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Enzyme-based Colorimetric and Potentiometric Biosensor for Detecting Pb (II) Ions in Milk

Kaur,Hardeep; Kumar,Sachin; Verma,Neelam
Fonte: Instituto de Tecnologia do Paraná - Tecpar Publicador: Instituto de Tecnologia do Paraná - Tecpar
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/08/2014 EN
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The aim of the present work was to study a simple colorimetric and potentiometric biosensor based on urease inhibition by Pb (II) ions for its estimation in milk samples. Urease immobilized on nylon membrane by hydrosol gel method was used as the biocomponent to demonstrate the metal effect on the enzyme activity using phenol red as the pH indicator. A lower limit detection of 38.6µm was achieved in the milk and the enzyme membranes were stable for more than two months at 4ºC. In potentiometric approach, response of an ion selective electrode (ISE) to changing ammonium ion concentration as a consequence of urease inhibition by Pb (II) ions was explored to achieve a detection limit of 9.66 µm. Lead specificity was attained by means of masking agents 1,10 - phenanthroline and sodium potassium tartarate. Validation of the developed biosensors was carried out with spiked milk samples.

The major surface protein complex of Treponema denticola depolarizes and induces ion channels in HeLa cell membranes.

Mathers, D A; Leung, W K; Fenno, J C; Hong, Y; McBride, B C
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /08/1996 EN
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The oral spirochete Treponema denticola is closely associated with periodontal diseases in humans. The 53-kDa major surface protein (Msp) located in the outer membrane of T. denticola serovar a (ATCC 35405) has both pore-forming activity and adhesin activity. We have used standard patch clamp recording methods to study the effects of a partially purified outer membrane complex containing Msp on HeLa cells. The Msp complex was free of the chymotrypsin-like proteinase also found in the outer membrane of T. denticola. Msp bound to several HeLa cell proteins, including a 65-kDa surface protein and a 96-kDa cytoplasmic protein. The Msp complex depolarized and increased the conductance of the HeLa cell membrane in a manner which was not strongly selective for Na+, K+, Ca2+, and Cl- ions. Cell-attached patches of HeLa cell membrane exposed to Msp complex exhibited short-lived channels with a slope conductance of 0.4 nS in physiologically normal saline. These studies show that Msp binds both a putative epithelial cell surface receptor and cytoplasmic proteins and that the Msp complex can form large conductance ion channels in the cytoplasmic membrane of epithelial cells. These properties may contribute to the cytopathic effects of T. denticola on host epithelial cells.

Bordetella pertussis major outer membrane porin protein forms small, anion-selective channels in lipid bilayer membranes.

Armstrong, S K; Parr, T R; Parker, C D; Hancock, R E
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /04/1986 EN
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The major outer membrane protein of molecular weight 40,000 (the 40K protein) of a virulent isolate of Bordetella pertussis was purified to apparent homogeneity. The purified protein formed an oligomer band (of apparent molecular weight 90,000) on sodium dodecyl sulfate-polyacrylamide gels after solubilization at low temperatures. The porin function of this protein was characterized by the black lipid bilayer method. The 40K protein formed channels smaller than all other constitutive major outer membrane porins studied to date. The average single-channel conductance in 1 M KCl was 0.56 nS. This was less than a third of the conductance previously observed for Escherichia coli porins. Zero-current potential measurements made of the porin to determine its ion selectivity revealed the porin to be more than 100-fold selective for anions over cations. The single-channel conductance was measured as a function of salt concentration. The data could be fitted to a Lineweaver-Burk plot suggesting an anion binding site with a Kd of 1.17 M Cl- and a maximum possible conductance through the channel of 1.28 nS.

Changes of extracellular potassium activity induced by electric current through brain tissue in the rat.

Gardner-Medwin, A R; Nicholson, C
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /02/1983 EN
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Ion-selective micro-electrodes have been used to measure K+ and Ca2+ activity changes in extracellular space beneath the surface of the neocortex and cerebellar cortex during current flow across the tissue surface in anaesthetized rats. Inward currents produced decreases of [K+]o and outward currents produced increases, with insignificant changes in [Ca2+]o. Changes of [K+]o were largest just under the surface of the tissue, but were detectable down to depths of ca. 1 mm. With appropriate sitting of electrodes in the cerebellar cortex, currents of 22 microA mm-2 for 400 sec produced changes averaging -42% for inward current and +66% for outward current. The [K+]o changes near the surface were most rapid immediately after the onset of current and more gradual after some tens of seconds. Deeper within the tissue the rate of change was more uniform and after the end of stimulation the return to base line was slower. The amplitude, depth dependence and time course of the [K+]o changes were in reasonable agreement with the results calculated for a model in which K+ moves partly through extracellular space but primarily through membranes and cytoplasm within the tissue. The [K+]o changes were not attributable to variations in neuronal activity...

Photoinitiated ion movements in bilayer membranes containing magnesium octaethylporphyrin.

Woodle, M C; Mauzerall, D
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /09/1986 EN
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A photocurrent produced by planar lipid bilayers containing Mg-octaethylporphyrin in the presence of oxygen has been investigated to determine if the current is due to movement of the MgOEP+ ion in the bilayer. Photoexcitation of the MgOEP is known to produce MgOEP+ in the bilayer when an electron acceptor is present. However, the aqueous electron acceptors ferricyanide and methyl viologen (MV+2) have opposite effects on the photocurrent. Ferricyanide decreases the photo current, even in the presence of oxygen, whereas methyl viologen increases the photocurrent, but only when oxygen is present. We attribute most of the photocurrent to the movement of superoxide anion. The difference in effect between ferricyanide and methyl viologen is attributed to the different rates of reduction of O2 by reduced MV+ (fast) vs. ferrocyanide (slow) and the known competition between ferricyanide and oxygen as the acceptor for the photoexcited porphyrin. It is inferred that most of the MgOEP is localized in the polar region of the lipid bilayer. Addition of ferrocyanide to the aqueous phase on one side of the bilayer, to trap MgOEP+ produced on the other side by MV+2, fails to increase the lifetime of the photovoltage. With a pH gradient across the bilayer...

Incorporation of ion channels from bovine rod outer segments into planar lipid bilayers.

Hanke, W; Kaupp, U B
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /11/1984 EN
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Membranes vesicles, prepared from bovine rod outer segments were fused with planar lipid bilayers. Two different ion channels were identified by recording currents from single channels. Both types of channels were selective for sodium rather than potassium and were impermeable to chloride ions. Unit conductances were 20 and 120 pS, respectively, in 150 mM sodium chloride. The channel with the larger unit conductance was sensitive to the transmembrane potential. This channel rapidly activated within less than 10 ms after a voltage jump to a more negative membrane potential and then inactivated after several seconds. The duration of the active period and the properties of the channel depended on the amplitude of the voltage jump. The channel of smaller unit conductance did not show any voltage-dependent activation or inactivation. Both types of channels were insensitive to light in the planar bilayer system. Channels incorporated into planar bilayers on a Teflon sandwich septum or on the tip of a glass micropipette gave similar results.

LF 16.0335, a novel potent and selective nonpeptide antagonist of the human bradykinin B2 receptor

Pruneau, Didier; Luccarini, Jean-Michel; Fouchet, Chantal; Defrêne, Evelyne; Franck, Rose-Marie; Loillier, Bruno; Duclos, Hervé; Robert, Claude; Cremers, Béatrice; Bélichard, Pierre; Paquet, Jean-Luc
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /09/1998 EN
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In the present paper, we describe the in vitro pharmacological properties of LF 16.0335 (1-[[3-[(2,4-dimethylquinolin-8-yl)oxymethyl]-2,4-dichloro-phenyl]sulphonyl] -2(S) - [[4 -[4-(aminoiminomethyl)phenylcarbonyl]piperazin-1-yl]carbonyl]pyrrolidine), a novel and potent nonpeptide antagonist of the human bradykinin (BK) B2 receptor.LF 16.0335 displaced [3H]-BK binding to membrane preparations from CHO cells expressing the cloned human B2 receptor, INT 407 cells and human umbilical vein with Ki values of 0.84±0.39 nM, 1.26±0.68 nM and 2.34±0.36 nM, respectively.In saturation binding studies performed in INT 407 cell membranes in the presence or absence of LF 16.0335, Bmax values of [3H]-BK were not significantly changed suggesting that LF 16.0335 behaves as a competitive antagonist.LF 16.0335 had no affinity for the cloned human kinin B1 receptor stably expressed in 293 cells. In addition, this compound at 1 μM did not significantly bind to a range of 40 different membrane receptors and eight ion channels except muscarinic M2 and M1 receptors for which an IC50 value of 0.9 and 1 μM was obtained.BK stimulates in a concentration-dependent manner phosphoinositosides (IPs) production in cultured INT 407 cells. Concentration-response-curves to BK were shifted to the right in the presence of LF 16.0335 (0.1 μM) without reduction of the maximum. LF 16.0335 inhibited the concentration-contraction curve to BK in the human umbilical vein giving a pA2 value of 8.30±0.30 with a Schild plot slope that was not different from unity.These results demonstrate that LF 16.0335 is a potent...

Mechanism of ion transport through the anion-selective channel of the Pseudomonas aeruginosa outer membrane

Fonte: The Rockefeller University Press Publicador: The Rockefeller University Press
Tipo: Artigo de Revista Científica
Publicado em 01/02/1987 EN
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Protein P trimers isolated and purified from Pseudomonas aeruginosa outer membrane were reconstituted in planar lipid bilayer membranes from diphytanoyl phosphatidylcholine. The protein trimers formed highly anion-specific channels with an average single channel conductance of 160 pS in 0.1 M Cl solution. A variety of different nonvalent anions were found to be permeable through the channel, which suggests a channel diameter between 0.5 and 0.7 nm. The selectivity for the halides followed the Eisenman sequence AVI (without At-). The ion transport through the protein P channel could be explained reasonably well by a one-site, two-barrier model. The stability constant of the binding of Cl- to the site was 20 M-1 at neutral pH. The binding of anions to the site was pH dependent, which suggested that several charges are involved in the closely spaced selectivity filter. Permeability ratios for different anions as calculated from bi-ionic potentials showed agreement with corresponding ratios of single channel conductances. The protein P channels were not voltage-gated and had lifetimes of the order of several minutes. The current-voltage curves were linear for membrane potentials up to 150 mV, which suggested that Nernst-Planck-type barriers rather than Eyring barriers were involved in the movement of anions through the protein P channel.

Sodium channel selectivity. Dependence on internal permeant ion concentration

Fonte: The Rockefeller University Press Publicador: The Rockefeller University Press
Tipo: Artigo de Revista Científica
Publicado em 01/08/1976 EN
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The selectivity of sodium channels in squid axon membranes was investigated with widely varying concentrations of internal ions. The selectivity ratio, PNa/PK, determined from reversal potentials decreases from 12.8 to 5.7 to 3.5 as the concentration of internal potassium is reduced from 530 to 180 to 50 mM, respectively. The internal KF perfusion medium can be diluted by tetramethylammonium (TMA), Tris, or sucrose solutions with the same decrease in PNa/PK. The changes in the selectivity ratio depend upon internal permeant ion concentration rather than ionic strength, membrane potential, or chloride permeability. Lowering the internal concentration of cesium, rubidium, guanidnium, or ammonium also reduces PNa/Pion. The selective sequence of the sodium channel is: Na greater than guanidinium greater than ammonium greater than K greater than Rb greater than Cs.

Intracellular K+ activity and its relation to basolateral membrane ion transport in Necturus gallbladder epithelium

Fonte: The Rockefeller University Press Publicador: The Rockefeller University Press
Tipo: Artigo de Revista Científica
Publicado em 01/07/1980 EN
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A study of the mechanisms of the effects of amphotericin B and ouabain on cell membrane and transepithelial potentials and intracellular K activity (alpha Ki) of Necturus gallbladder epithelium was undertaken with conventional and K-selective intracellular microelectrode techniques. Amphotericin B produced a mucosa-negative change of transepithelial potential (Vms) and depolarization of both apical and basolateral membranes. Rapid fall of alpha Ki was also observed, with the consequent reduction of the K equilibrium potential (EK) across both the apical and the basolateral membrane. It was also shown that, unless the mucosal bathing medium is rapidly exchanged, K accumulates in the unstirred fluid layers near the luminal membrane generating a paracellular K diffusion potential, which contributes to the Vms change. Exposure to ouabain resulted in a slow decrease of alpha Ki and slow depolarization of both cell membranes. Cell membrane potentials and alpha Ki could be partially restored by a brief (3-4 min) mucosal substitution of K for Na. Under all experimental conditions (control, amphotericin B, and ouabain), EK at the basolateral membrane was larger than the basolateral membrane equivalent emf (Eb). Therefore, the K chemical potential difference appears to account for Eb and the magnitude of the cell membrane potentials...

Chlorovirus-Mediated Membrane Depolarization of Chlorella Alters Secondary Active Transport of Solutes▿

Agarkova, Irina; Dunigan, David; Gurnon, James; Greiner, Timo; Barres, Julia; Thiel, Gerhard; Van Etten, James L.
Fonte: American Society for Microbiology (ASM) Publicador: American Society for Microbiology (ASM)
Tipo: Artigo de Revista Científica
EN
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Paramecium bursaria chlorella virus 1 (PBCV-1) is the prototype of a family of large, double-stranded DNA, plaque-forming viruses that infect certain eukaryotic chlorella-like green algae from the genus Chlorovirus. PBCV-1 infection results in rapid host membrane depolarization and potassium ion release. One interesting feature of certain chloroviruses is that they code for functional potassium ion-selective channel proteins (Kcv) that are considered responsible for the host membrane depolarization and, as a consequence, the efflux of potassium ions. This report examines the relationship between cellular depolarization and solute uptake. Annotation of the virus host Chlorella strain NC64A genome revealed 482 putative transporter-encoding genes; 224 are secondary active transporters. Solute uptake experiments using seven radioactive compounds revealed that virus infection alters the transport of all the solutes. However, the degree of inhibition varied depending on the solute. Experiments with nystatin, a drug known to depolarize cell membranes, produced changes in solute uptake that are similar but not identical to those that occurred during virus infection. Therefore, these studies indicate that chlorovirus infection causes a rapid and sustained depolarization of the host plasma membrane and that this depolarization leads to the inhibition of secondary active transporters that changes solute uptake.

Hydrogen Ion Buffering During Complete Brain Ischemia

KRAIG, RICHARD P.; PULSINELLI, WILLIAM A.; PLUM, FRED
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 09/09/1985 EN
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As a first step to quantify [H+] changes in brain during ischemia we used H+-selective microelectrodes and enzyme fluorometric techniques to describe the relationship between interstitial [H+] ([H+]o) and peak tissue lactate after cardiac arrest. We found a step function relationship between [H+]o and tissue lactate rather than the linear titration expected in a homogeneous protein solution. Within a blood glucose range from 3–7 mM, brain lactate rose from 8–13 mmol/kg along with a rise in [H+]o of 99 ± 6 nM (0.44 ± 0.02 pH). At higher blood glucose levels (17–80 mM), brain lactate accumulated to levels of 16–31 mmol/kg; concurrently [H+]o rose by 608 ± 16 nM (1.07 ± 0.02 pH). The unchanging level of [H+]o between 8–13 and 16–31 mmol/kg lactate implies that [H+]o is at a steady-state, but not equilibrium with respect to [H+] in other brain compartments. We propose that ion-transport characteristics of astroglia account for the observed relationship of [H+]o to tissue lactate during complete ischemia and suggest that brain infarction develops after plasma membranes in brain cells can no longer transport ions to regulate [H+].

Cation-Coordinating Properties of Perfluoro-15-Crown-5

Lai, Chun-Ze; Reardon, Molly E.; Boswell, Paul G.; Bühlmann, Philippe
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 01/01/2010 EN
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The coordinative properties of perfluoro-15-crown-5 with monocations were investigated using 19F NMR spectroscopy and ion-selective electrodes with perfluoro-15-crown-5 as the matrix of their sensor membranes and the fluorophilic tetrakis[3,5-bis(perfluorohexyl)phenyl]borate as ion exchanger site. The results show that perfluoro-15-crown-5 interacts weakly but significantly with Na+ and K+. Assuming 1:1 stoichiometry, the formal complexation constants were determined to be 5.5 and 1.7 M−1, respectively. This weak binding is consistent with the strong electron withdrawing nature of the many fluorine atoms in the perfluorocrown ether. While perfluorinated crown ethers have been known to form host–guest complexes with the anions O2− and F− in the gas phase, this is the first study that quantitatively confirms cation binding to a perfluorocrown ether.

Structural and biophysical properties of a synthetic channel-forming peptide: Designing a clinically relevant anion selective pore

Bukovnik, U.; Gao, J.; Cook, J.,G.A.; Shank, L.P.; Seabra, M.B.; Schultz, B.D.; Iwamoto, T.; Chen, J.; Tomich, J.M.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
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The design, synthesis, modeling and in vitro testing of channel-forming peptides derived from the cys-loop superfamily of ligand-gated ion channels are part of an ongoing research focus. Over 300 different sequences have been prepared based on the M2 transmembrane segment of the spinal cord glycine receptor α-subunit. A number of these sequences are water-soluble monomers that readily insert into biological membranes where they undergo supramolecular assembly, yielding channels with a range of selectivities and conductances. Selection of a sequence for further modifications to yield an optimal lead compound came down to a few key biophysical properties: low solution concentrations that yield channel activity, greater ensemble conductance, and enhanced ion selectivity. The sequence NK4-M2GlyR T19R, S22W (KKKKPARVGLGITTVLTMRTQW) addressed these criteria. The structure of this peptide has been analyzed by solution NMR as a monomer in detergent micelles, simulated as five-helix bundles in a membrane environment, modified by cysteine-scanning and studied for insertion efficiency in liposomes of selected lipid compositions. Taken together, these results define the structural and key biophysical properties of this sequence in a membrane. This model provides an initial scaffold from which rational substitutions can be proposed and tested to modulate anion selectivity.

Two-Step Mechanism of Membrane Disruption by Aβ through Membrane Fragmentation and Pore Formation

Sciacca, Michele F.M.; Kotler, Samuel A.; Brender, Jeffrey R.; Chen, Jennifer; Lee, Dong-kuk; Ramamoorthy, Ayyalusamy
Fonte: The Biophysical Society Publicador: The Biophysical Society
Tipo: Artigo de Revista Científica
Publicado em 22/08/2012 EN
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Disruption of cell membranes by Aβ is believed to be one of the key components of Aβ toxicity. However, the mechanism by which this occurs is not fully understood. Here, we demonstrate that membrane disruption by Aβ occurs by a two-step process, with the initial formation of ion-selective pores followed by nonspecific fragmentation of the lipid membrane during amyloid fiber formation. Immediately after the addition of freshly dissolved Aβ1–40, defects form on the membrane that share many of the properties of Aβ channels originally reported from single-channel electrical recording, such as cation selectivity and the ability to be blockaded by zinc. By contrast, subsequent amyloid fiber formation on the surface of the membrane fragments the membrane in a way that is not cation selective and cannot be stopped by zinc ions. Moreover, we observed that the presence of ganglioside enhances both the initial pore formation and the fiber-dependent membrane fragmentation process. Whereas pore formation by freshly dissolved Aβ1–40 is weakly observed in the absence of gangliosides, fiber-dependent membrane fragmentation can only be observed in their presence. These results provide insights into the toxicity of Aβ and may aid in the design of specific compounds to alleviate the neurodegeneration of Alzheimer’s disease.

Structural dynamics and topology of phosphorylated phospholamban homopentamer reveal its role in the regulation of calcium transport in sarcoplasmic reticulum

Vostrikov, Vitaly V.; Mote, Kaustubh R.; Verardi, Raffaello; Veglia, Gianluigi
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
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Phospholamban (PLN) inhibits the sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA), thereby regulating cardiac diastole. In membranes, PLN assembles into homopentamers that in both the phosphorylated and non-phosphorylated states have been proposed to form ion-selective channels. Here, we determined the structure of the phosphorylated pentamer using a combination of solution and solid-state nuclear magnetic resonance methods. We found that the pinwheel architecture of the homopentamer is preserved upon phosphorylation, with each monomer having an L-shaped conformation of each monomer. The TM domains form a hydrophobic pore of approximately 24 Å long, and 2 Å in diameter, which is inconsistent with canonical Ca2+ selective channels. Phosphorylation, however, enhances the conformational dynamics of the cytoplasmic region of PLN, causing the partial unwinding of the amphipathic helix. We propose that PLN oligomers act as storage for active monomers, keeping SERCA function within a physiological window.

Simple and Fast Method for Fabrication of Endoscopic Implantable Sensor Arrays

Tahirbegi, I. Bogachan; Alvira, Margarita; Mir, Mònica; Samitier, Josep
Fonte: MDPI Publicador: MDPI
Tipo: Artigo de Revista Científica
Publicado em 26/06/2014 EN
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Here we have developed a simple method for the fabrication of disposable implantable all-solid-state ion-selective electrodes (ISE) in an array format without using complex fabrication equipment or clean room facilities. The electrodes were designed in a needle shape instead of planar electrodes for a full contact with the tissue. The needle-shape platform comprises 12 metallic pins which were functionalized with conductive inks and ISE membranes. The modified microelectrodes were characterized with cyclic voltammetry, scanning electron microscope (SEM), and optical interferometry. The surface area and roughness factor of each microelectrode were determined and reproducible values were obtained for all the microelectrodes on the array. In this work, the microelectrodes were modified with membranes for the detection of pH and nitrate ions to prove the reliability of the fabricated sensor array platform adapted to an endoscope.

Fluorescent Analysis of the Cell-Selective Alzheimer's Disease Aβ Peptide Surface Membrane Binding: Influence of Membrane Components

Simakova, Olga; Arispe, Nelson J.
Fonte: SAGE-Hindawi Access to Research Publicador: SAGE-Hindawi Access to Research
Tipo: Artigo de Revista Científica
Publicado em 08/06/2011 EN
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We performed a fluorescent analysis of the binding of Aβ to the surface membrane of different types of cells lines such as PC12, GT1-7, and ex vivo neurons. Analyses were performed on sorted cells with membrane bound Aβ Competitive binding between Aβ phosphatidyl serine- (PtdSer-) specific binder annexin V and an anti-PtdSer antibody provided compelling data confirming the involvement of PtdSer as one of the surface membrane signal molecules for Aβ. We found that populations of cells that exhibited high surface membrane binding affinity for Aβ also show higher membrane cholesterol levels compared to cells that did not bind Aβ. This direct relationship was upheld in cholesterol-enriched or cholesterol-depleted cell membranes. We conclude that the initial process for the cell-selective binding by Aβ, to later conversion of elemental Aβ units into larger structures such as fibrils or to the potentially toxic ion channel aggregates, is highly influenced by the membrane content of PtdSer and cholesterol in the cell surface membrane.

Construcció de sensors electroquímics amb el nou ionofòr tetronasina i aplicació en estratègies analítiques avançades

Calvo Boluda, Daniel
Fonte: Bellaterra : Universitat Autònoma de Barcelona, Publicador: Bellaterra : Universitat Autònoma de Barcelona,
Tipo: Tesis i dissertacions electròniques; info:eu-repo/semantics/doctoralThesis Formato: application/pdf
Publicado em //2007 CAT; CAT
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Consultable des del TDX; Títol obtingut de la portada digitalitzada; L'interès que hi ha per trobar elèctrodes selectius d'ions (ISE) de millors característiques i el fet que l'antibiòtic tetronasina presenta uns equilibris d'intercanvi iònic en solució molt ràpids ens va fer plantejar l'ús d'aquest antibiòtic com a element electroactiu en ISE. La primera part de la investigació realitzada va correspondre a la construcció i avaluació de la resposta d'ISE basats en l'antibiòtic tetronasina per la detecció de l'ió sodi. A priori, aquest ió va ser el primer candidat degut a que els equilibris més ràpids en dissolució es devien a aquest ió. Es va replantejar l'ió principal pels ISE basats en tetronasina desprès de fer un exhaustiu estudi d'interferències, obtenint una resposta pel l'íó calci més gran que per l'ió sodi. El següent pas va ser construir ISE de calci i caracteritzar-los. La formulació òptima de la membrana selectiva d'ió calci emprava un 1% d'ionòfor, 0.2% d'additiu aniònic, 66% oNPOE i 33% PVC. La caracterització per aquests sensors va mostrar una resposta anormalment alta, del doble del predit per la llei de Nernst per ions divalents (65mV/dècada) a pH=5.0. Per la caracterització dels sensors desenvolupats i l'estudi del mecanisme de resposta també es va utilitzar la tècnica de la espectroscòpia electroquímica d'impedàncies. L'estudi de les característiques resistives de les membranes en el rang entre 50KHz-0.05Hz va confirmar l'elecció de la membrana selectiva òptima. El diagrama de Nyquist d'aquesta membrana en contacte amb una solució de CaCl2 10-3M mostrava un únic semicercle corresponent a la resistència oferida per la membrana (resistivitat<700 KOhms·cm) i a la capacitat (98 pF). L'ISE de millors característiques es va utilitzar per construir diferents eines analítiques avançades. La primera aplicació proposada va ser la de construir una llengua electrònica (LE)...

Cation binding at the air-water interface by macromolecules bearing pendant crown ethers moieties

Gold, Jeffrey; Teegarden, David; McGrane, Kathleen; Luca, David; Falcigno, Pasquale; Chen, Cindy; Smith, Thomas
Fonte: American Chemical Society: Journal of the American Chemical Society Publicador: American Chemical Society: Journal of the American Chemical Society
Tipo: Abstract Formato: 31371 bytes; application/pdf
EN_US
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In solution, the ion-binding characteristics of crown ethers and macromolecules containing macrocyclic ether moieties have been studied extensively. These ionophores are finding application in membranes, thin film sensors, and ion-selective electrodes. In these devices, interfacial binding equilibria are most pertinent. This paper presents the results of a detailed analysis of the pressure vs. area behavior of Langmuir films of poly(4’-vinylbenzo-18 crown-6), P18C6, spread on pure water and aqueous solutions of alkali metal salts. Our results show that the compression isotherms can be quantitatively related to the nature of the cation in the subphase and its concentration. At the air-water interface, the polymer is in a highly extended conformation and cooperative binding between proximate crown ether groups is precluded. Accordingly, the affinity of the polymer for Li+, Na+, K+, Rb+, and Cs+ at the airsolution interface mirrors that of the monomeric analogue, benzo-18-crown-6, in solution and is inverse to that of P18C6 in solution. Equilibrium binding constants for complexation of P18C6 to K+ at the air-water interface are comparable to those for binding of P18C6 to K+ in aqueous solution.