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Síntese e análise da sílica mesoporosa SBA-15 para incorporação de moléculas; Synthesis and analysis of mesoporous silica SBA-15 for incorporation of molecules

Garcia, Paulo Ricardo de Abreu Furtado
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 24/03/2015 PT
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Neste trabalho estudou-se a encapsulação de proteínas com diferentes pesos moleculares na sílica mesoporosa ordenada SBA-15 para avaliar sua aplicação como adjuvante imunológico. Para tanto, as proteínas IgG (150 kDa) e BSA (66,5 kDa) foram incorporadas à sílica mesoporosa com poros expandidos. Primeiramente estudou-se a dilatação dos poros utilizando-se um agente dilatador de estrutura no processo de síntese, através da preparação de amostras com diferentes quantidades de triisopropilbenzeno (TIPB). Resultados de isoterma de adsorção de nitrogênio (NAI) e espalhamento de raios X a baixo ângulo (SAXS) revelaram um aumento no diâmetro médio de poros da ordem de 23% e uma rede de poros mais desordenada. Para se ter uma estimativa das dimensões das proteínas, medidas de SAXS foram feitas e indicaram que ambas têm dimensões que permitiriam sua incorporação nos poros da SBA-15. As amostras com poros dilatados foram então utilizadas para a incorporação das proteínas IgG e BSA em solução tampão fosfato salina (PBS). Os resultados indicaram o preenchimento dos microporos pela solução de PBS com valor superior a 95%. Quanto ao preenchimento de mesoporos, observou-se maior variação no volume de poros e área superficial...

Can sieve-element plastids in Panicum maximum (Poaceae) leaves act in the blockage of injured sieve-tube elements?

Sousa Paiva, Elder Antonio; Machado, Silvia Rodrigues
Fonte: Elsevier Gmbh, Urban & Fischer Verlag Publicador: Elsevier Gmbh, Urban & Fischer Verlag
Tipo: Artigo de Revista Científica Formato: 327-331
ENG
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The ultrastructural features and the plastid changes caused by sample preparation were studied in sieve elements of Panicum maximum leaves. Samples of expanded leaves, taken near the ligule region, were fixed and processed by common light and transmission electron microscopy methods. In mature sieve-tube elements, the protoplast is electron-translucent and plastids are the most frequent organelles. Mitochondria and smooth endoplasmic reticulum segments are also visible and occupy a parietal position within the cell. The plastids are globular and show electron-dense proteinaceous inclusions in the stroma. The protein crystals are predominantly cuneate, but thin crystalloids and amorphous and/or filamentous proteins also occur. The presence of intact plastids plus others in different phases of plastid envelope rupture were interpreted as evidence that this rupture is a normal event in response to injury. This plastid envelope rupture is possibly activated by the release of pressure in the sieve-tube element. After plastid membrane vesiculation, the stroma and the protein crystals are dispersed within the sieve-element ground cytoplasm. The vesicles originating from the plastid envelope move to one cell pole, while protein crystalloids move to the opposite pole and agglomerate in the sieve-plate region. Our findings indicate that these protein crystalloids...

Matéria-prima da formação Corumbataí na região do pólo cerâmico de Santa Gertrudes, SP, com características naturais para fabricação de argila expandida

Moreno, M. M. T.; Zanardo, A.; Rocha, R. R.; Roveri, C. D.
Fonte: Associação Brasileira de Cerâmica Publicador: Associação Brasileira de Cerâmica
Tipo: Artigo de Revista Científica Formato: 342-348
POR
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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); Estudou-se um material da base da Formação Corumbataí, proveniente de uma mineração de argila, que apresenta restrições de uso em cerâmica devido à sua dureza e, principalmente, ao alto conteúdo de matéria orgânica. Verificou-se que o material apresenta características naturais ótimas para a fabricação de argila expandida diretamente a partir de fragmentos de rocha, mostrando comportamento piroplástico com expansão significativa se submetido à queima rápida. A caracterização da matéria-prima e do produto foi realizada mediante análise de carbono orgânico, difração de raios X, microscopia ótica e testes de queima. Foram determinadas as condições de queima para obter argila expandida utilizando forno de queima rápida e forno a rolos, ambos de laboratório, obtendo corpos com densidade variável (que podem chegar a valores menores que 0,5 g.cm-3) até o limite de expansão. Esta densidade é obtida devido à formação de poros fechados e uma película externa vítrea, que proporcionam uma resistência mecânica alta aos fragmentos expandidos.; This paper refers to the study of the material of the base of the Corumbataí formation (Parana Basin...

Anindobothrium n. gen. (Eucestoda : Tetraphyllidea) inhabiting marine and freshwater potamotrygonid stingrays

Marques, FPL; Brooks, D. R.; Lasso, C. A.
Fonte: Amer Soc Parasitologists Publicador: Amer Soc Parasitologists
Tipo: Artigo de Revista Científica Formato: 666-672
ENG
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Anindobothrium n. gen. is proposed to accommodate Caulobothrium anacolum inhabiting Himanturu schmardae from Colombia, and 2 new species, one inhabiting Potamotrygon orbigny in Brazil and the other inhabiting Paratrygon aereiba in Venezuela. Members of the new genus resemble members of Pararhinebothroides, Rhinebothroides, and Anthocephalum by having bothridia with poorly differentiated apical suckers and vasa deferentia expanded into external seminal vesicles. It further resembles Pararhinebothroides, Rhinebothroides, and Anthocephalum cairae by having vas deferens inserted near the poral rather than aporal end of the cirrus sac. The 3 species assigned to the new genus form an apparent monophyletic group, based on the possession of 3 putative synapomorphies: (1) genital pores in the anterior 1/4 of the proglottid, a trait that is unusual, but not unique, among phyllobothriids; (2) anteroventral ovarian lobes converging to the center of the proglottid, a character not previously reported for phyllobothriids; and (3) ovarian lobes comprising a loose network of digitiform processes.

Concentration of alpha-lactalbumin from cow milk whey through expanded bed adsorption using a hydrophobic resin

Conrado,L. S.; Veredas,V.; Nóbrega,E. S.; Santana,C. C.
Fonte: Brazilian Society of Chemical Engineering Publicador: Brazilian Society of Chemical Engineering
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/12/2005 EN
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The design of novel applications for the use of new high-density adsorbents in the direct recovery of proteins requires analysis of the fluid dynamics and mass transfer characteristics of the column used with the solid-liquid system. In this article we describe the operating parameters related to the use of a high-density, hydrophobic resin (Streamline® Phenyl) for the recovery of alpha-lactalbumin from cow milk whey in an expanded-bed adsorption mode of operation. The adsorption isotherm, kinetic curves and chromatographic curves for adsorption and elution were determined for alpha-lactalbumin recovered from whole whey. The experiments were used to confirm the theoretical model that involves the combination of resistance to the mass transfer in the liquid phase and diffusivity in the adsorbent resin pores. The model solution was obtained through the orthogonal collocation method. A nonlinear multivariable optimization method was used to fit the model to experimental results. A purity of 79% was obtained with the adsorption/elution protocol prior to any polishing procedure.

Low-temperature plasma nitriding of sintered PIM 316L austenitic stainless steel

Mendes,Aércio Fernando; Scheuer,Cristiano José; Joanidis,Ioanis Labhardt; Cardoso,Rodrigo Perito; Mafra,Márcio; Klein,Aloísio Nelmo; Brunatto,Silvio Francisco
Fonte: ABM, ABC, ABPol Publicador: ABM, ABC, ABPol
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/08/2014 EN
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This work reports experimental results on sintered PIM 316L stainless steel low-temperature plasma nitriding. The effect of treatment temperature and time on process kinetics, microstructure and surface characteristics of the nitrided samples were investigated. Nitriding was carried out at temperatures of 350, 380, 410 and 440 ºC , and times of 4, 8 and 16 h, using a gas mixture composed by 60% N2 + 20% H2 + 20% Ar, at a gas flow rate of 5.00 × 10-6 Nm³s-1, and a pressure of 800 Pa. The treated samples were characterized by scanning electron microscopy, X-ray diffractometry and microhardness measurements. Results indicate that low-temperature plasma nitriding is a diffusion controlled process. The calculated activation energy for nitrided layer growth was 111.4 kJmol-1. Apparently precipitation-free layers were produced in this study. It was also observed that the higher the treatment temperature and time the higher is the obtained surface hardness. Hardness up to 1343 HV0.025 was verified for samples nitrided at 440 ºC. Finally, the characterization of the treated surface indicates the formation of cracks, which were observed in regions adjacent to the original pores after the treatment.

Changes in ionic selectivity with changes in density of water in gels and cells

Wiggins, Philippa M.; van Ryn, René T.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /09/1990 EN
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Gels equilibrated with aqueous solutions of impermeant solutes reached a steady state in which, in the absence of a pressure difference, the activity of water in the pores of the gel was higher than that of water in the external solution. The chemical potential of water in the gel/polymer solution slurry was higher than that in the supernatant polymer solution removed from the gel. Water in the pores of the gel decreased in density to 0.96 as increasing osmotic stress was applied. It is argued that at constant temperature and pressure water can equilibrate between two compartments of unequal osmolality only by adjusting its molar volume. Experiments showed that when gel water had a higher activity than external water it was K+ selective; when it had a lower activity it was Na+ selective. It is proposed that a continuous spectrum of water structures can exist in these two compartment systems from dense, reactive, weakly-bonded water which selects highly hydrated ions, to expanded, stretched, unreactive, viscous water which is strongly hydrogen bonded and selects K+ and univalent anions. These findings are related to the state and properties of cytoplasmic water which is probably held under osmotic stress by the activity of the sodium pump.

Mechanism and kinetics of pore formation in membranes by water-soluble amphipathic peptides

Lee, Ming-Tao; Hung, Wei-Chin; Chen, Fang-Yu; Huang, Huey W.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
EN
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How antimicrobial peptides form pores in membranes is of interest as a fundamental membrane process. However, the underlying molecular mechanism, which has potential applications in therapeutics, nonviral gene transfer, and drug delivery, has been in dispute. We have resolved this mechanism by observing the time-dependent process of pore formation in individual giant unilamellar vesicles (GUVs) exposed to a melittin solution. An individual GUV first expanded its surface area at constant volume and then suddenly reversed to expanding its volume at constant area. The area expansion, the volume expansion, and the point of reversal all match the results of equilibrium measurements performed on peptide–lipid mixtures. The mechanism includes a negative feedback that makes peptide-induced pores stable with a well defined size, contrary to the suggestion that peptides disintegrate the membrane in a detergent-like manner.

Morphological Comparison and Taxonomic Utility of Copulatory Structures of Selected Nematode Species

Rammah, Abdallah; Hirschmann, Hedwig
Fonte: Society of Nematologists Publicador: Society of Nematologists
Tipo: Artigo de Revista Científica
Publicado em /07/1987 EN
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Spicules of 9 Meloidogyne, 2 Heterodera, 3 Globodera, and 12 other plant-parasitic, insect-parasitic, and free-living nematodes were excised and examined using scanning electron microscopy (SEM). Gubernacula of some of the species were also excised, and their structure was determined. The two spicules of all species examined were symmetrically identical in morphology. The spicule typically consisted of three parts: head, shaft, and blade with dorsal and ventral vela. The spicular nerve entered through the cytoplasmic core opening on the lateral outer surface of the spicule head and generally communicated with the exterior through one or two pores at the spicule tip. Spicules of Xiphinema sp. and Aporcelaimellus sp. were not composed of three typical parts, were less sclerotized, and lacked a cytoplasmic core opening and distal pores. Spicules of Aphelenchoides spp. had heads expanded into apex and rostrum and had very arcuate blades with thick dorsal and ventral edges (limbs). Gubernaculum shapes were stable within a species, but differed among species examined. The accessory structures of Hoplolaimus galeatus consisted of a tongue-shaped gubernaculum with two titillae at its distal end and a plate-like capitulum terminating distally in two flat...

Biocompatibility of Synthetic Poly(ester urethane)/Polyhedral Oligomeric Silsesquioxane Matrices with Embryonic Stem Cell Proliferation and Differentiation

Guo, Yan-Lin; Wang, Wenshou; Otaigbe, Joshua U.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /10/2010 EN
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Incorporation of polyhedral oligomeric silsesquioxanes (POSS) into poly (ester urethane)s (PEU) as a building block results in a PEU/POSS hybrid polymer with increased mechanical strength and thermostability. An attractive feature of the new polymer is that it forms a porous matrix when cast in the form of a thin film, making it potentially useful in tissue engineering. In this study, we present detailed microscopic analysis of the PEU/POSS matrix and demonstrate its biocompatibility with cell culture. The PEU/POSS polymer forms a continuous porous matrix with open pores and interconnected grooves. From SEM image analysis, it is calculated that there are about 950 pores per mm2 of the matrix area with pore size ranging from 1 to 15 μm in diameter. The area occupied by the pores represents approximately 7.6 % of matrix area. Using mouse embryonic stem cells (ESCs), we demonstrate that the PEU/POSS matrix provides excellent support for cell proliferation and differentiation. Under the cell culture condition optimized to maintain self-renewal, ESCs grown on a PEU/POSS matrix exhibit undifferentiated morphology, express pluripotency markers, and have similar growth rate to cells grown on gelatin. When induced for differentiation, ESCs underwent dramatic morphological change...

Regulation of Fusion Pore Closure and Compound Exocytosis in Neuroendocrine PC12 Cells by SCAMP1

Zhang, Jie; Castle, David
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
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During exocytosis, neuroendocrine cells can achieve partial release of stored secretory products from dense core vesicles (DCVs) by coupling endocytosis directly at fusion sites and without full discharge. The physiological role of partial secretion is of substantial interest. Much is known about SNARE-mediated initiation of exocytosis and dynamin-mediated completion of endocytosis, but little is known about coupling events. We have used real-time microscopy to examine the role of secretory carrier membrane protein SCAMP1 in exo-endocytic coupling in PC12 cells. While reduced SCAMP1 expression is known to impede dilation of newly opened fusion pores during onset of DCV exocytosis, we now show that SCAMP1 deficiency also inhibits closure of fusion pores after they have opened. Inhibition causes accumulation of fusion figures at the plasma membrane. Closure is recovered by restoring expression and accelerated slightly by overexpression. Interestingly, inhibited pore closure resulting from loss of SCAMP1 appears to increase secondary fusion of DCVs to already-fused DCVs (compound exocytosis). Unexpectedly, reinternalization of expanded DCV membranes following compound exocytosis appears to proceed normally in SCAMP1-deficient cells. SCAMP1’s apparent dual role in facilitating dilation and closure of fusion pores implicates its function in exo-endocytic coupling and in the regulation of partial secretion. Secondarily...

A new remarkable subterranean beetle of the Rhodopes: Paralovricia gen. n. beroni sp. n. belonging to Lovriciina new subtribe (Coleoptera, Carabidae, Trechinae, Bembidiini)

Giachino, Pier Mauro; Guéorguiev, Borislav; Vailati, Dante
Fonte: Pensoft Publishers Publicador: Pensoft Publishers
Tipo: Artigo de Revista Científica
Publicado em 09/07/2011 EN
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Paralovricia gen. n. beroni sp. n., belonging to the new subtribe Lovriciina, is described from two caves in the Western Rhodopes (Bulgaria): Kraypatnata peshtera, near Smilyan Village (Smolyan Municipality) and Snezhanka, near Peshtera Town (Peshtera Municipality). Three currently known genera, Lovricia Pretner, 1979, Neolovricia Lakota, Jalžić & Moravec, 2009 and Paralovricia gen. n. represent a monophyletic unit supported by important synapomorphies that allows to propose the establishment of the new subtribe Lovriciina, characterized by the following characters: last maxillary palpomeres very long and narrow, basal angles of pronotum without seta, elytra without discal setae, elytral umbilicate series of nine pores in which the main pores are the 2nd, 6th and 9th, apical recurrent striole absent and mesotibial apex expanded outward. Its systematic position within the subfamily Trechinae (sensu Lorenz 2005) is discussed and Lovriciina is placed near Anillina. Key to the genera of the subtribe is proposed. Distribution data and zoogeographical hypotheses are discussed.

Methods for Producing Scaffold-Free Engineered Cartilage Sheets from Auricular and Articular Chondrocyte Cell Sources and Attachment to Porous Tantalum

Whitney, G. Adam; Mera, Hisashi; Weidenbecher, Mark; Awadallah, Amad; Mansour, Joseph M.; Dennis, James E.
Fonte: Mary Ann Liebert, Inc. Publicador: Mary Ann Liebert, Inc.
Tipo: Artigo de Revista Científica
Publicado em /08/2012 EN
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Scaffold-free cartilage engineering techniques may provide a simple alternative to traditional methods employing scaffolds. We previously reported auricular chondrocyte-derived constructs for use in an engineered trachea model; however, the construct generation methods were not reported in detail. In this study, methods for cartilage construct generation from auricular and articular cell sources are described in detail, and the resulting constructs are compared for use in a joint resurfacing model. Attachment of cartilage sheets to porous tantalum is also investigated as a potential vehicle for future attachment to subchondral bone. Large scaffold-free cartilage constructs were produced from culture-expanded chondrocytes from skeletally mature rabbits, and redifferentiated in a chemically-defined culture medium. Auricular constructs contained more glycosaminoglycan (39.6±12.7 vs. 9.7±1.9 μg/mg wet weight, mean and standard deviation) and collagen (2.7±0.45 vs. 1.1±0.2 μg/mg wet weight, mean and standard deviation) than articular constructs. Aggregate modulus was also higher for auricular constructs vs. articular constructs (0.23±0.07 vs. 0.12±0.03 MPa, mean and standard deviation). Attachment of constructs to porous tantalum was achieved by neocartilage ingrowth into tantalum pores. These results demonstrate that large scaffold-free neocartilage constructs can be produced from mature culture-expanded chondrocytes in a chemically-defined medium...

Limits of Structural Plasticity in a Picornavirus Capsid Revealed by a Massively Expanded Equine Rhinitis A Virus Particle

Bakker, Saskia E.; Groppelli, Elisabetta; Pearson, Arwen R.; Stockley, Peter G.; Rowlands, David J.; Ranson, Neil A.
Fonte: American Society for Microbiology Publicador: American Society for Microbiology
Tipo: Artigo de Revista Científica
Publicado em /06/2014 EN
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The Picornaviridae family of small, nonenveloped viruses includes major pathogens of humans and animals. They have positive-sense, single-stranded RNA genomes, and the mechanism(s) by which these genomes are introduced into cells to initiate infection remains poorly understood. The structures of presumed uncoating intermediate particles of several picornaviruses show limited expansion and some increased porosity compared to the mature virions. Here, we present the cryo-electron microscopy structure of native equine rhinitis A virus (ERAV), together with the structure of a massively expanded ERAV particle, each at ∼17–Å resolution. The expanded structure has large pores on the particle 3-fold axes and has lost the RNA genome and the capsid protein VP4. The expanded structure thus illustrates both the limits of structural plasticity in such capsids and a plausible route by which genomic RNA might exit.

Porosity and distribution of water in perlite from the island of Milos, Greece

Kaufhold, Stephan; Reese, Anke; Schwiebacher, Werner; Dohrmann, Reiner; Grathoff, Georg H; Warr, Laurence N; Halisch, Matthias; Müller, Cornelia; Schwarz-Schampera, Ulrich; Ufer, Kristian
Fonte: Springer International Publishing Publicador: Springer International Publishing
Tipo: Artigo de Revista Científica
Publicado em 12/10/2014 EN
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A perlite sample representative of an operating mine in Milos was investigated with respect to the type and spatial distribution of water. A set of different methods was used which finally provided a consistent view on the water at least in this perlite. Infrared spectroscopy showed the presence of different water species (molecular water and hydroxyl groups / strongly bound water). The presence of more than 0.5 mass% smectite, however, could be excluded considering the cation exchange capacity results. The dehydration measured by thermal analysis occurred over a wide range of temperatures hence confirming the infrared spectroscopical results. Both methods point to the existence of a continuous spectrum of water binding energies. The spatial distribution of water and/or pores was investigated using different methods (CT: computer tomography, FIB: scanning electron microscopy including focused ion beam technology, IRM: infrared microscopy). Computer tomography (CT) showed large macropores (20 – 100 μm) and additionally revealed a mottled microstructure of the silicate matrix with low density areas up to a few μm in diameter. Scanning electron microscopy (FIB) confirmed the presence of μm sized pores and IRM showed the filling of these pores with water. In summary...

Isolation of an Asymmetric RNA Uncoating Intermediate for a Single-Stranded RNA Plant Virus

Bakker, Saskia E.; Ford, Robert J.; Barker, Amy M.; Robottom, Janice; Saunders, Keith; Pearson, Arwen R.; Ranson, Neil A.; Stockley, Peter G.
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
Publicado em 16/03/2012 EN
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We have determined the three-dimensional structures of both native and expanded forms of turnip crinkle virus (TCV), using cryo-electron microscopy, which allows direct visualization of the encapsidated single-stranded RNA and coat protein (CP) N-terminal regions not seen in the high-resolution X-ray structure of the virion. The expanded form, which is a putative disassembly intermediate during infection, arises from a separation of the capsid-forming domains of the CP subunits. Capsid expansion leads to the formation of pores that could allow exit of the viral RNA. A subset of the CP N-terminal regions becomes proteolytically accessible in the expanded form, although the RNA remains inaccessible to nuclease. Sedimentation velocity assays suggest that the expanded state is metastable and that expansion is not fully reversible. Proteolytically cleaved CP subunits dissociate from the capsid, presumably leading to increased electrostatic repulsion within the viral RNA. Consistent with this idea, electron microscopy images show that proteolysis introduces asymmetry into the TCV capsid and allows initial extrusion of the genome from a defined site. The apparent formation of polysomes in wheat germ extracts suggests that subsequent uncoating is linked to translation. The implication is that the viral RNA and its capsid play multiple roles during primary infections...

Efficiency of a Multi-Soil-Layering System on Wastewater Treatment Using Environment-Friendly Filter Materials

Ho, Chia-Chun; Wang, Pei-Hao
Fonte: MDPI Publicador: MDPI
Tipo: Artigo de Revista Científica
EN
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The multi-soil-layering (MSL) system primarily comprises two parts, specifically, the soil mixture layer (SML) and the permeable layer (PL). In Japan, zeolite is typically used as the permeable layer material. In the present study, zeolite was substituted with comparatively cheaper and more environmentally friendly materials, such as expanded clay aggregates, oyster shells, and already-used granular activated carbon collected from water purification plants. A series of indoor tests indicated that the suspended solid (SS) removal efficiency of granular activated carbon was between 76.2% and 94.6%; zeolite and expanded clay aggregates achieved similar efficiencies that were between 53.7% and 87.4%, and oyster shells presented the lowest efficiency that was between 29.8% and 61.8%. Further results show that the oyster shell system required an increase of wastewater retention time by 2 to 4 times that of the zeolite system to maintain similar chemical oxygen demand (COD) removal efficiency. Among the four MSL samples, the zeolite system and granular activated carbon system demonstrated a stable NH3-N removal performance at 92.3%–99.8%. The expanded clay aggregate system present lower removal performance because of its low adsorption capacity and excessively large pores...

Fusion pore expansion is a slow, discontinuous, and Ca2+-dependent process regulating secretion from alveolar type II cells

Haller, Thomas; Dietl, Paul; Pfaller, Kristian; Frick, Manfred; Mair, Norbert; Paulmichl, Markus; Hess, Michael W.; Fürst, Johannes; Maly, Karl
Fonte: The Rockefeller University Press Publicador: The Rockefeller University Press
Tipo: Artigo de Revista Científica
Publicado em 15/10/2001 EN
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In alveolar type II cells, the release of surfactant is considerably delayed after the formation of exocytotic fusion pores, suggesting that content dispersal may be limited by fusion pore diameter and subject to regulation at a postfusion level. To address this issue, we used confocal FRAP and N-(3-triethylammoniumpropyl)-4-(4-[dibutylamino]styryl) pyridinium dibromide (FM 1-43), a dye yielding intense localized fluorescence of surfactant when entering the vesicle lumen through the fusion pore (Haller, T., J. Ortmayr, F. Friedrich, H. Volkl, and P. Dietl. 1998. Proc. Natl. Acad. Sci. USA. 95:1579–1584). Thus, we have been able to monitor the dynamics of individual fusion pores up to hours in intact cells, and to calculate pore diameters using a diffusion model derived from Fick's law. After formation, fusion pores were arrested in a state impeding the release of vesicle contents, and expanded at irregular times thereafter. The expansion rate of initial pores and the probability of late expansions were increased by elevation of the cytoplasmic Ca2+ concentration. Consistently, content release correlated with the occurrence of Ca2+ oscillations in ATP-treated cells, and expanded fusion pores were detectable by EM. This study supports a new concept in exocytosis...

Expansion and apparent fluidity decrease of nuclear membranes induced by low Ca/Mg. Modulation of nuclear membrane lipid fluidity by the membrane-associated nuclear matrix proteins?

Fonte: The Rockefeller University Press Publicador: The Rockefeller University Press
Tipo: Artigo de Revista Científica
Publicado em 01/11/1978 EN
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Macronuclei isolated from Tetrahymena are contracted in form (average diameter: 10.2 micron) at a final Ca/Mg (3:2)concentration of 5 mM. Lowering the ion concentration to 1 mM induces an expansion of the average nuclear diameter to 12.2 micron. Both contracted and expanded nuclei are surrounded by a largely intact nuclear envelope as revealed by thin-sectioning electron microscopy. Nuclear swelling is accompanied by an expansion of the nuclear envelope as indicated by the decrease in the frequency of nuclear pore complexes from 52.6 to 42.1 pores/micron2 determined by freeze-etch electron microscopy. Contracted nuclear membranes reveal particle-devoid areas (average size: 0.21 micron2) on 59% of their fracture faces at the optimal growth temperature of 28 degrees C. About three-fifths of the number of these smooth areas disappear upon nuclear membrane expansion. Electron spin resonance using 5-doxylstearic acid as a spin label indicates a higher lipid fluidity in contracted than in expa,ded nuclear membranes. Moreover, a thermotropic lipid clustering occurs at approximately 17 degrees C only in expanded nuclear membranes. In contrast to the nuclear membrane- bound lipids, free lipids extracted from the nuclei rigidify with increasing Ca/Mg concentrations. Our findings are compatible with the view that the peripheral layer of the fundamental nuclear protein- framework...

Understanding water permeation in graphene oxide membranes

Wei, Ning; Peng, Xinsheng; Xu, Zhiping
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 05/02/2014
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Water transport through graphene-derived membranes has gained much interest recently due to its promising potential in filtration and separation applications. In this work, we explore water permeation in graphene oxide membranes using atomistic simulations, by considering flow through interlayer gallery, expanded pores such as wrinkles of interedge spaces, and pores within the sheet. We find that although flow enhancement can be established by nanoconfinement, fast water transport through pristine graphene channels is prohibited by a prominent side-pinning effect from capillaries formed between oxidized regions. We then discuss flow enhancement in situations according to several recent experiments. These understandings are finally integrated into a complete picture to understand water permeation through the layer-by-layer and porous microstructure and could guide rational design of functional membranes for energy and environmental applications.; Comment: arXiv admin note: text overlap with arXiv:1308.5367