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A hybrid electronic tongue for direct classification of baby liquid foods with or without gluten

Peres, António M.; Dias, L.G.; Veloso, Ana C.A.; Sousa, Mara E.B.C.; Machado, A.A.S.C.
Fonte: International Society of Electrochemistry Publicador: International Society of Electrochemistry
Tipo: Conferência ou Objeto de Conferência
ENG
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27.125742%
People suffering from celiac disease are gluten intolerant and inadvertent ingestion of gluten proteins must be avoided. Several techniques have been proposed to detect/quantify gluten proteins in foodstuffs: immunochemical methods, mass tandem spectrometry and polymerase chain reaction as well as gluten sensors [1]. Recently, a potentiometric electronic tongue (ET) with lipo/polymeric membranes has been used to detect gliadins, which are gluten proteins, in foodstuffs [2]. However, the use of these techniques requires the previous extraction of gluten proteins. This step can be a possible drawback since it is not possible to guarantee that the extraction has a 100% yield since the protein types overlap in solubility and extractability [3]. In this work, the feasibility of a hybrid multi-sensor ET, which combines repeated cross-sensitivity and ion selective sensors (Fig. 1), to discriminate gluten-free and gluten-containing liquid baby foods has been evaluated. The device was constructed using a screenprinted technique and directly applied in the liquid infant food samples. No extraction or dilution/dissolution step was required. In total, 5 “gluten-free” and 10 “glutencontaining” liquid baby foods of different flavors were purchased at local supermarkets and analyzed.

A hybrid electronic tongue for direct classification of baby liquid foods with or without gluten

Peres, A. M.; Dias, L. G.; Veloso, Ana C. A.; Sousa, M. E. B. C.; Machado, A. A. S. C.
Fonte: Universidade do Minho Publicador: Universidade do Minho
Tipo: Conferência ou Objeto de Conferência
Publicado em //2011 ENG
Relevância na Pesquisa
27.125742%
People suffering from celiac disease are gluten intolerant and inadvertent ingestion of gluten proteins must be avoided. Several techniques have been proposed to detect/quantify gluten proteins in foodstuffs: immunochemical methods, mass tandem spectrometry and polymerase chain reaction as well as gluten sensors [1]. Recently, a potentiometric electronic tongue (ET) with lipo/polymeric membranes has been used to detect gliadins, which are gluten proteins, in foodstuffs [2]. However, the use of these techniques requires the previous extraction of gluten proteins. This step can be a possible drawback since it is not possible to guarantee that the extraction has a 100% yield since the protein types overlap in solubility and extractability [3]. In this work, the feasibility of a hybrid multi-sensor ET, which combines repeated cross-sensitivity and ion selective sensors (Fig. 1), to discriminate gluten-free and gluten-containing liquid baby foods has been evaluated. The device was constructed using a screen- printed technique and directly applied in the liquid infant food samples. No extraction or dilution/dissolution step was required. In total...

Proof for a nonproteinaceous calcium-selective channel in Escherichia coli by total synthesis from (R)-3-hydroxybutanoic acid and inorganic polyphosphate

Das, Sudipto; Lengweiler, Urs D.; Seebach, Dieter; Reusch, Rosetta N.
Fonte: The National Academy of Sciences of the USA Publicador: The National Academy of Sciences of the USA
Tipo: Artigo de Revista Científica
Publicado em 19/08/1997 EN
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Traditionally, the structure and properties of natural products have been determined by total synthesis and comparison with authentic samples. We have now applied this procedure to the first nonproteinaceous ion channel, isolated from bacterial plasma membranes, and consisting of a complex of poly(3-hydroxybutyrate) and calcium polyphosphate. To this end, we have now synthesized the 128-mer of hydroxybutanoic acid and prepared a complex with inorganic calcium polyphosphate (average 65-mer), which was incorporated into a planar lipid bilayer of synthetic phospholipids. We herewith present data that demonstrate unambiguously that the completely synthetic complex forms channels that are indistinguishable in their voltage-dependent conductance, in their selectivity for divalent cations, and in their blocking behavior (by La3+) from channels isolated from Escherichia coli. The implications of our finding for prebiotic chemistry, biochemistry, and biology are discussed.

The nodulation-signaling protein NodO from Rhizobium leguminosarum biovar viciae forms ion channels in membranes.

Sutton, J M; Lea, E J; Downie, J A
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 11/10/1994 EN
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The secreted nodulation-signaling protein NodO was purified from the supernatant of cultures of Rhizobium leguminosarum biovar viciae. The native protein has a M(r) of approximately 67,000, suggesting that it exists as a dimer since the DNA sequence predicts a M(r) of 30,002. Pure NodO protein had no protease, pectinase, or cellulase activity, and no binding was observed to lipooligosaccharide nodulation factors. Although NodO is relatively hydrophilic, it appeared to insert into liposomes and was protected by liposomes from proteolytic cleavage. When added to planar lipid bilayers, NodO formed cation-selective channels that allowed the movement of monovalent cations (K+ and Na+) across the membrane. NodO is a Ca(2+)-binding protein; in the presence of high concentrations of Ca2+, channel activity was reduced. We hypothesize that NodO plays a role in nodulation signaling by stimulating uptake of nodulation factors or by forming cation-specific channels that function synergistically with the proposed lipooligosaccharide-induced depolarization of the plasma membrane of leguminous plants.

Interaction between Polyamines and Bacterial Outer Membranes as Investigated with Ion-Selective Electrodes

Katsu, Takashi; Nakagawa, Hideki; Yasuda, Keiko
Fonte: American Society for Microbiology Publicador: American Society for Microbiology
Tipo: Artigo de Revista Científica
Publicado em /04/2002 EN
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We analyzed the interaction between polyamines and the outer membrane of Escherichia coli cells using potentiometric measurements with Ca2+, tetraphenylphosphonium (TPP+), and K+ electrodes. The Ca2+ electrode was used to examine the ability of the polyamines to release Ca2+ from the outer membrane. The TPP+ electrode was used to examine the ability to permeabilize the outer membrane, since the uptake of TPP+ was enhanced when the permeability barrier of the outer membrane was disrupted. The K+ electrode was used to examine permeabilization in the cytoplasmic membrane by monitoring the efflux of K+ in cytosol. Although Ca2+ release was remarkably enhanced by increasing the number of amino groups in polyamines, no TPP+ uptake was observed with polyamines of a simple structure, such as ethylenediamine, spermidine, and spermine. TPP+ uptake was observed when appropriate lipophilic moieties were further attached to the polyamines with three or four amino groups, indicating that the existence of bulky moieties as well as the number of amino groups is important to induce outer membrane permeabilization. Thus, 1-naphthylacetylspermine and N,N′-bis[6-[[(2-methoxyphenyl)methyl]amino]hexyl]-1,8-octanediamine (methoctramine) were especially effective in increasing the permeability of the outer membrane of E. coli cells...

Ca2+-activated synexin forms highly selective, voltage-gated Ca2+ channels in phosphatidylserine bilayer membranes.

Pollard, H B; Rojas, E
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /05/1988 EN
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Synexin, a cytosolic protein that mediates Ca2+-dependent membrane fusion, was incorporated into acidic phospholipid bilayers, formed at the tip of a patch pipet. The pipet was filled with a high-Ca2+ solution (50 mM) and immersed in a chamber containing a low-Ca2+ solution (1 mM). Brief exposures of the bilayer to synexin increased the capacitance of the bilayer by a factor of 10 and decreased the membrane resistance by a factor of 20. Reduction of Ca2+ in the chamber to 1 microM caused an abrupt increase in the current required to hold the pipet potential at 0 mV. Under certain conditions channel events could be detected, often occurring in bursts. Consistently, open-time histograms were found to be voltage-dependent and to exhibit one time constant in the time range examined here. The slope conductance for the synexin channel was estimated as 10.2 +/- 2.1 pS for the large Ca2+ gradient with low chamber Ca2+. However, for symmetrical, low-Cl- solutions containing 25 mM Ca2+ the conductance was 26.5 +/- 5.2 pS. Ion-replacement studies showed the synexin channel to much prefer Ca2+ over Ba2+ or Mg2+. Cd2+, a potent blocker of other voltage-gated Ca2+ channels at 100 microM, blocked synexin channels only at very high concentrations (greater than or equal to 10 mM). Similarly...

High Affinity K+ Uptake in Maize Roots: A Lack of Coupling with H+ Efflux

Kochian, Leon V.; Shaff, Jon E.; Lucas, William J.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /11/1989 EN
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We report here on the putative coupling between a high affinity K+ uptake system which operates at low external K+ concentrations (Km = 10-20 micromolar), and H+ efflux in roots of intact, low-salt-grown maize plants. An experimental approach combining electrophysiological measurements, quantification of unidirectional K+(86Rb+) influx, and the simultaneous measurement of net K+ and H+ fluxes associated with individual cells at the root surface with K+- and H+-selective microelectrodes was utilized. A microelectrode system described previously (IA Newman, LV Kochian, MA Grusak, and WJ Lucas [1987] Plant Physiol 84: 1177-1184) was used to quantify net ion fluxes from the measurement of electrochemical potential gradients for K+ and H+ ions within the unstirred layer at the root surface. No evidence for coupling between K+ uptake and H+ efflux could be found based on: (a) extremely variable K+:H+ flux stoichiometries, with K+ uptake often well in excess of H+ efflux; (b) dramatic time-dependent variability in H+ extrusion when both fluxes were measured at a particular location along the root over time; and (c) a lack of pH sensitivity by the high affinity K+ uptake system (to changes in external pH) when net K+ uptake, unidirectional K+(86Rb+) influx...

The K+/Na+ Selectivity of a Cation Channel in the Plasma Membrane of Root Cells Does Not Differ in Salt-Tolerant and Salt-Sensitive Wheat Species 1

Schachtman, Daniel P.; Tyerman, Stephen D.; Terry, Bernard R.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /10/1991 EN
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The characteristics of cation outward rectifier channels were studied in protoplasts from wheat root (Triticum aestivum L. and Triticum turgidum L.) cells using the patch clamp technique. The cation outward rectifier channels were voltage-dependent with a single channel conductance of 32 ± 1 picosiemens in 100 millimolar KCl. Whole-cell currents were dominated by the activity of the cation outward rectifiers. The time- and voltage-dependence of these currents was accounted for by the summed behavior of individual channels recorded from outside-out detached patches. The K+/Na+ permeability ratio of these channels was measured in a salt-sensitive and salt-tolerant genotype of wheat that differ in rates of Na+ accumulation, using a voltage ramp protocol on protoplasts in the whole-cell configuration. Permeability ratios were calculated from shifts in reversal potentials following ion substitutions. There were no significant differences in the K+/Na+ permeability ratios of these channels in root cells from either of the two genotypes tested. The permeability ratio for K+/Cl− was greater than 50:1. The K+/Na+ permeability ratio averaged 30:1, which is two to four times more selective than the same type of channel in guard cells and suspension culture cells. Lowering the Ca2+ concentration in the bath solution to 0.1 millimolar in the presence of 100 millimolar Na+ had no significant effect on the K+/Na+ permeability ratios of the channel. It seems unlikely that the mechanism of salt tolerance in wheat is based on differences in the K+/Na+ selectivity of these channels.

Selective proton permeability and pH regulation of the influenza virus M2 channel expressed in mouse erythroleukaemia cells.

Chizhmakov, I V; Geraghty, F M; Ogden, D C; Hayhurst, A; Antoniou, M; Hay, A J
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 15/07/1996 EN
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1. The M2 protein of influenza A virus is implicated in transmembrane pH regulation during infection. Whole-cell patch clamp of mouse erythroleukaemia cells expressing the M2 protein in the surface membrane showed a conductance due to M2 which was specifically blocked by the anti-influenza drug rimantadine. 2. The ion selectivity of the rimantadine-sensitive current through M2 was determined. Reversal potentials were close to equilibrium potentials for transmembrane pH gradients and not to those for Na+, K+ or Cl- concentration gradients. M2 permeability to Na+ relative to H+ was estimated to be less than 6 x 10(-7). 3. The M2 conductance increased as external pH decreased below 8.5 and approached saturation at an external pH of 4, effects attributable to increased permeability due to increased driving potential and to activation by low external pH. Both activation and permeation could be described by interaction of protons with sites on M2, with apparent dissociation constants of approximately 0.1 microM and 1 microM, respectively, under physiological conditions. 4. The M2 protein can transfer protons selectively across membranes with the H+ electrochemical gradient, properties consistent with its role in modifying virion and trans-Golgi pH during virus infection.

Potassium transport of the frog retinal pigment epithelium: autoregulation of potassium activity in the subretinal space.

la Cour, M; Lund-Andersen, H; Zeuthen, T
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /06/1986 EN
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27.125742%
The K+ transport of the isolated retinal pigment epithelium from the bull-frog was studied using micropuncture with double-barrelled ion-selective micro-electrodes. Transient changes of intracellular values of electrical potential and K+ activity were monitored in response to abrupt changes in the K+ concentration on the retinal side of the tissue. The data were interpreted in terms of a simple three-compartment model of the epithelium in which the retinal (or apical) and choroidal (or basal) membranes separate the cellular compartment from the retinal and choroidal compartments. K+ transport across the retinal membrane was described by an active ouabain-sensitive K+ influx in parallel with a passive electrodiffusive K+ efflux. In steady state under control conditions, the active K+ influx (pump rate) averaged 0.18 X 10(-9) mol cm-2 s-1. The electrodiffusive K+ efflux was described by a K+ permeability, which in steady state under control conditions averaged 1.7 X 10(-5) cm s-1. K+ transport across the choroidal membrane was described as purely electrodiffusive. In steady state under control conditions, the K+ permeability of the choroidal membrane averaged 0.6 X 10(-5) cm s-1. When the K+ concentration on the retinal side of the tissue was increased from its control value...

Multiple types of voltage-dependent Ca2+-activated K+ channels of large conductance in rat brain synaptosomal membranes.

Farley, J.; Rudy, B.
Fonte: The Biophysical Society Publicador: The Biophysical Society
Tipo: Artigo de Revista Científica
Publicado em /06/1988 EN
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27.125742%
K+-selective ion channels from a mammalian brain synaptosomal membrane preparation were inserted into planar phospholipid bilayers on the tips of patch-clamp pipettes, and single-channel currents were measured. Multiple distinct classes of K+ channels were observed. We have characterized and described the properties of several types of voltage-dependent, Ca2+-activated K+ channels of large single-channel conductance (greater than 50 pS in symmetrical KCl solutions). One class of channels (Type I) has a 200-250-pS single-channel conductance. It is activated by internal calcium concentrations greater than 10(-7) M, and its probability of opening is increased by membrane depolarization. This channel is blocked by 1-3 mM internal concentrations of tetraethylammonium (TEA). These channels are similar to the BK channel described in a variety of tissues. A second novel group of voltage-dependent, Ca2+-activated K+ channels was also studied. These channels were more sensitive to internal calcium, but less sensitive to voltage than the large (Type I) channel. These channels were minimally affected by internal TEA concentrations of 10 mM, but were blocked by a 50 mM concentration. In this class of channels we found a wide range of relatively large unitary channel conductances (65-140 pS). Within this group we have characterized two types (75-80 pS and 120-125 pS) that also differ in gating kinetics. The various types of voltage-dependent...

Selective MPP+ uptake into synaptic dopamine vesicles: possible involvement in MPTP neurotoxicity.

Del Zompo, M.; Piccardi, M. P.; Ruiu, S.; Quartu, M.; Gessa, G. L.; Vaccari, A.
Fonte: Nature Publishing Group Publicador: Nature Publishing Group
Tipo: Artigo de Revista Científica
Publicado em /06/1993 EN
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27.125742%
1. In the present study we provide evidence for a saturable, Mg2+/ATP- and temperature-dependent, tetrabenazine-, dopamine-, and amphetamine-sensitive uptake of 1-methyl-4-phenylpyridinium ion (MPP+) in synaptic vesicles from mouse striatum. 2. Similarity in the properties of the vesicular uptake suggests that in the striatum dopamine and MPP+ share the vesicular carrier. 3. The presence of MPP+ vesicular uptake in dopamine-rich regions such as striatum, olfactory, tubercles and hypothalamus, as well as its absence in cerebellum, cortex and pons-medulla, suggest that monoamine vesicular carriers differ between highly and poorly dopamine-innervated regions. 4. The restriction of active MPP+ uptake to the dopaminergic regions, which reflects the previously shown distribution of [3H]-MPP+ binding sites in mouse brain membranes, indicates MPP+ as a marker of the vesicular carrier for dopamine in dopaminergic neurones. 5. A role in MPP+ neurotoxicity is suggested for this region-specific, vesicular storage of the toxin.

Identification of the functional core of the influenza A virus A/M2 proton-selective ion channel

Ma, Chunlong; Polishchuk, Alexei L.; Ohigashi, Yuki; Stouffer, Amanda L.; Schön, Arne; Magavern, Emma; Jing, Xianghong; Lear, James D.; Freire, Ernesto; Lamb, Robert A.; DeGrado, William F.; Pinto, Lawrence H.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
EN
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The influenza A virus M2 protein (A/M2) is a homotetrameric pH-activated proton transporter/channel that mediates acidification of the interior of endosomally encapsulated virus. This 97-residue protein has a single transmembrane (TM) helix, which associates to form homotetramers that bind the anti-influenza drug amantadine. However, the minimal fragment required for assembly and proton transport in cellular membranes has not been defined. Therefore, the conductance properties of truncation mutants expressed in Xenopus oocytes were examined. A short fragment spanning residues 21–61, M2(21-61), was inserted into the cytoplasmic membrane and had specific, amantadine-sensitive proton transport activity indistinguishable from that of full-length A/M2; an epitope-tagged version of an even shorter fragment, M2(21-51)-FLAG, had specific activity within a factor of 2 of the full-length protein. Furthermore, synthetic fragments including a peptide spanning residues 22–46 were found to transport protons into liposomes in an amantadine-sensitive manner. In addition, the functionally important His-37 residue pKa values are highly perturbed in the tetrameric form of the protein, a property conserved in the TM peptide and full-length A/M2 in both micelles and bilayers. These data demonstrate that the determinants for folding...

Water Dynamics and Interactions in Water-Polyether Binary Mixtures

Fenn, Emily E.; Moilanen, David E.; Levinger, Nancy E.; Fayer, Michael D.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 22/04/2009 EN
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Poly(ethylene) oxide (PEO) is a technologically important polymer with a wide range of applications including ion-exchange membranes, protein crystallization, and medical devices. PEO’s versatility arises from its special interactions with water. Water molecules may form hydrogen bond bridges between the ether oxygens of the backbone. While steady-state measurements and theoretical studies of PEO’s interactions with water abound, experiments measuring dynamic observables are quite sparse. A major question is the nature of the interactions of water with the ether oxygens as opposed to the highly hydrophilic PEO terminal hydroxyls. Here, we examine a wide range of mixtures of water and tetraethylene glycol dimethyl ether (TEGDE), a methyl-terminated derivative of PEO with 4 repeat units (5 ether oxygens) using ultrafast infrared polarization selective pump-probe measurements on water’s hydroxyl stretching mode to determine vibrational relaxation and orientational relaxation dynamics. The experiments focus on the dynamical interactions of water with the ether backbone because TEGDE does not have the PEO terminal hydroxyls. The experiments observe two distinct subensembles of water molecules: those that are hydrogen bonded to other waters and those that are associated with TEGDE molecules. The water orientational relaxation has a fast component of a few ps (water-like) followed by much slower decay of ∼20 ps (TEGDE associated). The two decay times vary only mildly with the water concentration. The two subensembles are evident even in very low water content samples...

An ion-channel-containing model membrane: structural determination by magnetic contrast neutron reflectometry†

Holt, Stephen A.; Le Brun, Anton P.; Majkrzak, Charles F.; McGillivray, Duncan J.; Heinrich, Frank; Lösche, Mathias; Lakey, Jeremy H.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em //2009 EN
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To many biophysical characterisation techniques, biological membranes appear as two-dimensional structures with details of their third dimension hidden within a 5 nm profile. Probing this structure requires methods able to discriminate multiple layers a few Ångströms thick. Given sufficient resolution, neutron methods can provide the required discrimination between different biochemical components, especially when selective deuteration is employed. We have used state-of-the-art neutron reflection methods, with resolution enhancement via magnetic contrast variation to study an oriented model membrane system. The model is based on the Escherichia coli outer membrane protein OmpF fixed to a gold surface via an engineered cysteine residue. Below the gold is buried a magnetic metal layer which, in a magnetic field, displays different scattering strengths to spin-up and spin-down neutrons. This provides two independent datasets from a single biological sample. Simultaneous fitting of the two datasets significantly refines the resulting model. A β-mercaptoethanol (βME) passivating surface, applied to the gold to prevent protein denaturation, is resolved for the first time as an 8.2 ± 0.6 Å thick layer, demonstrating the improved resolution and confirming that this layer remains after OmpF assembly. The thiolipid monolayer (35.3 ± 0.5 Å)...

Keeping active channels in their place: Membrane phosphoinositides regulate TRPM channel activity in a compartment-selective manner

Braun, Andrew P.
Fonte: Landes Bioscience Publicador: Landes Bioscience
Tipo: Artigo de Revista Científica
Publicado em 01/11/2012 EN
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We have long appreciated that the controlled movement of ions and solutes across the cell surface or plasma membrane affects every aspect of cell function, ranging from membrane excitability to metabolism to secretion, and is also critical for the long-term maintenance of cell viability. Studies examining these physiological transport processes have revealed a vast array of ion channels, transporters and ATPase-driven pumps that underlie these transmembrane ionic movements and how acquired or genetic disruption of these processes are linked to disease. More recently, it has become evident that the ongoing function of intracellular organelles and subcellular compartments also depends heavily on the controlled movement of ions to establish distinct pH or ionic environments. However, limited experimental access to these subcellular domains/structures has hampered scientific progress in this area, due in large part to the difficulty of applying proven functional assays, such as patch clamp and radiotracer methodologies, to these specialized membrane locations. Using both functional and immune-labeling assays, we now know that the types and complement of channels, transporters and pumps located within intracellular membranes and organelles often differ from those present on the plasma membrane. Moreover...

The pore of voltage-gated potassium ion channels is strained when closed

Fowler, Philip W.; Sansom, Mark S. P.
Fonte: Nature Pub. Group Publicador: Nature Pub. Group
Tipo: Artigo de Revista Científica
Publicado em 21/05/2013 EN
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Voltage-gated potassium channels form potassium-selective pores in cell membranes. They open or close in response to changes in the transmembrane potential and are essential for generating action potentials, and thus for the functioning of heart and brain. While a mechanism for how these channels close has been proposed, it is not clear what drives their opening. Here we use free energy molecular dynamics simulations to show that work must be done on the pore to reduce the kink in the pore-lining (S6) α-helices, thereby forming the helix bundle crossing and closing the channel. Strain is built up as the pore closes, which subsequently drives opening. We also determine the effect of mutating the PVPV motif that causes the kink in the S6 helix. Finally, an approximate upper limit on how far the S4 helix is displaced as the pore closes is estimated.

TRIC-B channels display labile gating: evidence from the TRIC-A knockout mouse model

Venturi, Elisa; Matyjaszkiewicz, Antoni; Pitt, Samantha J.; Tsaneva-Atanasova, Krasimira; Nishi, Miyuki; Yamazaki, Daiju; Takeshima, Hiroshi; Sitsapesan, Rebecca
Fonte: Springer Berlin Heidelberg Publicador: Springer Berlin Heidelberg
Tipo: Artigo de Revista Científica
EN
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Sarcoplasmic/endoplasmic reticulum (SR) and nuclear membranes contain two related cation channels named TRIC-A and TRIC-B. In many tissues, both subtypes are co-expressed, making it impossible to distinguish the distinct single-channel properties of each subtype. We therefore incorporated skeletal muscle SR vesicles derived from Tric-a-knockout mice into bilayers in order to characterise the biophysical properties of native TRIC-B without possible misclassification of the channels as TRIC-A, and without potential distortion of functional properties by detergent purification protocols. The native TRIC-B channels were ideally selective for cations. In symmetrical 210 mM K+, the maximum (full) open channel level (199 pS) was equivalent to that observed when wild-type SR vesicles were incorporated into bilayers. Analysis of TRIC-B gating revealed complex and variable behaviour. Four main sub-conductance levels were observed at approximately 80 % (161 pS), 60 % (123 pS), 46 % (93 pS), and 30 % (60 pS) of the full open state. Seventy-five percent of the channels were voltage sensitive with Po being markedly reduced at negative holding potentials. The frequent, rapid transitions between TRIC-B sub-conductance states prevented development of reliable gating models using conventional single-channel analysis. Instead...

Induction of Phosphoenolpyruvate Carboxykinase (PEPCK) during Acute Acidosis and Its Role in Acid Secretion by V-ATPase-Expressing Ionocytes

Furukawa, Fumiya; Tseng, Yung-Che; Liu, Sian-Tai; Chou, Yi-Ling; Lin, Ching-Chun; Sung, Po-Hsuan; Uchida, Katsuhisa; Lin, Li-Yih; Hwang, Pung-Pung
Fonte: Ivyspring International Publisher Publicador: Ivyspring International Publisher
Tipo: Artigo de Revista Científica
Publicado em 01/05/2015 EN
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Vacuolar-Type H+-ATPase (V-ATPase) takes the central role in pumping H+ through cell membranes of diverse organisms, which is essential for surviving acid-base fluctuating lifestyles or environments. In mammals, although glucose is believed to be an important energy source to drive V-ATPase, and phosphoenolpyruvate carboxykinase (PEPCK), a key enzyme for gluconeogenesis, is known to be activated in response to acidosis, the link between acid secretion and PEPCK activation remains unclear. In the present study, we used zebrafish larva as an in vivo model to show the role of acid-inducible PEPCK activity in glucose production to support higher rate of H+ secretion via V-ATPase, by utilizing gene knockdown, glucose supplementation, and non-invasive scanning ion-selective electrode technique (SIET). Zebrafish larvae increased V-ATPase-mediated acid secretion and transiently expression of Pck1, a zebrafish homolog of PEPCK, in response to acid stress. When pck1 gene was knocked down by specific morpholino, the H+ secretion via V-ATPase decreased, but this effect was rescued by supplementation of glucose into the yolk. By assessing changes in amino acid content and gene expression of respective enzymes, glutamine and glutamate appeared to be the major source for replenishment of Krebs cycle intermediates...

Electrokinetic Instability near Charge-Selective Hydrophobic Surfaces

Shelistov, V. S.; Demekhin, E. A.; Ganchenko, G. S.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 14/02/2014
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27.378804%
The influence of the texture of a hydrophobic surface on the electro-osmotic slip of the second kind and the electrokinetic instability near charge-selective surfaces (permselective membranes, electrodes, or systems of micro- and nanochannels) is investigated theoretically using a simple model based on the Rubinstein-Zaltzman approach. A simple formula is derived to evaluate the decrease in the instability threshold due to hydrophobicity. The study is complemented by numerical investigations both of linear and nonlinear instabilities near a hydrophobic membrane surface. Theory predicts a significant enhancement of the ion flux to the surface and shows a good qualitative agreement with the available experimental data.