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Caracterização de novas membranas de titanossilicatos microporosos por ensaios de permeabilidade

Lito, Patrícia Ferreira
Fonte: Universidade de Aveiro Publicador: Universidade de Aveiro
Tipo: Tese de Doutorado
POR
Relevância na Pesquisa
190.30375%
O interesse crescente das membranas inorgânicas deve-se à potencial aplicação em novas áreas de investigação e da indústria, e em alternativa a operações mais convencionais. Em particular, as membranas de titanossilicatos oferecem vantagens importantes sobre as de zeólitos, pois podem ser sintetizadas sem agentes estruturantes orgânicos, para evitar a calcinação subsequente usualmente responsável por defeitos irreversíveis, exibem novas possibilidades de substituição isomórfica da matriz, permitindo um ajuste mais fino das propriedades catalíticas e de adsorção, e são capazes de separar misturas com base em diferenças de afinidade e tamanho molecular (efeito de peneiro). Os objectivos principais deste trabalho foram: i) a caracterização dinâmica de membranas do tipo zeolítico sintetizadas no Laboratório Associado CICECO, realizando-se experiências de permeação com gases puros e misturas; ii) o desenvolvimento e validação de novos modelos para a transferência de massa multicomponente através de membranas porosas pela abordagem de Maxwell-Stefan, tendo em conta os mecanismos específicos encontrados, particularmente a contribuição por difusão superficial; e iii) a modelação dos pontos experimentais medidos...

Channel formation by antiapoptotic protein Bcl-2

Schendel, Sharon L.; Xie, Zhihua; Montal, Myrta Oblatt; Matsuyama, Shigemi; Montal, Mauricio; Reed, John C.
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 13/05/1997 EN
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184.31674%
Bcl-2 is the prototypical member of a large family of apoptosis-regulating proteins, consisting of blockers and promoters of cell death. The three-dimensional structure of a Bcl-2 homologue, Bcl-XL, suggests striking similarity to the pore-forming domains of diphtheria toxin and the bacterial colicins, prompting exploration of whether Bcl-2 is capable of forming pores in lipid membranes. Using chloride efflux from KCl-loaded unilamellar lipid vesicles as an assay, purified recombinant Bcl-2 protein exhibited pore-forming activity with properties similar to those of the bacterial toxins, diphtheria toxin, and colicins, i.e., dependence on low pH and acidic lipid membranes. In contrast, a mutant of Bcl-2 lacking the two core hydrophobic α-helices (helices 5 and 6), predicted to be required for membrane insertion and channel formation, produced only nonspecific effects. In planar lipid bilayers, where detection of single channels is possible, Bcl-2 formed discrete ion-conducting, cation-selective channels, whereas the Bcl-2 (Δh5, 6) mutant did not. The most frequent conductance observed (18 ± 2 pS in 0.5 M KCl at pH 7.4) is consistent with a four-helix bundle structure arising from Bcl-2 dimers. However, larger channel conductances (41 ± 2 pS and 90 ± 10 pS) also were detected with progressively lower occurrence...

A TRP homolog in Saccharomyces cerevisiae forms an intracellular Ca2+-permeable channel in the yeast vacuolar membrane

Palmer, Chris P.; Zhou, Xin-Liang; Lin, Junyu; Loukin, Stephen H.; Kung, Ching; Saimi, Yoshiro
Fonte: The National Academy of Sciences Publicador: The National Academy of Sciences
Tipo: Artigo de Revista Científica
EN
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193.81273%
The molecular identification of ion channels in internal membranes has made scant progress compared with the study of plasma membrane ion channels. We investigated a prominent voltage-dependent, cation-selective, and calcium-activated vacuolar ion conductance of 320 pS (yeast vacuolar conductance, YVC1) in Saccharomyces cerevisiae. Here we report on a gene, the deduced product of which possesses significant homology to the ion channel of the transient receptor potential (TRP) family. By using a combination of gene deletion and re-expression with direct patch clamping of the yeast vacuolar membrane, we show that this yeast TRP-like gene is necessary for the YVC1 conductance. In physiological conditions, tens of micromolar cytoplasmic Ca2+ activates the YVC1 current carried by cations including Ca2+ across the vacuolar membrane. Immunodetection of a tagged YVC1 gene product indicates that YVC1 is primarily localized in the vacuole and not other intracellular membranes. Thus we have identified the YVC1 vacuolar/lysosomal cation-channel gene. This report has implications for the function of TRP channels in other organisms and the possible molecular identification of vacuolar/lysosomal ion channels in other eukaryotes.

Human beta-adrenergic receptors. Simultaneous purification of beta 1- and beta 2-adrenergic-receptor peptides.

Bahouth, S W; Malbon, C C
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 01/12/1987 EN
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197.25445%
Beta-Adrenergic receptors from basal membranes of human placenta were purified from digitonin extracts by sequential rounds of affinity chromatography, hydrophobic chromatography, ion-exchange chromatography and steric-exclusion h.p.l.c. Basal membranes display both beta 1- and beta 2-adrenergic receptors, in the ratio 65:35. Affinity chromatography, hydrophobic chromatography on heptylamine-Sepharose and ion-exchange chromatography on DEAE-Sephacel removed most of the contaminating proteins, and final purification of the receptor to apparent homogeneity was achieved by steric-exclusion h.p.l.c. The purified receptors showed Mr 67000 on SDS/polyacrylamide-gel electrophoresis under reducing conditions. Specific binding of radioligand to the purified beta-adrenergic receptors displayed stereoselectivity, and the agonist competition profiles demonstrated the presence of both beta 1- and beta 2-receptors. By using the subtype-selective ligands CGP-20712A (beta 1-selective) and ICI-118,551 (beta 2-selective), the purified Mr-67000 species was shown to be composed of equivalent amounts of beta 1- and beta 2-adrenergic receptors. Affinity chromatography on Sepharose-alprenolol and sequential elution with 1 microM-CGP-20712A followed by 100 microM(-)-alprenolol permitted beta 1-adrenergic receptors to be resolved from the mixture of beta 1-/beta 2-adrenergic receptors. The pharmacologically distinct human beta 1 and beta 2-adrenergic receptors are shown to be structurally very similar peptides.

Anion, cation, and zwitterion selectivity of phospholemman channel molecules.

Kowdley, G C; Ackerman, S J; Chen, Z; Szabo, G; Jones, L R; Moorman, J R
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /01/1997 EN
Relevância na Pesquisa
195.17566%
Phospholemman (PLM), a 72-amino acid membrane protein with a single transmembrane domain, forms taurine-selective ion channels in lipid bilayers. Because taurine forms zwitterions, a taurine-selective channel might have binding sites for both anions and cations. Here we show that PLM channels indeed allow fluxes of both cations and anions, making instantaneous and voltage-dependent transitions among conformations with drastically different ion selectivity characteristics. This surprising and novel ion channel behavior offers a molecular explanation for selective taurine flux across cell membranes and may explain why molecules in the phospholemman family can induce cation- or anion-selective conductances when expressed in Xenopus oocytes.

The novel anticonvulsant MK-801 binds to the activated state of the N-methyl-D-aspartate receptor in rat brain.

Foster, A. C.; Wong, E. H.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /06/1987 EN
Relevância na Pesquisa
188.9574%
The influence of endogenous and exogenous acidic amino acids on the binding of [3H]-MK-801, a selective, non-competitive antagonist of N-methyl-D-aspartate (NMDA) receptors, has been investigated in rat cerebral cortex crude synaptic membranes (CSM). Removal of endogenous glutamate and aspartate from CSM by repeated washing reduced the affinity of [3H]-MK-801 for its binding site (with no change in the total number of binding sites) and increased NMDA-sensitive L-[3H]-glutamate binding. In washed CSM, competitive NMDA antagonists of the DL-alpha-amino-omega-phosphonocarboxylate series reduced [3H]-MK-801 binding and NMDA-sensitive L-[3H]-glutamate binding, the most active compounds being 2-amino-5-phosphonovalerate (AP5) and 2-amino-7-phosphono-heptanoate (AP7). Exogenous excitatory amino acid agonists enhanced the binding of [3H]-MK-801 to washed CSM by up to 700%. A selective involvement of NMDA receptors in these effects was indicated by the excellent correlation between EC50s for stimulation of [3H]-MK-801 binding and IC50s for inhibition of NMDA-sensitive L-[3H]-glutamate binding in the same membranes. The selective, competitive NMDA receptor antagonist D-AP5 blocked the L-glutamate-induced increase in [3H]-MK-801 binding in a competitive manner with a pA2 value of 6.0. These results seem to reflect a molecular interaction between two distinct components of the NMDA receptor complex: the transmitter recognition site and the site through which MK-801 exerts its antagonist effects...

The Effect of Valinomycin on Potassium and Sodium Permeability of HK and LK Sheep Red Cells

Tosteson, Daniel C.; Cook, P.; Andreoli, Thomas; Tieffenberg, M.
Fonte: The Rockefeller University Press Publicador: The Rockefeller University Press
Tipo: Artigo de Revista Científica
Publicado em 01/12/1967 EN
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189.46363%
A cyclic depsipeptide antibiotic, valinomycin, was found to produce increased selective permeability of the plasma membranes of HK and LK sheep red blood cells to potassium but not to sodium ions. The compound had relatively little effect on the active extrusion of sodium from HK sheep red blood cells or on the Na + K-stimulated ATPase activity of membranes derived from these cells. It is proposed that the selective cation permeability produced by this compound depends primarily on steric factors, particularly the relationship between the diameter of the ring and the effective diameter of the ion. The significance of these results for the problem of the mechanism of ionic selectivity in natural membranes is discussed.

Lytic Agents, Cell Permeability, and Monolayer Penetrability

Salton, M. R. J.
Fonte: The Rockefeller University Press Publicador: The Rockefeller University Press
Tipo: Artigo de Revista Científica
Publicado em 01/07/1968 EN
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187.70938%
Cell lysis induced by lytic agents is the terminal phase of a series of events leading to membrane disorganization and breadkdown with the release of cellular macromolecules. Permeability changes following exposure to lytic systems may range from selective effects on ion fluxes to gross membrane damage and cell leakage. Lysis can be conceived as an interfacial phenomenon, and the action of surface-active agents on erythrocytes has provided a model in which to investigate relationships between hemolysis and chemical structure, ionic charge, surface tension lowering, and ability to penetrate monolayers of membrane lipid components. Evidence suggests that lysis follows the attainment of surface pressures exceeding a "critical collapse" level and could involve membrane cholesterol or phospholipid. Similarities of chemical composition of membranes from various cell types could account for lytic responses observed on interaction with surface-active agents. Cell membranes usually contain about 20–30 % lipid and 50–75 % protein. One or two major phospholipids are present in all cell membranes, but sterols are not detectable in bacterial membranes other than those of the Mycoplasma group. The rigid cell wall in bacteria has an important bearing on their response to treatment with lytic agents. Removal of the wall renders the protoplast membrane sensitive to rapid lysis with surfactants. Isolated membranes of erythrocytes and bacteria are rapidly dissociated by surface-active agents. Products of dissociation of bacterial membranes have uniform behavior in the ultracentrifuge (sedimentation coefficients 2–3S). Dissociation of membrane proteins from lipids and the isolation and characterization of these proteins will provide a basis for investigating the specificity of interaction of lytic agents with biomembranes.

Flexibility of an Active Center in Sodium-Plus-Potassium Adenosine Triphosphatase

Post, R. L.; Kume, S.; Tobin, T.; Orcutt, B.; Sen, A. K.
Fonte: The Rockefeller University Press Publicador: The Rockefeller University Press
Tipo: Artigo de Revista Científica
Publicado em 01/07/1969 EN
Relevância na Pesquisa
189.32645%
In plasma membranes of intact cells an enzymatic pump actively transports sodium ions inward and potassium ions outward. In preparations of broken membranes it appears as an adenosine triphosphatase dependent on magnesium, sodium, and potassium ions together. In this adenosine triphosphatase a phosphorylated intermediate is formed from adenosine triphosphate in the presence of sodium ions and is hydrolyzed with the addition of potassium ions. The normal intermediate was not split by adenosine diphosphate. However, selective poisoning by N-ethylmaleimide or partial inhibition by a low magnesium ion concentration yielded an intermediate split by adenosine diphosphate and insensitive to potassium ions. Pulse experiments on the native enzyme supported further a hypothesis of a sequence of phosphorylated forms, the first being made reversibly from adenosine triphosphate in the presence of sodium ion and the second being made irreversiblyfrom the first and hydrolyzed in the presence of potassium ion. The cardioactive steriod inhibitor, ouabain, appeared to combine preferentially with the second form. Phosphorylation was at the same active site according to electrophoretic patterns of proteolytic phosphorylated fragments of both reactive forms. It is concluded that there is a conformational change in the active center for phosphorylation during the normal reaction sequence. This change may be linked to one required theoretically for active translocation of ions across the cell membrane.

Block of neuronal fast chloride channels by internal tetraethylammonium ions

Fonte: The Rockefeller University Press Publicador: The Rockefeller University Press
Tipo: Artigo de Revista Científica
Publicado em 01/07/1994 EN
Relevância na Pesquisa
188.36%
The classical potassium-selective ion channel blocker tetraethylammonium ion (TEA) was shown to block chloride-selective ion channels from excised surface membranes of acutely dissociated rat cortical neurons when applied to the formerly intracellular membrane surface. The patch voltage clamp method was used to record single channel currents from fast Cl channels in the presence of TEAi. At the filtering cut-off frequencies used (3-12.4 kHz, -3 dB) the TEAi-induced block appeared as a reduction in single channel current amplitude, which was interpreted as the result of extremely fast on the off rates for the blocking reaction. Under the conditions of these experiments, the magnitude of TEAi block was independent of membrane potential. Analysis of dose-response experimental results suggests that TEA binding resulted in a partial block of these channels with an equilibrium dissociation constant of approximately 12-15 mM. Analysis of amplitude distributions in the absence and presence of TEAi using the method of Yellen (1994. Journal of General Physiology. 84:157-186.) produced a similar equilibrium dissociation constant and provided a blocking rate constant of approximately 16,000 mM-1.s-1 and an unblocking rate constant of approximately 200...

Crystal structure of a concentrative nucleoside transporter from Vibrio cholerae at 2.4 Å

Johnson, Zachary Lee; Cheong, Cheom-Gil; Lee, Seok-Yong
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 11/03/2012 EN
Relevância na Pesquisa
194.58371%
Nucleosides are required for DNA and RNA synthesis, and the nucleoside adenosine plays a role in a variety of signaling processes 1,2. Transporting nucleosides across cell membranes provides the major source of nucleosides in many cell types and is also responsible for the termination of adenosine signaling. Due to their hydrophilic nature, nucleosides require a specialized class of integral membrane proteins, known as nucleoside transporters (NTs), for specific transport across cell membranes. In addition to nucleosides, NTs are important determinants for the transport of nucleoside-derived drugs across cell membranes 3–5. A wide range of nucleoside-derived drugs has been shown to depend, at least in part, on NTs for transport across cell membranes including anticancer drugs (e.g., Ara-C and gemcitabine) and antiviral drugs (e.g., AZT and ribavirin) 4,6–13. Concentrative nucleoside transporters (CNTs), members of the solute carrier transporter superfamily SLC28, use an ion gradient to actively transport nucleosides as well as nucleoside-derived drugs against their chemical gradients. The structural basis for selective ion-coupled nucleoside transport by CNTs is unknown. Here we present the crystal structure of a concentrative nucleoside transporter from Vibrio cholerae in complex with uridine at 2.4 Å. Our functional data show that the transporter utilizes a sodium gradient for nucleoside transport like its human orthologs. The structure reveals the overall architecture of this class of transporter...

Glutamate Receptors in Plants

DAVENPORT, ROMOLA
Fonte: Oxford University Press Publicador: Oxford University Press
Tipo: Artigo de Revista Científica
Publicado em /11/2002 EN
Relevância na Pesquisa
190.82959%
Ionotropic glutamate receptors function in animals as glutamate‐gated non‐selective cation channels. Numerous glutamate receptor‐like (GLR) genes have been identified in plant genomes, and plant GLRs are predicted, on the basis of sequence homology, to retain ligand‐binding and ion channel activity. Non‐selective cation channels are ubiquitous in plant membranes and may function in nutrient uptake, signalling and intra‐plant transport. However, there is little evidence for amino acid gating of plant ion channels. Recent evidence suggests that plant GLRs do encode non‐selective cation channels, but that these channels are not gated by amino acids. The functional properties of these proteins and their roles in plant physiology remain a mystery. The problems surrounding characterization and assignation of function to plant GLRs are discussed in this Botanical Briefing, and potential roles for GLR proteins as non‐selective cation channels involved in metabolic signalling are described.

Fabrication of Two-Dimensional Photonic Crystals in AlGaInP/GaInP Membranes by Inductively Coupled Plasma Etching

Chen, A.; Chua, Soo-Jin; Wang, B.; Fitzgerald, Eugene A.
Fonte: MIT - Massachusetts Institute of Technology Publicador: MIT - Massachusetts Institute of Technology
Tipo: Artigo de Revista Científica Formato: 1826863 bytes; application/pdf
EN
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267.662%
The fabrication process of two-dimensional photonic crystals in an AlGaInP/GaInP multi-quantum-well membrane structure is developed. The process includes high resolution electron-beam lithography, pattern transfer into SiO₂ etch mask by reactive ion etching, pattern transfer through AlGaInP/GaInP layer by inductively coupled plasma (ICP) etching and a selective undercut wet etch to create the freestanding membrane. The chlorine-based ICP etching conditions are optimized to achieve a vertical sidewall. The photonic crystal structures with periods of a=160-480nm are produced.; Singapore-MIT Alliance (SMA)

Supramolecular architectures for neural prostheses

Theogarajan, Luke Satish Kumar
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 230 leaves
ENG
Relevância na Pesquisa
188.36%
Neural prosthetic devices offer a means of restoring function that have been lost due to neural damage. The first part of this thesis investigates the design of a 15-channel, low-power, fully implantable stimulator chip. The chip is powered wirelessly and receives wireless commands. The chip features a CMOS only ASK detector, a single-differential converter based on a novel feedback loop, a low-power adaptive bandwidth DLL and 15 programmable current sources that can be controlled via four commands. Though it is feasible to build an implantable stimulator chip, the amount of power required to stimulate more than 16 channels is prohibitively large. Clearly, there is a need for a fundamentally different approach. The ultimate challenge is to design a self-sufficient neural interface. The ideal device will lend itself to seamless integration with the existing neural architecture. This necessitates that communication with the neural tissue should be performed via chemical rather than electrical messages. However, catastrophic destruction of neural tissue due to the release of large quantities of a neuroactive species, like neurotransmitters, precludes the storage of quantities large enough to suffice for the lifetime of the device. The ideal device then should actively sequester the chemical species from the body and release it upon receiving appropriate triggers in a power efficient manner. This thesis proposes the use of ionic gradients...

Ion channels induced in lipid bilayers by subvirion particles of the nonenveloped mammalian reoviruses.

Tosteson, M T; Nibert, M L; Fields, B N
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 15/11/1993 EN
Relevância na Pesquisa
267.662%
Mechanisms by which nonenveloped viruses penetrate cell membranes as an early step in infection are not well understood. Current ideas about the mode for cytosolic penetration by nonenveloped viruses include (i) formation of a membrane-spanning pore through which viral components enter the cell and (ii) local breakdown of the cellular membrane to provide direct access of infecting virus to the cell's interior. Here we report that of the three viral particles of nonenveloped mammalian reoviruses: virions, infectious subvirion particles, and cores (the last two forms generated from intact reovirus virions by proteolysis), only the infectious subvirion particles induced the formation of anion-selective, multisized channels in planar lipid bilayers under the experimental conditions used in this study. The value for the smallest size conductance varied depending on the lipid composition of the bilayer between 90 pS (Asolectin) and 300 pS (phosphatidylethanolamine:phosphatidylserine) and was found to be voltage independent. These findings are consistent with a proposal that the proteolytically activated infectious subviral particles mediate the interaction between virus and the lipid bilayer of a cell membrane during penetration. In addition...

Preparation and characterization of polymeric microspheres for Cr(VI) extraction

Valenzuela, F.; Marchese, José; Basualto Flores, Carlos Alfonso; Illanes, C.; Ochoa, N. A.
Fonte: ELSEVIER Publicador: ELSEVIER
Tipo: Artículo de revista
EN
Relevância na Pesquisa
267.662%
Microspheres (MS) from different polymers were prepared using two routes. Route A: process of phase inversion with solutions of polysulfone (PSf) in dichloromethane (DCM) and polyvinylpyrrolidone (PVP) as additive. Different weight ratios of PSf-PVP were used in the MS preparation. Route B: MS were obtained by cross-linking in emulsion using a commercial silicone as raw material. The obtained MS were analysed according to their morphological-structural characteristics and in relation to their Cr(VI) extraction capacity using impregnated MS with Aliquat 336. The results obtained showed that MS prepared with PSf-PVP have both less specific surfaces and relative porosities when the proportion of PVP in the mixture is increased. Extraction tests of ion Cr(VI) indicated that synthesized MS have adequate structural characteristics and interesting adsorptive properties which give rise to impregnating selective extractants. Impregnated microspheres with Aliquat 336 prepared from 2:1 PSf-PVP ratio achieved the highest Cr(VI) extractive performance (92% of Cr extraction for contact time of 60 min) and the best breakthrough point in column tests (up to 10 It in the first cycle).

Loss of pH Control in Plasmodium falciparum Parasites Subjected to Oxidative Stress

van Schalkwyk, Donelly A.; Saliba, Kevin J.; Biagini, Giancarlo A.; Bray, Patrick G.; Kirk, Kiaran
Fonte: Public Library of Science Publicador: Public Library of Science
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
267.662%
The intraerythrocytic malaria parasite is susceptible to oxidative stress and this may play a role in the mechanism of action of some antimalarial agents. Here we show that exposure of the intraerythrocytic malaria parasite to the oxidising agent hydrogen peroxide results in a fall in the intracellular ATP level and inhibition of the parasite's V-type H(+)-ATPase, causing a loss of pH control in both the parasite cytosol and the internal digestive vacuole. In contrast to the V-type H(+)-ATPase, the parasite's digestive vacuole H(+)-pyrophosphatase is insensitive to hydrogen peroxide-induced oxidative stress. This work provides insights into the effects of oxidative stress on the intraerythrocytic parasite, as well as providing an alternative possible explanation for a previous report that light-induced oxidative stress causes selective lysis of the parasite's digestive vacuole.; This work was supported by Australian National Health and Medical Research Council Grants 585473 (KJS and KK) and 418055 (KK), the Wellcome Trust (PGB) and the Leverhulme Trust (GAB). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

A model for enhanced and selective transport through biological membranes with alternating pores

Andreucci, D.; Bellaveglia, D.; Cirillo, E. N. M.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 28/02/2014
Relevância na Pesquisa
267.662%
We investigate the outflux of ions through the channels in a cell membrane. The channels undergo an open/close cycle according to a periodic schedule. Our study is based both on theoretical considerations relying on homogenization theory, and on Monte Carlo numerical simulations. We examine the onset of a limiting boundary behavior characterized by a constant ratio between the outflux and the local density, in the thermodynamics limit. The focus here is on the issue of selectivity, that is on the different behavior of the ion currents through the channel in the cases of the selected and non-selected species.; Comment: arXiv admin note: text overlap with arXiv:1307.4180

Electro-osmotic actuation for micropump applications

O'Brien, Sean
Fonte: Rochester Instituto de Tecnologia Publicador: Rochester Instituto de Tecnologia
Tipo: Tese de Doutorado
EN_US
Relevância na Pesquisa
184.9804%
An electro-osmotic actuation mechanism is explored for micropump applications where self contained, low power, miniaturized pumps are necessary. The principle of electro-osmosis through a cation selective membrane is used to develop a differential pressure which is used to deflect a pump membrane. In an electro-osmotic cell, there are electrolyte filled chambers on either side of an ion specific membrane. Hydrated cations migrate in an applied electric field, effectively pulling water molecules to the cathodic chamber. In such a setup, the polarity of the current can be periodically reversed causing the chambers to alternately fill and discharge. Since the chemical reactions are reversible, an operating window can be defined so that the electrodes do not degrade and gas bubbles do not form. Using data from the characterization of an ion specific membrane such as Nafion, design parameters were developed that could be used to build and operate a micropump using standard MEMS based fabrication and packaging technology. The design is compatible with a silicon substrate which could contain fluidic channels and chambers. Upper layers could be fabricated using laser cut plastic, Nafion membranes and elastomeric membranes. Characterization of the materials was done with an acrylic test cell that could be disassembled and reused [1]. Recommendations for the miniaturization and integration of the micropump were developed. Measurements of Nafion water transport properties were used to determine operating current requirements. Recommendations for the minimization of energy consumption is provided as related to chamber geometry. Possible explanations for anomalous effects observed during experimentation were explored through simulation.

Gravisensing: Ionic responses, cytoskeleton and amyloplast behaviour

Stomgren Allen, N; Chattaraj, P; Collings, David; Johannes, Eva
Fonte: Pergamon-Elsevier Ltd Publicador: Pergamon-Elsevier Ltd
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
267.662%
In Zea mays L., changes in orientation of stems are perceived by the pulvinal tissue, which responds to the stimulus by differential growth resulting in upward bending of the stem. Gravity is perceived in the bundle sheath cells, which contain amyloplasts that sediment to the new cell base when a change in the gravity vector occurs. The mechanism by which the mechanical signal is transduced into a physiological response is so far unknown for any gravity perceiving tissue. It is hypothesized that this involves interactions of amyloplasts with the plasma membrane and/or ER via cytoskeletal elements. To gain further insights into this process we monitored amyloplast movements in response to gravistimulation. In a pharmacological approach we investigated how the dynamics of plastid sedimentation are affected by actin and microtubule (MT) disrupting drugs. Dark grown caulonemal filaments of the moss Physcomitrella patens respond to gravity vector changes with a reorientation of tip growth away from the gravity vector. MT distributions in tip cells were monitored over time and MTs were seen to accumulate preferentially on the lower flank of the tip 30 min after a 90° turn. Using a self-referencing Ca2+ selective ion probe, we found that growing caulonemal filaments exhibit a Ca2+ influx at the apical dome...