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Sample records for activated ion channels

  1. Mechanically Activated Ion Channels.

    PubMed

    Ranade, Sanjeev S; Syeda, Ruhma; Patapoutian, Ardem

    2015-09-23

    Mechanotransduction, the conversion of physical forces into biochemical signals, is essential for various physiological processes such as the conscious sensations of touch and hearing, and the unconscious sensation of blood flow. Mechanically activated (MA) ion channels have been proposed as sensors of physical force, but the identity of these channels and an understanding of how mechanical force is transduced has remained elusive. A number of recent studies on previously known ion channels along with the identification of novel MA ion channels have greatly transformed our understanding of touch and hearing in both vertebrates and invertebrates. Here, we present an updated review of eukaryotic ion channel families that have been implicated in mechanotransduction processes and evaluate the qualifications of the candidate genes according to specified criteria. We then discuss the proposed gating models for MA ion channels and highlight recent structural studies of mechanosensitive potassium channels. PMID:26402601

  2. Detection of single ion channel activity with carbon nanotubes

    PubMed Central

    Zhou, Weiwei; Wang, Yung Yu; Lim, Tae-Sun; Pham, Ted; Jain, Dheeraj; Burke, Peter J.

    2015-01-01

    Many processes in life are based on ion currents and membrane voltages controlled by a sophisticated and diverse family of membrane proteins (ion channels), which are comparable in size to the most advanced nanoelectronic components currently under development. Here we demonstrate an electrical assay of individual ion channel activity by measuring the dynamic opening and closing of the ion channel nanopores using single-walled carbon nanotubes (SWNTs). Two canonical dynamic ion channels (gramicidin A (gA) and alamethicin) and one static biological nanopore (α-hemolysin (α-HL)) were successfully incorporated into supported lipid bilayers (SLBs, an artificial cell membrane), which in turn were interfaced to the carbon nanotubes through a variety of polymer-cushion surface functionalization schemes. The ion channel current directly charges the quantum capacitance of a single nanotube in a network of purified semiconducting nanotubes. This work forms the foundation for a scalable, massively parallel architecture of 1d nanoelectronic devices interrogating electrophysiology at the single ion channel level. PMID:25778101

  3. Detection of single ion channel activity with carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Zhou, Weiwei; Wang, Yung Yu; Lim, Tae-Sun; Pham, Ted; Jain, Dheeraj; Burke, Peter J.

    2015-03-01

    Many processes in life are based on ion currents and membrane voltages controlled by a sophisticated and diverse family of membrane proteins (ion channels), which are comparable in size to the most advanced nanoelectronic components currently under development. Here we demonstrate an electrical assay of individual ion channel activity by measuring the dynamic opening and closing of the ion channel nanopores using single-walled carbon nanotubes (SWNTs). Two canonical dynamic ion channels (gramicidin A (gA) and alamethicin) and one static biological nanopore (α-hemolysin (α-HL)) were successfully incorporated into supported lipid bilayers (SLBs, an artificial cell membrane), which in turn were interfaced to the carbon nanotubes through a variety of polymer-cushion surface functionalization schemes. The ion channel current directly charges the quantum capacitance of a single nanotube in a network of purified semiconducting nanotubes. This work forms the foundation for a scalable, massively parallel architecture of 1d nanoelectronic devices interrogating electrophysiology at the single ion channel level.

  4. Detection of single ion channel activity with carbon nanotubes.

    PubMed

    Zhou, Weiwei; Wang, Yung Yu; Lim, Tae-Sun; Pham, Ted; Jain, Dheeraj; Burke, Peter J

    2015-01-01

    Many processes in life are based on ion currents and membrane voltages controlled by a sophisticated and diverse family of membrane proteins (ion channels), which are comparable in size to the most advanced nanoelectronic components currently under development. Here we demonstrate an electrical assay of individual ion channel activity by measuring the dynamic opening and closing of the ion channel nanopores using single-walled carbon nanotubes (SWNTs). Two canonical dynamic ion channels (gramicidin A (gA) and alamethicin) and one static biological nanopore (α-hemolysin (α-HL)) were successfully incorporated into supported lipid bilayers (SLBs, an artificial cell membrane), which in turn were interfaced to the carbon nanotubes through a variety of polymer-cushion surface functionalization schemes. The ion channel current directly charges the quantum capacitance of a single nanotube in a network of purified semiconducting nanotubes. This work forms the foundation for a scalable, massively parallel architecture of 1d nanoelectronic devices interrogating electrophysiology at the single ion channel level. PMID:25778101

  5. Lipid bilayer array for simultaneous recording of ion channel activities

    NASA Astrophysics Data System (ADS)

    Hirano-Iwata, Ayumi; Nasu, Tomohiro; Oshima, Azusa; Kimura, Yasuo; Niwano, Michio

    2012-07-01

    This paper describes an array of stable and reduced-solvent bilayer lipid membranes (BLMs) formed in microfabricated silicon chips. BLMs were first vertically formed simultaneously and then turned 90° in order to realize a horizontal BLM array. Since the present BLMs are mechanically stable and robust, the BLMs survive this relatively tough process. Typically, a ˜60% yield in simultaneous BLM formation over 9 sites was obtained. Parallel recordings of gramicidin channel activities from different BLMs were demonstrated. The present system has great potential as a platform of BLM-based high throughput drug screening for ion channel proteins.

  6. Light-Activated Ion Channels for Remote Control of Neural Activity

    PubMed Central

    Chambers, James J.; Kramer, Richard H.

    2009-01-01

    Light-activated ion channels provide a new opportunity to precisely and remotely control neuronal activity for experimental applications in neurobiology. In the past few years, several strategies have arisen that allow light to control ion channels and therefore neuronal function. Light-based triggers for ion channel control include caged compounds, which release active neurotransmitters when photolyzed with light, and natural photoreceptive proteins, which can be expressed exogenously in neurons. More recently, a third type of light trigger has been introduced: a photoisomerizable tethered ligand that directly controls ion channel activity in a light-dependent manner. Beyond the experimental applications for light-gated ion channels, there may be clinical applications in which these light-sensitive ion channels could prove advantageous over traditional methods. Electrodes for neural stimulation to control disease symptoms are invasive and often difficult to reposition between cells in tissue. Stimulation by chemical agents is difficult to constrain to individual cells and has limited temporal accuracy in tissue due to diffusional limitations. In contrast, ion channels that can be directly activated with light allow control with unparalleled spatial and temporal precision. The goal of this chapter is to describe light-regulated ion channels and how they have been tailored to control different aspects of neural activity, and how to use these channels to manipulate and better understand development, function, and plasticity of neurons and neural circuits. PMID:19195553

  7. Structure and activity of the acid-sensing ion channels

    PubMed Central

    Sherwood, Thomas W.; Frey, Erin N.

    2012-01-01

    The acid-sensing ion channels (ASICs) are a family of proton-sensing channels expressed throughout the nervous system. Their activity is linked to a variety of complex behaviors including fear, anxiety, pain, depression, learning, and memory. ASICs have also been implicated in neuronal degeneration accompanying ischemia and multiple sclerosis. As a whole, ASICs represent novel therapeutic targets for several clinically important disorders. An understanding of the correlation between ASIC structure and function will help to elucidate their mechanism of action and identify potential therapeutics that specifically target these ion channels. Despite the seemingly simple nature of proton binding, multiple studies have shown that proton-dependent gating of ASICs is quite complex, leading to activation and desensitization through distinct structural components. This review will focus on the structural aspects of ASIC gating in response to both protons and the newly discovered activators GMQ and MitTx. ASIC modulatory compounds and their action on proton-dependent gating will also be discussed. This review is dedicated to the memory of Dale Benos, who made a substantial contribution to our understanding of ASIC activity. PMID:22843794

  8. Molecular candidates for cardiac stretch-activated ion channels

    PubMed Central

    Reed, Alistair; Kohl, Peter; Peyronnet, Rémi

    2014-01-01

    The heart is a mechanically-active organ that dynamically senses its own mechanical environment. This environment is constantly changing, on a beat-by-beat basis, with additional modulation by respiratory activity and changes in posture or physical activity, and further overlaid with more slowly occurring physiological (e.g. pregnancy, endurance training) or pathological challenges (e.g. pressure or volume overload). Far from being a simple pump, the heart detects changes in mechanical demand and adjusts its performance accordingly, both via heart rate and stroke volume alteration. Many of the underlying regulatory processes are encoded intracardially, and are thus maintained even in heart transplant recipients. Over the last three decades, molecular substrates of cardiac mechanosensitivity have gained increasing recognition in the scientific and clinical communities. Nonetheless, the processes underlying this phenomenon are still poorly understood. Stretch-activated ion channels (SAC) have been identified as one contributor to mechanosensitive autoregulation of the heartbeat. They also appear to play important roles in the development of cardiac pathologies – most notably stretch-induced arrhythmias. As recently discovered, some established cardiac drugs act, in part at least, via mechanotransduction pathways suggesting SAC as potential therapeutic targets. Clearly, identification of the molecular substrate of cardiac SAC is of clinical importance and a number of candidate proteins have been identified. At the same time, experimental studies have revealed variable–and at times contrasting–results regarding their function. Further complication arises from the fact that many ion channels that are not classically defined as SAC, including voltage and ligand-gated ion channels, can respond to mechanical stimulation. Here, we summarise what is known about the molecular substrate of the main candidates for cardiac SAC, before identifying potential further

  9. Ion permeation of AQP6 water channel protein. Single channel recordings after Hg2+ activation.

    PubMed

    Hazama, Akihiro; Kozono, David; Guggino, William B; Agre, Peter; Yasui, Masato

    2002-08-01

    Aquaporin-6 (AQP6) has recently been identified as an intracellular vesicle water channel with anion permeability that is activated by low pH or HgCl2. Here we present direct evidence of AQP6 channel gating using patch clamp techniques. Cell-attached patch recordings of AQP6 expressed in Xenopus laevis oocytes indicated that AQP6 is a gated channel with intermediate conductance (49 picosiemens in 100 mm NaCl) induced by 10 microm HgCl2. Current-voltage relationships were linear, and open probability was fairly constant at any given voltage, indicating that Hg2+-induced AQP6 conductance is voltage-independent. The excised outside-out patch recording revealed rapid activation of AQP6 channels immediately after application of 10 microm HgCl2. Reduction of both Na+ and Cl- concentrations from 100 to 30 mm did not shift the reversal potential of the Hg2+-induced AQP6 current, suggesting that Na+ is as permeable as Cl-. The Na+ permeability of Hg2+-induced AQP6 current was further demonstrated by 22Na+ influx measurements. Site-directed mutagenesis identified Cys-155 and Cys-190 residues as the sites of Hg2+ activation both for water permeability and ion conductance. The Hill coefficient from the concentration-response curve for Hg2+-induced conductance was 1.1 +/- 0.3. These data provide the first evidence of AQP6 channel gating at a single-channel level and suggest that each monomer contains the pore region for ions based on the number of Hg2+-binding sites and the kinetics of Hg2+-activation of the channel. PMID:12034750

  10. Ion channels activated by light in Limulus ventral photoreceptors

    PubMed Central

    1986-01-01

    The light-activated conductance of Limulus ventral photoreceptors was studied using the patch-clamp technique. Channels (40 pS) were observed whose probability of opening was greatly increased by light. In some cells the latency of channel activation was nearly the same as that of the macroscopic response, while in other cells the channel latency was much greater. Like the macroscopic conductance, channel activity was reduced by light adaptation but enhanced by the intracellular injection of the calcium chelator EGTA. The latter observation indicates that channel activation was not a secondary result of the light-induced rise in intracellular calcium. A two-microelectrode voltage-clamp method was used to measure the voltage dependence of the light-activated macroscopic conductance. It was found that this conductance is constant over a wide voltage range more negative than zero, but it increases markedly at positive voltages. The single channel currents measured over this same voltage range show that the single channel conductance is independent of voltage, but that channel gating properties are dependent on voltage. Both the mean channel open time and the opening rate increase at positive voltages. These properties change in a manner consistent with the voltage dependence of the macroscopic conductance. The broad range of similarities between the macroscopic and single channel currents supports the conclusion that the 40-pS channel that we have observed is the principal channel underlying the response to light in these photoreceptors. PMID:2419481

  11. Phosphoinositides regulate ion channels

    PubMed Central

    Hille, Bertil; Dickson, Eamonn J.; Kruse, Martin; Vivas, Oscar; Suh, Byung-Chang

    2014-01-01

    Phosphoinositides serve as signature motifs for different cellular membranes and often are required for the function of membrane proteins. Here, we summarize clear evidence supporting the concept that many ion channels are regulated by membrane phosphoinositides. We describe tools used to test their dependence on phosphoinositides, especially phosphatidylinositol 4,5-bisphosphate, and consider mechanisms and biological meanings of phosphoinositide regulation of ion channels. This lipid regulation can underlie changes of channel activity and electrical excitability in response to receptors. Since different intracellular membranes have different lipid compositions, the activity of ion channels still in transit towards their final destination membrane may be suppressed until they reach an optimal lipid environment. PMID:25241941

  12. Ion Channels in Regulation of Neuronal Regenerative Activities

    PubMed Central

    Chen, Dongdong; Yu, Shan Ping; Wei, Ling

    2014-01-01

    The regeneration of the nervous system is achieved by the regrowth of damaged neuronal axons, the restoration of damaged nerve cells, and the generation of new neurons to replace those that have been lost. In the central nervous system the regenerative ability is limited by various factors including damaged oligodendrocytes that are essential for neuronal axon myelination, an emerging glial scar, and secondary injury in the surrounding areas. Stem cell transplantation therapy has been shown to be a promising approach to treating neurodegenerative diseases because of the regenerative capability of stem cells that secrete neurotrophic factors and give rise to differentiated progeny. However, some issues of stem cell transplantation, such as survival, homing, and efficiency of neural differentiation after transplantation, still need to be improved. Ion channels allow for the exchange of ions between the intra- and extracellular spaces or between the cytoplasm and organelles. These ion channels maintain the ion homeostasis in the brain and play a key role in regulating the physiological function of the nervous system and allowing the processing of neuronal signals. In seeking a potential strategy to enhance the efficacy of stem cell therapy in neurological and neurodegenerative diseases, this review briefly summarizes the roles of ion channels in cell proliferation, differentiation, migration, chemotropic axon guidance of growth cones and axon outgrowth after injury. PMID:24399572

  13. Ion channels in microbes

    PubMed Central

    Martinac, Boris; Saimi, Yoshiro; Kung, Ching

    2008-01-01

    Summary Studies of ion channels have for long been dominated by the animalcentric, if not anthropocentric view of physiology. The structures and activities of ion channels had, however, evolved long before the appearance of complex multicellular organisms on Earth. The diversity of ion channels existing in cellular membranes of prokaryotes is a good example. Though at first it may appear as a paradox that most of what we know about the structure of eukaryotic ion channels is based on the structure of bacterial channels, this should not be surprising given the evolutionary relatedness of all living organisms and suitability of microbial cells for structural studies of biological macromolecules in a laboratory environment. Genome sequences of the human as well as various microbial, plant and animal organisms unambiguously established the evolutionary links, whereas crystallographic studies of the structures of major types of ion channels published over the last decade clearly demonstrated the advantage of using microbes as experimental organisms. The purpose of this review is not only to provide an account of acquired knowledge on microbial ion channels but also to show that the study of microbes and their ion channels may also hold a key to solving unresolved molecular mysteries in the future. PMID:18923187

  14. Fe(2+) substrate transport through ferritin protein cage ion channels influences enzyme activity and biomineralization.

    PubMed

    Behera, Rabindra K; Torres, Rodrigo; Tosha, Takehiko; Bradley, Justin M; Goulding, Celia W; Theil, Elizabeth C

    2015-09-01

    Ferritins, complex protein nanocages, form internal iron-oxy minerals (Fe2O3·H2O), by moving cytoplasmic Fe(2+) through intracage ion channels to cage-embedded enzyme (2Fe(2+)/O2 oxidoreductase) sites where ferritin biomineralization is initiated. The products of ferritin enzyme activity are diferric oxy complexes that are mineral precursors. Conserved, carboxylate amino acid side chains of D127 from each of three cage subunits project into ferritin ion channels near the interior ion channel exits and, thus, could direct Fe(2+) movement to the internal enzyme sites. Ferritin D127E was designed and analyzed to probe properties of ion channel size and carboxylate crowding near the internal ion channel opening. Glu side chains are chemically equivalent to, but longer by one -CH2 than Asp, side chains. Ferritin D127E assembled into normal protein cages, but diferric peroxo formation (enzyme activity) was not observed, when measured at 650 nm (DFP λ max). The caged biomineral formation, measured at 350 nm in the middle of the broad, nonspecific Fe(3+)-O absorption band, was slower. Structural differences (protein X-ray crystallography), between ion channels in wild type and ferritin D127E, which correlate with the inhibition of ferritin D127E enzyme activity include: (1) narrower interior ion channel openings/pores; (2) increased numbers of ion channel protein-metal binding sites, and (3) a change in ion channel electrostatics due to carboxylate crowding. The contributions of ion channel size and structure to ferritin activity reflect metal ion transport in ion channels are precisely regulated both in ferritin protein nanocages and membranes of living cells. PMID:26202907

  15. Active membrane having uniform physico-chemically functionalized ion channels

    DOEpatents

    Gerald, II, Rex E; Ruscic, Katarina J; Sears, Devin N; Smith, Luis J; Klingler, Robert J; Rathke, Jerome W

    2012-09-24

    The present invention relates to a physicochemically-active porous membrane for electrochemical cells that purports dual functions: an electronic insulator (separator) and a unidirectional ion-transporter (electrolyte). The electrochemical cell membrane is activated for the transport of ions by contiguous ion coordination sites on the interior two-dimensional surfaces of the trans-membrane unidirectional pores. One dimension of the pore surface has a macroscopic length (1 nm-1000 .mu.m) and is directed parallel to the direction of an electric field, which is produced between the cathode and the anode electrodes of an electrochemical cell. The membrane material is designed to have physicochemical interaction with ions. Control of the extent of the interactions between the ions and the interior pore walls of the membrane and other materials, chemicals, or structures contained within the pores provides adjustability of the ionic conductivity of the membrane.

  16. Phosphatidylinositol-3-kinase regulates mast cell ion channel activity.

    PubMed

    Lam, Rebecca S; Shumilina, Ekaterina; Matzner, Nicole; Zemtsova, Irina M; Sobiesiak, Malgorzata; Lang, Camelia; Felder, Edward; Dietl, Paul; Huber, Stephan M; Lang, Florian

    2008-01-01

    Stimulation of the mast cell IgE-receptor (FcepsilonRI) by antigen leads to stimulation of Ca(2+) entry with subsequent mast cell degranulation and release of inflammatory mediators. Ca(2+) further activates Ca(2+)-activated K(+) channels, which in turn provide the electrical driving force for Ca(2+) entry. Since phosphatidylinositol (PI)-3-kinase has previously been shown to be required for mast cell activation and degranulation, we explored, whether mast cell Ca(2+) and Ca(2+)-activated K(+) channels may be sensitive to PI3-kinase activity. Whole-cell patch clamp experiments and Fura-2 fluorescence measurements for determination of cytosolic Ca(2+) concentration were performed in mouse bone marrow-derived mast cells either treated or untreated with the PI3-kinase inhibitors LY-294002 (10 muM) and wortmannin (100 nM). Antigen-stimulated Ca(2+) entry but not Ca(2+) release from the intracellular stores was dramatically reduced upon PI3-kinase inhibition. Ca(2+) entry was further inhibited by TRPV blocker ruthenium red (10 muM). Ca(2+) entry following readdition after Ca(+)-store depletion with thapsigargin was again decreased by LY-294002, pointing to inhibition of store-operated channels (SOCs). Moreover, inhibition of PI3-kinase abrogated IgE-stimulated, but not ionomycin-induced stimulation of Ca(2+)-activated K(+) channels. These observations disclose PI3-kinase-dependent regulation of Ca(2+) entry and Ca(2+)-activated K(+)-channels, which in turn participate in triggering mast cell degranulation. PMID:18769043

  17. Zinc activates damage-sensing TRPA1 ion channels

    PubMed Central

    Hu, Hongzhen; Bandell, Michael; Petrus, Matt J.; Zhu, Michael X.; Patapoutian, Ardem

    2009-01-01

    Zinc is an essential biological trace element. It is required for the structure or function of over 300 proteins, and is increasingly recognized for its role in cell signaling. However, high concentrations of zinc have cytotoxic effects, and overexposure to zinc can cause pain and inflammation through unknown mechanisms. Here we show that zinc excites nociceptive somatosensory neurons and causes nociception in mice through TRPA1, a cation channel previously shown to mediate the pungency of wasabi and cinnamon through cysteine-modification. Zinc activates TRPA1 through a novel mechanism that requires zinc influx through TRPA1 channels and subsequent activation via specific intracellular cysteine and histidine residues. TRPA1 is highly sensitive to intracellular zinc, as low nanomolar concentrations activate TRPA1 and modulate its sensitivity. These findings identify TRPA1 as a major target for the sensory effects of zinc, and support an emerging role for zinc as a signaling molecule that can modulate sensory transmission. PMID:19202543

  18. Modulation of bone remodeling via mechanically activated ion channels

    NASA Technical Reports Server (NTRS)

    Duncan, Randall L. (Principal Investigator)

    1996-01-01

    A critical factor in the maintenance of bone mass is the physical forces imposed upon the skeleton. Removal of these forces, such as in a weightless environment, results in a rapid loss of bone, whereas application of exogenous mechanical strain has been shown to increase bone formation. Numerous flight and ground-based experiments indicate that the osteoblast is the key bone cell influenced by mechanical stimulation. Aside from early transient fluctuations in response to unloading, osteoclast number and activity seem unaffected by removal of strain. However, bone formation is drastically reduced in weightlessness and osteoblasts respond to mechanical strain with an increase in the activity of a number of second messenger pathways resulting in increased anabolic activity. Unfortunately, the mechanism by which the osteoblast converts physical stimuli into a biochemical message, a process we have termed biochemical coupling, remains elusive. Prior to the application of this grant, we had characterized a mechanosensitive, cation nonselective channel (SA-cat) in osteoblast-like osteosarcoma cells that we proposed is the initial signalling mechanism for mechanotransduction. During the execution of this grant, we have made considerable progress to further characterize this channel as well as to determine its role in the osteoblastic response to mechanical strain. To achieve these goals, we combined electrophysiologic techniques with cellular and molecular biology methods to examine the role of these channels in the normal function of the osteoblast in vitro.

  19. Relevance of Viroporin Ion Channel Activity on Viral Replication and Pathogenesis.

    PubMed

    Nieto-Torres, Jose L; Verdiá-Báguena, Carmina; Castaño-Rodriguez, Carlos; Aguilella, Vicente M; Enjuanes, Luis

    2015-07-01

    Modification of host-cell ionic content is a significant issue for viruses, as several viral proteins displaying ion channel activity, named viroporins, have been identified. Viroporins interact with different cellular membranes and self-assemble forming ion conductive pores. In general, these channels display mild ion selectivity, and, eventually, membrane lipids play key structural and functional roles in the pore. Viroporins stimulate virus production through different mechanisms, and ion channel conductivity has been proved particularly relevant in several cases. Key stages of the viral cycle such as virus uncoating, transport and maturation are ion-influenced processes in many viral species. Besides boosting virus propagation, viroporins have also been associated with pathogenesis. Linking pathogenesis either to the ion conductivity or to other functions of viroporins has been elusive for a long time. This article summarizes novel pathways leading to disease stimulated by viroporin ion conduction, such as inflammasome driven immunopathology. PMID:26151305

  20. Relevance of Viroporin Ion Channel Activity on Viral Replication and Pathogenesis

    PubMed Central

    Nieto-Torres, Jose L.; Verdiá-Báguena, Carmina; Castaño-Rodriguez, Carlos; Aguilella, Vicente M.; Enjuanes, Luis

    2015-01-01

    Modification of host-cell ionic content is a significant issue for viruses, as several viral proteins displaying ion channel activity, named viroporins, have been identified. Viroporins interact with different cellular membranes and self-assemble forming ion conductive pores. In general, these channels display mild ion selectivity, and, eventually, membrane lipids play key structural and functional roles in the pore. Viroporins stimulate virus production through different mechanisms, and ion channel conductivity has been proved particularly relevant in several cases. Key stages of the viral cycle such as virus uncoating, transport and maturation are ion-influenced processes in many viral species. Besides boosting virus propagation, viroporins have also been associated with pathogenesis. Linking pathogenesis either to the ion conductivity or to other functions of viroporins has been elusive for a long time. This article summarizes novel pathways leading to disease stimulated by viroporin ion conduction, such as inflammasome driven immunopathology. PMID:26151305

  1. Calcium ions open a selectivity filter gate during activation of the MthK potassium channel

    NASA Astrophysics Data System (ADS)

    Posson, David J.; Rusinova, Radda; Andersen, Olaf S.; Nimigean, Crina M.

    2015-09-01

    Ion channel opening and closing are fundamental to cellular signalling and homeostasis. Gates that control K+ channel activity were found both at an intracellular pore constriction and within the selectivity filter near the extracellular side but the specific location of the gate that opens Ca2+-activated K+ channels has remained elusive. Using the Methanobacterium thermoautotrophicum homologue (MthK) and a stopped-flow fluorometric assay for fast channel activation, we show that intracellular quaternary ammonium blockers bind to closed MthK channels. Since the blockers are known to bind inside a central channel cavity, past the intracellular entryway, the gate must be within the selectivity filter. Furthermore, the blockers access the closed channel slower than the open channel, suggesting that the intracellular entryway narrows upon pore closure, without preventing access of either the blockers or the smaller K+. Thus, Ca2+-dependent gating in MthK occurs at the selectivity filter with coupled movement of the intracellular helices.

  2. Mitochondrial Ion Channels

    PubMed Central

    O’Rourke, Brian

    2009-01-01

    In work spanning more than a century, mitochondria have been recognized for their multifunctional roles in metabolism, energy transduction, ion transport, inheritance, signaling, and cell death. Foremost among these tasks is the continuous production of ATP through oxidative phosphorylation, which requires a large electrochemical driving force for protons across the mitochondrial inner membrane. This process requires a membrane with relatively low permeability to ions to minimize energy dissipation. However, a wealth of evidence now indicates that both selective and nonselective ion channels are present in the mitochondrial inner membrane, along with several known channels on the outer membrane. Some of these channels are active under physiological conditions, and others may be activated under pathophysiological conditions to act as the major determinants of cell life and death. This review summarizes research on mitochondrial ion channels and efforts to identify their molecular correlates. Except in a few cases, our understanding of the structure of mitochondrial ion channels is limited, indicating the need for focused discovery in this area. PMID:17059356

  3. Chemoselective tarantula toxins report voltage activation of wild-type ion channels in live cells.

    PubMed

    Tilley, Drew C; Eum, Kenneth S; Fletcher-Taylor, Sebastian; Austin, Daniel C; Dupré, Christophe; Patrón, Lilian A; Garcia, Rita L; Lam, Kit; Yarov-Yarovoy, Vladimir; Cohen, Bruce E; Sack, Jon T

    2014-11-01

    Electrically excitable cells, such as neurons, exhibit tremendous diversity in their firing patterns, a consequence of the complex collection of ion channels present in any specific cell. Although numerous methods are capable of measuring cellular electrical signals, understanding which types of ion channels give rise to these signals remains a significant challenge. Here, we describe exogenous probes which use a novel mechanism to report activity of voltage-gated channels. We have synthesized chemoselective derivatives of the tarantula toxin guangxitoxin-1E (GxTX), an inhibitory cystine knot peptide that binds selectively to Kv2-type voltage gated potassium channels. We find that voltage activation of Kv2.1 channels triggers GxTX dissociation, and thus GxTX binding dynamically marks Kv2 activation. We identify GxTX residues that can be replaced by thiol- or alkyne-bearing amino acids, without disrupting toxin folding or activity, and chemoselectively ligate fluorophores or affinity probes to these sites. We find that GxTX-fluorophore conjugates colocalize with Kv2.1 clusters in live cells and are released from channels activated by voltage stimuli. Kv2.1 activation can be detected with concentrations of probe that have a trivial impact on cellular currents. Chemoselective GxTX mutants conjugated to dendrimeric beads likewise bind live cells expressing Kv2.1, and the beads are released by channel activation. These optical sensors of conformational change are prototype probes that can indicate when ion channels contribute to electrical signaling. PMID:25331865

  4. Molecular mechanism of ATP binding and ion channel activation in P2X receptors

    SciTech Connect

    Hattori, Motoyuki; Gouaux, Eric

    2012-10-24

    P2X receptors are trimeric ATP-activated ion channels permeable to Na{sup +}, K{sup +} and Ca{sup 2+}. The seven P2X receptor subtypes are implicated in physiological processes that include modulation of synaptic transmission, contraction of smooth muscle, secretion of chemical transmitters and regulation of immune responses. Despite the importance of P2X receptors in cellular physiology, the three-dimensional composition of the ATP-binding site, the structural mechanism of ATP-dependent ion channel gating and the architecture of the open ion channel pore are unknown. Here we report the crystal structure of the zebrafish P2X4 receptor in complex with ATP and a new structure of the apo receptor. The agonist-bound structure reveals a previously unseen ATP-binding motif and an open ion channel pore. ATP binding induces cleft closure of the nucleotide-binding pocket, flexing of the lower body {beta}-sheet and a radial expansion of the extracellular vestibule. The structural widening of the extracellular vestibule is directly coupled to the opening of the ion channel pore by way of an iris-like expansion of the transmembrane helices. The structural delineation of the ATP-binding site and the ion channel pore, together with the conformational changes associated with ion channel gating, will stimulate development of new pharmacological agents.

  5. The Earliest Ion Channels

    NASA Astrophysics Data System (ADS)

    Pohorille, A.; Wilson, M. A.; Wei, C.

    2009-12-01

    Supplying protocells with ions required assistance from channels spanning their membrane walls. The earliest channels were most likely short proteins that formed transmembrane helical bundles surrounding a water-filled pore. These simple aggregates were capable of transporting ions with efficiencies comparable to those of complex, contemporary ion channels. Channels with wide pores exhibited little ion selectivity but also imposed only modest constraints on amino acid sequences of channel-forming proteins. Channels with small pores could have been selective but also might have required a more precisely defined sequence of amino acids. In contrast to modern channels, their protocellular ancestors had only limited capabilities to regulate ion flux. It is postulated that subsequent evolution of ion channels progressed primarily to acquire precise regulation, and not high efficiency or selectivity. It is further proposed that channels and the surrounding membranes co-evolved.

  6. Ion channel modifying agents influence the electrical activity generated by canine intrinsic cardiac neurons in situ.

    PubMed

    Thompson, G W; Horackova, M; Armour, J A

    2000-04-01

    This study was designed to establish whether agents known to modify neuronal ion channels influence the behavior of mammalian intrinsic cardiac neurons in situ and, if so, in a manner consistent with that found previously in vitro. The activity generated by right atrial neurons was recorded extracellularly in varying numbers of anesthetized dogs before and during continuous local arterial infusion of several neuronal ion channel modifying agents. Veratridine (7.5 microM), the specific modifier of Na+-selective channels, increased neuronal activity (95% above control) in 80% of dogs tested (n = 25). The membrane depolarizing agent potassium chloride (40 mM) reduced neuronal activity (43% below control) in 84% of dogs tested (n = 19). The inhibitor of voltage-sensitive K+ channels, tetraethylammonium (10 mM), decreased neuronal activity (42% below control) in 73% of dogs tested (n = 11). The nonspecific potassium channel inhibitor barium chloride (5 mM) excited neurons (47% above control) in 13 of 19 animals tested. Cadmium chloride (200 microM), which inhibits Ca2+-selective channels and Ca2+-dependent K+ channels, increased neuronal activity (65% above control) in 79% of dogs tested (n = 14). The specific L-type Ca2+ channel blocking agent nifedipine (5 microM) reduced neuronal activity (52% blow control in 72% of 11 dogs tested), as did the nonspecific inhibitor of L-type Ca2+ channels, nickel chloride (5 mM) (36% below control in 69% of 13 dogs tested). Each agent induced either excitatory or inhibitory responses, depending on the agent tested. It is concluded that specific ion channels (I(Na), I(CaL), I(Kv), and I(KCa)) that have been associated with intrinsic cardiac neurons in vitro are involved in their capacity to generate action potentials in situ. PMID:10772056

  7. A Semi-Synthetic Ion Channel Platform for Detection of Phosphatase and Protease Activity

    PubMed Central

    Macrae, Michael X.; Blake, Steven; Jiang, Xiayun; Capone, Ricardo; Estes, Daniel J.; Mayer, Michael; Yang, Jerry

    2009-01-01

    Sensitive methods to probe the activity of enzymes are important for clinical assays and for elucidating the role of these proteins in complex biochemical networks. This paper describes a semi-synthetic ion channel platform for detecting the activity of two different classes of enzymes with high sensitivity. In the first case, this method uses single ion channel conductance measurements to follow the enzyme-catalyzed hydrolysis of a phosphate group attached to the C-terminus of gramicidin A (gA, an ion channel-forming peptide) in the presence of alkaline phosphatase (AP). Enzymatic hydrolysis of this phosphate group removes negative charges from the entrance of the gA pore, resulting in a product with measurably reduced single ion channel conductance compared to the original gA-phosphate substrate. This technique employs a standard, commercial bilayer setup and takes advantage of the catalytic turnover of enzymes and the amplification characteristics of ion flux through individual gA pores to detect picomolar concentrations of active AP in solution. Furthermore, this technique makes it possible to study the kinetics of an enzyme and provides an estimate for the observed rate constant (kcat) and the Michaelis constant (KM) by following the conversion of the gA-phosphate substrate to product over time in the presence of different concentrations of AP. In the second case, modification of gA with a substrate for proteolytic cleavage by anthrax lethal factor (LF) afforded a sensitive method for detection of LF activity, illustrating the utility of ion channel-based sensing for detection of a potential biowarfare agent. This ion channel-based platform represents a powerful, novel approach to monitor the activity of femtomoles to picomoles of two different classes of enzymes in solution. Furthermore, this platform has the potential for realizing miniaturized, cost-effective bioanalytical assays that complement currently established assays. PMID:19860382

  8. On Application Of Langevin Dynamics In Logarithmic Potential To Model Ion Channel Gate Activity.

    PubMed

    Wawrzkiewicz-Jałowiecka, Agata; Borys, Przemysław; Grzywna, Zbigniew J

    2015-12-01

    We model the activity of an ion channel gate by Langevin dynamics in a logarithmic potential. This approach enables one to describe the power-law dwell-time distributions of the considered system, and the long-term correlations between the durations of the subsequent channel states, or fractal scaling of statistical characteristics of the gate's movement with time. Activity of an ion channel gate is described as an overdamped motion of the reaction coordinate in a confining logarithmic potential, which ensures great flexibility of the model. Depending on the chosen parameters, it allows one to reproduce many types of gate dynamics within the family of non-Markovian, anomalous conformational diffusion processes. In this study we apply the constructed model to largeconductance voltage and Ca2+-activated potassium channels (BKCa). The interpretation of model assumptions and parameters is provided in terms of this biological system. Our results show good agreement with the experimental data. PMID:26317442

  9. [Cooperative phenomena in the activity of single ion channels].

    PubMed

    Geletiuk, V I; Kazachenko, V N

    1989-01-01

    Using the patch-voltage-clamp method kinetics of the fast potential-dependent K+-channels in molluscan neurones was investigated. It was found that under given experimental conditions the amplitudes of single current impulses have a wide spectrum. The amplitudes are proportional to a number of the current substates involved. Averaged fronts of the current impulses are S-shaped, and have duration greater than 1 ms. Averaged duration of the current impulses increases (from 0.25 to 30-40 ms) with the impulse amplitude (or with the number of the substates involved). There is a sharp bend of the dependence at the impulse amplitude 0.6-0.7 of maximal value. The phenomena investigated reflect, probably, cooperativity of the channel transitions between the substates. The degree of the cooperativity depends on the membrane potential value. PMID:2804147

  10. Ion conductance of the Ca(2+)-activated maxi-K+ channel from the embryonic rat brain.

    PubMed

    Mienville, J M; Clay, J R

    1997-01-01

    By using single-channel recording techniques, we measured the conductance (gK) of the Ca(2+)-activated Maxi-K+ channel from the embryonic rat brain, and examined its dependence on K+ ions present in equimolar concentrations on both sides of the membrane patch. With ionic strength maintained constant by substitution of N-methyl-D-glucamine for K+, gK has a sigmoidal dependence upon [K+]. This result has been obscured in previous work by variations in ionic strength, which has a marked effect on single-channel conductance, especially in the limit for which this variable approaches zero. The gK versus [K+] relationship is described, theoretically, by a three-barrier, two-binding-site model in which the barrier that an ion must cross to leave the channel is decreased as [K+] is increased. PMID:8994603

  11. Synthesis and characterization of a Redox-active artificial ion channel.

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The synthesis and characterization of an artificial ion channel containing both fluorescent and redox-active centers is described. fluorescence spectroscopy was used to study qualitative and quantitative aspects of the coordination of alkali metal cations and black lipid membrane studies were used ...

  12. Stochastically Gating Ion Channels Enable Patterned Spike Firing through Activity-Dependent Modulation of Spike Probability

    PubMed Central

    Dudman, Joshua T.; Nolan, Matthew F.

    2009-01-01

    The transformation of synaptic input into patterns of spike output is a fundamental operation that is determined by the particular complement of ion channels that a neuron expresses. Although it is well established that individual ion channel proteins make stochastic transitions between conducting and non-conducting states, most models of synaptic integration are deterministic, and relatively little is known about the functional consequences of interactions between stochastically gating ion channels. Here, we show that a model of stellate neurons from layer II of the medial entorhinal cortex implemented with either stochastic or deterministically gating ion channels can reproduce the resting membrane properties of stellate neurons, but only the stochastic version of the model can fully account for perithreshold membrane potential fluctuations and clustered patterns of spike output that are recorded from stellate neurons during depolarized states. We demonstrate that the stochastic model implements an example of a general mechanism for patterning of neuronal output through activity-dependent changes in the probability of spike firing. Unlike deterministic mechanisms that generate spike patterns through slow changes in the state of model parameters, this general stochastic mechanism does not require retention of information beyond the duration of a single spike and its associated afterhyperpolarization. Instead, clustered patterns of spikes emerge in the stochastic model of stellate neurons as a result of a transient increase in firing probability driven by activation of HCN channels during recovery from the spike afterhyperpolarization. Using this model, we infer conditions in which stochastic ion channel gating may influence firing patterns in vivo and predict consequences of modifications of HCN channel function for in vivo firing patterns. PMID:19214199

  13. Ion channels and migraine

    PubMed Central

    Yan, Jin; Dussor, Gregory

    2014-01-01

    Migraine is one of the most common neurological disorders. Despite its prevalence, the basic physiology of the molecules and mechanisms that contribute to migraine headache is still poorly understood, making the discovery of more effective treatments extremely difficult. The consistent presence of head-specific pain during migraine suggests an important role for activation of the peripheral nociceptors localized to the head. Accordingly, this review will cover the current understanding of the biological mechanisms leading to episodic activation and sensitization of the trigeminovascular pain pathway, focusing on recent advances regarding activation and modulation of ion channels. PMID:24697223

  14. NMR Structure and Ion Channel Activity of the p7 Protein from Hepatitis C Virus*

    PubMed Central

    Montserret, Roland; Saint, Nathalie; Vanbelle, Christophe; Salvay, Andrés Gerardo; Simorre, Jean-Pierre; Ebel, Christine; Sapay, Nicolas; Renisio, Jean-Guillaume; Böckmann, Anja; Steinmann, Eike; Pietschmann, Thomas; Dubuisson, Jean; Chipot, Christophe; Penin, François

    2010-01-01

    The small membrane protein p7 of hepatitis C virus forms oligomers and exhibits ion channel activity essential for virus infectivity. These viroporin features render p7 an attractive target for antiviral drug development. In this study, p7 from strain HCV-J (genotype 1b) was chemically synthesized and purified for ion channel activity measurements and structure analyses. p7 forms cation-selective ion channels in planar lipid bilayers and at the single-channel level by the patch clamp technique. Ion channel activity was shown to be inhibited by hexamethylene amiloride but not by amantadine. Circular dichroism analyses revealed that the structure of p7 is mainly α-helical, irrespective of the membrane mimetic medium (e.g. lysolipids, detergents, or organic solvent/water mixtures). The secondary structure elements of the monomeric form of p7 were determined by 1H and 13C NMR in trifluoroethanol/water mixtures. Molecular dynamics simulations in a model membrane were combined synergistically with structural data obtained from NMR experiments. This approach allowed us to determine the secondary structure elements of p7, which significantly differ from predictions, and to propose a three-dimensional model of the monomeric form of p7 associated with the phospholipid bilayer. These studies revealed the presence of a turn connecting an unexpected N-terminal α-helix to the first transmembrane helix, TM1, and a long cytosolic loop bearing the dibasic motif and connecting TM1 to TM2. These results provide the first detailed experimental structural framework for a better understanding of p7 processing, oligomerization, and ion channel gating mechanism. PMID:20667830

  15. Biophysics of CNG Ion Channels

    NASA Astrophysics Data System (ADS)

    Barry, Peter H.; Qu, Wei; Moorhouse, Andrew J.

    Cyclic nucleotide-gated (CNG) ion channels are cation-selective, opened by intracellular cyclic nucleotides like cAMP and cGMP, and present in many different neurons and non-neuronal cells. This chapter will concentrate primarily on the biophysical aspects of retinal and olfactory CNG channels, with special reference to ion permeation and selectivity and their underlying molecular basis, and will include a brief overview of the physiological function of CNG channels in both olfaction and phototransduction. We will review the subunit composition and molecular structure of the CNG channel and its similarity to the closely related potassium channels, and will also briefly outline the currently accepted molecular basis underlying activation of the channel and the location of the channel `gate'. We will then outline some general methodologies for investigating ion permeation and selectivity, before reviewing the ion permeation and selectivity properties of native and recombinant CNG channels. We will discuss divalent ion permeation through the channel and the mechanism of channel block by divalent ions. The chapter will conclude by discussing the results of recent experiments to investigate the molecular determinants of cation-anion selectivity in the channel.

  16. Sensing Nature's Electric Fields: Ion Channels as Active Elements of Linear Amplification

    NASA Astrophysics Data System (ADS)

    Bezrukov, Sergey M.

    2003-05-01

    Given the parameters of familiar cellular elements — voltage-sensitive ion channels, carriers, pumps, phospholipid insulators, and electrolytic conductors — is it possible to construct an amplifier whose sensitivity matches the 5 nV/cm threshold found in behavioral experiments on elasmobranch fish? Or, in addition to clever circuitry that uses commonly known elements and principles, do we need something else to understand this sensitivity? The resolution of this question is important not only for studies in sensory biophysics seeking to reveal underlying mechanisms and molecular structures. More generally, it deepens our appreciation of the stochastic nature of inter- and intra-cellular control circuits. Here I analyze a simplified circuit involving negative differential resistance of voltage-sensitive ion channels. The analysis establishes an off-equilibrium criterion for amplification, shows that ion channels are the dominant noise sources, and, by minimizing channel noise within the given constraints, demonstrates that generic voltage-sensitive ion channels are likely candidates for the active elements of the linear cellular amplifiers. Finally, I highlight a number of unsolved issues.

  17. Members of the Chloride Intracellular Ion Channel Protein Family Demonstrate Glutaredoxin-Like Enzymatic Activity

    PubMed Central

    Al Khamici, Heba; Brown, Louise J.; Hossain, Khondker R.; Hudson, Amanda L.; Sinclair-Burton, Alxcia A.; Ng, Jane Phui Mun; Daniel, Elizabeth L.; Hare, Joanna E.; Cornell, Bruce A.; Curmi, Paul M. G.; Davey, Mary W.; Valenzuela, Stella M.

    2015-01-01

    The Chloride Intracellular Ion Channel (CLIC) family consists of six evolutionarily conserved proteins in humans. Members of this family are unusual, existing as both monomeric soluble proteins and as integral membrane proteins where they function as chloride selective ion channels, however no function has previously been assigned to their soluble form. Structural studies have shown that in the soluble form, CLIC proteins adopt a glutathione S-transferase (GST) fold, however, they have an active site with a conserved glutaredoxin monothiol motif, similar to the omega class GSTs. We demonstrate that CLIC proteins have glutaredoxin-like glutathione-dependent oxidoreductase enzymatic activity. CLICs 1, 2 and 4 demonstrate typical glutaredoxin-like activity using 2-hydroxyethyl disulfide as a substrate. Mutagenesis experiments identify cysteine 24 as the catalytic cysteine residue in CLIC1, which is consistent with its structure. CLIC1 was shown to reduce sodium selenite and dehydroascorbate in a glutathione-dependent manner. Previous electrophysiological studies have shown that the drugs IAA-94 and A9C specifically block CLIC channel activity. These same compounds inhibit CLIC1 oxidoreductase activity. This work for the first time assigns a functional activity to the soluble form of the CLIC proteins. Our results demonstrate that the soluble form of the CLIC proteins has an enzymatic activity that is distinct from the channel activity of their integral membrane form. This CLIC enzymatic activity may be important for protecting the intracellular environment against oxidation. It is also likely that this enzymatic activity regulates the CLIC ion channel function. PMID:25581026

  18. Mechanisms of Rose Bengal inhibition on SecA ATPase and ion channel activities.

    PubMed

    Hsieh, Ying-Hsin; Huang, Ying-Ju; Jin, Jin-Shan; Yu, Liyan; Yang, Hsiuchin; Jiang, Chun; Wang, Binghe; Tai, Phang C

    2014-11-14

    SecA is an essential protein possessing ATPase activity in bacterial protein translocation for which Rose Bengal (RB) is the first reported sub-micromolar inhibitor in ATPase activity and protein translocation. Here, we examined the mechanisms of inhibition on various forms of SecA ATPase by conventional enzymatic assays, and by monitoring the SecA-dependent channel activity in the semi-physiological system in cells. We build on the previous observation that SecA with liposomes form active protein-conducting channels in the oocytes. Such ion channel activity is enhanced by purified Escherichia coli SecYEG-SecDF·YajC liposome complexes. Inhibition by RB could be monitored, providing correlation of in vitro activity and intact cell functionality. In this work, we found the intrinsic SecA ATPase is inhibited by RB competitively at low ATP concentration, and non-competitively at high ATP concentrations while the translocation ATPase with precursors and SecYEG is inhibited non-competitively by RB. The Inhibition by RB on SecA channel activity in the oocytes with exogenous ATP-Mg(2+), mimicking translocation ATPase activity, is also non-competitive. The non-competitive inhibition on channel activity has also been observed with SecA from other bacteria which otherwise would be difficult to examine without the cognate precursors and membranes. PMID:25450394

  19. Severe acute respiratory syndrome coronavirus envelope protein ion channel activity promotes virus fitness and pathogenesis.

    PubMed

    Nieto-Torres, Jose L; DeDiego, Marta L; Verdiá-Báguena, Carmina; Jimenez-Guardeño, Jose M; Regla-Nava, Jose A; Fernandez-Delgado, Raul; Castaño-Rodriguez, Carlos; Alcaraz, Antonio; Torres, Jaume; Aguilella, Vicente M; Enjuanes, Luis

    2014-05-01

    Deletion of Severe Acute Respiratory Syndrome Coronavirus (SARS-CoV) envelope (E) gene attenuates the virus. E gene encodes a small multifunctional protein that possesses ion channel (IC) activity, an important function in virus-host interaction. To test the contribution of E protein IC activity in virus pathogenesis, two recombinant mouse-adapted SARS-CoVs, each containing one single amino acid mutation that suppressed ion conductivity, were engineered. After serial infections, mutant viruses, in general, incorporated compensatory mutations within E gene that rendered active ion channels. Furthermore, IC activity conferred better fitness in competition assays, suggesting that ion conductivity represents an advantage for the virus. Interestingly, mice infected with viruses displaying E protein IC activity, either with the wild-type E protein sequence or with the revertants that restored ion transport, rapidly lost weight and died. In contrast, mice infected with mutants lacking IC activity, which did not incorporate mutations within E gene during the experiment, recovered from disease and most survived. Knocking down E protein IC activity did not significantly affect virus growth in infected mice but decreased edema accumulation, the major determinant of acute respiratory distress syndrome (ARDS) leading to death. Reduced edema correlated with lung epithelia integrity and proper localization of Na+/K+ ATPase, which participates in edema resolution. Levels of inflammasome-activated IL-1β were reduced in the lung airways of the animals infected with viruses lacking E protein IC activity, indicating that E protein IC function is required for inflammasome activation. Reduction of IL-1β was accompanied by diminished amounts of TNF and IL-6 in the absence of E protein ion conductivity. All these key cytokines promote the progression of lung damage and ARDS pathology. In conclusion, E protein IC activity represents a new determinant for SARS-CoV virulence. PMID:24788150

  20. Severe Acute Respiratory Syndrome Coronavirus Envelope Protein Ion Channel Activity Promotes Virus Fitness and Pathogenesis

    PubMed Central

    Nieto-Torres, Jose L.; DeDiego, Marta L.; Verdiá-Báguena, Carmina; Jimenez-Guardeño, Jose M.; Regla-Nava, Jose A.; Fernandez-Delgado, Raul; Castaño-Rodriguez, Carlos; Alcaraz, Antonio; Torres, Jaume; Aguilella, Vicente M.; Enjuanes, Luis

    2014-01-01

    Deletion of Severe Acute Respiratory Syndrome Coronavirus (SARS-CoV) envelope (E) gene attenuates the virus. E gene encodes a small multifunctional protein that possesses ion channel (IC) activity, an important function in virus-host interaction. To test the contribution of E protein IC activity in virus pathogenesis, two recombinant mouse-adapted SARS-CoVs, each containing one single amino acid mutation that suppressed ion conductivity, were engineered. After serial infections, mutant viruses, in general, incorporated compensatory mutations within E gene that rendered active ion channels. Furthermore, IC activity conferred better fitness in competition assays, suggesting that ion conductivity represents an advantage for the virus. Interestingly, mice infected with viruses displaying E protein IC activity, either with the wild-type E protein sequence or with the revertants that restored ion transport, rapidly lost weight and died. In contrast, mice infected with mutants lacking IC activity, which did not incorporate mutations within E gene during the experiment, recovered from disease and most survived. Knocking down E protein IC activity did not significantly affect virus growth in infected mice but decreased edema accumulation, the major determinant of acute respiratory distress syndrome (ARDS) leading to death. Reduced edema correlated with lung epithelia integrity and proper localization of Na+/K+ ATPase, which participates in edema resolution. Levels of inflammasome-activated IL-1β were reduced in the lung airways of the animals infected with viruses lacking E protein IC activity, indicating that E protein IC function is required for inflammasome activation. Reduction of IL-1β was accompanied by diminished amounts of TNF and IL-6 in the absence of E protein ion conductivity. All these key cytokines promote the progression of lung damage and ARDS pathology. In conclusion, E protein IC activity represents a new determinant for SARS-CoV virulence. PMID:24788150

  1. SecA Alone Can Promote Protein Translocation and Ion Channel Activity

    PubMed Central

    Hsieh, Ying-hsin; Zhang, Hao; Lin, Bor-ruei; Cui, Ningren; Na, Bing; Yang, Hsiuchin; Jiang, Chun; Sui, Sen-fang; Tai, Phang C.

    2011-01-01

    SecA is an essential component of the Sec-dependent protein translocation pathway across cytoplasmic membranes in bacteria. Escherichia coli SecA binds to cytoplasmic membranes at SecYEG high affinity sites and at phospholipid low affinity sites. It has been widely viewed that SecYEG functions as the essential protein-conducting channel through which precursors cross the membranes in bacterial Sec-dependent pathways, and that SecA functions as a motor to hydrolyze ATP in translocating precursors through SecYEG channels. We have now found that SecA alone can promote precursor translocation into phospholiposomes. Moreover, SecA-liposomes elicit ionic currents in Xenopus oocytes. Patch-clamp recordings further show that SecA alone promotes signal peptide- or precursor-dependent single channel activity. These activities were observed with the functional SecA at about 1–2 μm. The results show that SecA alone is sufficient to promote protein translocation into liposomes and to elicit ionic channel activity at the phospholipids low affinity binding sites, thus indicating that SecA is able to form the protein-conducting channels. Even so, such SecA-liposomes are less efficient than those with a full complement of Sec proteins, and lose the signal-peptide proofreading function, resembling the effects of PrlA mutations. Addition of purified SecYEG restores the signal peptide specificity and increases protein translocation and ion channel activities. These data show that SecA can promote protein translocation and ion channel activities both when it is bound to lipids at low affinity sites and when it is bound to SecYEG with high affinity. The latter of the two interactions confers high efficiency and specificity. PMID:22033925

  2. Photocontrol of Voltage-Gated Ion Channel Activity by Azobenzene Trimethylammonium Bromide in Neonatal Rat Cardiomyocytes.

    PubMed

    Frolova, Sheyda R; Gaiko, Olga; Tsvelaya, Valeriya A; Pimenov, Oleg Y; Agladze, Konstantin I

    2016-01-01

    The ability of azobenzene trimethylammonium bromide (azoTAB) to sensitize cardiac tissue excitability to light was recently reported. The dark, thermally relaxed trans- isomer of azoTAB suppressed spontaneous activity and excitation propagation speed, whereas the cis- isomer had no detectable effect on the electrical properties of cardiomyocyte monolayers. As the membrane potential of cardiac cells is mainly controlled by activity of voltage-gated ion channels, this study examined whether the sensitization effect of azoTAB was exerted primarily via the modulation of voltage-gated ion channel activity. The effects of trans- and cis- isomers of azoTAB on voltage-dependent sodium (INav), calcium (ICav), and potassium (IKv) currents in isolated neonatal rat cardiomyocytes were investigated using the whole-cell patch-clamp technique. The experiments showed that azoTAB modulated ion currents, causing suppression of sodium (Na+) and calcium (Ca2+) currents and potentiation of net potassium (K+) currents. This finding confirms that azoTAB-effect on cardiac tissue excitability do indeed result from modulation of voltage-gated ion channels responsible for action potential. PMID:27015602

  3. Photocontrol of Voltage-Gated Ion Channel Activity by Azobenzene Trimethylammonium Bromide in Neonatal Rat Cardiomyocytes

    PubMed Central

    Frolova, Sheyda R.; Gaiko, Olga; Tsvelaya, Valeriya A.; Pimenov, Oleg Y.; Agladze, Konstantin I.

    2016-01-01

    The ability of azobenzene trimethylammonium bromide (azoTAB) to sensitize cardiac tissue excitability to light was recently reported. The dark, thermally relaxed trans- isomer of azoTAB suppressed spontaneous activity and excitation propagation speed, whereas the cis- isomer had no detectable effect on the electrical properties of cardiomyocyte monolayers. As the membrane potential of cardiac cells is mainly controlled by activity of voltage-gated ion channels, this study examined whether the sensitization effect of azoTAB was exerted primarily via the modulation of voltage-gated ion channel activity. The effects of trans- and cis- isomers of azoTAB on voltage-dependent sodium (INav), calcium (ICav), and potassium (IKv) currents in isolated neonatal rat cardiomyocytes were investigated using the whole-cell patch-clamp technique. The experiments showed that azoTAB modulated ion currents, causing suppression of sodium (Na+) and calcium (Ca2+) currents and potentiation of net potassium (K+) currents. This finding confirms that azoTAB-effect on cardiac tissue excitability do indeed result from modulation of voltage-gated ion channels responsible for action potential. PMID:27015602

  4. Ultrasound modulates ion channel currents.

    PubMed

    Kubanek, Jan; Shi, Jingyi; Marsh, Jon; Chen, Di; Deng, Cheri; Cui, Jianmin

    2016-01-01

    Transcranial focused ultrasound (US) has been demonstrated to stimulate neurons in animals and humans, but the mechanism of this effect is unknown. It has been hypothesized that US, a mechanical stimulus, may mediate cellular discharge by activating mechanosensitive ion channels embedded within cellular membranes. To test this hypothesis, we expressed potassium and sodium mechanosensitive ion channels (channels of the two-pore-domain potassium family (K2P) including TREK-1, TREK-2, TRAAK; NaV1.5) in the Xenopus oocyte system. Focused US (10 MHz, 0.3-4.9 W/cm(2)) modulated the currents flowing through the ion channels on average by up to 23%, depending on channel and stimulus intensity. The effects were reversible upon repeated stimulation and were abolished when a channel blocker (ranolazine to block NaV1.5, BaCl2 to block K2P channels) was applied to the solution. These data reveal at the single cell level that focused US modulates the activity of specific ion channels to mediate transmembrane currents. These findings open doors to investigations of the effects of  US on ion channels expressed in neurons, retinal cells, or cardiac cells, which may lead to important medical applications. The findings may also pave the way to the development of sonogenetics: a non-invasive, US-based analogue of optogenetics. PMID:27112990

  5. Ultrasound modulates ion channel currents

    PubMed Central

    Kubanek, Jan; Shi, Jingyi; Marsh, Jon; Chen, Di; Deng, Cheri; Cui, Jianmin

    2016-01-01

    Transcranial focused ultrasound (US) has been demonstrated to stimulate neurons in animals and humans, but the mechanism of this effect is unknown. It has been hypothesized that US, a mechanical stimulus, may mediate cellular discharge by activating mechanosensitive ion channels embedded within cellular membranes. To test this hypothesis, we expressed potassium and sodium mechanosensitive ion channels (channels of the two-pore-domain potassium family (K2P) including TREK-1, TREK-2, TRAAK; NaV1.5) in the Xenopus oocyte system. Focused US (10 MHz, 0.3–4.9 W/cm2) modulated the currents flowing through the ion channels on average by up to 23%, depending on channel and stimulus intensity. The effects were reversible upon repeated stimulation and were abolished when a channel blocker (ranolazine to block NaV1.5, BaCl2 to block K2P channels) was applied to the solution. These data reveal at the single cell level that focused US modulates the activity of specific ion channels to mediate transmembrane currents. These findings open doors to investigations of the effects of  US on ion channels expressed in neurons, retinal cells, or cardiac cells, which may lead to important medical applications. The findings may also pave the way to the development of sonogenetics: a non-invasive, US-based analogue of optogenetics. PMID:27112990

  6. Marine Toxins Targeting Ion Channels

    PubMed Central

    Arias, Hugo R.

    2006-01-01

    This introductory minireview points out the importance of ion channels for cell communication. The basic concepts on the structure and function of ion channels triggered by membrane voltage changes, the so-called voltage-gated ion channels (VGICs), as well as those activated by neurotransmitters, the so-called ligand-gated ion channel (LGICs), are introduced. Among the most important VGIC superfamiles, we can name the voltage-gated Na+ (NaV), Ca2+ (CaV), and K+ (KV) channels. Among the most important LGIC super families, we can include the Cys-loop or nicotinicoid, the glutamate-activated (GluR), and the ATP-activated (P2XnR) receptor superfamilies. Ion channels are transmembrane proteins that allow the passage of different ions in a specific or unspecific manner. For instance, the activation of NaV, CaV, or KV channels opens a pore that is specific for Na+, Ca2+, or K+, respectively. On the other hand, the activation of certain LGICs such as nicotinic acetylcholine receptors, GluRs, and P2XnRs allows the passage of cations (e.g., Na+, K+, and/or Ca2+), whereas the activation of other LGICs such as type A γ-butyric acid and glycine receptors allows the passage of anions (e.g., Cl− and/or HCO3−). In this regard, the activation of NaV and CaV as well as ligand-gated cation channels produce membrane depolarization, which finally leads to stimulatory effects in the cell, whereas the activation of KV as well as ligand-gated anion channels induce membrane hyperpolarization that finally leads to inhibitory effects in the cell. The importance of these ion channel superfamilies is emphasized by considering their physiological functions throughout the body as well as their pathophysiological implicance in several neuronal diseases. In this regard, natural molecules, and especially marine toxins, can be potentially used as modulators (e.g., inhibitors or prolongers) of ion channel functions to treat or to alleviate a specific ion channel-linked disease (e

  7. Bacterial Ion Channels.

    PubMed

    Compton, Emma L R; Mindell, Joseph A

    2010-09-01

    Bacterial ion channels were known, but only in special cases, such as outer membrane porins in Escherichia coli and bacterial toxins that form pores in their target (bacterial or mammalian) membranes. The exhaustive coverage provided by a decade of bacterial genome sequencing has revealed that ion channels are actually widespread in bacteria, with homologs of a broad range of mammalian channel proteins coded throughout the bacterial and archaeal kingdoms. This review discusses four groups of bacterial channels: porins, mechano-sensitive (MS) channels, channel-forming toxins, and bacterial homologs of mammalian channels. The outer membrane (OM) of gram-negative bacteria blocks access of essential nutrients; to survive, the cell needs to provide a mechanism for nutrients to penetrate the OM. Porin channels provide this access by forming large, nonspecific aqueous pores in the OM that allow ions and vital nutrients to cross it and enter the periplasm. MS channels act as emergency release valves, allowing solutes to rapidly exit the cytoplasm and to dissipate the large osmotic disparity between the internal and external environments. MS channels are remarkable in that they do this by responding to forces exerted by the membrane itself. Some bacteria produce toxic proteins that form pores in trans, attacking and killing other organisms by virtue of their pore formation. The review focuses on those bacterial toxins that kill other bacteria, specifically the class of proteins called colicins. Colicins reveal the dangers of channel formation in the plasma membrane, since they kill their targets with exactly that approach. PMID:26443789

  8. Influence of proline position upon the ion channel activity of alamethicin.

    PubMed Central

    Kaduk, C; Duclohier, H; Dathe, M; Wenschuh, H; Beyermann, M; Molle, G; Bienert, M

    1997-01-01

    Alamethicin, a 20-residue peptaibol, induces voltage-dependent ion channels in lipid bilayers according to the barrel-stave model. To study relationships between the proline-14-induced kink region and the channel-forming behavior of the peptide, a set of alamethicin analogs with proline incorporated at positions 11, 12, 13, 14, 15, 16, and 17, respectively, as well as an analog with alanine instead of proline at position 14 were synthesized. Macroscopic conductance experiments show that the voltage dependence of the peptides is conserved although slightly influenced, but the apparent mean number of monomers forming the channels is significantly reduced when proline is not located at position 14. This is confirmed in single-channel experiments. The analogs with proline next to position 14 (i.e., 13, 15, 16) show stable conductance levels, but of reduced number, which follows the order Alam-P14 > Alam-P15 > Alam-P16 > Alam-P13. This reduction in the number of levels is connected with changes in the lifetime of the channels. Analogs with proline at position 11, 12, or 17 produce erratic, extremely short-lived current events that could not be resolved. The changes in functional properties are related to structural properties as probed by circular dichroism. The results indicate that proline at position 14 results in optimal channel activity, whereas channels formed by the analogs bearing proline at different positions are considerably less stable. PMID:9129817

  9. Simulating complex ion channel kinetics with IonChannelLab

    PubMed Central

    Covarrubias, Manuel; Sánchez-Rodríguez, Jorge E; Perez-Cornejo, Patricia; Arreola, Jorge

    2010-01-01

    In-silico simulation based on Markov chains is a powerful way to describe and predict the activity of many transport proteins including ion channels. However, modeling and simulation using realistic models of voltage- or ligand-gated ion channels exposed to a wide range of experimental conditions require building complex kinetic schemes and solving complicated differential equations. To circumvent these problems, we developed IonChannelLab a software tool that includes a user-friendly Graphical User Interface and a simulation library. This program supports channels with Ohmic or Goldman-Hodgkin-Katz behavior and can simulate the time-course of ionic and gating currents, single channel behavior and steady-state conditions. The program allows the simulation of experiments where voltage, ligand and ionic concentration are varied independently or simultaneously. PMID:20935453

  10. Mechanism for phosphoinositide selectivity and activation of TRPV1 ion channels

    PubMed Central

    Ufret-Vincenty, Carmen A.; Klein, Rebecca M.; Collins, Marcus D.; Rosasco, Mario G.; Martinez, Gilbert Q.

    2015-01-01

    Although PI(4,5)P2 is believed to play an essential role in regulating the activity of numerous ion channels and transporters, the mechanisms by which it does so are unknown. Here, we used the ability of the TRPV1 ion channel to discriminate between PI(4,5)P2 and PI(4)P to localize the region of TRPV1 sequence that interacts directly with the phosphoinositide. We identified a point mutation in the proximal C-terminal region after the TRP box, R721A, that inverted the selectivity of TRPV1. Although the R721A mutation produced only a 30% increase in the EC50 for activation by PI(4,5)P2, it decreased the EC50 for activation by PI(4)P by more than two orders of magnitude. We used chemically induced and voltage-activated phosphatases to determine that PI(4)P continued to support TRPV1 activity even after depletion of PI(4,5)P2 from the plasma membrane. Our data cannot be explained by a purely electrostatic mechanism for interaction between the phosphoinositide and the protein, similar to that of the MARCKS (myristoylated alanine-rich C kinase substrate) effector domain or the EGF receptor. Rather, conversion of a PI(4,5)P2-selective channel to a PI(4)P-selective channel indicates that a structured phosphoinositide-binding site mediates the regulation of TRPV1 activity and that the amino acid at position 721 likely interacts directly with the moiety at the 5′ position of the phosphoinositide. PMID:25918361

  11. Mechanism for phosphoinositide selectivity and activation of TRPV1 ion channels.

    PubMed

    Ufret-Vincenty, Carmen A; Klein, Rebecca M; Collins, Marcus D; Rosasco, Mario G; Martinez, Gilbert Q; Gordon, Sharona E

    2015-05-01

    Although PI(4,5)P2 is believed to play an essential role in regulating the activity of numerous ion channels and transporters, the mechanisms by which it does so are unknown. Here, we used the ability of the TRPV1 ion channel to discriminate between PI(4,5)P2 and PI(4)P to localize the region of TRPV1 sequence that interacts directly with the phosphoinositide. We identified a point mutation in the proximal C-terminal region after the TRP box, R721A, that inverted the selectivity of TRPV1. Although the R721A mutation produced only a 30% increase in the EC50 for activation by PI(4,5)P2, it decreased the EC50 for activation by PI(4)P by more than two orders of magnitude. We used chemically induced and voltage-activated phosphatases to determine that PI(4)P continued to support TRPV1 activity even after depletion of PI(4,5)P2 from the plasma membrane. Our data cannot be explained by a purely electrostatic mechanism for interaction between the phosphoinositide and the protein, similar to that of the MARCKS (myristoylated alanine-rich C kinase substrate) effector domain or the EGF receptor. Rather, conversion of a PI(4,5)P2-selective channel to a PI(4)P-selective channel indicates that a structured phosphoinositide-binding site mediates the regulation of TRPV1 activity and that the amino acid at position 721 likely interacts directly with the moiety at the 5' position of the phosphoinositide. PMID:25918361

  12. Structural Domains Underlying the Activation of Acid-Sensing Ion Channel 2a

    PubMed Central

    Schuhmacher, Laura-Nadine; Srivats, Shyam; Smith, Ewan St. John

    2015-01-01

    The acid-sensing ion channels (ASICs) are a family of ion channels expressed throughout the mammalian nervous system. The principal activator of ASICs is extracellular protons, and ASICs have been demonstrated to play a significant role in many physiologic and pathophysiologic processes, including synaptic transmission, nociception, and fear. However, not all ASICs are proton-sensitive: ASIC2a is activated by acid, whereas its splice variant ASIC2b is not. We made a series of chimeric ASIC2 proteins, and using whole-cell electrophysiology we have identified the minimal region of the ASIC2a extracellular domain that is required for ASIC2 proton activation: the first 87 amino acids after transmembrane domain 1. We next examined the function of different domains within the ASIC2b N-terminus and identified a region proximal to the first transmembrane domain that confers tachyphylaxis upon ASIC2a. We have thus identified domains of ASIC2 that are crucial to channel function and may be important for the function of other members of the ASIC family. PMID:25583083

  13. Ion channel-transporter interactions.

    PubMed

    Neverisky, Daniel L; Abbott, Geoffrey W

    2015-01-01

    All living cells require membrane proteins that act as conduits for the regulated transport of ions, solutes and other small molecules across the cell membrane. Ion channels provide a pore that permits often rapid, highly selective and tightly regulated movement of ions down their electrochemical gradient. In contrast, active transporters can move moieties up their electrochemical gradient. The secondary active transporters (such as SLC superfamily solute transporters) achieve this by coupling uphill movement of the substrate to downhill movement of another ion, such as sodium. The primary active transporters (including H(+)/K(+)-ATPases and Na(+)/K(+)-ATPases) utilize ATP hydrolysis as an energy source to power uphill transport. It is well known that proteins in each of these classes work in concert with members of the other classes to ensure, for example, ion homeostasis, ion secretion and restoration of ion balance following action potentials. More recently, evidence is emerging of direct physical interaction between true ion channels, and some primary or secondary active transporters. Here, we review the first known members of this new class of macromolecular complexes that we term "chansporters", explore their biological roles and discuss the pathophysiological consequences of their disruption. We compare functional and/or physical interactions between the ubiquitous KCNQ1 potassium channel and various active transporters, and examine other newly discovered chansporter complexes that suggest we may be seeing the tip of the iceberg in a newly emerging signaling modality. PMID:27098917

  14. Noxious cold ion channel TRPA1 is activated by pungent compounds and bradykinin.

    PubMed

    Bandell, Michael; Story, Gina M; Hwang, Sun Wook; Viswanath, Veena; Eid, Samer R; Petrus, Matt J; Earley, Taryn J; Patapoutian, Ardem

    2004-03-25

    Six members of the mammalian transient receptor potential (TRP) ion channels respond to varied temperature thresholds. The natural compounds capsaicin and menthol activate noxious heat-sensitive TRPV1 and cold-sensitive TRPM8, respectively. The burning and cooling perception of capsaicin and menthol demonstrate that these ion channels mediate thermosensation. We show that, in addition to noxious cold, pungent natural compounds present in cinnamon oil, wintergreen oil, clove oil, mustard oil, and ginger all activate TRPA1 (ANKTM1). Bradykinin, an inflammatory peptide acting through its G protein-coupled receptor, also activates TRPA1. We further show that phospholipase C is an important signaling component for TRPA1 activation. Cinnamaldehyde, the most specific TRPA1 activator, excites a subset of sensory neurons highly enriched in cold-sensitive neurons and elicits nociceptive behavior in mice. Collectively, these data demonstrate that TRPA1 activation elicits a painful sensation and provide a potential molecular model for why noxious cold can paradoxically be perceived as burning pain. PMID:15046718

  15. Low affinity block of native and cloned hyperpolarization-activated Ih channels by Ba2+ ions.

    PubMed

    van Welie, Ingrid; Wadman, Wytse J; van Hooft, Johannes A

    2005-01-10

    Ba2+ is commonly used to discriminate two classes of ion currents. The classical inward-rectifying K+ current, I(Kir), is blocked by low millimolar concentrations of Ba2+, whereas the hyperpolarization-activated cation current, I(h), is assumed not to be sensitive to Ba2+. Here we investigated the effects of Ba2+ on I(h) currents recorded from rat hippocampal CA1 pyramidal neurons, and on cloned I(h) channels composed of either HCN1 or HCN2 subunits transiently expressed in Human Embryonic Kidney (HEK) 293 cells. The results show that low millimolar concentrations of Ba2+ reduce the maximal I(h) conductance (IC50 approximately 3-5 mM) in both CA1 pyramidal neurons and in HEK 293 cells without specificity for HCN1 or HCN2 subunits. In addition, Ba2+ decreases the rate of activation and increases the rate of deactivation of I(h) currents. Neither the half-maximal voltage of activation, V(h), nor the reversal potential of the I(h) channels were affected by Ba2+. The combined results suggest that B2+, at concentrations commonly used to block I(Kir) currents, also reduces the conductance of I(h) channels without subunit specificity, and affects the kinetics of I(h) channel gating. PMID:15659289

  16. Stretch-activated ion channel Piezo1 directs lineage choice in human neural stem cells.

    PubMed

    Pathak, Medha M; Nourse, Jamison L; Tran, Truc; Hwe, Jennifer; Arulmoli, Janahan; Le, Dai Trang T; Bernardis, Elena; Flanagan, Lisa A; Tombola, Francesco

    2014-11-11

    Neural stem cells are multipotent cells with the ability to differentiate into neurons, astrocytes, and oligodendrocytes. Lineage specification is strongly sensitive to the mechanical properties of the cellular environment. However, molecular pathways transducing matrix mechanical cues to intracellular signaling pathways linked to lineage specification remain unclear. We found that the mechanically gated ion channel Piezo1 is expressed by brain-derived human neural stem/progenitor cells and is responsible for a mechanically induced ionic current. Piezo1 activity triggered by traction forces elicited influx of Ca(2+), a known modulator of differentiation, in a substrate-stiffness-dependent manner. Inhibition of channel activity by the pharmacological inhibitor GsMTx-4 or by siRNA-mediated Piezo1 knockdown suppressed neurogenesis and enhanced astrogenesis. Piezo1 knockdown also reduced the nuclear localization of the mechanoreactive transcriptional coactivator Yes-associated protein. We propose that the mechanically gated ion channel Piezo1 is an important determinant of mechanosensitive lineage choice in neural stem cells and may play similar roles in other multipotent stem cells. PMID:25349416

  17. Functional characterization of neurotransmitter activation and modulation in a nematode model ligand-gated ion channel.

    PubMed

    Heusser, Stephanie A; Yoluk, Özge; Klement, Göran; Riederer, Erika A; Lindahl, Erik; Howard, Rebecca J

    2016-07-01

    The superfamily of pentameric ligand-gated ion channels includes neurotransmitter receptors that mediate fast synaptic transmission in vertebrates, and are targets for drugs including alcohols, anesthetics, benzodiazepines, and anticonvulsants. However, the mechanisms of ion channel opening, gating, and modulation in these receptors leave many open questions, despite their pharmacological importance. Subtle conformational changes in both the extracellular and transmembrane domains are likely to influence channel opening, but have been difficult to characterize given the limited structural data available for human membrane proteins. Recent crystal structures of a modified Caenorhabditis elegans glutamate-gated chloride channel (GluCl) in multiple states offer an appealing model system for structure-function studies. However, the pharmacology of the crystallographic GluCl construct is not well established. To establish the functional relevance of this system, we used two-electrode voltage-clamp electrophysiology in Xenopus oocytes to characterize activation of crystallographic and native-like GluCl constructs by L-glutamate and ivermectin. We also tested modulation by ethanol and other anesthetic agents, and used site-directed mutagenesis to explore the role of a region of Loop F which was implicated in ligand gating by molecular dynamics simulations. Our findings indicate that the crystallographic construct functionally models concentration-dependent agonism and allosteric modulation of pharmacologically relevant receptors. Specific substitutions at residue Leu174 in loop F altered direct L-glutamate activation, consistent with computational evidence for this region's role in ligand binding. These insights demonstrate conservation of activation and modulation properties in this receptor family, and establish a framework for GluCl as a model system, including new possibilities for drug discovery. In this study, we elucidate the validity of a modified glutamate

  18. Pungent products from garlic activate the sensory ion channel TRPA1.

    PubMed

    Bautista, Diana M; Movahed, Pouya; Hinman, Andrew; Axelsson, Helena E; Sterner, Olov; Högestätt, Edward D; Julius, David; Jordt, Sven-Eric; Zygmunt, Peter M

    2005-08-23

    Garlic belongs to the Allium family of plants that produce organosulfur compounds, such as allicin and diallyl disulfide (DADS), which account for their pungency and spicy aroma. Many health benefits have been ascribed to Allium extracts, including hypotensive and vasorelaxant activities. However, the molecular mechanisms underlying these effects remain unknown. Intriguingly, allicin and DADS share structural similarities with allyl isothiocyanate, the pungent ingredient in wasabi and other mustard plants that induces pain and inflammation by activating TRPA1, an excitatory ion channel on primary sensory neurons of the pain pathway. Here we show that allicin and DADS excite an allyl isothiocyanate-sensitive subpopulation of sensory neurons and induce vasodilation by activating capsaicin-sensitive perivascular sensory nerve endings. Moreover, allicin and DADS activate the cloned TRPA1 channel when expressed in heterologous systems. These and other results suggest that garlic excites sensory neurons primarily through activation of TRPA1. Thus different plant genera, including Allium and Brassica, have developed evolutionary convergent strategies that target TRPA1 channels on sensory nerve endings to achieve chemical deterrence. PMID:16103371

  19. Influenza matrix protein 2 alters CFTR expression and function through its ion channel activity

    PubMed Central

    Londino, James D.; Lazrak, Ahmed; Jurkuvenaite, Asta; Collawn, James F.; Noah, James W.

    2013-01-01

    The human cystic fibrosis transmembrane conductance regulator (CFTR) is a cyclic AMP-activated chloride (Cl−) channel in the lung epithelium that helps regulate the thickness and composition of the lung epithelial lining fluid. We investigated whether influenza M2 protein, a pH-activated proton (H+) channel that traffics to the plasma membrane of infected cells, altered CFTR expression and function. M2 decreased CFTR activity in 1) Xenopus oocytes injected with human CFTR, 2) epithelial cells (HEK-293) stably transfected with CFTR, and 3) human bronchial epithelial cells (16HBE14o−) expressing native CFTR. This inhibition was partially reversed by an inhibitor of the ubiquitin-activating enzyme E1. Next we investigated whether the M2 inhibition of CFTR activity was due to an increase of secretory organelle pH by M2. Incubation of Xenopus oocytes expressing CFTR with ammonium chloride or concanamycin A, two agents that alkalinize the secretory pathway, inhibited CFTR activity in a dose-dependent manner. Treatment of M2- and CFTR-expressing oocytes with the M2 ion channel inhibitor amantadine prevented the loss in CFTR expression and activity; in addition, M2 mutants, lacking the ability to transport H+, did not alter CFTR activity in Xenopus oocytes and HEK cells. Expression of an M2 mutant retained in the endoplasmic reticulum also failed to alter CFTR activity. In summary, our data show that M2 decreases CFTR activity by increasing secretory organelle pH, which targets CFTR for destruction by the ubiquitin system. Alteration of CFTR activity has important consequences for fluid regulation and may potentially modify the immune response to viral infection. PMID:23457187

  20. THEMATICS analysis for functional ion channels

    NASA Astrophysics Data System (ADS)

    Shehadi, Ihsan A.

    Ion channels, as a group of integral membrane proteins, span the cell membrane forming ion-conducting pores that allow ions to traverse the hydrophobic lipid environment rapidly and selectively. The structure of the Streptomyces lividians (KcsA) and Mycobacterium tuberculosis ion channel (Mscl) potassium ion channel have provided the impetus and has helped further the understanding of the structural and functional studies of these channels. The KcsA adapts the voltage-gated mechanism for opening and closing of the channel. While Mcsl represents the mechanosensitive model of the channels. However, the mechanism of the opening and closing of these channels are not fully understood. Electrostatic methods (THEMATICS) are used to locate the site where closing and opening of the channels are controlled. Two clusters of amino acid residues are identified in each of the previously mentioned active models where net charges play an important role in controlling the mechanism of the opening and closure of the ion channels.0

  1. Prokineticin 2 potentiates acid-sensing ion channel activity in rat dorsal root ganglion neurons

    PubMed Central

    2012-01-01

    Background Prokineticin 2 (PK2) is a secreted protein and causes potent hyperalgesia in vivo, and is therefore considered to be a new pronociceptive mediator. However, the molecular targets responsible for the pronociceptive effects of PK2 are still poorly understood. Here, we have found that PK2 potentiates the activity of acid-sensing ion channels in the primary sensory neurons. Methods In the present study, experiments were performed on neurons freshly isolated from rat dorsal root ganglion by using whole-cell patch clamp and voltage-clamp recording techniques. Results PK2 dose-dependently enhanced proton-gated currents with an EC50 of 0.22 ± 0.06 nM. PK2 shifted the proton concentration-response curve upwards, with a 1.81 ± 0.11 fold increase of the maximal current response. PK2 enhancing effect on proton-gated currents was completely blocked by PK2 receptor antagonist. The potentiation was also abolished by intracellular dialysis of GF109203X, a protein kinase C inhibitor, or FSC-231, a protein interacting with C-kinase 1 inhibitor. Moreover, PK2 enhanced the acid-evoked membrane excitability of rat dorsal root ganglion neurons and caused a significant increase in the amplitude of the depolarization and the number of spikes induced by acid stimuli. Finally, PK2 exacerbated nociceptive responses to the injection of acetic acid in rats. Conclusion These results suggest that PK2 increases the activity of acid-sensing ion channels via the PK2 receptor and protein kinase C-dependent signal pathways in rat primary sensory neurons. Our findings support that PK2 is a proalgesic factor and its signaling likely contributes to acidosis-evoked pain by sensitizing acid-sensing ion channels. PMID:22642848

  2. Sequential formation of ion pairs during activation of a sodium channel voltage sensor

    PubMed Central

    DeCaen, Paul G.; Yarov-Yarovoy, Vladimir; Sharp, Elizabeth M.; Scheuer, Todd; Catterall, William A.

    2009-01-01

    Electrical signaling in biology depends upon a unique electromechanical transduction process mediated by the S4 segments of voltage-gated ion channels. These transmembrane segments are driven outward by the force of the electric field on positively charged amino acid residues termed “gating charges,” which are positioned at three-residue intervals in the S4 transmembrane segment, and this movement is coupled to opening of the pore. Here, we use the disulfide-locking method to demonstrate sequential ion pair formation between the fourth gating charge in the S4 segment (R4) and two acidic residues in the S2 segment during activation. R4 interacts first with E70 at the intracellular end of the S2 segment and then with D60 near the extracellular end. Analysis with the Rosetta Membrane method reveals the 3-D structures of the gating pore as these ion pairs are formed sequentially to catalyze the S4 transmembrane movement required for voltage-dependent activation. Our results directly demonstrate sequential ion pair formation that is an essential feature of the sliding helix model of voltage sensor function but is not compatible with the other widely discussed gating models. PMID:20007787

  3. Non-acidic activation of pain-related Acid-Sensing Ion Channel 3 by lipids.

    PubMed

    Marra, Sébastien; Ferru-Clément, Romain; Breuil, Véronique; Delaunay, Anne; Christin, Marine; Friend, Valérie; Sebille, Stéphane; Cognard, Christian; Ferreira, Thierry; Roux, Christian; Euller-Ziegler, Liana; Noel, Jacques; Lingueglia, Eric; Deval, Emmanuel

    2016-02-15

    Extracellular pH variations are seen as the principal endogenous signal that triggers activation of Acid-Sensing Ion Channels (ASICs), which are basically considered as proton sensors, and are involved in various processes associated with tissue acidification. Here, we show that human painful inflammatory exudates, displaying non-acidic pH, induce a slow constitutive activation of human ASIC3 channels. This effect is largely driven by lipids, and we identify lysophosphatidylcholine (LPC) and arachidonic acid (AA) as endogenous activators of ASIC3 in the absence of any extracellular acidification. The combination of LPC and AA evokes robust depolarizing current in DRG neurons at physiological pH 7.4, increases nociceptive C-fiber firing, and induces pain behavior in rats, effects that are all prevented by ASIC3 blockers. Lipid-induced pain is also significantly reduced in ASIC3 knockout mice. These findings open new perspectives on the roles of ASIC3 in the absence of tissue pH variation, as well as on the contribution of those channels to lipid-mediated signaling. PMID:26772186

  4. Expression and Activity of Acid-Sensing Ion Channels in the Mouse Anterior Pituitary

    PubMed Central

    Du, Jianyang; Reznikov, Leah R.; Welsh, Michael J.

    2014-01-01

    Acid sensing ion channels (ASICs) are proton-gated cation channels that are expressed in the nervous system and play an important role in fear learning and memory. The function of ASICs in the pituitary, an endocrine gland that contributes to emotions, is unknown. We sought to investigate which ASIC subunits were present in the pituitary and found mRNA expression for all ASIC isoforms, including ASIC1a, ASIC1b, ASIC2a, ASIC2b, ASIC3 and ASIC4. We also observed acid-evoked ASIC-like currents in isolated anterior pituitary cells that were absent in mice lacking ASIC1a. The biophysical properties and the responses to PcTx1, amiloride, Ca2+ and Zn2+ suggested that ASIC currents were mediated predominantly by heteromultimeric channels that contained ASIC1a and ASIC2a or ASIC2b. ASIC currents were also sensitive to FMRFamide (Phe-Met-Arg-Phe amide), suggesting that FMRFamide-like compounds might endogenously regulate pituitary ASICs. To determine whether ASICs might regulate pituitary cell function, we applied low pH and found that it increased the intracellular Ca2+ concentration. These data suggest that ASIC channels are present and functionally active in anterior pituitary cells and may therefore influence their function. PMID:25506946

  5. Expression and activity of acid-sensing ion channels in the mouse anterior pituitary.

    PubMed

    Du, Jianyang; Reznikov, Leah R; Welsh, Michael J

    2014-01-01

    Acid sensing ion channels (ASICs) are proton-gated cation channels that are expressed in the nervous system and play an important role in fear learning and memory. The function of ASICs in the pituitary, an endocrine gland that contributes to emotions, is unknown. We sought to investigate which ASIC subunits were present in the pituitary and found mRNA expression for all ASIC isoforms, including ASIC1a, ASIC1b, ASIC2a, ASIC2b, ASIC3 and ASIC4. We also observed acid-evoked ASIC-like currents in isolated anterior pituitary cells that were absent in mice lacking ASIC1a. The biophysical properties and the responses to PcTx1, amiloride, Ca2+ and Zn2+ suggested that ASIC currents were mediated predominantly by heteromultimeric channels that contained ASIC1a and ASIC2a or ASIC2b. ASIC currents were also sensitive to FMRFamide (Phe-Met-Arg-Phe amide), suggesting that FMRFamide-like compounds might endogenously regulate pituitary ASICs. To determine whether ASICs might regulate pituitary cell function, we applied low pH and found that it increased the intracellular Ca2+ concentration. These data suggest that ASIC channels are present and functionally active in anterior pituitary cells and may therefore influence their function. PMID:25506946

  6. ROS and intracellular ion channels.

    PubMed

    Kiselyov, Kirill; Muallem, Shmuel

    2016-08-01

    Oxidative stress is a well-known driver of numerous pathological processes involving protein and lipid peroxidation and DNA damage. The resulting increase of pro-apoptotic pressure drives tissue damage in a host of conditions, including ischemic stroke and reperfusion injury, diabetes, death in acute pancreatitis and neurodegenerative diseases. Somewhat less frequently discussed, but arguably as important, is the signaling function of oxidative stress stemming from the ability of oxidative stress to modulate ion channel activity. The evidence for the modulation of the intracellular ion channels and transporters by oxidative stress is constantly emerging and such evidence suggests new regulatory and pathological circuits that can be explored towards new treatments for diseases in which oxidative stress is an issue. In this review we summarize the current knowledge on the effects of oxidative stress on the intracellular ion channels and transporters and their role in cell function. PMID:26995054

  7. Ion Channel Engineering: Perspectives and Strategies

    PubMed Central

    Subramanyam, Prakash; Colecraft, Henry M.

    2014-01-01

    Ion channels facilitate the passive movement of ions down an electrochemical gradient and across lipid bilayers in cells. This phenomenon is essential for life, and underlies many critical homeostatic processes in cells. Ion channels are diverse and differ with respect to how they open and close (gating), and their ionic conductance/selectivity (permeation). Fundamental understanding of ion channel structure-function mechanisms, their physiological roles, how their dysfunction leads to disease, their utility as biosensors, and development of novel molecules to modulate their activity are important and active research frontiers. In this review, we focus on ion-channel engineering approaches that have been applied to investigate these aspects of ion channel function, with a major emphasis on voltage-gated ion channels. PMID:25205552

  8. Microbial Senses and Ion Channels

    NASA Astrophysics Data System (ADS)

    Kung, Ching; Zhou, Xin-Liang; Su, Zhen-Wei; Haynes, W. John; Loukin, Sephan H.; Saimi, Yoshiro

    The complexity of animals and plants is due largely to cellular arrangement. The structures and activities of macromolecules had, however, evolved in early microbes long before the appearance of this complexity. Among such molecules are those that sense light, heat, force, water, and ligands. Though historically and didactically associated with the nervous system, ion channels also have deep evolutionary roots. For example, force sensing with channels, which likely began as water sensing through membrane stretch generated by osmotic pressure, must be ancient and is universal in extant species. Extant microbial species, such as the model bacterium Escherichia coli and yeast Saccharomyces cerevisiae, are equipped with stretch-activated channels. The ion channel proteins MscL and MscS show clearly that these bacterial channels receive stretch forces from the lipid bilayer. TRPY1, the mechanosensitive channel in yeast, is being developed towards a similar basic understanding of channels of the TRP (transientreceptor- potential) superfamily. TRPY1 resides in the vacuolar membrane and releases Ca2+ from the vacuole to the cytoplasm upon hyperosmotic shock. Unlike in most TRP preparations from animals, the mechanosensitivity of TRPY1 can be examined directly under patch clamp in either whole-vacuole mode or excised patch mode. The combination of direct biophysical examination in vitro with powerful microbial genetics in vivo should complement the study of mechanosensations of complex animals and plants.

  9. Activation of mechanosensitive ion channel TRPV4 normalizes tumor vasculature and improves cancer therapy.

    PubMed

    Adapala, R K; Thoppil, R J; Ghosh, K; Cappelli, H C; Dudley, A C; Paruchuri, S; Keshamouni, V; Klagsbrun, M; Meszaros, J G; Chilian, W M; Ingber, D E; Thodeti, C K

    2016-01-21

    Tumor vessels are characterized by abnormal morphology and hyperpermeability that together cause inefficient delivery of chemotherapeutic agents. Although vascular endothelial growth factor has been established as a critical regulator of tumor angiogenesis, the role of mechanical signaling in the regulation of tumor vasculature or tumor endothelial cell (TEC) function is not known. Here we show that the mechanosensitive ion channel transient receptor potential vanilloid 4 (TRPV4) regulates tumor angiogenesis and tumor vessel maturation via modulation of TEC mechanosensitivity. We found that TECs exhibit reduced TRPV4 expression and function, which is correlated with aberrant mechanosensitivity towards extracellular matrix stiffness, increased migration and abnormal angiogenesis by TEC. Further, syngeneic tumor experiments revealed that the absence of TRPV4 induced increased vascular density, vessel diameter and reduced pericyte coverage resulting in enhanced tumor growth in TRPV4 knockout mice. Importantly, overexpression or pharmacological activation of TRPV4 restored aberrant TEC mechanosensitivity, migration and normalized abnormal angiogenesis in vitro by modulating Rho activity. Finally, a small molecule activator of TRPV4, GSK1016790A, in combination with anticancer drug cisplatin, significantly reduced tumor growth in wild-type mice by inducing vessel maturation. Our findings demonstrate TRPV4 channels to be critical regulators of tumor angiogenesis and represent a novel target for anti-angiogenic and vascular normalization therapies. PMID:25867067

  10. Activation of mechanosensitive ion channel TRPV4 normalizes tumor vasculature and improves cancer therapy

    PubMed Central

    Adapala, Ravi K.; Thoppil, Roslin J.; Ghosh, Kaustabh; Cappelli, Holly; Dudley, Andrew C.; Paruchuri, Sailaja; Keshamouni, Venkateshwar; Klagsbrun, Michael; Meszaros, J. Gary; Chilian, William M.; Ingber, Donald E.; Thodeti, Charles K.

    2016-01-01

    Tumor vessels are characterized by abnormal morphology and hyper-permeability that together cause inefficient delivery of chemotherapeutic agents. Although VEGF has been established as a critical regulator of tumor angiogenesis, the role of mechanical signaling in the regulation of tumor vasculature or tumor endothelial cell (TEC) function is not known. Here, we show that the mechanosensitive ion channel TRPV4 regulates tumor angiogenesis and tumor vessel maturation via modulation of TEC mechanosensitivity. We found that TEC exhibit reduced TRPV4 expression and function, which is correlated with aberrant mechanosensitivity towards ECM stiffness, increased migration and abnormal angiogenesis by TEC. Further, syngeneic tumor experiments revealed that the absence of TRPV4 induced increased vascular density, vessel diameter and reduced pericyte coverage resulting in enhanced tumor growth in TRPV4 KO mice. Importantly, overexpression or pharmacological activation of TRPV4 restored aberrant TEC mechanosensitivity, migration and normalized abnormal angiogenesis in vitro by modulating Rho activity. Finally, a small molecule activator of TRPV4, GSK1016790A, in combination with anti-cancer drug Cisplatin, significantly reduced tumor growth in WT mice by inducing vessel maturation. Our findings demonstrate TRPV4 channels to be critical regulators of tumor angiogenesis and represent a novel target for anti-angiogenic and vascular normalization therapies. PMID:25867067

  11. Ion permeation through light-activated channels in rhabdomeric photoreceptors. Role of divalent cations

    PubMed Central

    1996-01-01

    The receptor potential of rhabdomeric photoreceptors is mediated primarily by a Na influx, but other ions must also permeate through light-dependent channels to account for some properties of the photoresponse. We examined ion conduction in macroscopic and single- channel light-induced currents of Lima and Pecten photoreceptors. In the absence of Na, a fivefold change in extracellular K shifted the reversal voltage of the photocurrent (Vrev) by approximately 27 mV. Because the dependency of Vrev on [K]o was sub-Nernstian, and Vrev in each condition was more positive than Ek, some other ion(s) with a positive equilibrium potential must be implicated, in addition to K. We assessed the participation of calcium, an important candidate because of its involvement in light adaptation. Three strategies were adopted to minimize the impairments to cytosolic Ca homeostasis and loss of responsiveness that normally result from the required ionic manipulations: (a) Internal dialysis with Na-free solutions, to prevent reverse operation of the Na/Ca exchanger. (b) Rapid solution changes, temporally limiting exposure to potentially detrimental ionic conditions. (c) Single-channel recording, exposing only the cell- attached patch of membrane to the test solutions. An inward whole-cell photocurrent could be measured with Ca as the only extracellular charge carrier. Decreasing the [Ca]o to 0.5 mM reduced the response by 43% and displaced the reversal potential by -4.3 mV; the shift was larger (delta Vrev = -44 mV) when intracellular permeant cations were also removed. In all cases, however, the current carried by Ca was < 5% of that measured with normal [Na]o. Unitary light-activated currents were reduced in a similar way when the pipette contained only divalent cations, indicating a substantial selectivity for Na over Ca. The fall kinetics of the photoresponse was slower when external Ca was replaced by Ba, or when the membrane was depolarized; however, dialysis with 10 mM BAPTA

  12. Ion channeling revisited.

    SciTech Connect

    Doyle, Barney Lee; Corona, Aldo; Nguyen, Anh

    2014-09-01

    A MS Excel program has been written that calculates accidental, or unintentional, ion channeling in cubic bcc, fcc and diamond lattice crystals or polycrystalline materials. This becomes an important issue when simulating the creation by energetic neutrons of point displacement damage and extended defects using beams of ions. All of the tables and graphs in the three Ion Beam Analysis Handbooks that previously had to be manually looked up and read from were programed into Excel in handy lookup tables, or parameterized, for the case of the graphs, using rather simple exponential functions with different powers of the argument. The program then offers an extremely convenient way to calculate axial and planar half-angles and minimum yield or dechanneling probabilities, effects on half-angles of amorphous overlayers, accidental channeling probabilities for randomly oriented crystals or crystallites, and finally a way to automatically generate stereographic projections of axial and planar channeling half-angles. The program can generate these projections and calculate these probabilities for axes and [hkl] planes up to (555).

  13. Ion channel and lipid scramblase activity associated with expression of TMEM16F/ANO6 isoforms

    PubMed Central

    Scudieri, Paolo; Caci, Emanuela; Venturini, Arianna; Sondo, Elvira; Pianigiani, Giulia; Marchetti, Carla; Ravazzolo, Roberto; Pagani, Franco; Galietta, Luis J V

    2015-01-01

    Abstract TMEM16F, also known as ANO6, is a membrane protein that has been associated with phospholipid scramblase and ion channel activity. However, the characteristics of TMEM16F-dependent channels, particularly the ion selectivity, are a matter of debate. Furthermore, the direct involvement of TMEM16F in phospholipid scrambling has been questioned. We studied the properties of different TMEM16F variants generated by alternative splicing. Using whole-cell patch-clamp recordings, we found that V1, V2 and V5 variants generated membrane currents activated by very high (micromolar) intracellular Ca2+ concentrations and positive membrane potentials. These variants showed different degrees of Ca2+ sensitivity and kinetics of activation but similar ion permeability, characterized by a slight selectivity for Cl− over Na+. A fourth variant (V3) showing a unique carboxy-terminus was devoid of activity, in agreement with its intracellular localization. We also measured scramblase activity using the binding of annexin V to detect phosphatidylserine on the cell surface. V1, V2 and V5 variants were associated with calcium-dependent phosphatidylserine externalization. Interestingly, introduction of an activating mutation, D409G, produced a marked increase in the apparent Ca2+ sensitivity of TMEM16F-dependent channels. In parallel, this mutation also enhanced the extent of phosphatidylserine externalization that occurred even under resting conditions. These results support the conclusion that TMEM16F proteins are directly involved in dual activity, as a phospholipid scramblase and as an ion channel. Key points TMEM16F is a membrane protein with possible dual function as an ion channel and a phospholipid scramblase. The properties of ion channels associated with TMEM16F and the link between ion channel and scramblase activity are a matter of debate. We studied the properties of four isoforms of TMEM16F generated by alternative splicing. Upregulation of three TMEM16F isoforms or

  14. Overcoming mutagenicity and ion channel activity: optimization of selective spleen tyrosine kinase inhibitors.

    PubMed

    Ellis, J Michael; Altman, Michael D; Bass, Alan; Butcher, John W; Byford, Alan J; Donofrio, Anthony; Galloway, Sheila; Haidle, Andrew M; Jewell, James; Kelly, Nancy; Leccese, Erica K; Lee, Sandra; Maddess, Matthew; Miller, J Richard; Moy, Lily Y; Osimboni, Ekundayo; Otte, Ryan D; Reddy, M Vijay; Spencer, Kerrie; Sun, Binyuan; Vincent, Stella H; Ward, Gwendolyn J; Woo, Grace H C; Yang, Chiming; Houshyar, Hani; Northrup, Alan B

    2015-02-26

    Development of a series of highly kinome-selective spleen tyrosine kinase (Syk) inhibitors with favorable druglike properties is described. Early leads were discovered through X-ray crystallographic analysis, and a systematic survey of cores within a selected chemical space focused on ligand binding efficiency. Attenuation of hERG ion channel activity inherent within the initial chemotype was guided through modulation of physicochemical properties including log D, PSA, and pKa. PSA proved most effective for prospective compound design. Further profiling of an advanced compound revealed bacterial mutagenicity in the Ames test using TA97a Salmonella strain, and subsequent study demonstrated that this mutagenicity was pervasive throughout the series. Identification of intercalation as a likely mechanism for the mutagenicity-enabled modification of the core scaffold. Implementation of a DNA binding assay as a prescreen and models in DNA allowed resolution of the mutagenicity risk, affording molecules with favorable potency, selectivity, pharmacokinetic, and off-target profiles. PMID:25625541

  15. Activity of Palythoa caribaeorum Venom on Voltage-Gated Ion Channels in Mammalian Superior Cervical Ganglion Neurons

    PubMed Central

    Lazcano-Pérez, Fernando; Castro, Héctor; Arenas, Isabel; García, David E.; González-Muñoz, Ricardo; Arreguín-Espinosa, Roberto

    2016-01-01

    The Zoanthids are an order of cnidarians whose venoms and toxins have been poorly studied. Palythoa caribaeorum is a zoanthid commonly found around the Mexican coastline. In this study, we tested the activity of P. caribaeorum venom on voltage-gated sodium channel (NaV1.7), voltage-gated calcium channel (CaV2.2), the A-type transient outward (IA) and delayed rectifier (IDR) currents of KV channels of the superior cervical ganglion (SCG) neurons of the rat. These results showed that the venom reversibly delays the inactivation process of voltage-gated sodium channels and inhibits voltage-gated calcium and potassium channels in this mammalian model. The compounds responsible for these effects seem to be low molecular weight peptides. Together, these results provide evidence for the potential use of zoanthids as a novel source of cnidarian toxins active on voltage-gated ion channels. PMID:27164140

  16. Activity of Palythoa caribaeorum Venom on Voltage-Gated Ion Channels in Mammalian Superior Cervical Ganglion Neurons.

    PubMed

    Lazcano-Pérez, Fernando; Castro, Héctor; Arenas, Isabel; García, David E; González-Muñoz, Ricardo; Arreguín-Espinosa, Roberto

    2016-01-01

    The Zoanthids are an order of cnidarians whose venoms and toxins have been poorly studied. Palythoa caribaeorum is a zoanthid commonly found around the Mexican coastline. In this study, we tested the activity of P. caribaeorum venom on voltage-gated sodium channel (NaV1.7), voltage-gated calcium channel (CaV2.2), the A-type transient outward (IA) and delayed rectifier (IDR) currents of KV channels of the superior cervical ganglion (SCG) neurons of the rat. These results showed that the venom reversibly delays the inactivation process of voltage-gated sodium channels and inhibits voltage-gated calcium and potassium channels in this mammalian model. The compounds responsible for these effects seem to be low molecular weight peptides. Together, these results provide evidence for the potential use of zoanthids as a novel source of cnidarian toxins active on voltage-gated ion channels. PMID:27164140

  17. Ion channel activity of the CSFV p7 viroporin in surrogates of the ER lipid bilayer.

    PubMed

    Largo, Eneko; Verdiá-Báguena, Carmina; Aguilella, Vicente M; Nieva, José L; Alcaraz, Antonio

    2016-01-01

    Viroporins comprise a family of non-structural proteins that play significant and diverse roles during the replication cycle of many animal viruses. Consequently, they have become promising targets for inhibitory drug and vaccine development. Structure–function traits common to all members of the family are their small size (ca. 60–120 aa), high hydrophobicity, and the presence of helical domains that transverse the membrane and assemble into oligomeric-permeating structures therein. The possibility that viroporins show in particular conditions any kind of specificity in the transport of ions and small solutes remains a point of contention in the field. Here we have approached this issue using the Classical Swine Fever Virus (CSFV) protein p7 viroporin as a model. We have previously reported that CSFV-p7 induces release of ANTS (MW: 427.33) from lipid vesicles that emulate the Endoplasmic Reticulum (ER) membrane, and that this process is dependent on pH, modulated by the lipid composition, and recreated by a C-terminal transmembrane helix. Here we have assayed CSFV-p7 for its capacity to form ion-conducting channels in ER-like planar lipid membranes, and established whether this activity is subject to regulation by the same factors. The analysis of electrophysiological recordings in ER membrane surrogates suggests that CSFV-p7 forms pores wide enough to allow ANTS release. Moreover, we were able to discriminate between two pore structures with slightly different sizes and opposite ion selectivities. The fact that the relative abundances of each pore type depend crucially on membrane composition strengthens the view that the physicochemical properties of the lipid bilayers present in the cell endomembrane system modulate viroporin activity. PMID:26464198

  18. Ion Channels in Epithelial Cells

    NASA Astrophysics Data System (ADS)

    Palmer, Lawrence G.

    Ion channels in epithelial cells serve to move ions, and in some cases fluid, between compartments of the body. This function of the transfer of material is fundamentally different from that of the transfer of information, which is the main job of most channels in excitable cells. Nevertheless the basic construction of the channels is similar in many respects in the two tissue types. This chapter reviews the nature of channels in epithelia and discusses how their functions have evolved to accomplish the basic tasks for which they are responsible. I will focus on three channel types: epithelial Na+ channels, inward-rectifier K+ channels, and CFTR Cl- channels.

  19. Potentiation of acid-sensing ion channel activity by peripheral group I metabotropic glutamate receptor signaling.

    PubMed

    Gan, Xiong; Wu, Jing; Ren, Cuixia; Qiu, Chun-Yu; Li, Yan-Kun; Hu, Wang-Ping

    2016-05-01

    Glutamate activates peripheral group I metabotropic glutamate receptors (mGluRs) and contributes to inflammatory pain. However, it is still not clear the mechanisms are involved in group I mGluR-mediated peripheral sensitization. Herein, we report that group I mGluRs signaling sensitizes acid-sensing ion channels (ASICs) in dorsal root ganglion (DRG) neurons and contributes to acidosis-evoked pain. DHPG, a selective group I mGluR agonist, can potentiate the functional activity of ASICs, which mediated the proton-induced events. DHPG concentration-dependently increased proton-gated currents in DRG neurons. It shifted the proton concentration-response curve upwards, with a 47.3±7.0% increase of the maximal current response to proton. Group I mGluRs, especially mGluR5, mediated the potentiation of DHPG via an intracellular cascade. DHPG potentiation of proton-gated currents disappeared after inhibition of intracellular Gq/11 proteins, PLCβ, PKC or PICK1 signaling. Moreover, DHPG enhanced proton-evoked membrane excitability of rat DRG neurons and increased the amplitude of the depolarization and the number of spikes induced by acid stimuli. Finally, peripherally administration of DHPG dose-dependently exacerbated nociceptive responses to intraplantar injection of acetic acid in rats. Potentiation of ASIC activity by group I mGluR signaling in rat DRG neurons revealed a novel peripheral mechanism underlying group I mGluRs involvement in hyperalgesia. PMID:26946972

  20. Optical waveguide lightmode spectroscopic techniques for investigating membrane-bound ion channel activities.

    PubMed

    Székács, Inna; Kaszás, Nóra; Gróf, Pál; Erdélyi, Katalin; Szendrő, István; Mihalik, Balázs; Pataki, Agnes; Antoni, Ferenc A; Madarász, Emilia

    2013-01-01

    Optical waveguide lightmode spectroscopic (OWLS) techniques were probed for monitoring ion permeation through channels incorporated into artificial lipid environment. A novel sensor set-up was developed by depositing liposomes or cell-derived membrane fragments onto hydrophilic polytetrafluoroethylene (PTFE) membrane. The fibrous material of PTFE membrane could entrap lipoid vesicles and the water-filled pores provided environment for the hydrophilic domains of lipid-embedded proteins. The sensor surface was kept clean from the lipid holder PTFE membrane by a water- and ion-permeable polyethylene terephthalate (PET) mesh. The sensor set-up was tested with egg yolk lecithin liposomes containing gramicidin ion channels and with cell-derived membrane fragments enriched in GABA-gated anion channels. The method allowed monitoring the move of Na(+) and organic cations through gramicidin channels and detecting the Cl(-)-channel functions of the (α5β2γ2) GABAA receptor in the presence or absence of GABA and the competitive GABA-blocker bicuculline. PMID:24339925

  1. Optical Waveguide Lightmode Spectroscopic Techniques for Investigating Membrane-Bound Ion Channel Activities

    PubMed Central

    Székács, Inna; Kaszás, Nóra; Gróf, Pál; Erdélyi, Katalin; Szendrő, István; Mihalik, Balázs; Pataki, Ágnes; Antoni, Ferenc A.; Madarász, Emilia

    2013-01-01

    Optical waveguide lightmode spectroscopic (OWLS) techniques were probed for monitoring ion permeation through channels incorporated into artificial lipid environment. A novel sensor set-up was developed by depositing liposomes or cell-derived membrane fragments onto hydrophilic polytetrafluoroethylene (PTFE) membrane. The fibrous material of PTFE membrane could entrap lipoid vesicles and the water-filled pores provided environment for the hydrophilic domains of lipid-embedded proteins. The sensor surface was kept clean from the lipid holder PTFE membrane by a water- and ion-permeable polyethylene terephthalate (PET) mesh. The sensor set-up was tested with egg yolk lecithin liposomes containing gramicidin ion channels and with cell-derived membrane fragments enriched in GABA-gated anion channels. The method allowed monitoring the move of Na+ and organic cations through gramicidin channels and detecting the Cl–-channel functions of the (α5β2γ2) GABAA receptor in the presence or absence of GABA and the competitive GABA-blocker bicuculline. PMID:24339925

  2. Voltage-activated ion channels and Ca2+-induced Ca2+ release shape Ca2+ signaling in Merkel cells

    PubMed Central

    Piskorowski, Rebecca; Haeberle, Henry; Panditrao, Mayuri V.; Lumpkin, Ellen A.

    2008-01-01

    Ca2+ signaling and neurotransmission modulate touch-evoked responses in Merkel cell–neurite complexes. To identify mechanisms governing these processes, we analyzed voltage-activated ion channels and Ca2+ signaling in purified Merkel cells. Merkel cells in the intact skin were specifically labeled by antibodies against voltage-activated Ca2+ channels (CaV2.1) and voltage- and Ca2+-activated K+ (BKCa) channels. Voltage-clamp recordings revealed small Ca2+ currents, which produced Ca2+ transients that were amplified sevenfold by Ca2+-induced Ca2+ release. Merkel cells' voltage-activated K+ currents were carried predominantly by BKCa channels with inactivating and noninactivating components. Thus, Merkel cells, like hair cells, have functionally diverse BKCa channels. Finally, blocking K+ channels increased response magnitude and dramatically shortened Ca2+ transients evoked by mechanical stimulation. Together, these results demonstrate that Ca2+ signaling in Merkel cells is governed by the interplay of plasma membrane Ca2+ channels, store release and K+ channels, and they identify specific signaling mechanisms that may control touch sensitivity. PMID:18415122

  3. Acid-sensing ion channels regulate spontaneous inhibitory activity in the hippocampus: possible implications for epilepsy.

    PubMed

    Ievglevskyi, O; Isaev, D; Netsyk, O; Romanov, A; Fedoriuk, M; Maximyuk, O; Isaeva, E; Akaike, N; Krishtal, O

    2016-08-01

    Acid-sensing ion channels (ASICs) play an important role in numerous functions in the central and peripheral nervous systems ranging from memory and emotions to pain. The data correspond to a recent notion that each neuron and many glial cells of the mammalian brain express at least one member of the ASIC family. However, the mechanisms underlying the involvement of ASICs in neuronal activity are poorly understood. However, there are two exceptions, namely, the straightforward role of ASICs in proton-based synaptic transmission in certain brain areas and the role of the Ca(2+)-permeable ASIC1a subtype in ischaemic cell death. Using a novel orthosteric ASIC antagonist, we have found that ASICs specifically control the frequency of spontaneous inhibitory synaptic activity in the hippocampus. Inhibition of ASICs leads to a strong increase in the frequency of spontaneous inhibitory postsynaptic currents. This effect is presynaptic because it is fully reproducible in single synaptic boutons attached to isolated hippocampal neurons. In concert with this observation, inhibition of the ASIC current diminishes epileptic discharges in a low Mg(2+) model of epilepsy in hippocampal slices and significantly reduces kainate-induced discharges in the hippocampus in vivo Our results reveal a significant novel role for ASICs.This article is part of the themed issue 'Evolution brings Ca(2+) and ATP together to control life and death'. PMID:27377725

  4. Dehydrated Hereditary Stomatocytosislinked to gain-of-function mutations in mechanically activated PIEZO1 ion channels

    PubMed Central

    Albuisson, Juliette; Murthy, Swetha E.; Bandell, Michael; Coste, Bertrand; Louis-dit-Picard, Hélène; Mathur, Jayanti; Fénéant-Thibault, Madeleine; Tertian, Gérard; de Jaureguiberry, Jean-Pierre; Syfuss, Pierre-Yves; Cahalan, Stuart; Garçon, Loic; Toutain, Fabienne; Rohrlich, Pierre Simon; Delaunay, Jean; Picard, Véronique; Jeunemaitre, Xavier; Patapoutian, Ardem

    2013-01-01

    Dehydrated hereditary stomatocytosis (DHS) is a genetic condition with defective red blood cell (RBC) membrane properties that causes an imbalance in intracellular cation concentrations. Recently, two missense mutations inthe mechanically activated PIEZO1(FAM38A) ion channel were associated with DHS. However, it is not known how these mutations affect PIEZO1 function. Here, by combining linkage analysis and whole-exome sequencing in a large pedigree and Sanger sequencing in two additional kindreds and 11 unrelated DHS cases, we identifythree novel missense mutations and one recurrent duplication in PIEZO1, demonstrating that it is the major gene for DHS. All the DHS-associated mutations locate at C-terminal half of PIEZO1. Remarkably, we find that all PIEZO1 mutations give rise to mechanically activated currents that inactivate more slowly than wild-type currents. This gain-of-function PIEZO1 phenotype provides insight that helps to explain the increased permeability of cations in RBCs of DHS patients. Our findings also suggest a new role for mechanotransduction in RBC biology and pathophysiology. PMID:23695678

  5. Let It Go and Open Up, an Ensemble of Ion Channel Active States.

    PubMed

    Minor, Daniel L

    2016-02-11

    Ligand binding usually moves the target protein from an ensemble of inactive states to a well-defined active conformation. Matthies et al. flip this scheme around, finding that, for the magnesium channel CorA, loss of ligand binding induces an ensemble of conformations that turn the channel on. PMID:26871624

  6. Receptor-mediated activation of a plant Ca2+-permeable ion channel involved in pathogen defense

    PubMed Central

    Zimmermann, Sabine; Nürnberger, Thorsten; Frachisse, Jean-Marie; Wirtz, Wolfgang; Guern, Jean; Hedrich, Rainer; Scheel, Dierk

    1997-01-01

    Pathogen recognition at the plant cell surface typically results in the initiation of a multicomponent defense response. Transient influx of Ca2+ across the plasma membrane is postulated to be part of the signaling chain leading to pathogen resistance. Patch-clamp analysis of parsley protoplasts revealed a novel Ca2+-permeable, La3+-sensitive plasma membrane ion channel of large conductance (309 pS in 240 mM CaCl2). At an extracellular Ca2+ concentration of 1 mM, which is representative of the plant cell apoplast, unitary channel conductance was determined to be 80 pS. This ion channel (LEAC, for large conductance elicitor-activated ion channel) is reversibly activated upon treatment of parsley protoplasts with an oligopeptide elicitor derived from a cell wall protein of Phytophthora sojae. Structural features of the elicitor found previously to be essential for receptor binding, induction of defense-related gene expression, and phytoalexin formation are identical to those required for activation of LEAC. Thus, receptor-mediated stimulation of this channel appears to be causally involved in the signaling cascade triggering pathogen defense in parsley. PMID:11038609

  7. Dendrotoxins: structure-activity relationships and effects on potassium ion channels.

    PubMed

    Harvey, A L; Robertson, B

    2004-12-01

    Dendrotoxins are small proteins isolated from mamba (Dendroaspis) snakes. The original dendrotoxin was found in venom of the Eastern green mamba, Dendroaspis angusticeps, and related proteins were subsequently found in other mamba venoms. The dendrotoxins contain 57-60 amino acid residues cross-linked by three disulphide bridges, and they are homologous to Kunitz-type serine protease inhibitors, such as aprotinin (BPTI). The dendrotoxins have little or no anti-protease activity, but they block particular subtypes of voltage-dependent potassium channels of the Kv1 subfamily in neurones. Alpha-dendrotoxin from green mamba Dendroaspis angusticeps and toxin I from the black mamba Dendroaspis polylepis block cloned Kv1.1, Kv1.2 and Kv1.6 channels in the low nanomolar range; toxin K, also from the black mamba Dendroaspis polylepis, preferentially blocks Kv1.1 channels and is active at picomolar concentrations. Structural modifications and mutations to dendrotoxins have helped to define the molecular recognition properties of different types of K+ channels, although more work is needed to characterise the chemical features of the toxins that underlie their selectivity and potency at particular subtypes of channels. Dendrotoxins have been useful markers of subtypes of K+ channels in vivo, and dendrotoxins have become widely used as probes for studying the function of K+ channels in physiology and pathophysiology. With some pathological conditions being associated with voltage-gated K+ channels, analogues of dendrotoxins might have therapeutic potential. PMID:15579000

  8. Ion channel therapeutics for pain

    PubMed Central

    Skerratt, Sarah E; West, Christopher W

    2015-01-01

    Pain is a complex disease which can progress into a debilitating condition. The effective treatment of pain remains a challenge as current therapies often lack the desired level of efficacy or tolerability. One therapeutic avenue, the modulation of ion channel signaling by small molecules, has shown the ability to treat pain. However, of the 215 ion channels that exist in the human genome, with 85 ion channels having a strong literature link to pain, only a small number of these channels have been successfully drugged for pain. The focus of future research will be to fully explore the possibilities surrounding these unexplored ion channels. Toward this end, a greater understanding of ion channel modulation will be the greatest tool we have in developing the next generation of drugs for the treatment of pain. PMID:26218246

  9. Prolactin potentiates the activity of acid-sensing ion channels in female rat primary sensory neurons.

    PubMed

    Liu, Ting-Ting; Qu, Zu-Wei; Ren, Cuixia; Gan, Xiong; Qiu, Chun-Yu; Hu, Wang-Ping

    2016-04-01

    Prolactin (PRL) is a polypeptide hormone produced and released from the pituitary and extrapituitary tissues. It regulates activity of nociceptors and causes hyperalgesia in pain conditions, but little is known the molecular mechanism. We report here that PRL can exert a potentiating effect on the functional activity of acid-sensing ion channels (ASICs), key sensors for extracellular protons. First, PRL dose-dependently increased the amplitude of ASIC currents with an EC50 of (5.89 ± 0.28) × 10(-8) M. PRL potentiation of ASIC currents was also pH dependent. Second, PRL potentiation of ASIC currents was blocked by Δ1-9-G129R-hPRL, a PRL receptor antagonist, and removed by intracellular dialysis of either protein kinase C inhibitor GF109203X, protein interacting with C-kinase 1(PICK1) inhibitor FSC-231, or PI3K inhibitor AS605240. Third, PRL altered acidosis-evoked membrane excitability of DRG neurons and caused a significant increase in the amplitude of the depolarization and the number of spikes induced by acid stimuli. Four, PRL exacerbated nociceptive responses to injection of acetic acid in female rats. Finally, PRL displayed a stronger effect on ASIC mediated-currents and nociceptive behavior in intact female rats than OVX female and male rats and thus modulation of PRL may be gender-dependent. These results suggest that PRL up-regulates the activity of ASICs and enhances ASIC mediated nociceptive responses in female rats, which reveal a novel peripheral mechanism underlying PRL involvement in hyperalgesia. PMID:26188144

  10. Dual Activation of a Sex Pheromone-Dependent Ion Channel from Insect Olfactory Dendrites by Protein Kinase C Activators and Cyclic GMP

    NASA Astrophysics Data System (ADS)

    Zufall, Frank; Hatt, Hanns

    1991-10-01

    Olfactory transduction is thought to take place in the outer dendritic membrane of insect olfactory receptor neurons. Here we show that the outer dendritic plasma membrane of silkmoth olfactory receptor neurons seems to be exclusively equipped with a specific ion channel activated by low concentrations of the species-specific sex pheromone component. This so-called AC_1 channel has a conductance of 56 pS and is nonselectively permeable to cations. The AC_1 channel can be activated from the intracellular side by protein kinase C activators such as diacylglycerol and phorbolester and by cGMP but not by Ca2+, inositol 1,4,5-trisphosphate, or cAMP. Our results imply that phosphorylation of this ion channel by protein kinase C could be the crucial step in channel opening by sex pheromones.

  11. Dynamic ion-ion and water-ion interactions in ion channels.

    PubMed Central

    Wu, J V

    1992-01-01

    The dynamic interactions among ions and water molecules in ion channels are treated based on an assumption that ions at binding sites can be knocked off by both transient entering ions and local water molecules. The theory, when applied to a single-site model K+ channel, provides solutions for super- and subsaturations, flux-ratio exponent (n') greater than 1, osmotic streaming current, activity-dependent reversal potentials, and anomalous mole-fraction behavior. The analysis predicts that: (a) the saturation may but, in general, does not follow the Michaelis-Menten relation; (b) streaming current results from imbalanced water-ion knock-off interactions; (c) n' greater than 1 even for single-site channels, but it is unlikely to exceed 1.4 unless the pore is occupied by one or more ion(s); (d) in the calculation involving two permeant ion species with similar radii, the heavier ions show higher affinity; the ion-ion knock-off dissociation from the site is more effective when two interacting ions are identical. Therefore, the "multi-ion behaviors" found in most ion channels are the consequences of dynamic ion-ion and water-ion interactions. The presence of these interactions does not require two or more binding sites in channels. PMID:1376158

  12. Ion channels, channelopathies, and tooth formation.

    PubMed

    Duan, X

    2014-02-01

    The biological functions of ion channels in tooth development vary according to the nature of their gating, the species of ions passing through those gates, the number of gates, localization of channels, tissue expressing the channel, and interactions between cells and microenvironment. Ion channels feature unique and specific ion flux in ameloblasts, odontoblasts, and other tooth-specific cell lineages. Both enamel and dentin have active chemical systems orchestrating a variety of ion exchanges and demineralization and remineralization processes in a stage-dependent manner. An important role for ion channels is to regulate and maintain the calcium and pH homeostasis that are critical for proper enamel and dentin biomineralization. Specific functions of chloride channels, TRPVs, calcium channels, potassium channels, and solute carrier superfamily members in tooth formation have been gradually clarified in recent years. Mutations in these ion channels or transporters often result in disastrous changes in tooth development. The channelopathies of tooth include altered eruption (CLCN7, KCNJ2, TRPV3), root dysplasia (CLCN7, KCNJ2), amelogenesis imperfecta (KCNJ1, CFTR, AE2, CACNA1C, GJA1), dentin dysplasia (CLCN5), small teeth (CACNA1C, GJA1), tooth agenesis (CLCN7), and other impairments. The mechanisms leading to tooth channelopathies are primarily related to pH regulation, calcium homeostasis, or other alterations of the niche for tooth eruption and development. PMID:24076519

  13. Ion permeation through single channels activated by acetylcholine in denervated toad sartorius skeletal muscle fibers: effects of alkali cations.

    PubMed

    Quartararo, N; Barry, P H; Gage, P W

    1987-01-01

    The gigaohm seal technique was used to study ion permeation through acetylcholine-activated channels in cell-attached patches of the extrajunctional membrane of chronically denervated, enzyme-treated cells from the sartorius muscle of the toad Bufo marinus. The most frequently occurring channel type (greater than 95% of channel openings), provisionally classified as 'extrajunctional,' had a chord conductance of approximately 25 pS under normal conditions (-70 mV, 11 degrees C, Normal Toad Ringer's). The less frequently observed channel type (less than 5% of channel openings), classified as a 'junctional' type, had a conductance of 35 pS under the same conditions, and a similar null potential. In many patches, a small percentage (usually less than 2%) of openings of the extrajunctional channel displayed a lower conductance state. The shape of the I-V curves obtained for the extrajunctional channel depended on the predominant extracellular cation. For Cs and K, the I-V curves were essentially linear over the voltage range +50 to -150 mV across the patch, suggesting that the potential independent component of the energy profile within the channel was symmetrical. For Li, the I-V curve was very nonlinear, displaying a significant sublinearity at hyperpolarized potentials. Both an electrodiffusion and a symmetrical uniform four-barrier, three-site rate-theory model provided reasonable fits to the data, whereas symmetrical two-barrier, single-site rate-theory models did not. For the alkali cations examined, the relative permeability sequence was PCs greater than PK greater than PNa greater than PLi--a "proportional" selectivity sequence. This was different from the single channel conductance sequence which was found to be gamma K greater than gamma Cs greater than gamma Na greater than gamma Li implying that ions do not move independently through the channel. The relative binding constant sequence for the channel sites was found to be a "polarizability" sequence, i

  14. Gain-of-function mutations in the mechanically activated ion channel PIEZO2 cause a subtype of Distal Arthrogryposis

    PubMed Central

    Coste, Bertrand; Houge, Gunnar; Murray, Michael F.; Stitziel, Nathan; Bandell, Michael; Giovanni, Monica A.; Philippakis, Anthony; Hoischen, Alexander; Riemer, Gunnar; Steen, Unni; Steen, Vidar Martin; Mathur, Jayanti; Cox, James; Lebo, Matthew; Rehm, Heidi; Weiss, Scott T.; Wood, John N.; Maas, Richard L.; Sunyaev, Shamil R.; Patapoutian, Ardem

    2013-01-01

    Mechanotransduction, the pathway by which mechanical forces are translated to biological signals, plays important but poorly characterized roles in physiology. PIEZOs are recently identified, widely expressed, mechanically activated ion channels that are hypothesized to play a role in mechanotransduction in mammals. Here, we describe two distinct PIEZO2 mutations in patients with a subtype of Distal Arthrogryposis Type 5 characterized by generalized autosomal dominant contractures with limited eye movements, restrictive lung disease, and variable absence of cruciate knee ligaments. Electrophysiological studies reveal that the two PIEZO2 mutations affect biophysical properties related to channel inactivation: both E2727del and I802F mutations cause the PIEZO2-dependent, mechanically activated currents to recover faster from inactivation, while E2727del also causes a slowing of inactivation. Both types of changes in kinetics result in increased channel activity in response to a given mechanical stimulus, suggesting that Distal Arthrogryposis Type 5 can be caused by gain-of-function mutations in PIEZO2. We further show that overexpression of mutated PIEZO2 cDNAs does not cause constitutive activity or toxicity to cells, indicating that the observed phenotype is likely due to a mechanotransduction defect. Our studies identify a type of channelopathy and link the dysfunction of mechanically activated ion channels to developmental malformations and joint contractures. PMID:23487782

  15. Calcium-Activated SK Channels Influence Voltage-Gated Ion Channels to Determine the Precision of Firing in Globus Pallidus Neurons

    PubMed Central

    Deister, Christopher A.; Chan, C. Savio; Surmeier, D. James; Wilson, Charles J.

    2012-01-01

    Globus pallidus (GP) neurons fire rhythmically in the absence of synaptic input, suggesting that they may encode their inputs as changes in the phase of their rhythmic firing. Action potential afterhyperpolarization (AHP) enhances precision of firing by ensuring that the ion channels recover from inactivation by the same amount on each cycle. Voltage-clamp experiments in slices showed that the longest component of the GP neuron’s AHP is blocked by apamin, a selective antagonist of calcium-activated SK channels. Application of 100 nm apamin also disrupted the precision of firing in perforated-patch and cell-attached recordings. SK channel blockade caused a small depolarization in spike threshold and made it more variable, but there was no reduction in the maximal rate of rise during an action potential. Thus, the firing irregularity was not caused solely by a reduction in voltage-gated Na+ channel availability. Subthreshold voltage ramps triggered a large outward current that was sensitive to the initial holding potential and had properties similar to the A-type K+ current in GP neurons. In numerical simulations, the availability of both Na+ and A-type K+ channels during autonomous firing were reduced when SK channels were removed, and a nearly equal reduction in Na+ and K+ subthreshold-activated ion channel availability produced a large decrease in the neuron’s slope conductance near threshold. This change made the neuron more sensitive to intrinsically generated noise. In vivo, this change would also enhance the sensitivity of GP neurons to small synaptic inputs. PMID:19571136

  16. Myrsinane, Premyrsinane, and Cyclomyrsinane Diterpenes from Euphorbia falcata as Potassium Ion Channel Inhibitors with Selective G Protein-Activated Inwardly Rectifying Ion Channel (GIRK) Blocking Effects.

    PubMed

    Vasas, Andrea; Forgo, Peter; Orvos, Péter; Tálosi, László; Csorba, Attila; Pinke, Gyula; Hohmann, Judit

    2016-08-26

    GIRK channels are activated by a large number of G protein-coupled receptors and regulate the electrical activity of neurons, cardiac atrial myocytes, and β-pancreatic cells. Abnormalities in GIRK channel function have been implicated in the pathophysiology of neuropathic pain, drug addiction, and cardiac arrhythmias. In the heart, GIRK channels are selectively expressed in the atrium, and their activation inhibits pacemaker activity, thereby slowing the heart rate. In the present study, 19 new diterpenes, falcatins A-S (1-19), and the known euphorprolitherin D (20) were isolated from Euphorbia falcata. The compounds were assayed on stable transfected HEK-hERG (Kv11.1) and HEK-GIRK1/4 (Kir3.1 and Kir3.4) cells. Blocking activity on GIRK channels was exerted by 13 compounds (61-83% at 10 μM), and, among them, five possessed low potency on the hERG channel (4-20% at 10 μM). These selective activities suggest that myrsinane-related diterpenes are potential lead compounds for the treatment of atrial fibrillation. PMID:27441737

  17. Cholesterol binding to ion channels

    PubMed Central

    Levitan, Irena; Singh, Dev K.; Rosenhouse-Dantsker, Avia

    2014-01-01

    Numerous studies demonstrated that membrane cholesterol is a major regulator of ion channel function. The goal of this review is to discuss significant advances that have been recently achieved in elucidating the mechanisms responsible for cholesterol regulation of ion channels. The first major insight that comes from growing number of studies that based on the sterol specificity of cholesterol effects, show that several types of ion channels (nAChR, Kir, BK, TRPV) are regulated by specific sterol-protein interactions. This conclusion is supported by demonstrating direct saturable binding of cholesterol to a bacterial Kir channel. The second major advance in the field is the identification of putative cholesterol binding sites in several types of ion channels. These include sites at locations associated with the well-known cholesterol binding motif CRAC and its reversed form CARC in nAChR, BK, and TRPV, as well as novel cholesterol binding regions in Kir channels. Notably, in the majority of these channels, cholesterol is suggested to interact mainly with hydrophobic residues in non-annular regions of the channels being embedded in between transmembrane protein helices. We also discuss how identification of putative cholesterol binding sites is an essential step to understand the mechanistic basis of cholesterol-induced channel regulation. Clearly, however, these are only the first few steps in obtaining a general understanding of cholesterol-ion channels interactions and their roles in cellular and organ functions. PMID:24616704

  18. Stretch-activated single ion channel currents in tissue-cultured embryonic chick skeletal muscle.

    PubMed Central

    Guharay, F; Sachs, F

    1984-01-01

    The membrane of tissue-cultured chick pectoral muscle contains an ionic channel which is activated by membrane stretch. Nicotinic channels and Ca2+-activated K+ channels are not affected by stretch. In 150 mM-external K+ and 150 mM-internal Na+ the channel has a conductance of 70 pS, linear current-voltage relationship between -50 and -140 mV and a reversal potential of +30 mV. Kinetic analysis of single-channel records indicates that there are one open (O) and three closed (C) states. The data can be fitted by the reaction scheme: C1-C2-C3-O. Only the rate constant that governs the C1-C2 transition (k1,2) is stretch-sensitive. None of the rates are voltage-sensitive. The rate constant k1,2 varies with the square of the tension as k1, 2 = k0 X e alpha T2, where alpha is a constant describing the sensitivity to stretch and T is the tension. A typical value of alpha is 0.08 (dyn cm-1)-2. Following exposure to cytochalasin B the channel becomes more sensitive to stretch. The stretch-sensitivity constant, alpha, increases from 0.08 to 2.4 (dyn cm-1)-2. The probability of the channel being open is strongly dependent upon the extracellular K+ concentration. With a suction of 2 cmHg the probability increases from 0.004 in normal saline (5 mM-K+) to 0.26 in 150 mM-K+. The channel appears to gather force from a large area of membrane (greater than 3 X 10(5) A2), probably by a cytochalasin-resistant cytoskeletal network. PMID:6086918

  19. Cardiac ion channels in health and disease.

    PubMed

    Amin, Ahmad S; Tan, Hanno L; Wilde, Arthur A M

    2010-01-01

    Cardiac electrical activity depends on the coordinated propagation of excitatory stimuli through the heart and, as a consequence, the generation of action potentials in individual cardiomyocytes. Action potential formation results from the opening and closing (gating) of ion channels that are expressed within the sarcolemma of cardiomyocytes. Ion channels possess distinct genetic, molecular, pharmacologic, and gating properties and exhibit dissimilar expression levels within different cardiac regions. By gating, ion channels permit ion currents across the sarcolemma, thereby creating the different phases of the action potential (e.g., resting phase, depolarization, repolarization). The importance of ion channels in maintaining normal heart rhythm is reflected by the increased incidence of arrhythmias in inherited diseases that are linked to mutations in genes encoding ion channels or their accessory proteins and in acquired diseases that are associated with changes in ion channel expression levels or gating properties. This review discusses ion channels that contribute to action potential formation in healthy hearts and their role in inherited and acquired diseases. PMID:19875343

  20. Acid-sensitive ion channels and receptors.

    PubMed

    Holzer, Peter

    2009-01-01

    Acidosis is a noxious condition associated with inflammation, ischaemia or defective acid containment. As a consequence, acid sensing has evolved as an important property of afferent neurons with unmyelinated and thinly myelinated nerve fibres. Protons evoke multiple currents in primary afferent neurons, which are carried by several acid-sensitive ion channels. Among these, acid-sensing ion channels (ASICs) and transient receptor potential (TRP) vanilloid-1 (TRPV1) ion channels have been most thoroughly studied. ASICs survey moderate decreases in extracellular pH, whereas TRPV1 is activated only by severe acidosis resulting in pH values below 6. Two-pore-domain K(+) (K(2P)) channels are differentially regulated by small deviations of extra- or intracellular pH from physiological levels. Other acid-sensitive channels include TRPV4, TRPC4, TRPC5, TRPP2 (PKD2L1), ionotropic purinoceptors (P2X), inward rectifier K(+) channels, voltage-activated K(+) channels, L-type Ca(2+) channels, hyperpolarization-activated cyclic nucleotide gated channels, gap junction channels, and Cl(-) channels. In addition, acid-sensitive G protein coupled receptors have also been identified. Most of these molecular acid sensors are expressed by primary sensory neurons, although to different degrees and in various combinations. Emerging evidence indicates that many of the acid-sensitive ion channels and receptors play a role in acid sensing, acid-induced pain and acid-evoked feedback regulation of homeostatic reactions. The existence and apparent redundancy of multiple pH surveillance systems attests to the concept that acid-base regulation is a vital issue for cell and tissue homeostasis. Since upregulation and overactivity of acid sensors appear to contribute to various forms of chronic pain, acid-sensitive ion channels and receptors are considered as targets for novel analgesic drugs. This approach will only be successful if the pathological implications of acid sensors can be differentiated

  1. Acid-sensitive ion channels and receptors

    PubMed Central

    Holzer, Peter

    2015-01-01

    Acidosis is a noxious condition associated with inflammation, ischaemia or defective acid containment. As a consequence, acid sensing has evolved as an important property of afferent neurons with unmyelinated and thinly myelinated nerve fibres. Protons evoke multiple currents in primary afferent neurons, which are carried by several acid-sensitive ion channels. Among these, acid-sensing ion channels (ASICs) and transient receptor potential (TRP) vanilloid-1 (TRPV1) ion channels have been most thoroughly studied. ASICs survey moderate decreases in extracellular pH whereas TRPV1 is activated only by severe acidosis resulting in pH values below 6. Two-pore domain K+ (K2P) channels are differentially regulated by small deviations of extra- or intracellular pH from physiological levels. Other acid-sensitive channels comprise TRPV4, TRPC4, TRPC5, TRPP2 (PKD2L1), ionotropic purinoceptors (P2X), inward rectifier K+ channels, voltage-activated K+ channels, L-type Ca2+ channels, hyperpolarization-activated cyclic nucleotide-gated channels, gap junction channels, and Cl− channels. In addition, acid-sensitive G protein-coupled receptors have also been identified. Most of these molecular acid sensors are expressed by primary sensory neurons, although to different degrees and in various combinations. Emerging evidence indicates that many of the acid-sensitive ion channels and receptors play a role in acid sensing, acid-induced pain and acid-evoked feedback regulation of homeostatic reactions. The existence and apparent redundancy of multiple pH surveillance systems attests to the concept that acid-base regulation is a vital issue for cell and tissue homeostasis. Since upregulation and overactivity of acid sensors appear to contribute to various forms of chronic pain, acid-sensitive ion channels and receptors are considered as targets for novel analgesic drugs. This approach will only be successful if the pathological implications of acid sensors can be differentiated

  2. Structure-activity and interaction effects of 14 different pyrethroids on voltage-gated chloride ion channels.

    PubMed

    Burr, Steven A; Ray, David E

    2004-02-01

    We have proposed that since the type II pyrethroids deltamethrin and cypermethrin, but not the type I pyrethroid cismethrin act on chloride channels, this could contribute to the bimodal nature of pyrethroid poisoning syndromes. We now examine a wider range of pyrethroid structures on the activity of these calcium-independent voltage-gated maxi-chloride channels. Excised inside-out membrane patches from differentiated mouse neuroblastoma cells were used, and mean channel open probabilities calculated. For single dosing at 10 microM, bioallethrin, beta-cyfluthrin, cypermethrin, deltamethrin, and fenpropathrin were all found to significantly decrease open channel probability (p < 0.05). Bifenthrin, bioresmethrin, cispermethrin, cisresmethrin, cyfluthrin isomers 2 and 4, lambda-cyhalothrin, esfenvalerate, and tefluthrin, did not significantly alter open channel probability (p > 0.05). Since the type II pyrethroids, esfenvalerate, and lambda-cyhalothrin were ineffective, we must conclude that actions at the chloride ion channel target cannot in themselves account for the differences between the two types of poisoning syndrome. Sequential dosing with type II pyrethroids caused no further chloride ion channel closure. The type I pyrethroid cisresmethrin did however prevent a subsequent effect by the mixed type pyrethroid fenpropathrin. In contrast, the type I pyrethroid cispermethrin did not prevent a subsequent effect due to the type II pyrethroid deltamethrin. The difference in effect may be the result of differences in potency, as deltamethrin had a greater effect than fenpropathrin. It therefore appears clear that in some combinations the type I and type II pyrethroids can compete and may bind to the same chloride channel target site. PMID:14657519

  3. Intracellular ion channels and cancer.

    PubMed

    Leanza, Luigi; Biasutto, Lucia; Managò, Antonella; Gulbins, Erich; Zoratti, Mario; Szabò, Ildikò

    2013-01-01

    Several types of channels play a role in the maintenance of ion homeostasis in subcellular organelles including endoplasmatic reticulum, nucleus, lysosome, endosome, and mitochondria. Here we give a brief overview of the contribution of various mitochondrial and other organellar channels to cancer cell proliferation or death. Much attention is focused on channels involved in intracellular calcium signaling and on ion fluxes in the ATP-producing organelle mitochondria. Mitochondrial K(+) channels (Ca(2+)-dependent BKCa and IKCa, ATP-dependent KATP, Kv1.3, two-pore TWIK-related Acid-Sensitive K(+) channel-3 (TASK-3)), Ca(2+) uniporter MCU, Mg(2+)-permeable Mrs2, anion channels (voltage-dependent chloride channel VDAC, intracellular chloride channel CLIC) and the Permeability Transition Pore (MPTP) contribute importantly to the regulation of function in this organelle. Since mitochondria play a central role in apoptosis, modulation of their ion channels by pharmacological means may lead to death of cancer cells. The nuclear potassium channel Kv10.1 and the nuclear chloride channel CLIC4 as well as the endoplasmatic reticulum (ER)-located inositol 1,4,5-trisphosphate (IP3) receptor, the ER-located Ca(2+) depletion sensor STIM1 (stromal interaction molecule 1), a component of the store-operated Ca(2+) channel and the ER-resident TRPM8 are also mentioned. Furthermore, pharmacological tools affecting organellar channels and modulating cancer cell survival are discussed. The channels described in this review are summarized on Figure 1. Overall, the view is emerging that intracellular ion channels may represent a promising target for cancer treatment. PMID:24027528

  4. Hyperpolarization-activated ion channels as targets for nitric oxide signalling in deep cerebellar nuclei

    PubMed Central

    Wilson, Gary W; Garthwaite, John

    2010-01-01

    Most biological effects of nitric oxide (NO) in the brain are mediated by guanylyl cyclase-coupled NO receptors, whose activation results in increased intracellular cGMP levels. Apart from protein kinase activation little is known about subsequent cGMP signal transduction. In optic nerve axons, hyperpolarization-activated cyclic nucleotide-modulated cation (HCN) channels, which bind cGMP or cAMP directly, were recently suggested to be a target. The aim here was to test this possibility more directly. Neurones of the rat deep cerebellar nuclei were selected for this purpose, their suitability being attested by immunocytochemistry showing that the principal neurones expressed guanylyl cyclase protein and that NO synthase-containing fibres were abundant in the neuropil. Using whole-cell voltage-clamp recording, HCN channels in the neurones were activated in response to isoprenaline and exogenous cAMP but only occasionally did they respond to NO, although exogenous cGMP was routinely effective. With the less invasive sharp microelectrode recording technique, however, exogenous NO modulated the channels reproducibly, as measured by the size of the HCN channel-mediated voltage sag following hyperpolarization. Moreover, NO also blunted the subsequent rebound depolarizing potentials, consistent with it increasing the hyperpolarization-activated current. Optimizing the whole-cell solution to improve the functioning of NO-activated guanylyl cyclase failed to restore NO sensitivity. Minimizing cellular dialysis by using the perforated-patch technique, however, was successful. The results provide evidence that HCN channels are potential downstream mediators of NO signalling in deep cerebellar nuclei neurones and suggest that the more general importance of this transduction pathway may have been overlooked previously because of unsuitable recording methods. PMID:20529121

  5. Measuring Ion Channels on Solid Supported Membranes

    PubMed Central

    Schulz, Patrick; Dueck, Benjamin; Mourot, Alexandre; Hatahet, Lina; Fendler, Klaus

    2009-01-01

    Abstract Application of solid supported membranes (SSMs) for the functional investigation of ion channels is presented. SSM-based electrophysiology, which has been introduced previously for the investigation of active transport systems, is expanded for the analysis of ion channels. Membranes or liposomes containing ion channels are adsorbed to an SSM and a concentration gradient of a permeant ion is applied. Transient currents representing ion channel transport activity are recorded via capacitive coupling. We demonstrate the application of the technique to liposomes reconstituted with the peptide cation channel gramicidin, vesicles from native tissue containing the nicotinic acetylcholine receptor, and membranes from a recombinant cell line expressing the ionotropic P2X2 receptor. It is shown that stable ion gradients, both inside as well as outside directed, can be applied and currents are recorded with an excellent signal/noise ratio. For the nicotinic acetylcholine receptor and the P2X2 receptor excellent assay quality factors of Z′ = 0.55 and Z′ = 0.67, respectively, are obtained. This technique opens up new possibilities in cases where conventional electrophysiology fails like the functional characterization of ion channels from intracellular compartments. It also allows for robust fully automatic assays for drug screening. PMID:19580777

  6. Calcium-dependent regulation of Rab activation and vesicle fusion by an intracellular P2X ion channel.

    PubMed

    Parkinson, Katie; Baines, Abigail E; Keller, Thomas; Gruenheit, Nicole; Bragg, Laricia; North, R Alan; Thompson, Christopher R L

    2014-01-01

    Rab GTPases play key roles in the delivery, docking and fusion of intracellular vesicles. However, the mechanism by which spatial and temporal regulation of Rab GTPase activity is controlled is poorly understood. Here we describe a mechanism by which localized calcium release through a vesicular ion channel controls Rab GTPase activity. We show that activation of P2XA, an intracellular ion channel localized to the Dictyostelium discoideum contractile vacuole system, results in calcium efflux required for downregulation of Rab11a activity and efficient vacuole fusion. Vacuole fusion and Rab11a downregulation require the activity of CnrF, an EF-hand-containing Rab GAP found in a complex with Rab11a and P2XA. CnrF Rab GAP activity for Rab11a is enhanced by the presence of calcium and the EF-hand domain. These findings suggest that P2XA activation results in vacuolar calcium release, which triggers activation of CnrF Rab GAP activity and subsequent downregulation of Rab11a to allow vacuole fusion. PMID:24335649

  7. Ion Channels in Nerve Membranes

    ERIC Educational Resources Information Center

    Ehrenstein, Gerald

    1976-01-01

    Discusses research that indicates that nerve membranes, which play a key role in the conduction of impulses, are traversed by protein channels with ion pathways opened and closed by the membrane electric field. (Author/MLH)

  8. Activation of acid-sensing ion channels by localized proton transient reveals their role in proton signaling

    PubMed Central

    Zeng, Wei-Zheng; Liu, Di-Shi; Liu, Lu; She, Liang; Wu, Long-Jun; Xu, Tian-Le

    2015-01-01

    Extracellular transients of pH alterations likely mediate signal transduction in the nervous system. Neuronal acid-sensing ion channels (ASICs) act as sensors for extracellular protons, but the mechanism underlying ASIC activation remains largely unknown. Here, we show that, following activation of a light-activated proton pump, Archaerhodopsin-3 (Arch), proton transients induced ASIC currents in both neurons and HEK293T cells co-expressing ASIC1a channels. Using chimera proteins that bridge Arch and ASIC1a by a glycine/serine linker, we found that successful coupling occurred within 15 nm distance. Furthermore, two-cell sniffer patch recording revealed that regulated release of protons through either Arch or voltage-gated proton channel Hv1 activated neighbouring cells expressing ASIC1a channels. Finally, computational modelling predicted the peak proton concentration at the intercellular interface to be at pH 6.7, which is acidic enough to activate ASICs in vivo. Our results highlight the pathophysiological role of proton signalling in the nervous system. PMID:26370138

  9. Hyperpolarization-activated cation and T-type calcium ion channel expression in porcine and human renal pacemaker tissues.

    PubMed

    Hurtado, Romulo; Smith, Carl S

    2016-05-01

    Renal pacemaker activity triggers peristaltic upper urinary tract contractions that propel waste from the kidney to the bladder, a process prone to congenital defects that are the leading cause of pediatric kidney failure. Recently, studies have discovered that hyperpolarization-activated cation (HCN) and T-type calcium (TTC) channel conductances underlie murine renal pacemaker activity, setting the origin and frequency and coordinating upper urinary tract peristalsis. Here, we determined whether this ion channel expression is conserved in the porcine and human urinary tracts, which share a distinct multicalyceal anatomy with multiple pacemaker sites. Double chromagenic immunohistochemistry revealed that HCN isoform 3 is highly expressed at the porcine minor calyces, the renal pacemaker tissues, whereas the kidney and urinary tract smooth muscle lacked this HCN expression. Immunofluorescent staining demonstrated that HCN(+) cells are integrated within the porcine calyx smooth muscle, and that they co-express TTC channel isoform Cav3.2. In humans, the anatomic structure of the minor calyx pacemaker was assayed via hematoxylin and eosin analyses, and enabled the visualization of the calyx smooth muscle surrounding adjacent papillae. Strikingly, immunofluorescence revealed that HCN3(+) /Cav3.2(+) cells are also localized to the human minor calyx smooth muscle. Collectively, these data have elucidated a conserved molecular signature of HCN and TTC channel expression in porcine and human calyx pacemaker tissues. These findings provide evidence for the mechanisms that can drive renal pacemaker activity in the multi-calyceal urinary tract, and potential causes of obstructive uropathies. PMID:26805464

  10. Ion Channel Blockers as Antimicrobial Agents, Efflux Inhibitors, and Enhancers of Macrophage Killing Activity against Drug Resistant Mycobacterium tuberculosis

    PubMed Central

    Perdigão, João; Couto, Isabel; Portugal, Isabel; Martins, Marta; Amaral, Leonard; Anes, Elsa; Viveiros, Miguel

    2016-01-01

    Given the ability of M. tuberculosis to survive as an intracellular pathogen and its propensity to develop resistance to the existing antituberculosis drugs, its treatment requires new approaches. Here the antimycobacterial properties of verapamil, thioridazine, chlorpromazine, flupenthixol and haloperidol were investigated against a panel of drug resistant M. tuberculosis strains, both in vitro and on human-infected macrophages. These compounds are efflux inhibitors that share among them the characteristic of being ion channel blockers. In vitro, all compounds exhibited synergistic inhibitory activities when combined with isoniazid and rifampicin, and were able to inhibit active efflux, demonstrating their role as efflux inhibitors. Gene expression analysis showed that M. tuberculosis efflux genes were overexpressed in response to antibiotic exposure, in vitro and within macrophages, irrespective of their resistance pattern. These compounds displayed a rapid and high killing activity against M. tuberculosis, associated with a decrease in intracellular ATP levels demonstrating that the bactericidal action of the ion channel blockers against M. tuberculosis clinical strains is associated with their interference with energy metabolism. The compounds led to a decrease in the intracellular mycobacterial load by increasing phagosome acidification and activating lysosomal hydrolases. The results presented in this study enable us to propose the following mechanism of action for these compounds: a) in the bacteria, the compounds generate a cascade of events involving the inhibition of the respiratory chain complexes and energy production for efflux activity. Indirectly, this reduce the resistance level to antituberculosis drugs potentiating their activity; b) on the host cell, the treatment with the ion channel blockers increases phagosome acidification and induces the expression of phagosomal hydrolases, leading to bacterial growth restriction irrespective of their

  11. Ion Channel Blockers as Antimicrobial Agents, Efflux Inhibitors, and Enhancers of Macrophage Killing Activity against Drug Resistant Mycobacterium tuberculosis.

    PubMed

    Machado, Diana; Pires, David; Perdigão, João; Couto, Isabel; Portugal, Isabel; Martins, Marta; Amaral, Leonard; Anes, Elsa; Viveiros, Miguel

    2016-01-01

    Given the ability of M. tuberculosis to survive as an intracellular pathogen and its propensity to develop resistance to the existing antituberculosis drugs, its treatment requires new approaches. Here the antimycobacterial properties of verapamil, thioridazine, chlorpromazine, flupenthixol and haloperidol were investigated against a panel of drug resistant M. tuberculosis strains, both in vitro and on human-infected macrophages. These compounds are efflux inhibitors that share among them the characteristic of being ion channel blockers. In vitro, all compounds exhibited synergistic inhibitory activities when combined with isoniazid and rifampicin, and were able to inhibit active efflux, demonstrating their role as efflux inhibitors. Gene expression analysis showed that M. tuberculosis efflux genes were overexpressed in response to antibiotic exposure, in vitro and within macrophages, irrespective of their resistance pattern. These compounds displayed a rapid and high killing activity against M. tuberculosis, associated with a decrease in intracellular ATP levels demonstrating that the bactericidal action of the ion channel blockers against M. tuberculosis clinical strains is associated with their interference with energy metabolism. The compounds led to a decrease in the intracellular mycobacterial load by increasing phagosome acidification and activating lysosomal hydrolases. The results presented in this study enable us to propose the following mechanism of action for these compounds: a) in the bacteria, the compounds generate a cascade of events involving the inhibition of the respiratory chain complexes and energy production for efflux activity. Indirectly, this reduce the resistance level to antituberculosis drugs potentiating their activity; b) on the host cell, the treatment with the ion channel blockers increases phagosome acidification and induces the expression of phagosomal hydrolases, leading to bacterial growth restriction irrespective of their

  12. Ion Channels in Brain Metastasis.

    PubMed

    Klumpp, Lukas; Sezgin, Efe C; Eckert, Franziska; Huber, Stephan M

    2016-01-01

    Breast cancer, lung cancer and melanoma exhibit a high metastatic tropism to the brain. Development of brain metastases severely worsens the prognosis of cancer patients and constrains curative treatment options. Metastasizing to the brain by cancer cells can be dissected in consecutive processes including epithelial-mesenchymal transition, evasion from the primary tumor, intravasation and circulation in the blood, extravasation across the blood-brain barrier, formation of metastatic niches, and colonization in the brain. Ion channels have been demonstrated to be aberrantly expressed in tumor cells where they regulate neoplastic transformation, malignant progression or therapy resistance. Moreover, many ion channel modulators are FDA-approved drugs and in clinical use proposing ion channels as druggable targets for future anti-cancer therapy. The present review article aims to summarize the current knowledge on the function of ion channels in the different processes of brain metastasis. The data suggest that certain channel types involving voltage-gated sodium channels, ATP-release channels, ionotropic neurotransmitter receptors and gap junction-generating connexins interfere with distinct processes of brain metastazation. PMID:27618016

  13. The ion-channel laser

    SciTech Connect

    Whittum, D.H.; Sessler, A.M. ); Dawson, J.M. . Dept. of Physics)

    1990-01-01

    A relativistic electron beam propagating through a plasma in the ion-focused regime exhibits an electromagnetic instability at a resonant frequency {omega} {approximately} 2{gamma}{sup 2} {omega}{sub {beta}}. Growth is enhanced by optical guiding in the ion channel, which acts as dielectric waveguide, with fiber parameter V {approximately} 2 (I/I{sub A}){sup 1/2}. A 1-D theory for such an ion-channel laser'' is formulated, scaling laws are derived and numerical examples are given. Possible experimental evidence is noted. 23 refs., 1 fig., 1 tab.

  14. The ion channel TRPV1 regulates the activation and proinflammatory properties of CD4+ T cells

    PubMed Central

    Bertin, Samuel; Aoki-Nonaka, Yukari; de Jong, Petrus Rudolf; Stanwood, Shawna R.; Srikanth, Sonal; Lee, Jihyung; To, Keith; Abramson, Lior; Yu, Timothy; Han, Tiffany; Touma, Ranim; Li, Xiangli; González-Navajas, José M.; Herdman, Scott; Corr, Maripat; Fu, Guo; Dong, Hui; Gwack, Yousang; Franco, Alessandra; Jefferies, Wilfred A.; Raz, Eyal

    2016-01-01

    TRPV1 is a Ca2+-permeable channel mostly studied as a pain receptor in sensory neurons. However, its role in other cell types is poorly understood. Here, we demonstrate that TRPV1 is functionally expressed in CD4+ T cells where it acts as a non-store-operated Ca2+ channel and contributes to T cell receptor (TCR)-induced Ca2+ influx, TCR signaling and T cell activation. In models of T cell-mediated colitis, TRPV1 promotes colitogenic T cell responses and intestinal inflammation. Furthermore, genetic and pharmacological inhibition of TRPV1 in human CD4+ T cells recapitulates the phenotype of murine Trpv1−/− CD4+ T cells. These findings suggest that TRPV1 inhibition could represent a new therapeutic strategy to restrain proinflammatory T cell responses. PMID:25282159

  15. Demystifying Mechanosensitive Piezo Ion Channels.

    PubMed

    Xu, X Z Shawn

    2016-06-01

    Mechanosensitive channels mediate touch, hearing, proprioception, and blood pressure regulation. Piezo proteins, including Piezo1 and Piezo2, represent a new class of mechanosensitive channels that have been reported to play key roles in most, if not all, of these modalities. The structural architecture and molecular mechanisms by which Piezos act as mechanosensitive channels, however, remain mysterious. Two new studies have now provided critical insights into the atomic structure and molecular basis of the ion permeation and mechano-gating properties of the Piezo1 channel. PMID:27164907

  16. Structural mechanism underlying capsaicin binding and activation of the TRPV1 ion channel.

    PubMed

    Yang, Fan; Xiao, Xian; Cheng, Wei; Yang, Wei; Yu, Peilin; Song, Zhenzhen; Yarov-Yarovoy, Vladimir; Zheng, Jie

    2015-07-01

    Capsaicin bestows spiciness by activating TRPV1 channel with exquisite potency and selectivity. Although a capsaicin-bound channel structure was previously resolved by cryo-EM at 4.2- to 4.5-Å resolution, capsaicin was registered as a small electron density, reflecting neither its chemical structure nor specific ligand-channel interactions--important details required for mechanistic understanding. We obtained the missing atomic-level details by iterative computation and confirmed them by systematic site-specific functional tests. We observed that the bound capsaicin takes a 'tail-up, head-down' configuration. The vanillyl and amide groups form specific interactions to anchor its bound position, while the aliphatic tail may sample a range of conformations, making it invisible in cryo-EM images. Capsaicin stabilizes TRPV1's open state by 'pull-and-contact' interactions between the vanillyl group and the S4-S5 linker. Our study provides a structural mechanism for the agonistic function of capsaicin and its analogs, and demonstrates an effective approach to obtain atomic-level information from cryo-EM structures. PMID:26053297

  17. Structural mechanism underlying capsaicin binding and activation of TRPV1 ion channel

    PubMed Central

    Cheng, Wei; Yang, Wei; Yu, Peilin; Song, Zhenzhen; Yarov-Yarovoy, Vladimir; Zheng, Jie

    2015-01-01

    Capsaicin bestows spiciness by activating TRPV1 channel with exquisite potency and selectivity. Capsaicin-bound channel structure was previously resolved by cryo-EM at 4.2-to-4.5 Å resolution, however important details required for mechanistic understandings are unavailable: capsaicin was registered as a small electron density, reflecting neither its chemical structure nor specific ligand-channel interactions. We obtained the missing atomic-level details by iterative computation, which were confirmed by systematic site-specific functional tests. We observed that the bound capsaicin takes “tail-up, head-down” configurations. The vanillyl and amide groups form specific interactions to anchor its bound position, while the aliphatic tail may sample a range of conformations, making it invisible in cryo-EM images. Capsaicin stabilizes the open state by “pull-and-contact” interactions between the vanillyl group and the S4-S5 linker. Our study provided a structural mechanism for the agonistic function of capsaicin and its analogs, and demonstrated an effective approach to obtain atomic level information from cryo-EM structures. PMID:26053297

  18. Gingerol activates noxious cold ion channel TRPA1 in gastrointestinal tract.

    PubMed

    Yang, Meng-Qi; Ye, Lin-Lan; Liu, Xiao-Ling; Qi, Xiao-Ming; Lv, Jia-Di; Wang, Gang; Farhan, Ulah-Khan; Waqas, Nawaz; Chen, Ding-Ding; Han, Lei; Zhou, Xiao-Hui

    2016-06-01

    TRPA1 channels are non-selective cation channels that could be activated by plant-derived pungent products, including gingerol, a main active constituent of ginger. Ginger could improve the digestive function; however whether ginger improves the digestive function through activating TRPA1 receptor in gastrointestinal tract has not been investigated. In the present study, gingerol was used to stimulate cell lines (RIN14B or STC-1) while depletion of extracellular calcium. TRPA1 inhibitor (rethenium red) and TRPA1 gene silencing via TRPA1-specific siRNA were also used for mechanistic studies. The intracellular calcium and secretion of serotonin or cholecystokinin were measured by fura-2/AM and ELISA. Stimulation of those cells with gingerol increased intracellular calcium levels and the serotonin or cholecystokinin secretion. The gingerol-induced intracellular calcium increase and secretion (serotonin or cholecystokinin) release were completely blocked by ruthenium red, EGTA, and TRPA1-specific siRNA. In summary, our results suggested that gingerol derived from ginger might improve the digestive function through secretion releasing from endocrine cells of the gut by inducing TRPA1-mediated calcium influx. PMID:27473961

  19. Functional Expression of a Ca(2+)-activated Cl(-) Channel Modulator Involved in Ion Transport and Epithelial Cell Differentiation.

    PubMed

    Yamazaki, Jun

    2016-01-01

      Cl(-)-permeable channels and transporters expressed on the cell membranes of various mammalian cell types play pivotal roles in the transport of electrolytes and water, pH regulation, cell volume and membrane excitability, and are therefore expected to be useful molecular targets for drug discovery. Both TMEM16A (a possible candidate for Ca(2+)-regulated Cl(-) channels recently identified) and cystic fibrosis transmembrane conductance regulator (CFTR) (or cAMP-regulated Cl(-) channels) have been known to be involved in Cl(-) secretion and reabsorption in the rat salivary gland. Crosstalk between two types of regulatory pathways through these two types of channels has also been described. Previously, we demonstrated that CLCA, a Ca(2+)-activated Cl(-) channel modulator, was involved in Cl(-) absorption in rat salivary ducts. In addition to Ca(2+), basal NF-κB activity in a mouse keratinocyte line was shown to be involved in the transcriptional regulation of CLCA. Conversely, a truncated isoform of CLCA was found in undifferentiated epithelial cells present in the rat epidermal basal layers. Under regulation by Ca(2+) and PKC, the surface expression of β1-integrin and cell adhesion were decreased in the CLCA-overexpressing cells. Knockdown of this isoform elevated the expression of β1-integrin in rat epidermis in vivo. These results indicate that the specific differentiation-dependent localization of CLCA, and transcriptional regulation through Ca(2+), are likely to affect ion permeability and the adhesive potential of epithelial cells. In summary, these types of Cl(-) channels and their modulators may function in a coordinated manner in regulating the functions of epithelial cells under different physiological conditions. PMID:26935091

  20. Monitoring charge flux to quantify unusual ligand-induced ion channel activity for use in biological nanopore-based sensors.

    PubMed

    Macazo, Florika C; White, Ryan J

    2014-06-01

    The utility of biological nanopores for the development of sensors has become a growing area of interest in analytical chemistry. Their emerging use in chemical analysis is a result of several ideal characteristics. First, they provide reproducible control over nanoscale pore sizes with an atomic level of precision. Second, they are amenable to resistive-pulse type measurement systems when embedded into an artificial lipid bilayer. A single binding event causes a change in the flow of millions of ions across the membrane per second that is readily measured as a change in current with excellent signal-to-noise ratio. To date, ion channel-based biosensors have been limited to well-behaved proteins. Most demonstrations of using ion channels as sensors have been limited to proteins that remain in the open, conducting state, unless occupied by an analyte of interest. Furthermore, these proteins are nonspecific, requiring chemical, biochemical, or genetic manipulations to impart chemical specificity. Here, we report on the use of the pore-forming abilities of heat shock cognate 70 (Hsc70) to quantify a specific analyte. Hsc70 reconstitutes into phospholipid membranes and opens to form multiple conductance states specifically in the presence of ATP. We introduce the measurement of "charge flux" to characterize the ATP-regulated multiconductance nature of Hsc70, which enables sensitive quantification of ATP (100 μM-4 mM). We believe that monitoring protein-induced charge flux across a bilayer membrane represents a universal method for quantitatively monitoring ion-channel activity. This measurement has the potential to broaden the library of usable proteins in the development of nanopore-based biosensors. PMID:24794413

  1. Thermosensitive Ion Channel Activation in Single Neuronal Cells by Using Surface-Engineered Plasmonic Nanoparticles.

    PubMed

    Nakatsuji, Hirotaka; Numata, Tomohiro; Morone, Nobuhiro; Kaneko, Shuji; Mori, Yasuo; Imahori, Hiroshi; Murakami, Tatsuya

    2015-09-28

    Controlling cell functions using external photoresponsive nanomaterials has enormous potential for the development of cell-engineering technologies and intractable disease therapies, but the former currently requires genetic modification of the target cells. We present a method using plasma-membrane-targeted gold nanorods (pm-AuNRs) prepared with a cationic protein/lipid complex to activate a thermosensitive cation channel, TRPV1, in intact neuronal cells. Highly localized photothermal heat generation mediated by the pm-AuNRs induced Ca(2+) influx solely by TRPV1 activation. In contrast, the use of previously reported cationic AuNRs that are coated with a conventional synthetic polymer also led to photoinduced Ca(2+) influx, but this influx resulted from membrane damage. Our method provides an optogenetic platform without the need for prior genetic engineering of the target cells and might be useful for novel TRPV1-targeted phototherapeutic approaches. PMID:26249533

  2. Single-Channel Recording of Ligand-Gated Ion Channels.

    PubMed

    Plested, Andrew J R

    2016-01-01

    Single-channel recordings reveal the microscopic properties of individual ligand-gated ion channels. Such recordings contain much more information than measurements of ensemble behavior and can yield structural and functional information about the receptors that participate in fast synaptic transmission in the brain. With a little care, a standard patch-clamp electrophysiology setup can be adapted for single-channel recording in a matter of hours. Thenceforth, it is a realistic aim to record single-molecule activity with microsecond resolution from arbitrary cell types, including cell lines and neurons. PMID:27480725

  3. BK channels: multiple sensors, one activation gate.

    PubMed

    Yang, Huanghe; Zhang, Guohui; Cui, Jianmin

    2015-01-01

    Ion transport across cell membranes is essential to cell communication and signaling. Passive ion transport is mediated by ion channels, membrane proteins that create ion conducting pores across cell membrane to allow ion flux down electrochemical gradient. Under physiological conditions, majority of ion channel pores are not constitutively open. Instead, structural region(s) within these pores breaks the continuity of the aqueous ion pathway, thereby serves as activation gate(s) to control ions flow in and out. To achieve spatially and temporally regulated ion flux in cells, many ion channels have evolved sensors to detect various environmental stimuli or the metabolic states of the cell and trigger global conformational changes, thereby dynamically operate the opening and closing of their activation gate. The sensors of ion channels can be broadly categorized as chemical sensors and physical sensors to respond to chemical (such as neural transmitters, nucleotides and ions) and physical (such as voltage, mechanical force and temperature) signals, respectively. With the rapidly growing structural and functional information of different types of ion channels, it is now critical to understand how ion channel sensors dynamically control their gates at molecular and atomic level. The voltage and Ca(2+) activated BK channels, a K(+) channel with an electrical sensor and multiple chemical sensors, provide a unique model system for us to understand how physical and chemical energy synergistically operate its activation gate. PMID:25705194

  4. BK channels: multiple sensors, one activation gate

    PubMed Central

    Yang, Huanghe; Zhang, Guohui; Cui, Jianmin

    2015-01-01

    Ion transport across cell membranes is essential to cell communication and signaling. Passive ion transport is mediated by ion channels, membrane proteins that create ion conducting pores across cell membrane to allow ion flux down electrochemical gradient. Under physiological conditions, majority of ion channel pores are not constitutively open. Instead, structural region(s) within these pores breaks the continuity of the aqueous ion pathway, thereby serves as activation gate(s) to control ions flow in and out. To achieve spatially and temporally regulated ion flux in cells, many ion channels have evolved sensors to detect various environmental stimuli or the metabolic states of the cell and trigger global conformational changes, thereby dynamically operate the opening and closing of their activation gate. The sensors of ion channels can be broadly categorized as chemical sensors and physical sensors to respond to chemical (such as neural transmitters, nucleotides and ions) and physical (such as voltage, mechanical force and temperature) signals, respectively. With the rapidly growing structural and functional information of different types of ion channels, it is now critical to understand how ion channel sensors dynamically control their gates at molecular and atomic level. The voltage and Ca2+ activated BK channels, a K+ channel with an electrical sensor and multiple chemical sensors, provide a unique model system for us to understand how physical and chemical energy synergistically operate its activation gate. PMID:25705194

  5. Bright ion channels and lipid bilayers.

    PubMed

    Szymański, Wiktor; Yilmaz, Duygu; Koçer, Armağan; Feringa, Ben L

    2013-12-17

    If we look at a simple organism such as a zebrafish under a microscope, we would see many cells working in harmony. If we zoomed in, we would observe each unit performing its own tasks in a special aqueous environment isolated from the other units by a lipid bilayer approximately 5 nm thick. These confined units are social: they communicate with one another by sensing and responding to the chemical changes in their environment through receptors and ion channels. These channels control the highly specific and selective passage of ions from one side of the cell to the other and are embedded in lipid bilayers. The movement of ions through ion channels supports excitation and electrical signaling in the nervous system. Ion channels have fascinated scientists not only because of their specificity and selectivity, but also for their functions, the serious consequences when they malfunction, and the other potential applications of these molecules. Light is a useful trigger to control and manipulate ion channels externally. With the many state-of-the-art optical technologies available, light offers a high degree of spatial and temporal control, millisecond precision, and noninvasive intervention and does not change the chemical environment of the system of interest. In this Account, we discuss research toward the dynamic control of lipid bilayer assembly and channel function, particularly the transport across the lipid bilayer-ion channel barrier of cells using light. We first summarize the manipulation of ion channel activity with light to modulate the channel's natural activity. Based on the type of photoswitch employed, we can achieve novel functionalities with these channels, and control neural activity. Then we discuss the recent developments in light-induced transport through lipid bilayers. We focus on three different approaches: the incorporation of photoswitchable copolymers into the lipids, the doping of the lipid bilayer with photosensitive amphiphiles and the

  6. Energy channeling from trapped to passing fast ions mediated by GAE/CAE activity in NSTX

    NASA Astrophysics Data System (ADS)

    Medley, S. S.; Belova, E.; Kramer, G.; Podesta, M.; Liu, D.

    2013-10-01

    In the National Spherical Torus Experiment, an increased charge exchange neutral flux localized at the neutral beam full injection energy is measured by the E||B Neutral Particle Analyzer. Termed the High-Energy Feature (HEF), it appears on the beam-injected energetic ion spectrum in discharges where NTM or kink modes (f < 10 kHz) are absent, TAE activity (f ~ 10-150 kHz) is weak and CAE/GAE activity (f ~ 400 - 1200 kHz) is robust. The HEF exhibits a growth time of t ~ 20-80 ms and develops a slowing down distribution that continues to evolve over periods > 100 ms. HEFs are observed only in H-mode discharges with NB power Pb >= 4 MW and in the pitch range v||/v ~ 0.7 - 0.9. The HEF appears to be caused by a CAE/GAE wave-particle interaction that modifies the fast ion distribution, fi(E,v||/v,r). This mechanism was studied using the SPIRAL code that evolves an initial TRANSP-calculated fi(E,v||/v,r) distribution in the presence of background plasma profiles under drive from wave-particle resonances with CAE/GAE Alfvén eigenmodes. Supported by U.S. Department of Energy under Contract No. DE-AC02-09CH11466.

  7. Ion channels in development and cancer.

    PubMed

    Bates, Emily

    2015-01-01

    Ion channels have emerged as regulators of developmental processes. In model organisms and in people with mutations in ion channels, disruption of ion channel function can affect cell proliferation, cell migration, and craniofacial and limb patterning. Alterations of ion channel function affect morphogenesis in fish, frogs, mammals, and flies, demonstrating that ion channels have conserved roles in developmental processes. One model suggests that ion channels affect proliferation and migration through changes in cell volume. However, ion channels have not explicitly been placed in canonical developmental signaling cascades until recently. This review gives examples of ion channels that influence developmental processes, offers a potential underlying molecular mechanism involving bone morphogenetic protein (BMP) signaling, and finally explores exciting possibilities for manipulating ion channels to influence cell fate for regenerative medicine and to impact disease. PMID:26566112

  8. Improved Ion-Channel Biosensors

    NASA Technical Reports Server (NTRS)

    Nadeau, Jay; White, Victor; Dougherty, Dennis; Maurer, Joshua

    2004-01-01

    An effort is underway to develop improved biosensors of a type based on ion channels in biomimetic membranes. These sensors are microfabricated from silicon and other materials compatible with silicon. As described, these sensors offer a number of advantages over prior sensors of this type.

  9. P2Y1 Receptor Activation of the TRPV4 Ion Channel Enhances Purinergic Signaling in Satellite Glial Cells.

    PubMed

    Rajasekhar, Pradeep; Poole, Daniel P; Liedtke, Wolfgang; Bunnett, Nigel W; Veldhuis, Nicholas A

    2015-11-27

    Transient receptor potential (TRP) ion channels of peripheral sensory pathways are important mediators of pain, itch, and neurogenic inflammation. They are expressed by primary sensory neurons and by glial cells in the central nervous system, but their expression and function in satellite glial cells (SGCs) of sensory ganglia have not been explored. SGCs tightly ensheath neurons of sensory ganglia and can regulate neuronal excitability in pain and inflammatory states. Using a modified dissociation protocol, we isolated neurons with attached SGCs from dorsal root ganglia of mice. SGCs, which were identified by expression of immunoreactive Kir4.1 and glutamine synthetase, were closely associated with neurons, identified using the pan-neuronal marker NeuN. A subpopulation of SGCs expressed immunoreactive TRP vanilloid 4 (TRPV4) and responded to the TRPV4-selective agonist GSK1016790A by an influx of Ca(2+) ions. SGCs did not express functional TRPV1, TRPV3, or TRP ankyrin 1 channels. Responses to GSK1016790A were abolished by the TRPV4 antagonist HC067047 and were absent in SGCs from Trpv4(-/-) mice. The P2Y1-selective agonist 2-methylthio-ADP increased [Ca(2+)]i in SGCs, and responses were prevented by the P2Y1-selective antagonist MRS2500. P2Y1 receptor-mediated responses were enhanced in TRPV4-expressing SGCs and HEK293 cells, suggesting that P2Y1 couples to and activates TRPV4. PKC inhibitors prevented P2Y1 receptor activation of TRPV4. Our results provide the first evidence for expression of TRPV4 in SGCs and demonstrate that TRPV4 is a purinergic receptor-operated channel in SGCs of sensory ganglia. PMID:26475857

  10. Regulation of Ion Channels by Pyridine Nucleotides

    PubMed Central

    Kilfoil, Peter J.; Tipparaju, Srinivas M.; Barski, Oleg A.; Bhatnagar, Aruni

    2014-01-01

    Recent research suggests that in addition to their role as soluble electron carriers, pyridine nucleotides [NAD(P)(H)] also regulate ion transport mechanisms. This mode of regulation seems to have been conserved through evolution. Several bacterial ion–transporting proteins or their auxiliary subunits possess nucleotide-binding domains. In eukaryotes, the Kv1 and Kv4 channels interact with pyridine nucleotide–binding β-subunits that belong to the aldo-keto reductase superfamily. Binding of NADP+ to Kvβ removes N-type inactivation of Kv currents, whereas NADPH stabilizes channel inactivation. Pyridine nucleotides also regulate Slo channels by interacting with their cytosolic regulator of potassium conductance domains that show high sequence homology to the bacterial TrkA family of K+ transporters. These nucleotides also have been shown to modify the activity of the plasma membrane KATP channels, the cystic fibrosis transmembrane conductance regulator, the transient receptor potential M2 channel, and the intracellular ryanodine receptor calcium release channels. In addition, pyridine nucleotides also modulate the voltage-gated sodium channel by supporting the activity of its ancillary subunit—the glycerol-3-phosphate dehydrogenase-like protein. Moreover, the NADP+ metabolite, NAADP+, regulates intracellular calcium homeostasis via the 2-pore channel, ryanodine receptor, or transient receptor potential M2 channels. Regulation of ion channels by pyridine nucleotides may be required for integrating cell ion transport to energetics and for sensing oxygen levels or metabolite availability. This mechanism also may be an important component of hypoxic pulmonary vasoconstriction, memory, and circadian rhythms, and disruption of this regulatory axis may be linked to dysregulation of calcium homeostasis and cardiac arrhythmias. PMID:23410881

  11. Arabidopsis MSL10 Has a Regulated Cell Death Signaling Activity That Is Separable from Its Mechanosensitive Ion Channel Activity[C][W

    PubMed Central

    Veley, Kira M.; Maksaev, Grigory; Frick, Elizabeth M.; January, Emma; Kloepper, Sarah C.; Haswell, Elizabeth S.

    2014-01-01

    Members of the MscS superfamily of mechanosensitive ion channels function as osmotic safety valves, releasing osmolytes under increased membrane tension. MscS homologs exhibit diverse topology and domain structure, and it has been proposed that the more complex members of the family might have novel regulatory mechanisms or molecular functions. Here, we present a study of MscS-Like (MSL)10 from Arabidopsis thaliana that supports these ideas. High-level expression of MSL10-GFP in Arabidopsis induced small stature, hydrogen peroxide accumulation, ectopic cell death, and reactive oxygen species- and cell death-associated gene expression. Phosphomimetic mutations in the MSL10 N-terminal domain prevented these phenotypes. The phosphorylation state of MSL10 also regulated its ability to induce cell death when transiently expressed in Nicotiana benthamiana leaves but did not affect subcellular localization, assembly, or channel behavior. Finally, the N-terminal domain of MSL10 was sufficient to induce cell death in tobacco, independent of phosphorylation state. We conclude that the plant-specific N-terminal domain of MSL10 is capable of inducing cell death, this activity is regulated by phosphorylation, and MSL10 has two separable activities—one as an ion channel and one as an inducer of cell death. These findings further our understanding of the evolution and significance of mechanosensitive ion channels. PMID:25052715

  12. A Latin American Perspective on Ion Channels.

    PubMed

    Elgoyhen, Ana Belén; Barajas-López, Carlos

    2016-09-01

    Ion channels, both ligand- and voltage-gated, play fundamental roles in many physiologic processes. Alteration in ion channel function underlies numerous pathologies, including hypertension, diabetes, chronic pain, epilepsy, certain cancers, and neuromuscular diseases. In addition, an increasing number of inherited and de novo ion channel mutations have been shown to contribute to disease states. Ion channels are thus a major class of pharmacotherapeutic targets. PMID:27535998

  13. The role of stretch-activated ion channels in acute respiratory distress syndrome: finally a new target?

    PubMed

    Schwingshackl, Andreas

    2016-09-01

    Mechanical ventilation (MV) and oxygen therapy (hyperoxia; HO) comprise the cornerstones of life-saving interventions for patients with acute respiratory distress syndrome (ARDS). Unfortunately, the side effects of MV and HO include exacerbation of lung injury by barotrauma, volutrauma, and propagation of lung inflammation. Despite significant improvements in ventilator technologies and a heightened awareness of oxygen toxicity, besides low tidal volume ventilation few if any medical interventions have improved ARDS outcomes over the past two decades. We are lacking a comprehensive understanding of mechanotransduction processes in the healthy lung and know little about the interactions between simultaneously activated stretch-, HO-, and cytokine-induced signaling cascades in ARDS. Nevertheless, as we are unraveling these mechanisms we are gathering increasing evidence for the importance of stretch-activated ion channels (SACs) in the activation of lung-resident and inflammatory cells. In addition to the discovery of new SAC families in the lung, e.g., two-pore domain potassium channels, we are increasingly assigning mechanosensing properties to already known Na(+), Ca(2+), K(+), and Cl(-) channels. Better insights into the mechanotransduction mechanisms of SACs will improve our understanding of the pathways leading to ventilator-induced lung injury and lead to much needed novel therapeutic approaches against ARDS by specifically targeting SACs. This review 1) summarizes the reasons why the time has come to seriously consider SACs as new therapeutic targets against ARDS, 2) critically analyzes the physiological and experimental factors that currently limit our knowledge about SACs, and 3) outlines the most important questions future research studies need to address. PMID:27521425

  14. Investigation of Ion Channel Activities of Gramicidin A in the Presence of Ionic Liquids Using Model Cell Membranes

    PubMed Central

    Ryu, Hyunil; Lee, Hwankyu; Iwata, Seigo; Choi, Sangbaek; Ki Kim, Moon; Kim, Young-Rok; Maruta, Shinsaku; Min Kim, Sun; Jeon, Tae-Joon

    2015-01-01

    Ionic liquids (ILs) are considered to be green solvents because of their non-volatility. Although ILs are relatively safe in the atmospheric environment, they may be toxic in other environments. Our previous research showed that the cytotoxicity of ILs to biological organisms is attributable to interference with cell membranes by IL insertion. However, the effects of ILs on ion channels, which play important roles in cell homeostasis, have not been comprehensively studied to date. In this work, we studied the interactions between ILs and lipid bilayer membranes with gramicidin A ion channels. We used two methods, namely electrical and fluorescence measurements of ions that permeate the membrane. The lifetimes of channels were increased by all the ILs tested in this work via stabilizing the compressed structure of the lipid bilayer and the rate of ion flux through gA channels was decreased by changing the membrane surface charge. The former effect, which increased the rate of ion flux, was dominant at high salt concentrations, whereas the latter, which decreased the rate of ion flux, was dominant at low salt concentrations. The effects of ILs increased with increasing concentration and alkyl chain length. The experimental results were further studied using molecular dynamics simulations. PMID:26189604

  15. Investigation of Ion Channel Activities of Gramicidin A in the Presence of Ionic Liquids Using Model Cell Membranes.

    PubMed

    Ryu, Hyunil; Lee, Hwankyu; Iwata, Seigo; Choi, Sangbaek; Kim, Moon Ki; Kim, Young-Rok; Maruta, Shinsaku; Kim, Sun Min; Jeon, Tae-Joon

    2015-01-01

    Ionic liquids (ILs) are considered to be green solvents because of their non-volatility. Although ILs are relatively safe in the atmospheric environment, they may be toxic in other environments. Our previous research showed that the cytotoxicity of ILs to biological organisms is attributable to interference with cell membranes by IL insertion. However, the effects of ILs on ion channels, which play important roles in cell homeostasis, have not been comprehensively studied to date. In this work, we studied the interactions between ILs and lipid bilayer membranes with gramicidin A ion channels. We used two methods, namely electrical and fluorescence measurements of ions that permeate the membrane. The lifetimes of channels were increased by all the ILs tested in this work via stabilizing the compressed structure of the lipid bilayer and the rate of ion flux through gA channels was decreased by changing the membrane surface charge. The former effect, which increased the rate of ion flux, was dominant at high salt concentrations, whereas the latter, which decreased the rate of ion flux, was dominant at low salt concentrations. The effects of ILs increased with increasing concentration and alkyl chain length. The experimental results were further studied using molecular dynamics simulations. PMID:26189604

  16. Unique battery with an active membrane separator having uniform physico-chemically functionalized ion channels and a method making the same

    DOEpatents

    Gerald, II, Rex E.; Ruscic, Katarina J.; Sears, Devin N.; Smith, Luis J.; Klingler, Robert J.; Rathke, Jerome W.

    2012-02-21

    The invention relates to a unique battery having an active, porous membrane and method of making the same. More specifically the invention relates to a sealed battery system having a porous, metal oxide membrane with uniform, physicochemically functionalized ion channels capable of adjustable ionic interaction. The physicochemically-active porous membrane purports dual functions: an electronic insulator (separator) and a unidirectional ion-transporter (electrolyte). The electrochemical cell membrane is activated for the transport of ions by contiguous ion coordination sites on the interior two-dimensional surfaces of the trans-membrane unidirectional pores. The membrane material is designed to have physicochemical interaction with ions. Control of the extent of the interactions between the ions and the interior pore walls of the membrane and other materials, chemicals, or structures contained within the pores provides adjustability of the ionic conductivity of the membrane.

  17. Ion channel regulation by protein S-acylation

    PubMed Central

    2014-01-01

    Protein S-acylation, the reversible covalent fatty-acid modification of cysteine residues, has emerged as a dynamic posttranslational modification (PTM) that controls the diversity, life cycle, and physiological function of numerous ligand- and voltage-gated ion channels. S-acylation is enzymatically mediated by a diverse family of acyltransferases (zDHHCs) and is reversed by acylthioesterases. However, for most ion channels, the dynamics and subcellular localization at which S-acylation and deacylation cycles occur are not known. S-acylation can control the two fundamental determinants of ion channel function: (1) the number of channels resident in a membrane and (2) the activity of the channel at the membrane. It controls the former by regulating channel trafficking and the latter by controlling channel kinetics and modulation by other PTMs. Ion channel function may be modulated by S-acylation of both pore-forming and regulatory subunits as well as through control of adapter, signaling, and scaffolding proteins in ion channel complexes. Importantly, cross-talk of S-acylation with other PTMs of both cysteine residues by themselves and neighboring sites of phosphorylation is an emerging concept in the control of ion channel physiology. In this review, I discuss the fundamentals of protein S-acylation and the tools available to investigate ion channel S-acylation. The mechanisms and role of S-acylation in controlling diverse stages of the ion channel life cycle and its effect on ion channel function are highlighted. Finally, I discuss future goals and challenges for the field to understand both the mechanistic basis for S-acylation control of ion channels and the functional consequence and implications for understanding the physiological function of ion channel S-acylation in health and disease. PMID:24821965

  18. Differential hERG ion channel activity of ultrasmall gold nanoparticles

    PubMed Central

    Leifert, Annika; Pan, Yu; Kinkeldey, Anne; Schiefer, Frank; Setzler, Julia; Scheel, Olaf; Lichtenbeld, Hera; Schmid, Günter; Wenzel, Wolfgang; Jahnen-Dechent, Willi; Simon, Ulrich

    2013-01-01

    Understanding the mechanism of toxicity of nanomaterials remains a challenge with respect to both mechanisms involved and product regulation. Here we show toxicity of ultrasmall gold nanoparticles (AuNPs). Depending on the ligand chemistry, 1.4-nm-diameter AuNPs failed electrophysiology-based safety testing using human embryonic kidney cell line 293 cells expressing human ether-á-go-go-Related gene (hERG), a Food and Drug Administration-established drug safety test. In patch-clamp experiments, phosphine-stabilized AuNPs irreversibly blocked hERG channels, whereas thiol-stabilized AuNPs of similar size had no effect in vitro, and neither particle blocked the channel in vivo. We conclude that safety regulations may need to be reevaluated and adapted to reflect the fact that the binding modality of surface functional groups becomes a relevant parameter for the design of nanoscale bioactive compounds. PMID:23630249

  19. Differential hERG ion channel activity of ultrasmall gold nanoparticles.

    PubMed

    Leifert, Annika; Pan, Yu; Kinkeldey, Anne; Schiefer, Frank; Setzler, Julia; Scheel, Olaf; Lichtenbeld, Hera; Schmid, Günter; Wenzel, Wolfgang; Jahnen-Dechent, Willi; Simon, Ulrich

    2013-05-14

    Understanding the mechanism of toxicity of nanomaterials remains a challenge with respect to both mechanisms involved and product regulation. Here we show toxicity of ultrasmall gold nanoparticles (AuNPs). Depending on the ligand chemistry, 1.4-nm-diameter AuNPs failed electrophysiology-based safety testing using human embryonic kidney cell line 293 cells expressing human ether-á-go-go-Related gene (hERG), a Food and Drug Administration-established drug safety test. In patch-clamp experiments, phosphine-stabilized AuNPs irreversibly blocked hERG channels, whereas thiol-stabilized AuNPs of similar size had no effect in vitro, and neither particle blocked the channel in vivo. We conclude that safety regulations may need to be reevaluated and adapted to reflect the fact that the binding modality of surface functional groups becomes a relevant parameter for the design of nanoscale bioactive compounds. PMID:23630249

  20. The exceptionally high reactivity of Cys 621 is critical for electrophilic activation of the sensory nerve ion channel TRPA1.

    PubMed

    Bahia, Parmvir K; Parks, Thomas A; Stanford, Katherine R; Mitchell, David A; Varma, Sameer; Stevens, Stanley M; Taylor-Clark, Thomas E

    2016-06-01

    Activation of the sensory nerve ion channel TRPA1 by electrophiles is the key mechanism that initiates nociceptive signaling, and leads to defensive reflexes and avoidance behaviors, during oxidative stress in mammals. TRPA1 is rapidly activated by subtoxic levels of electrophiles, but it is unclear how TRPA1 outcompetes cellular antioxidants that protect cytosolic proteins from electrophiles. Here, using physiologically relevant exposures, we demonstrate that electrophiles react with cysteine residues on mammalian TRPA1 at rates that exceed the reactivity of typical cysteines by 6,000-fold and that also exceed the reactivity of antioxidant enzymes. We show that TRPA1 possesses a complex reactive cysteine profile in which C621 is necessary for electrophile-induced binding and activation. Modeling of deprotonation energies suggests that K620 contributes to C621 reactivity and mutation of K620 alone greatly reduces the effect of electrophiles on TRPA1. Nevertheless, binding of electrophiles to C621 is not sufficient for activation, which also depends on the function of another reactive cysteine (C665). Together, our results demonstrate that TRPA1 acts as an effective electrophilic sensor because of the exceptionally high reactivity of C621. PMID:27241698

  1. Ion channels and transporters in lymphocyte function and immunity

    PubMed Central

    Feske, Stefan; Skolnik, Edward Y.; Prakriya, Murali

    2013-01-01

    Preface Lymphocyte function is regulated by a network of ion channels and transporters in the plasma membrane of T and B cells. They modulate the cytoplasmic concentrations of diverse cations such as calcium, magnesium and zinc, which function as second messengers to regulate critical lymphocyte effector functions including cytokine production, differentiation and cytotoxicity. The repertoire of ion conducting proteins includes calcium release-activated calcium (CRAC) channels, P2X receptors, transient receptor potential (TRP) channels, potassium channels as well as magnesium and zinc transporters. This review discusses the roles of several ions channels and transporters in lymphocyte function and immunity. PMID:22699833

  2. Erythrocyte ion channels in regulation of apoptosis.

    PubMed

    Lang, Florian; Birka, Christina; Myssina, Svetlana; Lang, Karl S; Lang, Philipp A; Tanneur, Valerie; Duranton, Christophe; Wieder, Thomas; Huber, Stephan M

    2004-01-01

    Erythrocytes lack mitochondria and nuclei, key organelles in the regulation of apoptosis. Until recently, erythrocytes were thus not considered subject to this type of cell death. However, exposure of erythrocytes to the Ca2+ ionophore ionomycin was shown to induce cell shrinkage, cell membrane blebbing and breakdown of phosphatidylserine asymmetry with subsequent phosphatidylserine exposure at the cell surface, all typical features of apoptosis. Further studies revealed the participation of ion channels in the regulation of erythrocyte "apoptosis." Osmotic shock, oxidative stress and energy depletion all activate a Ca2(+)-permeable non-selective cation channel in the erythrocyte cell membrane. The subsequent increase of Ca2+ concentration stimulates a scramblase leading to breakdown of cell membrane phosphatidylserine asymmetry and activates Ca2+ sensitive K+ (Gardos) channels leading to KCl loss and (further) cell shrinkage. Phosphatidylserine exposure and cell shrinkage are blunted in the nominal absence of extracellular Ca2+, in the presence of the cation channel inhibitors amiloride or ethylisopropylamiloride, at increased extracellular K+ or in the presence of the Gardos channel inhibitors clotrimazole or charybdotoxin. Thus, increase of cytosolic Ca2+ and cellular loss of K+ participate in the triggering of erythrocyte scramblase. Nevertheless, phosphatidylserine exposure is not completely abrogated in the nominal absence of Ca2+, pointing to additional Ca2(+)-independent pathways. One of those is activation of sphingomyelinase with subsequent formation of ceramide which in turn leads to stimulation of erythrocyte scramblase. The exposure of phosphatidylserine at the extracellular face of the cell membrane stimulates phagocytes to engulf the apoptotic erythrocytes. Thus, sustained activation of the cation channels eventually leads to clearance of affected erythrocytes from peripheral blood. Erythropoietin inhibits the non-selective cation channel and thus

  3. Calcium homeostasis modulator (CALHM) ion channels.

    PubMed

    Ma, Zhongming; Tanis, Jessica E; Taruno, Akiyuki; Foskett, J Kevin

    2016-03-01

    Calcium homeostasis modulator 1 (CALHM1), formerly known as FAM26C, was recently identified as a physiologically important plasma membrane ion channel. CALHM1 and its Caenorhabditis elegans homolog, CLHM-1, are regulated by membrane voltage and extracellular Ca(2+) concentration ([Ca(2+)]o). In the presence of physiological [Ca(2+)]o (∼1.5 mM), CALHM1 and CLHM-1 are closed at resting membrane potentials but can be opened by strong depolarizations. Reducing [Ca(2+)]o increases channel open probability, enabling channel activation at negative membrane potentials. Together, voltage and Ca(2+) o allosterically regulate CALHM channel gating. Through convergent evolution, CALHM has structural features that are reminiscent of connexins and pannexins/innexins/LRRC8 (volume-regulated anion channel (VRAC)) gene families, including four transmembrane helices with cytoplasmic amino and carboxyl termini. A CALHM1 channel is a hexamer of CALHM1 monomers with a functional pore diameter of ∼14 Å. CALHM channels discriminate poorly among cations and anions, with signaling molecules including Ca(2+) and ATP able to permeate through its pore. CALHM1 is expressed in the brain where it plays an important role in cortical neuron excitability induced by low [Ca(2+)]o and in type II taste bud cells in the tongue that sense sweet, bitter, and umami tastes where it functions as an essential ATP release channel to mediate nonsynaptic neurotransmitter release. CLHM-1 is expressed in C. elegans sensory neurons and body wall muscles, and its genetic deletion causes locomotion defects. Thus, CALHM is a voltage- and Ca(2+) o-gated ion channel, permeable to large cations and anions, that plays important roles in physiology. PMID:26603282

  4. Conductance of Ion Channels - Theory vs. Experiment

    NASA Technical Reports Server (NTRS)

    Pohorille, Andrew; Wilson, Michael; Mijajlovic, Milan

    2013-01-01

    Transmembrane ion channels mediate a number of essential physiological processes in a cell ranging from regulating osmotic pressure to transmission of neural signals. Kinetics and selectivity of ion transport is of critical importance to a cell and, not surprisingly, it is a subject of numerous experimental and theoretical studies. In this presentation we will analyze in detail computer simulations of two simple channels from fungi - antiamoebin and trichotoxin. Each of these channels is made of an alpha-helical bundle of small, nongenomically synthesized peptides containing a number of rare amino acids and exhibits strong antimicrobial activity. We will focus on calculating ionic conductance defined as the ratio of ionic current through the channel to applied voltage. From molecular dynamics simulations, conductance can be calculated in at least two ways, each involving different approximations. Specifically, the current, given as the number of charges transferred through the channel per unit of time, can be obtained from the number of events in which ions cross the channel during the simulation. This method works well for large currents (high conductance values and/or applied voltages). If the number of crossing events is small, reliable estimates of current are difficult to achieve. Alternatively, conductance can be estimated assuming that ion transport can be well approximated as diffusion in the external potential given by the free energy profile. Then, the current can be calculated by solving the one-dimensional diffusion equation in this external potential and applied voltage (the generalized Nernst-Planck equation). To do so three ingredients are needed: the free energy profile, the position-dependent diffusion coefficient and the diffusive flux of ions into the channel. All these quantities can be obtained from molecular dynamics simulations. An important advantage of this method is that it can be used equally well to estimating large and small currents

  5. High throughput screening technologies for ion channels

    PubMed Central

    Yu, Hai-bo; Li, Min; Wang, Wei-ping; Wang, Xiao-liang

    2016-01-01

    Ion channels are involved in a variety of fundamental physiological processes, and their malfunction causes numerous human diseases. Therefore, ion channels represent a class of attractive drug targets and a class of important off-targets for in vitro pharmacological profiling. In the past decades, the rapid progress in developing functional assays and instrumentation has enabled high throughput screening (HTS) campaigns on an expanding list of channel types. Chronologically, HTS methods for ion channels include the ligand binding assay, flux-based assay, fluorescence-based assay, and automated electrophysiological assay. In this review we summarize the current HTS technologies for different ion channel classes and their applications. PMID:26657056

  6. Plant Ion Channels: Gene Families, Physiology, and Functional Genomics Analyses

    PubMed Central

    Ward, John M.; Mäser, Pascal; Schroeder, Julian I.

    2016-01-01

    Distinct potassium, anion, and calcium channels in the plasma membrane and vacuolar membrane of plant cells have been identified and characterized by patch clamping. Primarily owing to advances in Arabidopsis genetics and genomics, and yeast functional complementation, many of the corresponding genes have been identified. Recent advances in our understanding of ion channel genes that mediate signal transduction and ion transport are discussed here. Some plant ion channels, for example, ALMT and SLAC anion channel subunits, are unique. The majority of plant ion channel families exhibit homology to animal genes; such families include both hyperpolarization-and depolarization-activated Shaker-type potassium channels, CLC chloride transporters/channels, cyclic nucleotide–gated channels, and ionotropic glutamate receptor homologs. These plant ion channels offer unique opportunities to analyze the structural mechanisms and functions of ion channels. Here we review gene families of selected plant ion channel classes and discuss unique structure-function aspects and their physiological roles in plant cell signaling and transport. PMID:18842100

  7. ICEPO: the ion channel electrophysiology ontology

    PubMed Central

    Hinard, V.; Britan, A.; Rougier, J.S.; Bairoch, A.; Abriel, H.; Gaudet, P.

    2016-01-01

    Ion channels are transmembrane proteins that selectively allow ions to flow across the plasma membrane and play key roles in diverse biological processes. A multitude of diseases, called channelopathies, such as epilepsies, muscle paralysis, pain syndromes, cardiac arrhythmias or hypoglycemia are due to ion channel mutations. A wide corpus of literature is available on ion channels, covering both their functions and their roles in disease. The research community needs to access this data in a user-friendly, yet systematic manner. However, extraction and integration of this increasing amount of data have been proven to be difficult because of the lack of a standardized vocabulary that describes the properties of ion channels at the molecular level. To address this, we have developed Ion Channel ElectroPhysiology Ontology (ICEPO), an ontology that allows one to annotate the electrophysiological parameters of the voltage-gated class of ion channels. This ontology is based on a three-state model of ion channel gating describing the three conformations/states that an ion channel can adopt: closed, open and inactivated. This ontology supports the capture of voltage-gated ion channel electrophysiological data from the literature in a structured manner and thus enables other applications such as querying and reasoning tools. Here, we present ICEPO (ICEPO ftp site: ftp://ftp.nextprot.org/pub/current_release/controlled_vocabularies/), as well as examples of its use. PMID:27055825

  8. ICEPO: the ion channel electrophysiology ontology.

    PubMed

    Hinard, V; Britan, A; Rougier, J S; Bairoch, A; Abriel, H; Gaudet, P

    2016-01-01

    Ion channels are transmembrane proteins that selectively allow ions to flow across the plasma membrane and play key roles in diverse biological processes. A multitude of diseases, called channelopathies, such as epilepsies, muscle paralysis, pain syndromes, cardiac arrhythmias or hypoglycemia are due to ion channel mutations. A wide corpus of literature is available on ion channels, covering both their functions and their roles in disease. The research community needs to access this data in a user-friendly, yet systematic manner. However, extraction and integration of this increasing amount of data have been proven to be difficult because of the lack of a standardized vocabulary that describes the properties of ion channels at the molecular level. To address this, we have developed Ion Channel ElectroPhysiology Ontology (ICEPO), an ontology that allows one to annotate the electrophysiological parameters of the voltage-gated class of ion channels. This ontology is based on a three-state model of ion channel gating describing the three conformations/states that an ion channel can adopt: closed, open and inactivated. This ontology supports the capture of voltage-gated ion channel electrophysiological data from the literature in a structured manner and thus enables other applications such as querying and reasoning tools. Here, we present ICEPO (ICEPO ftp site:ftp://ftp.nextprot.org/pub/current_release/controlled_vocabularies/), as well as examples of its use. PMID:27055825

  9. Zebrafish acid-sensing ion channel (ASIC) 4, characterization of homo- and heteromeric channels, and identification of regions important for activation by H+.

    PubMed

    Chen, Xuanmao; Polleichtner, Georg; Kadurin, Ivan; Gründer, Stefan

    2007-10-19

    There are four genes for acid-sensing ion channels (ASICs) in the genome of mammalian species. Whereas ASIC1 to ASIC3 form functional H+-gated Na+ channels, ASIC4 is not gated by H+, and its function is unknown. Zebrafish has two ASIC4 paralogs: zASIC4.1 and zASIC4.2. Whereas zASIC4.1 is gated by extracellular H+, zASIC4.2 is not. This differential response to H+ makes zASIC4 paralogs a good model to study the properties of this ion channel. In this study, we found that surface expression of homomeric zASIC4.2 is higher than that of zASIC4.1. Surface expression of zASIC4.1 was much increased by formation of heteromeric channels, suggesting that zASIC4.1 contributes to heteromeric ASICs in zebrafish neurons. Robust surface expression of H+-insensitive zASIC4.2 suggests that zASIC4.2 functions as a homomer and is gated by an as yet unknown stimulus, different from H+. Moreover, we identified a small region just distal to the first transmembrane domain that is crucial for the differential H+ response of the two paralogs. This post-TM1 domain may have a general role in gating of members of this gene family. PMID:17686779

  10. Pharmacological investigation of the bioluminescence signaling pathway of the dinoflagellate Lingulodinium polyedrum: evidence for the role of stretch-activated ion channels.

    PubMed

    Jin, Kelly; Klima, Jason C; Deane, Grant; Dale Stokes, Malcolm; Latz, Michael I

    2013-08-01

    Dinoflagellate bioluminescence serves as a whole-cell reporter of mechanical stress, which activates a signaling pathway that appears to involve the opening of voltage-sensitive ion channels and release of calcium from intracellular stores. However, little else is known about the initial signaling events that facilitate the transduction of mechanical stimuli. In the present study using the red tide dinoflagellate Lingulodinium polyedrum (Stein) Dodge, two forms of dinoflagellate bioluminescence, mechanically stimulated and spontaneous flashes, were used as reporter systems to pharmacological treatments that targeted various predicted signaling events at the plasma membrane level of the signaling pathway. Pretreatment with 200 μM Gadolinium III (Gd(3+) ), a nonspecific blocker of stretch-activated and some voltage-gated ion channels, resulted in strong inhibition of both forms of bioluminescence. Pretreatment with 50 μM nifedipine, an inhibitor of L-type voltage-gated Ca(2+) channels that inhibits mechanically stimulated bioluminescence, did not inhibit spontaneous bioluminescence. Treatment with 1 mM benzyl alcohol, a membrane fluidizer, was very effective in stimulating bioluminescence. Benzyl alcohol-stimulated bioluminescence was inhibited by Gd(3+) but not by nifedipine, suggesting that its role is through stretch activation via a change in plasma membrane fluidity. These results are consistent with the presence of stretch-activated and voltage-gated ion channels in the bioluminescence mechanotransduction signaling pathway, with spontaneous flashing associated with a stretch-activated component at the plasma membrane. PMID:27007206

  11. United in Diversity: Mechanosensitive Ion Channels in Plants

    PubMed Central

    Hamilton, Eric S.; Schlegel, Angela M.; Haswell, Elizabeth S.

    2015-01-01

    Mechanosensitive (MS) ion channels are a common mechanism for perceiving and responding to mechanical force. This class of mechanoreceptors is capable of transducing membrane tension directly into ion flux. In plant systems, MS ion channels have been proposed to play a wide array of roles, from the perception of touch and gravity to the osmotic homeostasis of intracellular organelles. Three families of plant MS ion channels have been identified: the MscS-like (MSL), Mid1-complementing activity (MCA), and two-pore potassium (TPK) families. Channels from these families vary widely in structure and function, localize to multiple cellular compartments, and conduct chloride, calcium, and/or potassium ions. However, they are still likely to represent only a fraction of the MS ion channel diversity in plant systems. PMID:25494462

  12. 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

  13. The alpha-5 segment of Bacillus thuringiensis delta-endotoxin: in vitro activity, ion channel formation and molecular modelling.

    PubMed Central

    Gazit, E; Bach, D; Kerr, I D; Sansom, M S; Chejanovsky, N; Shai, Y

    1994-01-01

    A peptide with a sequence corresponding to the highly conserved alpha-5 segment of the Cry delta-endotoxin family (amino acids 193-215 of Bacillus thuringiensis CryIIIA [Gazit and Shai (1993) Biochemistry 32, 3429-3436]), was investigated with respect to its interaction with insect membranes, cytotoxicity in vitro towards Spodoptera frugiperda (Sf-9) cells, and its propensity to form ion channels in planar lipid membranes (PLMs). Selectively labelled analogues of alpha-5 at either the N-terminal amino acid or the epsilon-amine of its lysine, were used to monitor the interaction of the peptides with insect membranes. The fluorescent emission spectra of the 7-nitrobenz-2-oxa-1,3-diazole-4-yl (NBD)-labelled alpha-5 peptides displayed a blue shift upon binding to insect (Spodoptera littoralis) mid-gut membranes, reflecting the relocation of the fluorescent probes to an environment of increased apolarity, i.e. within the lipidic constituent of the membrane. Moreover, midgut membrane-bound NBD-labelled alpha-5 peptides were protected from enzymic proteolysis. Functional characterization of alpha-5 has revealed that it is cytotoxic to Sf-9 insect cells, and that it forms ion channels in PLMs with conductances ranging from 30 to 1000 pS. A proline-substituted analogue of alpha-5 is less cytolytic and slightly more exposed to enzymic digestion. Molecular modelling utilizing simulated annealing via molecular dynamics suggests that a transbilayer pore may be formed by alpha-5 monomers that assemble to form a left-handed coiled coil of approximately parallel helices. These findings further support a role for alpha-5 in the toxic mechanism of delta-endotoxins, and assign alpha-5 as one of the transmembrane helices which form the toxic pore. The suggested role is consistent with the recent finding that cleavage of CryIVB delta-endotoxin in a loop between alpha-5 and alpha-6 is highly important for its larvicidal activity [Angsuthanasombat, Crickmore and Ellar (1993) FEMS

  14. Optical control of an ion channel gate.

    PubMed

    Lemoine, Damien; Habermacher, Chloé; Martz, Adeline; Méry, Pierre-François; Bouquier, Nathalie; Diverchy, Fanny; Taly, Antoine; Rassendren, François; Specht, Alexandre; Grutter, Thomas

    2013-12-17

    The powerful optogenetic pharmacology method allows the optical control of neuronal activity by photoswitchable ligands tethered to channels and receptors. However, this approach is technically demanding, as it requires the design of pharmacologically active ligands. The development of versatile technologies therefore represents a challenging issue. Here, we present optogating, a method in which the gating machinery of an ATP-activated P2X channel was reprogrammed to respond to light. We found that channels covalently modified by azobenzene-containing reagents at the transmembrane segments could be reversibly turned on and off by light, without the need of ATP, thus revealing an agonist-independent, light-induced gating mechanism. We demonstrate photocontrol of neuronal activity by a light-gated, ATP-insensitive P2X receptor, providing an original tool devoid of endogenous sensitivity to delineate P2X signaling in normal and pathological states. These findings open new avenues to specifically activate other ion channels independently of their natural stimulus. PMID:24297890

  15. Mechanosensitive Ion Channels in Cardiovascular Physiology

    PubMed Central

    Teng, Jinfeng; Loukin, Steve; Kung, Ching

    2014-01-01

    EC coupling is subjected to a mechanical feedback, which originates from physical force-sensing ion channels in the pericardium and elsewhere. Reviewed here are the most recent developments that greatly advanced our understanding of these mechanosensitive (MS) channels, including TRPs and K2p’s. Patch clamp has continued to demonstrate the direct channel activation by membrane stretch. Crystallography and cryo-electron microscopy have revealed the structures of several MS channels at atomic resolution. Some have been purified to homogeneity, reconstituted into lipid bilayer, and still retain their ability to respond to stretch force. A force-from-lipid (FFL) theory has been advanced that emphasizes the strong binding between channel proteins and lipids. Through these bonds, the sharp lateral tension (akin to surface tension) of the bilayer can transmit added force to the channel protein. Like temperature sensitivity, sensitivity to mechanical force is far more pervasive than we previously realize, and is especially important to the beating heart. PMID:26778915

  16. Ion channels versus ion pumps: the principal difference, in principle

    PubMed Central

    Gadsby, David C.

    2009-01-01

    Two kinds of border guards control the incessant traffic of ions across cell membranes: ion channels and ion pumps. When open, channels let selected ions diffuse rapidly down electrical and concentration gradients, whereas ion pumps labour tirelessly to maintain the gradients, by consuming energy to slowly move ions against them. Because of their diametrically opposed tasks and their divergent speeds, channels and pumps have traditionally been viewed as completely different entities, as alike as chalk and cheese. But new structural and mechanistic information about both classes of these molecular machines challenges this comfortable separation, forcing its reevaluation. PMID:19339978

  17. Ion Channels in Innate and Adaptive Immunity

    PubMed Central

    Feske, Stefan; Wulff, Heike; Skolnik, Edward Y.

    2016-01-01

    Ion channels and transporters mediate the transport of charged ions across hydrophobic lipid membranes. In immune cells, divalent cations such as calcium, magnesium, and zinc have important roles as second messengers to regulate intracellular signaling pathways. By contrast, monovalent cations such as sodium and potassium mainly regulate the membrane potential, which indirectly controls the influx of calcium and immune cell signaling. Studies investigating human patients with mutations in ion channels and transporters, analysis of gene-targeted mice, or pharmacological experiments with ion channel inhibitors have revealed important roles of ionic signals in lymphocyte development and in innate and adaptive immune responses. We here review the mechanisms underlying the function of ion channels and transporters in lymphocytes and innate immune cells and discuss their roles in lymphocyte development, adaptive and innate immune responses, and autoimmunity, as well as recent efforts to develop pharmacological inhibitors of ion channels for immunomodulatory therapy. PMID:25861976

  18. Ion channels enable electrical communication within bacterial communities

    PubMed Central

    Prindle, Arthur; Liu, Jintao; Asally, Munehiro; Ly, San; Garcia-Ojalvo, Jordi; Süel, Gürol M.

    2016-01-01

    The study of bacterial ion channels has provided fundamental insights into the structural basis of neuronal signaling. However, the native role of ion channels in bacteria has remained elusive. Here we show that ion channels conduct long-range electrical signals within bacterial biofilm communities through spatially propagating waves of potassium. These waves result from a positive feedback loop, in which a metabolic trigger induces release of intracellular potassium, which in turn depolarizes neighboring cells. Propagating through the biofilm, this wave of depolarization coordinates metabolic states among cells in the interior and periphery of the biofilm. Deletion of the potassium channel abolishes this response. As predicted by a mathematical model, we further show that spatial propagation can be hindered by specific genetic perturbations to potassium channel gating. Together, these results demonstrate a function for ion channels in bacterial biofilms, and provide a prokaryotic paradigm for active, long-range electrical signaling in cellular communities. PMID:26503040

  19. The Control of Male Fertility by Spermatozoan Ion Channels

    PubMed Central

    Lishko, Polina V.; Kirichok, Yuriy; Ren, Dejian; Navarro, Betsy; Chung, Jean-Ju

    2014-01-01

    Ion channels control the sperm ability to fertilize the egg by regulating sperm maturation in the female reproductive tract and by triggering key sperm physiological responses required for successful fertilization such as hyperactivated motility, chemotaxis, and the acrosome reaction. CatSper, a pH-regulated, calcium-selective ion channel, and KSper (Slo3) are core regulators of sperm tail calcium entry and sperm hyperactivated motility. Many other channels had been proposed as regulating sperm activity without direct measurements. With the development of the sperm patch-clamp technique, CatSper and KSper have been confirmed as the primary spermatozoan ion channels. In addition, the voltage-gated proton channel Hv1 has been identified in human sperm tail, and the P2X2 ion channel has been identified in the midpiece of mouse sperm. Mutations and deletions in sperm-specific ion channels affect male fertility in both mice and humans without affecting other physiological functions. The uniqueness of sperm ion channels makes them ideal pharmaceutical targets for contraception. In this review we discuss how ion channels regulate sperm physiology. PMID:22017176

  20. Ion Channel Expression in the Developing Enteric Nervous System

    PubMed Central

    Stamp, Lincon A.; Fegan, Emily; Dent, Stephan; Cooper, Edward C.; Lomax, Alan E.; Anderson, Colin R.; Bornstein, Joel C.; Young, Heather M.; McKeown, Sonja J.

    2015-01-01

    The enteric nervous system arises from neural crest-derived cells (ENCCs) that migrate caudally along the embryonic gut. The expression of ion channels by ENCCs in embryonic mice was investigated using a PCR-based array, RT-PCR and immunohistochemistry. Many ion channels, including chloride, calcium, potassium and sodium channels were already expressed by ENCCs at E11.5. There was an increase in the expression of numerous ion channel genes between E11.5 and E14.5, which coincides with ENCC migration and the first extension of neurites by enteric neurons. Previous studies have shown that a variety of ion channels regulates neurite extension and migration of many cell types. Pharmacological inhibition of a range of chloride or calcium channels had no effect on ENCC migration in cultured explants or neuritogenesis in vitro. The non-selective potassium channel inhibitors, TEA and 4-AP, retarded ENCC migration and neuritogenesis, but only at concentrations that also resulted in cell death. In summary, a large range of ion channels is expressed while ENCCs are colonizing the gut, but we found no evidence that ENCC migration or neuritogenesis requires chloride, calcium or potassium channel activity. Many of the ion channels are likely to be involved in the development of electrical excitability of enteric neurons. PMID:25798587

  1. Photochemical control of endogenous ion channels and cellular excitability.

    PubMed

    Fortin, Doris L; Banghart, Matthew R; Dunn, Timothy W; Borges, Katharine; Wagenaar, Daniel A; Gaudry, Quentin; Karakossian, Movses H; Otis, Thomas S; Kristan, William B; Trauner, Dirk; Kramer, Richard H

    2008-04-01

    Light-activated ion channels provide a precise and noninvasive optical means for controlling action potential firing, but the genes encoding these channels must first be delivered and expressed in target cells. Here we describe a method for bestowing light sensitivity onto endogenous ion channels that does not rely on exogenous gene expression. The method uses a synthetic photoisomerizable small molecule, or photoswitchable affinity label (PAL), that specifically targets K+ channels. PALs contain a reactive electrophile, enabling covalent attachment of the photoswitch to naturally occurring nucleophiles in K+ channels. Ion flow through PAL-modified channels is turned on or off by photoisomerizing PAL with different wavelengths of light. We showed that PAL treatment confers light sensitivity onto endogenous K+ channels in isolated rat neurons and in intact neural structures from rat and leech, allowing rapid optical regulation of excitability without genetic modification. PMID:18311146

  2. Surface dynamics of voltage-gated ion channels.

    PubMed

    Heine, Martin; Ciuraszkiewicz, Anna; Voigt, Andreas; Heck, Jennifer; Bikbaev, Arthur

    2016-07-01

    Neurons encode information in fast changes of the membrane potential, and thus electrical membrane properties are critically important for the integration and processing of synaptic inputs by a neuron. These electrical properties are largely determined by ion channels embedded in the membrane. The distribution of most ion channels in the membrane is not spatially uniform: they undergo activity-driven changes in the range of minutes to days. Even in the range of milliseconds, the composition and topology of ion channels are not static but engage in highly dynamic processes including stochastic or activity-dependent transient association of the pore-forming and auxiliary subunits, lateral diffusion, as well as clustering of different channels. In this review we briefly discuss the potential impact of mobile sodium, calcium and potassium ion channels and the functional significance of this for individual neurons and neuronal networks. PMID:26891382

  3. Structure and selectivity in bestrophin ion channels

    SciTech Connect

    Yang, Tingting; Liu, Qun; Kloss, Brian; Bruni, Renato; Kalathur, Ravi C.; Guo, Youzhong; Kloppmann, Edda; Rost, Burkhard; Colecraft, Henry M.; Hendrickson, Wayne A.

    2014-09-25

    Human bestrophin 1 (hBest1) is a calcium-activated chloride channel from the retinal pigment epithelium, where it can suffer mutations associated with vitelliform macular degeneration, or Best disease. We describe the structure of a bacterial homolog (KpBest) of hBest1 and functional characterizations of both channels. KpBest is a pentamer that forms a five-helix transmembrane pore, closed by three rings of conserved hydrophobic residues, and has a cytoplasmic cavern with a restricted exit. From electrophysiological analysis of structure-inspired mutations in KpBest and hBest1, we find a subtle control of ion selectivity in the bestrophins, including reversal of anion/cation selectivity, and dramatic activation by mutations at the exit restriction. Lastly, a homology model of hBest1 shows the locations of disease-causing mutations and suggests possible roles in regulation.

  4. Mitochondrial ion channels as oncological targets.

    PubMed

    Leanza, L; Zoratti, M; Gulbins, E; Szabo, I

    2014-12-01

    Mitochondria, the key bioenergetic intracellular organelles, harbor a number of proteins with proven or hypothetical ion channel functions. Growing evidence points to the important contribution of these channels to the regulation of mitochondrial function, such as ion homeostasis imbalances profoundly affecting energy transducing processes, reactive oxygen species production and mitochondrial integrity. Given the central role of mitochondria in apoptosis, their ion channels with the potential to compromise mitochondrial function have become promising targets for the treatment of malignancies. Importantly, in vivo evidence demonstrates the involvement of the proton-transporting uncoupling protein, a mitochondrial potassium channel, the outer membrane located porin and the permeability transition pore in tumor progression/control. In this review, we focus on mitochondrial channels that have been assigned a definite role in cell death regulation and possess clear oncological relevance. Overall, based on in vivo and in vitro genetic and pharmacological evidence, mitochondrial ion channels are emerging as promising targets for cancer treatment. PMID:24469031

  5. Modeling ion channels: Past, present, and future

    PubMed Central

    2014-01-01

    Ion channels are membrane-bound enzymes whose catalytic sites are ion-conducting pores that open and close (gate) in response to specific environmental stimuli. Ion channels are important contributors to cell signaling and homeostasis. Our current understanding of gating is the product of 60 plus years of voltage-clamp recording augmented by intervention in the form of environmental, chemical, and mutational perturbations. The need for good phenomenological models of gating has evolved in parallel with the sophistication of experimental technique. The goal of modeling is to develop realistic schemes that not only describe data, but also accurately reflect mechanisms of action. This review covers three areas that have contributed to the understanding of ion channels: traditional Eyring kinetic theory, molecular dynamics analysis, and statistical thermodynamics. Although the primary emphasis is on voltage-dependent channels, the methods discussed here are easily generalized to other stimuli and could be applied to any ion channel and indeed any macromolecule. PMID:24935742

  6. Stretch induced endothelin-1 secretion by adult rat astrocytes involves calcium influx via stretch-activated ion channels (SACs)

    SciTech Connect

    Ostrow, Lyle W.; Suchyna, Thomas M.; Sachs, Frederick

    2011-06-24

    Highlights: {yields} Endothelin-1 expression by adult rat astrocytes correlates with cell proliferation. {yields} Stretch-induced ET-1 is inhibited by GsMtx-4, a specific inhibitor of Ca{sup 2+} permeant SACs. {yields} The less specific SAC inhibitor streptomycin also inhibits ET-1 secretion. {yields} Stretch-induced ET-1 production depends on a calcium influx. {yields} SAC pharmacology may provide a new class of therapeutic agents for CNS pathology. -- Abstract: The expression of endothelins (ETs) and ET-receptors is often upregulated in brain pathology. ET-1, a potent vasoconstrictor, also inhibits the expression of astrocyte glutamate transporters and is mitogenic for astrocytes, glioma cells, neurons, and brain capillary endothelia. We have previously shown that mechanical stress stimulates ET-1 production by adult rat astrocytes. We now show in adult astrocytes that ET-1 production is driven by calcium influx through stretch-activated ion channels (SACs) and the ET-1 production correlates with cell proliferation. Mechanical stimulation using biaxial stretch (<20%) of a rubber substrate increased ET-1 secretion, and 4 {mu}M GsMTx-4 (a specific inhibitor of SACs) inhibited secretion by 30%. GsMTx-4 did not alter basal ET-1 levels in the absence of stretch. Decreasing the calcium influx by lowering extracellular calcium also inhibited stretch-induced ET-1 secretion without effecting ET-1 secretion in unstretched controls. Furthermore, inhibiting SACs with the less specific inhibitor streptomycin also inhibited stretch-induced ET-1 secretion. The data can be explained with a simple model in which ET-1 secretion depends on an internal Ca{sup 2+} threshold. This coupling of mechanical stress to the astrocyte endothelin system through SACs has treatment implications, since all pathology deforms the surrounding parenchyma.

  7. Enhancement of acid-sensing ion channel activity by metabotropic P2Y UTP receptors in primary sensory neurons.

    PubMed

    Ren, Cuixia; Gan, Xiong; Wu, Jing; Qiu, Chun-Yu; Hu, Wang-Ping

    2016-03-01

    Peripheral purinergic signaling plays an important role in nociception. Increasing evidence suggests that metabotropic P2Y receptors are also involved, but little is known about the underlying mechanism. Herein, we report that selective P2Y receptor agonist uridine 5'-triphosphate (UTP) can exert an enhancing effect on the functional activity of acid-sensing ion channels (ASICs), key sensors for extracellular protons, in rat dorsal root ganglia (DRG) neurons. First, UTP dose-dependently increased the amplitude of ASIC currents. UTP also shifted the concentration-response curve for proton upwards, with a 56.6 ± 6.4% increase of the maximal current response to proton. Second, UTP potentiation of proton-gated currents can be mimicked by adenosine 5'-triphosphate (ATP), but not by P2Y1 receptor agonist ADP. Potentiation of UTP was blocked by P2Y receptor antagonist suramin and by inhibition of intracellular G protein, phospholipase C (PLC), protein kinase C (PKC), or protein interacting with C-kinase 1 (PICK1) signaling. Third, UTP altered acidosis-evoked membrane excitability of DRG neurons and caused a significant increase in the amplitude of the depolarization and the number of spikes induced by acid stimuli. Finally, UTP dose-dependently exacerbated nociceptive responses to injection of acetic acid in rats. These results suggest that UTP enhanced ASIC-mediated currents and nociceptive responses, which reveal a novel peripheral mechanism underlying UTP-sensitive P2Y2 receptor involvement in hyperalgesia by sensitizing ASICs in primary sensory neurons. PMID:26538146

  8. Ion Channels in Obesity: Pathophysiology and Potential Therapeutic Targets.

    PubMed

    Vasconcelos, Luiz H C; Souza, Iara L L; Pinheiro, Lílian S; Silva, Bagnólia A

    2016-01-01

    Obesity is a multifactorial disease related to metabolic disorders and associated with genetic determinants. Currently, ion channels activity has been linked to many of these disorders, in addition to the central regulation of food intake, energetic balance, hormone release and response, as well as the adipocyte cell proliferation. Therefore, the objective of this work is to review the current knowledge about the influence of ion channels in obesity development. This review used different sources of literature (Google Scholar, PubMed, Scopus, and Web of Science) to assess the role of ion channels in the pathophysiology of obesity. Ion channels present diverse key functions, such as the maintenance of physiological homeostasis and cell proliferation. Cell biology and pharmacological experimental evidences demonstrate that proliferating cells exhibit ion channel expression, conductance, and electrical properties different from the resting cells. Thereby, a large variety of ion channels has been identified in the pathogenesis of obesity such as potassium, sodium, calcium and chloride channels, nicotinic acetylcholine receptor and transient receptor potential channels. The fundamental involvement of these channels on the generation of obesity leads to the progress in the knowledge about the mechanisms responsible for the obesity pathophysiology, consequently emerging as new targets for pharmacological modulation. PMID:27065858

  9. Ion Channels in Obesity: Pathophysiology and Potential Therapeutic Targets

    PubMed Central

    Vasconcelos, Luiz H. C.; Souza, Iara L. L.; Pinheiro, Lílian S.; Silva, Bagnólia A.

    2016-01-01

    Obesity is a multifactorial disease related to metabolic disorders and associated with genetic determinants. Currently, ion channels activity has been linked to many of these disorders, in addition to the central regulation of food intake, energetic balance, hormone release and response, as well as the adipocyte cell proliferation. Therefore, the objective of this work is to review the current knowledge about the influence of ion channels in obesity development. This review used different sources of literature (Google Scholar, PubMed, Scopus, and Web of Science) to assess the role of ion channels in the pathophysiology of obesity. Ion channels present diverse key functions, such as the maintenance of physiological homeostasis and cell proliferation. Cell biology and pharmacological experimental evidences demonstrate that proliferating cells exhibit ion channel expression, conductance, and electrical properties different from the resting cells. Thereby, a large variety of ion channels has been identified in the pathogenesis of obesity such as potassium, sodium, calcium and chloride channels, nicotinic acetylcholine receptor and transient receptor potential channels. The fundamental involvement of these channels on the generation of obesity leads to the progress in the knowledge about the mechanisms responsible for the obesity pathophysiology, consequently emerging as new targets for pharmacological modulation. PMID:27065858

  10. Bis-triazolyl diguanosine derivatives as synthetic transmembrane ion channels.

    PubMed

    Kumar, Y Pavan; Das, Rabindra Nath; Schütte, Ole Mathis; Steinem, Claudia; Dash, Jyotirmayee

    2016-06-01

    In nature, ion channels facilitate the transport of ions across biological membranes. The development of artificial ion channels that can mimic the fundamental functions of the natural ones would be of great importance to biological research. Artificial ion channels based on nucleoside derivatives are expected to be biocompatible with functions that can be controlled by the presence or absence of biologically relevant molecules. This protocol describes the detailed procedures for the synthesis and ion-channel activity of four diguanosine derivatives, each made up of two guanosine moieties separated by a covalent linker (e.g., PEG). The procedure describes the preparation of guanosine azide and guanosine alkine building blocks, as well as the preparation of four distinct synthetic linkers each containing either two alkynes or two azides. The diguanosine derivatives are synthesized using a 'one-pot' modular synthetic approach based on Cu(I)-catalyzed azide and alkyne cycloaddition. The ion-channel activity of these diguanosine derivatives for the transportation of ions across a phospholipid bilayer is investigated using voltage-clamp experiment. By using the PEG-containing diguanosine as an example, we describe how to determine the ion-channel activity in the presence of different metal ions (e.g., Na(+), K(+) and Cs(+)) and the inhibition of the ion-channel activity using the nucleobase cytosine. The approximate time frame for the synthesis of the PEG dinucleoside is 3 d, and that for the experiments to evaluate its ability to transport K(+) ion across a phospholipid bilayer is ∼8-10 h. PMID:27149327

  11. Equivalence of trans paths in ion channels

    NASA Astrophysics Data System (ADS)

    Alvarez, Juan; Hajek, Bruce

    2006-04-01

    We explore stochastic models for the study of ion transport in biological cells. Analysis of these models explains and explores an interesting feature of ion transport observed by biophysicists. Namely, the average time it takes ions to cross certain ion channels is the same in either direction, even if there is an electric potential difference across the channels. It is shown for simple single ion models that the distribution of a path (i.e., the history of location versus time) of an ion crossing the channel in one direction has the same distribution as the time-reversed path of an ion crossing the channel in the reverse direction. Therefore, not only is the mean duration of these paths equal, but other measures, such as the variance of passage time or the mean time a path spends within a specified section of the channel, are also the same for both directions of traversal. The feature is also explored for channels with interacting ions. If a system of interacting ions is in reversible equilibrium (net flux is zero), then the equivalence of the left-to-right trans paths with the time-reversed right-to-left trans paths still holds. However, if the system is in equilibrium, but not reversible equilibrium, then such equivalence need not hold.

  12. Structure and selectivity in bestrophin ion channels

    DOE PAGESBeta

    Yang, Tingting; Liu, Qun; Kloss, Brian; Bruni, Renato; Kalathur, Ravi C.; Guo, Youzhong; Kloppmann, Edda; Rost, Burkhard; Colecraft, Henry M.; Hendrickson, Wayne A.

    2014-09-25

    Human bestrophin 1 (hBest1) is a calcium-activated chloride channel from the retinal pigment epithelium, where it can suffer mutations associated with vitelliform macular degeneration, or Best disease. We describe the structure of a bacterial homolog (KpBest) of hBest1 and functional characterizations of both channels. KpBest is a pentamer that forms a five-helix transmembrane pore, closed by three rings of conserved hydrophobic residues, and has a cytoplasmic cavern with a restricted exit. From electrophysiological analysis of structure-inspired mutations in KpBest and hBest1, we find a subtle control of ion selectivity in the bestrophins, including reversal of anion/cation selectivity, and dramatic activationmore » by mutations at the exit restriction. Lastly, a homology model of hBest1 shows the locations of disease-causing mutations and suggests possible roles in regulation.« less

  13. Understanding autoimmunity: The ion channel perspective.

    PubMed

    RamaKrishnan, Anantha Maharasi; Sankaranarayanan, Kavitha

    2016-07-01

    Ion channels are integral membrane proteins that orchestrate the passage of ions across the cell membrane and thus regulate various key physiological processes of the living system. The stringently regulated expression and function of these channels hold a pivotal role in the development and execution of various cellular functions. Malfunction of these channels results in debilitating diseases collectively termed channelopathies. In this review, we highlight the role of these proteins in the immune system with special emphasis on the development of autoimmunity. The role of ion channels in various autoimmune diseases is also listed out. This comprehensive review summarizes the ion channels that could be used as molecular targets in the development of new therapeutics against autoimmune disorders. PMID:26854401

  14. Dendritic Ion Channel Trafficking and Plasticity

    PubMed Central

    Shah, Mala M.; Hammond, Rebecca S.; Hoffman, Dax

    2010-01-01

    Dendrites, the elaborate processes emerging from neuronal cell bodies, receive most excitatory synaptic inputs. Voltage- and calcium-gated ion channels are abundant in dendrites and modify the shape, propagation and integration of synaptic signals. These ion channels also determine intrinsic dendritic excitability and are therfore important for the induction and manifestation of Hebbian and non-Hebbian plasticity. Revealingly, dendritic channels have distinct expression patterns and biophysical properties from those present in other neuronal compartments. Recent evidence suggests that dendritic ion channels are locally regulated, perhaps contributing to different forms of plasticity. In this review, we will discuss the implications of regulating dendritic ion channel function and trafficking in the context of plasticity and information processing. PMID:20363038

  15. Acid-sensing ion channels under hypoxia

    PubMed Central

    Yingjun, Guo; Xun, Qu

    2013-01-01

    Hypoxia represents the lack of oxygen below the basic level, and the range of known channels related to hypoxia is continually increasing. Since abnormal hypoxia initiates pathological processes in numerous diseases via, to a great degree, producing acidic microenvironment, the significance of these channels in this environment has, until now, remained completely unknown. However, recent discovery of acid-sensing ion channels (ASICs) have enhanced our understanding of the hypoxic channelome. They belong to the degenerin/epithelial Na+ channel family and function once extracellular pH decreases to a certain level. So does the ratiocination emerge that ASICs participate in many hypoxia-induced pathological processes, including pain, apoptosis, malignancy, which all appear to involve them. Since evidence suggests that activity of ASICs is altered under pathological hypoxia, future studies are needed to deeply explore the relationship between ASICs and hypoxia, which may provide a progressive understanding of hypoxic effects in cancer, arthritis, intervertebral disc degeneration, ischemic brain injury and so on. PMID:23764948

  16. Caveolae, Ion Channels and Cardiac Arrhythmias

    PubMed Central

    Balijepalli, Ravi C.; Kamp, Timothy J.

    2009-01-01

    Caveolae are specialized membrane microdomains enriched in cholesterol and sphingolipids which are present in multiple cell types including cardiomyocytes. Along with the essential scaffolding protein caveolin-3, a number of different ion channels and transporters have been localized to caveolae in the heart including L-type Ca2+ channels (Cav1.2), Na+ channels (Nav1.5), pacemaker channels (HCN4), Na+/Ca2+ exchnager (NCX1) and others. Closely associated with these channels are specific macromolecular signaling complexes that provide highly localized regulation of the channels. Mutations in the caveolin-3 gene (CAV3) have been linked with the congenital long QT syndrome (LQT9), and mutations in caveolar-localized ion channels may contribute to other inherited arrhythmias. Changes in the caveolar microdomain in acquired heart disease may also lead to dysregulation and dysfunction of ion channels, altering the risk of arrhythmias in conditions such as heart failure. This review highlights the existing evidence identifying and characterizing ion channels localized to caveolae in cardiomyocytes and their role in arrhythmogenesis. PMID:19351512

  17. Pair creation in heavy ion channeling

    NASA Astrophysics Data System (ADS)

    Belov, N. A.; Harman, Z.

    2016-04-01

    Heavy ions channeled through crystals with multi-GeV kinetic energies can create electron-positron pairs. In the framework of the ion, the energy of virtual photons arising from the periodic crystal potential may exceed the threshold 2mec2. The repeated periodic collisions with the crystal ions yield high pair production rates. When the virtual photon frequency matches a nuclear transition in the ion, the production rate can be resonantly increased. In this two-step excitation-pair conversion scheme, the excitation rates are coherently enhanced, and scale approximately quadratically with the number of crystal sites along the channel.

  18. Role of Dynamics in the Autoinhibition and Activation of the Hyperpolarization-activated Cyclic Nucleotide-modulated (HCN) Ion Channels*♦

    PubMed Central

    VanSchouwen, Bryan; Akimoto, Madoka; Sayadi, Maryam; Fogolari, Federico; Melacini, Giuseppe

    2015-01-01

    The hyperpolarization-activated cyclic nucleotide-modulated (HCN) ion channels control rhythmicity in neurons and cardiomyocytes. Cyclic AMP allosterically modulates HCN through the cAMP-dependent formation of a tetrameric gating ring spanning the intracellular region (IR) of HCN, to which cAMP binds. Although the apo versus holo conformational changes of the cAMP-binding domain (CBD) have been previously mapped, only limited information is currently available on the HCN IR dynamics, which have been hypothesized to play a critical role in the cAMP-dependent gating of HCN. Here, using molecular dynamics simulations validated and complemented by experimental NMR and CD data, we comparatively analyze HCN IR dynamics in the four states of the thermodynamic cycle arising from the coupling between cAMP binding and tetramerization equilibria. This extensive set of molecular dynamics trajectories captures the active-to-inactive transition that had remained elusive for other CBDs, and it provides unprecedented insight on the role of IR dynamics in HCN autoinhibition and its release by cAMP. Specifically, the IR tetramerization domain becomes more flexible in the monomeric states, removing steric clashes that the apo-CDB structure would otherwise impose. Furthermore, the simulations reveal that the active/inactive structural transition for the apo-monomeric CBD occurs through a manifold of pathways that are more divergent than previously anticipated. Upon cAMP binding, these pathways become disallowed, pre-confining the CBD conformational ensemble to a tetramer-compatible state. This conformational confinement primes the IR for tetramerization and thus provides a model of how cAMP controls HCN channel gating. PMID:25944904

  19. Ion Channel Probes for Scanning Ion Conductance Microscopy

    PubMed Central

    2015-01-01

    The sensitivity and selectivity of ion channels provide an appealing opportunity for sensor development. Here, we describe ion channel probes (ICPs), which consist of multiple ion channels reconstituted into lipid bilayers suspended across the opening of perflourinated glass micropipets. When incorporated with a scanning ion conductance microscope (SICM), ICPs displayed a distance-dependent current response that depended on the number of ion channels in the membrane. With distance-dependent current as feedback, probes were translated laterally, to demonstrate the possibility of imaging with ICPs. The ICP platform yields several potential advantages for SICM that will enable exciting opportunities for incorporation of chemical information into imaging and for high-resolution imaging. PMID:25425190

  20. Ion channels in cancer: future perspectives and clinical potential.

    PubMed

    Lang, Florian; Stournaras, Christos

    2014-03-19

    Ion transport across the cell membrane mediated by channels and carriers participate in the regulation of tumour cell survival, death and motility. Moreover, the altered regulation of channels and carriers is part of neoplastic transformation. Experimental modification of channel and transporter activity impacts tumour cell survival, proliferation, malignant progression, invasive behaviour or therapy resistance of tumour cells. A wide variety of distinct Ca(2+) permeable channels, K(+) channels, Na(+) channels and anion channels have been implicated in tumour growth and metastasis. Further experimental information is, however, needed to define the specific role of individual channel isoforms critically important for malignancy. Compelling experimental evidence supports the assumption that the pharmacological inhibition of ion channels or their regulators may be attractive targets to counteract tumour growth, prevent metastasis and overcome therapy resistance of tumour cells. This short review discusses the role of Ca(2+) permeable channels, K(+) channels, Na(+) channels and anion channels in tumour growth and metastasis and the therapeutic potential of respective inhibitors. PMID:24493756

  1. Ion channels, phosphorylation and mammalian sperm capacitation

    PubMed Central

    Visconti, Pablo E; Krapf, Dario; de la Vega-Beltrán, José Luis; Acevedo, Juan José; Darszon, Alberto

    2011-01-01

    Sexually reproducing animals require an orchestrated communication between spermatozoa and the egg to generate a new individual. Capacitation, a maturational complex phenomenon that occurs in the female reproductive tract, renders spermatozoa capable of binding and fusing with the oocyte, and it is a requirement for mammalian fertilization. Capacitation encompasses plasma membrane reorganization, ion permeability regulation, cholesterol loss and changes in the phosphorylation state of many proteins. Novel tools to study sperm ion channels, image intracellular ionic changes and proteins with better spatial and temporal resolution, are unraveling how modifications in sperm ion transport and phosphorylation states lead to capacitation. Recent evidence indicates that two parallel pathways regulate phosphorylation events leading to capacitation, one of them requiring activation of protein kinase A and the second one involving inactivation of ser/thr phosphatases. This review examines the involvement of ion transporters and phosphorylation signaling processes needed for spermatozoa to achieve capacitation. Understanding the molecular mechanisms leading to fertilization is central for societies to deal with rising male infertility rates, to develop safe male gamete-based contraceptives and to preserve biodiversity through better assisted fertilization strategies. PMID:21540868

  2. Exogenous acetate ion reaches the type II copper centre in CueO through the water-excretion channel and potentially affects the enzymatic activity.

    PubMed

    Komori, Hirofumi; Kataoka, Kunishige; Tanaka, Sakiko; Matsuda, Nana; Higuchi, Yoshiki; Sakurai, Takeshi

    2016-07-01

    The acetate-bound form of the type II copper was found in the X-ray structure of the multicopper oxidase CueO crystallized in acetate buffer in addition to the conventional OH(-)-bound form as the major resting form. The acetate ion was retained bound to the type II copper even after prolonged exposure of a CueO crystal to X-ray radiation, which led to the stepwise reduction of the Cu centres. However, in this study, when CueO was crystallized in citrate buffer the OH(-)-bound form was present exclusively. This fact shows that an exogenous acetate ion reaches the type II Cu centre through the water channel constructed between domains 1 and 3 in the CueO molecule. It was also found that the enzymatic activity of CueO is enhanced in the presence of acetate ions in the solvent water. PMID:27380373

  3. Structural mechanisms underlying the function of epithelial sodium channel/acid-sensing ion channel

    PubMed Central

    Carattino, Marcelo D.

    2013-01-01

    Purpose of review The epithelial sodium channel/degenerin family encompasses a group of cation-selective ion channels that are activated or modulated by a variety of extracellular stimuli. This review describes findings that provide new insights into the molecular mechanisms that control the function of these channels. Recent findings Epithelial sodium channels facilitate Na+ reabsorption in the distal nephron and hence have a role in fluid volume homeostasis and arterial blood pressure regulation. Acid-sensing ion channels are broadly distributed in the nervous system where they contribute to the sensory processes. The atomic structure of acid-sensing ion channel 1 illustrates the complex trimeric architecture of these proteins. Each subunit has two transmembrane spanning helices, a highly organized ectodomain and intracellular N-terminus and C-terminus. Recent findings have begun to elucidate the structural elements that allow these channels to sense and respond to extracellular factors. This review emphasizes the roles of the extracellular domain in sensing changes in the extracellular milieu and of the residues in the extracellular–transmembrane domains interface in coupling extracellular changes to the pore of the channel. Summary Epithelial sodium channels and acid-sensing ion channels have evolved to sense extracellular cues. Future research should be directed toward elucidating how changes triggered by extracellular factors translate into pore opening and closing events. PMID:21709553

  4. The ion channel TRPV1 regulates the activation and proinflammatory properties of CD4⁺ T cells.

    PubMed

    Bertin, Samuel; Aoki-Nonaka, Yukari; de Jong, Petrus Rudolf; Nohara, Lilian L; Xu, Hongjian; Stanwood, Shawna R; Srikanth, Sonal; Lee, Jihyung; To, Keith; Abramson, Lior; Yu, Timothy; Han, Tiffany; Touma, Ranim; Li, Xiangli; González-Navajas, José M; Herdman, Scott; Corr, Maripat; Fu, Guo; Dong, Hui; Gwack, Yousang; Franco, Alessandra; Jefferies, Wilfred A; Raz, Eyal

    2014-11-01

    TRPV1 is a Ca(2+)-permeable channel studied mostly as a pain receptor in sensory neurons. However, its role in other cell types is poorly understood. Here we found that TRPV1 was functionally expressed in CD4(+) T cells, where it acted as a non-store-operated Ca(2+) channel and contributed to T cell antigen receptor (TCR)-induced Ca(2+) influx, TCR signaling and T cell activation. In models of T cell-mediated colitis, TRPV1 promoted colitogenic T cell responses and intestinal inflammation. Furthermore, genetic and pharmacological inhibition of TRPV1 in human CD4(+) T cells recapitulated the phenotype of mouse Trpv1(-/-) CD4(+) T cells. Our findings suggest that inhibition of TRPV1 could represent a new therapeutic strategy for restraining proinflammatory T cell responses. PMID:25282159

  5. Multitude of ion channels in the regulation of transmitter release.

    PubMed Central

    Rahamimoff, R; Butkevich, A; Duridanova, D; Ahdut, R; Harari, E; Kachalsky, S G

    1999-01-01

    The presynaptic nerve terminal is of key importance in communication in the nervous system. Its primary role is to release transmitter quanta on the arrival of an appropriate stimulus. The structural basis of these transmitter quanta are the synaptic vesicles that fuse with the surface membrane of the nerve terminal, to release their content of neurotransmitter molecules and other vesicular components. We subdivide the control of quantal release into two major classes: the processes that take place before the fusion of the synaptic vesicle with the surface membrane (the pre-fusion control) and the processes that occur after the fusion of the vesicle (the post-fusion control). The pre-fusion control is the main determinant of transmitter release. It is achieved by a wide variety of cellular components, among them the ion channels. There are reports of several hundred different ion channel molecules at the surface membrane of the nerve terminal, that for convenience can be grouped into eight major categories. They are the voltage-dependent calcium channels, the potassium channels, the calcium-gated potassium channels, the sodium channels, the chloride channels, the non-selective channels, the ligand gated channels and the stretch-activated channels. There are several categories of intracellular channels in the mitochondria, endoplasmic reticulum and the synaptic vesicles. We speculate that the vesicle channels may be of an importance in the post-fusion control of transmitter release. PMID:10212476

  6. Ion Channels and Signaling in the Pituitary Gland

    PubMed Central

    Stojilkovic, Stanko S.; Tabak, Joël; Bertram, Richard

    2010-01-01

    Endocrine pituitary cells are neuronlike; they express numerous voltage-gated sodium, calcium, potassium, and chloride channels and fire action potentials spontaneously, accompanied by a rise in intracellular calcium. In some cells, spontaneous electrical activity is sufficient to drive the intracellular calcium concentration above the threshold for stimulus-secretion and stimulus-transcription coupling. In others, the function of these action potentials is to maintain the cells in a responsive state with cytosolic calcium near, but below, the threshold level. Some pituitary cells also express gap junction channels, which could be used for intercellular Ca2+ signaling in these cells. Endocrine cells also express extracellular ligand-gated ion channels, and their activation by hypothalamic and intrapituitary hormones leads to amplification of the pacemaking activity and facilitation of calcium influx and hormone release. These cells also express numerous G protein-coupled receptors, which can stimulate or silence electrical activity and action potential-dependent calcium influx and hormone release. Other members of this receptor family can activate calcium channels in the endoplasmic reticulum, leading to a cell type-specific modulation of electrical activity. This review summarizes recent findings in this field and our current understanding of the complex relationship between voltage-gated ion channels, ligand-gated ion channels, gap junction channels, and G protein-coupled receptors in pituitary cells. PMID:20650859

  7. Na Channel β Subunits: Overachievers of the Ion Channel Family.

    PubMed

    Brackenbury, William J; Isom, Lori L

    2011-01-01

    Voltage-gated Na(+) channels (VGSCs) in mammals contain a pore-forming α subunit and one or more β subunits. There are five mammalian β subunits in total: β1, β1B, β2, β3, and β4, encoded by four genes: SCN1B-SCN4B. With the exception of the SCN1B splice variant, β1B, the β subunits are type I topology transmembrane proteins. In contrast, β1B lacks a transmembrane domain and is a secreted protein. A growing body of work shows that VGSC β subunits are multifunctional. While they do not form the ion channel pore, β subunits alter gating, voltage-dependence, and kinetics of VGSCα subunits and thus regulate cellular excitability in vivo. In addition to their roles in channel modulation, β subunits are members of the immunoglobulin superfamily of cell adhesion molecules and regulate cell adhesion and migration. β subunits are also substrates for sequential proteolytic cleavage by secretases. An example of the multifunctional nature of β subunits is β1, encoded by SCN1B, that plays a critical role in neuronal migration and pathfinding during brain development, and whose function is dependent on Na(+) current and γ-secretase activity. Functional deletion of SCN1B results in Dravet Syndrome, a severe and intractable pediatric epileptic encephalopathy. β subunits are emerging as key players in a wide variety of physiopathologies, including epilepsy, cardiac arrhythmia, multiple sclerosis, Huntington's disease, neuropsychiatric disorders, neuropathic and inflammatory pain, and cancer. β subunits mediate multiple signaling pathways on different timescales, regulating electrical excitability, adhesion, migration, pathfinding, and transcription. Importantly, some β subunit functions may operate independently of α subunits. Thus, β subunits perform critical roles during development and disease. As such, they may prove useful in disease diagnosis and therapy. PMID:22007171

  8. Hypoxia. 4. Hypoxia and ion channel function

    PubMed Central

    Polak, Jan

    2011-01-01

    The ability to sense and respond to oxygen deprivation is required for survival; thus, understanding the mechanisms by which changes in oxygen are linked to cell viability and function is of great importance. Ion channels play a critical role in regulating cell function in a wide variety of biological processes, including neuronal transmission, control of ventilation, cardiac contractility, and control of vasomotor tone. Since the 1988 discovery of oxygen-sensitive potassium channels in chemoreceptors, the effect of hypoxia on an assortment of ion channels has been studied in an array of cell types. In this review, we describe the effects of both acute and sustained hypoxia (continuous and intermittent) on mammalian ion channels in several tissues, the mode of action, and their contribution to diverse cellular processes. PMID:21178108

  9. CRACking ion channel targets: 2nd annual Ion Channel Targets Conference. 12-13 September 2006, Boston, MA, USA.

    PubMed

    Mathes, Chris

    2007-01-01

    The 2nd Annual Ion Channel Targets (ICT) Conference (by Select Bioscience LLC) was held in Boston on 12-13 September 2006. A healthy mixture of scientists from pharma, biotech and academic sectors attended the meeting. The speaker list reflected this mixture. In general, the conference focused on new ion channel targets and the methods for studying them in detail. Keynote lectures from Professors David Clapham (Harvard Medical School, USA) and Reinhold Penner (University of Hawaii, USA) set the tone by highlighting recent findings with a voltage-gated proton channel (Clapham), cation channel in sperm (Clapham) and the calcium-release-activated calcium channel (Penner). Also described at ICT were voltage-gated sodium, potassium, transmembrane-receptor-potential channels, as well as ligand-gated nicotinic acetylcholine (nAChR) and GABA type A receptors. PMID:17150038

  10. Acid-sensing ion channels interact with and inhibit BK K+ channels

    PubMed Central

    Petroff, Elena Yermolaieva; Price, Margaret P.; Snitsarev, Vladislav; Gong, Huiyu; Korovkina, Victoria; Abboud, Francois M.; Welsh, Michael J.

    2008-01-01

    Acid-sensing ion channels (ASICs) are neuronal non-voltage-gated cation channels that are activated when extracellular pH falls. They contribute to sensory function and nociception in the peripheral nervous system, and in the brain they contribute to synaptic plasticity and fear responses. Some of the physiologic consequences of disrupting ASIC genes in mice suggested that ASIC channels might modulate neuronal function by mechanisms in addition to their H+-evoked opening. Within ASIC channel's large extracellular domain, we identified sequence resembling that in scorpion toxins that inhibit K+ channels. Therefore, we tested the hypothesis that ASIC channels might inhibit K+ channel function by coexpressing ASIC1a and the high-conductance Ca2+- and voltage-activated K+ (BK) channel. We found that ASIC1a associated with BK channels and inhibited their current. Reducing extracellular pH disrupted the association and relieved the inhibition. BK channels, in turn, altered the kinetics of ASIC1a current. In addition to BK, ASIC1a inhibited voltage-gated Kv1.3 channels. Other ASIC channels also inhibited BK, although acidosis-dependent relief of inhibition varied. These results reveal a mechanism of ion channel interaction and reciprocal regulation. Finding that a reduced pH activated ASIC1a and relieved BK inhibition suggests that extracellular protons may enhance the activity of channels with opposing effects on membrane voltage. The wide and varied expression patterns of ASICs, BK, and related K+ channels suggest broad opportunities for this signaling system to alter neuronal function. PMID:18287010

  11. The Origins of Transmembrane Ion Channels

    NASA Technical Reports Server (NTRS)

    Pohorille, Andrew; Wilson, Michael A.

    2012-01-01

    Even though membrane proteins that mediate transport of ions and small molecules across cell walls are among the largest and least understood biopolymers in contemporary cells, it is still possible to shed light on their origins and early evolution. The central observation is that transmembrane portions of most ion channels are simply bundles of -helices. By combining results of experimental and computer simulation studies on synthetic models and natural channels, mostly of non-genomic origin, we show that the emergence of -helical channels was protobiologically plausible, and did not require highly specific amino acid sequences. Despite their simple structure, such channels could possess properties that, at the first sight, appear to require markedly larger complexity. Specifically, we explain how the antiamoebin channels, which are made of identical helices, 16 amino acids in length, achieve efficiency comparable to that of highly evolved channels. We further show that antiamoebin channels are extremely flexible, compared to modern, genetically coded channels. On the basis of our results, we propose that channels evolved further towards high structural complexity because they needed to acquire stable rigid structures and mechanisms for precise regulation rather than improve efficiency. In general, even though architectures of membrane proteins are not nearly as diverse as those of water-soluble proteins, they are sufficiently flexible to adapt readily to the functional demands arising during evolution.

  12. Carbon monoxide: an emerging regulator of ion channels

    PubMed Central

    Wilkinson, William J; Kemp, Paul J

    2011-01-01

    Abstract Carbon monoxide is rapidly emerging as an important cellular messenger, regulating a wide range of physiological processes. Crucial to its role in both physiology and disease is its ability differentially to regulate several classes of ion channels, including examples from calcium-activated K+ (BKCa), voltage-activated K+ (Kv) and Ca2+ channel (L-type) families, ligand-gated P2X receptors (P2X2 and P2X4), tandem P domain K+ channels (TREK1) and the epithelial Na+ channel (ENaC). The mechanisms by which CO regulates these ion channels are still unclear and remain somewhat controversial. However, available structure–function studies suggest that a limited range of amino acid residues confer CO sensitivity, either directly or indirectly, to particular ion channels and that cellular redox state appears to be important to the final integrated response. Whatever the molecular mechanism by which CO regulates ion channels, endogenous production of this gasotransmitter has physiologically important roles and is currently being explored as a potential therapeutic. PMID:21521759

  13. [Interaction of melittin with ion channels of excitable membranes].

    PubMed

    Zherelova, O M; Kabanova, N V; Kazachenko, V N; Chaĭlakhian, L M

    2007-01-01

    The effect of the neurotoxin melittin on the activation of ion channels of excitable membrane, the plasmalemma of Characeae algae cells, isolated membrane patches of neurons of mollusc L. stagnalis and Vero cells was studied by the method of intracellular perfusion and the patch-clamp technique in inside-out configuration. It was shown that melittin disturbs the conductivity of plasmalemma and modifieds Ca(2+)-channels of plant membrane. The leakage current that appears by the action of melittin can be restored by substituting calmodulin for melittin. Melittin modifies K(+)-channels of animal cell membrane by disrupting the phospholipid matrix and forms conductive structures in the membrane by interacting with channel proteins, which is evidenced by the appearance of additional ion channels. PMID:17477057

  14. Functional Insights from Glutamate Receptor Ion Channel Structures

    PubMed Central

    Kumar, Janesh; Mayer, Mark L.

    2014-01-01

    X-ray crystal structures for the soluble amino terminal and ligand binding domains of glutamate receptor ion channels, combined with a 3.6 Å resolution structure of the full length AMPA receptor GluA2 homotetramer, provide unique insights into the mechanisms of iGluR assembly and function. Increasingly sophisticated biochemical, computational and electrophysiological experiments are beginning to reveal the mechanism of action of partial agonists, and yield new models for the mechanism of action of allosteric modulators. Newly identified NMDA receptor ligands acting at novel sites offer hope for development of subtype selective modulators. Many issues remain unsolved, including the role of the ATD in AMPA receptor signaling, and the mechanisms by which auxiliary proteins regulate receptor activity. The structural basis for ion permeation and ion channel block also remain areas of uncertainty, and despite substantial progress, molecular dynamics simulations have yet to reveal how binding of glutamate opens the ion channel pore. PMID:22974439

  15. Mitochondrial Ion Channels in Cancer Transformation

    PubMed Central

    Madamba, Stephen M.; Damri, Kevin N.; Dejean, Laurent M.; Peixoto, Pablo M.

    2015-01-01

    Cancer transformation involves reprograming of mitochondrial function to avert cell death mechanisms, monopolize energy metabolism, accelerate mitotic proliferation, and promote metastasis. Mitochondrial ion channels have emerged as promising therapeutic targets because of their connection to metabolic and apoptotic functions. This mini review discusses how mitochondrial channels may be associated with cancer transformation and expands on the possible involvement of mitochondrial protein import complexes in pathophysiological process. PMID:26090338

  16. Thermally activated TRPV3 channels.

    PubMed

    Luo, Jialie; Hu, Hongzhen

    2014-01-01

    TRPV3 is a temperature-sensitive transient receptor potential (TRP) ion channel. The TRPV3 protein functions as a Ca(2+)-permeable nonselective cation channel with six transmembrane domains forming a tetrameric complex. TRPV3 is known to be activated by warm temperatures, synthetic small-molecule chemicals, and natural compounds from plants. Its function is regulated by a variety of physiological factors including extracellular divalent cations and acidic pH, intracellular adenosine triphosphate, membrane voltage, and arachidonic acid. TRPV3 shows a broad expression pattern in both neuronal and non-neuronal tissues including epidermal keratinocytes, epithelial cells in the gut, endothelial cells in blood vessels, and neurons in dorsal root ganglia and CNS. TRPV3 null mice exhibit abnormal hair morphogenesis and compromised skin barrier function. Recent advances suggest that TRPV3 may play critical roles in inflammatory skin disorders, itch, and pain sensation. Thus, identification of selective TRPV3 activators and inhibitors could potentially lead to beneficial pharmacological interventions in several diseases. The intent of this review is to summarize our current knowledge of the tissue expression, structure, function, and mechanisms of activation of TRPV3. PMID:25366242

  17. Electrical Heart Defibrillation with Ion Channel Blockers

    NASA Astrophysics Data System (ADS)

    Feeney, Erin; Clark, Courtney; Puwal, Steffan

    Heart disease is the leading cause of mortality in the United States. Rotary electrical waves within heart muscle underlie electrical disorders of the heart termed fibrillation; their propagation and breakup leads to a complex distribution of electrical activation of the tissue (and of the ensuing mechanical contraction that comes from electrical activation). Successful heart defibrillation has, thus far, been limited to delivering large electrical shocks to activate the entire heart and reset its electrical activity. In theory, defibrillation of a system this nonlinear should be possible with small electrical perturbations (stimulations). A successful algorithm for such a low-energy defibrillator continues to elude researchers. We propose to examine in silica whether low-energy electrical stimulations can be combined with antiarrhythmic, ion channel-blocking drugs to achieve a higher rate of defibrillation and whether the antiarrhythmic drugs should be delivered before or after electrical stimulation has commenced. Progress toward a more successful, low-energy defibrillator will greatly minimize the adverse effects noted in defibrillation and will assist in the development of pediatric defibrillators.

  18. The Earliest Ion Channels in Protocellular Membranes

    NASA Technical Reports Server (NTRS)

    Mijajlovic, Milan; Pohorille, Andrew; Wilson, Michael; Wei, Chenyu

    2010-01-01

    Cellular membranes with their hydrophobic interior are virtually impermeable to ions. Bulk of ion transport through them is enabled through ion channels. Ion channels of contemporary cells are complex protein molecules which span the membrane creating a cylindrical pore filled with water. Protocells, which are widely regarded as precursors to modern cells, had similarly impermeable membranes, but the set of proteins in their disposal was much simpler and more limited. We have been, therefore, exploring an idea that the first ion channels in protocellular membranes were formed by much smaller peptide molecules that could spontaneously selfassemble into short-lived cylindrical bundles in a membrane. Earlier studies have shown that a group of peptides known as peptaibols is capable of forming ion channels in lipid bilayers when they are exposed to an electric field. Peptaibols are small, non-genetically encoded peptides produced by some fungi as a part of their system of defense against bacteria. They are usually only 14-20 residues long, which is just enough to span the membrane. Their sequence is characterized by the presence of non-standard amino acids which, interestingly, are also expected to have existed on the early earth. In particular, the presence of 2-aminoisobutyric acid (AIB) gives peptaibols strong helix forming propensities. Association of the helices inside membranes leads to the formation of cylindrical bundles, typically containing 4 to 10 monomers. Although peptaibols are excellent candidates for models of the earliest ion channels their structures, which are stabilized only by van der Waals forces and occasional hydrogen bonds between neighboring helices, are not very stable. Although it might properly reflect protobiological reality, it is also a major obstacle in studying channel behavior. For this reason we focused on two members of the peptaibol family, trichotoxin and antiamoebin, which are characterized by a single conductance level. This

  19. The earliest ion channels in protocellular membranes

    NASA Astrophysics Data System (ADS)

    Mijajlovic, Milan; Pohorille, Andrew; Wilson, Michael; Wei, Chenyu

    Cellular membranes with their hydrophobic interior are virtually impermeable to ions. Bulk of ion transport through them is enabled through ion channels. Ion channels of contemporary cells are complex protein molecules which span the membrane creating a cylindrical pore filled with water. Protocells, which are widely regarded as precursors to modern cells, had similarly impermeable membranes, but the set of proteins in their disposal was much simpler and more limited. We have been, therefore, exploring an idea that the first ion channels in protocellular membranes were formed by much smaller peptide molecules that could spontaneously self-assemble into short-lived cylindrical bundles in a membrane. Earlier studies have shown that a group of peptides known as peptaibols is capable of forming ion channels in lipid bilayers when they are exposed to an electric field. Peptaibols are small, non-genetically encoded peptides produced by some fungi as a part of their system of defense against bacteria. They are usually only 14-20 residues long, which is just enough to span the membrane. Their sequence is characterized by the presence of non-standard amino acids which, interestingly, are also expected to have existed on the early earth. In particular, the presence of 2-aminoisobutyric acid (AIB) gives peptaibols strong helix forming propensities. Association of the helices inside membranes leads to the formation of cylindrical bundles, typically containing 4 to 10 monomers. Although peptaibols are excellent candidates for models of the earliest ion channels their struc-tures, which are stabilized only by van der Waals forces and occasional hydrogen bonds between neighboring helices, are not very stable. Although it might properly reflect protobiological real-ity, it is also a major obstacle in studying channel behavior. For this reason we focused on two members of the peptaibol family, trichotoxin and antiamoebin, which are characterized by a single conductance level. This

  20. Impact of mechanical stress on ion transport in native lung epithelium (Xenopus laevis): short-term activation of Na+, Cl (-) and K+ channels.

    PubMed

    Bogdan, Roman; Veith, Christine; Clauss, Wolfgang; Fronius, Martin

    2008-09-01

    Epithelia, in general, and the lung epithelium, in particular, are exposed to mechanical forces, but little is known about their impact on pulmonary ion transport. In our present study, we employed transepithelial ion transport measurements on Xenopus lung preparations using custom-built Ussing chambers. Tissues were exposed to mechanical stress by increasing the water column (5 cm) at one side of the tissues. Apical exposure to hydrostatic pressure significantly decreased the short circuit current (I (SC): 24 +/- 1%, n = 152), slightly decreased the transepithelial resistance (R (T): 7 +/- 2%, n = 152), but increased the apical membrane capacitance (C (M): 16 +/- 6%, n = 9). The pressure-induced effect was sensitive to Na+ (amiloride), Cl(-) (DIDS, NFA, NPPB) and K+ channel blockers (Ba2+), glibenclamide). Further on, it was accompanied by increased extracellular ATP levels. The results show that mechanical stress leads to an activation of Na+, Cl(-), and K+ conductances in a native pulmonary epithelium resulting in a net decrease of ion absorption. This could be of considerable interest, since an altered ion transport may contribute to pathophysiological conditions, e.g., the formation of pulmonary edema during artificial ventilation. PMID:18581136

  1. Oxidative Stress and Maxi Calcium-Activated Potassium (BK) Channels

    PubMed Central

    Hermann, Anton; Sitdikova, Guzel F.; Weiger, Thomas M.

    2015-01-01

    All cells contain ion channels in their outer (plasma) and inner (organelle) membranes. Ion channels, similar to other proteins, are targets of oxidative impact, which modulates ion fluxes across membranes. Subsequently, these ion currents affect electrical excitability, such as action potential discharge (in neurons, muscle, and receptor cells), alteration of the membrane resting potential, synaptic transmission, hormone secretion, muscle contraction or coordination of the cell cycle. In this chapter we summarize effects of oxidative stress and redox mechanisms on some ion channels, in particular on maxi calcium-activated potassium (BK) channels which play an outstanding role in a plethora of physiological and pathophysiological functions in almost all cells and tissues. We first elaborate on some general features of ion channel structure and function and then summarize effects of oxidative alterations of ion channels and their functional consequences. PMID:26287261

  2. The influence of lipids on voltage-gated ion channels

    PubMed Central

    Jiang, Qiu-Xing; Gonen, Tamir

    2012-01-01

    Voltage-gated ion channels are responsible for transmitting electrochemical signals in both excitable and non-excitable cells. Structural studies of voltage-gated potassium and sodium channels by X-ray crystallography have revealed atomic details on their voltage-sensor domains and pore domains, and were put in context of disparate mechanistic views on the voltage-driven conformational changes in these proteins. Functional investigation of voltage-gated channels in membranes, however, showcased a mechanism of lipid-dependent gating for voltage-gated channels, suggesting that the lipids play an indispensible and critical role in the proper gating of many of these channels. Structure determination of membrane-embedded voltage-gated ion channels appears to be the next frontier in fully addressing the mechanism by which the voltage sensor domains control channel opening. Currently electron crystallography is the only structural biology method in which a membrane protein of interest is crystallized within a complete lipid-bilayer mimicking the native environment of a biological membrane. At a sufficiently high resolution, an electron crystallographic structure could reveal lipids, the channel and their mutual interactions at the atomic level. Electron crystallography is therefore a promising avenue toward understanding how lipids modulate channel activation through close association with the voltage sensor domains. PMID:22483432

  3. Emergence of ion channel modal gating from independent subunit kinetics.

    PubMed

    Bicknell, Brendan A; Goodhill, Geoffrey J

    2016-09-01

    Many ion channels exhibit a slow stochastic switching between distinct modes of gating activity. This feature of channel behavior has pronounced implications for the dynamics of ionic currents and the signaling pathways that they regulate. A canonical example is the inositol 1,4,5-trisphosphate receptor (IP3R) channel, whose regulation of intracellular Ca(2+) concentration is essential for numerous cellular processes. However, the underlying biophysical mechanisms that give rise to modal gating in this and most other channels remain unknown. Although ion channels are composed of protein subunits, previous mathematical models of modal gating are coarse grained at the level of whole-channel states, limiting further dialogue between theory and experiment. Here we propose an origin for modal gating, by modeling the kinetics of ligand binding and conformational change in the IP3R at the subunit level. We find good agreement with experimental data over a wide range of ligand concentrations, accounting for equilibrium channel properties, transient responses to changing ligand conditions, and modal gating statistics. We show how this can be understood within a simple analytical framework and confirm our results with stochastic simulations. The model assumes that channel subunits are independent, demonstrating that cooperative binding or concerted conformational changes are not required for modal gating. Moreover, the model embodies a generally applicable principle: If a timescale separation exists in the kinetics of individual subunits, then modal gating can arise as an emergent property of channel behavior. PMID:27551100

  4. The transient receptor potential family of ion channels.

    PubMed

    Nilius, Bernd; Owsianik, Grzegorz

    2011-01-01

    The transient receptor potential (TRP) multigene superfamily encodes integral membrane proteins that function as ion channels. Members of this family are conserved in yeast, invertebrates and vertebrates. The TRP family is subdivided into seven subfamilies: TRPC (canonical), TRPV (vanilloid), TRPM (melastatin), TRPP (polycystin), TRPML (mucolipin), TRPA (ankyrin) and TRPN (NOMPC-like); the latter is found only in invertebrates and fish. TRP ion channels are widely expressed in many different tissues and cell types, where they are involved in diverse physiological processes, such as sensation of different stimuli or ion homeostasis. Most TRPs are non-selective cation channels, only few are highly Ca2+ selective, some are even permeable for highly hydrated Mg2+ ions. This channel family shows a variety of gating mechanisms, with modes of activation ranging from ligand binding, voltage and changes in temperature to covalent modifications of nucleophilic residues. Activated TRP channels cause depolarization of the cellular membrane, which in turn activates voltage-dependent ion channels, resulting in a change of intracellular Ca2+ concentration; they serve as gatekeeper for transcellular transport of several cations (such as Ca2+ and Mg2+), and are required for the function of intracellular organelles (such as endosomes and lysosomes). Because of their function as intracellular Ca2+ release channels, they have an important regulatory role in cellular organelles. Mutations in several TRP genes have been implicated in diverse pathological states, including neurodegenerative disorders, skeletal dysplasia, kidney disorders and pain, and ongoing research may help find new therapies for treatments of related diseases. PMID:21401968

  5. The transient receptor potential family of ion channels

    PubMed Central

    2011-01-01

    Summary The transient receptor potential (TRP) multigene superfamily encodes integral membrane proteins that function as ion channels. Members of this family are conserved in yeast, invertebrates and vertebrates. The TRP family is subdivided into seven subfamilies: TRPC (canonical), TRPV (vanilloid), TRPM (melastatin), TRPP (polycystin), TRPML (mucolipin), TRPA (ankyrin) and TRPN (NOMPC-like); the latter is found only in invertebrates and fish. TRP ion channels are widely expressed in many different tissues and cell types, where they are involved in diverse physiological processes, such as sensation of different stimuli or ion homeostasis. Most TRPs are non-selective cation channels, only few are highly Ca2+ selective, some are even permeable for highly hydrated Mg2+ ions. This channel family shows a variety of gating mechanisms, with modes of activation ranging from ligand binding, voltage and changes in temperature to covalent modifications of nucleophilic residues. Activated TRP channels cause depolarization of the cellular membrane, which in turn activates voltage-dependent ion channels, resulting in a change of intracellular Ca2+ concentration; they serve as gatekeeper for transcellular transport of several cations (such as Ca2+ and Mg2+), and are required for the function of intracellular organelles (such as endosomes and lysosomes). Because of their function as intracellular Ca2+ release channels, they have an important regulatory role in cellular organelles. Mutations in several TRP genes have been implicated in diverse pathological states, including neurodegenerative disorders, skeletal dysplasia, kidney disorders and pain, and ongoing research may help find new therapies for treatments of related diseases. PMID:21401968

  6. Mitochondrial ion channels as therapeutic targets

    PubMed Central

    Peixoto, Pablo M.; Ryu, Shin-Young; Kinnally, Kathleen W.

    2010-01-01

    The study of mitochondrial ion channels changed our perception of these double-wrapped organelles from being just the power house of a cell to the guardian of a cell's fate. Mitochondria communicate with the cell through these special channels. Most of the time, the message is encoded by ion flow across the mitochondrial outer and inner membranes. Potassium, sodium, calcium, protons, nucleotides, and proteins traverse the mitochondrial membranes in an exquisitely regulated manner to control a myriad of processes, from respiration and mitochondrial morphology to cell proliferation and cell death. This review is an update on both well established and putative mitochondrial channels regarding their composition, function, regulation, and therapeutic potential. PMID:20178788

  7. Targeting ion channels in cystic fibrosis.

    PubMed

    Mall, Marcus A; Galietta, Luis J V

    2015-09-01

    Mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene cause a characteristic defect in epithelial ion transport that plays a central role in the pathogenesis of cystic fibrosis (CF). Hence, pharmacological correction of this ion transport defect by targeting of mutant CFTR, or alternative ion channels that may compensate for CFTR dysfunction, has long been considered as an attractive approach to a causal therapy of this life-limiting disease. The recent introduction of the CFTR potentiator ivacaftor into the therapy of a subgroup of patients with specific CFTR mutations was a major milestone and enormous stimulus for seeking effective ion transport modulators for all patients with CF. In this review, we discuss recent breakthroughs and setbacks with CFTR modulators designed to rescue mutant CFTR including the common mutation F508del. Further, we examine the alternative chloride channels TMEM16A and SLC26A9, as well as the epithelial sodium channel ENaC as alternative targets in CF lung disease, which remains the major cause of morbidity and mortality in patients with CF. Finally, we will focus on the hurdles that still need to be overcome to make effective ion transport modulation therapies available for all patients with CF irrespective of their CFTR genotype. PMID:26115565

  8. Ion/water channels for embryo implantation barrier.

    PubMed

    Liu, Xin-Mei; Zhang, Dan; Wang, Ting-Ting; Sheng, Jian-Zhong; Huang, He-Feng

    2014-05-01

    Successful implantation involves three distinct processes, namely the embryo apposition, attachment, and penetration through the luminal epithelium of the endometrium to establish a vascular link to the mother. After penetration, stromal cells underlying the epithelium differentiate and surround the embryo to form the embryo implantation barrier, which blocks the passage of harmful substances to the embryo. Many ion/water channel proteins were found to be involved in the process of embryo implantation. First, ion/water channel proteins play their classical role in establishing a resting membrane potential, shaping action potentials and other electrical signals by gating the flow of ions across the cell membrane. Second, most of ion/water channel proteins are regulated by steroid hormone (estrogen or progesterone), which may have important implications to the embryo implantation. Last but not least, these proteins do not limit themselves as pure channels but also function as an initiator of a series of consequences once activated by their ligand/stimulator. Herein, we discuss these new insights in recent years about the contribution of ion/water channels to the embryo implantation barrier construction during early pregnancy. PMID:24789983

  9. Dysfunctional HCN ion channels in neurological diseases

    PubMed Central

    DiFrancesco, Jacopo C.; DiFrancesco, Dario

    2015-01-01

    Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels are expressed as four different isoforms (HCN1-4) in the heart and in the central and peripheral nervous systems. HCN channels are activated by membrane hyperpolarization at voltages close to resting membrane potentials and carry the hyperpolarization-activated current, dubbed If (funny current) in heart and Ih in neurons. HCN channels contribute in several ways to neuronal activity and are responsible for many important cellular functions, including cellular excitability, generation, and modulation of rhythmic activity, dendritic integration, transmission of synaptic potentials, and plasticity phenomena. Because of their role, defective HCN channels are natural candidates in the search for potential causes of neurological disorders in humans. Several data, including growing evidence that some forms of epilepsy are associated with HCN mutations, support the notion of an involvement of dysfunctional HCN channels in different experimental models of the disease. Additionally, some anti-epileptic drugs are known to modify the activity of the Ih current. HCN channels are widely expressed in the peripheral nervous system and recent evidence has highlighted the importance of the HCN2 isoform in the transmission of pain. HCN channels are also present in the midbrain system, where they finely regulate the activity of dopaminergic neurons, and a potential role of these channels in the pathogenesis of Parkinson’s disease has recently emerged. The function of HCN channels is regulated by specific accessory proteins, which control the correct expression and modulation of the neuronal Ih current. Alteration of these proteins can severely interfere with the physiological channel function, potentially predisposing to pathological conditions. In this review we address the present knowledge of the association between HCN dysfunctions and neurological diseases, including clinical, genetic, and physiopathological

  10. More Than a Pore: Ion Channel Signaling Complexes

    PubMed Central

    Fakler, Bernd; Kaczmarek, Leonard K.; Isom, Lori L.

    2014-01-01

    Voltage- and ligand-gated ion channels form the molecular basis of cellular excitability. With >400 members and accounting for ∼1.5% of the human genome, ion channels are some of the most well studied of all proteins in heterologous expression systems. Yet, ion channels often exhibit unexpected properties in vivo because of their interaction with a variety of signaling/scaffolding proteins. Such interactions can influence the function and localization of ion channels, as well as their coupling to intracellular second messengers and pathways, thus increasing the signaling potential of these ion channels in neurons. Moreover, functions have been ascribed to ion channels that are largely independent of their ion-conducting roles. Molecular and functional dissection of the ion channel proteome/interactome has yielded new insights into the composition of ion channel complexes and how their dysregulation leads to human disease. PMID:25392484

  11. A Method for Activation of Endogenous Acid-sensing Ion Channel 1a (ASIC1a) in the Nervous System with High Spatial and Temporal Precision

    PubMed Central

    Li, Tianbo; Yang, Youshan; Canessa, Cecilia M.

    2014-01-01

    Protons activate acid-sensing ion channel 1a (ASIC1a) in the central nervous system (CNS) although the impact of such activation on brain outputs remains elusive. Progress elucidating the functional roles of ASIC1a in the CNS has been hindered by technical difficulties of achieving acidification with spatial and temporal precision. We have implemented a method to control optically the opening of ASIC1a in brain slices and also in awake animals. The light-driven H+ pump ArchT was expressed in astrocytes of mouse cortex by injection of adenoviral vectors containing a strong and astrocyte-specific promoter. Illumination with amber light acidified the surrounding interstitium and led to activation of endogenous ASIC1a channels and firing of action potentials in neurons localized in close proximity to ArchT-expressing astrocytes. We conclude that this optogenetic method offers a minimally invasive approach that enables examining the biological consequences of ASIC1a currents in any structure of the CNS and in the modulation of animal behaviors. PMID:24727474

  12. Regulation of CFTR ion channel gating by MgATP.

    PubMed

    Aleksandrov, A A; Riordan, J R

    1998-07-10

    Single channel currents of wild-type CFTR reconstituted in lipid bilayers were recorded to study the temperature dependence of channel gating between +20 degrees C and +40 degrees C. The opening of the channel was highly temperature dependent and required an activation energy of about 100 kJ/mol. Closing of the channel was only weakly temperature dependent with an activation energy close to that of diffusion in water. We found no significant difference in the free energy between the open and closed states. Most of the excess energy needed to activate channel opening is used to diminish the entropy of the open state. This structural reorganization is initiated by ATP binding followed by interconversion to the open channel structure as the CFTR-ATP-Mg complex passes to the transition state for hydrolysis. The energy of the CFTR-ATP-Mg interaction in the transition state is responsible for the CFTR ion channel opening rather than the energy of ATP hydrolysis. Channel closing is a diffusion limited process and does not require additional ATP binding. PMID:9684873

  13. 3-Azatetracyclo[5.2.1.15,8.01,5]undecane derivatives: from wild-type inhibitors of the M2 ion channel of influenza A virus to derivatives with potent activity against the V27A mutant

    PubMed Central

    Rey-Carrizo, Matias; Torres, Eva; Ma, Chunlong; Barniol-Xicota, Marta; Wang, Jun; Wu, Yibing; Naesens, Lieve; DeGrado, William F.; Lamb, Robert A.; Pinto, Lawrence H.; Vázquez, Santiago

    2013-01-01

    We have synthesized and characterized a series of compounds containing the 3-azatetracyclo[5.2.1.15,8.01,5]undecane scaffold designed as analogs of amantadine, an inhibitor of the M2 proton channel of influenza A virus. Inhibition of the wild-type (wt) M2 channel and the amantadine-resistant A/M2-S31N and A/M2-V27A mutant ion channels were measured in Xenopus oocytes using two-electrode voltage clamp (TEV) assays. Most of the novel compounds inhibited the wt ion channel in the low micromolar range. Of note, several compounds inhibited the A/M2 V27A mutant ion channel, one of them with submicromolar IC50. None of the compounds was found to inhibit the S31N mutant ion channel. The antiviral activity of three novel dual wt and A/M2-V27A channels inhibitors was confirmed by influenza virus yield assays. PMID:24237039

  14. Regulation of heartbeat by G protein-coupled ion channels.

    PubMed

    Brown, A M

    1990-12-01

    The coupling of ion channels to receptors by G proteins is the subject of this American Physiological Society Walter B. Cannon Memorial "Physiology in Perspective" Lecture. This subject is particularly appropriate because it includes a molecular explanation of a homeostatic mechanism involving the autonomic nervous system and the latter subject preoccupied Dr. Cannon during most of his career. With the use of reconstitution methods, we and others have shown that heterotrimeric guanine nucleotide-binding (G) proteins couple receptors to ion channels by both membrane-delimited, direct pathways and cytoplasmic second messenger pathways. Furthermore, one set of receptors may be coupled to as many as three different sets of ion channels to form networks. Dual G protein pathways lead to the prediction of biphasic ion current responses in cell signaling, and this prediction was confirmed. In sinoatrial pacemaker cells, the pacemaking hyperpolarization-activated inward current (If) is directly regulated by the G proteins Gs and Go, and the two can act simultaneously. This could explain the classical observation that vagal inhibition of heart rate is greater during sympathetic stimulation. Because deactivation of the muscarinic response occurs much faster than the G protein alpha-subunit hydrolyzes guanosine 5'-triphosphate, we looked for accessory cellular factors. A surprising result was that the small monomeric ras G protein blocked the muscarinic pathway. The significance of this observation is unknown, but it appears that small and large G proteins may interact in ion channel signaling pathways. PMID:1701981

  15. Contribution of Automated Technologies to Ion Channel Drug Discovery.

    PubMed

    Picones, Arturo; Loza-Huerta, Arlet; Segura-Chama, Pedro; Lara-Figueroa, Cesar O

    2016-01-01

    Automated technologies are now resolving the historical relegation that ion channels have endured as targets for the new drug discovery and development global efforts. The richness and adequacy of functional assay methodologies, remarkably fluorescence-based detection of ions fluxes and patch-clamp electrophysiology recording of ionic currents, are now automated and increasingly employed for the analysis of ion channel activity. While the former is currently the most commonly applied, the latter is finally reaching the throughput capacity to be engaged in the primary screening of chemical libraries conformed by hundreds of thousands of compounds. The use of automated instrumentation for the study of ion channel functionality (and dysfunctionality), particularly in the search for novel pharmacological agents with therapeutic purposes, has now reached out beyond the industrial setting, its original natural enclave, and is making its way into a growing number of academic labs and core facilities. The present chapter reviews the increasing contributions accomplished by a variety of different key automated technologies which have revolutionized the strategies to approach the discovery and development of new drugs targeting ion channels. PMID:27038379

  16. Protein 4.1 and the control of ion channels.

    PubMed

    Baines, Anthony J; Bennett, Pauline M; Carter, Edward W; Terracciano, Cesare

    2009-01-01

    The classical function of 4.1R in red blood cells is to contribute to the mechanochemical properties of the membrane by promoting the interaction between spectrin and actin. More recently, it has been recognized that 4.1R is required for the stable cell surface accumulation of a number of erythrocyte membrane proteins. 4.1R is one member of the mammalian 4.1 family - the others being 4.1N, 4.1G and 4.1B - and is expressed in many cell types other than erythrocytes. Recently we have examined the phenotype of hearts from 4.1R knockout mice. Although they had a generally normal morphology, these hearts exhibited bradycardia, and prolongation of both action potentials and QT intervals. Electrophysiological analysis revealed anomalies in a range of ion channel activities. In addition, the immunoreactivity of voltage-gated Na(+) channel NaV1.5 was reduced, indicating a role for 4.1R in the cellular accumulation of this ion channel. 4.1 proteins also have roles in the accumulation of at least two other classes of ion channel. In epithelia, 4.1 interacts with the store-operated channel TRPC4. In neurons, the ligand-gated channels GluR1 and GluR4 require 4.1 proteins for cell surface accumulation. The spectrum of transmembrane proteins that bind to 4.1 proteins overlaps with that of ankyrin. A hypothesis to investigate in the future is that differential regulation of 4.1 and ankyrins (e.g. by PIP(2)) allows highly selective control of cell surface accumulation and transport activity of a specific range of ion channels. PMID:19272819

  17. Targeting Ion Channels: An Important Therapeutic Implication in Gastrointestinal Dysmotility in Patients With Spinal Cord Injury

    PubMed Central

    Radulovic, Miroslav; Anand, Preeti; Korsten, Mark A; Gong, Bing

    2015-01-01

    Gastrointestinal (GI) dysmotility is a severe, and common complication in patients with spinal cord injury (SCI). Current therapeutic methods using acetylcholine analogs or laxative agents have unwanted side effects, besides often fail to have desired effect. Various ion channels such as ATP-sensitive potassium (KATP) channel, calcium ions (Ca2+)-activated potassium ions (K+) channels, voltage-sensitive Ca2+ channels and chloride ion (Cl−) channels are abundantly expressed in GI tissues, and play an important role in regulating GI motility. The release of neurotransmitters from the enteric nerve terminal, innervating GI interstitial cells of Cajal (ICC), and smooth muscle cells (SMC), causes inactivation of K+ and Cl− channels, increasing Ca2+ influx into cytoplasm, resulting in membrane depolarization and smooth muscle contraction. Thus, agents directly regulating ion channels activity either in ICC or in SMC may affect GI peristalsis and would be potential therapeutic target for the treatment of GI dysmotility with SCI. PMID:26424038

  18. Oxidation of ion channels in the aging nervous system.

    PubMed

    Patel, Rahul; Sesti, Federico

    2016-05-15

    Ion channels are integral membrane proteins that allow passive diffusion of ions across membranes. In neurons and in other excitable cells, the harmonious coordination between the numerous types of ion channels shape and propagate electrical signals. Increased accumulation of reactive oxidative species (ROS), and subsequent oxidation of proteins, including ion channels, is a hallmark feature of aging and may contribute to cell failure as a result. In this review we discuss the effects of ROS on three major types of ion channels of the central nervous system, namely the potassium (K(+)), calcium (Ca(2+)) and sodium (Na(+)) channels. We examine two general mechanisms through which ROS affect ion channels: via direct oxidation of specific residues and via indirect interference of pathways that regulate the channels. The overall status of the present studies indicates that the interaction of ion channels with ROS is multimodal and pervasive in the central nervous system and likely constitutes a general mechanism of aging susceptibility. PMID:26947620

  19. Ion channels and apoptosis in cancer

    PubMed Central

    Bortner, Carl D.; Cidlowski, John A.

    2014-01-01

    Humans maintain a constant cell number throughout their lifespan. This equilibrium of cell number is accomplished when cell proliferation and cell death are kept balanced, achieving a steady-state cell number. Abnormalities in cell growth or cell death can lead to an overabundance of cells known as neoplasm or tumours. While the perception of cancer is often that of an uncontrollable rate of cell growth or increased proliferation, a decrease in cell death can also lead to tumour formation. Most cells when detached from their normal tissue die. However, cancer cells evade cell death, tipping the balance to an overabundance of cell number. Therefore, overcoming this resistance to cell death is a decisive factor in the treatment of cancer. Ion channels play a critical role in cancer in regards to cell proliferation, malignant angiogenesis, migration and metastasis. Additionally, ion channels are also known to be critical components of apoptosis. In this review, we discuss the modes of cell death focusing on the ability of cancer cells to evade apoptosis. Specifically, we focus on the role ion channels play in controlling and regulating life/death decisions and how they can be used to overcome resistance to apoptosis in the treatment of cancer. PMID:24493752

  20. Insight toward epithelial Na+ channel mechanism revealed by the acid-sensing ion channel 1 structure.

    PubMed

    Stockand, James D; Staruschenko, Alexander; Pochynyuk, Oleh; Booth, Rachell E; Silverthorn, Dee U

    2008-09-01

    The epithelial Na(+) channel/degenerin (ENaC/DEG) protein family includes a diverse group of ion channels, including nonvoltage-gated Na(+) channels of epithelia and neurons, and the acid-sensing ion channel 1 (ASIC1). In mammalian epithelia, ENaC helps regulate Na(+) and associated water transport, making it a critical determinant of systemic blood pressure and pulmonary mucosal fluidity. In the nervous system, ENaC/DEG proteins are related to sensory transduction. While the importance and physiological function of these ion channels are established, less is known about their structure. One hallmark of the ENaC/DEG channel family is that each channel subunit has only two transmembrane domains connected by an exceedingly large extracellular loop. This subunit structure was recently confirmed when Jasti and colleagues determined the crystal structure of chicken ASIC1, a neuronal acid-sensing ENaC/DEG channel. By mapping ENaC to the structural coordinates of cASIC1, as we do here, we hope to provide insight toward ENaC structure. ENaC, like ASIC1, appears to be a trimeric channel containing 1alpha, 1beta, and 1gamma subunit. Heterotrimeric ENaC and monomeric ENaC subunits within the trimer possibly contain many of the major secondary, tertiary, and quaternary features identified in cASIC1 with a few subtle but critical differences. These differences are expected to have profound effects on channel behavior. In particular, they may contribute to ENaC insensitivity to acid and to its constitutive activity in the absence of time- and ligand-dependent inactivation. Experiments resulting from this comparison of cASIC1 and ENaC may help clarify unresolved issues related to ENaC architecture, and may help identify secondary structures and residues critical to ENaC function. PMID:18459164

  1. A single-cell correlative nanoelectromechanosensing approach to detect cancerous transformation: monitoring the function of F-actin microfilaments in the modulation of the ion channel activity

    NASA Astrophysics Data System (ADS)

    AbdolahadThe Authors With Same Contributions., Mohammad; Saeidi, Ali; Janmaleki, Mohsen; Mashinchian, Omid; Taghinejad, Mohammad; Taghinejad, Hossein; Azimi, Soheil; Mahmoudi, Morteza; Mohajerzadeh, Shams

    2015-01-01

    Cancerous transformation may be dependent on correlation between electrical disruptions in the cell membrane and mechanical disruptions of cytoskeleton structures. Silicon nanotube (SiNT)-based electrical probes, as ultra-accurate signal recorders with subcellular resolution, may create many opportunities for fundamental biological research and biomedical applications. Here, we used this technology to electrically monitor cellular mechanosensing. The SiNT probe was combined with an electrically activated glass micropipette aspiration system to achieve a new cancer diagnostic technique that is based on real-time correlation between mechanical and electrical behaviour of single cells. Our studies demonstrated marked changes in the electrical response following increases in the mechanical aspiration force in healthy cells. In contrast, such responses were extremely weak for malignant cells. Confocal microscopy results showed the impact of actin microfilament remodelling on the reduction of the electrical response for aspirated cancer cells due to the significant role of actin in modulating the ion channel activity in the cell membrane.Cancerous transformation may be dependent on correlation between electrical disruptions in the cell membrane and mechanical disruptions of cytoskeleton structures. Silicon nanotube (SiNT)-based electrical probes, as ultra-accurate signal recorders with subcellular resolution, may create many opportunities for fundamental biological research and biomedical applications. Here, we used this technology to electrically monitor cellular mechanosensing. The SiNT probe was combined with an electrically activated glass micropipette aspiration system to achieve a new cancer diagnostic technique that is based on real-time correlation between mechanical and electrical behaviour of single cells. Our studies demonstrated marked changes in the electrical response following increases in the mechanical aspiration force in healthy cells. In contrast, such

  2. A gating mechanism of pentameric ligand-gated ion channels

    PubMed Central

    Calimet, Nicolas; Simoes, Manuel; Changeux, Jean-Pierre; Karplus, Martin; Taly, Antoine; Cecchini, Marco

    2013-01-01

    Pentameric ligand-gated ion channels (pLGICs) play a central role in intercellular communication in the nervous system and are involved in fundamental processes such as attention, learning, and memory. They are oligomeric protein assemblies that convert a chemical signal into an ion flux through the postsynaptic membrane, but the molecular mechanism of gating ions has remained elusive. Here, we present atomistic molecular dynamics simulations of the prokaryotic channels from Gloeobacter violaceus (GLIC) and Erwinia chrysanthemi (ELIC), whose crystal structures are thought to represent the active and the resting states of pLGICs, respectively, and of the eukaryotic glutamate-gated chloride channel from Caenorhabditis elegans (GluCl), whose open-channel structure was determined complexed with the positive allosteric modulator ivermectin. Structural observables extracted from the trajectories of GLIC and ELIC are used as progress variables to analyze the time evolution of GluCl, which was simulated in the absence of ivermectin starting from the structure with bound ivermectin. The trajectory of GluCl with ivermectin removed shows a sequence of structural events that couple agonist unbinding from the extracellular domain to ion-pore closing in the transmembrane domain. Based on these results, we propose a structural mechanism for the allosteric communication leading to deactivation/activation of the GluCl channel. This model of gating emphasizes the coupling between the quaternary twisting and the opening/closing of the ion pore and is likely to apply to other members of the pLGIC family. PMID:24043807

  3. Ion channel networks in the control of cerebral blood flow.

    PubMed

    Longden, Thomas A; Hill-Eubanks, David C; Nelson, Mark T

    2016-03-01

    One hundred and twenty five years ago, Roy and Sherrington made the seminal observation that neuronal stimulation evokes an increase in cerebral blood flow.(1) Since this discovery, researchers have attempted to uncover how the cells of the neurovascular unit-neurons, astrocytes, vascular smooth muscle cells, vascular endothelial cells and pericytes-coordinate their activity to control this phenomenon. Recent work has revealed that ionic fluxes through a diverse array of ion channel species allow the cells of the neurovascular unit to engage in multicellular signaling processes that dictate local hemodynamics.In this review we center our discussion on two major themes: (1) the roles of ion channels in the dynamic modulation of parenchymal arteriole smooth muscle membrane potential, which is central to the control of arteriolar diameter and therefore must be harnessed to permit changes in downstream cerebral blood flow, and (2) the striking similarities in the ion channel complements employed in astrocytic endfeet and endothelial cells, enabling dual control of smooth muscle from either side of the blood-brain barrier. We conclude with a discussion of the emerging roles of pericyte and capillary endothelial cell ion channels in neurovascular coupling, which will provide fertile ground for future breakthroughs in the field. PMID:26661232

  4. Ankyrin-based Cellular Pathways for Cardiac Ion Channel and Transporter Targeting and Regulation

    PubMed Central

    Cunha, Shane R.; Mohler, Peter J.

    2010-01-01

    The coordinate activities of ion channels and transporters regulate myocyte membrane excitability and normal cardiac function. Dysfunction in cardiac ion channel and transporter function may result in cardiac arrhythmias and sudden cardiac death. While the past fifteen years have linked defects in ion channel biophysical properties with human disease, more recent findings illustrate that ion channel and transporter localization within cardiomyocytes is equally critical for normal membrane excitability and tissue function. Ankyrins are a family of multifunctional adapter proteins required for the expression, membrane localization, and regulation of select cardiac ion channels and transporters. Notably, loss of ankyrin expression in mice, and ankyrin loss-of-function in humans is now associated with defects in myocyte excitability and cardiac physiology. Here, we provide an overview of the roles of ankyrin polypeptides in cardiac physiology, as well as review other recently identified pathways required for the membrane expression and regulation of key cardiac ion channels and transporters. PMID:20934528

  5. The CFTR ion channel: gating, regulation, and anion permeation.

    PubMed

    Hwang, Tzyh-Chang; Kirk, Kevin L

    2013-01-01

    Cystic fibrosis transmembrane conductance regulator (CFTR) is an ATP-gated anion channel with two remarkable distinctions. First, it is the only ATP-binding cassette (ABC) transporter that is known to be an ion channel--almost all others function as transport ATPases. Second, CFTR is the only ligand-gated channel that consumes its ligand (ATP) during the gating cycle--a consequence of its enzymatic activity as an ABC transporter. We discuss these special properties of CFTR in the context of its evolutionary history as an ABC transporter. Other topics include the mechanisms by which CFTR gating is regulated by phosphorylation of its unique regulatory domain and our current view of the CFTR permeation pathway (or pore). Understanding these basic operating principles of the CFTR channel is central to defining the mechanisms of action of prospective cystic fibrosis drugs and to the development of new, rational treatment strategies. PMID:23284076

  6. Flipping the Photoswitch: Ion Channels Under Light Control.

    PubMed

    McKenzie, Catherine K; Sanchez-Romero, Inmaculada; Janovjak, Harald

    2015-01-01

    Nature has incorporated small photochromic molecules, colloquially termed 'photoswitches', in photoreceptor proteins to sense optical cues in phototaxis and vision. While Nature's ability to employ light-responsive functionalities has long been recognized, it was not until recently that scientists designed, synthesized and applied synthetic photochromes to manipulate many of which open rapidly and locally in their native cell types, biological processes with the temporal and spatial resolution of light. Ion channels in particular have come to the forefront of proteins that can be put under the designer control of synthetic photochromes. Photochromic ion channel controllers are comprised of three classes, photochromic soluble ligands (PCLs), photochromic tethered ligands (PTLs) and photochromic crosslinkers (PXs), and in each class ion channel functionality is controlled through reversible changes in photochrome structure. By acting as light-dependent ion channel agonists, antagonist or modulators, photochromic controllers effectively converted a wide range of ion channels, including voltage-gated ion channels, 'leak channels', tri-, tetra- and pentameric ligand-gated ion channels, and temperature-sensitive ion channels, into man-made photoreceptors. Control by photochromes can be reversible, unlike in the case of 'caged' compounds, and non-invasive with high spatial precision, unlike pharmacology and electrical manipulation. Here, we introduce design principles of emerging photochromic molecules that act on ion channels and discuss the impact that these molecules are beginning to have on ion channel biophysics and neuronal physiology. PMID:26381942

  7. Gated Ion Channel-Based Biosensor Device

    NASA Astrophysics Data System (ADS)

    Separovic, Frances; Cornell, Bruce A.

    A biosensor device based on the ion channel gramicidin A (gA) incorporated into a bilayer membrane is described. This generic immunosensing device utilizes gA coupled to an antibody and assembled in a lipid membrane. The membrane is chemically tethered to a gold electrode, which reports on changes in the ionic conduction of the lipid bilayer. Binding of a target molecule in the bathing solution to the antibody causes the gramicidin channels to switch from predominantly conducting dimers to predominantly nonconducting monomers. Conventional a.c. impedance spectroscopy between the gold and a counter electrode in the bathing solution is used to measure changes in the ionic conductivity of the membrane. This approach permits the quantitative detection of a range of target species, including bacteria, proteins, toxins, DNA sequences, and drug molecules.

  8. High temperature ion channels and pores

    NASA Technical Reports Server (NTRS)

    Kang, Xiaofeng (Inventor); Gu, Li Qun (Inventor); Cheley, Stephen (Inventor); Bayley, Hagan (Inventor)

    2011-01-01

    The present invention includes an apparatus, system and method for stochastic sensing of an analyte to a protein pore. The protein pore may be an engineer protein pore, such as an ion channel at temperatures above 55.degree. C. and even as high as near 100.degree. C. The analyte may be any reactive analyte, including chemical weapons, environmental toxins and pharmaceuticals. The analyte covalently bonds to the sensor element to produce a detectable electrical current signal. Possible signals include change in electrical current. Detection of the signal allows identification of the analyte and determination of its concentration in a sample solution. Multiple analytes present in the same solution may also be detected.

  9. Crystal structure of a heterotetrameric NMDA receptor ion channel

    PubMed Central

    Karakas, Erkan; Furukawa, Hiro

    2014-01-01

    N -methyl-D-aspartate (NMDA) receptors belong to the family of ionotropic glutamate receptors, which mediate most excitatory synaptic transmission in mammalian brains. Calcium permeation triggered by activation of NMDA receptors is the pivotal event for initiation of neuronal plasticity. Here we show the crystal structure of the intact heterotetrameric GluN1/GluN2B NMDA receptor ion channel at 4 Å. The NMDA receptors are arranged as a dimer of GluN1-GluN2B heterodimers with the two-fold symmetry axis running through the entire molecule composed of an amino terminal domain (ATD), a ligand-binding domain (LBD), and a transmembrane domain (TMD). The ATD and LBD are much more highly packed in the NMDA receptors than non-NMDA receptors, which may explain why ATD regulates ion channel activity in NMDA receptors but not in non-NMDA receptors. PMID:24876489

  10. Single-Molecule Ion Channel Conformational Dynamics in Living Cells

    NASA Astrophysics Data System (ADS)

    Lu, H. Peter

    2014-03-01

    Stochastic and inhomogeneous conformational changes regulate the function and dynamics of ion channels that are crucial for cell functions, neuronal signaling, and brain functions. Such complexity makes it difficult, if not impossible, to characterize ion channel dynamics using conventional electrical recording alone since that the measurement does not specifically interrogate the associated conformational changes but rather the consequences of the conformational changes. Recently, new technology developments on single-molecule spectroscopy, and especially, the combined approaches of using single ion channel patch-clamp electrical recording and single-molecule fluorescence imaging have provided us the capability of probing ion channel conformational changes simultaneously with the electrical single channel recording. By combining real-time single-molecule fluorescence imaging measurements with real-time single-channel electric current measurements in artificial lipid bilayers and in living cell membranes, we were able to probe single ion-channel-protein conformational changes simultaneously, and thus providing an understanding the dynamics and mechanism of ion-channel proteins at the molecular level. The function-regulating and site-specific conformational changes of ion channels are now measurable under physiological conditions in real-time, one molecule at a time. We will focus our discussion on the new development and results of real-time imaging of the dynamics of gramicidin, colicin, and NMDA receptor ion channels in lipid bilayers and living cells. Our results shed light on new perspectives of the intrinsic interplay of lipid membrane dynamics, solvation dynamics, and the ion channel functions.

  11. Theory of the ion-channel laser

    SciTech Connect

    Whittum, D.H.

    1990-09-01

    A relativistic electron beam propagating through a plasma in the ion-focussed regime exhibits an electromagnetic instability with peak growth rate near a resonant frequency {omega}{approximately}2 {gamma}{sup 2} {omega}{beta}, where {gamma} is the Lorentz factor and {omega}{beta} is the betatron frequency. The physical basis for this instability is that an ensemble of relativistic simple harmonic oscillators, weakly driven by an electromagnetic wave, will lose energy to the wave through axial bunching. This bunching'' corresponds to the development of an rf component in the beam current, and a coherent centroid oscillation. The subject of this thesis is the theory of a laser capitalizing on this electromagnetic instability. A historical perspective is offered. The basic features of relativistic electron beam propagation in the ion-focussed regime are reviewed. The ion-channel laser (ICL) instability is explored theoretically through an eikonal formalism, analgous to the KMR'' formalism for the free-electron laser (FEL). The dispersion relation is derived, and the dependence of growth rate on three key parameters is explored. Finite temperature effects are assessed. From this work it is found that the typical gain length for amplification is longer than the Rayleigh length and we go on to consider three mechanisms which will tend to guide waveguide. First, we consider the effect of the ion channel as a dielectric waveguide. We consider next the use of a conducting waveguide, appropriate for a microwave amplifier. Finally, we examine a form of optical guiding'' analgous to that found in the FEL. The eikonal formalism is used to model numerically the instability through and beyond saturation. Results are compared with the numerical simulation of the full equations of motion, and with the analytic scalings. The analytical requirement on detuning spread is confirmed.

  12. Peptides inhibitors of acid-sensing ion channels.

    PubMed

    Diochot, S; Salinas, M; Baron, A; Escoubas, P; Lazdunski, M

    2007-02-01

    Acid-sensing ion channels (ASICs) channels are proton-gated cationic channels mainly expressed in central and peripheric nervous system and related to the epithelial amiloride-sensitive Na(+) channels and to the degenerin family of ion channels. ASICs comprise four proteins forming functional channel subunits (ASIC1a, ASIC1b, ASIC2a, and ASIC3) and two proteins (ASIC2b and ASIC4) without yet known activators. Functional channels are activated by external pH variations ranging from pH(0.5) 6.8 to 4.0 and currents are characterized by either rapid kinetics of inactivation (ASIC1a, ASIC1b, ASIC3) or slow kinetics of inactivation (ASIC2a) and sometimes the presence of a plateau phase (ASIC3). ASIC1a and ASIC3, which are expressed in nociceptive neurons, have been implicated in inflammation and knockout mice studies support the role of ASIC3 in various pain processes. ASIC1a seems more related to synaptic plasticity, memory, learning and fear conditioning in the CNS. ASIC2a contributes to hearing in the cochlea, sour taste sensation, and visual transduction in the retina. The pharmacology of ASICs is limited to rather nonselective drugs such as amiloride, nonsteroid anti-inflammatory drugs, and neuropeptides. Recently, two peptides, PcTx1 and APETx2, isolated from a spider and a sea anemone, have been characterized as selective and high-affinity inhibitors for ASIC1a and ASIC3 channels, respectively. PcTx1 inhibits ASIC1a homomers with an affinity of 0.7 nM (IC(50)) without any effect on ASIC1a containing heteromers and thus helped to characterize ASIC1a homomeric channels in peripheric and central neurons. PcTx1 acts as a gating modifier since it shifts the channel from the resting to an inactivated state by increasing its affinity for H(+). APETx2 is less selective since it inhibits several ASIC3-containing channels (IC(50) from 63 nM to 2 microM) and to date its mode of action is unknown. Nevertheless, APETx2 structure is related to other sea anemone peptides, which

  13. Ion channels in mesenchymal stem cells from rat bone marrow.

    PubMed

    Li, Gui-Rong; Deng, Xiu-Ling; Sun, Haiying; Chung, Stephen S M; Tse, Hung-Fat; Lau, Chu-Pak

    2006-06-01

    Mesenchymal stem cells (MSCs) from bone marrow are believed to be an ideal cell source for cardiomyoplasty; however, cellular electrophysiology is not understood. The present study was designed to investigate ion channels in undifferentiated rat MSCs. It was found that three types of outward currents were present in rat MSCs, including a small portion of Ca(2+)-activated K(+) channel (I(KCa)) sensitive to inhibition by iberiotoxin and/or clotromazole, a delayed rectifier K(+) current (IK(DR)), and a transient outward K(+) current (I(to)). In addition, tetrodotoxin (TTX)-sensitive sodium current (I(Na.TTX)) and nifedipine-sensitive L-type Ca(2+) current (I(Ca.L)) were found in a small population of rat MSCs. Moreover, reverse transcription-polymerase chain reaction revealed the molecular evidence of mRNA for the functional ionic currents, including Slo and KCNN4 for I(KCa); Kv1.4 for I(to); Kv1.2 and Kv2.1 for IK(DR); SCN2a1 for I(Na.TTX); and CCHL2a for I(Ca.L). These results demonstrate for the first time that multiple functional ion channel currents (i.e., I(KCa), I(to), IK(DR), I(Na.TTX), and I(Ca.L)) are present in rat MSCs from bone marrow; however, physiological roles of these ion channels remain to be studied. PMID:16484345

  14. Acid-sensing ion channels and transient-receptor potential ion channels in zebrafish taste buds.

    PubMed

    Levanti, M; Randazzo, B; Viña, E; Montalbano, G; Garcia-Suarez, O; Germanà, A; Vega, J A; Abbate, F

    2016-09-01

    Sensory information from the environment is required for life and survival, and it is detected by specialized cells which together make up the sensory system. The fish sensory system includes specialized organs that are able to detect mechanical and chemical stimuli. In particular, taste buds are small organs located on the tongue in terrestrial vertebrates that function in the perception of taste. In fish, taste buds occur on the lips, the flanks, and the caudal (tail) fins of some species and on the barbels of others. In fish taste receptor cells, different classes of ion channels have been detected which, like in mammals, presumably participate in the detection and/or transduction of chemical gustatory signals. However, since some of these ion channels are involved in the detection of additional sensory modalities, it can be hypothesized that taste cells sense stimuli other than those specific for taste. This mini-review summarizes current knowledge on the presence of transient-receptor potential (TRP) and acid-sensing (ASIC) ion channels in the taste buds of teleosts, especially adult zebrafish. Up to now ASIC4, TRPC2, TRPA1, TRPV1 and TRPV4 ion channels have been found in the sensory cells, while ASIC2 was detected in the nerves supplying the taste buds. PMID:27513962

  15. Ion channels modulating mouse dendritic cell functions.

    PubMed

    Matzner, Nicole; Zemtsova, Irina M; Nguyen, Thi Xuan; Duszenko, Michael; Shumilina, Ekaterina; Lang, Florian

    2008-11-15

    Ca(2+)-mediated signal transduction pathways play a central regulatory role in dendritic cell (DC) responses to diverse Ags. However, the mechanisms leading to increased [Ca(2+)](i) upon DC activation remained ill-defined. In the present study, LPS treatment (100 ng/ml) of mouse DCs resulted in a rapid increase in [Ca(2+)](i), which was due to Ca(2+) release from intracellular stores and influx of extracellular Ca(2+) across the cell membrane. In whole-cell voltage-clamp experiments, LPS-induced currents exhibited properties similar to the currents through the Ca(2+) release-activated Ca(2+) channels (CRAC). These currents were highly selective for Ca(2+), exhibited a prominent inward rectification of the current-voltage relationship, and showed an anomalous mole fraction and a fast Ca(2+)-dependent inactivation. In addition, the LPS-induced increase of [Ca(2+)](i) was sensitive to margatoxin and ICAGEN-4, both inhibitors of voltage-gated K(+) (Kv) channels Kv1.3 and Kv1.5, respectively. MHC class II expression, CCL21-dependent migration, and TNF-alpha and IL-6 production decreased, whereas phagocytic capacity increased in LPS-stimulated DCs in the presence of both Kv channel inhibitors as well as the I(CRAC) inhibitor SKF-96365. Taken together, our results demonstrate that Ca(2+) influx in LPS-stimulated DCs occurs via Ca(2+) release-activated Ca(2+) channels, is sensitive to Kv channel activity, and is in turn critically important for DC maturation and functions. PMID:18981098

  16. Principles Governing Metal Ion Selectivity in Ion Channel Proteins

    NASA Astrophysics Data System (ADS)

    Lim, Carmay

    2014-03-01

    Our research interests are to (i) unravel the principles governing biological processes and use them to identify novel drug targets and guide drug design, and (ii) develop new methods for studying macromolecular interactions. This talk will provide an overview of our work in these two areas and an example of how our studies have helped to unravel the principles underlying the conversion of Ca2+-selective to Na+-selective channels. Ion selectivity of four-domain voltage-gated Ca2+(Cav) and sodium (Nav) channels, which is controlled by the selectivity filter (SF, the narrowest region of an open pore), is crucial for electrical signaling. Over billions of years of evolution, mutation of the Glu from domain II/III in the EEEE/DEEA SF of Ca2+-selective Cav channels to Lys made these channels Na+-selective. This talk will delineate the physical principles why Lys is sufficient for Na+/Ca2+selectivity and why the DEKA SF is more Na+-selective than the DKEA one.

  17. [Acid-Sensing Ion Channels (ASICs) in pain].

    PubMed

    Lingueglia, Eric

    2014-01-01

    The discovery of new drug targets represents a real opportunity for developing fresh strategies against pain. Ion channels are interesting targets because they are directly involved in the detection and the transmission of noxious stimuli by sensory fibres of the peripheral nervous system and by neurons of the spinal cord. Acid-Sensing Ion Channels (ASICs) have emerged as important players in the pain pathway. They are neuronal, voltage-independent depolarizing sodium channels activated by extracellular protons. The ASIC family comprises several subunits that need to associate into homo- or hetero-trimers to form a functional channel. The ASIC1 and ASIC3 isoforms are particularly important in sensory neurons, whereas ASIC1a, alone or in association with ASIC2, is essential in the central nervous system. The potent analgesic effects associated with their inhibition in animals (which can be comparable to those of morphine) and data suggesting a role in human pain illustrate the therapeutic potential of these channels. PMID:24948015

  18. Ion channel recordings on an injection-molded polymer chip.

    PubMed

    Tanzi, Simone; Matteucci, Marco; Christiansen, Thomas Lehrmann; Friis, Søren; Christensen, Mette Thylstrup; Garnaes, Joergen; Wilson, Sandra; Kutchinsky, Jonatan; Taboryski, Rafael

    2013-12-21

    In this paper, we demonstrate recordings of the ion channel activity across the cell membrane in a biological cell by employing the so-called patch clamping technique on an injection-molded polymer microfluidic device. The findings will allow direct recordings of ion channel activity to be made using the cheapest materials and production platform to date and with the potential for very high throughput. The employment of cornered apertures for cell capture allowed the fabrication of devices without through holes and via a scheme comprising master origination by dry etching in a silicon substrate, electroplating in nickel and injection molding of the final part. The most critical device parameters were identified as the length of the patching capillary and the very low surface roughness on the inside of the capillary. The cross-sectional shape of the orifice was found to be less critical, as both rectangular and semicircular profiles seemed to have almost the same ability to form tight seals with cells with negligible leak currents. The devices were functionally tested using human embryonic kidney cells expressing voltage-gated sodium channels (Nav1.7) and benchmarked against a commercial state-of-the-art system for automated ion channel recordings. These experiments considered current-voltage (IV) relationships for activation and inactivation of the Nav1.7 channels and their sensitivity to a local anesthetic, lidocaine. Both IVs and lidocaine dose-response curves obtained from the injection-molded polymer device were in good agreement with data obtained from the commercial system. PMID:24154831

  19. Ion channel genes and human neurological disease: Recent progress, prospects, and challenges

    PubMed Central

    Cooper, Edward C.; Jan, Lily Yeh

    1999-01-01

    What do epilepsy, migraine headache, deafness, episodic ataxia, periodic paralysis, malignant hyperthermia, and generalized myotonia have in common? These human neurological disorders can be caused by mutations in genes for ion channels. Many of the channel diseases are “paroxysmal disorders” whose principal symptoms occur intermittently in individuals who otherwise may be healthy and active. Some of the ion channels that cause human neurological disease are old acquaintances previously cloned and extensively studied by channel specialists. In other cases, however, disease-gene hunts have led the way to the identification of new channel genes. Progress in the study of ion channels has made it possible to analyze the effects of human neurological disease-causing channel mutations at the level of the single channel, the subcellular domain, the neuronal network, and the behaving organism. PMID:10220366

  20. The effect of hyperpolarization-activated cyclic nucleotide-gated ion channel inhibitors on the vagal control of guinea pig airway smooth muscle tone

    PubMed Central

    McGovern, Alice E; Robusto, Jed; Rakoczy, Joanna; Simmons, David G; Phipps, Simon; Mazzone, Stuart B

    2014-01-01

    BACKGROUND AND PURPOSE Subtypes of the hyperpolarization-activated cyclic nucleotide-gated (HCN) family of cation channels are widely expressed on nerves and smooth muscle cells in many organ systems, where they serve to regulate membrane excitability. Here we have assessed whether HCN channel inhibitors alter the function of airway smooth muscle or the neurons that regulate airway smooth muscle tone. EXPERIMENTAL APPROACH The effects of the HCN channel inhibitors ZD7288, zatebradine and Cs+ were assessed on agonist and nerve stimulation-evoked changes in guinea pig airway smooth muscle tone using tracheal strips in vitro, an innervated tracheal tube preparation ex vivo or in anaesthetized mechanically ventilated guinea pigs in vivo. HCN channel expression in airway nerves was assessed using immunohistochemistry, PCR and in situ hybridization. KEY RESULTS HCN channel inhibition did not alter airway smooth muscle reactivity in vitro to exogenously administered smooth muscle spasmogens, but significantly potentiated smooth muscle contraction evoked by the sensory nerve stimulant capsaicin and electrical field stimulation of parasympathetic cholinergic postganglionic neurons. Sensory nerve hyperresponsiveness was also evident in in vivo following HCN channel blockade. Cs+, but not ZD7288, potentiated preganglionic nerve-dependent airway contractions and over time induced autorhythmic preganglionic nerve activity, which was not mimicked by inhibitors of potassium channels. HCN channel expression was most evident in vagal sensory ganglia and airway nerve fibres. CONCLUSIONS AND IMPLICATIONS HCN channel inhibitors had a previously unrecognized effect on the neural regulation of airway smooth muscle tone, which may have implications for some patients receiving HCN channel inhibitors for therapeutic purposes. PMID:24762027

  1. Chapter Five - Ubiquitination of Ion Channels and Transporters.

    PubMed

    Lamothe, S M; Zhang, S

    2016-01-01

    Ion channels and transporters play essential roles in excitable cells including cardiac, skeletal, and smooth muscle cells, neurons, and endocrine cells. Their dysfunction underlies the pathology of various diseases. Thus, the tight regulation of these transmembrane proteins is essential for cell physiology. While the ubiquitin system is involved in many aspects of cellular processes, this chapter focuses on the ubiquitin-mediated degradation of ion channels and transporters. Ubiquitination of ion channels and transporters is multifaceted and occurs at various cellular compartments such as the plasma membrane and the endoplasmic reticulum. While various molecules are involved in the ubiquitination of ion channels and transporters, E3 ubiquitin ligases play a central role in selectively targeting substrates for ubiquitination and will be a major focus in this chapter. To date, the Nedd4 family of E3 ubiquitin ligases and their regulations of ion channels and transporters have been extensively studied. In this chapter, we will first review Nedd4/Nedd4-2 and their regulations. We will then discuss how E3 ubiquitin ligases, especially Nedd4-2, regulate various ion channels and transporters including epithelial Na(+) channels, voltage-gated Na(+) channels, KCNQ and hERG K(+) channels, Cl(-) channels such as CFTR, transporters such as Na(+)/K(+) ATPase, and gap junctions. Furthermore, diseases caused by improper ubiquitination of ion channels and transporters will be discussed to highlight the process of ubiquitination and its biological as well as clinical significance. PMID:27378758

  2. Ion channels and the control of blood pressure

    PubMed Central

    Baker, Emma H

    2000-01-01

    Ion channels exist in all cells and are enormously varied in structure, function and regulation. Some progress has been made in understanding the role that ion channels play in the control of blood pressure, but the discipline is still in its infancy. Ion channels provide many different targets for intervention in disorders of blood pressure and exciting advances have been made in this field. It is possible that new drugs, as well as antisense nucleotide technology or gene therapy directed towards ion channels, may form a new class of treatments for high and low blood pressure in the future. PMID:10718773

  3. Computer-Aided Drug Discovery and Design Targeting Ion Channels.

    PubMed

    Zhang, Qiansen; Gao, Zhaobing; Yang, Huaiyu

    2016-01-01

    Ion channels are widely expressed in living cells and play critical roles in various cellular biological functions. Dysfunctional ion channels can cause a variety of diseases, making ion channels attractive targets for drug discovery. Computational approaches, such as molecular docking and molecular dynamic simulations, provide economic and efficient tools for finding modulators of ion channels and for elucidating the action mechanisms of small molecules. In this review, we focus primarily on four types of ion channels (voltage-gated, ligand-gated, acid-sensing, and virus matrix 2 ion channels). The current advancements in computer-aided drug discovery and design targeting ion channels are summarized. First, ligand-based studies for drug design are briefly outlined. Then, we focus on the structurebased studies targeting pore domains, endogenous binding sites and allosteric sites of ion channels. Moreover, we also review the contribution of computational methods to the field of ligand binding and unbinding pathways of ion channels. Finally, we propose future developments for the field. PMID:26975507

  4. The CFTR Ion Channel: Gating, Regulation, and Anion Permeation

    PubMed Central

    Hwang, Tzyh-Chang; Kirk, Kevin L.

    2013-01-01

    Cystic fibrosis transmembrane conductance regulator (CFTR) is an ATP-gated anion channel with two remarkable distinctions. First, it is the only ATP-binding cassette (ABC) transporter that is known to be an ion channel—almost all others function as transport ATPases. Second, CFTR is the only ligand-gated channel that consumes its ligand (ATP) during the gating cycle—a consequence of its enzymatic activity as an ABC transporter. We discuss these special properties of CFTR in the context of its evolutionary history as an ABC transporter. Other topics include the mechanisms by which CFTR gating is regulated by phosphorylation of its unique regulatory domain and our current view of the CFTR permeation pathway (or pore). Understanding these basic operating principles of the CFTR channel is central to defining the mechanisms of action of prospective cystic fibrosis drugs and to the development of new, rational treatment strategies. PMID:23284076

  5. Channelpedia: An Integrative and Interactive Database for Ion Channels

    PubMed Central

    Ranjan, Rajnish; Khazen, Georges; Gambazzi, Luca; Ramaswamy, Srikanth; Hill, Sean L.; Schürmann, Felix; Markram, Henry

    2011-01-01

    Ion channels are membrane proteins that selectively conduct ions across the cell membrane. The flux of ions through ion channels drives electrical and biochemical processes in cells and plays a critical role in shaping the electrical properties of neurons. During the past three decades, extensive research has been carried out to characterize the molecular, structural, and biophysical properties of ion channels. This research has begun to elucidate the role of ion channels in neuronal function and has subsequently led to the development of computational models of ion channel function. Although there have been substantial efforts to consolidate these findings into easily accessible and coherent online resources, a single comprehensive resource is still lacking. The success of these initiatives has been hindered by the sheer diversity of approaches and the variety in data formats. Here, we present “Channelpedia” (http://channelpedia.net), which is designed to store information related to ion channels and models and is characterized by an efficient information management framework. Composed of a combination of a database and a wiki-like discussion platform Channelpedia allows researchers to collaborate and synthesize ion channel information from literature. Equipped to automatically update references, Channelpedia integrates and highlights recent publications with relevant information in the database. It is web based, freely accessible and currently contains 187 annotated ion channels with 45 Hodgkin–Huxley models. PMID:22232598

  6. Oxytocin inhibits the activity of acid-sensing ion channels through the vasopressin, V1A receptor in primary sensory neurons

    PubMed Central

    Qiu, Fang; Qiu, Chun-Yu; Cai, Huilan; Liu, Ting-Ting; Qu, Zu-Wei; Yang, Zhifan; Li, Jia-Da; Zhou, Qun-Yong; Hu, Wang-Ping

    2014-01-01

    BACKGROUND AND PURPOSE A growing number of studies have demonstrated that oxytocin (OT) plays an analgesic role in modulation of nociception and pain. Most work to date has focused on the central mechanisms of OT analgesia, but little is known about whether peripheral mechanisms are also involved. Acid-sensing ion channels (ASICs) are distributed in peripheral sensory neurons and participate in nociception. Here, we investigated the effects of OT on the activity of ASICs in dorsal root ganglion (DRG) neurons. EXPERIMENTAL APPROACH Electrophysiological experiments were performed on neurons from rat DRG. Nociceptive behaviour was induced by acetic acid in rats and mice lacking vasopressin, V1A receptors. KEY RESULTS OT inhibited the functional activity of native ASICs. Firstly, OT dose-dependently decreased the amplitude of ASIC currents in DRG neurons. Secondly, OT inhibition of ASIC currents was mimicked by arginine vasopressin (AVP) and completely blocked by the V1A receptor antagonist SR49059, but not by the OT receptor antagonist L-368899. Thirdly, OT altered acidosis-evoked membrane excitability of DRG neurons and significantly decreased the amplitude of the depolarization and number of action potentials induced by acid stimuli. Finally, peripherally administered OT or AVP inhibited nociceptive responses to intraplantar injection of acetic acid in rats. Both OT and AVP also induced an analgesic effect on acidosis-evoked pain in wild-type mice, but not in V1A receptor knockout mice. CONCLUSIONS AND IMPLICATIONS These results reveal a novel peripheral mechanism for the analgesic effect of OT involving the modulation of native ASICs in primary sensory neurons mediated by V1A receptors. PMID:24641084

  7. Structural basis for ion permeation mechanism in pentameric ligand-gated ion channels

    PubMed Central

    Sauguet, Ludovic; Poitevin, Frédéric; Murail, Samuel; Van Renterghem, Catherine; Moraga-Cid, Gustavo; Malherbe, Laurie; Thompson, Andrew W; Koehl, Patrice; Corringer, Pierre-Jean; Baaden, Marc; Delarue, Marc

    2013-01-01

    To understand the molecular mechanism of ion permeation in pentameric ligand-gated ion channels (pLGIC), we solved the structure of an open form of GLIC, a prokaryotic pLGIC, at 2.4 Å. Anomalous diffraction data were used to place bound anions and cations. This reveals ordered water molecules at the level of two rings of hydroxylated residues (named Ser6′ and Thr2′) that contribute to the ion selectivity filter. Two water pentagons are observed, a self-stabilized ice-like water pentagon and a second wider water pentagon, with one sodium ion between them. Single-channel electrophysiology shows that the side-chain hydroxyl of Ser6′ is crucial for ion translocation. Simulations and electrostatics calculations complemented the description of hydration in the pore and suggest that the water pentagons observed in the crystal are important for the ion to cross hydrophobic constriction barriers. Simulations that pull a cation through the pore reveal that residue Ser6′ actively contributes to ion translocation by reorienting its side chain when the ion is going through the pore. Generalization of these findings to the pLGIC family is proposed. PMID:23403925

  8. Application of ion-sensitive field effect transistors for ion channel screening.

    PubMed

    Walsh, Kenneth B; DeRoller, Nicholas; Zhu, Yihao; Koley, Goutam

    2014-04-15

    Cell-based screening assays are now widely used for identifying compounds that serve as ion channel modulators. However, instrumentation for the automated, real-time analysis of ion flux from clonal and primary cells is lacking. This study describes the initial development of an ion-sensitive field effect transistor (ISFET)-based screening assay for the acquisition of K(+) efflux data from cells cultured in multi-well plates. Silicon-based K(+)-sensitive ISFETs were tested for their electrical response to varying concentrations of KCl and were found to display a linear response relationship to KCl in the range of 10 µM-1 mM. The ISFETs, along with reference electrodes, were inserted into fast-flow chambers containing either human colonic T84 epithelial cells or U251-MG glioma cells. Application of the Ca(2+) ionophore A23187 (1 µM), to activate Ca(2+)-activated non-selective cation (NSC) channels (T84 cells) and large conductance Ca(2+)-activated K(+) (BK) channels (U251 cells), resulted in time-dependent increases in the extracellular K(+) concentration ([K(+)]o) as measured with the ISFETs. Treatment of the cells with blockers of either the NSC or BK channels, caused a strong inhibition of the A23187-induced increase in [K(+)]o. These results were consistent with ion current measurements obtained using the whole-cell arrangement of the patch clamp procedure. In addition, K(+) efflux data could be acquired in parallel from multiple cell chambers using the ISFET sensors. Given the non-invasive properties of the probes, the ISFET-based assay should be adaptable for screening ion channels in various cell types. PMID:24315877

  9. Bioinspired Artificial Sodium and Potassium Ion Channels.

    PubMed

    Rodríguez-Vázquez, Nuria; Fuertes, Alberto; Amorín, Manuel; Granja, Juan R

    2016-01-01

    In Nature, all biological systems present a high level of compartmentalization in order to carry out a wide variety of functions in a very specific way. Hence, they need ways to be connected with the environment for communication, homeostasis equilibrium, nutrition, waste elimination, etc. The biological membranes carry out these functions; they consist of physical insulating barriers constituted mainly by phospholipids. These amphipathic molecules spontaneously aggregate in water to form bilayers in which the polar groups are exposed to the aqueous media while the non-polar chains self-organize by aggregating to each other to stay away from the aqueous media. The insulating properties of membranes are due to the formation of a hydrophobic bilayer covered at both sides by the hydrophilic phosphate groups. Thus, lipophilic molecules can permeate the membrane freely, while the small charged or very hydrophilic molecules require the assistance of other membrane components in order to overcome the energetic cost implied in crossing the non-polar region of the bilayer. Most of the large polar species (such as oligosaccharides, polypeptides or nucleic acids) cross into and out of the cell via endocytosis and exocytosis, respectively. Nature has created a series of systems (carriers and pores) in order to control the balance of small hydrophilic molecules and ions. The most important structures to achieve these goals are the ionophoric proteins that include the channel proteins, such as the sodium and potassium channels, and ionic transporters, including the sodium/potassium pumps or calcium/sodium exchangers among others. Inspired by these, scientists have created non-natural synthetic transporting structures to mimic the natural systems. The progress in the last years has been remarkable regarding the efficient transport of Na(+) and K(+) ions, despite the fact that the selectivity and the ON/OFF state of the non-natural systems remain a present and future challenge

  10. Zinc as Allosteric Ion Channel Modulator: Ionotropic Receptors as Metalloproteins.

    PubMed

    Peralta, Francisco Andrés; Huidobro-Toro, Juan Pablo

    2016-01-01

    Zinc is an essential metal to life. This transition metal is a structural component of many proteins and is actively involved in the catalytic activity of cell enzymes. In either case, these zinc-containing proteins are metalloproteins. However, the amino acid residues that serve as ligands for metal coordination are not necessarily the same in structural proteins compared to enzymes. While crystals of structural proteins that bind zinc reveal a higher preference for cysteine sulfhydryls rather than histidine imidazole rings, catalytic enzymes reveal the opposite, i.e., a greater preference for the histidines over cysteines for catalysis, plus the influence of carboxylic acids. Based on this paradigm, we reviewed the putative ligands of zinc in ionotropic receptors, where zinc has been described as an allosteric modulator of channel receptors. Although these receptors do not strictly qualify as metalloproteins since they do not normally bind zinc in structural domains, they do transitorily bind zinc at allosteric sites, modifying transiently the receptor channel's ion permeability. The present contribution summarizes current information showing that zinc allosteric modulation of receptor channels occurs by the preferential metal coordination to imidazole rings as well as to the sulfhydryl groups of cysteine in addition to the carboxyl group of acid residues, as with enzymes and catalysis. It is remarkable that most channels, either voltage-sensitive or transmitter-gated receptor channels, are susceptible to zinc modulation either as positive or negative regulators. PMID:27384555

  11. Acid-sensing ion channels in pathological conditions

    PubMed Central

    Chu, Xiang-Ping; Xiong, Zhi-Gang

    2013-01-01

    Acid-sensing ion channels (ASICs), a novel family of proton-gated amiloride-sensitive cation channels, are expressed primarily in neurons of peripheral sensory and central nervous systems. Recent studies have shown that activation of ASICs, particularly the ASIC1a channels, plays a critical role in neuronal injury associated with neurological disorders such as brain ischemia, multiple sclerosis, and spinal cord injury, etc. In normal conditions in vitro, ASIC1a channels desensitize rapidly in the presence of a continuous acidosis or following a pre-exposure to minor pH drop, raising doubt for their contributions to the acidosis-mediated neuronal injury. It is now known that the properties of ASICs can be dramatically modulated by signaling molecules or biochemical changes associated with pathological conditions. Modulation of ASICs by these molecules can lead to dramatically enhanced and/or prolonged activities of these channels thus promoting their pathological functions. Understanding of how ASICs behave in pathological conditions may help define new strategies for the treatment and/or prevention of neuronal injury associated with various neurological disorders. PMID:23224900

  12. Axial channeling of boron ions into silicon

    NASA Astrophysics Data System (ADS)

    La Ferla, A.; Galvagno, G.; Raineri, V.; Setola, R.; Rimini, E.; Carbera, A.; Gasparotto, A.

    1992-04-01

    Channeling boron implants were performed into (100) and (110) silicon substrates in the energy range 80-700 keV. The dose ranged between 3.5 × 10 11 and 1 × 10 15 atoms/cm 2. The axial channeling concentration profiles of implanted B + were compared with that obtained for incidence along the random direction of the crystal and with that obtained by implantation in amorphous silicon. The electrical and chemical boron distributions were obtained by spreading resistance and secondary ion mass spectrometry measurements, respectively. The inelastic stopping power, Sc, was extracted from the experimental maximum ranges for the [100] and [110] axis. The energ dependence of the electronic stopping power is given by Sc = KEp with p[100] = 0.469±0.010 and p[110] = 0.554±0.004. Simulations obtained by the MARLOWE code, using the Oen-Robinson impact parameter dependent formula, for the electronic energy loss reproduce quite well the experimental depth profiles.

  13. Synthetic ion channels: from pores to biological applications.

    PubMed

    Gokel, George W; Negin, Saeedeh

    2013-12-17

    In this Account, we describe the development of several diverse families of synthetic, membrane-active amphiphiles that form pores and facilitate transport within membrane bilayers. For the most part, the compounds are amphiphiles that insert into the bilayer and form pores either on their own or by self-assembly. The first family of synthetic ion channels prepared in our lab, the hydraphiles, used crown ethers as head groups and as a polar central element. In a range of biophysical studies, we showed that the hydraphiles formed unimolecular pores that spanned the bilayer. They mediated the transport of Na(+) and K(+) but were blocked by Ag(+). The hydraphiles are nonrectifying and disrupt ion homeostasis. As a result, these synthetic ion channels are toxic to various bacteria and yeast, a feature that has been used therapeutically in direct injection chemotherapy. We also developed a family of amphiphilic heptapeptide ion transporters that selected Cl(-) >10-fold over K(+) and showed voltage dependent gating. The formed pores were approximately dimeric, and variations in the N- and C-terminal anchor chains and the acids affected transport rates. Surprisingly, the longer N-terminal anchor chains led to less transport but greater Cl(-) selectivity. A proline residue, which is present in the ClC protein channel's conductance pore, proved to be critical for Cl(-) transport selectivity. Pyrogallol[4]arenes are macrocycles formed by acid-catalyzed condensation of four 1,2,3- trihydroxybenzenes with four aldehydes. The combination of 12 hydroxyl groups on one face of the macrocycle and four pendant alkyl chains conferred considerable amphiphilicity to these compounds. The pyrogallol[4]arenes inserted into bilayer membranes and conducted ions. Based on our experimental evidence, the ions passed through a self-assembled pore comprising four or five amphiphiles rather than passing through the central opening of a single macrocycle. Pyrogallol[4]arenes constructed with

  14. Modeling negative ion defect migration through the gramicidin A channel.

    PubMed

    Nemukhin, Alexander V; Kaliman, Ilya A; Moskovsky, Alexander A

    2009-08-01

    The results of potential of mean force (PMF) calculations for the distinct stages of proton conduction through the gramicidin A channel, including proton migration, reorientation of the water file and negative ion defect migration, are presented. The negative ion defect migration mechanism was hypothesized in experimental studies but was not considered previously in molecular dynamics simulations. The model system consisted of the peptide chains constructed on the base of the structure PDBID:1JNO, the inner file of nine water molecules and external clusters of water molecules placed at both ends of the channel. Potential energy functions were computed with the CHARMM/PM6/TIP3P parameters. The results obtained for proton migration and water file reorientation are basically consistent with those reported previously by Pómès and Roux (Biophys J 82:2304, 2002) within the similar approach. For the newly considered mechanism of negative ion defect migration from the channel center to the end of the water file we obtain the energy 3.8 kcal mol(-1) which is not considerably different from the activation energy of water reorientation, 5.4 kcal mol(-1). Therefore this mechanism may principally compete for the rate-limiting step in proton conduction in gramicidin. PMID:19198898

  15. Ion channels and transporters in tumour cell migration and invasion

    PubMed Central

    Schwab, Albrecht; Stock, Christian

    2014-01-01

    Cell migration is a central component of the metastatic cascade requiring a concerted action of ion channels and transporters (migration-associated transportome), cytoskeletal elements and signalling cascades. Ion transport proteins and aquaporins contribute to tumour cell migration and invasion among other things by inducing local volume changes and/or by modulating Ca2+ and H+ signalling. Targeting cell migration therapeutically bears great clinical potential, because it is a prerequisite for metastasis. Ion transport proteins appear to be attractive candidate target proteins for this purpose because they are easily accessible as membrane proteins and often overexpressed or activated in cancer. Importantly, a number of clinically widely used drugs are available whose anticipated efficacy as anti-tumour drugs, however, has now only begun to be evaluated. PMID:24493750

  16. Ligand-gated ion channel interacting proteins and their role in neuroprotection

    PubMed Central

    Li, Shupeng; Wong, Albert H. C.; Liu, Fang

    2014-01-01

    Ion channel receptors are a vital component of nervous system signaling, allowing rapid and direct conversion of a chemical neurotransmitter message to an electrical current. In recent decades, it has become apparent that ionotropic receptors are regulated by protein-protein interactions with other ion channels, G-protein coupled receptors and intracellular proteins. These other proteins can also be modulated by these interactions with ion channel receptors. This bidirectional functional cross-talk is important for critical cellular functions such as excitotoxicity in pathological and disease states like stroke, and for the basic dynamics of activity-dependent synaptic plasticity. Protein interactions with ion channel receptors can therefore increase the computational capacity of neuronal signaling cascades and also represent a novel target for therapeutic intervention in neuropsychiatric disease. This review will highlight some examples of ion channel receptor interactions and their potential clinical utility for neuroprotection. PMID:24847210

  17. Trafficking Mechanisms Underlying Neuronal Voltage-gated Ion Channel Localization at the Axon Initial Segment

    PubMed Central

    Vacher, Helene; Trimmer, James S.

    2012-01-01

    Summary Voltage-gated ion channels are diverse and fundamental determinants of neuronal intrinsic excitability. Voltage-gated K+ (Kv) and Na+ (Nav) channels play complex yet fundamentally important roles in determining intrinsic excitability. The Kv and Nav channels located at the axon initial segment (AIS) play a unique and especially important role in generating neuronal output in the form of anterograde axonal and backpropagating action potentials, Aberrant intrinsic excitability in individual neurons within networks contributes to synchronous neuronal activity leading to seizures. Mutations in ion channel genes gives rise to a variety of seizure-related “Channelopathies”, and many of the ion channel subunits associated with epilepsy mutations are localized at the AIS, making this a hotspot for epileptogenesis. Here we review the cellular mechanisms that underlie the trafficking of Kv and Nav channels found at the AIS, and how Kv and Nav channel mutations associated with epilepsy can alter these processes. PMID:23216576

  18. Hypoxia-Dependent Reactive Oxygen Species Signaling in the Pulmonary Circulation: Focus on Ion Channels

    PubMed Central

    Veit, Florian; Pak, Oleg; Brandes, Ralf P.

    2015-01-01

    Abstract Significance: An acute lack of oxygen in the lung causes hypoxic pulmonary vasoconstriction, which optimizes gas exchange. In contrast, chronic hypoxia triggers a pathological vascular remodeling causing pulmonary hypertension, and ischemia can cause vascular damage culminating in lung edema. Recent Advances: Regulation of ion channel expression and gating by cellular redox state is a widely accepted mechanism; however, it remains a matter of debate whether an increase or a decrease in reactive oxygen species (ROS) occurs under hypoxic conditions. Ion channel redox regulation has been described in detail for some ion channels, such as Kv channels or TRPC6. However, in general, information on ion channel redox regulation remains scant. Critical Issues and Future Directions: In addition to the debate of increased versus decreased ROS production during hypoxia, we aim here at describing and deciphering why different oxidants, under different conditions, can cause both activation and inhibition of channel activity. While the upstream pathways affecting channel gating are often well described, we need a better understanding of redox protein modifications to be able to determine the complexity of ion channel redox regulation. Against this background, we summarize the current knowledge on hypoxia-induced ROS-mediated ion channel signaling in the pulmonary circulation. Antioxid. Redox Signal. 22, 537–552 PMID:25545236

  19. Trails of Kilovolt Ions Created by Subsurface Channeling

    SciTech Connect

    Redinger, Alex; Standop, Sebastian; Michely, Thomas; Rosandi, Yudi; Urbassek, Herbert M.

    2010-02-19

    Using scanning tunneling microscopy, we observe the damage trails produced by keV noble-gas ions incident at glancing angles onto Pt(111). Surface vacancies and adatoms aligned along the ion trajectory constitute the ion trails. Atomistic simulations reveal that these straight trails are produced by nuclear (elastic) collisions with surface layer atoms during subsurface channeling of the projectiles. In a small energy window around 5 keV, Xe{sup +} ions create vacancy grooves that mark the ion trajectory with atomic precision. The asymmetry of the adatom production on the two sides of the projectile path is traced back to the asymmetry of the ion's subsurface channel.

  20. Allosterism and Structure in Thermally Activated Transient Receptor Potential Channels.

    PubMed

    Diaz-Franulic, Ignacio; Poblete, Horacio; Miño-Galaz, Germán; González, Carlos; Latorre, Ramón

    2016-07-01

    The molecular sensors that mediate temperature changes in living organisms are a large family of proteins known as thermosensitive transient receptor potential (TRP) ion channels. These membrane proteins are polymodal receptors that can be activated by cold or hot temperatures, depending on the channel subtype, voltage, and ligands. The stimuli sensors are allosterically coupled to a pore domain, increasing the probability of finding the channel in its ion conductive conformation. In this review we first discuss the allosteric coupling between the temperature and voltage sensor modules and the pore domain, and then discuss the thermodynamic foundations of thermo-TRP channel activation. We provide a structural overview of the molecular determinants of temperature sensing. We also posit an anisotropic thermal diffusion model that may explain the large temperature sensitivity of TRP channels. Additionally, we examine the effect of several ligands on TRP channel function and the evidence regarding their mechanisms of action. PMID:27297398

  1. Target Promiscuity and Heterogeneous Effects of Tarantula Venom Peptides Affecting Na+ and K+ Ion Channels*

    PubMed Central

    Redaelli, Elisa; Cassulini, Rita Restano; Silva, Deyanira Fuentes; Clement, Herlinda; Schiavon, Emanuele; Zamudio, Fernando Z.; Odell, George; Arcangeli, Annarosa; Clare, Jeffrey J.; Alagón, Alejandro; de la Vega, Ricardo C. Rodríguez; Possani, Lourival D.; Wanke, Enzo

    2010-01-01

    Venom-derived peptide modulators of ion channel gating are regarded as essential tools for understanding the molecular motions that occur during the opening and closing of ion channels. In this study, we present the characterization of five spider toxins on 12 human voltage-gated ion channels, following observations about the target promiscuity of some spider toxins and the ongoing revision of their “canonical” gating-modifying mode of action. The peptides were purified de novo from the venom of Grammostola rosea tarantulas, and their sequences were confirmed by Edman degradation and mass spectrometry analysis. Their effects on seven tetrodotoxin-sensitive Na+ channels, the three human ether-à-go-go (hERG)-related K+ channels, and two human Shaker-related K+ channels were extensively characterized by electrophysiological techniques. All the peptides inhibited ion conduction through all the Na+ channels tested, although with distinctive patterns. The peptides also affected the three pharmaceutically relevant hERG isoforms differently. At higher concentrations, all peptides also modified the gating of the Na+ channels by shifting the activation to more positive potentials, whereas more complex effects were recorded on hERG channels. No effects were evident on the two Shaker-related K+ channels at concentrations well above the IC50 value for the affected channels. Given the sequence diversity of the tested peptides, we propose that tarantula toxins should be considered both as multimode and target-promiscuous ion channel modulators; both features should not be ignored when extracting mechanistic interpretations about ion channel gating. Our observations could also aid in future structure-function studies and might help the development of novel ion channel-specific drugs. PMID:19955179

  2. Ion Channels in Native Chloroplast Membranes: Challenges and Potential for Direct Patch-Clamp Studies

    PubMed Central

    Pottosin, Igor; Dobrovinskaya, Oxana

    2015-01-01

    Photosynthesis without any doubt depends on the activity of the chloroplast ion channels. The thylakoid ion channels participate in the fine partitioning of the light-generated proton-motive force (p.m.f.). By regulating, therefore, luminal pH, they affect the linear electron flow and non-photochemical quenching. Stromal ion homeostasis and signaling, on the other hand, depend on the activity of both thylakoid and envelope ion channels. Experimentally, intact chloroplasts and swollen thylakoids were proven to be suitable for direct measurements of the ion channels activity via conventional patch-clamp technique; yet, such studies became infrequent, although their potential is far from being exhausted. In this paper we wish to summarize existing challenges for direct patch-clamping of native chloroplast membranes as well as present available results on the activity of thylakoid Cl− (ClC?) and divalent cation-permeable channels, along with their tentative roles in the p.m.f. partitioning, volume regulation, and stromal Ca2+ and Mg2+ dynamics. Patch-clamping of the intact envelope revealed both large-conductance porin-like channels, likely located in the outer envelope membrane and smaller conductance channels, more compatible with the inner envelope location. Possible equivalent model for the sandwich-like arrangement of the two envelope membranes within the patch electrode will be discussed, along with peculiar properties of the fast-activated cation channel in the context of the stromal pH control. PMID:26733887

  3. Energetics of ion conduction through the K+ channel

    NASA Astrophysics Data System (ADS)

    Bernèche, Simon; Roux, Benoît

    2001-11-01

    K+ channels are transmembrane proteins that are essential for the transmission of nerve impulses. The ability of these proteins to conduct K+ ions at levels near the limit of diffusion is traditionally described in terms of concerted mechanisms in which ion-channel attraction and ion-ion repulsion have compensating effects, as several ions are moving simultaneously in single file through the narrow pore. The efficiency of such a mechanism, however, relies on a delicate energy balance-the strong ion-channel attraction must be perfectly counterbalanced by the electrostatic ion-ion repulsion. To elucidate the mechanism of ion conduction at the atomic level, we performed molecular dynamics free energy simulations on the basis of the X-ray structure of the KcsA K+ channel. Here we find that ion conduction involves transitions between two main states, with two and three K+ ions occupying the selectivity filter, respectively; this process is reminiscent of the `knock-on' mechanism proposed by Hodgkin and Keynes in 1955. The largest free energy barrier is on the order of 2-3kcalmol-1, implying that the process of ion conduction is limited by diffusion. Ion-ion repulsion, although essential for rapid conduction, is shown to act only at very short distances. The calculations show also that the rapidly conducting pore is selective.

  4. Modelling modal gating of ion channels with hierarchical Markov models

    PubMed Central

    Fackrell, Mark; Crampin, Edmund J.; Taylor, Peter

    2016-01-01

    Many ion channels spontaneously switch between different levels of activity. Although this behaviour known as modal gating has been observed for a long time it is currently not well understood. Despite the fact that appropriately representing activity changes is essential for accurately capturing time course data from ion channels, systematic approaches for modelling modal gating are currently not available. In this paper, we develop a modular approach for building such a model in an iterative process. First, stochastic switching between modes and stochastic opening and closing within modes are represented in separate aggregated Markov models. Second, the continuous-time hierarchical Markov model, a new modelling framework proposed here, then enables us to combine these components so that in the integrated model both mode switching as well as the kinetics within modes are appropriately represented. A mathematical analysis reveals that the behaviour of the hierarchical Markov model naturally depends on the properties of its components. We also demonstrate how a hierarchical Markov model can be parametrized using experimental data and show that it provides a better representation than a previous model of the same dataset. Because evidence is increasing that modal gating reflects underlying molecular properties of the channel protein, it is likely that biophysical processes are better captured by our new approach than in earlier models. PMID:27616917

  5. Acid-sensing ion channels: trafficking and synaptic function

    PubMed Central

    2013-01-01

    Extracellular acidification occurs in the brain with elevated neural activity, increased metabolism, and neuronal injury. This reduction in pH can have profound effects on brain function because pH regulates essentially every single biochemical reaction. Therefore, it is not surprising to see that Nature evolves a family of proteins, the acid-sensing ion channels (ASICs), to sense extracellular pH reduction. ASICs are proton-gated cation channels that are mainly expressed in the nervous system. In recent years, a growing body of literature has shown that acidosis, through activating ASICs, contributes to multiple diseases, including ischemia, multiple sclerosis, and seizures. In addition, ASICs play a key role in fear and anxiety related psychiatric disorders. Several recent reviews have summarized the importance and therapeutic potential of ASICs in neurological diseases, as well as the structure-function relationship of ASICs. However, there is little focused coverage on either the basic biology of ASICs or their contribution to neural plasticity. This review will center on these topics, with an emphasis on the synaptic role of ASICs and molecular mechanisms regulating the spatial distribution and function of these ion channels. PMID:23281934

  6. The Thumb Domain Mediates Acid-sensing Ion Channel Desensitization.

    PubMed

    Krauson, Aram J; Carattino, Marcelo D

    2016-05-20

    Acid-sensing ion channels (ASICs) are cation-selective proton-gated channels expressed in neurons that participate in diverse physiological processes, including nociception, synaptic plasticity, learning, and memory. ASIC subunits contain intracellular N and C termini, two transmembrane domains that constitute the pore, and a large extracellular loop with defined domains termed the finger, β-ball, thumb, palm, and knuckle. Here we examined the contribution of the finger, β-ball, and thumb domains to activation and desensitization through the analysis of chimeras and the assessment of the effect of covalent modification of introduced Cys at the domain-domain interfaces. Our studies with ASIC1a-ASIC2a chimeras showed that swapping the thumb domain between subunits results in faster channel desensitization. Likewise, the covalent modification of Cys residues at selected positions in the β-ball-thumb interface accelerates the desensitization of the mutant channels. Studies of accessibility with thiol-reactive reagents revealed that the β-ball and thumb domains reside apart in the resting state but that they become closer to each other in response to extracellular acidification. We propose that the thumb domain moves upon continuous exposure to an acidic extracellular milieu, assisting with the closing of the pore during channel desensitization. PMID:27015804

  7. Neurosensory mechanotransduction through acid-sensing ion channels

    PubMed Central

    Chen, Chih-Cheng; Wong, Chia-Wen

    2013-01-01

    Acid-sensing ion channels (ASICs) are voltage-insensitive cation channels responding to extracellular acidification. ASIC proteins have two transmembrane domains and a large extracellular domain. The molecular topology of ASICs is similar to that of the mechanosensory abnormality 4- or 10-proteins expressed in touch receptor neurons and involved in neurosensory mechanotransduction in nematodes. The ASIC proteins are involved in neurosensory mechanotransduction in mammals. The ASIC isoforms are expressed in Merkel cell–neurite complexes, periodontal Ruffini endings and specialized nerve terminals of skin and muscle spindles, so they might participate in mechanosensation. In knockout mouse models, lacking an ASIC isoform produces defects in neurosensory mechanotransduction of tissue such as skin, stomach, colon, aortic arch, venoatrial junction and cochlea. The ASICs are thus implicated in touch, pain, digestive function, baroreception, blood volume control and hearing. However, the role of ASICs in mechanotransduction is still controversial, because we lack evidence that the channels are mechanically sensitive when expressed in heterologous cells. Thus, ASIC channels alone are not sufficient to reconstruct the path of transducing molecules of mechanically activated channels. The mechanotransducers associated with ASICs need further elucidation. In this review, we discuss the expression of ASICs in sensory afferents of mechanoreceptors, findings of knockout studies, technical issues concerning studies of neurosensory mechanotransduction and possible missing links. Also we propose a molecular model and a new approach to disclose the molecular mechanism underlying the neurosensory mechanotransduction. PMID:23490035

  8. Transient receptor potential melastatin 3 is a phosphoinositide-dependent ion channel

    PubMed Central

    Badheka, Doreen; Borbiro, Istvan

    2015-01-01

    Phosphoinositides are emerging as general regulators of the functionally diverse transient receptor potential (TRP) ion channel family. Phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) has been reported to positively regulate many TRP channels, but in several cases phosphoinositide regulation is controversial. TRP melastatin 3 (TRPM3) is a heat-activated ion channel that is also stimulated by chemical agonists, such as pregnenolone sulfate. Here, we used a wide array of approaches to determine the effects of phosphoinositides on TRPM3. We found that channel activity in excised inside-out patches decreased over time (rundown), an attribute of PI(4,5)P2-dependent ion channels. Channel activity could be restored by application of either synthetic dioctanoyl (diC8) or natural arachidonyl stearyl (AASt) PI(4,5)P2. The PI(4,5)P2 precursor phosphatidylinositol 4-phosphate (PI(4)P) was less effective at restoring channel activity. TRPM3 currents were also restored by MgATP, an effect which was inhibited by two different phosphatidylinositol 4-kinase inhibitors, or by pretreatment with a phosphatidylinositol-specific phospholipase C (PI-PLC) enzyme, indicating that MgATP acted by generating phosphoinositides. In intact cells, reduction of PI(4,5)P2 levels by chemically inducible phosphoinositide phosphatases or a voltage-sensitive 5′-phosphatase inhibited channel activity. Activation of PLC via muscarinic receptors also inhibited TRPM3 channel activity. Overall, our data indicate that TRPM3 is a phosphoinositide-dependent ion channel and that decreasing PI(4,5)P2 abundance limits its activity. As all other members of the TRPM family have also been shown to require PI(4,5)P2 for activity, our data establish PI(4,5)P2 as a general positive cofactor of this ion channel subfamily. PMID:26123195

  9. Improvement in fusion reactor performance due to ion channeling

    SciTech Connect

    Emmert, G.A.; El-Guebaly, L.A.; Kulcinski, G.L.; Santarius, J.F.; Sviatoslavsky, I.N.; Meade, D.M.

    1994-11-01

    Ion channeling is a recent idea for improving the performance of fusion reactors by increasing the fraction of the fusion power deposited in the ions. In this paper the authors assess the effect of ion channeling on D-T and D-{sup 3}He reactors. The figures of merit used are the fusion power density and the cost of electricity. It is seen that significant ion channeling can lead to about a 50-65% increase in the fusion power density. For the Apollo D-{sup 3}He reactor concept the reduction in the cost of electricity can be as large as 30%.

  10. Novel perspectives in cancer therapy: Targeting ion channels.

    PubMed

    Arcangeli, Annarosa; Becchetti, Andrea

    2015-01-01

    By controlling ion fluxes at multiple time scales, ion channels shape rapid cell signals, such as action potential and synaptic transmission, as well as much slower processes, such as mitosis and cell migration. As is currently increasingly recognized, a variety of channel types are involved in cancer hallmarks, and regulate specific stages of neoplastic progression. Long-term in vitro work has established that inhibition of these ion channels impairs the growth of cancer cells. Recently, these studies have been followed up in vivo, hence revealing that ion channels constitute promising pharmacological targets in oncology. The channel proteins can be often accessed from the extracellular milieu, which allows use of lower drug doses and decrease untoward toxicity. However, because of the central physiological roles exerted by ion channels in excitable cells, other types of side effects may arise, the gravest of which is cardiac arrhythmia. A paradigmatic case is offered by Kv11.1 (hERG1) channels. HERG1 blockers attenuate the progression of both hematologic malignancies and solid tumors, but may also lead to the lengthening of the electrocardiographic QT interval, thus predisposing the patient to ventricular arrhythmias. These side effects can be avoided by specifically inhibiting the channel isoforms which are highly expressed in certain tumors, such as Kv11.1B and the neonatal forms of voltage-gated Na(+) channels. Preclinical studies are also being explored in breast and prostate cancer (targeting voltage-gated Na(+) channels), and gliomas (targeting CLC-3). Overall, the possible approaches to improve the efficacy and safety of ion channel targeting in oncology include: (1) the development of specific inhibitors for the channel subtypes expressed in specific tumors; (2) drug delivery into the tumor by using antibodies or nanotechnology-based approaches; (3) combination regimen therapy and (4) blocking specific conformational states of the ion channel. We believe

  11. Extracellular zinc ion regulates transient receptor potential melastatin 5 (TRPM5) channel activation through its interaction with a pore loop domain.

    PubMed

    Uchida, Kunitoshi; Tominaga, Makoto

    2013-09-01

    The transient receptor potential melastatin 5 (TRPM5) channel is a monovalent cation channel activated by intracellular Ca(2+). Expression of this channel is restricted to taste cells, the pancreas and brainstem, and is thought to be involved in controlling membrane potentials. Its endogenous ligands are not well characterized. Here, we show that extracellular application of Zn(2+) inhibits TRPM5 activity. In whole-cell patch-clamp recordings, extracellular application of ZnCl2 inhibited step-pulse-induced TRPM5 currents with 500 nM free intracellular Ca(2+) in a dose-dependent manner (IC50 = 4.3 μM at -80 mV). ZnSO4 also inhibited TRPM5 activity. Extracellular application of ZnCl2 inhibited TRPM5 activation at several temperatures. Furthermore, inhibition by 30 μM ZnCl2 was impaired in TRPM5 mutants in which His at 896, and Glu at 926 and/or Glu at 939 in the outer pore loop were replaced with Gln. From these results, we conclude that extracellular Zn(2+) inhibits TRPM5 channels, and the residues in the outer pore loop of TRPM5 are critically involved in the inhibition. PMID:23884414

  12. Extracellular Zinc Ion Regulates Transient Receptor Potential Melastatin 5 (TRPM5) Channel Activation through Its Interaction with a Pore Loop Domain

    PubMed Central

    Uchida, Kunitoshi; Tominaga, Makoto

    2013-01-01

    The transient receptor potential melastatin 5 (TRPM5) channel is a monovalent cation channel activated by intracellular Ca2+. Expression of this channel is restricted to taste cells, the pancreas and brainstem, and is thought to be involved in controlling membrane potentials. Its endogenous ligands are not well characterized. Here, we show that extracellular application of Zn2+ inhibits TRPM5 activity. In whole-cell patch-clamp recordings, extracellular application of ZnCl2 inhibited step-pulse-induced TRPM5 currents with 500 nm free intracellular Ca2+ in a dose-dependent manner (IC50 = 4.3 μm at −80 mV). ZnSO4 also inhibited TRPM5 activity. Extracellular application of ZnCl2 inhibited TRPM5 activation at several temperatures. Furthermore, inhibition by 30 μm ZnCl2 was impaired in TRPM5 mutants in which His at 896, and Glu at 926 and/or Glu at 939 in the outer pore loop were replaced with Gln. From these results, we conclude that extracellular Zn2+ inhibits TRPM5 channels, and the residues in the outer pore loop of TRPM5 are critically involved in the inhibition. PMID:23884414

  13. Mechano-sensitivity of epithelial sodium channels (ENaCs): laminar shear stress increases ion channel open probability.

    PubMed

    Althaus, Mike; Bogdan, Roman; Clauss, Wolfgang G; Fronius, Martin

    2007-08-01

    Epithelial cells are exposed to a variety of mechanical forces, but little is known about the impact of these forces on epithelial ion channels. Here we show that mechanical activation of epithelial sodium channels (ENaCs), which are essential for electrolyte and water balance, occurs via an increased ion channel open probability. ENaC activity of heterologously expressed rat (rENaC) and Xenopus (xENaC) orthologs was measured by whole-cell as well as single-channel recordings. Laminar shear stress (LSS), producing shear forces in physiologically relevant ranges, was used to mechanically stimulate ENaCs and was able to activate ENaC currents in whole-cell recordings. Preceding pharmacological activation of rENaC with Zn2+ and xENaC with gadolinium and glibenclamide largely prevented LSS-activated currents. In contrast, proteolytic cleavage with trypsin potentiated the LSS effect on rENaC whereas the LSS effect on xENaC was reversed (inhibition of xENaC current). Further, we found that exposure of excised outside-out patches to LSS led to an increased ion channel open probability without affecting the number of active channels. We suggest that mechano-sensitivity of ENaC may represent a ubiquitous feature for the physiology of epithelia, providing a putative mechanism for coupling transepithelial Na+ reabsorption to luminal transport. PMID:17426066

  14. Zinc as Allosteric Ion Channel Modulator: Ionotropic Receptors as Metalloproteins

    PubMed Central

    Peralta, Francisco Andrés; Huidobro-Toro, Juan Pablo

    2016-01-01

    Zinc is an essential metal to life. This transition metal is a structural component of many proteins and is actively involved in the catalytic activity of cell enzymes. In either case, these zinc-containing proteins are metalloproteins. However, the amino acid residues that serve as ligands for metal coordination are not necessarily the same in structural proteins compared to enzymes. While crystals of structural proteins that bind zinc reveal a higher preference for cysteine sulfhydryls rather than histidine imidazole rings, catalytic enzymes reveal the opposite, i.e., a greater preference for the histidines over cysteines for catalysis, plus the influence of carboxylic acids. Based on this paradigm, we reviewed the putative ligands of zinc in ionotropic receptors, where zinc has been described as an allosteric modulator of channel receptors. Although these receptors do not strictly qualify as metalloproteins since they do not normally bind zinc in structural domains, they do transitorily bind zinc at allosteric sites, modifying transiently the receptor channel’s ion permeability. The present contribution summarizes current information showing that zinc allosteric modulation of receptor channels occurs by the preferential metal coordination to imidazole rings as well as to the sulfhydryl groups of cysteine in addition to the carboxyl group of acid residues, as with enzymes and catalysis. It is remarkable that most channels, either voltage-sensitive or transmitter-gated receptor channels, are susceptible to zinc modulation either as positive or negative regulators. PMID:27384555

  15. Computational study of a calcium release-activated calcium channel

    NASA Astrophysics Data System (ADS)

    Talukdar, Keka; Shantappa, Anil

    2016-05-01

    The naturally occurring proteins that form hole in membrane are commonly known as ion channels. They play multiple roles in many important biological processes. Deletion or alteration of these channels often leads to serious problems in the physiological processes as it controls the flow of ions through it. The proper maintenance of the flow of ions, in turn, is required for normal health. Here we have investigated the behavior of a calcium release-activated calcium ion channel with pdb entry 4HKR in Drosophila Melanogaster. The equilibrium energy as well as molecular dynamics simulation is performed first. The protein is subjected to molecular dynamics simulation to find their energy minimized value. Simulation of the protein in the environment of water and ions has given us important results too. The solvation energy is also found using Charmm potential.

  16. Ion Permeation and Mechanotransduction Mechanisms of Mechanosensitive Piezo Channels.

    PubMed

    Zhao, Qiancheng; Wu, Kun; Geng, Jie; Chi, Shaopeng; Wang, Yanfeng; Zhi, Peng; Zhang, Mingmin; Xiao, Bailong

    2016-03-16

    Piezo proteins have been proposed as the long-sought-after mechanosensitive cation channels in mammals that play critical roles in various mechanotransduction processes. However, the molecular bases that underlie their ion permeation and mechanotransduction have remained functionally undefined. Here we report our finding of the miniature pore-forming module of Piezo1 that resembles the pore architecture of other trimeric channels and encodes the essential pore properties. We further identified specific residues within the pore module that determine unitary conductance, pore blockage and ion selectivity for divalent and monovalent cations and anions. The non-pore-containing region of Piezo1 confers mechanosensitivity to mechano-insensitive trimeric acid-sensing ion channels, demonstrating that Piezo1 channels possess intrinsic mechanotransduction modules separate from their pore modules. In conclusion, this is the first report on the bona fide pore module and mechanotransduction components of Piezo channels, which define their ion-conducting properties and gating by mechanical stimuli, respectively. PMID:26924440

  17. Pathophysiological and protective roles of mitochondrial ion channels

    PubMed Central

    O’Rourke, Brian

    2000-01-01

    Mitochondria possess a highly permeable outer membrane and an inner membrane that was originally thought to be relatively impermeable to ions to prevent dissipation of the electrochemical gradient for protons. Although recent evidence has revealed a rich diversity of ion channels in both membranes, the purpose of these channels remains incompletely determined. Pores in the outer membrane are fundamental participants in apoptotic cell death, and this process may also involve permeability transition pores on the inner membrane. Novel functions are now being assigned to other ion channels of the inner membrane. Examples include protection against ischaemic injury by mitochondrial KATP channels and the contribution of inner membrane anion channels to spontaneous mitochondrial oscillations in cardiac myocytes. The central role of mitochondria in both the normal function of the cell and in its demise makes these channels prime targets for future research and drug development. PMID:11080248

  18. Ion Channels as Drug Targets in Central Nervous System Disorders

    PubMed Central

    Waszkielewicz, A.M; Gunia, A; Szkaradek, N; Słoczyńska, K; Krupińska, S; Marona, H

    2013-01-01

    Ion channel targeted drugs have always been related with either the central nervous system (CNS), the peripheral nervous system, or the cardiovascular system. Within the CNS, basic indications of drugs are: sleep disorders, anxiety, epilepsy, pain, etc. However, traditional channel blockers have multiple adverse events, mainly due to low specificity of mechanism of action. Lately, novel ion channel subtypes have been discovered, which gives premises to drug discovery process led towards specific channel subtypes. An example is Na+ channels, whose subtypes 1.3 and 1.7-1.9 are responsible for pain, and 1.1 and 1.2 – for epilepsy. Moreover, new drug candidates have been recognized. This review is focusing on ion channels subtypes, which play a significant role in current drug discovery and development process. The knowledge on channel subtypes has developed rapidly, giving new nomenclatures of ion channels. For example, Ca2+ channels are not any more divided to T, L, N, P/Q, and R, but they are described as Cav1.1-Cav3.3, with even newer nomenclature α1A-α1I and α1S. Moreover, new channels such as P2X1-P2X7, as well as TRPA1-TRPV1 have been discovered, giving premises for new types of analgesic drugs. PMID:23409712

  19. Ion transport in a model gramicidin channel. Structure and thermodynamics.

    PubMed Central

    Roux, B; Karplus, M

    1991-01-01

    The potential of mean force for Na+ and K+ ions as a function of position in the interior of a periodic poly(L,D)-alanine model for the gramicidin beta-helix is calculated with a detailed atomic model and realistic interactions. The calculated free energy barriers are 4.5 kcal/mol for Na+ and 1.0 kcal/mol for K+. A decomposition of the free energy demonstrates that the water molecules make a significant contribution to the free energy of activation. There is an increase in entropy at the transition state associated with greater fluctuations. Analysis reveals that the free energy profile of ions in the periodic channel is controlled not by the large interaction energy involving the ion but rather by the weaker water-water, water-peptide and peptide-peptide hydrogen bond interactions. The interior of the channel retains much of the solvation properties of a liquid in its interactions with the cations. Of particular importance is the flexibility of the helix, which permits it to respond to the presence of an ion in a fluidlike manner. The distortion of the helix is local (limited to a few carbonyls) because the structure is too flexible to transmit a perturbation to large distances. The plasticity of the structure (i.e., the property to deform without generating a large energy stress) appears to be an essential factor in the transport of ions, suggesting that a rigid helix model would be inappropriate. Images FIGURE 1 FIGURE 10 PMID:1714305

  20. TRPM2: a multifunctional ion channel for calcium signalling

    PubMed Central

    Sumoza-Toledo, Adriana; Penner, Reinhold

    2011-01-01

    The transient potential receptor melastatin-2 (TRPM2) channel has emerged as an important Ca2+ signalling mechanism in a variety of cells, contributing to cellular functions that include cytokine production, insulin release, cell motility and cell death. Its ability to respond to reactive oxygen species has made TRPM2 a potential therapeutic target for chronic inflammation, neurodegenerative diseases, and oxidative stress-related pathologies. TRPM2 is a non-selective, calcium (Ca2+)-permeable cation channel of the melastatin-related transient receptor potential (TRPM) ion channel subfamily. It is activated by intracellular adenosine diphosphate ribose (ADPR) through a diphosphoribose hydrolase domain in its C-terminus and regulated through a variety of factors, including synergistic facilitation by [Ca2+]i, cyclic ADPR, H2O2, NAADP, and negative feedback regulation by AMP and permeating protons (pH). In addition to its role mediating Ca2+ influx into the cells, TRPM2 can also function as a lysosomal Ca2+ release channel, contributing to cell death. The physiological and pathophysiological context of ROS-mediated events makes TRPM2 a promising target for the development of therapeutic tools of inflammatory and degenerative diseases. PMID:21135052

  1. Ovarian cancer: Ion channel and aquaporin expression as novel targets of clinical potential.

    PubMed

    Frede, Julia; Fraser, Scott P; Oskay-Özcelik, Gülten; Hong, Yeosun; Ioana Braicu, E; Sehouli, Jalid; Gabra, Hani; Djamgoz, Mustafa B A

    2013-07-01

    Ovarian cancer is associated with limited overall survival, due to problems in early detection and therapy. Membrane ion channels have been proposed to play a significant, concerted role in the cancer process, from initial proliferation to metastasis, and promise to be early, functional biomarkers. We review the evidence for ion channel and aquaporin expression and functioning in human ovarian cancer cells and tissues. In vitro, K(+) channels, mainly voltage-gated, including Ca(2+)-activated channels, have been found to control the cell cycle, as in other cancers. Voltage-gated, volume-regulated and intracellular Cl(-) channels have been detected in vitro and in vivo and shown to be involved in proliferation, adhesion and invasion. Evidence for 'transient receptor potential', voltage-gated sodium and calcium channels, which have been shown to contribute to pathogenesis of other carcinomas, is also emerging in ovarian cancer. Aquaporins may be involved in cell growth, migration and formation of ascites via increased water permeability of micro-vessels. It is concluded that functional expression of ion channels and their regulation by steroid hormones and growth factors are an integral part of ovarian cancer development and progression. Furthermore, ion channels may be involved in multidrug resistance, commonly associated with treatment of ovarian cancer. We propose that ion channel studies can facilitate our understanding of the pathobiology of ovarian cancer and, ultimately, can serve as viable novel targets for its clinical management. PMID:23683551

  2. Structural mechanism for the regulation of HCN ion channels by the accessory protein TRIP8b

    PubMed Central

    DeBerg, Hannah A.; Bankston, John R.; Rosenbaum, Joel C.; Brzovic, Peter S.; Zagotta, William N.; Stoll, Stefan

    2015-01-01

    Summary Hyperpolarization-activated cyclic nucleotide-gated (HCN) ion channels underlie the cationic Ih current present in many neurons. The direct binding of cAMP to HCN channels increases the rate and extent of channel opening and results in a depolarizing shift in the voltage dependence of activation. TRIP8b is an accessory protein that regulates the cell surface expression and dendritic localization of HCN channels and reduces the cyclic nucleotide dependence of these channels. Here we use electron paramagnetic resonance (EPR) to show that TRIP8b binds to the apo state of the cyclic nucleotide-binding domain (CNBD) of HCN2 channels without changing the overall domain structure. With EPR and nuclear magnetic resonance (NMR), we locate TRIP8b relative to the HCN channel and identify the binding interface on the CNBD. These data provide a structural framework for understanding how TRIP8b regulates the cyclic nucleotide dependence of HCN channels. PMID:25800552

  3. Synthesis, structure activity relationship, radiolabeling and preclinical evaluation of high affinity ligands for the ion channel of the N-methyl-d-aspartate receptor as potential imaging probes for positron emission tomography.

    PubMed

    Klein, Pieter J; Christiaans, Johannes A M; Metaxas, Athanasios; Schuit, Robert C; Lammertsma, Adriaan A; van Berckel, Bart N M; Windhorst, Albert D

    2015-03-01

    The N-methyl-d-aspartate receptor (NMDAr) is involved in many neurological and psychiatric disorders including Alzheimer's disease and schizophrenia. Currently, it is not possible to assess NMDAr availability in vivo. The purpose of this study was to develop a positron emission tomography (PET) ligand for the NMDAr ion channel. A series of di- and tri-N-substituted diarylguanidines was synthesized. In addition, in vitro binding affinity for the NMDAr ion channel in rat forebrain membrane fractions was assessed. Compounds 10, 11 and 32 were radiolabeled with either carbon-11 or fluorine-18. Ligands [(11)C]10 and [(18)F]32 were evaluated ex vivo in B6C3 mice. Biodistribution studies showed higher uptake of [(11)C]10 and [(18)F]32 in forebrain regions compared with cerebellum. In addition, for [(11)C]10 54% and for [(18)F]32 70% of activity in the brain at 60min was due to intact tracer. Pre-treatment with MK-801 (0.6mg·kg(-1), ip) slightly decreased uptake in NMDAr-specific regions for [(18)F]32, but not for [(11)C]10. As such [(18)F]32 has the best characteristics as a PET tracer for the ion channel of the NMDAr. PMID:25648682

  4. Block of ATP-Binding Cassette B19 Ion Channel Activity by 5-Nitro-2-(3-Phenylpropylamino)-Benzoic Acid Impairs Polar Auxin Transport and Root Gravitropism1[OPEN

    PubMed Central

    Cho, Misuk; Henry, Elizabeth M.; Lewis, Daniel R.; Wu, Guosheng; Muday, Gloria K.

    2014-01-01

    Polar transport of the hormone auxin through tissues and organs depends on membrane proteins, including some B-subgroup members of the ATP-binding cassette (ABC) transporter family. The messenger RNA level of at least one B-subgroup ABCB gene in Arabidopsis (Arabidopsis thaliana), ABCB19, increases upon treatment with the anion channel blocker 5-nitro-2-(3-phenylpropylamino)-benzoic acid (NPPB), possibly to compensate for an inhibitory effect of the drug on ABCB19 activity. Consistent with this hypothesis, NPPB blocked ion channel activity associated with ABCB19 expressed in human embryonic kidney cells as measured by patch-clamp electrophysiology. NPPB inhibited polar auxin transport through Arabidopsis seedling roots similarly to abcb19 mutations. NPPB also inhibited shootward auxin transport, which depends on the related ABCB4 protein. NPPB substantially decreased ABCB4 and ABCB19 protein levels when cycloheximide concomitantly inhibited new protein synthesis, indicating that blockage by NPPB enhances the degradation of ABCB transporters. Impairing the principal auxin transport streams in roots with NPPB caused aberrant patterns of auxin signaling reporters in root apices. Formation of the auxin-signaling gradient across the tips of gravity-stimulated roots, and its developmental consequence (gravitropism), were inhibited by micromolar concentrations of NPPB that did not affect growth rate. These results identify ion channel activity of ABCB19 that is blocked by NPPB, a compound that can now be considered an inhibitor of polar auxin transport with a defined molecular target. PMID:25324509

  5. Ion channel remodeling in vascular smooth muscle during hypertension: Implications for novel therapeutic approaches

    PubMed Central

    Joseph, Biny K.; Thakali, Keshari M.; Moore, Christopher L.; Rhee, Sung W.

    2013-01-01

    Ion channels are multimeric, transmembrane proteins that selectively mediate ion flux across the plasma membrane in a variety of cells including vascular smooth muscle cells (VSMCs). The dynamic interplay of Ca2+ and K+ channels on the plasma membrane of VSMCs plays a pivotal role in modulating the vascular tone of small arteries and arterioles. The abnormally-elevated arterial tone observed in hypertension thus points to an aberrant expression and function of Ca2+ and K+ channels in the VSMCs. In this short review, we focus on the three well-studied ion channels in VSMCs, namely the L-type Ca2+ (CaV1.2) channels, the voltage-gated K+ (KV) channels, and the large-conductance Ca2+-activated K+ (BK) channels. First, we provide a brief overview on the physiological role of vascular CaV1.2, KV and BK channels in regulating arterial tone. Second, we discuss the current understanding of the expression changes and regulation of CaV1.2, KV and BK channels in the vasculature during hypertension. Third, based on available proof-of-concept studies, we describe the potential therapeutic approaches targeting these vascular ion channels in order to restore blood pressure to normotensive levels. PMID:23376354

  6. Diversity of folds in animal toxins acting on ion channels.

    PubMed Central

    Mouhat, Stéphanie; Jouirou, Besma; Mosbah, Amor; De Waard, Michel; Sabatier, Jean-Marc

    2004-01-01

    Animal toxins acting on ion channels of excitable cells are principally highly potent short peptides that are present in limited amounts in the venoms of various unrelated species, such as scorpions, snakes, sea anemones, spiders, insects, marine cone snails and worms. These toxins have been used extensively as invaluable biochemical and pharmacological tools to characterize and discriminate between the various ion channel types that differ in ionic selectivity, structure and/or cell function. Alongside the huge molecular and functional diversity of ion channels, a no less impressive structural diversity of animal toxins has been indicated by the discovery of an increasing number of polypeptide folds that are able to target these ion channels. Indeed, it appears that these peptide toxins have evolved over time on the basis of clearly distinct architectural motifs, in order to adapt to different ion channel modulating strategies (pore blockers compared with gating modifiers). Herein, we provide an up-to-date overview of the various types of fold from animal toxins that act on ion channels selective for K+, Na+, Ca2+ or Cl- ions, with special emphasis on disulphide bridge frameworks and structural motifs associated with these peptide folds. PMID:14674883

  7. Surface potentials and the calculated selectivity of ion channels.

    PubMed Central

    Miedema, Henk

    2002-01-01

    Ion channels catalyze the transport of ions across biological membranes. A proper understanding of ion-channel functioning is essential to our knowledge of cell physiology, and, in this context, ion-channel selectivity is a key concept. The extent to which a channel permeates two ion species, a and b, is expressed by the permeability ratio, P(a)/P(b). This paper addresses a complication in the calculation of P(a)/P(b) that is related to the existence of surface potentials (psi) and that so far has not been fully appreciated. This paper shows the rather surprising effect of psi on the calculated P(a)/P(b) of a channel that is permeable to two ion species of different valence. If we ignore psi, we conclude, for instance, P(a) > P(b). If we implement psi in the calculation of P(a)/P(b), we may, however, conclude exactly the reverse, i.e., P(a) < P(b). Because electrostatic potentials arise at the surface of essentially all biological membranes, this paper argues for a more critical evaluation of ion channel selectivity measurements. PMID:11751304

  8. Cyclisation increases the stability of the sea anemone peptide APETx2 but decreases its activity at acid-sensing ion channel 3.

    PubMed

    Jensen, Jonas E; Mobli, Mehdi; Brust, Andreas; Alewood, Paul F; King, Glenn F; Rash, Lachlan D

    2012-07-01

    APETx2 is a peptide isolated from the sea anemone Anthopleura elegantissima. It is the most potent and selective inhibitor of acid-sensing ion channel 3 (ASIC3) and it is currently in preclinical studies as a novel analgesic for the treatment of chronic inflammatory pain. As a peptide it faces many challenges in the drug development process, including the potential lack of stability often associated with therapeutic peptides. In this study we determined the susceptibility of wild-type APETx2 to trypsin and pepsin and tested the applicability of backbone cyclisation as a strategy to improve its resistance to enzymatic degradation. Cyclisation with either a six-, seven- or eight-residue linker vastly improved the protease resistance of APETx2 but substantially decreased its potency against ASIC3. This suggests that either the N- or C-terminus of APETx2 is involved in its interaction with the channel, which we confirmed by making N- and C-terminal truncations. Truncation of either terminus, but especially the N-terminus, has detrimental effects on the ability of APETx2 to inhibit ASIC3. The current work indicates that cyclisation is unlikely to be a suitable strategy for stabilising APETx2, unless linkers can be engineered that do not interfere with binding to ASIC3. PMID:22851922

  9. Cyclisation Increases the Stability of the Sea Anemone Peptide APETx2 but Decreases Its Activity at Acid-Sensing Ion Channel 3

    PubMed Central

    Jensen, Jonas E.; Mobli, Mehdi; Brust, Andreas; Alewood, Paul F.; King, Glenn F.; Rash, Lachlan D.

    2012-01-01

    APETx2 is a peptide isolated from the sea anemone Anthopleura elegantissima. It is the most potent and selective inhibitor of acid-sensing ion channel 3 (ASIC3) and it is currently in preclinical studies as a novel analgesic for the treatment of chronic inflammatory pain. As a peptide it faces many challenges in the drug development process, including the potential lack of stability often associated with therapeutic peptides. In this study we determined the susceptibility of wild-type APETx2 to trypsin and pepsin and tested the applicability of backbone cyclisation as a strategy to improve its resistance to enzymatic degradation. Cyclisation with either a six-, seven- or eight-residue linker vastly improved the protease resistance of APETx2 but substantially decreased its potency against ASIC3. This suggests that either the N- or C-terminus of APETx2 is involved in its interaction with the channel, which we confirmed by making N- and C-terminal truncations. Truncation of either terminus, but especially the N-terminus, has detrimental effects on the ability of APETx2 to inhibit ASIC3. The current work indicates that cyclisation is unlikely to be a suitable strategy for stabilising APETx2, unless linkers can be engineered that do not interfere with binding to ASIC3. PMID:22851922

  10. Structural analysis of calmodulin binding to ion channels demonstrates the role of its plasticity in regulation.

    PubMed

    Kovalevskaya, Nadezda V; van de Waterbeemd, Michiel; Bokhovchuk, Fedir M; Bate, Neil; Bindels, René J M; Hoenderop, Joost G J; Vuister, Geerten W

    2013-11-01

    The Ca²⁺-binding protein calmodulin (CaM) is a well-known regulator of ion-channel activity. Consequently, the Protein Data Bank contains many structures of CaM in complex with different fragments of ion channels that together display a variety of binding modes. In addition to the canonical interaction, in which CaM engages its target with both its domains, many of the ion-channel-CaM complexes demonstrate alternative non-canonical binding modes that depend on the target and experimental conditions. Based on these findings, several mechanisms of ion-channel regulation by CaM have been proposed, all exploiting its plasticity and flexibility in interacting with its targets. In this review, we focus on complexes of CaM with either the voltage-gated calcium channels; the voltage-gated sodium channels or the small conductance calcium-activated potassium channels, for which both structural and functional data are available. For each channel, the functional relevance of these structural data and possible mechanism of calcium-dependent (in)activation and/or facilitation are discussed in detail. PMID:23609407

  11. Spiral wave death, breakup induced by ion channel poisoning on regular Hodgkin-Huxley neuronal networks

    NASA Astrophysics Data System (ADS)

    Ma, Jun; Huang, Long; Tang, Jun; Ying, He-Ping; Jin, Wu-Yin

    2012-11-01

    The electric activities of neurons are often affected by ion channel poisoning, in particularly, interrupting normal transduction of signals within the brain. This may be due to changes in conductance and the number of active channels. Tetraethylammonium, for example, is known to cause ion channel poisoning of potassium channels, while tetrodotoxin has similar detrimental effects on sodium channels. The occurrence of spiral waves in neuronal systems was observed frequently in the past, and it was argued that these waves of excitation may play an important role by the propagation of electric signals across the quiescent regions of the brain. In this work, the parameters xk and xNa determine the ratio, with regards to the total number of ion channels, of active potassium and sodium channels, respectively, and they are taken to be representative also for the degree of channel poisoning. In the numerical studies, a well developed stable rotating spiral wave is used as the initial state to be controlled by the ion channel poisoning. We show that, under noise-free conditions, spiral waves are terminated whenever xk and xNa are set lower than a given threshold. However, breakup of spiral wave occurs if the intensity of the channel noise increases. In order to quantify these observations, we use a simple but robust synchronization measure, which captures succinctly the transition from spiral waves to homogeneous neuronal activity and/or broken turbulent state. The critical thresholds can be inferred from the abrupt changes occurring in the corresponding dependencies of synchronization versus the xk and xNa ratios. Furthermore, the sampled membrane potentials of a single neuron are recorded to detect the periodical spiral wave in a feasible way and the results could be dependent of the position of node (or site) to be monitored. Notably, small synchronization factors can be tightly associated to states where the formation of spiral waves is robust to channel poisoning and

  12. Antibody therapeutics targeting ion channels: are we there yet?

    PubMed Central

    Sun, Han; Li, Min

    2013-01-01

    The combination of technological advances, genomic sequences and market success is catalyzing rapid development of antibody-based therapeutics. Cell surface receptors and ion channel proteins are well known drug targets, but the latter has seen less success. The availability of crystal structures, better understanding of gating biophysics and validation of physiological roles now form an excellent foundation to pursue antibody-based therapeutics targeting ion channels to treat a variety of diseases. PMID:23381110

  13. The dynamics of small excitable ion channel clusters

    NASA Astrophysics Data System (ADS)

    Shuai, J. W.; Jung, P.

    2006-06-01

    Through computational modeling we predict that small sodium ion channel clusters on small patches of membrane can encode electric signals most efficiently at certain magic cluster sizes. We show that this effect can be traced back to algebraic features of small integers and are universal for channels with a simple gating dynamics. We further explore physiologic conditions under which such effects can occur.

  14. Three Homologous Subunits Form a High Affinity Peptide-gated Ion Channel in Hydra*

    PubMed Central

    Dürrnagel, Stefan; Kuhn, Anne; Tsiairis, Charisios D.; Williamson, Michael; Kalbacher, Hubert; Grimmelikhuijzen, Cornelis J. P.; Holstein, Thomas W.; Gründer, Stefan

    2010-01-01

    Recently, three ion channel subunits of the degenerin (DEG)/epithelial Na+ channel (ENaC) gene family have been cloned from the freshwater polyp Hydra magnipapillata, the Hydra Na+ channels (HyNaCs) 2–4. Two of them, HyNaC2 and HyNaC3, co-assemble to form an ion channel that is gated by the neuropeptides Hydra-RFamides I and II. The HyNaC2/3 channel is so far the only cloned ionotropic receptor from cnidarians and, together with the related ionotropic receptor FMRFamide-activated Na+ channel (FaNaC) from snails, the only known peptide-gated ionotropic receptor. The HyNaC2/3 channel has pore properties, like a low Na+ selectivity and a low amiloride affinity, that are different from other channels of the DEG/ENaC gene family, suggesting that a component of the native Hydra channel might still be lacking. Here, we report the cloning of a new ion channel subunit from Hydra, HyNaC5. The new subunit is closely related to HyNaC2 and -3 and co-localizes with HyNaC2 and -3 to the base of the tentacles. Coexpression in Xenopus oocytes of HyNaC5 with HyNaC2 and -3 largely increases current amplitude after peptide stimulation and affinity of the channel to Hydra-RFamides I and II. Moreover, the HyNaC2/3/5 channel has altered pore properties and amiloride affinity, more similarly to other DEG/ENaC channels. Collectively, our results suggest that the three homologous subunits HyNaC2, -3, and -5 form a peptide-gated ion channel in Hydra that could contribute to fast synaptic transmission. PMID:20159980

  15. The venom of the fishing spider Dolomedes sulfurous contains various neurotoxins acting on voltage-activated ion channels in rat dorsal root ganglion neurons.

    PubMed

    Wang, Hengyun; Zhang, Fan; Li, Dan; Xu, Shiyan; He, Juan; Yu, Hai; Li, Jiayan; Liu, Zhonghua; Liang, Songping

    2013-04-01

    Dolomedes sulfurous is a venomous spider distributed in the south of China and characterized with feeding on fish. The venom exhibits great diversity and contains hundreds of peptides as revealed by off-line RP-HPLC/MALDI-TOF-MS analysis. The venom peptides followed a triple-modal distribution, with 40.7% of peptides falling in the mass range of 1000-3000 Da, 25.6% peptides in the 7000-9000 Da range and 23.5% peptides in the 3000-5000 Da range. This distribution modal is rather different from these of peptides from other spider venoms analyzed. The venom could inhibit voltage-activated Na(+), K(+) and Ca(2+) channels in rat DRG neurons as revealed by voltage-clamp analysis. Significantly, the venom exhibited inhibitory effects on TTX-R Na(+) and T-type Ca(2+) currents, suggesting that there exist both channel antagonists which might be valuable tools for investigation of both channels and drug development. Additionally, intrathoracically injection of venom could cause serve neurotoxic effects on zebrafish and death at higher concentrations. The LD50 value was calculated to be 28.8 μg/g body weight. Our results indicated that the venom of D. sulfurous contain diverse neurotoxins which serve to capture prey. Intensive studies will be necessary to investigate the structures and functions of specific peptides of the venom in the future. PMID:23391637

  16. Computational Tools for Interpreting Ion Channel pH-Dependence

    PubMed Central

    Sazanavets, Ivan; Warwicker, Jim

    2015-01-01

    Activity in many biological systems is mediated by pH, involving proton titratable groups with pKas in the relevant pH range. Experimental analysis of pH-dependence in proteins focusses on particular sidechains, often with mutagenesis of histidine, due to its pKa near to neutral pH. The key question for algorithms that predict pKas is whether they are sufficiently accurate to effectively narrow the search for molecular determinants of pH-dependence. Through analysis of inwardly rectifying potassium (Kir) channels and acid-sensing ion channels (ASICs), mutational effects on pH-dependence are probed, distinguishing between groups described as pH-coupled or pH-sensor. Whereas mutation can lead to a shift in transition pH between open and closed forms for either type of group, only for pH-sensor groups does mutation modulate the amplitude of the transition. It is shown that a hybrid Finite Difference Poisson-Boltzmann (FDPB) – Debye-Hückel continuum electrostatic model can filter mutation candidates, providing enrichment for key pH-coupled and pH-sensor residues in both ASICs and Kir channels, in comparison with application of FDPB alone. PMID:25915903

  17. Computational Tools for Interpreting Ion Channel pH-Dependence.

    PubMed

    Sazanavets, Ivan; Warwicker, Jim

    2015-01-01

    Activity in many biological systems is mediated by pH, involving proton titratable groups with pKas in the relevant pH range. Experimental analysis of pH-dependence in proteins focusses on particular sidechains, often with mutagenesis of histidine, due to its pKa near to neutral pH. The key question for algorithms that predict pKas is whether they are sufficiently accurate to effectively narrow the search for molecular determinants of pH-dependence. Through analysis of inwardly rectifying potassium (Kir) channels and acid-sensing ion channels (ASICs), mutational effects on pH-dependence are probed, distinguishing between groups described as pH-coupled or pH-sensor. Whereas mutation can lead to a shift in transition pH between open and closed forms for either type of group, only for pH-sensor groups does mutation modulate the amplitude of the transition. It is shown that a hybrid Finite Difference Poisson-Boltzmann (FDPB) - Debye-Hückel continuum electrostatic model can filter mutation candidates, providing enrichment for key pH-coupled and pH-sensor residues in both ASICs and Kir channels, in comparison with application of FDPB alone. PMID:25915903

  18. Structure of the TRPA1 ion channel suggests regulatory mechanisms

    PubMed Central

    Paulsen, Candice E.; Armache, Jean-Paul; Gao, Yuan; Cheng, Yifan; Julius, David

    2015-01-01

    The TRPA1 ion channel (a.k.a the ‘wasabi receptor’) is a detector of noxious chemical agents encountered in our environment or produced endogenously during tissue injury or drug metabolism. These include a broad class of electrophiles that activate the channel through covalent protein modification. TRPA1 antagonists hold potential for treating neurogenic inflammatory conditions provoked or exacerbated by irritant exposure. Despite compelling reasons to understand TRPA1 function, structural mechanisms underlying channel regulation remain obscure. Here, we use single-particle electron cryo-microscopy to determine the structure of full-length human TRPA1 to ~4Å resolution in the presence of pharmacophores, including a potent antagonist. A number of unexpected features are revealed, including an extensive coiled-coil assembly domain stabilized by polyphosphate co-factors and a highly integrated nexus that converges on an unpredicted TRP-like allosteric domain. These findings provide novel insights into mechanisms of TRPA1 regulation, and establish a blueprint for structure-based design of analgesic and anti-inflammatory agents. PMID:25855297

  19. Tuning the ion selectivity of tetrameric cation channels by changing the number of ion binding sites

    SciTech Connect

    Derebe, Mehabaw G.; Sauer, David B.; Zeng, Weizhong; Alam, Amer; Shi, Ning; Jiang, Youxing

    2015-11-30

    Selective ion conduction across ion channel pores is central to cellular physiology. To understand the underlying principles of ion selectivity in tetrameric cation channels, we engineered a set of cation channel pores based on the nonselective NaK channel and determined their structures to high resolution. These structures showcase an ensemble of selectivity filters with a various number of contiguous ion binding sites ranging from 2 to 4, with each individual site maintaining a geometry and ligand environment virtually identical to that of equivalent sites in K{sup +} channel selectivity filters. Combined with single channel electrophysiology, we show that only the channel with four ion binding sites is K{sup +} selective, whereas those with two or three are nonselective and permeate Na{sup +} and K{sup +} equally well. These observations strongly suggest that the number of contiguous ion binding sites in a single file is the key determinant of the channel's selectivity properties and the presence of four sites in K{sup +} channels is essential for highly selective and efficient permeation of K{sup +} ions.

  20. Mass-dependent channel electron multiplier operation. [for ion detection

    NASA Technical Reports Server (NTRS)

    Fields, S. A.; Burch, J. L.; Oran, W. A.

    1977-01-01

    The absolute counting efficiency and pulse height distributions of a continuous-channel electron multiplier used in the detection of hydrogen, argon and xenon ions are assessed. The assessment technique, which involves the post-acceleration of 8-eV ion beams to energies from 100 to 4000 eV, provides information on counting efficiency versus post-acceleration voltage characteristics over a wide range of ion mass. The charge pulse height distributions for H2 (+), A (+) and Xe (+) were measured by operating the experimental apparatus in a marginally gain-saturated mode. It was found that gain saturation occurs at lower channel multiplier operating voltages for light ions such as H2 (+) than for the heavier ions A (+) and Xe (+), suggesting that the technique may be used to discriminate between these two classes of ions in electrostatic analyzers.

  1. Small iminium ions block gramicidin channels in lipid bilayers.

    PubMed Central

    Hemsley, G; Busath, D

    1991-01-01

    Guanidinium and acetamidinium, when added to the bathing solution in concentrations of approximately 0.1M, cause brief blocks in the single channel potassium currents from channels formed in planar lipid bilayers by gramicidin A. Single channel lifetimes are not affected indicating that the channel structure is not modified by the blockers. Guanidinium block durations and interblock times are approximately exponential in distribution. Block frequencies increase with guanidinium concentration whereas block durations are unaffected. Increases in membrane potential cause an increase in block frequency as expected for a positively charged blocker but a decrease in block duration suggesting that the block is relieved when the blocker passes through the channel. At low pH, urea, formamide, and acetamide cause similar blocks suggesting that the protonated species of these molecules also block. Arginine and several amines do not block. This indicates that only iminium ions which are small enough to enter the channel can cause blocks in gramicidin channels. PMID:1712240

  2. Principles of selective ion transport in channels and pumps.

    PubMed

    Gouaux, Eric; Mackinnon, Roderick

    2005-12-01

    The transport of ions across the membranes of cells and organelles is a prerequisite for many of life's processes. Transport often involves very precise selectivity for specific ions. Recently, atomic-resolution structures have been determined for channels or pumps that are selective for sodium, potassium, calcium, and chloride: four of the most abundant ions in biology. From these structures we can begin to understand the principles of selective ion transport in terms of the architecture and detailed chemistry of the ion conduction pathways. PMID:16322449

  3. Patch Clamp Recording of Ion Channels Expressed in Xenopus Oocytes

    PubMed Central

    L Brown, Austin; E. Johnson, Brandon; B. Goodman, Miriam

    2008-01-01

    Since its development by Sakmann and Neher 1, 2, the patch clamp has become established as an extremely useful technique for electrophysiological measurement of single or multiple ion channels in cells. This technique can be applied to ion channels in both their native environment and expressed in heterologous cells, such as oocytes harvested from the African clawed frog, Xenopus laevis. Here, we describe the well-established technique of patch clamp recording from Xenopus oocytes. This technique is used to measure the properties of expressed ion channels either in populations (macropatch) or individually (single-channel recording). We focus on techniques to maximize the quality of oocyte preparation and seal generation. With all factors optimized, this technique gives a probability of successful seal generation over 90 percent. The process may be optimized differently by every researcher based on the factors he or she finds most important, and we present the approach that have lead to the greatest success in our hands. PMID:19078941

  4. Alternative paradigms for ion channelopathies: disorders of ion channel membrane trafficking and posttranslational modification.

    PubMed

    Curran, Jerry; Mohler, Peter J

    2015-01-01

    Channelopathies are a diverse set of disorders associated with defects in ion channel (and transporter) function. Although the vast majority of channelopathies are linked with inherited mutations that alter ion channel biophysical properties, another group of similar disorders has emerged that alter ion channel synthesis, membrane trafficking, and/or posttranslational modifications. In fact, some electrical and episodic disorders have now been identified that are not defects in the ion channel but instead reflect dysfunction in an ion channel (or transporter) regulatory protein. This review focuses on alternative paradigms for physiological disorders associated with protein biosynthesis, folding, trafficking, and membrane retention. Furthermore, the review highlights the role of aberrant posttranslational modifications in acquired channelopathies. PMID:25293528

  5. Turning a Poor Ion Channel into a Good Pump

    NASA Astrophysics Data System (ADS)

    Astumian, Dean

    2003-05-01

    We consider a membrane protein that can exist in two configurations, either one of which acts as a poor ion channel, allowing ions to slowly leak across the membrane from high to low elctrochemical potential. We show that random external fluctuations can provide the energy to turn this poor channel into a good pump that drives ion transport from low to high electrochemical potential. We discuss this result in terms of a gambling analogy, and point to possible implications for fields as far ranging as population biology, economics, and actuarial science.

  6. The ion channel inverse problem: neuroinformatics meets biophysics.

    PubMed

    Cannon, Robert C; D'Alessandro, Giampaolo

    2006-08-25

    Ion channels are the building blocks of the information processing capability of neurons: any realistic computational model of a neuron must include reliable and effective ion channel components. Sophisticated statistical and computational tools have been developed to study the ion channel structure-function relationship, but this work is rarely incorporated into the models used for single neurons or small networks. The disjunction is partly a matter of convention. Structure-function studies typically use a single Markov model for the whole channel whereas until recently whole-cell modeling software has focused on serial, independent, two-state subunits that can be represented by the Hodgkin-Huxley equations. More fundamentally, there is a difference in purpose that prevents models being easily reused. Biophysical models are typically developed to study one particular aspect of channel gating in detail, whereas neural modelers require broad coverage of the entire range of channel behavior that is often best achieved with approximate representations that omit structural features that cannot be adequately constrained. To bridge the gap so that more recent channel data can be used in neural models requires new computational infrastructure for bringing together diverse sources of data to arrive at best-fit models for whole-cell modeling. We review the current state of channel modeling and explore the developments needed for its conclusions to be integrated into whole-cell modeling. PMID:16933979

  7. Postranslational Modification of Ion Channels in Colonic Inflammation.

    PubMed

    Akbarali, Hamid I; Kang, Minho

    2015-01-01

    Voltage-gated ion channels are key regulators of cell excitability. There is significant evidence that these channels are subject to modulation by redox status of the cells. Here we review the post-translational modifications of ion channels that occur in colonic inflammation. The redox mechanisms involve tyrosine nitration, covalent modification of cysteine residues and sulfhydration by hydrogen sulfide in experimental colitis. In the setting of colonic inflammation, modifications of cysteine and tyrosine are likely to occur at several sites within the same channel complex. In this review we describe alterations in channel function due to specific modifications of tyrosine and cysteine residues by reactive nitrogen, oxygen and hydrogen-sulfide resulting in altered motility. PMID:26411766

  8. Targeting ion channels for the treatment of gastrointestinal motility disorders

    PubMed Central

    Beyder, Arthur

    2012-01-01

    Gastrointestinal (GI) functional and motility disorders are highly prevalent and responsible for long-term morbidity and sometimes mortality in the affected patients. It is estimated that one in three persons has a GI functional or motility disorder. However, diagnosis and treatment of these widespread conditions remains challenging. This partly stems from the multisystem pathophysiology, including processing abnormalities in the central and peripheral (enteric) nervous systems and motor dysfunction in the GI wall. Interstitial cells of Cajal (ICCs) are central to the generation and propagation of the cyclical electrical activity and smooth muscle cells (SMCs) are responsible for electromechanical coupling. In these and other excitable cells voltage-sensitive ion channels (VSICs) are the main molecular units that generate and regulate electrical activity. Thus, VSICs are potential targets for intervention in GI motility disorders. Research in this area has flourished with advances in the experimental methods in molecular and structural biology and electrophysiology. However, our understanding of the molecular mechanisms responsible for the complex and variable electrical behavior of ICCs and SMCs remains incomplete. In this review, we focus on the slow waves and action potentials in ICCs and SMCs. We describe the constituent VSICs, which include voltage-gated sodium (NaV), calcium (CaV), potassium (KV, KCa), chloride (Cl–) and nonselective ion channels (transient receptor potentials [TRPs]). VSICs have significant structural homology and common functional mechanisms. We outline the approaches and limitations and provide examples of targeting VSICs at the pores, voltage sensors and alternatively spliced sites. Rational drug design can come from an integrated view of the structure and mechanisms of gating and activation by voltage or mechanical stress. PMID:22282704

  9. Hydrogen peroxide affects ion channels in lily pollen grain protoplasts.

    PubMed

    Breygina, M A; Abramochkin, D V; Maksimov, N M; Yermakov, I P

    2016-09-01

    Ion homeostasis plays a central role in polarisation and polar growth. In several cell types ion channels are controlled by reactive oxygen species (ROS). One of the most important cells in the plant life cycle is the male gametophyte, which grows under the tight control of both ion fluxes and ROS balance. The precise relationship between these two factors in pollen tubes has not been completely elucidated, and in pollen grains it has never been studied to date. In the present study we used a simple model - protoplasts obtained from lily pollen grains at the early germination stage - to reveal the effect of H2 O2 on cation fluxes crucial for pollen germination. Here we present direct evidence for two ROS-sensitive currents on the pollen grain plasma membrane: the hyperpolarisation-activated calcium current, which is strongly enhanced by H2 O2 , and the outward potassium current, which is modestly enhanced by H2 O2 . We used low concentrations of H2 O2 that do not cause an intracellular oxidative burst and do not damage cells, as demonstrated with fluorescent staining. PMID:27115728

  10. Aluminium and hydrogen ions inhibit a mechanosensory calcium-selective cation channel

    NASA Technical Reports Server (NTRS)

    Ding, J. P.; Pickard, B. G.

    1993-01-01

    The tension-dependent activity of mechanosensory calcium-selective cation channels in excised plasmalemmal patches from onion bulb scale epidermis is modulated by pH in the physiologically meaningful range between 4.5 and 7.2. It is rapidly lowered by lowering pH and rapidly raised by raising pH. Channel activity is effectively inhibited by low levels of aluminium ions and activity can be partially restored by washing for a few minutes. We suggest that under normal conditions the sensitivity of the mechanosensory channels to pH of the wall free space plays important roles in regulation of plant activities such as growth. We further suggest that, when levels of acid and aluminium ions in the soil solution are high, they might inhibit similar sensory channels in cells of the root tip, thus contributing critically to the acid soil syndrome.

  11. Control of Neuronal Voltage-Gated Calcium Ion Channels From RNA to Protein

    PubMed Central

    Lipscombe, Diane; Allen, Summer E; Toro, Cecilia P.

    2013-01-01

    Voltage-gated calcium (CaV) ion channels convert neuronal activity into rapid intracellular calcium signals to trigger a myriad of cellular responses. Their involvement in major neurological and psychiatric diseases, and importance as therapeutic targets, has propelled interest in subcellular-specific mechanisms that align CaV channel activity to specific tasks. Here we highlight recent studies that delineate mechanisms controlling the expression of CaV channels at the level of RNA and protein. We discuss the roles of RNA editing and alternative pre-mRNA splicing in generating CaV channel isoforms with activities specific to the demands of individual cells; the roles of ubiquitination and accessory proteins in regulating CaV channel expression; and the specific binding partners which contribute to both pre- and post- synaptic CaV channel function. PMID:23907011

  12. Control of neuronal voltage-gated calcium ion channels from RNA to protein.

    PubMed

    Lipscombe, Diane; Allen, Summer E; Toro, Cecilia P

    2013-10-01

    Voltage-gated calcium ion (CaV) channels convert neuronal activity into rapid intracellular calcium signals to trigger a myriad of cellular responses. Their involvement in major neurological and psychiatric diseases, and importance as therapeutic targets, has propelled interest in subcellular-specific mechanisms that align CaV channel activity to specific tasks. Here, we highlight recent studies that delineate mechanisms controlling the expression of CaV channels at the level of RNA and protein. We discuss the roles of RNA editing and alternative pre-mRNA splicing in generating CaV channel isoforms with activities specific to the demands of individual cells; the roles of ubiquitination and accessory proteins in regulating CaV channel expression; and the specific binding partners that contribute to both pre- and postsynaptic CaV channel function. PMID:23907011

  13. Pharmacological targeting of ion channels for cancer therapy: In vivo evidences.

    PubMed

    Leanza, Luigi; Managò, Antonella; Zoratti, Mario; Gulbins, Erich; Szabo, Ildiko

    2016-06-01

    Since the discovery of the participation of various ion channels in the regulation of cell proliferation and programmed cell death two decades ago, the field exploring ion channel function in relation to cancer has undergone rapid development. Although the mechanisms accounting for the impact of ion channel modulators on cancer growth have not been fully clarified in all cases, numerous in vivo experiments targeting diverse ion channels in various cancer models illustrate the great potentiality of this approach and promote ion channels to the class of oncological targets. In the present review we give an updated overview of the field and critically discuss the promising results obtained in pre-clinical models using specific pharmacological modulators of calcium, sodium, potassium and anion-permeable ion channels, whose expression is often altered in tumor cells and tissues. The most, especially critical issues are specificity of action and side-effects. Interestingly, some of the most potent drugs are natural products, and several of the active compounds are already used in the clinic for other purposes. In these latter cases involving drug repositioning we may expect a faster progression from preclinical to clinical studies. This article is part of a Special Issue entitled: Calcium and Cell Fate. Guest Editors: Jacques Haiech, Claus Heizmann, Joachim Krebs, Thierry Capiod and Olivier Mignen. PMID:26658642

  14. Ion fluxes through nanopores and transmembrane channels

    NASA Astrophysics Data System (ADS)

    Bordin, J. R.; Diehl, A.; Barbosa, M. C.; Levin, Y.

    2012-03-01

    We introduce an implicit solvent Molecular Dynamics approach for calculating ionic fluxes through narrow nanopores and transmembrane channels. The method relies on a dual-control-volume grand-canonical molecular dynamics (DCV-GCMD) simulation and the analytical solution for the electrostatic potential inside a cylindrical nanopore recently obtained by Levin [Europhys. Lett.EULEEJ0295-507510.1209/epl/i2006-10240-4 76, 163 (2006)]. The theory is used to calculate the ionic fluxes through an artificial transmembrane channel which mimics the antibacterial gramicidin A channel. Both current-voltage and current-concentration relations are calculated under various experimental conditions. We show that our results are comparable to the characteristics associated to the gramicidin A pore, especially the existence of two binding sites inside the pore and the observed saturation in the current-concentration profiles.

  15. Stochastic differential equation models for ion channel noise in Hodgkin-Huxley neurons.

    PubMed

    Goldwyn, Joshua H; Imennov, Nikita S; Famulare, Michael; Shea-Brown, Eric

    2011-04-01

    The random transitions of ion channels between conducting and nonconducting states generate a source of internal fluctuations in a neuron, known as channel noise. The standard method for modeling the states of ion channels nonlinearly couples continuous-time Markov chains to a differential equation for voltage. Beginning with the work of R. F. Fox and Y.-N. Lu [Phys. Rev. E 49, 3421 (1994)], there have been attempts to generate simpler models that use stochastic differential equation (SDEs) to approximate the stochastic spiking activity produced by Markov chain models. Recent numerical investigations, however, have raised doubts that SDE models can capture the stochastic dynamics of Markov chain models.We analyze three SDE models that have been proposed as approximations to the Markov chain model: one that describes the states of the ion channels and two that describe the states of the ion channel subunits. We show that the former channel-based approach can capture the distribution of channel noise and its effects on spiking in a Hodgkin-Huxley neuron model to a degree not previously demonstrated, but the latter two subunit-based approaches cannot. Our analysis provides intuitive and mathematical explanations for why this is the case. The temporal correlation in the channel noise is determined by the combinatorics of bundling subunits into channels, but the subunit-based approaches do not correctly account for this structure. Our study confirms and elucidates the findings of previous numerical investigations of subunit-based SDE models. Moreover, it presents evidence that Markov chain models of the nonlinear, stochastic dynamics of neural membranes can be accurately approximated by SDEs. This finding opens a door to future modeling work using SDE techniques to further illuminate the effects of ion channel fluctuations on electrically active cells. PMID:21599202

  16. EPR Studies of Gating Mechanisms in Ion Channels

    PubMed Central

    Chakrapani, Sudha

    2015-01-01

    Ion channels open and close in response to diverse stimuli, and the molecular events underlying these processes are extensively modulated by ligands of both endogenous and exogenous origin. In the past decade, high-resolution structures of several channel types have been solved, providing unprecedented details of the molecular architecture of these membrane proteins. Intrinsic conformational flexibility of ion channels critically governs their functions. However, the dynamics underlying gating mechanisms and modulations are obscured in the information from crystal structures. While nuclear magnetic resonance spectroscopic methods allow direct measurements of protein dynamics, they are limited by the large size of these membrane protein assemblies in detergent micelles or lipid membranes. Electron paramagnetic resonance (EPR) spectroscopy has emerged as a key biophysical tool to characterize structural dynamics of ion channels and to determine stimulus-driven conformational transition between functional states in a physiological environment. This review will provide an overview of the recent advances in the field of voltage- and ligand-gated channels and highlight some of the challenges and controversies surrounding the structural information available. It will discuss general methods used in site-directed spin labeling and EPR spectroscopy and illustrate how findings from these studies have narrowed the gap between high-resolution structures and gating mechanisms in membranes, and have thereby helped reconcile seemingly disparate models of ion channel function. PMID:25950970

  17. Potassium ion channels and allergic asthma.

    PubMed

    Kocmalova, M; Oravec, M; Adamkov, M; Sadlonova, V; Kazimierova, I; Medvedova, I; Joskova, M; Franova, S; Sutovska, M

    2015-01-01

    High-conductive calcium-sensitive potassium channels (BK+Ca) and ATP-sensitive potassium (K+ATP) channels play a significant role in the airway smooth muscle cell and goblet cell function, and cytokine production. The present study evaluated the therapeutic potential of BK+Ca and K+ATP openers, NS 1619 and pinacidil, respectively, in an experimental model of allergic inflammation. Airway allergic inflammation was induced with ovalbumine in guinea pigs during 21 days, which was followed by a 14-day treatment with BK+Ca and K+ATP openers. The outcome measures were airway smooth muscle cells reactivity in vivo and in vitro, cilia beating frequency and the level of exhaled NO (ENO), and the level of pro-inflammatory cytokines in the plasma and bronchoalveolar lavage fluid. The openers of both channels decreased airway smooth muscle cells reactivity, cilia beating frequency, and cytokine levels in the serum. Furthermore, NS1619 reduced ENO and inflammatory cells infiltration. The findings confirmed the presence of beneficial effects of BK+Ca and K+ATP openers on airway defence mechanisms. Although both openers dampened pro-inflammatory cytokines and mast cells infiltration, an evident anti-inflammatory effect was provided only by NS1619. Therefore, we conclude that particularly BK+Ca channels represent a promising new drug target in treatment of airway's allergic inflammation. PMID:25315623

  18. Molecular Dynamical Study on Ion Channeling through Peptide Nanotube

    NASA Astrophysics Data System (ADS)

    Sumiya, Norihito; Igami, Daiki; Takeda, Kyozaburo

    2011-12-01

    We theoretically study the possibility of ion channeling through peptide nanotubes (PNTs). After designing the minimal peptide nanorings (PNRs) and their aggregated form (peptide nanotubes, PNT) computationally, we carry out molecular dynamics (MD) calculations for cation channeling. The present MD calculations show that cation channeling through PNTs occurs. Furthermore, inter-ring hydrogen bonds (HBs) survive and maintain the tubular form of PNTs during cation channeling. We introduce mobility such that cation channeling can be evaluated quantitatively. As the ionic radius of the cation becomes smaller, the effective relaxation time τ becomes larger. Accordingly, mobilities of 10-2˜10-3[cm2/volt/sec] are calculated. In contrast, when an anion (F-) passes through the PNT, the inter-ring HBs are broken, thus inducing breakdown of the peptide backbone. Consequently, H atoms from the broken HBs surround the channeling anion (F-) and halt its motion.

  19. Ion Concentration- and Voltage-Dependent Push and Pull Mechanisms of Potassium Channel Ion Conduction

    PubMed Central

    Kasahara, Kota; Shirota, Matsuyuki; Kinoshita, Kengo

    2016-01-01

    The mechanism of ion conduction by potassium channels is one of the central issues in physiology. In particular, it is still unclear how the ion concentration and the membrane voltage drive ion conduction. We have investigated the dynamics of the ion conduction processes in the Kv1.2 pore domain, by molecular dynamics (MD) simulations with several different voltages and ion concentrations. By focusing on the detailed ion movements through the pore including selectivity filter (SF) and cavity, we found two major conduction mechanisms, called the III-IV-III and III-II-III mechanisms, and the balance between the ion concentration and the voltage determines the mechanism preference. In the III-IV-III mechanism, the outermost ion in the pore is pushed out by a new ion coming from the intracellular fluid, and four-ion states were transiently observed. In the III-II-III mechanism, the outermost ion is pulled out first, without pushing by incoming ions. Increases in the ion concentration and voltage accelerated ion conductions, but their mechanisms were different. The increase in the ion concentrations facilitated the III-IV-III conductions, while the higher voltages increased the III-II-III conductions, indicating that the pore domain of potassium channels permeates ions by using two different driving forces: a push by intracellular ions and a pull by voltage. PMID:26950215

  20. Ion Concentration- and Voltage-Dependent Push and Pull Mechanisms of Potassium Channel Ion Conduction.

    PubMed

    Kasahara, Kota; Shirota, Matsuyuki; Kinoshita, Kengo

    2016-01-01

    The mechanism of ion conduction by potassium channels is one of the central issues in physiology. In particular, it is still unclear how the ion concentration and the membrane voltage drive ion conduction. We have investigated the dynamics of the ion conduction processes in the Kv1.2 pore domain, by molecular dynamics (MD) simulations with several different voltages and ion concentrations. By focusing on the detailed ion movements through the pore including selectivity filter (SF) and cavity, we found two major conduction mechanisms, called the III-IV-III and III-II-III mechanisms, and the balance between the ion concentration and the voltage determines the mechanism preference. In the III-IV-III mechanism, the outermost ion in the pore is pushed out by a new ion coming from the intracellular fluid, and four-ion states were transiently observed. In the III-II-III mechanism, the outermost ion is pulled out first, without pushing by incoming ions. Increases in the ion concentration and voltage accelerated ion conductions, but their mechanisms were different. The increase in the ion concentrations facilitated the III-IV-III conductions, while the higher voltages increased the III-II-III conductions, indicating that the pore domain of potassium channels permeates ions by using two different driving forces: a push by intracellular ions and a pull by voltage. PMID:26950215

  1. Rapid optical control of nociception with an ion-channel photoswitch.

    PubMed

    Mourot, Alexandre; Fehrentz, Timm; Le Feuvre, Yves; Smith, Caleb M; Herold, Christian; Dalkara, Deniz; Nagy, Frédéric; Trauner, Dirk; Kramer, Richard H

    2012-04-01

    Local anesthetics effectively suppress pain sensation, but most of these compounds act nonselectively, inhibiting activity of all neurons. Moreover, their actions abate slowly, preventing precise spatial and temporal control of nociception. We developed a photoisomerizable molecule, quaternary ammonium-azobenzene-quaternary ammonium (QAQ), that enables rapid and selective optical control of nociception. QAQ is membrane-impermeant and has no effect on most cells, but it infiltrates pain-sensing neurons through endogenous ion channels that are activated by noxious stimuli, primarily TRPV1. After QAQ accumulates intracellularly, it blocks voltage-gated ion channels in the trans form but not the cis form. QAQ enables reversible optical silencing of mouse nociceptive neuron firing without exogenous gene expression and can serve as a light-sensitive analgesic in rats in vivo. Because intracellular QAQ accumulation is a consequence of nociceptive ion-channel activity, QAQ-mediated photosensitization is a platform for understanding signaling mechanisms in acute and chronic pain. PMID:22343342

  2. Structural basis of ion permeation gating in Slo2.1 K+ channels

    PubMed Central

    Garg, Priyanka; Gardner, Alison; Garg, Vivek

    2013-01-01

    The activation gate of ion channels controls the transmembrane flux of permeant ions. In voltage-gated K+ channels, the aperture formed by the S6 bundle crossing can widen to open or narrow to close the ion permeation pathway, whereas the selectivity filter gates ion flux in cyclic-nucleotide gated (CNG) and Slo1 channels. Here we explore the structural basis of the activation gate for Slo2.1, a weakly voltage-dependent K+ channel that is activated by intracellular Na+ and Cl−. Slo2.1 channels were heterologously expressed in Xenopus laevis oocytes and activated by elevated [NaCl]i or extracellular application of niflumic acid. In contrast to other voltage-gated channels, Slo2.1 was blocked by verapamil in an activation-independent manner, implying that the S6 bundle crossing does not gate the access of verapamil to its central cavity binding site. The structural basis of Slo2.1 activation was probed by Ala scanning mutagenesis of the S6 segment and by mutation of selected residues in the pore helix and S5 segment. Mutation to Ala of three S6 residues caused reduced trafficking of channels to the cell surface and partial (K256A, I263A, Q273A) or complete loss (E275A) of channel function. P271A Slo2.1 channels trafficked normally, but were nonfunctional. Further mutagenesis and intragenic rescue by second site mutations suggest that Pro271 and Glu275 maintain the inner pore in an open configuration by preventing formation of a tight S6 bundle crossing. Mutation of several residues in S6 and S5 predicted by homology modeling to contact residues in the pore helix induced a gain of channel function. Substitution of the pore helix residue Phe240 with polar residues induced constitutive channel activation. Together these findings suggest that (1) the selectivity filter and not the bundle crossing gates ion permeation and (2) dynamic coupling between the pore helix and the S5 and S6 segments mediates Slo2.1 channel activation. PMID:24166878

  3. Toxic β-Amyloid (Aβ) Alzheimer's Ion Channels: From Structure to Function and Design

    NASA Astrophysics Data System (ADS)

    Nussinov, Ruth

    2012-02-01

    Full-length amyloid beta peptides (Aβ1-40/42) form neuritic amyloid plaques in Alzheimer's disease (AD) patients and are implicated in AD pathology. Recent biophysical and cell biological studies suggest a direct mechanism of amyloid beta toxicity -- ion channel mediated loss of calcium homeostasis. Truncated amyloid beta fragments (Aβ11-42 and Aβ17-42), commonly termed as non-amyloidogenic are also found in amyloid plaques of Alzheimer's disease (AD) and in the preamyloid lesions of Down's syndrome (DS), a model system for early onset AD study. Very little is known about the structure and activity of these smaller peptides although they could be key AD and DS pathological agents. Using complementary techniques of explicit solvent molecular dynamics (MD) simulations, atomic force microscopy (AFM), channel conductance measurements, cell calcium uptake assays, neurite degeneration and cell death assays, we have shown that non-amyloidogenic Aβ9-42 and Aβ17-42 peptides form ion channels with loosely attached subunits and elicit single channel conductances. The subunits appear mobile suggesting insertion of small oligomers, followed by dynamic channel assembly and dissociation. These channels allow calcium uptake in APP-deficient cells and cause neurite degeneration in human cortical neurons. Channel conductance, calcium uptake and neurite degeneration are selectively inhibited by zinc, a blocker of amyloid ion channel activity. Thus truncated Aβ fragments could account for undefined roles played by full length Aβs and provide a novel mechanism of AD and DS pathology. The emerging picture from our large-scale simulations is that toxic ion channels formed by β-sheets are highly polymorphic, and spontaneously break into loosely interacting dynamic units (though still maintaining ion channel structures as imaged with AFM), that associate and dissociate leading to toxic ion flux. This sharply contrasts intact conventional gated ion channels that consist of tightly

  4. Ion binding in the Open HCN Pacemaker Channel Pore: Fast Mechanisms to Shape “Slow” Channels

    PubMed Central

    Lyashchenko, Alex K.; Tibbs, Gareth R.

    2008-01-01

    IH pacemaker channels carry a mixed monovalent cation current that, under physiological ion gradients, reverses at ∼−34 mV, reflecting a 4:1 selectivity for K over Na. However, IH channels display anomalous behavior with respect to permeant ions such that (a) open channels do not exhibit the outward rectification anticipated assuming independence; (b) gating and selectivity are sensitive to the identity and concentrations of externally presented permeant ions; (c) the channels' ability to carry an inward Na current requires the presence of external K even though K is a minor charge carrier at negative voltages. Here we show that open HCN channels (the hyperpolarization-activated, cyclic nucleotide sensitive pore forming subunits of IH) undergo a fast, voltage-dependent block by intracellular Mg in a manner that suggests the ion binds close to, or within, the selectivity filter. Eliminating internal divalent ion block reveals that (a) the K dependence of conduction is mediated via K occupancy of site(s) within the pore and that asymmetrical occupancy and/or coupling of these sites to flux further shapes ion flow, and (b) the kinetics of equilibration between K-vacant and K-occupied states of the pore (10–20 μs or faster) is close to the ion transit time when the pore is occupied by K alone (∼0.5–3 μs), a finding that indicates that either ion:ion repulsion involving Na is adequate to support flux (albeit at a rate below our detection threshold) and/or the pore undergoes rapid, permeant ion-sensitive equilibration between nonconducting and conducting configurations. Biophysically, further exploration of the Mg site and of interactions of Na and K within the pore will tell us much about the architecture and operation of this unusual pore. Physiologically, these results suggest ways in which “slow” pacemaker channels may contribute dynamically to the shaping of fast processes such as Na-K or Ca action potentials. PMID:18270171

  5. Role of TRP ion channels in cancer and tumorigenesis.

    PubMed

    Shapovalov, George; Ritaine, Abigael; Skryma, Roman; Prevarskaya, Natalia

    2016-05-01

    Transient receptor potential (TRP) channels are recently identified proteins that form a versatile family of ion channels, the majority of which are calcium permeable and exhibit complex regulatory patterns with sensitivity to multiple environmental factors. While this sensitivity has captured early attention, leading to recognition of TRP channels as environmental and chemical sensors, many later studies concentrated on the regulation of intracellular calcium by TRP channels. Due to mutations, dysregulation of ion channel gating or expression levels, normal spatiotemporal patterns of local Ca(2+) distribution become distorted. This causes deregulation of downstream effectors sensitive to changes in Ca(2+) homeostasis that, in turn, promotes pathophysiological cancer hallmarks, such as enhanced survival, proliferation and invasion. These observations give rise to the appreciation of the important contributions that TRP channels make to many cellular processes controlling cell fate and positioning these channels as important players in cancer regulation. This review discusses the accumulated scientific knowledge focused on TRP channel involvement in regulation of cell fate in various transformed tissues. PMID:26842901

  6. Effects of monoterpenes on ion channels of excitable cells.

    PubMed

    Oz, Murat; Lozon, Yosra; Sultan, Ahmed; Yang, Keun-Hang Susan; Galadari, Sehamuddin

    2015-08-01

    Monoterpenes are a structurally diverse group of phytochemicals and a major constituent of plant-derived 'essential oils'. Monoterpenes such as menthol, carvacrol, and eugenol have been utilized for therapeutical purposes and food additives for centuries and have been reported to have anti-inflammatory, antioxidant and analgesic actions. In recent years there has been increasing interest in understanding the pharmacological actions of these molecules. There is evidence indicating that monoterpenes can modulate the functional properties of several types of voltage and ligand-gated ion channels, suggesting that some of their pharmacological actions may be mediated by modulations of ion channel function. In this report, we review the literature concerning the interaction of monoterpenes with various ion channels. PMID:25956464

  7. Functional properties of ion channels and transporters in tumour vascularization

    PubMed Central

    Fiorio Pla, Alessandra; Munaron, Luca

    2014-01-01

    Vascularization is crucial for solid tumour growth and invasion, providing metabolic support and sustaining metastatic dissemination. It is now accepted that ion channels and transporters play a significant role in driving the cancer growth at all stages. They may represent novel therapeutic, diagnostic and prognostic targets for anti-cancer therapies. On the other hand, although the expression and role of ion channels and transporters in the vascular endothelium is well recognized and subject of recent reviews, only recently has their involvement in tumour vascularization been recognized. Here, we review the current literature on ion channels and transporters directly involved in the angiogenic process. Particular interest will be focused on tumour angiogenesis in vivo as well as in the different steps that drive this process in vitro, such as endothelial cell proliferation, migration, adhesion and tubulogenesis. Moreover, we compare the ‘transportome’ system of tumour vascular network with the physiological one. PMID:24493751

  8. Ion selectivity and gating mechanisms of FNT channels

    PubMed Central

    Waight, Andrew B.; Czyzewski, Bryan K.; Wang, Da-Neng

    2013-01-01

    The phospholipid bilayer has evolved to be a protective and selective barrier by which the cell maintains high concentrations of life sustaining organic and inorganic material. As gatekeepers responsible for an immense amount of bidirectional chemical traffic between the cytoplasm and extracellular milieu, ion channels have been studied in detail since their postulated existence nearly three-quarters of a century ago. Over the past fifteen years, we have begun to understand how selective permeability can be achieved for both cationic and anionic ions. Our mechanistic knowledge has expanded recently with studies of a large family of anion channels, the Formate Nitrite Transport (FNT) family. This family has proven amenable to structural studies at a resolution high enough to reveal intimate details of ion selectivity and gating. With five representative members having yielded a total of 15 crystal structures, this family represents one of the richest sources of structural information for anion channels. PMID:23773802

  9. Tarantula toxins use common surfaces for interacting with Kv and ASIC ion channels.

    PubMed

    Gupta, Kanchan; Zamanian, Maryam; Bae, Chanhyung; Milescu, Mirela; Krepkiy, Dmitriy; Tilley, Drew C; Sack, Jon T; Yarov-Yarovoy, Vladimir; Kim, Jae Il; Swartz, Kenton J

    2015-01-01

    Tarantula toxins that bind to voltage-sensing domains of voltage-activated ion channels are thought to partition into the membrane and bind to the channel within the bilayer. While no structures of a voltage-sensor toxin bound to a channel have been solved, a structural homolog, psalmotoxin (PcTx1), was recently crystalized in complex with the extracellular domain of an acid sensing ion channel (ASIC). In the present study we use spectroscopic, biophysical and computational approaches to compare membrane interaction properties and channel binding surfaces of PcTx1 with the voltage-sensor toxin guangxitoxin (GxTx-1E). Our results show that both types of tarantula toxins interact with membranes, but that voltage-sensor toxins partition deeper into the bilayer. In addition, our results suggest that tarantula toxins have evolved a similar concave surface for clamping onto α-helices that is effective in aqueous or lipidic physical environments. PMID:25948544

  10. Tonic PKA Activity Regulates SK Channel Nanoclustering and Somatodendritic Distribution.

    PubMed

    Abiraman, Krithika; Sah, Megha; Walikonis, Randall S; Lykotrafitis, George; Tzingounis, Anastasios V

    2016-06-01

    Small-conductance calcium-activated potassium (SK) channels mediate a potassium conductance in the brain and are involved in synaptic plasticity, learning, and memory. SK channels show a distinct subcellular localization that is crucial for their neuronal functions. However, the mechanisms that control this spatial distribution are unknown. We imaged SK channels labeled with fluorophore-tagged apamin and monitored SK channel nanoclustering at the single molecule level by combining atomic force microscopy and toxin (i.e., apamin) pharmacology. Using these two complementary approaches, we found that native SK channel distribution in pyramidal neurons, across the somatodendritic domain, depends on ongoing cyclic adenosine monophosphate (cAMP)-protein kinase A (PKA) levels, strongly limiting SK channel expression at the pyramidal neuron soma. Furthermore, tonic cAMP-PKA levels also controlled whether SK channels were expressed in nanodomains as single entities or as a group of multiple channels. Our study reveals a new level of regulation of SK channels by cAMP-PKA and suggests that ion channel topography and nanoclustering might be under the control of second messenger cascades. PMID:27107637

  11. Identification and characterization of a bacterial hydrosulphide ion channel

    SciTech Connect

    Czyzewski, Bryan K.; Wang, Da-Neng

    2012-10-26

    The hydrosulphide ion (HS{sup -}) and its undissociated form, hydrogen sulphide (H{sub 2}S), which are believed to have been critical to the origin of life on Earth, remain important in physiology and cellular signalling. As a major metabolite in anaerobic bacterial growth, hydrogen sulphide is a product of both assimilatory and dissimilatory sulphate reduction. These pathways can reduce various oxidized sulphur compounds including sulphate, sulphite and thiosulphate. The dissimilatory sulphate reduction pathway uses this molecule as the terminal electron acceptor for anaerobic respiration, in which process it produces excess amounts of H{sub 2}S. The reduction of sulphite is a key intermediate step in all sulphate reduction pathways. In Clostridium and Salmonella, an inducible sulphite reductase is directly linked to the regeneration of NAD{sup +}, which has been suggested to have a role in energy production and growth, as well as in the detoxification of sulphite. Above a certain concentration threshold, both H{sub 2}S and HS{sup -} inhibit cell growth by binding the metal centres of enzymes and cytochrome oxidase, necessitating a release mechanism for the export of this toxic metabolite from the cell. Here we report the identification of a hydrosulphide ion channel in the pathogen Clostridium difficile through a combination of genetic, biochemical and functional approaches. The HS{sup -} channel is a member of the formate/nitrite transport family, in which about 50 hydrosulphide ion channels form a third subfamily alongside those for formate (FocA) and for nitrite (NirC). The hydrosulphide ion channel is permeable to formate and nitrite as well as to HS{sup -} ions. Such polyspecificity can be explained by the conserved ion selectivity filter observed in the channel's crystal structure. The channel has a low open probability and is tightly regulated, to avoid decoupling of the membrane proton gradient.

  12. Ion channel profile of TRPM8 cold receptors reveals a role of TASK-3 potassium channels in thermosensation.

    PubMed

    Morenilla-Palao, Cruz; Luis, Enoch; Fernández-Peña, Carlos; Quintero, Eva; Weaver, Janelle L; Bayliss, Douglas A; Viana, Félix

    2014-09-11

    Animals sense cold ambient temperatures through the activation of peripheral thermoreceptors that express TRPM8, a cold- and menthol-activated ion channel. These receptors can discriminate a very wide range of temperatures from innocuous to noxious. The molecular mechanism responsible for the variable sensitivity of individual cold receptors to temperature is unclear. To address this question, we performed a detailed ion channel expression analysis of cold-sensitive neurons, combining bacterial artificial chromosome (BAC) transgenesis with a molecular-profiling approach in fluorescence-activated cell sorting (FACS)-purified TRPM8 neurons. We found that TASK-3 leak potassium channels are highly enriched in a subpopulation of these sensory neurons. The thermal threshold of TRPM8 cold neurons is decreased during TASK-3 blockade and in mice lacking TASK-3, and, most importantly, these mice display hypersensitivity to cold. Our results demonstrate a role of TASK-3 channels in thermosensation, showing that a channel-based combinatorial strategy in TRPM8 cold thermoreceptors leads to molecular specialization and functional diversity. PMID:25199828

  13. Calcium-permeable ion channels in the kidney.

    PubMed

    Zhou, Yiming; Greka, Anna

    2016-06-01

    Calcium ions (Ca(2+)) are crucial for a variety of cellular functions. The extracellular and intracellular Ca(2+) concentrations are thus tightly regulated to maintain Ca(2+) homeostasis. The kidney, one of the major organs of the excretory system, regulates Ca(2+) homeostasis by filtration and reabsorption. Approximately 60% of the Ca(2+) in plasma is filtered, and 99% of that is reabsorbed by the kidney tubules. Ca(2+) is also a critical signaling molecule in kidney development, in all kidney cellular functions, and in the emergence of kidney diseases. Recently, studies using genetic and molecular biological approaches have identified several Ca(2+)-permeable ion channel families as important regulators of Ca(2+) homeostasis in kidney. These ion channel families include transient receptor potential channels (TRP), voltage-gated calcium channels, and others. In this review, we provide a brief and systematic summary of the expression, function, and pathological contribution for each of these Ca(2+)-permeable ion channels. Moreover, we discuss their potential as future therapeutic targets. PMID:27029425

  14. Interaction of ion channels and receptors with PDZ domain proteins.

    PubMed

    Kornau, H C; Seeburg, P H; Kennedy, M B

    1997-06-01

    The complex anatomy of neurons demands a high degree of functional organization. Therefore, membrane receptors and ion channels are often localized to selected subcellular sites and coupled to specific signal transduction machineries. PDZ domains have come into focus as protein interaction modules that mediate the binding of a class of submembraneous proteins to membrane receptors and ion channels and thus subserve these organizational aspects. The structures of two PDZ domains have been resolved, which has led to a structural understanding of the specificity of interactions of various PDZ domains with their respective partners. The functional implications of PDZ domain interactions are now being addressed in vitro and in vivo. PMID:9232802

  15. Ion channels and the transduction of light signals

    NASA Technical Reports Server (NTRS)

    Spalding, E. P.; Evans, M. L. (Principal Investigator)

    2000-01-01

    Studies of biological light-sensing mechanisms are revealing important roles for ion channels. Photosensory transduction in plants is no exception. In this article, the evidence that ion channels perform such signal-transducing functions in the complex array of mechanisms that bring about plant photomorphogenesis will be reviewed and discussed. The examples selected for discussion range from light-gradient detection in unicellular algae to the photocontrol of stem growth in Arabidopsis. Also included is some discussion of the technical aspects of studies that combine electrophysiology and photobiology.

  16. Four basic residues critical for the ion selectivity and pore blocker sensitivity of TMEM16A calcium-activated chloride channels.

    PubMed

    Peters, Christian J; Yu, Haibo; Tien, Jason; Jan, Yuh Nung; Li, Min; Jan, Lily Yeh

    2015-03-17

    TMEM16A (transmembrane protein 16) (Anoctamin-1) forms a calcium-activated chloride channel (CaCC) that regulates a broad array of physiological properties in response to changes in intracellular calcium concentration. Although known to conduct anions according to the Eisenman type I selectivity sequence, the structural determinants of TMEM16A anion selectivity are not well-understood. Reasoning that the positive charges on basic residues are likely contributors to anion selectivity, we performed whole-cell recordings of mutants with alanine substitution for basic residues within the putative pore region and identified four residues on four different putative transmembrane segments that significantly increased the permeability of the larger halides and thiocyanate relative to that of chloride. Because TMEM16A permeation properties are known to shift with changes in intracellular calcium concentration, we further examined the calcium dependence of anion selectivity. We found that WT TMEM16A but not mutants with alanine substitution at those four basic residues exhibited a clear decline in the preference for larger anions as intracellular calcium was increased. Having implicated these residues as contributing to the TMEM16A pore, we scrutinized candidate small molecules from a high-throughput CaCC inhibitor screen to identify two compounds that act as pore blockers. Mutations of those four putative pore-lining basic residues significantly altered the IC50 of these compounds at positive voltages. These findings contribute to our understanding regarding anion permeation of TMEM16A CaCC and provide valuable pharmacological tools to probe the channel pore. PMID:25733897

  17. Collective Diffusion Model for Ion Conduction through Microscopic Channels

    PubMed Central

    Liu, Yingting; Zhu, Fangqiang

    2013-01-01

    Ion conduction through microscopic channels is of central importance in both biology and nanotechnology. To better understand the current-voltage (I-V) dependence of ion channels, here we describe and prove a collective diffusion model that quantitatively relates the spontaneous ion permeation at equilibrium to the stationary ionic fluxes driven by small voltages. The model makes it possible to determine the channel conductance in the linear I-V range from equilibrium simulations without the application of a voltage. To validate the theory, we perform molecular-dynamics simulations on two channels—a conical-shaped nanopore and the transmembrane pore of an α-hemolysin—under both equilibrium and nonequilibrium conditions. The simulations reveal substantial couplings between the motions of cations and anions, which are effectively captured by the collective coordinate in the model. Although the two channels exhibit very different linear ranges in the I-V curves, in both cases the channel conductance at small voltages is in reasonable agreement with the prediction from the equilibrium simulation. The simulations also suggest that channel charges, rather than geometric asymmetry, play a more prominent role in current rectification. PMID:23442858

  18. Briefing in application of machine learning methods in ion channel prediction.

    PubMed

    Lin, Hao; Chen, Wei

    2015-01-01

    In cells, ion channels are one of the most important classes of membrane proteins which allow inorganic ions to move across the membrane. A wide range of biological processes are involved and regulated by the opening and closing of ion channels. Ion channels can be classified into numerous classes and different types of ion channels exhibit different functions. Thus, the correct identification of ion channels and their types using computational methods will provide in-depth insights into their function in various biological processes. In this review, we will briefly introduce and discuss the recent progress in ion channel prediction using machine learning methods. PMID:25961077

  19. Briefing in Application of Machine Learning Methods in Ion Channel Prediction

    PubMed Central

    2015-01-01

    In cells, ion channels are one of the most important classes of membrane proteins which allow inorganic ions to move across the membrane. A wide range of biological processes are involved and regulated by the opening and closing of ion channels. Ion channels can be classified into numerous classes and different types of ion channels exhibit different functions. Thus, the correct identification of ion channels and their types using computational methods will provide in-depth insights into their function in various biological processes. In this review, we will briefly introduce and discuss the recent progress in ion channel prediction using machine learning methods. PMID:25961077

  20. Voltage Sensor in Voltage-gated ion channels

    NASA Astrophysics Data System (ADS)

    Bezanilla, Francisco

    2006-03-01

    Voltage-gated ion channels are intrinsic membrane proteins that play a fundamental role in the generation and propagation of the nerve impulse. Their salient characteristic is that the probability of the ion channel of being open depends steeply on the voltage across the membrane where those channels are inserted. Thus, in a membrane containing many channels, the ionic conductance is controlled by the membrane potential. The voltage exerts its control on the channel by reorienting intrinsic charges in the protein, generally arginine or lysine residues located in the 4th transmembrane segment of the channel protein, a region that has been called the voltage sensor. Upon changing the membrane potential, the charged groups reorient in the field generating a transient current (gating current). The properties of the gating current may be studied with a small number of channels to infer the operation of the sensor at the single molecule level by noise analysis or with a large number of channels to infer the details of the energy landscape the sensor traverses in opening the pore. This information is global in nature and cannot pinpoint the exact origin of the charge movement that generates the gating current. The movement of physical charges in the protein has been inferred with site-directed mutagenesis of the charged residues to histidine that allows the study of proton accessibility. The actual movement has been studied with fluorescence spectroscopy, fluorescence resonance energy transfer. The combined information of site-directed mutagenesis, gating currents, fluorescence studies and emerging crystal structures have started to delineate a physical representation of the conformational changes responsible for voltage sensing that lead to the opening of the conduction pore in voltage-gated ion channels.

  1. Structure of Thermally Activated TRP Channels

    PubMed Central

    Cohen, Matthew R.; Moiseenkova-Bell, Vera Y.

    2015-01-01

    Temperature sensation is important for adaptation and survival of organisms. While temperature has the potential to affect all biological macromolecules, organisms have evolved specific thermosensitive molecular detectors that are able to transduce temperature changes into physiologically relevant signals. Among these thermosensors are ion channels from the transient receptor potential (TRP) family. Prime candidates include TRPV1–4, TRPA1, and TRPM8 (the so-called “thermoTRP” channels), which are expressed in sensory neurons and gated at specific temperatures. Electrophysiological and thermodynamic approaches have been employed to determine the nature by which thermoTRPs detect temperature and couple temperature changes to channel gating. To further understand how thermoTRPs sense temperature, high-resolution structures of full-length thermoTRPs channels will be required. Here, we will discuss current progress in unraveling the structures of thermoTRP channels. PMID:25366237

  2. Crystal orientation mapping via ion channeling: An alternative to EBSD.

    PubMed

    Langlois, C; Douillard, T; Yuan, H; Blanchard, N P; Descamps-Mandine, A; Van de Moortèle, B; Rigotti, C; Epicier, T

    2015-10-01

    A new method, which we name ion CHanneling ORientation Determination (iCHORD), is proposed to obtain orientation maps on polycrystals via ion channeling. The iChord method exploits the dependence between grain orientation and ion beam induced secondary electron image contrast. At each position of the region of interest, intensity profiles are obtained from a series of images acquired with different orientations with respect to the ion beam. The profiles are then compared to a database of theoretical profiles of known orientation. The Euler triplet associated to the most similar theoretical profile gives the orientation at that position. The proof-of-concept is obtained on a titanium nitride sample. The potentialities of iCHORD as an alternative to EBSD are then discussed. PMID:26094201

  3. Voltage is a partial activator of rat thermosensitive TRP channels

    PubMed Central

    Matta, José A; Ahern, Gerard P

    2007-01-01

    TRPV1 and TRPM8 are sensory nerve ion channels activated by heating and cooling, respectively. A variety of physical and chemical stimuli activate these receptors in a synergistic manner but the underlying mechanisms are unclear. Both channels are voltage sensitive, and temperature and ligands modulate this voltage dependence. Thus, a voltage-sensing mechanism has become an attractive model to explain the generalized gating of these and other thermo-sensitive TRP channels. We show here using whole-cell and single channel measurements that voltage produces only a partial activation of TRPV1 and TRPM8. At room temperature (20–25°C) membrane depolarization evokes responses that saturate at ∼50–60% of the maximum open probability. Furthermore, high concentrations of capsaicin (10 μm), resiniferatoxin (5 μm) and menthol (6 mm) reveal voltage-independent gating. Similarly, other modes of TRPV1 regulation including heat, protein kinase C-dependent phosphorylation, and protons enhance both the efficacy and sensitivity of voltage activation. In contrast, the TRPV1 antagonist capsazepine produces the opposite effects. These data can be explained by an allosteric model in which voltage, temperature, agonists and inverse agonists are independently coupled, either positively or negatively, to channel gating. Thus, voltage acts separately but in concert with other stimuli to regulate channel activation, and, therefore, a voltage-sensitive mechanism is unlikely to represent a final, gating mechanism for these channels. PMID:17932142

  4. Adjuvant Effect of an Alternative Plasticizer, Diisopropyl Adipate, on a Contact Hypersensitivity Mouse Model: Link with Sensory Ion Channel TRPA1 Activation.

    PubMed

    Kurohane, Kohta; Kimura, Ayako; Terasawa, Rie; Sahara, Yurina; Kobayashi, Kamiyu; Suzuki, Wakana; Matsuoka, Takeshi; Watanabe, Tatsuo; Imai, Yasuyuki

    2015-01-01

    Due to health concerns about phthalate esters, the use of alternative plasticizers is being considered. Phthalate esters enhance skin sensitization to fluorescein isothiocyanate (FITC) in mouse models. We have demonstrated that phthalate esters stimulate transient receptor potential ankyrin 1 (TRPA1) cation channels expressed on sensory neurons. We also found a correlation between TRPA1 activation and the enhancing effect on FITC-induced contact hypersensitivity (CHS) when testing various types of phthalate esters. Here we investigated the effects of an alternative plasticizer, diisopropyl adipate (DIA). Activation of TRPA1 by DIA was demonstrated by calcium mobilization using Chinese hamster ovary cells expressing TRPA1 in vitro. The effect of DIA was inhibited by a TRPA1-specific antagonist, HC-030031. The presence of DIA or dibutyl phthalate (DBP; positive control) during skin sensitization of BALB/c mice to FITC augmented the CHS response, as revealed by the level of ear-swelling. The enhancing effect of DIA was inhibited by in vivo pretreatment with HC-030031. FITC-presenting CD11c(+) dendritic cell (DC)-trafficking to draining lymph nodes was facilitated both by DIA and by DBP. DBP and DIA were similarly active in the enhancement of interferon-γ production by draining lymph nodes, but the effect on interleukin-4 production was weaker with DIA. Overall, DIA activated TRPA1 and enhanced FITC-induced CHS, as DBP did. The adjuvant effects of adipate esters may need to be considered because they are used as ingredients in cosmetics and drug formulations topically applied to the skin. PMID:25959058

  5. Ion channels in human red blood cell membrane: actors or relics?

    PubMed

    Thomas, Serge L Y; Bouyer, Guillaume; Cueff, Anne; Egée, Stéphane; Glogowska, Edyta; Ollivaux, Céline

    2011-04-15

    During the past three decades, electrophysiological studies revealed that human red blood cell membrane is endowed with a large variety of ion channels. The physiological role of these channels, if any, remains unclear; they do not participate in red cell homeostasis which is rather based on the almost total absence of cationic permeability and minute anionic conductance. They seem to be inactive in the "resting cell." However, when activated experimentally, ion channels can lead to a very high single cell conductance and potentially induce disorders, with the major risks of fast dehydration and dissipation of gradients. Could there be physiological conditions under which the red cell needs to activate these high conductances, or are ion channels relics of a function lost in anucleated cells? It has been demonstrated that they play a key role in diseases such as sickle cell anemia or malaria. This short overview of ion channels identified to-date in the human red cell membrane is an attempt to propose a dynamic role for these channels in circulating cells in health and disease. PMID:21429775

  6. Biophysics, pathophysiology, and pharmacology of ion channel gating pores

    PubMed Central

    Moreau, Adrien; Gosselin-Badaroudine, Pascal; Chahine, Mohamed

    2014-01-01

    Voltage sensor domains (VSDs) are a feature of voltage gated ion channels (VGICs) and voltage sensitive proteins. They are composed of four transmembrane (TM) segments (S1–S4). Currents leaking through VSDs are called omega or gating pore currents. Gating pores are caused by mutations of the highly conserved positively charged amino acids in the S4 segment that disrupt interactions between the S4 segment and the gating charge transfer center (GCTC). The GCTC separates the intracellular and extracellular water crevices. The disruption of S4–GCTC interactions allows these crevices to communicate and create a fast activating and non-inactivating alternative cation-selective permeation pathway of low conductance, or a gating pore. Gating pore currents have recently been shown to cause periodic paralysis phenotypes. There is also increasing evidence that gating pores are linked to several other familial diseases. For example, gating pores in Nav1.5 and Kv7.2 channels may underlie mixed arrhythmias associated with dilated cardiomyopathy (DCM) phenotypes and peripheral nerve hyperexcitability (PNH), respectively. There is little evidence for the existence of gating pore blockers. Moreover, it is known that a number of toxins bind to the VSD of a specific domain of Na+ channels. These toxins may thus modulate gating pore currents. This focus on the VSD motif opens up a new area of research centered on developing molecules to treat a number of cell excitability disorders such as epilepsy, cardiac arrhythmias, and pain. The purpose of the present review is to summarize existing knowledge of the pathophysiology, biophysics, and pharmacology of gating pore currents and to serve as a guide for future studies aimed at improving our understanding of gating pores and their pathophysiological roles. PMID:24772081

  7. Theoretical and computational models of biological ion channels

    NASA Astrophysics Data System (ADS)

    Roux, Benoit

    2004-03-01

    A theoretical framework for describing ion conduction through biological molecular pores is established and explored. The framework is based on a statistical mechanical formulation of the transmembrane potential (1) and of the equilibrium multi-ion potential of mean forces through selective ion channels (2). On the basis of these developments, it is possible to define computational schemes to address questions about the non-equilibrium flow of ions through ion channels. In the case of narrow channels (gramicidin or KcsA), it is possible to characterize the ion conduction in terms of the potential of mean force of the ions along the channel axis (i.e., integrating out the off-axis motions). This has been used for gramicidin (3) and for KcsA (4,5). In the case of wide pores (i.e., OmpF porin), this is no longer a good idea, but it is possible to use a continuum solvent approximations. In this case, a grand canonical monte carlo brownian dynamics algorithm was constructed for simulating the non-equilibrium flow of ions through wide pores. The results were compared with those from the Poisson-Nernst-Planck mean-field electrodiffusion theory (6-8). References; 1. B. Roux, Biophys. J. 73:2980-2989 (1997); 2. B. Roux, Biophys. J. 77, 139-153 (1999); 3. Allen, Andersen and Roux, PNAS (2004, in press); 4. Berneche and Roux. Nature, 414:73-77 (2001); 5. Berneche and Roux. PNAS, 100:8644-8648 (2003); 6. W. Im and S. Seefeld and B. Roux, Biophys. J. 79:788-801 (2000); 7. W. Im and B. Roux, J. Chem. Phys. 115:4850-4861 (2001); 8. W. Im and B. Roux, J. Mol. Biol. 322:851-869 (2002).

  8. Scorpion venom components that affect ion-channels function

    PubMed Central

    Quintero-Hernández, V.; Jiménez-Vargas, J.M.; Gurrola, G.B.; Valdivia, H.H.F.; Possani, L.D.

    2014-01-01

    SUMMARY The number and types of venom components that affect ion-channel function are reviewed. These are the most important venom components responsible for human intoxication, deserving medical attention, often requiring the use of specific anti-venoms. Special emphasis is given to peptides that recognize Na+-, K+- and Ca++-channels of excitable cells. Knowledge generated by direct isolation of peptides from venom and components deduced from cloned genes, whose amino acid sequences are deposited into databanks are now adays in the order of 1.5 thousands, out of an estimate biodiversity closed to 300,000. Here the diversity of components is briefly reviewed with mention to specific references. Structural characteristic are discussed with examples taken from published work. The principal mechanisms of action of the three different types of peptides are also reviewed. Na+-channel specific venom components usually are modifier of the open and closing kinetic mechanisms of the ion-channels, whereas peptides affecting K+-channels are normally pore blocking agents. The Ryanodine Ca++-channel specific peptides are known for causing sub-conducting stages of the channels conductance and some were shown to be able to internalize penetrating inside the muscle cells. PMID:23891887

  9. Apocalmodulin Itself Promotes Ion Channel Opening and Ca2+ Regulation

    PubMed Central

    Adams, Paul J.; Ben-Johny, Manu; Dick, Ivy E.; Inoue, Takanari; Yue, David T.

    2014-01-01

    SUMMARY The Ca2+-free form of calmodulin (apoCaM) often appears inert, modulating target molecules only upon conversion to its Ca2+-bound form. This schema has appeared to govern voltage-gated Ca2+ channels, where apoCaM has been considered a dormant Ca2+ sensor, associated with channels, but awaiting the binding of Ca2+ ions before inhibiting channel opening to provide vital feedback inhibition. Using single-molecule measurements of channels and chemical dimerization to elevate apoCaM, we find that apoCaM binding on its own markedly upregulates opening, rivaling the strongest forms of modulation. Upon Ca2+ binding to this CaM, inhibition may simply reverse the initial upregulation. As RNA edited and spliced channel variants show different affinities for apoCaM, the apoCaM-dependent control mechanisms may underlie the functional diversity of these variants and explain an elongation of neuronal action potentials by apoCaM. More broadly, voltage-gated Na channels adopt this same modulatory principle. ApoCaM thus imparts potent and pervasive ion-channel regulation. PMID:25417111

  10. [Ion channels and demyelination: basis of a treatment of experimental autoimmune encephalomyelitis (EAE) by potassium channel blockers].

    PubMed

    Devaux, J; Beeton, C; Béraud, E; Crest, M

    2004-05-01

    Voltage-gated potassium channels (Kv channels) are ion channels, openings of which provide an outward flow of potassium ions repolarising the cell. In neurons, Kv channels play a crucial role in action potential repolarisation and in shaping neuronal excitability. In non-excitable cells, such as T lymphocytes, Kv channels and calcium-activated K+ channels (KCa channels) determine the driving force for Ca2+ entry. During T cell activation the calcium entry depolarises the cell and increases the cytosolic calcium concentration, which in return activates Kv and KCa channels. K+ channel opening repolarises the cell and drives the membrane potential to a negative voltage. The roles of Kv channels in nervous and immune systems have been investigated here by means of a rat experimental autoimmune disease of the central nervous system, the experimental autoimmune encephalomyelitis (EAE). EAE is characterised clinically by paralysis, and pathologically by inflammatory cell infiltrations into the brain and the spinal cord. Among the inflammatory cells, T lymphocytes play a major role. Hence, EAE can be adoptively transferred into syngenic animals by the injection of T cells reactive to myelin antigens. During adoptive-EAE, somato-sensory evoked potentials recorded along the spinal tracts decrease in amplitude and axonal propagation is disrupted. We have analysed the consequences of Kv channels blockade by peptidyl toxins on central nerve conduction, on T cell activation and on the time course of EAE. In rat optic nerves, Kv channels have been identified up from postnatal day 1. Their blockade by kaliotoxin (a scorpion toxin) or by dendrotoxin-I (a snake toxin) enlarges the compound action potentials, demonstrating the participation of Kv channels to spike repolarisation. This effect disappears at adult age due to the sequestration of Kv channels under the myelin, in the paranodal regions. During acute demyelination by lysophosphatidyl-choline, the surface area of compound

  11. New Insights on Astrocyte Ion Channels: Critical for Homeostasis and Neuron-Glia Signaling

    PubMed Central

    Khakh, Baljit S.; Skatchkov, Serguei N.; Lee, C. Justin; Rouach, Nathalie

    2015-01-01

    Initial biophysical studies on glial cells nearly 50 years ago identified these cells as being electrically silent. These first studies also demonstrated a large K+ conductance, which led to the notion that glia may regulate extracellular K+ levels homeostatically. This view has now gained critical support from the study of multiple disease models discussed herein. Dysfunction of a major astrocyte K+ channel, Kir4.1, appears as an early pathological event underlying neuronal phenotypes in several neurodevelopmental and neurodegenerative diseases. An expanding list of other astrocyte ion channels, including the calcium-activated ion channel BEST-1, hemichannels, and two-pore domain K+ channels, all contribute to astrocyte biology and CNS function and underpin new forms of crosstalk between neurons and glia. Once considered merely the glue that holds the brain together, it is now increasingly recognized that astrocytes contribute in several fundamental ways to neuronal function. Emerging new insights and future perspectives of this active research area are highlighted within. SIGNIFICANCE STATEMENT The critical role of astrocyte potassium channels in CNS homeostasis has been reemphasized by recent studies conducted in animal disease models. Emerging evidence also supports the signaling role mediated by astrocyte ion channels such as BEST1, hemichannels, and two-pore channels, which enable astrocytes to interact with neurons and regulate synaptic transmission and plasticity. This minisymposium highlights recent developments and future perspectives of these research areas. PMID:26468182

  12. BK channel activation: structural and functional insights

    PubMed Central

    Lee, Urvi S.; Cui, Jianmin

    2010-01-01

    The voltage and Ca2+ activated K+ (BK) channels are involved in the regulation of neurotransmitter release and neuronal excitability. Structurally, BK channels are homologous to voltage- and ligand-gated K+ channels, having a voltage sensor and pore as the membrane-spanning domain and a cytosolic domain containing metal binding sites. Recently published electron cryomicroscopy (cryo-EM) and X-ray crystallographic structures of the BK channel provided the first look into the assembly of these domains, corroborating the close interactions among these domains during channel gating that have been suggested by functional studies. This review discusses these latest findings and an emerging new understanding about BK channel gating and implications for diseases such as epilepsy, in which mutations in BK channel genes have been associated. PMID:20663573

  13. Ion Selectivity Mechanism in a Bacterial Pentameric Ligand-Gated Ion Channel

    SciTech Connect

    Fritsch, Sebastian; Ivanov, Ivaylo; Wang, Hailong; Cheng, Xiaolin

    2010-01-01

    The proton-gated ion channel from Gloeobacter violaceus (GLIC) is a prokaryotic homolog of the eukaryotic nicotinic acetylcholine receptor that responds to the binding of neurotransmitter acetylcholine and mediates fast signal transmission. Recent emergence of a high-resolution crystal structure of GLIC captured in a potentially open state allowed detailed, atomic-level insight into ion conduction and selectivity mechanisms in these channels. Herein, we have examined the barriers to ion conduction and origins of ion selectivity in the GLIC channel by the construction of potential-of-mean-force profiles for sodium and chloride ions inside the transmembrane region. Our calculations reveal that the GLIC channel is open for a sodium ion to transport, but presents a 11 kcal/mol free energy barrier for a chloride ion. Our collective findings identify three distinct contributions to the observed preference for the permeant ions. First, there is a substantial contribution due to a ring of negatively charged glutamate residues (E-2 ) at the narrow intracellular end of the channel. The negative electrostatics of this region and the ability of the glutamate side chains to directly bind cations would strongly favor the passage of sodium ions while hindering translocation of chloride ions. Second, our results imply a significant hydrophobic contribution to selectivity linked to differences in the desolvation penalty for the sodium versus chloride ions in the central hydrophobic region of the pore. This hydrophobic contribution is evidenced by the large free energy barriers experienced by Cl in the middle of the pore for both GLIC and the E-2 A mutant. Finally, there is a distinct contribution arising from the overall negative electrostatics of the channel.

  14. Ion homeostasis, channels, and transporters: an update on cellular mechanisms.

    PubMed

    Dubyak, George R

    2004-12-01

    The steady-state maintenance of highly asymmetric concentrations of the major inorganic cations and anions is a major function of both plasma membranes and the membranes of intracellular organelles. Homeostatic regulation of these ionic gradients is critical for most functions. Due to their charge, the movements of ions across biological membranes necessarily involves facilitation by intrinsic membrane transport proteins. The functional characterization and categorization of membrane transport proteins was a major focus of cell physiological research from the 1950s through the 1980s. On the basis of these functional analyses, ion transport proteins were broadly divided into two classes: channels and carrier-type transporters (which include exchangers, cotransporters, and ATP-driven ion pumps). Beginning in the mid-1980s, these functional analyses of ion transport and homeostasis were complemented by the cloning of genes encoding many ion channels and transporter proteins. Comparison of the predicted primary amino acid sequences and structures of functionally similar ion transport proteins facilitated their grouping within families and superfamilies of structurally related membrane proteins. Postgenomics research in ion transport biology increasingly involves two powerful approaches. One involves elucidation of the molecular structures, at the atomic level in some cases, of model ion transport proteins. The second uses the tools of cell biology to explore the cell-specific function or subcellular localization of ion transport proteins. This review will describe how these approaches have provided new, and sometimes surprising, insights regarding four major questions in current ion transporter research. 1) What are the fundamental differences between ion channels and ion transporters? 2) How does the interaction of an ion transport protein with so-called adapter proteins affect its subcellular localization or regulation by various intracellular signal transduction

  15. Laser Microsurgery Permits Fungal Plasma Membrane Single-Ion-Channel Resolution at the Hyphal Tip

    PubMed Central

    Véry, Anne-Aliénor; Davies, Julia M.

    1998-01-01

    A method for formation of high-electrical-resistance seals on the Neurospora crassa plasma membrane, allowing resolution of single-ion-channel activity by patch clamp electrophysiology, is reported. Laser microsurgery permits access to the hyphal apex without enzymatic cell wall digestion and loss of morphological polarity. Cell wall reformation is delayed by brefeldin. This method can allow full characterization of apical plasma membrane channels, which are implicated in tip growth. PMID:16349556

  16. A Change in the Ion Selectivity of Ligand-Gated Ion Channels Provides a Mechanism to Switch Behavior.

    PubMed

    Pirri, Jennifer K; Rayes, Diego; Alkema, Mark J

    2015-01-01

    Behavioral output of neural networks depends on a delicate balance between excitatory and inhibitory synaptic connections. However, it is not known whether network formation and stability is constrained by the sign of synaptic connections between neurons within the network. Here we show that switching the sign of a synapse within a neural circuit can reverse the behavioral output. The inhibitory tyramine-gated chloride channel, LGC-55, induces head relaxation and inhibits forward locomotion during the Caenorhabditis elegans escape response. We switched the ion selectivity of an inhibitory LGC-55 anion channel to an excitatory LGC-55 cation channel. The engineered cation channel is properly trafficked in the native neural circuit and results in behavioral responses that are opposite to those produced by activation of the LGC-55 anion channel. Our findings indicate that switches in ion selectivity of ligand-gated ion channels (LGICs) do not affect network connectivity or stability and may provide an evolutionary and a synthetic mechanism to change behavior. PMID:26348462

  17. SLO2 Channels Are Inhibited by All Divalent Cations That Activate SLO1 K+ Channels.

    PubMed

    Budelli, Gonzalo; Sun, Qi; Ferreira, Juan; Butler, Alice; Santi, Celia M; Salkoff, Lawrence

    2016-04-01

    Two members of the family of high conductance K(+)channels SLO1 and SLO2 are both activated by intracellular cations. However, SLO1 is activated by Ca(2+)and other divalent cations, while SLO2 (Slack or SLO2.2 from rat) is activated by Na(+) Curiously though, we found that SLO2.2 is inhibited by all divalent cations that activate SLO1, with Zn(2+)being the most effective inhibitor with an IC50of ∼8 μmin contrast to Mg(2+), the least effective, with an IC50of ∼ 1.5 mm Our results suggest that divalent cations are not SLO2 pore blockers, but rather inhibit channel activity by an allosteric modification of channel gating. By site-directed mutagenesis we show that a histidine residue (His-347) downstream of S6 reduces inhibition by divalent cations. An analogous His residue present in some CNG channels is an inhibitory cation binding site. To investigate whether inhibition by divalent cations is conserved in an invertebrate SLO2 channel we cloned the SLO2 channel fromDrosophila(dSLO2) and compared its properties to those of rat SLO2.2. We found that, like rat SLO2.2, dSLO2 was also activated by Na(+)and inhibited by divalent cations. Inhibition of SLO2 channels in mammals andDrosophilaby divalent cations that have second messenger functions may reflect the physiological regulation of these channels by one or more of these ions. PMID:26823461

  18. Ion channel voltage sensors: structure, function, and pathophysiology.

    PubMed

    Catterall, William A

    2010-09-23

    Voltage-gated ion channels generate electrical signals in species from bacteria to man. Their voltage-sensing modules are responsible for initiation of action potentials and graded membrane potential changes in response to synaptic input and other physiological stimuli. Extensive structure-function studies, structure determination, and molecular modeling are now converging on a sliding-helix mechanism for electromechanical coupling in which outward movement of gating charges in the S4 transmembrane segments catalyzed by sequential formation of ion pairs pulls the S4-S5 linker, bends the S6 segment, and opens the pore. Impairment of voltage-sensor function by mutations in Na+ channels contributes to several ion channelopathies, and gating pore current conducted by mutant voltage sensors in Na(V)1.4 channels is the primary pathophysiological mechanism in hypokalemic periodic paralysis. The emerging structural model for voltage sensor function opens the way to development of a new generation of ion-channel drugs that act on voltage sensors rather than blocking the pore. PMID:20869590

  19. Targeting ion channels for the treatment of autoimmune neuroinflammation

    PubMed Central

    Bittner, Stefan

    2013-01-01

    Pharmacological targeting of ion channels has long been recognized as an attractive strategy for the treatment of various diseases. Multiple sclerosis (MS) is an autoimmune disorder of the central nervous system with a prominent neurodegenerative component. A multitude of different cell types are involved in the complex pathophysiology of this disorder, including cells of the immune system (e.g. T and B lymphocytes and microglia), the neurovascular unit (e.g. endothelial cells and astrocytes) and the central nervous system (e.g. astrocytes and neurons). The pleiotropic expression and function of ion channels gives rise to the attractive opportunity of targeting different players and pathophysiological aspects of MS by the modulation of ion channel function in a cell-type and context-specific manner. We discuss the emerging knowledge about ion channels in the context of autoimmune neuroinflammation. While some pharmacological targets are at the edge of clinical translation, others have only recently been discovered and are still under investigation. Special focus is given to those candidates that could be attractive novel targets for future therapeutic approaches in neuroimmune autoinflammation. PMID:23997817

  20. Voltage-Dependent Gating in a “Voltage Sensor-Less” Ion Channel

    PubMed Central

    Kurata, Harley T.; Rapedius, Markus; Kleinman, Marc J.; Baukrowitz, Thomas .; Nichols, Colin G.

    2010-01-01

    The voltage sensitivity of voltage-gated cation channels is primarily attributed to conformational changes of a four transmembrane segment voltage-sensing domain, conserved across many levels of biological complexity. We have identified a remarkable point mutation that confers significant voltage dependence to Kir6.2, a ligand-gated channel that lacks any canonical voltage-sensing domain. Similar to voltage-dependent Kv channels, the Kir6.2[L157E] mutant exhibits time-dependent activation upon membrane depolarization, resulting in an outwardly rectifying current-voltage relationship. This voltage dependence is convergent with the intrinsic ligand-dependent gating mechanisms of Kir6.2, since increasing the membrane PIP2 content saturates Po and eliminates voltage dependence, whereas voltage activation is more dramatic when channel Po is reduced by application of ATP or poly-lysine. These experiments thus demonstrate an inherent voltage dependence of gating in a “ligand-gated” K+ channel, and thereby provide a new view of voltage-dependent gating mechanisms in ion channels. Most interestingly, the voltage- and ligand-dependent gating of Kir6.2[L157E] is highly sensitive to intracellular [K+], indicating an interaction between ion permeation and gating. While these two key features of channel function are classically dealt with separately, the results provide a framework for understanding their interaction, which is likely to be a general, if latent, feature of the superfamily of cation channels. PMID:20208975

  1. Super-Resolution Scanning Patch-Clamp Reveals Clustering of Functional Ion Channels in the Adult Ventricular Myocyte

    PubMed Central

    Bhargava, Anamika; Lin, Xianming; Novak, Pavel; Mehta, Kinneri; Korchev, Yuri

    2013-01-01

    Rationale Compartmentation of ion channels on the cardiomyocyte surface is important for electrical propagation and electromechanical coupling. The specialized T-tubule and costameric structures facilitate spatial coupling of various ion channels and receptors. Existing methods like immunofluorescence and patch-clamp techniques are limited in their ability to localize functional ion channels. As such, a correlation between channel protein location and channel function remains incomplete. Objective To validate a method that permits to routinely image the topography of a live cardiomyocyte, and then study clustering of functional ion channels from a specific microdomain. Methods and Results We used scanning ion conductance microscopy and conventional cell-attached patch-clamp with a software modification that allows controlled increase of pipette tip diameter. The sharp nanopipette used for topography scan was modified into a larger patch pipette which can be positioned with nanoscale precision to a specific site of interest (crest, groove or T-tubules of cardiomyocytes), and sealed to the membrane for cell-attached recording of ion channels. Using this method, we significantly increased the probability of detecting activity of L-type calcium channels in the T-tubules of ventricular cardiomyocytes. We also demonstrated that active sodium channels do not distribute homogenously on the sarcolemma but rather, they segregate into clusters of various densities -most crowded in the crest region- that are surrounded by areas virtually free of functional sodium channels. Conclusions Our new method substantially increases the throughput of recording location-specific functional ion channels on the cardiomyocyte sarcolemma, thus allowing characterization of ion channels in relation to the microdomain in which they reside. PMID:23438901

  2. Ion movement through gramicidin A channels. Single-channel measurements at very high potentials.

    PubMed Central

    Andersen, O S

    1983-01-01

    The patch-clamp technique of Mueller (1975, Ann. N.Y. Acad. Sci., 274:247-264) and Neher and Sakmann (1976, Nature (Lond.), 260:799-802) was modified to be suitable for single-channel measurements in lipid bilayers at potentials up to 500 mV. This method was used to study gramicidin A single-channel current-voltage characteristics. It was found that the sublinear current-voltage behavior normally observed at low permeant ion concentrations and rather low potentials (V less than or equal to 200 mV) continues to be seen all the way up to 500 mV. This phenomenon is characteristic of the low permeant ion situation in which the channel is far from saturation, and implies that the overall rate constant for association between ion and channel is very weakly, if at all, voltage dependent. The magnitude of the single channel currents at 500 mV is consistent with the notion that the aqueous convergence conductance is a significant factor in determining the permeability characteristics of the gramicidin A channel. PMID:6188500

  3. Role of Ion Channels in the Sperm Acrosome Reaction.

    PubMed

    Beltrán, Carmen; Treviño, Claudia L; Mata-Martínez, Esperanza; Chávez, Julio C; Sánchez-Cárdenas, Claudia; Baker, Mark; Darszon, Alberto

    2016-01-01

    The acrosome reaction (AR) is a unique exocytotic process where the acrosome, a single membrane-delimited specialized organelle, overlying the nucleus in the sperm head of many species, fuses with the overlying plasma membrane. This reaction, triggered by physiological inducers from the female gamete, its vicinity, or other stimuli, discharges the acrosomal content modifying the plasma membrane, incorporating the inner acrosomal membrane, and exposing it to the extracellular medium. The AR is essential for sperm-egg coat penetration, fusion with the eggs' plasma membrane, and fertilization. As in most exocytotic processes Ca(2+) is crucial for the AR, as well as intracellular pH and membrane potential changes. Thus, among the required processes needed for this reaction, ion permeability changes involving channels are pivotal. In spite of the key role ion channels play in the AR, their identity and regulation is not fully understood. Though molecular and pharmacological evidence indicates that various ionic channels participate during the AR, such as store-operated Ca(2+) channels and voltage-dependent Ca(2+) channels, whole cell patch clamp recordings have failed to detect some of them until now. Since sperm display a very high resistance and a minute cytoplasmic volume, very few channels are needed to achieve large membrane potential and concentration changes. Functional detection of few channels in the morphologically complex and tiny sperm poses technical problems, especially when their conductance is very small, as in the case of SOCs. Single channel recordings and novel fluorescence microscopy strategies will help to define the participation of ionic channels in the intertwined signaling network that orchestrates the AR. PMID:27194349

  4. Airway irritation and cough evoked by acid: from human to ion channel

    PubMed Central

    Gu, Qihai; Lee, Lu-Yuan

    2011-01-01

    Inhalation or aspiration of acid solution evokes airway defense responses such as cough and reflex bronchoconstriction, resulting from activation of vagal bronchopulmonary C-fibers and Aδ afferents. The stimulatory effect of hydrogen ion on these sensory nerves is generated by activation of two major types of ion channels expressed in these neurons: a rapidly activating and inactivating current mediated through ASICs, and a slow sustaining current via activation of TRPV1. Recent studies have shown that these acid-evoked responses are elevated during airway inflammatory reaction, revealing the potential convergence of a wide array of inflammatory signaling on these ion channels. Since pH in the airway fluid drops substantially in patients with inflammatory airway diseases, these heightened stimulatory effects of acid on airway sensory nerves may play a part in the manifestation of airway irritation and excessive cough under those pathophysiological conditions. PMID:21543258

  5. Chemical rescue of histidine selectivity filter mutants of the M2 ion channel of influenza A virus.

    PubMed

    Venkataraman, Padmavati; Lamb, Robert A; Pinto, Lawrence H

    2005-06-01

    The influenza virus M2 proton-selective ion channel activity facilitates virus uncoating, a process that occurs in the acidic environment of the endosome. The M2 channel causes acidification of the interior of the virus particle, which results in viral protein-protein dissociation. The M2 protein is a homotetramer that contains in its aqueous pore a histidine residue (His-37) that acts as a selectivity filter and a tryptophan residue (Trp-41) that acts as a channel gate. Substitution of His-37 modifies M2 ion channel properties drastically. However, the results of such experiments are difficult to interpret because substitution of His-37 could cause gross structural changes to the channel pore. We described here experiments in which partial or, in some cases, full rescue of specific M2 ion channel properties of His-37 substitution mutants was achieved by addition of imidazole to the bathing medium. Chemical rescue was demonstrated for three histidine substitution mutant ion channels (M2-H37G, M2-H37S, and M2-H37T) and for two double mutants in which the Trp-41 channel gate was also mutated (H37G/W41Y and H37G/W41A). Currents of the M2-H37G mutant ion channel were inhibited by Cu(II), which has been shown to coordinate with His-37 in the wild-type channel. Chemical rescue was very specific for imidazole. Buffer molecules that were neutral when protonated (4-morpholineethanesulfonic acid and 3-morpholino-2-hydroxypropanesulfonic acid) did not rescue ion channel activity of the M2-H37G mutant ion channel, but 1-methylimidazole did provide partial rescue of function. These results were consistent with a model for proton transport through the pore of the wild-type channel in which the imidazole side chain of His-37 acted as an intermediate proton acceptor/donor group. PMID:15784624

  6. Energetics of Multi-Ion Conduction Pathways in Potassium Ion Channels

    PubMed Central

    2013-01-01

    Potassium ion channels form pores in cell membranes, allowing potassium ions through while preventing the passage of sodium ions. Despite numerous high-resolution structures, it is not yet possible to relate their structure to their single molecule function other than at a qualitative level. Over the past decade, there has been a concerted effort using molecular dynamics to capture the thermodynamics and kinetics of conduction by calculating potentials of mean force (PMF). These can be used, in conjunction with the electro-diffusion theory, to predict the conductance of a specific ion channel. Here, we calculate seven independent PMFs, thereby studying the differences between two potassium ion channels, the effect of the CHARMM CMAP forcefield correction, and the sensitivity and reproducibility of the method. Thermodynamically stable ion–water configurations of the selectivity filter can be identified from all the free energy landscapes, but the heights of the kinetic barriers for potassium ions to move through the selectivity filter are, in nearly all cases, too high to predict conductances in line with experiment. This implies it is not currently feasible to predict the conductance of potassium ion channels, but other simpler channels may be more tractable. PMID:24353479

  7. Pressure effects on stopping power of solids for channeled ions

    NASA Astrophysics Data System (ADS)

    Pathak, A. P.; Cruz, S. A.; Soullard, J.

    2005-01-01

    Pressure effects on the energy loss of swift channeled ions through silicon are considered. This is accomplished by estimating the changes in orbital charge densities and the corresponding mean ionization potentials, induced by increasing pressure. The bulk density for the compressed material is obtained from available experimental information on the corresponding equation of state for pressures up to 11.3 GPa, beyond which a structural phase transformation occurs. The high pressure is simulated by first caging the individual Si atom in a small spherical volume V and estimated as P=-partial derivative E/partial derivative V, where E is the total electronic energy for a particular confinement volume. The energy is selfconsistently calculated through a recently developed shell-wise version of the Thomas-Fermi-Dirac-Weizsacker density functional, which compares favorably with ab initio calculations on the basis of a cluster model where the Si atom is surrounded by neon (helium) atoms (in a molecular scheme). The resulting individual electronic shell charge densities are then averaged along planar channels to find the effective charge densities needed in the channeling energy loss calculations for channeled ions. The position dependence of the energy loss in the channels for the free and high-pressure case is calculated for 5 Me V protons and alpha particles along the (110) planar channels.

  8. The Tenth Annual Ion Channel Retreat, Vancouver, Canada, June 25–27, 2012

    PubMed Central

    Kimlicka, Lynn; Liang, Sophia; Brugger, Saranna; Liang, Dong

    2013-01-01

    Abstract Ten years after Aurora Biomed (Vancouver, British Columbia, Canada) hosted the inaugural Ion Channel Retreat, this event is recognized as a leading conference for ion channel researchers. Held annually in Vancouver, this meeting consistently provides an outlet for researchers to share their findings while learning about new concepts, methods, and technologies. Researchers use this forum to discuss and debate a spectrum of topics from ion channel research and technology to drug discovery and safety. The Retreat covered key subjects in the ion channel industry, including ion channels as disease targets, transient receptor protein channels as pain and disease targets, ion channels as pain targets, ion channel structure and function, ion channel screening technologies, cardiac safety and toxicology, and cardiac function and pharmacology. PMID:23679851

  9. Nonselective block by La3+ of Arabidopsis ion channels involved in signal transduction

    NASA Technical Reports Server (NTRS)

    Lewis, B. D.; Spalding, E. P.; Evans, M. L. (Principal Investigator)

    1998-01-01

    Lanthanide ions such as La3+ are frequently used as blockers to test the involvement of calcium channels in plant and animal signal transduction pathways. For example, the large rise in cytoplasmic Ca2+ concentration triggered by cold shock in Arabidopsis seedlings is effectively blocked by 10 mM La3+ and we show here that the simultaneous large membrane depolarization is similarly blocked. However, a pharmacological tool is only as useful as it is selective and the specificity of La3+ for calcium channels was brought into question by our finding that it also blocked a blue light (BL)-induced depolarization that results from anion channel activation and believed not to involve calcium channels. This unexpected inhibitory effect of La3+ on the BL-induced depolarization is explained by our finding that 10 mM La3+ directly and completely blocked the BL-activated anion channel when applied to excised patches. We have investigated the ability of La3+ to block noncalcium channels in Arabidopsis. In addition to the BL-activated anion channel, 10 mM La3+ blocked a cation channel and a stretch-activated channel in patches of plasma membrane excised from hypocotyl cells. In root cells, 10 mM La3+ inhibited the activity of an outward-rectifying potassium channel at the whole cell and single-channel level by 47% and 58%, respectively. We conclude that La3+ is a nonspecific blocker of multiple ionic conductances in Arabidopsis and may disrupt signal transduction processes independently of any effect on Ca2+ channels.

  10. Optical electrophysiology for probing function and pharmacology of voltage-gated ion channels

    PubMed Central

    Zhang, Hongkang; Reichert, Elaine; Cohen, Adam E

    2016-01-01

    Voltage-gated ion channels mediate electrical dynamics in excitable tissues and are an important class of drug targets. Channels can gate in sub-millisecond timescales, show complex manifolds of conformational states, and often show state-dependent pharmacology. Mechanistic studies of ion channels typically involve sophisticated voltage-clamp protocols applied through manual or automated electrophysiology. Here, we develop all-optical electrophysiology techniques to study activity-dependent modulation of ion channels, in a format compatible with high-throughput screening. Using optical electrophysiology, we recapitulate many voltage-clamp protocols and apply to Nav1.7, a channel implicated in pain. Optical measurements reveal that a sustained depolarization strongly potentiates the inhibitory effect of PF-04856264, a Nav1.7-specific blocker. In a pilot screen, we stratify a library of 320 FDA-approved compounds by binding mechanism and kinetics, and find close concordance with patch clamp measurements. Optical electrophysiology provides a favorable tradeoff between throughput and information content for studies of NaV channels, and possibly other voltage-gated channels. DOI: http://dx.doi.org/10.7554/eLife.15202.001 PMID:27215841

  11. Ion channel noise can explain firing correlation in auditory nerves.

    PubMed

    Moezzi, Bahar; Iannella, Nicolangelo; McDonnell, Mark D

    2016-10-01

    Neural spike trains are commonly characterized as a Poisson point process. However, the Poisson assumption is a poor model for spiking in auditory nerve fibres because it is known that interspike intervals display positive correlation over long time scales and negative correlation over shorter time scales. We have therefore developed a biophysical model based on the well-known Meddis model of the peripheral auditory system, to produce simulated auditory nerve fibre spiking statistics that more closely match the firing correlations observed in empirical data. We achieve this by introducing biophysically realistic ion channel noise to an inner hair cell membrane potential model that includes fractal fast potassium channels and deterministic slow potassium channels. We succeed in producing simulated spike train statistics that match empirically observed firing correlations. Our model thus replicates macro-scale stochastic spiking statistics in the auditory nerve fibres due to modeling stochasticity at the micro-scale of potassium channels. PMID:27480847

  12. Nicotine effect on cardiovascular system and ion channels.

    PubMed

    Hanna, Salma Toma

    2006-03-01

    Smoking is a leading cause of cardiovascular disease, hypertension, myocardial infarction, and stroke. Nicotine is one of the components of cigarette smoke. Nicotine effects on the cardiovascular system reflect the activity of the nicotine receptors centrally and on peripheral autonomic ganglia. It has been found that cigarette smoke extract-induced contraction of porcine coronary arteries is related to superoxide anion-mediated degradation of nitric oxide. Treatment of rabbit aortas with an oxygen free radicals scavenger attenuated cigarette smoke impairment of arterial relaxation. Treatment of smokers with vitamin C, an antioxidant, improved impaired endothelium-dependent reactivity of large peripheral arteries. Thus it appears that chronic smoking and acute exposure to cigarette smoke extract may alter endothelium-dependent reactivity via the production of oxygen derived free radicals. This review discusses the effects of nicotine on resistance arterioles, compliance arteries, smooth muscle cells, and ion channels in the cardiovascular system. We discuss studies performed on humans, nicotine-exposed animals, and cell cultures yielding varying and inconsistent results that may be due to differences in experimental design, species, and the dose of exposure. Nicotine exposure appears to induce a combination of free radical production, vascular wall adhesion, and a reduction of fibrinolytic activity in the plasma. PMID:16633075

  13. Finite element simulation of the gating mechanism of mechanosensitive ion channels

    NASA Astrophysics Data System (ADS)

    Bavi, Navid; Qin, Qinghua; Martinac, Boris

    2013-08-01

    In order to eliminate limitations of existing experimental or computational methods (such as patch-clamp technique or molecular dynamic analysis) a finite element (FE) model for multi length-scale and time-scale investigation on the gating mechanism of mechanosensitive (MS) ion channels has been established. Gating force value (from typical patch clamping values) needed to activate Prokaryotic MS ion channels was applied as tensional force to the FE model of the lipid bilayer. Making use of the FE results, we have discussed the effects of the geometrical and the material properties of the Escherichia coli MscL mechanosensitive ion channel opening in relation to the membrane's Young's modulus (which will vary depending on the cell type or cholesterol density in an artificial membrane surrounding the MscL ion channel). The FE model has shown that when the cell membrane stiffens the required channel activation force increases considerably. This is in agreement with experimental results taken from the literature. In addition, the present study quantifies the relationship between the membrane stress distribution around a `hole' for modeling purposes and the stress concentration in the place transmembrane proteins attached to the hole by applying an appropriate mesh refinement as well as well defining contact condition in these areas.

  14. Nanoscale ion sequestration to determine the polarity selectivity of ion conductance in carriers and channels.

    PubMed

    Cranfield, Charles G; Bettler, Taren; Cornell, Bruce

    2015-01-01

    The nanoscale spacing between a tethered lipid bilayer membrane (tBLM) and its supporting gold electrode can be utilized to determine the polarity selectivity of the conduction of ion channels and ion carriers embedded in a membrane. The technique relies upon a bias voltage sequestering or eliminating ions, of a particular polarity, into or out of the aqueous electrolyte region between the gold electrode and the tethered membrane. A demonstration is given, using ac swept frequency impedance spectrometry, of the bias polarity dependence of the ionophore conductance of gramicidin A, a cationic selective channel, and valinomycin, a potassium ion selective carrier. We further use pulsed amperometry to show that the intrinsic voltage dependence of the ion conduction is actually selective of the polarity of the transported ion and not simply of the direction of the ionic current flow. PMID:25474616

  15. Thermal Responsive Ion Selectivity of Uranyl Peroxide Nanocages: An Inorganic Mimic of K(+) Ion Channels.

    PubMed

    Gao, Yunyi; Szymanowski, Jennifer E S; Sun, Xinyu; Burns, Peter C; Liu, Tianbo

    2016-06-01

    An actinyl peroxide cage cluster, Li48+m K12 (OH)m [UO2 (O2 )(OH)]60 (H2 O)n (m≈20 and n≈310; U60 ), discriminates precisely between Na(+) and K(+) ions when heated to certain temperatures, a most essential feature for K(+) selective filters. The U60 clusters demonstrate several other features in common with K(+) ion channels, including passive transport of K(+) ions, a high flux rate, and the dehydration of U60 and K(+) ions. These qualities make U60 (a pure inorganic cluster) a promising ion channel mimic in an aqueous environment. Laser light scattering (LLS) and isothermal titration calorimetry (ITC) studies revealed that the tailorable ion selectivity of U60 clusters is a result of the thermal responsiveness of the U60 hydration shells. PMID:27105921

  16. Ion Selectivity Mechanism in a Bacterial Pentameric Ligand-Gated Ion Channel

    SciTech Connect

    Fritsch, Sebastian M; Ivanov, Ivaylo N; Wang, Hailong; Cheng, Xiaolin

    2011-01-01

    The proton-gated ion channel from Gloeobacter violaceus (GLIC) is a prokaryotic homolog of the eukaryotic nicotinic acetylcholine receptor (nAChR) that responds to the binding of neurotransmitter acetylcholine and mediates fast signal transmission. Recent emergence of a high resolution crystal structure of GLIC captured in a potentially open state allowed detailed, atomic-level insight into ion conduction and selectivity mechanisms in these channels. Herein, we have examined the barriers to ion conduction and origins of ion selectivity in the GLIC channel by the construction of potential of mean force (PMF) profiles for sodium and chloride ions inside the transmembrane region. Our calculations reveal that the GLIC channel is open for a sodium ion to transport, but presents a ~10 kcal/mol free energy barrier for a chloride ion, which arises primarily from the unfavorable interactions with a ring of negatively charged glutamate residues (E-2 ) at the intracellular end and a ring of hydrophobic residues (I9 ) in the middle of the transmembrane domain. Our collective findings further suggest that the charge selection mechanism can, to a large extent, be attributed to the narrow intracellular end and a ring of glutamate residues in this position their strong negative electrostatics and ability to bind cations. By contrast, E19 at the extracellular entrance only plays a minor role in ion selectivity of GLIC. In addition to electrostatics, both ion hydration and protein dynamics are found to be crucial for ion conduction as well, which explains why a chloride ion experiences a much greater barrier than a sodium ion in the hydrophobic region of the pore.

  17. Molecular dynamics of ion transport through the open conformation of a bacterial voltage-gated sodium channel

    PubMed Central

    Ulmschneider, Martin B.; Bagnéris, Claire; McCusker, Emily C.; DeCaen, Paul G.; Delling, Markus; Clapham, David E.; Ulmschneider, Jakob P.; Wallace, B. A.

    2013-01-01

    The crystal structure of the open conformation of a bacterial voltage-gated sodium channel pore from Magnetococcus sp. (NaVMs) has provided the basis for a molecular dynamics study defining the channel’s full ion translocation pathway and conductance process, selectivity, electrophysiological characteristics, and ion-binding sites. Microsecond molecular dynamics simulations permitted a complete time-course characterization of the protein in a membrane system, capturing the plethora of conductance events and revealing a complex mixture of single and multi-ion phenomena with decoupled rapid bidirectional water transport. The simulations suggest specific localization sites for the sodium ions, which correspond with experimentally determined electron density found in the selectivity filter of the crystal structure. These studies have also allowed us to identify the ion conductance mechanism and its relation to water movement for the NavMs channel pore and to make realistic predictions of its conductance properties. The calculated single-channel conductance and selectivity ratio correspond closely with the electrophysiology measurements of the NavMs channel expressed in HEK 293 cells. The ion translocation process seen in this voltage-gated sodium channel is clearly different from that exhibited by members of the closely related family of voltage-gated potassium channels and also differs considerably from existing proposals for the conductance process in sodium channels. These studies simulate sodium channel conductance based on an experimentally determined structure of a sodium channel pore that has a completely open transmembrane pathway and activation gate. PMID:23542377

  18. Epithelial Sodium and Acid-Sensing Ion Channels

    NASA Astrophysics Data System (ADS)

    Kellenberger, Stephan

    The epithelial Na+ channel (ENaC) and acid-sensing ion channels (ASICs) are non-voltage-gated Na+ channels that form their own subfamilies within the ENaC/degenerin ion channel family. ASICs are sensors of extracellular pH, and ENaC, whose main function is trans-epithelial Na+ transport, can sense extra- and intra-cellular Na+. In aldosterone-responsive epithelial cells of the kidney, ENaC plays a critical role in the control of sodium balance, blood volume and blood pressure. In airway epithelia, ENaC has a distinct role in controlling fluid reabsorption at the air-liquid interface, thereby determining the rate of mucociliary transport. In taste receptor cells of the tongue, ENaC is involved in salt taste sensation. ASICs have emerged as key sensors for extracellular protons in central and peripheral neurons. Although not all of their physiological and pathological functions are firmly established yet, there is good evidence for a role of ASICs in the brain in learning, expression of fear, and in neurodegeneration after ischaemic stroke. In sensory neurons, ASICs are involved in nociception and mechanosensation. ENaC and ASIC subunits share substantial sequence homology and the conservation of several functional domains. This chapter summarises our current understanding of the physiological functions and of the mechanisms of ion permeation, gating and regulation of ENaC and ASICs.

  19. Convergence of ion channel genome content in early animal evolution.

    PubMed

    Liebeskind, Benjamin J; Hillis, David M; Zakon, Harold H

    2015-02-24

    Multicellularity has evolved multiple times, but animals are the only multicellular lineage with nervous systems. This fact implies that the origin of nervous systems was an unlikely event, yet recent comparisons among extant taxa suggest that animal nervous systems may have evolved multiple times independently. Here, we use ancestral gene content reconstruction to track the timing of gene family expansions for the major families of ion-channel proteins that drive nervous system function. We find that animals with nervous systems have broadly similar complements of ion-channel types but that these complements likely evolved independently. We also find that ion-channel gene family evolution has included large loss events, two of which were immediately followed by rounds of duplication. Ctenophores, cnidarians, and bilaterians underwent independent bouts of gene expansion in channel families involved in synaptic transmission and action potential shaping. We suggest that expansions of these family types may represent a genomic signature of expanding nervous system complexity. Ancestral nodes in which nervous systems are currently hypothesized to have originated did not experience large expansions, making it difficult to distinguish among competing hypotheses of nervous system origins and suggesting that the origin of nerves was not attended by an immediate burst of complexity. Rather, the evolution of nervous system complexity appears to resemble a slow fuse in stem animals followed by many independent bouts of gene gain and loss. PMID:25675537

  20. Convergence of ion channel genome content in early animal evolution

    PubMed Central

    Liebeskind, Benjamin J.; Hillis, David M.; Zakon, Harold H.

    2015-01-01

    Multicellularity has evolved multiple times, but animals are the only multicellular lineage with nervous systems. This fact implies that the origin of nervous systems was an unlikely event, yet recent comparisons among extant taxa suggest that animal nervous systems may have evolved multiple times independently. Here, we use ancestral gene content reconstruction to track the timing of gene family expansions for the major families of ion-channel proteins that drive nervous system function. We find that animals with nervous systems have broadly similar complements of ion-channel types but that these complements likely evolved independently. We also find that ion-channel gene family evolution has included large loss events, two of which were immediately followed by rounds of duplication. Ctenophores, cnidarians, and bilaterians underwent independent bouts of gene expansion in channel families involved in synaptic transmission and action potential shaping. We suggest that expansions of these family types may represent a genomic signature of expanding nervous system complexity. Ancestral nodes in which nervous systems are currently hypothesized to have originated did not experience large expansions, making it difficult to distinguish among competing hypotheses of nervous system origins and suggesting that the origin of nerves was not attended by an immediate burst of complexity. Rather, the evolution of nervous system complexity appears to resemble a slow fuse in stem animals followed by many independent bouts of gene gain and loss. PMID:25675537

  1. Equilibrium selectivity alone does not create K+-selective ion conduction in K+ channels

    NASA Astrophysics Data System (ADS)

    Liu, Shian; Lockless, Steve W.

    2013-11-01

    Potassium (K+) channels are selective for K+ over Na+ ions during their transport across membranes. We and others have previously shown that tetrameric K+ channels are primarily occupied by K+ ions in their selectivity filters under physiological conditions, demonstrating the channel’s intrinsic equilibrium preference for K+ ions. Based on this observation, we hypothesize that the preference for K+ ions over Na+ ions in the filter determines its selectivity during ion conduction. Here, we ask whether non-selective cation channels, which share an overall structure and similar individual ion-binding sites with K+ channels, have an ion preference at equilibrium. The variants of the non-selective Bacillus cereus NaK cation channel we examine are all selective for K+ over Na+ ions at equilibrium. Thus, the detailed architecture of the K+ channel selectivity filter, and not only its equilibrium ion preference, is fundamental to the generation of selectivity during ion conduction.

  2. Structure and Energetics of Allosteric Regulation of HCN2 Ion Channels by Cyclic Nucleotides*

    PubMed Central

    DeBerg, Hannah A.; Brzovic, Peter S.; Flynn, Galen E.; Zagotta, William N.; Stoll, Stefan

    2016-01-01

    Hyperpolarization-activated cyclic nucleotide-gated (HCN) ion channels play an important role in regulating electrical activity in the heart and brain. They are gated by the binding of cyclic nucleotides to a conserved, intracellular cyclic nucleotide-binding domain (CNBD), which is connected to the channel pore by a C-linker region. Binding of cyclic nucleotides increases the rate and extent of channel activation and shifts it to less hyperpolarized voltages. We probed the allosteric mechanism of different cyclic nucleotides on the CNBD and on channel gating. Electrophysiology experiments showed that cAMP, cGMP, and cCMP were effective agonists of the channel and produced similar increases in the extent of channel activation. In contrast, electron paramagnetic resonance (EPR) and nuclear magnetic resonance (NMR) on the isolated CNBD indicated that the induced conformational changes and the degrees of stabilization of the active conformation differed for the three cyclic nucleotides. We explain these results with a model where different allosteric mechanisms in the CNBD all converge to have the same effect on the C-linker and render all three cyclic nucleotides similarly potent activators of the channel. PMID:26559974

  3. Structure and Energetics of Allosteric Regulation of HCN2 Ion Channels by Cyclic Nucleotides.

    PubMed

    DeBerg, Hannah A; Brzovic, Peter S; Flynn, Galen E; Zagotta, William N; Stoll, Stefan

    2016-01-01

    Hyperpolarization-activated cyclic nucleotide-gated (HCN) ion channels play an important role in regulating electrical activity in the heart and brain. They are gated by the binding of cyclic nucleotides to a conserved, intracellular cyclic nucleotide-binding domain (CNBD), which is connected to the channel pore by a C-linker region. Binding of cyclic nucleotides increases the rate and extent of channel activation and shifts it to less hyperpolarized voltages. We probed the allosteric mechanism of different cyclic nucleotides on the CNBD and on channel gating. Electrophysiology experiments showed that cAMP, cGMP, and cCMP were effective agonists of the channel and produced similar increases in the extent of channel activation. In contrast, electron paramagnetic resonance (EPR) and nuclear magnetic resonance (NMR) on the isolated CNBD indicated that the induced conformational changes and the degrees of stabilization of the active conformation differed for the three cyclic nucleotides. We explain these results with a model where different allosteric mechanisms in the CNBD all converge to have the same effect on the C-linker and render all three cyclic nucleotides similarly potent activators of the channel. PMID:26559974

  4. Redox Regulation of Ion Channels in the Pulmonary Circulation

    PubMed Central

    Weir, Edward Kenneth

    2015-01-01

    Abstract Significance: The pulmonary circulation is a low-pressure, low-resistance, highly compliant vasculature. In contrast to the systemic circulation, it is not primarily regulated by a central nervous control mechanism. The regulation of resting membrane potential due to ion channels is of integral importance in the physiology and pathophysiology of the pulmonary vasculature. Recent Advances: Redox-driven ion conductance changes initiated by direct oxidation, nitration, and S-nitrosylation of the cysteine thiols and indirect phosphorylation of the threonine and serine residues directly affect pulmonary vascular tone. Critical Issues: Molecular mechanisms of changes in ion channel conductance, especially the identification of the sites of action, are still not fully elucidated. Future Directions: Further investigation of the interaction between redox status and ion channel gating, especially the physiological significance of S-glutathionylation and S-nitrosylation, could result in a better understanding of the physiological and pathophysiological importance of these mediators in general and the implications of such modifications in cellular functions and related diseases and their importance for targeted treatment strategies. Antioxid. Redox Signal. 22, 465–485. PMID:24702125

  5. 50 years of ion channeling in materials science

    NASA Astrophysics Data System (ADS)

    Vantomme, André

    2016-03-01

    In the early days of ion beam analysis, i.e. the early 60s, channeling was discovered and brought to maturity via a combined effort in experimental, computational and theoretical research. It was soon realized that the probability for nuclear interaction (such as nuclear scattering, nuclear reactions, ionization followed by X-ray emission…) would significantly decrease when steering the ion beam along a crystallographic direction of a single crystal. Hence, this effect would be optimally suited to investigate a wide range of materials properties related to their crystal structure, such as defects, elastic strain, the lattice site of impurities, as well as phonon-related properties. In this paper, I will briefly review some of the pioneering work, which led to the discovery and theoretical understanding of ion channeling. Subsequently, a number of applications will be discussed where the strength of the ion beam analysis technique allows deducing information which is often hardly (or not) attainable by other techniques. Throughout the paper, I will reflect on the future of channeling in materials research, and pay special attention to potential pitfalls, challenges and opportunities.

  6. NOTE: Dielectrophoretic analysis of changes in cytoplasmic ion levels due to ion channel blocker action reveals underlying differences between drug-sensitive and multidrug-resistant leukaemic cells

    NASA Astrophysics Data System (ADS)

    Duncan, L.; Shelmerdine, H.; Hughes, M. P.; Coley, H. M.; Hübner, Y.; Labeed, F. H.

    2008-01-01

    Dielectrophoresis (DEP)—the motion of particles in non-uniform AC fields—has been used in the investigation of cell electrophysiology. The technique offers the advantages of rapid determination of the conductance and capacitance of membrane and cytoplasm. However, it is unable to directly determine the ionic strengths of individual cytoplasmic ions, which has potentially limited its application in assessing cell composition. In this paper, we demonstrate how dielectrophoresis can be used to investigate the cytoplasmic ion composition by using ion channel blocking agents. By blocking key ion transporters individually, it is possible to determine their overall contribution to the free ions in the cytoplasm. We use this technique to evaluate the relative contributions of chloride, potassium and calcium ions to the cytoplasmic conductivities of drug sensitive and resistant myelogenous leukaemic (K562) cells in order to determine the contributions of individual ion channel activity in mediating multi-drug resistance in cancer. Results indicate that whilst K+ and Ca2+ levels were extremely similar between sensitive and resistant lines, levels of Cl- were elevated by three times to that in the resistant line, implying increased chloride channel activity. This result is in line with current theories of MDR, and validates the use of ion channel blockers with DEP to investigate ion channel function.

  7. Supramolecular Assemblies and Localized Regulation of Voltage-Gated Ion Channels

    PubMed Central

    Dai, Shuiping; Hall, Duane D.; Hell, Johannes W.

    2009-01-01

    This review addresses the localized regulation of voltage-gated ion channels by phosphorylation. Comprehensive data on channel regulation by associated protein kinases, phosphatases, and related regulatory proteins are mainly available for voltage-gated Ca2+ channels, which form the main focus of this review. Other voltage-gated ion channels and especially Kv7.1-3 (KCNQ1-3), the large- and small-conductance Ca2+-activated K+ channels BK and SK2, and the inward-rectifying K+ channels Kir3 have also been studied to quite some extent and will be included. Regulation of the L-type Ca2+ channel Cav1.2 by PKA has been studied most thoroughly as it underlies the cardiac fight-or-flight response. A prototypical Cav1.2 signaling complex containing the β2 adrenergic receptor, the heterotrimeric G protein Gs, adenylyl cyclase, and PKA has been identified that supports highly localized via cAMP. The type 2 ryanodine receptor as well as AMPA- and NMDA-type glutamate receptors are in close proximity to Cav1.2 in cardiomyocytes and neurons, respectively, yet independently anchor PKA, CaMKII, and the serine/threonine phosphatases PP1, PP2A, and PP2B, as is discussed in detail. Descriptions of the structural and functional aspects of the interactions of PKA, PKC, CaMKII, Src, and various phosphatases with Cav1.2 will include comparisons with analogous interactions with other channels such as the ryanodine receptor or ionotropic glutamate receptors. Regulation of Na+ and K+ channel phosphorylation complexes will be discussed in separate papers. This review is thus intended for readers interested in ion channel regulation or in localization of kinases, phosphatases, and their upstream regulators. PMID:19342611

  8. Organization of Ion Channels in the Myelinated Nerve Fiber

    NASA Astrophysics Data System (ADS)

    Waxman, Stephen G.; Murdoch Ritchie, J.

    1985-06-01

    The functional organization of the mammalian myelinated nerve fiber is complex and elegant. In contrast to nonmyelinated axons, whose membranes have a relatively uniform structure, the mammalian myelinated axon exhibits a high degree of regional specialization that extends to the location of voltage-dependent ion channels within the axon membrane. Sodium and potassium channels are segregated into complementary membrane domains, with a distribution reflecting that of the overlying Schwann or glial cells. This complexity of organization has important implications for physiology and pathophysiology, particularly with respect to the development of myelinated fibers.

  9. From Toxins Targeting Ligand Gated Ion Channels to Therapeutic Molecules

    PubMed Central

    Nasiripourdori, Adak; Taly, Valérie; Grutter, Thomas; Taly, Antoine

    2011-01-01

    Ligand-gated ion channels (LGIC) play a central role in inter-cellular communication. This key function has two consequences: (i) these receptor channels are major targets for drug discovery because of their potential involvement in numerous human brain diseases; (ii) they are often found to be the target of plant and animal toxins. Together this makes toxin/receptor interactions important to drug discovery projects. Therefore, toxins acting on LGIC are presented and their current/potential therapeutic uses highlighted. PMID:22069709

  10. Acid-sensing ion channels in pain and disease

    PubMed Central

    Wemmie, John A.; Taugher, Rebecca J.; Kreple, Collin J.

    2015-01-01

    Why do neurons sense extracellular acid? In large part, this question has driven increasing investigation on acid-sensing ion channels (ASICs) in the CNS and the peripheral nervous system for the past two decades. Significant progress has been made in understanding the structure and function of ASICs at the molecular level. Studies aimed at clarifying their physiological importance have suggested roles for ASICs in pain, neurological and psychiatric disease. This Review highlights recent findings linking these channels to physiology and disease. In addition, it discusses some of the implications for therapy and points out questions that remain unanswered. PMID:23783197

  11. Main ion channels and receptors associated with visceral hypersensitivity in irritable bowel syndrome

    PubMed Central

    de Carvalho Rocha, Heraldo Arcela; Dantas, Bruna Priscilla Vasconcelos; Rolim, Thaísa Leite; Costa, Bagnólia Araújo; de Medeiros, Arnaldo Correia

    2014-01-01

    Irritable bowel syndrome (IBS) is a very frequent functional gastrointestinal disorder characterized by recurrent abdominal pain or discomfort and alteration of bowel habits. The IBS physiopathology is extremely complex. Visceral hypersensitivity plays an important role in the pathogenesis of abdominal pain in both in vitro and in vivo models of this functional disorder. In order to obtain a general view of the participation of the main ion channels and receptors regarding the visceral hypersensitivity in the IBS and to describe their chemical structure, a literature review was carried out. A bibliographical research in the following electronic databases: Pubmed and Virtual Library in Health (BVS) was fulfilled by using the search terms “ion channels” “or” “receptors” “and” “visceral hypersensitivity” “or” “visceral nociception” “and” “irritable bowel syndrome”. Original and review articles were considered for data acquisition. The activation of the ATP ion-gated channels, voltage-gated sodium (Nav) and calcium (Cav) channels, as well as the activation of protease-activated receptors (PAR2), transient receptor potential vanilloide-1, serotonin, cannabinoids and cholecystokinin are involved in the genesis of visceral hypersensitivity in IBS. The involvement of ion channels and receptors concerning visceral hypersensitivity is noteworthy in IBS models. PMID:24976114

  12. Function and regulation of TRPP2 ion channel revealed by a gain-of-function mutant.

    PubMed

    Arif Pavel, Mahmud; Lv, Caixia; Ng, Courtney; Yang, Lei; Kashyap, Parul; Lam, Clarissa; Valentino, Victoria; Fung, Helen Y; Campbell, Thomas; Møller, Simon Geir; Zenisek, David; Holtzman, Nathalia G; Yu, Yong

    2016-04-26

    Mutations in polycystin-1 and transient receptor potential polycystin 2 (TRPP2) account for almost all clinically identified cases of autosomal dominant polycystic kidney disease (ADPKD), one of the most common human genetic diseases. TRPP2 functions as a cation channel in its homomeric complex and in the TRPP2/polycystin-1 receptor/ion channel complex. The activation mechanism of TRPP2 is unknown, which significantly limits the study of its function and regulation. Here, we generated a constitutively active gain-of-function (GOF) mutant of TRPP2 by applying a mutagenesis scan on the S4-S5 linker and the S5 transmembrane domain, and studied functional properties of the GOF TRPP2 channel. We found that extracellular divalent ions, including Ca(2+), inhibit the permeation of monovalent ions by directly blocking the TRPP2 channel pore. We also found that D643, a negatively charged amino acid in the pore, is crucial for channel permeability. By introducing single-point ADPKD pathogenic mutations into the GOF TRPP2, we showed that different mutations could have completely different effects on channel activity. The in vivo function of the GOF TRPP2 was investigated in zebrafish embryos. The results indicate that, compared with wild type (WT), GOF TRPP2 more efficiently rescued morphological abnormalities, including curly tail and cyst formation in the pronephric kidney, caused by down-regulation of endogenous TRPP2 expression. Thus, we established a GOF TRPP2 channel that can serve as a powerful tool for studying the function and regulation of TRPP2. The GOF channel may also have potential application for developing new therapeutic strategies for ADPKD. PMID:27071085

  13. Mutant SOD1 Forms Ion Channel: Implications for ALS Pathophysiology

    PubMed Central

    Allen, Michael J.; Lacroix, Jérome J.; Ramachandran, Srinivasan; Capone, Ricardo; Whitlock, Jenny L.; Ghadge, Ghanashyam D.; Arnsdorf, Morton F.; Roos, Raymond P.; Lal, Ratnesh

    2011-01-01

    Point mutations in the gene encoding copper-zinc superoxide dismutase (SOD1) impart a gain-of-function to this protein that underlies 20-25% of all familial amyotrophic lateral sclerosis (FALS) cases. However, the specific mechanism of mutant SOD1 toxicity has remained elusive. Using the complementary techniques of atomic force microscopy (AFM), electrophysiology, and cell and molecular biology, here we examine the structure and activity of A4VSOD1, a mutant SOD1. AFM of A4VSOD1 reconstituted in lipid membrane shows discrete tetrameric pore-like structure with outer and inner diameters 12.2 and 3.0 nm respectively. Electrophysiological recordings show distinct ionic conductances across bilayer for A4VSOD1 and none for wild-type SOD1. Mouse neuroblastoma cells exposed to A4VSOD1 undergo membrane depolarization and increases in intracellular calcium. These results provide compelling new evidence that a mutant SOD1 is capable of disrupting cellular homeostasis via an unregulated ion channel mechanism. Such a “toxic channel” mechanism presents a new therapeutic direction for ALS research. PMID:21930207

  14. Effects of Bisphenol A on ion channels: Experimental evidence and molecular mechanisms.

    PubMed

    Soriano, Sergi; Ripoll, Cristina; Alonso-Magdalena, Paloma; Fuentes, Esther; Quesada, Ivan; Nadal, Angel; Martinez-Pinna, Juan

    2016-07-01

    Bisphenol A (BPA) is an endocrine-disrupting chemical (EDC) produced in huge quantities in the manufacture of polycarbonate plastics and epoxy resins. It is present in most humans in developed countries, acting as a xenoestrogen and it is considered an environmental risk factor associated to several diseases. Among the whole array of identified mechanisms by which BPA can interfere with physiological processes in living organisms, changes on ion channel activity is one of the most poorly understood. There is still little evidence about BPA regulation of ion channel expression and function. However, this information is key to understand how BPA disrupts excitable and non-excitable cells, including neurons, endocrine cells and muscle cells. This report is the result of a comprehensive literature review on the effects of BPA on ion channels. We conclude that there is evidence to say that these important molecules may be key end-points for EDCs acting as xenoestrogens. However, more research on channel-mediated BPA effects is needed. Particularly, mechanistic studies to unravel the pathophysiological actions of BPA on ion channels at environmentally relevant doses. PMID:26930576

  15. The Transcription Factors Islet and Lim3 Combinatorially Regulate Ion Channel Gene Expression

    PubMed Central

    Wolfram, Verena; Southall, Tony D.; Günay, Cengiz; Prinz, Astrid A.; Brand, Andrea H.

    2014-01-01

    Expression of appropriate ion channels is essential to allow developing neurons to form functional networks. Our previous studies have identified LIM-homeodomain (HD) transcription factors (TFs), expressed by developing neurons, that are specifically able to regulate ion channel gene expression. In this study, we use the technique of DNA adenine methyltransferase identification (DamID) to identify putative gene targets of four such TFs that are differentially expressed in Drosophila motoneurons. Analysis of targets for Islet (Isl), Lim3, Hb9, and Even-skipped (Eve) identifies both ion channel genes and genes predicted to regulate aspects of dendritic and axonal morphology. Significantly, some ion channel genes are bound by more than one TF, consistent with the possibility of combinatorial regulation. One such gene is Shaker (Sh), which encodes a voltage-dependent fast K+ channel (Kv1.1). DamID reveals that Sh is bound by both Isl and Lim3. We used body wall muscle as a test tissue because in conditions of low Ca2+, the fast K+ current is carried solely by Sh channels (unlike neurons in which a second fast K+ current, Shal, also contributes). Ectopic expression of isl, but not Lim3, is sufficient to reduce both Sh transcript and Sh current level. By contrast, coexpression of both TFs is additive, resulting in a significantly greater reduction in both Sh transcript and current compared with isl expression alone. These observations provide evidence for combinatorial activity of Isl and Lim3 in regulating ion channel gene expression. PMID:24523544

  16. Ion channels and receptor as targets for the control of parasitic nematodes

    PubMed Central

    Wolstenholme, Adrian J.

    2011-01-01

    Many of the anthelmintic drugs in use today act on the nematode nervous system. Ion channel targets have some obvious advantages. They tend to act quickly, which means that they will clear many infections rapidly. They produce very obvious effects on the worms, typically paralyzing them, and these effects are suitable for use in rapid and high-throughput assays. Many of the ion channels and enzymes targeted can also be incorporated into such assays. The macrocyclic lactones bind to an allosteric site on glutamate-gated chloride channels, either directly activating the channel or enhancing the effect of the normal agonist, glutamate. Many old and new anthelmintics, including tribendimidine and the amino-acetonitrile derivatives, act as agonists at nicotinic acetylcholine receptors; derquantel is an antagonist at these receptors. Nematodes express many different types of nicotinic receptor and this diversity means that they are likely to remain important targets for the foreseeable future. Emodepside may have multiple effects, affecting both a potassium channel and a pre-synaptic G protein-coupled receptor; although few other current drugs act at such targets, this example indicates that they may be more important in the future. The nematode nervous system contains many other ion channels and receptors that have not so far been exploited in worm control but which should be explored in the development of effective new compounds. PMID:24533259

  17. Binding of Capsaicin to the TRPV1 Ion Channel.

    PubMed

    Darré, Leonardo; Domene, Carmen

    2015-12-01

    Transient receptor potential (TRP) ion channels constitute a notable family of cation channels involved in the ability of an organisms to detect noxious mechanical, thermal, and chemical stimuli that give rise to the perception of pain, taste, and changes in temperature. One of the most experimentally studied agonist of TRP channels is capsaicin, which is responsible for the burning sensation produced when chili pepper is in contact with organic tissues. Thus, understanding how this molecule interacts and regulates TRP channels is essential to high impact pharmacological applications, particularly those related to pain treatment. The recent publication of a three-dimensional structure of the vanilloid receptor 1 (TRPV1) in the absence and presence of capsaicin from single particle electron cryomicroscopy experiments provides the opportunity to explore these questions at the atomic level. In the present work, molecular docking and unbiased and biased molecular dynamics simulations were employed to generate a structural model of the capsaicin-channel complex. In addition, the standard free energy of binding was estimated using alchemical transformations coupled with conformational, translational, and orientational restraints on the ligand. Key binding modes consistent with previous experimental data are identified, and subtle but essential dynamical features of the binding site are characterized. These observations shed some light into how TRPV1 interacts with capsaicin, and may help to refine design parameters for new TRPV1 antagonists, and potentially guide further developments of TRP channel modulators. PMID:26502196

  18. Novel Activation of Voltage-gated K+ Channels by Sevoflurane*

    PubMed Central

    Barber, Annika F.; Liang, Qiansheng; Covarrubias, Manuel

    2012-01-01

    Voltage-gated ion channels are modulated by halogenated inhaled general anesthetics, but the underlying molecular mechanisms are not understood. Alkanols and halogenated inhaled anesthetics such as halothane and isoflurane inhibit the archetypical voltage-gated Kv3 channel homolog K-Shaw2 by stabilizing the resting/closed states. By contrast, sevoflurane, a more heavily fluorinated ether commonly used in general anesthesia, specifically activates K-Shaw2 currents at relevant concentrations (0.05–1 mm) in a rapid and reversible manner. The concentration dependence of this modulation is consistent with the presence of high and low affinity interactions (KD = 0.06 and 4 mm, respectively). Sevoflurane (<1 mm) induces a negative shift in the conductance-voltage relation and increases the maximum conductance. Furthermore, suggesting possible roles in general anesthesia, mammalian Kv1.2 and Kv1.5 channels display similar changes. Quantitative description of the observations by an economical allosteric model indicates that sevoflurane binding favors activation gating and eliminates an unstable inactivated state outside the activation pathway. This study casts light on the mechanism of the novel sevoflurane-dependent activation of Kv channels, which helps explain how closely related inhaled anesthetics achieve specific actions and suggests strategies to develop novel Kv channel activators. PMID:23038249

  19. Automatable lipid bilayer formation for ion channel studies

    NASA Astrophysics Data System (ADS)

    Poulos, Jason L.; Bang, Hyunwoo; Jeon, Tae-Joon; Schmidt, Jacob J.

    2008-08-01

    Transmembrane proteins and ion channels are important drug targets and have been explored as single molecule sensors. For these proteins to function normally they must be integrated within lipid bilayers; however, the labor and skill required to create artificial lipid bilayers have the limited the possible applications utilizing these proteins. In order to reduce the complexity and cost of lipid bilayer formation and measurement, we have modified a previously published lipid bilayer formation technique using mechanically contacted monolayers so that the process is automatable, requiring minimal operator input. Measurement electronics are integrated with the fluid handling system, greatly reducing the time and operator feedback characteristically required of traditional bilayer experiments. To demonstrate the biological functionality of the resultant bilayers and the system's capabilities as a membrane platform, the ion channel gramicidin A was incorporated and measured with this system.

  20. Biomimetic Nanotubes Based on Cyclodextrins for Ion-Channel Applications.

    PubMed

    Mamad-Hemouch, Hajar; Ramoul, Hassen; Abou Taha, Mohammad; Bacri, Laurent; Huin, Cécile; Przybylski, Cédric; Oukhaled, Abdelghani; Thiébot, Bénédicte; Patriarche, Gilles; Jarroux, Nathalie; Pelta, Juan

    2015-11-11

    Biomimetic membrane channels offer a great potential for fundamental studies and applications. Here, we report the fabrication and characterization of short cyclodextrin nanotubes, their insertion into membranes, and cytotoxicity assay. Mass spectrometry and high-resolution transmission electron microscopy were used to confirm the synthesis pathway leading to the formation of short nanotubes and to describe their structural parameters in terms of length, diameter, and number of cyclodextrins. Our results show the control of the number of cyclodextrins threaded on the polyrotaxane leading to nanotube synthesis. Structural parameters obtained by electron microscopy are consistent with the distribution of the number of cyclodextrins evaluated by mass spectrometry from the initial polymer distribution. An electrophysiological study at single molecule level demonstrates the ion channel formation into lipid bilayers, and the energy penalty for the entry of ions into the confined nanotube. In the presence of nanotubes, the cell physiology is not altered. PMID:26471761

  1. Laser induced electron acceleration in an ion-channel guiding

    SciTech Connect

    Esmaeilzadeh, Mahdi; Taghavi, Amin; Hanifpour, Maryam

    2011-09-15

    Direct electron acceleration by a propagating laser pulse of circular polarization in an ion-channel guiding is studied by developing a relativistic three-dimensional single particle code. The electron chaotic dynamic is also studied using time series, power spectrum, and Liapunov exponent. It is found that the electron motion is regular (non-chaotic) for laser pulse with short time duration, while for long enough time duration, the electron motion may be chaotic. In the case of non-chaotic motion, the electron can gain and retain very high energy in the presence of ion-channel before reaching the steady-state, whereas in the case of chaotic motion, the electron gains energy and then loses it very rapidly in an unpredictable manner.

  2. Ion permeation properties of the glutamate receptor channel in cultured embryonic Drosophila myotubes.

    PubMed Central

    Chang, H; Ciani, S; Kidokoro, Y

    1994-01-01

    Ion permeation properties of the glutamate receptor channel in cultured myotubes of Drosophila embryos were studied using the inside-out configuration of the patch-clamp technique. Lowering the NaCl concentration in the bath (intracellular solution), while maintaining that of the external solution constant, caused a shift of the reversal potential in the positive direction, thus indicating a higher permeability of the channel to Na+ than to Cl- (PCl/PNa < 0.04), and suggesting that the channel is cation selective. With 145 mM Na+ on both sides of the membrane, the single-channel current-voltage relation was almost linear in the voltage range between -80 and +80 mV, the conductance showing some variability in the range between 140 and 170 pS. All monovalent alkali cations tested, as well as NH4+, permeated the channel effectively. Using the Goldman-Hodgkin-Katz equation for the reversal potential, the permeability ratios with respect to Na+ were estimated to be: 1.32 for K+, 1.18 for NH4+, 1.15 for Rb+, 1.09 for Cs+, and 0.57 for Li+. Divalent cations, i.e. Mg2+ and Ca2+, in the external solution depressed not only the inward but also the outward Na+ currents, although reversal potential measurements indicated that both ions have considerably higher permeabilities than Na+ (PMg/PNa = 2.31; PCa/PNa = 9.55). The conductance-activity relation for Na+ was described by a hyperbolic curve. The maximal conductance was about 195 pS and the half-saturating activity 45 mM. This result suggests that Na+ ions bind to sites in the channel. All data were fitted by a model based on the Eyring's reaction rate theory, in which the receptor channel is a one-ion pore with three energy barriers and two internal sites. PMID:7519261

  3. Amino acid-sensing ion channels in plants

    SciTech Connect

    Spalding, Edgar P.

    2014-08-12

    The title of our project is “Amino acid-sensing ion channels in plants”. Its goals are two-fold: to determine the molecular functions of glutamate receptor-like (GLR) proteins, and to elucidate their biological roles (physiological or developmental) in plants. Here is our final technical report. We were highly successful in two of the three aims, modestly successful in the third.

  4. Ion channels go to Stockholm--this time as proteins.

    PubMed

    Miller, Christopher

    2003-12-18

    The 2003 Nobel Prize in Chemistry was awarded to two structural biologists, Roderick Mackinnon of Rockefeller University and Peter Agre of Johns Hopkins University, for their groundbreaking work on the structure and function of ion channels. In recognition of the outstanding impact that MacKinnon's work has had for neuroscience, Chris Miller traces MacKinnon's scientific path to the Nobel Prize. PMID:14687537

  5. Ion Channel Voltage Sensors: Structure, Function, and Pathophysiology

    PubMed Central

    Catterall, William A.

    2010-01-01

    Voltage-gated ion channels generate electrical signals in species from bacteria to man. Their voltage-sensing modules are responsible for initiation of action potentials and graded membrane potential changes in response to synaptic input and other physiological stimuli. Extensive structure-function studies, structure determination, and molecular modeling are now converging on a sliding-helix mechanism for electromechanical coupling in which outward movement of gating charges in the S4 transmembrane segments catalyzed by sequential formation of ion pairs pulls the S4-S5 linker, bends the S6 segment, and opens the pore. Impairment of voltage-sensor function by mutations in Na+ channels contributes to several ion channelopathies, and gating pore current conducted by mutant voltage sensors in NaV1.4 channels is the primary pathophysiological mechanism in Hypokalemic Periodic Paralysis. The emerging structural model for voltage sensor function opens the way to development of a new generation of ionchannel drugs that act on voltage sensors rather than blocking the pore. PMID:20869590

  6. Regulation of lysosomal ion homeostasis by channels and transporters.

    PubMed

    Xiong, Jian; Zhu, Michael X

    2016-08-01

    Lysosomes are the major organelles that carry out degradation functions. They integrate and digest materials compartmentalized by endocytosis, phagocytosis or autophagy. In addition to more than 60 hydrolases residing in the lysosomes, there are also ion channels and transporters that mediate the flux or transport of H(+), Ca(2+), Na(+), K(+), and Cl(-) across the lysosomal membranes. Defects in ionic exchange can lead to abnormal lysosome morphology, defective vesicle trafficking, impaired autophagy, and diseases such as neurodegeneration and lysosomal storage disorders. The latter are characterized by incomplete lysosomal digestion and accumulation of toxic materials inside enlarged intracellular vacuoles. In addition to degradation, recent studies have revealed the roles of lysosomes in metabolic pathways through kinases such as mechanistic target of rapamycin (mTOR) and transcriptional regulation through calcium signaling molecules such as transcription factor EB (TFEB) and calcineurin. Owing to the development of new approaches including genetically encoded fluorescence probes and whole endolysosomal patch clamp recording techniques, studies on lysosomal ion channels have made remarkable progress in recent years. In this review, we will focus on the current knowledge of lysosome-resident ion channels and transporters, discuss their roles in maintaining lysosomal function, and evaluate how their dysfunction can result in disease. PMID:27430889

  7. Peptidomimetic Star Polymers for Targeting Biological Ion Channels.

    PubMed

    Chen, Rong; Lu, Derong; Xie, Zili; Feng, Jing; Jia, Zhongfan; Ho, Junming; Coote, Michelle L; Wu, Yingliang; Monteiro, Michael J; Chung, Shin-Ho

    2016-01-01

    Four end-functionalized star polymers that could attenuate the flow of ionic currents across biological ion channels were first de novo designed computationally, then synthesized and tested experimentally on mammalian K+ channels. The 4-arm ethylene glycol conjugate star polymers with lysine or a tripeptide attached to the end of each arm were specifically designed to mimic the action of scorpion toxins on K+ channels. Molecular dynamics simulations showed that the lysine side chain of the polymers physically occludes the pore of Kv1.3, a target for immuno-suppression therapy. Two of the compounds tested were potent inhibitors of Kv1.3. The dissociation constants of these two compounds were computed to be 0.1 μM and 0.7 μM, respectively, within 3-fold to the values derived from subsequent experiments. These results demonstrate the power of computational methods in molecular design and the potential of star polymers as a new infinitely modifiable platform for ion channel drug discovery. PMID:27007701

  8. The Concise Guide to Pharmacology 2013/14: Ion Channels

    PubMed Central

    Alexander, Stephen PH; Benson, Helen E; Faccenda, Elena; Pawson, Adam J; Sharman, Joanna L; Catterall, William A; Spedding, Michael; Peters, John A; Harmar, Anthony J

    2013-01-01

    The Concise Guide to PHARMACOLOGY 2013/14 provides concise overviews of the key properties of over 2000 human drug targets with their pharmacology, plus links to an open access knowledgebase of drug targets and their ligands (www.guidetopharmacology.org), which provides more detailed views of target and ligand properties. The full contents can be found at http://onlinelibrary.wiley.com/doi/10.1111/bph.12444/full. Ion channels are one of the seven major pharmacological targets into which the Guide is divided, with the others being G protein-coupled receptors, ligand-gated ion channels, catalytic receptors, nuclear hormone receptors, transporters and enzymes. These are presented with nomenclature guidance and summary information on the best available pharmacological tools, alongside key references and suggestions for further reading. A new landscape format has easy to use tables comparing related targets. It is a condensed version of material contemporary to late 2013, which is presented in greater detail and constantly updated on the website www.guidetopharmacology.org, superseding data presented in previous Guides to Receptors and Channels. It is produced in conjunction with NC-IUPHAR and provides the official IUPHAR classification and nomenclature for human drug targets, where appropriate. It consolidates information previously curated and displayed separately in IUPHAR-DB and the Guide to Receptors and Channels, providing a permanent, citable, point-in-time record that will survive database updates. PMID:24528239

  9. Peptidomimetic Star Polymers for Targeting Biological Ion Channels

    PubMed Central

    Chen, Rong; Lu, Derong; Xie, Zili; Feng, Jing; Jia, Zhongfan; Ho, Junming; Coote, Michelle L.; Wu, Yingliang; Monteiro, Michael J.; Chung, Shin-Ho

    2016-01-01

    Four end-functionalized star polymers that could attenuate the flow of ionic currents across biological ion channels were first de novo designed computationally, then synthesized and tested experimentally on mammalian K+ channels. The 4-arm ethylene glycol conjugate star polymers with lysine or a tripeptide attached to the end of each arm were specifically designed to mimic the action of scorpion toxins on K+ channels. Molecular dynamics simulations showed that the lysine side chain of the polymers physically occludes the pore of Kv1.3, a target for immuno-suppression therapy. Two of the compounds tested were potent inhibitors of Kv1.3. The dissociation constants of these two compounds were computed to be 0.1 μM and 0.7 μM, respectively, within 3-fold to the values derived from subsequent experiments. These results demonstrate the power of computational methods in molecular design and the potential of star polymers as a new infinitely modifiable platform for ion channel drug discovery. PMID:27007701

  10. International Union of Basic and Clinical Pharmacology. LXXVI. Current Progress in the Mammalian TRP Ion Channel Family

    PubMed Central

    Wu, Long-Jun; Sweet, Tara-Beth

    2010-01-01

    Transient receptor potential (TRP) channels are a large family of ion channel proteins, surpassed in number in mammals only by voltage-gated potassium channels. TRP channels are activated and regulated through strikingly diverse mechanisms, making them suitable candidates for cellular sensors. They respond to environmental stimuli such as temperature, pH, osmolarity, pheromones, taste, and plant compounds, and intracellular stimuli such as Ca2+ and phosphatidylinositol signal transduction pathways. However, it is still largely unknown how TRP channels are activated in vivo. Despite the uncertainties, emerging evidence using TRP channel knockout mice indicates that these channels have broad function in physiology. Here we review the recent progress on the physiology, pharmacology and pathophysiological function of mammalian TRP channels. PMID:20716668

  11. Active channel for Fanno Creek, Oregon

    USGS Publications Warehouse

    Sobieszczyk, Steven

    2011-01-01

    Fanno Creek is a tributary to the Tualatin River and flows though parts of the southwest Portland metropolitan area. The stream is heavily influenced by urban runoff and shows characteristic flashy streamflow and poor water quality commonly associated with urban streams. This data set represents the active, wetted channel as derived from light detection and ranging (LiDAR) data and aerial photographic imagery. The wetted channel boundary is equivalent to the extent of water observed during a 2-yr high flow event.

  12. Hydrostatic and osmotic pressure activated channel in plant vacuole

    PubMed Central

    Alexandre, Joel; Lassalles, Jean-Paul

    1991-01-01

    The vacuolar membrane of red beet vacuoles contains a channel which was not gated by voltage or Ca2+ ions. Its unit conductance was 20 pS in 200 mM symmetrical KCl solutions. It was stretch activated: the conductance remained constant but the probability of opening was increased by suction or pressure applied to a membrane patch. A 1.5-kNm-2 suction applied to isolated patches or a 0.08-kNm-2 pressure applied to a 45-μm diameter vacuole induced an e-fold change in the mean current. A 75% inhibition of the channel current was obtained with 10 μM Gd3+ on the cytoplasmic side. The channel was more permeable for K+ than for Cl- (PK/PCl ∼ 3). A possible clustering for this channel was suggested by the recordings of the patch current. The channel properties were not significantly affected by a change in sorbitol osmolality in the solutions under isoosmotic conditions, between 0.6 and 1 mol/kg sorbitol. However, the channel was very sensitive to an osmotic gradient. A 0.2-mol/kg sorbitol gradient induced a two-fold increase in unit conductance and a thirty-fold increase in the mean patch current of the channel. A current was measured, when the osmotic gradient was the only driving force applied to the vacuolar membrane. The hydrostatic and osmotic pressure (HOP) activated channel described in this paper could be gated in vivo condition by a change in osmolality, without the need of a change in the turgor pressure in the cell. The HOP channel represents a possible example of an osmoreceptor for plant cells. PMID:19431814

  13. Cyclic nucleotide-activated channels in carp olfactory receptor cells.

    PubMed

    Kolesnikov, S S; Kosolapov, A V

    1993-07-25

    When applied from the cytoplasmic side, cyclic 3',5'-adenosine and guanosine monophosphates reversibly increased the ion permeability of inside-out patches of carp olfactory neuron plasma membrane. The cAMP (cGMP)-induced permeability via cAMP (cGMP) concentration was fitted by Hill's equation with the exponents of 1.07 +/- 0.15 (1.12 +/- 0.05) and EC50 = 1.3 +/- 0.6 microM (0.9 +/- 0.3 microM). Substitution of NaCl in the bathing solution by chlorides of other alkali metals resulted in a slight shift of reversal potential of the cyclic nucleotide-dependent (CN) current, which indicates a weak selectivity of the channels. Permeability coefficients calculated by Goldman-Hodgkin-Katz's equation corresponded to the following relation: PNa/PK/PLi/PRb/PCs = 1:0.98:0.94:0.70:0.61. Ca2+ and Mg2+ in physiological concentrations blocked the channels activated by cyclic nucleotides (CN-channels). In the absence of divalent cations the conductance of single CN-channels was equal to 51 +/- 9 pS in 100 mM NaCl solution. Channel density did not exceed 1 micron-2. The maximal open state probability of the channel (Po) tended towards 1.0 at a high concentration of cAMP or cGMP. Dichlorobenzamil decreased Po without changing the single CN-channel' conductance. CN-channels exhibited burst activity. Mean open and closed times as well as the burst duration depended on agonist concentration. A kinetic model with four states (an inactivated, a closed and two open ones) is suggested to explain the regularities of CN-channel gating and dose-response relations. PMID:8334139

  14. An external sodium ion binding site controls allosteric gating in TRPV1 channels.

    PubMed

    Jara-Oseguera, Andres; Bae, Chanhyung; Swartz, Kenton J

    2016-01-01

    TRPV1 channels in sensory neurons are integrators of painful stimuli and heat, yet how they integrate diverse stimuli and sense temperature remains elusive. Here, we show that external sodium ions stabilize the TRPV1 channel in a closed state, such that removing the external ion leads to channel activation. In studying the underlying mechanism, we find that the temperature sensors in TRPV1 activate in two steps to favor opening, and that the binding of sodium to an extracellular site exerts allosteric control over temperature-sensor activation and opening of the pore. The binding of a tarantula toxin to the external pore also exerts control over temperature-sensor activation, whereas binding of vanilloids influences temperature-sensitivity by largely affecting the open/closed equilibrium. Our results reveal a fundamental role of the external pore in the allosteric control of TRPV1 channel gating and provide essential constraints for understanding how these channels can be tuned by diverse stimuli. PMID:26882503

  15. Modulation of acid-sensing ion channels: molecular mechanisms and therapeutic potential

    PubMed Central

    Chu, Xiang-Ping; Papasian, Christopher J; Wang, John Q; Xiong, Zhi-Gang

    2011-01-01

    Increases in extracellular proton concentrations, which takes place in physiological conditions such as synaptic signaling and pathological conditions such as tissue inflammation, ischemic stroke, traumatic brain injury, and epileptic seizure, activates a unique family of membrane ion channels; the acid-sensing ion channels (ASICs). All ASICs belong to amiloride-sensitive degenerin/epithelial Na+ channel superfamily. Four genes encoded at seven sub-units have been identified. ASICs are expressed primarily in neurons and have been shown to play critical roles in synaptic plasticity, learning/memory, fear conditioning, sensory transduction, pain perception, ischemic brain injury, seizure, and other neurological as well as psychological disorders. Although protons are the primary activator for ASICs, the properties and/or level of expression of these channels are modulated dramatically by neuropeptides, di-and polyvalent cations, inflammatory mediators, associated proteins, and protein phosphorylations, etc. Modulation of ASICs can result in profound changes in the activities and functions of these channels in both physiological and pathological processes. In this article, we provide an up to date review on the modulations of ASICs by exogenous agents and endogenous signaling molecules. A better understanding of how ASICs can be modulated should help define new strategies to counteract the deleterious effects of dysregulated ASIC activity. PMID:22162785

  16. An external sodium ion binding site controls allosteric gating in TRPV1 channels

    PubMed Central

    Jara-Oseguera, Andres; Bae, Chanhyung; Swartz, Kenton J

    2016-01-01

    TRPV1 channels in sensory neurons are integrators of painful stimuli and heat, yet how they integrate diverse stimuli and sense temperature remains elusive. Here, we show that external sodium ions stabilize the TRPV1 channel in a closed state, such that removing the external ion leads to channel activation. In studying the underlying mechanism, we find that the temperature sensors in TRPV1 activate in two steps to favor opening, and that the binding of sodium to an extracellular site exerts allosteric control over temperature-sensor activation and opening of the pore. The binding of a tarantula toxin to the external pore also exerts control over temperature-sensor activation, whereas binding of vanilloids influences temperature-sensitivity by largely affecting the open/closed equilibrium. Our results reveal a fundamental role of the external pore in the allosteric control of TRPV1 channel gating and provide essential constraints for understanding how these channels can be tuned by diverse stimuli. DOI: http://dx.doi.org/10.7554/eLife.13356.001 PMID:26882503

  17. The Effect of Hydrophobic Monoamines on Acid-Sensing Ion Channels ASIC1B

    PubMed Central

    Nagaeva, E. I.; Potapieva, N. N.; Tikhonov, D. B.

    2015-01-01

    Acid-sensing ion channels (ASICs) are widely distributed in both the central and peripheral nervous systems of vertebrates. The pharmacology of these receptors remains poorly investigated, while the search for new ASIC modulators is very important. Recently, we found that some monoamines, which are blockers of NMDA receptors, inhibit and/or potentiate acid-sensing ion channels, depending on the subunit composition of the channels. The effect of 9-aminoacridine, IEM-1921, IEM-2117, and memantine both on native receptors and on recombinant ASIC1a, ASIC2a, and ASIC3 homomers was studied. In the present study, we have investigated the effect of these four compounds on homomeric ASIC1b channels. Experiments were performed on recombinant receptors expressed in CHO cells using the whole-cell patch clamp technique. Only two compounds, 9-aminoacridine and memantine, inhibited ASIC1b channels. IEM-1921 and IEM-2117 were inactive even at a 1000 μM concentration. In most aspects, the effect of the compounds on ASIC1b was similar to their effect on ASIC1a. The distinguishing feature of homomeric ASIC1b channels is a steep activation-dependence, indicating cooperative activation by protons. In our experiments, the curve of the concentration dependence of ASIC1b inhibition by 9-aminoacridine also had a slope (Hill coefficient) of 3.8, unlike ASIC1a homomers, for which the Hill coefficient was close to 1. This finding indicates that the inhibitory effect of 9-aminoacridine is associated with changes in the activation properties of acid-sensing ion channels. PMID:26085950

  18. Progress in Development of Improved Ion-Channel Biosensors

    NASA Technical Reports Server (NTRS)

    Nadeau, Jay L.; White, Victor E.; Maurer, Joshua A.; Dougherty, Dennis A.

    2008-01-01

    Further improvements have recently been made in the development of the devices described in Improved Ion-Channel Biosensors (NPO-30710), NASA Tech Briefs, Vol. 28, No. 10 (October 2004), page 30. As discussed in more detail in that article, these sensors offer advantages of greater stability, greater lifetime, and individual electrical addressability, relative to prior ion-channel biosensors. In order to give meaning to a brief description of the recent improvements, it is necessary to recapitulate a substantial portion of the text of the cited previous article. The figure depicts one sensor that incorporates the recent improvements, and can be helpful in understanding the recapitulated text, which follows: These sensors are microfabricated from silicon and other materials compatible with silicon. Typically, the sensors are fabricated in arrays in silicon wafers on glass plates. Each sensor in the array can be individually electrically addressed, without interference with its neighbors. Each sensor includes a well covered by a thin layer of silicon nitride, in which is made a pinhole for the formation of a lipid bilayer membrane. In one stage of fabrication, the lower half of the well is filled with agarose, which is allowed to harden. Then the upper half of the well is filled with a liquid electrolyte (which thereafter remains liquid) and a lipid bilayer is painted over the pinhole. The liquid contains a protein that forms an ion channel on top of the hardened agarose. The combination of enclosure in the well and support by the hardened agarose provides the stability needed to keep the membrane functional for times as long as days or even weeks. An electrode above the well, another electrode below the well, and all the materials between the electrodes together constitute a capacitor. What is measured is the capacitive transient current in response to an applied voltage pulse. One notable feature of this sensor, in comparison with prior such sensors, is a

  19. A Theoretical Model for Calculating Voltage Sensitivity of Ion Channels and the Application on Kv1.2 Potassium Channel

    PubMed Central

    Yang, Huaiyu; Gao, Zhaobing; Li, Ping; Yu, Kunqian; Yu, Ye; Xu, Tian-Le; Li, Min; Jiang, Hualiang

    2012-01-01

    Voltage sensing confers conversion of a change in membrane potential to signaling activities underlying the physiological processes. For an ion channel, voltage sensitivity is usually experimentally measured by fitting electrophysiological data to Boltzmann distributions. In our study, a two-state model of the ion channel and equilibrium statistical mechanics principle were used to test the hypothesis of empirically calculating the overall voltage sensitivity of an ion channel on the basis of its closed and open conformations, and determine the contribution of individual residues to the voltage sensing. We examined the theoretical paradigm by performing experimental measurements with Kv1.2 channel and a series of mutants. The correlation between the calculated values and the experimental values is at respective level, R2 = 0.73. Our report therefore provides in silico prediction of key conformations and has identified additional residues critical for voltage sensing. PMID:22768937

  20. Allosteric regulation of pentameric ligand-gated ion channels

    PubMed Central

    Taly, Antoine; Hénin, Jérôme; Changeux, Jean-Pierre; Cecchini, Marco

    2014-01-01

    Pentameric ligand-gated ion channels (pLGICs) play a central role in intercellular communications in the nervous system by converting the binding of a chemical messenger—a neurotransmitter—into an ion flux through the postsynaptic membrane. They are oligomeric assemblies that provide prototypical examples of allosterically regulated integral membrane proteins. Here, we present an overview of the most recent advances on the signal transduction mechanism based on the X-ray structures of both prokaryotic and invertebrate eukaryotic pLGICs and on atomistic Molecular Dynamics simulations. The present results suggest that ion gating involves a large structural reorganization of the molecule mediated by two distinct quaternary transitions, a global twisting and the blooming of the extracellular domain, which can be modulated by ligand binding at the topographically distinct orthosteric and allosteric sites. The emerging model of gating is consistent with a wealth of functional studies and will boost the development of novel pharmacological strategies. PMID:25478624

  1. Point Mutations in the Transmembrane Region of the Clic1 Ion Channel Selectively Modify Its Biophysical Properties

    PubMed Central

    Averaimo, Stefania; Abeti, Rosella; Savalli, Nicoletta; Brown, Louise J.; Curmi, Paul M. G.; Breit, Samuel N.; Mazzanti, Michele

    2013-01-01

    Chloride intracellular Channel 1 (CLIC1) is a metamorphic protein that changes from a soluble cytoplasmic protein into a transmembrane protein. Once inserted into membranes, CLIC1 multimerises and is able to form chloride selective ion channels. Whilst CLIC1 behaves as an ion channel both in cells and in artificial lipid bilayers, its structure in the soluble form has led to some uncertainty as to whether it really is an ion channel protein. CLIC1 has a single putative transmembrane region that contains only two charged residues: arginine 29 (Arg29) and lysine 37 (Lys37). As charged residues are likely to have a key role in ion channel function, we hypothesized that mutating them to neutral alanine to generate K37A and R29A CLIC1 would alter the electrophysiological characteristics of CLIC1. By using three different electrophysiological approaches: i) single channel Tip-Dip in artificial bilayers using soluble recombinant CLIC1, ii) cell-attached and iii) whole-cell patch clamp recordings in transiently transfected HEK cells, we determined that the K37A mutation altered the single-channel conductance while the R29A mutation affected the single-channel open probability in response to variation in membrane potential. Our results show that mutation of the two charged amino acids (K37 and R29) in the putative transmembrane region of CLIC1 alters the biophysical properties of the ion channel in both artificial bilayers and cells. Hence these charged residues are directly involved in regulating its ion channel activity. This strongly suggests that, despite its unusual structure, CLIC1 itself is able to form a chloride ion channel. PMID:24058583

  2. Regulation of Intestinal Glucose Absorption by Ion Channels and Transporters

    PubMed Central

    Chen, Lihong; Tuo, Biguang; Dong, Hui

    2016-01-01

    The absorption of glucose is electrogenic in the small intestinal epithelium. The major route for the transport of dietary glucose from intestinal lumen into enterocytes is the Na+/glucose cotransporter (SGLT1), although glucose transporter type 2 (GLUT2) may also play a role. The membrane potential of small intestinal epithelial cells (IEC) is important to regulate the activity of SGLT1. The maintenance of membrane potential mainly depends on the activities of cation channels and transporters. While the importance of SGLT1 in glucose absorption has been systemically studied in detail, little is currently known about the regulation of SGLT1 activity by cation channels and transporters. A growing line of evidence suggests that cytosolic calcium ([Ca2+]cyt) can regulate the absorption of glucose by adjusting GLUT2 and SGLT1. Moreover, the absorption of glucose and homeostasis of Ca2+ in IEC are regulated by cation channels and transporters, such as Ca2+ channels, K+ channels, Na+/Ca2+ exchangers, and Na+/H+ exchangers. In this review, we consider the involvement of these cation channels and transporters in the regulation of glucose uptake in the small intestine. Modulation of them may be a potential strategy for the management of obesity and diabetes. PMID:26784222

  3. Mn ions pass through calcium channels. A possible explanation

    PubMed Central

    1983-01-01

    The divalent transition-metal cations Fe, Co, and Ni were used to test the hypothesis that Mn ions pass through calcium channels because Mn ions have a relatively low energy of hydration. The test ions were applied to the bath and comparisons were made of their effects on Ca or Mn spikes elicited from myoepithelial cells of the proventriculus of the polychaete worm Syllis spongiphila. Control experiments showed that (a) results obtained using deoxygenated solutions (required to stabilize Fe2+ ions) could be compared with those using solutions containing oxygen, and (b) the test cations did not measurably affect the electrical coupling between cells. Ca spikes were reversibly abolished by the test cations in the order of effectiveness: Fe (16.1 mM +/- 1.0, SE; n = 15) = Co (14.6 mM +/- 0.8; n = 27) less than Ni (8.3 mM +/- 0.7; n = 16). The test cations diminished Mn spikes by decreasing maximum rates of rise (Fe = Co less than Ni) and overshoot amplitudes (Fe less than Co less than Ni). The test cations also increased the current intensity required for Ca (Fe = Co less than Ni) or Mn spike initiation (Fe less than Co less than Ni). Since the energies of hydration of Fe, Co, and Ni increase stepwise from that of Mn, and the effectiveness of these ions in diminishing Ca and Mn spikes increased in the order Fe less than or equal to Co less than Ni, these data support the hypothesis that Mn ions pass through Ca channels because they shed waters of hydration relatively easily. An additional observation was that, at below-blocking concentrations, the test cations caused decreased duration of Mn spikes and increased duration of Ca spikes. PMID:6308126

  4. Chemical activation of the mechanotransduction channel Piezo1

    PubMed Central

    Syeda, Ruhma; Xu, Jie; Dubin, Adrienne E; Coste, Bertrand; Mathur, Jayanti; Huynh, Truc; Matzen, Jason; Lao, Jianmin; Tully, David C; Engels, Ingo H; Petrassi, H Michael; Schumacher, Andrew M; Montal, Mauricio; Bandell, Michael; Patapoutian, Ardem

    2015-01-01

    Piezo ion channels are activated by various types of mechanical stimuli and function as biological pressure sensors in both vertebrates and invertebrates. To date, mechanical stimuli are the only means to activate Piezo ion channels and whether other modes of activation exist is not known. In this study, we screened ∼3.25 million compounds using a cell-based fluorescence assay and identified a synthetic small molecule we termed Yoda1 that acts as an agonist for both human and mouse Piezo1. Functional studies in cells revealed that Yoda1 affects the sensitivity and the inactivation kinetics of mechanically induced responses. Characterization of Yoda1 in artificial droplet lipid bilayers showed that Yoda1 activates purified Piezo1 channels in the absence of other cellular components. Our studies demonstrate that Piezo1 is amenable to chemical activation and raise the possibility that endogenous Piezo1 agonists might exist. Yoda1 will serve as a key tool compound to study Piezo1 regulation and function. DOI: http://dx.doi.org/10.7554/eLife.07369.001 PMID:26001275

  5. Autocrine-Based Selection of Drugs That Target Ion Channels from Combinatorial Venom Peptide Libraries.

    PubMed

    Zhang, Hongkai; Du, Mingjuan; Xie, Jia; Liu, Xiao; Sun, Jingying; Wang, Wei; Xin, Xiu; Possani, Lourival D; Yea, Kyungmoo; Lerner, Richard A

    2016-08-01

    Animal venoms represent a rich source of pharmacologically active peptides that interact with ion channels. However, a challenge to discovering drugs remains because of the slow pace at which venom peptides are discovered and refined. An efficient autocrine-based high-throughput selection system was developed to discover and refine venom peptides that target ion channels. The utility of this system was demonstrated by the discovery of novel Kv1.3 channel blockers from a natural venom peptide library that was formatted for autocrine-based selection. We also engineered a Kv1.3 blocker peptide (ShK) derived from sea anemone to generate a subtype-selective Kv1.3 blocker with a long half-life in vivo. PMID:27197631

  6. A family of fluoride-specific ion channels with dual-topology architecture

    PubMed Central

    Stockbridge, Randy B; Robertson, Janice L; Kolmakova-Partensky, Ludmila; Miller, Christopher

    2013-01-01

    Fluoride ion, ubiquitous in soil, water, and marine environments, is a chronic threat to microorganisms. Many prokaryotes, archea, unicellular eukaryotes, and plants use a recently discovered family of F− exporter proteins to lower cytoplasmic F− levels to counteract the anion’s toxicity. We show here that these ‘Fluc’ proteins, purified and reconstituted in liposomes and planar phospholipid bilayers, form constitutively open anion channels with extreme selectivity for F− over Cl−. The active channel is a dimer of identical or homologous subunits arranged in antiparallel transmembrane orientation. This dual-topology assembly has not previously been seen in ion channels but is known in multidrug transporters of the SMR family, and is suggestive of an evolutionary antecedent of the inverted repeats found within the subunits of many membrane transport proteins. DOI: http://dx.doi.org/10.7554/eLife.01084.001 PMID:23991286

  7. The role of cystic fibrosis transmembrane conductance regulator phenylalanine 508 side chain in ion channel gating.

    PubMed

    Cui, Liying; Aleksandrov, Luba; Hou, Yue-Xian; Gentzsch, Martina; Chen, Jey-Hsin; Riordan, John R; Aleksandrov, Andrei A

    2006-04-15

    Cystic fibrosis transmembrane conductance regulator (CFTR) is an ion channel employing the ABC transporter structural motif. Deletion of a single residue (Phe508) in the first nucleotide-binding domain (NBD1), which occurs in most patients with cystic fibrosis, impairs both maturation and function of the protein. However, substitution of the Phe508 with small uncharged amino acids, including cysteine, is permissive for maturation. To explore the possible role of the phenylalanine aromatic side chain in channel gating we introduced a cysteine at this position in cysless CFTR, enabling its selective chemical modification by sulfhydryl reagents. Both cysless and wild-type CFTR ion channels have identical mean open times when activated by different nucleotide ligands. Moreover, both channels could be locked in an open state by introducing an ATPase inhibiting mutation (E1371S). However, the introduction of a single cysteine (F508C) prevented the cysless E1371S channel from maintaining the permanently open state, allowing closing to occur. Chemical modification of cysless E1371S/F508C by sulfhydryl reagents was used to probe the role of the side chain in ion channel function. Specifically, benzyl-methanethiosulphonate modification of this variant restored the gating behaviour to that of cysless E1371S containing the wild-type phenylalanine at position 508. This provides the first direct evidence that a specific interaction of the Phe508 aromatic side chain plays a role in determining the residency time in the closed state. Thus, despite the fact that this aromatic side chain is not essential for CFTR folding, it is important in the ion channel function. PMID:16484308

  8. The role of cystic fibrosis transmembrane conductance regulator phenylalanine 508 side chain in ion channel gating

    PubMed Central

    Cui, Liying; Aleksandrov, Luba; Hou, Yue-Xian; Gentzsch, Martina; Chen, Jey-Hsin; Riordan, John R; Aleksandrov, Andrei A

    2006-01-01

    Cystic fibrosis transmembrane conductance regulator (CFTR) is an ion channel employing the ABC transporter structural motif. Deletion of a single residue (Phe508) in the first nucleotide-binding domain (NBD1), which occurs in most patients with cystic fibrosis, impairs both maturation and function of the protein. However, substitution of the Phe508 with small uncharged amino acids, including cysteine, is permissive for maturation. To explore the possible role of the phenylalanine aromatic side chain in channel gating we introduced a cysteine at this position in cysless CFTR, enabling its selective chemical modification by sulfhydryl reagents. Both cysless and wild-type CFTR ion channels have identical mean open times when activated by different nucleotide ligands. Moreover, both channels could be locked in an open state by introducing an ATPase inhibiting mutation (E1371S). However, the introduction of a single cysteine (F508C) prevented the cysless E1371S channel from maintaining the permanently open state, allowing closing to occur. Chemical modification of cysless E1371S/F508C by sulfhydryl reagents was used to probe the role of the side chain in ion channel function. Specifically, benzyl-methanethiosulphonate modification of this variant restored the gating behaviour to that of cysless E1371S containing the wild-type phenylalanine at position 508. This provides the first direct evidence that a specific interaction of the Phe508 aromatic side chain plays a role in determining the residency time in the closed state. Thus, despite the fact that this aromatic side chain is not essential for CFTR folding, it is important in the ion channel function. PMID:16484308

  9. [Ion channels and water channels--a prerequisite for living cells and electric signals in the brain].

    PubMed

    Storm, Johan F

    2003-12-01

    Water channels and ion channels are membrane proteins that transport water and ions into and out of cells with high selectivity and efficiency. Peter Agre and Roderick MacKinnon were awarded the Nobel Prize in chemistry 2003 for their discoveries of the structure of water channels and ion channel proteins, thus explaining basal mechanisms that are fundamental to all forms of life and in particular to the electrical signalling in the brain. These scientific achievements answer questions that biophysicists and physiologists have discussed since the 19th century. PMID:14713970

  10. The role of ion channels in the hypoxia-induced aggressiveness of glioblastoma

    PubMed Central

    Sforna, Luigi; Cenciarini, Marta; Belia, Silvia; D’Adamo, Maria Cristina; Pessia, Mauro; Franciolini, Fabio; Catacuzzeno, Luigi

    2015-01-01

    The malignancy of glioblastoma multiform (GBM), the most common and aggressive form of human brain tumors, strongly correlates with the presence of hypoxic areas, but the mechanisms controlling the hypoxia-induced aggressiveness are still unclear. GBM cells express a number of ion channels whose activity supports cell volume changes and increases in the cytosolic Ca2+ concentration, ultimately leading to cell proliferation, migration or death. In several cell types it has previously been shown that low oxygen levels regulate the expression and activity of these channels, and more recent data indicate that this also occurs in GBM cells. Based on these findings, it may be hypothesized that the modulation of ion channel activity or expression by the hypoxic environment may participate in the acquisition of the aggressive phenotype observed in GBM cells residing in a hypoxic environment. If this hypothesis will be confirmed, the use of available ion channels modulators may be considered for implementing novel therapeutic strategies against these tumors. PMID:25642170

  11. Structural plasticity and dynamic selectivity of acid-sensing ion channel-spider toxin complexes

    SciTech Connect

    Baconguis, Isabelle; Gouaux, Eric

    2012-07-29

    Acid-sensing ion channels (ASICs) are voltage-independent, amiloride-sensitive channels involved in diverse physiological processes ranging from nociception to taste. Despite the importance of ASICs in physiology, we know little about the mechanism of channel activation. Here we show that psalmotoxin activates non-selective and Na+-selective currents in chicken ASIC1a at pH7.25 and 5.5, respectively. Crystal structures of ASIC1a–psalmotoxin complexes map the toxin binding site to the extracellular domain and show how toxin binding triggers an expansion of the extracellular vestibule and stabilization of the open channel pore. At pH7.25 the pore is approximately 10Å in diameter, whereas at pH5.5 the pore is largely hydrophobic and elliptical in cross-section with dimensions of approximately 5 by 7Å, consistent with a barrier mechanism for ion selectivity. These studies define mechanisms for activation of ASICs, illuminate the basis for dynamic ion selectivity and provide the blueprints for new therapeutic agents.

  12. Calcium-activated potassium channels and endothelial dysfunction: therapeutic options?

    PubMed Central

    Félétou, Michel

    2009-01-01

    The three subtypes of calcium-activated potassium channels (KCa) of large, intermediate and small conductance (BKCa, IKCa and SKCa) are present in the vascular wall. In healthy arteries, BKCa channels are preferentially expressed in vascular smooth muscle cells, while IKCa and SKCa are preferentially located in endothelial cells. The activation of endothelial IKCa and SKCa contributes to nitric oxide (NO) generation and is required to elicit endothelium-dependent hyperpolarizations. In the latter responses, the hyperpolarization of the smooth muscle cells is evoked either via electrical coupling through myo-endothelial gap junctions or by potassium ions, which by accumulating in the intercellular space activate the inwardly rectifying potassium channel Kir2.1 and/or the Na+/K+-ATPase. Additionally, endothelium-derived factors such as cytochrome P450-derived epoxyeicosatrienoic acids and under some circumstances NO, prostacyclin, lipoxygenase products and hydrogen peroxide (H2O2) hyperpolarize and relax the underlying smooth muscle cells by activating BKCa. In contrast, cytochrome P450-derived 20-hydroxyeicosatetraenoic acid and various endothelium-derived contracting factors inhibit BKCa. Aging and cardiovascular diseases are associated with endothelial dysfunctions that can involve a decrease in NO bioavailability, alterations of EDHF-mediated responses and/or enhanced production of endothelium-derived contracting factors. Because potassium channels are involved in these endothelium-dependent responses, activation of endothelial and/or smooth muscle KCa could prevent the occurrence of endothelial dysfunction. Therefore, direct activators of these potassium channels or compounds that regulate their activity or their expression may be of some therapeutic interest. Conversely, blockers of IKCa may prevent restenosis and that of BKCa channels sepsis-dependent hypotension. PMID:19187341

  13. Computer Simulation Studies of Ion Channels at High Temperatures

    NASA Astrophysics Data System (ADS)

    Song, Hyun Deok

    The gramicidin channel is the smallest known biological ion channel, and it exhibits cation selectivity. Recently, Dr. John Cuppoletti's group at the University of Cincinnati showed that the gramicidin channel can function at high temperatures (360 ˜ 380K) with significant currents. This finding may have significant implications for fuel cell technology. In this thesis, we have examined the gramicidin channel at 300K, 330K, and 360K by computer simulation. We have investigated how the temperature affects the current and differences in magnitude of free energy between the two gramicidin forms, the helical dimer (HD) and the double helix (DH). A slight decrease of the free energy barrier inside the gramicidin channel and increased diffusion at high temperatures result in an increase of current. An applied external field of 0.2V/nm along the membrane normal results in directly observable ion transport across the channels at high temperatures for both HD and DH forms. We found that higher temperatures also affect the probability distribution of hydrogen bonds, the bending angle, the distance between dimers, and the size of the pore radius for the helical dimer structure. These findings may be related to the gating of the gramicidin channel. Methanococcus jannaschii (MJ) is a methane-producing thermophile, which was discovered at a depth of 2600m in a Pacific Ocean vent in 1983. It has the ability to thrive at high temperatures and high pressures, which are unfavorable for most life forms. There have been some experiments to study its stability under extreme conditions, but still the origin of the stability of MJ is not exactly known. MJ0305 is the chloride channel protein from the thermophile MJ. After generating a structure of MJ0305 by homology modeling based on the Ecoli ClC templates, we examined the thermal stability, and the network stability from the change of network entropy calculated from the adjacency matrices of the protein. High temperatures increase the

  14. Ion conduction and conformational flexibility of a bacterial voltage-gated sodium channel.

    PubMed

    Boiteux, Céline; Vorobyov, Igor; Allen, Toby W

    2014-03-01

    Voltage-gated Na(+) channels play an essential role in electrical signaling in the nervous system and are key pharmacological targets for a range of disorders. The recent solution of X-ray structures for the bacterial channel NavAb has provided an opportunity to study functional mechanisms at the atomic level. This channel's selectivity filter exhibits an EEEE ring sequence, characteristic of mammalian Ca(2+), not Na(+), channels. This raises the fundamentally important question: just what makes a Na(+) channel conduct Na(+) ions? Here we explore ion permeation on multimicrosecond timescales using the purpose-built Anton supercomputer. We isolate the likely protonation states of the EEEE ring and observe a striking flexibility of the filter that demonstrates the necessity for extended simulations to study conduction in this channel. We construct free energy maps to reveal complex multi-ion conduction via knock-on and "pass-by" mechanisms, involving concerted ion and glutamate side chain movements. Simulations in mixed ionic solutions reveal relative energetics for Na(+), K(+), and Ca(2+) within the pore that are consistent with the modest selectivity seen experimentally. We have observed conformational changes in the pore domain leading to asymmetrical collapses of the activation gate, similar to proposed inactivated structures of NavAb, with helix bending involving conserved residues that are critical for slow inactivation. These structural changes are shown to regulate access to fenestrations suggested to be pathways for lipophilic drugs and provide deeper insight into the molecular mechanisms connecting drug activity and slow inactivation. PMID:24550503

  15. Nerve membrane ion channels as the target site of environmental toxicants

    SciTech Connect

    Narahashi, T.

    1987-04-01

    There are many environmentally important chemicals which exhibit potent effects on the nervous system. Since nerve excitation takes place in a fraction of a second, electrophysiological methods provide the authors with the most straightforward approach to the study of the mechanisms of action of environmental toxicants on the nervous system. Aquatic animals such as crayfish, lobster, squid, and marine snails represent extremely useful materials for such electrophysiological studies, because much of the authors knowledge of nerve excitation is derived from those animals. Nerve excitation takes place as a result of opening and closing of ion channels of the membrane. These functions are independent of metabolic energy, and can be measured most effectively by voltage clamp techniques as applied to the giant axons of the crayfish and the squid. Patch clamp techniques developed during the past 10 years have added a new dimension to the electrophysiological investigation. These techniques allow them to measure the activity of individual ion channels, thereby making it possible to analyze the interaction of toxic molecules directly with single ion channels. Examples are given summarizing electrophysiological studies of environmental neurotoxicants. The abdominal nerve cords and neuromuscular preparations isolated from the crayfish are convenient materials for bioassay of certain environmental toxicants such as pyrethroids, chlorinated hydrocarbons, and other insecticides. Only a small fraction of the flux through the sodium channel, less than 1%, must be modified by pyrethroids for the animal to develop symptoms of poisoning. Such a toxicological application from channel to animal is important is understanding the potent toxic effect.

  16. Na(+) -Activated K(+) Channels in Rat Supraoptic Neurones.

    PubMed

    Bansal, V; Fisher, T E

    2016-06-01

    The magnocellular neurosecretory cells (MNCs) of the hypothalamus secrete the neurohormones vasopressin and oxytocin. The systemic release of these hormones depends on the rate and pattern of MNC firing and it is therefore important to identify the ion channels that contribute to the electrical behaviour of MNCs. In the present study, we report evidence for the presence of Na(+) -activated K(+) (KN a ) channels in rat MNCs. KN a channels mediate outwardly rectifying K(+) currents activated by the increases in intracellular Na(+) that occur during electrical activity. Although the molecular identity of native KN a channels is unclear, their biophysical properties are consistent with those of expressed Slick (slo 2.1) and Slack (slo 2.2) proteins. Using immunocytochemistry and Western blot experiments, we found that both Slick and Slack proteins are expressed in rat MNCs. Using whole cell voltage clamp techniques on acutely isolated rat MNCs, we found that inhibiting Na(+) influx by the addition of the Na(+) channel blocker tetrodotoxin or the replacement of Na(+) in the external solution with Li(+) caused a significant decrease in sustained outward currents. Furthermore, the evoked outward current density was significantly higher in rat MNCs using patch pipettes containing 60 mm Na(+) than it was when patch pipettes containing 0 mm Na(+) were used. Our data show that functional KN a channels are expressed in rat MNCs. These channels could contribute to the activity-dependent afterhyperpolarisations that have been identified in the MNCs and thereby play a role in the regulation of their electrical behaviour. PMID:27091544

  17. Charging the Quantum Capacitance of Graphene with a Single Biological Ion Channel

    PubMed Central

    2015-01-01

    The interaction of cell and organelle membranes (lipid bilayers) with nanoelectronics can enable new technologies to sense and measure electrophysiology in qualitatively new ways. To date, a variety of sensing devices have been demonstrated to measure membrane currents through macroscopic numbers of ion channels. However, nanoelectronic based sensing of single ion channel currents has been a challenge. Here, we report graphene-based field-effect transistors combined with supported lipid bilayers as a platform for measuring, for the first time, individual ion channel activity. We show that the supported lipid bilayers uniformly coat the single layer graphene surface, acting as a biomimetic barrier that insulates (both electrically and chemically) the graphene from the electrolyte environment. Upon introduction of pore-forming membrane proteins such as alamethicin and gramicidin A, current pulses are observed through the lipid bilayers from the graphene to the electrolyte, which charge the quantum capacitance of the graphene. This approach combines nanotechnology with electrophysiology to demonstrate qualitatively new ways of measuring ion channel currents. PMID:24754625

  18. Novel Insights into Acid-Sensing Ion Channels: Implications for Degenerative Diseases

    PubMed Central

    Zhou, Ren-Peng; Wu, Xiao-Shan; Wang, Zhi-Sen; Xie, Ya-Ya; Ge, Jin-Fang; Chen, Fei-Hu

    2016-01-01

    Degenerative diseases often strike older adults and are characterized by progressive deterioration of cells, eventually leading to tissue and organ degeneration for which limited effective treatment options are currently available. Acid-sensing ion channels (ASICs), a family of extracellular H+-activated ligand-gated ion channels, play critical roles in physiological and pathological conditions. Aberrant activation of ASICs is reported to regulate cell apoptosis, differentiation and autophagy. Accumulating evidence has highlighted a dramatic increase and activation of ASICs in degenerative disorders, including multiple sclerosis, Parkinson’s disease, Huntington’s disease, intervertebral disc degeneration and arthritis. In this review, we have comprehensively discussed the critical roles of ASICs and their potential utility as therapeutic targets in degenerative diseases. PMID:27493834

  19. Phosphoinositide control of membrane protein function: a frontier led by studies on ion channels.

    PubMed

    Logothetis, Diomedes E; Petrou, Vasileios I; Zhang, Miao; Mahajan, Rahul; Meng, Xuan-Yu; Adney, Scott K; Cui, Meng; Baki, Lia

    2015-01-01

    Anionic phospholipids are critical constituents of the inner leaflet of the plasma membrane, ensuring appropriate membrane topology of transmembrane proteins. Additionally, in eukaryotes, the negatively charged phosphoinositides serve as key signals not only through their hydrolysis products but also through direct control of transmembrane protein function. Direct phosphoinositide control of the activity of ion channels and transporters has been the most convincing case of the critical importance of phospholipid-protein interactions in the functional control of membrane proteins. Furthermore, second messengers, such as [Ca(2+)]i, or posttranslational modifications, such as phosphorylation, can directly or allosterically fine-tune phospholipid-protein interactions and modulate activity. Recent advances in structure determination of membrane proteins have allowed investigators to obtain complexes of ion channels with phosphoinositides and to use computational and experimental approaches to probe the dynamic mechanisms by which lipid-protein interactions control active and inactive protein states. PMID:25293526

  20. Novel Insights into Acid-Sensing Ion Channels: Implications for Degenerative Diseases.

    PubMed

    Zhou, Ren-Peng; Wu, Xiao-Shan; Wang, Zhi-Sen; Xie, Ya-Ya; Ge, Jin-Fang; Chen, Fei-Hu

    2016-08-01

    Degenerative diseases often strike older adults and are characterized by progressive deterioration of cells, eventually leading to tissue and organ degeneration for which limited effective treatment options are currently available. Acid-sensing ion channels (ASICs), a family of extracellular H(+)-activated ligand-gated ion channels, play critical roles in physiological and pathological conditions. Aberrant activation of ASICs is reported to regulate cell apoptosis, differentiation and autophagy. Accumulating evidence has highlighted a dramatic increase and activation of ASICs in degenerative disorders, including multiple sclerosis, Parkinson's disease, Huntington's disease, intervertebral disc degeneration and arthritis. In this review, we have comprehensively discussed the critical roles of ASICs and their potential utility as therapeutic targets in degenerative diseases. PMID:27493834

  1. Developmental Profile of Ion Channel Specializations in the Avian Nucleus Magnocellularis

    PubMed Central

    Hong, Hui; Rollman, Lisia; Feinstein, Brooke; Sanchez, Jason Tait

    2016-01-01

    Ultrafast and temporally precise action potentials (APs) are biophysical specializations of auditory brainstem neurons; properties necessary for encoding sound localization and communication cues. Fundamental to these specializations are voltage dependent potassium (KV) and sodium (NaV) ion channels. Here, we characterized the functional development of these ion channels and quantified how they shape AP properties in the avian cochlear nucleus magnocellularis (NM). We report that late developing NM neurons (embryonic [E] days 19–21) generate fast APs that reliably phase lock to sinusoidal inputs at 75 Hz. In contrast, early developing neurons (activated potassium (K+HVA) channels were blocked, APs for all ages became significantly slower. This was most evident for early developing neurons where the ratio of K+HVA current accounted for ~85% of the total KV response. This ratio dropped to ~50% for late developing neurons, suggesting a developmental upregulation of low-voltage activated potassium (K+LVA) channels. Indeed, blockade of K+LVA eliminated remaining current and increased neural excitability for late developing neurons. We also report developmental changes in the amplitude, kinetics and voltage dependence of NaV currents. For early developing neurons, increase in NaV current amplitude was due to channel density while channel conductance dominated for late developing neurons. From E10 to E21, NaV channel currents became faster but differed in their voltage dependence; early developing neurons (channel inactivation voltages while late developing NM neurons (>E19) contained NaV channels that inactivate at more

  2. Crystal structures of a double-barrelled fluoride ion channel

    PubMed Central

    Stockbridge, Randy B.; Kolmakova-Partensky, Ludmila; Shane, Tania; Koide, Akiko; Koide, Shohei; Miller, Christopher; Newstead, Simon

    2016-01-01

    To contend with hazards posed by environmental fluoride, microorganisms export this anion through F--specific ion channels of the Fluc family1–4. Since the recent discovery of Fluc channels, numerous idiosyncratic features of these proteins have been unearthed, including extreme selectivity for F- over Cl- and dual-topology dimeric assembly5–6. To understand the chemical basis for F- permeation and how the antiparallel subunits convene to form a F--selective pore, we solved crystal structures of two bacterial Fluc homologues in complex with three different monobody inhibitors, with and without F- present, to a maximum resolution of 2.1 Å. The structures reveal a surprising “double-barrelled” channel architecture in which two F- ion pathways span the membrane and the dual-topology arrangement includes a centrally coordinated cation, most likely Na+. F- selectivity is proposed to arise from the very narrow pores and an unusual anion coordination that exploits the quadrupolar edges of conserved phenylalanine rings. PMID:26344196

  3. Ion Channels in the Eye: Involvement in Ocular Pathologies.

    PubMed

    Giblin, Jonathan P; Comes, Nuria; Strauss, Olaf; Gasull, Xavier

    2016-01-01

    The eye is the sensory organ of vision. There, the retina transforms photons into electrical signals that are sent to higher brain areas to produce visual sensations. In the light path to the retina, different types of cells and tissues are involved in maintaining the transparency of avascular structures like the cornea or lens, while others, like the retinal pigment epithelium, have a critical role in the maintenance of photoreceptor function by regenerating the visual pigment. Here, we have reviewed the roles of different ion channels expressed in ocular tissues (cornea, conjunctiva and neurons innervating the ocular surface, lens, retina, retinal pigment epithelium, and the inflow and outflow systems of the aqueous humor) that are involved in ocular disease pathophysiologies and those whose deletion or pharmacological modulation leads to specific diseases of the eye. These include pathologies such as retinitis pigmentosa, macular degeneration, achromatopsia, glaucoma, cataracts, dry eye, or keratoconjunctivitis among others. Several disease-associated ion channels are potential targets for pharmacological intervention or other therapeutic approaches, thus highlighting the importance of these channels in ocular physiology and pathophysiology. PMID:27038375

  4. Crystal structures of a double-barrelled fluoride ion channel.

    PubMed

    Stockbridge, Randy B; Kolmakova-Partensky, Ludmila; Shane, Tania; Koide, Akiko; Koide, Shohei; Miller, Christopher; Newstead, Simon

    2015-09-24

    To contend with hazards posed by environmental fluoride, microorganisms export this anion through F(-)-specific ion channels of the Fluc family. Since the recent discovery of Fluc channels, numerous idiosyncratic features of these proteins have been unearthed, including strong selectivity for F(-) over Cl(-) and dual-topology dimeric assembly. To understand the chemical basis for F(-) permeation and how the antiparallel subunits convene to form a F(-)-selective pore, here we solve the crystal structures of two bacterial Fluc homologues in complex with three different monobody inhibitors, with and without F(-) present, to a maximum resolution of 2.1 Å. The structures reveal a surprising 'double-barrelled' channel architecture in which two F(-) ion pathways span the membrane, and the dual-topology arrangement includes a centrally coordinated cation, most likely Na(+). F(-) selectivity is proposed to arise from the very narrow pores and an unusual anion coordination that exploits the quadrupolar edges of conserved phenylalanine rings. PMID:26344196

  5. The mechanosensory calcium-selective ion channel: key component of a plasmalemmal control centre?

    NASA Technical Reports Server (NTRS)

    Pickard, B. G.; Ding, J. P.

    1993-01-01

    Mechanosensory calcium-selective ion channels probably serve to detect not only mechanical stress but also electrical, thermal, and diverse chemical stimuli. Because all stimuli result in a common output, most notably a shift in second messenger calcium concentration, the channels are presumed to serve as signal integrators. Further, insofar as second messenger calcium in turn gives rise to mechanical, electrical, and diverse chemical changes, the channels are postulated to initiate regulatory feedbacks. It is proposed that the channels and the feedback loops play a wide range of roles in regulating normal plant function, as well as in mediating disturbance of normal function by environmental stressors and various pathogens. In developing evidence for the physiological performance of the channel, a model for a cluster of regulatory plasmalemmal proteins and cytoskeletal elements grouped around a set of wall-to-membrane and transmembrane linkers has proved useful. An illustration of how the model might operate is presented. It is founded on the demonstration that several xenobiotics interfere both with normal channel behaviour and with gravitropic reception. Accordingly, the first part of the illustration deals with how the channels and the control system within which they putatively operate might initiate gravitropism. Assuming that gravitropism is an asymmetric expression of growth, the activities of the channels and the plasmalemmal control system are extrapolated to account for regulation of both rate and allometry of cell expansion. Finally, it is discussed how light, hormones, redox agents and herbicides could in principle affect growth via the putative plasmalemmal control cluster or centre.

  6. A Numerical Approach to Ion Channel Modelling Using Whole-Cell Voltage-Clamp Recordings and a Genetic Algorithm

    PubMed Central

    Gurkiewicz, Meron; Korngreen, Alon

    2007-01-01

    The activity of trans-membrane proteins such as ion channels is the essence of neuronal transmission. The currently most accurate method for determining ion channel kinetic mechanisms is single-channel recording and analysis. Yet, the limitations and complexities in interpreting single-channel recordings discourage many physiologists from using them. Here we show that a genetic search algorithm in combination with a gradient descent algorithm can be used to fit whole-cell voltage-clamp data to kinetic models with a high degree of accuracy. Previously, ion channel stimulation traces were analyzed one at a time, the results of these analyses being combined to produce a picture of channel kinetics. Here the entire set of traces from all stimulation protocols are analysed simultaneously. The algorithm was initially tested on simulated current traces produced by several Hodgkin-Huxley–like and Markov chain models of voltage-gated potassium and sodium channels. Currents were also produced by simulating levels of noise expected from actual patch recordings. Finally, the algorithm was used for finding the kinetic parameters of several voltage-gated sodium and potassium channels models by matching its results to data recorded from layer 5 pyramidal neurons of the rat cortex in the nucleated outside-out patch configuration. The minimization scheme gives electrophysiologists a tool for reproducing and simulating voltage-gated ion channel kinetics at the cellular level. PMID:17784781

  7. Transient receptor potential ion channels in primary sensory neurons as targets for novel analgesics

    PubMed Central

    Sousa-Valente, J; Andreou, A P; Urban, L; Nagy, I

    2014-01-01

    The last decade has witnessed an explosion in novel findings relating to the molecules involved in mediating the sensation of pain in humans. Transient receptor potential (TRP) ion channels emerged as the greatest group of molecules involved in the transduction of various physical stimuli into neuronal signals in primary sensory neurons, as well as, in the development of pain. Here, we review the role of TRP ion channels in primary sensory neurons in the development of pain associated with peripheral pathologies and possible strategies to translate preclinical data into the development of effective new analgesics. Based on available evidence, we argue that nociception-related TRP channels on primary sensory neurons provide highly valuable targets for the development of novel analgesics and that, in order to reduce possible undesirable side effects, novel analgesics should prevent the translocation from the cytoplasm to the cell membrane and the sensitization of the channels rather than blocking the channel pore or binding sites for exogenous or endogenous activators. LINKED ARTICLES This article is part of a themed section on the pharmacology of TRP channels. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2014.171.issue-10 PMID:24283624

  8. Voltage-Gated Ion Channels in Cancer Cell Proliferation

    PubMed Central

    Rao, Vidhya R.; Perez-Neut, Mathew; Kaja, Simon; Gentile, Saverio

    2015-01-01

    Changes of the electrical charges across the surface cell membrane are absolutely necessary to maintain cellular homeostasis in physiological as well as in pathological conditions. The opening of ion channels alter the charge distribution across the surface membrane as they allow the diffusion of ions such as K+, Ca++, Cl−, Na+. Traditionally, voltage-gated ion channels (VGIC) are known to play fundamental roles in controlling rapid bioelectrical signaling including action potential and/or contraction. However, several investigations have revealed that these classes of proteins can also contribute significantly to cell mitotic biochemical signaling, cell cycle progression, as well as cell volume regulation. All these functions are critically important for cancer cell proliferation. Interestingly, a variety of distinct VGICs are expressed in different cancer cell types, including metastasis but not in the tissues from which these tumors were generated. Given the increasing evidence suggesting that VGIC play a major role in cancer cell biology, in this review we discuss the role of distinct VGIC in cancer cell proliferation and possible therapeutic potential of VIGC pharmacological manipulation. PMID:26010603

  9. Sea anemone peptide with uncommon β-hairpin structure inhibits acid-sensing ion channel 3 (ASIC3) and reveals analgesic activity.

    PubMed

    Osmakov, Dmitry I; Kozlov, Sergey A; Andreev, Yaroslav A; Koshelev, Sergey G; Sanamyan, Nadezhda P; Sanamyan, Karen E; Dyachenko, Igor A; Bondarenko, Dmitry A; Murashev, Arkadii N; Mineev, Konstantin S; Arseniev, Alexander S; Grishin, Eugene V

    2013-08-01

    Three novel peptides were isolated from the venom of the sea anemone Urticina grebelnyi. All of them are 29 amino acid peptides cross-linked by two disulfide bridges, with a primary structure similar to other sea anemone peptides belonging to structural group 9a. The structure of the gene encoding the shared precursor protein of the identified peptides was determined. One peptide, π-AnmTX Ugr 9a-1 (short name Ugr 9-1), produced a reversible inhibition effect on both the transient and the sustained current of human ASIC3 channels expressed in Xenopus laevis oocytes. It completely blocked the transient component (IC50 10 ± 0.6 μM) and partially (48 ± 2%) inhibited the amplitude of the sustained component (IC50 1.44 ± 0.19 μM). Using in vivo tests in mice, Ugr 9-1 significantly reversed inflammatory and acid-induced pain. The other two novel peptides, AnmTX Ugr 9a-2 (Ugr 9-2) and AnmTX Ugr 9a-3 (Ugr 9-3), did not inhibit the ASIC3 current. NMR spectroscopy revealed that Ugr 9-1 has an uncommon spatial structure, stabilized by two S-S bridges, with three classical β-turns and twisted β-hairpin without interstrand disulfide bonds. This is a novel peptide spatial structure that we propose to name boundless β-hairpin. PMID:23801332

  10. Sea Anemone Peptide with Uncommon β-Hairpin Structure Inhibits Acid-sensing Ion Channel 3 (ASIC3) and Reveals Analgesic Activity*

    PubMed Central

    Osmakov, Dmitry I.; Kozlov, Sergey A.; Andreev, Yaroslav A.; Koshelev, Sergey G.; Sanamyan, Nadezhda P.; Sanamyan, Karen E.; Dyachenko, Igor A.; Bondarenko, Dmitry A.; Murashev, Arkadii N.; Mineev, Konstantin S.; Arseniev, Alexander S.; Grishin, Eugene V.

    2013-01-01

    Three novel peptides were isolated from the venom of the sea anemone Urticina grebelnyi. All of them are 29 amino acid peptides cross-linked by two disulfide bridges, with a primary structure similar to other sea anemone peptides belonging to structural group 9a. The structure of the gene encoding the shared precursor protein of the identified peptides was determined. One peptide, π-AnmTX Ugr 9a-1 (short name Ugr 9-1), produced a reversible inhibition effect on both the transient and the sustained current of human ASIC3 channels expressed in Xenopus laevis oocytes. It completely blocked the transient component (IC50 10 ± 0.6 μm) and partially (48 ± 2%) inhibited the amplitude of the sustained component (IC50 1.44 ± 0.19 μm). Using in vivo tests in mice, Ugr 9-1 significantly reversed inflammatory and acid-induced pain. The other two novel peptides, AnmTX Ugr 9a-2 (Ugr 9-2) and AnmTX Ugr 9a-3 (Ugr 9-3), did not inhibit the ASIC3 current. NMR spectroscopy revealed that Ugr 9-1 has an uncommon spatial structure, stabilized by two S-S bridges, with three classical β-turns and twisted β-hairpin without interstrand disulfide bonds. This is a novel peptide spatial structure that we propose to name boundless β-hairpin. PMID:23801332

  11. TRPV3 channels mediate strontium-induced mouse egg activation

    PubMed Central

    Carvacho, Ingrid; Lee, Hoi Chang; Fissore, Rafael A.; Clapham, David E.

    2014-01-01

    SUMMARY In mammals, calcium influx is required for oocyte maturation and egg activation. The molecular identities of the calcium-permeant channels that underlie the initiation of embryonic development are not established. Here, we describe a Transient Receptor Potential (TRP) ion channel current activated by TRP agonists that is absent in TrpV3−/− eggs. TRPV3 current is differentially expressed during oocyte maturation, reaching a peak of maximum density and activity at metaphase of meiosis II (MII), the stage of fertilization. Selective activation of TRPV3 channels provokes egg activation by mediating massive calcium entry. Widely used to activate eggs, strontium application is known to yield normal offspring in combination with somatic cell nuclear transfer. We show that TRPV3 is required for strontium influx, as TrpV3−/− eggs failed to permeate Sr2+ or undergo strontium-induced activation. We propose that TRPV3 is the major mediator of calcium influx in mouse eggs and is a putative target for artificial egg activation. PMID:24316078

  12. Structure and permeability of ion-channels by integrated AFM and waveguide TIRF microscopy.

    PubMed

    Ramachandran, Srinivasan; Arce, Fernando Teran; Patel, Nirav R; Quist, Arjan P; Cohen, Daniel A; Lal, Ratnesh

    2014-01-01

    Membrane ion channels regulate key cellular functions and their activity is dependent on their 3D structure. Atomic force microscopy (AFM) images 3D structure of membrane channels placed on a solid substrate. Solid substrate prevents molecular transport through ion channels thus hindering any direct structure-function relationship analysis. Here we designed a ~70 nm nanopore to suspend a membrane, allowing fluidic access to both sides. We used these nanopores with AFM and total internal reflection fluorescence microscopy (TIRFM) for high resolution imaging and molecular transport measurement. Significantly, membranes over the nanopore were stable for repeated AFM imaging. We studied structure-activity relationship of gap junction hemichannels reconstituted in lipid bilayers. Individual hemichannels in the membrane overlying the nanopore were resolved and transport of hemichannel-permeant LY dye was visualized when the hemichannel was opened by lowering calcium in the medium. This integrated technique will allow direct structure-permeability relationship of many ion channels and receptors. PMID:24651823

  13. The TRPM2 ion channel is required for sensitivity to warmth.

    PubMed

    Tan, Chun-Hsiang; McNaughton, Peter A

    2016-08-25

    Thermally activated ion channels are known to detect the entire thermal range from extreme heat (TRPV2), painful heat (TRPV1, TRPM3 and ANO1), non-painful warmth (TRPV3 and TRPV4) and non-painful coolness (TRPM8) through to painful cold (TRPA1). Genetic deletion of each of these ion channels, however, has only modest effects on thermal behaviour in mice, with the exception of TRPM8, the deletion of which has marked effects on the perception of moderate coolness in the range 10-25 °C. The molecular mechanism responsible for detecting non-painful warmth, in particular, is unresolved. Here we used calcium imaging to identify a population of thermally sensitive somatosensory neurons which do not express any of the known thermally activated TRP channels. We then used a combination of calcium imaging, electrophysiology and RNA sequencing to show that the ion channel generating heat sensitivity in these neurons is TRPM2. Autonomic neurons, usually thought of as exclusively motor, also express TRPM2 and respond directly to heat. Mice in which TRPM2 had been genetically deleted showed a striking deficit in their sensation of non-noxious warm temperatures, consistent with the idea that TRPM2 initiates a 'warm' signal which drives cool-seeking behaviour. PMID:27533035

  14. Moving Fe2+ from ferritin ion channels to catalytic OH centers depends on conserved protein cage carboxylates

    PubMed Central

    Behera, Rabindra K.; Theil, Elizabeth C.

    2014-01-01

    Ferritin biominerals are protein-caged metabolic iron concentrates used for iron–protein cofactors and oxidant protection (Fe2+ and O2 sequestration). Fe2+ passage through ion channels in the protein cages, like membrane ion channels, required for ferritin biomineral synthesis, is followed by Fe2+ substrate movement to ferritin enzyme (Fox) sites. Fe2+ and O2 substrates are coupled via a diferric peroxo (DFP) intermediate, λmax 650 nm, which decays to [Fe3+–O–Fe3+] precursors of caged ferritin biominerals. Structural studies show multiple conformations for conserved, carboxylate residues E136 and E57, which are between ferritin ion channel exits and enzymatic sites, suggesting functional connections. Here we show that E136 and E57 are required for ferritin enzyme activity and thus are functional links between ferritin ion channels and enzymatic sites. DFP formation (Kcat and kcat/Km), DFP decay, and protein-caged hydrated ferric oxide accumulation decreased in ferritin E57A and E136A; saturation required higher Fe2+ concentrations. Divalent cations (both ion channel and intracage binding) selectively inhibit ferritin enzyme activity (block Fe2+ access), Mn2+ << Co2+ < Cu2+ < Zn2+, reflecting metal ion–protein binding stabilities. Fe2+–Cys126 binding in ferritin ion channels, observed as Cu2+–S–Cys126 charge-transfer bands in ferritin E130D UV-vis spectra and resistance to Cu2+ inhibition in ferritin C126S, was unpredicted. Identifying E57 and E136 links in Fe2+ movement from ferritin ion channels to ferritin enzyme sites completes a bucket brigade that moves external Fe2+ into ferritin enzymatic sites. The results clarify Fe2+ transport within ferritin and model molecular links between membrane ion channels and cytoplasmic destinations. PMID:24843174

  15. Identification of the Energetic Plume Ion Escape Channel at Mars

    NASA Astrophysics Data System (ADS)

    Johnson, B. C.; Liemohn, M. W.; Fraenz, M.; Barabash, S.

    2013-12-01

    Mars lacks a global dipole magnetic field. The resulting induced magnetosphere arising from Mars' atmosphere's direct interaction with the solar wind differs significantly from that of Venus. The weak gravitational field of Mars creates scale heights so large that the exosphere extends out beyond the Induced Magnetosphere Boundary (IMB), where newly ionized exospheric oxygen is exposed to high speed shocked solar wind flow and the associated strong convective electric field (E). The weaker Interplanetary Magnetic Field (IMF) at Mars, combined with this s