33 in [001]-textured PbTiO 3 ceramics where domain wall motions are absent.« less

Giant piezoelectric voltage coefficient in grain-oriented modified PbTiO3 material

PubMed Central

Yan, Yongke; Zhou, Jie E.; Maurya, Deepam; Wang, Yu U.; Priya, Shashank

2016-01-01

A rapid surge in the research on piezoelectric sensors is occurring with the arrival of the Internet of Things. Single-phase oxide piezoelectric materials with giant piezoelectric voltage coefficient (g, induced voltage under applied stress) and high Curie temperature (Tc) are crucial towards providing desired performance for sensing, especially under harsh environmental conditions. Here, we report a grain-oriented (with 95% <001> texture) modified PbTiO3 ceramic that has a high Tc (364 °C) and an extremely large g33 (115 × 10−3 Vm N−1) in comparison with other known single-phase oxide materials. Our results reveal that self-polarization due to grain orientation along the spontaneous polarization direction plays an important role in achieving large piezoelectric response in a domain motion-confined material. The phase field simulations confirm that the large piezoelectric voltage coefficient g33 originates from maximized piezoelectric strain coefficient d33 and minimized dielectric permittivity ɛ33 in [001]-textured PbTiO3 ceramics where domain wall motions are absent. PMID:27725634

Hydrophobic interactions between the voltage sensor and pore mediate inactivation in Kv11.1 channels

PubMed Central

Perry, Matthew D.; Wong, Sophia; Ng, Chai Ann

2013-01-01

Kv11.1 channels are critical for the maintenance of a normal heart rhythm. The flow of potassium ions through these channels is controlled by two voltage-regulated gates, termed “activation” and “inactivation,” located at opposite ends of the pore. Crucially in Kv11.1 channels, inactivation gating occurs much more rapidly, and over a distinct range of voltages, compared with activation gating. Although it is clear that the fourth transmembrane segments (S4), within each subunit of the tetrameric channel, are important for controlling the opening and closing of the activation gate, their role during inactivation gating is much less clear. Here, we use rate equilibrium free energy relationship (REFER) analysis to probe the contribution of the S4 “voltage-sensor” helix during inactivation of Kv11.1 channels. Contrary to the important role that charged residues play during activation gating, it is the hydrophobic residues (Leu529, Leu530, Leu532, and Val535) that are the key molecular determinants of inactivation gating. Within the context of an interconnected multi-domain model of Kv11.1 inactivation gating, our REFER analysis indicates that the S4 helix and the S4–S5 linker undergo a conformational rearrangement shortly after that of the S5 helix and S5P linker, but before the S6 helix. Combining REFER analysis with double mutant cycle analysis, we provide evidence for a hydrophobic interaction between residues on the S4 and S5 helices. Based on a Kv11.1 channel homology model, we propose that this hydrophobic interaction forms the basis of an intersubunit coupling between the voltage sensor and pore domain that is an important mediator of inactivation gating. PMID:23980196

Design and Simulation Test of an Open D-Dot Voltage Sensor

PubMed Central

Bai, Yunjie; Wang, Jingang; Wei, Gang; Yang, Yongming

2015-01-01

Nowadays, sensor development focuses on miniaturization and non-contact measurement. According to the D-dot principle, a D-dot voltage sensor with a new structure was designed based on the differential D-dot sensor with a symmetrical structure, called an asymmetric open D-dot voltage sensor. It is easier to install. The electric field distribution of the sensor was analyzed through Ansoft Maxwell and an open D-dot voltage sensor was designed. This open D-voltage sensor is characteristic of accessible insulating strength and small electric field distortion. The steady and transient performance test under 10 kV-voltage reported satisfying performances of the designed open D-dot voltage sensor. It conforms to requirements for a smart grid measuring sensor in intelligence, miniaturization and facilitation. PMID:26393590

Research and Experiments on a Unipolar Capacitive Voltage Sensor

PubMed Central

Zhou, Qiang; He, Wei; Li, Songnong; Hou, Xingzhe

2015-01-01

Voltage sensors are an important part of the electric system. In service, traditional voltage sensors need to directly contact a high-voltage charged body. Sensors involve a large volume, complex insulation structures, and high design costs. Typically an iron core structure is adopted. As a result, ferromagnetic resonance can occur easily during practical application. Moreover, owing to the multilevel capacitor divider, the sensor cannot reflect the changes of measured voltage in time. Based on the electric field coupling principle, this paper designs a new voltage sensor; the unipolar structure design solves many problems of traditional voltage sensors like the great insulation design difficulty and high costs caused by grounding electrodes. A differential signal input structure is adopted for the detection circuit, which effectively restrains the influence of the common-mode interference signal. Through sensor modeling, simulation and calculations, the structural design of the sensor electrode was optimized, miniaturization of the sensor was realized, the voltage division ratio of the sensor was enhanced, and the phase difference of sensor measurement was weakened. The voltage sensor is applied to a single-phase voltage class line of 10 kV for testing. According to the test results, the designed sensor is able to meet the requirements of accurate and real-time measurement for voltage of the charged conductor as well as to provide a new method for electricity larceny prevention and on-line monitoring of the power grid in an electric system. Therefore, it can satisfy the development demands of the smart power grid. PMID:26307992

Free-energy landscape of ion-channel voltage-sensor-domain activation.

PubMed

Delemotte, Lucie; Kasimova, Marina A; Klein, Michael L; Tarek, Mounir; Carnevale, Vincenzo

2015-01-06

Voltage sensor domains (VSDs) are membrane-bound protein modules that confer voltage sensitivity to membrane proteins. VSDs sense changes in the transmembrane voltage and convert the electrical signal into a conformational change called activation. Activation involves a reorganization of the membrane protein charges that is detected experimentally as transient currents. These so-called gating currents have been investigated extensively within the theoretical framework of so-called discrete-state Markov models (DMMs), whereby activation is conceptualized as a series of transitions across a discrete set of states. Historically, the interpretation of DMM transition rates in terms of transition state theory has been instrumental in shaping our view of the activation process, whose free-energy profile is currently envisioned as composed of a few local minima separated by steep barriers. Here we use atomistic level modeling and well-tempered metadynamics to calculate the configurational free energy along a single transition from first principles. We show that this transition is intrinsically multidimensional and described by a rough free-energy landscape. Remarkably, a coarse-grained description of the system, based on the use of the gating charge as reaction coordinate, reveals a smooth profile with a single barrier, consistent with phenomenological models. Our results bridge the gap between microscopic and macroscopic descriptions of activation dynamics and show that choosing the gating charge as reaction coordinate masks the topological complexity of the network of microstates participating in the transition. Importantly, full characterization of the latter is a prerequisite to rationalize modulation of this process by lipids, toxins, drugs, and genetic mutations.

Voltage-Dependent Gating: Novel Insights from KCNQ1 Channels

PubMed Central

Cui, Jianmin

2016-01-01

Gating of voltage-dependent cation channels involves three general molecular processes: voltage sensor activation, sensor-pore coupling, and pore opening. KCNQ1 is a voltage-gated potassium (Kv) channel whose distinctive properties have provided novel insights on fundamental principles of voltage-dependent gating. 1) Similar to other Kv channels, KCNQ1 voltage sensor activation undergoes two resolvable steps; but, unique to KCNQ1, the pore opens at both the intermediate and activated state of voltage sensor activation. The voltage sensor-pore coupling differs in the intermediate-open and the activated-open states, resulting in changes of open pore properties during voltage sensor activation. 2) The voltage sensor-pore coupling and pore opening require the membrane lipid PIP2 and intracellular ATP, respectively, as cofactors, thus voltage-dependent gating is dependent on multiple stimuli, including the binding of intracellular signaling molecules. These mechanisms underlie the extraordinary KCNE1 subunit modification of the KCNQ1 channel and have significant physiological implications. PMID:26745405

Components of gating charge movement and S4 voltage-sensor exposure during activation of hERG channels.

PubMed

Wang, Zhuren; Dou, Ying; Goodchild, Samuel J; Es-Salah-Lamoureux, Zeineb; Fedida, David

2013-04-01

The human ether-á-go-go-related gene (hERG) K(+) channel encodes the pore-forming α subunit of the rapid delayed rectifier current, IKr, and has unique activation gating kinetics, in that the α subunit of the channel activates and deactivates very slowly, which focuses the role of IKr current to a critical period during action potential repolarization in the heart. Despite its physiological importance, fundamental mechanistic properties of hERG channel activation gating remain unclear, including how voltage-sensor movement rate limits pore opening. Here, we study this directly by recording voltage-sensor domain currents in mammalian cells for the first time and measuring the rates of voltage-sensor modification by [2-(trimethylammonium)ethyl] methanethiosulfonate chloride (MTSET). Gating currents recorded from hERG channels expressed in mammalian tsA201 cells using low resistance pipettes show two charge systems, defined as Q(1) and Q(2), with V(1/2)'s of -55.7 (equivalent charge, z = 1.60) and -54.2 mV (z = 1.30), respectively, with the Q(2) charge system carrying approximately two thirds of the overall gating charge. The time constants for charge movement at 0 mV were 2.5 and 36.2 ms for Q(1) and Q(2), decreasing to 4.3 ms for Q(2) at +60 mV, an order of magnitude faster than the time constants of ionic current appearance at these potentials. The voltage and time dependence of Q2 movement closely correlated with the rate of MTSET modification of I521C in the outermost region of the S4 segment, which had a V(1/2) of -64 mV and time constants of 36 ± 8.5 ms and 11.6 ± 6.3 ms at 0 and +60 mV, respectively. Modeling of Q(1) and Q(2) charge systems showed that a minimal scheme of three transitions is sufficient to account for the experimental findings. These data point to activation steps further downstream of voltage-sensor movement that provide the major delays to pore opening in hERG channels.

The output voltage model and experiment of magnetostrictive displacement sensor based on Weidemann effect

NASA Astrophysics Data System (ADS)

Wang, Bowen; Li, Yuanyuan; Xie, Xinliang; Huang, Wenmei; Weng, Ling; Zhang, Changgeng

2018-05-01

Based on the Wiedemann effect and inverse magnetostritive effect, the output voltage model of a magnetostrictive displacement sensor has been established. The output voltage of the magnetostrictive displacement sensor is calculated in different magnetic fields. It is found that the calculating result is in an agreement with the experimental one. The theoretical and experimental results show that the output voltage of the displacement sensor is linearly related to the magnetostrictive differences, (λl-λt), of waveguide wires. The measured output voltages for Fe-Ga and Fe-Ni wire sensors are 51.5mV and 36.5mV, respectively, and the output voltage of Fe-Ga wire sensor is obviously higher than that of Fe-Ni wire sensor under the same magnetic field. The model can be used to predict the output voltage of the sensor and to provide guidance for the optimization design of the sensor.

Improved detection of electrical activity with a voltage probe based on a voltage-sensing phosphatase.

PubMed

Tsutsui, Hidekazu; Jinno, Yuka; Tomita, Akiko; Niino, Yusuke; Yamada, Yoshiyuki; Mikoshiba, Katsuhiko; Miyawaki, Atsushi; Okamura, Yasushi

2013-09-15

  One of the most awaited techniques in modern physiology is the sensitive detection of spatiotemporal electrical activity in a complex network of excitable cells. The use of genetically encoded voltage probes has been expected to enable such analysis. However, in spite of recent progress, existing probes still suffer from low signal amplitude and/or kinetics too slow to detect fast electrical activity. Here, we have developed an improved voltage probe named Mermaid2, which is based on the voltage-sensor domain of the voltage-sensing phosphatase from Ciona intestinalis and Förster energy transfer between a pair of fluorescent proteins. In mammalian cells, Mermaid2 permits ratiometric readouts of fractional changes of more than 50% over a physiologically relevant voltage range with fast kinetics, and it was used to follow a train of action potentials at frequencies of up to 150 Hz. Mermaid2 was also able to detect single action potentials and subthreshold voltage responses in hippocampal neurons in vitro, in addition to cortical electrical activity evoked by sound stimuli in single trials in living mice.

Single calcium channel domain gating of synaptic vesicle fusion at fast synapses; analysis by graphic modeling

PubMed Central

Stanley, Elise F

2015-01-01

At fast-transmitting presynaptic terminals Ca2+ enter through voltage gated calcium channels (CaVs) and bind to a synaptic vesicle (SV) -associated calcium sensor (SV-sensor) to gate fusion and discharge. An open CaV generates a high-concentration plume, or nanodomain of Ca2+ that dissipates precipitously with distance from the pore. At most fast synapses, such as the frog neuromuscular junction (NMJ), the SV sensors are located sufficiently close to individual CaVs to be gated by single nanodomains. However, at others, such as the mature rodent calyx of Held (calyx of Held), the physiology is more complex with evidence that CaVs that are both close and distant from the SV sensor and it is argued that release is gated primarily by the overlapping Ca2+ nanodomains from many CaVs. We devised a 'graphic modeling' method to sum Ca2+ from individual CaVs located at varying distances from the SV-sensor to determine the SV release probability and also the fraction of that probability that can be attributed to single domain gating. This method was applied first to simplified, low and high CaV density model release sites and then to published data on the contrasting frog NMJ and the rodent calyx of Held native synapses. We report 3 main predictions: the SV-sensor is positioned very close to the point at which the SV fuses with the membrane; single domain-release gating predominates even at synapses where the SV abuts a large cluster of CaVs, and even relatively remote CaVs can contribute significantly to single domain-based gating. PMID:26457441

The conserved phenylalanine in the K+ channel voltage-sensor domain creates a barrier with unidirectional effects.

PubMed

Schwaiger, Christine S; Liin, Sara I; Elinder, Fredrik; Lindahl, Erik

2013-01-08

Voltage-gated ion channels are crucial for regulation of electric activity of excitable tissues such as nerve cells, and play important roles in many diseases. During activation, the charged S4 segment in the voltage sensor domain translates across a hydrophobic core forming a barrier for the gating charges. This barrier is critical for channel function, and a conserved phenylalanine in segment S2 has previously been identified to be highly sensitive to substitutions. Here, we have studied the kinetics of K(v)1-type potassium channels (Shaker and K(v)1.2/2.1 chimera) through site-directed mutagenesis, electrophysiology, and molecular simulations. The F290L mutation in Shaker (F233L in K(v)1.2/2.1) accelerates channel closure by at least a factor 50, although opening is unaffected. Free energy profiles with the hydrophobic neighbors of F233 mutated to alanine indicate that the open state with the fourth arginine in S4 above the hydrophobic core is destabilized by ∼17 kJ/mol compared to the first closed intermediate. This significantly lowers the barrier of the first deactivation step, although the last step of activation is unaffected. Simulations of wild-type F233 show that the phenyl ring always rotates toward the extracellular side both for activation and deactivation, which appears to help stabilize a well-defined open state. Copyright © 2013 Biophysical Society. Published by Elsevier Inc. All rights reserved.

Expression, purification, and reconstitution of the voltage-sensing domain from Ci-VSP.

PubMed

Li, Qufei; Jogini, Vishwanath; Wanderling, Sherry; Cortes, D Marien; Perozo, Eduardo

2012-10-16

The voltage-sensing domain (VSD) is the common scaffold responsible for the functional behavior of voltage-gated ion channels, voltage sensitive enzymes, and proton channels. Because of the position of the voltage dependence of the available VSD structures, at present, they all represent the activated state of the sensor. Yet in the absence of a consensus resting state structure, the mechanistic details of voltage sensing remain controversial. The voltage dependence of the VSD from Ci-VSP (Ci-VSD) is dramatically right shifted, so that at 0 mV it presumably populates the putative resting state. Appropriate biochemical methods are an essential prerequisite for generating sufficient amounts of Ci-VSD protein for high-resolution structural studies. Here, we present a simple and robust protocol for the expression of eukaryotic Ci-VSD in Escherichia coli at milligram levels. The protein is pure, homogeneous, monodisperse, and well-folded after solubilization in Anzergent 3-14 at the analyzed concentration (~0.3 mg/mL). Ci-VSD can be reconstituted into liposomes of various compositions, and initial site-directed spin labeling and electron paramagnetic resonance (EPR) spectroscopic measurements indicate its first transmembrane segment folds into an α-helix, in agreement with the homologous region of other VSDs. On the basis of our results and enhanced relaxation EPR spectroscopy measurement, Ci-VSD reconstitutes essentially randomly in proteoliposomes, precluding straightforward application of transmembrane voltages in combination with spectroscopic methods. Nevertheless, these results represent an initial step that makes the resting state of a VSD accessible to a variety of biophysical and structural approaches, including X-ray crystallography, spectroscopic methods, and electrophysiology in lipid bilayers.

Expression, Purification and Reconstitution of the Voltage Sensing Domain from Ci-VSP

PubMed Central

Li, Qufei; Jogini, Vishwanath; Wanderling, Sherry; Cortes, D. Marien; Perozo, Eduardo

2013-01-01

The voltage-sensing domain (VSD) is the common scaffold responsible for the functional behavior of voltage gated ion channels, voltage sensitive enzymes and proton channels. Because of the position of the voltage dependence of the available VSD structures, at present, they all represent the activated state of the sensor. Yet, in the absence of a consensus resting state structure, the mechanistic details of voltage sensing remain controversial. The voltage dependence of the VSD from Ci-VSP (Ci-VSD) is dramatically right shifted, so that at 0 mV It presumably populates the putative resting state. Appropriate biochemical methods are an essential prerequisite to generate sufficient amounts of Ci-VSD protein for high-resolution structural studies. Here, we present a simple and robust protocol for the Escherichia coli expression of eukaryotic Ci-VSD at milligram levels. The protein is pure, homogeneous, mono-disperse and well folded after solubilization in Anzergent 3-14 at the analyzed concentration (~ 0.3 mg/mL). Ci-VSD can be reconstituted into liposomes of various compositions and initial site-directed spin labeling and EPR spectroscopic measurements indicate its first transmembrane segment folds into an α-helix, in agreement to the homologous region of other VSDs. Based on current results and enhanced relaxation EPR spectroscopy measurement, Ci-VSD reconstitutes essentially randomly in proteo-liposomes, precluding straightforward application of transmembrane voltages in combination with spectroscopic methods. Nevertheless, the present results represent an initial step that makes the resting state of a VSD accessible to a variety of biophysical and structural approaches, including X-ray crystallography, spectroscopic methods and electrophysiology in lipid bilayers. PMID:22989304

Structure of the cold- and menthol-sensing ion channel TRPM8.

PubMed

Yin, Ying; Wu, Mengyu; Zubcevic, Lejla; Borschel, William F; Lander, Gabriel C; Lee, Seok-Yong

2018-01-12

Transient receptor potential melastatin (TRPM) cation channels are polymodal sensors that are involved in a variety of physiological processes. Within the TRPM family, member 8 (TRPM8) is the primary cold and menthol sensor in humans. We determined the cryo-electron microscopy structure of the full-length TRPM8 from the collared flycatcher at an overall resolution of ~4.1 ångstroms. Our TRPM8 structure reveals a three-layered architecture. The amino-terminal domain with a fold distinct among known TRP structures, together with the carboxyl-terminal region, forms a large two-layered cytosolic ring that extensively interacts with the transmembrane channel layer. The structure suggests that the menthol-binding site is located within the voltage-sensor-like domain and thus provides a structural glimpse of the design principle of the molecular transducer for cold and menthol sensation. Copyright © 2018 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.

Structural characterization of the voltage sensor domain and voltage-gated K+- channel proteins vectorially-oriented within a single bilayer membrane at the solid/vapor and solid/liquid interfaces via neutron interferometry

PubMed Central

Gupta, S.; Dura, J.A.; Freites, J.A.; Tobias, D.J.; Blasie, J. K.

2012-01-01

The voltage-sensor domain (VSD) is a modular 4-helix bundle component that confers voltage sensitivity to voltage-gated cation channels in biological membranes. Despite extensive biophysical studies and the recent availability of x-ray crystal structures for a few voltage-gated potassium (Kv-) channels and a voltage-gate sodium (Nav-) channel, a complete understanding of the cooperative mechanism of electromechanical coupling, interconverting the closed-to-open states (i.e. non-conducting to cation conducting) remains undetermined. Moreover, the function of these domains is highly dependent on the physical-chemical properties of the surrounding lipid membrane environment. The basis for this work was provided by a recent structural study of the VSD from a prokaryotic Kv-channel vectorially-oriented within a single phospholipid (POPC; 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine) membrane investigated by x-ray interferometry at the solid/moist He (or solid/vapor) and solid/liquid interfaces thus achieving partial to full hydration, respectively (Gupta et. al. Phys. Rev E. 2011, 84). Here, we utilize neutron interferometry to characterize this system in substantially greater structural detail at the sub-molecular level, due to its inherent advantages arising from solvent contrast variation coupled with the deuteration of selected sub-molecular membrane components, especially important for the membrane at the solid/liquid interface. We demonstrate the unique vectorial orientation of the VSD and the retention of its molecular conformation manifest in the asymmetric profile structure of the protein within the profile structure of this single bilayer membrane system. We definitively characterize the asymmetric phospholipid bilayer solvating the lateral surfaces of the VSD protein within the membrane. The profile structures of both the VSD protein and phospholipid bilayer depend upon the hydration state of the membrane. We also determine the distribution of water and exchangeable hydrogen throughout the profile structure of both the VSD itself and the VSD:POPC membrane. These two experimentally-determined water and exchangeable hydrogen distribution profiles are in good agreement with molecular dynamics simulations of the VSD protein vectorially-oriented within a fully hydrated POPC bilayer membrane, supporting the existence of the VSD’s water pore. This approach was extended to the full-length Kv-channel (KvAP) at solid/liquid interface, providing the separate profile structures of the KvAP protein and the POPC bilayer within the reconstituted KvAP:POPC membrane. PMID:22686684

An ultra low energy biomedical signal processing system operating at near-threshold.

PubMed

Hulzink, J; Konijnenburg, M; Ashouei, M; Breeschoten, A; Berset, T; Huisken, J; Stuyt, J; de Groot, H; Barat, F; David, J; Van Ginderdeuren, J

2011-12-01

This paper presents a voltage-scalable digital signal processing system designed for the use in a wireless sensor node (WSN) for ambulatory monitoring of biomedical signals. To fulfill the requirements of ambulatory monitoring, power consumption, which directly translates to the WSN battery lifetime and size, must be kept as low as possible. The proposed processing platform is an event-driven system with resources to run applications with different degrees of complexity in an energy-aware way. The architecture uses effective system partitioning to enable duty cycling, single instruction multiple data (SIMD) instructions, power gating, voltage scaling, multiple clock domains, multiple voltage domains, and extensive clock gating. It provides an alternative processing platform where the power and performance can be scaled to adapt to the application need. A case study on a continuous wavelet transform (CWT)-based heart-beat detection shows that the platform not only preserves the sensitivity and positive predictivity of the algorithm but also achieves the lowest energy/sample for ElectroCardioGram (ECG) heart-beat detection publicly reported today.

Pado, a fluorescent protein with proton channel activity can optically monitor membrane potential, intracellular pH, and map gap junctions.

PubMed

Kang, Bok Eum; Baker, Bradley J

2016-04-04

An in silico search strategy was developed to identify potential voltage-sensing domains (VSD) for the development of genetically encoded voltage indicators (GEVIs). Using a conserved charge distribution in the S2 α-helix, a single in silico search yielded most voltage-sensing proteins including voltage-gated potassium channels, voltage-gated calcium channels, voltage-gated sodium channels, voltage-gated proton channels, and voltage-sensing phosphatases from organisms ranging from mammals to bacteria and plants. A GEVI utilizing the VSD from a voltage-gated proton channel identified from that search was able to optically report changes in membrane potential. In addition this sensor was capable of manipulating the internal pH while simultaneously reporting that change optically since it maintains the voltage-gated proton channel activity of the VSD. Biophysical characterization of this GEVI, Pado, demonstrated that the voltage-dependent signal was distinct from the pH-dependent signal and was dependent on the movement of the S4 α-helix. Further investigation into the mechanism of the voltage-dependent optical signal revealed that inhibiting the dimerization of the fluorescent protein greatly reduced the optical signal. Dimerization of the FP thereby enabled the movement of the S4 α-helix to mediate a fluorescent response.

Pado, a fluorescent protein with proton channel activity can optically monitor membrane potential, intracellular pH, and map gap junctions

PubMed Central

Kang, Bok Eum; Baker, Bradley J.

2016-01-01

An in silico search strategy was developed to identify potential voltage-sensing domains (VSD) for the development of genetically encoded voltage indicators (GEVIs). Using a conserved charge distribution in the S2 α-helix, a single in silico search yielded most voltage-sensing proteins including voltage-gated potassium channels, voltage-gated calcium channels, voltage-gated sodium channels, voltage-gated proton channels, and voltage-sensing phosphatases from organisms ranging from mammals to bacteria and plants. A GEVI utilizing the VSD from a voltage-gated proton channel identified from that search was able to optically report changes in membrane potential. In addition this sensor was capable of manipulating the internal pH while simultaneously reporting that change optically since it maintains the voltage-gated proton channel activity of the VSD. Biophysical characterization of this GEVI, Pado, demonstrated that the voltage-dependent signal was distinct from the pH-dependent signal and was dependent on the movement of the S4 α-helix. Further investigation into the mechanism of the voltage-dependent optical signal revealed that inhibiting the dimerization of the fluorescent protein greatly reduced the optical signal. Dimerization of the FP thereby enabled the movement of the S4 α-helix to mediate a fluorescent response. PMID:27040905

Apo-states of calmodulin and CaBP1 control CaV1 voltage-gated calcium channel function through direct competition for the IQ domain

PubMed Central

Findeisen, Felix; Rumpf, Christine; Minor, Daniel L.

2013-01-01

In neurons, binding of calmodulin (CaM) or calcium-binding protein 1 (CaBP1) to the CaV1 (L-type) voltage-gated calcium channel IQ domain endows the channel with diametrically opposed properties. CaM causes calcium-dependent inactivation (CDI) and limits calcium entry, whereas CaBP1 blocks CDI and allows sustained calcium influx. Here, we combine isothermal titration calorimetry (ITC) with cell-based functional measurements and mathematical modeling to show that these calcium sensors behave in a competitive manner that is explained quantitatively by their apo-state binding affinities for the IQ domain. This competition can be completely blocked by covalent tethering of CaM to the channel. Further, we show that Ca2+/CaM has a sub-picomolar affinity for the IQ domain that is achieved without drastic alteration of calcium binding properties. The observation that the apo-forms of CaM and CaBP1 compete with each other demonstrates a simple mechanism for direct modulation of CaV1 function and suggests a means by which excitable cells may dynamically tune CaV activity. PMID:23811053

Gating Charge Calculations by Computational Electrophysiology Simulations.

PubMed

Machtens, Jan-Philipp; Briones, Rodolfo; Alleva, Claudia; de Groot, Bert L; Fahlke, Christoph

2017-04-11

Electrical cell signaling requires adjustment of ion channel, receptor, or transporter function in response to changes in membrane potential. For the majority of such membrane proteins, the molecular details of voltage sensing remain insufficiently understood. Here, we present a molecular dynamics simulation-based method to determine the underlying charge movement across the membrane-the gating charge-by measuring electrical capacitor properties of membrane-embedded proteins. We illustrate the approach by calculating the charge transfer upon membrane insertion of the HIV gp41 fusion peptide, and validate the method on two prototypical voltage-dependent proteins, the Kv1.2 K + channel and the voltage sensor of the Ciona intestinalis voltage-sensitive phosphatase, against experimental data. We then use the gating charge analysis to study how the T1 domain modifies voltage sensing in Kv1.2 channels and to investigate the voltage dependence of the initial binding of two Na + ions in Na + -coupled glutamate transporters. Our simulation approach quantifies various mechanisms of voltage sensing, enables direct comparison with experiments, and supports mechanistic interpretation of voltage sensitivity by fractional amino acid contributions. Copyright © 2017 Biophysical Society. Published by Elsevier Inc. All rights reserved.

KCNE1 constrains the voltage sensor of Kv7.1 K+ channels.

PubMed

Shamgar, Liora; Haitin, Yoni; Yisharel, Ilanit; Malka, Eti; Schottelndreier, Hella; Peretz, Asher; Paas, Yoav; Attali, Bernard

2008-04-09

Kv7 potassium channels whose mutations cause cardiovascular and neurological disorders are members of the superfamily of voltage-gated K(+) channels, comprising a central pore enclosed by four voltage-sensing domains (VSDs) and sharing a homologous S4 sensor sequence. The Kv7.1 pore-forming subunit can interact with various KCNE auxiliary subunits to form K(+) channels with very different gating behaviors. In an attempt to characterize the nature of the promiscuous gating of Kv7.1 channels, we performed a tryptophan-scanning mutagenesis of the S4 sensor and analyzed the mutation-induced perturbations in gating free energy. Perturbing the gating energetics of Kv7.1 bias most of the mutant channels towards the closed state, while fewer mutations stabilize the open state or the inactivated state. In the absence of auxiliary subunits, mutations of specific S4 residues mimic the gating phenotypes produced by co-assembly of Kv7.1 with either KCNE1 or KCNE3. Many S4 perturbations compromise the ability of KCNE1 to properly regulate Kv7.1 channel gating. The tryptophan-induced packing perturbations and cysteine engineering studies in S4 suggest that KCNE1 lodges at the inter-VSD S4-S1 interface between two adjacent subunits, a strategic location to exert its striking action on Kv7.1 gating functions.

KCNE1 Constrains the Voltage Sensor of Kv7.1 K+ Channels

PubMed Central

Yisharel, Ilanit; Malka, Eti; Schottelndreier, Hella; Peretz, Asher; Paas, Yoav; Attali, Bernard

2008-01-01

Kv7 potassium channels whose mutations cause cardiovascular and neurological disorders are members of the superfamily of voltage-gated K+ channels, comprising a central pore enclosed by four voltage-sensing domains (VSDs) and sharing a homologous S4 sensor sequence. The Kv7.1 pore-forming subunit can interact with various KCNE auxiliary subunits to form K+ channels with very different gating behaviors. In an attempt to characterize the nature of the promiscuous gating of Kv7.1 channels, we performed a tryptophan-scanning mutagenesis of the S4 sensor and analyzed the mutation-induced perturbations in gating free energy. Perturbing the gating energetics of Kv7.1 bias most of the mutant channels towards the closed state, while fewer mutations stabilize the open state or the inactivated state. In the absence of auxiliary subunits, mutations of specific S4 residues mimic the gating phenotypes produced by co-assembly of Kv7.1 with either KCNE1 or KCNE3. Many S4 perturbations compromise the ability of KCNE1 to properly regulate Kv7.1 channel gating. The tryptophan-induced packing perturbations and cysteine engineering studies in S4 suggest that KCNE1 lodges at the inter-VSD S4-S1 interface between two adjacent subunits, a strategic location to exert its striking action on Kv7.1 gating functions. PMID:18398469

Voltage Sensor

NASA Technical Reports Server (NTRS)

1996-01-01

Under a Lewis Research Center Small Business Innovation Research contract, SRICO, Inc. developed a fiber optic voltage sensor to measure voltage in electronic systems in spacecraft. The sensor uses glass and light to sense and transmit electricity, and is relatively safe and accurate. SRICO then commercialized the sensor for measurement of electric field and voltage in applications such as electric power systems and hazardous environments, lightning detection, and fiber optic communication systems.

Stabilization of the Activated hERG Channel Voltage Sensor by Depolarization Involves the S4-S5 Linker.

PubMed

Thouta, Samrat; Hull, Christina M; Shi, Yu Patrick; Sergeev, Valentine; Young, James; Cheng, Yen M; Claydon, Thomas W

2017-01-24

Slow deactivation of hERG channels is critical for preventing cardiac arrhythmia yet the mechanistic basis for the slow gating transition is unclear. Here, we characterized the temporal sequence of events leading to voltage sensor stabilization upon membrane depolarization. Progressive increase in step depolarization duration slowed voltage-sensor return in a biphasic manner (τ fast = 34 ms, τ slow  = 2.5 s). The faster phase of voltage-sensor return slowing correlated with the kinetics of pore opening. The slower component occurred over durations that exceeded channel activation and was consistent with voltage sensor relaxation. The S4-S5 linker mutation, G546L, impeded the faster phase of voltage sensor stabilization without attenuating the slower phase, suggesting that the S4-S5 linker is important for communications between the pore gate and the voltage sensor during deactivation. These data also demonstrate that the mechanisms of pore gate-opening-induced and relaxation-induced voltage-sensor stabilization are separable. Deletion of the distal N-terminus (Δ2-135) accelerated off-gating current, but did not influence the relative contribution of either mechanism of stabilization of the voltage sensor. Lastly, we characterized mode-shift behavior in hERG channels, which results from stabilization of activated channel states. The apparent mode-shift depended greatly on recording conditions. By measuring slow activation and deactivation at steady state we found the "true" mode-shift to be ∼15 mV. Interestingly, the "true" mode-shift of gating currents was ∼40 mV, much greater than that of the pore gate. This demonstrates that voltage sensor return is less energetically favorable upon repolarization than pore gate closure. We interpret this to indicate that stabilization of the activated voltage sensor limits the return of hERG channels to rest. The data suggest that this stabilization occurs as a result of reconfiguration of the pore gate upon opening by a mechanism that is influenced by the S4-S5 linker, and by a separable voltage-sensor intrinsic relaxation mechanism. Copyright © 2017 Biophysical Society. Published by Elsevier Inc. All rights reserved.

Study of electric field distorted by space charges under positive lightning impulse voltage

NASA Astrophysics Data System (ADS)

Wang, Zezhong; Geng, Yinan

2018-03-01

Actually, many insulation problems are related to electric fields. And measuring electric fields is an important research topic of high-voltage engineering. In particular, the electric field distortion caused by space charge is the basis of streamer theory, and thus quantitatively measuring the Poisson electric field caused by space charge is significant to researching the mechanism of air gap discharge. In this paper, we used our photoelectric integrated sensor to measure the electric field distribution in a 1-m rod-plane gap under positive lightning impulse voltage. To verify the reliability of this quantitative measurement, we compared the measured results with calculated results from a numerical simulation. The electric-field time domain waveforms on the axis of the 1-m rod-plane out of the space charge zone were measured with various electrodes. The Poisson electric fields generated by space charge were separated from the Laplace electric field generated by applied voltages, and the amplitudes and variations were measured for various applied voltages and at various locations. This work also supplies the feasible basis for directly measuring strong electric field under high voltage.

Structures of closed and open states of a voltage-gated sodium channel

PubMed Central

Lenaeus, Michael J.; Gamal El-Din, Tamer M.; Ramanadane, Karthik; Pomès, Régis; Zheng, Ning; Catterall, William A.

2017-01-01

Bacterial voltage-gated sodium channels (BacNavs) serve as models of their vertebrate counterparts. BacNavs contain conserved voltage-sensing and pore-forming domains, but they are homotetramers of four identical subunits, rather than pseudotetramers of four homologous domains. Here, we present structures of two NaVAb mutants that capture tightly closed and open states at a resolution of 2.8–3.2 Å. Introduction of two humanizing mutations in the S6 segment (NaVAb/FY: T206F and V213Y) generates a persistently closed form of the activation gate in which the intracellular ends of the four S6 segments are drawn tightly together to block ion permeation completely. This construct also revealed the complete structure of the four-helix bundle that forms the C-terminal domain. In contrast, truncation of the C-terminal 40 residues in NavAb/1–226 captures the activation gate in an open conformation, revealing the open state of a BacNav with intact voltage sensors. Comparing these structures illustrates the full range of motion of the activation gate, from closed with its orifice fully occluded to open with an orifice of ∼10 Å. Molecular dynamics and free-energy simulations confirm designation of NaVAb/1–226 as an open state that allows permeation of hydrated Na+, and these results also support a hydrophobic gating mechanism for control of ion permeation. These two structures allow completion of a closed–open–inactivated conformational cycle in a single voltage-gated sodium channel and give insight into the structural basis for state-dependent binding of sodium channel-blocking drugs. PMID:28348242

Niflumic acid alters gating of HCN2 pacemaker channels by interaction with the outer region of S4 voltage sensing domains.

PubMed

Cheng, Lan; Sanguinetti, Michael C

2009-05-01

Niflumic acid, 2-[[3-(trifluoromethyl)phenyl]amino]pyridine-3-carboxylic acid (NFA), is a nonsteroidal anti-inflammatory drug that also blocks or modifies the gating of many ion channels. Here, we investigated the effects of NFA on hyperpolarization-activated cyclic nucleotide-gated cation (HCN) pacemaker channels expressed in X. laevis oocytes using site-directed mutagenesis and the two-electrode voltage-clamp technique. Extracellular NFA acted rapidly and caused a slowing of activation and deactivation and a hyperpolarizing shift in the voltage dependence of HCN2 channel activation (-24.5 +/- 1.2 mV at 1 mM). Slowed channel gating and reduction of current magnitude was marked in oocytes treated with NFA, while clamped at 0 mV but minimal in oocytes clamped at -100 mV, indicating the drug preferentially interacts with channels in the closed state. NFA at 0.1 to 3 mM shifted the half-point for channel activation in a concentration-dependent manner, with an EC(50) of 0.54 +/- 0.068 mM and a predicted maximum shift of -38 mV. NFA at 1 mM also reduced maximum HCN2 conductance by approximately 20%, presumably by direct block of the pore. The rapid onset and state-dependence of NFA-induced changes in channel gating suggests an interaction with the extracellular region of the S4 transmembrane helix, the primary voltage-sensing domain of HCN2. Neutralization (by mutation to Gln) of any three of the outer four basic charged residues in S4, but not single mutations, abrogated the NFA-induced shift in channel activation. We conclude that NFA alters HCN2 gating by interacting with the extracellular end of the S4 voltage sensor domains.

Charge movement in gating-locked HCN channels reveals weak coupling of voltage sensors and gate.

PubMed

Ryu, Sujung; Yellen, Gary

2012-11-01

HCN (hyperpolarization-activated cyclic nucleotide gated) pacemaker channels have an architecture similar to that of voltage-gated K(+) channels, but they open with the opposite voltage dependence. HCN channels use essentially the same positively charged voltage sensors and intracellular activation gates as K(+) channels, but apparently these two components are coupled differently. In this study, we examine the energetics of coupling between the voltage sensor and the pore by using cysteine mutant channels for which low concentrations of Cd(2+) ions freeze the open-closed gating machinery but still allow the sensors to move. We were able to lock mutant channels either into open or into closed states by the application of Cd(2+) and measure the effect on voltage sensor movement. Cd(2+) did not immobilize the gating charge, as expected for strict coupling, but rather it produced shifts in the voltage dependence of voltage sensor charge movement, consistent with its effect of confining transitions to either closed or open states. From the magnitude of the Cd(2+)-induced shifts, we estimate that each voltage sensor produces a roughly three- to sevenfold effect on the open-closed equilibrium, corresponding to a coupling energy of ∼1.3-2 kT per sensor. Such coupling is not only opposite in sign to the coupling in K(+) channels, but also much weaker.

Study and Experiment on Non-Contact Voltage Sensor Suitable for Three-Phase Transmission Line

PubMed Central

Zhou, Qiang; He, Wei; Xiao, Dongping; Li, Songnong; Zhou, Kongjun

2015-01-01

A voltage transformer, as voltage signal detection equipment, plays an important role in a power system. Presently, more and more electric power systems are adopting potential transformer and capacitance voltage transformers. Transformers are often large in volume and heavyweight, their insulation design is difficult, and an iron core or multi-grade capacitance voltage division structure is generally adopted. As a result, the detection accuracy of transformer is reduced, a huge phase difference exists between detection signal and voltage signal to be measured, and the detection signal cannot accurately and timely reflect the change of conductor voltage signal to be measured. By aiming at the current problems of electric transformation, based on electrostatic induction principle, this paper designed a non-contact voltage sensor and gained detection signal of the sensor through electrostatic coupling for the electric field generated by electric charges of the conductor to be measured. The insulation structure design of the sensor is simple and its volume is small; phase difference of sensor measurement is effectively reduced through optimization design of the electrode; and voltage division ratio and measurement accuracy are increased. The voltage sensor was tested on the experimental platform of simulating three-phase transmission line. According to the result, the designed non-contact voltage sensor can realize accurate and real-time measurement for the conductor voltage. It can be applied to online monitoring for the voltage of three-phase transmission line or three-phase distribution network line, which is in accordance with the development direction of the smart grid. PMID:26729119

Study and Experiment on Non-Contact Voltage Sensor Suitable for Three-Phase Transmission Line.

PubMed

Zhou, Qiang; He, Wei; Xiao, Dongping; Li, Songnong; Zhou, Kongjun

2015-12-30

A voltage transformer, as voltage signal detection equipment, plays an important role in a power system. Presently, more and more electric power systems are adopting potential transformer and capacitance voltage transformers. Transformers are often large in volume and heavyweight, their insulation design is difficult, and an iron core or multi-grade capacitance voltage division structure is generally adopted. As a result, the detection accuracy of transformer is reduced, a huge phase difference exists between detection signal and voltage signal to be measured, and the detection signal cannot accurately and timely reflect the change of conductor voltage signal to be measured. By aiming at the current problems of electric transformation, based on electrostatic induction principle, this paper designed a non-contact voltage sensor and gained detection signal of the sensor through electrostatic coupling for the electric field generated by electric charges of the conductor to be measured. The insulation structure design of the sensor is simple and its volume is small; phase difference of sensor measurement is effectively reduced through optimization design of the electrode; and voltage division ratio and measurement accuracy are increased. The voltage sensor was tested on the experimental platform of simulating three-phase transmission line. According to the result, the designed non-contact voltage sensor can realize accurate and real-time measurement for the conductor voltage. It can be applied to online monitoring for the voltage of three-phase transmission line or three-phase distribution network line, which is in accordance with the development direction of the smart grid.

On Certain New Methodology for Reducing Sensor and Readout Electronics Circuitry Noise in Digital Domain

NASA Technical Reports Server (NTRS)

Kizhner, Semion; Miko, Joseph; Bradley, Damon; Heinzen, Katherine

2008-01-01

NASA Hubble Space Telescope (HST) and upcoming cosmology science missions carry instruments with multiple focal planes populated with many large sensor detector arrays. These sensors are passively cooled to low temperatures for low-level light (L3) and near-infrared (NIR) signal detection, and the sensor readout electronics circuitry must perform at extremely low noise levels to enable new required science measurements. Because we are at the technological edge of enhanced performance for sensors and readout electronics circuitry, as determined by thermal noise level at given temperature in analog domain, we must find new ways of further compensating for the noise in the signal digital domain. To facilitate this new approach, state-of-the-art sensors are augmented at their array hardware boundaries by non-illuminated reference pixels, which can be used to reduce noise attributed to sensors. There are a few proposed methodologies of processing in the digital domain the information carried by reference pixels, as employed by the Hubble Space Telescope and the James Webb Space Telescope Projects. These methods involve using spatial and temporal statistical parameters derived from boundary reference pixel information to enhance the active (non-reference) pixel signals. To make a step beyond this heritage methodology, we apply the NASA-developed technology known as the Hilbert- Huang Transform Data Processing System (HHT-DPS) for reference pixel information processing and its utilization in reconfigurable hardware on-board a spaceflight instrument or post-processing on the ground. The methodology examines signal processing for a 2-D domain, in which high-variance components of the thermal noise are carried by both active and reference pixels, similar to that in processing of low-voltage differential signals and subtraction of a single analog reference pixel from all active pixels on the sensor. Heritage methods using the aforementioned statistical parameters in the digital domain (such as statistical averaging of the reference pixels themselves) zeroes out the high-variance components, and the counterpart components in the active pixels remain uncorrected. This paper describes how the new methodology was demonstrated through analysis of fast-varying noise components using the Hilbert-Huang Transform Data Processing System tool (HHT-DPS) developed at NASA and the high-level programming language MATLAB (Trademark of MathWorks Inc.), as well as alternative methods for correcting for the high-variance noise component, using an HgCdTe sensor data. The NASA Hubble Space Telescope data post-processing, as well as future deep-space cosmology projects on-board instrument data processing from all the sensor channels, would benefit from this effort.

An RF-induced voltage sensor for investigating pacemaker safety in MRI.

PubMed

Barbier, Thérèse; Piumatti, Roberto; Hecker, Bertrand; Odille, Freddy; Felblinger, Jacques; Pasquier, Cédric

2014-12-01

Magnetic resonance imaging (MRI) is inadvisable for patients with pacemakers, as radiofrequency (RF) voltages induced in the pacemaker leads may cause the device to malfunction. Our goal is to develop a sensor to measure such RF-induced voltages during MRI safety tests. A sensor was designed (16.6 cm(2)) for measuring voltages at the connection between the pacemaker lead and its case. The induced voltage is demodulated, digitized, and transferred by optical fibres. The sensor was calibrated on the bench using RF pulses of known amplitude and duration. Then the sensor was tested during MRI scanning at 1.5 T in a saline gel filled phantom. Bench tests showed measurement errors below 5% with a (-40 V; +40 V) range, a precision of 0.06 V, and a temporal resolution of 24.2 μs. In MRI tests, variability in the measured voltages was below 3.7% for 996 measurements with different sensors and RF exposure. Coupling between the sensor and the MRI electromagnetic environment was estimated with a second sensor connected and was below 6.2%. For a typical clinical MRI sequence, voltages around ten Vp were detected. We have built an accurate and reproducible tool for measuring RF-induced voltages in pacemaker leads during MR safety investigations. The sensor might also be used with other conducting cables including those used for electrocardiography and neurostimulation.

Electro-optic voltage sensor with Multiple Beam Splitting

DOEpatents

Woods, Gregory K.; Renak, Todd W.; Crawford, Thomas M.; Davidson, James R.

2000-01-01

A miniature electro-optic voltage sensor system capable of accurate operation at high voltages without use of the dedicated voltage dividing hardware. The invention achieves voltage measurement without significant error contributions from neighboring conductors or environmental perturbations. The invention employs a transmitter, a sensor, a detector, and a signal processor. The transmitter produces a beam of electromagnetic radiation which is routed into the sensor. Within the sensor the beam undergoes the Pockels electro-optic effect. The electro-optic effect produces a modulation of the beam's polarization, which is in turn converted to a pair of independent conversely-amplitude-modulated signals, from which the voltage of the E-field is determined by the signal processor. The use of converse AM signals enables the signal processor to better distinguish signal from noise. The sensor converts the beam by splitting the beam in accordance with the axes of the beam's polarization state (an ellipse) into at least two AM signals. These AM signals are fed into a signal processor and processed to determine the voltage between a ground conductor and the conductor on which voltage is being measured.

Mobile patient monitoring based on impedance-loaded SAW-sensors.

PubMed

Karilainen, Anna; Finnberg, Thomas; Uelzen, Thorsten; Dembowski, Klaus; Müller, Jörg

2004-11-01

A remotely requestable, passive, short-range sensor network for measuring small voltages is presented. The sensor system is able to simultaneously monitor six small voltages in millivolt-range, and it can be used for Holter-electrocardiogram (ECG) and other biopotential monitoring, or in industrial applications. The sensors are based on a surface acoustic wave (SAW) delay line with voltage-dependent, impedance loading on a reflector interdigital transducer (IDT). The load circuit impedance is varied by the capacitance of the voltage-controlled varactor. High resolution is achieved by developing a MOS-capacitor with a thin oxide, low flat-band voltage, and zero-voltage capacitance in the space-charge region, as well as a high-Q-microcoil by thick metal electroplating. Simultaneous monitoring of multiple potentials is realized by time-division-multiplexing of different sensor signals.

Electrooptic polymer voltage sensor and method of manufacture thereof

NASA Technical Reports Server (NTRS)

Gottsche, Allan (Inventor); Perry, Joseph W. (Inventor)

1993-01-01

An optical voltage sensor utilizing an electrooptic polymer is disclosed for application to electric power distribution systems. The sensor, which can be manufactured at low cost in accordance with a disclosed method, measures voltages across a greater range than prior art sensors. The electrooptic polymer, which replaces the optical crystal used in prior art sensors, is sandwiched directly between two high voltage electrodes. Voltage is measured by fiber optical means, and no voltage division is required. The sample of electrooptic polymer is fabricated in a special mold and later mounted in a sensor housing. Alternatively, mold and sensor housing may be identical. The sensor housing is made out of a machinable polymeric material and is equipped with two opposing optical windows. The optical windows are mounted in the bottom of machined holes in the wall of the mold. These holes provide for mounting of the polarizing optical components and for mounting of the fiber optic connectors. One connecting fiber is equipped with a light emitting diode as a light source. Another connecting fiber is equipped with a photodiode as a detector.

A localized interaction surface for voltage-sensing domains on the pore domain of a K+ channel.

PubMed

Li-Smerin, Y; Hackos, D H; Swartz, K J

2000-02-01

Voltage-gated K+ channels contain a central pore domain and four surrounding voltage-sensing domains. How and where changes in the structure of the voltage-sensing domains couple to the pore domain so as to gate ion conduction is not understood. The crystal structure of KcsA, a bacterial K+ channel homologous to the pore domain of voltage-gated K+ channels, provides a starting point for addressing this question. Guided by this structure, we used tryptophan-scanning mutagenesis on the transmembrane shell of the pore domain in the Shaker voltage-gated K+ channel to localize potential protein-protein and protein-lipid interfaces. Some mutants cause only minor changes in gating and when mapped onto the KcsA structure cluster away from the interface between pore domain subunits. In contrast, mutants producing large changes in gating tend to cluster near this interface. These results imply that voltage-sensing domains interact with localized regions near the interface between adjacent pore domain subunits.

An optical fiber Bragg grating and piezoelectric ceramic voltage sensor

NASA Astrophysics Data System (ADS)

Yang, Qing; He, Yanxiao; Sun, Shangpeng; Luo, Mandan; Han, Rui

2017-10-01

Voltage measurement is essential in many fields like power grids, telecommunications, metallurgy, railways, and oil production. A voltage-sensing unit, consisting of fiber Bragg gratings (FBGs) and piezoelectric ceramics, based on which an optical over-voltage sensor was proposed and fabricated in this paper. No demodulation devices like spectrometer or Fabry-Perot filter were needed to gain the voltage signal, and a relatively large sensing frequency range was acquired in this paper; thus, the cost of the sensing system is more acceptable in engineering application. The voltage to be measured was directly applied to the piezoelectric ceramic, and deformation of the ceramics and the grating would be caused because of the inverse piezoelectric effect. With a reference grating, the output light intensity change will be caused by the FBG center wavelength change; thus, the relationship between the applied voltage and the output light intensity was established. Validation of the sensor was accomplished in the frequency range from 50 Hz to 20 kHz and switching impulse waves with a test platform; good linearity of the input-output characteristic was achieved. A temperature validation test was completed, showing that the sensor maintains good temperature stability. Experimental results show that the optical over-voltage sensor can be used for voltage monitoring, and if applied with a voltage divider, the sensor can be used to measure high voltage.

An optical fiber Bragg grating and piezoelectric ceramic voltage sensor.

PubMed

Yang, Qing; He, Yanxiao; Sun, Shangpeng; Luo, Mandan; Han, Rui

2017-10-01

Voltage measurement is essential in many fields like power grids, telecommunications, metallurgy, railways, and oil production. A voltage-sensing unit, consisting of fiber Bragg gratings (FBGs) and piezoelectric ceramics, based on which an optical over-voltage sensor was proposed and fabricated in this paper. No demodulation devices like spectrometer or Fabry-Perot filter were needed to gain the voltage signal, and a relatively large sensing frequency range was acquired in this paper; thus, the cost of the sensing system is more acceptable in engineering application. The voltage to be measured was directly applied to the piezoelectric ceramic, and deformation of the ceramics and the grating would be caused because of the inverse piezoelectric effect. With a reference grating, the output light intensity change will be caused by the FBG center wavelength change; thus, the relationship between the applied voltage and the output light intensity was established. Validation of the sensor was accomplished in the frequency range from 50 Hz to 20 kHz and switching impulse waves with a test platform; good linearity of the input-output characteristic was achieved. A temperature validation test was completed, showing that the sensor maintains good temperature stability. Experimental results show that the optical over-voltage sensor can be used for voltage monitoring, and if applied with a voltage divider, the sensor can be used to measure high voltage.

Profiling of Current Transients in Capacitor Type Diamond Sensors.

PubMed

Gaubas, Eugenijus; Ceponis, Tomas; Meskauskaite, Dovile; Kazuchits, Nikolai

2015-06-08

The operational characteristics of capacitor-type detectors based on HPHT and CVD diamond have been investigated using perpendicular and parallel injection of carrier domain regimes. Simulations of the drift-diffusion current transients have been implemented by using dynamic models based on Shockley-Ramo's theorem, under injection of localized surface domains and of bulk charge carriers. The bipolar drift-diffusion regimes have been analyzed for the photo-induced bulk domain (packet) of excess carriers. The surface charge formation and polarization effects dependent on detector biasing voltage have been revealed. The screening effects ascribed to surface charge and to dynamics of extraction of the injected bulk excess carrier domain have been separated and explained. The parameters of drift mobility of the electrons μ(e) = 4000 cm2/Vs and holes μ(h) = 3800 cm2/Vs have been evaluated for CVD diamond using the perpendicular profiling of currents. The coefficient of carrier ambipolar diffusion D(a) = 97 cm2/s and the carrier recombination lifetime τ(R,CVD) ≌ 110 ns in CVD diamond were extracted by combining analysis of the transients of the sensor current and the microwave probed photoconductivity. The carrier trapping with inherent lifetime τR,HPHT ≌ 2 ns prevails in HPHT diamond.

Electro-optic voltage sensor for sensing voltage in an E-field

DOEpatents

Woods, G.K.; Renak, T.W.

1999-04-06

A miniature electro-optic voltage sensor system capable of accurate operation at high voltages is disclosed. The system employs a transmitter, a sensor disposed adjacent to but out of direct electrical contact with a conductor on which the voltage is to be measured, a detector, and a signal processor. The transmitter produces a beam of electromagnetic radiation which is routed into the sensor where the beam undergoes the Pockels electro-optic effect. The electro-optic effect causes phase shifting in the beam, which is in turn converted to a pair of independent beams, from which the voltage of a system based on its E-field is determined when the two beams are normalized by the signal processor. The sensor converts the beam by splitting the beam in accordance with the axes of the beam`s polarization state (an ellipse whose ellipticity varies between -1 and +1 in proportion to voltage) into at least two AM signals. These AM signals are fed into a signal processor and processed to determine the voltage between a ground conductor and the conductor on which voltage is being measured. 18 figs.

Electro-optic voltage sensor for sensing voltage in an E-field

DOEpatents

Woods, Gregory K.; Renak, Todd W.

1999-01-01

A miniature electro-optic voltage sensor system capable of accurate operation at high voltages. The system employs a transmitter, a sensor disposed adjacent to but out of direct electrical contact with a conductor on which the voltage is to be measured, a detector, and a signal processor. The transmitter produces a beam of electromagnetic radiation which is routed into the sensor where the beam undergoes the Pockels electro-optic effect. The electro-optic effect causes phase shifting in the beam, which is in turn converted to a pair of independent beams, from which the voltage of a system based on its E-field is determined when the two beams are normalized by the signal processor. The sensor converts the beam by splitting the beam in accordance with the axes of the beam's polarization state (an ellipse whose ellipticity varies between -1 and +1 in proportion to voltage) into at least two AM signals. These AM signals are fed into a signal processor and processed to determine the voltage between a ground conductor and the conductor on which voltage is being measured.

A Calmodulin C-Lobe Ca2+-Dependent Switch Governs Kv7 Channel Function.

PubMed

Chang, Aram; Abderemane-Ali, Fayal; Hura, Greg L; Rossen, Nathan D; Gate, Rachel E; Minor, Daniel L

2018-02-21

Kv7 (KCNQ) voltage-gated potassium channels control excitability in the brain, heart, and ear. Calmodulin (CaM) is crucial for Kv7 function, but how this calcium sensor affects activity has remained unclear. Here, we present X-ray crystallographic analysis of CaM:Kv7.4 and CaM:Kv7.5 AB domain complexes that reveal an Apo/CaM clamp conformation and calcium binding preferences. These structures, combined with small-angle X-ray scattering, biochemical, and functional studies, establish a regulatory mechanism for Kv7 CaM modulation based on a common architecture in which a CaM C-lobe calcium-dependent switch releases a shared Apo/CaM clamp conformation. This C-lobe switch inhibits voltage-dependent activation of Kv7.4 and Kv7.5 but facilitates Kv7.1, demonstrating that mechanism is shared by Kv7 isoforms despite the different directions of CaM modulation. Our findings provide a unified framework for understanding how CaM controls different Kv7 isoforms and highlight the role of membrane proximal domains for controlling voltage-gated channel function. VIDEO ABSTRACT. Copyright © 2018 Elsevier Inc. All rights reserved.

Voltage-sensing domain mode shift is coupled to the activation gate by the N-terminal tail of hERG channels.

PubMed

Tan, Peter S; Perry, Matthew D; Ng, Chai Ann; Vandenberg, Jamie I; Hill, Adam P

2012-09-01

Human ether-a-go-go-related gene (hERG) potassium channels exhibit unique gating kinetics characterized by unusually slow activation and deactivation. The N terminus of the channel, which contains an amphipathic helix and an unstructured tail, has been shown to be involved in regulation of this slow deactivation. However, the mechanism of how this occurs and the connection between voltage-sensing domain (VSD) return and closing of the gate are unclear. To examine this relationship, we have used voltage-clamp fluorometry to simultaneously measure VSD motion and gate closure in N-terminally truncated constructs. We report that mode shifting of the hERG VSD results in a corresponding shift in the voltage-dependent equilibrium of channel closing and that at negative potentials, coupling of the mode-shifted VSD to the gate defines the rate of channel closure. Deletion of the first 25 aa from the N terminus of hERG does not alter mode shifting of the VSD but uncouples the shift from closure of the cytoplasmic gate. Based on these observations, we propose the N-terminal tail as an adaptor that couples voltage sensor return to gate closure to define slow deactivation gating in hERG channels. Furthermore, because the mode shift occurs on a time scale relevant to the cardiac action potential, we suggest a physiological role for this phenomenon in maximizing current flow through hERG channels during repolarization.

Design of a New Built-in UHF Multi-Frequency Antenna Sensor for Partial Discharge Detection in High-Voltage Switchgears.

PubMed

Zhang, Xiaoxing; Cheng, Zheng; Gui, Yingang

2016-07-26

In this study a new built-in ultrahigh frequency (UHF) antenna sensor was designed and applied in a high-voltage switchgear for partial discharge (PD) detection. The casing of the switchgear was initially used as the ground plane of the antenna sensor, which integrated the sensor into the high-voltage switchgear. The Koch snowflake patch was adopted as the radiation patch of the antenna to overcome the disadvantages of common microstrip antennas, and the feed position and the dielectric layer thickness were simulated in detail. Simulation results show that the antenna sensor possessed four resonant points with good impedance matching from 300 MHz to 1000 MHz, and it also presented good multi-frequency performance in the entire working frequency band. PD detection experiments were conducted in the high-voltage switchgear, and the fabricated antenna sensor was effectively built into the high-voltage switchgear. In order to reflect the advantages of the built-in antenna sensor, another external UHF antenna sensor was used as a comparison to simultaneously detect PD. Experimental results demonstrated that the built-in antenna sensor possessed high detection sensitivity and strong anti-interference capacity, which ensured the practicability of the design. In addition, it had more high-voltage switchgear PD detection advantages than the external sensor.

Design of a New Built-in UHF Multi-Frequency Antenna Sensor for Partial Discharge Detection in High-Voltage Switchgears

PubMed Central

Zhang, Xiaoxing; Cheng, Zheng; Gui, Yingang

2016-01-01

In this study a new built-in ultrahigh frequency (UHF) antenna sensor was designed and applied in a high-voltage switchgear for partial discharge (PD) detection. The casing of the switchgear was initially used as the ground plane of the antenna sensor, which integrated the sensor into the high-voltage switchgear. The Koch snowflake patch was adopted as the radiation patch of the antenna to overcome the disadvantages of common microstrip antennas, and the feed position and the dielectric layer thickness were simulated in detail. Simulation results show that the antenna sensor possessed four resonant points with good impedance matching from 300 MHz to 1000 MHz, and it also presented good multi-frequency performance in the entire working frequency band. PD detection experiments were conducted in the high-voltage switchgear, and the fabricated antenna sensor was effectively built into the high-voltage switchgear. In order to reflect the advantages of the built-in antenna sensor, another external UHF antenna sensor was used as a comparison to simultaneously detect PD. Experimental results demonstrated that the built-in antenna sensor possessed high detection sensitivity and strong anti-interference capacity, which ensured the practicability of the design. In addition, it had more high-voltage switchgear PD detection advantages than the external sensor. PMID:27472331

Electro-optic voltage sensor with beam splitting

DOEpatents

Woods, Gregory K.; Renak, Todd W.; Davidson, James R.; Crawford, Thomas M.

2002-01-01

The invention is a miniature electro-optic voltage sensor system capable of accurate operation at high voltages without use of the dedicated voltage dividing hardware typically found in the prior art. The invention achieves voltage measurement without significant error contributions from neighboring conductors or environmental perturbations. The invention employs a transmitter, a sensor, a detector, and a signal processor. The transmitter produces a beam of electromagnetic radiation which is routed into the sensor. Within the sensor the beam undergoes the Pockels electro-optic effect. The electro-optic effect produces a modulation of the beam's polarization, which is in turn converted to a pair of independent conversely-amplitude-modulated signals, from which the voltage of the E-field is determined by the signal processor. The use of converse AM signals enables the signal processor to better distinguish signal from noise. The sensor converts the beam by splitting the beam in accordance with the axes of the beam's polarization state (an ellipse) into at least two AM signals. These AM signals are fed into a signal processor and processed to determine the voltage between a ground conductor and the conductor on which voltage is being measured.

Sensitive bistable magnetic sensors using twisted amorphous magnetostrictive ribbons due to Matteucci effect

NASA Astrophysics Data System (ADS)

Mohri, K.; Takeuchi, S.

1982-11-01

New sensitive magnetic-field sensors are presented using twisted amorphous magnetostrictive ribbons such as Fe80B20 and Fe81-xCrxB17Si2. Sharp voltage pulses are induced between ends of the ribbon of as short as 25 mm or at the terminals of the detecting coil against external fields of as low as 1 Oe and 0.01 Hz-6 kHz. The domain nucleation field at the bistable flux reversal is very constant for 130 °C, 600 h using Fe79Cr2B17Si2, and a possible maximum operating temperature is about 180 °C. Small sized magnetic sensors without any windings for detecting rotational speed, distance, and other mechanical quantities are realized using the twisted ribbons by combining with small magnets. These sensitive and reliable magnetic sensors with digital outputs are suitable for applications in industrial robots and automobiles controlled with microcomputers.

Non-contact current and voltage sensor having detachable housing incorporating multiple ferrite cylinder portions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Carpenter, Gary D.; El-Essawy, Wael; Ferreira, Alexandre Peixoto

2016-04-26

A detachable current and voltage sensor provides an isolated and convenient device to measure current passing through a conductor such as an AC branch circuit wire, as well as providing an indication of an electrostatic potential on the wire, which can be used to indicate the phase of the voltage on the wire, and optionally a magnitude of the voltage. The device includes a housing formed from two portions that mechanically close around the wire and that contain the current and voltage sensors. The current sensor is a ferrite cylinder formed from at least three portions that form the cylindermore » when the sensor is closed around the wire with a hall effect sensor disposed in a gap between two of the ferrite portions along the circumference to measure current. A capacitive plate or wire is disposed adjacent to, or within, the ferrite cylinder to provide the indication of the voltage.« less

Apo states of calmodulin and CaBP1 control CaV1 voltage-gated calcium channel function through direct competition for the IQ domain.

PubMed

Findeisen, Felix; Rumpf, Christine H; Minor, Daniel L

2013-09-09

In neurons, binding of calmodulin (CaM) or calcium-binding protein 1 (CaBP1) to the CaV1 (L-type) voltage-gated calcium channel IQ domain endows the channel with diametrically opposed properties. CaM causes calcium-dependent inactivation and limits calcium entry, whereas CaBP1 blocks calcium-dependent inactivation (CDI) and allows sustained calcium influx. Here, we combine isothermal titration calorimetry with cell-based functional measurements and mathematical modeling to show that these calcium sensors behave in a competitive manner that is explained quantitatively by their apo-state binding affinities for the IQ domain. This competition can be completely blocked by covalent tethering of CaM to the channel. Further, we show that Ca(2+)/CaM has a sub-picomolar affinity for the IQ domain that is achieved without drastic alteration of calcium-binding properties. The observation that the apo forms of CaM and CaBP1 compete with each other demonstrates a simple mechanism for direct modulation of CaV1 function and suggests a means by which excitable cells may dynamically tune CaV activity. Copyright © 2013 The Authors. Published by Elsevier Ltd.. All rights reserved.

Non-contact current and voltage sensor

DOEpatents

Carpenter, Gary D; El-Essawy, Wael; Ferreira, Alexandre Peixoto; Keller, Thomas Walter; Rubio, Juan C; Schappert, Michael A

2014-03-25

A detachable current and voltage sensor provides an isolated and convenient device to measure current passing through a conductor such as an AC branch circuit wire, as well as providing an indication of an electrostatic potential on the wire, which can be used to indicate the phase of the voltage on the wire, and optionally a magnitude of the voltage. The device includes a housing that contains the current and voltage sensors, which may be a ferrite cylinder with a hall effect sensor disposed in a gap along the circumference to measure current, or alternative a winding provided through the cylinder along its axis and a capacitive plate or wire disposed adjacent to, or within, the ferrite cylinder to provide the indication of the voltage.

RF current sensor

DOEpatents

Moore, James A.; Sparks, Dennis O.

1998-11-10

An RF sensor having a novel current sensing probe and a voltage sensing probe to measure voltage and current. The current sensor is disposed in a transmission line to link all of the flux generated by the flowing current in order to obtain an accurate measurement. The voltage sensor is a flat plate which operates as a capacitive plate to sense voltage on a center conductor of the transmission line, in which the measured voltage is obtained across a resistance leg of a R-C differentiator circuit formed by the characteristic impedance of a connecting transmission line and a capacitance of the plate, which is positioned proximal to the center conductor.

Electro-optical voltage sensor head

DOEpatents

Woods, Gregory K.

1998-01-01

A miniature electro-optic voltage sensor system capable of accurate operation at high voltages. The system employs a transmitter, a sensor disposed adjacent to but out of direct electrical contact with a conductor on which the voltage is to be measured, a detector, and a signal processor. The transmitter produces a beam of electromagnetic radiation which is routed into the sensor where the beam undergoes the Pockels electro-optic effect. The electro-optic effect causes phase shifting in the beam, which is in turn converted to a pair of independent beams, from which the voltage of a system based on its E-field is determined when the two beams are normalized by the signal processor. The sensor converts the beam by splitting the beam in accordance with the axes of the beam's polarization state (an ellipse whose ellipticity varies between -1 and +1 in proportion to voltage) into at least two AM signals. These AM signals are fed into a signal processor and processed to determine the voltage between a ground conductor and the conductor on which voltage is being measured.

Electro-optical voltage sensor head

DOEpatents

Woods, G.K.

1998-03-24

A miniature electro-optic voltage sensor system capable of accurate operation at high voltages is disclosed. The system employs a transmitter, a sensor disposed adjacent to but out of direct electrical contact with a conductor on which the voltage is to be measured, a detector, and a signal processor. The transmitter produces a beam of electromagnetic radiation which is routed into the sensor where the beam undergoes the Pockels electro-optic effect. The electro-optic effect causes phase shifting in the beam, which is in turn converted to a pair of independent beams, from which the voltage of a system based on its E-field is determined when the two beams are normalized by the signal processor. The sensor converts the beam by splitting the beam in accordance with the axes of the beam`s polarization state (an ellipse whose ellipticity varies between -1 and +1 in proportion to voltage) into at least two AM signals. These AM signals are fed into a signal processor and processed to determine the voltage between a ground conductor and the conductor on which voltage is being measured. 6 figs.

Molecular Coupling between Voltage Sensor and Pore Opening in the Arabidopsis Inward Rectifier K+ Channel KAT1

PubMed Central

Latorre, Ramon; Olcese, Riccardo; Basso, Claudia; Gonzalez, Carlos; Muñoz, Fabian; Cosmelli, Diego; Alvarez, Osvaldo

2003-01-01

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. PMID:14517271

Nonsensing residues in S3-S4 linker's C terminus affect the voltage sensor set point in K+ channels.

PubMed

Carvalho-de-Souza, Joao L; Bezanilla, Francisco

2018-02-05

Voltage sensitivity in ion channels is a function of highly conserved arginine residues in their voltage-sensing domains (VSDs), but this conservation does not explain the diversity in voltage dependence among different K + channels. Here we study the non-voltage-sensing residues 353 to 361 in Shaker K + channels and find that residues 358 and 361 strongly modulate the voltage dependence of the channel. We mutate these two residues into all possible remaining amino acids (AAs) and obtain Q-V and G-V curves. We introduced the nonconducting W434F mutation to record sensing currents in all mutants except L361R, which requires K + depletion because it is affected by W434F. By fitting Q-Vs with a sequential three-state model for two voltage dependence-related parameters ( V 0 , the voltage-dependent transition from the resting to intermediate state and V 1 , from the latter to the active state) and G-Vs with a two-state model for the voltage dependence of the pore domain parameter ( V 1/2 ), Spearman's coefficients denoting variable relationships with hydrophobicity, available area, length, width, and volume of the AAs in 358 and 361 positions could be calculated. We find that mutations in residue 358 shift Q-Vs and G-Vs along the voltage axis by affecting V 0 , V 1 , and V 1/2 according to the hydrophobicity of the AA. Mutations in residue 361 also shift both curves, but V 0 is affected by the hydrophobicity of the AA in position 361, whereas V 1 and V 1/2 are affected by size-related AA indices. Small-to-tiny AAs have opposite effects on V 1 and V 1/2 in position 358 compared with 361. We hypothesize possible coordination points in the protein that residues 358 and 361 would temporarily and differently interact with in an intermediate state of VSD activation. Our data contribute to the accumulating knowledge of voltage-dependent ion channel activation by adding functional information about the effects of so-called non-voltage-sensing residues on VSD dynamics. © 2018 Carvalho-de-Souza and Bezanilla.

Voltage-dependent K+ channel gating and voltage sensor toxin sensitivity depend on the mechanical state of the lipid membrane.

PubMed

Schmidt, Daniel; MacKinnon, Roderick

2008-12-09

Voltage-dependent K(+) (Kv) channels underlie action potentials through gating conformational changes that are driven by membrane voltage. In this study of the paddle chimera Kv channel, we demonstrate that the rate of channel opening, the voltage dependence of the open probability, and the maximum achievable open probability depend on the lipid membrane environment. The activity of the voltage sensor toxin VsTx1, which interferes with voltage-dependent gating by partitioning into the membrane and binding to the channel, also depends on the membrane. Membrane environmental factors that influence channel function are divisible into two general categories: lipid compositional and mechanical state. The mechanical state can have a surprisingly large effect on the function of a voltage-dependent K(+) channel, including its pharmacological interaction with voltage sensor toxins. The dependence of VSTx1 activity on the mechanical state of the membrane leads us to hypothesize that voltage sensor toxins exert their effect by perturbing the interaction forces that exist between the channel and the membrane.

Voltage-dependent K+ channel gating and voltage sensor toxin sensitivity depend on the mechanical state of the lipid membrane

PubMed Central

Schmidt, Daniel; MacKinnon, Roderick

2008-01-01

Voltage-dependent K+ (Kv) channels underlie action potentials through gating conformational changes that are driven by membrane voltage. In this study of the paddle chimera Kv channel, we demonstrate that the rate of channel opening, the voltage dependence of the open probability, and the maximum achievable open probability depend on the lipid membrane environment. The activity of the voltage sensor toxin VsTx1, which interferes with voltage-dependent gating by partitioning into the membrane and binding to the channel, also depends on the membrane. Membrane environmental factors that influence channel function are divisible into two general categories: lipid compositional and mechanical state. The mechanical state can have a surprisingly large effect on the function of a voltage-dependent K+ channel, including its pharmacological interaction with voltage sensor toxins. The dependence of VSTx1 activity on the mechanical state of the membrane leads us to hypothesize that voltage sensor toxins exert their effect by perturbing the interaction forces that exist between the channel and the membrane. PMID:19050073

Non-intrusive high voltage measurement using slab coupled optical sensors

NASA Astrophysics Data System (ADS)

Stan, Nikola; Chadderdon, Spencer; Selfridge, Richard H.; Schultz, Stephen M.

2014-03-01

We present an optical fiber non-intrusive sensor for measuring high voltage transients. The sensor converts the unknown voltage to electric field, which is then measured using slab-coupled optical fiber sensor (SCOS). Since everything in the sensor except the electrodes is made of dielectric materials and due to the small field sensor size, the sensor is minimally perturbing to the measured voltage. We present the details of the sensor design, which eliminates arcing and minimizes local dielectric breakdown using Teflon blocks and insulation of the whole structure with transformer oil. The structure has a capacitance of less than 3pF and resistance greater than 10 GΩ. We show the measurement of 66.5 kV pulse with a 32.6μs time constant. The measurement matches the expected value of 67.8 kV with less than 2% error.

3′ Phosphatase activity toward phosphatidylinositol 3,4-bisphosphate [PI(3,4)P2] by voltage-sensing phosphatase (VSP)

PubMed Central

Kurokawa, Tatsuki; Takasuga, Shunsuke; Sakata, Souhei; Yamaguchi, Shinji; Horie, Shigeo; Homma, Koichi J.; Sasaki, Takehiko; Okamura, Yasushi

2012-01-01

Voltage-sensing phosphatases (VSPs) consist of a voltage-sensor domain and a cytoplasmic region with remarkable sequence similarity to phosphatase and tensin homolog deleted on chromosome 10 (PTEN), a tumor suppressor phosphatase. VSPs dephosphorylate the 5′ position of the inositol ring of both phosphatidylinositol 3,4,5-trisphosphate [PI(3,4,5)P3] and phosphatidylinositol 4,5-bisphosphate [PI(4,5)P2] upon voltage depolarization. However, it is unclear whether VSPs also have 3′ phosphatase activity. To gain insights into this question, we performed in vitro assays of phosphatase activities of Ciona intestinalis VSP (Ci-VSP) and transmembrane phosphatase with tensin homology (TPTE) and PTEN homologous inositol lipid phosphatase (TPIP; one human ortholog of VSP) with radiolabeled PI(3,4,5)P3. TLC assay showed that the 3′ phosphate of PI(3,4,5)P3 was not dephosphorylated, whereas that of phosphatidylinositol 3,4-bisphosphate [PI(3,4)P2] was removed by VSPs. Monitoring of PI(3,4)P2 levels with the pleckstrin homology (PH) domain from tandem PH domain-containing protein (TAPP1) fused with GFP (PHTAPP1-GFP) by confocal microscopy in amphibian oocytes showed an increase of fluorescence intensity during depolarization to 0 mV, consistent with 5′ phosphatase activity of VSP toward PI(3,4,5)P3. However, depolarization to 60 mV showed a transient increase of GFP fluorescence followed by a decrease, indicating that, after PI(3,4,5)P3 is dephosphorylated at the 5′ position, PI(3,4)P2 is then dephosphorylated at the 3′ position. These results suggest that substrate specificity of the VSP changes with membrane potential. PMID:22645351

3' Phosphatase activity toward phosphatidylinositol 3,4-bisphosphate [PI(3,4)P2] by voltage-sensing phosphatase (VSP).

PubMed

Kurokawa, Tatsuki; Takasuga, Shunsuke; Sakata, Souhei; Yamaguchi, Shinji; Horie, Shigeo; Homma, Koichi J; Sasaki, Takehiko; Okamura, Yasushi

2012-06-19

Voltage-sensing phosphatases (VSPs) consist of a voltage-sensor domain and a cytoplasmic region with remarkable sequence similarity to phosphatase and tensin homolog deleted on chromosome 10 (PTEN), a tumor suppressor phosphatase. VSPs dephosphorylate the 5' position of the inositol ring of both phosphatidylinositol 3,4,5-trisphosphate [PI(3,4,5)P(3)] and phosphatidylinositol 4,5-bisphosphate [PI(4,5)P(2)] upon voltage depolarization. However, it is unclear whether VSPs also have 3' phosphatase activity. To gain insights into this question, we performed in vitro assays of phosphatase activities of Ciona intestinalis VSP (Ci-VSP) and transmembrane phosphatase with tensin homology (TPTE) and PTEN homologous inositol lipid phosphatase (TPIP; one human ortholog of VSP) with radiolabeled PI(3,4,5)P(3). TLC assay showed that the 3' phosphate of PI(3,4,5)P(3) was not dephosphorylated, whereas that of phosphatidylinositol 3,4-bisphosphate [PI(3,4)P(2)] was removed by VSPs. Monitoring of PI(3,4)P(2) levels with the pleckstrin homology (PH) domain from tandem PH domain-containing protein (TAPP1) fused with GFP (PH(TAPP1)-GFP) by confocal microscopy in amphibian oocytes showed an increase of fluorescence intensity during depolarization to 0 mV, consistent with 5' phosphatase activity of VSP toward PI(3,4,5)P(3). However, depolarization to 60 mV showed a transient increase of GFP fluorescence followed by a decrease, indicating that, after PI(3,4,5)P(3) is dephosphorylated at the 5' position, PI(3,4)P(2) is then dephosphorylated at the 3' position. These results suggest that substrate specificity of the VSP changes with membrane potential.

Kv7.1 ion channels require a lipid to couple voltage sensing to pore opening.

PubMed

Zaydman, Mark A; Silva, Jonathan R; Delaloye, Kelli; Li, Yang; Liang, Hongwu; Larsson, H Peter; Shi, Jingyi; Cui, Jianmin

2013-08-06

Voltage-gated ion channels generate dynamic ionic currents that are vital to the physiological functions of many tissues. These proteins contain separate voltage-sensing domains, which detect changes in transmembrane voltage, and pore domains, which conduct ions. Coupling of voltage sensing and pore opening is critical to the channel function and has been modeled as a protein-protein interaction between the two domains. Here, we show that coupling in Kv7.1 channels requires the lipid phosphatidylinositol 4,5-bisphosphate (PIP2). We found that voltage-sensing domain activation failed to open the pore in the absence of PIP2. This result is due to loss of coupling because PIP2 was also required for pore opening to affect voltage-sensing domain activation. We identified a critical site for PIP2-dependent coupling at the interface between the voltage-sensing domain and the pore domain. This site is actually a conserved lipid-binding site among different K(+) channels, suggesting that lipids play an important role in coupling in many ion channels.

Profile structures of the voltage-sensor domain and the voltage-gated K+-channel vectorially oriented in a single phospholipid bilayer membrane at the solid-vapor and solid-liquid interfaces determined by x-ray interferometry

PubMed Central

Gupta, S.; Liu, J.; Strzalka, J.; Blasie, J. K.

2011-01-01

One subunit of the prokaryotic voltage-gated potassium ion channel from Aeropyrum pernix (KvAP) is comprised of six transmembrane α helices, of which S1–S4 form the voltage-sensor domain (VSD) and S5 and S6 contribute to the pore domain (PD) of the functional homotetramer. However, the mechanism of electromechanical coupling interconverting the closed-to-open (i.e., nonconducting-to-K+-conducting) states remains undetermined. Here, we have vectorially oriented the detergent (OG)-solubilized VSD in single monolayers by two independent approaches, namely “directed-assembly” and “self-assembly,” to achieve a high in-plane density. Both utilize Ni coordination chemistry to tether the protein to an alkylated inorganic surface via its C-terminal His6 tag. Subsequently, the detergent is replaced by phospholipid (POPC) via exchange, intended to reconstitute a phospholipid bilayer environment for the protein. X-ray interferometry, in which interference with a multilayer reference structure is used to both enhance and phase the specular x-ray reflectivity from the tethered single membrane, was used to determine directly the electron density profile structures of the VSD protein solvated by detergent versus phospholipid, and with either a moist He (moderate hydration) or bulk aqueous buffer (high hydration) environment to preserve a native structure conformation. Difference electron density profiles, with respect to the multilayer substrate itself, for the VSD-OG monolayer and VSD-POPC membranes at both the solid-vapor and solid-liquid interfaces, reveal the profile structures of the VSD protein dominating these profiles and further indicate a successful reconstitution of a lipid bilayer environment. The self-assembly approach was similarly extended to the intact full-length KvAP channel for comparison. The spatial extent and asymmetry in the profile structures of both proteins confirm their unidirectional vectorial orientation within the reconstituted membrane and indicate retention of the protein’s folded three-dimensional tertiary structure upon completion of membrane bilayer reconstitution. Moreover, the resulting high in-plane density of vectorially oriented protein within a fully hydrated single phospholipid bilayer membrane at the solid-liquid interface will enable investigation of their conformational states as a function of the transmembrane electric potential. PMID:22060407

Reduced voltage sensitivity in a K+-channel voltage sensor by electric field remodeling

PubMed Central

González-Pérez, Vivian; Stack, Katherine; Boric, Katica; Naranjo, David

2010-01-01

Propagation of the nerve impulse relies on the extreme voltage sensitivity of Na+ and K+ channels. The transmembrane movement of four arginine residues, located at the fourth transmembrane segment (S4), in each of their four voltage-sensing domains is mostly responsible for the translocation of 12 to 13 eo across the transmembrane electric field. Inserting additional positively charged residues between the voltage-sensing arginines in S4 would, in principle, increase voltage sensitivity. Here we show that either positively or negatively charged residues added between the two most external sensing arginines of S4 decreased voltage sensitivity of a Shaker voltage-gated K+-channel by up to ≈50%. The replacement of Val363 with a charged residue displaced inwardly the external boundaries of the electric field by at least 6 Å, leaving the most external arginine of S4 constitutively exposed to the extracellular space and permanently excluded from the electric field. Both the physical trajectory of S4 and its electromechanical coupling to open the pore gate seemed unchanged. We propose that the separation between the first two sensing charges at resting is comparable to the thickness of the low dielectric transmembrane barrier they must cross. Thus, at most a single sensing arginine side chain could be found within the field. The conserved hydrophobic nature of the residues located between the voltage-sensing arginines in S4 may shape the electric field geometry for optimal voltage sensitivity in voltage-gated ion channels. PMID:20194763

Profiling of Current Transients in Capacitor Type Diamond Sensors

PubMed Central

Gaubas, Eugenijus; Ceponis, Tomas; Meskauskaite, Dovile; Kazuchits, Nikolai

2015-01-01

The operational characteristics of capacitor-type detectors based on HPHT and CVD diamond have been investigated using perpendicular and parallel injection of carrier domain regimes. Simulations of the drift-diffusion current transients have been implemented by using dynamic models based on Shockley-Ramo’s theorem, under injection of localized surface domains and of bulk charge carriers. The bipolar drift-diffusion regimes have been analyzed for the photo-induced bulk domain (packet) of excess carriers. The surface charge formation and polarization effects dependent on detector biasing voltage have been revealed. The screening effects ascribed to surface charge and to dynamics of extraction of the injected bulk excess carrier domain have been separated and explained. The parameters of drift mobility of the electrons μe = 4000 cm2/Vs and holes μh = 3800 cm2/Vs have been evaluated for CVD diamond using the perpendicular profiling of currents. The coefficient of carrier ambipolar diffusion Da = 97 cm2/s and the carrier recombination lifetime τR,CVD ≌ 110 ns in CVD diamond were extracted by combining analysis of the transients of the sensor current and the microwave probed photoconductivity. The carrier trapping with inherent lifetime τR,HPHT ≌ 2 ns prevails in HPHT diamond. PMID:26061200

OBSAPS Data Acquisition System: Operator’s Manual and System Overview

DTIC Science & Technology

2011-05-01

Explanation of Druck Voltage to Depth Conversion used during OBSAPS (April-May’11)   25   Druck  Pressure  sensor  conversion  from...for H-91, PA Voltage, PA Current and Sonobuoy and Druck pressure sensor analog inputs. 6. Software settable thresholds for H-91, PA Voltage, PA...17. Custom dry side box for Druck Pressure Sensor supply voltage and dropping resistor. 18. Battery 9-30VDC for supplying Druck power 19. Druck PTX

Voltage sensor and dielectric material

DOEpatents

Yakymyshyn, Christopher Paul; Yakymyshyn, Pamela Jane; Brubaker, Michael Allen

2006-10-17

A voltage sensor is described that consists of an arrangement of impedance elements. The sensor is optimized to provide an output ratio that is substantially immune to changes in voltage, temperature variations or aging. Also disclosed is a material with a large and stable dielectric constant. The dielectric constant can be tailored to vary with position or direction in the material.

Simulating the Activation of Voltage Sensing Domain for a Voltage-Gated Sodium Channel Using Polarizable Force Field.

PubMed

Sun, Rui-Ning; Gong, Haipeng

2017-03-02

Voltage-gated sodium (Na V ) channels play vital roles in the signal transduction of excitable cells. Upon activation of a Na V channel, the change of transmembrane voltage triggers conformational change of the voltage sensing domain, which then elicits opening of the pore domain and thus allows an influx of Na + ions. Description of this process with atomistic details is in urgent demand. In this work, we simulated the partial activation process of the voltage sensing domain of a prokaryotic Na V channel using a polarizable force field. We not only observed the conformational change of the voltage sensing domain from resting to preactive state, but also rigorously estimated the free energy profile along the identified reaction pathway. Comparison with the control simulation using an additive force field indicates that voltage-gating thermodynamics of Na V channels may be inaccurately described without considering the electrostatic polarization effect.

The S4–S5 Linker Acts as a Signal Integrator for hERG K+ Channel Activation and Deactivation Gating

PubMed Central

Ng, Chai Ann; Perry, Matthew D.; Tan, Peter S.; Hill, Adam P.; Kuchel, Philip W.; Vandenberg, Jamie I.

2012-01-01

Human ether-à-go-go-related gene (hERG) K+ channels have unusual gating kinetics. Characterised by slow activation/deactivation but rapid inactivation/recovery from inactivation, the unique gating kinetics underlie the central role hERG channels play in cardiac repolarisation. The slow activation and deactivation kinetics are regulated in part by the S4–S5 linker, which couples movement of the voltage sensor domain to opening of the activation gate at the distal end of the inner helix of the pore domain. It has also been suggested that cytosolic domains may interact with the S4–S5 linker to regulate activation and deactivation kinetics. Here, we show that the solution structure of a peptide corresponding to the S4–S5 linker of hERG contains an amphipathic helix. The effects of mutations at the majority of residues in the S4–S5 linker of hERG were consistent with the previously identified role in coupling voltage sensor movement to the activation gate. However, mutations to Ser543, Tyr545, Gly546 and Ala548 had more complex phenotypes indicating that these residues are involved in additional interactions. We propose a model in which the S4–S5 linker, in addition to coupling VSD movement to the activation gate, also contributes to interactions that stabilise the closed state and a separate set of interactions that stabilise the open state. The S4–S5 linker therefore acts as a signal integrator and plays a crucial role in the slow deactivation kinetics of the channel. PMID:22359612

Structure of the polycystic kidney disease TRP channel Polycystin-2 (PC2).

PubMed

Grieben, Mariana; Pike, Ashley C W; Shintre, Chitra A; Venturi, Elisa; El-Ajouz, Sam; Tessitore, Annamaria; Shrestha, Leela; Mukhopadhyay, Shubhashish; Mahajan, Pravin; Chalk, Rod; Burgess-Brown, Nicola A; Sitsapesan, Rebecca; Huiskonen, Juha T; Carpenter, Elisabeth P

2017-02-01

Mutations in either polycystin-1 (PC1 or PKD1) or polycystin-2 (PC2, PKD2 or TRPP1) cause autosomal-dominant polycystic kidney disease (ADPKD) through unknown mechanisms. Here we present the structure of human PC2 in a closed conformation, solved by electron cryomicroscopy at 4.2-Å resolution. The structure reveals a novel polycystin-specific 'tetragonal opening for polycystins' (TOP) domain tightly bound to the top of a classic transient receptor potential (TRP) channel structure. The TOP domain is formed from two extensions to the voltage-sensor-like domain (VSLD); it covers the channel's endoplasmic reticulum lumen or extracellular surface and encloses an upper vestibule, above the pore filter, without blocking the ion-conduction pathway. The TOP-domain fold is conserved among the polycystins, including the homologous channel-like region of PC1, and is the site of a cluster of ADPKD-associated missense variants. Extensive contacts among the TOP-domain subunits, the pore and the VSLD provide ample scope for regulation through physical and chemical stimuli.

Capacitively coupled RF voltage probe having optimized flux linkage

DOEpatents

Moore, James A.; Sparks, Dennis O.

1999-02-02

An RF sensor having a novel current sensing probe and a voltage sensing probe to measure voltage and current. The current sensor is disposed in a transmission line to link all of the flux generated by the flowing current in order to obtain an accurate measurement. The voltage sensor is a flat plate which operates as a capacitive plate to sense voltage on a center conductor of the transmission line, in which the measured voltage is obtained across a resistance leg of a R-C differentiator circuit formed by the characteristic impedance of a connecting transmission line and a capacitance of the plate, which is positioned proximal to the center conductor.

Design of Edible Oil Degradation Tool by Using Electromagnetic Field Absorbtion Principle which was Characterized to Peroxide Number

NASA Astrophysics Data System (ADS)

Isnen, M.; Nasution, T. I.; Perangin-angin, B.

2016-08-01

The identification of changes in oil quality has been conducted by indicating the change of dielectric constant which was showed by sensor voltage. Sensor was formed from two parallel flats that worked by electromagnetic wave propagation principle. By measuring its amplitude of electromagnetic wave attenuation caused by interaction between edible oil samples and the sensor, dielectric constant could be identified and estimated as well as peroxide number. In this case, the parallel flats were connected to an electric oscillator 700 kHz. Furthermore, sensor system could showed measurable voltage differences for each different samples. The testing carried out to five oil samples after undergoing an oxidation treatment at fix temperature of 235oC for 0, 5, 10, 15 and 20 minutes. Iodometry method testing showed peroxide values about 1.99, 9.95, 5.96, 11.86, and 15.92 meq/kg respectively with rising trend. Besides that, the testing result by sensor system showed voltages values 1.139, 1.147, 1.165, 1.173, and 1.176 volts with rising trend, respectively. It means that the higher sensor voltages showed the higher damage rate of edible oil when the change in sensor voltage was caused by the change in oil dielectric constant in which heating process caused damage in edible oil molecules structure. The more damage of oil structure caused the more difficulties of oil molecules to polarize and it is indicated by smaller dielectric constant. Therefore electric current would be smaller when sensor voltage was higher. On the other side, the higher sensor voltage means the smaller dielectric constant and the higher peroxide number.

Interactions between charged residues in the transmembrane segments of the voltage-sensing domain in the hERG channel.

PubMed

Zhang, M; Liu, J; Jiang, M; Wu, D-M; Sonawane, K; Guy, H R; Tseng, G-N

2005-10-01

Studies on voltage-gated K channels such as Shaker have shown that positive charges in the voltage-sensor (S4) can form salt bridges with negative charges in the surrounding transmembrane segments in a state-dependent manner, and different charge pairings can stabilize the channels in closed or open states. The goal of this study is to identify such charge interactions in the hERG channel. This knowledge can provide constraints on the spatial relationship among transmembrane segments in the channel's voltage-sensing domain, which are necessary for modeling its structure. We first study the effects of reversing S4's positive charges on channel activation. Reversing positive charges at the outer (K525D) and inner (K538D) ends of S4 markedly accelerates hERG activation, whereas reversing the 4 positive charges in between either has no effect or slows activation. We then use the 'mutant cycle analysis' to test whether D456 (outer end of S2) and D411 (inner end of S1) can pair with K525 and K538, respectively. Other positive charges predicted to be able, or unable, to interact with D456 or D411 are also included in the analysis. The results are consistent with predictions based on the distribution of these charged residues, and confirm that there is functional coupling between D456 and K525 and between D411 and K538.

Probing α-3(10) transitions in a voltage-sensing S4 helix.

PubMed

Kubota, Tomoya; Lacroix, Jérôme J; Bezanilla, Francisco; Correa, Ana M

2014-09-02

The S4 helix of voltage sensor domains (VSDs) transfers its gating charges across the membrane electrical field in response to changes of the membrane potential. Recent studies suggest that this process may occur via the helical conversion of the entire S4 between α and 310 conformations. Here, using LRET and FRET, we tested this hypothesis by measuring dynamic changes in the transmembrane length of S4 from engineered VSDs expressed in Xenopus oocytes. Our results suggest that the native S4 from the Ciona intestinalis voltage-sensitive phosphatase (Ci-VSP) does not exhibit extended and long-lived 310 conformations and remains mostly α-helical. Although the S4 of NavAb displays a fully extended 310 conformation in x-ray structures, its transplantation in the Ci-VSP VSD scaffold yielded similar results as the native Ci-VSP S4. Taken together, our study does not support the presence of long-lived extended α-to-310 helical conversions of the S4 in Ci-VSP associated with voltage activation. Copyright © 2014 Biophysical Society. Published by Elsevier Inc. All rights reserved.

Packet personal radiation monitor

DOEpatents

Phelps, J.E.

1988-03-31

A personal radiation monitor of the chirper type is provided for detecting ionizing radiation. A battery powered high voltage power supply is used to generate and apply a high voltage bias to a G-M tube radiation sensor. The high voltage is monitored by a low-loss sensing network which generates a feedback signal to control the high voltage power supply such that the high voltage bias is recharged to +500 VDC when the current pulses of the sensor, generated by the detection of ionizing radiatonevents, discharges the high voltage bias to +450 VDC. During the high voltage recharge period an audio transducer is activated to produce an audible ''chirp''. The rate of the ''chirps'' is controlled by the rate at which the high voltage bias is recharged, which is proportional to the radiation field intensity to which the sensor is exposed. The chirp rate sensitivity is set to be approximately 1.5 (chirps/min/MR/hr.). The G-M tube sensor is used in a current sensing mode so that the device does not paralyze in a high radiation field. 2 figs.

Packet personal radiation monitor

DOEpatents

Phelps, James E.

1989-01-01

A personal radiation monitor of the chirper type is provided for detecting ionizing radiation. A battery powered high voltage power supply is used to generate and apply a high voltage bias to a G-M tube radiation sensor. The high voltage is monitored by a low-loss sensing network which generates a feedback signal to control the high voltage power supply such that the high voltage bias is recharged to +500 VDC when the current pulses of the sensor, generated by the detection of ionizing radiation events, discharges the high voltage bias to +450 VDC. During the high voltage recharge period an audio transducer is activated to produce an audible "chirp". The rate of the "chirps" is controlled by the rate at which the high voltage bias is recharged, which is proportional to the radiation field intensity to which the sensor is exposed. The chirp rate sensitivity is set to be approximately 1.5 (chirps/min/MR/hr.). The G-M tube sensor is used in a current sensing mode so that the device does not paralyze in a high radiation field.

Design, experiments and simulation of voltage transformers on the basis of a differential input D-dot sensor.

PubMed

Wang, Jingang; Gao, Can; Yang, Jie

2014-07-17

Currently available traditional electromagnetic voltage sensors fail to meet the measurement requirements of the smart grid, because of low accuracy in the static and dynamic ranges and the occurrence of ferromagnetic resonance attributed to overvoltage and output short circuit. This work develops a new non-contact high-bandwidth voltage measurement system for power equipment. This system aims at the miniaturization and non-contact measurement of the smart grid. After traditional D-dot voltage probe analysis, an improved method is proposed. For the sensor to work in a self-integrating pattern, the differential input pattern is adopted for circuit design, and grounding is removed. To prove the structure design, circuit component parameters, and insulation characteristics, Ansoft Maxwell software is used for the simulation. Moreover, the new probe was tested on a 10 kV high-voltage test platform for steady-state error and transient behavior. Experimental results ascertain that the root mean square values of measured voltage are precise and that the phase error is small. The D-dot voltage sensor not only meets the requirement of high accuracy but also exhibits satisfactory transient response. This sensor can meet the intelligence, miniaturization, and convenience requirements of the smart grid.

Modular Apparatus and Method for Attaching Multiple Devices

NASA Technical Reports Server (NTRS)

Okojie, Robert S (Inventor)

2015-01-01

A modular apparatus for attaching sensors and electronics is disclosed. The modular apparatus includes a square recess including a plurality of cavities and a reference cavity such that a pressure sensor can be connected to the modular apparatus. The modular apparatus also includes at least one voltage input hole and at least one voltage output hole operably connected to each of the plurality of cavities such that voltage can be applied to the pressure sensor and received from the pressure sensor.

Low-voltage 96 dB snapshot CMOS image sensor with 4.5 nW power dissipation per pixel.

PubMed

Spivak, Arthur; Teman, Adam; Belenky, Alexander; Yadid-Pecht, Orly; Fish, Alexander

2012-01-01

Modern "smart" CMOS sensors have penetrated into various applications, such as surveillance systems, bio-medical applications, digital cameras, cellular phones and many others. Reducing the power of these sensors continuously challenges designers. In this paper, a low power global shutter CMOS image sensor with Wide Dynamic Range (WDR) ability is presented. This sensor features several power reduction techniques, including a dual voltage supply, a selective power down, transistors with different threshold voltages, a non-rationed logic, and a low voltage static memory. A combination of all these approaches has enabled the design of the low voltage "smart" image sensor, which is capable of reaching a remarkable dynamic range, while consuming very low power. The proposed power-saving solutions have allowed the maintenance of the standard architecture of the sensor, reducing both the time and the cost of the design. In order to maintain the image quality, a relation between the sensor performance and power has been analyzed and a mathematical model, describing the sensor Signal to Noise Ratio (SNR) and Dynamic Range (DR) as a function of the power supplies, is proposed. The described sensor was implemented in a 0.18 um CMOS process and successfully tested in the laboratory. An SNR of 48 dB and DR of 96 dB were achieved with a power dissipation of 4.5 nW per pixel.

Low-Voltage 96 dB Snapshot CMOS Image Sensor with 4.5 nW Power Dissipation per Pixel

PubMed Central

Spivak, Arthur; Teman, Adam; Belenky, Alexander; Yadid-Pecht, Orly; Fish, Alexander

2012-01-01

Modern “smart” CMOS sensors have penetrated into various applications, such as surveillance systems, bio-medical applications, digital cameras, cellular phones and many others. Reducing the power of these sensors continuously challenges designers. In this paper, a low power global shutter CMOS image sensor with Wide Dynamic Range (WDR) ability is presented. This sensor features several power reduction techniques, including a dual voltage supply, a selective power down, transistors with different threshold voltages, a non-rationed logic, and a low voltage static memory. A combination of all these approaches has enabled the design of the low voltage “smart” image sensor, which is capable of reaching a remarkable dynamic range, while consuming very low power. The proposed power-saving solutions have allowed the maintenance of the standard architecture of the sensor, reducing both the time and the cost of the design. In order to maintain the image quality, a relation between the sensor performance and power has been analyzed and a mathematical model, describing the sensor Signal to Noise Ratio (SNR) and Dynamic Range (DR) as a function of the power supplies, is proposed. The described sensor was implemented in a 0.18 um CMOS process and successfully tested in the laboratory. An SNR of 48 dB and DR of 96 dB were achieved with a power dissipation of 4.5 nW per pixel. PMID:23112588

KCNE1 divides the voltage sensor movement in KCNQ1/KCNE1 channels into two steps

NASA Astrophysics Data System (ADS)

Barro-Soria, Rene; Rebolledo, Santiago; Liin, Sara I.; Perez, Marta E.; Sampson, Kevin J.; Kass, Robert S.; Larsson, H. Peter

2014-04-01

The functional properties of KCNQ1 channels are highly dependent on associated KCNE-β subunits. Mutations in KCNQ1 or KCNE subunits can cause congenital channelopathies, such as deafness, cardiac arrhythmias and epilepsy. The mechanism by which KCNE1-β subunits slow the kinetics of KCNQ1 channels is a matter of current controversy. Here we show that KCNQ1/KCNE1 channel activation occurs in two steps: first, mutually independent voltage sensor movements in the four KCNQ1 subunits generate the main gating charge movement and underlie the initial delay in the activation time course of KCNQ1/KCNE1 currents. Second, a slower and concerted conformational change of all four voltage sensors and the gate, which opens the KCNQ1/KCNE1 channel. Our data show that KCNE1 divides the voltage sensor movement into two steps with widely different voltage dependences and kinetics. The two voltage sensor steps in KCNQ1/KCNE1 channels can be pharmacologically isolated and further separated by a disease-causing mutation.

Lab-on-chip components for molecular detection

NASA Astrophysics Data System (ADS)

Adam, Tijjani; Dhahi, Th S.; Mohammed, Mohammed; Hashim, U.; Noriman, N. Z.; Dahham, Omar S.

2017-09-01

We successfully fabricated Lab on chip components and integrated for possible use in biomedical application. The sensor was fabricated by using conventional photolithography method integrated with PDMS micro channels for smooth delivery of sample to the sensing domain. The sensor was silanized and aminated with 3-Aminopropyl triethoxysilane (APTES) to functionalize the surface with biomolecules and create molecular binding chemistry. The resulting Si-O-Si- components were functionalized with oligonucleotides probe of HPV, which interacted with the single stranded HPV DNA target to create a field across on the device. The fabrication, immobilization and hybridization processes were characterized with current voltage (I-V) characterization (KEITHLEY, 6487). The sensor show selectivity for the HPV DNA target in a linear range from concentration 0.1 nM to 1 µM. This strategy presented a simple, rapid and sensitive platform for HPV detection and would become a powerful tool for pathogenic microorganisms screening in clinical diagnosis.

In-situ Monitoring of Internal Local Temperature and Voltage of Proton Exchange Membrane Fuel Cells

PubMed Central

Lee, Chi-Yuan; Fan, Wei-Yuan; Hsieh, Wei-Jung

2010-01-01

The distribution of temperature and voltage of a fuel cell are key factors that influence performance. Conventional sensors are normally large, and are also useful only for making external measurements of fuel cells. Centimeter-scale sensors for making invasive measurements are frequently unable to accurately measure the interior changes of a fuel cell. This work focuses mainly on fabricating flexible multi-functional microsensors (for temperature and voltage) to measure variations in the local temperature and voltage of proton exchange membrane fuel cells (PEMFC) that are based on micro-electro-mechanical systems (MEMS). The power density at 0.5 V without a sensor is 450 mW/cm2, and that with a sensor is 426 mW/cm2. Since the reaction area of a fuel cell with a sensor is approximately 12% smaller than that without a sensor, but the performance of the former is only 5% worse. PMID:22163556

In-situ monitoring of internal local temperature and voltage of proton exchange membrane fuel cells.

PubMed

Lee, Chi-Yuan; Fan, Wei-Yuan; Hsieh, Wei-Jung

2010-01-01

The distribution of temperature and voltage of a fuel cell are key factors that influence performance. Conventional sensors are normally large, and are also useful only for making external measurements of fuel cells. Centimeter-scale sensors for making invasive measurements are frequently unable to accurately measure the interior changes of a fuel cell. This work focuses mainly on fabricating flexible multi-functional microsensors (for temperature and voltage) to measure variations in the local temperature and voltage of proton exchange membrane fuel cells (PEMFC) that are based on micro-electro-mechanical systems (MEMS). The power density at 0.5 V without a sensor is 450 mW/cm(2), and that with a sensor is 426 mW/cm(2). Since the reaction area of a fuel cell with a sensor is approximately 12% smaller than that without a sensor, but the performance of the former is only 5% worse.

PIP2-dependent coupling is prominent in Kv7.1 due to weakened interactions between S4-S5 and S6

NASA Astrophysics Data System (ADS)

Kasimova, Marina A.; Zaydman, Mark A.; Cui, Jianmin; Tarek, Mounir

2015-01-01

Among critical aspects of voltage-gated potassium (Kv) channels' functioning is the effective communication between their two composing domains, the voltage sensor (VSD) and the pore. This communication, called coupling, might be transmitted directly through interactions between these domains and, as recently proposed, indirectly through interactions with phosphatidylinositol-4,5-bisphosphate (PIP2), a minor lipid of the inner plasma membrane leaflet. Here, we show how the two components of coupling, mediated by protein-protein or protein-lipid interactions, both contribute in the Kv7.1 functioning. On the one hand, using molecular dynamics simulations, we identified a Kv7.1 PIP2 binding site that involves residues playing a key role in PIP2-dependent coupling. On the other hand, combined theoretical and experimental approaches have shown that the direct interaction between the segments of the VSD (S4-S5) and the pore (S6) is weakened by electrostatic repulsion. Finally, we conclude that due to weakened protein-protein interactions, the PIP2-dependent coupling is especially prominent in Kv7.1.

Strain Sensing Characteristics of Rubbery Carbon Nanotube Composite for Flexible Sensors.

PubMed

Choi, Gyong Rak; Park, Hyung-ki; Huh, Hoon; Kim, Young-Ju; Ham, Heon; Kim, Hyoun Woo; Lim, Kwon Taek; Kim, Sung Yong; Kang, Inpil

2016-02-01

In this study, the piezoresistive properties of CNT (Carbon Nanotube)/EPDM composite are characterized for the applications of a flexible sensor. The CNT/EPDM composites were prepared by using a Brabender mixer with MWCNT (Multi-walled Carbon Nanotube) and organoclay. The static and quasi-dynamic voltage output responses of the composite sensor were also experimentally studied and were compared with those of a conventional foil strain gage. The voltage output by using a signal processing system was fairly stable and it shows somehow linear responses at both of loading and unloading cases with hysteresis. The voltage output was distorted under a quasi-dynamic test due to its unsymmetrical piezoresistive characteristics. The CNT/EPDM sensor showed quite tardy response to its settling time test under static deflections and that would be a hurdle for its real time applications. Furthermore, since the CNT/EPDM sensor does not have directional voltage output to tension and compression, it only could be utilized as a mono-directional force sensor such as a compressive touch sensor.

Capacitively-coupled inductive sensors for measurements of pulsed currents and pulsed magnetic fields

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ekdahl, C.A.

In experiments involving pulsed high magnetic fields the appearance of the full induced voltage at the output terminals of large-area inductive sensors such as diamagnetic loops and Rogowski belts imposes severe requirements on the insulation near the output. Capacitive detection of the inductive-sensor output voltage provides an ideal geometry for high-voltage insulation, and also accomplishes the necessary voltage division. An inductive-shunt current monitor was designed to utilize the capacitive-detection principle. The contruction of this device and its performance are described in this paper.

Microscopic origin of gating current fluctuations in a potassium channel voltage sensor.

PubMed

Freites, J Alfredo; Schow, Eric V; White, Stephen H; Tobias, Douglas J

2012-06-06

Voltage-dependent ion channels open and close in response to changes in membrane electrical potential due to the motion of their voltage-sensing domains (VSDs). VSD charge displacements within the membrane electric field are observed in electrophysiology experiments as gating currents preceding ionic conduction. The elementary charge motions that give rise to the gating current cannot be observed directly, but appear as discrete current pulses that generate fluctuations in gating current measurements. Here we report direct observation of gating-charge displacements in an atomistic molecular dynamics simulation of the isolated VSD from the KvAP channel in a hydrated lipid bilayer on the timescale (10-μs) expected for elementary gating charge transitions. The results reveal that gating-charge displacements are associated with the water-catalyzed rearrangement of salt bridges between the S4 arginines and a set of conserved acidic side chains on the S1-S3 transmembrane segments in the hydrated interior of the VSD. Copyright © 2012 Biophysical Society. Published by Elsevier Inc. All rights reserved.

Voltage-gated proton (H(v)1) channels, a singular voltage sensing domain.

PubMed

Castillo, Karen; Pupo, Amaury; Baez-Nieto, David; Contreras, Gustavo F; Morera, Francisco J; Neely, Alan; Latorre, Ramon; Gonzalez, Carlos

2015-11-14

The main role of voltage-gated proton channels (Hv1) is to extrude protons from the intracellular milieu when, mediated by different cellular processes, the H(+) concentration increases. Hv1 are exquisitely selective for protons and their structure is homologous to the voltage sensing domain (VSD) of other voltage-gated ion channels like sodium, potassium, and calcium channels. In clear contrast to the classical voltage-dependent channels, Hv1 lacks a pore domain and thus permeation necessarily occurs through the voltage sensing domain. Hv1 channels are activated by depolarizing voltages, and increases in internal proton concentration. It has been proposed that local conformational changes of the transmembrane segment S4, driven by depolarization, trigger the molecular rearrangements that open Hv1. However, it is still unclear how the electromechanical coupling is achieved between the VSD and the potential pore, allowing the proton flux from the intracellular to the extracellular side. Here we provide a revised view of voltage activation in Hv1 channels, offering a comparative scenario with other voltage sensing channels domains. Copyright © 2015 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.

Crystal structure of the cytoplasmic phosphatase and tensin homolog (PTEN)-like region of Ciona intestinalis voltage-sensing phosphatase provides insight into substrate specificity and redox regulation of the phosphoinositide phosphatase activity.

PubMed

Matsuda, Makoto; Takeshita, Kohei; Kurokawa, Tatsuki; Sakata, Souhei; Suzuki, Mamoru; Yamashita, Eiki; Okamura, Yasushi; Nakagawa, Atsushi

2011-07-01

Ciona intestinalis voltage-sensing phosphatase (Ci-VSP) has a transmembrane voltage sensor domain and a cytoplasmic region sharing similarity to the phosphatase and tensin homolog (PTEN). It dephosphorylates phosphatidylinositol 4,5-bisphosphate and phosphatidylinositol 3,4,5-trisphosphate upon membrane depolarization. The cytoplasmic region is composed of a phosphatase domain and a putative membrane interaction domain, C2. Here we determined the crystal structures of the Ci-VSP cytoplasmic region in three distinct constructs, wild-type (248-576), wild-type (236-576), and G365A mutant (248-576). The crystal structure of WT-236 and G365A-248 had the disulfide bond between the catalytic residue Cys-363 and the adjacent residue Cys-310. On the other hand, the disulfide bond was not present in the crystal structure of WT-248. These suggest the possibility that Ci-VSP is regulated by reactive oxygen species as found in PTEN. These structures also revealed that the conformation of the TI loop in the active site of the Ci-VSP cytoplasmic region was distinct from the corresponding region of PTEN; Ci-VSP has glutamic acid (Glu-411) in the TI loop, orienting toward the center of active site pocket. Mutation of Glu-411 led to acquirement of increased activity toward phosphatidylinositol 3,5-bisphosphate, suggesting that this site is required for determining substrate specificity. Our results provide the basic information of the enzymatic mechanism of Ci-VSP.

The hitchhiker’s guide to the voltage-gated sodium channel galaxy

PubMed Central

2016-01-01

Eukaryotic voltage-gated sodium (Nav) channels contribute to the rising phase of action potentials and served as an early muse for biophysicists laying the foundation for our current understanding of electrical signaling. Given their central role in electrical excitability, it is not surprising that (a) inherited mutations in genes encoding for Nav channels and their accessory subunits have been linked to excitability disorders in brain, muscle, and heart; and (b) Nav channels are targeted by various drugs and naturally occurring toxins. Although the overall architecture and behavior of these channels are likely to be similar to the more well-studied voltage-gated potassium channels, eukaryotic Nav channels lack structural and functional symmetry, a notable difference that has implications for gating and selectivity. Activation of voltage-sensing modules of the first three domains in Nav channels is sufficient to open the channel pore, whereas movement of the domain IV voltage sensor is correlated with inactivation. Also, structure–function studies of eukaryotic Nav channels show that a set of amino acids in the selectivity filter, referred to as DEKA locus, is essential for Na+ selectivity. Structures of prokaryotic Nav channels have also shed new light on mechanisms of drug block. These structures exhibit lateral fenestrations that are large enough to allow drugs or lipophilic molecules to gain access into the inner vestibule, suggesting that this might be the passage for drug entry into a closed channel. In this Review, we will synthesize our current understanding of Nav channel gating mechanisms, ion selectivity and permeation, and modulation by therapeutics and toxins in light of the new structures of the prokaryotic Nav channels that, for the time being, serve as structural models of their eukaryotic counterparts. PMID:26712848

Design, Experiments and Simulation of Voltage Transformers on the Basis of a Differential Input D-dot Sensor

PubMed Central

Wang, Jingang; Gao, Can; Yang, Jie

2014-01-01

Currently available traditional electromagnetic voltage sensors fail to meet the measurement requirements of the smart grid, because of low accuracy in the static and dynamic ranges and the occurrence of ferromagnetic resonance attributed to overvoltage and output short circuit. This work develops a new non-contact high-bandwidth voltage measurement system for power equipment. This system aims at the miniaturization and non-contact measurement of the smart grid. After traditional D-dot voltage probe analysis, an improved method is proposed. For the sensor to work in a self-integrating pattern, the differential input pattern is adopted for circuit design, and grounding is removed. To prove the structure design, circuit component parameters, and insulation characteristics, Ansoft Maxwell software is used for the simulation. Moreover, the new probe was tested on a 10 kV high-voltage test platform for steady-state error and transient behavior. Experimental results ascertain that the root mean square values of measured voltage are precise and that the phase error is small. The D-dot voltage sensor not only meets the requirement of high accuracy but also exhibits satisfactory transient response. This sensor can meet the intelligence, miniaturization, and convenience requirements of the smart grid. PMID:25036333

System for improving measurement accuracy of transducer by measuring transducer temperature and resistance change using thermoelectric voltages

NASA Technical Reports Server (NTRS)

Anderson, Karl F. (Inventor); Parker, Allen R., Jr. (Inventor)

1993-01-01

A constant current loop measuring system measures a property including the temperature of a sensor responsive to an external condition being measured. The measuring system includes thermocouple conductors connected to the sensor, sensing first and second induced voltages responsive to the external condition. In addition, the measuring system includes a current generator and reverser generating a constant current, and supplying the constant current to the thermocouple conductors in forward and reverse directions generating first and second measured voltages, and a determining unit receiving the first and second measured voltages from the current generator and reverser, and determining the temperature of the sensor responsive to the first and second measured voltages.

Color regeneration from reflective color sensor using an artificial intelligent technique.

PubMed

Saracoglu, Ömer Galip; Altural, Hayriye

2010-01-01

A low-cost optical sensor based on reflective color sensing is presented. Artificial neural network models are used to improve the color regeneration from the sensor signals. Analog voltages of the sensor are successfully converted to RGB colors. The artificial intelligent models presented in this work enable color regeneration from analog outputs of the color sensor. Besides, inverse modeling supported by an intelligent technique enables the sensor probe for use of a colorimetric sensor that relates color changes to analog voltages.

A Monolithic CMOS Magnetic Hall Sensor with High Sensitivity and Linearity Characteristics

PubMed Central

Huang, Haiyun; Wang, Dejun; Xu, Yue

2015-01-01

This paper presents a fully integrated linear Hall sensor by means of 0.8 μm high voltage complementary metal-oxide semiconductor (CMOS) technology. This monolithic Hall sensor chip features a highly sensitive horizontal switched Hall plate and an efficient signal conditioner using dynamic offset cancellation technique. An improved cross-like Hall plate achieves high magnetic sensitivity and low offset. A new spinning current modulator stabilizes the quiescent output voltage and improves the reliability of the signal conditioner. The tested results show that at the 5 V supply voltage, the maximum Hall output voltage of the monolithic Hall sensor microsystem, is up to ±2.1 V and the linearity of Hall output voltage is higher than 99% in the magnetic flux density range from ±5 mT to ±175 mT. The output equivalent residual offset is 0.48 mT and the static power consumption is 20 mW. PMID:26516864

A Monolithic CMOS Magnetic Hall Sensor with High Sensitivity and Linearity Characteristics.

PubMed

Huang, Haiyun; Wang, Dejun; Xu, Yue

2015-10-27

This paper presents a fully integrated linear Hall sensor by means of 0.8 μm high voltage complementary metal-oxide semiconductor (CMOS) technology. This monolithic Hall sensor chip features a highly sensitive horizontal switched Hall plate and an efficient signal conditioner using dynamic offset cancellation technique. An improved cross-like Hall plate achieves high magnetic sensitivity and low offset. A new spinning current modulator stabilizes the quiescent output voltage and improves the reliability of the signal conditioner. The tested results show that at the 5 V supply voltage, the maximum Hall output voltage of the monolithic Hall sensor microsystem, is up to ±2.1 V and the linearity of Hall output voltage is higher than 99% in the magnetic flux density range from ±5 mT to ±175 mT. The output equivalent residual offset is 0.48 mT and the static power consumption is 20 mW.

Functional diversity of potassium channel voltage-sensing domains.

PubMed

Islas, León D

2016-01-01

Voltage-gated potassium channels or Kv's are membrane proteins with fundamental physiological roles. They are composed of 2 main functional protein domains, the pore domain, which regulates ion permeation, and the voltage-sensing domain, which is in charge of sensing voltage and undergoing a conformational change that is later transduced into pore opening. The voltage-sensing domain or VSD is a highly conserved structural motif found in all voltage-gated ion channels and can also exist as an independent feature, giving rise to voltage sensitive enzymes and also sustaining proton fluxes in proton-permeable channels. In spite of the structural conservation of VSDs in potassium channels, there are several differences in the details of VSD function found across variants of Kvs. These differences are mainly reflected in variations in the electrostatic energy needed to open different potassium channels. In turn, the differences in detailed VSD functioning among voltage-gated potassium channels might have physiological consequences that have not been explored and which might reflect evolutionary adaptations to the different roles played by Kv channels in cell physiology.

Functional diversity of potassium channel voltage-sensing domains

PubMed Central

Islas, León D.

2016-01-01

Abstract Voltage-gated potassium channels or Kv's are membrane proteins with fundamental physiological roles. They are composed of 2 main functional protein domains, the pore domain, which regulates ion permeation, and the voltage-sensing domain, which is in charge of sensing voltage and undergoing a conformational change that is later transduced into pore opening. The voltage-sensing domain or VSD is a highly conserved structural motif found in all voltage-gated ion channels and can also exist as an independent feature, giving rise to voltage sensitive enzymes and also sustaining proton fluxes in proton-permeable channels. In spite of the structural conservation of VSDs in potassium channels, there are several differences in the details of VSD function found across variants of Kvs. These differences are mainly reflected in variations in the electrostatic energy needed to open different potassium channels. In turn, the differences in detailed VSD functioning among voltage-gated potassium channels might have physiological consequences that have not been explored and which might reflect evolutionary adaptations to the different roles played by Kv channels in cell physiology. PMID:26794852

Three-dimensional structural damage localization system and method using layered two-dimensional array of capacitance sensors

NASA Technical Reports Server (NTRS)

Curry, Mark A (Inventor); Senibi, Simon D (Inventor); Banks, David L (Inventor)

2010-01-01

A system and method for detecting damage to a structure is provided. The system includes a voltage source and at least one capacitor formed as a layer within the structure and responsive to the voltage source. The system also includes at least one sensor responsive to the capacitor to sense a voltage of the capacitor. A controller responsive to the sensor determines if damage to the structure has occurred based on the variance of the voltage of the capacitor from a known reference value. A method for sensing damage to a structure involves providing a plurality of capacitors and a controller, and coupling the capacitors to at least one surface of the structure. A voltage of the capacitors is sensed using the controller, and the controller calculates a change in the voltage of the capacitors. The method can include signaling a display system if a change in the voltage occurs.

An electrostatic potassium channel opener targeting the final voltage sensor transition

PubMed Central

Börjesson, Sara I.

2011-01-01

Free polyunsaturated fatty acids (PUFAs) modulate the voltage dependence of voltage-gated ion channels. As an important consequence thereof, PUFAs can suppress epileptic seizures and cardiac arrhythmia. However, molecular details for the interaction between PUFA and ion channels are not well understood. In this study, we have localized the site of action for PUFAs on the voltage-gated Shaker K channel by introducing positive charges on the channel surface, which potentiated the PUFA effect. Furthermore, we found that PUFA mainly affects the final voltage sensor movement, which is closely linked to channel opening, and that specific charges at the extracellular end of the voltage sensor are critical for the PUFA effect. Because different voltage-gated K channels have different charge profiles, this implies channel-specific PUFA effects. The identified site and the pharmacological mechanism will potentially be very useful in future drug design of small-molecule compounds specifically targeting neuronal and cardiac excitability. PMID:21624947

Non-perturbing voltage measurement in a coaxial cable with slab-coupled optical sensors.

PubMed

Stan, Nikola; Seng, Frederick; Shumway, LeGrand; King, Rex; Schultz, Stephen

2017-08-20

Voltage in a coaxial cable is measured by an electric-field optical fiber sensor exploiting the proportionality of voltage and electric field in a fixed structure. The sensor is inserted in a hole drilled through the dielectric of the RG-218 coaxial cable and sealed with epoxy to displace all air and prevent the adverse effects of charge buildup during high-voltage measurements. It is shown that the presence of the sensor in the coaxial cable does not significantly increase electrical reflections in the cable. A slab-coupled optical fiber sensor (SCOS) is used for its compact size and dielectric make. The dynamic range of 50 dB is shown experimentally with detection of signals as low as 1 V and up to 157 kV. A low corner of 0.3 Hz is demonstrated and the SCOS is shown to be able to measure 90 ns rise time.

A Fiber-Optic Sensor for Acoustic Emission Detection in a High Voltage Cable System

PubMed Central

Zhang, Tongzhi; Pang, Fufei; Liu, Huanhuan; Cheng, Jiajing; Lv, Longbao; Zhang, Xiaobei; Chen, Na; Wang, Tingyun

2016-01-01

We have proposed and demonstrated a Michelson interferometer-based fiber sensor for detecting acoustic emission generated from the partial discharge (PD) of the accessories of a high-voltage cable system. The developed sensor head is integrated with a compact and relatively high sensitivity cylindrical elastomer. Such a sensor has a broadband frequency response and a relatively high sensitivity in a harsh environment under a high-voltage electric field. The design and fabrication of the sensor head integrated with the cylindrical elastomer is described, and a series of experiments was conducted to evaluate the sensing performance. The experimental results demonstrate that the sensitivity of our developed sensor for acoustic detection of partial discharges is 1.7 rad/(m⋅Pa). A high frequency response up to 150 kHz is achieved. Moreover, the relatively high sensitivity for the detection of PD is verified in both the laboratory environment and gas insulated switchgear. The obtained results show the great potential application of a Michelson interferometer-based fiber sensor integrated with a cylindrical elastomer for in-situ monitoring high-voltage cable accessories for safety work. PMID:27916900

Temperature and Voltage Coupling to Channel Opening in Transient Receptor Potential Melastatin 8 (TRPM8)*♦

PubMed Central

Raddatz, Natalia; Castillo, Juan P.; Gonzalez, Carlos; Alvarez, Osvaldo; Latorre, Ramon

2014-01-01

Expressed in somatosensory neurons of the dorsal root and trigeminal ganglion, the transient receptor potential melastatin 8 (TRPM8) channel is a Ca2+-permeable cation channel activated by cold, voltage, phosphatidylinositol 4,5-bisphosphate, and menthol. Although TRPM8 channel gating has been characterized at the single channel and macroscopic current levels, there is currently no consensus regarding the extent to which temperature and voltage sensors couple to the conduction gate. In this study, we extended the range of voltages where TRPM8-induced ionic currents were measured and made careful measurements of the maximum open probability the channel can attain at different temperatures by means of fluctuation analysis. The first direct measurements of TRPM8 channel temperature-driven conformational rearrangements provided here suggest that temperature alone is able to open the channel and that the opening reaction is voltage-independent. Voltage is a partial activator of TRPM8 channels, because absolute open probability values measured with fully activated voltage sensors are less than 1, and they decrease as temperature rises. By unveiling the fast temperature-dependent deactivation process, we show that TRPM8 channel deactivation is well described by a double exponential time course. The fast and slow deactivation processes are temperature-dependent with enthalpy changes of 27.2 and 30.8 kcal mol−1. The overall Q10 for the closing reaction is about 33. A three-tiered allosteric model containing four voltage sensors and four temperature sensors can account for the complex deactivation kinetics and coupling between voltage and temperature sensor activation and channel opening. PMID:25352597

Free-energy landscape of ion-channel voltage-sensor–domain activation

PubMed Central

Delemotte, Lucie; Kasimova, Marina A.; Klein, Michael L.; Tarek, Mounir; Carnevale, Vincenzo

2015-01-01

Voltage sensor domains (VSDs) are membrane-bound protein modules that confer voltage sensitivity to membrane proteins. VSDs sense changes in the transmembrane voltage and convert the electrical signal into a conformational change called activation. Activation involves a reorganization of the membrane protein charges that is detected experimentally as transient currents. These so-called gating currents have been investigated extensively within the theoretical framework of so-called discrete-state Markov models (DMMs), whereby activation is conceptualized as a series of transitions across a discrete set of states. Historically, the interpretation of DMM transition rates in terms of transition state theory has been instrumental in shaping our view of the activation process, whose free-energy profile is currently envisioned as composed of a few local minima separated by steep barriers. Here we use atomistic level modeling and well-tempered metadynamics to calculate the configurational free energy along a single transition from first principles. We show that this transition is intrinsically multidimensional and described by a rough free-energy landscape. Remarkably, a coarse-grained description of the system, based on the use of the gating charge as reaction coordinate, reveals a smooth profile with a single barrier, consistent with phenomenological models. Our results bridge the gap between microscopic and macroscopic descriptions of activation dynamics and show that choosing the gating charge as reaction coordinate masks the topological complexity of the network of microstates participating in the transition. Importantly, full characterization of the latter is a prerequisite to rationalize modulation of this process by lipids, toxins, drugs, and genetic mutations. PMID:25535341

Zn{sup 2+} induces apoptosis in human highly metastatic SHG-44 glioma cells, through inhibiting activity of the voltage-gated proton channel Hv1

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Yifan; Zhang, Shangrong; Li, Shu Jie, E-mail: shujieli@nankai.edu.cn

Highlights: •Hv1 is expressed in highly metastatic glioma cell. •Zn{sup 2+} ions induces apoptosis in highly metastatic glioma cells. •Zn{sup 2+} ions markedly inhibit proton secretion. •Zn{sup 2+} ions reduce the gelatinase activity. •Inhibition of Hv1 activity via Zn{sup 2+} ions can effectively retard the cancer growth. -- Abstract: In contrast to the voltage-gated K{sup +} channels, the voltage-gated proton channel Hv1 contains a voltage-sensor domain but lacks a pore domain. Here, we showed that Hv1 is expressed in the highly metastatic glioma cell SHG-44, but lowly in the poorly metastatic glioma cell U-251. Inhibition of Hv1 activity by 140more » μM zinc chloride induces apoptosis in the human highly metastatic glioma cells. Zn{sup 2+} ions markedly inhibit proton secretion, and reduce the gelatinase activity in the highly metastatic glioma cells. In vivo, the glioma tumor sizes of the implantation of the SHG-44 xenografts in nude mice that were injected zinc chloride solution, were dramatically smaller than that in the controlled groups. The results demonstrated that the inhibition of Hv1 activity via Zn{sup 2+} ions can effectively retard the cancer growth and suppress the cancer metastasis by the decrease of proton extrusion and the down-regulation of gelatinase activity. Our results suggest that Zn{sup 2+} ions may be used as a potential anti-glioma drug for glioma therapy.« less

Modulation of BK channel voltage gating by different auxiliary β subunits

PubMed Central

Contreras, Gustavo F.; Neely, Alan; Alvarez, Osvaldo; Gonzalez, Carlos; Latorre, Ramon

2012-01-01

Calcium- and voltage-activated potassium channels (BK) are regulated by a multiplicity of signals. The prevailing view is that different BK gating mechanisms converge to determine channel opening and that these gating mechanisms are allosterically coupled. In most instances the pore forming α subunit of BK is associated with one of four alternative β subunits that appear to target specific gating mechanisms to regulate the channel activity. In particular, β1 stabilizes the active configuration of the BK voltage sensor having a large effect on BK Ca2+ sensitivity. To determine the extent to which β subunits regulate the BK voltage sensor, we measured gating currents induced by the pore-forming BK α subunit alone and with the different β subunits expressed in Xenopus oocytes (β1, β2IR, β3b, and β4). We found that β1, β2, and β4 stabilize the BK voltage sensor in the active conformation. β3 has no effect on voltage sensor equilibrium. In addition, β4 decreases the apparent number of charges per voltage sensor. The decrease in the charge associated with the voltage sensor in α β4 channels explains most of their biophysical properties. For channels composed of the α subunit alone, gating charge increases slowly with pulse duration as expected if a significant fraction of this charge develops with a time course comparable to that of K+ current activation. In the presence of β1, β2, and β4 this slow component develops in advance of and much more rapidly than ion current activation, suggesting that BK channel opening proceeds in two steps. PMID:23112204

Otoferlin acts as a Ca2+ sensor for vesicle fusion and vesicle pool replenishment at auditory hair cell ribbon synapses

PubMed Central

Goutman, Juan D; Auclair, Sarah Marie; Boutet de Monvel, Jacques; Tertrais, Margot; Emptoz, Alice; Parrin, Alexandre; Nouaille, Sylvie; Guillon, Marc; Sachse, Martin; Ciric, Danica; Bahloul, Amel; Hardelin, Jean-Pierre; Sutton, Roger Bryan; Avan, Paul; Krishnakumar, Shyam S; Rothman, James E

2017-01-01

Hearing relies on rapid, temporally precise, and sustained neurotransmitter release at the ribbon synapses of sensory cells, the inner hair cells (IHCs). This process requires otoferlin, a six C2-domain, Ca2+-binding transmembrane protein of synaptic vesicles. To decipher the role of otoferlin in the synaptic vesicle cycle, we produced knock-in mice (Otof Ala515,Ala517/Ala515,Ala517) with lower Ca2+-binding affinity of the C2C domain. The IHC ribbon synapse structure, synaptic Ca2+ currents, and otoferlin distribution were unaffected in these mutant mice, but auditory brainstem response wave-I amplitude was reduced. Lower Ca2+ sensitivity and delay of the fast and sustained components of synaptic exocytosis were revealed by membrane capacitance measurement upon modulations of intracellular Ca2+ concentration, by varying Ca2+ influx through voltage-gated Ca2+-channels or Ca2+ uncaging. Otoferlin thus functions as a Ca2+ sensor, setting the rates of primed vesicle fusion with the presynaptic plasma membrane and synaptic vesicle pool replenishment in the IHC active zone. PMID:29111973

Otoferlin acts as a Ca2+ sensor for vesicle fusion and vesicle pool replenishment at auditory hair cell ribbon synapses.

PubMed

Michalski, Nicolas; Goutman, Juan D; Auclair, Sarah Marie; Boutet de Monvel, Jacques; Tertrais, Margot; Emptoz, Alice; Parrin, Alexandre; Nouaille, Sylvie; Guillon, Marc; Sachse, Martin; Ciric, Danica; Bahloul, Amel; Hardelin, Jean-Pierre; Sutton, Roger Bryan; Avan, Paul; Krishnakumar, Shyam S; Rothman, James E; Dulon, Didier; Safieddine, Saaid; Petit, Christine

2017-11-07

Hearing relies on rapid, temporally precise, and sustained neurotransmitter release at the ribbon synapses of sensory cells, the inner hair cells (IHCs). This process requires otoferlin, a six C 2 -domain, Ca 2+ -binding transmembrane protein of synaptic vesicles. To decipher the role of otoferlin in the synaptic vesicle cycle, we produced knock-in mice ( Otof Ala515,Ala517/Ala515,Ala517 ) with lower Ca 2+ -binding affinity of the C 2 C domain. The IHC ribbon synapse structure, synaptic Ca 2+ currents, and otoferlin distribution were unaffected in these mutant mice, but auditory brainstem response wave-I amplitude was reduced. Lower Ca 2+ sensitivity and delay of the fast and sustained components of synaptic exocytosis were revealed by membrane capacitance measurement upon modulations of intracellular Ca 2+ concentration, by varying Ca 2+ influx through voltage-gated Ca 2+ -channels or Ca 2+ uncaging. Otoferlin thus functions as a Ca 2+ sensor, setting the rates of primed vesicle fusion with the presynaptic plasma membrane and synaptic vesicle pool replenishment in the IHC active zone.

A common pathway for charge transport through voltage-sensing domains.

PubMed

Chanda, Baron; Bezanilla, Francisco

2008-02-07

Voltage-gated ion channels derive their voltage sensitivity from the movement of specific charged residues in response to a change in transmembrane potential. Several studies on mechanisms of voltage sensing in ion channels support the idea that these gating charges move through a well-defined permeation pathway. This gating pathway in a voltage-gated ion channel can also be mutated to transport free cations, including protons. The recent discovery of proton channels with sequence homology to the voltage-sensing domains suggests that evolution has perhaps exploited the same gating pathway to generate a bona fide voltage-dependent proton transporter. Here we will discuss implications of these findings on the mechanisms underlying charge (and ion) transport by voltage-sensing domains.

Non-contact current and voltage sensing method using a clamshell housing and a ferrite cylinder

DOE Office of Scientific and Technical Information (OSTI.GOV)

Carpenter, Gary D.; El-Essawy, Wael; Ferreira, Alexandre Peixoto

2016-04-26

A method of measurement using a detachable current and voltage sensor provides an isolated and convenient technique for to measuring current passing through a conductor such as an AC branch circuit wire, as well as providing an indication of an electrostatic potential on the wire, which can be used to indicate the phase of the voltage on the wire, and optionally a magnitude of the voltage. The device includes a housing that contains the current and voltage sensors, which may be a ferrite cylinder with a hall effect sensor disposed in a gap along the circumference to measure current, ormore » alternative a winding provided through the cylinder along its axis and a capacitive plate or wire disposed adjacent to, or within, the ferrite cylinder to provide the indication of the voltage.« less

The isolated voltage sensing domain of the Shaker potassium channel forms a voltage-gated cation channel.

PubMed

Zhao, Juan; Blunck, Rikard

2016-10-06

Domains in macromolecular complexes are often considered structurally and functionally conserved while energetically coupled to each other. In the modular voltage-gated ion channels the central ion-conducting pore is surrounded by four voltage sensing domains (VSDs). Here, the energetic coupling is mediated by interactions between the S4-S5 linker, covalently linking the domains, and the proximal C-terminus. In order to characterize the intrinsic gating of the voltage sensing domain in the absence of the pore domain, the Shaker Kv channel was truncated after the fourth transmembrane helix S4 (Shaker-iVSD). Shaker-iVSD showed significantly altered gating kinetics and formed a cation-selective ion channel with a strong preference for protons. Ion conduction in Shaker-iVSD developed despite identical primary sequence, indicating an allosteric influence of the pore domain. Shaker-iVSD also displays pronounced 'relaxation'. Closing of the pore correlates with entry into relaxation suggesting that the two processes are energetically related.

Multiple modes of a-type potassium current regulation.

PubMed

Cai, Shi-Qing; Li, Wenchao; Sesti, Federico

2007-01-01

Voltage-dependent potassium (K+) channels (Kv) regulate cell excitability by controlling the movement of K+ ions across the membrane in response to changes in the cell voltage. The Kv family, which includes A-type channels, constitute the largest group of K+ channel genes within the superfamily of Na+, Ca2+ and K+ voltage-gated channels. The name "A-type" stems from the typical profile of these currents that results form the opposing effects of fast activation and inactivation. In neuronal cells, A-type currents (I(A)), determine the interval between two consecutive action potentials during repetitive firing. In cardiac muscle, A-type currents (I(to)), control the initial repolarization of the myocardium. Structurally, A-type channels are tetramers of alpha-subunits each containing six putative transmembrane domains including a voltage-sensor. A-type channels can be modulated by means of protein-protein interactions with so-called beta-subunits that control inactivation voltage sensitivity and other properties, and by post-transcriptional modifications such as phosphorylation or oxidation. Recently a new mode of A-type regulation has been discovered in the form of a class of hybrid beta-subunits that posses their own enzymatic activity. Here, we review the biophysical and physiological properties of these multiple modes of A-type channel regulation.

Biased low differential input impedance current receiver/converter device and method for low noise readout from voltage-controlled detectors

DOEpatents

Degtiarenko, Pavel V [Williamsburg, VA; Popov, Vladimir E [Newport News, VA

2011-03-22

A first stage electronic system for receiving charge or current from voltage-controlled sensors or detectors that includes a low input impedance current receiver/converter device (for example, a transimpedance amplifier), which is directly coupled to the sensor output, a source of bias voltage, and the device's power supply (or supplies), which use the biased voltage point as a baseline.

Phase-Discriminating Capacitive Sensor System

NASA Technical Reports Server (NTRS)

Vranish, John M.; Rahim, Wadi

1993-01-01

Crosstalk eliminated by maintaining voltages on all electrodes at same amplitude, phase, and frequency. Each output feedback-derived control voltage, change of which indicates proximity-induced change in capacitance of associated sensing electrode. Sensors placed close together, enabling imaging of sort. Images and/or output voltages used to guide robots in proximity to various objects.

An allosteric model of the molecular interactions of excitation- contraction coupling in skeletal muscle

PubMed Central

1993-01-01

A contact interaction is proposed to exist between the voltage sensor of the transverse tubular membrane of skeletal muscle and the calcium release channel of the sarcoplasmic reticulum. This interaction is given a quantitative formulation inspired in the Monod, Wyman, and Changeux model of allosteric transitions in hemoglobin (Monod, J., J. Wyman, and J.-P. Changeux. 1965. Journal of Molecular Biology. 12:88- 118), and analogous to one proposed by Marks and Jones for voltage- dependent Ca channels (Marks, T. N., and S. W. Jones. 1992. Journal of General Physiology. 99:367-390). The allosteric protein is the calcium release channel, a homotetramer, with two accessible states, closed and open. The kinetics and equilibrium of this transition are modulated by voltage sensors (dihydropyridine receptors) pictured as four units per release channel, each undergoing independent voltage-driven transitions between two states (resting and activating). For each voltage sensor that moves to the activating state, the tendency of the channel to open increases by an equal (large) factor. The equilibrium and kinetic equations of the model are solved and shown to reproduce well a number of experimentally measured relationships including: charge movement (Q) vs. voltage, open probability of the release channel (Po) vs. voltage, the transfer function relationship Po vs. Q, and the kinetics of charge movement, release activation, and deactivation. The main consequence of the assumption of allosteric coupling is that primary effects on the release channel are transmitted backward to the voltage sensor and give secondary effects. Thus, the model reproduces well the effects of perchlorate, described in the two previous articles, under the assumption that the primary effect is to increase the intrinsic tendency of the release channel to open, with no direct effects on the voltage sensor. This modification of the open-closed equilibrium of the release channel causes a shift in the equilibrium dependency of charge movement with voltage. The paradoxical slowing of charge movement by perchlorate also results from reciprocal effects of the channel on the allosterically coupled voltage sensors. The observations of the previous articles plus the simulations in this article constitute functional evidence of allosteric transmission. PMID:8245819

Voltage Sensors Monitor Harmful Static

NASA Technical Reports Server (NTRS)

2009-01-01

A tiny sensor, small enough to be worn on clothing, now monitors voltage changes near sensitive instruments after being created to alert Agency workers to dangerous static buildup near fuel operations and avionics. San Diego s Quasar Federal Systems received a Small Business Innovation Research (SBIR) contract from Kennedy Space Center to develop its remote voltage sensor (RVS), a dime-sized electrometer designed to measure triboelectric changes in the environment. One of the unique qualities of the RVS is that it can detect static at greater distances than previous devices, measuring voltage changes from a few centimeters to a few meters away, due to its much-improved sensitivity.

How does KCNE1 regulate the Kv7.1 potassium channel? Model-structure, mutations, and dynamics of the Kv7.1-KCNE1 complex.

PubMed

Gofman, Yana; Shats, Simona; Attali, Bernard; Haliloglu, Turkan; Ben-Tal, Nir

2012-08-08

The voltage-gated potassium channel Kv7.1 and its auxiliary subunit KCNE1 are expressed in the heart and give rise to the major repolarization current. The interaction of Kv7.1 with the single transmembrane helix of KCNE1 considerably slows channel activation and deactivation, raises single-channel conductance, and prevents slow voltage-dependent inactivation. We built a Kv7.1-KCNE1 model-structure. The model-structure agrees with previous disulfide mapping studies and enables us to derive molecular interpretations of electrophysiological recordings that we obtained for two KCNE1 mutations. An elastic network analysis of Kv7.1 fluctuations in the presence and absence of KCNE1 suggests a mechanistic perspective on the known effects of KCNE1 on Kv7.1 function: slow deactivation is attributed to the low mobility of the voltage-sensor domains upon KCNE1 binding, abolishment of voltage-dependent inactivation could result from decreased fluctuations in the external vestibule, and amalgamation of the fluctuations in the pore region is associated with enhanced ion conductivity. Copyright © 2012 Elsevier Ltd. All rights reserved.

Gas Composition Sensing Using Carbon Nanotube Arrays

NASA Technical Reports Server (NTRS)

Li, Jing; Meyyappan, Meyya

2012-01-01

This innovation is a lightweight, small sensor for inert gases that consumes a relatively small amount of power and provides measurements that are as accurate as conventional approaches. The sensing approach is based on generating an electrical discharge and measuring the specific gas breakdown voltage associated with each gas present in a sample. An array of carbon nanotubes (CNTs) in a substrate is connected to a variable-pulse voltage source. The CNT tips are spaced appropriately from the second electrode maintained at a constant voltage. A sequence of voltage pulses is applied and a pulse discharge breakdown threshold voltage is estimated for one or more gas components, from an analysis of the current-voltage characteristics. Each estimated pulse discharge breakdown threshold voltage is compared with known threshold voltages for candidate gas components to estimate whether at least one candidate gas component is present in the gas. The procedure can be repeated at higher pulse voltages to estimate a pulse discharge breakdown threshold voltage for a second component present in the gas. The CNTs in the gas sensor have a sharp (low radius of curvature) tip; they are preferably multi-wall carbon nanotubes (MWCNTs) or carbon nanofibers (CNFs), to generate high-strength electrical fields adjacent to the tips for breakdown of the gas components with lower voltage application and generation of high current. The sensor system can provide a high-sensitivity, low-power-consumption tool that is very specific for identification of one or more gas components. The sensor can be multiplexed to measure current from multiple CNT arrays for simultaneous detection of several gas components.

Breakdown voltage reduction by field emission in multi-walled carbon nanotubes based ionization gas sensor

DOE Office of Scientific and Technical Information (OSTI.GOV)

Saheed, M. Shuaib M.; Muti Mohamed, Norani; Arif Burhanudin, Zainal, E-mail: zainabh@petronas.com.my

2014-03-24

Ionization gas sensors using vertically aligned multi-wall carbon nanotubes (MWCNT) are demonstrated. The sharp tips of the nanotubes generate large non-uniform electric fields at relatively low applied voltage. The enhancement of the electric field results in field emission of electrons that dominates the breakdown mechanism in gas sensor with gap spacing below 14 μm. More than 90% reduction in breakdown voltage is observed for sensors with MWCNT and 7 μm gap spacing. Transition of breakdown mechanism, dominated by avalanche electrons to field emission electrons, as decreasing gap spacing is also observed and discussed.

Optical fiber voltage sensor based on Michelsion interferometer using Fabry-Perot demodulation interferometer

NASA Astrophysics Data System (ADS)

Chen, Xinwei; He, Shengnan; Li, Dandan; Wang, Kai; Fan, Yan'en; Wu, Shuai

2014-11-01

We present an optical fiber voltage sensor by Michelsion interferometer (MI) employing a Fabry-Perot (F-P) interferometer and the DC phase tracking (DCPT) signal processing method. By mounting a MI fabricated by an optical fiber coupler on a piezoelectric (PZT) transducer bar, a dynamic strain would be generated to change the optical path difference (OPD) of the interferometer when the measured voltage was applied on the PZT. Applying an F-P interferometer to demodulate the optical intensity variation output of the MI, the voltage can be obtained. The experiment results show that the relationship between the optical intensity variation and the voltage applied on the PZT is approximately linear. Furthermore, the phase generate carrier (PGC) algorithm was applied to demodulate the output of the sensor also.

Study of surface properties of ATLAS12 strip sensors and their radiation resistance

NASA Astrophysics Data System (ADS)

Mikestikova, M.; Allport, P. P.; Baca, M.; Broughton, J.; Chisholm, A.; Nikolopoulos, K.; Pyatt, S.; Thomas, J. P.; Wilson, J. A.; Kierstead, J.; Kuczewski, P.; Lynn, D.; Hommels, L. B. A.; Ullan, M.; Bloch, I.; Gregor, I. M.; Tackmann, K.; Hauser, M.; Jakobs, K.; Kuehn, S.; Mahboubi, K.; Mori, R.; Parzefall, U.; Clark, A.; Ferrere, D.; Sevilla, S. Gonzalez; Ashby, J.; Blue, A.; Bates, R.; Buttar, C.; Doherty, F.; McMullen, T.; McEwan, F.; O'Shea, V.; Kamada, S.; Yamamura, K.; Ikegami, Y.; Nakamura, K.; Takubo, Y.; Unno, Y.; Takashima, R.; Chilingarov, A.; Fox, H.; Affolder, A. A.; Casse, G.; Dervan, P.; Forshaw, D.; Greenall, A.; Wonsak, S.; Wormald, M.; Cindro, V.; Kramberger, G.; Mandić, I.; Mikuž, M.; Gorelov, I.; Hoeferkamp, M.; Palni, P.; Seidel, S.; Taylor, A.; Toms, K.; Wang, R.; Hessey, N. P.; Valencic, N.; Hanagaki, K.; Dolezal, Z.; Kodys, P.; Bohm, J.; Stastny, J.; Bevan, A.; Beck, G.; Milke, C.; Domingo, M.; Fadeyev, V.; Galloway, Z.; Hibbard-Lubow, D.; Liang, Z.; Sadrozinski, H. F.-W.; Seiden, A.; To, K.; French, R.; Hodgson, P.; Marin-Reyes, H.; Parker, K.; Jinnouchi, O.; Hara, K.; Sato, K.; Hagihara, M.; Iwabuchi, S.; Bernabeu, J.; Civera, J. V.; Garcia, C.; Lacasta, C.; Marti i Garcia, S.; Rodriguez, D.; Santoyo, D.; Solaz, C.; Soldevila, U.

2016-09-01

A radiation hard n+-in-p micro-strip sensor for the use in the Upgrade of the strip tracker of the ATLAS experiment at the High Luminosity Large Hadron Collider (HL-LHC) has been developed by the "ATLAS ITk Strip Sensor collaboration" and produced by Hamamatsu Photonics. Surface properties of different types of end-cap and barrel miniature sensors of the latest sensor design ATLAS12 have been studied before and after irradiation. The tested barrel sensors vary in "punch-through protection" (PTP) structure, and the end-cap sensors, whose stereo-strips differ in fan geometry, in strip pitch and in edge strip ganging options. Sensors have been irradiated with proton fluences of up to 1×1016 neq/cm2, by reactor neutron fluence of 1×1015 neq/cm2 and by gamma rays from 60Co up to dose of 1 MGy. The main goal of the present study is to characterize the leakage current for micro-discharge breakdown voltage estimation, the inter-strip resistance and capacitance, the bias resistance and the effectiveness of PTP structures as a function of bias voltage and fluence. It has been verified that the ATLAS12 sensors have high breakdown voltage well above the operational voltage which implies that different geometries of sensors do not influence their stability. The inter-strip isolation is a strong function of irradiation fluence, however the sensor performance is acceptable in the expected range for HL-LHC. New gated PTP structure exhibits low PTP onset voltage and sharp cut-off of effective resistance even at the highest tested radiation fluence. The inter-strip capacitance complies with the technical specification required before irradiation and no radiation-induced degradation was observed. A summary of ATLAS12 sensors tests is presented including a comparison of results from different irradiation sites. The measured characteristics are compared with the previous prototype of the sensor design, ATLAS07.

Voltage- and ATP-dependent structural rearrangements of the P2X2 receptor associated with the gating of the pore

PubMed Central

Keceli, Batu; Kubo, Yoshihiro

2014-01-01

P2X2 is an extracellular ATP-gated cation channel which has a voltage-dependent gating property even though it lacks a canonical voltage sensor. It is a trimer in which each subunit has two transmembrane helices and a large extracellular domain. The three inter-subunit ATP binding sites are linked to the pore forming transmembrane (TM) domains by β-strands. We analysed structural rearrangements of the linker strands between the ATP binding site and TM domains upon ligand binding and voltage change, electrophysiologically in Xenopus oocytes, using mutants carrying engineered thiol-modifiable cysteine residues. (1) We demonstrated that the double mutant D315C&I67C (at β-14 and β-1, respectively) shows a 2- to 4-fold increase in current amplitude after treatment with a reducing reagent, dithiothreitol (DTT). Application of the thiol-reactive metal Cd2+ induced current decline due to bond formation between D315C and I67C. This effect was not observed in wild type (WT) or in single point mutants. (2) Cd2+-induced current decline was analysed in hyperpolarized and depolarized conditions with different pulse protocols, and also in the presence and absence of ATP. (3) Current decline induced by Cd2+ could be clearly observed in the presence of ATP, but was not clear in the absence of ATP, showing a state-dependent modification. (4) In the presence of ATP, Cd2+ modification was significantly faster in hyperpolarized than in depolarized conditions, showing voltage-dependent structural rearrangements of the linker strands. (5) Experiments using tandem trimeric constructs (TTCs) with controlled number and position of mutations in the trimer showed that the bridging by Cd2+ between 315 and 67 was not intra- but inter-subunit. (6) Finally, we performed similar analyses of a pore mutant T339S, which makes the channel activation voltage insensitive. Cd2+ modification rates of T339S were similar in hyperpolarized and depolarized conditions. Taking these results together, we demonstrated that structural rearrangements of the linker region of the P2X2 receptor channel are induced not only by ligand binding but also by membrane potential change. PMID:25172943

Microbial fuel cells as power supply of a low-power temperature sensor

NASA Astrophysics Data System (ADS)

Khaled, Firas; Ondel, Olivier; Allard, Bruno

2016-02-01

Microbial fuel cells (MFCs) show great promise as a concomitant process for water treatment and as renewable energy sources for environmental sensors. The small energy produced by MFCs and the low output voltage limit the applications of MFCs. Specific converter topologies are required to step-up the output voltage of a MFC. A Power Management Unit (PMU) is proposed for operation at low input voltage and at very low power in a completely autonomous way to capture energy from MFCs with the highest possible efficiency. The application of sensors for monitoring systems in remote locations is an important approach. MFCs could be an alternative energy source in this case. Powering a sensor with MFCs may prove the fact that wastewater may be partly turned into renewable energy for realistic applications. The Power Management Unit is demonstrated for 3.6 V output voltage at 1 mW continuous power, based on a low-cost 0.7-L MFC. A temperature sensor may operate continuously on 2-MFCs in continuous flow mode. A flyback converter under discontinuous conduction mode is also tested to power the sensor. One continuously fed MFC was able to efficiently and continuously power the sensor.

Simulation of Electrostatic Actuation in Interdigitated Comb Drive MEMS Resonator for Energy Harvester Applications

NASA Astrophysics Data System (ADS)

Sathya, S.; Pavithra, M.; Muruganand, S.

2016-09-01

This paper presents an actuation mechanism based on the interdigitated comb drive MEMS resonator. The important role of that device is to establish MEMS resonators for the second order systems. Comb drive model is one of the basic model which uses the principle of electrostatic and force can be generated for the capacitive sensors. This work is done by overlapping movable and fixed comb fingers which produces an energy. The specific range of the polyimide material properties of young's modulus of 3.1GPa and density of 1300 Kg/m3. Results are shown in the structural domain performance of a lateral motion which corresponds to the applying voltage between the interdigitated comb fingers. It has laterally driven about 40pm with driving voltage. Also the resonance frequency 24Hz and 15Hz with high quality factors are depending on the spring length 260pm and 360pm and structure thickness of 2μm and 5 μm. Here Finite element method (FEM) is used to simulate the various physics scenario and it is designed as two dimensional structure multiphysics domain. The prototype of comb drive MEMS resonator has been suitable for energy harvesting system applications.

FLASH X-RAY (FXR) LINEAR INDUCTION ACCELERATOR (LIA) OPTIMIZATION Sensor Delay Correction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ong, M M; Houck, T L; Kreitzer, B R

2006-05-01

The radiographic goal of the FXR Optimization Project is to generate an x-ray pulse with peak energy of 19 MeV, spot-size of 1.5 mm, a dose of 500 rad, and duration of 60 ns. The electrical objectives are to generate a 3 kA electron-beam and refine our 16 MV accelerator so that the voltage does not vary more than 1%-rms. In a multi-cell linear induction accelerator, like FXR, the timing of the acceleration pulses relative to the beam is critical. The pulses must be timed optimally so that a cell is at full voltage before the beam arrives and doesmore » not drop until the beam passes. In order to stay within the energy-variation budget, the synchronization between the cells and beam arrival must be controlled to a couple of nanoseconds. Therefore, temporal measurements must be accurate to a fraction of a nanosecond. FXR Optimization Project developed a one-giga-sample per second (gs/s) data acquisition system to record beam sensor data. Signal processing algorithms were written to determine cell timing with an uncertainty of a fraction of a nanosecond. However, the uncertainty in the sensor delay was still a few nanoseconds. This error had to be reduced if we are to improve the quality of the electron beam. Two types of sensors are used to align the cell voltage pulse against the beam current. The beam current is measured with resistive-wall sensors. The cell voltages are read with capacitive voltage monitors. Sensor delays can be traced to two mechanisms: (1) the sensors are not co-located at the beam and cell interaction points, and (2) the sensors have different length jumper cables and other components that connect them to the standard-length coaxial cables of the data acquisition system. Using the physical locations and dimensions of the sensor components, and the dielectric constant of the materials, delay times were computed. Relative to the cell voltage, the beam current was theoretically reporting late by 7.7 ns. Two experiments were performed to verify and refine the sensor delay correction. In the first experiment, the beam was allowed to drift through a cell that was not pulsed. The beam induces a potential into the cell that is read by the voltage monitor. Analysis of the data indicated that the beam sensor signal was likely 7.1 ns late. In the second experiment, the beam current is calculated from the injector diode voltage that is the sum of the cell voltages. A 7 ns correction produced a very good match between the signals from the two types of sensors. For simplicity, we selected a correction factor that advanced the current signals by 7 ns. This should reduce the uncertainty in the temporal measurements to less than 1 ns.« less

A Comparison of Two Sensors Used to Measure High-Voltage, Fast-Risetime Signals in Coaxial Cable

NASA Astrophysics Data System (ADS)

Farr, Everett G.; Atchley, Lanney M.; Ellibee, Donald E.; Carey, William J.; Altgilbers, Larry L.

We consider here two sensors that are commonly used to measure high-voltage fast-risetime signals in coaxial cable. One sensor measures the current in the cable, and is called a Current-Viewing Resistor, or CVR. In this design, the cable jacket is cut, a portion of the cable jacket is removed, and a number of resistors are inserted in parallel across the gap, thereby creating a low resistance in series with the outer cable jacket. The voltage across these resistors is proportional to the current in the coax. The second sensor measures the derivative of the voltage in the coax. It is fabricated from a "sawed-off" SMA connector that is inserted through a small hole in the cable jacket. In this paper we characterize the accuracy of both sensors when used with RG-220 cable, and we discuss the situations when one might prefer one measurement type over the other.

Low-voltage organic strain sensor on plastic using polymer/high- K inorganic hybrid gate dielectrics

NASA Astrophysics Data System (ADS)

Jung, Soyoun; Ji, Taeksoo; Varadan, Vijay K.

2007-12-01

In this paper, gate-induced pentacene semiconductor strain sensors based on hybrid-gate dielectrics using poly-vinylphenol (PVP) and high-K inorganic, Ta IIO 5 are fabricated on flexible substrates, polyethylene naphthalate (PEN). The Ta IIO 5 gate dielectric layer is combined with a thin PVP layer to obtain very smooth and hydrophobic surfaces which improve the molecular structures of pentacene films. The PVP-Ta IIO 5 hybrid-gate dielectric films exhibit a high dielectric capacitance and low leakage current. The sensors adopting thin film transistor (TFT)-like structures show a significantly reduced operating voltage (~6V), and good device characteristics with a field-effect mobility of 1.89 cm2/V•s, a threshold voltage of -0.5 V, and an on/off ratio of 10 3. The strain sensor, one of the practical applications in large-area organic electronics, was characterized with different bending radii of 50, 40, 30, and 20 mm. The sensor output signals were significantly improved with low-operating voltages.

A novel method for in-situ monitoring of local voltage, temperature and humidity distributions in fuel cells using flexible multi-functional micro sensors.

PubMed

Lee, Chi-Yuan; Fan, Wei-Yuan; Chang, Chih-Ping

2011-01-01

In this investigation, micro voltage, temperature and humidity sensors were fabricated and integrated for the first time on a stainless steel foil using micro-electro-mechanical systems (MEMS). These flexible multi-functional micro sensors have the advantages of high temperature resistance, flexibility, smallness, high sensitivity and precision of location. They were embedded in a proton exchange membrane fuel cell (PEMFC) and used to simultaneously measure variations in the inner voltage, temperature and humidity. The accuracy and reproducibility of the calibrated results obtained using the proposed micro sensors is excellent. The experimental results indicate that, at high current density and 100%RH or 75%RH, the relative humidity midstream and downstream saturates due to severe flooding. The performance of the PEM fuel cell can be stabilized using home-made flexible multi-functional micro sensors by the in-situ monitoring of local voltage, temperature and humidity distributions within it.

A Novel Method for In-Situ Monitoring of Local Voltage, Temperature and Humidity Distributions in Fuel Cells Using Flexible Multi-Functional Micro Sensors

PubMed Central

Lee, Chi-Yuan; Fan, Wei-Yuan; Chang, Chih-Ping

2011-01-01

In this investigation, micro voltage, temperature and humidity sensors were fabricated and integrated for the first time on a stainless steel foil using micro-electro-mechanical systems (MEMS). These flexible multi-functional micro sensors have the advantages of high temperature resistance, flexibility, smallness, high sensitivity and precision of location. They were embedded in a proton exchange membrane fuel cell (PEMFC) and used to simultaneously measure variations in the inner voltage, temperature and humidity. The accuracy and reproducibility of the calibrated results obtained using the proposed micro sensors is excellent. The experimental results indicate that, at high current density and 100%RH or 75%RH, the relative humidity midstream and downstream saturates due to severe flooding. The performance of the PEM fuel cell can be stabilized using home-made flexible multi-functional micro sensors by the in-situ monitoring of local voltage, temperature and humidity distributions within it. PMID:22319361

Genotype–phenotype correlations in neonatal epilepsies caused by mutations in the voltage sensor of Kv7.2 potassium channel subunits

PubMed Central

Miceli, Francesco; Soldovieri, Maria Virginia; Ambrosino, Paolo; Barrese, Vincenzo; Migliore, Michele; Cilio, Maria Roberta; Taglialatela, Maurizio

2013-01-01

Mutations in the KV7.2 gene encoding for voltage-dependent K+ channel subunits cause neonatal epilepsies with wide phenotypic heterogeneity. Two mutations affecting the same positively charged residue in the S4 domain of KV7.2 have been found in children affected with benign familial neonatal seizures (R213W mutation) or with neonatal epileptic encephalopathy with severe pharmacoresistant seizures and neurocognitive delay, suppression-burst pattern at EEG, and distinct neuroradiological features (R213Q mutation). To examine the molecular basis for this strikingly different phenotype, we studied the functional characteristics of mutant channels by using electrophysiological techniques, computational modeling, and homology modeling. Functional studies revealed that, in homomeric or heteromeric configuration with KV7.2 and/or KV7.3 subunits, both mutations markedly destabilized the open state, causing a dramatic decrease in channel voltage sensitivity. These functional changes were (i) more pronounced for channels incorporating R213Q- than R213W-carrying KV7.2 subunits; (ii) proportional to the number of mutant subunits incorporated; and (iii) fully restored by the neuronal Kv7 activator retigabine. Homology modeling confirmed a critical role for the R213 residue in stabilizing the activated voltage sensor configuration. Modeling experiments in CA1 hippocampal pyramidal cells revealed that both mutations increased cell firing frequency, with the R213Q mutation prompting more dramatic functional changes compared with the R213W mutation. These results suggest that the clinical disease severity may be related to the extent of the mutation-induced functional K+ channel impairment, and set the preclinical basis for the potential use of Kv7 openers as a targeted anticonvulsant therapy to improve developmental outcome in neonates with KV7.2 encephalopathy. PMID:23440208

The isolated voltage sensing domain of the Shaker potassium channel forms a voltage-gated cation channel

PubMed Central

Zhao, Juan; Blunck, Rikard

2016-01-01

Domains in macromolecular complexes are often considered structurally and functionally conserved while energetically coupled to each other. In the modular voltage-gated ion channels the central ion-conducting pore is surrounded by four voltage sensing domains (VSDs). Here, the energetic coupling is mediated by interactions between the S4-S5 linker, covalently linking the domains, and the proximal C-terminus. In order to characterize the intrinsic gating of the voltage sensing domain in the absence of the pore domain, the Shaker Kv channel was truncated after the fourth transmembrane helix S4 (Shaker-iVSD). Shaker-iVSD showed significantly altered gating kinetics and formed a cation-selective ion channel with a strong preference for protons. Ion conduction in Shaker-iVSD developed despite identical primary sequence, indicating an allosteric influence of the pore domain. Shaker-iVSD also displays pronounced 'relaxation'. Closing of the pore correlates with entry into relaxation suggesting that the two processes are energetically related. DOI: http://dx.doi.org/10.7554/eLife.18130.001 PMID:27710769

Imaging Voltage in Genetically Defined Neuronal Subpopulations with a Cre Recombinase-Targeted Hybrid Voltage Sensor.

PubMed

Bayguinov, Peter O; Ma, Yihe; Gao, Yu; Zhao, Xinyu; Jackson, Meyer B

2017-09-20

Genetically encoded voltage indicators create an opportunity to monitor electrical activity in defined sets of neurons as they participate in the complex patterns of coordinated electrical activity that underlie nervous system function. Taking full advantage of genetically encoded voltage indicators requires a generalized strategy for targeting the probe to genetically defined populations of cells. To this end, we have generated a mouse line with an optimized hybrid voltage sensor (hVOS) probe within a locus designed for efficient Cre recombinase-dependent expression. Crossing this mouse with Cre drivers generated double transgenics expressing hVOS probe in GABAergic, parvalbumin, and calretinin interneurons, as well as hilar mossy cells, new adult-born neurons, and recently active neurons. In each case, imaging in brain slices from male or female animals revealed electrically evoked optical signals from multiple individual neurons in single trials. These imaging experiments revealed action potentials, dynamic aspects of dendritic integration, and trial-to-trial fluctuations in response latency. The rapid time response of hVOS imaging revealed action potentials with high temporal fidelity, and enabled accurate measurements of spike half-widths characteristic of each cell type. Simultaneous recording of rapid voltage changes in multiple neurons with a common genetic signature offers a powerful approach to the study of neural circuit function and the investigation of how neural networks encode, process, and store information. SIGNIFICANCE STATEMENT Genetically encoded voltage indicators hold great promise in the study of neural circuitry, but realizing their full potential depends on targeting the sensor to distinct cell types. Here we present a new mouse line that expresses a hybrid optical voltage sensor under the control of Cre recombinase. Crossing this line with Cre drivers generated double-transgenic mice, which express this sensor in targeted cell types. In brain slices from these animals, single-trial hybrid optical voltage sensor recordings revealed voltage changes with submillisecond resolution in multiple neurons simultaneously. This imaging tool will allow for the study of the emergent properties of neural circuits and permit experimental tests of the roles of specific types of neurons in complex circuit activity. Copyright © 2017 the authors 0270-6474/17/379305-15$15.00/0.

A frequency-sensing readout using piezoelectric sensors for sensing of physiological signals.

PubMed

Buxi, Dilpreet; Redouté, Jean-Michel; Yuce, Mehmet Rasit

2014-01-01

Together with a charge or voltage amplifier, piezoelectric sensors are commonly used to pick up physiological vibrations from the body. As an alternative to chopper or auto-zero amplifiers, frequency sensing is known in literature to provide advantages of noise immunity, interfacing to digital readout systems as well as tunable range of sensing. A frequency-sensing readout circuit for sensing low voltage signals from piezoelectric sensors is successfully developed and tested in this work. The output voltage of a piezoelectric sensor is fed to a varactor, which is part of an Colpitts LC oscillator. The oscillation frequency is converted into a voltage using a phase locked loop. The circuit is compared to a reference design in terms of linearity, noise and transfer function. The readout has a input-referred noise voltage of 2.24μV/√Hz and consumes 15 mA at 5V supply. Arterial pulse wave signals and the cardiac vibrations from the chest are measured from one subject to show the proof of concept of the proposed readout. The results of this work are intended to contribute towards alternative low noise analog front end designs for piezoelectric sensors.

Integrative Approach with Electrophysiological and Theoretical Methods Reveals a New Role of S4 Positively Charged Residues in PKD2L1 Channel Voltage-Sensing.

PubMed

Numata, Tomohiro; Tsumoto, Kunichika; Yamada, Kazunori; Kurokawa, Tatsuki; Hirose, Shinichi; Nomura, Hideki; Kawano, Mitsuhiro; Kurachi, Yoshihisa; Inoue, Ryuji; Mori, Yasuo

2017-08-29

Numerical model-based simulations provide important insights into ion channel gating when experimental limitations exist. Here, a novel strategy combining numerical simulations with patch clamp experiments was used to investigate the net positive charges in the putative transmembrane segment 4 (S4) of the atypical, positively-shifted voltage-dependence of polycystic kidney disease 2-like 1 (PKD2L1) channel. Charge-neutralising mutations (K452Q, K455Q and K461Q) in S4 reduced gating charges, positively shifted the Boltzmann-type activation curve [i.e., open probability (P open )-V curve] and altered the time-courses of activation/deactivation of PKD2L1, indicating that this region constitutes part of a voltage sensor. Numerical reconstruction of wild-type (WT) and mutant PKD2L1-mediated currents necessitated, besides their voltage-dependent gating parameters, a scaling factor that describes the voltage-dependence of maximal conductance, G max . Subsequent single-channel conductance (γ) measurements revealed that voltage-dependence of G max in WT can be explained by the inward-rectifying property of γ, which is greatly changed in PKD2L1 mutants. Homology modelling based on PKD2 and Na V Ab structures suggest that such voltage dependence of P open and γ in PKD2L1 could both reflect the charged state of the S4 domain. The present conjunctive experimental and theoretical approaches provide a framework to explore the undetermined mechanism(s) regulating TRP channels that possess non-classical voltage-dependent properties.

Results of the 2015 testbeam of a 180 nm AMS High-Voltage CMOS sensor prototype

DOE Office of Scientific and Technical Information (OSTI.GOV)

Benoit, M.; de Mendizabal, J. Bilbao; Casse, G.

We investigated the active pixel sensors based on the High-Voltage CMOS technology as a viable option for the future pixel tracker of the ATLAS experiment at the High-Luminosity LHC. Our paper reports on the testbeam measurements performed at the H8 beamline of the CERN Super Proton Synchrotron on a High-Voltage CMOS sensor prototype produced in 180 nm AMS technology. These results in terms of tracking efficiency and timing performance, for different threshold and bias conditions, are shown.

Results of the 2015 testbeam of a 180 nm AMS High-Voltage CMOS sensor prototype

DOE PAGES

Benoit, M.; de Mendizabal, J. Bilbao; Casse, G.; ...

2016-07-21

We investigated the active pixel sensors based on the High-Voltage CMOS technology as a viable option for the future pixel tracker of the ATLAS experiment at the High-Luminosity LHC. Our paper reports on the testbeam measurements performed at the H8 beamline of the CERN Super Proton Synchrotron on a High-Voltage CMOS sensor prototype produced in 180 nm AMS technology. These results in terms of tracking efficiency and timing performance, for different threshold and bias conditions, are shown.

Piezoelectric bimorph optical-fiber sensor.

PubMed

Sun, Fengguo; Xiao, Gaozhi; Zhang, Zhiyi; Grover, Chander P

2004-03-20

We propose and demonstrate a novel high-voltage optical-fiber sensor. This sensor consists of an emitting fiber, a receiving fiber, and a piezoelectric bimorph transducer. The emitting fiber is fixed in a base, whereas the receiving fiber is mounted on the free end of the piezoelectric bimorph transducer. When a voltage is applied to the piezoelectric bimorph transducer, its free end is displaced over a distance delta. The displacement induces a loss in the optical coupling between the emitting and the receiving fiber. The voltage can be measured by monitoring the coupling loss.

Frequency domain analysis of droplet-based electrostatic transducers

NASA Astrophysics Data System (ADS)

Allegretto, Graham; Dobashi, Yuta; Dixon, Katelyn; Wyss, Justin; Yao, Dickson; Madden, John D. W.

2018-07-01

Squeezing a water droplet between two electrodes can generate a potential difference by converting some of the mechanical energy in vibrations into electrical energy. By utilizing the high capacitance inherent to electric double layers, and the surface charging at a polymer/water interface, we demonstrate a sensor that generates up to 892 mV peak-to-peak between 1 and 100 Hz, in response to a 250 μm deformation. This frequency response is described and explained using a linearized model in which the interfacial charge acts as the priming voltage, removing the need for external charging normally required in capacitive generators. The model suggests how to design the cell for maximum power output and provides an intuitive understanding of the high pass nature of the sensor. It successfully predicts the point of maximum power transfer.

Time varying voltage combustion control and diagnostics sensor

DOEpatents

Chorpening, Benjamin T [Morgantown, WV; Thornton, Jimmy D [Morgantown, WV; Huckaby, E David [Morgantown, WV; Fincham, William [Fairmont, WV

2011-04-19

A time-varying voltage is applied to an electrode, or a pair of electrodes, of a sensor installed in a fuel nozzle disposed adjacent the combustion zone of a continuous combustion system, such as of the gas turbine engine type. The time-varying voltage induces a time-varying current in the flame which is measured and used to determine flame capacitance using AC electrical circuit analysis. Flame capacitance is used to accurately determine the position of the flame from the sensor and the fuel/air ratio. The fuel and/or air flow rate (s) is/are then adjusted to provide reduced flame instability problems such as flashback, combustion dynamics and lean blowout, as well as reduced emissions. The time-varying voltage may be an alternating voltage and the time-varying current may be an alternating current.

An LMS Programming Scheme and Floating-Gate Technology Enabled Trimmer-Less and Low Voltage Flame Detection Sensor.

PubMed

Iglesias-Rojas, Juan Carlos; Gomez-Castañeda, Felipe; Moreno-Cadenas, Jose Antonio

2017-06-14

In this paper, a Least Mean Square (LMS) programming scheme is used to set the offset voltage of two operational amplifiers that were built using floating-gate transistors, enabling a 0.95 V RMS trimmer-less flame detection sensor. The programming scheme is capable of setting the offset voltage over a wide range of values by means of electron injection. The flame detection sensor consists of two programmable offset operational amplifiers; the first amplifier serves as a 26 μV offset voltage follower, whereas the second amplifier acts as a programmable trimmer-less voltage comparator. Both amplifiers form the proposed sensor, whose principle of functionality is based on the detection of the electrical changes produced by the flame ionization. The experimental results show that it is possible to measure the presence of a flame accurately after programming the amplifiers with a maximum of 35 LMS-algorithm iterations. Current commercial flame detectors are mainly used in absorption refrigerators and large industrial gas heaters, where a high voltage AC source and several mechanical trimmings are used in order to accurately measure the presence of the flame.

An LMS Programming Scheme and Floating-Gate Technology Enabled Trimmer-Less and Low Voltage Flame Detection Sensor

PubMed Central

Iglesias-Rojas, Juan Carlos; Gomez-Castañeda, Felipe; Moreno-Cadenas, Jose Antonio

2017-01-01

In this paper, a Least Mean Square (LMS) programming scheme is used to set the offset voltage of two operational amplifiers that were built using floating-gate transistors, enabling a 0.95 VRMS trimmer-less flame detection sensor. The programming scheme is capable of setting the offset voltage over a wide range of values by means of electron injection. The flame detection sensor consists of two programmable offset operational amplifiers; the first amplifier serves as a 26 μV offset voltage follower, whereas the second amplifier acts as a programmable trimmer-less voltage comparator. Both amplifiers form the proposed sensor, whose principle of functionality is based on the detection of the electrical changes produced by the flame ionization. The experimental results show that it is possible to measure the presence of a flame accurately after programming the amplifiers with a maximum of 35 LMS-algorithm iterations. Current commercial flame detectors are mainly used in absorption refrigerators and large industrial gas heaters, where a high voltage AC source and several mechanical trimmings are used in order to accurately measure the presence of the flame. PMID:28613250

Phosphatidic acid modulation of Kv channel voltage sensor function.

PubMed

Hite, Richard K; Butterwick, Joel A; MacKinnon, Roderick

2014-10-06

Membrane phospholipids can function as potent regulators of ion channel function. This study uncovers and investigates the effect of phosphatidic acid on Kv channel gating. Using the method of reconstitution into planar lipid bilayers, in which protein and lipid components are defined and controlled, we characterize two effects of phosphatidic acid. The first is a non-specific electrostatic influence on activation mediated by electric charge density on the extracellular and intracellular membrane surfaces. The second is specific to the presence of a primary phosphate group, acts only through the intracellular membrane leaflet and depends on the presence of a particular arginine residue in the voltage sensor. Intracellular phosphatidic acid accounts for a nearly 50 mV shift in the midpoint of the activation curve in a direction consistent with stabilization of the voltage sensor's closed conformation. These findings support a novel mechanism of voltage sensor regulation by the signaling lipid phosphatidic acid.

Alpha-Particle Gas-Pressure Sensor

NASA Technical Reports Server (NTRS)

Buehler, M. C.; Bell, L. D.; Hecht, M. H.

1996-01-01

An approximate model was developed to establish design curves for the saturation region and a more complete model developed to characterize the current-voltage curves for an alpha-particle pressure sensor. A simple two-parameter current-voltage expression was developed to describe the dependence of the ion current on pressure. The parameters are the saturation-current pressure coefficient and mu/D, the ion mobility/diffusion coefficient. The sensor is useful in the pressure range between 0.1 and 1000 mb using a 1 - mu Ci(241) Am source. Experimental results, taken between 1 and up to 200 mb, show the sensor operates with an anode voltage of 5 V and a sensitivity of 20 fA/mb in nitrogen.

Voltage-sensing phosphatase modulation by a C2 domain.

PubMed

Castle, Paul M; Zolman, Kevin D; Kohout, Susy C

2015-01-01

The voltage-sensing phosphatase (VSP) is the first example of an enzyme controlled by changes in membrane potential. VSP has four distinct regions: the transmembrane voltage-sensing domain (VSD), the inter-domain linker, the cytosolic catalytic domain, and the C2 domain. The VSD transmits the changes in membrane potential through the inter-domain linker activating the catalytic domain which then dephosphorylates phosphatidylinositol phosphate (PIP) lipids. The role of the C2, however, has not been established. In this study, we explore two possible roles for the C2: catalysis and membrane-binding. The Ci-VSP crystal structures show that the C2 residue Y522 lines the active site suggesting a contribution to catalysis. When we mutated Y522 to phenylalanine, we found a shift in the voltage dependence of activity. This suggests hydrogen bonding as a mechanism of action. Going one step further, when we deleted the entire C2 domain, we found voltage-dependent enzyme activity was no longer detectable. This result clearly indicates the entire C2 is necessary for catalysis as well as for modulating activity. As C2s are known membrane-binding domains, we tested whether the VSP C2 interacts with the membrane. We probed a cluster of four positively charged residues lining the top of the C2 and suggested by previous studies to interact with phosphatidylinositol 4,5-bisphosphate [PI(4,5)P2] (Kalli et al., 2014). Neutralizing those positive charges significantly shifted the voltage dependence of activity to higher voltages. We tested membrane binding by depleting PI(4,5)P2 from the membrane using the 5HT2C receptor and found that the VSD motions as measured by voltage clamp fluorometry (VCF) were not changed. These results suggest that if the C2 domain interacts with the membrane to influence VSP function it may not occur exclusively through PI(4,5)P2. Together, this data advances our understanding of the VSP C2 by demonstrating a necessary and critical role for the C2 domain in VSP function.

Voltage-sensing phosphatase modulation by a C2 domain

PubMed Central

Castle, Paul M.; Zolman, Kevin D.; Kohout, Susy C.

2015-01-01

The voltage-sensing phosphatase (VSP) is the first example of an enzyme controlled by changes in membrane potential. VSP has four distinct regions: the transmembrane voltage-sensing domain (VSD), the inter-domain linker, the cytosolic catalytic domain, and the C2 domain. The VSD transmits the changes in membrane potential through the inter-domain linker activating the catalytic domain which then dephosphorylates phosphatidylinositol phosphate (PIP) lipids. The role of the C2, however, has not been established. In this study, we explore two possible roles for the C2: catalysis and membrane-binding. The Ci-VSP crystal structures show that the C2 residue Y522 lines the active site suggesting a contribution to catalysis. When we mutated Y522 to phenylalanine, we found a shift in the voltage dependence of activity. This suggests hydrogen bonding as a mechanism of action. Going one step further, when we deleted the entire C2 domain, we found voltage-dependent enzyme activity was no longer detectable. This result clearly indicates the entire C2 is necessary for catalysis as well as for modulating activity. As C2s are known membrane-binding domains, we tested whether the VSP C2 interacts with the membrane. We probed a cluster of four positively charged residues lining the top of the C2 and suggested by previous studies to interact with phosphatidylinositol 4,5-bisphosphate [PI(4,5)P2] (Kalli et al., 2014). Neutralizing those positive charges significantly shifted the voltage dependence of activity to higher voltages. We tested membrane binding by depleting PI(4,5)P2 from the membrane using the 5HT2C receptor and found that the VSD motions as measured by voltage clamp fluorometry (VCF) were not changed. These results suggest that if the C2 domain interacts with the membrane to influence VSP function it may not occur exclusively through PI(4,5)P2. Together, this data advances our understanding of the VSP C2 by demonstrating a necessary and critical role for the C2 domain in VSP function. PMID:25904865

A Power-Frequency Electric Field Sensor for Portable Measurement

PubMed Central

Xiao, Dongping; Ma, Qichao; Xie, Yutong; Zheng, Qi

2018-01-01

In this paper, a new type of electric field sensor is proposed for the health and safety protection of inspection staff in high-voltage environments. Compared with the traditional power frequency electric field measurement instruments, the portable instrument has some special performance requirements and, thus, a new kind of double spherical shell sensor is presented. First, the mathematical relationships between the induced voltage of the sensor, the output voltage of the measurement circuit, and the original electric field in free space are deduced theoretically. These equations show the principle of the proposed sensor to measure the electric field and the effect factors of the measurement. Next, the characteristics of the sensor are analyzed through simulation. The simulation results are in good agreement with the theoretical analysis. The influencing rules of the size and material of the sensor on the measurement results are summarized. Then, the proposed sensor and the matching measurement system are used in a physical experiment. After calibration, the error of the measurement system is discussed. Lastly, the directional characteristic of the proposed sensor is experimentally tested. PMID:29614753

A Power-Frequency Electric Field Sensor for Portable Measurement.

PubMed

Xiao, Dongping; Ma, Qichao; Xie, Yutong; Zheng, Qi; Zhang, Zhanlong

2018-03-31

In this paper, a new type of electric field sensor is proposed for the health and safety protection of inspection staff in high-voltage environments. Compared with the traditional power frequency electric field measurement instruments, the portable instrument has some special performance requirements and, thus, a new kind of double spherical shell sensor is presented. First, the mathematical relationships between the induced voltage of the sensor, the output voltage of the measurement circuit, and the original electric field in free space are deduced theoretically. These equations show the principle of the proposed sensor to measure the electric field and the effect factors of the measurement. Next, the characteristics of the sensor are analyzed through simulation. The simulation results are in good agreement with the theoretical analysis. The influencing rules of the size and material of the sensor on the measurement results are summarized. Then, the proposed sensor and the matching measurement system are used in a physical experiment. After calibration, the error of the measurement system is discussed. Lastly, the directional characteristic of the proposed sensor is experimentally tested.

Fractional Modeling of the AC Large-Signal Frequency Response in Magnetoresistive Current Sensors

PubMed Central

Arias, Sergio Iván Ravello; Muñoz, Diego Ramírez; Moreno, Jaime Sánchez; Cardoso, Susana; Ferreira, Ricardo; de Freitas, Paulo Jorge Peixeiro

2013-01-01

Fractional calculus is considered when derivatives and integrals of non-integer order are applied over a specific function. In the electrical and electronic domain, the transfer function dependence of a fractional filter not only by the filter order n, but additionally, of the fractional order α is an example of a great number of systems where its input-output behavior could be more exactly modeled by a fractional behavior. Following this aim, the present work shows the experimental ac large-signal frequency response of a family of electrical current sensors based in different spintronic conduction mechanisms. Using an ac characterization set-up the sensor transimpedance function Zt(if) is obtained considering it as the relationship between sensor output voltage and input sensing current, Zt(jf)=Vo,sensor(jf)/Isensor(jf). The study has been extended to various magnetoresistance sensors based in different technologies like anisotropic magnetoresistance (AMR), giant magnetoresistance (GMR), spin-valve (GMR-SV) and tunnel magnetoresistance (TMR). The resulting modeling shows two predominant behaviors, the low-pass and the inverse low-pass with fractional index different from the classical integer response. The TMR technology with internal magnetization offers the best dynamic and sensitivity properties opening the way to develop actual industrial applications. PMID:24351648

A Multi-Modality CMOS Sensor Array for Cell-Based Assay and Drug Screening.

PubMed

Chi, Taiyun; Park, Jong Seok; Butts, Jessica C; Hookway, Tracy A; Su, Amy; Zhu, Chengjie; Styczynski, Mark P; McDevitt, Todd C; Wang, Hua

2015-12-01

In this paper, we present a fully integrated multi-modality CMOS cellular sensor array with four sensing modalities to characterize different cell physiological responses, including extracellular voltage recording, cellular impedance mapping, optical detection with shadow imaging and bioluminescence sensing, and thermal monitoring. The sensor array consists of nine parallel pixel groups and nine corresponding signal conditioning blocks. Each pixel group comprises one temperature sensor and 16 tri-modality sensor pixels, while each tri-modality sensor pixel can be independently configured for extracellular voltage recording, cellular impedance measurement (voltage excitation/current sensing), and optical detection. This sensor array supports multi-modality cellular sensing at the pixel level, which enables holistic cell characterization and joint-modality physiological monitoring on the same cellular sample with a pixel resolution of 80 μm × 100 μm. Comprehensive biological experiments with different living cell samples demonstrate the functionality and benefit of the proposed multi-modality sensing in cell-based assay and drug screening.

EIT-based fabric pressure sensing.

PubMed

Yao, A; Yang, C L; Seo, J K; Soleimani, M

2013-01-01

This paper presents EIT-based fabric sensors that aim to provide a pressure mapping using the current carrying and voltage sensing electrodes attached to the boundary of the fabric patch. Pressure-induced shape change over the sensor area makes a change in the conductivity distribution which can be conveyed to the change of boundary current-voltage data. This boundary data is obtained through electrode measurements in EIT system. The corresponding inverse problem is to reconstruct the pressure and deformation map from the relationship between the applied current and the measured voltage on the fabric boundary. Taking advantage of EIT in providing dynamical images of conductivity changes due to pressure induced shape change, the pressure map can be estimated. In this paper, the EIT-based fabric sensor was presented for circular and rectangular sensor geometry. A stretch sensitive fabric was used in circular sensor with 16 electrodes and a pressure sensitive fabric was used in a rectangular sensor with 32 electrodes. A preliminary human test was carried out with the rectangular sensor for foot pressure mapping showing promising results.

A High-Temperature Piezoresistive Pressure Sensor with an Integrated Signal-Conditioning Circuit.

PubMed

Yao, Zong; Liang, Ting; Jia, Pinggang; Hong, Yingping; Qi, Lei; Lei, Cheng; Zhang, Bin; Xiong, Jijun

2016-06-18

This paper focuses on the design and fabrication of a high-temperature piezoresistive pressure sensor with an integrated signal-conditioning circuit, which consists of an encapsulated pressure-sensitive chip, a temperature compensation circuit and a signal-conditioning circuit. A silicon on insulation (SOI) material and a standard MEMS process are used in the pressure-sensitive chip fabrication, and high-temperature electronic components are adopted in the temperature-compensation and signal-conditioning circuits. The entire pressure sensor achieves a hermetic seal and can be operated long-term in the range of -50 °C to 220 °C. Unlike traditional pressure sensor output voltage ranges (in the dozens to hundreds of millivolts), the output voltage of this sensor is from 0 V to 5 V, which can significantly improve the signal-to-noise ratio and measurement accuracy in practical applications of long-term transmission based on experimental verification. Furthermore, because this flexible sensor's output voltage is adjustable, general follow-up pressure transmitter devices for voltage converters need not be used, which greatly reduces the cost of the test system. Thus, the proposed high-temperature piezoresistive pressure sensor with an integrated signal-conditioning circuit is expected to be highly applicable to pressure measurements in harsh environments.

Electro-optic voltage sensor head

DOEpatents

Crawford, T.M.; Davidson, J.R.; Woods, G.K.

1999-08-17

The invention is an electro-optic voltage sensor head designed for integration with existing types of high voltage transmission and distribution apparatus. The sensor head contains a transducer, which comprises a transducing material in which the Pockels electro-optic effect is observed. In the practice of the invention at least one beam of electromagnetic radiation is routed into the transducing material of the transducer in the sensor head. The beam undergoes an electro-optic effect in the sensor head when the transducing material is subjected to an E-field. The electro-optic effect is observed as a differential phase a shift, also called differential phase modulation, of the beam components in orthogonal planes of the electromagnetic radiation. In the preferred embodiment the beam is routed through the transducer along an initial axis and then reflected by a retro-reflector back substantially parallel to the initial axis, making a double pass through the transducer for increased measurement sensitivity. The preferred embodiment of the sensor head also includes a polarization state rotator and at least one beam splitter for orienting the beam along major and minor axes and for splitting the beam components into two signals which are independent converse amplitude-modulated signals carrying E-field magnitude and hence voltage information from the sensor head by way of optic fibers. 6 figs.

Electro-optic voltage sensor head

DOEpatents

Crawford, Thomas M.; Davidson, James R.; Woods, Gregory K.

1999-01-01

The invention is an electro-optic voltage sensor head designed for integration with existing types of high voltage transmission and distribution apparatus. The sensor head contains a transducer, which comprises a transducing material in which the Pockels electro-optic effect is observed. In the practice of the invention at least one beam of electromagnetic radiation is routed into the transducing material of the transducer in the sensor head. The beam undergoes an electro-optic effect in the sensor head when the transducing material is subjected to an E-field. The electro-optic effect is observed as a differential phase a shift, also called differential phase modulation, of the beam components in orthogonal planes of the electromagnetic radiation. In the preferred embodiment the beam is routed through the transducer along an initial axis and then reflected by a retro-reflector back substantially parallel to the initial axis, making a double pass through the transducer for increased measurement sensitivity. The preferred embodiment of the sensor head also includes a polarization state rotator and at least one beam splitter for orienting the beam along major and minor axes and for splitting the beam components into two signals which are independent converse amplitude-modulated signals carrying E-field magnitude and hence voltage information from the sensor head by way of optic fibers.

Design and modeling of magnetically driven electric-field sensor for non-contact DC voltage measurement in electric power systems.

PubMed

Wang, Decai; Li, Ping; Wen, Yumei

2016-10-01

In this paper, the design and modeling of a magnetically driven electric-field sensor for non-contact DC voltage measurement are presented. The magnetic drive structure of the sensor is composed of a small solenoid and a cantilever beam with a cylindrical magnet mounted on it. The interaction of the magnet and the solenoid provides the magnetic driving force for the sensor. Employing magnetic drive structure brings the benefits of low driving voltage and large vibrating displacement, which consequently results in less interference from the drive signal. In the theoretical analyses, the capacitance calculation model between the wire and the sensing electrode is built. The expression of the magnetic driving force is derived by the method of linear fitting. The dynamical model of the magnetic-driven cantilever beam actuator is built by using Euler-Bernoulli theory and distributed parameter method. Taking advantage of the theoretical model, the output voltage of proposed sensor can be predicted. The experimental results are in good agreement with the theoretical results. The proposed sensor shows a favorable linear response characteristic. The proposed sensor has a measuring sensitivity of 9.87 μV/(V/m) at an excitation current of 37.5 mA. The electric field intensity resolution can reach 10.13 V/m.

Biophysical characterization of the fluorescent protein voltage probe VSFP2.3 based on the voltage-sensing domain of Ci-VSP.

PubMed

Lundby, Alicia; Akemann, Walther; Knöpfel, Thomas

2010-11-01

A voltage sensitive phosphatase was discovered in the ascidian Ciona intestinalis. The phosphatase, Ci-VSP, contains a voltage-sensing domain homologous to those known from voltage-gated ion channels, but unlike ion channels, the voltage-sensing domain of Ci-VSP can reside in the cell membrane as a monomer. We fused the voltage-sensing domain of Ci-VSP to a pair of fluorescent reporter proteins to generate a genetically encodable voltage-sensing fluorescent probe, VSFP2.3. VSFP2.3 is a fluorescent voltage probe that reports changes in membrane potential as a FRET (fluorescence resonance energy transfer) signal. Here we report sensing current measurements from VSFP2.3, and show that VSFP2.3 carries 1.2 e sensing charges, which are displaced within 1.5 ms. The sensing currents become faster at higher temperatures, and the voltage dependence of the decay time constants is temperature dependent. Neutralization of an arginine in S4, previously suggested to be a sensing charge, and measuring associated sensing currents indicate that this charge is likely to reside at the membrane-aqueous interface rather than within the membrane electric field. The data presented give us insights into the voltage-sensing mechanism of Ci-VSP, which will allow us to further improve the sensitivity and kinetics of the family of VSFP proteins.

High-voltage pixel sensors for ATLAS upgrade

NASA Astrophysics Data System (ADS)

Perić, I.; Kreidl, C.; Fischer, P.; Bompard, F.; Breugnon, P.; Clemens, J.-C.; Fougeron, D.; Liu, J.; Pangaud, P.; Rozanov, A.; Barbero, M.; Feigl, S.; Capeans, M.; Ferrere, D.; Pernegger, H.; Ristic, B.; Muenstermann, D.; Gonzalez Sevilla, S.; La Rosa, A.; Miucci, A.; Nessi, M.; Iacobucci, G.; Backhaus, M.; Hügging, Fabian; Krüger, H.; Hemperek, T.; Obermann, T.; Wermes, N.; Garcia-Sciveres, M.; Quadt, A.; Weingarten, J.; George, M.; Grosse-Knetter, J.; Rieger, J.; Bates, R.; Blue, A.; Buttar, C.; Hynds, D.

2014-11-01

The high-voltage (HV-) CMOS pixel sensors offer several good properties: a fast charge collection by drift, the possibility to implement relatively complex CMOS in-pixel electronics and the compatibility with commercial processes. The sensor element is a deep n-well diode in a p-type substrate. The n-well contains CMOS pixel electronics. The main charge collection mechanism is drift in a shallow, high field region, which leads to a fast charge collection and a high radiation tolerance. We are currently evaluating the use of the high-voltage detectors implemented in 180 nm HV-CMOS technology for the high-luminosity ATLAS upgrade. Our approach is replacing the existing pixel and strip sensors with the CMOS sensors while keeping the presently used readout ASICs. By intelligence we mean the ability of the sensor to recognize a particle hit and generate the address information. In this way we could benefit from the advantages of the HV sensor technology such as lower cost, lower mass, lower operating voltage, smaller pitch, smaller clusters at high incidence angles. Additionally we expect to achieve a radiation hardness necessary for ATLAS upgrade. In order to test the concept, we have designed two HV-CMOS prototypes that can be readout in two ways: using pixel and strip readout chips. In the case of the pixel readout, the connection between HV-CMOS sensor and the readout ASIC can be established capacitively.

Structural basis for gating and activation of RyR1

PubMed Central

des Georges, Amédée; Clarke, Oliver B.; Zalk, Ran; Yuan, Qi; Condon, Kendall J.; Grassucci, Robert A.; Hendrickson, Wayne A.; Marks, Andrew R.; Frank, Joachim

2016-01-01

Summary The type-1 ryanodine receptor (RyR1) is an intracellular calcium (Ca2+) release channel required for skeletal muscle contraction. Here we present cryo-EM reconstructions of RyR1 in multiple functional states revealing the structural basis of channel gating and ligand-dependent activation. Binding sites for the channel activators Ca2+, ATP and caffeine were identified at interdomain interfaces of the C-terminal domain. Either ATP or Ca2+ alone induce conformational changes in the cytoplasmic assembly (‘priming’), without pore dilation. In contrast, in the presence of all three activating ligands, high-resolution reconstructions of open and closed states of RyR1 were obtained from the same sample, enabling analyses of conformational changes associated with gating. Gating involves global conformational changes in the cytosolic assembly accompanied by local changes in the transmembrane domain, which include bending of the S6 transmembrane segment and consequent pore dilation, displacement and deformation of the S4-S5 linker, and conformational changes in the pseudo-voltage-sensor domain. PMID:27662087

Electro-optic high voltage sensor

DOEpatents

Davidson, James R.; Seifert, Gary D.

2003-09-16

A small sized electro-optic voltage sensor capable of accurate measurement of high voltages without contact with a conductor or voltage source is provided. When placed in the presence of an electric field, the sensor receives an input beam of electromagnetic radiation. A polarization beam displacer separates the input beam into two beams with orthogonal linear polarizations and causes one linearly polarized beam to impinge a crystal at a desired angle independent of temperature. The Pockels effect elliptically polarizes the beam as it travels through the crystal. A reflector redirects the beam back through the crystal and the beam displacer. On the return path, the polarization beam displacer separates the elliptically polarized beam into two output beams of orthogonal linear polarization. The system may include a detector for converting the output beams into electrical signals and a signal processor for determining the voltage based on an analysis of the output beams.

Unfolding of a Temperature-Sensitive Domain Controls Voltage-Gated Channel Activation.

PubMed

Arrigoni, Cristina; Rohaim, Ahmed; Shaya, David; Findeisen, Felix; Stein, Richard A; Nurva, Shailika Reddy; Mishra, Smriti; Mchaourab, Hassane S; Minor, Daniel L

2016-02-25

Voltage-gated ion channels (VGICs) are outfitted with diverse cytoplasmic domains that impact function. To examine how such elements may affect VGIC behavior, we addressed how the bacterial voltage-gated sodium channel (BacNa(V)) C-terminal cytoplasmic domain (CTD) affects function. Our studies show that the BacNa(V) CTD exerts a profound influence on gating through a temperature-dependent unfolding transition in a discrete cytoplasmic domain, the neck domain, proximal to the pore. Structural and functional studies establish that the BacNa(V) CTD comprises a bi-partite four-helix bundle that bears an unusual hydrophilic core whose integrity is central to the unfolding mechanism and that couples directly to the channel activation gate. Together, our findings define a general principle for how the widespread four-helix bundle cytoplasmic domain architecture can control VGIC responses, uncover a mechanism underlying the diverse BacNa(V) voltage dependencies, and demonstrate that a discrete domain can encode the temperature-dependent response of a channel. Copyright © 2016 Elsevier Inc. All rights reserved.

Unfolding of a temperature-sensitive domain controls voltage-gated channel activation

PubMed Central

Arrigoni, Cristina; Rohaim, Ahmed; Shaya, David; Findeisen, Felix; Stein, Richard A.; Nurva, Shailika Reddy; Mishra, Smriti; Mchaourab, Hassane S.; Minor, Daniel L.

2016-01-01

Voltage-gated ion channels (VGICs) are outfitted with diverse cytoplasmic domains that impact function. To examine how such elements may affect VGIC behavior, we addressed how the bacterial voltage-gated sodium channel (BacNaV) C-terminal cytoplasmic domain (CTD) affects function. Our studies show that the BacNaV CTD exerts a profound influence on gating through a temperature-dependent unfolding transition in a discrete cytoplasmic domain, the neck domain, proximal to the pore. Structural and functional studies establish that the BacNaV CTD comprises a bi-partite four-helix bundle that bears an unusual hydrophilic core whose integrity is central to the unfolding mechanism and that couples directly to the channel activation gate. Together, our findings define a general principle for how the widespread four-helix bundle cytoplasmic domain architecture can control VGIC responses, uncover a mechanism underlying the diverse BacNaV voltage dependencies, and demonstrate that a discrete domain can encode the temperature dependent response of a channel. PMID:26919429

Coupling between the Voltage-sensing and Pore Domains in a Voltage-gated Potassium Channel

PubMed Central

Schow, Eric V.; Freites, J. Alfredo; Nizkorodov, Alex; White, Stephen H.; Tobias, Douglas J.

2012-01-01

Voltage-dependent potassium (Kv), sodium (Nav), and calcium channels open and close in response to changes in transmembrane (TM) potential, thus regulating cell excitability by controlling ion flow across the membrane. An outstanding question concerning voltage gating is how voltage-induced conformational changes of the channel voltage-sensing domains (VSDs) are coupled through the S4-S5 interfacial linking helices to the opening and closing of the pore domain (PD). To investigate the coupling between the VSDs and the PD, we generated a closed Kv channel configuration from Aeropyrum pernix (KvAP) using atomistic simulations with experiment-based restraints on the VSDs. Full closure of the channel required, in addition to the experimentally determined TM displacement, that the VSDs be displaced both inwardly and laterally around the PD. This twisting motion generates a tight hydrophobic interface between the S4-S5 linkers and the C-terminal ends of the pore domain S6 helices in agreement with available experimental evidence. PMID:22425907

Coupling between the voltage-sensing and pore domains in a voltage-gated potassium channel.

PubMed

Schow, Eric V; Freites, J Alfredo; Nizkorodov, Alex; White, Stephen H; Tobias, Douglas J

2012-07-01

Voltage-dependent potassium (Kv), sodium (Nav), and calcium channels open and close in response to changes in transmembrane (TM) potential, thus regulating cell excitability by controlling ion flow across the membrane. An outstanding question concerning voltage gating is how voltage-induced conformational changes of the channel voltage-sensing domains (VSDs) are coupled through the S4-S5 interfacial linking helices to the opening and closing of the pore domain (PD). To investigate the coupling between the VSDs and the PD, we generated a closed Kv channel configuration from Aeropyrum pernix (KvAP) using atomistic simulations with experiment-based restraints on the VSDs. Full closure of the channel required, in addition to the experimentally determined TM displacement, that the VSDs be displaced both inwardly and laterally around the PD. This twisting motion generates a tight hydrophobic interface between the S4-S5 linkers and the C-terminal ends of the pore domain S6 helices in agreement with available experimental evidence.

Location of the β4 transmembrane helices in the BK potassium channel

PubMed Central

Wu, Roland S.; Chudasama, Neelesh; Zakharov, Sergey I.; Doshi, Darshan; Motoike, Howard; Liu, Guoxia; Yao, Yongneng; Niu, Xiaowei; Deng, Shi-Xian; Landry, Donald W.; Karlin, Arthur; Marx, Steven O.

2009-01-01

Large-conductance, voltage- and Ca2+-gated potassium (BK) channels control excitability in a number of cell types. BK channels are composed of α subunits, which contain the voltage-sensor domains and the Ca2+- sensor domains, and form the pore, and often one of four types of β subunits, which modulate the channel in a cell-specific manner. β4 is expressed in neurons throughout the brain. Deletion of β4 in mice causes temporal lobe epilepsy. Compared to channels composed of α alone, channels composed of α and β4 activate and deactivate more slowly. We inferred the locations of the two β4 transmembrane (TM) helices, TM1 and TM2, relative to the seven αTM helices, S0-S6, from the extent of disulfide bond formation between cysteines substituted in the extracellular flanks of these TM helices. We found that β4 TM2 is close to α S0 and that β4 TM1 is close to both α S1 and S2. At least at their extracellular ends, TM1 and TM2 are not close to S3 through S6. In six of eight of the most highly crosslinked cysteine pairs, four crosslinks from TM2 to S0 and one each from TM1 to S1 and S2 had small effects on the V50 and on the rates of activation and deactivation. That disulfide crosslinking caused only small functional perturbations is consistent with the proximity of the extracellular ends of TM2 to S0 and of TM1 to S1 and to S2, in both the open and closed states. PMID:19571123

A second generation expert system for checking and diagnosing AXAF's electric power system

NASA Technical Reports Server (NTRS)

Bykat, Alex

1992-01-01

AXAF - Advanced X-ray Astrophysics Facility - is a third NASA's great space observatory. Each of these observatories is intended to cover different parts of the electromagnetic spectrum (x-ray for AXAF) and to provide high resolution images of celestial sources in our universe. While the spacecraft is in orbit, the electric power system (EPS) performance is monitored via sensors measuring voltages, currents, pressures, and temperatures. The sensor data are sent from the spacecraft to the ground station as telemetry and analyzed on arrival. Monitoring, diagnosis and maintenance of such EPS is an arduous task which requires expertise and constant attention of the ground personnel. To help the ground crew in this task, much of it should be automated and delegated to expert systems, which draw engineer's attention to possible malfunctions and allows him to review the telemetry to determine the source of the trouble, diagnose the suspected fault and to propose a corrective action. Those systems are built on assumptions such as: (1) domain knowledge is available and can be represented as a set of rules; (2) domain knowledge is circumscribed, static, and monotonic; and (3) expert decision making can be emulated by a logical inference mechanism.

Development of a Synthetic Switch to Control Protein Stability in Eukaryotic Cells with Light.

PubMed

Taxis, Christof

2017-01-01

In eukaryotic cells, virtually all regulatory processes are influenced by proteolysis. Thus, synthetic control of protein stability is a powerful approach to influence cellular behavior. To achieve this, selected target proteins are modified with a conditional degradation sequence (degron) that responds to a distinct signal. For development of a synthetic degron, an appropriate sensor domain is fused with a degron such that activity of the degron is under control of the sensor. This chapter describes the development of a light-activated, synthetic degron in the model organism Saccharomyces cerevisiae. This photosensitive degron module is composed of the light-oxygen-voltage (LOV) 2 photoreceptor domain of Arabidopsis thaliana phototropin 1 and a degron derived from murine ornithine decarboxylase (ODC). Excitation of the photoreceptor with blue light induces a conformational change that leads to exposure and activation of the degron. Subsequently, the protein is targeted for degradation by the proteasome. Here, the strategy for degron module development and optimization is described in detail together with experimental aspects, which were pivotal for successful implementation of light-controlled proteolysis. The engineering of the photosensitive degron (psd) module may well serve as a blueprint for future development of sophisticated synthetic switches.

A new 9T global shutter pixel with CDS technique

NASA Astrophysics Data System (ADS)

Liu, Yang; Ma, Cheng; Zhou, Quan; Wang, Xinyang

2015-04-01

Benefiting from motion blur free, Global shutter pixel is very widely used in the design of CMOS image sensors for high speed applications such as motion vision, scientifically inspection, etc. In global shutter sensors, all pixel signal information needs to be stored in the pixel first and then waiting for readout. For higher frame rate, we need very fast operation of the pixel array. There are basically two ways for the in pixel signal storage, one is in charge domain, such as the one shown in [1], this needs complicated process during the pixel fabrication. The other one is in voltage domain, one example is the one in [2], this pixel is based on the 4T PPD technology and normally the driving of the high capacitive transfer gate limits the speed of the array operation. In this paper we report a new 9T global shutter pixel based on 3-T partially pinned photodiode (PPPD) technology. It incorporates three in-pixel storage capacitors allowing for correlated double sampling (CDS) and pipeline operation of the array (pixel exposure during the readout of the array). Only two control pulses are needed for all the pixels at the end of exposure which allows high speed exposure control.

Emergence of domains and nonlinear transport in the zero-resistance state.

PubMed

Dmitriev, I A; Khodas, M; Mirlin, A D; Polyakov, D G

2013-11-15

We study transport in the domain state, the so-called zero-resistance state, that emerges in a two-dimensional electron system in which the combined action of microwave radiation and magnetic field produces a negative absolute conductivity. We show that the voltage-biased system has a rich phase diagram in the system size and voltage plane, with second- and first-order transitions between the domain and homogeneous states for small and large voltages, respectively. We find the residual negative dissipative resistance in the stable domain state.

A micro-power precision amplifier for converting the output of light sensors to a voltage readable by miniature data loggers.

PubMed

Phillips, Nathan; Bond, Barbara J.

1999-07-01

To record photosynthetically active radiation (PAR) simultaneously at a number of points throughout a forest canopy, we developed a simple, inexpensive (< $10 US) current-to-voltage converter that processes the current generated by a photodiode radiation sensor to a voltage range that is recordable with a miniature data logger. The converter, which weighs less than 75 g and has a volume of only 100 cm(3), is built around an ultra-low power OP-90 precision operational amplifier, which consumes less than 0.5 mA at 9 V when converting the output of a Li-Cor LI-190SA quantum sensor exposed to photosynthetically active radiation (PAR) of 2500 &mgr;mol m(-2) s(-1) or only 5 &mgr;A in low light. A small 9-V battery thus powers the amplifier for more than 1000 h of continuous operation. Correlations between photometer readings and voltage output from the current-to-voltage converter were high and linear at both high and low PAR. Sixteen Li-Cor LI-190SA quantum sensors each equipped with current-to-voltage converters and connected to a miniature data logger were deployed in the upper branches of a Panamanian tropical rainforest canopy. Each unit performed reliably during a one- or two-week evaluation.

Self-calibrated humidity sensor in CMOS without post-processing.

PubMed

Nizhnik, Oleg; Higuchi, Kohei; Maenaka, Kazusuke

2012-01-01

A 1.1 μW power dissipation, voltage-output humidity sensor with 10% relative humidity accuracy was developed in the LFoundry 0.15 μm CMOS technology without post-processing. The sensor consists of a woven lateral array of electrodes implemented in CMOS top metal, a humidity-sensitive layer of Intervia Photodielectric 8023D-10, a CMOS capacitance to voltage converter, and the self-calibration circuitry.

A Spherical Electro Optic High Voltage Sensor

DTIC Science & Technology

1989-06-01

electro - optic (EO) crystal is introduced for photonic measurement of pulsed high-voltage fields. A spherical shape is used in order to reduce electric field gradients in the vicinity of the sensor. The sensor is pure dielectric and is interrogated remotely using a laser. The sensor does not require the connection of any conducting components, which results in the highest electrical isolation. The spherical nature of the crystal coupled with the incident laser beam, and crossed polarizers (intensity modulation scheme). automatically produces interference figures. The

IE Data Processing.

DTIC Science & Technology

1984-10-01

RN4 DMT P6 CAnQ fram P4 Satellite ID-343567656469B Sensor Bias Node Voltages 1 1.27 0. 2 7.54 6.31 3 16.42 15.26 4 28.93 27.87 NmDber of sectors per...Monitor Interoretation Event Yloitor Voltage Change Sensor Operation Mode Cange Duration Frequency 0 20 Elec: Density Cal2 1024 ion: Density 1 K 2, 3of...34"Event monitor voltage decreases linearly fron 500 to 100 during electron sweep. • Event monitor voltage increases linearly from 10 to 500 during

The monitoring of transient regimes on machine tools based on speed, acceleration and active electric power absorbed by motors

NASA Astrophysics Data System (ADS)

Horodinca, M.

2016-08-01

This paper intend to propose some new results related with computer aided monitoring of transient regimes on machine-tools based on the evolution of active electrical power absorbed by the electric motor used to drive the main kinematic chains and the evolution of rotational speed and acceleration of the main shaft. The active power is calculated in numerical format using the evolution of instantaneous voltage and current delivered by electrical power system to the electric motor. The rotational speed and acceleration of the main shaft are calculated based on the signal delivered by a sensor. Three real-time analogic signals are acquired with a very simple computer assisted setup which contains a voltage transformer, a current transformer, an AC generator as rotational speed sensor, a data acquisition system and a personal computer. The data processing and analysis was done using Matlab software. Some different transient regimes were investigated; several important conclusions related with the advantages of this monitoring technique were formulated. Many others features of the experimental setup are also available: to supervise the mechanical loading of machine-tools during cutting processes or for diagnosis of machine-tools condition by active electrical power signal analysis in frequency domain.

Fiber-optic sensors for aerospace electrical measurements: An update

NASA Technical Reports Server (NTRS)

Patterson, Richard L.; Rose, A. H.; Tang, D.; Day, G. W.

1991-01-01

Fiber-optic sensors are being developed for electrical current, voltage, and power measurements in aerospace applications. These sensors are presently designed to cover ac frequencies from 60 Hz to 20 kHz. The current sensor, based on the Faraday effect in optical fiber, is in advanced development after some initial testing. Concentration is on packaging methods and ways to maintain consistent sensitivity with changes in temperature. The voltage sensor, utilizing the Pockels effect in a crystal, has excelled in temperature tests. This paper reports on the development of these sensors, the results of evaluation, improvements now in progress, and the future direction of the work.

Chemical sensors are hybrid-input memristors

NASA Astrophysics Data System (ADS)

Sysoev, V. I.; Arkhipov, V. E.; Okotrub, A. V.; Pershin, Y. V.

2018-04-01

Memristors are two-terminal electronic devices whose resistance depends on the history of input signal (voltage or current). Here we demonstrate that the chemical gas sensors can be considered as memristors with a generalized (hybrid) input, namely, with the input consisting of the voltage, analyte concentrations and applied temperature. The concept of hybrid-input memristors is demonstrated experimentally using a single-walled carbon nanotubes chemical sensor. It is shown that with respect to the hybrid input, the sensor exhibits some features common with memristors such as the hysteretic input-output characteristics. This different perspective on chemical gas sensors may open new possibilities for smart sensor applications.

Crystal Structures of Apparent Saccharide Sensors from Histidine Kinase Receptors Prevalent in a Human Gut Symbiont

PubMed Central

Zhang, Zhen; Liu, Qun; Hendrickson, Wayne A.

2014-01-01

The adult human gut presents a complicated ecosystem where host-bacterium symbiosis plays an important role. Bacteroides thetaiotaomicron is a predominant member of the gut microflora, providing the human digestive tract with a large number of glycolytic enzymes. Expression of many of these enzymes appears to be controlled by histidine kinase receptors that are fused into unusual hybrid two-component systems that share homologous periplasmic sensor domains. These sensor domains belong to the third most populated (HK3) family based on a previous bioinformatics analysis of predicted histidine kinase sensors. Here, we present crystal structures of two sensor domains representative of the HK3 family. Each sensor is folded into three domains: two seven-bladed β-propeller domains and one β-sandwich domain. Both sensors form dimers in crystals and one sensor appears to be physiologically relevant. The folding characteristics in the individual domains, the domain organization, and the oligomeric architecture are all unique to the HK3 sensors. The sequence analysis of the HK3 sensors indicates that these sensors are shared among other signaling molecules, implying a combinatorial molecular evolution. PMID:24995510

Use of external cavity quantum cascade laser compliance voltage in real-time trace gas sensing of multiple chemicals

NASA Astrophysics Data System (ADS)

Phillips, Mark C.; Taubman, Matthew S.; Kriesel, Jason

2015-01-01

We describe a prototype trace gas sensor designed for real-time detection of multiple chemicals. The sensor uses an external cavity quantum cascade laser (ECQCL) swept over its tuning range of 940-1075 cm-1 (9.30-10.7 μm) at a 10 Hz repetition rate. The sensor was designed for operation in multiple modes, including gas sensing within a multi-pass Heriott cell and intracavity absorption sensing using the ECQCL compliance voltage. In addition, the ECQCL compliance voltage was used to reduce effects of long-term drifts in the ECQCL output power. The sensor was characterized for noise, drift, and detection of chemicals including ammonia, methanol, ethanol, isopropanol, Freon- 134a, Freon-152a, and diisopropyl methylphosphonate (DIMP). We also present use of the sensor for mobile detection of ammonia downwind of cattle facilities, in which concentrations were recorded at 1-s intervals.

Expression and testing in plants of ArcLight, a genetically-encoded voltage indicator used in neuroscience research.

PubMed

Matzke, Antonius J M; Matzke, Marjori

2015-10-12

It is increasingly appreciated that electrical controls acting at the cellular and supra-cellular levels influence development and initiate rapid responses to environmental cues. An emerging method for non-invasive optical imaging of electrical activity at cell membranes uses genetically-encoded voltage indicators (GEVIs). Developed by neuroscientists to chart neuronal circuits in animals, GEVIs comprise a fluorescent protein that is fused to a voltage-sensing domain. One well-known GEVI, ArcLight, undergoes strong shifts in fluorescence intensity in response to voltage changes in mammalian cells. ArcLight consists of super-ecliptic (SE) pHluorin (pH-sensitive fluorescent protein) with an A227D substitution, which confers voltage sensitivity in neurons, fused to the voltage-sensing domain of the voltage-sensing phosphatase of C iona i ntestinalis (Ci-VSD). In an ongoing effort to adapt tools of optical electrophysiology for plants, we describe here the expression and testing of ArcLight and various derivatives in different membranes of root cells in Arabidopsis thaliana. Transgenic constructs were designed to express ArcLight and various derivatives targeted to the plasma membrane and nuclear membranes of Arabidopsis root cells. In transgenic seedlings, changes in fluorescence intensity of these reporter proteins following extracellular ATP (eATP) application were monitored using a fluorescence microscope equipped with a high speed camera. Coordinate reductions in fluorescence intensity of ArcLight and Ci-VSD-containing derivatives were observed at both the plasma membrane and nuclear membranes following eATP treatments. However, similar responses were observed for derivatives lacking the Ci-VSD. The dispensability of the Ci-VSD suggests that in plants, where H(+) ions contribute substantially to electrical activities, the voltage-sensing ability of ArcLight is subordinate to the pH sensitivity of its SEpHluorin base. The transient reduction of ArcLight fluorescence triggered by eATP most likely reflects changes in pH and not membrane voltage. The pH sensitivity of ArcLight precludes its use as a direct sensor of membrane voltage in plants. Nevertheless, ArcLight and derivatives situated in the plasma membrane and nuclear membranes may offer robust, fluorescence intensity-based pH indicators for monitoring concurrent changes in pH at these discrete membrane systems. Such tools will assist analyses of pH as a signal and/or messenger at the cell surface and the nuclear periphery in living plants.

Phosphatidic acid modulation of Kv channel voltage sensor function

PubMed Central

Hite, Richard K; Butterwick, Joel A; MacKinnon, Roderick

2014-01-01

Membrane phospholipids can function as potent regulators of ion channel function. This study uncovers and investigates the effect of phosphatidic acid on Kv channel gating. Using the method of reconstitution into planar lipid bilayers, in which protein and lipid components are defined and controlled, we characterize two effects of phosphatidic acid. The first is a non-specific electrostatic influence on activation mediated by electric charge density on the extracellular and intracellular membrane surfaces. The second is specific to the presence of a primary phosphate group, acts only through the intracellular membrane leaflet and depends on the presence of a particular arginine residue in the voltage sensor. Intracellular phosphatidic acid accounts for a nearly 50 mV shift in the midpoint of the activation curve in a direction consistent with stabilization of the voltage sensor's closed conformation. These findings support a novel mechanism of voltage sensor regulation by the signaling lipid phosphatidic acid. DOI: http://dx.doi.org/10.7554/eLife.04366.001 PMID:25285449

Design of a Humidity Sensor Tag for Passive Wireless Applications.

PubMed

Wu, Xiang; Deng, Fangming; Hao, Yong; Fu, Zhihui; Zhang, Lihua

2015-10-07

This paper presents a wireless humidity sensor tag for low-cost and low-power applications. The proposed humidity sensor tag, based on radio frequency identification (RFID) technology, was fabricated in a standard 0.18 μm complementary metal oxide semiconductor (CMOS) process. The top metal layer was deposited to form the interdigitated electrodes, which were then filled with polyimide as the humidity sensing layer. A two-stage rectifier adopts a dynamic bias-voltage generator to boost the effective gate-source voltage of the switches in differential-drive architecture, resulting in a flat power conversion efficiency curve. The capacitive sensor interface, based on phase-locked loop (PLL) theory, employs a simple architecture and can work with 0.5 V supply voltage. The measurement results show that humidity sensor tag achieves excellent linearity, hysteresis and stability performance. The total power-dissipation of the sensor tag is 2.5 μW, resulting in a maximum operating distance of 23 m under 4 W of radiation power of the RFID reader.

Design of a Humidity Sensor Tag for Passive Wireless Applications

PubMed Central

Wu, Xiang; Deng, Fangming; Hao, Yong; Fu, Zhihui; Zhang, Lihua

2015-01-01

This paper presents a wireless humidity sensor tag for low-cost and low-power applications. The proposed humidity sensor tag, based on radio frequency identification (RFID) technology, was fabricated in a standard 0.18 μm complementary metal oxide semiconductor (CMOS) process. The top metal layer was deposited to form the interdigitated electrodes, which were then filled with polyimide as the humidity sensing layer. A two-stage rectifier adopts a dynamic bias-voltage generator to boost the effective gate-source voltage of the switches in differential-drive architecture, resulting in a flat power conversion efficiency curve. The capacitive sensor interface, based on phase-locked loop (PLL) theory, employs a simple architecture and can work with 0.5 V supply voltage. The measurement results show that humidity sensor tag achieves excellent linearity, hysteresis and stability performance. The total power-dissipation of the sensor tag is 2.5 μW, resulting in a maximum operating distance of 23 m under 4 W of radiation power of the RFID reader. PMID:26457707

Structural interactions between lipids, water and S1-S4 voltage-sensing domains.

PubMed

Krepkiy, Dmitriy; Gawrisch, Klaus; Swartz, Kenton J

2012-11-02

Membrane proteins serve crucial signaling and transport functions, yet relatively little is known about their structures in membrane environments or how lipids interact with these proteins. For voltage-activated ion channels, X-ray structures suggest that the mobile voltage-sensing S4 helix would be exposed to the membrane, and functional studies reveal that lipid modification can profoundly alter channel activity. Here, we use solid-state NMR to investigate structural interactions of lipids and water with S1-S4 voltage-sensing domains and to explore whether lipids influence the structure of the protein. Our results demonstrate that S1-S4 domains exhibit extensive interactions with lipids and that these domains are heavily hydrated when embedded in a membrane. We also find evidence for preferential interactions of anionic lipids with S1-S4 domains and that these interactions have lifetimes on the timescale of ≤ 10(-3)s. Arg residues within S1-S4 domains are well hydrated and are positioned in close proximity to lipids, exhibiting local interactions with both lipid headgroups and acyl chains. Comparative studies with a positively charged lipid lacking a phosphodiester group reveal that this lipid modification has only modest effects on the structure and hydration of S1-S4 domains. Taken together, our results demonstrate that Arg residues in S1-S4 voltage-sensing domains reside in close proximity to the hydrophobic interior of the membrane yet are well hydrated, a requirement for carrying charge and driving protein motions in response to changes in membrane voltage. Published by Elsevier Ltd.

Structural interactions between lipids, water and S1-S4 voltage-sensing domains

PubMed Central

Krepkiy, Dmitriy; Gawrisch, Klaus; Swartz, Kenton J.

2012-01-01

Membrane proteins serve crucial signaling and transport functions, yet relatively little is known about their structures in membrane environments or how lipids interact with these proteins. For voltage-activated ion channels, X-ray structures suggest that the mobile voltage-sensing S4 helix would be exposed to the membrane, and functional studies reveal that lipid modification can profoundly alter channel activity. Here we use solid-state NMR to investigate structural interactions of lipids and water with S1-S4 voltage-sensing domains, and to explore whether lipids influence the structure of the protein. Our results demonstrate that S1-S4 domains exhibit extensive interactions with lipids, and that these domains are heavily hydrated when embedded in a membrane. We also find evidence for preferential interactions of anionic lipids with S1-S4 domains, and that these interactions have lifetimes on the timescale of 10−3s. Arg residues within S1-S4 domains are well-hydrated and are positioned in close proximity to lipids, exhibiting local interactions with both lipid head groups and acyl chains. Comparative studies with a positively charged lipid lacking a phosphodiester group reveal that this lipid modification has only modest effects on the structure and hydration of S1-S4 domains. Taken together, our results demonstrate that Arg residues in S1-S4 voltage-sensing domains reside in close proximity to the hydrophobic interior of the membrane, yet are well-hydrated, a requirement for carrying charge and driving protein motions in response to changes in membrane voltage. PMID:22858867

Optical fiber sensor of partial discharges in High Voltage DC experiments

NASA Astrophysics Data System (ADS)

Búa-Núñez, I.; Azcárraga-Ramos, C. G.; Posada-Román, J. E.; Garcia-Souto, J. A.

2014-05-01

A setup simulating High Voltage DC (HVDC) transformers barriers was developed to demonstrate the effectiveness of an optical fiber (OF) sensor in detecting partial discharges (PD) under these peculiar conditions. Different PD detection techniques were compared: electrical methods, and acoustic methods. Standard piezoelectric sensors (R15i-AST) and the above mentioned OF sensors were used for acoustic detection. The OF sensor was able to detect PD acoustically with a sensitivity better than the other detection methods. The multichannel instrumentation system was tested in real HVDC conditions with the aim of analyzing the behavior of the insulation (mineral oil/pressboard).

UV-visible sensors based on polymorphous silicon

NASA Astrophysics Data System (ADS)

Guedj, Cyril S.; Cabarrocas, Pere R. i.; Massoni, Nicolas; Moussy, Norbert; Morel, Damien; Tchakarov, Svetoslav; Bonnassieux, Yvan

2003-09-01

UV-based imaging systems can be used for low-altitude rockets detection or biological agents identification (for instance weapons containing ANTHRAX). Compared to conventional CCD technology, CMOS-based active pixel sensors provide several advantages, including excellent electro-optical performances, high integration, low voltage operation, low power consumption, low cost, long lifetime, and robustness against environment. The monolithic integration of UV, visible and infrared detectors on the same uncooled CMOS smart system would therefore represent a major advance in the combat field, for characterization and representation of targets and backgrounds. In this approach, we have recently developped a novel technology using polymorphous silicon. This new material, fully compatible with above-IC silicon technology, is made of nanometric size ordered domains embedded in an amorphous matrix. The typical quantum efficiency of detectors made of this nano-material reach up to 80 % at 550 nm and 30 % in the UV range, depending of the design and the growth parameters. Furthermore, a record dark current of 20 pA/cm2 at -3 V has been reached. In addition, this new generation of sensors is significantly faster and more stable than their amorphous silicon counterparts. In this paper, we will present the relationship between the sensor technology and the overall performances.

Radial displacement sensor for non-contact bearings

NASA Technical Reports Server (NTRS)

McCormick, John A. (Inventor); Sixsmith, Herbert (Inventor)

1998-01-01

A radial position sensor includes four capacitive electrodes oriented about a shaft, arranged in two diametrically opposite pairs. Sensor circuitry generates an output signal in proportion to the capacitance between the electrodes and the shaft; the capacitance between an electrode and the shaft increases as the shaft approaches the electrode and decreases as the shaft recedes from the electrode. The sensor circuitry applies an alternating voltage to one electrode of a pair and a 180 degree out of phase alternating voltage to the other electrode of the pair. The electrical responses of the two electrodes to their respective input signals are summed to form a radial deviation signal which is relatively free from the alternating voltage and accurately represents the position of the shaft relative to the electrodes of the pair.

Fabrication and Characteristics of an nc-Si/c-Si Heterojunction MOSFETs Pressure Sensor

PubMed Central

Zhao, Xiaofeng; Wen, Dianzhong; Li, Gang

2012-01-01

A novel nc-Si/c-Si heterojunction MOSFETs pressure sensor is proposed in this paper, with four p-MOSFETs with nc-Si/c-Si heterojunction as source and drain. The four p-MOSFETs are designed and fabricated on a square silicon membrane by CMOS process and MEMS technology where channel resistances of the four nc-Si/c-Si heterojunction MOSFETs form a Wheatstone bridge. When the additional pressure is P, the nc-Si/c-Si heterojunction MOSFETs pressure sensor can measure this additional pressure P. The experimental results show that when the supply voltage is 3 V, length-width (L:W) ratio is 2:1, and the silicon membrane thickness is 75 μm, the full scale output voltage of the pressure sensor is 15.50 mV at room temperature, and pressure sensitivity is 0.097 mV/kPa. When the supply voltage and L:W ratio are the same as the above, and the silicon membrane thickness is 45 μm, the full scale output voltage is 43.05 mV, and pressure sensitivity is 2.153 mV/kPa. Therefore, the sensor has higher sensitivity and good temperature characteristics compared to the traditional piezoresistive pressure sensor. PMID:22778646

A High-Temperature Piezoresistive Pressure Sensor with an Integrated Signal-Conditioning Circuit

PubMed Central

Yao, Zong; Liang, Ting; Jia, Pinggang; Hong, Yingping; Qi, Lei; Lei, Cheng; Zhang, Bin; Xiong, Jijun

2016-01-01

This paper focuses on the design and fabrication of a high-temperature piezoresistive pressure sensor with an integrated signal-conditioning circuit, which consists of an encapsulated pressure-sensitive chip, a temperature compensation circuit and a signal-conditioning circuit. A silicon on insulation (SOI) material and a standard MEMS process are used in the pressure-sensitive chip fabrication, and high-temperature electronic components are adopted in the temperature-compensation and signal-conditioning circuits. The entire pressure sensor achieves a hermetic seal and can be operated long-term in the range of −50 °C to 220 °C. Unlike traditional pressure sensor output voltage ranges (in the dozens to hundreds of millivolts), the output voltage of this sensor is from 0 V to 5 V, which can significantly improve the signal-to-noise ratio and measurement accuracy in practical applications of long-term transmission based on experimental verification. Furthermore, because this flexible sensor’s output voltage is adjustable, general follow-up pressure transmitter devices for voltage converters need not be used, which greatly reduces the cost of the test system. Thus, the proposed high-temperature piezoresistive pressure sensor with an integrated signal-conditioning circuit is expected to be highly applicable to pressure measurements in harsh environments. PMID:27322288

0.5 V and 0.43 pJ/bit Capacitive Sensor Interface for Passive Wireless Sensor Systems

PubMed Central

Beriain, Andoni; Gutierrez, Iñigo; Solar, Hector; Berenguer, Roc

2015-01-01

This paper presents an ultra low-power and low-voltage pulse-width modulation based ratiometric capacitive sensor interface. The interface was designed and fabricated in a standard 90 nm CMOS 1P9M technology. The measurements show an effective resolution of 10 bits using 0.5 V of supply voltage. The active occupied area is only 0.0045 mm2 and the Figure of Merit (FOM), which takes into account the energy required per conversion bit, is 0.43 pJ/bit. Furthermore, the results show low sensitivity to PVT variations due to the proposed ratiometric architecture. In addition, the sensor interface was connected to a commercial pressure transducer and the measurements of the resulting complete pressure sensor show a FOM of 0.226 pJ/bit with an effective linear resolution of 7.64 bits. The results validate the use of the proposed interface as part of a pressure sensor, and its low-power and low-voltage characteristics make it suitable for wireless sensor networks and low power consumer electronics. PMID:26343681

0.5 V and 0.43 pJ/bit Capacitive Sensor Interface for Passive Wireless Sensor Systems.

PubMed

Beriain, Andoni; Gutierrez, Iñigo; Solar, Hector; Berenguer, Roc

2015-08-28

This paper presents an ultra low-power and low-voltage pulse-width modulation based ratiometric capacitive sensor interface. The interface was designed and fabricated in a standard 90 nm CMOS 1P9M technology. The measurements show an effective resolution of 10 bits using 0.5 V of supply voltage. The active occupied area is only 0.0045 mm2 and the Figure of Merit (FOM), which takes into account the energy required per conversion bit, is 0.43 pJ/bit. Furthermore, the results show low sensitivity to PVT variations due to the proposed ratiometric architecture. In addition, the sensor interface was connected to a commercial pressure transducer and the measurements of the resulting complete pressure sensor show a FOM of 0.226 pJ/bit with an effective linear resolution of 7.64 bits. The results validate the use of the proposed interface as part of a pressure sensor, and its low-power and low-voltage characteristics make it suitable for wireless sensor networks and low power consumer electronics.

EIT-Based Fabric Pressure Sensing

PubMed Central

Yao, A.; Yang, C. L.; Seo, J. K.; Soleimani, M.

2013-01-01

This paper presents EIT-based fabric sensors that aim to provide a pressure mapping using the current carrying and voltage sensing electrodes attached to the boundary of the fabric patch. Pressure-induced shape change over the sensor area makes a change in the conductivity distribution which can be conveyed to the change of boundary current-voltage data. This boundary data is obtained through electrode measurements in EIT system. The corresponding inverse problem is to reconstruct the pressure and deformation map from the relationship between the applied current and the measured voltage on the fabric boundary. Taking advantage of EIT in providing dynamical images of conductivity changes due to pressure induced shape change, the pressure map can be estimated. In this paper, the EIT-based fabric sensor was presented for circular and rectangular sensor geometry. A stretch sensitive fabric was used in circular sensor with 16 electrodes and a pressure sensitive fabric was used in a rectangular sensor with 32 electrodes. A preliminary human test was carried out with the rectangular sensor for foot pressure mapping showing promising results. PMID:23533538

A low power on-chip class-E power amplifier for remotely powered implantable sensor systems

NASA Astrophysics Data System (ADS)

Ture, Kerim; Kilinc, Enver G.; Dehollain, Catherine

2015-06-01

This paper presents a low power fully integrated class-E power amplifier and its integration with remotely powered sensor system. The class-E power amplifier is suitable solution for low-power applications due to its high power efficiency. However, the required high inductance values which make the on-chip integration of the power amplifier difficult. The designed power amplifier is fully integrated in the remotely powered sensor system and fabricated in 0.18 μm CMOS process. The power is transferred to the implantable sensor system at 13.56 MHz by using an inductively coupled remote powering link. The induced AC voltage on the implant coil is converted into a DC voltage by a passive full-wave rectifier. A voltage regulator is used to suppress the ripples and create a clean and stable 1.8 V supply voltage for the sensor and communication blocks. The data collected from the sensors is transmitted by on-off keying modulated low-power transmitter at 1.2 GHz frequency. The transmitter is composed of a LC tank oscillator and a fully on-chip class-E power amplifier. An additional output network is used for the power amplifier which makes the integration of the power amplifier fully on-chip. The integrated power amplifier with 0.2 V supply voltage has a drain efficiency of 31.5% at -10 dBm output power for 50 Ω load. The measurement results verify the functionality of the power amplifier and the remotely powered implantable sensor system. The data communication is also verified by using a commercial 50 Ω chip antenna and has 600 kbps data rate at 1 m communication distance.

Ultra Low Energy Binary Decision Diagram Circuits Using Few Electron Transistors

NASA Astrophysics Data System (ADS)

Saripalli, Vinay; Narayanan, Vijay; Datta, Suman

Novel medical applications involving embedded sensors, require ultra low energy dissipation with low-to-moderate performance (10kHz-100MHz) driving the conventional MOSFETs into sub-threshold operation regime. In this paper, we present an alternate ultra-low power computing architecture using Binary Decision Diagram based logic circuits implemented using Single Electron Transistors (SETs) operating in the Coulomb blockade regime with very low supply voltages. We evaluate the energy - performance tradeoff metrics of such BDD circuits using time domain Monte Carlo simulations and compare them with the energy-optimized CMOS logic circuits. Simulation results show that the proposed approach achieves better energy-delay characteristics than CMOS realizations.

Effect of Sensors on the Reliability and Control Performance of Power Circuits in the Web of Things (WoT)

PubMed Central

Bae, Sungwoo; Kim, Myungchin

2016-01-01

In order to realize a true WoT environment, a reliable power circuit is required to ensure interconnections among a range of WoT devices. This paper presents research on sensors and their effects on the reliability and response characteristics of power circuits in WoT devices. The presented research can be used in various power circuit applications, such as energy harvesting interfaces, photovoltaic systems, and battery management systems for the WoT devices. As power circuits rely on the feedback from voltage/current sensors, the system performance is likely to be affected by the sensor failure rates, sensor dynamic characteristics, and their interface circuits. This study investigated how the operational availability of the power circuits is affected by the sensor failure rates by performing a quantitative reliability analysis. In the analysis process, this paper also includes the effects of various reconstruction and estimation techniques used in power processing circuits (e.g., energy harvesting circuits and photovoltaic systems). This paper also reports how the transient control performance of power circuits is affected by sensor interface circuits. With the frequency domain stability analysis and circuit simulation, it was verified that the interface circuit dynamics may affect the transient response characteristics of power circuits. The verification results in this paper showed that the reliability and control performance of the power circuits can be affected by the sensor types, fault tolerant approaches against sensor failures, and the response characteristics of the sensor interfaces. The analysis results were also verified by experiments using a power circuit prototype. PMID:27608020

IKs channels open slowly because KCNE1 accessory subunits slow the movement of S4 voltage sensors in KCNQ1 pore-forming subunits

PubMed Central

Ruscic, Katarina J.; Miceli, Francesco; Villalba-Galea, Carlos A.; Dai, Hui; Mishina, Yukiko; Bezanilla, Francisco; Goldstein, Steve A. N.

2013-01-01

Human IKs channels activate slowly with the onset of cardiac action potentials to repolarize the myocardium. IKs channels are composed of KCNQ1 (Q1) pore-forming subunits that carry S4 voltage-sensor segments and KCNE1 (E1) accessory subunits. Together, Q1 and E1 subunits recapitulate the conductive and kinetic properties of IKs. How E1 modulates Q1 has been unclear. Investigators have variously posited that E1 slows the movement of S4 segments, slows opening and closing of the conduction pore, or modifies both aspects of electromechanical coupling. Here, we show that Q1 gating current can be resolved in the absence of E1, but not in its presence, consistent with slowed movement of the voltage sensor. E1 was directly demonstrated to slow S4 movement with a fluorescent probe on the Q1 voltage sensor. Direct correlation of the kinetics of S4 motion and ionic current indicated that slowing of sensor movement by E1 was both necessary and sufficient to determine the slow-activation time course of IKs. PMID:23359697

A Quantitative Evaluation of Drive Pattern Selection for Optimizing EIT-Based Stretchable Sensors

PubMed Central

Nefti-Meziani, Samia; Carbonaro, Nicola

2017-01-01

Electrical Impedance Tomography (EIT) is a medical imaging technique that has been recently used to realize stretchable pressure sensors. In this method, voltage measurements are taken at electrodes placed at the boundary of the sensor and are used to reconstruct an image of the applied touch pressure points. The drawback with EIT-based sensors, however, is their low spatial resolution due to the ill-posed nature of the EIT reconstruction. In this paper, we show our performance evaluation of different EIT drive patterns, specifically strategies for electrode selection when performing current injection and voltage measurements. We compare voltage data with Signal-to-Noise Ratio (SNR) and Boundary Voltage Changes (BVC), and study image quality with Size Error (SE), Position Error (PE) and Ringing (RNG) parameters, in the case of one-point and two-point simultaneous contact locations. The study shows that, in order to improve the performance of EIT based sensors, the electrode selection strategies should dynamically change correspondingly to the location of the input stimuli. In fact, the selection of one drive pattern over another can improve the target size detection and position accuracy up to 4.7% and 18%, respectively. PMID:28858252

A Quantitative Evaluation of Drive Pattern Selection for Optimizing EIT-Based Stretchable Sensors.

PubMed

Russo, Stefania; Nefti-Meziani, Samia; Carbonaro, Nicola; Tognetti, Alessandro

2017-08-31

Electrical Impedance Tomography (EIT) is a medical imaging technique that has been recently used to realize stretchable pressure sensors. In this method, voltage measurements are taken at electrodes placed at the boundary of the sensor and are used to reconstruct an image of the applied touch pressure points. The drawback with EIT-based sensors, however, is their low spatial resolution due to the ill-posed nature of the EIT reconstruction. In this paper, we show our performance evaluation of different EIT drive patterns, specifically strategies for electrode selection when performing current injection and voltage measurements. We compare voltage data with Signal-to-Noise Ratio (SNR) and Boundary Voltage Changes (BVC), and study image quality with Size Error (SE), Position Error (PE) and Ringing (RNG) parameters, in the case of one-point and two-point simultaneous contact locations. The study shows that, in order to improve the performance of EIT based sensors, the electrode selection strategies should dynamically change correspondingly to the location of the input stimuli. In fact, the selection of one drive pattern over another can improve the target size detection and position accuracy up to 4.7% and 18%, respectively.

Fiber-optic sensors for aerospace electrical measurements - An update

NASA Technical Reports Server (NTRS)

Patterson, Richard L.; Rose, A. H.; Tang, D.; Day, G. W.

1991-01-01

The authors report the progress made on the development of aerospace current and voltage sensors which use fiber-optic and optical sensing heads. These sensors are presently designed to cover ac frequencies from 60 Hz to 20 kHz. The current sensor, based on the Faraday effect in optical fiber, is in advanced development after some initial testing. The emphasis is on packaging methods and ways to maintain consistent sensitivity with changes in temperature. The voltage sensor, utilizing the Pockels effect in a crystal, has excelled in temperature tests. The authors report on the development of these sensors. The authors also relate the technology used in the sensors, the results of evaluation, improvements being made, and the future direction of the work.

A dark green fluorescent protein as an acceptor for measurement of Förster resonance energy transfer.

PubMed

Murakoshi, Hideji; Shibata, Akihiro C E; Nakahata, Yoshihisa; Nabekura, Junichi

2015-10-15

Measurement of Förster resonance energy transfer by fluorescence lifetime imaging microscopy (FLIM-FRET) is a powerful method for visualization of intracellular signaling activities such as protein-protein interactions and conformational changes of proteins. Here, we developed a dark green fluorescent protein (ShadowG) that can serve as an acceptor for FLIM-FRET. ShadowG is spectrally similar to monomeric enhanced green fluorescent protein (mEGFP) and has a 120-fold smaller quantum yield. When FRET from mEGFP to ShadowG was measured using an mEGFP-ShadowG tandem construct with 2-photon FLIM-FRET, we observed a strong FRET signal with low cell-to-cell variability. Furthermore, ShadowG was applied to a single-molecule FRET sensor to monitor a conformational change of CaMKII and of the light oxygen voltage (LOV) domain in HeLa cells. These sensors showed reduced cell-to-cell variability of both the basal fluorescence lifetime and response signal. In contrast to mCherry- or dark-YFP-based sensors, our sensor allowed for precise measurement of individual cell responses. When ShadowG was applied to a separate-type Ras FRET sensor, it showed a greater response signal than did the mCherry-based sensor. Furthermore, Ras activation and translocation of its effector ERK2 into the nucleus could be observed simultaneously. Thus, ShadowG is a promising FLIM-FRET acceptor.

Optical fiber voltage sensors for broad temperature ranges

NASA Technical Reports Server (NTRS)

Rose, A. H.; Day, G. W.

1992-01-01

We describe the development of an optical fiber ac voltage sensor for aircraft and spacecraft applications. Among the most difficult specifications to meet for this application is a temperature stability of +/- 1 percent from -65 C to +125 C. This stability requires a careful selection of materials, components, and optical configuration with further compensation using an optical-fiber temperature sensor located near the sensing element. The sensor is a polarimetric design, based on the linear electro-optic effect in bulk Bi4Ge3O12. The temperature sensor is also polarimetric, based on the temperature dependence of the birefringence of bulk SiO2. The temperature sensor output is used to automatically adjust the calibration of the instrument.

Derivation of Hodgkin-Huxley equations for a Na+ channel from a master equation for coupled activation and inactivation

NASA Astrophysics Data System (ADS)

Vaccaro, S. R.

2016-11-01

The Na+ current in nerve and muscle membranes may be described in terms of the activation variable m (t ) and the inactivation variable h (t ) , which are dependent on the transitions of S4 sensors of each of the Na+ channel domains DI to DIV. The time-dependence of the Na+ current and the rate equations satisfied by m (t ) and h (t ) may be derived from the solution to a master equation that describes the coupling between two or three activation sensors regulating the Na+ channel conductance and a two-stage inactivation process. If the inactivation rate from the closed or open states increases as the S4 sensors activate, a more general form of the Hodgkin-Huxley expression for the open-state probability may be derived where m (t ) is dependent on both activation and inactivation processes. The voltage dependence of the rate functions for inactivation and recovery from inactivation are consistent with the empirically determined expressions and exhibit saturation for both depolarized and hyperpolarized clamp potentials.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kapusta, P.; Kisielewski, B.

In this paper the overvoltage protection modules (OVP) for the power supply (PS) system of the Belle II pixel detector (PXD) are described. The aim of the OVP is to protect the detector and associated electronics against overvoltage conditions. Most critical in the system are voltages supplying the front-end ASICs. The PXD detector consists of the DEPFET sensor modules with integrated chips like the Drain Current Digitizer, the Switcher and the Data Handling Processor. These chips, implemented in modern sub-micron technologies, are quite vulnerable to variations in the supply voltages. The PXD will be placed in the Belle II experimentmore » as close as possible to the interaction point, where access during experiment is very limited or even impossible, thus the PS and OVP systems exploit the remote-sensing method. Overvoltage conditions are due to failures of the PS itself, wrong setting of the output voltages or transient voltages coming out of hard noisy environment of the experiment. The OVP modules are parts of the PS modules. For powering the PXD 40 PS modules are placed 15 m outside the Belle II spectrometer. Each one is equipped with the OVP board. All voltages (22) are grouped in 4 domains: Analog, Digital, Steering and Gate which have independent grounds. The OVP boards are designed from integrated circuits from Linear Technology. All configurations were simulated with the Spice program. The control electronics is designed in a Xilinx CPLD. Two types of integrated circuits were used. LT4356 surge stopper protects loads from high voltage transients. The output voltages are limited to a safe value and also protect loads against over current faults. For less critical voltages, the LTC2912 voltage monitors are used that detect under-voltage and overvoltage events. It has to be noted that the OVP system is working independently of any other protection of the PS system, which increases its overall reliability. (authors)« less

Comparative sequence analysis suggests a conserved gating mechanism for TRP channels

PubMed Central

Palovcak, Eugene; Delemotte, Lucie; Klein, Michael L.

2015-01-01

The transient receptor potential (TRP) channel superfamily plays a central role in transducing diverse sensory stimuli in eukaryotes. Although dissimilar in sequence and domain organization, all known TRP channels act as polymodal cellular sensors and form tetrameric assemblies similar to those of their distant relatives, the voltage-gated potassium (Kv) channels. Here, we investigated the related questions of whether the allosteric mechanism underlying polymodal gating is common to all TRP channels, and how this mechanism differs from that underpinning Kv channel voltage sensitivity. To provide insight into these questions, we performed comparative sequence analysis on large, comprehensive ensembles of TRP and Kv channel sequences, contextualizing the patterns of conservation and correlation observed in the TRP channel sequences in light of the well-studied Kv channels. We report sequence features that are specific to TRP channels and, based on insight from recent TRPV1 structures, we suggest a model of TRP channel gating that differs substantially from the one mediating voltage sensitivity in Kv channels. The common mechanism underlying polymodal gating involves the displacement of a defect in the H-bond network of S6 that changes the orientation of the pore-lining residues at the hydrophobic gate. PMID:26078053

An Improved Targeted cAMP Sensor to Study the Regulation of Adenylyl Cyclase 8 by Ca2+ Entry through Voltage-Gated Channels

PubMed Central

Everett, Katy L.; Cooper, Dermot M. F.

2013-01-01

Here we describe an improved sensor with reduced pH sensitivity tethered to adenylyl cyclase (AC) 8. The sensor was used to study cAMP dynamics in the AC8 microdomain of MIN6 cells, a pancreatic β-cell line. In these cells, AC8 was activated by Ca2+ entry through L-type voltage-gated channels following depolarisation. This activation could be reconstituted in HEK293 cells co-expressing AC8 and either the α1C or α1D subunit of L-type voltage-gated Ca2+ channels. The development of this improved sensor opens the door to the study of cAMP microdomains in excitable cells that have previously been challenging due to the sensitivity of fluorescent proteins to pH changes. PMID:24086669

Voltage-sensing domain of voltage-gated proton channel Hv1 shares mechanism of block with pore domains.

PubMed

Hong, Liang; Pathak, Medha M; Kim, Iris H; Ta, Dennis; Tombola, Francesco

2013-01-23

Voltage-gated sodium, potassium, and calcium channels are made of a pore domain (PD) controlled by four voltage-sensing domains (VSDs). The PD contains the ion permeation pathway and the activation gate located on the intracellular side of the membrane. A large number of small molecules are known to inhibit the PD by acting as open channel blockers. The voltage-gated proton channel Hv1 is made of two VSDs and lacks the PD. The location of the activation gate in the VSD is unknown and open channel blockers for VSDs have not yet been identified. Here, we describe a class of small molecules which act as open channel blockers on the Hv1 VSD and find that a highly conserved phenylalanine in the charge transfer center of the VSD plays a key role in blocker binding. We then use one of the blockers to show that Hv1 contains two intracellular and allosterically coupled gates. Copyright © 2013 Elsevier Inc. All rights reserved.

Calmodulin and calcium differentially regulate the neuronal Nav1.1 voltage-dependent sodium channel

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gaudioso, Christelle; Carlier, Edmond; Youssouf, Fahamoe

2011-07-29

Highlights: {yields} Both Ca{sup ++}-Calmodulin (CaM) and Ca{sup ++}-free CaM bind to the C-terminal region of Nav1.1. {yields} Ca{sup ++} and CaM have both opposite and convergent effects on I{sub Nav1.1}. {yields} Ca{sup ++}-CaM modulates I{sub Nav1.1} amplitude. {yields} CaM hyperpolarizes the voltage-dependence of activation, and increases the inactivation rate. {yields} Ca{sup ++} alone antagonizes CaM for both effects, and depolarizes the voltage-dependence of inactivation. -- Abstract: Mutations in the neuronal Nav1.1 voltage-gated sodium channel are responsible for mild to severe epileptic syndromes. The ubiquitous calcium sensor calmodulin (CaM) bound to rat brain Nav1.1 and to the human Nav1.1 channelmore » expressed by a stably transfected HEK-293 cell line. The C-terminal region of the channel, as a fusion protein or in the yeast two-hybrid system, interacted with CaM via a consensus C-terminal motif, the IQ domain. Patch clamp experiments on HEK1.1 cells showed that CaM overexpression increased peak current in a calcium-dependent way. CaM had no effect on the voltage-dependence of fast inactivation, and accelerated the inactivation kinetics. Elevating Ca{sup ++} depolarized the voltage-dependence of fast inactivation and slowed down the fast inactivation kinetics, and for high concentrations this effect competed with the acceleration induced by CaM alone. Similarly, the depolarizing action of calcium antagonized the hyperpolarizing shift of the voltage-dependence of activation due to CaM overexpression. Fluorescence spectroscopy measurements suggested that Ca{sup ++} could bind the Nav1.1 C-terminal region with micromolar affinity.« less

Tunable, multiwavelength-swept fiber laser based on nematic liquid crystal device for fiber-optic electric-field sensor

NASA Astrophysics Data System (ADS)

Lee, Hyun Ji; Kim, Sung-Jo; Ko, Myeong Ock; Kim, Jong-Hyun; Jeon, Min Yong

2018-03-01

We propose a tunable multiwavelength-swept laser based on a nematic liquid crystal (NLC) Fabry-Perot (FP) etalon, which is embedded in the resonator of a wavelength-swept laser. We achieve the continuous wavelength tuning of the multiwavelength-swept laser by applying the electric field to the NLC FP etalon. The free spectral range of the fabricated NLC FP etalon is approximately 7.9 nm. When the electric field applied to the NLC FP etalon exceeds the threshold value (Fréedericksz threshold voltage), the output of the multiwavelength-swept laser can be tuned continuously. The tuning range of the multiwavelength-swept laser can be achieved at a value greater than 75 nm, which has a considerably wider tunable range than a conventional multiwavelength laser based on an NLC FP etalon. The slope efficiencies in the spectral and temporal domains for the tunable multiwavelength-swept laser are 22.2 nm/(mVrms / μm) and 0.17 ms/(mVrms / μm), respectively in the linear region. Therefore, the developed multiwavelength-swept laser based on the NLC FP etalon can be applied to an electric-field sensor. Because the wavelength measurement and time measurement have a linear relationship, the electric-field sensor can detect a rapid change in the electric-field intensity by measuring the peak change of the pulse in the temporal domain using the NLC FP etalon-based multiwavelength-swept laser.

Measurement and analysis of time-domain characteristics of corona-generated radio interference from a single positive corona source

NASA Astrophysics Data System (ADS)

Li, Xuebao; Li, Dayong; Chen, Bo; Cui, Xiang; Lu, Tiebing; Li, Yinfei

2018-04-01

The corona-generated electromagnetic interference commonly known as radio interference (RI) has become a limiting factor for the design of high voltage direct current transmission lines. In this paper, a time-domain measurement system is developed to measure the time-domain characteristics of corona-generated RI from a single corona source under a positive corona source. In the experiments, the corona current pulses are synchronously measured through coupling capacitors. The one-to-one relationship between the corona current pulse and measured RI voltage pulse is observed. The statistical characteristics of pulse parameters are analyzed, and the correlations between the corona current pulse and RI voltage pulse in the time-domain and frequency-domain are analyzed. Depending on the measured corona current pulses, the time-domain waveform of corona-generated RI is calculated on the basis of the propagation model of corona current on the conductor, the dipolar model for electric field calculation, and the antenna model for inducing voltage calculation. The well matched results between measured and simulated waveforms of RI voltage can show the validity of the measurement and calculation method presented in this paper, which also further show the close correlation between corona current and corona-generated RI.

Dimeric Structure of the Blue Light Sensor Protein Photozipper in the Active State.

PubMed

Ozeki, Kohei; Tsukuno, Hiroyuki; Nagashima, Hiroki; Hisatomi, Osamu; Mino, Hiroyuki

2018-02-06

The light oxygen voltage-sensing (LOV) domain plays a crucial role in blue light (BL) sensing in plants and microorganisms. LOV domains are usually associated with the effector domains and regulate the activities of effector domains in a BL-dependent manner. Photozipper (PZ) is monomeric in the dark state. BL induces reversible dimerization of PZ and subsequently increases its affinity for the target DNA sequence. In this study, we report the analyses of PZ by pulsed electron-electron double resonance (PELDOR). The neutral flavin radical was formed by BL illumination in the presence of dithiothreitol in the LOV-C254S (without the bZIP domain) and PZ-C254S mutants, where the cysteine residue responsible for adduct formation was replaced with serine. The magnetic dipole interactions of 3 MHz between the neutral radicals were detected in both LOV-C254S and PZ-C254S, indicating that these mutants are dimeric in the radical state. The PELDOR simulation showed that the distance between the radical pair is close to that estimated from the dimeric crystal structure in the "light state" [Heintz, U., and Schlichting, I. (2016) eLife 5, e11860], suggesting that in the radical state, LOV domains in PZ-C254S form a dimer similar to that of LOV-C254S, which lacks the bZIP domain.

Transduction of Voltage and Ca2+ Signals by Slo1 BK Channels

PubMed Central

Hoshi, T.; Pantazis, A.; Olcese, R.

2013-01-01

Large-conductance Ca2+- and voltage-gated K+ channels are activated by an increase in intracellular Ca2+ concentration and/or depolarization. The channel activation mechanism is well described by an allosteric model encompassing the gate, voltage sensors, and Ca2+ sensors, and the model is an excellent framework to understand the influences of auxiliary β and γ subunits and regulatory factors such as Mg2+. Recent advances permit elucidation of structural correlates of the biophysical mechanism. PMID:23636263

Field-Polarity-Dependent Domain Growth in Epitaxial BaTiO 3 Films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Roth, Robert; Guo, Er-Jia; Rafique, Mohsin

The growth of circular tip-induced domains has been studied in epitaxial BaTiO 3 (BTO) films as a function of writing voltage and time using piezoresponse force microscopy (PFM). While abundant for Pb(Zr,Ti)O 3 (PZT) films, such studies are rare for BTO. Strong relaxation of written domains is observed in the form of reduction of the PFM amplitude inside the area of written domains which occurs additionally to a decrease of the domain radius. The domain wall velocity observed for negative tip voltage is systematically smaller than that for positive tip voltage. Based on maps of the positive and negative switchingmore » fields, the effective driving field for both polarities has been estimated. The polarity-dependent effective field cannot account for the different velocities, indicating a polarity-dependent mobility of the domain walls.« less

Field-Polarity-Dependent Domain Growth in Epitaxial BaTiO 3 Films

DOE PAGES

Roth, Robert; Guo, Er-Jia; Rafique, Mohsin; ...

2018-03-23

The growth of circular tip-induced domains has been studied in epitaxial BaTiO 3 (BTO) films as a function of writing voltage and time using piezoresponse force microscopy (PFM). While abundant for Pb(Zr,Ti)O 3 (PZT) films, such studies are rare for BTO. Strong relaxation of written domains is observed in the form of reduction of the PFM amplitude inside the area of written domains which occurs additionally to a decrease of the domain radius. The domain wall velocity observed for negative tip voltage is systematically smaller than that for positive tip voltage. Based on maps of the positive and negative switchingmore » fields, the effective driving field for both polarities has been estimated. The polarity-dependent effective field cannot account for the different velocities, indicating a polarity-dependent mobility of the domain walls.« less

A Simple Sensor Model for THUNDER Actuators

NASA Technical Reports Server (NTRS)

Campbell, Joel F.; Bryant, Robert G.

2009-01-01

A quasi-static (low frequency) model is developed for THUNDER actuators configured as displacement sensors based on a simple Raleigh-Ritz technique. This model is used to calculate charge as a function of displacement. Using this and the calculated capacitance, voltage vs. displacement and voltage vs. electrical load curves are generated and compared with measurements. It is shown this model gives acceptable results and is useful for determining rough estimates of sensor output for various loads, laminate configurations and thicknesses.

Low-resistance strip sensors for beam-loss event protection

NASA Astrophysics Data System (ADS)

Ullán, M.; Benítez, V.; Quirion, D.; Zabala, M.; Pellegrini, G.; Lozano, M.; Lacasta, C.; Soldevila, U.; García, C.; Fadeyev, V.; Wortman, J.; DeFilippis, J.; Shumko, M.; Grillo, A. A.; Sadrozinski, H. F.-W.

2014-11-01

AC-coupled silicon strip sensors can be damaged in case of a beam loss due to the possibility of a large charge accumulation in the bulk, developing very high voltages across the coupling capacitors which can destroy them. Punch-through structures are currently used to avoid this problem helping to evacuate the accumulated charge as large voltages are developing. Nevertheless, previous experiments, performed with laser pulses, have shown that these structures can become ineffective in relatively long strips. The large value of the implant resistance can effectively isolate the "far" end of the strip from the punch-through structure leading to large voltages. We present here our developments to fabricate low-resistance strip sensors to avoid this problem. The deposition of a conducting material in contact with the implants drastically reduces the strip resistance, assuring the effectiveness of the punch-through structures. First devices have been fabricated with this new technology. Initial results with laser tests show the expected reduction in peak voltages on the low resistivity implants. Other aspects of the sensor performance, including the signal formation, are not affected by the new technology.

Effect of electrode gap on the sensing properties of multiwalled carbon nanotubes based gas sensor

NASA Astrophysics Data System (ADS)

Saheed, Mohamed Shuaib Mohamed; Mohamed, Norani Muti; Burhanudin, Zainal Arif

2016-11-01

Vertically aligned multiwalled carbon nanotubes (MWCNT) were grown on Si substrate coated with alumina and iron using chemical vapor deposition. Electrode gap of 10, 25 and 50 µm were adopted to determine the effect of varying gap spacing on the sensing properties such as voltage breakdown, sensitivity and selectivity for three gases namely argon, carbon dioxide and ammonia. Argon has the lowest voltage breakdown for every electrode gap. The fabricated MWCNT based gas sensor drastically reduced the voltage breakdown by 89.5% when the electrode spacing is reduced from 50 µm to 10 µm. The reduction is attributed to the high non-uniform electric field between the electrodes caused by the protrusion of nanotips. The sensor shows good sensitivity and selectivity with the ability to detect the gas in the mixture with air provided that the concentration is ≥ 20% where the voltage breakdown will be close to the pure gas.

Fiber-optic voltage sensor with cladded fiber and evanescent wave variation detection

DOEpatents

Wood, Charles B.

1992-01-01

A fiber optic voltage sensor is described which includes a source of light, a reference fiber for receiving a known percentage of the light and an electrostrictive element having terminals across which is applied, a voltage to be measured. The electrostrictive element is responsive to the applied voltage to assume an altered physical state. A measuring fiber also receives a known percentage of light from the light source and is secured about the electrostrictive element. The measuring fiber is provided with a cladding and exhibits an evanescent wave in the cladding. The measuring fiber has a known length which is altered when the electrostrictive element assumes its altered physical state. A differential sensor is provided which senses the intensity of light in both the reference fiber and the measuring fiber and provides an output indicative of the difference between the intensities.

A high resolution on-chip delay sensor with low supply-voltage sensitivity for high-performance electronic systems.

PubMed

Sheng, Duo; Lai, Hsiu-Fan; Chan, Sheng-Min; Hong, Min-Rong

2015-02-13

An all-digital on-chip delay sensor (OCDS) circuit with high delay-measurement resolution and low supply-voltage sensitivity for efficient detection and diagnosis in high-performance electronic system applications is presented. Based on the proposed delay measurement scheme, the quantization resolution of the proposed OCDS can be reduced to several picoseconds. Additionally, the proposed cascade-stage delay measurement circuit can enhance immunity to supply-voltage variations of the delay measurement resolution without extra self-biasing or calibration circuits. Simulation results show that the delay measurement resolution can be improved to 1.2 ps; the average delay resolution variation is 0.55% with supply-voltage variations of ±10%. Moreover, the proposed delay sensor can be implemented in an all-digital manner, making it very suitable for high-performance electronic system applications as well as system-level integration.

Fiber-optic voltage sensor with cladded fiber and evanescent wave variation detection

DOEpatents

Wood, C.B.

1992-12-15

A fiber optic voltage sensor is described which includes a source of light, a reference fiber for receiving a known percentage of the light and an electrostrictive element having terminals across which is applied, a voltage to be measured. The electrostrictive element is responsive to the applied voltage to assume an altered physical state. A measuring fiber also receives a known percentage of light from the light source and is secured about the electrostrictive element. The measuring fiber is provided with a cladding and exhibits an evanescent wave in the cladding. The measuring fiber has a known length which is altered when the electrostrictive element assumes its altered physical state. A differential sensor is provided which senses the intensity of light in both the reference fiber and the measuring fiber and provides an output indicative of the difference between the intensities. 3 figs.

Computational investigation of single-wall carbon nanotube functionalized with palladium nanoclusters as hydrogen sulfide gas sensor

NASA Astrophysics Data System (ADS)

Bagherzadeh-Nobari, S.; Hosseini-Istadeh, K.; Kalantarinejad, R.; Elahi, S. M.; Shokri, A. A.

2018-03-01

Our aim is to study theoretically, the sensitivity of a hydrogen sulfide gas sensor, with regard to electrical conductance behavior. Our senor consists of a semiconductor single-wall carbon nanotube (SWCNT), functionalized with palladium nanoclusters, sandwiched between two gold electrodes. Initially, we have computed the optimized structure of the sensor, via molecular dynamic simulations. Then by using non-equilibrium Green's function method, combined with density functional theory, the electronic and transport properties of the sensor were calculated, and compared before and after adsorption of H2S gas, at different bias voltages. The highest sensitivity is achieved at 40 mV bias voltage. In this bias voltage, H2S gas adsorption causes a significant decrease of current, because as a result of charge transfer from the CNT and palladium nanoclusters, to H2S gas, majority carriers (electrons) decrease. The results show that CNT decorated with palladium nanoclusters can be a promising candidate in gas-sensorics.

Development and Preliminary Evaluation of a Spray Deposition Sensing System for Improving Pesticide Application.

PubMed

Kesterson, Melissa A; Luck, Joe D; Sama, Michael P

2015-12-17

An electronic, resistance-based sensor array and data acquisition system was developed to measure spray deposition from hydraulic nozzles. The sensor surface consisted of several parallel tin plated copper traces of varying widths with varying gap widths. The system contained an embedded microprocessor to monitor output voltage corresponding to spray deposition every second. In addition, a wireless module was used to transmit the voltage values to a remote laptop. Tests were conducted in two stages to evaluate the performance of the sensor array in an attempt to quantify the spray deposition. Initial tests utilized manual droplet placement on the sensor surface to determine the effects of temperature and droplet size on voltage output. Secondary testing utilized a spray chamber to pass nozzles at different speeds above the sensor surface to determine if output varied based on different application rates or spray droplet classification. Results from this preliminary analysis indicated that manual droplets of 5 and 10 μL resulted in significantly different values from the sensors while temperature did not consistently affect output. Spray chamber test results indicated that different application rates and droplet sizes could be determined using the sensor array.

Development and Preliminary Evaluation of a Spray Deposition Sensing System for Improving Pesticide Application

PubMed Central

Kesterson, Melissa A.; Luck, Joe D.; Sama, Michael P.

2015-01-01

An electronic, resistance-based sensor array and data acquisition system was developed to measure spray deposition from hydraulic nozzles. The sensor surface consisted of several parallel tin plated copper traces of varying widths with varying gap widths. The system contained an embedded microprocessor to monitor output voltage corresponding to spray deposition every second. In addition, a wireless module was used to transmit the voltage values to a remote laptop. Tests were conducted in two stages to evaluate the performance of the sensor array in an attempt to quantify the spray deposition. Initial tests utilized manual droplet placement on the sensor surface to determine the effects of temperature and droplet size on voltage output. Secondary testing utilized a spray chamber to pass nozzles at different speeds above the sensor surface to determine if output varied based on different application rates or spray droplet classification. Results from this preliminary analysis indicated that manual droplets of 5 and 10 μL resulted in significantly different values from the sensors while temperature did not consistently affect output. Spray chamber test results indicated that different application rates and droplet sizes could be determined using the sensor array. PMID:26694417

Piezoelectric Active Humidity Sensors Based on Lead-Free NaNbO₃ Piezoelectric Nanofibers.

PubMed

Gu, Li; Zhou, Di; Cao, Jun Cheng

2016-06-07

The development of micro-/nano-scaled energy harvesters and the self-powered sensor system has attracted great attention due to the miniaturization and integration of the micro-device. In this work, lead-free NaNbO₃ piezoelectric nanofibers with a monoclinic perovskite structure were synthesized by the far-field electrospinning method. The flexible active humidity sensors were fabricated by transferring the nanofibers from silicon to a soft polymer substrate. The sensors exhibited outstanding piezoelectric energy-harvesting performance with output voltage up to 2 V during the vibration process. The output voltage generated by the NaNbO₃ sensors exhibited a negative correlation with the environmental humidity varying from 5% to 80%, where the peak-to-peak value of the output voltage generated by the sensors decreased from 0.40 to 0.07 V. The sensor also exhibited a short response time, good selectively against ethanol steam, and great temperature stability. The piezoelectric active humidity sensing property could be attributed to the increased leakage current in the NaNbO₃ nanofibers, which was generated due to proton hopping among the H₃O⁺ groups in the absorbed H₂O layers under the driving force of the piezoelectric potential.

Interactions among DIV voltage-sensor movement, fast inactivation, and resurgent Na current induced by the NaVβ4 open-channel blocking peptide

PubMed Central

Lewis, Amanda H.

2013-01-01

Resurgent Na current flows as voltage-gated Na channels recover through open states from block by an endogenous open-channel blocking protein, such as the NaVβ4 subunit. The open-channel blocker and fast-inactivation gate apparently compete directly, as slowing the onset of fast inactivation increases resurgent currents by favoring binding of the blocker. Here, we tested whether open-channel block is also sensitive to deployment of the DIV voltage sensor, which facilitates fast inactivation. We expressed NaV1.4 channels in HEK293t cells and assessed block by a free peptide replicating the cytoplasmic tail of NaVβ4 (the “β4 peptide”). Macroscopic fast inactivation was disrupted by mutations of DIS6 (L443C/A444W; “CW” channels), which reduce fast-inactivation gate binding, and/or by the site-3 toxin ATX-II, which interferes with DIV movement. In wild-type channels, the β4 peptide competed poorly with fast inactivation, but block was enhanced by ATX. With the CW mutation, large peptide-induced resurgent currents were present even without ATX, consistent with increased open-channel block upon depolarization and slower deactivation after blocker unbinding upon repolarization. The addition of ATX greatly increased transient current amplitudes and further enlarged resurgent currents, suggesting that pore access by the blocker is actually decreased by full deployment of the DIV voltage sensor. ATX accelerated recovery from block at hyperpolarized potentials, however, suggesting that the peptide unbinds more readily when DIV voltage-sensor deployment is disrupted. These results are consistent with two open states in Na channels, dependent on the DIV voltage-sensor position, which differ in affinity for the blocking protein. PMID:23940261

Noise-enhanced chaos in a weakly coupled GaAs/(Al,Ga)As superlattice.

PubMed

Yin, Zhizhen; Song, Helun; Zhang, Yaohui; Ruiz-García, Miguel; Carretero, Manuel; Bonilla, Luis L; Biermann, Klaus; Grahn, Holger T

2017-01-01

Noise-enhanced chaos in a doped, weakly coupled GaAs/Al_{0.45}Ga_{0.55}As superlattice has been observed at room temperature in experiments as well as in the results of the simulation of nonlinear transport based on a discrete tunneling model. When external noise is added, both the measured and simulated current-versus-time traces contain irregularly spaced spikes for particular applied voltages, which separate a regime of periodic current oscillations from a region of no current oscillations at all. In the voltage region without current oscillations, the electric-field profile consist of a low-field domain near the emitter contact separated by a domain wall consisting of a charge accumulation layer from a high-field regime closer to the collector contact. With increasing noise amplitude, spontaneous chaotic current oscillations appear over a wider bias voltage range. For these bias voltages, the domain boundary between the two electric-field domains becomes unstable and very small current or voltage fluctuations can trigger the domain boundary to move toward the collector and induce chaotic current spikes. The experimentally observed features are qualitatively very well reproduced by the simulations. Increased noise can consequently enhance chaotic current oscillations in semiconductor superlattices.

Noise-enhanced chaos in a weakly coupled GaAs/(Al,Ga)As superlattice

NASA Astrophysics Data System (ADS)

Yin, Zhizhen; Song, Helun; Zhang, Yaohui; Ruiz-García, Miguel; Carretero, Manuel; Bonilla, Luis L.; Biermann, Klaus; Grahn, Holger T.

2017-01-01

Noise-enhanced chaos in a doped, weakly coupled GaAs /Al0.45Ga0.55As superlattice has been observed at room temperature in experiments as well as in the results of the simulation of nonlinear transport based on a discrete tunneling model. When external noise is added, both the measured and simulated current-versus-time traces contain irregularly spaced spikes for particular applied voltages, which separate a regime of periodic current oscillations from a region of no current oscillations at all. In the voltage region without current oscillations, the electric-field profile consist of a low-field domain near the emitter contact separated by a domain wall consisting of a charge accumulation layer from a high-field regime closer to the collector contact. With increasing noise amplitude, spontaneous chaotic current oscillations appear over a wider bias voltage range. For these bias voltages, the domain boundary between the two electric-field domains becomes unstable and very small current or voltage fluctuations can trigger the domain boundary to move toward the collector and induce chaotic current spikes. The experimentally observed features are qualitatively very well reproduced by the simulations. Increased noise can consequently enhance chaotic current oscillations in semiconductor superlattices.

Humidity detection using chitosan film based sensor

NASA Astrophysics Data System (ADS)

Nasution, T. I.; Nainggolan, I.; Dalimunthe, D.; Balyan, M.; Cuana, R.; Khanifah, S.

2018-02-01

A humidity sensor made of the natural polymer chitosan has been successfully fabricated in the film form by a solution casting method. Humidity testing was performed by placing a chitosan film sensor in a cooling machine room, model KT-2000 Ahu. The testing results showed that the output voltage values of chitosan film sensor increased with the increase in humidity percentage. For the increase in humidity percentage from 30 to 90% showed that the output voltage of chitosan film sensor increased from 32.19 to 138.75 mV. It was also found that the sensor evidenced good repeatability and stability during the testing. Therefore, chitosan has a great potential to be used as new sensing material for the humidity detection of which was cheaper and environmentally friendly.

Breathing of voltage dependent anion channel as revealed by the fractal property of its gating

NASA Astrophysics Data System (ADS)

Manna, Smarajit; Banerjee, Jyotirmoy; Ghosh, Subhendu

2007-12-01

The gating of voltage dependent anion channel (VDAC) depends on the movement of voltage sensors in the transmembrane region, but the actual mechanism is still not well understood. With a view to understand the phenomenon we have analyzed the current recordings of VDAC in lipid bilayer membrane (BLM) and found that the data show self-similarity and fractal characteristics. We look for the microscopic and molecular basis of fractal behavior of gating of VDAC. A model describing the oscillatory dynamics of voltage sensors of VDAC in the transmembrane region under applied potential has been proposed which gives rise to the aforesaid fractal behavior.

Use of multi-functional flexible micro-sensors for in situ measurement of temperature, voltage and fuel flow in a proton exchange membrane fuel cell.

PubMed

Lee, Chi-Yuan; Chan, Pin-Cheng; Lee, Chung-Ju

2010-01-01

Temperature, voltage and fuel flow distribution all contribute considerably to fuel cell performance. Conventional methods cannot accurately determine parameter changes inside a fuel cell. This investigation developed flexible and multi-functional micro sensors on a 40 μm-thick stainless steel foil substrate by using micro-electro-mechanical systems (MEMS) and embedded them in a proton exchange membrane fuel cell (PEMFC) to measure the temperature, voltage and flow. Users can monitor and control in situ the temperature, voltage and fuel flow distribution in the cell. Thereby, both fuel cell performance and lifetime can be increased.

Ultrananocrystalline Diamond Cantilever Wide Dynamic Range Acceleration/Vibration /Pressure Sensor

DOEpatents

Krauss, Alan R.; Gruen, Dieter M.; Pellin, Michael J.; Auciello, Orlando

2003-09-02

An ultrananocrystalline diamond (UNCD) element formed in a cantilever configuration is used in a highly sensitive, ultra-small sensor for measuring acceleration, shock, vibration and static pressure over a wide dynamic range. The cantilever UNCD element may be used in combination with a single anode, with measurements made either optically or by capacitance. In another embodiment, the cantilever UNCD element is disposed between two anodes, with DC voltages applied to the two anodes. With a small AC modulated voltage applied to the UNCD cantilever element and because of the symmetry of the applied voltage and the anode-cathode gap distance in the Fowler-Nordheim equation, any change in the anode voltage ratio V1/V2 required to maintain a specified current ratio precisely matches any displacement of the UNCD cantilever element from equilibrium. By measuring changes in the anode voltage ratio required to maintain a specified current ratio, the deflection of the UNCD cantilever can be precisely determined. By appropriately modulating the voltages applied between the UNCD cantilever and the two anodes, or limit electrodes, precise independent measurements of pressure, uniaxial acceleration, vibration and shock can be made. This invention also contemplates a method for fabricating the cantilever UNCD structure for the sensor.

Ultrananocrystalline diamond cantilever wide dynamic range acceleration/vibration/pressure sensor

DOEpatents

Krauss, Alan R [Naperville, IL; Gruen, Dieter M [Downers Grove, IL; Pellin, Michael J [Naperville, IL; Auciello, Orlando [Bolingbrook, IL

2002-07-23

An ultrananocrystalline diamond (UNCD) element formed in a cantilever configuration is used in a highly sensitive, ultra-small sensor for measuring acceleration, shock, vibration and static pressure over a wide dynamic range. The cantilever UNCD element may be used in combination with a single anode, with measurements made either optically or by capacitance. In another embodiment, the cantilever UNCD element is disposed between two anodes, with DC voltages applied to the two anodes. With a small AC modulated voltage applied to the UNCD cantilever element and because of the symmetry of the applied voltage and the anode-cathode gap distance in the Fowler-Nordheim equation, any change in the anode voltage ratio V1/N2 required to maintain a specified current ratio precisely matches any displacement of the UNCD cantilever element from equilibrium. By measuring changes in the anode voltage ratio required to maintain a specified current ratio, the deflection of the UNCD cantilever can be precisely determined. By appropriately modulating the voltages applied between the UNCD cantilever and the two anodes, or limit electrodes, precise independent measurements of pressure, uniaxial acceleration, vibration and shock can be made. This invention also contemplates a method for fabricating the cantilever UNCD structure for the sensor.

Thermally Stable, Piezoelectric and Pyroelectric Polymeric Substrates and Method Relating Thereto

NASA Technical Reports Server (NTRS)

Simpson, Joycelyn O. (Inventor); St.Claire, Terry L. (Inventor)

2002-01-01

A thermally stable, piezoelectric and pyroelectric polymeric substrate was prepared, This thermally stable, piezoelectric and pyroelectric polymeric substrate may be used to prepare electromechanical transducers, thermomechanical transducers, accelerometers, acoustic sensors, infrared sensors, pressure sensors, vibration sensors, impact sensors. in-situ temperature sensors, in-situ stress/strain sensors, micro actuators, switches. adjustable fresnel lenses, speakers, tactile sensors, weather sensors, micro positioners, ultrasonic devices, power generators, tunable reflectors, microphones, and hydrophones. The process for preparing these polymeric substrates includes: providing a polymeric substrate having a softening temperature greater than 100 C; depositing a metal electrode material onto the polymer film; attaching a plurality of electrical leads to the metal electrode coated polymeric substrates; heating the metal electrode coated polymeric substrate in a low dielectric medium; applying a voltage to the heated metal electrode coated polymeric substrate to induce polarization; and cooling the polarized metal electrode coated polymeric electrode while maintaining a constant voltage.

Thermally Stable, Piezoelectric and Pyroelectric Polymeric Substrates

NASA Technical Reports Server (NTRS)

Simpson, Joycely O. (Inventor); St.Clair, Terry L. (Inventor)

1999-01-01

A thermally stable, piezoelectric and pyroelectric polymeric substrate was prepared. This thermally stable, piezoelectric and pyroelectric polymeric substrate may be used to prepare electromechanical transducers, thermomechanical transducers, accelerometers. acoustic sensors, infrared sensors, pressure sensors, vibration sensors, impact sensors, in-situ temperature sensors, in-situ stress/strain sensors, micro actuators, switches, adjustable fresnel lenses, speakers, tactile sensors. weather sensors, micro positioners, ultrasonic devices, power generators, tunable reflectors, microphones, and hydrophones. The process for preparing these polymeric substrates includes: providing a polymeric substrate having a softening temperature greater than 1000 C; depositing a metal electrode material onto the polymer film; attaching a plurality of electrical leads to the metal electrode coated polymeric substrate; heating the metal electrode coated polymeric substrate in a low dielectric medium; applying a voltage to the heated metal electrode coated polymeric substrate to induce polarization; and cooling the polarized metal electrode coated polymeric electrode while maintaining a constant voltage.

Method of Making Thermally Stable, Piezoelectric and Proelectric Polymeric Substrates

NASA Technical Reports Server (NTRS)

Simpson, Joycelyn O. (Inventor); St.Clair, Terry L. (Inventor)

1999-01-01

A thermally stable, piezoelectric and pyroelectric polymeric substrate was prepared. This thermally stable, piezoelectric and pyroelectric polymeric substrate may be used to prepare electromechanical transducers, thermomechanical transducers, accelerometers, acoustic sensors, infrared sensors, pressure sensors, vibration sensors, impact sensors. in-situ temperature sensors, in-situ stress/strain sensors, micro actuators, switches, adjustable fresnel lenses, speakers, tactile sensors, weather sensors, micro positioners, ultrasonic devices, power generators, tunable reflectors, microphones, and hydrophones. The process for preparing these polymeric substrates includes: providing a polymeric substrate having a softening temperature greater than 100 C; depositing a metal electrode material onto the polymer film; attaching a plurality of electrical leads to the metal electrode coated polymeric substrate; heating the metal electrode coated polymeric substrate in a low dielectric medium: applying a voltage to the heated metal electrode coated polymeric substrate to induce polarization; and cooling the polarized metal electrode coated polymeric electrode while maintaining a constant voltage.

A genetically encoded tool kit for manipulating and monitoring membrane phosphatidylinositol 4,5-bisphosphate in intact cells.

PubMed

Hertel, Fabian; Switalski, Agathe; Mintert-Jancke, Elisa; Karavassilidou, Katharina; Bender, Kirsten; Pott, Lutz; Kienitz, Marie-Cécile

2011-01-01

Most ion channels are regulated by phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P(2)) in the cell membrane by diverse mechanisms. Important molecular tools to study ion channel regulation by PtdIns(4,5)P(2) in living cells have been developed in the past. These include fluorescent PH-domains as sensors for Förster resonance energy transfer (FRET), to monitor changes in plasma membrane(.) For controlled and reversible depletion of PtdIns(4,5)P(2), voltage-sensing phosphoinositide phosphatases (VSD) have been demonstrated as a superior tool, since they are independent of cellular signaling pathways. Combining these methods in intact cells requires multiple transfections. We used self-cleaving viral 2A-peptide sequences for adenovirus driven expression of the PH-domain of phospholipase-Cδ1 (PLCδ1) fused to ECFP and EYFP respectively and Ciona intestinalis VSP (Ci-VSP), from a single open reading frame (ORF) in adult rat cardiac myocytes. Expression and correct targeting of ECFP-PH-PLCδ1(,) EYFP-PH-PLCδ1, and Ci-VSP from a single tricistronic vector containing 2A-peptide sequences first was demonstrated in HEK293 cells by voltage-controlled FRET measurements and Western blotting. Adult rat cardiac myocytes expressed Ci-VSP and the two fluorescent PH-domains within 4 days after gene transfer using the vector integrated into an adenoviral construct. Activation of Ci-VSP by depolarization resulted in rapid changes in FRET ratio indicating depletion of PtdIns(4,5)P(2) in the plasma membrane. This was paralleled by inhibition of endogenous G protein activated K(+) (GIRK) current. By comparing changes in FRET and current, a component of GIRK inhibition by adrenergic receptors unrelated to depletion of PtdIns(4,5)P(2) was identified. Expression of a FRET sensor pair and Ci-VSP from a single ORF provides a useful approach to study regulation of ion channels by phosphoinositides in cell lines and transfection-resistant postmitotic cells. Generally, adenoviral constructs containing self-cleaving 2A-peptide sequences are highly suited for simultaneous transfer of multiple genes in adult cardiac myocytes.

Modular chemiresistive sensor

DOE Office of Scientific and Technical Information (OSTI.GOV)

Alam, Maksudul M.; Sampathkumaran, Uma

The present invention relates to a modular chemiresistive sensor. In particular, a modular chemiresistive sensor for hypergolic fuel and oxidizer leak detection, carbon dioxide monitoring and detection of disease biomarkers. The sensor preferably has two gold or platinum electrodes mounted on a silicon substrate where the electrodes are connected to a power source and are separated by a gap of 0.5 to 4.0 .mu.M. A polymer nanowire or carbon nanotube spans the gap between the electrodes and connects the electrodes electrically. The electrodes are further connected to a circuit board having a processor and data storage, where the processor canmore » measure current and voltage values between the electrodes and compare the current and voltage values with current and voltage values stored in the data storage and assigned to particular concentrations of a pre-determined substance such as those listed above or a variety of other substances.« less

Impact of Reflow on the Output Characteristics of Piezoelectric Microelectromechanical System Devices

NASA Astrophysics Data System (ADS)

Nogami, Hirofumi; Kobayashi, Takeshi; Okada, Hironao; Masuda, Takashi; Maeda, Ryutaro; Itoh, Toshihiro

2012-09-01

An animal health monitoring system and a wireless sensor node aimed at preventing the spread of animal-transmitted diseases and improving pastoral efficiency which are especially suitable for chickens, were developed. The sensor node uses a piezoelectric microelectromechanical system (MEMS) device and an event-driven system that is activated by the movements of a chicken. The piezoelectric MEMS device has two functions: a) it measures the activity of a chicken and b) switches the micro-control unit (MCU) of the wireless sensor node from the sleep mode. The piezoelectric MEMS device is required to produce high output voltages when the chicken moves. However, after the piezoelectric MEMS device was reflowed to the wireless sensor node, the output voltages of the piezoelectric MEMS device decreased. The main reason for this might be the loss of residual polarization, which is affected by the thermal load during the reflow process. After the reflow process, we were not able to apply a voltage to the piezoelectric MEMS device; thus, the piezoelectric output voltage was not increased by repoling the piezoelectric MEMS device. To address the thermal load of the reflow process, we established a thermal poling treatment, which achieves a higher temperature than the reflow process. We found that on increasing the thermal poling temperature, the piezoelectric output voltages did not decreased low significantly. Thus, we considered that a thermal poling temperature higher than that of the reflow process prevents the piezoelectric output voltage reduction caused by the thermal load.

A novel method of temperature compensation for piezoresistive microcantilever-based sensors.

PubMed

Han, Jianqiang; Wang, Xiaofei; Yan, Tianhong; Li, Yan; Song, Meixuan

2012-03-01

Microcantilever with integrated piezoresistor has been applied to in situ surface stress measurement in the field of biochemical sensors. It is well known that piezoresistive cantilever-based sensors are sensitive to ambient temperature changing due to highly temperature-dependent piezoresistive effect and mismatch in thermal expansion of composite materials. This paper proposes a novel method of temperature drift compensation for microcantilever-based sensors with a piezoresistive full Wheatstone bridge integrated at the clamped ends by subtracting the amplified output voltage of the reference cantilever from the output voltage of the sensing cantilever through a simple temperature compensating circuit. Experiments show that the temperature drift of microcantilever sensors can be significantly reduced by the method.

Design Considerations for Aural Vital Signs Using PZT Piezoelectric Ceramics Sensor Based on the Computerization Method.

PubMed

Noimanee, Suranan; Tunkasiri, Tawee; Siriwitayakorn, Kingkeo; Tantrakoon, Jerapong

2007-11-11

The purpose was to illustrate how system developed for measurement of the aural vital signs such as patient's heart and lung sounds in the hospital. For heart sounds measurement must operate the frequency response between 20 - 800 Hz, and lung sounds measurement must operate the frequency response between 160 - 4,000 Hz. The method was designed PZT piezoelectric ceramics for both frequency response in the same PZT sensor. It converts a signal from aural vital sign form to voltage signal. The signal is suitably amplified and re-filtered in band pass frequency band. It is converted to digital signal by an analog to digital conversion circuitry developed for the purpose. The results were that all signals can fed to personal computer through the sound card port. With the supporting software for drawing of graphic on the screen, the signal for a specific duration is accessed and stored in the computer's memory in term of each patient's data. In conclusion, the data of each patient call dot pcg (.pcg) for drawing graph and dot wave (.wave) for sound listening or automatic sending via electronic mail to the physician for later analysis of interpreting the sounds on the basis of their time domain and frequency domain representation to diagnose heart disorders.

The orientation and molecular movement of a k(+) channel voltage-sensing domain.

PubMed

Gandhi, Chris S; Clark, Eliana; Loots, Eli; Pralle, Arnd; Isacoff, Ehud Y

2003-10-30

Voltage-gated channels operate through the action of a voltage-sensing domain (membrane segments S1-S4) that controls the conformation of gates located in the pore domain (membrane segments S5-S6). Recent structural studies on the bacterial K(v)AP potassium channel have led to a new model of voltage sensing in which S4 lies in the lipid at the channel periphery and moves through the membrane as a unit with a portion of S3. Here we describe accessibility probing and disulfide scanning experiments aimed at determining how well the K(v)AP model describes the Drosophila Shaker potassium channel. We find that the S1-S3 helices have one end that is externally exposed, S3 does not undergo a transmembrane motion, and S4 lies in close apposition to the pore domain in the resting and activated state.

Electro-optic voltage sensor for sensing voltage in an E-field

DOEpatents

Davidson, James R.; Crawford, Thomas M.; Seifert, Gary D.

2002-03-26

A miniature electro-optic voltage sensor and system capable of accurate operation at high voltages has a sensor body disposed in an E-field. The body receives a source beam of electromagnetic radiation. A polarization beam displacer separates the source light beam into two beams with orthogonal linear polarizations. A wave plate rotates the linear polarization to rotated polarization. A transducer utilizes Pockels electro-optic effect and induces a differential phase shift on the major and minor axes of the rotated polarization in response to the E-field. A prism redirects the beam back through the transducer, wave plate, and polarization beam displacer. The prism also converts the rotated polarization to circular or elliptical polarization. The wave plate rotates the major and minor axes of the circular or elliptical polarization to linear polarization. The polarization beam displacer separates the beam into two beams of orthogonal linear polarization representing the major and minor axes. The system may have a transmitter for producing the beam of electro-magnetic radiation; a detector for converting the two beams into electrical signals; and a signal processor for determining the voltage.

Development of CMOS Imager Block for Capsule Endoscope

NASA Astrophysics Data System (ADS)

Shafie, S.; Fodzi, F. A. M.; Tung, L. Q.; Lioe, D. X.; Halin, I. A.; Hasan, W. Z. W.; Jaafar, H.

2014-04-01

This paper presents the development of imager block to be associated in a capsule endoscopy system. Since the capsule endoscope is used to diagnose gastrointestinal diseases, the imager block must be in small size which is comfortable for the patients to swallow. In this project, a small size 1.5V button battery is used as the power supply while the voltage supply requirements for other components such as microcontroller and CMOS image sensor are higher. Therefore, a voltage booster circuit is proposed to boost up the voltage supply from 1.5V to 3.3V. A low power microcontroller is used to generate control pulses for the CMOS image sensor and to convert the 8-bits parallel data output to serial data to be transmitted to the display panel. The results show that the voltage booster circuit was able to boost the voltage supply from 1.5V to 3.3V. The microcontroller precisely controls the CMOS image sensor to produce parallel data which is then serialized again by the microcontroller. The serial data is then successfully translated to 2fps image and displayed on computer.

Control systems using modal domain optical fiber sensors for smart structure applications

NASA Technical Reports Server (NTRS)

Lindner, Douglas K.; Reichard, Karl M.

1991-01-01

Recently, a new class of sensors has emerged for structural control which respond to environmental changes over a significant gauge length; these sensors are called distributed-effect sensors. These sensors can be fabricated with spatially varying sensitivity to the distributed measurand, and can be configured to measure a variety of structural parameters which can not be measured directly using point sensors. Examples of distributed-effect sensors include piezoelectric film, holographic sensors, and modal domain optical fiber sensors. Optical fiber sensors are particularly attractive for smart structure applications because they are flexible, have low mass, and can easily be embedded directly into materials. In this paper we describe the implementation of weighted modal domain optical fiber sensors. The mathematical model of the modal domain optical fiber sensor model is described and used to derive an expression for the sensor sensitivity. The effects of parameter variations on the sensor sensitivity are demonstrated to illustrate methods of spatially varying the sensor sensitivity.

Photon Counting Imaging with an Electron-Bombarded Pixel Image Sensor

PubMed Central

Hirvonen, Liisa M.; Suhling, Klaus

2016-01-01

Electron-bombarded pixel image sensors, where a single photoelectron is accelerated directly into a CCD or CMOS sensor, allow wide-field imaging at extremely low light levels as they are sensitive enough to detect single photons. This technology allows the detection of up to hundreds or thousands of photon events per frame, depending on the sensor size, and photon event centroiding can be employed to recover resolution lost in the detection process. Unlike photon events from electron-multiplying sensors, the photon events from electron-bombarded sensors have a narrow, acceleration-voltage-dependent pulse height distribution. Thus a gain voltage sweep during exposure in an electron-bombarded sensor could allow photon arrival time determination from the pulse height with sub-frame exposure time resolution. We give a brief overview of our work with electron-bombarded pixel image sensor technology and recent developments in this field for single photon counting imaging, and examples of some applications. PMID:27136556

Early-onset epileptic encephalopathy caused by gain-of-function mutations in the voltage sensor of Kv7.2 and Kv7.3 potassium channel subunits.

PubMed

Miceli, Francesco; Soldovieri, Maria Virginia; Ambrosino, Paolo; De Maria, Michela; Migliore, Michele; Migliore, Rosanna; Taglialatela, Maurizio

2015-03-04

Mutations in Kv7.2 (KCNQ2) and Kv7.3 (KCNQ3) genes, encoding for voltage-gated K(+) channel subunits underlying the neuronal M-current, have been associated with a wide spectrum of early-onset epileptic disorders ranging from benign familial neonatal seizures to severe epileptic encephalopathies. The aim of the present work has been to investigate the molecular mechanisms of channel dysfunction caused by voltage-sensing domain mutations in Kv7.2 (R144Q, R201C, and R201H) or Kv7.3 (R230C) recently found in patients with epileptic encephalopathies and/or intellectual disability. Electrophysiological studies in mammalian cells transfected with human Kv7.2 and/or Kv7.3 cDNAs revealed that each of these four mutations stabilized the activated state of the channel, thereby producing gain-of-function effects, which are opposite to the loss-of-function effects produced by previously found mutations. Multistate structural modeling revealed that the R201 residue in Kv7.2, corresponding to R230 in Kv7.3, stabilized the resting and nearby voltage-sensing domain states by forming an intricate network of electrostatic interactions with neighboring negatively charged residues, a result also confirmed by disulfide trapping experiments. Using a realistic model of a feedforward inhibitory microcircuit in the hippocampal CA1 region, an increased excitability of pyramidal neurons was found upon incorporation of the experimentally defined parameters for mutant M-current, suggesting that changes in network interactions rather than in intrinsic cell properties may be responsible for the neuronal hyperexcitability by these gain-of-function mutations. Together, the present results suggest that gain-of-function mutations in Kv7.2/3 currents may cause human epilepsy with a severe clinical course, thus revealing a previously unexplored level of complexity in disease pathogenetic mechanisms. Copyright © 2015 the authors 0270-6474/15/353782-12$15.00/0.

Optical fiber extrinsic Fabry-Perot interferometer sensors for ultrasound detection

NASA Astrophysics Data System (ADS)

Sun, Qingguo; Chen, Na; Ding, Yuetong; Chen, Zhenyi; Wang, Tingyun

2009-11-01

In this paper, a new method is proposed to fabricate an optical fiber extrinsic Fabry-Perot interferometer (EFPI) as an ultrasonic sensor. An acoustic emission detecting system is constructed based on multiple EFPI sensors and demodulation circuit. Ultrasound detection experiments were done from both traditional piezoelectric transducer (PZT) and high voltage discharge. In the experiments, strong ultrasound signals were detected in both cases. The signal attenuation related to the distance and the angle between the acoustic emission source and the FP sensor are obtained. The results indicate that the receiving angle of the FP sensor is nearly 90° and the maximum detection distance in the air is more than 200cm. Furthermore, four sensors are used to locate the position of the ultrasound source produced by high voltage discharge.

Fluorescent Protein Voltage Probes Derived from ArcLight that Respond to Membrane Voltage Changes with Fast Kinetics

PubMed Central

Han, Zhou; Jin, Lei; Platisa, Jelena; Cohen, Lawrence B.; Baker, Bradley J.; Pieribone, Vincent A.

2013-01-01

We previously reported the discovery of a fluorescent protein voltage probe, ArcLight, and its derivatives that exhibit large changes in fluorescence intensity in response to changes of plasma membrane voltage. ArcLight allows the reliable detection of single action potentials and sub-threshold activities in individual neurons and dendrites. The response kinetics of ArcLight (τ1-on ~10 ms, τ2-on ~ 50 ms) are comparable with most published genetically-encoded voltage probes. However, probes using voltage-sensing domains other than that from the Ciona intestinalis voltage sensitive phosphatase exhibit faster kinetics. Here we report new versions of ArcLight, in which the Ciona voltage-sensing domain was replaced with those from chicken, zebrafish, frog, mouse or human. We found that the chicken and zebrafish-based ArcLight exhibit faster kinetics, with a time constant (τ) less than 6ms for a 100 mV depolarization. Although the response amplitude of these two probes (8-9%) is not as large as the Ciona-based ArcLight (~35%), they are better at reporting action potentials from cultured neurons at higher frequency. In contrast, probes based on frog, mouse and human voltage sensing domains were either slower than the Ciona-based ArcLight or had very small signals. PMID:24312287

Domain switching kinetics in ferroelectric-resistive BiFeO3 thin film memories

NASA Astrophysics Data System (ADS)

Meng, Jianwei; Jiang, Jun; Geng, Wenping; Chen, Zhihui; Zhang, Wei; Jiang, Anquan

2015-02-01

We fabricated (00l) BiFeO3 (BFO) thin films in different growth modes on SrRuO3/SrTiO3 substrates using a pulsed laser deposition technique. X-ray diffraction patterns show an out-of-plane lattice constant of 4.03 Å and ferroelectric polarization of 82 µC/cm2 for the BFO thin film in a layer-by-layer growth mode (2D-BFO), larger than 3.96 Å and 51 µC/cm2 for the thin film in the 3D-island formation growth mode (3D-BFO). The 2D-BFO thin film at 300 K shows switchable on/off diode currents upon polarization flipping near a negative coercive voltage, which is nevertheless absent from the above 3D-BFO thin film. From a positive-up-negative-down pulse characterization technique, we measured domain switching current transients as well as polarization-voltage (Pf-Vf) hysteresis loops in both semiconducting thin films. Pf-Vf hysteresis loops after 1 µs-retention time show the preferred domain orientation pointing to bottom electrodes in a 3D-BFO thin film. The poor retention of the domains pointing to top electrodes can be improved considerably in a 2D-BFO thin film. From these measurements, we extracted domain switching time dependence of coercive voltage at temperatures of 78-300 K. From these dependences, we found coercive voltages in semiconducting ferroelectric thin films much higher than those in insulating thin films, disobeying the traditional Merz equation. Finally, an equivalent resistance model in description of free-carrier compensation of the front domain boundary charge is developed to interpret this difference. This equivalent resistance can be coincidently extracted either from domain switching time dependence of coercive voltage or from applied voltage dependence of domain switching current, which drops almost linearly with the temperature until down to 0 in a ferroelectric insulator at 78 K.

Use of Multi-Functional Flexible Micro-Sensors for in situ Measurement of Temperature, Voltage and Fuel Flow in a Proton Exchange Membrane Fuel Cell

PubMed Central

Lee, Chi-Yuan; Chan, Pin-Cheng; Lee, Chung-Ju

2010-01-01

Temperature, voltage and fuel flow distribution all contribute considerably to fuel cell performance. Conventional methods cannot accurately determine parameter changes inside a fuel cell. This investigation developed flexible and multi-functional micro sensors on a 40 μm-thick stainless steel foil substrate by using micro-electro-mechanical systems (MEMS) and embedded them in a proton exchange membrane fuel cell (PEMFC) to measure the temperature, voltage and flow. Users can monitor and control in situ the temperature, voltage and fuel flow distribution in the cell. Thereby, both fuel cell performance and lifetime can be increased. PMID:22163545

Temperature Induced Voltage Offset Drifts in Silicon Carbide Pressure Sensors

NASA Technical Reports Server (NTRS)

Okojie, Robert S.; Lukco, Dorothy; Nguyen, Vu; Savrun, Ender

2012-01-01

We report the reduction of transient drifts in the zero pressure offset voltage in silicon carbide (SiC) pressure sensors when operating at 600 C. The previously observed maximum drift of +/- 10 mV of the reference offset voltage at 600 C was reduced to within +/- 5 mV. The offset voltage drifts and bridge resistance changes over time at test temperature are explained in terms of the microstructure and phase changes occurring within the contact metallization, as analyzed by Auger electron spectroscopy and field emission scanning electron microscopy. The results have helped to identify the upper temperature reliable operational limit of this particular metallization scheme to be 605 C.

Structural Characterization of the Predominant Family of Histidine Kinase Sensor Domains

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Z.; Hendrickson, W

2010-01-01

Histidine kinase (HK) receptors are used ubiquitously by bacteria to monitor environmental changes, and they are also prevalent in plants, fungi, and other protists. Typical HK receptors have an extracellular sensor portion that detects a signal, usually a chemical ligand, and an intracellular transmitter portion that includes both the kinase domain itself and the site for histidine phosphorylation. While kinase domains are highly conserved, sensor domains are diverse. HK receptors function as dimers, but the molecular mechanism for signal transduction across cell membranes remains obscure. In this study, eight crystal structures were determined from five sensor domains representative of themore » most populated family, family HK1, found in a bioinformatic analysis of predicted sensor domains from transmembrane HKs. Each structure contains an inserted repeat of PhoQ/DcuS/CitA (PDC) domains, and similarity between sequence and structure is correlated across these and other double-PDC sensor proteins. Three of the five sensors crystallize as dimers that appear to be physiologically relevant, and comparisons between ligated structures and apo-state structures provide insights into signal transmission. Some HK1 family proteins prove to be sensors for chemotaxis proteins or diguanylate cyclase receptors, implying a combinatorial molecular evolution.« less

Multi-Domain SDN Survivability for Agricultural Wireless Sensor Networks.

PubMed

Huang, Tao; Yan, Siyu; Yang, Fan; Liu, Jiang

2016-11-06

Wireless sensor networks (WSNs) have been widely applied in agriculture field; meanwhile, the advent of multi-domain software-defined networks (SDNs) have improved the wireless resource utilization rate and strengthened network management. In recent times, multi-domain SDNs have been applied to agricultural sensor networks, namely multi-domain software-defined wireless sensor networks (SDWSNs). However, when the SDNs controlling agriculture networks suddenly become unavailable, whether intra-domain or inter-domain, sensor network communication is abnormal because of the loss of control. Moreover, there are controller and switch info-updating problems even if the controller becomes available again. To resolve these problems, this paper proposes a new approach based on an Open vSwitch extension for multi-domain SDWSNs, which can enhance agriculture network survivability and stability. We achieved this by designing a connection-state mechanism, a communication mechanism on both L2 and L3, and an info-updating mechanism based on Open vSwitch. The experimental results show that, whether it is agricultural inter-domain or intra-domain during the controller failure period, the sensor switches can enter failure recovery mode as soon as possible so that the sensor network keeps a stable throughput, a short failure recovery time below 300 ms, and low packet loss. Further, the domain can smoothly control the domain network again once the controller becomes available. This approach based on an Open vSwitch extension can enhance the survivability and stability of multi-domain SDWSNs in precision agriculture.

Multi-Domain SDN Survivability for Agricultural Wireless Sensor Networks

PubMed Central

Huang, Tao; Yan, Siyu; Yang, Fan; Liu, Jiang

2016-01-01

Wireless sensor networks (WSNs) have been widely applied in agriculture field; meanwhile, the advent of multi-domain software-defined networks (SDNs) have improved the wireless resource utilization rate and strengthened network management. In recent times, multi-domain SDNs have been applied to agricultural sensor networks, namely multi-domain software-defined wireless sensor networks (SDWSNs). However, when the SDNs controlling agriculture networks suddenly become unavailable, whether intra-domain or inter-domain, sensor network communication is abnormal because of the loss of control. Moreover, there are controller and switch info-updating problems even if the controller becomes available again. To resolve these problems, this paper proposes a new approach based on an Open vSwitch extension for multi-domain SDWSNs, which can enhance agriculture network survivability and stability. We achieved this by designing a connection-state mechanism, a communication mechanism on both L2 and L3, and an info-updating mechanism based on Open vSwitch. The experimental results show that, whether it is agricultural inter-domain or intra-domain during the controller failure period, the sensor switches can enter failure recovery mode as soon as possible so that the sensor network keeps a stable throughput, a short failure recovery time below 300 ms, and low packet loss. Further, the domain can smoothly control the domain network again once the controller becomes available. This approach based on an Open vSwitch extension can enhance the survivability and stability of multi-domain SDWSNs in precision agriculture. PMID:27827971

Electrochemical sensor for monitoring electrochemical potentials of fuel cell components

DOEpatents

Kunz, Harold R.; Breault, Richard D.

1993-01-01

An electrochemical sensor comprised of wires, a sheath, and a conduit can be utilized to monitor fuel cell component electric potentials during fuel cell shut down or steady state. The electrochemical sensor contacts an electrolyte reservoir plate such that the conduit wicks electrolyte through capillary action to the wires to provide water necessary for the electrolysis reaction which occurs thereon. A voltage is applied across the wires of the electrochemical sensor until hydrogen evolution occurs at the surface of one of the wires, thereby forming a hydrogen reference electrode. The voltage of the fuel cell component is then determined with relation to the hydrogen reference electrode.

Low power wireless sensor networks for infrastructure monitoring

NASA Astrophysics Data System (ADS)

Ghaed, Mohammad Hassan; Ghahramani, Mohammad Mahdi; Chen, Gregory; Fojtik, Matthew; Blaauw, David; Flynn, Michael P.; Sylvester, Dennis

2012-04-01

Sensors with long lifetimes are ideal for infrastructure monitoring. Miniaturized sensor systems are only capable of storing small amounts of energy. Prior work has increased sensor lifetime through the reduction of supply voltage , necessitating voltage conversion from storage elements such as batteries. Sensor lifetime can be further extended by harvesting from solar, vibrational, or thermal energy. Since harvested energy is sporadic, it must be detected and stored. Harvesting sources do not provide voltage levels suitable for secondary power sources, necessitating DC-DC upconversion. We demonstrate a 8.75mm3 sensor system with a near-threshold ARM microcontroller, custom 3.3fW/bit SRAM, two 1mm2 solar cells, a thin-film Li-ion battery, and integrated power management unit. The 7.7μW system enters a 550pW data-retentive sleep state between measurements and harvests solar energy to enable energy autonomy. Our receiver and transmitter architectures benefit from a design strategy that employs mixed signal and digital circuit schemes that perform well in advanced CMOS integrated circuit technologies. A prototype transmitter implemented in 0.13μm CMOS satisfies the requirements for Zigbee, but consumes far less power consumption than state-of-the-art commercial devices.

Mutation of I696 and W697 in the TRP box of vanilloid receptor subtype I modulates allosteric channel activation.

PubMed

Gregorio-Teruel, Lucia; Valente, Pierluigi; González-Ros, José Manuel; Fernández-Ballester, Gregorio; Ferrer-Montiel, Antonio

2014-03-01

The transient receptor potential vanilloid receptor subtype I (TRPV1) channel acts as a polymodal sensory receptor gated by chemical and physical stimuli. Like other TRP channels, TRPV1 contains in its C terminus a short, conserved domain called the TRP box, which is necessary for channel gating. Substitution of two TRP box residues-I696 and W697-with Ala markedly affects TRPV1's response to all activating stimuli, which indicates that these two residues play a crucial role in channel gating. We systematically replaced I696 and W697 with 18 native l-amino acids (excluding cysteine) and evaluated the effect on voltage- and capsaicin-dependent gating. Mutation of I696 decreased channel activation by either voltage or capsaicin; furthermore, gating was only observed with substitution of hydrophobic amino acids. Substitution of W697 with any of the 18 amino acids abolished gating in response to depolarization alone, shifting the threshold to unreachable voltages, but not capsaicin-mediated gating. Moreover, vanilloid-activated responses of W697X mutants showed voltage-dependent gating along with a strong voltage-independent component. Analysis of the data using an allosteric model of activation indicates that mutation of I696 and W697 primarily affects the allosteric coupling constants of the ligand and voltage sensors to the channel pore. Together, our findings substantiate the notion that inter- and/or intrasubunit interactions at the level of the TRP box are critical for efficient coupling of stimulus sensing and gate opening. Perturbation of these interactions markedly reduces the efficacy and potency of the activating stimuli. Furthermore, our results identify these interactions as potential sites for pharmacological intervention.

Voltage-dependent gating and gating charge measurements in the Kv1.2 potassium channel

PubMed Central

Ishida, Itzel G.; Rangel-Yescas, Gisela E.; Carrasco-Zanini, Julia

2015-01-01

Much has been learned about the voltage sensors of ion channels since the x-ray structure of the mammalian voltage-gated potassium channel Kv1.2 was published in 2005. High resolution structural data of a Kv channel enabled the structural interpretation of numerous electrophysiological findings collected in various ion channels, most notably Shaker, and permitted the development of meticulous computational simulations of the activation mechanism. The fundamental premise for the structural interpretation of functional measurements from Shaker is that this channel and Kv1.2 have the same characteristics, such that correlation of data from both channels would be a trivial task. We tested these assumptions by measuring Kv1.2 voltage-dependent gating and charge per channel. We found that the Kv1.2 gating charge is near 10 elementary charges (eo), ∼25% less than the well-established 13–14 eo in Shaker. Next, we neutralized positive residues in the Kv1.2 S4 transmembrane segment to investigate the cause of the reduction of the gating charge and found that, whereas replacing R1 with glutamine decreased voltage sensitivity to ∼50% of the wild-type channel value, mutation of the subsequent arginines had a much smaller effect. These data are in marked contrast to the effects of charge neutralization in Shaker, where removal of the first four basic residues reduces the gating charge by roughly the same amount. In light of these differences, we propose that the voltage-sensing domains (VSDs) of Kv1.2 and Shaker might undergo the same physical movement, but the septum that separates the aqueous crevices in the VSD of Kv1.2 might be thicker than Shaker’s, accounting for the smaller Kv1.2 gating charge. PMID:25779871

Symmetric voltage-controlled variable resistance

NASA Technical Reports Server (NTRS)

Vanelli, J. C.

1978-01-01

Feedback network makes resistance of field-effect transistor (FET) same for current flowing in either direction. It combines control voltage with source and load voltages to give symmetric current/voltage characteristics. Since circuit produces same magnitude output voltage for current flowing in either direction, it introduces no offset in presense of altering polarity signals. It is therefore ideal for sensor and effector circuits in servocontrol systems.

Mapping Capacitive Coupling Among Pixels in a Sensor Array

NASA Technical Reports Server (NTRS)

Seshadri, Suresh; Cole, David M.; Smith, Roger M.

2010-01-01

An improved method of mapping the capacitive contribution to cross-talk among pixels in an imaging array of sensors (typically, an imaging photodetector array) has been devised for use in calibrating and/or characterizing such an array. The method involves a sequence of resets of subarrays of pixels to specified voltages and measurement of the voltage responses of neighboring non-reset pixels.

A copper-coated fiber Bragg grating current sensor

NASA Astrophysics Data System (ADS)

Jia, Danping; Zhao, Limin; Lin, Yingwen

2005-01-01

Conventional current transformer (CT) is based on the principles of electric magnetic induction with copper wire windings and iron cores, it is widely used in power systems. But it emerges more weakness as the applied voltage and power capacity more and more increase. Over the past 20 years optical current sensors have received significant attention by a number of groups around the world as next generation high voltage measurement devices, with a view to replacing iron-corn current transformers in the electric power industry. In the opposite side of conventional current transformer, optical fiber current sensor provides a solution of the existed problems. It brings the significant advantages that they are non-conductive and lightweight, which can allow for much simpler insulation and mounting designs as the application voltage increase to1000kV or more to day. In addition, optical sensors do not exhibit hysteresis and provide a much large dynamic range and frequency response than iron-core CT. Optical fiber Bragg grating current sensor is the most potential important one among the optical current sensors, but its current transferred sensibility and the capability of anti-variance of temperature and stress still in a lower level. In this paper, a copper coated Bragg grating current sensor are described. The sensibility is improved significantly.

The Design and Characterization of a Prototype Wideband Voltage Sensor Based on a Resistive Divider

PubMed Central

Garnacho, Fernando; Khamlichi, Abderrahim; Rovira, Jorge

2017-01-01

The most important advantage of voltage dividers over traditional voltage transformers is that voltage dividers do not have an iron core with non-linear hysteresis characteristics. The voltage dividers have a linear behavior with respect to over-voltages and a flat frequency response larger frequency range. The weak point of a voltage divider is the influence of external high-voltage (HV) and earth parts in its vicinity. Electrical fields arising from high voltages in neighboring phases and from ground conductors and structures are one of their main sources for systematic measurement errors. This paper describes a shielding voltage divider for a 24 kV medium voltage network insulated in SF6 composed of two resistive-capacitive dividers, one integrated within the other, achieving a flat frequency response up to 10 kHz for ratio error and up to 5 kHz for phase displacement error. The metal shielding improves its immunity against electric and magnetic fields. The characterization performed on the built-in voltage sensor shows an accuracy class of 0.2 for a frequency range from 20 Hz to 5 kHz and a class of 0.5 for 1 Hz up to 20 Hz. A low temperature effect is also achieved for operation conditions of MV power grids. PMID:29149085

The Design and Characterization of a Prototype Wideband Voltage Sensor Based on a Resistive Divider.

PubMed

Garnacho, Fernando; Khamlichi, Abderrahim; Rovira, Jorge

2017-11-17

The most important advantage of voltage dividers over traditional voltage transformers is that voltage dividers do not have an iron core with non-linear hysteresis characteristics. The voltage dividers have a linear behavior with respect to over-voltages and a flat frequency response larger frequency range. The weak point of a voltage divider is the influence of external high-voltage (HV) and earth parts in its vicinity. Electrical fields arising from high voltages in neighboring phases and from ground conductors and structures are one of their main sources for systematic measurement errors. This paper describes a shielding voltage divider for a 24 kV medium voltage network insulated in SF6 composed of two resistive-capacitive dividers, one integrated within the other, achieving a flat frequency response up to 10 kHz for ratio error and up to 5 kHz for phase displacement error. The metal shielding improves its immunity against electric and magnetic fields. The characterization performed on the built-in voltage sensor shows an accuracy class of 0.2 for a frequency range from 20 Hz to 5 kHz and a class of 0.5 for 1 Hz up to 20 Hz. A low temperature effect is also achieved for operation conditions of MV power grids.

Voltage control of magnetic single domains in Ni discs on ferroelectric BaTiO3

NASA Astrophysics Data System (ADS)

Ghidini, M.; Zhu, B.; Mansell, R.; Pellicelli, R.; Lesaine, A.; Moya, X.; Crossley, S.; Nair, B.; Maccherozzi, F.; Barnes, C. H. W.; Cowburn, R. P.; Dhesi, S. S.; Mathur, N. D.

2018-06-01

For 1 µm-diameter Ni discs on a BaTiO3 substrate, the local magnetization direction is determined by ferroelectric domain orientation as a consequence of growth strain, such that single-domain discs lie on single ferroelectric domains. On applying a voltage across the substrate, ferroelectric domain switching yields non-volatile magnetization rotations of 90°, while piezoelectric effects that are small and continuous yield non-volatile magnetization reversals that are non-deterministic. This demonstration of magnetization reversal without ferroelectric domain switching implies reduced fatigue, and therefore represents a step towards applications.

Molecular basis of the remarkable species selectivity of an insecticidal sodium channel toxin from the African spider Augacephalus ezendami

NASA Astrophysics Data System (ADS)

Herzig, Volker; Ikonomopoulou, Maria; Smith, Jennifer J.; Dziemborowicz, Sławomir; Gilchrist, John; Kuhn-Nentwig, Lucia; Rezende, Fernanda Oliveira; Moreira, Luciano Andrade; Nicholson, Graham M.; Bosmans, Frank; King, Glenn F.

2016-07-01

The inexorable decline in the armament of registered chemical insecticides has stimulated research into environmentally-friendly alternatives. Insecticidal spider-venom peptides are promising candidates for bioinsecticide development but it is challenging to find peptides that are specific for targeted pests. In the present study, we isolated an insecticidal peptide (Ae1a) from venom of the African spider Augacephalus ezendami (family Theraphosidae). Injection of Ae1a into sheep blowflies (Lucilia cuprina) induced rapid but reversible paralysis. In striking contrast, Ae1a was lethal to closely related fruit flies (Drosophila melanogaster) but induced no adverse effects in the recalcitrant lepidopteran pest Helicoverpa armigera. Electrophysiological experiments revealed that Ae1a potently inhibits the voltage-gated sodium channel BgNaV1 from the German cockroach Blattella germanica by shifting the threshold for channel activation to more depolarized potentials. In contrast, Ae1a failed to significantly affect sodium currents in dorsal unpaired median neurons from the American cockroach Periplaneta americana. We show that Ae1a interacts with the domain II voltage sensor and that sensitivity to the toxin is conferred by natural sequence variations in the S1-S2 loop of domain II. The phyletic specificity of Ae1a provides crucial information for development of sodium channel insecticides that target key insect pests without harming beneficial species.

A Novel High-Sensitivity, Low-Power, Liquid Crystal Temperature Sensor

PubMed Central

Algorri, José Francisco; Urruchi, Virginia; Bennis, Noureddine; Sánchez-Pena, José Manuel

2014-01-01

A novel temperature sensor based on nematic liquid crystal permittivity as a sensing magnitude, is presented. This sensor consists of a specific micrometric structure that gives considerable advantages from other previous related liquid crystal (LC) sensors. The analytical study reveals that permittivity change with temperature is introduced in a hyperbolic cosine function, increasing the sensitivity term considerably. The experimental data has been obtained for ranges from −6 °C to 100 °C. Despite this, following the LC datasheet, theoretical ranges from −40 °C to 109 °C could be achieved. These results have revealed maximum sensitivities of 33 mVrms/°C for certain temperature ranges; three times more than of most silicon temperature sensors. As it was predicted by the analytical study, the micrometric size of the proposed structure produces a high output voltage. Moreover the voltage's sensitivity to temperature response can be controlled by the applied voltage. This response allows temperature measurements to be carried out without any amplification or conditioning circuitry, with very low power consumption. PMID:24721771

Enhanced low current, voltage, and power dissipation measurements via Arduino Uno microcontroller with modified commercially available sensors

NASA Astrophysics Data System (ADS)

Tanner, Meghan; Eckel, Ryan; Senevirathne, Indrajith

The versatility, simplicity, and robustness of Arduino microcontroller architecture have won a huge following with increasingly serious engineering and physical science applications. Arduino microcontroller environment coupled with commercially available sensors have been used to systematically measure, record, and analyze low currents, low voltages and corresponding dissipated power for assessing secondary physical properties in a diverse array of engineering systems. Setup was assembled via breadboard, wire, and simple soldering with an Arduino Uno with ATmega328P microcontroller connected to a PC. The microcontroller was programmed with Arduino Software while the bootloader was used to upload the code. Commercial Hall effect current sensor modules ACS712 and INA169 current shunt monitor was used to measure corresponding low to ultra-low currents and voltages. Stable measurement data was obtained via sensors and compared with corresponding oscilloscope measurements to assess reliability and uncertainty. Sensor breakout boards were modified to enhance the sensitivity of the measurements and to expand the applicability. Discussion of these measurements will focus on capabilities, capacities and limitations of the systems with examples of possible applications. Lock Haven Nanotechnology Program.

Domain wall conductivity in KTiOPO4 crystals

NASA Astrophysics Data System (ADS)

Lindgren, G.; Canalias, C.

2017-07-01

We study the local ionic conductivity of ferroelectric domain walls and domains in KTiOPO4 single-crystals. We show a fourfold increase in conductivity at the domain walls, compared to that of the domains, attributed to an increased concentration of defects. Our current-voltage measurements reveal memristive-like behavior associated with topographic changes and permanent charge displacement. This behavior is observed for all the voltage sweep-rates at the domain walls, while it only occurs for low frequencies at the domains. We attribute these findings to the redistribution of ions due to the applied bias and their effect on the tip-sample barrier.

Design of an Auto-zeroed, Differential, Organic Thin-film Field-effect Transistor Amplifier for Sensor Applications

NASA Technical Reports Server (NTRS)

Binkley, David M.; Verma, Nikhil; Crawford, Robert L.; Brandon, Erik; Jackson, Thomas N.

2004-01-01

Organic strain gauge and other sensors require high-gain, precision dc amplification to process their low-level output signals. Ideally, amplifiers would be fabricated using organic thin-film field-effect transistors (OTFT's) adjacent to the sensors. However, OTFT amplifiers exhibit low gain and high input-referred dc offsets that must be effectively managed. This paper presents a four-stage, cascaded differential OTFT amplifier utilizing switched capacitor auto-zeroing. Each stage provides a nominal voltage gain of four through a differential pair driving low-impedance active loads, which provide common-mode output voltage control. p-type pentacence OTFT's are used for the amplifier devices and auto-zero switches. Simulations indicate the amplifier provides a nominal voltage gain of 280 V/V and effectively amplifies a 1-mV dc signal in the presence of 500-mV amplifier input-referred dc offset voltages. Future work could include the addition of digital gain calibration and offset correction of residual offsets associated with charge injection imbalance in the differential circuits.

Understanding blue-light photoreceptors

NASA Astrophysics Data System (ADS)

Crane, Brian

Blue-light sensing proteins coordinate many biological processes that include phototropism, photomorphism, stress responses, virulence and the entrainment of circadian clocks. Three major types of blue-light sensors all bind flavin nucleotides as chromophores, but the photochemistry employed and conformational responses invoked differ considerably among the classes. Nevertheless, photoinduced electron transfer reactions play a key role in many mechanisms. How such reactivity leads to conformational signaling will be discussed for both cryptochromes (CRYs) and light- oxygen- voltage (LOV) domains. In CRYs, blue-light mediated flavin reduction promotes proton transfer within the active center that then leads to displacement of a key signaling element. For LOV proteins, blue light causes formation of a covalent cysteinyl-flavin adduct, which rearranges hydrogen bonding and restructures the N-terminal region of the protein. Interestingly, a new class of LOV-like sensor does not undergo adduct formation and instead can operate by flavin photoreduction, like CRY. Conserved aspects of reactivity in these proteins provide lessons for the design of new photosensors, which may find use as tools in optogenetics Supported by NIH GM079679.

Study of V-OTDR stability for dynamic strain measurement in piezoelectric vibration

NASA Astrophysics Data System (ADS)

Ren, Meiqi; Lu, Ping; Chen, Liang; Bao, Xiaoyi

2016-09-01

In a phase-sensitive optical-time domain reflectometry (Φ-OTDR) system, the challenge for dynamic strain measurement lies in large intensity fluctuations from trace to trace. The intensity fluctuation caused by stochastic characteristics of Rayleigh backscattering sets detection limit for the minimum strength of vibration measurement and causes the large measurement uncertainty. Thus, a trace-to-trace correlation coefficient is introduced to quantify intensity fluctuation of Φ-OTDR traces and stability of the sensor system theoretically and experimentally. A novel approach of measuring dynamic strain induced by various driving voltages of lead zirconate titanate (PZT) in Φ-OTDR is also demonstrated. Piezoelectric vibration signals are evaluated through analyzing peak values of fast Fourier transform spectra at the fundamental frequency and high-order harmonics based on Bessel functions. High trace-to-trace correlation coefficients varying from 0.824 to 0.967 among 100 measurements are obtained in experimental results, showing the good stability of our sensor system, as well as small uncertainty of measured peak values.

Image sensor system with bio-inspired efficient coding and adaptation.

PubMed

Okuno, Hirotsugu; Yagi, Tetsuya

2012-08-01

We designed and implemented an image sensor system equipped with three bio-inspired coding and adaptation strategies: logarithmic transform, local average subtraction, and feedback gain control. The system comprises a field-programmable gate array (FPGA), a resistive network, and active pixel sensors (APS), whose light intensity-voltage characteristics are controllable. The system employs multiple time-varying reset voltage signals for APS in order to realize multiple logarithmic intensity-voltage characteristics, which are controlled so that the entropy of the output image is maximized. The system also employs local average subtraction and gain control in order to obtain images with an appropriate contrast. The local average is calculated by the resistive network instantaneously. The designed system was successfully used to obtain appropriate images of objects that were subjected to large changes in illumination.

Electro-optic high voltage sensor

DOEpatents

Davidson, James R.; Seifert, Gary D.

2002-01-01

A small sized electro-optic voltage sensor capable of accurate measurement of high levels of voltages without contact with a conductor or voltage source is provided. When placed in the presence of an electric field, the sensor receives an input beam of electromagnetic radiation into the sensor. A polarization beam displacer serves as a filter to separate the input beam into two beams with orthogonal linear polarizations. The beam displacer is oriented in such a way as to rotate the linearly polarized beams such that they enter a Pockels crystal having at a preferred angle of 45 degrees. The beam displacer is therefore capable of causing a linearly polarized beam to impinge a crystal at a desired angle independent of temperature. The Pockels electro-optic effect induces a differential phase shift on the major and minor axes of the input beam as it travels through the Pockels crystal, which causes the input beam to be elliptically polarized. A reflecting prism redirects the beam back through the crystal and the beam displacer. On the return path, the polarization beam displacer separates the elliptically polarized beam into two output beams of orthogonal linear polarization representing the major and minor axes. The system may include a detector for converting the output beams into electrical signals, and a signal processor for determining the voltage based on an analysis of the output beams. The output beams are amplitude modulated by the frequency of the electric field and the amplitude of the output beams is proportional to the magnitude of the electric field, which is related to the voltage being measured.

Eddy Current Method for Fatigue Testing

NASA Technical Reports Server (NTRS)

Simpson, John W. (Inventor); Fulton, James P. (Inventor); Wincheski, Russell A. (Inventor); Todhunter, Ronald G. (Inventor); Namkung, Min (Inventor); Nath, Shridhar C. (Inventor)

1997-01-01

Flux-focusing electromagnetic sensor using a ferromagnetic flux-focusing lens simplifies inspections and increases detectability of fatigue cracks and material loss in high conductivity material. A ferrous shield isolates a high-turn pick-up coil from an excitation coil. Use of the magnetic shield produces a null voltage output across the receiving coil in presence of an unflawed sample. Redistribution of the current flow in the sample caused by the presence of flaws. eliminates the shielding condition and a large output voltage is produced, yielding a clear unambiguous flaw signal. Maximum sensor output is obtained when positioned symmetrically above the crack. By obtaining position of maximum sensor output, it is possible to track the fault and locate the area surrounding its tip. Accuracy of tip location is enhanced by two unique features of the sensor; a very high signal-to-noise ratio of the probe's output resulting in an extremely smooth signal peak across the fault, and a rapidly decaying sensor output outside a small area surrounding the crack tip enabling the search region to be clearly defined. Under low frequency operation, material thinning due to corrosion causes incomplete shielding of the pick-up coil. Low frequency output voltage of the probe is therefore a direct indicator of thickness of the test sample. Fatigue testing a conductive material is accomplished by applying load to the material, applying current to the sensor, scanning the material with the sensor, monitoring the sensor output signal, adjusting material load based on the sensor output signal of the sensor, and adjusting position of the sensor based on its output signal.

Low-Cost Linear Optical Sensors.

ERIC Educational Resources Information Center

Kinsey, Kenneth F.; Meisel, David D.

1994-01-01

Discusses the properties and application of three light-to-voltage optical sensors. The sensors have been used for sensing diffraction patterns, the inverse-square law, and as a fringe counter with an interferometer. (MVL)

Design and calibration of a six-axis MEMS sensor array for use in scoliosis correction surgery

NASA Astrophysics Data System (ADS)

Benfield, David; Yue, Shichao; Lou, Edmond; Moussa, Walied A.

2014-08-01

A six-axis sensor array has been developed to quantify the 3D force and moment loads applied in scoliosis correction surgery. Initially this device was developed to be applied during scoliosis correction surgery and augmented onto existing surgical instrumentation, however, use as a general load sensor is also feasible. The development has included the design, microfabrication, deployment and calibration of a sensor array. The sensor array consists of four membrane devices, each containing piezoresistive sensing elements, generating a total of 16 differential voltage outputs. The calibration procedure has made use of a custom built load application frame, which allows quantified forces and moments to be applied and compared to the outputs from the sensor array. Linear or non-linear calibration equations are generated to convert the voltage outputs from the sensor array back into 3D force and moment information for display or analysis.

Analysis of periplasmic sensor domains from Anaeromyxobacter dehalogenans 2CP-C: Structure of one sensor domain from a histidine kinase and another from a chemotaxis protein

PubMed Central

Pokkuluri, P Raj; Dwulit-Smith, Jeff; Duke, Norma E; Wilton, Rosemarie; Mack, Jamey C; Bearden, Jessica; Rakowski, Ella; Babnigg, Gyorgy; Szurmant, Hendrik; Joachimiak, Andrzej; Schiffer, Marianne

2013-01-01

Anaeromyxobacter dehalogenans is a δ-proteobacterium found in diverse soils and sediments. It is of interest in bioremediation efforts due to its dechlorination and metal-reducing capabilities. To gain an understanding on A. dehalogenans' abilities to adapt to diverse environments we analyzed its signal transduction proteins. The A. dehalogenans genome codes for a large number of sensor histidine kinases (HK) and methyl-accepting chemotaxis proteins (MCP); among these 23 HK and 11 MCP proteins have a sensor domain in the periplasm. These proteins most likely contribute to adaptation to the organism's surroundings. We predicted their three-dimensional folds and determined the structures of two of the periplasmic sensor domains by X-ray diffraction. Most of the domains are predicted to have either PAS-like or helical bundle structures, with two predicted to have solute-binding protein fold, and another predicted to have a 6-phosphogluconolactonase like fold. Atomic structures of two sensor domains confirmed the respective fold predictions. The Adeh_2942 sensor (HK) was found to have a helical bundle structure, and the Adeh_3718 sensor (MCP) has a PAS-like structure. Interestingly, the Adeh_3718 sensor has an acetate moiety bound in a binding site typical for PAS-like domains. Future work is needed to determine whether Adeh_3718 is involved in acetate sensing by A. dehalogenans. PMID:23897711

Binding modes and functional surface of anti-mammalian scorpion α-toxins to sodium channels.

PubMed

Chen, Rong; Chung, Shin-Ho

2012-10-02

Scorpion α-toxins bind to the voltage-sensing domains of voltage-gated sodium (Na(V)) channels and interfere with the inactivation mechanisms. The functional surface of α-toxins has been shown to contain an NC-domain consisting of the five-residue turn (positions 8-12) and the C-terminus (positions 56-64) and a core-domain centered on the residue 18. The NC- and core-domains are interconnected by the linker-domain (positions 8-18). Here with atomistic molecular dynamics simulations, we examine the binding modes between two α-toxins, the anti-mammalian AahII and the anti-insect LqhαIT, and the voltage-sensing domain of rat Na(V)1.2, a subtype of Na(V) channels expressed in nerve cells. Both toxins are docked to the extracellular side of the voltage-sensing domain of Na(V)1.2 using molecular dynamics simulations, with the linker-domain assumed to wedge into the binding pocket. Several salt bridges and hydrophobic clusters are observed to form between the NC- and core-domains of the toxins and Na(V)1.2 and stabilize the toxin-channel complexes. The binding modes predicted are consistent with available mutagenesis data and can readily explain the relative affinities of AahII and LqhαIT for Na(V)1.2. The dissociation constants for the two toxin-channel complexes are derived, which compare favorably with experiment. Our models demonstrate that the functional surface of anti-mammalian scorpion α-toxins is centered on the linker-domain, similar to that of β-toxins.

Electro-chemical coupling in the voltage-dependent phosphatase Ci-VSP

PubMed Central

Kohout, Susy C.; Bell, Sarah C.; Liu, Lijun; Xu, Qiang; Minor, Daniel L.; Isacoff, Ehud Y.

2010-01-01

In the voltage sensing phosphatase, Ci-VSP, a voltage sensing domain (VSD) controls a lipid phosphatase domain (PD). The mechanism by which the domains are allosterically coupled is not well understood. Using an in vivo assay, we find that the inter-domain linker that connects the VSD to the PD is essential for coupling the full-length protein. Biochemical assays show that the linker is also needed for activity in the isolated PD. We identify a late step of VSD motion in the full-length protein that depends on the linker. Strikingly, this VSD motion is found to require PI(4,5)P2, a substrate of Ci-VSP. These results suggest that the voltage-driven motion of the VSD turns the enzyme on by rearranging the linker into an activated conformation, and that this activated conformation is stabilized by PI(4,5)P2. We propose that Ci-VSP activity is self-limited because its decrease of PI(4,5)P2 levels decouples the VSD from the enzyme. PMID:20364128

Wireless Sensor Network for Radiometric Detection and Assessment of Partial Discharge in High-Voltage Equipment

NASA Astrophysics Data System (ADS)

Upton, D. W.; Saeed, B. I.; Mather, P. J.; Lazaridis, P. I.; Vieira, M. F. Q.; Atkinson, R. C.; Tachtatzis, C.; Garcia, M. S.; Judd, M. D.; Glover, I. A.

2018-03-01

Monitoring of partial discharge (PD) activity within high-voltage electrical environments is increasingly used for the assessment of insulation condition. Traditional measurement techniques employ technologies that either require off-line installation or have high power consumption and are hence costly. A wireless sensor network is proposed that utilizes only received signal strength to locate areas of PD activity within a high-voltage electricity substation. The network comprises low-power and low-cost radiometric sensor nodes which receive the radiation propagated from a source of PD. Results are reported from several empirical tests performed within a large indoor environment and a substation environment using a network of nine sensor nodes. A portable PD source emulator was placed at multiple locations within the network. Signal strength measured by the nodes is reported via WirelessHART to a data collection hub where it is processed using a location algorithm. The results obtained place the measured location within 2 m of the actual source location.

Evaluation of low-cost electro-chemical sensors for environmental monitoring of ozone, nitrogen dioxide, and carbon monoxide.

PubMed

Afshar-Mohajer, Nima; Zuidema, Christopher; Sousan, Sinan; Hallett, Laura; Tatum, Marcus; Rule, Ana M; Thomas, Geb; Peters, Thomas M; Koehler, Kirsten

2018-02-01

Development of an air quality monitoring network with high spatio-temporal resolution requires installation of a large number of air pollutant monitors. However, state-of-the-art monitors are costly and may not be compatible with wireless data logging systems. In this study, low-cost electro-chemical sensors manufactured by Alphasense Ltd. for detection of CO and oxidative gases (predominantly O 3 and NO 2 ) were evaluated. The voltages from three oxidative gas sensors and three CO sensors were recorded every 2.5 sec when exposed to controlled gas concentrations in a 0.125-m 3 acrylic glass chamber. Electro-chemical sensors for detection of oxidative gases demonstrated sensitivity to both NO 2 and O 3 with similar voltages recorded when exposed to equivalent environmental concentrations of NO 2 or O 3 gases, when evaluated separately. There was a strong linear relationship between the recorded voltages and target concentrations of oxidative gases (R 2 > 0.98) over a wide range of concentrations. Although a strong linear relationship was also observed for CO concentrations below 12 ppm, a saturation effect was observed wherein the voltage only changes minimally for higher CO concentrations (12-50 ppm). The nonlinear behavior of the CO sensors implied their unsuitability for environments where high CO concentrations are expected. Using a manufacturer-supplied shroud, sensors were tested at 2 different flow rates (0.25 and 0.5 Lpm) to mimic field calibration of the sensors with zero air and a span gas concentration (2 ppm NO2 or 15 ppm CO). As with all electrochemical sensors, the tested devices were subject to drift with a bias up to 20% after 9 months of continuous operation. Alphasense CO sensors were found to be a proper choice for occupational and environmental CO monitoring with maximum concentration of 12 ppm, especially due to the field-ready calibration capability. Alphasense oxidative gas sensors are usable only if it is valuable to know the sum of the NO 2 and O 3 concentrations.

Modal domain fiber optic sensor for closed loop vibration control of a flexible beam

NASA Technical Reports Server (NTRS)

Cox, D.; Thomas, D.; Reichard, K.; Lindner, D.; Claus, R. O.

1990-01-01

The use of a modal domain sensor in a vibration control experiment is described. An optical fiber is bonded along the length of a flexible beam. A control signal derived from the output of the modal domain sensor is used to suppress vibrations induced in the beam. A distributed effect model for the modal domain sensor is developed and combined with models of the beam and actuator dynamics to produce a system suitable for control design.

In search of a consensus model of the resting state of a voltage-sensing domain.

PubMed

Vargas, Ernesto; Bezanilla, Francisco; Roux, Benoît

2011-12-08

Voltage-sensing domains (VSDs) undergo conformational changes in response to the membrane potential and are the critical structural modules responsible for the activation of voltage-gated channels. Structural information about the key conformational states underlying voltage activation is currently incomplete. Through the use of experimentally determined residue-residue interactions as structural constraints, we determine and refine a model of the Kv channel VSD in the resting conformation. The resulting structural model is in broad agreement with results that originate from various labs using different techniques, indicating the emergence of a consensus for the structural basis of voltage sensing. Copyright © 2011 Elsevier Inc. All rights reserved.

A finite state machine read-out chip for integrated surface acoustic wave sensors

NASA Astrophysics Data System (ADS)

Rakshit, Sambarta; Iliadis, Agis A.

2015-01-01

A finite state machine based integrated sensor circuit suitable for the read-out module of a monolithically integrated SAW sensor on Si is reported. The primary sensor closed loop consists of a voltage controlled oscillator (VCO), a peak detecting comparator, a finite state machine (FSM), and a monolithically integrated SAW sensor device. The output of the system oscillates within a narrow voltage range that correlates with the SAW pass-band response. The period of oscillation is of the order of the SAW phase delay. We use timing information from the FSM to convert SAW phase delay to an on-chip 10 bit digital output operating on the principle of time to digital conversion (TDC). The control inputs of this digital conversion block are generated by a second finite state machine operating under a divided system clock. The average output varies with changes in SAW center frequency, thus tracking mass sensing events in real time. Based on measured VCO gain of 16 MHz/V our system will convert a 10 kHz SAW frequency shift to a corresponding mean voltage shift of 0.7 mV. A corresponding shift in phase delay is converted to a one or two bit shift in the TDC output code. The system can handle alternate SAW center frequencies and group delays simply by adjusting the VCO control and TDC delay control inputs. Because of frequency to voltage and phase to digital conversion, this topology does not require external frequency counter setups and is uniquely suitable for full monolithic integration of autonomous sensor systems and tags.

A solar charge and discharge controller for wireless sensor nodes

NASA Astrophysics Data System (ADS)

Dang, Yibo; Shen, Shu

2018-02-01

Aiming at the energy supply problem that restricts the life of wireless sensor nodes, a solar energy charge and discharge controller suitable for wireless sensor nodes is designed in this paper. A Microcontroller is used as the core of the solar charge and discharge controller. The software of the solar charge and discharge controller adopts the C language to realize the program of the main control module. Firstly, the function of monitoring solar panel voltage and lithium battery voltage are simulated by Protel software, and the charge time is tested in cloudy and overcast outdoor environment. The results of the experiment show that our controller meets the power supply demand of wireless sensor nodes.

Development of N+ in P pixel sensors for a high-luminosity large hadron collider

NASA Astrophysics Data System (ADS)

Kamada, Shintaro; Yamamura, Kazuhisa; Unno, Yoshinobu; Ikegami, Yoichi

2014-11-01

Hamamatsu Photonics K. K. is developing an N+ in a p planar pixel sensor with high radiation tolerance for the high-luminosity large hadron collider (HL-LHC). The N+ in the p planar pixel sensor is a candidate for the HL-LHC and offers the advantages of high radiation tolerance at a reasonable price compared with the N+ in an n planar sensor, the three-dimensional sensor, and the diamond sensor. However, the N+ in the p planar pixel sensor still presents some problems that need to be solved, such as its slim edge and the danger of sparks between the sensor and readout integrated circuit. We are now attempting to solve these problems with wafer-level processes, which is important for mass production. To date, we have obtained a 250-μm edge with an applied bias voltage of 1000 V. To protect against high-voltage sparks from the edge, we suggest some possible designs for the N+ edge.

A novel NaV1.5 voltage sensor mutation associated with severe atrial and ventricular arrhythmias.

PubMed

Wang, Hong-Gang; Zhu, Wandi; Kanter, Ronald J; Silva, Jonathan R; Honeywell, Christina; Gow, Robert M; Pitt, Geoffrey S

2016-03-01

Inherited autosomal dominant mutations in cardiac sodium channels (NaV1.5) cause various arrhythmias, such as long QT syndrome and Brugada syndrome. Although dozens of mutations throughout the protein have been reported, there are few reported mutations within a voltage sensor S4 transmembrane segment and few that are homozygous. Here we report analysis of a novel lidocaine-sensitive recessive mutation, p.R1309H, in the NaV1.5 DIII/S4 voltage sensor in a patient with a complex arrhythmia syndrome. We expressed the wild type or mutant NaV1.5 heterologously for analysis with the patch-clamp and voltage clamp fluorometry (VCF) techniques. p.R1309H depolarized the voltage-dependence of activation, hyperpolarized the voltage-dependence of inactivation, and slowed recovery from inactivation, thereby reducing the channel availability at physiologic membrane potentials. Additionally, p.R1309H increased the "late" Na(+) current. The location of the mutation in DIIIS4 prompted testing for a gating pore current. We observed an inward current at hyperpolarizing voltages that likely exacerbates the loss-of-function defects at resting membrane potentials. Lidocaine reduced the gating pore current. The p.R1309H homozygous NaV1.5 mutation conferred both gain-of-function and loss-of-function effects on NaV1.5 channel activity. Reduction of a mutation-induced gating pore current by lidocaine suggested a therapeutic mechanism. Copyright © 2016 Elsevier Ltd. All rights reserved.

alpha-helical structural elements within the voltage-sensing domains of a K(+) channel.

PubMed

Li-Smerin, Y; Hackos, D H; Swartz, K J

2000-01-01

Voltage-gated K(+) channels are tetramers with each subunit containing six (S1-S6) putative membrane spanning segments. The fifth through sixth transmembrane segments (S5-S6) from each of four subunits assemble to form a central pore domain. A growing body of evidence suggests that the first four segments (S1-S4) comprise a domain-like voltage-sensing structure. While the topology of this region is reasonably well defined, the secondary and tertiary structures of these transmembrane segments are not. To explore the secondary structure of the voltage-sensing domains, we used alanine-scanning mutagenesis through the region encompassing the first four transmembrane segments in the drk1 voltage-gated K(+) channel. We examined the mutation-induced perturbation in gating free energy for periodicity characteristic of alpha-helices. Our results are consistent with at least portions of S1, S2, S3, and S4 adopting alpha-helical secondary structure. In addition, both the S1-S2 and S3-S4 linkers exhibited substantial helical character. The distribution of gating perturbations for S1 and S2 suggest that these two helices interact primarily with two environments. In contrast, the distribution of perturbations for S3 and S4 were more complex, suggesting that the latter two helices make more extensive protein contacts, possibly interfacing directly with the shell of the pore domain.

The Molecular Basis of Polyunsaturated Fatty Acid Interactions with the Shaker Voltage-Gated Potassium Channel

PubMed Central

Yazdi, Samira; Stein, Matthias; Elinder, Fredrik; Andersson, Magnus; Lindahl, Erik

2016-01-01

Voltage-gated potassium (KV) channels are membrane proteins that respond to changes in membrane potential by enabling K+ ion flux across the membrane. Polyunsaturated fatty acids (PUFAs) induce channel opening by modulating the voltage-sensitivity, which can provide effective treatment against refractory epilepsy by means of a ketogenic diet. While PUFAs have been reported to influence the gating mechanism by electrostatic interactions to the voltage-sensor domain (VSD), the exact PUFA-protein interactions are still elusive. In this study, we report on the interactions between the Shaker KV channel in open and closed states and a PUFA-enriched lipid bilayer using microsecond molecular dynamics simulations. We determined a putative PUFA binding site in the open state of the channel located at the protein-lipid interface in the vicinity of the extracellular halves of the S3 and S4 helices of the VSD. In particular, the lipophilic PUFA tail covered a wide range of non-specific hydrophobic interactions in the hydrophobic central core of the protein-lipid interface, while the carboxylic head group displayed more specific interactions to polar/charged residues at the extracellular regions of the S3 and S4 helices, encompassing the S3-S4 linker. Moreover, by studying the interactions between saturated fatty acids (SFA) and the Shaker KV channel, our study confirmed an increased conformational flexibility in the polyunsaturated carbon tails compared to saturated carbon chains, which may explain the specificity of PUFA action on channel proteins. PMID:26751683

Deconvolution of Voltage Sensor Time Series and Electro-diffusion Modeling Reveal the Role of Spine Geometry in Controlling Synaptic Strength.

PubMed

Cartailler, Jerome; Kwon, Taekyung; Yuste, Rafael; Holcman, David

2018-03-07

Most synaptic excitatory connections are made on dendritic spines. But how the voltage in spines is modulated by its geometry remains unclear. To investigate the electrical properties of spines, we combine voltage imaging data with electro-diffusion modeling. We first present a temporal deconvolution procedure for the genetically encoded voltage sensor expressed in hippocampal cultured neurons and then use electro-diffusion theory to compute the electric field and the current-voltage conversion. We extract a range for the neck resistances of 〈R〉=100±35MΩ. When a significant current is injected in a spine, the neck resistance can be inversely proportional to its radius, but not to the radius square, as predicted by Ohm's law. We conclude that the postsynaptic voltage cannot only be modulated by changing the number of receptors, but also by the spine geometry. Thus, spine morphology could be a key component in determining synaptic transduction and plasticity. Copyright © 2018 Elsevier Inc. All rights reserved.

Charge immobilization of the voltage sensor in domain IV is independent of sodium current inactivation.

PubMed

Sheets, Michael F; Hanck, Dorothy A

2005-02-15

Recovery from fast inactivation in voltage-dependent Na+ channels is associated with a slow component in the time course of gating charge during repolarization (i.e. charge immobilization), which results from the slow movement of the S4 segments in domains III and IV (S4-DIII and S4-DIV). Previous studies have shown that the non-specific removal of fast inactivation by the proteolytic enzyme pronase eliminated charge immobilization, while the specific removal of fast inactivation (by intracellular MTSET modification of a cysteine substituted for the phenylalanine in the IFM motif, ICMMTSET, in the inactivation particle formed by the linker between domains III and IV) only reduced the amount of charge immobilization by nearly one-half. To investigate the molecular origin of the remaining slow component of charge immobilization we studied the human cardiac Na+ channel (hH1a) in which the outermost arginine in the S4-DIV, which contributes approximately 20% to total gating charge (Qmax), was mutated to a cysteine (R1C-DIV). Gating charge could be fully restored in R1C-DIV by exposure to extracellular MTSEA, a positively charged methanethiosulphonate reagent. The RIC-DIV mutation was combined with ICMMTSET to remove fast inactivation, and the gating currents of R1C-DIV-ICM(MTSET) were recorded before and after modification with MTSEAo. Prior to MTSEAo, the time course of the gating charge during repolarization (off-charge) was best described by a single fast time constant. After MTSEA, the off-charge had both fast and slow components, with the slow component accounting for nearly 35% of Qmax. These results demonstrate that the slow movement of the S4-DIV during repolarization is not dependent upon the normal binding of the inactivation particle.

An All Oxide-Based Imperceptible Thin-Film Transistor with Humidity Sensing Properties

PubMed Central

Kim, Kyung Su; Ahn, Cheol Hyoun; Kang, Won Jun; Cho, Sung Woon; Jung, Sung Hyeon; Yoon, Dae Ho; Cho, Hyung Koun

2017-01-01

We have examined the effects of oxygen content and thickness in sputtered InSnO (ITO) electrodes, especially for the application of imperceptible amorphous-InGaZnO (a-IGZO) thin-film transistors (TFTs) in humidity sensors. The imperceptible a-IGZO TFT with 50-nm ITO electrodes deposited at Ar:O2 = 29:0.3 exhibited good electrical performances with Vth of −0.23 V, SS of 0.34 V/dec, µFE of 7.86 cm2/V∙s, on/off ratio of 8.8 × 107, and has no degradation for bending stress up to a 3.5-mm curvature. The imperceptible oxide TFT sensors showed the highest sensitivity for the low and wide gate bias of −1~2 V under a wide range of relative humidity (40–90%) at drain voltage 1 V, resulting in low power consumption by the sensors. Exposure to water vapor led to a negative shift in the threshold voltage (or current enhancement), and an increase in relative humidity induced continuous threshold voltage shift. In particular, compared to conventional resistor-type sensors, the imperceptible oxide TFT sensors exhibited extremely high sensitivity from a current amplification of >103. PMID:28772888

An All Oxide-Based Imperceptible Thin-Film Transistor with Humidity Sensing Properties.

PubMed

Kim, Kyung Su; Ahn, Cheol Hyoun; Kang, Won Jun; Cho, Sung Woon; Jung, Sung Hyeon; Yoon, Dae Ho; Cho, Hyung Koun

2017-05-13

We have examined the effects of oxygen content and thickness in sputtered InSnO (ITO) electrodes, especially for the application of imperceptible amorphous-InGaZnO ( a -IGZO) thin-film transistors (TFTs) in humidity sensors. The imperceptible a -IGZO TFT with 50-nm ITO electrodes deposited at Ar:O₂ = 29:0.3 exhibited good electrical performances with V th of -0.23 V, SS of 0.34 V/dec, µ FE of 7.86 cm²/V∙s, on/off ratio of 8.8 × 10⁷, and has no degradation for bending stress up to a 3.5-mm curvature. The imperceptible oxide TFT sensors showed the highest sensitivity for the low and wide gate bias of -1~2 V under a wide range of relative humidity (40-90%) at drain voltage 1 V, resulting in low power consumption by the sensors. Exposure to water vapor led to a negative shift in the threshold voltage (or current enhancement), and an increase in relative humidity induced continuous threshold voltage shift. In particular, compared to conventional resistor-type sensors, the imperceptible oxide TFT sensors exhibited extremely high sensitivity from a current amplification of >10³.

The First Extracellular Linker Is Important for Several Aspects of the Gating Mechanism of Human TRPA1 Channel

PubMed Central

Marsakova, Lenka; Barvik, Ivan; Zima, Vlastimil; Zimova, Lucie; Vlachova, Viktorie

2017-01-01

Transient receptor potential ankyrin 1 (TRPA1) is an excitatory ion channel involved in pain, inflammation and itching. This channel gates in response to many irritant and proalgesic agents, and can be modulated by calcium and depolarizing voltage. While the closed-state structure of TRPA1 has been recently resolved, also having its open state is essential for understanding how this channel works. Here we use molecular dynamics simulations combined with electrophysiological measurements and systematic mutagenesis to predict and explore the conformational changes coupled to the expansion of the presumptive channel's lower gate. We show that, upon opening, the upper part of the sensor module approaches the pore domain of an adjacent subunit and the conformational dynamics of the first extracellular flexible loop may govern the voltage-dependence of multimodal gating, thereby serving to stabilize the open state of the channel. These results are generally important in understanding the structure and function of TRPA1 and offer new insights into the gating mechanism of TRPA1 and related channels. PMID:28197074

Carbon monoxide gas sensing using zinc oxide deposited by successive ionic layer adhesion and reaction

NASA Astrophysics Data System (ADS)

Florido, E. A.; Dagaas, N. A. C.

2017-05-01

This study was aimed to determine the carbon monoxide (CO) gas sensing capability of zinc oxide (ZnO) film fabricated by successive ionic layer adsorption and reaction (SILAR) on glass substrate. Films consisting of a mixture of flower-like clusters of ZnO nanorods and nanowires were observed using scanning electron microscopy (SEM). Current-voltage characterization of the samples showed an average resistivity of 13.0 Ω-m. Carbon monoxide gas was synthesized by mixing the required amount of formic acid and excess sulfuric acid to produce CO gas concentrations of 100, 200, 300, 400, and 500 parts per million (ppm) v/v with five trials for each concentration. Two sets of data were obtained. One set consisted of the voltage response of the single film sensor while the other set were obtained from the double film sensor. The voltage response for the single film sensor and the double film sensor showed an average sensitivity of 0.0038 volts per ppm and 0.0024 volts per ppm, respectively. The concentration the single film can detect with a 2V output is 526 ppm while the double film sensor can detect up to 833 ppm with a 2V output. This shows that using the double film sensor is advantageous compared to single film sensor, because of its higher concentration range due to the larger surface area for the gas to interact. Moreover, the measured average resistance for the single film sensor was 10 MΩ while for the double film sensor the average resistance was 5 MΩ.

The Integration and Applications of Organic Thin Film Transistors and Ferroelectric Polymers

NASA Astrophysics Data System (ADS)

Hsu, Yu-Jen

Organic thin film transistors and ferroelectric polymer (polyvinylidene difluoride) sheet material are integrated to form various sensors for stress/strain, acoustic wave, and Infrared (heat) sensing applications. Different from silicon-based transistors, organic thin film transistors can be fabricated and processed in room-temperature and integrated with a variety of substrates. On the other hand, polyvinylidene difluoride (PVDF) exhibits ferroelectric properties that are highly useful for sensor applications. The wide frequency bandwidth (0.001 Hz to 10 GHz), vast dynamic range (100n to 10M psi), and high elastic compliance (up to 3 percent) make PVDF a more suitable candidate over ceramic piezoelectric materials for thin and flexible sensor applications. However, the low Curie temperature may have impeded its integration with silicon technology. Organic thin film transistors, however, do not have the limitation of processing temperature, hence can serve as transimpedance amplifiers to convert the charge signal generated by PVDF into current signal that are more measurable and less affected by any downstream parasitics. Piezoelectric sensors are useful for a range of applications, but passive arrays suffer from crosstalk and signal attenuation which have complicated the development of array-based PVDF sensors. We have used organic field effect transistors, which are compatible with the low Curie temperature of a flexible piezoelectric polymer,PVDF, to monolithically fabricate transimpedance amplifiers directly on the sensor surface and convert the piezoelectric charge signal into a current signal which can be detected even in the presence of parasitic capacitances. The device couples the voltage generated by the PVDF film under strain into the gate of the organic thin film transistors (OFET) using an arrangement that allows the full piezoelectric voltage to couple to the channel, while also increasing the charge retention time. A bipolar detector is created by using a UV-Ozone treatment to shift the threshold voltage and increase the current of the transistor under both compressive and tensile strain. An array of strain sensors which maps the strain field on a PVDF film surface is demonstrated in this work. The strain sensor experience inspires a tone analyzer built using distributed resonator architecture on a tensioned piezoelectric PVDF sheet. This sheet is used as both the resonator and detection element. Two architectures are demonstrated; one uses distributed directly addressed elements as a proof of concept, and the other integrates organic thin film transistor-based transimpedance amplifiers monolithically with the PVDF sheet to convert the piezoelectric charge signal into a current signal for future applications such as sound field imaging. The PVDF sheet material is instrumented along its length and the amplitude response at 15 sites is recorded and analyzed as a function of the frequency of excitation. The determination of the dominant frequency component of an incoming sound is demonstrated using linear system decomposition of the time-averaged response of the sheet using no time domain detection. Our design allows for the determination of the spectral composition of a sound using the mechanical signal processing provided by the amplitude response and eliminates the need for time-domain electronic signal processing of the incoming signal. The concepts of the PVDF strain sensor and the tone analyzer trigger the idea of an active matrix microphone through the integration of organic thin film transistors with a freestanding piezoelectric polymer sheet. Localized acoustic pressure detection is enabled by switch transistors and local transimpedance amplification built into the active matrix architecture. The frequency of detection ranges from DC to 15KHz; the bandwidth is extended using an architecture that provides for virtually zero gate/source and gate/drain capacitance at the sensing transistors and low overlap capacitance at the switch transistors. A series of measurements are taken to demonstrate localized acoustic wave detection, high pitch sound diffraction pattern mapping, and directional listening. This system permits the direct visualization of a two dimensional sound field in a format that was previously inaccessible. In addition to the piezoelectric property, pyroelectricity is also exhibited by PVDF and is essential in the world of sensors. An integration of PVDF and OFET for the IR heat sensing is demonstrated to prove the concept of converting pyroelectric charge signal to a electric current signal. The basic pyroelectricity of PVDF sheet is first examined before making a organic transistor integrated IR sensor. Then, two types of architectures are designed and tested. The first one uses the structure similar to the PVDF strain sensor, and the second one uses a PVDF capacitor to gate the integrated OFETs. The conversion from pyroelectric signal to transistor current signal is observed and characterized. This design provides a flexible and gain-tunable version for IR heat sensors.

Light regulates attachment, exopolysaccharide production, and nodulation in Rhizobium leguminosarum through a LOV-histidine kinase photoreceptor

PubMed Central

Bonomi, Hernán R.; Posadas, Diana M.; Paris, Gastón; Carrica, Mariela del Carmen; Frederickson, Marcus; Pietrasanta, Lía Isabel; Bogomolni, Roberto A.; Zorreguieta, Angeles; Goldbaum, Fernando A.

2012-01-01

Rhizobium leguminosarum is a soil bacterium that infects root hairs and induces the formation of nitrogen-fixing nodules on leguminous plants. Light, oxygen, and voltage (LOV)-domain proteins are blue-light receptors found in higher plants and many algae, fungi, and bacteria. The genome of R. leguminosarum bv. viciae 3841, a pea-nodulating endosymbiont, encodes a sensor histidine kinase containing a LOV domain at the N-terminal end (R-LOV-HK). R-LOV-HK has a typical LOV domain absorption spectrum with broad bands in the blue and UV-A regions and shows a truncated photocycle. Here we show that the R-LOV-HK protein regulates attachment to an abiotic surface and production of flagellar proteins and exopolysaccharide in response to light. Also, illumination of bacterial cultures before inoculation of pea roots increases the number of nodules per plant and the number of intranodular bacteroids. The effects of light on nodulation are dependent on a functional lov gene. The results presented in this work suggest that light, sensed by R-LOV-HK, is an important environmental factor that controls adaptive responses and the symbiotic efficiency of R. leguminosarum. PMID:22773814

Blue light-induced LOV domain dimerization enhances the affinity of Aureochrome 1a for its target DNA sequence

PubMed Central

Heintz, Udo; Schlichting, Ilme

2016-01-01

The design of synthetic optogenetic tools that allow precise spatiotemporal control of biological processes previously inaccessible to optogenetic control has developed rapidly over the last years. Rational design of such tools requires detailed knowledge of allosteric light signaling in natural photoreceptors. To understand allosteric communication between sensor and effector domains, characterization of all relevant signaling states is required. Here, we describe the mechanism of light-dependent DNA binding of the light-oxygen-voltage (LOV) transcription factor Aureochrome 1a from Phaeodactylum tricornutum (PtAu1a) and present crystal structures of a dark state LOV monomer and a fully light-adapted LOV dimer. In combination with hydrogen/deuterium-exchange, solution scattering data and DNA-binding experiments, our studies reveal a light-sensitive interaction between the LOV and basic region leucine zipper DNA-binding domain that together with LOV dimerization results in modulation of the DNA affinity of PtAu1a. We discuss the implications of these results for the design of synthetic LOV-based photosensors with application in optogenetics. DOI: http://dx.doi.org/10.7554/eLife.11860.001 PMID:26754770

Superior Sensor Making Sense in Military, Medicine

NASA Technical Reports Server (NTRS)

2004-01-01

A fiber-optic voltage sensor developed a decade ago for NASA's aircraft and space power systems has been the building block for a string of new sensor products offering safe, accurate detection and measurement for electrically noisy and hazardous environments.

Gating of the two-pore cation channel AtTPC1 in the plant vacuole is based on a single voltage-sensing domain.

PubMed

Jaślan, D; Mueller, T D; Becker, D; Schultz, J; Cuin, T A; Marten, I; Dreyer, I; Schönknecht, G; Hedrich, R

2016-09-01

The two-pore cation channel TPC1 operates as a dimeric channel in animal and plant endomembranes. Each subunit consists of two homologous Shaker-like halves, with 12 transmembrane domains in total (S1-S6, S7-S12). In plants, TPC1 channels reside in the vacuolar membrane, and upon voltage stimulation, give rise to the well-known slow-activating SV currents. Here, we combined bioinformatics, structure modelling, site-directed mutagenesis, and in planta patch clamp studies to elucidate the molecular mechanisms of voltage-dependent channel gating in TPC1 in its native plant background. Structure-function analysis of the Arabidopsis TPC1 channel in planta confirmed that helix S10 operates as the major voltage-sensing site, with Glu450 and Glu478 identified as possible ion-pair partners for voltage-sensing Arg537. The contribution of helix S4 to voltage sensing was found to be negligible. Several conserved negative residues on the luminal site contribute to calcium binding, stabilizing the closed channel. During evolution of plant TPC1s from two separate Shaker-like domains, the voltage-sensing function in the N-terminal Shaker-unit (S1-S4) vanished. © 2016 German Botanical Society and The Royal Botanical Society of the Netherlands.

Fiber-coupled LED gas sensor and its application to online monitoring of ecoefficient dielectric insulation gases in high-voltage circuit breakers.

PubMed

Kramer, Axel; Over, Daniel; Stoller, Patrick; Paul, Thomas A

2017-05-20

Novel dielectric insulation gases used as alternatives to sulfur hexafluoride in gas-insulated switchgear (GIS) include several mixtures containing fluorinated organic compounds. We developed a fiber-optic analyzer enabling concentration measurement of fluoroketones used in medium- and high-voltage switchgear applications by ABB, with concurrent compensation of disturbing effects caused by dust and dirt. The sensor enables measurements in GIS and even in operating high-voltage circuit breakers. The online availability of concentration readings of fluoroketones is important for development tests, but can also be applied for monitoring or diagnostics of field installations.

A pH sensor with a double-gate silicon nanowire field-effect transistor

NASA Astrophysics Data System (ADS)

Ahn, Jae-Hyuk; Kim, Jee-Yeon; Seol, Myeong-Lok; Baek, David J.; Guo, Zheng; Kim, Chang-Hoon; Choi, Sung-Jin; Choi, Yang-Kyu

2013-02-01

A pH sensor composed of a double-gate silicon nanowire field-effect transistor (DG Si-NW FET) is demonstrated. The proposed DG Si-NW FET allows the independent addressing of the gate voltage and hence improves the sensing capability through an application of asymmetric gate voltage between the two gates. One gate is a driving gate which controls the current flow, and the other is a supporting gate which amplifies the shift of the threshold voltage, which is a sensing metric, and which arises from changes in the pH. The pH signal is also amplified through modulation of the gate oxide thickness.

Magnetic sensor for high temperature using a laminate composite of magnetostrictive material and piezoelectric material

NASA Astrophysics Data System (ADS)

Ueno, Toshiyuki; Higuchi, Toshiro

2005-05-01

A high sensitive and heat-resistive magnetic sensor using a magnetostrictive/piezoelectric laminate composite is investigated. The sensing principle is based on the magnetostrictive- and piezoelectric effect, whereby a detected yoke displacement is transduced into a voltage on the piezoelectric materials. The sensor is intended to detect the displacement of a ferromagnetic object in a high temperature environment, where conventional magnetic sensors are not useful. Such applications include sensors in engine of automobile and machinery used in material processing. The sensor features combination of a laminate composite of magnetostrictive/piezoelectric materials with high Curie temperatures and an appropriate magnetic circuit to convert mechanical displacement to sensor voltages and suppress temperature fluctuation. This paper describes the sensing principle and shows experimental results using a composite of Terfenol-D and Lithium Niobate to assure high sensitivity of 50V/mm at bias gap of 0.1mm and a temperature operating range over 200 °C.

Structure of a eukaryotic voltage-gated sodium channel at near-atomic resolution.

PubMed

Shen, Huaizong; Zhou, Qiang; Pan, Xiaojing; Li, Zhangqiang; Wu, Jianping; Yan, Nieng

2017-03-03

Voltage-gated sodium (Na v ) channels are responsible for the initiation and propagation of action potentials. They are associated with a variety of channelopathies and are targeted by multiple pharmaceutical drugs and natural toxins. Here, we report the cryogenic electron microscopy structure of a putative Na v channel from American cockroach (designated Na v PaS) at 3.8 angstrom resolution. The voltage-sensing domains (VSDs) of the four repeats exhibit distinct conformations. The entrance to the asymmetric selectivity filter vestibule is guarded by heavily glycosylated and disulfide bond-stabilized extracellular loops. On the cytoplasmic side, a conserved amino-terminal domain is placed below VSD I , and a carboxy-terminal domain binds to the III-IV linker. The structure of Na v PaS establishes an important foundation for understanding function and disease mechanism of Na v and related voltage-gated calcium channels. Copyright © 2017, American Association for the Advancement of Science.

Microhotplate Temperature Sensor Calibration and BIST.

PubMed

Afridi, M; Montgomery, C; Cooper-Balis, E; Semancik, S; Kreider, K G; Geist, J

2011-01-01

In this paper we describe a novel long-term microhotplate temperature sensor calibration technique suitable for Built-In Self Test (BIST). The microhotplate thermal resistance (thermal efficiency) and the thermal voltage from an integrated platinum-rhodium thermocouple were calibrated against a freshly calibrated four-wire polysilicon microhotplate-heater temperature sensor (heater) that is not stable over long periods of time when exposed to higher temperatures. To stress the microhotplate, its temperature was raised to around 400 °C and held there for days. The heater was then recalibrated as a temperature sensor, and microhotplate temperature measurements were made based on the fresh calibration of the heater, the first calibration of the heater, the microhotplate thermal resistance, and the thermocouple voltage. This procedure was repeated 10 times over a period of 80 days. The results show that the heater calibration drifted substantially during the period of the test while the microhotplate thermal resistance and the thermocouple-voltage remained stable to within about plus or minus 1 °C over the same period. Therefore, the combination of a microhotplate heater-temperature sensor and either the microhotplate thermal resistance or an integrated thin film platinum-rhodium thermocouple can be used to provide a stable, calibrated, microhotplate-temperature sensor, and the combination of the three sensor is suitable for implementing BIST functionality. Alternatively, if a stable microhotplate-heater temperature sensor is available, such as a properly annealed platinum heater-temperature sensor, then the thermal resistance of the microhotplate and the electrical resistance of the platinum heater will be sufficient to implement BIST. It is also shown that aluminum- and polysilicon-based temperature sensors, which are not stable enough for measuring high microhotplate temperatures (>220 °C) without impractically frequent recalibration, can be used to measure the silicon substrate temperature if never exposed to temperatures above about 220 °C.

A CMOS Luminescence Intensity and Lifetime Dual Sensor Based on Multicycle Charge Modulation.

PubMed

Fu, Guoqing; Sonkusale, Sameer R

2018-06-01

Luminescence plays an important role in many scientific and industrial applications. This paper proposes a novel complementary metal-oxide-semiconductor (CMOS) sensor chip that can realize both luminescence intensity and lifetime sensing. To enable high sensitivity, we propose parasitic insensitive multicycle charge modulation scheme for low-light lifetime extraction benefiting from simplicity, accuracy, and compatibility with deeply scaled CMOS process. The designed in-pixel capacitive transimpedance amplifier (CTIA) based structure is able to capture the weak luminescence-induced voltage signal by accumulating photon-generated charges in 25 discrete gated 10-ms time windows and 10-μs pulsewidth. A pinned photodiode on chip with 1.04 pA dark current is utilized for luminescence detection. The proposed CTIA-based circuitry can achieve 2.1-mV/(nW/cm 2 ) responsivity and 4.38-nW/cm 2 resolution at 630 nm wavelength for intensity measurement and 45-ns resolution for lifetime measurement. The sensor chip is employed for measuring time constants and luminescence lifetimes of an InGaN-based white light-emitting diode at different wavelengths. In addition, we demonstrate accurate measurement of the lifetime of an oxygen sensitive chromophore with sensitivity to oxygen concentration of 7.5%/ppm and 6%/ppm in both intensity and lifetime domain. This CMOS-enabled oxygen sensor was then employed to test water quality from different sources (tap water, lakes, and rivers).

Foundry Technologies Focused on Environmental and Ecological Applications

NASA Astrophysics Data System (ADS)

Roizin, Ya.; Lisiansky, M.; Pikhay, E.

Solutions allowing fabrication of remote control systems with integrated sensors (motes) were introduced as a part of CMOS foundry production platform and verified on silicon. The integrated features include sensors employing principles previously verified in the development of ultra-low power consuming non-volatile memories (C-Flash, MRAM) and components allowing low-power energy harvesting (low voltage rectifiers, high -voltage solar cells). The developed systems are discussed with emphasis on their environmental and security applications.

System and method for calibrating a rotary absolute position sensor

NASA Technical Reports Server (NTRS)

Davis, Donald R. (Inventor); Permenter, Frank Noble (Inventor); Radford, Nicolaus A (Inventor)

2012-01-01

A system includes a rotary device, a rotary absolute position (RAP) sensor generating encoded pairs of voltage signals describing positional data of the rotary device, a host machine, and an algorithm. The algorithm calculates calibration parameters usable to determine an absolute position of the rotary device using the encoded pairs, and is adapted for linearly-mapping an ellipse defined by the encoded pairs to thereby calculate the calibration parameters. A method of calibrating the RAP sensor includes measuring the rotary position as encoded pairs of voltage signals, linearly-mapping an ellipse defined by the encoded pairs to thereby calculate the calibration parameters, and calculating an absolute position of the rotary device using the calibration parameters. The calibration parameters include a positive definite matrix (A) and a center point (q) of the ellipse. The voltage signals may include an encoded sine and cosine of a rotary angle of the rotary device.

Sensors for Using Times of Flight to Measure Flow Velocities

NASA Technical Reports Server (NTRS)

Fralick, Gutave; Wrbanek, John D.; Hwang, Danny; Turso, James

2006-01-01

Thin-film sensors for measuring flow velocities in terms of times of flight are undergoing development. These sensors are very small and can be mounted flush with surfaces of airfoils, ducts, and other objects along which one might need to measure flows. Alternatively or in addition, these sensors can be mounted on small struts protruding from such surfaces for acquiring velocity measurements at various distances from the surfaces for the purpose of obtaining boundary-layer flow-velocity profiles. These sensors are related to, but not the same as, hot-wire anemometers. Each sensor includes a thin-film, electrically conductive loop, along which an electric current is made to flow to heat the loop to a temperature above that of the surrounding fluid. Instantaneous voltage fluctuations in segments of the loop are measured by means of electrical taps placed at intervals along the loop. These voltage fluctuations are caused by local fluctuations in electrical resistance that are, in turn, caused by local temperature fluctuations that are, in turn, caused by fluctuations in flow-induced cooling and, hence, in flow velocity. The differential voltage as a function of time, measured at each pair of taps, is subjected to cross-correlation processing with the corresponding quantities measured at other pairs of taps at different locations on the loop. The cross-correlations yield the times taken by elements of fluid to travel between the pairs of taps. Then the component of velocity along the line between any two pairs of taps is calculated simply as the distance between the pairs of taps divided by the travel time. Unlike in the case of hot-wire anemometers, there is no need to obtain calibration data on voltage fluctuations versus velocity fluctuations because, at least in principle, the correlation times are independent of the calibration data.

Characterization of the Functional Domains of a Mammalian Voltage-Sensitive Phosphatase.

PubMed

Rosasco, Mario G; Gordon, Sharona E; Bajjalieh, Sandra M

2015-12-15

Voltage-sensitive phosphatases (VSPs) are proteins that directly couple changes in membrane electrical potential to inositol lipid phosphatase activity. VSPs thus couple two signaling pathways that are critical for cellular functioning. Although a number of nonmammalian VSPs have been characterized biophysically, mammalian VSPs are less well understood at both the physiological and biophysical levels. In this study, we aimed to address this gap in knowledge by determining whether the VSP from mouse, Mm-VSP, is expressed in the brain and contains a functional voltage-sensing domain (VSD) and a phosphatase domain. We report that Mm-VSP is expressed in neurons and is developmentally regulated. To address whether the functions of the VSD and phosphatase domain are retained in Mm-VSP, we took advantage of the modular nature of these domains and expressed each independently as a chimeric protein in a heterologous expression system. We found that the Mm-VSP VSD, fused to a viral potassium channel, was able to drive voltage-dependent gating of the channel pore. The Mm-VSP phosphatase domain, fused to the VSD of a nonmammalian VSP, was also functional: activation resulted in PI(4,5)P2 depletion that was sufficient to inhibit the PI(4,5)P2-regulated KCNQ2/3 channels. While testing the functionality of the VSD and phosphatase domain, we observed slight differences between the activities of Mm-VSP-based chimeras and those of nonmammalian VSPs. Although the properties of VSP chimeras may not completely reflect the properties of native VSPs, the differences we observed in voltage-sensing and phosphatase activity provide a starting point for future experiments to investigate the function of Mm-VSP and other mammalian VSPs. In conclusion, our data reveal that both the VSD and the lipid phosphatase domain of Mm-VSP are functional, indicating that Mm-VSP likely plays an important role in mouse neurophysiology. Copyright © 2015 Biophysical Society. Published by Elsevier Inc. All rights reserved.

Characterization of the RcsC sensor kinase from Erwinia amylovora and other enterobacteria

USDA-ARS?s Scientific Manuscript database

RcsC is a hybrid sensor kinase which contains a sensor domain, a histidine kinase domain and a receiver domain. We have previously demonstrated that, while the Erwinia amylovora rcsC mutant produces more amylovoran than the wild type strain in vitro, the mutant remains avirulent on both immature pea...

α-Helical Structural Elements within the Voltage-Sensing Domains of a K+ Channel

PubMed Central

Li-Smerin, Yingying; Hackos, David H.; Swartz, Kenton J.

2000-01-01

Voltage-gated K+ channels are tetramers with each subunit containing six (S1–S6) putative membrane spanning segments. The fifth through sixth transmembrane segments (S5–S6) from each of four subunits assemble to form a central pore domain. A growing body of evidence suggests that the first four segments (S1–S4) comprise a domain-like voltage-sensing structure. While the topology of this region is reasonably well defined, the secondary and tertiary structures of these transmembrane segments are not. To explore the secondary structure of the voltage-sensing domains, we used alanine-scanning mutagenesis through the region encompassing the first four transmembrane segments in the drk1 voltage-gated K+ channel. We examined the mutation-induced perturbation in gating free energy for periodicity characteristic of α-helices. Our results are consistent with at least portions of S1, S2, S3, and S4 adopting α-helical secondary structure. In addition, both the S1–S2 and S3–S4 linkers exhibited substantial helical character. The distribution of gating perturbations for S1 and S2 suggest that these two helices interact primarily with two environments. In contrast, the distribution of perturbations for S3 and S4 were more complex, suggesting that the latter two helices make more extensive protein contacts, possibly interfacing directly with the shell of the pore domain. PMID:10613917

Active control of flexural vibrations in beams

NASA Technical Reports Server (NTRS)

Gerhold, Carl H.

1987-01-01

The feasibility of using piezoelectric actuators to control the flexural oscillations of large structures in space is investigated. Flexural oscillations are excited by impulsive loads. The vibratory response can degrade the pointing accuracy of cameras and antennae, and can cause high stresses at structural node points. Piezoelectric actuators have the advantage of exerting localized bending moments. In this way, vibration is controlled without exciting rigid body modes. The actuators are used in collocated sensor/driver pairs to form a feedback control system. The sensor produces a voltage that is proportional to the dynamic stress at the sensor location, and the driver produces a force that is proportional to the voltage applied to it. The analog control system amplifies and phase shifts the sensor signal to produce the voltage signal that is applied to the driver. The feedback control is demonstrated to increase the first mode damping in a cantilever beam by up to 100 percent, depending on the amplifier gain. The damping efficiency of the control system when the piezoelectrics are not optimally positioned at points of high stress in the beam is evaluated.

Temperature and Humidity Sensor Powered by an Individual Microbial Fuel Cell in a Power Management System.

PubMed

Zheng, Qi; Xiong, Lei; Mo, Bing; Lu, Weihong; Kim, Suki; Wang, Zhenyu

2015-09-11

Microbial fuel cells (MFCs) are of increasing interest as bioelectrochemical systems for decomposing organic materials and converting chemical energy into electricity. The main challenge for this technology is that the low power and voltage of the devices restricts the use of MFCs in practical applications. In this paper, a power management system (PMS) is developed to store the energy and export an increased voltage. The designed PMS successfully increases the low voltage generated by an individual MFC to a high potential of 5 V, capable of driving a wireless temperature and humidity sensor based on nRF24L01 data transmission modules. With the PMS, MFCs can intermittently power the sensor for data transmission to a remote receiver. It is concluded that even an individual MFC can supply the energy required to power the sensor and telemetry system with the designed PMS. The presented PMS can be widely used for unmanned environmental monitoring such as wild rivers, lakes, and adjacent water areas, and offers promise for further advances in MFC technology.

Temperature and Humidity Sensor Powered by an Individual Microbial Fuel Cell in a Power Management System

PubMed Central

Zheng, Qi; Xiong, Lei; Mo, Bing; Lu, Weihong; Kim, Suki; Wang, Zhenyu

2015-01-01

Microbial fuel cells (MFCs) are of increasing interest as bioelectrochemical systems for decomposing organic materials and converting chemical energy into electricity. The main challenge for this technology is that the low power and voltage of the devices restricts the use of MFCs in practical applications. In this paper, a power management system (PMS) is developed to store the energy and export an increased voltage. The designed PMS successfully increases the low voltage generated by an individual MFC to a high potential of 5 V, capable of driving a wireless temperature and humidity sensor based on nRF24L01 data transmission modules. With the PMS, MFCs can intermittently power the sensor for data transmission to a remote receiver. It is concluded that even an individual MFC can supply the energy required to power the sensor and telemetry system with the designed PMS. The presented PMS can be widely used for unmanned environmental monitoring such as wild rivers, lakes, and adjacent water areas, and offers promise for further advances in MFC technology. PMID:26378546

Vibration sensing in flexible structures using a distributed-effect modal domain optical fiber sensor

NASA Technical Reports Server (NTRS)

Reichard, Karl M.; Lindner, Douglas K.; Claus, Richard O.

1991-01-01

Modal domain optical fiber sensors have recently been employed in the implementation of system identification algorithms and the closed-loop control of vibrations in flexible structures. The mathematical model of the modal domain optical fiber sensor used in these applications, however, only accounted for the effects of strain in the direction of the fiber's longitudinal axis. In this paper, we extend this model to include the effects of arbitrary stress. Using this sensor model, we characterize the sensor's sensitivity and dynamic range.

The voltage-sensor quartet

PubMed Central

Bankston, J. R.; Kass, R. S.

2009-01-01

Decoding the workings of voltage-gated sodium channels is crucial because their mutation leads to severe disease and their activity is modulated by toxins and drugs. An innovative approach now allows such investigations. PMID:19005542

Rain Drop Charge Sensor

NASA Astrophysics Data System (ADS)

S, Sreekanth T.

begin{center} Large Large Rain Drop Charge Sensor Sreekanth T S*, Suby Symon*, G. Mohan Kumar (1) , S. Murali Das (2) *Atmospheric Sciences Division, Centre for Earth Science Studies, Thiruvananthapuram 695011 (1) D-330, Swathi Nagar, West Fort, Thiruvananthapuram 695023 (2) Kavyam, Manacaud, Thiruvananthapuram 695009 begin{center} ABSTRACT To study the inter-relations with precipitation electricity and precipitation microphysical parameters a rain drop charge sensor was designed and developed at CESS Electronics & Instrumentation Laboratory. Simultaneous measurement of electric charge and fall speed of rain drops could be done using this charge sensor. A cylindrical metal tube (sensor tube) of 30 cm length is placed inside another thick metal cover opened at top and bottom for electromagnetic shielding. Mouth of the sensor tube is exposed and bottom part is covered with metal net in the shielding cover. The instrument is designed in such a way that rain drops can pass only through unhindered inside the sensor tube. When electrically charged rain drops pass through the sensor tube, it is charged to the same magnitude of drop charge but with opposite polarity. The sensor tube is electrically connected the inverted input of a current to voltage converter operational amplifier using op-amp AD549. Since the sensor is electrically connected to the virtual ground of the op-amp, the charge flows to the ground and the generated current is converted to amplified voltage. This output voltage is recorded using a high frequency (1kHz) voltage recorder. From the recorded pulse, charge magnitude, polarity and fall speed of rain drop are calculated. From the fall speed drop diameter also can be calculated. The prototype is now under test running at CESS campus. As the magnitude of charge in rain drops is an indication of accumulated charge in clouds in lightning, this instrument has potential application in the field of risk and disaster management. By knowing the charge magnitude of initial drops from a precipitation event, gross cloud charge can be estimated and necessary precautions can be taken during convective cloud events. Being a site of high lightning incidence in tropics, Kerala state is affected in India and calls for much attention in lightning hazards mitigation. Installing this charge sensor and atmospheric electric field mill, an attempt to a better warning system can be attempted.

Toward developing long-life water quality sensors for the ISS using planar REDOX and conductivity sensors

NASA Technical Reports Server (NTRS)

Buehler, M. G.; Kuhlman, G. M.; Keymeulen, D.; Myung, N.; Kounaves, S. P.

2003-01-01

REDOX and conductivity sensors are metal electrodes that are used to detect ionic species in solution by measuring the electrochemical cell current as the voltage is scanned. This paper describes the construction of the sensors, the potentiostat electronics, the measurement methodology, and applications to water quality measurements.

Inductive Position Sensor

NASA Technical Reports Server (NTRS)

Youngquist, Robert C. (Inventor); Simmons, Stephen M. (Inventor)

2015-01-01

An inductive position sensor uses three parallel inductors, each of which has an axial core that is an independent magnetic structure. A first support couples first and second inductors and separate them by a fixed distance. A second support coupled to a third inductor disposed between the first and second inductors. The first support and second support are configured for relative movement as distance changes from the third inductor to each of the first and second inductors. An oscillating current is supplied to the first and second inductors. A device measures a phase component of a source voltage generating the oscillating current and a phase component of voltage induced in the third inductor when the oscillating current is supplied to the first and second inductors such that the phase component of the voltage induced overlaps the phase component of the source voltage.

Effect of Embedded Pd Microstructures on the Flat-Band-Voltage Operation of Room Temperature ZnO-Based Liquid Petroleum Gas Sensors

PubMed Central

Ali, Ghusoon M.; Thompson, Cody V.; Jasim, Ali K.; Abdulbaqi, Isam M.; Moore, James C.

2013-01-01

Three methods were used to fabricate ZnO-based room temperature liquid petroleum gas (LPG) sensors having interdigitated metal-semiconductor-metal (MSM) structures. Specifically, devices with Pd Schottky contacts were fabricated with: (1) un-doped ZnO active layers; (2) Pd-doped ZnO active layers; and (3) un-doped ZnO layers on top of Pd microstructure arrays. All ZnO films were grown on p-type Si(111) substrates by the sol-gel method. For devices incorporating a microstructure array, Pd islands were first grown on the substrate by thermal evaporation using a 100 μm mesh shadow mask. We have estimated the sensitivity of the sensors for applied voltage from –5 to 5 V in air ambient, as well as with exposure to LPG in concentrations from 500 to 3,500 ppm at room temperature (300 K). The current-voltage characteristics were studied and parameters such as leakage current, barrier height, reach-through voltage, and flat-band voltage were extracted. We include contributions due to the barrier height dependence on the electric field and tunneling through the barrier for the studied MSM devices. The Pd-enhanced devices demonstrated a maximum gas response at flat-band voltages. The study also revealed that active layers consisting of Pd microstructure embedded ZnO films resulted in devices exhibiting greater gas-response as compared to those using Pd-doped ZnO thin films or un-doped active layers.

Nanostructured cavity devices for extracellular stimulation of HL-1 cells

NASA Astrophysics Data System (ADS)

Czeschik, Anna; Rinklin, Philipp; Derra, Ulrike; Ullmann, Sabrina; Holik, Peter; Steltenkamp, Siegfried; Offenhäusser, Andreas; Wolfrum, Bernhard

2015-05-01

Microelectrode arrays (MEAs) are state-of-the-art devices for extracellular recording and stimulation on biological tissue. Furthermore, they are a relevant tool for the development of biomedical applications like retina, cochlear and motor prostheses, cardiac pacemakers and drug screening. Hence, research on functional cell-sensor interfaces, as well as the development of new surface structures and modifications for improved electrode characteristics, is a vivid and well established field. However, combining single-cell resolution with sufficient signal coupling remains challenging due to poor cell-electrode sealing. Furthermore, electrodes with diameters below 20 µm often suffer from a high electrical impedance affecting the noise during voltage recordings. In this study, we report on a nanocavity sensor array for voltage-controlled stimulation and extracellular action potential recordings on cellular networks. Nanocavity devices combine the advantages of low-impedance electrodes with small cell-chip interfaces, preserving a high spatial resolution for recording and stimulation. A reservoir between opening aperture and electrode is provided, allowing the cell to access the structure for a tight cell-sensor sealing. We present the well-controlled fabrication process and the effect of cavity formation and electrode patterning on the sensor's impedance. Further, we demonstrate reliable voltage-controlled stimulation using nanostructured cavity devices by capturing the pacemaker of an HL-1 cell network.Microelectrode arrays (MEAs) are state-of-the-art devices for extracellular recording and stimulation on biological tissue. Furthermore, they are a relevant tool for the development of biomedical applications like retina, cochlear and motor prostheses, cardiac pacemakers and drug screening. Hence, research on functional cell-sensor interfaces, as well as the development of new surface structures and modifications for improved electrode characteristics, is a vivid and well established field. However, combining single-cell resolution with sufficient signal coupling remains challenging due to poor cell-electrode sealing. Furthermore, electrodes with diameters below 20 µm often suffer from a high electrical impedance affecting the noise during voltage recordings. In this study, we report on a nanocavity sensor array for voltage-controlled stimulation and extracellular action potential recordings on cellular networks. Nanocavity devices combine the advantages of low-impedance electrodes with small cell-chip interfaces, preserving a high spatial resolution for recording and stimulation. A reservoir between opening aperture and electrode is provided, allowing the cell to access the structure for a tight cell-sensor sealing. We present the well-controlled fabrication process and the effect of cavity formation and electrode patterning on the sensor's impedance. Further, we demonstrate reliable voltage-controlled stimulation using nanostructured cavity devices by capturing the pacemaker of an HL-1 cell network. Electronic supplementary information (ESI) available: Comparison of non-filtered and Savitzky-Golay filtered action potential recordings, electrical signals and corresponding optical signals. See DOI: 10.1039/c5nr01690h

A Smart Voltage and Current Monitoring System for Three Phase Inverters Using an Android Smartphone Application

PubMed Central

Mnati, Mohannad Jabbar; Van den Bossche, Alex; Chisab, Raad Farhood

2017-01-01

In this paper, a new smart voltage and current monitoring system (SVCMS) technique is proposed. It monitors a three phase electrical system using an Arduino platform as a microcontroller to read the voltage and current from sensors and then wirelessly send the measured data to monitor the results using a new Android application. The integrated SVCMS design uses an Arduino Nano V3.0 as the microcontroller to measure the results from three voltage and three current sensors and then send this data, after calculation, to the Android smartphone device of an end user using Bluetooth HC-05. The Arduino Nano V3.0 controller and Bluetooth HC-05 are a cheap microcontroller and wireless device, respectively. The new Android smartphone application that monitors the voltage and current measurements uses the open source MIT App Inventor 2 software. It allows for monitoring some elementary fundamental voltage power quality properties. An effort has been made to investigate what is possible using available off-the-shelf components and open source software. PMID:28420132

A Smart Voltage and Current Monitoring System for Three Phase Inverters Using an Android Smartphone Application.

PubMed

Mnati, Mohannad Jabbar; Van den Bossche, Alex; Chisab, Raad Farhood

2017-04-15

In this paper, a new smart voltage and current monitoring system (SVCMS) technique is proposed. It monitors a three phase electrical system using an Arduino platform as a microcontroller to read the voltage and current from sensors and then wirelessly send the measured data to monitor the results using a new Android application. The integrated SVCMS design uses an Arduino Nano V3.0 as the microcontroller to measure the results from three voltage and three current sensors and then send this data, after calculation, to the Android smartphone device of an end user using Bluetooth HC-05. The Arduino Nano V3.0 controller and Bluetooth HC-05 are a cheap microcontroller and wireless device, respectively. The new Android smartphone application that monitors the voltage and current measurements uses the open source MIT App Inventor 2 software. It allows for monitoring some elementary fundamental voltage power quality properties. An effort has been made to investigate what is possible using available off-the-shelf components and open source software.

Study and Control of Various Corona Modes in an Atmospheric Pressure Weakly Ionized Plasma Reactor Using a Current Sensor Characterized by a Broad Frequency Band

NASA Astrophysics Data System (ADS)

Islam, Rokibul; Pedrow, Patrick; Lekobou, William; Englund, Karl

2013-09-01

A broad band current sensor is being used to monitor the various phenomena (primary streamers, secondary streamers, back corona, etc.) associated with an atmospheric pressure needle-array-to-grounded-screen corona discharge. The reactor consists of a PVC tube and the needle array consists of nickel coated steel electrodes with radius of curvature about 50 μ . The grounded screen is made from stainless steel mesh and applied voltage has a frequency of 60 Hz with an RMS value ranging from 0 to 10 kV. The voltage sensor is a resistive divider and the current sensor is a viewing resistor with value 50 Ω. The feed gas stream is presently (argon + acetylene) or (argon + oxygen) with the argon acting as carrier gas and the acetylene and oxygen acting as precursor gases. Voltage and current are captured with a LeCroy 9350AL 500MHz oscilloscope and analyzed with Matlab using digital signal processing algorithms. The goals of the research are 1) to measure reactor electrical power on a real time basis; 2) to provide real time control of the applied voltage and thus avoid spark conditions; and 3) to identify the various corona modes present in the reactor. Processing of substrates takes place downstream from the grounded screen, outside of the harsh corona discharge environment.

Point mutation of a conserved aspartate, D69, in the muscarinic M2 receptor does not modify voltage-sensitive agonist potency.

PubMed

Ågren, Richard; Sahlholm, Kristoffer; Nilsson, Johanna; Århem, Peter

2018-01-29

The muscarinic M 2 receptor (M 2 R) has been shown to display voltage-sensitive agonist binding, based on G protein-activated inward rectifier potassium channel (GIRK) opening and radioligand binding at different membrane voltages. A conserved aspartate in transmembrane segment (TM) II of M 2 R, D69, has been proposed as the voltage sensor. While a recent paper instead presented evidence of tyrosines in TMs III, VI, and VII acting as voltage sensors, these authors were not able to record GIRK channel activation by a D69N mutant M 2 R. In the present study, we succeeded in recording ACh-induced GIRK channel activation by this mutant at -80 and 0 mV. The acetylcholine EC 50 was about 2.5-fold higher at 0 mV, a potency shift very similar to that observed at wild-type M 2 R, indicating that voltage sensitivity persists at the D69N mutant. Thus, our present observations corroborate the notion that D69 is not responsible for voltage sensitivity of the M 2 R. Copyright © 2018 Elsevier Inc. All rights reserved.

Magnetic susceptibility well-logging unit with single power supply thermoregulation system

DOE Office of Scientific and Technical Information (OSTI.GOV)

Seeley, R. L.

1985-11-05

The magnetic susceptibility well-logging unit with single power supply thermoregulation system provides power from a single surface power supply over a well-logging cable to an integrated circuit voltage regulator system downhole. This voltage regulator system supplies regulated voltages to a temperature control system and also to a Maxwell bridge sensing unit which includes the solenoid of a magnetic susceptibility probe. The temperature control system is provided with power from the voltage regulator system and operates to permit one of several predetermined temperatures to be chosen, and then operates to maintain the solenoid of a magnetic susceptibility probe at this chosenmore » temperature. The temperature control system responds to a temperature sensor mounted upon the probe solenoid to cause resistance heaters concentrically spaced from the probe solenoid to maintain the chosen temperature. A second temperature sensor on the probe solenoid provides a temperature signal to a temperature transmitting unit, which initially converts the sensed temperature to a representative voltage. This voltage is then converted to a representative current signal which is transmitted by current telemetry over the well logging cable to a surface electronic unit which then reconverts the current signal to a voltage signal.« less

A Miniature Magnetic-Force-Based Three-Axis AC Magnetic Sensor with Piezoelectric/Vibrational Energy-Harvesting Functions.

PubMed

Hung, Chiao-Fang; Yeh, Po-Chen; Chung, Tien-Kan

2017-02-08

In this paper, we demonstrate a miniature magnetic-force-based, three-axis, AC magnetic sensor with piezoelectric/vibrational energy-harvesting functions. For magnetic sensing, the sensor employs a magnetic-mechanical-piezoelectric configuration (which uses magnetic force and torque, a compact, single, mechanical mechanism, and the piezoelectric effect) to convert x -axis and y -axis in-plane and z -axis magnetic fields into piezoelectric voltage outputs. Under the x -axis magnetic field (sine-wave, 100 Hz, 0.2-3.2 gauss) and the z -axis magnetic field (sine-wave, 142 Hz, 0.2-3.2 gauss), the voltage output with the sensitivity of the sensor are 1.13-26.15 mV with 8.79 mV/gauss and 1.31-8.92 mV with 2.63 mV/gauss, respectively. In addition, through this configuration, the sensor can harness ambient vibrational energy, i.e., possessing piezoelectric/vibrational energy-harvesting functions. Under x -axis vibration (sine-wave, 100 Hz, 3.5 g) and z -axis vibration (sine-wave, 142 Hz, 3.8 g), the root-mean-square voltage output with power output of the sensor is 439 mV with 0.333 μW and 138 mV with 0.051 μW, respectively. These results show that the sensor, using this configuration, successfully achieves three-axis magnetic field sensing and three-axis vibration energy-harvesting. Due to these features, the three-axis AC magnetic sensor could be an important design reference in order to develop future three-axis AC magnetic sensors, which possess energy-harvesting functions, for practical industrial applications, such as intelligent vehicle/traffic monitoring, processes monitoring, security systems, and so on.

A Miniature Magnetic-Force-Based Three-Axis AC Magnetic Sensor with Piezoelectric/Vibrational Energy-Harvesting Functions

PubMed Central

Hung, Chiao-Fang; Yeh, Po-Chen; Chung, Tien-Kan

2017-01-01

In this paper, we demonstrate a miniature magnetic-force-based, three-axis, AC magnetic sensor with piezoelectric/vibrational energy-harvesting functions. For magnetic sensing, the sensor employs a magnetic–mechanical–piezoelectric configuration (which uses magnetic force and torque, a compact, single, mechanical mechanism, and the piezoelectric effect) to convert x-axis and y-axis in-plane and z-axis magnetic fields into piezoelectric voltage outputs. Under the x-axis magnetic field (sine-wave, 100 Hz, 0.2–3.2 gauss) and the z-axis magnetic field (sine-wave, 142 Hz, 0.2–3.2 gauss), the voltage output with the sensitivity of the sensor are 1.13–26.15 mV with 8.79 mV/gauss and 1.31–8.92 mV with 2.63 mV/gauss, respectively. In addition, through this configuration, the sensor can harness ambient vibrational energy, i.e., possessing piezoelectric/vibrational energy-harvesting functions. Under x-axis vibration (sine-wave, 100 Hz, 3.5 g) and z-axis vibration (sine-wave, 142 Hz, 3.8 g), the root-mean-square voltage output with power output of the sensor is 439 mV with 0.333 μW and 138 mV with 0.051 μW, respectively. These results show that the sensor, using this configuration, successfully achieves three-axis magnetic field sensing and three-axis vibration energy-harvesting. Due to these features, the three-axis AC magnetic sensor could be an important design reference in order to develop future three-axis AC magnetic sensors, which possess energy-harvesting functions, for practical industrial applications, such as intelligent vehicle/traffic monitoring, processes monitoring, security systems, and so on. PMID:28208693

Uncooled tunneling infrared sensor

NASA Technical Reports Server (NTRS)

Kenny, Thomas W. (Inventor); Kaiser, William J. (Inventor); Podosek, Judith A. (Inventor); Vote, Erika C. (Inventor); Muller, Richard E. (Inventor); Maker, Paul D. (Inventor)

1995-01-01

An uncooled infrared tunneling sensor in which the only moving part is a diaphragm which is deflected into contact with a micromachined silicon tip electrode prepared by a novel lithographic process. Similarly prepared deflection electrodes employ electrostatic force to control the deflection of a silicon nitride, flat diaphragm membrane. The diaphragm exhibits a high resonant frequency which reduces the sensor's sensitivity to vibration. A high bandwidth feedback circuit controls the tunneling current by adjusting the deflection voltage to maintain a constant deflection of the membrane. The resulting infrared sensor can be miniaturized to pixel dimensions smaller than 100 .mu.m. An alternative embodiment is implemented using a corrugated membrane to permit large deflection without complicated clamping and high deflection voltages. The alternative embodiment also employs a pinhole aperture in a membrane to accommodate environmental temperature variation and a sealed chamber to eliminate environmental contamination of the tunneling electrodes and undesireable accoustic coupling to the sensor.

Dimerization of the voltage-sensing phosphatase controls its voltage-sensing and catalytic activity.

PubMed

Rayaprolu, Vamseedhar; Royal, Perrine; Stengel, Karen; Sandoz, Guillaume; Kohout, Susy C

2018-05-07

Multimerization is a key characteristic of most voltage-sensing proteins. The main exception was thought to be the Ciona intestinalis voltage-sensing phosphatase (Ci-VSP). In this study, we show that multimerization is also critical for Ci-VSP function. Using coimmunoprecipitation and single-molecule pull-down, we find that Ci-VSP stoichiometry is flexible. It exists as both monomers and dimers, with dimers favored at higher concentrations. We show strong dimerization via the voltage-sensing domain (VSD) and weak dimerization via the phosphatase domain. Using voltage-clamp fluorometry, we also find that VSDs cooperate to lower the voltage dependence of activation, thus favoring the activation of Ci-VSP. Finally, using activity assays, we find that dimerization alters Ci-VSP substrate specificity such that only dimeric Ci-VSP is able to dephosphorylate the 3-phosphate from PI(3,4,5)P 3 or PI(3,4)P 2 Our results indicate that dimerization plays a significant role in Ci-VSP function. © 2018 Rayaprolu et al.

Voltage-sensitive rhodol with enhanced two-photon brightness.

PubMed

Kulkarni, Rishikesh U; Kramer, Daniel J; Pourmandi, Narges; Karbasi, Kaveh; Bateup, Helen S; Miller, Evan W

2017-03-14

We have designed, synthesized, and applied a rhodol-based chromophore to a molecular wire-based platform for voltage sensing to achieve fast, sensitive, and bright voltage sensing using two-photon (2P) illumination. Rhodol VoltageFluor-5 (RVF5) is a voltage-sensitive dye with improved 2P cross-section for use in thick tissue or brain samples. RVF5 features a dichlororhodol core with pyrrolidyl substitution at the nitrogen center. In mammalian cells under one-photon (1P) illumination, RVF5 demonstrates high voltage sensitivity (28% ΔF/F per 100 mV) and improved photostability relative to first-generation voltage sensors. This photostability enables multisite optical recordings from neurons lacking tuberous sclerosis complex 1, Tsc1, in a mouse model of genetic epilepsy. Using RVF5, we show that Tsc1 KO neurons exhibit increased activity relative to wild-type neurons and additionally show that the proportion of active neurons in the network increases with the loss of Tsc1. The high photostability and voltage sensitivity of RVF5 is recapitulated under 2P illumination. Finally, the ability to chemically tune the 2P absorption profile through the use of rhodol scaffolds affords the unique opportunity to image neuronal voltage changes in acutely prepared mouse brain slices using 2P illumination. Stimulation of the mouse hippocampus evoked spiking activity that was readily discerned with bath-applied RVF5, demonstrating the utility of RVF5 and molecular wire-based voltage sensors with 2P-optimized fluorophores for imaging voltage in intact brain tissue.

Optical sensors for electrical elements of a medium voltage distribution network

NASA Astrophysics Data System (ADS)

De Maria, Letizia; Bartalesi, Daniele; Serragli, Paolo; Paladino, Domenico

2012-04-01

The aging of most of the components of the National transmission and distribution system can potentially influence the reliability of power supply in a Medium Voltage (MV) network. In order to prevent possible dangerous situations, selected diagnostic indicators on electrical parts exploiting reliable and potentially low-cost sensors are required. This paper presents results concerning two main research activities regarding the development and application of innovative optical sensors for the diagnostic of MV electrical components. The first concerns a multi-sensor prototype for the detection of pre-discharges in MV switchboards: it is the combination of three different types of sensors operating simultaneously to detect incipient failure and to reduce the occurrence of false alarms. The system is real-time controlled by an embedded computer through a LabView interface. The second activity refers to a diagnostic tool to provide significant real-time information about early aging of MV/Low Voltage (LV) transformers by means of its vibration fingerprint. A miniaturized Optical Micro-Electro-Mechanical System (MEMS) based unit has been assembled for vibration measurements, wireless connected to a remote computer and controlled via LabView interface. Preliminary comparative tests were carried out with standard piezoelectric accelerometers on a conventional MV/LV test transformer under open circuit and in short-circuited configuration.

Characterization of AC current sensor based on giant magnetoresistance and coil for power meter design

NASA Astrophysics Data System (ADS)

Dhani, H. S.; Aminudin, A.; Waslaluddin

2018-05-01

Electric current is the basic variable of measurement in instrumentation system. One of the current measurements had been developed was based on magnetic sensor. Giant Magnetoresistance (GMR) produces an output voltage when it detects the magnetic field from electric current flow. The purpose of this study was to characterize the response of GMR when variation number of coil was given. The characterization was the GMR voltage response to the AC current values from 0.01 A to 5.00 A. The linearity of the relation was reaching saturation point when the magnetic field measured higher than 10.5 Oe at room temperature. As the number of coil increased, the earlier saturation occurred. To see the sensitivity of the sensor response, the data graph was cut off at 1.56 A AC. From this research, we got single coil was ideal to measure electric current higher than 1.56 A AC, as the relation of GMR voltage to the current tended to maintain its linearity. For measurement of 1.56 A AC and less, coil number addition would increase the sensitivity of sensor response. This research hopefully will be benefit for further development using an electric current measurement based on GMR magnetic sensor for power meter design.

The Analog Revolution and Its On-Going Role in Modern Analytical Measurements.

PubMed

Enke, Christie G

2015-12-15

The electronic revolution in analytical instrumentation began when we first exceeded the two-digit resolution of panel meters and chart recorders and then took the first steps into automated control. It started with the first uses of operational amplifiers (op amps) in the analog domain 20 years before the digital computer entered the analytical lab. Their application greatly increased both accuracy and precision in chemical measurement and they provided an elegant means for the electronic control of experimental quantities. Later, laboratory and personal computers provided an unlimited readout resolution and enabled programmable control of instrument parameters as well as storage and computation of acquired data. However, digital computers did not replace the op amp's critical role of converting the analog sensor's output to a robust and accurate voltage. Rather it added a new role: converting that voltage into a number. These analog operations are generally the limiting portions of our computerized instrumentation systems. Operational amplifier performance in gain, input current and resistance, offset voltage, and rise time have improved by a remarkable 3-4 orders of magnitude since their first implementations. Each 10-fold improvement has opened the doors for the development of new techniques in all areas of chemical analysis. Along with some interesting history, the multiple roles op amps play in modern instrumentation are described along with a number of examples of new areas of analysis that have been enabled by their improvements.

Architecture for distributed actuation and sensing using smart piezoelectric elements

NASA Astrophysics Data System (ADS)

Etienne-Cummings, Ralph; Pourboghrat, Farzad; Maruboyina, Hari K.; Abrate, Serge; Dhali, Shirshak K.

1998-07-01

We discuss vibration control of a cantilevered plate with multiple sensors and actuators. An architecture is chosen to minimize the number of control and sensing wires required. A custom VLSI chip, integrated with the sensor/actuator elements, controls the local behavior of the plate. All the actuators are addressed in parallel; local decode logic selects which actuator is stimulated. Downloaded binary data controls the applied voltage and modulation frequency for each actuator, and High Voltage MOSFETs are used to activate them. The sensors, which are independent adjacent piezoelectric ceramic elements, can be accessed in a random or sequential manner. An A/D card and GPIB interconnected test equipment allow a PC to read the sensors' outputs and dictate the actuation procedure. A visual programming environment is used to integrate the sensors, controller and actuators. Based on the constitutive relations for the piezoelectric material, simple models for the sensors and actuators are derived. A two level hierarchical robust controller is derived for motion control and for damping of vibrations.

A CMOS Pressure Sensor Tag Chip for Passive Wireless Applications

PubMed Central

Deng, Fangming; He, Yigang; Li, Bing; Zuo, Lei; Wu, Xiang; Fu, Zhihui

2015-01-01

This paper presents a novel monolithic pressure sensor tag for passive wireless applications. The proposed pressure sensor tag is based on an ultra-high frequency RFID system. The pressure sensor element is implemented in the 0.18 µm CMOS process and the membrane gap is formed by sacrificial layer release, resulting in a sensitivity of 1.2 fF/kPa within the range from 0 to 600 kPa. A three-stage rectifier adopts a chain of auxiliary floating rectifier cells to boost the gate voltage of the switching transistors, resulting in a power conversion efficiency of 53% at the low input power of −20 dBm. The capacitive sensor interface, using phase-locked loop archietcture, employs fully-digital blocks, which results in a 7.4 bits resolution and 0.8 µW power dissipation at 0.8 V supply voltage. The proposed passive wireless pressure sensor tag costs a total 3.2 µW power dissipation. PMID:25806868

A CMOS pressure sensor tag chip for passive wireless applications.

PubMed

Deng, Fangming; He, Yigang; Li, Bing; Zuo, Lei; Wu, Xiang; Fu, Zhihui

2015-03-23

This paper presents a novel monolithic pressure sensor tag for passive wireless applications. The proposed pressure sensor tag is based on an ultra-high frequency RFID system. The pressure sensor element is implemented in the 0.18 µm CMOS process and the membrane gap is formed by sacrificial layer release, resulting in a sensitivity of 1.2 fF/kPa within the range from 0 to 600 kPa. A three-stage rectifier adopts a chain of auxiliary floating rectifier cells to boost the gate voltage of the switching transistors, resulting in a power conversion efficiency of 53% at the low input power of -20 dBm. The capacitive sensor interface, using phase-locked loop archietcture, employs fully-digital blocks, which results in a 7.4 bits resolution and 0.8 µW power dissipation at 0.8 V supply voltage. The proposed passive wireless pressure sensor tag costs a total 3.2 µW power dissipation.

Sensing Properties of a Novel Temperature Sensor Based on Field Assisted Thermal Emission.

PubMed

Pan, Zhigang; Zhang, Yong; Cheng, Zhenzhen; Tong, Jiaming; Chen, Qiyu; Zhang, Jianpeng; Zhang, Jiaxiang; Li, Xin; Li, Yunjia

2017-02-27

The existing temperature sensors using carbon nanotubes (CNTs) are limited by low sensitivity, complicated processes, or dependence on microscopy to observe the experimental results. Here we report the fabrication and successful testing of an ionization temperature sensor featuring non-self-sustaining discharge. The sharp tips of nanotubes generate high electric fields at relatively low voltages, lowering the work function of electrons emitted by CNTs, and thereby enabling the safe operation of such sensors. Due to the temperature effect on the electron emission of CNTs, the collecting current exhibited an exponential increase with temperature rising from 20 °C to 100 °C. Additionally, a higher temperature coefficient of 0.04 K -1 was obtained at 24 V voltage applied on the extracting electrode, higher than the values of other reported CNT-based temperature sensors. The triple-electrode ionization temperature sensor is easy to fabricate and converts the temperature change directly into an electrical signal. It shows a high temperature coefficient and good application potential.

Sensing Properties of a Novel Temperature Sensor Based on Field Assisted Thermal Emission

PubMed Central

Pan, Zhigang; Zhang, Yong; Cheng, Zhenzhen; Tong, Jiaming; Chen, Qiyu; Zhang, Jianpeng; Zhang, Jiaxiang; Li, Xin; Li, Yunjia

2017-01-01

The existing temperature sensors using carbon nanotubes (CNTs) are limited by low sensitivity, complicated processes, or dependence on microscopy to observe the experimental results. Here we report the fabrication and successful testing of an ionization temperature sensor featuring non-self-sustaining discharge. The sharp tips of nanotubes generate high electric fields at relatively low voltages, lowering the work function of electrons emitted by CNTs, and thereby enabling the safe operation of such sensors. Due to the temperature effect on the electron emission of CNTs, the collecting current exhibited an exponential increase with temperature rising from 20 °C to 100 °C. Additionally, a higher temperature coefficient of 0.04 K−1 was obtained at 24 V voltage applied on the extracting electrode, higher than the values of other reported CNT-based temperature sensors. The triple-electrode ionization temperature sensor is easy to fabricate and converts the temperature change directly into an electrical signal. It shows a high temperature coefficient and good application potential. PMID:28264427

Optical microphone with fiber Bragg grating and signal processing techniques

NASA Astrophysics Data System (ADS)

Tosi, Daniele; Olivero, Massimo; Perrone, Guido

2008-06-01

In this paper, we discuss the realization of an optical microphone array using fiber Bragg gratings as sensing elements. The wavelength shift induced by acoustic waves perturbing the sensing Bragg grating is transduced into an intensity modulation. The interrogation unit is based on a fixed-wavelength laser source and - as receiver - a photodetector with proper amplification; the system has been implemented using devices for standard optical communications, achieving a low-cost interrogator. One of the advantages of the proposed approach is that no voltage-to-strain calibration is required for tracking dynamic shifts. The optical sensor is complemented by signal processing tools, including a data-dependent frequency estimator and adaptive filters, in order to improve the frequency-domain analysis and mitigate the effects of disturbances. Feasibility and performances of the optical system have been tested measuring the output of a loudspeaker. With this configuration, the sensor is capable of correctly detecting sounds up to 3 kHz, with a frequency response that exhibits a top sensitivity within the range 200-500 Hz; single-frequency input sounds inducing an axial strain higher than ~10nɛ are correctly detected. The repeatability range is ~0.1%. The sensor has also been applied for the detection of pulsed stimuli generated from a metronome.

Calcium Activated K+ Channels in The Electroreceptor of the Skate Confirmed by Cloning. Details of Subunits and Splicing

PubMed Central

King, Benjamin L.; Shi, Ling Fang; Kao, Peter; Clusin, William T.

2015-01-01

Elasmobranchs detect small potentials using excitable cells of the ampulla of Lorenzini which have calcium-activated K+ channels, first described in l974. A distinctive feature of the outward current in voltage clamped ampullae is its apparent insensitivity to voltage. The sequence of a BK channel α isoform expressed in the ampulla of the skate was characterized. A signal peptide is present at the beginning of the gene. When compared to human isoform 1 (the canonical sequence), the largest difference was absence of a 59 amino acid region from the S8-S9 intracellular linker that contains the strex regulatory domain. The ampulla isoform was also compared with the isoform predicted˜ in late skate embryos where strex was also absent. The BK voltage sensors were conserved in both skate isoforms. Differences between the skate and human BK channel included alternative splicing. Alternative splicing occurs at seven previously defined sites that are characteristic for BK channels in general and hair cells in particular. Skate BK sequences were highly similar to the Australian ghost shark and several other vertebrate species. Based on alignment of known BK sequences with the skate genome and transcriptome, there are at least two isoforms of Kcnma1α expressed in the skate. One of the β subunits (β4), which is known to decrease voltage sensitivity, was also identified in the skate genome and transcriptome and in the ampulla. These studies advance our knowledge of BK channels and suggest further studies in the ampulla and other excitable tissues. PMID:26687710

KCNE1 remodels the voltage sensor of Kv7.1 to modulate channel function.

PubMed

Wu, Dick; Pan, Hua; Delaloye, Kelli; Cui, Jianmin

2010-12-01

The KCNE1 auxiliary subunit coassembles with the Kv7.1 channel and modulates its properties to generate the cardiac I(Ks) current. Recent biophysical evidence suggests that KCNE1 interacts with the voltage-sensing domain (VSD) of Kv7.1. To investigate the mechanism of how KCNE1 affects the VSD to alter the voltage dependence of channel activation, we perturbed the VSD of Kv7.1 by mutagenesis and chemical modification in the absence and presence of KCNE1. Mutagenesis of S4 in Kv7.1 indicates that basic residues in the N-terminal half (S4-N) and C-terminal half (S4-C) of S4 are important for stabilizing the resting and activated states of the channel, respectively. KCNE1 disrupts electrostatic interactions involving S4-C, specifically with the lower conserved glutamate in S2 (Glu(170) or E2). Likewise, Trp scanning of S4 shows that mutations to a cluster of residues in S4-C eliminate current in the presence of KCNE1. In addition, KCNE1 affects S4-N by enhancing MTS accessibility to the top of the VSD. Consistent with the structure of Kv channels and previous studies on the KCNE1-Kv7.1 interaction, these results suggest that KCNE1 alters the interactions of S4 residues with the surrounding protein environment, possibly by changing the protein packing around S4, thereby affecting the voltage dependence of Kv7.1. Copyright © 2010 Biophysical Society. Published by Elsevier Inc. All rights reserved.

Temperature compensated and self-calibrated current sensor

DOEpatents

Yakymyshyn, Christopher Paul; Brubaker, Michael Allen; Yakymyshyn, Pamela Jane

2007-09-25

A method is described to provide temperature compensation and reduction of drift due to aging for a current sensor based on a plurality of magnetic field sensors positioned around a current carrying conductor. The offset voltage signal generated by each magnetic field sensor is used to correct variations in the output signal due to temperature variations and aging.

Structure and Orientation of a Voltage-Sensor Toxin in Lipid Membranes

PubMed Central

Jung, Hyun Ho; Jung, Hoi Jong; Milescu, Mirela; Lee, Chul Won; Lee, Seungkyu; Lee, Ju Yeon; Eu, Young-Jae; Kim, Ha Hyung; Swartz, Kenton J.; Kim, Jae Il

2010-01-01

Abstract Amphipathic protein toxins from tarantula venom inhibit voltage-activated potassium (Kv) channels by binding to a critical helix-turn-helix motif termed the voltage sensor paddle. Although these toxins partition into membranes to bind the paddle motif, their structure and orientation within the membrane are unknown. We investigated the interaction of a tarantula toxin named SGTx with membranes using both fluorescence and NMR spectroscopy. Depth-dependent fluorescence-quenching experiments with brominated lipids suggest that Trp30 in SGTx is positioned ∼9 Å from the center of the bilayer. NMR spectra reveal that the inhibitor cystine knot structure of the toxin does not radically change upon membrane partitioning. Transferred cross-saturation NMR experiments indicate that the toxin's hydrophobic protrusion contacts the hydrophobic core of the membrane, whereas most surrounding polar residues remain at interfacial regions of the bilayer. The inferred orientation of the toxin reveals a twofold symmetry in the arrangement of basic and hydrophobic residues, a feature that is conserved among tarantula toxins. These results have important implications for regions of the toxin involved in recognizing membranes and voltage-sensor paddles, and for the mechanisms by which tarantula toxins alter the activity of different types of ion channels. PMID:20643084

Local twin domains and tip-voltage-induced domain switching of monoclinic M C phase in Pb ( M g 1 / 3 N b 2 / 3 ) O 3 - 0.34 PbTi O 3 single crystal revealed by piezoresponse force microscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Ruixue; Yang, Bin; Luo, Zhenlin

2016-08-29

Here, the monoclinic (M) phases in high-performance relaxor-based ferroelectric single crystals have been recognized to be a vital structural factor for the outstanding piezoelectric property. However, due to the complexity of the structure in M phases, the understanding about it is still limited. In this paper, the local twin domains and tip-voltage-induced domain switching of the M C phase in Pb(Mg 1/3Nb 2/3)O 3 - 0.34PbTiO 3 (PMN-0.34PT) single crystal have been intensively investigated by piezoresponse force microscopy (PFM). By theoretically analyzing the experimental patterns of domain walls on the (001) C face, the specific M C twin domains inmore » the initial annealed state of a selected area have been clarified, and the polarization orientation of the M C phase in this sample is determined to be at an angle of 29 degrees to the < 001 > C directions. In addition, based on the evolution of domains and the motion of domain walls under the step-increased PFM tip dc voltage (V dc), the switching process and features of different types of M C domain variants are visually revealed« less

Dual-mode self-validating resistance/Johnson noise thermometer system

DOEpatents

Shepard, Robert L.; Blalock, Theron V.; Roberts, Michael J.

1993-01-01

A dual-mode Johnson noise and DC resistance thermometer capable of use in control systems where prompt indications of temperature changes and long term accuracy are needed. A resistance-inductance-capacitance (RLC) tuned circuit produces a continuous voltage signal for Johnson noise temperature measurement. The RLC circuit provides a mean-squared noise voltage that depends only on the capacitance used and the temperature of the sensor. The sensor has four leads for simultaneous coupling to a noise signal processor and to a DC resistance signal processor.

Prediction of Trace Element based Energizing Sensor Control System using PWM

NASA Astrophysics Data System (ADS)

Zukri, Mohammad Nizar Bin Mohamed; Abu Bakar, Elmi Bin; Uchiyama, Naoki; Abdullah, Mohamad Nazir Bin

2018-05-01

A real-time system for field-work monitoring wastewater laden with heavy metal in industrial discharge through wireless communication network was developed. The monitoring system poses an interesting challenge in order to determine existing metal ion in the solution whereas the previous result only consider total dissolve ion. This paper aims to distinguish the metal ion based on reaction determination in solution. The control algorithm was implemented as generating voltage input for energize conductivity sensor since the voltage corresponding to oxidation and reaction based on standard reduction potential. Implementation of ATmega2560 microcontroller for control voltage fed on sensor equivalent to controlling the PWM duty cycle. PID controller was designed uses a microcontroller (Arduino) platform with manual tuning for identify reaction process and sufficient voltage input. From the experimental result, is found that the proposed PI controller has excellent tracking and measurement performance. Low-pass filter was applied in programming to make the system understand that signal has achieved stable. The development of hardware and software of the closed loop system has an enhancement of measurement performance and high feasibility for SME’s company in economic point of view. The desired objective is to achieve a system with the stable measurement and sufficient voltage supply. This system will provide an accurate and precise control efficiently without using costly component and complicated circuit.

Proline Scan of the hERG Channel S6 Helix Reveals the Location of the Intracellular Pore Gate

PubMed Central

Thouta, Samrat; Sokolov, Stanislav; Abe, Yuki; Clark, Sheldon J.; Cheng, Yen M.; Claydon, Tom W.

2014-01-01

In Shaker-like channels, the activation gate is formed at the bundle crossing by the convergence of the inner S6 helices near a conserved proline-valine-proline motif, which introduces a kink that allows for electromechanical coupling with voltage sensor motions via the S4-S5 linker. Human ether-a-go-go-related gene (hERG) channels lack the proline-valine-proline motif and the location of the intracellular pore gate and how it is coupled to S4 movement is less clear. Here, we show that proline substitutions within the S6 of hERG perturbed pore gate closure, trapping channels in the open state. Performing a proline scan of the inner S6 helix, from Ile655 to Tyr667 revealed that gate perturbation occurred with proximal (I655P-Q664P), but not distal (R665P-Y667P) substitutions, suggesting that Gln664 marks the position of the intracellular gate in hERG channels. Using voltage-clamp fluorimetry and gating current analysis, we demonstrate that proline substitutions trap the activation gate open by disrupting the coupling between the voltage-sensing unit and the pore of the channel. We characterize voltage sensor movement in one such trapped-open mutant channel and demonstrate the kinetics of what we interpret to be intrinsic hERG voltage sensor movement. PMID:24606930

HOPG/ZnO/HOPG pressure sensor

NASA Astrophysics Data System (ADS)

Jahangiri, Mojtaba; Yousefiazari, Ehsan; Ghalamboran, Milad

2017-12-01

Pressure sensor is one of the most commonly used sensors in the research laboratories and industries. These are generally categorized in three different classes of absolute pressure sensors, gauge pressure sensors, and differential pressure sensors. In this paper, we fabricate and assess the pressure sensitivity of the current vs. voltage diagrams in a graphite/ZnO/graphite structure. Zinc oxide layers are deposited on highly oriented pyrolytic graphite (HOPG) substrates by sputtering a zinc target under oxygen plasma. The top electrode is also a slice of HOPG which is placed on the ZnO layer and connected to the outside electronic circuits. By recording the I-V characteristics of the device under different forces applied to the top HOPG electrode, the pressure sensitivity is demonstrated; at the optimum biasing voltage, the device current changes 10 times upon changing the pressure level on the top electrode by 20 times. Repeatability and reproducibility of the observed effect is studied on the same and different samples. All the materials used for the fabrication of this pressure sensor are biocompatible, the fabricated device is anticipated to find potential applications in biomedical engineering.

A multi-agent approach to intelligent monitoring in smart grids

NASA Astrophysics Data System (ADS)

Vallejo, D.; Albusac, J.; Glez-Morcillo, C.; Castro-Schez, J. J.; Jiménez, L.

2014-04-01

In this paper, we propose a scalable multi-agent architecture to give support to smart grids, paying special attention to the intelligent monitoring of distribution substations. The data gathered by multiple sensors are used by software agents that are responsible for monitoring different aspects or events of interest, such as normal voltage values or unbalanced intensity values that can end up blowing fuses and decreasing the quality of service of end consumers. The knowledge bases of these agents have been built by means of a formal model for normality analysis that has been successfully used in other surveillance domains. The architecture facilitates the integration of new agents and can be easily configured and deployed to monitor different environments. The experiments have been conducted over a power distribution network.

Anomalous domain inversion in LiNbO3 single crystals investigated by scanning probe microscopy

NASA Astrophysics Data System (ADS)

Lilienblum, M.; Soergel, E.

2011-09-01

Ferroelectric domains were written in lithium niobate (LiNbO3) single crystals by applying voltage pulses to the tip of a scanning force microscope. The generated domains are subsequently imaged by piezoresponse force microscopy. As it has been previously observed not only full domains but also doughnut-shaped ones arise from tip-based domain formation. In this contribution, we present our experiments which were carried out with 10-20 μm thin LiNbO3 single crystals. We show that by choosing appropriate writing parameters, domains of predetermined shape (full or doughnut) can be reliably generated. In addition to the duration and the amplitude of the voltage pulse the moment of the retraction of the tip from the sample surface was found to be a crucial parameter for reproducible domain formation.

Localization and Molecular Determinants of the Hanatoxin Receptors on the Voltage-Sensing Domains of a K+ Channel

PubMed Central

Li-Smerin, Yingying; Swartz, Kenton J.

2000-01-01

Hanatoxin inhibits voltage-gated K+ channels by modifying the energetics of activation. We studied the molecular determinants and physical location of the Hanatoxin receptors on the drk1 voltage-gated K+ channel. First, we made multiple substitutions at three previously identified positions in the COOH terminus of S3 to examine whether these residues interact intimately with the toxin. We also examined a region encompassing S1–S3 using alanine-scanning mutagenesis to identify additional determinants of the toxin receptors. Finally, guided by the structure of the KcsA K+ channel, we explored whether the toxin interacts with the peripheral extracellular surface of the pore domain in the drk1 K+ channel. Our results argue for an intimate interaction between the toxin and the COOH terminus of S3 and suggest that the Hanatoxin receptors are confined within the voltage-sensing domains of the channel, at least 20–25 Å away from the central pore axis. PMID:10828242

Electrical coupling of single cardiac rat myocytes to field-effect and bipolar transistors.

PubMed

Kind, Thomas; Issing, Matthias; Arnold, Rüdiger; Müller, Bernt

2002-12-01

A novel bipolar transistor for extracellular recording the electrical activity of biological cells is presented, and the electrical behavior compared with the field-effect transistor (FET). Electrical coupling is examined between single cells separated from the heart of adults rats (cardiac myocytes) and both types of transistors. To initiate a local extracellular voltage, the cells are periodically stimulated by a patch pipette in voltage clamp and current clamp mode. The local extracellular voltage is measured by the planar integrated electronic sensors: the bipolar and the FET. The small signal transistor currents correspond to the local extracellular voltage. The two types of sensor transistors used here were developed and manufactured in the laboratory of our institute. The manufacturing process and the interfaces between myocytes and transistors are described. The recordings are interpreted by way of simulation based on the point-contact model and the single cardiac myocyte model.

Variable Rail Voltage Control of a Brushless DC (BLDC) Motor

DTIC Science & Technology

2013-01-01

Variable Rail Voltage Control of a Brushless DC ( BLDC ) Motor by Yuan Chen, Joseph Conroy, and William Nothwang ARL-TR-6308 January 2013...TR-6308 January 2013 Variable Rail Voltage Control of a Brushless DC ( BLDC ) Motor Yuan Chen, Joseph Conroy, and William Nothwang Sensors...DATES COVERED (From - To) 4. TITLE AND SUBTITLE Variable Rail Voltage Control of a Brushless DC ( BLDC ) Motor 5a. CONTRACT NUMBER 5b. GRANT

Fiber optic sensors and systems at the Federal University of Rio de Janeiro

NASA Astrophysics Data System (ADS)

Werneck, Marcelo M.; dos Santos, Paulo A. M.; Ferreira, Aldo P.; Maggi, Luis E.; de Carvalho, Carlos R., Jr.; Ribeiro, R. M.

1998-08-01

As widely known, fiberoptics (FO) are being used in a large variety of sensors and systems particularly for their small dimensions and low cost, large bandwidth and favorable dielectric properties. These properties have allowed us to develop sensors and systems for general applications and, particularly, for biomedical engineering. The intravascular pressure sensor was designed for small dimensions and high bandwidth. The system is based on light-intensity modulation technique and uses a 2 mm-diameter elastomer membrane as the sensor element and a pigtailed laser as a light source. The optical power output curve was linear for pressures within the range of 0 to 300 mmHg. The real time optical biosensor uses the evanescent field technique for monitoring Escherichia coli growth in culture media. The optical biosensor monitors interactions between the analytic (bacteria) and the evanescent field of an optical fiber passing through it. The FO based high voltage and current sensor is a measuring system designed for monitoring voltage and current in high voltage transmission lines. The linearity of the system is better than 2% in both ranges of 0 to 25 kV and 0 to 1000 A. The optical flowmeter uses a cross-correlation technique that analyses two light beams crossing the flow separated by a fixed distance. The x-ray image sensor uses a scintillating FO array, one FO for each image pixel to form an image of the x-ray field. The systems described in these paper use general-purpose components including optical fibers and optoelectronic devices, which are readily available, and of low cost.

Research progress in fiber optic sensors and systems at the Federal University of Rio de Janeiro

NASA Astrophysics Data System (ADS)

Werneck, Marcelo M.; Ferreira, Aldo P.; Maggi, Luis E.; De Carvalho, C. C.; Ribeiro, R. M.

1999-02-01

As widely known, fiberoptics (FO) are being used in a large variety of sensor an systems particularly for their small dimensions and low cost, large bandwidth and favorable dielectric properties. These properties have allowed us to develop sensor and systems for general applications and, particularly, for biomedical engineering. The intravasculator pressure sensor was designed for small dimensions and high bandwidth. The system is based on light- intensity modulation technique and use a 2 mm-diameter elastomer membrane as the sensor element and a pigtailed laser as a light source. The optical power out put curve was linear for pressures within the range of 0 to 300 mmHg. The real time optical biosensor uses the evanescent field technique for monitoring Escherichia coli growth in culture media. The optical biosensor monitors interactions between the analytic and the evanescent field of an optical fiber passing through it. The FO based high voltage and current sensor is a measuring system designed for monitoring voltage and current in high voltage transmission lines. The linearity of the system is better than 2 percent in both ranges of 0 to 25 kV and 0 to 1000 A. The optical flowmeter uses a cross-correlation technique that analyzes two light beams crossing the flow separated by a fixed distance. The x-ray image sensor uses a scintillating FO array, one FO for each image pixel to form an image of the x-ray field. The systems described in this paper use general-purpose components including optical fibers and optoelectronic devices, which are readily available, and of low cost.

UHF front-end feeding RFID-based body sensor networks by exploiting the reader signal

NASA Astrophysics Data System (ADS)

Pasca, M.; Colella, R.; Catarinucci, L.; Tarricone, L.; D'Amico, S.; Baschirotto, A.

2016-05-01

This paper presents an integrated, high-sensitivity UHF radio frequency identification (RFID) power management circuit for body sensor network applications. The circuit consists of a two-stage RF-DC Dickson's rectifier followed by an integrated five-stage DC-DC Pelliconi's charge pump driven by an ultralow start-up voltage LC oscillator. The DC-DC charge pump interposed between the RF-DC rectifier and the output load provides the RF to load isolation avoiding losses due to the diodes reverse saturation current. The RF-DC rectifier has been realized on FR4 substrate, while the charge pump and the oscillator have been realized in 180 nm complementary metal oxide semiconductor (CMOS) technology. Outdoor measurements demonstrate the ability of the power management circuit to provide 400 mV output voltage at 14 m distance from the UHF reader, in correspondence of -25 dBm input signal power. As demonstrated in the literature, such output voltage level is suitable to supply body sensor network nodes.

Fabrication of Ultra-Thin Printed Organic TFT CMOS Logic Circuits Optimized for Low-Voltage Wearable Sensor Applications.

PubMed

Takeda, Yasunori; Hayasaka, Kazuma; Shiwaku, Rei; Yokosawa, Koji; Shiba, Takeo; Mamada, Masashi; Kumaki, Daisuke; Fukuda, Kenjiro; Tokito, Shizuo

2016-05-09

Ultrathin electronic circuits that can be manufactured by using conventional printing technologies are key elements necessary to realize wearable health sensors and next-generation flexible electronic devices. Due to their low level of power consumption, complementary (CMOS) circuits using both types of semiconductors can be easily employed in wireless devices. Here, we describe ultrathin CMOS logic circuits, for which not only the source/drain electrodes but also the semiconductor layers were printed. Both p-type and n-type organic thin film transistor devices were employed in a D-flip flop circuit in the newly developed stacked structure and exhibited excellent electrical characteristics, including good carrier mobilities of 0.34 and 0.21 cm(2) V(-1) sec(-1), and threshold voltages of nearly 0 V with low operating voltages. These printed organic CMOS D-flip flop circuits exhibit operating frequencies of 75 Hz and demonstrate great potential for flexible and printed electronics technology, particularly for wearable sensor applications with wireless connectivity.

Fabrication of Ultra-Thin Printed Organic TFT CMOS Logic Circuits Optimized for Low-Voltage Wearable Sensor Applications

PubMed Central

Takeda, Yasunori; Hayasaka, Kazuma; Shiwaku, Rei; Yokosawa, Koji; Shiba, Takeo; Mamada, Masashi; Kumaki, Daisuke; Fukuda, Kenjiro; Tokito, Shizuo

2016-01-01

Ultrathin electronic circuits that can be manufactured by using conventional printing technologies are key elements necessary to realize wearable health sensors and next-generation flexible electronic devices. Due to their low level of power consumption, complementary (CMOS) circuits using both types of semiconductors can be easily employed in wireless devices. Here, we describe ultrathin CMOS logic circuits, for which not only the source/drain electrodes but also the semiconductor layers were printed. Both p-type and n-type organic thin film transistor devices were employed in a D-flip flop circuit in the newly developed stacked structure and exhibited excellent electrical characteristics, including good carrier mobilities of 0.34 and 0.21 cm2 V−1 sec−1, and threshold voltages of nearly 0 V with low operating voltages. These printed organic CMOS D-flip flop circuits exhibit operating frequencies of 75 Hz and demonstrate great potential for flexible and printed electronics technology, particularly for wearable sensor applications with wireless connectivity. PMID:27157914

The twisted ion-permeation pathway of a resting voltage-sensing domain.

PubMed

Tombola, Francesco; Pathak, Medha M; Gorostiza, Pau; Isacoff, Ehud Y

2007-02-01

Proteins containing voltage-sensing domains (VSDs) translate changes in membrane potential into changes in ion permeability or enzymatic activity. In channels, voltage change triggers a switch in conformation of the VSD, which drives gating in a separate pore domain, or, in channels lacking a pore domain, directly gates an ion pathway within the VSD. Neither mechanism is well understood. In the Shaker potassium channel, mutation of the first arginine residue of the S4 helix to a smaller uncharged residue makes the VSD permeable to ions ('omega current') in the resting conformation ('S4 down'). Here we perform a structure-guided perturbation analysis of the omega conductance to map its VSD permeation pathway. We find that there are four omega pores per channel, which is consistent with one conduction path per VSD. Permeating ions from the extracellular medium enter the VSD at its peripheral junction with the pore domain, and then plunge into the core of the VSD in a curved conduction pathway. Our results provide a model of the resting conformation of the VSD.

Comparative study of 0° X-cut and Y + 36°-cut lithium niobate high-voltage sensing

NASA Astrophysics Data System (ADS)

Patel, N.; Branch, D. W.; Schamiloglu, E.; Cular, S.

2015-08-01

A comparison study between Y + 36° and 0° X-cut lithium niobate (LiNbO3) was performed to evaluate the influence of crystal cut on the acoustic propagation to realize a piezoelectric high-voltage sensor. The acoustic time-of-flight for each crystal cut was measured when applying direct current (DC), alternating current (AC), and pulsed voltages. Results show that the voltage-induced shift in the acoustic wave propagation time scaled quadratically with voltage for DC and AC voltages applied to X-cut crystals. For the Y + 36° crystal, the voltage-induced shift scales linearly with DC voltages and quadratically with AC voltages. When applying 5 μs voltage pulses to both crystals, the voltage-induced shift scaled linearly with voltage. For the Y + 36° cut, the voltage-induced shift from applying DC voltages ranged from 10 to 54 ps and 35 to 778 ps for AC voltages at 640 V over the frequency range of 100 Hz-100 kHz. Using the same conditions as the Y + 36° cut, the 0° X-cut crystal sensed a shift of 10-273 ps for DC voltages and 189-813 ps for AC voltage application. For 5 μs voltage pulses, the 0° X-cut crystal sensed a voltage induced shift of 0.250-2 ns and the Y + 36°-cut crystal sensed a time shift of 0.115-1.6 ns. This suggests a frequency sensitive response to voltage where the influence of the crystal cut was not a significant contributor under DC, AC, or pulsed voltage conditions. The measured DC data were compared to a 1-D impedance matrix model where the predicted incremental length changed as a function of voltage. When the voltage source error was eliminated through physical modeling from the uncertainty budget, the combined uncertainty of the sensor (within a 95% confidence interval) decreased to 0.0033% using a Y + 36°-cut crystal and 0.0032% using an X-cut crystal for all the voltage conditions used in this experiment.

Comparative study of 0° X-cut and Y + 36°-cut lithium niobate high-voltage sensing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Patel, N.; Department of Electrical and Computer Engineering, MSC01 1100, University of New Mexico, Albuquerque, New Mexico 87131-0001; Branch, D. W.

2015-08-15

A comparison study between Y + 36° and 0° X-cut lithium niobate (LiNbO{sub 3}) was performed to evaluate the influence of crystal cut on the acoustic propagation to realize a piezoelectric high-voltage sensor. The acoustic time-of-flight for each crystal cut was measured when applying direct current (DC), alternating current (AC), and pulsed voltages. Results show that the voltage-induced shift in the acoustic wave propagation time scaled quadratically with voltage for DC and AC voltages applied to X-cut crystals. For the Y + 36° crystal, the voltage-induced shift scales linearly with DC voltages and quadratically with AC voltages. When applying 5more » μs voltage pulses to both crystals, the voltage-induced shift scaled linearly with voltage. For the Y + 36° cut, the voltage-induced shift from applying DC voltages ranged from 10 to 54 ps and 35 to 778 ps for AC voltages at 640 V over the frequency range of 100 Hz–100 kHz. Using the same conditions as the Y + 36° cut, the 0° X-cut crystal sensed a shift of 10–273 ps for DC voltages and 189–813 ps for AC voltage application. For 5 μs voltage pulses, the 0° X-cut crystal sensed a voltage induced shift of 0.250–2 ns and the Y + 36°-cut crystal sensed a time shift of 0.115–1.6 ns. This suggests a frequency sensitive response to voltage where the influence of the crystal cut was not a significant contributor under DC, AC, or pulsed voltage conditions. The measured DC data were compared to a 1-D impedance matrix model where the predicted incremental length changed as a function of voltage. When the voltage source error was eliminated through physical modeling from the uncertainty budget, the combined uncertainty of the sensor (within a 95% confidence interval) decreased to 0.0033% using a Y + 36°-cut crystal and 0.0032% using an X-cut crystal for all the voltage conditions used in this experiment.« less

Comparative study of 0° X-cut and Y+36°-cut lithium niobate high-voltage sensing

DOE PAGES

Patel, N.; Branch, D. W.; Schamiloglu, E.; ...

2015-08-11

A comparison study between Y+36° and 0° X-cut lithium niobate (LiNbO 3) was performed to evaluate the influence of crystal cut on the acoustic propagation to realize a piezoelectric high-voltage sensor. The acoustic time-of-flight for each crystal cut was measured when applying direct current (DC), alternating current (AC), and pulsed voltages. Results show that the voltage-induced shift in the acoustic wave propagation time scaled quadratically with voltage for DC and AC voltages applied to X-cut crystals. For the Y+36° crystal, the voltage-induced shift scales linearly with DC voltages and quadratically with AC voltages. When applying 5 μs voltage pulses tomore » both crystals, the voltage-induced shift scaled linearly with voltage. For the Y+36° cut, the voltage-induced shift from applying DC voltages ranged from 10 to 54 ps and 35 to 778 ps for AC voltages at 640 V over the frequency range of 100 Hz–100 kHz. Using the same conditions as the Y+36° cut, the 0° X-cut crystal sensed a shift of 10–273 ps for DC voltages and 189–813 ps for AC voltage application. For 5 μs voltage pulses, the 0° X-cut crystal sensed a voltage induced shift of 0.250–2 ns and the Y+36°-cut crystal sensed a time shift of 0.115–1.6 ns. This suggests a frequency sensitive response to voltage where the influence of the crystal cut was not a significant contributor under DC, AC, or pulsed voltage conditions. The measured DC data were compared to a 1-D impedance matrix model where the predicted incremental length changed as a function of voltage. Furthermore, when the voltage source error was eliminated through physical modeling from the uncertainty budget, the combined uncertainty of the sensor (within a 95% confidence interval) decreased to 0.0033% using a Y + 36°-cut crystal and 0.0032% using an X-cut crystal for all the voltage conditions used in this experiment.« less

Toward Quantifying the Electrostatic Transduction Mechanism in Carbon Nanotube Biomolecular Sensors

NASA Astrophysics Data System (ADS)

Lerner, Mitchell; Kybert, Nicholas; Mendoza, Ryan; Dailey, Jennifer; Johnson, A. T. Charlie

2013-03-01

Despite the great promise of carbon nanotube field-effect transistors (CNT FETs) for applications in chemical and biochemical detection, a quantitative understanding of sensor responses is lacking. To explore the role of electrostatics in sensor transduction, experiments were conducted with a set of similar compounds designed to adsorb onto the CNT FET via a pyrene linker group and take on a set of known charge states under ambient conditions. Acidic and basic species were observed to induce threshold voltage shifts of opposite sign, consistent with gating of the CNT FET by local charges due to protonation or deprotonation of the pyrene compounds by interfacial water. The magnitude of the gate voltage shift was controlled by the distance between the charged group and the CNT. Additionally, functionalization with an uncharged pyrene compound showed a threshold shift ascribed to its molecular dipole moment. This work illustrates a method for producing CNT FETs with controlled values of the turnoff gate voltage, and more generally, these results will inform the development of quantitative models for the response of CNT FET chemical and biochemical sensors. As an example, the results of an experiment detecting biomarkers of Lyme disease will be discussed in the context of this model.

A 12-bit high-speed column-parallel two-step single-slope analog-to-digital converter (ADC) for CMOS image sensors.

PubMed

Lyu, Tao; Yao, Suying; Nie, Kaiming; Xu, Jiangtao

2014-11-17

A 12-bit high-speed column-parallel two-step single-slope (SS) analog-to-digital converter (ADC) for CMOS image sensors is proposed. The proposed ADC employs a single ramp voltage and multiple reference voltages, and the conversion is divided into coarse phase and fine phase to improve the conversion rate. An error calibration scheme is proposed to correct errors caused by offsets among the reference voltages. The digital-to-analog converter (DAC) used for the ramp generator is based on the split-capacitor array with an attenuation capacitor. Analysis of the DAC's linearity performance versus capacitor mismatch and parasitic capacitance is presented. A prototype 1024 × 32 Time Delay Integration (TDI) CMOS image sensor with the proposed ADC architecture has been fabricated in a standard 0.18 μm CMOS process. The proposed ADC has average power consumption of 128 μW and a conventional rate 6 times higher than the conventional SS ADC. A high-quality image, captured at the line rate of 15.5 k lines/s, shows that the proposed ADC is suitable for high-speed CMOS image sensors.

Voltage-Gated Channel Mechanosensitivity: Fact or Friction?

PubMed Central

Morris, Catherine E.

2011-01-01

The heart is a continually active pulsatile fluid pump. It generates appropriate forces by precisely timed and spaced engagement of its contractile machinery. Largely, it makes its own control signals, the most crucial of which are precisely timed and spaced fluxes of ions across the sarcolemma, achieved by the timely opening and closing of diverse voltage-gated channels (VGC). VGCs have four voltage sensors around a central ion-selective pore that opens and closes under the influence of membrane voltage. Operation of any VGC is secondarily tuned by the mechanical state (i.e., structure) of the bilayer in which it is embedded. Rates of opening and closing, in other words, vary with bilayer structure. Thus, in the intensely mechanical environment of the myocardium and its vasculature, VGCs kinetics might be routinely modulated by reversible and irreversible nano-scale changes in bilayer structure. If subtle bilayer deformations are routine in the pumping heart, VGCs could be subtly transducing bilayer mechanical signals, thereby tuning cardiac rhythmicity, collectively contributing to mechano-electric feedback. Reversible bilayer deformations would be expected with changing shear flows and tissue distension, while irreversible bilayer restructuring occurs with ischemia, inflammation, membrane remodeling, etc. I suggest that tools now available could be deployed to help probe whether/how the inherent mechanosensitivity of VGCs – an attribute substantially reflecting the dependence of voltage sensor stability on bilayer structure – contributes to cardiac rhythmicity. Chief among these tools are voltage sensor toxins (whose inhibitory efficacy varies with the mechanical state of bilayer) and arrhythmia-inducing VGC mutants with distinctive mechano-phenotypes. PMID:21660289

Actuation stability test of the LISA pathfinder inertial sensor front-end electronics

NASA Astrophysics Data System (ADS)

Mance, Davor; Gan, Li; Weber, Bill; Weber, Franz; Zweifel, Peter

In order to limit the residual stray forces on the inertial sensor test mass in LISA pathfinder, √ it is required that the fluctuation of the test mass actuation voltage is within 2ppm/ Hz. The actuation voltage stability test on the flight hardware of the inertial sensor front-end electronics (IS FEE) is presented in this paper. This test is completed during the inertial sensor integration at EADS Astrium Friedrichshafen, Germany. The standard measurement method using voltmeter is not sufficient for verification, since the instrument low frequency √ fluctuation is higher than the 2ppm/ Hz requirement. In this test, by using the differential measurement method and the lock-in amplifier, the actuation stability performance is verified and the quality of the IS FEE hardware is confirmed by the test results.

Carbon Nanotube Tape Vibrating Gyroscope

NASA Technical Reports Server (NTRS)

Tucker, Dennis Stephen (Inventor)

2016-01-01

A vibrating gyroscope includes a piezoelectric strip having length and width dimensions. The piezoelectric strip includes a piezoelectric material and carbon nanotubes (CNTs) substantially aligned and polled along the strip's length dimension. A spindle having an axis of rotation is coupled to the piezoelectric strip. The axis of rotation is parallel to the strip's width dimension. A first capacitance sensor is mechanically coupled to the spindle for rotation therewith. The first capacitance sensor is positioned at one of the strip's opposing ends and is spaced apart from one of the strip's opposing faces. A second capacitance sensor is mechanically coupled to the spindle for rotation therewith. The second capacitance sensor is positioned at another of the strip's opposing ends and is spaced apart from another of the strip's opposing faces. A voltage source applies an AC voltage to the piezoelectric strip.

Regulation of Na+ channel inactivation by the DIII and DIV voltage-sensing domains.

PubMed

Hsu, Eric J; Zhu, Wandi; Schubert, Angela R; Voelker, Taylor; Varga, Zoltan; Silva, Jonathan R

2017-03-06

Functional eukaryotic voltage-gated Na + (Na V ) channels comprise four domains (DI-DIV), each containing six membrane-spanning segments (S1-S6). Voltage sensing is accomplished by the first four membrane-spanning segments (S1-S4), which together form a voltage-sensing domain (VSD). A critical Na V channel gating process, inactivation, has previously been linked to activation of the VSDs in DIII and DIV. Here, we probe this interaction by using voltage-clamp fluorometry to observe VSD kinetics in the presence of mutations at locations that have been shown to impair Na V channel inactivation. These locations include the DIII-DIV linker, the DIII S4-S5 linker, and the DIV S4-S5 linker. Our results show that, within the 10-ms timeframe of fast inactivation, the DIV-VSD is the primary regulator of inactivation. However, after longer 100-ms pulses, the DIII-DIV linker slows DIII-VSD deactivation, and the rate of DIII deactivation correlates strongly with the rate of recovery from inactivation. Our results imply that, over the course of an action potential, DIV-VSDs regulate the onset of fast inactivation while DIII-VSDs determine its recovery. © 2017 Hsu et al.

Voltage-sensitive rhodol with enhanced two-photon brightness

PubMed Central

Kulkarni, Rishikesh U.; Kramer, Daniel J.; Pourmandi, Narges; Karbasi, Kaveh; Bateup, Helen S.

2017-01-01

We have designed, synthesized, and applied a rhodol-based chromophore to a molecular wire-based platform for voltage sensing to achieve fast, sensitive, and bright voltage sensing using two-photon (2P) illumination. Rhodol VoltageFluor-5 (RVF5) is a voltage-sensitive dye with improved 2P cross-section for use in thick tissue or brain samples. RVF5 features a dichlororhodol core with pyrrolidyl substitution at the nitrogen center. In mammalian cells under one-photon (1P) illumination, RVF5 demonstrates high voltage sensitivity (28% ΔF/F per 100 mV) and improved photostability relative to first-generation voltage sensors. This photostability enables multisite optical recordings from neurons lacking tuberous sclerosis complex 1, Tsc1, in a mouse model of genetic epilepsy. Using RVF5, we show that Tsc1 KO neurons exhibit increased activity relative to wild-type neurons and additionally show that the proportion of active neurons in the network increases with the loss of Tsc1. The high photostability and voltage sensitivity of RVF5 is recapitulated under 2P illumination. Finally, the ability to chemically tune the 2P absorption profile through the use of rhodol scaffolds affords the unique opportunity to image neuronal voltage changes in acutely prepared mouse brain slices using 2P illumination. Stimulation of the mouse hippocampus evoked spiking activity that was readily discerned with bath-applied RVF5, demonstrating the utility of RVF5 and molecular wire-based voltage sensors with 2P-optimized fluorophores for imaging voltage in intact brain tissue. PMID:28242676

Microhotplate Temperature Sensor Calibration and BIST

PubMed Central

Afridi, M.; Montgomery, C.; Cooper-Balis, E.; Semancik, S.; Kreider, K. G.; Geist, J.

2011-01-01

In this paper we describe a novel long-term microhotplate temperature sensor calibration technique suitable for Built-In Self Test (BIST). The microhotplate thermal resistance (thermal efficiency) and the thermal voltage from an integrated platinum-rhodium thermocouple were calibrated against a freshly calibrated four-wire polysilicon microhotplate-heater temperature sensor (heater) that is not stable over long periods of time when exposed to higher temperatures. To stress the microhotplate, its temperature was raised to around 400 °C and held there for days. The heater was then recalibrated as a temperature sensor, and microhotplate temperature measurements were made based on the fresh calibration of the heater, the first calibration of the heater, the microhotplate thermal resistance, and the thermocouple voltage. This procedure was repeated 10 times over a period of 80 days. The results show that the heater calibration drifted substantially during the period of the test while the microhotplate thermal resistance and the thermocouple-voltage remained stable to within about plus or minus 1 °C over the same period. Therefore, the combination of a microhotplate heater-temperature sensor and either the microhotplate thermal resistance or an integrated thin film platinum-rhodium thermocouple can be used to provide a stable, calibrated, microhotplate-temperature sensor, and the combination of the three sensor is suitable for implementing BIST functionality. Alternatively, if a stable microhotplate-heater temperature sensor is available, such as a properly annealed platinum heater-temperature sensor, then the thermal resistance of the microhotplate and the electrical resistance of the platinum heater will be sufficient to implement BIST. It is also shown that aluminum- and polysilicon-based temperature sensors, which are not stable enough for measuring high microhotplate temperatures (>220 °C) without impractically frequent recalibration, can be used to measure the silicon substrate temperature if never exposed to temperatures above about 220 °C. PMID:26989603

Electron tunneling infrared sensor module with integrated control circuitry

NASA Technical Reports Server (NTRS)

Boyadzhyan-Sevak, Vardkes V. (Inventor)

2001-01-01

In an integrated electron tunneling sensor, an automatic tunneling control circuit varies a high voltage bias applied to the sensor deflection electrode in response to changes in sensor output to maintain the proper gap between the sensor tip and membrane. The control circuit ensures stable tunneling activity in the presence of large signals and other disturbances to the sensor. Output signals from the module may be derived from the amplified sensor output. The integrated sensor module is particularly well adapted for use in blood glucose measurement and monitoring system.

Structural mechanism of voltage-dependent gating in an isolated voltage-sensing domain.

PubMed

Li, Qufei; Wanderling, Sherry; Paduch, Marcin; Medovoy, David; Singharoy, Abhishek; McGreevy, Ryan; Villalba-Galea, Carlos A; Hulse, Raymond E; Roux, Benoît; Schulten, Klaus; Kossiakoff, Anthony; Perozo, Eduardo

2014-03-01

The transduction of transmembrane electric fields into protein motion has an essential role in the generation and propagation of cellular signals. Voltage-sensing domains (VSDs) carry out these functions through reorientations of positive charges in the S4 helix. Here, we determined crystal structures of the Ciona intestinalis VSD (Ci-VSD) in putatively active and resting conformations. S4 undergoes an ~5-Å displacement along its main axis, accompanied by an ~60° rotation. This movement is stabilized by an exchange in countercharge partners in helices S1 and S3 that generates an estimated net charge transfer of ~1 eo. Gating charges move relative to a ''hydrophobic gasket' that electrically divides intra- and extracellular compartments. EPR spectroscopy confirms the limited nature of S4 movement in a membrane environment. These results provide an explicit mechanism for voltage sensing and set the basis for electromechanical coupling in voltage-dependent enzymes and ion channels.

Temporal resistance variation of the second generation HTS tape during superconducting-to-normal state transition.

PubMed

Malginov, Vladimir A; Malginov, Andrey V; Fleishman, Leonid S

2013-01-01

The quench process in high-temperature superconducting (HTS) wires plays an important role in superconducting power devices, such as fault current limiters, magnets, cables, etc. The superconducting device should survive after the overheating due to quench. We studied the evolution of the resistance of the YBCO tape wire during the quench process with 1 ms time resolution for various excitation voltages. The resistive normal zone was found to be located in a domain of about 1-4 cm long. The normal state nucleation begins in 40-60 ms after voltage is applied across the HTS tape. In subsequent 200-300 ms other normal state regions appear. The normal domain heating continues in the following 5-10s that results in a factor of 2-3 increase of its resistance. Formation of the normal domain during the quench process follows the same stages for different excitation voltages. Characteristic domain sizes, lifetimes and temperatures are determined for all stages.

Precision liquid level sensor

DOEpatents

Field, M.E.; Sullivan, W.H.

A precision liquid level sensor utilizes a balanced bridge, each arm including an air dielectric line. Changes in liquid level along one air dielectric line imbalance the bridge and create a voltage which is directly measurable across the bridge.

Experimental study for the reproduction of sudden unintended acceleration incidents.

PubMed

Park, Sungji; Choi, Youngsuk; Choi, Woongchul

2016-10-01

A few cases of the sudden unintended acceleration have been reported over the last few years [1-11] and some of them seemed to be somewhat related to an electronic throttle control (ETC) system [11,12]. In this experimental study, efforts were made to reproduce the cases of sudden unintended acceleration possibly related to the ETC. Typically, an ETC of the engine is managed based on signals from airflow sensor, throttle position sensor and acceleration pedal sensor. With this typical sensor configuration in mind, these sensor signals were checked for noise levels. However, none of them showed any clear relationship with the sudden unintended acceleration mainly due to the robustness of the ETC logic software. As an alternative approach, supply voltage to an engine control unit (ECU) was tempered intentionally to observe any clues for the incidents. The observed results with the supply voltage drop and fluctuation tests were rather astonishing. The throttle valve position went all the way up to 100% for around one second when the battery voltage plunged down to 7V periodically despite that the acceleration pedal position was kept steady. As an effort to confirm the case, multiple tries were made systematically on a chassis dynamometer as well as on the test road. In this paper, detailed procedures and findings are reported accordingly. Copyright © 2016 Elsevier Ireland Ltd. All rights reserved.