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Desenvolvimento de membranas e filmes auto-suportados a partir da polianilina : síntense, caracterização e aplicação; Development of membrane and freestanding film as of polyaniline : synthesis, characterization and application

Müller, Franciélli; Ferreira, Carlos Arthur; Amado, Franco Dani Rico; Rodrigues, Marco Antonio Siqueira
Fonte: Universidade Federal do Rio Grande do Sul Publicador: Universidade Federal do Rio Grande do Sul
Tipo: Artigo de Revista Científica Formato: application/pdf
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Polímeros condutores são uma nova classe de polímeros que tem recebido especial interesse para a produção de membranas e filmes. A polianilina (PANI) destaca-se entre eles por sua elevada estabilidade química, fácil polimerização e baixo custo. O objetivo deste trabalho foi desenvolver uma blenda de polímero convencional (HIPS) com polímero condutor (PANI-CSA) e um filme de polianilina auto-suportado, usando ácido canforsulfônico (CSA) como dopante primário e 4-cloro-3-metil fenol (CMC) como dopante secundário. Estes dois materiais foram empregados como membranas íon-seletivas em um sistema de eletrodiálise para remoção de níquel de soluções. A membrana e o filme foram caracterizados por condutividade elétrica, MEV, espectroscopia FTIR, Raman e TGA. Os resultados obtidos apontam para a possibilidade de aplicação da membrana seletiva para eletrodiálise. A extração de níquel para a membrana sintetizada se mostrou semelhante à extração para a membrana comercial. O filme auto-suportado apesar de exibir boa resistência mecânica no estado sólido apresentou comportamento pouco satisfatório quando colocado em imersão com a solução de trabalho para eletrodiálise, devido ao seu estado quebradiço.; Conducting polymers are a new class of polymers that has received particular interest for the production of membranes and films. The polyaniline (PANI) is distinguished among conducting polymers for its high chemical stability...

Caracterização química e atividade biológica de peptídeos presentes na peçonha do escorpião brasileiro Opisthacanthus cayaporum

Camargos, Thalita Soares
Fonte: Universidade de Brasília Publicador: Universidade de Brasília
Tipo: Dissertação
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Dissertação (mestrado)—Universidade de Brasília, Faculdade de Ciências da Saúde, 2009.; A peçonha de escorpiões é conhecida por ser uma complexa mistura de moléculas capazes de exercer as mais diversas funções. As mais estudadas são as que atuam em canais iônicos, especialmente nos canais seletivos aos íons Na+ e K+, os responsáveis pela transmissão da informação nervosa. Além dessas moléculas, existe uma família de peptídeos sem pontes dissulfeto, chamados de NDBP (Non Dissulfide Brigded Peptides), que podem agir como formadores de poros em membranas, como antimicrobianos e citolíticos, e/ou potencializadores de bradicinina. O presente trabalho demonstra a riqueza de moléculas presentes na peçonha do escorpião brasileiro Opisthacanthus cayaporum. A caracterização de uma molécula bloqueadora de canal para K+, membro da família das κ-KTx, sistematicamente chamada de κ-KTx2.5, mostrou que esta molécula forma α-hélices em ambiente hidrofílico e é capaz de bloquear canais de K+ dos subtipos hKV1.1 e 1.4. As sequências parciais de uma molécula da família das Escorpinas e de um NDBP também são descritas no presente trabalho. __________________________________________________________________________________________ ABSTRACT; Scorpions venom is a rich source of molecules with variable functions. The most studied are those that act on ion channels...

Development of a K(+)-channel probe and its use for identification of an intracellular plant membrane K+ channel.

Mi, F; Berkowitz, G A
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 11/04/1995 EN
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Polyclonal antibodies were generated against a 9-amino acid, synthetic peptide corresponding to the selectivity filter in the pore region of K(+)-channel proteins. The sequence of amino acids in the ion-conducting pore region of K+ channels is the only highly conserved region of members of this protein family. The objectives of the present work were (i) to determine whether the anti-channel pore peptide antibody was immunoreactive with known K(+)-channel proteins and (ii) to demonstrate the usefulness of the antibody by employing it to identify a newly discovered K(+)-channel protein. Anti-channel pore peptide was immunoreactive with various K(+)-channel subtypes native to a number of different species. Immunoblot analysis demonstrated affinity of the antibody for the drk1, maxi-K, and KAT1 K(+)-channel proteins. Studies also suggested that the anti-channel pore peptide antibody did not immunoreact with membrane proteins other than K+ channels. The anti-channel pore peptide antibody was used to establish the identity of a 62-kDa chloroplast inner envelope polypeptide as a putative component of a K(+)-channel protein. It was concluded that an antibody generated against the conserved pore region/selectivity filter of K+ channels has broad but selective affinity for this class of proteins. This K(+)-channel probe may be a useful tool for identification of K(+)-channel proteins in native membranes.

N-methyl-D-aspartate receptor plasticity in kindling: quantitative and qualitative alterations in the N-methyl-D-aspartate receptor-channel complex.

Yeh, G C; Bonhaus, D W; Nadler, J V; McNamara, J O
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /10/1989 EN
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Kindling is an animal model of epilepsy and neuronal plasticity produced by periodic electrical stimulation of the brain. Electrophysiologic studies indicate that this phenomenon is associated with increased participation of N-methyl-D-aspartate (NMDA) receptors in excitatory synaptic transmission. Biochemical studies suggest that a change intrinsic to the NMDA receptor-channel complex may contribute to the increase in NMDA receptor-mediated synaptic transmission. We tested this idea by measuring the binding of 3-[(+)-2-(carboxypiperazin-4-yl)][1,2-3H]propyl-1-phosphonic acid ([3H]CPP), [3H]glycine, and tritiated N-[(1-thienyl)cyclohexyl]piperidine [( 3H]TCP) to rat hippocampal membranes. In this preparation these ligands are selective for the NMDA receptor, the strychnine-insensitive glycine receptor, and the NMDA receptor-gated ion channel, respectively. Kindling increased the density of CPP, glycine, and TCP binding sites in hippocampal membranes by 47%, 42%, and 25%, respectively. No significant changes were detected in the affinity of these binding sites. Surprisingly, alterations in the glycine binding site were detected in animals sacrificed 1 month but not 1 day after the final kindling stimulation. Thus, delayed upregulation of the NMDA receptor-channel complex may be one molecular mechanism that maintains the long-lasting hyperexcitability of hippocampal neurons in kindled animals.

A monoclonal immunotoxin acting on the Na+ channel, with properties similar to those of a scorpion toxin.

Barhanin, J; Meiri, H; Romey, G; Pauron, D; Lazdunski, M
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /03/1985 EN
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We describe the properties of a monoclonal antibody against the Na+ channel. The antibody, 72.38, competitively inhibited (Ki = 1.5 X 10(-9) M) the binding of an 125I-labeled toxin from the Brazilian scorpion Tityus serrulatus (125I-TiTX gamma) to Na+ channels of rat brain membranes. No significant inhibition of binding of a number of other Na+ channel toxins was observed. The inhibition of 125I-TiTX gamma binding also was observed with the solubilized Na+ channel from rat brain membranes (Ki = 2 X 10(-9) M). Antibody 72.38 antagonized 125I-TiTX gamma binding to Na+ channels from different animal species (fish, avian, and mammalian) and from different tissues (electroplax, brain, heart, and muscle). Moreover, 72.38 has been used for immunofluorescence labeling of Na+ channels in rat sciatic nodes of Ranvier and cultured dorsal root ganglion cells. Electrophysiological experiments on rat muscle cells fully confirmed the similarity between TiTX gamma and 72.38 seen in binding experiments. Both produce slow oscillations of the membrane potential accompanied by bursts of action potentials which are due to a selective action on the Na+ channel. TiTX gamma and 72.38 are without effect on the ion selectivity of the Na+ channel, but they both drastically change the voltage-dependence of activation and inactivation of the Na+ channel.

Equilibrium Potentials of Membrane Electrodes

Wang, Jui H.; Copeland, Eva
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /07/1973 EN
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A simple thermodynamic theory of the equilibrium potentials of membrane electrodes is formulated and applied to the glass electrode for measurement of pH. The new formulation assumes the selective adsorption or binding of specific ions on the surface of the membrane which may or may not be permeable to the ion, and includes the conventional derivation based on reversible ion transport across membranes as a special case. To test the theory, a platinum wire was coated with a mixture of stearic acid and methyl-tri-n-octyl-ammonium stearate. When this coated electrode was immersed in aqueous phosphate solution, its potential was found to be a linear function of pH from pH 2 to 12 with a slope equal to the theoretical value of 59.0 mV per pH unit at 24°.

Phospholipase C-delta1 and oxytocin receptor signalling: evidence of its role as an effector.

Park, E S; Won, J H; Han, K J; Suh, P G; Ryu, S H; Lee, H S; Yun, H Y; Kwon, N S; Baek, K J
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 01/04/1998 EN
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Although the oxytocin receptor modulates intracellular Ca2+ ion levels in myometrium, the identities of signal molecules have not been clearly clarified. Our previous studies on oxytocin receptor signalling demonstrated that 80 kDa Ghalpha is a signal mediator [Baek, Kwon, Lee, Kim, Muralidhar and Im (1996) Biochem. J. 315, 739-744]. To elucidate the effector in the oxytocin receptor signalling pathway, we evaluated the oxytocin-mediated activation of phospholipase C (PLC) by using solubilized membranes from human myometrium and a three-component preparation containing the oxytocin receptor-Ghalpha-PLC-delta1 complex. PLC-delta1 activity in the three-component preparation, as well as PLC activity in solubilized membranes, was increased by oxytocin in the presence of Ca2+ and activated Ghalpha (GTP-bound Ghalpha). Furthermore the stimulated PLC-delta1 activity resulting from activation of Ghalpha via the oxytocin receptor was significantly attenuated by the selective oxytocin antagonist desGly-NH2d(CH2)5[Tyr(Me)2,Thr4]ornithine vasotocin or GDP. Consistent with these observations, co-immunoprecipitation and co-immunoadsorption of PLC-delta1 in the three-component preparation by anti-Gh7alpha antibody resulted in the PLC-delta1 being tightly coupled to activated Ghalpha on stimulation of the oxytocin receptor. These results indicate that PLC-delta1 is the effector for Ghalpha-mediated oxytocin receptor signalling.

Flux, coupling, and selectivity in ionic channels of one conformation.

Chen, D P; Eisenberg, R S
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /08/1993 EN
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Ions crossing biological membranes are described as a concentration of charge flowing through a selective open channel of one conformation and analyzed by a combination of Poisson and Nernst-Planck equations and boundary conditions, called the PNP theory for short. The ion fluxes in this theory interact much as ion fluxes interact in biological channels and mediated transporters, provided the theoretical channel contains permanent charge and has selectivity created by (electro-chemical) resistance at its ends. Interaction occurs because the flux of different ionic species depends on the same electric field. That electric field is a variable, changing with experimental conditions because the screening (i.e., shielding) of the permanent charge within the channel changes with experimental conditions. For example, the screening of charge and the shape of the electric field depend on the concentration of all ionic species on both sides of the channel. As experimental interventions vary the screening, the electric field varies, and thus the flux of each ionic species varies conjointly, and is, in that sense, coupled. Interdependence and interaction are the rule, independence is the exception, in this channel.

Binding constants of Li+, K+, and Tl+ in the gramicidin channel determined from water permeability measurements.

Dani, J A; Levitt, D G
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /08/1981 EN
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In an open circuit there can be no net cation flux through membranes containing only cation-selective channels, because electroneutrality must be maintained. If the channels are so narrow that water and cations cannot pass by each other, then the net water flux through those "single-file" channels that contain a cation is zero. It is therefore possible to determine the cation binding constants from the decrease in the average water permeability per channel as the cation concentration in the solution is increased. Three different methods were used to determine the osmotic water permeability of gramicidin channels in lipid bilayer membranes. The osmotic water permeability coefficient per gramicidin channel in the absence of cations was found to be 6 x 10(-14) cm3/s. As the cation concentration was raised, the water permeability decreased and a binding constant was determined from a quantitative fit to the data. When the data were fitted assuming a maximum of one ion per channel, the dissociation constant was 115 mM for Li+, 69 mM for K+, and 2 mM for Tl+.

Functional Na+ Channels in Cell Adhesion probed by Transistor Recording

Schmidtner, Markus; Fromherz, Peter
Fonte: Biophysical Society Publicador: Biophysical Society
Tipo: Artigo de Revista Científica
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Cell membranes in a tissue are in close contact to each other, embedded in the extracellular matrix. Standard electrophysiological methods are not able to characterize ion channels under these conditions. Here we consider the area of cell adhesion on a solid substrate as a model system. We used HEK 293 cells cultured on fibronectin and studied the activation of NaV1.4 sodium channels in the adherent membrane with field-effect transistors in a silicon substrate. Under voltage clamp, we compared the transistor response with the whole-cell current. We observed that the extracellular voltage in the cell-chip contact was proportional to the total membrane current. The relation was calibrated by alternating-current stimulation. We found that Na+ channels are present in the area of cell adhesion on fibronectin with a functionality and a density that is indistinguishable from the free membrane. The experiment provides a basis for studying selective accumulation and depletion of ion channels in cell adhesion and also for a development of cell-based biosensoric devices and neuroelectronic systems.

STUDIES ON THE ELIMINATION OF DYES IN THE GASTRIC AND PANCREATIC SECRETIONS, AND INFERENCES THEREFROM CONCERNING THE MECHANISMS OF SECRETION OF ACID AND BASE

Ingraham, Raymond C.; Visscher, Maurice B.
Fonte: The Rockefeller University Press Publicador: The Rockefeller University Press
Tipo: Artigo de Revista Científica
Publicado em 20/05/1935 EN
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1. All dyes appearing in gastric juice after intravenous injection in the dog are characterized by having their chromogen in the electropositive ion under suitable conditions. 2. All dyes eliminated in pancreatic juice ionize with the chromogen electronegative under proper circumstances. 3. The amphoteric characteristics of certain dyestuffs, as well as the changes in charge associated with reversible reduction in others, have been taken into consideration, and the lack of success of previous investigators in finding a common characteristic of dyes secreted by the gastric glands differentiating them from those secreted by the pancreas, has been shown to have been due to failure to take these potentialities of the dyestuffs into account. 4. Several possible hypotheses concerning the mechanism of selectivity to dyestuffs have been considered. Differences in distribution in acid, neutral, and alkaline phases will not account for selective secretion without postulating also specific membrane permeability. It is pointed out that the theory most thoroughly in accord with all the facts observed is based upon the pore concept. To restrain electronegative dyes by polar adsorption, the pores of the membranes of the gastric glands would have to be positively charged. Such pores would constitute an electrostatic filter...

Polycystin-2 cation channel function in the human syncytiotrophoblast is regulated by microtubular structures

Montalbetti, Nicolás; Li, Qiang; Wu, Yuliang; Chen, Xing-Zhen; Cantiello, Horacio F
Fonte: Blackwell Science Inc Publicador: Blackwell Science Inc
Tipo: Artigo de Revista Científica
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Polycystin-2 (PC2), encoded by PKD2, which is one of the genes whose mutations cause polycystic kidney disease, is abundantly produced in the apical domain of the syncytiotrophoblast (hST) of term human placenta. PC2, a TRP-type (TRPP2) non-selective cation channel, is present in primary cilia of renal epithelial cells, a microtubule-based ancillary structure with sensory function. The hST has abundant cytoskeletal structures, and actin filament dynamics regulate PC2 channel function in this epithelium. However, it is expected that the apical hST excludes microtubular structures. Here, we demonstrated by Western blot and immunocytochemical analyses that hST apical vesicles indeed contain microtubule structural components, including tubulin isoforms, acetylated α-tubulin, and the kinesin motor proteins KIF3A and KIF3B. PC2 and tubulin were substantially colocalized in hST vesicles. Treatment of hST vesicles with either the microtubular disrupter colchicine (15 μm) or the microtubular stabilizer paclitaxel (taxol, 15 μm) resulted in distinct patterns of microtubular re-organization and PC2 redistribution. We also observed that changes in microtubular dynamics regulate PC2 channel function. Addition of colchicine rapidly inhibited PC2 channel activity in lipid-bilayer reconstituted hST membranes. Addition of either tubulin and GTP...

Characterization of the basolateral membrane conductance of Necturus urinary bladder

Fonte: The Rockefeller University Press Publicador: The Rockefeller University Press
Tipo: Artigo de Revista Científica
Publicado em 01/04/1987 EN
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Necturus urinary bladders stripped of serosal muscle and connective tissue were impaled through their basolateral membranes with microelectrodes in experiments that permitted rapid changes in the ion composition of the serosal solution. The transepithelial electrical properties exhibited a marked seasonal variation that could be attributed to variations in the conductance of the shunt pathway, apical membrane selectivity, and basolateral Na+ transport. In contrast, the passive electrical properties of the basolateral membrane remained constant throughout the year. The apparent transference numbers (Ti) of the basolateral membrane for K+ and Cl- were determined from the effect on the basolateral membrane equivalent electromotive force of a sudden increase in the serosal K+ concentration from 2.5 to 50 mM/liter or a decrease in the Cl- concentration from 101 to 10 mM/liter. TK and TCl were 0.71 +/- 0.05 and 0.04 +/- 0.01, respectively. The basolateral K+ conductance could be blocked by Ba2+ (0.5 mM), Cs+ (10 mM), or Rb+ (10 mM), but was unaffected by 3,4- diaminopyridine (100 microM), decamethonium (100 microM), or tetraethylammonium (10 mM). We conclude that a highly selective K+ conductance dominates the electrical properties of the basolateral membrane and that this conductance is different from those found in nerve and muscle membranes.

Developments in the Field of Conducting and Non-conducting Polymer Based Potentiometric Membrane Sensors for Ions Over the Past Decade

Faridbod, Farnoush; Ganjali, Mohammad Reza; Dinarvand, Rassoul; Norouzi, Parviz
Fonte: Molecular Diversity Preservation International (MDPI) Publicador: Molecular Diversity Preservation International (MDPI)
Tipo: Artigo de Revista Científica
Publicado em 03/04/2008 EN
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Many research studies have been conducted on the use of conjugated polymers in the construction of chemical sensors including potentiometric, conductometric and amperometric sensors or biosensors over the last decade. The induction of conductivity on conjugated polymers by treating them with suitable oxidizing agents won Heeger, MacDiarmid and Shirakawa the 2000 Nobel Prize in Chemistry. Common conjugated polymers are poly(acetylene)s, poly(pyrrole)s, poly(thiophene)s, poly(terthiophene)s, poly(aniline)s, poly(fluorine)s, poly(3-alkylthiophene)s, polytetrathiafulvalenes, poly-napthalenes, poly(p-phenylene sulfide), poly(p-phenylenevinylene)s, poly(3,4-ethylene-dioxythiophene), polyparaphenylene, polyazulene, polyparaphenylene sulfide, poly-carbazole and polydiaminonaphthalene. More than 60 sensors for inorganic cations and anions with different characteristics based on conducting polymers have been reported. There have also been reports on the application of non-conducting polymers (nCPs), i.e. PVC, in the construction of potentiometric membrane sensors for determination of more than 60 inorganic cations and anions. However, the leakage of ionophores from the membranes based on these polymers leads to relatively lower life times. In this article...

Effect of Diaminopropionic acid (Dap) on the Biophysical Properties of a Modified Synthetic Channel-Forming Peptide

Bukovnik, Urska; Sala-Rabanal, Monica; Francis, Simonne; Frazier, Shawnalea J.; Schultz, Bruce D.; Nichols, Colin G.; Tomich, John M.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
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Channel replacement therapy, based on synthetic channel-forming peptides (CFPs) with the ability to supersede defective endogenous ion channels, is a novel treatment modality that may augment existing interventions against multiple diseases. Previously, we derived CFPs from the second transmembrane segment of the α-subunit of the glycine receptor, M2GlyR, which forms chloride-selective channels in its native form. The best candidate, NK4-M2GlyR T19R, S22W (p22-T19R, S22W), was water-soluble, incorporated into cell membranes and was non-immunogenic, but lacked the structural properties for high conductance and anion selectivity when assembled into a pore. Further studies suggested that the threonine residues at positions 13, 17 and 20 line the pore of assembled p22-T19R, S22W, and here we used 2, 3-diaminopropionic acid (Dap) substitutions to introduce positive charges to the pore-lining interface of the predicted p22-T19R, S22W channel. Dap-substituted p22-T19R, S22W peptides retained the α-helical secondary structure characteristic of their parent peptide, and induced short-circuit transepithelial currents when exposed to the apical membrane of Madin-Darby canine kidney (MDCK) cells; the sequences containing multiple Dap-substituted residues induced larger currents than the peptides with single or no Dap-substitutions. To gain further insights into the effects of Dap residues on the properties of the putative pore...

mTORC2 regulates renal tubule sodium uptake by promoting ENaC activity

Gleason, Catherine E.; Frindt, Gustavo; Cheng, Chih-Jen; Ng, Michael; Kidwai, Atif; Lang, Florian; Baum, Michel; Palmer, Lawrence G.; Pearce, David; Rashmi, Priyanka
Fonte: American Society for Clinical Investigation Publicador: American Society for Clinical Investigation
Tipo: Artigo de Revista Científica
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The epithelial Na+ channel (ENaC) is essential for Na+ homeostasis, and dysregulation of this channel underlies many forms of hypertension. Recent studies suggest that mTOR regulates phosphorylation and activation of serum/glucocorticoid regulated kinase 1 (SGK1), which is known to inhibit ENaC internalization and degradation; however, it is not clear whether mTOR contributes to the regulation of renal tubule ion transport. Here, we evaluated the effect of selective mTOR inhibitors on kidney tubule Na+ and K+ transport in WT and Sgk1–/– mice, as well as in isolated collecting tubules. We found that 2 structurally distinct competitive inhibitors (PP242 and AZD8055), both of which prevent all mTOR-dependent phosphorylation, including that of SGK1, caused substantial natriuresis, but not kaliuresis, in WT mice, which indicates that mTOR preferentially influences ENaC function. PP242 also substantially inhibited Na+ currents in isolated perfused cortical collecting tubules. Accordingly, patch clamp studies on cortical tubule apical membranes revealed that mTOR inhibition markedly reduces ENaC activity, but does not alter activity of K+ inwardly rectifying channels (ROMK channels). Together, these results demonstrate that mTOR regulates kidney tubule ion handling and suggest that mTOR regulates Na+ homeostasis through SGK1-dependent modulation of ENaC activity.

ZnO Nanostructure-Based Intracellular Sensor

Asif, Muhammad H.; Danielsson, Bengt; Willander, Magnus
Fonte: MDPI Publicador: MDPI
Tipo: Artigo de Revista Científica
Publicado em 21/05/2015 EN
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Recently ZnO has attracted much interest because of its usefulness for intracellular measurements of biochemical species by using its semiconducting, electrochemical, catalytic properties and for being biosafe and biocompatible. ZnO thus has a wide range of applications in optoelectronics, intracellular nanosensors, transducers, energy conversion and medical sciences. This review relates specifically to intracellular electrochemical (glucose and free metal ion) biosensors based on functionalized zinc oxide nanowires/nanorods. For intracellular measurements, the ZnO nanowires/nanorods were grown on the tip of a borosilicate glass capillary (0.7 µm in diameter) and functionalized with membranes or enzymes to produce intracellular selective metal ion or glucose sensors. Successful intracellular measurements were carried out using ZnO nanowires/nanorods grown on small tips for glucose and free metal ions using two types of cells, human fat cells and frog oocytes. The sensors in this study were used to detect real-time changes of metal ions and glucose across human fat cells and frog cells using changes in the electrochemical potential at the interface of the intracellular micro-environment. Such devices are helpful in explaining various intracellular processes involving ions and glucose.

Characterization and regulation of a chloride channel from bovine tracheal epithelium.

Duszyk, M; Liu, D; Kamosinska, B; French, A S; Man, S F
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 15/11/1995 EN
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1. The patch-clamp technique was used to characterize chloride channels from the apical membranes of bovine tracheal epithelial cells. Application of GTP gamma S or NaF to excised patches revealed the existence of a novel type of Cl- channel regulated by G-proteins in a membrane-delimited manner. 2. The channel had a linear current-voltage relationship, with a conductance of 100-120 pS. Its open probability was independent of voltage. 3. The channel was highly anion selective (permeability ratio, PNa/PCl = 0.06 +/- 0.04) and had the halide permeability sequence: I- > Br- > or = Cl- > F-, corresponding to the Eisenman I sequence. This suggested that neither ionic size nor diffusion rate determined ion permeation through the channel. 4. The mole fraction behaviour was studied using fluoride and chloride ions. Mixtures of ions produced currents that would be expected from the linear combination of the two ions acting independently, indicating relatively simple permeation through the pore and compatible with a single ion binding site. 5. The channel was inhibited by the stilbene disulphonates SITS (4-acetamido-4'-isothiocyanatostilbene-2, 2'-disulphonic acid) and DNDS (4,4'-dinitrostilbene-2,2'-sulphonic acid). SITS introduced voltage dependence to channel gating and indicated the possible involvement of lysine residues in the channel permeation pathway. 6. NaF was unable to activate Cl- channels in the presence of the aluminum chelator...

A planar lipid bilayer in an electric field: membrane instability, flow field and electrical impedance

Ziebert, Falko; Lacoste, David
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 22/02/2011
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For many biotechnological applications it would be useful to better understand the effects produced by electric fields on lipid membranes. This review discusses several aspects of the electrostatic properties of a planar lipid membrane with its surrounding electrolyte in a normal DC or AC electric field. In the planar geometry, the analysis of electrokinetic equations can be carried out quite far, allowing to characterize analytically the steady state and the dynamics of the charge accumulation in the Debye layers, which results from the application of the electric field. For a conductive membrane in an applied DC electric field, we characterize the corrections to the elastic moduli, the appearance of a membrane undulation instability and the associated flows which are built up near the membrane. For a membrane in an applied AC electric field, we analytically derive the impedance from the underlying electrokinetic equations. We discuss different relevant effects due to the membrane conductivity or due to the bulk diffusion coefficients of the ions. Of particular interest is the case where the membrane has selective conductivity for only one type of ion. These results, and future extensions thereof, should be useful for the interpretation of impedance spectroscopy data used to characterize e.g. ion channels embedded in planar bilayers.; Comment: 33 pages...

Developing germanium on nothing (GON) nanowire arrays

Thomas, Paul
Fonte: Rochester Instituto de Tecnologia Publicador: Rochester Instituto de Tecnologia
Tipo: Tese de Doutorado
EN_US
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Advanced crystal growth techniques enable novel devices and circuit designs to further scale and integrate heterogeneous structures for CMOS, MEMS/NEMS, and optoelectronic applications. In particular, nanowires (NW) are among the promising structures derived from these developments. Research has demonstrated the utility of NWs as a channel material for gate-all-around transistors, high sensitivity biological/chemical sensors, photodetectors, as well as a whole spectrum of LEDs and lasers. However, NW based devices are not without their fabrication challenges. Relatively simple structures for CMOS or MEMS/NEMS processes are difficult to reproduce when many NW based devices rely on a dropcast process. This thesis demonstrates a method for producing Germanium on Nothing (GON) NW arrays on a Si substrate that forgoes dropcasting and, instead, creates NWs via selective material removal methods commonly utilized by industry. GON NW arrays are formed through the sequential use of E-beam lithography, selective wet chemical etching, and reactive ion etching. Global oxide thinning in BOE leaves a thin masking layer that protects the underlying Si, preventing etching in a TMAH solution. GON regions are defined by E-beam lithography and are subject to a RIE which creates release points in the remaining SiO2. Unmasked Si is then etched by a TMAH solution...