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1

Cell fractionation.  

PubMed

Proteins within a cell are localized into specific cellular compartments, allowing compartmentalization of distinct tasks. If we consider lipid bilayers as compartments, then gram-negative bacteria such as Pseudomonas aeruginosa can target proteins to five distinct locations: the cytoplasm, the inner membrane, the periplasm, the outer membrane, and the extracellular environment. In this chapter, we describe how the different compartments can be selectively isolated by a combination of centrifugation and disruption techniques. Fractionation of the cells into subcellular compartments enables protein enrichment and is essential to accurately determine the localization of specific proteins, which is the first step towards understanding the function of a protein in the cell. PMID:24818905

Ize, Bérengère; Viarre, Véronique; Voulhoux, Romé

2014-01-01

2

Preparation of membrane fraction from herpes simplex virus-infected cells which induce cytotoxic T lymphocytes.  

PubMed

The immunogenic capacity of herpes simplex virus (HSV)-infected cells and their subcellular membrane fractions was investigated by assessing the anti-HSV cytotoxic T lymphocyte (CTL) response in cultures of spleen lymphocytes from HSV-primed BALB/c mice. Methylchloranthrane-induced fibrosarcoma (Meth A) cells infected with HSV (HSV-Meth A) were fixed either with glutaraldehyde or by heating at 56 C to preserve their immunogenic competence and then used as a stimulator. Microsomes and plasma membranes were prepared from HSV-Meth A and their immunogenic activities were determined. Through the recovery of stimulatory activity in the plasma membrane fraction was half of that in the microsome fraction, the activity in the former was much more stable than in the latter and the plasma membrane fraction proved to be well qualified as an immunogen for anti-HSV CTL induction. Upon purification, the specific activity of the membrane fraction, on the basis of protein concentration, increased 43-fold. PMID:6606107

Hitsumoto, Y; Sonoda, S; Okuyama, M; Miki, Y; Utsumi, S

1983-01-01

3

The post-synthetic sorting of endogenous membrane proteins examined by the simultaneous purification of apical and basolateral plasma membrane fractions from Caco-2 cells.  

PubMed Central

A subcellular fractionation method to isolate simultaneously apical and basolateral plasma membrane fractions from the human adenocarcinoma cell line Caco-2, grown on filter supports, is described. The method employs sucrose-density-gradient centrifugation and differential precipitation. The apical membrane fraction was enriched 14-fold in sucrase-isomaltase and 21-fold in 5'-nucleotidase compared with the homogenate. The basolateral membrane fraction was enriched 20-fold relative to the homogenate in K(+)-stimulated p-nitrophenylphosphatase. Alkaline phosphatase was enriched 15-fold in the apical membrane fraction and 3-fold in the basolateral membrane fraction. Analytical density-gradient centrifugation showed that this enzyme was a true constituent of both fractions, and experiments measuring alkaline phosphatase release following treatment with phosphatidylinositol-specific phospholipase C showed that in both membrane fractions the enzyme was glycosyl-phosphatidylinositol-linked. There was very little contamination of either membrane fraction by marker enzymes of the Golgi complex, mitochondria or lysosomes. Both membrane fractions were greater than 10-fold purified with respect to the endoplasmic reticulum marker enzyme alpha-glucosidase. Protein composition analysis of purified plasma membrane fractions together with domain-specific cell surface biotinylation experiments revealed the presence of both common and unique integral membrane proteins in each plasma membrane domain. The post-synthetic transport of endogenous integral plasma membrane proteins was examined using the devised subcellular fractionation procedure in conjunction with pulse-chase labelling experiments and immunoprecipitation. Five common integral membrane proteins immunoprecipitated by an antiserum raised against a detergent extract of the apical plasma membrane fraction were delivered with the same time course to each cell-surface domain. Images Fig. 1. Fig. 3. Fig. 4. Fig. 5. PMID:1315518

Ellis, J A; Jackman, M R; Luzio, J P

1992-01-01

4

Fraction reduction in membrane systems.  

PubMed

Fraction reduction is a basic computation for rational numbers. P system is a new computing model, while the current methods for fraction reductions are not available in these systems. In this paper, we propose a method of fraction reduction and discuss how to carry it out in cell-like P systems with the membrane structure and the rules with priority designed. During the application of fraction reduction rules, synchronization is guaranteed by arranging some special objects in these rules. Our work contributes to performing the rational computation in P systems since the rational operands can be given in the form of fraction. PMID:24772037

Guo, Ping; Zhang, Hong; Chen, Haizhu; Liu, Ran

2014-01-01

5

Fraction Reduction in Membrane Systems  

PubMed Central

Fraction reduction is a basic computation for rational numbers. P system is a new computing model, while the current methods for fraction reductions are not available in these systems. In this paper, we propose a method of fraction reduction and discuss how to carry it out in cell-like P systems with the membrane structure and the rules with priority designed. During the application of fraction reduction rules, synchronization is guaranteed by arranging some special objects in these rules. Our work contributes to performing the rational computation in P systems since the rational operands can be given in the form of fraction. PMID:24772037

Zhang, Hong

2014-01-01

6

Fractional order models of viscoelasticity as an alternative in the analysis of red blood cell (RBC) membrane mechanics  

PubMed Central

New lumped-element models of red blood cell mechanics can be constructed using fractional order generalizations of springs and dashpots. Such ‘spring-pots’ exhibit a fractional order viscoelastic behavior that captures a wide spectrum of experimental results through power-law expressions in both the time and frequency domains. The system dynamics is fully described by linear fractional order differential equations derived from first order stress–strain relationships using the tools of fractional calculus. Changes in the composition or structure of the membrane are conveniently expressed in the fractional order of the model system. This approach provides a concise way to describe and quantify the biomechanical behavior of membranes, cells and tissues. PMID:20090192

Craiem, Damian; Magin, Richard L

2011-01-01

7

Inhibition of adhesion of Clostridium difficile to human intestinal cells after treatment with serum and intestinal fluid isolated from mice immunized with nontoxigenic C. difficile membrane fraction.  

PubMed

Diarrhea and pseudomembrane colitis caused by Clostridium difficile infection is a global health concern because of the high recurrence rate after standard antibiotic therapy. Vaccination presents a powerful countermeasure against disease recurrence. In this study, mice vaccinated with the nontoxigenic C. difficile membrane fraction generated a marked immune response to the antigen, as demonstrated by the serum IgG and intestinal fluid IgA levels. Significantly, pretreatment with harvested IgG- and IgA-containing fluids was sufficient to prevent in vitro adhesion of C. difficile to human Caco-2 intestinal cells. These results highlight the potential of nontoxigenic C. difficile membrane fraction as a vaccine candidate for C. difficile infection. PMID:25745878

Senoh, Mitsutoshi; Iwaki, Masaaki; Yamamoto, Akihiko; Kato, Haru; Fukuda, Tadashi; Shibayama, Keigo

2015-04-01

8

A novel regulatory mechanism for trimeric GTP-binding proteins in the membrane and secretory granule fractions of human and rodent beta cells.  

PubMed Central

Recently we described roles for heterotrimeric and low-molecular-mass GTP-binding proteins in insulin release from normal rat islets. During these studies, we observed that a protein with an apparent molecular mass (37 kDa) similar to that of the beta subunit of trimeric GTP-binding proteins underwent phosphorylation in each of five classes of insulin-secreting cells. Incubation of the beta cell total membrane fraction or the isolated secretory granule fraction (but not the cytosolic fraction) with [gamma-32P]ATP or [gamma-32P]GTP resulted in the phosphorylation of this protein, which was selectively immunoprecipitated by an anti-serum directed against the common beta subunit of trimeric G-proteins. Disruption of the alpha beta gamma trimer (by pretreatment with either fluoroaluminate or guanosine 5'(-)[gamma-thio]triphosphate) prevented beta subunit phosphorylation. Based on differential sensitivities to pH, heat and the histidine-selective reagent diethyl pyrocarbonate (and reversal of the latter by hydroxylamine), the phosphorylated amino acid was presumptively identified as histidine. Incubation of pure beta subunit alone or in combination with the exogenous purified alpha subunit of transducin did not result in the phosphorylation of the beta subunit, but addition of the islet cell membrane fraction did support this event, suggesting that membrane localization (or a membrane-associated factor) is required for beta subunit phosphorylation. Incubation of phosphorylated beta subunit with G alpha.GDP accelerated the dephosphorylation of the beta subunit, accompanied by the formation of G alpha-GTP. Immunoblotting detected multiple alpha subunits (of Gi, G(o) and Gq) and at least one beta subunit in the secretory granule fraction of normal rat islets and insulinoma cells. These data describe a potential alternative mechanism for the activation of GTP-binding proteins in beta cells which contrasts with the classical receptor-agonist mechanism: G beta undergoes transient phosphorylation at a histidine residue by a GTP-specific protein kinase; this phosphate, in turn, may be transferred via a classical Ping-Pong mechanism to G alpha.GDP (inactive), yielding the active configuration G alpha.GTP in secretory granules (a strategic location to modulate exocytosis). PMID:8546716

Kowluru, A; Seavey, S E; Rhodes, C J; Metz, S A

1996-01-01

9

Identification of SNAP receptors in rat adipose cell membrane fractions and in SNARE complexes co-immunoprecipitated with epitope-tagged N-ethylmaleimide-sensitive fusion protein.  

PubMed

The vesicle-associated membrane proteins [VAMPs; vesicle SNAP receptors (v-SNAREs)] present on GLUT4-enriched vesicles prepared from rat adipose cells [Cain, Trimble and Lienhard (1992) J. Biol. Chem. 267, 11681-11684] have been identified as synaptobrevin 2 (VAMP 2) and cellubrevin (VAMP 3) by using isoform-specific antisera. Additional antisera identify syntaxins 2 and 4 as the predominant target membrane SNAP receptors (t-SNAREs) in the plasma membranes (PM), with syntaxin 3 at one-twentieth the level. Syntaxins 2 and 4 are enriched 5-10-fold in PM compared with low-density microsomes (LDM). Insulin treatment results in an 11-fold increase in immunodetectable GLUT4 in PM and smaller (approx. 2-fold) increases in VAMP 2 and VAMP 3, whereas the subcellular distributions of the syntaxins are not altered by insulin treatment. To determine which of the SNAP receptors (SNAREs) in PM might participate in SNARE complexes with proteins from GLUT4 vesicles, complexes were immunoprecipitated with anti-myc antibody from solubilized membranes after the addition of myc-epitope-tagged N-ethylmaleimide-sensitive fusion protein (NSF) and recombinant alpha-soluble NSF attachment protein (alpha-SNAP). These complexes contain VAMPs 2 and 3 and syntaxin 4, but not syntaxins 2 or 3. Complex formation requires ATP and is disrupted by ATP hydrolysis. When all membrane fractions are prepared from basal cells, few or no VAMPs and no syntaxin 4 are immunoprecipitated in SNARE complexes obtained from LDM alone (or from immunoisolated GLUT4 vesicles). The content of syntaxin 4 depends on the presence of PM, and participation of VAMPs 2 and 3 is enhanced 4-6-fold by the addition of solubilized GLUT4 vesicles to PM. The latter increase is greater than can be explained by the 2-fold higher levels of VAMPs added to the reaction mixture. When all membrane fractions are prepared from insulin-stimulated cells, SNARE complexes formed from PM alone contain similar levels of syntaxin 4 but 5-6-fold higher levels of VAMPs 2 and 3 compared with PM alone from basal cells. Addition of GLUT4 vesicle proteins to PM from insulin-treated cells results in a further 2-fold increase in VAMP 2 recovered in SNARE complexes. Therefore the VAMPs in PM of insulin-treated but not basal cells, and in GLUT4-vesicles from cells in either condition, are in a form that readily forms a SNARE complex with PM t-SNAREs and NSF. Insulin seems to activate PM and/or GLUT4 vesicles so as to increase the efficiency of SNARE complex formation. PMID:8973549

Timmers, K I; Clark, A E; Omatsu-Kanbe, M; Whiteheart, S W; Bennett, M K; Holman, G D; Cushman, S W

1996-12-01

10

Composite fuel cell membranes  

SciTech Connect

A bilayer or trilayer composite ion exchange membrane is described suitable for use in a fuel cell. The composite membrane has a high equivalent weight thick layer in order to provide sufficient strength and low equivalent weight surface layers for improved electrical performance in a fuel cell. In use, the composite membrane is provided with electrode surface layers. The composite membrane can be composed of a sulfonic fluoropolymer in both core and surface layers.

Plowman, K.R.; Rehg, T.J.; Davis, L.W.; Carl, W.P.; Cisar, A.J.; Eastland, C.S.

1997-08-05

11

Composite fuel cell membranes  

DOEpatents

A bilayer or trilayer composite ion exchange membrane suitable for use in a fuel cell. The composite membrane has a high equivalent weight thick layer in order to provide sufficient strength and low equivalent weight surface layers for improved electrical performance in a fuel cell. In use, the composite membrane is provided with electrode surface layers. The composite membrane can be composed of a sulfonic fluoropolymer in both core and surface layers.

Plowman, Keith R. (Lake Jackson, TX); Rehg, Timothy J. (Lake Jackson, TX); Davis, Larry W. (West Columbia, TX); Carl, William P. (Marble Falls, TX); Cisar, Alan J. (Cypress, TX); Eastland, Charles S. (West Columbia, TX)

1997-01-01

12

Mechanosensitivity of cell membranes  

Microsoft Academic Search

Physical and biophysical mechanisms of mechano-sensitivity of cell membranes are reviewed. The possible roles of the lipid matrix and of the cytoskeleton in membrane mechanoreception are discussed. Techniques for generation of static strains and dynamic curvatures of membrane patches are considered. A unified model for stress-activated and stress-inactivated ion channels under static strains is described. A review of work on

Alexander G. Petrov; Peter N. R. Usherwood

1994-01-01

13

Membrane in cancer cells  

SciTech Connect

This book contains papers presented at a conference on membranes in cancer cells. Topics covered include Oncogenies, hormones, and free-radical processes in malignant transformation in vitro and Superoxide onion may trigger DNA strand breaks in human granulorytes by acting as a membrane target.

Galeotti, T.; Cittadini, A.; Neri, G.; Scarpa, A.

1988-01-01

14

Membrane Cells for Brine Electrolysis.  

ERIC Educational Resources Information Center

Membrane cells were developed as alternatives to mercury and diaphragm cells for the electrolysis of brine. Compares the three types of cells, focusing on the advantages and disadvantages of membrane cells. (JN)

Tingle, M.

1982-01-01

15

Cell Membranes Tutorial  

NSDL National Science Digital Library

New from The Biology Project of the University of Arizona, this online tutorial "introduces the dynamic complexes of proteins, carbohydrates, and lipids that comprise cell membranes," and relates how membranes "are important for regulating ion and molecular traffic flow between cells." Each section of this Web site takes the form of a multiple choice question. Answer the question correctly, and a brief explanation of each answer choice will be displayed. Answer the question incorrectly, and a short but helpful tutorial with colorful diagrams will help get you on the right track. This would be an valuable Web site for students wishing to test themselves on cell membrane structure and function, but would not be especially useful for those new to the subject.

2002-01-01

16

Cell Membranes Tutorial  

NSDL National Science Digital Library

New from The Biology Project of the University of Arizona, this online tutorial introduces the dynamic complexes of proteins, carbohydrates, and lipids that comprise cell membranes, and relates how membranes are important for regulating ion and molecular traffic flow between cells. Each section of this Web site takes the form of a multiple choice question. Answer the question correctly, and a brief explanation of each answer choice will be displayed. Answer the question incorrectly, and a short but helpful tutorial with colorful diagrams will help get you on the right track. This would be an valuable Web site for students wishing to test themselves on cell membrane structure and function, but would not be especially useful for those new to the subject.

2002-01-01

17

BIOCHEMICAL CHARACTERIZATION OF MEMBRANE FRACTIONS IN MURINE SPERM: IDENTIFICATION OF THREE DISTINCT SUB-TYPES OF MEMBRANE RAFTS  

PubMed Central

Despite enormous interest in membrane raft microdomains, no studies in any cell type have defined the relative compositions of the raft fractions on the basis of their major components—sterols, phospholipids, and proteins—or additional raft-associating lipids such as the ganglioside, GM1. Our previous localization data in live sperm showed that the plasma membrane overlying the acrosome represents a stabilized platform enriched in GM1 and sterols. These findings, along with the physiological requirement for sterol efflux for sperm to function, prompted us to characterize sperm membrane fractions biochemically. After confirming limitations of commonly-used detergent-based approaches, we utilized a non-detergent-based method, separating membrane fractions that were reproducibly distinct based on sterol, GM1, phospholipid and protein compositions (both mass amounts and molar ratios). Based on fraction buoyancy and biochemical composition, we identified at least three highly reproducible subtypes of membrane raft. Electron microscopy revealed that raft fractions were free of visible contaminants and were separated by buoyancy rather than morphology. Quantitative proteomic comparisons and fluorescence localization of lipids suggested that different organelles contributed differentially to individual raft sub-types, but that multiple membrane microdomain sub-types could exist within individual domains. This has important implications for scaffolding functions broadly associated with rafts. Most importantly, we show that the common practice of characterizing membrane domains as either “raft” or “non-raft” oversimplifies the actual biochemical complexity of cellular membranes. PMID:19006178

Asano, Atsushi; Selvaraj, Vimal; Buttke, Danielle E.; Nelson, Jacquelyn L.; Green, Karin M.; Evans, James E.; Travis, Alexander J.

2009-01-01

18

Gas phase fractionation method using porous ceramic membrane  

DOEpatents

Flaw-free porous ceramic membranes fabricated from metal sols and coated onto a porous support are advantageously used in gas phase fractionation methods. Mean pore diameters of less than 40 .ANG., preferably 5-20 .ANG. and most preferably about 15 .ANG., are permeable at lower pressures than existing membranes. Condensation of gases in small pores and non-Knudsen membrane transport mechanisms are employed to facilitate and increase membrane permeability and permselectivity.

Peterson, Reid A. (Madison, WI); Hill, Jr., Charles G. (Madison, WI); Anderson, Marc A. (Madison, WI)

1996-01-01

19

Fuel cell membrane humidification  

DOEpatents

A polymer electrolyte membrane fuel cell assembly has an anode side and a cathode side separated by the membrane and generating electrical current by electrochemical reactions between a fuel gas and an oxidant. The anode side comprises a hydrophobic gas diffusion backing contacting one side of the membrane and having hydrophilic areas therein for providing liquid water directly to the one side of the membrane through the hydrophilic areas of the gas diffusion backing. In a preferred embodiment, the hydrophilic areas of the gas diffusion backing are formed by sewing a hydrophilic thread through the backing. Liquid water is distributed over the gas diffusion backing in distribution channels that are separate from the fuel distribution channels.

Wilson, Mahlon S. (Los Alamos, NM)

1999-01-01

20

Inhibition of Adenosine Triphosphatase Activity from a Plasma Membrane Fraction of Acer pseudoplatanus Cells by 2,2,2-Trichloroethyl 3,4-Dichlorocarbanilate 12  

PubMed Central

2,2,2-Trichloroethyl 3,4-dichlorocarbanilate (SW26) is toxic for Acer pseudoplatanus cell cultures. It inhibited the cellular proton extrusion and depolarized the plasmalemma. In vitro, it inhibited the plasma membrane ATPase. SW 26 was also inhibitory to membrane ATPases of other origins—plant (maize shoot), fungus (Schizosaccharomyces pombe), and animal (dog kidney)—with about the same efficiency (7.5 micromolar < I50 < 22 micromolar). It did not inhibit the oligomycin-sensitive ATPase from purified plant mitochondria, nor molybdate-sensitive soluble phosphatases. SW26 was more specific for plasma membrane ATPases than diethylstilbestrol or vanadate. A Lineweaver-Burk plot analysis showed that inhibition kinetics were purely noncompetitive (Ki = 14.7 micromolar) below 20 micromolar. Above this concentration, the inhibition pattern was not consistent with Michaelis-Menten kinetics, and a Hill plot representation revealed a positive cooperativity. PMID:16664702

Blein, Jean-Pierre; de Cherade, Xavier; Bergon, Michel; Calmon, Jean-Pierre; Scalla, René

1986-01-01

21

Cell Membrane Color Sheet and Build a Cell Membrane  

NSDL National Science Digital Library

Students color-code a schematic of a cell and its cell membrane structures. Then they complete the "Build-a-Membrane" activity found at http://learn.genetics.utah.edu. This reinforces their understanding of the structure and function of animal cells, and shows them the importance of being able to construct a tangible model of something that is otherwise difficult to see.

VU Bioengineering RET Program,

22

Antigenicity of basement membrane fractions obtained from rat seminiferous tubules.  

PubMed

A noncollagenous fraction of basement membrane (D-STBM) obtained from rat testes was submitted to sodium dodecyl sulfate-polyacrylamide slab gel electrophoresis (SDS-PAGE), and eight well-defined bands were detected. A cross-reaction with an antiserum against laminin was revealed by immunoblotting in five bands, with molecular weights ranging from 54 to 64 kDa. No further resolution of these components could be obtained by size exclusion and ionic exchange chromatography. Fifty-two percent of the rats immunized with D-STBM and adjuvants developed a mild multifocal damage of the testis. The lesions were characterized by foci of seminiferous tubules with different degrees of sloughing and/or atrophy of the germinal epithelium. Giant multinucleated cells were frequently seen, and mild interstitial mononuclear cell infiltrates were also detected. By immunofluorescence, deposits of rat IgG with a faint discontinuous linear pattern were observed along the walls of the seminiferous tubules. Circulating antibodies to D-STBM were detected by ELISA in 100% of the rats, whereas in a cross-reaction with laminin antibodies were detected in only 63%. All rats studied revealed a positive delayed type of hypersensitivity (DTH) response to D-STBM. None of the control rats injected with saline and adjuvants presented circulating antibodies to D-STBM or laminin or a positive DTH reaction to D-STBM. Some control group rats (10%) revealed few isolated seminiferous tubules with some degree of sloughing of the germinal epithelium. PMID:2483053

Areces, L B; Biscoglio de Jimenez Bonino, M; Cascone, O; Puig, R; Denduchis, B

1989-08-01

23

Characterization of outer membrane protein fractions of Bdellovibrionales.  

PubMed

Bdellovibrio-and-like organisms (BALOs) are predatory bacteria that prey upon Gram-negative bacteria and are taxonomically subsumed in the order Bdellovibrionales. Despite their unique lifestyle, these bacteria show remarkable genotypic diversities. The outer membrane of the predators is likely to play an important role during the recognition and invasion stage, as well as in the intraperiplasmic growth phase. In this study, the outer membrane protein fractions of type strains of Bdellovibrio, Bacteriovorax and Peredibacter were investigated, revealing the presence of outer membrane proteins (Omps) similar to the major Omps of Bdellovibrio bacteriovorus. The primary structures of these Omps of Bdellovibrio sp. W, Bacteriovorax stolpii and Peredibacter starrii were elucidated by a combined mass spectrometric-reverse genetic approach. The similarity between the analyzed Omps of the investigated BALOs ranges from 32% to 89% showing conserved amino acid regions in their primary structure. PMID:15668021

Beck, Sebastian; Schwudke, Dominik; Appel, Bernd; Linscheid, Michael; Strauch, Eckhard

2005-02-01

24

Rapid Fractionation of Wheat Leaf Protoplasts Using Membrane Filtration 1  

PubMed Central

A technique is presented for measuring the in vivo metabolite levels in the chloroplast stroma, the cytosol, and the mitochondrial matrix of wheat (Triticum aestivum, var `Timmo') leaf protoplasts, in which membrane filtration is used to prepare fractions enriched in the different subcellular fractions within 0.1 seconds after disruption of the protoplasts. By closing a syringe, protoplasts are forced through a net and disrupted, diluting the cytosol into the medium and also releasing intact chloroplasts and mitochondria which can then be immediately removed on membrane filters placed behind the nylon net. By varying the membrane filters, different filtrates are obtained corresponding to (a) mainly cytosol, or (b) cytosol and mitochondria with only low levels of chloroplasts; alternatively, (c) the entire protoplast contents are obtained by omitting the filters. The filtrates are immediately split, half flowing into HClO4 where they are immediately quenched for subsequent metabolite analyses; the other half flows into detergent and is used to monitor the exact distribution of marker enzymes in each individual fractionation. Using the measured distributions of metabolite and of marker enzymes in the three filtrates, the subcellular distribution of the metabolite can be algebraically calculated. The method is presented using ATP as an example. The quench time (0.1 second) made possible by membrane filtration is considerably faster than has been possible in the previously developed techniques using silicone oil centrifugation for chloroplasts (1 second) or mitochondria (1 minute). This rapid quench makes it possible to investigate subcellular pools which have a rapid turnover, like the adenine nucleotides. PMID:16662652

Lilley, Ross McC.; Stitt, Mark; Mader, Gerhard; Heldt, Hans W.

1982-01-01

25

Identifying polyvinylidene fluoride ultrafiltration membrane fouling behavior of different effluent organic matter fractions using colloidal probes.  

PubMed

The interaction forces between effluent organic matter (EfOM) fractions and membrane were measured by atomic force microscopy in conjunction with self-made membrane material colloidal probes. The inter-EfOM-fraction and intra-EfOM-fraction interactions were investigated using corresponding EfOM-fraction-coated colloidal probe. We combined this analysis with corresponding fouling experiments to identify the EfOM fractions responsible for polyvinylidene fluoride (PVDF) ultrafiltration membrane fouling. Results show that hydrophilic and hydrophobic fractions were the dominant fractions responsible for membrane fouling and flux decline in the initial and later filtration stages, respectively, which was mainly attributed to the stronger PVDF-hydrophilic fraction and intra-hydrophobic-fraction interaction forces. This phenomenon, in conjunction with the fact that each interaction force of PVDF-EfOM fraction was stronger than corresponding intra-EfOM-fraction force, suggests that the elimination of the PVDF-hydrophilic fraction interaction force is the best strategy for controlling EfOM fouling. Moreover, the inter-EfOM-fraction interaction force was mainly controlled by the corresponding intra-EfOM-fraction interaction forces. And, while the membrane-EfOM fraction and intra-EfOM-fraction interactions for each type of EfOM fraction are equivalent, the EfOM fractions with the molecular weight smaller than the molecular weight cutoff of the membranes used were mainly responsible for membrane fouling rather than the relatively high-molecular-weight fractions. PMID:24631880

Miao, Rui; Wang, Lei; Lv, Yongtao; Wang, Xudong; Feng, Ling; Liu, Ziwen; Huang, Danxi; Yang, Yongzhe

2014-05-15

26

The First Cell Membranes  

Microsoft Academic Search

Organic compounds are synthesized in the interstellar medium and can be delivered to planetary surfaces such as the early Earth, where they mix with endogenous species. Some of these compounds are amphiphilic, having polar and nonpolar groups on the same molecule. Amphiphilic compounds spontaneously self-assemble into more complex structures such as bimolecular layers, which in turn form closed membranous vesicles.

David Deamer; Jason P. Dworkin; Scott A. Sandford; Max P. Bernstein; Louis J. Allamandola

2002-01-01

27

Electropermeabilization of the cell membrane.  

PubMed

Membrane electropermeabilization is the observation that the permeability of a cell membrane can be transiently increased when a micro-millisecond external electric field pulse is applied on a cell suspension or on a tissue. Applicative aspects for the transfer of foreign molecules (macromolecules) into the cytoplasm are routinely used. But only a limited knowledge about what is really occurring in the cell and its membranes at the molecular levels is available. This chapter is a critical attempt to report the present state of the art and to point out some of the still open problems. The experimental facts associated to membrane electropermeabilization are firstly reported. They are valid on biological and model systems. Secondly, soft matter approaches give access to the bioelectrochemical description of the thermodynamical constraints supporting the destabilization of simplified models of the biological membrane. It is indeed described as a thin dielectric leaflet, where a molecular transport takes place by electrophoresis and then diffusion. This naïve approach is due to the lack of details on the structural aspects affecting the living systems as shown in a third part. Membranes are part of the cell machinery. The critical property of cells as being an open system from the thermodynamical point of view is almost never present. Computer simulations are now contributing to our knowledge on electropermeabilization. The last part of this chapter is a (very) critical report of all the efforts that have been performed. The final conclusion remains that we still do not know all the details on the reversible structural and dynamical alterations of the cell membrane (and cytoplasm) supporting its electropermeabilization. We have a long way in basic and translational researches to reach a pertinent description. PMID:24510809

Teissie, Justin

2014-01-01

28

Pervaporation membranes in direct methanol fuel cells  

Microsoft Academic Search

The membranes in direct methanol fuel cells must both conduct protons and serve as a barrier for methanol. Nafion, the most common fuel cell membrane, is an excellent conductor but a poor barrier. Polyvinyl alcohol pervaporation membranes are good methanol barriers but poor conductors. These and most other pervaporation membranes offer no significant advantages over Nafion in methanol fuel cell

Bryan S. Pivovar; Yuxin Wang; E. L. Cussler

1999-01-01

29

Corrugated Membrane Fuel Cell Structures  

SciTech Connect

One of the most challenging aspects of traditional PEM fuel cell stacks is the difficulty achieving the platinum catalyst utilization target of 0.2 gPt/kWe set forth by the DOE. Good catalyst utilization can be achieved with state-of-the-art catalyst coated membranes (CCM) when low catalyst loadings (<0.3 mg/cm2) are used at a low current. However, when low platinum loadings are used, the peak power density is lower than conventional loadings, requiring a larger total active area and a larger bipolar plate. This results in a lower overall stack power density not meeting the DOE target. By corrugating the fuel cell membrane electrode structure, Ion Power?s goal is to realize both the Pt utilization targets as well as the power density targets of the DOE. This will be achieved by demonstrating a fuel cell single cell (50 cm2) with a twofold increase in the membrane active area over the geometric area of the cell by corrugating the MEA structure. The corrugating structure must be able to demonstrate the target properties of < 10 mOhm-cm2 electrical resistance at > 20 psi compressive strength over the active area, in combination with offering at least 80% of power density that can be achieved by using the same MEA in a flat plate structure. Corrugated membrane fuel cell structures also have the potential to meet DOE power density targets by essentially packaging more membrane area into the same fuel cell volume as compared to conventional stack constructions.

Grot, Stephen [President, Ion Power Inc.] President, Ion Power Inc.

2013-09-30

30

In Vitro Enzymatic Reduction Kinetics of Mineral Oxides by Membrane Fractions from Shewanella oneidensis MR-1  

SciTech Connect

This study documents the first example of in vitro solid-phase mineral oxide reduction by enzyme-containing membrane fractions. Previous in vitro studies have only reported the reduction of aqueous ions. Total membrane (TM) fractions from iron-grown cultures of Shewanella oneidensis MR-1 were isolated and shown to catalyze the reduction of goethite, hematite, birnessite, and ramsdellite/pyrolusite using formate. In contrast, nicotinamide adenine dinucleotide (NADH) and succinate cannot function as electron donors. The significant implications of observations related to this cell-free system are: (i) both iron and manganese mineral oxides are reduced by the TM fraction, but aqueous U(VI) is not; (ii) TM fractions from anaerobically grown, but not aerobically grown, cells can reduce the mineral oxides; (iii) electron shuttles and iron chelators are not needed for this in vitro reduction, documenting conclusively that reduction can occur by direct contact with the mineral oxide; (iv) electron shuttles and EDTA stimulate the in vitro Fe(III) reduction, documenting that exogenous molecules can enhance rates of enzymatic mineral reduction; and (v) multiple membrane components are involved in solid-phase oxide reduction. The membrane fractions, consisting of liposomes of cytoplasmic and outer membrane segments, contain at least 100 proteins including the enzyme that oxidizes formate, formate dehydrogenase. Mineral oxide reduction was inhibited by the addition of detergent Triton X-100, which solubilizes membranes and their associated proteins, consistent with the involvement of multiple electron carriers that are disrupted by detergent addition. In contrast, formate dehydrogenase activity was not inhibited by Triton X-100. The addition of anthraquinone-2,6-disulfonate (AQDS) and menaquinone-4 was unable to restore activity; however, menadione (MD) restored 33% of the activity. The addition of AQDS and MD to reactions without added detergent increased the rate of goethite reduction. The Michaelis-Menten K{sub m} values of 71 {+-} 22 m{sup 2}/L for hematite and 50 {+-} 16 m{sup 2}/L for goethite were calculated as a function of surface area of the two insoluble minerals. V{sub max} was determined to be 123 {+-} 14 and 156 {+-} 13 nmol Fe(II)/min/mg of TM protein for hematite and goethite, respectively. These values are consistent with in vivo rates of reduction reported in the literature. These observations are consistent with our conclusion that the enzymatic reduction of mineral oxides is an effective probe that will allow elucidation of molecular chemistry of the membrane-mineral interface where electron transfer occurs.

Ruebush,S.; Icopini, G.; Brantley, S.; Tien, M.

2006-01-01

31

In vitro enzymatic reduction kinetics of mineral oxides by membrane fractions from Shewanella oneidensis MR-1  

NASA Astrophysics Data System (ADS)

This study documents the first example of in vitro solid-phase mineral oxide reduction by enzyme-containing membrane fractions. Previous in vitro studies have only reported the reduction of aqueous ions. Total membrane (TM) fractions from iron-grown cultures of Shewanella oneidensis MR-1 were isolated and shown to catalyze the reduction of goethite, hematite, birnessite, and ramsdellite/pyrolusite using formate. In contrast, nicotinamide adenine dinucleotide (NADH) and succinate cannot function as electron donors. The significant implications of observations related to this cell-free system are: (i) both iron and manganese mineral oxides are reduced by the TM fraction, but aqueous U(VI) is not; (ii) TM fractions from anaerobically grown, but not aerobically grown, cells can reduce the mineral oxides; (iii) electron shuttles and iron chelators are not needed for this in vitro reduction, documenting conclusively that reduction can occur by direct contact with the mineral oxide; (iv) electron shuttles and EDTA stimulate the in vitro Fe(III) reduction, documenting that exogenous molecules can enhance rates of enzymatic mineral reduction; and (v) multiple membrane components are involved in solid-phase oxide reduction. The membrane fractions, consisting of liposomes of cytoplasmic and outer membrane segments, contain at least 100 proteins including the enzyme that oxidizes formate, formate dehydrogenase. Mineral oxide reduction was inhibited by the addition of detergent Triton X-100, which solubilizes membranes and their associated proteins, consistent with the involvement of multiple electron carriers that are disrupted by detergent addition. In contrast, formate dehydrogenase activity was not inhibited by Triton X-100. The addition of anthraquinone-2,6-disulfonate (AQDS) and menaquinone-4 was unable to restore activity; however, menadione (MD) restored 33% of the activity. The addition of AQDS and MD to reactions without added detergent increased the rate of goethite reduction. The Michaelis-Menten Km values of 71 ± 22 m 2/L for hematite and 50 ± 16 m 2/L for goethite were calculated as a function of surface area of the two insoluble minerals. Vmax was determined to be 123 ± 14 and 156 ± 13 nmol Fe(II)/min/mg of TM protein for hematite and goethite, respectively. These values are consistent with in vivo rates of reduction reported in the literature. These observations are consistent with our conclusion that the enzymatic reduction of mineral oxides is an effective probe that will allow elucidation of molecular chemistry of the membrane-mineral interface where electron transfer occurs.

Ruebush, Shane S.; Icopini, Gary A.; Brantley, Susan L.; Tien, Ming

2006-01-01

32

Red cell membrane disorders.  

PubMed

Disorders of the erythrocyte membrane, including hereditary spherocytosis, hereditary elliptocytosis, hereditary pyropoikilocytosis, and hereditary stomatocytosis, comprise an important group of inherited hemolytic anemias. These syndromes are characterized by marked clinical and laboratory heterogeneity. Recent molecular studies have revealed that there is also significant genetic heterogeneity in these disorders. This is particularly true for the spherocytosis syndromes where each kindred has a private mutation in one of the spherocytosis genes. Treatment with splenectomy is curative in most patients. Splenectomy via a laparoscopic approach has become the surgical method of choice. Growing recognition and understanding of the long-term risks and complications of splenectomy, including cardiovascular disease, thrombotic disorders, and pulmonary hypertension, and the emergence of penicillin-resistant pneumococci, a concern for infection in overwhelming postsplenectomy infection, have led to reevaluation of the role of splenectomy. Recent management guidelines acknowledge these important considerations when entertaining splenectomy and recommend detailed discussion between health care providers, patient, and family. PMID:16304353

Gallagher, Patrick G

2005-01-01

33

The Cell Membrane and Nanotechnology  

NSDL National Science Digital Library

This activity is from the Wisconsin Online Resource Center, which is a digital library of web-based learning objects. Barbara Liang created this resource, and it examines nanotechnology applications that are based on cell membrane structure and function. The brief activity contains animated illustrations and interactives that help students grasp nanotechnology concepts.

Liang, Barbara

34

Membrane proteome analysis of glioblastoma cell invasion.  

PubMed

Glioblastoma multiforme (GBM) tumor invasion is facilitated by cell migration and degradation of the extracellular matrix. Invadopodia are actin-rich structures that protrude from the plasma membrane in direct contact with the extracellular matrix and are proposed to participate in epithelial-mesenchymal transition. We characterized the invasiveness of 9 established GBM cell lines using an invadopodia assay and performed quantitative mass spectrometry-based proteomic analyses on enriched membrane fractions. All GBM cells produced invadopodia, with a 65% difference between the most invasive cell line (U87MG) and the least invasive cell line (LN229) (p = 0.0001). Overall, 1,141 proteins were identified in the GBM membrane proteome; the levels of 49 proteins correlated with cell invasiveness. Ingenuity Pathway Analysis predicted activation "cell movement" (z-score = 2.608, p = 3.94E) in more invasive cells and generated a network of invasion-associated proteins with direct links to key regulators of invadopodia formation. Gene expression data relating to the invasion-associated proteins ITGA5 (integrin ?5), CD97, and ANXA1 (annexin A1) showed prognostic significance in independent GBM cohorts. Fluorescence microscopy demonstrated ITGA5, CD97, and ANXA1 localization in invadopodia assays, and small interfering RNA knockdown of ITGA5 reduced invadopodia formation in U87MG cells. Thus, invasion-associated proteins, including ITGA5, may prove to be useful anti-invasive targets; volociximab, a therapeutic antibody against integrin ?5?1, may be useful for treatment of patients with GBM. PMID:25853691

Mallawaaratchy, Duthika M; Buckland, Michael E; McDonald, Kerrie L; Li, Cheryl C Y; Ly, Linda; Sykes, Erin K; Christopherson, Richard I; Kaufman, Kimberley L

2015-05-01

35

A Major Fraction of Glycosphingolipids in Model and Cellular Cholesterol-containing Membranes Is Undetectable by Their Binding Proteins*  

PubMed Central

Glycosphingolipids (GSLs) accumulate in cholesterol-enriched cell membrane domains and provide receptors for protein ligands. Lipid-based “aglycone” interactions can influence GSL carbohydrate epitope presentation. To evaluate this relationship, Verotoxin binding its receptor GSL, globotriaosyl ceramide (Gb3), was analyzed in simple GSL/cholesterol, detergent-resistant membrane vesicles by equilibrium density gradient centrifugation. Vesicles separated into two Gb3/cholesterol-containing populations. The lighter, minor fraction (<5% total GSL), bound VT1, VT2, IgG/IgM mAb anti-Gb3, HIVgp120 or Bandeiraea simplicifolia lectin. Only IgM anti-Gb3, more tolerant of carbohydrate modification, bound both vesicle fractions. Post-embedding cryo-immuno-EM confirmed these results. This appears to be a general GSL-cholesterol property, because similar receptor-inactive vesicles were separated for other GSL-protein ligand systems; cholera toxin (CTx)-GM1, HIVgp120-galactosyl ceramide/sulfatide. Inclusion of galactosyl or glucosyl ceramide (GalCer and GlcCer) rendered VT1-unreactive Gb3/cholesterol vesicles, VT1-reactive. We found GalCer and GlcCer bind Gb3, suggesting GSL-GSL interaction can counter cholesterol masking of Gb3. The similar separation of Vero cell membrane-derived vesicles into minor “binding,” and major “non-binding” fractions when probed with VT1, CTx, or anti-SSEA4 (a human GSL stem cell marker), demonstrates potential physiological relevance. Cell membrane GSL masking was cholesterol- and actin-dependent. Cholesterol depletion of Vero and HeLa cells enabled differential VT1B subunit labeling of “available” and “cholesterol-masked” plasma membrane Gb3 pools by fluorescence microscopy. Thus, the model GSL/cholesterol vesicle studies predicted two distinct membrane GSL formats, which were demonstrated within the plasma membrane of cultured cells. Cholesterol masking of most cell membrane GSLs may impinge many GSL receptor functions. PMID:20716521

Mahfoud, Radhia; Manis, Adam; Binnington, Beth; Ackerley, Cameron; Lingwood, Clifford A.

2010-01-01

36

The effect of passive mixing on pressure drop and oxygen mass fraction using opposing channel flow field design in a Proton Exchange Membrane Fuel Cell  

NASA Astrophysics Data System (ADS)

This study investigates a flow field with opposing channel design. Previous studies on flow field designs have been focused on improving fuel utilization which often leads to increased pressure drop. This increased pressure drop is typical because standard designs employ either a single flow channel to clear blockages or dead end condition to force the flow through the gas diffusion layer. The disadvantage with these designs is the increased resistance to the flow which requires higher pressure, which becomes a parasitic loss that lowers the system efficiency. For this study the focus was to reduce the pressure drop by providing a less resistive path to the flow. To achieve a less resistive path, the inlet channel was split into two opposing channels. These channels are then recombined only to be split again for the next leg. Therefore, the split channel design should reduce the pressure drop which reduces the parasitic load and ultimately contributes to higher system efficiency. In addition the recombining of the streams at each leg should induce mixing. Having opposing channels should also increase cross flow under the lands to reduce mass transfer loses. The cathode side of the fuel cell is especially sensitive to the mass transport losses since air (oxygen mixed with nitrogen) is used for supplying oxygen unlike the anode side which uses pure hydrogen. To test the hypothesis of having benefits from an opposing channel design, both an experimental and analytical approach was taken. For the experiment, a serpentine flow field and opposing channel flow field plates were compared over several flow rates with compressed air. To test the hypothesis of increased mass transfer, the two flow fields were modeled using a CFD software package, COMSOL. It was found that the opposing channel configuration for high flow rate with multiple entry and exit conditions exhibited significant improvement over the single serpentine channel. Pressure drop was ? less than the serpentine channel with similar conditions. Simulations for mass transfer show that recombining of the flow streams generate more uniform current density unlike the serpentine configuration where the current density was concentrated at the entrance of the flow stream. The background section provides a brief overview of the governing equations, the theory of flow field operation and previous bodies of work on flow field design. Recommendations are made for further verification of the design using a real working cell based on the results.

Singh, Anant Bir

37

Effect of oral ingestion of different fractions of Allium cepa on the blood and erythrocyte membrane lipids and certain membrane-bound enzymes in rats.  

PubMed

The effect of oral ingestion of different fractions of onion (Allium cepa)--extract, residue, and whole--at a dose level equivalent to intake of 50 g of onion per day for a 70-kg man, for 30 days, to male adult, normal, albino rats was studied on blood and erythrocyte membrane lipids and certain membrane-bound enzymes. Onion extract and residue showed hypercholesterolemic effect, while whole onion showed hypocholesterolemic effect in blood. In erythrocyte membranes, all the fractions had hypocholesterolemic and hypolipidemic effect, which was accompanied by changes in the erythrocyte membrane enzymes studied, i.e., alkaline and acid phosphatase, 5'-nucleotidase, total and Mg2+ ATPase. The above study indicated that it is safer to take whole onion rather than onion residue or extract, because whole onion could lower the blood cholesterol level even in normal condition and has a less pronounced effect on the micro-environment of the cells. PMID:2525181

Ahluwalia, P; Mohindroo, A

1989-04-01

38

Membrane degradation mechanisms in polymer electrolyte membrane fuel cells  

NASA Astrophysics Data System (ADS)

Membrane degradation and failure is one of the most important factors limiting the lifetime of polymer electrolyte membrane fuel cells (PEMFCs). Increasing the membrane life by developing degradation mitigation strategies in the cell or developing a new membrane with improved life requires a detailed understanding of the membrane degradation mechanism during operation in a PEMFC. An in-situ and nondestructive technique, which relies on the measurement of the membrane degradation rate in a fuel cell, was used to study the chemical/electrochemical mode of membrane degradation. NafionRTM membrane was used for the degradation study and fluoride emission rate (FER) as measured from the fuel cell effluent water analysis was used as a quantitative indicator of the membrane degradation rate. The degradation mechanism was studied by a detailed investigation of the effect of reactants, catalyst properties (location, potential, catalyst type, interaction with O2 and H2O), cell current, membrane thickness, NafionRTM counterion, and direction of water movement on the membrane degradation rate. Based on the experimental findings it is shown that commonly known membrane degradation mechanisms involving formation of active oxygen species from H 2O2 decomposition or the direct formation of active oxygen species in the oxygen reduction reaction are not the dominating membrane degradation mechanisms in PEMFCs. It is proposed that molecular H2 and O 2 react on the surface of Pt catalyst to form the membrane degrading species. Depending upon the catalyst location the source of H2 or O2 or both is from the reactant crossover through the membrane. The reaction mechanism is chemical in nature and depends upon the catalyst surface properties and the relative concentrations of H2 and O 2 at the catalyst. The membrane degradation rate also depends on the residence time of the species in the membrane and the reaction volume i.e. the membrane thickness. Thus, the membrane degradation may not be limited only to the polymer surface in contact with Pt catalyst. The sulfonic acid groups in the NafionRTM side chain are key to the mechanism by which the radical species attack the polymer.

Mittal, Vishal Onkarmal

39

Water-soluble proteins of the human red cell membrane  

Microsoft Academic Search

Summary Procedures were developed for preparation of red cell membranes almost free of hemoglobin but with minimal loss of membrane proteins. Two water-soluble protein fractions are described, each constituting about 25% of the ghost protein. The first is ionically bonded and can be solubilized in water rapidly at pH 7.0 and more slowly at higher ionic strength solutions, with a

J. Th. Hoogeveen; R. Juliano; J. Coleman; A. Rothstein

1970-01-01

40

Membrane Cells in Chlor Alkali Application  

E-print Network

MEMBRANE CELLS IN COLOR ALKALI APPLICATION Dr. K. Lesker, UHDE GmbH ABSTRACT The worldwide chlorine/caustic soda production has reached approximately 40 million tpy. Despite the stagnation of the chlorine demand in thc wcstcrn world, e... of the per fluorinated ion exchange membrane 1968-72 Development of the membrane process 1Membranes for > 30% of NaOH IY81 first conversion of a diaphragm plant In a membrane chloralkali...

Lesker, K.

41

Analyzing Subcellular mRNA Localization via Cell Fractionation  

PubMed Central

Summary The partitioning of secretory and membrane protein-encoding mRNAs to the endoplasmic reticulum (ER), and their translation on ER-associated ribosomes, governs access to the secretory/exocytic pathways of the cell. As mRNAs encoding secretory and membrane proteins comprise approximately 30% of the transcriptome, the localization of mRNAs to the ER represents an extraordinarily prominent, ubiquitous, and yet poorly understood RNA localization phenomenon. The partitioning of mRNAs to the ER is generally thought to be achieved by the signal recognition particle (SRP) pathway. In this pathway, mRNA localization to the ER is determined by the translation product – translation yields an N-terminal signal sequence or topogenic signal that is recognized by the SRP and the resulting mRNA-ribosome-SRP complex is then recruited to the ER membrane. Recent studies have demonstrated that mRNAs can be localized to the ER via a signal sequence and/or translation-independent pathway(s) and that discrete sets of cytosolic protein-encoding mRNAs are enriched on the ER membrane, though they lack an encoded signal sequence. These key findings reopen investigations into the mechanism(s) that govern mRNA localization to the ER. In this contribution, we describe two independent methods that can be utilized to study this important and poorly understood aspect of eukaryotic cell biology. These methods comprise two independent means of fractionating tissue culture cells to yield free/cytosolic polyribosomes and ER membrane-bound polyribosomes. Detailed methods for the fractionation and characterization of the two polyribosome pools are provided. PMID:21431749

Jagannathan, Sujatha; Nwosu, Christine; Nicchitta, Christopher V.

2013-01-01

42

Altered membrane-cytoskeleton linkage and membrane blebbing in energy-depleted renal proximal tubular cells.  

PubMed

The effects of energy depletion on two membrane-cytoskeletal linker proteins (ezrin and myosin-1 beta) and membrane bleb formation were studied in isolated rabbit proximal tubule cells. Measurements of cytoskeletal-membrane interactions by using the laser optic trap method revealed a stronger association of control tubule membrane with the apical cytoskeleton compared with the basal cytoskeleton. Energy depletion weakened the apical membrane-cytoskeleton interactions to a greater degree. Biochemical studies demonstrated that energy depletion altered both ezrin and myosin-1 beta. The salt-insensitive ezrin fraction dissociated from the cytoskeleton; myosin-1beta redistributed from the peripheral cytoskeleton to a perinuclear/nuclear complex. These changes in ezrin and myosin-1 beta and the weakening of the membrane-cytoskeleton interactions correlated with the release of brush-border membrane blebs observed by differential interference contrast microscopy. Permeability of membrane blebs was also evaluated during energy depletion and indicated an increased permeabilization of basal blebs to 3-kDa dextrans. These results support the hypothesis that alterations in membrane-cytoskeleton linkers facilitate the formation and detachment of blebs by weakening membrane-cytoskeleton interactions. PMID:11249853

Chen, J; Wagner, M C

2001-04-01

43

Hydrophilic fraction of natural organic matter causing irreversible fouling of microfiltration and ultrafiltration membranes.  

PubMed

Although membrane filtration is a promising technology in the field of drinking water treatment, persistent membrane fouling remains a major disadvantage. For more efficient operation, causative agents of membrane fouling need to be identified. Membrane fouling can be classified into physically reversible and irreversible fouling on basis of the removability of the foulants by physical cleaning. Four types of natural organic matter (NOM) in river water used as a source of drinking water were fractionated into hydrophobic and hydrophilic fractions, and their potential to develop irreversible membrane fouling was evaluated by a bench-scale filtration experiment together with spectroscopic and chromatographic analyses. In this study, only dissolved NOM was investigated without consideration of interactions of NOM fractions with particulate matter. Results demonstrated that despite identical total organic carbon (TOC), fouling development trends were significantly different between hydrophilic and hydrophobic fractions. The hydrophobic fractions did not increase membrane resistance, while the hydrophilic fractions caused severe loss of membrane permeability. These results were identical with the case when the calcium was added to hydrophobic and hydrophilic fractions. The largest difference in NOM characteristics between hydrophobic and hydrophilic fractions was the presence or absence of macromolecules; the primary constituent causing irreversible fouling was inferred to be "biopolymers", including carbohydrates and proteins. In addition, the results demonstrated that the extent of irreversible fouling was considerably different depending on the combination of membrane materials and NOM characteristics. Despite identical nominal pore size (0.1 ?m), a polyvinylidene fluoride (PVDF) membrane was found to be more rapidly fouled than a PE membrane. This is probably explained by the generation of strong hydrogen bonding between hydroxyl groups of biopolymers and fluorine of the PVDF membrane. On the basis of these findings, it was suggested that the higher fouling potential of the hydrophilic fraction of the dissolved NOMs from various natural water sources are mainly attributed to macromolecules, or biopolymers. PMID:24565803

Yamamura, Hiroshi; Okimoto, Kenji; Kimura, Katsuki; Watanabe, Yoshimasa

2014-05-01

44

Membrane heterogeneity in murine stem cells  

SciTech Connect

The cell membrane's role in hemopoietic differentiation and regulation is increasingly evident. Certain fluorescent molecules interact with membrane components at the molecular level. The organic dye merocyanine 540(MCN) is such a tool for studying hemopoietic stem cell membranes at the molecular level. This paper present work involving biologic interactions of MCN with CLL (chronic lymphocytic leukemia) and hemopoietic cell membranes. The authors work indicates that MNC staining reveals membrane differences that accompany cellular transformation and differentiation. Changes in MNC fluorescene indicate that hemopoietic cells are heterogeneous with respect to membrane properties, and sensitivity to MNC photoinactivation reveals that membrane properties may change as a function of differentiative state between pluripotent and committed granulocytic precursor cells.

Myers, C.P.; Kerk, D.K.; Norman, A.

1980-01-01

45

Characterization and storage of malaria antigens: Fractionation of Plasmodium knowlesi-induced antigens of rhesus monkey erythrocyte membranes*  

PubMed Central

In order to characterize parasite-induced host cell membrane antigens, the plasma membranes of Plasmodium knowlesi-infected rhesus erythrocytes have been compared with those of normal red cells and purified schizonts by immunochemical and biochemical techniques. Host cell membranes and schizonts were separated by differential centrifugation following nitrogen decompression. Isolated schizonts were further fractionated into several subcellular compartments. Crossed-immune electrophoresis, against monkey anti-schizont serum, of Triton X-100-solubilized material identified 7 P. knowlesi-specific antigens, of which 4 could be detected only in the host cell membranes. These membranes also contained 3 proteins, with relative molecular masses of 55 000, 65 000 and 90 000 and isoelectric points at pH 4.5, 4.5 and 5.2, respectively, which are lacking in normal membranes. Pulse-chase experiments with (14C)-glucosamine showed that these parasite-induced host cell membrane components are glycoproteins. ImagesFig. 1Fig. 2 PMID:120762

Schmidt-Ullrich, R.; Wallach, D. F. H.; Lightholder, J.

1979-01-01

46

Actinide transport across cell membranes.  

PubMed

Protactinium uptake into the normal liver does not exceed 3%, but when the phospholipid levels in the liver are elevated by administration of thioacetamide this uptake increases to 31%. Phosphatidic acid, which is absent from the normal liver, has been shown to extract protactinium into organic solvents. However, phosphatidylserine, a component of normal liver cell membranes, does not extract protactinium. It might be conjectured that this is why so little protactinium is taken up by the normal liver. The hypothesis is advanced that phosphatidylserine, which is known to complex plutonium, americium and curium, may regulate the uptake of these elements by liver. PMID:7373293

Bulman, R A; Griffin, R J

1980-01-01

47

The Proton Exchange Membrane (PEM) Fuel Cell  

NSDL National Science Digital Library

This page is an introduction to the Proton Exchange Membrane (PEM) fuel cell. It uses flash animation to explain in greater detail what the PEM fuel cell consists of and how it works. The website has an introductory animation which is followed by more in depth description of the proton exchange membrane fuel cell.

48

Resistance of cell membranes to different detergents  

Microsoft Academic Search

Partial resistance of cell membranes to solubilization with mild detergents and the analysis of isolated detergent-resistant membranes (DRMs) have been used operationally to define membrane domains. Given the multitude of detergents used for this purpose, we sought to investigate whether extraction with different detergents might reflect the same underlying principle of domain formation. We therefore compared the protein and lipid

Sebastian Schuck; Masanori Honsho; Kim Ekroos; Andrej Shevchenko; Kai Simons

2003-01-01

49

Polymer electrolyte membrane assembly for fuel cells  

NASA Technical Reports Server (NTRS)

An electrolyte membrane for use in a fuel cell can contain sulfonated polyphenylether sulfones. The membrane can contain a first sulfonated polyphenylether sulfone and a second sulfonated polyphenylether sulfone, wherein the first sulfonated polyphenylether and the second sulfonated polyphenylether sulfone have equivalent weights greater than about 560, and the first sulfonated polyphenylether and the second sulfonated polyphenylether sulfone also have different equivalent weights. Also, a membrane for use in a fuel cell can contain a sulfonated polyphenylether sulfone and an unsulfonated polyphenylether sulfone. Methods for manufacturing a membrane electrode assemblies for use in fuel cells can include roughening a membrane surface. Electrodes and methods for fabricating such electrodes for use in a chemical fuel cell can include sintering an electrode. Such membranes and electrodes can be assembled into chemical fuel cells.

Yen, Shiao-Ping S. (Inventor); Kindler, Andrew (Inventor); Yavrouian, Andre (Inventor); Halpert, Gerald (Inventor)

2002-01-01

50

Polymer electrolyte membrane assembly for fuel cells  

NASA Technical Reports Server (NTRS)

An electrolyte membrane for use in a fuel cell can contain sulfonated polyphenylether sulfones. The membrane can contain a first sulfonated polyphenylether sulfone and a second sulfonated polyphenylether sulfone, wherein the first sulfonated polyphenylether and the second sulfonated polyphenylether sulfone have equivalent weights greater than about 560, and the first sulfonated polyphenylether and the second sulfonated polyphenylether sulfone also have different equivalent weights. Also, a membrane for use in a fuel cell can contain a sulfonated polyphenylether sulfone and an unsulfonated polyphenylether sulfone. Methods for manufacturing a membrane electrode assemblies for use in fuel cells can include roughening a membrane surface. Electrodes and methods for fabricating such electrodes for use in a chemical fuel cell can include sintering an electrode. Such membranes and electrodes can be assembled into chemical fuel cells.

Yen, Shiao-Ping S. (Inventor); Kindler, Andrew (Inventor); Yavrouian, Andre (Inventor); Halpert, Gerald (Inventor)

2000-01-01

51

Characterisation of cell-wall polysaccharides from mandarin segment membranes.  

PubMed

In an attempt to develop a process of enzymatic peeling of mandarin segments suitable for use on an industrial scale, the cell wall fraction of the segment membrane of Satsuma mandarin fruits was extracted to obtain a chelating agent-soluble pectin fraction (ChSS), a dilute sodium hydroxide-soluble pectin fraction (DASS), a 1M sodium hydroxide-soluble hemicellulose fraction (1MASS), a 4M sodium hydroxide-soluble hemicellulose fraction (4MASS) and a cellulose-rich residue (3.1, 0.9, 0.4, 0.7 and 1.6%w/w of fresh membrane, respectively). The ChSS pectin consisted mainly of galacturonic acid followed by arabinose and galactose. The DASS fraction contained less galacturonic acid and more neutral sugars than ChSS. Eighty-nine percent of the galacturonic acid present in the segment membranes was recovered in the above two pectin fractions. The two hemicellulosic fractions consisted of two different molecular weight populations, which also differed in their sugar composition. Arabinose, xylose, mannose, galactose and glucose were the main sugar constituents of these hemicellulose fractions. In addition to an (arabino)xylan and a xyloglucan, the presence of an arabinogalactan is suggested by the sugar composition of both hemicelluloses. The pectin fractions were also characterised by their degradability by the pectic enzymes polygalacturonase, pectinmethylesterase and rhamnogalacturonan hydrolase. However the degree of degradation of the pectin fractions by enzymes differed, and the amount of the polymeric materials resistant to further degradation and the oligomeric products also differed. Using pectic enzymes it is possible to obtain peeled mandarin segments ready to eat or for canning. PMID:25577048

Coll-Almela, Luis; Saura-López, Domingo; Laencina-Sánchez, José; Schols, Henk A; Voragen, Alfons G J; Ros-García, José María

2015-05-15

52

Isolation of a hemidesmosome-rich fraction from a human squamous cell carcinoma cell line.  

PubMed

Hemidesmosomes are cell-to-matrix adhesion complexes anchoring keratinocytes to basement membranes. For the first time, we present a method to prepare a fraction from human cultured cells that are highly enriched in hemidesmosomal proteins. Using DJM-1 cells derived from human squamous cell carcinoma, accumulation of hemidesmosomes was observed when these cells were cultured for more than 10 days in a commercial serum-free medium without supplemental calcium. Electron microscopy demonstrated that numerous electron-dense adhesion structures were present along the basal cell membranes of DJM-1 cells cultured under the aforementioned conditions. After removing cellular materials using an ammonia solution, hemidesmosomal proteins and deposited extracellular matrix were collected and separated by electrophoresis. There were eight major polypeptides, which were determined to be plectin, BP230, BP180, integrin ?6 and ?4 subunits, and laminin-332 by immunoblotting and mass spectrometry. Therefore, we designated this preparation as a hemidesmosome-rich fraction. This fraction contained laminin-332 exclusively in its unprocessed form, which may account for the promotion of laminin deposition, and minimal amounts of Lutheran blood group protein, a nonhemidesmosomal transmembrane protein. This hemidesmosome-rich fraction would be useful not only for biological research on hemidesmosomes but also for developing a serum test for patients with blistering skin diseases. PMID:24726610

Hirako, Yoshiaki; Yonemoto, Yuki; Yamauchi, Tomoe; Nishizawa, Yuji; Kawamoto, Yoshiyuki; Owaribe, Katsushi

2014-06-10

53

Effect of various hepatic membrane fractions on microtubule assembly- with special emphasis on the role of membrane phospholipids  

PubMed Central

This report describes an interaction between rat brain microtubule protein and various hepatic fractions in vitro. Purified preparations of Golgi membranes, plasma membrane, rough and smooth endoplasmic reticulum, nuclear membranes, and mitochondria were obtained from the livers of 200-g rats. Several concentrations of fresh or sonicated frozen membranes were incubated with twice-cycled rat brain microtubule protein in a microtubule assembly buffer for 60 min at 30 degrees C. Changes in microtubule assembly were assessed either by quantitative electron microscopy on negatively stained samples or by spectrophotometric methods. The results show that all the tested membranes "bound" microtubule protein, preventing assembly: Golgi and plasma membranes, as well as mitochondria, were especially potent in this regard. To identify the membrane-associated components responsible for microtubule protein binding, the membranes were extracted with methanol-chloroform, and liposomes were prepared from the resulting lipids. Microtubule protein incubated with these liposomes showed a differential ability to assemble that was similar to the effect obtained with intact membranes. Membrane-extracted phospholipids were identified as the lipid component responsible for these changes, with the negatively charged phospholipids (cardiolipin and phosphatidylserine) being uniquely active. These findings indicate that hepatic membranes differentially interact with brain microtubule protein; this interaction may be dependent on membrane phospholipids. PMID:7251654

1981-01-01

54

Advanced composite polymer electrolyte fuel cell membranes  

SciTech Connect

A new type of reinforced composite perfluorinated polymer electrolyte membrane, GORE-SELECT{trademark} (W.L. Gore & Assoc.), is characterized and tested for fuel cell applications. Very thin membranes (5-20 {mu}m thick) are available. The combination of reinforcement and thinness provides high membrane, conductances (80 S/cm{sup 2} for a 12 {mu}m thick membrane at 25{degrees}C) and improved water distribution in the operating fuel cell without sacrificing longevity or durability. In contrast to nonreinforced perfluorinated membranes, the x-y dimensions of the GORE-SELECT membranes are relatively unaffected by the hydration state. This feature may be important from the viewpoints of membrane/electrode interface stability and fuel cell manufacturability.

Wilson, M.S.; Zawodzinski, T.A.; Gottesfeld, S.; Kolde, J.A.; Bahar, B.

1995-09-01

55

Development of ionomer membranes for fuel cells  

Microsoft Academic Search

In this contribution an overview is given about the state-of-the-art at the membrane development for proton-conductive polymer (composite) membranes for the application membrane fuel cells, focusing on the membrane developments in this field performed at ICVT.For preparation of the polymers, processes have been developed for sulfonated arylene main-chain polymers as well as for arylene main-chain polymers containing basic N-containing groups,

Jochen A. Kerres

2001-01-01

56

Fuel cell ion-exchange membrane investigation  

NASA Technical Reports Server (NTRS)

The present deficiencies in the fluorocarbon sulfonic acid membrane used as the solid polymer electrolyte in the H2/O2 fuel cell are studied. Considered are: Adhesives selection, elastomeric formulations, scavenger exploration, and membrane characterization. The significant data are interpreted and recommendations are given for both short and long range further investigations in two of the four major areas: membrane adhesives and membrane stabilization.

Toy, M. S.

1972-01-01

57

Membrane Organization and Dynamics in Cell Polarity  

PubMed Central

The establishment and maintenance of cell polarity is important to a wide range of biological processes ranging from chemotaxis to embryogenesis. An essential feature of cell polarity is the asymmetric organization of proteins and lipids in the plasma membrane. In this article, we discuss how polarity regulators such as small GTP-binding proteins and phospholipids spatially and kinetically control vesicular trafficking and membrane organization. Conversely, we discuss how membrane trafficking contributes to cell polarization through delivery of polarity determinants and regulators to the plasma membrane. PMID:20066116

Orlando, Kelly; Guo, Wei

2009-01-01

58

Live cell imaging of membrane / cytoskeleton interactions and membrane topology  

PubMed Central

We elucidate the interaction between actin and specific membrane components, using real time live cell imaging, by delivering probes that enable access to components, that cannot be accessed genetically. We initially investigated the close interplay between Phosphatidylinositol 4,5-bisphosphate (PIP2) and the F-actin network. We show that, during the early stage of cell adhesion, PIP2 forms domains within the filopodia membrane. We studied these domains alongside cell spreading and observed that these very closely follow the actin tread-milling. We show that this mechanism is associated with an active transport of PIP2 rich organelles from the cell perinuclear area to the edge, along actin fibers. Finally, mapping other phospholipids and membrane components we observed that the PIP2 domains formation is correlated with sphingosine and cholesterol rafts. PMID:25205456

Chierico, Luca; Joseph, Adrian S.; Lewis, Andrew L.; Battaglia, Giuseppe

2014-01-01

59

Proton Exchange Membranes for Fuel Cells  

SciTech Connect

Proton exchange membrane, also known as polymer electrolyte membrane, fuel cells (PEMFCs) offer the promise of efficient conversion of chemical energy of fuel, such as hydrogen or methanol, into electricity with minimal pollution. Their widespread use to power zero-emission automobiles as part of a hydrogen economy can contribute to enhanced energy security and reduction in greenhouse gas emissions. However, the commercial viability of PEMFC technology is hindered by high cost associated with the membrane electrode assembly (MEA) and poor membrane durability under prolonged operation at elevated temperature. Membranes for automotive fuel cell applications need to perform well over a period comparable to the life of an automotive engine and under heavy load cycling including start-stop cycling under sub-freezing conditions. The combination of elevated temperature, changes in humidity levels, physical stresses and harsh chemical environment contribute to membrane degradation. Perfluorinated sulfonic acid (PFSA)-based membranes, such as Nafion®, have been the mainstay of PEMFC technology. Their limitations, in terms of cost and poor conductivity at low hydration, have led to continuing research into membranes that have good proton conductivity at elevated temperatures above 120 °C and under low humidity conditions. Such membranes have the potential to avoid catalyst poisoning, simplify fuel cell design and reduce the cost of fuel cells. Hydrocarbon-based membranes are being developed as alternatives to PFSA membranes, but concerns about chemical and mechanical stability and durability remain. Novel anhydrous membranes based on polymer gels infused with protic ionic liquids have also been recently proposed, but considerable fundamental research is needed to understand proton transport in novel membranes and evaluate durability under fuel cell operating conditions. In order to advance this promising technology, it is essential to rationally design the next generation of PEMs based on an understanding of chemistry, membrane morphology and proton transport obtained from experiment, theory and computer simulation.

Devanathan, Ramaswami

2010-11-01

60

Optical rheology for live cell membranes  

E-print Network

We present a novel optical methodology including both instrumentation and theory aimed at retrieving the full viscoelastic information of cell membrane material properties. Red blood cells (RBC) are chosen for this study ...

Park, YongKeun, S.M. Massachusetts Institute of Technology

2007-01-01

61

Membrane proteomic analysis of pancreatic cancer cells  

PubMed Central

Background Pancreatic cancer is one of the most aggressive human tumors due to its high potential of local invasion and metastasis. The aim of this study was to characterize the membrane proteomes of pancreatic ductal adenocarcinoma (PDAC) cells of primary and metastatic origins, and to identify potential target proteins related to metastasis of pancreatic cancer. Methods Membrane/membrane-associated proteins were isolated from AsPC-1 and BxPC-3 cells and identified with a proteomic approach based on SDS-PAGE, in-gel tryptic digestion and liquid chromatography with tandem mass spectrometry (LC-MS/MS). X! Tandem was used for database searching against the SwissProt human protein database. Results We identified 221 & 208 proteins from AsPC-1 and BxPC-3 cells, respectively, most of which are membrane or membrane-associated proteins. A hundred and nine proteins were found in both cell lines while the others were present in either AsPC-1 or BxPC-3 cells. Differentially expressed proteins between two cell lines include modulators of cell adhesion, cell motility or tumor invasion as well as metabolic enzymes involved in glycolysis, tricarboxylic acid cycle, or nucleotide/lipid metabolism. Conclusion Membrane proteomes of AsPC-1 (metastatic) and BxPC-3 (primary) cells are remarkably different. The differentially expressed membrane proteins may serve as potential targets for diagnostic and therapeutic interventions. PMID:20831833

2010-01-01

62

Identification of tonoplast and plasma membrane in membrane fractions from garden cress ( Lepidium sativum L.) with and without filipin treatment  

Microsoft Academic Search

Membranes from roots of Lepidium sativum L. were investigated in situ and after fractionation by applying morphological and biochemical methods. After freeze-fracture combined with filipin labelling the tonoplast and the plasma membrane could be easily characterized by the frequency of intramembranous particles and the arrangement of filipin-induced lesions. On tonoplast vesicles, the filipin-induced lesions were arranged in clusters of different

B. Dorp; D. Volkmann; G. F. E. Scherer

1986-01-01

63

Proteomic Profiling of the Outer Membrane Fraction of the Obligate Intracellular Bacterial Pathogen Ehrlichia ruminantium  

PubMed Central

The outer membrane proteins (OMPs) of Gram-negative bacteria play a crucial role in virulence and pathogenesis. Identification of these proteins represents an important goal for bacterial proteomics, because it aids in vaccine development. Here, we have developed such an approach for Ehrlichia ruminantium, the obligate intracellular bacterium that causes heartwater. A preliminary whole proteome analysis of elementary bodies, the extracellular infectious form of the bacterium, had been performed previously, but information is limited about OMPs in this organism and about their role in the protective immune response. Identification of OMPs is also essential for understanding Ehrlichia’s OM architecture, and how the bacterium interacts with the host cell environment. First, we developed an OMP extraction method using the ionic detergent sarkosyl, which enriched the OM fraction. Second, proteins were separated via one-dimensional electrophoresis, and digested peptides were analyzed via nano-liquid chromatographic separation coupled with mass spectrometry (LC-MALDI-TOF/TOF). Of 46 unique proteins identified in the OM fraction, 18 (39%) were OMPs, including 8 proteins involved in cell structure and biogenesis, 4 in transport/virulence, 1 porin, and 5 proteins of unknown function. These experimental data were compared to the predicted subcellular localization of the entire E. ruminantium proteome, using three different algorithms. This work represents the most complete proteome characterization of the OM fraction in Ehrlichia spp. The study indicates that suitable subcellular fractionation experiments combined with straightforward computational analysis approaches are powerful for determining the predominant subcellular localization of the experimentally observed proteins. We identified proteins potentially involved in E. ruminantium pathogenesis, which are good novel targets for candidate vaccines. Thus, combining bioinformatics and proteomics, we discovered new OMPs for E. ruminantium that are valuable data for those investigating new vaccines against this organism. In summary, we provide both pioneering data and novel insights into the pathogenesis of this obligate intracellular bacterium. PMID:25710494

Moumène, Amal; Marcelino, Isabel; Ventosa, Miguel; Gros, Olivier; Lefrançois, Thierry; Vachiéry, Nathalie

2015-01-01

64

Proteomic Profiling of the Outer Membrane Fraction of the Obligate Intracellular Bacterial Pathogen Ehrlichia ruminantium.  

PubMed

The outer membrane proteins (OMPs) of Gram-negative bacteria play a crucial role in virulence and pathogenesis. Identification of these proteins represents an important goal for bacterial proteomics, because it aids in vaccine development. Here, we have developed such an approach for Ehrlichia ruminantium, the obligate intracellular bacterium that causes heartwater. A preliminary whole proteome analysis of elementary bodies, the extracellular infectious form of the bacterium, had been performed previously, but information is limited about OMPs in this organism and about their role in the protective immune response. Identification of OMPs is also essential for understanding Ehrlichia's OM architecture, and how the bacterium interacts with the host cell environment. First, we developed an OMP extraction method using the ionic detergent sarkosyl, which enriched the OM fraction. Second, proteins were separated via one-dimensional electrophoresis, and digested peptides were analyzed via nano-liquid chromatographic separation coupled with mass spectrometry (LC-MALDI-TOF/TOF). Of 46 unique proteins identified in the OM fraction, 18 (39%) were OMPs, including 8 proteins involved in cell structure and biogenesis, 4 in transport/virulence, 1 porin, and 5 proteins of unknown function. These experimental data were compared to the predicted subcellular localization of the entire E. ruminantium proteome, using three different algorithms. This work represents the most complete proteome characterization of the OM fraction in Ehrlichia spp. The study indicates that suitable subcellular fractionation experiments combined with straightforward computational analysis approaches are powerful for determining the predominant subcellular localization of the experimentally observed proteins. We identified proteins potentially involved in E. ruminantium pathogenesis, which are good novel targets for candidate vaccines. Thus, combining bioinformatics and proteomics, we discovered new OMPs for E. ruminantium that are valuable data for those investigating new vaccines against this organism. In summary, we provide both pioneering data and novel insights into the pathogenesis of this obligate intracellular bacterium. PMID:25710494

Moumène, Amal; Marcelino, Isabel; Ventosa, Miguel; Gros, Olivier; Lefrançois, Thierry; Vachiéry, Nathalie; Meyer, Damien F; Coelho, Ana V

2015-01-01

65

Membrane processes relevant for the polymer electrolyte fuel cell  

E-print Network

Membrane processes relevant for the polymer electrolyte fuel cell Aleksander Kolstad Chemical. The important aspects concerning the Polymer Electrolyte Membrane Fuel Cell, more commonly known as Proton

Kjelstrup, Signe

66

Membrane Stability during Biopreservation of Blood Cells.  

PubMed

SUMMARY: Storage methods, which can be taken into consideration for red blood cells and platelets, include liquid storage, cryopreservation and freeze-drying. Red blood cells can be hypothermically stored at refrigerated temperatures, whereas platelets are chilling sensitive and therefore cannot be stored at temperatures below 20 °C. Here we give an overview of available cryopreservation and freeze-drying procedures for blood cells and discuss the effects of these procedures on cells, particularly on cellular membranes. Cryopreservation and freeze-drying may result in chemical and structural modifications of cellular membranes. Membranes undergo phase and permeability changes during freezing and drying. Cryo- and lyoprotective agents prevent membrane damage by different mechanisms. Cryoprotective agents are preferentially excluded from membrane surfaces. They decrease the activation energy for water transport during freezing and control the rate of cellular dehydration. Lyoprotectants are thought to stabilize membranes during drying by forming direct hydrogen bonding interactions with phospholipid head groups. In addition, lyoprotectants can form a glassy state at room temperature. Recently liposomes have been investigated to stabilize blood cells during freezing and freeze-drying. Liposomes modify the composition of cellular membranes by lipid and cholesterol transfer, which can stabilize or destabilize the low temperature response of cells. PMID:21566710

Stoll, Christoph; Wolkers, Willem F

2011-01-01

67

Proton Exchange Membranes for Fuel Cell Applications  

Microsoft Academic Search

This paper presents an overview of the key requirements for the proton exchange membranes (PEM) used in fuel cell applications, along with a description of the membrane materials currently being used and their ability to meet these requirements. Also discussed are some of the new materials, technologies, and research directions being pursued to try to meet the demanding performance and

Steven J. Hamrock; Michael A. Yandrasits

2006-01-01

68

Proton conducting membrane for fuel cells  

DOEpatents

An ion conducting membrane comprising dendrimeric polymers covalently linked into a network structure. The dendrimeric polymers have acid functional terminal groups and may be covalently linked via linking compounds, cross-coupling reactions, or copolymerization reactions. The ion conducting membranes may be produced by various methods and used in fuel cells.

Colombo, Daniel G.; Krumpelt, Michael; Myers, Deborah J.; Kopasz, John P.

2007-03-27

69

Proton conducting membrane for fuel cells  

DOEpatents

An ion conducting membrane comprising dendrimeric polymers covalently linked into a network structure. The dendrimeric polymers have acid functional terminal groups and may be covalently linked via linking compounds, cross-coupling reactions, or copolymerization reactions. The ion conducting membranes may be produced by various methods and used in fuel cells.

Colombo, Daniel G.; Krumpelt, Michael; Myers, Deborah J.; Kopasz, John P.

2005-12-20

70

Functional fluoropolymers for fuel cell membranes  

Microsoft Academic Search

Various routes to synthesise functional fluoropolymers used in membranes for fuel cell applications are presented. They can be separated into three main families of alternatives. The first concerns the direct radical copolymerisation of fluoroalkenes with fluorinated functional monomers. The latter are either fluorinated vinyl ethers, ?,?,?-trifluorostyrenes or trifluorovinyl oxy-aromatic monomers bearing sulfonic or phosphonic acids. The resulting membranes are the

R. Souzy; B. Ameduri; B. Boutevin; G. Gebel; P. Capron

2005-01-01

71

Functional fluoropolymers for fuel cell membranes  

Microsoft Academic Search

Various routes to synthesize functional fluoropolymers used in membranes for fuel cell applications are presented. They can be separated into three main families of alternatives. The first concerns the direct radical copolymerization of fluoroalkenes with fluorinated functional monomers. The latter are either fluorinated vinyl ethers, ?,?,?-trifluorostyrenes or trifluorovinyl oxy aromatic monomers bearing sulfonic or phosphonic acids. The resulting membranes are

Renaud Souzy; Bruno Ameduri

2005-01-01

72

Membrane Elastic Properties and Cell Function  

PubMed Central

Recent studies indicate that the cell membrane, interacting with its attached cytoskeleton, is an important regulator of cell function, exerting and responding to forces. We investigate this relationship by looking for connections between cell membrane elastic properties, especially surface tension and bending modulus, and cell function. Those properties are measured by pulling tethers from the cell membrane with optical tweezers. Their values are determined for all major cell types of the central nervous system, as well as for macrophage. Astrocytes and glioblastoma cells, which are considerably more dynamic than neurons, have substantially larger surface tensions. Resting microglia, which continually scan their environment through motility and protrusions, have the highest elastic constants, with values similar to those for resting macrophage. For both microglia and macrophage, we find a sharp softening of bending modulus between their resting and activated forms, which is very advantageous for their acquisition of phagocytic functions upon activation. We also determine the elastic constants of pure cell membrane, with no attached cytoskeleton. For all cell types, the presence of F-actin within tethers, contrary to conventional wisdom, is confirmed. Our findings suggest the existence of a close connection between membrane elastic constants and cell function. PMID:23844071

Pontes, Bruno; Ayala, Yareni; Fonseca, Anna Carolina C.; Romão, Luciana F.; Amaral, Rac?ele F.; Salgado, Leonardo T.; Lima, Flavia R.; Farina, Marcos; Viana, Nathan B.; Moura-Neto, Vivaldo; Nussenzveig, H. Moysés

2013-01-01

73

Detection of Molecular Charges at Cell Membrane  

NASA Astrophysics Data System (ADS)

Molecular charges at the cell membrane have been successfully detected using cell-based field-effect devices. Mouse fibroblast cells were adhered to the Si3N4 gate surface of the field-effect devices. The negative charges of sialic acid at the surface of the cell membrane could be detected as a shift of the flatband voltage of the field-effect devices. Quantitative analysis of molecular charges at the cell membrane could be demonstrated in relation to the number of adhered cells on the Si3N4 gate surface. The platform based on the field-effect devices is suitable for a simple, accurate and non-invasive system for cell functional analysis.

Sakata, Toshiya; Miyahara, Yuji

2008-01-01

74

Comparison of methods used to separate the inner and outer membranes of cell envelopes of Campylobacter spp.  

PubMed

The outer membrane of Campylobacter coli, C. jejuni and C. fetus cell envelopes appeared as three fractions after sucrose gradient centrifugation. Each outer membrane fraction was contaminated with succinate dehydrogenase activity from the cytoplasmic membrane fraction. Similarly the inner membrane fraction was contaminated with 2-ketodeoxyoctonate and outer membrane proteins including the porin(s). The separation of these two membranes was not facilitated by variations in lysozyme treatment, cell age, presence or absence of flagella, or longer lipopolysaccharide chain length. Sodium lauroyl sarcosinate extraction resulted in an outer membrane fraction which contained some inner membrane contamination and produced multiple bands upon sucrose gradient centrifugation. Triton X-100 extraction removed the inner membrane from the outer membrane and Triton X-100/EDTA treatment extracted lipopolysaccharide-rich regions of the outer membrane which contained almost exclusively the Campylobacter porin(s). These data indicated that the inner and outer membranes of the Campylobacter cell envelope were very difficult to separate, possibly because of extensive fusions between these two membranes. PMID:2474628

Page, W J; Taylor, D E

1988-11-01

75

A vacuolar-type proton pump in a vesicle fraction enriched with potassium transporting plasma membranes from tobacco hornworm midgut  

SciTech Connect

Mg-ATP dependent electrogenic proton transport, monitored with fluorescent acridine orange, 9-aminoacridine, and oxonol V, was investigated in a fraction enriched with potassium transporting goblet cell apical membranes of Manduca sexta larval midgut. Proton transport and the ATPase activity from the goblet cell apical membrane exhibited similar substrate specificity and inhibitor sensitivity. ATP and GTP were far better substrates than UTP, CTP, ADP, and AMP. Azide and vanadate did not inhibit proton transport, whereas 100 microM N,N'-dicyclohexylcarbodiimide and 30 microM N-ethylmaleimide were inhibitors. The pH gradient generated by ATP and limiting its hydrolysis was 2-3 pH units. Unlike the ATPase activity, proton transport was not stimulated by KCl. In the presence of 20 mM KCl, a proton gradient could not be developed or was dissipated. Monovalent cations counteracted the proton gradient in an order of efficacy like that for stimulation of the membrane-bound ATPase activity: K+ = Rb+ much greater than Li+ greater than Na+ greater than choline (chloride salts). Like proton transport, the generation of an ATP dependent and azide- and vanadate-insensitive membrane potential (vesicle interior positive) was prevented largely by 100 microM N,N'-dicyclohexylcarbodiimide and 30 microM N-ethylmaleimide. Unlike proton transport, the membrane potential was not affected by 20 mM KCl. In the presence of 150 mM choline chloride, the generation of a membrane potential was suppressed, whereas the pH gradient increased 40%, indicating an anion conductance in the vesicle membrane. Altogether, the results led to the following new hypothesis of electrogenic potassium transport in the lepidopteran midgut. A vacuolar-type electrogenic ATPase pumps protons across the apical membrane of the goblet cell, thus energizing electroneutral proton/potassium antiport. The result is a net active and electrogenic potassium flux.

Wieczorek, H.; Weerth, S.; Schindlbeck, M.; Klein, U.

1989-07-05

76

Alternate Fuel Cell Membranes for Energy Independence  

SciTech Connect

The overall objective of this project was the development and evaluation of novel hydrocarbon fuel cell (FC) membranes that possess high temperature performance and long term chemical/mechanical durability in proton exchange membrane (PEM) fuel cells (FC). The major research theme was synthesis of aromatic hydrocarbon polymers of the poly(arylene ether sulfone) (PAES) type containing sulfonic acid groups tethered to the backbone via perfluorinated alkylene linkages and in some cases also directly attached to the phenylene groups along the backbone. Other research themes were the use of nitrogen-based heterocyclics instead of acid groups for proton conduction, which provides high temperature, low relative humidity membranes with high mechanical/thermal/chemical stability and pendant moieties that exhibit high proton conductivities in the absence of water, and synthesis of block copolymers consisting of a proton conducting block coupled to poly(perfluorinated propylene oxide) (PFPO) blocks. Accomplishments of the project were as follows: 1) establishment of a vertically integrated program of synthesis, characterization, and evaluation of FC membranes, 2) establishment of benchmark membrane performance data based on Nafion for comparison to experimental membrane performance, 3) development of a new perfluoroalkyl sulfonate monomer, N,N-diisopropylethylammonium 2,2-bis(p-hydroxyphenyl) pentafluoropropanesulfonate (HPPS), 4) synthesis of random and block copolymer membranes from HPPS, 5) synthesis of block copolymer membranes containing high-acid-concentration hydrophilic blocks consisting of HPPS and 3,3'-disulfonate-4,4'-dichlorodiphenylsulfone (sDCDPS), 6) development of synthetic routes to aromatic polymer backbones containing pendent 1H-1,2,3-triazole moieties, 7) development of coupling strategies to create phase-separated block copolymers between hydrophilic sulfonated prepolymers and commodity polymers such as PFPO, 8) establishment of basic performance properties of experimental membranes, 9) fabrication and FC performance testing of membrane electrode assemblies (MEA) from experimental membranes, and 10) measurement of ex situ and in situ membrane durability of experimental membranes. Although none of the experimental hydrocarbon membranes that issued from the project displayed proton conductivities that met DOE requirements, the project contributed to our basic understanding of membrane structure-property relationships in a number of key respects. An important finding of the benchmark studies is that physical degradation associated with humidity and temperature variations in the FC tend to open new fuel crossover pathways and act synergistically with chemical degradation to accelerate overall membrane degradation. Thus, for long term membrane survival and efficient fuel utilization, membranes must withstand internal stresses due to humidity and temperature changes. In this respect, rigid aromatic hydrocarbon fuel cell membranes, e.g. PAES, offer an advantage over un-modified Nafion membranes. The benchmark studies also showed that broadband dielectric spectroscopy is a potentially powerful tool in assessing shifts in the fundamental macromolecular dynamics caused by Nafion chemical degradation, and thus, this technique is of relevance in interrogating proton exchange membrane durability in fuel cells and macromolecular dynamics as coupled to proton migration, which is of fundamental relevance in proton exchange membranes in fuel cells. A key finding from the hydrocarbon membrane synthesis effort was that rigid aromatic polymers containing isolated ion exchange groups tethered tightly to the backbone (short tether), such as HPPS, provide excellent mechanical and durability properties but do not provide sufficient conductivity, in either random or block configuration, when used as the sole ion exchange monomer. However, we continue to hypothesize that longer tethers, and tethered groups spaced more closely within the hydrophilic chain elements of the polymer, will yield highly conductive materials with excellent mech

Storey, Robson, F.; Mauritz, Kenneth, A.; Patton, Derek, L.; Savin, Daniel, A.

2012-12-18

77

Advanced membrane electrode assemblies for fuel cells  

DOEpatents

A method of preparing advanced membrane electrode assemblies (MEA) for use in fuel cells. A base polymer is selected for a base membrane. An electrode composition is selected to optimize properties exhibited by the membrane electrode assembly based on the selection of the base polymer. A property-tuning coating layer composition is selected based on compatibility with the base polymer and the electrode composition. A solvent is selected based on the interaction of the solvent with the base polymer and the property-tuning coating layer composition. The MEA is assembled by preparing the base membrane and then applying the property-tuning coating layer to form a composite membrane. Finally, a catalyst is applied to the composite membrane.

Kim, Yu Seung; Pivovar, Bryan S.

2012-07-24

78

Advanced membrane electrode assemblies for fuel cells  

DOEpatents

A method of preparing advanced membrane electrode assemblies (MEA) for use in fuel cells. A base polymer is selected for a base membrane. An electrode composition is selected to optimize properties exhibited by the membrane electrode assembly based on the selection of the base polymer. A property-tuning coating layer composition is selected based on compatibility with the base polymer and the electrode composition. A solvent is selected based on the interaction of the solvent with the base polymer and the property-tuning coating layer composition. The MEA is assembled by preparing the base membrane and then applying the property-tuning coating layer to form a composite membrane. Finally, a catalyst is applied to the composite membrane.

Kim, Yu Seung; Pivovar, Bryan S

2014-02-25

79

Fractionation of monomeric and polymeric anthocyainins from Concord grape (Vitis labrusca L.) juice by membrane ultrafiltration.  

PubMed

Concord grape juice with 20% polymeric and 60% monomeric anthocyanin (Acy) forms was ultrafiltrated using polyvinylidene fluoride flat sheet membranes ranging from 10 to 1000 K molecular weight cutoff (MWCO) to obtain different permeate and retentate fractions. Permeate flux, membrane resistance, Acy rejection, fouling, Acy content and composition, color properties, and antioxidant activity (AOX) were characterized. Results showed that permeate flux declined with lower MWCO, while membrane resistance increased and related exponentially with fouling. Anthocyanin membrane rejection differed for polymeric and monomeric Acy forms. Polymeric Acy increased (36-66%) and monomeric Acy decreased (12-20%) in retentate fractions with membrane pore size of <100K MWCO, while polymeric Acy decreased (11-28%) and monomeric Acy increased (5-7%) in permeate fractions. Fraction properties showed that AOX related linearly with the total phenolic content, while lightness and chroma color properties related linearly to the monomeric Acy content. These results indicate that ultrafiltration can be used to tailor monomeric and polymeric Acy fractions with potential effects in color and bioactive properties. PMID:17665929

Kalbasi, Ahmad; Cisneros-Zevallos, Luis

2007-08-22

80

Cell Surface Membrane Antigen Phenotype of Human Gastrointestinal Mast Cells  

Microsoft Academic Search

Background: Mast cells (MC) are important effector cells of allergic and inflammatory reactions in diverse organs. These cells interact with a number of other immune cells and structural cells in the tissues as well as with proinflammatory mediators and cytokines. The various interactions are considered to be mediated through distinct cell surface membrane receptors on MC. Methods:In the present study,

Maria-Theresa Krauth; Yasamin Majlesi; Stefan Florian; Alexandra Böhm; Alexander W. Hauswirth; Minoo Ghannadan; Friedrich Wimazal; Markus Raderer; Friedrich Wrba; Peter Valent

2005-01-01

81

Durability of PEM Fuel Cell Membranes  

NASA Astrophysics Data System (ADS)

Durability is still a critical limiting factor for the commercialization of polymer electrolyte membrane (PEM) fuel cells, a leading energy conversion technology for powering future hydrogen fueled automobiles, backup power systems (e.g., for base transceiver station of cellular networks), portable electronic devices, etc. Ionic conducting polymer (ionomer) electrolyte membranes are the critical enabling materials for the PEM fuel cells. They are also widely used as the central functional elements in hydrogen generation (e.g., electrolyzers), membrane cell for chlor-alkali production, etc. A perfluorosulfonic acid (PFSA) polymer with the trade name Nafion® developed by DuPont™ is the most widely used PEM in chlor-alkali cells and PEM fuel cells. Similar PFSA membranes have been developed by Dow Chemical, Asahi Glass, and lately Solvay Solexis. Frequently, such membranes serve the dual function of reactant separation and selective ionic conduction between two otherwise separate compartments. For some applications, the compromise of the "separation" function via the degradation and mechanical failure of the electrolyte membrane can be the life-limiting factor; this is particularly the case for PEM in hydrogen/oxygen fuel cells.

Huang, Xinyu; Reifsnider, Ken

82

MYADM regulates Rac1 targeting to ordered membranes required for cell spreading and migration.  

PubMed

Membrane organization into condensed domains or rafts provides molecular platforms for selective recruitment of proteins. Cell migration is a general process that requires spatiotemporal targeting of Rac1 to membrane rafts. The protein machinery responsible for making rafts competent to recruit Rac1 remains elusive. Some members of the MAL family of proteins are involved in specialized processes dependent on this type of membrane. Because condensed membrane domains are a general feature of the plasma membrane of all mammalian cells, we hypothesized that MAL family members with ubiquitous expression and plasma membrane distribution could be involved in the organization of membranes for cell migration. We show that myeloid-associated differentiation marker (MYADM), a protein with unique features within the MAL family, colocalizes with Rac1 in membrane protrusions at the cell surface and distributes in condensed membranes. MYADM knockdown (KD) cells had altered membrane condensation and showed deficient incorporation of Rac1 to membrane raft fractions and, similar to Rac1 KD cells, exhibited reduced cell spreading and migration. Results of rescue-of-function experiments by expression of MYADM or active Rac1L61 in cells knocked down for Rac1 or MYADM, respectively, are consistent with the idea that MYADM and Rac1 act on parallel pathways that lead to similar functional outcomes. PMID:21325632

Aranda, Juan F; Reglero-Real, Natalia; Kremer, Leonor; Marcos-Ramiro, Beatriz; Ruiz-Sáenz, Ana; Calvo, María; Enrich, Carlos; Correas, Isabel; Millán, Jaime; Alonso, Miguel A

2011-04-15

83

Motility and plasma membrane integrity of spermatozoa in fractionated stallion ejaculates after storage.  

PubMed

With the aim of investigating properties of stallion seminal plasma to eventually improve semen-handling techniques, sperm motility and plasma membrane integrity were analysed in different fractions of the ejaculates after storage. Semen was collected using a computer-controlled automated phantom that separates the ejaculates into five successive cups. Samples containing seminal plasma and skim milk extender were compared with samples stored in skim milk extender after the removal of seminal plasma by centrifugation. Fractionated ejaculates were stored cooled for 24 h after dilution with extender (Expt 1) or frozen in liquid nitrogen (Expt 2). In Expt 1, cup 1 was pre-sperm fluid, cups 2 and 3 sperm-rich fractions, and cup 4 sperm-poor fractions. In Expt 2, cups 1 and 2 were sperm-rich fractions, and cups 3 and 4 sperm-poor fractions. One sample (WE) represented the whole ejaculate in both experiments. Motility parameters were determined with a Hamilton-Thorn Motility Analyzer, and plasma membrane integrity was assessed using carboxyfluorescein diacetate and propidium iodide staining and fluorescence microscopy. The removal of seminal plasma lowered motility values, but not plasma membrane integrity, in both experiments. No significant differences between cups were observed after cooled storage. The cups differed significantly in most post-thaw motility parameters, and the sperm-rich fraction showed higher post-thaw motility than the whole ejaculate. PMID:16420325

Kareskoski, A M; Reilas, T; Andersson, M; Katila, T

2006-02-01

84

Structure and thermotropic phase behaviour of detergent-resistant membrane raft fractions isolated from human and ruminant erythrocytes  

Microsoft Academic Search

Detergent-resistant membrane raft fractions have been prepared from human, goat, and sheep erythrocyte ghosts using Triton X-100. The structure and thermotropic phase behaviour of the fractions have been examined by freeze-fracture electron microscopy and synchrotron X-ray diffraction methods. The raft fractions are found to consist of vesicles and multilamellar structures indicating considerable rearrangement of the original ghost membrane. Few membrane-associated

Peter J. Quinn; Cedric Tessier; Dominique Rainteau; Kamen S. Koumanov; Claude Wolf

2005-01-01

85

Mechanical tension drives cell membrane fusion.  

PubMed

Membrane fusion is an energy-consuming process that requires tight juxtaposition of two lipid bilayers. Little is known about how cells overcome energy barriers to bring their membranes together for fusion. Previously, we have shown that cell-cell fusion is an asymmetric process in which an "attacking" cell drills finger-like protrusions into the "receiving" cell to promote cell fusion. Here, we show that the receiving cell mounts a Myosin II (MyoII)-mediated mechanosensory response to its invasive fusion partner. MyoII acts as a mechanosensor, which directs its force-induced recruitment to the fusion site, and the mechanosensory response of MyoII is amplified by chemical signaling initiated by cell adhesion molecules. The accumulated MyoII, in turn, increases cortical tension and promotes fusion pore formation. We propose that the protrusive and resisting forces from fusion partners put the fusogenic synapse under high mechanical tension, which helps to overcome energy barriers for membrane apposition and drives cell membrane fusion. PMID:25684354

Kim, Ji Hoon; Ren, Yixin; Ng, Win Pin; Li, Shuo; Son, Sungmin; Kee, Yee-Seir; Zhang, Shiliang; Zhang, Guofeng; Fletcher, Daniel A; Robinson, Douglas N; Chen, Elizabeth H

2015-03-01

86

Fuel cell subassemblies incorporating subgasketed thrifted membranes  

DOEpatents

A fuel cell roll good subassembly is described that includes a plurality of individual electrolyte membranes. One or more first subgaskets are attached to the individual electrolyte membranes. Each of the first subgaskets has at least one aperture and the first subgaskets are arranged so the center regions of the individual electrolyte membranes are exposed through the apertures of the first subgaskets. A second subgasket comprises a web having a plurality of apertures. The second subgasket web is attached to the one or more first subgaskets so the center regions of the individual electrolyte membranes are exposed through the apertures of the second subgasket web. The second subgasket web may have little or no adhesive on the subgasket surface facing the electrolyte membrane.

Iverson, Eric J; Pierpont, Daniel M; Yandrasits, Michael A; Hamrock, Steven J; Obradovich, Stephan J; Peterson, Donald G

2014-01-28

87

Basement Membranes: Cell Scaffoldings and Signaling Platforms  

PubMed Central

Basement membranes are widely distributed extracellular matrices that coat the basal aspect of epithelial and endothelial cells and surround muscle, fat, and Schwann cells. These extracellular matrices, first expressed in early embryogenesis, are self-assembled on competent cell surfaces through binding interactions among laminins, type IV collagens, nidogens, and proteoglycans. They form stabilizing extensions of the plasma membrane that provide cell adhesion and that act as solid-phase agonists. Basement membranes play a role in tissue and organ morphogenesis and help maintain function in the adult. Mutations adversely affecting expression of the different structural components are associated with developmental arrest at different stages as well as postnatal diseases of muscle, nerve, brain, eye, skin, vasculature, and kidney. PMID:21421915

Yurchenco, Peter D.

2011-01-01

88

Membrane depolarization in LAN1 cells  

Microsoft Academic Search

We investigated the influence of ion compositions on the membrane potential in LA-N-1 human neuroblastoma cells using bisoxonol\\u000a as a potential-sensitive fluorescent dye. The ability of K+, ouabain, veratridine, and maitotoxin to induce membrane depolarization was evaluated. Increasing concentrations of K+ ions from 10 to 50 mM caused a dose-dependent increase of bisoxonol fluorescence, which was completely independent on Na+

Giuseppe Sorrentino; Maria R. Monsurrõ; Indrapal N. Singh; Julian N. Kanfer

1997-01-01

89

Interaction of human CBG with cell membranes.  

PubMed

Specific binding sites for corticosteroid-binding globulin (CBG) and its pregnancy-associated variant (pCBG), having a modified carbohydrate moiety, were found in the plasma membranes of human liver, decidual endometrium and placental syncytiotrophoblast. The membrane binding was influenced by the conformation of the glycoprotein molecules and structure of their carbohydrate chains. CBG receptor was solubilized from the endometrium membrane and partially characterized. It was found to have a subunit structure, with a homooligomeric sialoglycoprotein consisting of four 20 kDa protomeric species being involved in the recognition of the CBG molecules complexed with progesterone or cortisol. A kinetic study using membrane microvesicles derived from the syncytiotrophoblast brush border revealed that neither CBG nor pCBG restricted cortisol accumulation in the intravesicular space, whereas only normal CBG could penetrate the syncytiotrophoblast membrane. Action of the CBG-cortisol complex on trophoblast cells resulted in the activation of membrane adenylate cyclase and growth of the cAMP accumulation within these cells. Collectively, these findings suggest that both normal CBG and pCBG are involved in the guided transport of steroid hormones to the target cells and transmembrane transfer of hormones and/or hormonal signals. PMID:1659892

Strel'chyonok, O A; Avvakumov, G V

1991-01-01

90

Membrane potential dynamics of grid cells.  

PubMed

During navigation, grid cells increase their spike rates in firing fields arranged on a markedly regular triangular lattice, whereas their spike timing is often modulated by theta oscillations. Oscillatory interference models of grid cells predict theta amplitude modulations of membrane potential during firing field traversals, whereas competing attractor network models predict slow depolarizing ramps. Here, using in vivo whole-cell recordings, we tested these models by directly measuring grid cell intracellular potentials in mice running along linear tracks in virtual reality. Grid cells had large and reproducible ramps of membrane potential depolarization that were the characteristic signature tightly correlated with firing fields. Grid cells also demonstrated intracellular theta oscillations that influenced their spike timing. However, the properties of theta amplitude modulations were not consistent with the view that they determine firing field locations. Our results support cellular and network mechanisms in which grid fields are produced by slow ramps, as in attractor models, whereas theta oscillations control spike timing. PMID:23395984

Domnisoru, Cristina; Kinkhabwala, Amina A; Tank, David W

2013-03-14

91

Blend Concepts for Fuel Cell Membranes  

NASA Astrophysics Data System (ADS)

Differently cross-linked blend membranes were prepared from commercial arylene main-chain polymers from the classes of poly(ether-ketones) and poly(ethersulfones) modified with sulfonate groups, sulfinate cross-linking groups and basic N-groups. The following membrane types have been prepared: (a) van-der Waals/dipole-dipole blends by mixing a polysulfonate with unmodified PSU. This membrane type showed a heterogeneous morphology, leading to extreme swelling and even dissolution of the sulfonated component at elevated temperatures. (b) Hydrogen bridge blends by mixing a polysulfonate with a polyamide or polyetherimide. This membrane type showed a partially heterogeneous morphology, also leading to extreme swelling/dissolution of the sulfonated blend component at elevated temperatures. (c) Acid-base blends by mixing a polysulfonate with a polymeric N-base (self-developed/commercial). With this membrane type, we could reach a wide variability of properties by variation of different parameters. Membranes showing excellent stability and good fuel cell performance up to 100°C (PEFC) and 130°C (DMFC) were obtained. (d) Covalently cross-linked (blend) membranes by either mixing of a polysulfonate with a polysulfinate or by preparation of a polysulfinatesulfonate, followed by reaction of the sulfinate groups in solution with a dihalogeno compound under S-alkylation. Membranes were prepared that showed effective suppression of swelling without H+-conductivity loss. The membranes showed good PEFC (up to 100°C) and DMFC (up to 130°C) performance. (e) Covalent-ionically cross-linked blend membranes by mixing polysulfonates with polysulfinates and polybases or by mixing a polysulfonate with a polymer carrying both sulfinate and basic N-groups. The covalent-ionically cross-linked membranes were tested in DMFC up to 110°C and showed a good performance. (f) Differently cross-linked organic-inorganic blend composite membranes via different procedures. The best results were obtained with blend membranes having a layered zirconium phosphate “ZrP” phase: They were transparent, and showed good H+;-conductivity and stability. Application of one of these composite membranes to a PEFC yielded good performance up to T=115°C.

Kerres, Jochen

92

High density cell culture by membrane-based cell recycle.  

PubMed

Enhancement of productivity of a bioprocess necessitates continuous operation of bioreactors with high biomass concentrations than are possible in conventional batch, fedbatch or continuous modes of culture. Membrane-based cell recycle has been effectively used to maintain high cell concentrations in bioreactors. This review compares membranebased cell recycle operation with other such high density cell culture systems as immobilized cell reactors and reactors with cell recycle by centrifugation or gravity sedimentation. A theoretical of production of primary and secondary metabolites in membrane-based recycle systems is presented. Operation of this type of system is discussed with examples from aerobic and anaerobic fermentations. PMID:14548467

Chang, H N; Yoo, I K; Kim, B S

1994-01-01

93

Fractions!  

NSDL National Science Digital Library

Practice all of the activities to help you learn fractions! Go through all five levels of Fractions Review Activities Practice Naming Fractions Do you remember how to do Fraction Sets? Play these games when you have finished the top three activities: Cross the River Pizza Party Fractions Rescue Island Adding Subtracting Fractions SPLAT Mrs. Anderson's Fraction Games Action Fraction Soccer Shootout Fraction Multiplication Soccer Shootout Fraction Division Dirt Bike Fractions Comparisons ...

Miss Lerdahl

2011-02-01

94

Polyphosphoinositides are present in plasma membranes isolated from fusogenic carrot cells  

Microsoft Academic Search

Fusogenic carrot cells grown in suspension culture were labeled 12 hours with myo-(2-³H)inositol. Plasma membranes were isolated from the prelabeled fusogenic carrot cells by both aqueous polymer two-phase partitioning and Renografin density gradients. With both methods, the plasma membrane-enriched fractions, as identified by marker enzymes, were enriched in (³H)inositol-labeled phosphatidylinositol monophosphate (PIP) and phosphatidylinositol bisphosphate (PIPâ). An additional (³H)inositol-labeled lipid,

J. J. Wheeler; W. F. Boss

1987-01-01

95

Subcellular fractionation of stored red blood cells reveals a compartment-based protein carbonylation evolution.  

PubMed

During blood banking, erythrocytes undergo storage lesions, altering or degrading their metabolism, rheological properties, and protein content. Carbonylation is a hallmark of protein oxidative lesions, thus of red blood cell oxidative stress. In order to improve global erythrocyte protein carbonylation assessment, subcellular fractionation has been established, allowing us to work on four different protein populations, namely soluble hemoglobin, hemoglobin-depleted soluble fraction, integral membrane and cytoskeleton membrane protein fractions. Carbonylation in erythrocyte-derived microparticles has also been investigated. Carbonylated proteins were derivatized with 2,4-dinitrophenylhydrazine (2,4-DNPH) and quantified by western blot analyses. In particular, carbonylation in the cytoskeletal membrane fraction increased remarkably between day 29 and day 43 (P<0.01). Moreover, protein carbonylation within microparticles released during storage showed a two-fold increase along the storage period (P<0.01). As a result, carbonylation of cytoplasmic and membrane protein fractions differs along storage, and the present study allows explaining two distinct steps in global erythrocyte protein carbonylation evolution during blood banking. This article is part of a Special Issue entitled: Integrated omics. PMID:22580360

Delobel, Julien; Prudent, Michel; Rubin, Olivier; Crettaz, David; Tissot, Jean-Daniel; Lion, Niels

2012-12-01

96

A Hybrid Microbial Fuel Cell Membrane Bioreactor with a Conductive Ultrafiltration Membrane Biocathode for Wastewater Treatment  

E-print Network

A Hybrid Microbial Fuel Cell Membrane Bioreactor with a Conductive Ultrafiltration Membrane-biocathode microbial fuel cell- membrane bioreactor (MFC-MBR) system was developed to achieve simultaneous wastewater these goals. A microbial fuel cell (MFC) is a technology that uses exoelectrogenic biofilms on the anode

97

Release of extracellular membrane vesicles from microvilli of epithelial cells is enhanced by depleting membrane cholesterol  

Microsoft Academic Search

We previously reported on the occurrence of prominin-1-carrying membrane vesicles that are released into body fluids from microvilli of epithelial cells. This release has been implicated in cell differentiation. Here we have characterized these vesicles released from the differentiated Caco-2 cells. We find that in these vesicles, prominin-1 directly interacts with membrane cholesterol and is associated with a membrane microdomain.

Anne-Marie Marzesco; Michaela Wilsch-Bräuninger; Véronique Dubreuil; Peggy Janich; Katja Langenfeld; Christoph Thiele; Wieland B. Huttner; Denis Corbeil

2009-01-01

98

Fractional occurrence of defects in membranes and mechanically driven interleaflet phospholipid transport  

NASA Astrophysics Data System (ADS)

The picture of biological membranes as uniform, homogeneous bileaflet structures has been revised in recent times due to the growing recognition that these structures can undergo significant fluctuations both in local curvature and in thickness. In particular, evidence has been obtained that a temporary, localized disordering of the lipid bilayer structure (defects) may serve as a principal pathway for movement of lipid molecules from one leaflet of the membrane to the other. How frequently these defects occur and how long they remain open are important unresolved questions. In this report, we calculate the rate of molecular transport through a transient defect in the membrane and compare this result to measurements of the net transbilayer flux of lipid molecules measured in an experiment in which the lipid flux is driven by differences between the mechanical stress in the two leaflets of the membrane bilayer. Based on this comparison, we estimate the frequency of defect occurrence in the membrane. The occurrence of defects is rare: the probability of finding a defect in 1.0 ?m2 of a lecithin membrane is estimated to be ~6.0×10-6. Based on this fractional occurrence of defects, the free energy of defect formation is estimated to be ~1.0×10-19 J. The calculations provide support for a model in which interleaflet transport in membranes is accelerated by mechanically driven lipid flow.

Raphael, Robert M.; Waugh, Richard E.; Svetina, Saša.; Žekš, Boštjan

2001-11-01

99

Integration of Cell Membranes and Nanotube Transistors  

E-print Network

Integration of Cell Membranes and Nanotube Transistors Keith Bradley, Alona Davis, Jean. As the nanoelectronic device, we use a nanotube network transistor, which incorporates many individual nanotubes as transistors, and that the two systems interact. Further, we use the interaction to study the charge

Gruner, George

100

Membrane electrode assembly for a fuel cell  

NASA Technical Reports Server (NTRS)

A catalyst ink for a fuel cell including a catalytic material and poly(vinylidene fluoride). The ink may be applied to a substrate to form an electrode, or bonded with other electrode layers to form a membrane electrode assembly (MEA).

Prakash, Surya (Inventor); Narayanan, Sekharipuram R. (Inventor); Atti, Anthony (Inventor); Olah, George (Inventor); Smart, Marshall C. (Inventor)

2006-01-01

101

Corrugated Membrane Fuel Cell 2010 DOE Hydrogen Program Fuel Cell  

E-print Network

Corrugated Membrane Fuel Cell Structures Structures 2010 DOE Hydrogen Program Fuel Cell 2010 DOE Hydrogen Program Fuel Cell Project Kick-Off Principle Investigator: Dr. Stephen Grot Presenter: Dr structure Compared to MEA in a flat plate structure 9 #12;Technical Accomplishments Titanium Screen as Gas

102

Natural organic matter (NOM) fouling of ultrafiltration membranes: fractionation of NOM in surface water and characterisation by LC-OCD  

Microsoft Academic Search

Natural organic matter (NOM) plays a significant role in fouling of ultrafiltration membranes in drinking water treatment processes. The aim of this study was to obtain a better understanding of the interactions between the fractional components of NOM and a hydrophilic PES\\/PVP hollow fiber ultrafiltration membrane (150–200 kDa). NOM was fractionated into hydrophobic, transphilic and hydrophilic acid fractions according to

Maria D. Kennedy; Hyoung K. Chun; Victor A. Quintanilla Yangalia; Bas G. J. Heijman; Jan C. Schippers

2005-01-01

103

Sodium selectivity of Reissner's membrane epithelial cells  

PubMed Central

Background Sodium absorption by Reissner's membrane is thought to contribute to the homeostasis of the volume of cochlear endolymph. It was previously shown that the absorptive transepithelial current was blocked by amiloride and benzamil. The most commonly-observed target of these drugs is the epithelial sodium channel (ENaC), which is composed of the three subunits ?-,?- and ?-ENaC. However, other less-selective cation channels have also been observed to be sensitive to benzamil and amiloride. The aim of this study was to determine whether Reissner's membrane epithelial cells could support parasensory K+ absorption via amiloride- and benzamil-sensitive electrogenic pathways. Results We determined the molecular and functional expression of candidate cation channels with gene array (GEO GSE6196), RT-PCR, and whole-cell patch clamp. Transcript expression analysis of Reissner's membrane detected no amiloride-sensitive acid-sensing ion channels (ASIC1a, ASIC2a, ASIC2b) nor amiloride-sensitive cyclic-nucleotide gated channels (CNGA1, CNGA2, CNGA4, CNGB3). By contrast, ?-,?- and ?-ENaC were all previously reported as present in Reissner's membrane. The selectivity of the benzamil-sensitive cation currents was observed in whole-cell patch clamp recordings under Cl--free conditions where cations were the only permeant species. The currents were carried by Na+ but not K+, and the permeability of Li+ was greater than that of Na+ in Reissner's membrane. Complete replacement of bath Na+ with the inpermeable cation NMDG+ led to the same inward current as with benzamil in a Na+ bath. Conclusions These results are consistent with the amiloride/benzamil-sensitive absorptive flux of Reissner's membrane mediated by a highly Na+-selective channel that has several key characteristics in common with ???-ENaC. The amiloride-sensitive pathway therefore absorbs only Na+ in this epithelium and does not provide a parasensory K+ efflux route from scala media. PMID:21284860

2011-01-01

104

Activation of intrinsic apoptotic signaling pathway in cancer cells by Cymbopogon citratus polysaccharide fractions.  

PubMed

Essential oils of Cymbopogon citratus were already reported to have wide ranging medical and industrial applications. However, information on polysaccharides from the plant and their anticancer activities are limited. In the present study, polysaccharides from C. citratus were extracted and fractionated by anion exchange and gel filtration chromatography. Two different polysaccharide fractions such as F1 and F2 were obtained, and these fractions were found to have distinct acidic polysaccharides as characterized by their molecular weight and sugar content. NMR spectral analysis revealed the presence of (1?4) linked b-d-Xylofuranose moiety in these polysaccharides. Using these polysaccharide fractions F1 and F2, anti-inflammatory and anticancer activities were evaluated against cancer cells in vitro and the mechanism of action of the polysaccharides in inducing apoptosis in cancer cells via intrinsic pathway was also proposed. Two different reproductive cancer cells such as Siha and LNCap were employed for in vitro studies on cytotoxicity, induction of apoptosis and apoptotic DNA fragmentation, changes in mitochondrial membrane potential, and profiles of gene and protein expression in response to treatment of cells by the polysaccharide fractions. These polysaccharide fractions exhibited potential cytotoxic and apoptotic effects on carcinoma cells, and they induced apoptosis in these cells through the events of up-regulation of caspase 3, down-regulation of bcl-2 family genes followed by cytochrome c release. PMID:24702929

Thangam, Ramar; Sathuvan, Malairaj; Poongodi, Arasu; Suresh, Veeraperumal; Pazhanichamy, Kalailingam; Sivasubramanian, Srinivasan; Kanipandian, Nagarajan; Ganesan, Nalini; Rengasamy, Ramasamy; Thirumurugan, Ramasamy; Kannan, Soundarapandian

2014-07-17

105

Sputter-deposited fuel cell membranes and electrodes  

NASA Technical Reports Server (NTRS)

A method for preparing a membrane for use in a fuel cell membrane electrode assembly includes the steps of providing an electrolyte membrane, and sputter-depositing a catalyst onto the electrolyte membrane. The sputter-deposited catalyst may be applied to multiple sides of the electrolyte membrane. A method for forming an electrode for use in a fuel cell membrane electrode assembly includes the steps of obtaining a catalyst, obtaining a backing, and sputter-depositing the catalyst onto the backing. The membranes and electrodes are useful for assembling fuel cells that include an anode electrode, a cathode electrode, a fuel supply, and an electrolyte membrane, wherein the electrolyte membrane includes a sputter-deposited catalyst, and the sputter-deposited catalyst is effective for sustaining a voltage across a membrane electrode assembly in the fuel cell.

Narayanan, Sekharipuram R. (Inventor); Jeffries-Nakamura, Barbara (Inventor); Chun, William (Inventor); Ruiz, Ron P. (Inventor); Valdez, Thomas I. (Inventor)

2001-01-01

106

Investigation of Transient Phenomena of Proton Exchange Membrane Fuel Cells  

E-print Network

Investigation of Transient Phenomena of Proton Exchange Membrane Fuel Cells by Roongrojana of Proton Exchange Membrane Fuel Cells by Roongrojana Songprakorp BSc, Prince of Songkhla University to the modeling and under- standing of the dynamic behavior of proton exchange membrane fuel cells (PEMFCs

Victoria, University of

107

Durability aspects of polymer electrolyte membrane fuel cells  

NASA Astrophysics Data System (ADS)

In order for the successful adoption of proton exchange membrane (PEM) fuel cell technology, it is imperative that durability is understood, quantified and improved. A number of mechanisms are known to contribute to PEMFC membrane electrode assembly (MEA) performance degradation. In this dissertation, we show, via experiments, some of the various processes that degrade the proton exchange membrane in a PEM fuel cell; and catalyst poisoning due to hydrogen sulfide (H2S) and siloxane. The effect of humidity on the chemical stability of two types of membranes, [i.e., perfluorosulfonic acid type (PFSA, NafionRTM 112) and biphenyl sulfone hydrocarbon type, (BPSH-35)] was studied by subjecting the MEAs to open-circuit voltage (OCV) decay and potential cycling tests at elevated temperatures and low inlet gas relative humidities. The BPSH-35 membranes showed poor chemical stability in ex situ Fenton tests compared to that of NafionRTM membranes. However, under fuel cell conditions, BPSH-35 MEAs outperformed NafionRTM 112 MEAs in both the OCV decay and potential cycling tests. For both membranes, (i) at a given temperature, membrane degradation was more pronounced at lower humidities and (ii) at a given relative humidity operation, increasing the cell temperature accelerated membrane degradation. Mechanical stability of these two types of membranes was also studied using relative humidity (RH) cycling. Hydrogen peroxide (H2O2) formation rates in a proton exchange membrane (PEM) fuel cell were estimated by studying the oxygen reduction reaction (ORR) on a rotating ring disc electrode (RRDE). Fuel cell conditions were replicated by depositing a film of Pt/Vulcan XC-72 catalyst onto the disk and by varying the temperature, dissolved O2 concentration and the acidity levels in HClO4. The HClO4 acidity was correlated to ionomer water activity and hence fuel cell humidity. H 2O2 formation rates showed a linear dependence on oxygen concentration and square dependence on water activity. The H2O 2 selectivity in ORR was independent of oxygen concentration but increased with decrease in water activity (i.e., decreased humidity). Presences of trace impurities (such as CO, H2S, NH3, etc.) in the fuel also affect PEMFC durability. Among these impurities, H 2S causes significantly higher performance loss and irreversible catalytic poisoning. A concise mechanism for the poisoning kinetics of H2S on composite solid polymer electrolyte Pt (SPE-Pt) electrode was validated experimentally by charge balances and theoretically by a model, which predicted the oxidation current as a function of the applied potential. H2S dissociatively adsorbed onto SPE-Pt electrode as linear and bridge bonded sulfur (S) species and, under favorable potentials, underwent electro-oxidation to sulfur and then to sulfur dioxide (SO2). Fraction of the adsorbed S species remained as 'hard-to-oxidize' adsorbents and caused irreversible loss of catalytic activity. Deactivation of bridge sites occurred first followed by the loss of linear sites. A method to estimate the catalytic sites irreversibly lost due to sulfur poisoning was developed.

Sethuraman, Vijay Anand

108

Design and optimization of polymer electrolyte membrane (PEM) fuel cells  

NASA Astrophysics Data System (ADS)

The performance of polymer electrolyte membrane (PEM) fuel cells is studied using a single-phase two-dimensional electrochemical model. The model is coupled with a nonlinear constrained optimization algorithm to determine an optimum design of the fuel cell with respect to the operation and the geometrical parameters of cathode such as the air inlet pressure, the cathode thickness and length and the width of shoulders in the interdigitated air distributor. In addition, the robustness of the optimum design of the fuel cell with respect to uncertainties in several electrochemical reaction and species transport parameters (e.g., gas diffusivity, agglomerate particle size, etc.) is tested using a statistical sensitivity analysis. The results of the optimization analysis show that higher current densities at a constant cell voltage are obtained as the inlet air pressure and the fraction of the cathode length associated with a shoulder of the interdigitated air distributor are increased, and as the cathode thickness and the length of the cathode per one interdigitated gas distributor shoulder are decreased. The statistical sensitivity analysis results, on the other hand, show that the equilibrium cathode/membrane potential difference has the largest effect on the predicted polarization curve of the fuel cell. However, the optimal design of the cathode side of the fuel cell is found not to be affected by the uncertainties in the model parameters such as the equilibrium cathode/membrane potential difference. The results obtained are rationalized in terms of the effect of the fuel-cell design on the air flow fields and the competition between the rates of species transport to and from the cathode active layer and the kinetics of the oxygen reduction half-reaction.

Grujicic, M.; Chittajallu, K. M.

2004-04-01

109

Catalytic membranes for fuel cells  

DOEpatents

A fuel cell of the present invention comprises a cathode and an anode, one or both of the anode and the cathode including a catalyst comprising a bundle of longitudinally aligned graphitic carbon nanotubes including a catalytically active transition metal incorporated longitudinally and atomically distributed throughout the graphitic carbon walls of said nanotubes. The nanotubes also include nitrogen atoms and/or ions chemically bonded to the graphitic carbon and to the transition metal. Preferably, the transition metal comprises at least one metal selected from the group consisting of Fe, Co, Ni, Mn, and Cr.

Liu, Di-Jia (Naperville, IL); Yang, Junbing (Bolingbrook, IL); Wang, Xiaoping (Naperville, IL)

2011-04-19

110

Free Energy Difference in Indolicidin Attraction to Eukaryotic and Prokaryotic Model Cell Membranes  

E-print Network

Free Energy Difference in Indolicidin Attraction to Eukaryotic and Prokaryotic Model Cell Membranes and structural determinants of indolicidin interactions with eukaryotic and prokaryotic cell membranes using and prokaryotic cell membranes. Indolicidin was preferentially attracted to the model prokaryotic cell membrane

111

Dynamics of photoinduced cell plasma membrane injury.  

PubMed

We have developed a video microscopy system designed for real-time measurement of single cell damage during photolysis under well defined physicochemical and photophysical conditions. Melanoma cells cultured in vitro were treated with the photosensitizer (PS), tin chlorin e6 (SnCe6) or immunoconjugate (SnCe6 conjugated to a anti-ICAM monoclonal antibody), and illuminated with a 10 mW He/Ne laser at a 630 nm wavelength. Cell membrane integrity was assessed using the vital dye calcein-AM. In experiments in which the laser power density and PS concentration were varied, it was determined that the time lag before cell rupture was inversely proportional to the estimated singlet oxygen flux to the cell surface. Microscopic examination of the lytic event indicated that photo-induced lysis was caused by a point rupture of the plasma membrane. The on-line nature of this microscopy system offers an opportunity to monitor the dynamics of the cell damage process and to gain insights into the mechanism governing photolytic cell injury processes. PMID:7612864

Thorpe, W P; Toner, M; Ezzell, R M; Tompkins, R G; Yarmush, M L

1995-05-01

112

Beauvericin induced erythrocyte cell membrane scrambling.  

PubMed

Beauvericin is a mycotoxin with antiviral, antibacterial, nematicidal, insecticidal, cytotoxic, and apoptotic activity. Similar to nucleated cells erythrocytes may undergo suicidal death or eryptosis, which is characterized by cell shrinkage and phosphatidylserine exposure at the erythrocyte surface. Eryptosis may be triggered by energy depletion leading to increase of cytosolic Ca²+ activity. The present study thus explored whether beauvericin is able to trigger eryptosis and influence eryptosis following energy depletion. Cell membrane scrambling was estimated from binding of annexin V to phosphatidylserine at the erythrocyte surface, cell volume from forward scatter in FACS analysis, cytosolic Ca²+ concentration from Fluo3 fluorescence, cytosolic ATP concentration from a luciferase-assay and ion channel activity with whole cell patch clamp. Exposure to beauvericin (? 5 ?M) significantly decreased erythrocyte ATP concentration and increased cytosolic Ca²+ concentration as well as annexin V-binding. The effect of beauvericin on annexin V binding was significantly blunted by removal of extracellular Ca²+. Glucose depletion (48 h) was followed by, increase of Fluo3 fluorescence, decrease of forward scatter and increase of annexin V-binding. Beauvericin (? 1 ?M) augmented the effect of glucose withdrawal on Fluo3 fluorescence and annexin V-binding, but significantly blunted the effect of glucose withdrawal on forward scatter, an effect paralleled by inhibition of Ca²+ activated K+ channels. The present observations disclose novel effects of beauvericin, i.e. stimulation of Ca²+ entry with subsequent cell membrane scrambling and inhibition of Ca²+ activated K+ channels with blunting of cell shrinkage. PMID:21296643

Qadri, Syed M; Kucherenko, Yuliya; Lang, Florian

2011-04-28

113

Correlation of cell membrane dynamics and cell motility  

PubMed Central

Background Essential events of cell development and homeostasis are revealed by the associated changes of cell morphology and therefore have been widely used as a key indicator of physiological states and molecular pathways affecting various cellular functions via cytoskeleton. Cell motility is a complex phenomenon primarily driven by the actin network, which plays an important role in shaping the morphology of the cells. Most of the morphology based features are approximated from cell periphery but its dynamics have received none to scant attention. We aim to bridge the gap between membrane dynamics and cell states from the perspective of whole cell movement by identifying cell edge patterns and its correlation with cell dynamics. Results We present a systematic study to extract, classify, and compare cell dynamics in terms of cell motility and edge activity. Cell motility features extracted by fitting a persistent random walk were used to identify the initial set of cell subpopulations. We propose algorithms to extract edge features along the entire cell periphery such as protrusion and retraction velocity. These constitute a unique set of multivariate time-lapse edge features that are then used to profile subclasses of cell dynamics by unsupervised clustering. Conclusions By comparing membrane dynamic patterns exhibited by each subclass of cells, correlated trends of edge and cell movements were identified. Our findings are consistent with published literature and we also identified that motility patterns are influenced by edge features from initial time points compared to later sampling intervals. PMID:22372978

2011-01-01

114

Solubilization and Partial Purification of the Adenosine Triphosphatase from a Corn Root Plasma Membrane Fraction  

PubMed Central

The K+-stimulated ATPase was partially purified from a plasma membrane fraction from corn roots (WF9 × Mo 17) by solubilization with 30 millimolar octyl-?-d-glucopyranoside followed by precipitation with dilute ammonium sulfate. The specific activity of the enzyme was increased about five times by this procedure. The molecular weight of the detergent-extracted ATPase complex was estimated to be at least 500,000 daltons by chromatography on a Bio-Gel A-5m column. Negative staining electron microscopy indicated that the detergent-extracted material consisted of amorphous particles, while the ammonium sulfate precipitate was composed of uniform vesicles with an average diameter of 100 nanometers. The protein composition of the ammonium sulfate precipitate was significantly different from that of the plasma membrane fraction when compared by sodium dodecyl sulfate gel electrophoresis. The characteristics of the partially purified ATPase resembled those of the plasma membrane associated enzyme. The ATPase required Mg2+, was further stimulated by K+, was almost completely inhibited by 0.1 millimolar diethylstilbestrol, and was not affected by 5.0 micrograms per milliliter oligomycin. Although the detergents sodium cholate, deoxycholate, Triton X-100 and Lubrol WX also solubilized some membrane protein, none solubilized the K+-stimulated ATPase activity. Low concentrations of each detergent, including octyl-?-d-glucopyranoside, activated the ATPase and higher concentrations inactivated the enzyme. These results suggest that the plasma membrane ATPase is a large, integral membrane protein or protein complex that requires lipids to maintain its activity. Images PMID:16661309

Dupont, Frances M.; Leonard, Robert T.

1980-01-01

115

Unraveling sterol-dependent membrane phenotypes by analysis of protein abundance-ratio distributions in different membrane fractions under biochemical and endogenous sterol depletion.  

PubMed

During the last decade, research on plasma membrane focused increasingly on the analysis of so-called microdomains. It has been shown that function of many membrane-associated proteins involved in signaling and transport depends on their conditional segregation within sterol-enriched membrane domains. High throughput proteomic analysis of sterol-protein interactions are often based on analyzing detergent resistant membrane fraction enriched in sterols and associated proteins, which also contain proteins from these microdomain structures. Most studies so far focused exclusively on the characterization of detergent resistant membrane protein composition and abundances. This approach has received some criticism because of its unspecificity and many co-purifying proteins. In this study, by a label-free quantitation approach, we extended the characterization of membrane microdomains by particularly studying distributions of each protein between detergent resistant membrane and detergent-soluble fractions (DSF). This approach allows a more stringent definition of dynamic processes between different membrane phases and provides a means of identification of co-purifying proteins. We developed a random sampling algorithm, called Unicorn, allowing for robust statistical testing of alterations in the protein distribution ratios of the two different fractions. Unicorn was validated on proteomic data from methyl-?-cyclodextrin treated plasma membranes and the sterol biosynthesis mutant smt1. Both, chemical treatment and sterol-biosynthesis mutation affected similar protein classes in their membrane phase distribution and particularly proteins with signaling and transport functions. PMID:24030099

Zauber, Henrik; Szymanski, Witold; Schulze, Waltraud X

2013-12-01

116

Analyzing the effects of surface distribution of pores in cell electroporation for a cell membrane containing cholesterol  

E-print Network

This paper presents a model and numerical analysis of transmembrane potential induced in biological cell membrane under the influence of externally applied electric field (i.e., electroporation). This model differs from the established models in two distinct ways. Firstly, it incorporates the presence of cholesterol (~20% mole-fraction) in the membrane. Secondly, it considers the dependence of pore distribution on the variation of transmembrane potential from one region of the cell to the other. Formulation is based on the role of membrane tension and electrical forces in the formation of pores in a cell membrane, which is considered as an infinitesimally thin insulator. The model has been used to explore the creation and evolution of pores and to determine the number and size of pores as function of applied electric field (magnitude & duration). Results show that the presence of cholesterol enhances poration by changing the membrane tension. Analysis indicate that the number of pores, average pore radii ...

Shil, Pratip; Vidyasagar, Pandit B

2007-01-01

117

Cell-to-cell transfer of bacterial outer membrane lipoproteins.  

PubMed

Myxococcus xanthus cells can glide forward by retracting type IV pili. Tgl, an outer membrane lipoprotein, is necessary to assemble pili. Tgl mutants can be transiently "stimulated" if brought into end-to-end contact with tgl+ donor cells. By separating the stimulated recipient cells from donor cells, we found that Tgl protein was transferred from the donors to the rescued recipient cells. Mutants lacking CglB lipoprotein, which is part of a second gliding engine, could also be stimulated, and CglB protein was transferred from donor to recipient cells. The high transfer efficiency of Tgl and CglB proteins suggests that donor and recipient cells briefly fuse their outer membranes. PMID:15994555

Nudleman, Eric; Wall, Daniel; Kaiser, Dale

2005-07-01

118

Fuel cell membranes and crossover prevention  

DOEpatents

A membrane electrode assembly for use with a direct organic fuel cell containing a formic acid fuel includes a solid polymer electrolyte having first and second surfaces, an anode on the first surface and a cathode on the second surface and electrically linked to the anode. The solid polymer electrolyte has a thickness t:.gtoreq..times..times..times..times. ##EQU00001## where C.sub.f is the formic acid fuel concentration over the anode, D.sub.f is the effective diffusivity of the fuel in the solid polymer electrolyte, K.sub.f is the equilibrium constant for partition coefficient for the fuel into the solid polymer electrolyte membrane, I is Faraday's constant n.sub.f is the number of electrons released when 1 molecule of the fuel is oxidized, and j.sub.f.sup.c is an empirically determined crossover rate of fuel above which the fuel cell does not operate.

Masel, Richard I. (Champaign, IL); York, Cynthia A. (Newington, CT); Waszczuk, Piotr (White Bear Lake, MN); Wieckowski, Andrzej (Champaign, IL)

2009-08-04

119

New membranes for direct methanol fuel cells  

Microsoft Academic Search

The performance of direct methanol fuel cells (DMFC) is limited by the cross-over of methanol through the electrolyte. Electrolyte membranes prepared by blending of sulfonated arylene main-chain polymers like sulfonated PEEK Victrex (sPEEK) or sulfonated PSU Udel (sPSU) with basic polymers like poly(4-vinylpyridine) (P4VP) or polybenzimidazole (PBI) show excellent chemical and thermal stability, good proton-conductivity, and good performance in H2

L. Jörissen; V. Gogel; J. Kerres; J. Garche

2002-01-01

120

Oscillations of membrane potential in L cells  

Microsoft Academic Search

Summary Effects of divalent cations on oscillations of membrane potentials (i.e., spontaneous repetitive hyperpolarizing responses) and on hyperpolarizing responses induced by electrical stimuli as well as on resting potentials were studied in large nondividing L cells. Deprivation of Ca2+ from the external medium inhibited these hyperpolarizing responses accompanying slight depolarization of the resting potential. Sr2+ or Mn2+ applied to the

Yasunobu Okada; Wakoh Tsuchiya; Akira Inouye

1979-01-01

121

Membrane catalyst layer for fuel cells  

DOEpatents

A gas reaction fuel cell incorporates a thin catalyst layer between a solid polymer electrolyte (SPE) membrane and a porous electrode backing. The catalyst layer is preferably less than about 10 .mu.m in thickness with a carbon supported platinum catalyst loading less than about 0.35 mgPt/cm.sup.2. The film is formed as an ink that is spread and cured on a film release blank. The cured film is then transferred to the SPE membrane and hot pressed into the surface to form a catalyst layer having a controlled thickness and catalyst distribution. Alternatively, the catalyst layer is formed by applying a Na.sup.+ form of a perfluorosulfonate ionomer directly to the membrane, drying the film at a high temperature, and then converting the film back to the protonated form of the ionomer. The layer has adequate gas permeability so that cell performance is not affected and has a density and particle distribution effective to optimize proton access to the catalyst and electronic continuity for electron flow from the half-cell reaction occurring at the catalyst.

Wilson, Mahlon S. (Los Alamos, NM)

1993-01-01

122

Effect of Diphenyl Ether Herbicides on Oxidation of Protoporphyrinogen to Protoporphyrin in Organellar and Plasma Membrane Enriched Fractions of Barley 1  

PubMed Central

In barley (Hordeum vulgare L.) root cells, activity for oxidizing protoporphyrinogen to protoporphyrin (protoporphyrinogen oxidase), a step in chlorophyll and heme synthesis, was found both in the crude mitochondrial fraction and in a plasma membrane enriched fraction separated by a sucrose gradient technique utilized for preparing plasma membranes. The specific activity (expressed as nanomoles of protoporphyrin formed per hour per milligram protein) in the mitochondrial fraction was 8 and in the plasma membrane enriched fraction was 4 to 6. The plasma membrane enriched fraction exhibited minimal cytochrome oxidase activity and no carotenoid content, indicating little contamination with mitochondrial or plastid membranes. Etioplasts from etiolated barley leaves exhibited a protoporphyrinogen oxidase specific activity of 7 to 12. Protoporphyrinogen oxidase activity in the barley root mitochondrial fraction and etioplast extracts was more than 90% inhibited by assay in the presence of the diphenyl ether herbicide acifluorfen methyl, but the activity in the plasma membrane enriched fraction exhibited much less inhibition by this herbicide (12 to 38% inhibition) under the same assay conditions. Acifluorfen-methyl inhibition of the organellar (mitochondrial or plastid) enzyme was maximal upon preincubation of the enzyme with 4 mm dithiothreitol, although a lesser degree of inhibition was noted if the organellar enzyme was preincubated in the presence of other reductants such as glutathione or ascorbate. Acifluorfen-methyl caused only 20% inhibition if the enzyme was preincubated in buffer without reductants. Incubation of barley etioplast extracts with the earlier tetrapyrrole precursor coproporphyrinogen and acifluorfen-methyl resulted in the accumulation of protoporphyrinogen, which could be converted to protoporphyrin even in the presence of the herbicide by the addition of the plasma membrane enriched fraction from barley roots. These findings have implications for the toxicity of diphenyl ether herbicides, whose light induced tissue damage is apparently caused by accumulation of the photoreactive porphyrin intermediate, protoporphyrin, when the organellar protoporphyrinogen oxidase enzyme is inhibited by herbicides. Our results suggest that the protoporphyrinogen that accumulates as a result of herbicide inhibition of the organellar enzyme can be oxidized to protoporphyrin by a protoporphyrinogen oxidizing activity that is located at sites such as the plasma membrane, which is much less sensitive to inhibition by diphenylether herbicides. PMID:16668371

Jacobs, Judith M.; Jacobs, Nicholas J.; Sherman, Timothy D.; Duke, Stephen O.

1991-01-01

123

Fractions  

NSDL National Science Digital Library

Welcome to Fractions. This program uses three different Internet sites to learn fractions. On each site you will learn the basics of fractions and how to add, and multiply fractions. The three sites are Fractions, Mathsisfun.com and Who wants pizza?; a fun way to learn fractions. Even if you have never understood fractions before, you will understand them after visiting all three web sites. Two students will work together so that you can help eachother. Take turns using the keyboard so that each person gets a chance at the computer. . Let\\'s begin by going to the first site, \\"Fractions\\". Click on the line under \\"Beginning Fractions\\". Scroll down to the red border where it says \\"Fractions\\" and read the material about fractions. Click on \\"Start Fractions\\" and then click on the box that shows what fraction of the box is ...

Richard S. Melenson

2005-11-25

124

Electroosmotic flow through polymer electrolyte membranes in PEM fuel cells  

Microsoft Academic Search

Water management is critically important for polymer electrolyte membrane fuel cells (PEMFC), and is complicated by the electroosmotic flow of water from anode to cathode through the polymer electrolyte membrane. In this study, electroosmotic flow in polymer electrolyte membranes is modeled incorporating the electrokinetic effect, and key parameters affecting the PEM fuel cell performance are identified. The governing Poisson–Boltzmann and

G. Karimi; X. Li

2005-01-01

125

Fuel cell membrane hydration and fluid metering  

DOEpatents

A hydration system includes fuel cell fluid flow plate(s) and injection port(s). Each plate has flow channel(s) with respective inlet(s) for receiving respective portion(s) of a given stream of reactant fluid for a fuel cell. Each injection port injects a portion of liquid water directly into its respective flow channel. This serves to hydrate at least corresponding part(s) of a given membrane of the corresponding fuel cell(s). The hydration system may be augmented by a metering system including flow regulator(s). Each flow regulator meters an injecting at inlet(s) of each plate of respective portions of liquid into respective portion(s) of a given stream of fluid by corresponding injection port(s).

Jones, Daniel O. (Glenville, NY); Walsh, Michael M. (Fairfield, CT)

2003-01-01

126

Fuel cell membrane hydration and fluid metering  

DOEpatents

A hydration system includes fuel cell fluid flow plate(s) and injection port(s). Each plate has flow channel(s) with respective inlet(s) for receiving respective portion(s) of a given stream of reactant fluid for a fuel cell. Each injection port injects a portion of liquid water directly into its respective flow channel in order to mix its respective portion of liquid water with the corresponding portion of the stream. This serves to hydrate at least corresponding part(s) of a given membrane of the corresponding fuel cell(s). The hydration system may be augmented by a metering system including flow regulator(s). Each flow regulator meters an injecting at inlet(s) of each plate of respective portions of liquid into respective portion(s) of a given stream of fluid by corresponding injection port(s).

Jones, Daniel O. (Glenville, NY); Walsh, Michael M. (Fairfield, CT)

1999-01-01

127

Recruitment of activating NK-cell receptors 2B4 and NKG2D to membrane microdomains in mammalian cells is dependent on their transmembrane regions.  

PubMed

Membrane microdomains play an important role in the regulation of natural killer (NK) cell activities. These cholesterol-rich membrane domains are enriched at the activating immunological synapse and several activating NK-cell receptors are known to localize to membrane microdomains upon receptor engagement. In contrast, inhibitory receptors do not localize in these specialized membrane domains. In addition, the functional competence of educated NK cells correlates with a confinement of activating receptors in membrane microdomains. However, the molecular basis for this confinement is unknown. Here, we investigate the structural requirements for the recruitment of the human-activating NK-cell receptors NKG2D and 2B4 to detergent-resistant membrane fractions in the murine BA/F3 cell line and in the human NK-cell line NKL. This stimulation-dependent recruitment occurred independently of the intracellular domains of the receptors. However, either interfering with the association between NKG2D and DAP10, or mutating the transmembrane region of 2B4 impacted the recruitment of the receptors to detergent-resistant membrane fractions and modulated the function of 2B4 in NK cells. Our data suggest a potential interaction between the transmembrane region of NK-cell receptors and membrane lipids as a molecular mechanism involved in determining the membrane confinement of activating NK-cell receptors. PMID:25545687

Gütgemann, Stephan A; Sandusky, Mina M; Wingert, Sabine; Claus, Maren; Watzl, Carsten

2015-04-01

128

Basolateral plasma membranes of intestinal epithelial cells. Identification by lactoperoxidase-catalysed iodination and isolation after density perturbation with digitonin.  

PubMed Central

Lactoperoxidase-catalysed iodination was used to label intestinal epithelial cell sheets with 125I. The iodination was carried out under conditions that allowed little penetration of lactoperoxidase into the cells and membrane-bound 125I therefore provided an effective marker for following plasma-membrane fragments through subcellular-fractionation procedures. 2. After homogenization and isopycnic zonal centrifugation through sucrose gradients two peaks of membrane-bound 125I were detected. One coincided with brush border enzymes such as alkaline phosphatase, disaccharidases and L-leucine B-naphthylamidase, whereas the other was coincident with the major peak of (Na++K+)-stimulated ATPase (adenosine triphosphatase), which has been thought to be concentrated in the basolateral plasma membranes of these cells. Neither peak of 125I reflected the distribution of any marker for an intracellular organelle. 3. A larger proportion of the (Na++K+)-stimulated ATPase, and thus of the basolateral plasma-membrane material, was found in a crude 'mitochondrial' fraction. It was not readiily separated from mitochondria by conventional techniques of subcellular fractionation. 4. Treatment of the 'mitochondrial' fraction with digitonin increased the density of basolateral plasma membrane but had little effect on mitochondrial density. A purified preparation of digitonin-loaded basolateral plasma membranes was isolated at a density of 1.20-1.22 by isopycnic centrifugation. 5. The enzymic composition of this preparation of basolateral plasma membranes is compared with previous preparations isolated from intestinal mucosal 'scrape' materials and from isolated cells. Images PLATE 1 PMID:129058

Lewis, B A; Elkin, A; Michell, R H; Coleman, R

1975-01-01

129

Microfabrication of High-Resolution Porous Membranes for Cell Culture  

PubMed Central

Microporous membranes are widely utilized in cell biology to study cell-cell signaling and cell migration. However, the thickness and low porosity of commercial track-etched membranes limit the quality of cell imaging and the degree of cell-cell contact that can be achieved on such devices. We employ photolithography-based microfabrication to achieve porous membranes with pore diameter as small as 0.9 ?m, up to 40% porosity, and less than 5% variation in pore size. Through the use of a soap release layer, membranes as thin as 1 ?m can be achieved. The thin membranes minimally disrupt contrast enhancement optics, thus allowing good quality imaging of unlabeled cells under white light, unlike commercial membranes. In addition, the polymer membrane materials display low autofluorescence even after patterning, facilitating high quality fluorescence microscopy. Finally, confocal imaging suggests that substantial cell-cell contact is possible through the pores of these thin membranes. This membrane technology can enhance existing uses of porous membranes in cell biology as well as enable new types of experiments. PMID:24567663

Kim, Monica Y.; Li, David Jiang; Pham, Long K.; Wong, Brandon G.

2014-01-01

130

Computational Modeling and Optimization of Proton Exchange Membrane Fuel Cells  

E-print Network

Computational Modeling and Optimization of Proton Exchange Membrane Fuel Cells by Marc Secanell and Optimization of Proton Exchange Membrane Fuel Cells by Marc Secanell Gallart Bachelor in Engineering cells. In this thesis, a computational framework for fuel cell analysis and optimization is presented

Victoria, University of

131

Double-layer ionomer membrane for improving fuel cell performance.  

PubMed

A double-layer ionomer membrane, thin-layer Nafion (perfluorinated sulfonic acid polymer) on a sulfonated aromatic block copolymer (SPK-bl-1), was prepared for improving fuel cell performance. Each component of the double-layer membrane showed similar phase-separated morphologies to those of the original membranes. A fuel cell with the double-layer membrane exhibited lower ohmic resistance and higher cathode performance than those with the original SPK-bl-1 membrane despite their comparable water uptake and proton conductivity. Detailed electrochemical analyses of fuel cell data suggested that the thin Nafion interlayer contributed to improving the interfacial contact between the SPK-bl-1 membrane and the cathode catalyst layer and to mitigating excessive drying of the membrane. The results provide new insight on designing high-performance fuel cells with nonfluorinated ionomer membranes such as sulfonated aromatic polymers. PMID:24988282

Mochizuki, Takashi; Uchida, Makoto; Uchida, Hiroyuki; Watanabe, Masahiro; Miyatake, Kenji

2014-08-27

132

Interaction between Cell Penetrating pVEC and cell membranes  

NASA Astrophysics Data System (ADS)

Vascular Endothelial Cadherin (VEC) is a transmembrane-spanning glycoprotein that belongs to the family of cell adhesion molecules and plays an active role in control of vascular permeability and angiogenesis. PVEC, an 18 amino acid domain, has been shown to be able to traverse cell membranes with attached macromolecules. pVEC is an amphiphilic molecule with a high content of basic amino acids resulting in a net positive charge. Electrostatic and hydrophobic interactions can perturb membrane self-assembly and stability and are likely to be responsible for peptide uptake. We use synchrotron x-ray scattering and confocal microscopy to examine the phase behavior of the pVEC lipid system, and its relation to membrane permeation mechanisms.

Mishra, Abhijit; Hwee Lai, Ghee; Schmidt, Nathan; Wong, Gerard

2011-03-01

133

Membrane disorder and phospholipid scrambling in electropermeabilized and viable cells.  

PubMed

Membrane electropermeabilization relies on the transient permeabilization of the plasma membrane of cells submitted to electric pulses. This method is widely used in cell biology and medicine due to its efficiency to transfer molecules while limiting loss of cell viability. However, very little is known about the consequences of membrane electropermeabilization at the molecular and cellular levels. Progress in the knowledge of the involved mechanisms is a biophysical challenge. As a transient loss of membrane cohesion is associated with membrane permeabilization, our main objective was to detect and visualize at the single-cell level the incidence of phospholipid scrambling and changes in membrane order. We performed studies using fluorescence microscopy with C6-NBD-PC and FM1-43 to monitor phospholipid scrambling and membrane order of mammalian cells. Millisecond permeabilizing pulses induced membrane disorganization by increasing the translocation of phosphatidylcholines according to an ATP-independent process. The pulses induced the formation of long-lived permeant structures that were present during membrane resealing, but were not associated with phosphatidylcholine internalization. These pulses resulted in a rapid phospholipid flip/flop within less than 1s and were exclusively restricted to the regions of the permeabilized membrane. Under such electrical conditions, phosphatidylserine externalization was not detected. Moreover, this electrically-mediated membrane disorganization was not correlated with loss of cell viability. Our results could support the existence of direct interactions between the movement of membrane zwitterionic phospholipids and the electric field. PMID:24583083

Escoffre, Jean-Michel; Bellard, Elisabeth; Faurie, Cécile; Sébaï, Sarra C; Golzio, Muriel; Teissié, Justin; Rols, Marie-Pierre

2014-07-01

134

Cell membrane structure of human giant-celled glioblastoma  

Microsoft Academic Search

A giant-cell glioblastoma was examined by electron microscopy and by the freeze-fracture technique. The cell membranes bordering the extensive extracellular space often showed complicated undulations and peripheral vacuoles as well as occasional microvilli or filopodia. The undulations were mainly composed of plasmalemmal vesicles as well as of large (400–800 nm in diameter) and small (30–50 nm in diameter) localized protrusions

Eiichi Tani; Masaru Nakano; Tetsuya Itagaki; Toyokazu Fukumori

1978-01-01

135

Ion transport through cell membrane channels  

E-print Network

We discuss various models of ion transport through cell membrane channels. Recent experimental data shows that sizes of ion channels are compared to those of ions and that only few ions may be simultaneously in any single channel. Theoretical description of ion transport in such channels should therefore take into account interactions between ions and between ions and channel proteins. This is not satisfied by macroscopic continuum models based on Poisson-Nernst-Planck equations. More realistic descriptions of ion transport are offered by microscopic Brownian and molecular dynamics. One should also take into account a dynamical character of the channel structure. This is not yet addressed in the literature

Jan Gomulkiewicz; Jacek Miekisz; Stanislaw Miekisz

2007-06-05

136

Leishmania donovani: Immunostimulatory Cellular Responses of Membrane and Soluble Protein Fractions of Splenic Amastigotes in Cured Patient and Hamsters  

PubMed Central

Visceral leishmaniasis (VL), caused by the intracellular parasite Leishmania donovani, L. chagasi and L. infantum is characterized by defective cell-mediated immunity (CMI) and is usually fatal if not treated properly. An estimated 350 million people worldwide are at risk of acquiring infection with Leishmania parasites with approximately 500,000 cases of VL being reported each year. In the absence of an efficient and cost-effective antileishmanial drug, development of an appropriate long-lasting vaccine against VL is the need of the day. In VL, the development of a CMI, capable of mounting Th1-type of immune responses, play an important role as it correlate with recovery from and resistance to disease. Resolution of infection results in lifelong immunity against the disease which indicates towards the feasibility of a vaccine against the disease. Most of the vaccination studies in Leishmaniasis have been focused on promastigote- an infective stage of parasite with less exploration of pathogenic amastigote form, due to the cumbersome process of its purified isolation. In the present study, we have isolated and purified splenic amastigotes of L. donovani, following the traditional protocol with slight modification. These were fractionated into five membranous and soluble subfractions each i.e MAF1-5 and SAF1-5 and were subjected for evaluation of their ability to induce cellular responses. Out of five sub-fractions from each of membrane and soluble, only four viz. MAF2, MAF3, SAF2 and SAF3 were observed to stimulate remarkable lymphoproliferative, IFN-?, IL-12 responses and Nitric Oxide production, in Leishmania-infected cured/exposed patients and hamsters. Results suggest the presence of Th-1 type immunostimulatory molecules in these sub-fractions which may further be exploited for developing a successful subunit vaccine from the less explored pathogenic stage against VL. PMID:22292030

Tandon, Rati; Samant, Mukesh; Sundar, Shyam; Dube, Anuradha

2012-01-01

137

Water and methanol uptakes in Nafion membranes and membrane effects on direct methanol cell performance  

Microsoft Academic Search

This paper compares direct methanol fuel cells (DMFCs) employing two types of Nafion{reg{underscore}sign} (E.I.DuPont de Nemours and Company) membranes of different equivalent weight (EW). Methanol and water uptakes in 1,100 and 1,200 EW Nafion membranes were determined by weighing PâOâ-dried and methanol solution-equilibrated membranes. Both methanol and water uptakes in the 1,200 EW membrane were about 70--74% of those in

X. Ren; T. E. Springer; S. Gottesfeld

2000-01-01

138

Membrane Purification Cell for Aluminum Recycling  

SciTech Connect

Recycling mixed aluminum scrap usually requires adding primary aluminum to the scrap stream as a diluent to reduce the concentration of non-aluminum constituents used in aluminum alloys. Since primary aluminum production requires approximately 10 times more energy than melting scrap, the bulk of the energy and carbon dioxide emissions for recycling are associated with using primary aluminum as a diluent. Eliminating the need for using primary aluminum as a diluent would dramatically reduce energy requirements, decrease carbon dioxide emissions, and increase scrap utilization in recycling. Electrorefining can be used to extract pure aluminum from mixed scrap. Some example applications include producing primary grade aluminum from specific scrap streams such as consumer packaging and mixed alloy saw chips, and recycling multi-alloy products such as brazing sheet. Electrorefining can also be used to extract valuable alloying elements such as Li from Al-Li mixed scrap. This project was aimed at developing an electrorefining process for purifying aluminum to reduce energy consumption and emissions by 75% compared to conventional technology. An electrolytic molten aluminum purification process, utilizing a horizontal membrane cell anode, was designed, constructed, operated and validated. The electrorefining technology could also be used to produce ultra-high purity aluminum for advanced materials applications. The technical objectives for this project were to: - Validate the membrane cell concept with a lab-scale electrorefining cell; - Determine if previously identified voltage increase issue for chloride electrolytes holds for a fluoride-based electrolyte system; - Assess the probability that voltage change issues can be solved; and - Conduct a market and economic analysis to assess commercial feasibility. The process was tested using three different binary alloy compositions (Al-2.0 wt.% Cu, Al-4.7 wt.% Si, Al-0.6 wt.% Fe) and a brazing sheet scrap composition (Al-2.8 wt.% Si-0.7 wt.% Fe-0.8 wt.% Mn),. Purification factors (defined as the initial impurity concentration divided by the final impurity concentration) of greater than 20 were achieved for silicon, iron, copper, and manganese. Cell performance was measured using its current and voltage characteristics and composition analysis of the anode, cathode, and electrolytes. The various cells were autopsied as part of the study. Three electrolyte systems tested were: LiCl-10 wt. % AlCl3, LiCl-10 wt. % AlCl3-5 wt.% AlF3 and LiF-10 wt.% AlF3. An extended four-day run with the LiCl-10 wt.% AlCl3-5 wt.% AlF3 electrolyte system was stable for the entire duration of the experiment, running at energy requirements about one third of the Hoopes and the conventional Hall-Heroult process. Three different anode membranes were investigated with respect to their purification performance and survivability: a woven graphite cloth with 0.05 cm nominal thickness & > 90 % porosity, a drilled rigid membrane with nominal porosity of 33%, and another drilled rigid graphite membrane with increased thickness. The latter rigid drilled graphite was selected as the most promising membrane design. The economic viability of the membrane cell to purify scrap is sensitive to primary & scrap aluminum prices, and the cost of electricity. In particular, it is sensitive to the differential between scrap and primary aluminum price which is highly variable and dependent on the scrap source. In order to be economically viable, any scrap post-processing technology in the U.S. market must have a total operating cost well below the scrap price differential of $0.20-$0.40 per lb to the London Metal Exchange (LME), a margin of 65%-85% of the LME price. The cost to operate the membrane cell is estimated to be < $0.24/lb of purified aluminum. The energy cost is estimated to be $0.05/lb of purified aluminum with the remaining costs being repair and maintenance, electrolyte, labor, taxes and depreciation. The bench-scale work on membrane purification cell process has demonstrated technological advantages and subs

David DeYoung; James Wiswall; Cong Wang

2011-11-29

139

Aptamer Directly Evolved from Live Cells Recognizes Membrane Bound Immunoglobin  

E-print Network

into diseased cells (1). The origin of these protein transformations can be due to genetic alternations and, and Weihong Tan The identification of tumor related cell membrane protein targets is important of membrane proteins that play an essential role in dis- ease progression and in transforming healthy cells

Tan, Weihong

140

Isolation and Characterization of Glycophorin from Carp Red Blood Cell Membranes  

PubMed Central

We isolated a high-purity carp glycophorin from carp erythrocyte membranes following extraction using the lithium diiodosalicylate (LIS)-phenol method and streptomycin treatment. The main carp glycophorin was observed to locate at the position of the carp and human band-3 proteins on an SDS-polyacrylamide gel. Only the N-glycolylneuraminic acid (NeuGc) form of sialic acid was detected in the carp glycophorin. The oligosaccharide fraction was separated into two components (P-1 and P-2) using a Glyco-Pak DEAE column. We observed bacteriostatic activity against five strains of bacteria, including two known fish pathogens. Fractions from the carp erythrocyte membrane, the glycophorin oligosaccharide and the P-1 also exhibited bacteriostatic activity; whereas the glycolipid fraction and the glycophorin fraction without sialic acid did not show the activity. The carp glycophorin molecules attach to the flagellum of V. anguillarum or the cell surface of M. luteus and inhibited bacterial growth. PMID:25110961

Aoki, Takahiko; Chimura, Kenji; Nakao, Nobuhiro; Mizuno, Yasuko

2014-01-01

141

Kinetics and mechanism of cell membrane electrofusion.  

PubMed Central

A new quantitative approach to study cell membrane electrofusion has been developed. Erythrocyte ghosts were brought into close contact using dielectrophoresis and then treated with one square or even exponentially decaying fusogenic pulse. Individual fusion events were followed by lateral diffusion of the fluorescent lipid analogue 1,1'-dihexadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (Dil) from originally labeled to unlabeled adjacent ghosts. It was found that ghost fusion can be described as a first-order rate process with corresponding rate constants; a true fusion rate constant, k(f), for the square waveform pulse and an effective fusion rate constant, k(ef), for the exponential pulse. Compared with the fusion yield, the fusion rate constants are more fundamental characteristics of the fusion process and have implications for its mechanisms. Values of k(f) for rabbit and human erythrocyte ghosts were obtained at different electric field strength and temperatures. Arrhenius k(f) plots revealed that the activation energy of ghost electrofusion is in the range of 6-10 kT. Measurements were also made with the rabbit erythrocyte ghosts exposed to 42 degrees C for 10 min (to disrupt the spectrin network) or 0.1-1.0 mM uranyl acetate (to stabilize the bilayer lipid matrix of membranes). A correlation between the dependence of the fusion and previously published pore-formation rate constants for all experimental conditions suggests that the cell membrane electrofusion process involve pores formed during reversible electrical breakdown. A statistical analysis of fusion products (a) further supports the idea that electrofusion is a stochastic process and (b) shows that the probability of ghost electrofusion is independent of the presence of Dil as a label as well as the number of fused ghosts. PMID:1617138

Abidor, I G; Sowers, A E

1992-01-01

142

Integrin-like proteins are localized to plasma membrane fractions, not plastids, in Arabidopsis  

NASA Technical Reports Server (NTRS)

Integrins are a large family of integral membrane proteins that function in signal transduction in animal systems. These proteins are conserved in vertebrates, invertebrates, and fungi. Evidence from previous research suggests that integrin-like proteins may be present in plants as well, and that these proteins may function in signal transduction during gravitropism. In past studies, researchers have used monoclonal and polyclonal antibodies to localize beta 1 integrin-like proteins in plants. However, there is a disparity between data collected from these studies, especially since molecular weights obtained from these investigations range from 55-120 kDa for integrin-like proteins. To date, a complete investigation which employs all three basic immunolabeling procedures, immunoblotting, immunofluorescence microscopy, and immunogold labeling, in addition to extensive fractionation and exhaustive controls, has been lacking. In this paper, we demonstrate that use of a polyclonal antibody against the cytoplasmic domain of avian beta 1-integrin can produce potential artifacts in immunolocalization studies. However, these problems can be eliminated through use of starchless mutants or proper specimen preparation prior to electrophoresis. We also show that this antibody, when applied within the described parameters and with careful controls, identifies a large (100 kDa) integrin-like protein that is localized to plasma membrane fractions in Arabidopsis.

Swatzell, L. J.; Edelmann, R. E.; Makaroff, C. A.; Kiss, J. Z.

1999-01-01

143

Membrane electrolyte issues in direct methanol fuel cells  

SciTech Connect

The authors discuss here the effect of methanol, water, and proton transport through membrane electrolytes on the performance of direct methanol polymer electrolyte fuel cells (DMPEFCs). After a discussion of the issues involved in defining such transport parameters, the authors present some data on methanol and water uptake and transport through Nafion 117 membranes. Finally, strategies for improving membrane performance in DMPEFCs are discussed.

Zawodzinski, T.A. Jr.; Wilson, M.S.; Bett, J.A.; Gottesfeld, S. [Los Alamos National Lab., NM (United States). Electronic and Electrochemical Materials and Device Group

1994-12-31

144

Humidification studies on polymer electrolyte membrane fuel cell  

Microsoft Academic Search

Two methods of humidifying the anode gas, namely, external and membrane humidification, for a polymer electrolyte membrane fuel (PEMFC) cell are explained. It is found that the water of solvation of protons decreases with increase in the current density and the electrode area. This is due to insufficient external humidification. In a membrane-based humidification, an optimum set of parameters, such

P Sridhar; Ramkumar Perumal; N Rajalakshmi; M Raja; K. S Dhathathreyan

2001-01-01

145

Xyloglucan biosynthesis by Golgi membranes from suspension-cultured sycamore (Acer pseudoplatanus) cells  

SciTech Connect

Xyloglucan is a major hemicellulose polysaccharide in plant cell walls. Biosynthesis of such cell wall polysaccharides is closely linked to the process of plant cell growth and development. Xyloglucan polysaccharides consist of a {beta}-1,4 glucan backbone synthesized by xyloglucan synthase and sidechains of xylose, galactose, and fucose added by other transferase enzymes. Most plant Golgi and plasma membranes also contain glucan synthases I II, which make {beta}-1,4 and {beta}-1,3 glucans, respectively. All of these enzymes have very similar activities. Cell walls on suspension-cultured cells from Acer pseudoplatanus (sycamore maple) were enzymatically softened prior to cell disruption by passing through a 30 {mu}m nylon screen. Cell membranes from homogenates were separated by ultracentrifugation on top-loaded or flotation sucrose density gradients. Samples were collected by gradient fractionation and assayed for membrane markers and xyloglucan and glucan synthase activities. Standard marker assays (cyt. c reductase for eR, IDPase UDPase for Golgi, and eosin 5{prime}-malelmide binding for plasma membrane) showed partial separation of these three membrane types. Golgi and plasma membrane markers overlapped in most gradients. Incorporation of {sup 14}C-labeled sugars from UDP-glucose and UDP-xylose was used to detect xyloglucan synthase, glucan synthases I II, and xylosyl transferase in Golgi membrane fractions. These activities overlapped, although distinct peaks of xyloglucan synthase and xylosyl transferase were found. Ca{sup ++} had a stimulatory effect on glucan synthases I II, while Mn{sup ++} had an inhibitory effect on glucan synthase I in the presence of Ca{sup ++}. The similarity of these various synthase activities demonstrates the need for careful structural characterization of newly synthesized polysaccharides.

White, A.R.; Xin, Yi (North Dakota State Univ., Fargo (USA))

1990-05-01

146

Nonhumidified High-Temperature Membranes Developed for Proton Exchange Membrane Fuel Cells  

NASA Technical Reports Server (NTRS)

Fuel cells are being considered for a wide variety of aerospace applications. One of the most versatile types of fuel cells is the proton-exchange-membrane (PEM) fuel cell. PEM fuel cells can be easily scaled to meet the power and space requirements of a specific application. For example, small 100-W PEM fuel cells are being considered for personal power for extravehicular activity suit applications, whereas larger PEM fuel cells are being designed for primary power in airplanes and in uninhabited air vehicles. Typically, PEM fuel cells operate at temperatures up to 80 C. To increase the efficiency and power density of the fuel cell system, researchers are pursuing methods to extend the operating temperature of the PEM fuel cell to 180 C. The most widely used membranes in PEM fuel cells are Nafion 112 and Nafion 117--sulfonated perfluorinated polyethers that were developed by DuPont. In addition to their relatively high cost, the properties of these membranes limit their use in a PEM fuel cell to around 80 C. The proton conductivity of Nafion membranes significantly decreases above 80 C because the membrane dehydrates. The useful operating range of Nafion-based PEM fuel cells can be extended to over 100 C if ancillary equipment, such as compressors and humidifiers, is added to maintain moisture levels within the membrane. However, the addition of these components reduces the power density and increases the complexity of the fuel cell system.

Kinder, James D.

2005-01-01

147

Polymer-electrolyte membrane, electrochemical fuel cell, and related method  

DOEpatents

A polymer-electrolyte membrane is presented. The polymer-electrolyte membrane comprises an acid-functional polymer, and an additive incorporated in at least a portion of the membrane. The additive comprises a fluorinated cycloaliphatic additive, a hydrophobic cycloaliphatic additive, or combinations thereof, wherein the additive has a boiling point greater than about 120.degree. C. An electrochemical fuel cell including the polymer-electrolyte membrane, and a related method, are also presented.

Krishnan, Lakshmi; Yeager, Gary William; Soloveichik, Grigorii Lev

2014-12-09

148

Chemicals and energy co-generation from direct hydrocarbons/oxygen proton exchange membrane fuel cell  

NASA Astrophysics Data System (ADS)

A proton exchange membrane fuel cell for chemicals and energy co-generation was set up with hydrocarbons ethane, propane and butane as fuels, and the electrochemical performance of the cell was studied by using linear potential sweep, alternating current impedance and gas chromatography. The cell performance can be improved to a great extent by increasing the platinum load in the catalyst, by treating the membrane with phosphoric acid and by elevating temperature. The improvement of cell performance by the increase of platinum load is ascribed to the increase of reaction sites for hydrocarbon oxidation, that by phosphoric acid treatment to the increase of proton conductivity in Nafion membrane, and that by elevating temperature to the improvement in thermodynamic as well as kinetic aspects. Only a small fraction of the hydrocarbon is converted to carbon dioxide in this cell during its power generation. The current efficiency is 5% for the conversion of ethane to carbon dioxide in the ethane/oxygen fuel cell with 20% carbon-supported platinum as catalyst and phosphoric acid-treated membrane as proton exchange membrane at 0.2 V, 80 °C and ambient pressure. The reaction activity of hydrocarbons at the anode is in the order of propane, butane and ethane. The possible chemicals produced from the cell were hydrocarbons with more than six carbons, which are inactive at the anode under cell conditions.

Li, W. S.; Lu, D. S.; Luo, J. L.; Chuang, K. T.

149

Enzymatic Oxidation of Cholesterol: Properties and Functional Effects of Cholestenone in Cell Membranes  

PubMed Central

Bacterial cholesterol oxidase is commonly used as an experimental tool to reduce cellular cholesterol content. That the treatment also generates the poorly degradable metabolite 4-cholesten-3-one (cholestenone) has received less attention. Here, we investigated the membrane partitioning of cholestenone using simulations and cell biological experiments and assessed the functional effects of cholestenone in human cells. Atomistic simulations predicted that cholestenone reduces membrane order, undergoes faster flip-flop and desorbs more readily from membranes than cholesterol. In primary human fibroblasts, cholestenone was released from membranes to physiological extracellular acceptors more avidly than cholesterol, but without acceptors it remained in cells over a day. To address the functional effects of cholestenone, we studied fibroblast migration during wound healing. When cells were either cholesterol oxidase treated or part of cellular cholesterol was exchanged for cholestenone with cyclodextrin, cell migration during 22 h was markedly inhibited. Instead, when a similar fraction of cholesterol was removed using cyclodextrin, cells replenished their cholesterol content in 3 h and migrated similarly to control cells. Thus, cholesterol oxidation produces long-term functional effects in cells and these are in part due to the generated membrane active cholestenone. PMID:25157633

Neuvonen, Maarit; Manna, Moutusi; Mokkila, Sini; Javanainen, Matti; Rog, Tomasz; Liu, Zheng; Bittman, Robert; Vattulainen, Ilpo; Ikonen, Elina

2014-01-01

150

The application of Dow Chemical's perfluorinated membranes in proton-exchange membrane fuel cells  

NASA Technical Reports Server (NTRS)

Dow Chemical's research activities in fuel cells revolve around the development of perfluorosulfonic acid membranes useful as the proton transport medium and separator. Some of the performance characteristics which are typical for such membranes are outlined. The results of tests utilizing a new experimental membrane useful in proton-exchange membrane fuel cells are presented. The high voltage at low current densities can lead to higher system efficiencies while, at the same time, not sacrificing other critical properties pertinent to membrane fuel cell operation. A series of tests to determine response times indicated that on-off cycles are on the order of 80 milliseconds to reach 90 percent of full power. The IR free voltage at 100 amps/sq ft was determined and the results indicating a membrane/electrode package resistance to be .15 ohm-sq cm at 100 amps/sq ft.

Eisman, G. A.

1989-01-01

151

In Vivo Incorporation of Radioactive Metabolites by Golgi Apparatus and Other Cell Fractions of Onion Stem 12  

PubMed Central

Incorporation in vivo of various 14C-labeled substrates into dictyosomes of onion (Allium cepa) stem was determined, and comparisons were made with other cell fractions on a nitrogen basis. Tissue explants were incubated for varying times in the presence of the radioactive metabolites supplied in the external medium. Fractions were then obtained from homogenates stabilized with glutaraldehyde. Purified fractions containing dictyosomes (individual stacks of cisternae) of the Golgi apparatus were obtained by centrifugation in a sucrose gradient also yielding a smooth membrane fraction free of dictyosomes. Dictyosomes were preferentially labeled with choline-1,2-14C and acetate-2-14C, suggesting that plant Golgi apparatus participate in the synthesis or modification of membrane lipids. Dictyosomes were also labeled with glucose-U-14C and leucine-U-14C, but on a molar basis incorporation was less than with choline or acetate. Images PMID:16657393

Morré, D. James

1970-01-01

152

Exo70 Generates Membrane Curvature for Morphogenesis and Cell Migration  

PubMed Central

Dynamic shape changes of the plasma membrane are fundamental to many processes ranging from morphogenesis and cell migration to phagocytosis and viral propagation. Here we demonstrate that Exo70, a component of the exocyst complex, induces tubular membrane invaginations towards the lumen of synthetic vesicles in vitro and generates protrusions on the surface of cells. Biochemical analyses using Exo70 mutants and independent molecular dynamics simulations based on Exo70 structure demonstrate that Exo70 generates negative membrane curvature through an oligomerization-based mechanism. In cells, the membrane-deformation function of Exo70 is required for protrusion formation and directional cell migration. Exo70 thus represents a membrane-bending protein that may couple actin dynamics and plasma membrane remodeling for morphogenesis. PMID:23948253

Zhao, Yuting; Liu, Jianglan; Yang, Changsong; Capraro, Benjamin R.; Baumgart, Tobias; Bradley, Ryan P.; Ramakrishnan, N.; Xu, Xiaowei; Radhakrishnan, Ravi; Svitkina, Tatyana; Guo, Wei

2013-01-01

153

Dense-cored membranous structures in smooth muscle cells of the vas deferens of the rat.  

PubMed

Smooth muscle cells from rat vas deferens were studied by electron microscopy. Vesicular and tubular membranous structures containing an electron-opaque material were found in the smooth muscle cells. Similar structures were also found in a subfraction (F3) of microsomes of vas deferens smooth muscle which was shown to be rich in both plasma membrane and putative endoplasmic reticulum markers. Treatment of the tissues with calcium-free Krebs solution containing EGTA prior to fixation eliminated almost completely the presence of these dense-cored membranous structures (DMS), whereas incubation of the subcellular membrane fraction with EGTA solution had no effect on the appearance of the DMS. Plasma membrane infoldings were found in the smooth muscle cells extending well into their interior. Horseradish peroxidase penetrates vesicles in a location similar to that of DMS in smooth muscle cells, suggesting that some of the DMS may be connected to the extracellular space. We conclude that the dense-core material within the DMS is calcium dependent. We also suggest that some of the DMS represent infoldings of the plasma membrane extending into the cell's interior. PMID:6697383

Lee, R M; Kwan, C Y; Daniel, E E

1984-01-01

154

Conductivity Measurements of Synthesized Heteropoly Acid Membranes for Proton Exchange Membrane Fuel Cells  

SciTech Connect

Fuel cell technology is receiving attention due to its potential to be a pollution free method of electricity production when using renewably produced hydrogen as fuel. In a Proton Exchange Membrane (PEM) fuel cell H2 and O2 react at separate electrodes, producing electricity, thermal energy, and water. A key component of the PEM fuel cell is the membrane that separates the electrodes. DuPont’s Nafion® is the most commonly used membrane in PEM fuel cells; however, fuel cell dehydration at temperatures near 100°C, resulting in poor conductivity, is a major hindrance to fuel cell performance. Recent studies incorporating heteropoly acids (HPAs) into membranes have shown an increase in conductivity and thus improvement in performance. HPAs are inorganic materials with known high proton conductivities. The primary objective of this work is to measure the conductivity of Nafion, X-Ionomer membranes, and National Renewable Energy Laboratory (NREL) Developed Membranes that are doped with different HPAs at different concentrations. Four-point conductivity measurements using a third generation BekkTech? conductivity test cell are used to determine membrane conductivity. The effect of multiple temperature and humidification levels is also examined. While the classic commercial membrane, Nafion, has a conductivity of approximately 0.10 S/cm, measurements for membranes in this study range from 0.0030 – 0.58 S/cm, depending on membrane type, structure of the HPA, and the relative humidity. In general, the X-ionomer with H6P2W21O71 HPA gave the highest conductivity and the Nafion with the 12-phosphotungstic (PW12) HPA gave the lowest. The NREL composite membranes had conductivities on the order of 0.0013 – 0.025 S/cm.

Record, K.A.; Haley, B.T.; Turner, J.

2006-01-01

155

Effects of membrane fluidity on hormone action in cultured cells  

E-print Network

fibroblasts (8, 9) and has been shown to increase small molecule transport into the cell and increase rates of DNA and RNA synthesis (R, 10, 11). Increased rates of protein synthesis (12), phosphorylation of membrane proteins (13), The citations... on the outside of the plasma membrane of target cells. The recep- tor-ligand complexes migrate laterally in the plane of the membrane and become associated into clusters, which then move into regions of coated pits where they undergo endocytosis...

Williams, Gary Wayne

1982-01-01

156

Fractions  

NSDL National Science Digital Library

This interactive Flash applet can be used to compare and explore equivalence among fractions, decimals and percentages. It allows a child or teacher to represent fractions on one or more fraction strips, and to color individual parts. Each displayed strip can be labelled as a fraction, a decimal (to three decimal places) or a percentage; the ratio of yellow to green parts of each strip can also be displayed. It lends itself well to use with an interactive white board. A pdf guide to this collection of teaching applets is cataloged separately.

2006-01-01

157

Hemoglobin s polymerization and red cell membrane changes.  

PubMed

Different pathways lead from the simple point mutation in hemoglobin to the membrane changes that characterize the altered interaction of the sickle red blood cell with its environment, including endothelial cells, white blood cells, and platelets. Polymerization and oxidation-induced damage to both lipid and protein components of the red cell membrane, as well as the generation of bioreactive membrane material (microparticles), has a profound effect on all tissues and organs, and defines the vasculopathy of the patient with sickle cell disease. PMID:24589260

Kuypers, Frans A

2014-04-01

158

Electron-beam direct processing on living cell membrane  

SciTech Connect

We demonstrated a direct processing on a living Hep G2 cell membrane in conventional cultivation conditions using an electron beam. Electron beam-induced deposition from liquid precursor 3,4-ethylenedioxythiophene and ablation was performed on the living cells. The 2.5-10 keV electron beam which was irradiated through a 100-nm-thick SiN nanomembrane could induce a deposition pattern and a ablation on a living cell membrane. This electron beam direct processing can provide simple in-situ cell surface modification for an analytical method of living cell membrane dynamic.

Hoshino, Takayuki [Department of Bio-Applications and Systems Engineering, Tokyo University of Agriculture and Technology, 2-24-16 Naka-cho, Koganei, Tokyo 184-8588 (Japan); Morishima, Keisuke [Department of Bio-Applications and Systems Engineering, Tokyo University of Agriculture and Technology, 2-24-16 Naka-cho, Koganei, Tokyo 184-8588 (Japan); Department of Mechanical Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871 Japan (Japan)

2011-10-24

159

Salt splitting in a three-compartment membrane electrolysis cell  

Microsoft Academic Search

A three-compartment membrane cell was used to investigate the electrohydrolysis of sodium sulphate for the regeneration of acid and base. The membranes used were Pall R1010 cation exchange and Pall R1030 anion exchange. The effect of flow rate, current density and initial salt concentration on the performance of the cell (current efficiencies, transport properties and product concentrations) are reported. The

N Tzanetakis; WM Taama; K Scott

2002-01-01

160

Ion Transport Through Cell Membrane Channels Jan Gomulkiewicz1  

E-print Network

1 Ion Transport Through Cell Membrane Channels Jan Gomulkiewicz1 , Jacek Mikisz2 , and Stanislaw various models of ion transport through cell membrane channels. Recent experimental data shows that sizes of ion channels are compared to those of ions and that only few ions may be simultaneously in any single

Miekisz, Jacek

161

Basement Membrane Collagen: Degradation by Migrating Endothelial Cells  

Microsoft Academic Search

One of the first steps in neovascularizaton is dissolution of the basement membrane at the point of endothelial outgrowth. An assay was developed to determine whether basement membrane collagens (types IV and V) are degraded by endothelial cells migrating toward a chemotactic stimulus. Fetal bovine endothelial cells were placed on one side of a filter containing the collagen substrate, and

Tea Kalebic; S. Garbisa; B. Glaser; L. A. Liotta

1983-01-01

162

Mathematical modeling of proton exchange membrane fuel cells  

Microsoft Academic Search

A one-dimensional non-isothermal model of a proton exchange membrane (PEM) fuel cell has been developed to investigate the effect of various design and operating conditions on the cell performance, thermal response and water management, and to understand the underlying mechanism. The model includes variable membrane hydration, ternary gas mixtures for both reactant streams, phase change of water in the electrodes

Andrew Rowe; Xianguo Li

2001-01-01

163

THE ENZYMATIC IODINATION OF THE RED CELL MEMBRANE  

Microsoft Academic Search

An enzymatic iodination procedure utilizing lactoperoxidase (LPO), radioactive iodide, and hydrogen peroxide generated by a glucose oxidase-glucose system has been described and utilized for a study of the red cell membrane . 97 % of the incorporated isotope is in the erythrocyte ghost and 3 % is associated with hemoglobin . No significant labeling of the red cell membrane occurs

ANN L. HUBBARD; ZANVIL A. COHN

1972-01-01

164

Functional fluoropolymers for fuel cell membranes and B. Amduri1  

E-print Network

1 Functional fluoropolymers for fuel cell membranes R. Souzy1 and B. Améduri1 * 1) Laboratory@cit.enscm.fr. Abstract Various routes to synthesise functional fluoropolymers used in membranes for fuel cells-g-poly(M) graft copolymers (where FP and M stand for fluoropolymer and monomer, respectively) obtained

Paris-Sud XI, Université de

165

Self-humidifying polymer electrolyte membranes for fuel cells  

Microsoft Academic Search

Polymer electrolyte fuel cells have attracted enormous interest as a primary power source for electric vehicles. Water management in the electrolyte is one of the complicated problems to be overcome. A new self-humidifying electrolyte membrane is proposed to solve this problem. Self-humidification allows the use of very thin membranes, simultaneously allowing high performance of the cell. Use of the new,

Masahiro Watanabe; Hiroyuki Uchida; Yasuhiro Seki; Masaomi Emori; P. Stonehart

1996-01-01

166

Resealing dynamics of a cell membrane after electroporation Martin Bier  

E-print Network

V resting potential, a relaxation back to an almost zero current takes place. Figure 3 shows the currents obResealing dynamics of a cell membrane after electroporation Martin Bier Department of Physics, East The membrane of a living cell consists of a bilayer of amphipolar lipid molecules as well as much larger

Bier, Martin

167

Membrane Nanowaves in Single and Collective Cell Migration  

PubMed Central

We report the characterization of three-dimensional membrane waves for migrating single and collective cells and describe their propagation using wide-field optical profiling technique with nanometer resolution. We reveal the existence of small and large membrane waves the amplitudes of which are in the range of ?3–7 nm to ?16–25 nm respectively, through the cell. For migrating single-cells, the amplitude of these waves is about 30 nm near the cell edge. Two or more different directions of propagation of the membrane nanowaves inside the same cell can be observed. After increasing the migration velocity by BMP-2 treatment, only one wave direction of propagation exists with an increase in the average amplitude (more than 80 nm near the cell edge). Furthermore for collective-cell migration, these membrane nanowaves are attenuated on the leader cells and poor transmission of these nanowaves to follower cells was observed. After BMP-2 treatment, the membrane nanowaves are transmitted from the leader cell to several rows of follower cells. Surprisingly, the vast majority of the observed membrane nanowaves is shared between the adjacent cells. These results give a new view on how single and collective-cells modulate their motility. This work has significant implications for the therapeutic use of BMPs for the regeneration of skin tissue. PMID:24846182

Zouani, Omar F.; Gocheva, Veronika; Durrieu, Marie-Christine

2014-01-01

168

Vaccination of feedlot cattle with extracts and membrane fractions from two Mycoplasma bovis isolates results in strong humoral immune responses but does not protect against an experimental challenge.  

PubMed

Mycoplasma bovis is one of the most significant contributors to the bovine respiratory syndrome (BRD) that causes major losses in feedlot and dairy farms. Current experimental vaccines against M. bovis are ineffective and in some cases seem to enhance disease. Experimental infection with M. bovis induces a predominantly Th2 response and high levels of IgG1, which is an inferior opsonin and hence lacks protective capacity. In an attempt to induce a balanced (Th1/Th2) immune response, we have used CpG ODN 2007 as an adjuvant in a trial involving vaccination of cattle with M. bovis total extracts and/or membrane fractions and subsequent intranasal inoculation with an infective dose of M. bovis prepared from two different clinical isolates. Significant IgG1 serum responses were observed against both, extracts and fractions while IgG2 responses were significant against the extracts only. Proliferation of peripheral blood mononuclear cells (PBMC) after incubation with M. bovis cells was only observed in post-challenge samples of cattle vaccinated with both extracts and fractions but not in samples of cattle immunized with the membrane fractions alone. All groups showed transient weight losses and increased temperatures however, there were no significant differences in clinical parameters and survival rates between the groups. PMID:23340004

Mulongo, Musa; Prysliak, Tracy; Perez-Casal, Jose

2013-02-27

169

Large Deformation Mechanics of Plasma Membrane Chained Vesicles in Cells  

NASA Astrophysics Data System (ADS)

The clathrin-coated pits, vesicles and chained vesicles on the inner surface of the plasma membrane facilitate the cell to transport specific extracellular macromolecules. This cellular process is strongly involved with large mechanical deformations of the plasma membrane accompanied by changes in membrane curvature. The assembly of the clathrin coat is thought to provide curvature into the membrane. Hence, effects of in-plane shear elasticity due to these coat structure may be significant on the vesicular mechanics. In this study, large deformation mechanics of plasma membrane chained vesicles in cells have been formulated based on minimization of bending and in-plane shear strain energy of the membrane. Effects of outer surrounding cytoplasmic flat membrane upon mechanically stable shapes of the vesicles were revealed, while effects of in-plane shear elasticity were partly discussed.

Kosawada, Tadashi; Sanada, Kouichi; Takano, Tetsuo

170

Live-cell imaging of receptors around postsynaptic membranes.  

PubMed

This protocol describes how to image the trafficking of glutamate receptors around excitatory postsynaptic membrane formed on an adhesion protein-coated glass surface. The protocol was developed to clarify how receptors move during the induction of synaptic plasticity. Dissociated neurons are cultured on a coverslip coated with neurexin, which induces the formation of postsynaptic membrane-like structures on the glass surface. A glutamate receptor tagged with a fluorescent protein is then transfected into neurons, and it is observed with total internal reflection fluorescence microscopy. The whole process takes about 3 weeks. Changes in the amount of cell-surface receptors caused by neuronal activities can be quantified, and individual exocytosis events of receptors can be clearly observed around the pseudo-postsynaptic membrane. This protocol has potential applications for studies of movements of membrane proteins around other specialized regions of the cell membrane, such as the inhibitory postsynaptic membrane, the presynaptic membrane or the immunological synapses. PMID:24336472

Tanaka, Hiromitsu; Fujii, Shumpei; Hirano, Tomoo

2014-01-01

171

Sustainable Energy Systems Lab: Proton Exchange Membrane Fuel Cell  

NSDL National Science Digital Library

This lab introduces the operation of a proton exchange membrane fuel cell. Students will become familiar with a Simulink model of a proton exchange membrane fuel cell, obtain the nonlinear voltage-current and power-current characteristics for a typical fuel cell, determine the maximum power point and obtain a linear voltage equation for the fuel cell as a function of the current. This document may be downloaded in Microsoft Word file format.

172

Purification and characterization of a CMP-sialic:LcOse4Cer sialyltransferase from human colorectal carcinoma cell membranes  

Microsoft Academic Search

Purified lactotetraosylceramide (Gal beta 1----3GlcNAc beta 1----3Gal beta 1----4Glc1-Cer) was tested for its ability to accept (14C)sialic acid from CMP-(14C)sialic into monosialoganglioside fractions in the presence of membrane fractions purified from human colorectal carcinoma cells (SW1116). Membrane fractions were isolated by three different methods: sucrose density centrifugation, CMP-agarose gel column chromatography, and LcOse4 gel chromatography. We optimized the incubation conditions

Vis Liepkans; Alain Jolif; Goran Larson

1988-01-01

173

The Stirred Tank Reactor Polymer Electrolyte Membrane Fuel Cell  

E-print Network

The design and operation of a differential Polymer Electrolyte Membrane (PEM) fuel cell is described. The fuel cell design is based on coupled Stirred Tank Reactors (STR); the gas phase in each reactor compartment was well mixed. The characteristic times for reactant flow, gas phase diffusion and reaction were chosen so that the gas compositions at both the anode and cathode are uniform. The STR PEM fuel cell is one-dimensional; the only spatial gradients are transverse to the membrane. The STR PEM fuel cell was employed to examine fuel cell start- up, and its dynamic responses to changes in load, temperature and reactant flow rates. Multiple time scales in systems response are found to correspond to water absorption by the membrane, water transport through the membrane and stress-related mechanical changes of the membrane.

Benziger, J; Karnas, E; Moxley, J; Teuscher, C; Kevrekidis, Yu G; Benziger, Jay

2003-01-01

174

Cell membrane thermal gradients induced by electromagnetic fields  

NASA Astrophysics Data System (ADS)

While electromagnetic fields induce structural changes in cell membranes, particularly electroporation, much remains to be understood about membrane level temperature gradients. For instance, microwaves induce cell membrane temperature gradients (?T) and bioeffects with little bulk temperature change. Recent calculations suggest that nanosecond pulsed electric fields (nsPEFs) may also induce such gradients that may additionally impact the electroporation threshold. Here, we analytically and numerically calculate the induced ?T as a function of pulse duration and pulse repetition rate. We relate ?T to the thermally induced cell membrane electric field (Em) by assuming the membrane behaves as a thermoelectric such that Em ˜ ?T. Focusing initially on applying nsPEFs to a uniform membrane, we show that reducing pulse duration and increasing pulse repetition rate (or using higher frequency for alternating current (AC) fields) maximizes the magnitude and duration of ?T and, concomitantly, Em. The maximum ?T initially occurs at the interface between the cell membrane and extracellular fluid before becoming uniform across the membrane, potentially enabling initial molecular penetration and subsequent transport across the membrane. These results, which are equally applicable to AC fields, motivate further studies to elucidate thermoelectric behavior in a model membrane system and the coupling of the Em induced by ?T with that created directly by the applied field.

Garner, Allen L.; Deminsky, Maxim; Bogdan Neculaes, V.; Chashihin, V.; Knizhnik, Andrey; Potapkin, Boris

2013-06-01

175

Characterization of a graphene oxide membrane fuel cell  

NASA Astrophysics Data System (ADS)

The electrical, mechanical, and compositional characterization of a graphene oxide membrane is presented, and its application as an electrolyte material in a polymer electrolyte membrane fuel cell is explored. Self-supporting graphene oxide membranes were prepared by a simple vacuum filtration process and, for the first time, characterized as the electrolyte in a fuel cell operating in an elevated temperature range (30-80 °C), with a maximum power density of ?34 mW cm-2, approaching that of a Nafion electrolyte based cell prepared and tested under similar conditions. Evidence for partial membrane reduction was found at higher temperatures and is believed to originate from more easily released, higher energy oxide groups, such as epoxides. We also discuss the morphology, the mechanical properties, chemical composition, and electrical conductivity of the graphene oxide membranes, with comparisons made to conventional Nafion membranes.

Bayer, T.; Bishop, S. R.; Nishihara, M.; Sasaki, K.; Lyth, S. M.

2014-12-01

176

Nafion\\/mordenite hybrid membrane for high-temperature operation of polymer electrolyte membrane fuel cell  

Microsoft Academic Search

Nafion\\/mordenite hybrid membranes for the operation of polymer electrolyte membrane fuel cells (PEMFCs) above 100 °C were prepared by mixing of H+-form mordenite powder and perfluorosulfonylfluoride copolymer resin. PEMFC operation above 100 °C reduces CO poisoning as well as passivation of the Pt anode electrocatalyst by other condensable species. The physico-chemical properties of hybrid membranes were investigated by tensile strength

Sang-Hee Kwak; Tae-Hyun Yang; Chang-Soo Kim; Ki Hyun Yoon

2003-01-01

177

Nafion\\/Analcime and Nafion\\/Faujasite composite membranes for polymer electrolyte membrane fuel cells  

Microsoft Academic Search

The Nafion\\/zeolite composite membranes were synthesized for polymer electrolyte fuel cells (PEMFCs) by adding zeolite in the matrix of Nafion polymer. Two kinds of zeolites, Analcime and Faujasite, having different Si\\/Al ratio were used. The physico-chemical properties of the composite membranes such as water uptake, ion-exchange capacity, hydrogen permeability, and proton conductivity were determined. The fabricated composite membranes showed the

Paisan Kongkachuichay; Siraprapa Pimprom

2010-01-01

178

Preparation and performance of nano silica\\/Nafion composite membrane for proton exchange membrane fuel cells  

Microsoft Academic Search

Composite membranes made from Nafion ionomer with nano phosphonic acid-functionalised silica and colloidal silica were prepared and evaluated for proton exchange membrane fuel cells (PEMFCs) operating at elevated temperature and low relative humidity (RH). The phosphonic acid-functionalised silica additive obtained from a sol–gel process was well incorporated into Nafion membrane. The particle size determined using transmission electron microscope (TEM) had

Keping Wang; Scott McDermid; Jing Li; Natalia Kremliakova; Paul Kozak; Chaojie Song; Yanghua Tang; Jianlu Zhang; Jiujun Zhang

2008-01-01

179

Nafion\\/PTFE\\/silicate membranes for high-temperature proton exchange membrane fuel cells  

Microsoft Academic Search

Fuel cell performance of membrane electrode assemblies (MEAs) prepared from poly(tetrafluoroethylene)\\/Nafion\\/silicate (PNS) membrane and Nafion-112 membrane were investigated. Due to the low conductivity of PTFE and silicate, PNS had a higher proton resistance than Nafion-112. However, in this work we show that PNS performs better than Nafion-112 for a high current density i>500mA\\/cm2 operation with a low inlet gas humidity.

Guo-Bin Jung; Fang-Bor Weng; Ay Su; Jiun-Sheng Wang; T. Leon Yu; Hsiu-Li Lin; Tein-Fu Yang; Shih-Hung Chan

2008-01-01

180

Studying the Nucleated Mammalian Cell Membrane by Single Molecule Approaches  

PubMed Central

The cell membrane plays a key role in compartmentalization, nutrient transportation and signal transduction, while the pattern of protein distribution at both cytoplasmic and ectoplasmic sides of the cell membrane remains elusive. Using a combination of single-molecule techniques, including atomic force microscopy (AFM), single molecule force spectroscopy (SMFS) and stochastic optical reconstruction microscopy (STORM), to study the structure of nucleated cell membranes, we found that (1) proteins at the ectoplasmic side of the cell membrane form a dense protein layer (4 nm) on top of a lipid bilayer; (2) proteins aggregate to form islands evenly dispersed at the cytoplasmic side of the cell membrane with a height of about 10–12 nm; (3) cholesterol-enriched domains exist within the cell membrane; (4) carbohydrates stay in microdomains at the ectoplasmic side; and (5) exposed amino groups are asymmetrically distributed on both sides. Based on these observations, we proposed a Protein Layer-Lipid-Protein Island (PLLPI) model, to provide a better understanding of cell membrane structure, membrane trafficking and viral fusion mechanisms. PMID:24806512

Wang, Feng; Wu, Jiazhen; Gao, Jing; Liu, Shuheng; Jiang, Junguang; Jiang, Shibo; Wang, Hongda

2014-01-01

181

Biodegradation characteristics and size fractionation of landfill leachate for integrated membrane treatment.  

PubMed

The fate of organics and nitrogen during the biological treatment with MBR and subsequent membrane filtration processes (nano filtration, NF; reverse osmosis, RO) were investigated for a landfill leachate. The chemical oxygen demand (COD) and total Kjeldahl nitrogen (TKN) removal performances of membrane bioreactor (MBR) were obtained to be around 89% and 85%, respectively. The effluent COD of MBR was measured to be 1935 mg/L (30 kDa) which is much lower than experimentally determined soluble inert COD of 3200 mg/L using 0.45 ?m filter. The readily and slowly biodegradable COD fractions were estimated to be 17% and 52% of raw influent COD, respectively. The respirometry based modeling test performed on raw leachate exhibited much slower degradation kinetics compared to municipal wastewater. A unique subset of model parameters was extracted from batch respirometry by using acclimated MBR sludge. The sequential ultrafiltration (UF) experiments (particle size distribution, PSD) revealed that most of the organics was below 2 nm filter mesh size. In addition, NF/RO post treatment after MBR system was required to increase COD and total nitrogen (TN) removal performances up to 99%. Relatively lower salt rejection rates around 94% was obtained for RO system as a post treatment of MBR system. PMID:23856313

Insel, Güçlü; Dagdar, Mina; Dogruel, Serdar; Dizge, Nadir; Ubay Cokgor, Emine; Keskinler, Bülent

2013-09-15

182

Apparent 2-D diffusivity in a ruffled cell membrane.  

PubMed

Most biological cell membranes have a microtopology that increases their surface area, including a highly ruffled surface in the case of leukocytes. Thus, molecular membrane diffusivities as measured by fluorescence recovery after photobleaching or other methods are decreased when projected onto a plane. We use a two-dimensional crested cycloid as a parameterized surface to simulate the random-walk diffusion of a molecule within a ruffled membrane. The apparent 2-D diffusivity was then calculated when the ruffled membrane is projected onto a plane. It is shown that the apparent diffusivity decreases as a function of the membrane area, to the -1.4 power. PMID:15019499

King, Michael R

2004-04-01

183

In-situ membrane hydration measurement of proton exchange membrane fuel cells  

NASA Astrophysics Data System (ADS)

Achieving proper membrane hydration control is one of the most critical aspects of PEM fuel cell development. This article describes the development and application of a novel 50 cm2 fuel cell device to study the in-situ membrane hydration by measuring the through-thickness membrane swelling via an array of linear variable differential transducers. Using this setup either as an air/air (dummy) cell or as a hydrogen/air (operating) cell, we performed a series of hydration and dehydration experiments by cycling the RH of the inlet gas streams at 80 °C. From the linear relationship between the under-the-land swelling and the over-the-channel water content, the mechanical constraint within the fuel cell assembly can suppress the membrane water uptake by 11%-18%. The results from the air/air humidity cycling test show that the membrane can equilibrate within 120 s for all RH conditions and that membrane can reach full hydration at a RH higher than 140% in spite of the use of a liquid water impermeable Carbel MP30Z microporous layer. This result confirms that the U.S. DOE's humidity cycling mechanical durability protocol induces sufficient humidity swings to maximize hygrothermal mechanical stresses. This study shows that the novel experimental technique can provide a robust and accurate means to study the in-situ hydration of thin membranes subject to a wide range of fuel cell conditions.

Lai, Yeh-Hung; Fly, Gerald W.; Clapham, Shawn

2015-01-01

184

In vitro antioxidant properties of chicken skin enzymatic protein hydrolysates and membrane fractions.  

PubMed

Chicken thigh and breast skin proteins were hydrolysed using alcalase or a combination of pepsin and pancreatin (PP), each at concentrations of 1-4%. The chicken skin protein hydrolysates (CSPHs) were then fractionated by membrane ultrafiltration into different molecular weight peptides (<1, 1-3, 3-5 and 5-10kDa) and analysed for antioxidant properties. Results showed that the CSPHs had a significantly (p<0.05) lower scavenging activity against DPPH radicals when compared to reduced glutathione. The chicken breast skin hydrolysates had significantly higher DPPH scavenging activity than the chicken thigh skin hydrolysates. DPPH scavenging and metal ion chelation increased significantly (p<0.05) from 29-40% to 86-89%, respectively with increasing proteolytic enzyme concentration. In contrast, the antioxidant properties decreased as peptide size increased. We conclude that CSPHs and their peptide fractions may be used as ingredients in the formulation of functional foods and nutraceuticals for the control and management of oxidative stress-related diseases. PMID:24360464

Onuh, John O; Girgih, Abraham T; Aluko, Rotimi E; Aliani, Michel

2014-05-01

185

Fractionation of protein hydrolysates of fish and chicken using membrane ultrafiltration: investigation of antioxidant activity.  

PubMed

In this work, chicken and fish peptides were obtained using the proteolytic enzymes ?-Chymotrypsin and Flavourzyme. The muscle was hydrolyzed for 4 h, and the resulting peptides were evaluated. Hydrolysates were produced from Argentine croaker (Umbrina canosai) with a degree of hydrolysis (DH) of 25.9 and 27.6% and from chicken (Gallus domesticus) with DH of 17.8 and 20.6% for Flavourzyme and ?-Chymotrypsin, respectively. Membrane ultrafiltration was used to separate fish and chicken hydrolysates from Flavourzyme and ?-Chymotrypsin based on molecular weight cutoff of >1,000, <1,000 and >500, and <500 Da, to produce fractions (F1,000, F1,000-500, and F500) with antioxidant activity. Fish hydrolysates produced with Flavourzyme (FHF) and ?-Chymotrypsin showed 60.8 and 50.9% of peptides with a molecular weight of <3 kDa in its composition, respectively. To chicken hydrolysates produced with Flavourzyme and ?-Chymotrypsin (CHC) was observed 83 and 92.4% of peptides with a molecular weight of <3 kDa. The fraction that showed, in general, higher antioxidant potential was F1,000 from FHF. When added 40 mg/mL of FHF and CHC, 93 and 80% of lipid oxidation in ground beef homogenates was inhibited, respectively. The composition of amino acids indicated higher amino acids hydrophobic content and amino acids containing sulfuric residues for FHF, which showed antioxidant potential. PMID:24449375

Centenaro, Graciela Salete; Salas-Mellado, Myriam; Pires, Carla; Batista, Irineu; Nunes, Maria L; Prentice, Carlos

2014-03-01

186

Cell membrane potentials induced during exposure to EMP fields  

SciTech Connect

Internal current densities and electric fields induced in the human body during exposure to EMP fields are reviewed and used to predict resulting cell membrane potentials. Using several different approaches, membrane potentials of about 100 mV are predicted. These values are comparable to the static membrane potentials maintained by cells as a part of normal physiological function, but the EMP-induced potentials persist for only about 10 ns. Possible biological implications of EMP-induced membrane potentials including conformational changes and electroporation are discussed.

Gailey, P.C.; Easterly, C.E.

1994-09-01

187

Inorganic–Polymer Composite Membranes for Proton Exchange Membrane Fuel Cells  

Microsoft Academic Search

Composite membranes consisting primarily of a polymer and an inorganic proton conducting particle or a proton conducting polymer containing inorganic particles for use as proton exchange membranes in low and intermediate temperature fuel cells are reviewed. The chemistry of major inorganic additives that have been used is described in terms of their structure and intrinsic ability to conduct protons. Composites

Andrew M. Herring

2006-01-01

188

Catalyst layers for proton exchange membrane fuel cells prepared by electrospray deposition on Nafion membrane  

Microsoft Academic Search

The electrospray deposition method has been used for preparation of catalyst layers for proton exchange membrane fuel cells (PEMFC) on Nafion membrane. Deposition of Pt\\/C+ionomer suspensions on Nafion 212 gives rise to layers with a globular morphology, in contrast with the dendritic growth observed for the same layers when deposited on the gas diffusion layer, GDL (microporous carbon black layer

A. M. Chaparro; P. Ferreira-Aparicio; M. A. Folgado; A. J. Martín; L. Daza

2011-01-01

189

Humidification studies on polymer electrolyte membrane fuel cell  

NASA Astrophysics Data System (ADS)

Two methods of humidifying the anode gas, namely, external and membrane humidification, for a polymer electrolyte membrane fuel (PEMFC) cell are explained. It is found that the water of solvation of protons decreases with increase in the current density and the electrode area. This is due to insufficient external humidification. In a membrane-based humidification, an optimum set of parameters, such as gas flow rate, area and type of the membrane, must be chosen to achieve effective humidification. The present study examines the dependence of water pick-up by hydrogen on the temperature, area and thickness of the membrane in membrane humidification. Since the performance of the fuel cell is dependent more on hydrogen humidification than on oxygen humidification, the scope of the work is restricted to the humidification of hydrogen using Nafion ® membrane. An examination is made on the dependence of water pick-up by hydrogen in membrane humidification on the temperature, area and thickness of the membrane. The dependence of fuel cell performance on membrane humidification and external humidification in the anode gas is also considered.

Sridhar, P.; Perumal, Ramkumar; Rajalakshmi, N.; Raja, M.; Dhathathreyan, K. S.

190

Cell Membranes Under Hydrostatic Pressure Subjected to Micro-Injection  

NASA Astrophysics Data System (ADS)

The work is concerned with the determination of the mechanical behaviour of cell membranes under uniform hydrostatic pressure subject to micro-injections. For that purpose, assuming that the shape of the deformed cell membrane is axisymmetric a variational statement of the problem is developed on the ground of the so-called spontaneous curvature model. In this setting, the cell membrane is regarded as an axisymmetric surface in the three-dimensional Euclidean space providing a stationary value of the shape energy functional under the constraint of fixed total area and fixed enclosed volume. The corresponding Euler-Lagrange equations and natural boundary conditions are derived, analyzed and used to express the forces and moments in the membrane. Several examples of such surfaces representing possible shapes of cell membranes under pressure subjected to micro injection are determined numerically.

Vassilev, Vassil M.; Kostadinov, Kostadin G.; Mladenov, Ivaïlo M.; Shulev, Assen A.; Stoilov, Georgi I.; Djondjorov, Peter A.

2011-04-01

191

Alternative Sources of Adult Stem Cells: Human Amniotic Membrane  

Microsoft Academic Search

\\u000a Human amniotic membrane is a highly promising cell source for tissue engineering. The cells thereof, human amniotic epithelial\\u000a cells (hAEC) and human amniotic mesenchymal stromal cells (hAMSC), may be immunoprivileged, they represent an early developmental\\u000a status, and their application is ethically uncontroversial. Cell banking strategies may use freshly isolated cells or involve\\u000a in vitro expansion to increase cell numbers. Therefore,

Susanne Wolbank; Martijn van Griensven; Regina Grillari-Voglauer; Anja Peterbauer-Scherb

2010-01-01

192

How helminths use excretory secretory fractions to modulate dendritic cells  

PubMed Central

It is well known that helminth parasites have immunomodulatory effects on their hosts. They characteristically cause a skew toward TH2 immunity, stimulate Treg cells while simultaneously inhibiting TH1 and TH17 responses. Additionally, they induce eosinophilia and extensive IgE release. The exact mechanism of how the worms achieve this effect have yet to be fully elucidated; however, parasite-derived secretions and their interaction with antigen presenting cells have been centrally implicated. Herein, we will review the effects of helminth excretory-secretory fractions on dendritic cells and discuss how this interaction is crucial in shaping the host response. PMID:23221477

White, Rhiannon R.; Artavanis-Tsakonas, Katerina

2012-01-01

193

Computational Modeling of Electrolyte/Cathode Interfaces in Proton Exchange Membrane Fuel Cells  

E-print Network

Computational Modeling of Electrolyte/Cathode Interfaces in Proton Exchange Membrane Fuel Cells Dr Proton exchange membrane fuel cells (PEMFCs) are alternative energy conversion devices that efficiently

Bjørnstad, Ottar Nordal

194

Measurement of the nonlinear elasticity of red blood cell membranes  

PubMed Central

The membranes of human red blood cells (RBCs) are a composite of a fluid lipid bilayer and a triangular network of semiflexible filaments (spectrin). We perform cellular microrheology using the dynamic membrane fluctuations of the RBCs to extract the elastic moduli of this composite membrane. By applying known osmotic stresses we measure the changes in the elastic constants under imposed strain and thereby determine the nonlinear elastic properties of the membrane. We find that the elastic nonlinearities of the shear modulus in tensed RBC membranes can be well-understood in terms of a simple worm-like chain model. Our results show that the elasticity of the spectrin network can mostly account for the area compression modulus at physiological osmolality, suggesting that the lipid bilayer has significant excess area. As the cell swells, the elastic contribution from the now tensed lipid membrane becomes dominant. PMID:21728589

Park, YongKeun; Best, Catherine A.; Kuriabova, Tatiana; Henle, Mark L.; Feld, Michael S.; Levine, Alex J.; Popescu, Gabriel

2012-01-01

195

Cell-Cell Communication Via Extracellular Membrane Vesicles and Its Role in the Immune Response  

PubMed Central

The host immune response involves a variety of cell types, including specialized immune and non-immune cells. The delicate coordination among these cells via close communication is central for the proper operation of immune system. Cell-cell communication is mediated by a complex network that includes soluble factors such as cytokines, chemokines, and metabolites exported from cells, as well as membrane-bound receptors and their ligands. Cell-cell communication is also mediated by membrane vesicles (e.g., exosomes, ectosomes), which are either shed by distant cells or exchanged by cells that are making direct contact. Intercellular communication via extracellular membrane vesicles has drawn much attention recently, as they have been shown to carry various biomolecules that modulate the activities of recipient cells. In this review, I will discuss current views on cell-cell communication via extra-cellular membrane vesicles, especially shedded membrane vesicles, and their effects on the control of the immune system. PMID:23807045

Hwang, Inkyu

2013-01-01

196

Membrane hydraulic permeability changes during cooling of mammalian cells.  

PubMed

In order to predict optimal cooling rates for cryopreservation of cells, the cell-specific membrane hydraulic permeability and corresponding activation energy for water transport need to be experimentally determined. These parameters should preferably be determined at subzero temperatures in the presence of ice. There is, however, a lack of methods to study membrane properties of cells in the presence of ice. We have used Fourier transform infrared spectroscopy to study freezing-induced membrane dehydration of mouse embryonic fibroblast (3T3) cells and derived the subzero membrane hydraulic permeability and the activation energy for water transport from these data. Coulter counter measurements were used to determine the suprazero membrane hydraulic permeability parameters from cellular volume changes of cells exposed to osmotic stress. The activation energy for water transport in the ice phase is about three fold greater compared to that at suprazero temperatures. The membrane hydraulic permeability at 0 °C that was extrapolated from suprazero measurements is about five fold greater compared to that extrapolated from subzero measurements. This difference is likely due to a freezing-induced dehydration of the bound water around the phospholipid head groups. Using Fourier transform infrared spectroscopy, two distinct water transport processes, that of free and membrane bound water, can be identified during freezing with distinct activation energies. Dimethylsulfoxide, a widely used cryoprotective agent, did not prevent freezing-induced membrane dehydration but decreased the activation energy for water transport. PMID:21126509

Akhoondi, Maryam; Oldenhof, Harriëtte; Stoll, Christoph; Sieme, Harald; Wolkers, Willem F

2011-03-01

197

How the antimicrobial peptides destroy bacteria cell membrane: Translocations vs. membrane buckling  

NASA Astrophysics Data System (ADS)

In this study, coarse grained Dissipative Particle Dynamics simulation with implementation of electrostatic interactions is developed in constant pressure and surface tension ensemble to elucidate how the antimicrobial peptide molecules affect bilayer cell membrane structure and kill bacteria. We find that peptides with different chemical-physical properties exhibit different membrane obstructing mechanisms. Peptide molecules can destroy vital functions of the affected bacteria by translocating across their membranes via worm-holes, or by associating with membrane lipids to form hydrophilic cores trapped inside the hydrophobic domain of the membranes. In the latter scenario, the affected membranes are strongly corrugated (buckled) in accord with very recent experimental observations [G. E. Fantner et al., Nat. Nanotech., 5 (2010), pp. 280-285].

Golubovic, Leonardo; Gao, Lianghui; Chen, Licui; Fang, Weihai

2012-02-01

198

Red cell membrane remodeling in sickle cell anemia. Sequestration of membrane lipids and proteins in Heinz bodies.  

PubMed Central

In red cells from patients with sickle cell anemia, hemoglobin S denatures and forms Heinz bodies. Binding of Heinz bodies to the inner surface of the sickle cell membrane promotes clustering and colocalization of the membrane protein band 3, outer surface-bound autologous IgG and, to some extent, the membrane proteins glycophorin and ankyrin. Loss of transbilayer lipid asymmetry is also found in certain populations of sickle red cells. The lateral distribution of sickle cell membrane lipids has not been examined, however. In this report, we examine by fluorescence microscopy the incorporation and distribution of the fluorescent phospholipid analogues 7-nitro-2,1,3-benzoxadiazol-4-yl (NBD)-phosphatidylserine and NBD-phosphatidylcholine in sickle red cells. Both phospholipid analogues are observed to accumulate prominently at sites of Heinz bodies. Accumulation at sites of Heinz bodies is also shown by 1,'1-dihexadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate, a fluorescent lipid analogue that readily crosses membranes, but not by fluorescein-phosphatidylethanolamine, an analogue that is localized to the outer leaflet of the membrane. Double labeling and confocal microscopy techniques show that NBD-lipids, band 3 protein, protein 4.1, ankyrin, and spectrin are all sequestered within sickle red cells and colocalized at sites of Heinz bodies. We propose that Heinz bodies provide a hydrophobic surface on which sickle red cell membrane lipids and proteins are sequestered. PMID:8550846

Liu, S C; Yi, S J; Mehta, J R; Nichols, P E; Ballas, S K; Yacono, P W; Golan, D E; Palek, J

1996-01-01

199

Composite polymer membranes for proton exchange membrane fuel cells operating at elevated temperatures and reduced humidities  

Microsoft Academic Search

Proton Exchange Membrane Fuel Cells (PEMFCs) are the leading candidate in the fuel cell technology due to the high power density, solid electrolyte, and low operational temperature. However, PEMFCs operating in the normal temperature range (60-80°C) face problems including poor carbon monoxide tolerance and heat rejection. The poisoning effect can be significantly relieved by operating the fuel cell at elevated

Tao Zhang

2006-01-01

200

Improved Membrane Materials for PEM Fuel Cell Application  

SciTech Connect

The overall goal of this project is to collect and integrate critical structure/property information in order to develop methods that lead to significant improvements in the durability and performance of polymer electrolyte membrane fuel cell (PEMFC) materials. This project is focused on the fundamental improvement of PEMFC membrane materials with respect to chemical, mechanical and morphological durability as well as the development of new inorganically-modified membranes.

Kenneth A. Mauritz; Robert B. Moore

2008-06-30

201

The Flocculating Cationic Polypetide from Moringa oleifera Seeds Damages Bacterial Cell Membranes by Causing Membrane Fusion.  

PubMed

A cationic protein isolated from the seeds of the Moringa oleifera tree has been extensively studied for use in water treatment in developing countries and has been proposed for use in antimicrobial and therapeutic applications. However, the molecular basis for the antimicrobial action of this peptide, Moringa oleifera cationic protein (MOCP), has not been previously elucidated. We demonstrate here that a dominant mechanism of MOCP antimicrobial activity is membrane fusion. We used a combination of cryogenic electron microscopy (cryo-EM) and fluorescence assays to observe and study the kinetics of fusion of membranes in liposomes representing model microbial cells. We also conducted cryo-EM experiments on E. coli cells where MOCP was seen to fuse the inner and outer membranes. Coarse-grained molecular dynamics simulations of membrane vesicles with MOCP molecules were used to elucidate steps in peptide adsorption, stalk formation, and fusion between membranes. PMID:25845029

Shebek, Kevin; Schantz, Allen B; Sines, Ian; Lauser, Kathleen; Velegol, Stephanie; Kumar, Manish

2015-04-21

202

An Experimental and Theoretical Analysis of Ultrasound-Induced Permeabilization of Cell Membranes  

PubMed Central

Application of ultrasound transiently permeabilizes cell membranes and offers a nonchemical, nonviral, and noninvasive method for cellular drug delivery. Although the ability of ultrasound to increase transmembrane transport has been well demonstrated, a systematic dependence of transport on ultrasound parameters is not known. This study examined cell viability and cellular uptake of calcein using 3T3 mouse cell suspension as a model system. Cells were exposed to varying acoustic energy doses at four different frequencies in the low frequency regime (20–100 kHz). At all frequencies, cell viability decreased with increasing acoustic energy dose, while the fraction of cells exhibiting uptake of calcein showed a maximum at an intermediate energy dose. Acoustic spectra under various ultrasound conditions were also collected and assessed for the magnitude of broadband noise and subharmonic peaks. While the cell viability and transport data did not show any correlation with subharmonic (f/2) emission, they correlated with the broadband noise, suggesting a dominant contribution of transient cavitation. A theoretical model was developed to relate reversible and irreversible membrane permeabilization to the number of transient cavitation events. The model showed that nearly every stage of transient cavitation, including bubble expansion, collapse, and subsequent shock waves may contribute to membrane permeabilization. For each mechanism, the volume around the bubble within which bubbles induce reversible and irreversible membrane permeabilization was determined. Predictions of the model are consistent with experimental data. PMID:12719239

Sundaram, Jagannathan; Mellein, Berlyn R.; Mitragotri, Samir

2003-01-01

203

Distribution of Intact and Core Membrane Lipids of Archaeal Glycerol Dialkyl Glycerol Tetraethers among Size-Fractionated Particulate Organic Matter in Hood Canal, Puget Sound  

PubMed Central

There is great interest in the membrane lipids of archaea (glycerol dialkyl glycerol tetraethers [GDGTs]) as tracers of archaeal biomass because of their utility as paleoproxies and because of the biogeochemical importance of archaea. While core GDGTs (formed by hydrolysis of polar head groups of intact GDGTs after cell death) are appropriate for paleostudies, they have also been used to trace archaeal populations. Also, despite the small size (0.2 by 0.7 ?m) of cultivated marine archaea, 0.7-?m glass-fiber filters (GFFs) are typically used to collect GDGTs from natural waters. We quantified both core and intact GDGTs in free-living (0.2- to 0.7-?m), suspended (0.7- to 60-?m), and aggregate (>60-?m) particle size fractions in Puget Sound (Washington State). On average, the free-living fraction contained 36% of total GDGTs, 90% of which were intact. The intermediate-size fraction contained 62% of GDGTs, and 29% of these were intact. The aggregate fraction contained 2% of the total GDGT pool, and 29% of these were intact. Our results demonstrate that intact GDGTs are largely in the free-living fraction. Because only intact GDGTs are present in living cells, protocols that target this size fraction and analyze the intact GDGT pool are necessary to track living populations in marine waters. Core GDGT enrichment in larger-size fractions indicates that archaeal biomass may quickly become attached or entrained in particles once the archaea are dead or dying. While the concentrations of the two pools were generally not correlated, the similar sizes of the core and intact GDGT pools suggest that core GDGTs are removed from the water column on timescales similar to those of cell replication, on timescales of days to weeks. PMID:22226949

Huguet, Carme; Truxal, Laura T.

2012-01-01

204

Wisconsin Online Resource Center: Construction of the Cell Membrane  

NSDL National Science Digital Library

Hosted by the Wisconsin Online Resource Center, this fun and informative web-based tutorial on the Construction of the Cell Membrane was created by Barbara Liang and Chad Blohowiak. Although the site content is geared for an older audience, the tutorial is so clear and easy to navigate that younger students curious about cells will enjoy it as well. Through the process of building the molecular structure of an animated cell membrane, site visitors will learn "the makeup and the basis for cell membrane function." The 23-page tutorial is fairly brief and interactive with questions and assignments such as placing the fibrous receptor or glycoprotein into the cell membrane. This site also has link for downloading the required software plug-in.

Blohowiak, Chad

205

Homotypic fusion of endoplasmic reticulum membranes in plant cells  

PubMed Central

The endoplasmic reticulum (ER) is a membrane-bounded organelle whose membrane comprises a network of tubules and sheets. The formation of these characteristic shapes and maintenance of their continuity through homotypic membrane fusion appears to be critical for the proper functioning of the ER. The atlastins (ATLs), a family of ER-localized dynamin-like GTPases, have been identified as fusogens of the ER membranes in metazoans. Mutations of the ATL proteins in mammalian cells cause morphological defects in the ER, and purified Drosophila ATL mediates membrane fusion in vitro. Plant cells do not possess ATL, but a family of similar GTPases, named root hair defective 3 (RHD3), are likely the functional orthologs of ATLs. In this review, we summarize recent advances in our understanding of how RHD3 proteins play a role in homotypic ER fusion. We also discuss the possible physiological significance of forming a tubular ER network in plant cells. PMID:24385977

Zhang, Miao; Hu, Junjie

2013-01-01

206

Identification of effluent organic matter fractions responsible for low-pressure membrane fouling.  

PubMed

Anion exchange resin (AER), powder activated carbon (PAC) adsorption and ozonation treatments were applied on biologically treated wastewater effluent with the objective to modify the effluent organic matter (EfOM) matrix. Both AER and PAC led to significant total organic carbon (TOC) removal, while the TOC remained nearly constant after ozonation. Liquid Chromatography-Organic Carbon Detection (LC-OCD) analysis showed that the AER treatment preferentially removed high and intermediate molecular weight (MW) humic-like structures while PAC removed low MW compounds. Only a small reduction of the high MW colloids (i.e. biopolymers) was observed for AER and PAC treatments. Ozonation induced a large reduction of the biopolymers and an important increase of the low MW humic substances (i.e. building blocks). Single-cycle microfiltration (MF) and ultrafiltration (UF) tests were conducted using commercially available hollow fibres at a constant flux. After reconcentration to their original organic carbon content, the EfOM matrix modified by AER and PAC treatments exhibited higher UF membrane fouling compared to untreated effluent; result that correlated with the higher concentration of biopolymers. On the contrary, ozonation which induced a significant degradation of the biopolymers led to a minor flux reduction for both UF and MF filtration tests. Based on a single filtration, results indicate that biopolymers play a major role in low pressure membrane fouling and that intermediate and low MW compounds have minor impact. Thus, this approach has shown to be a valid methodology to identify the foulant fractions of EfOM. PMID:22884373

Filloux, Emmanuelle; Gallard, Hervé; Croue, Jean-Philippe

2012-11-01

207

Catalytic membranes for CO oxidation in fuel cells  

DOEpatents

A hydrogen permeable membrane, which includes a polymer stable at temperatures of about 200 C having clay impregnated with Pt or Au or Ru or Pd particles or mixtures thereof with average diameters of less than about 10 nanometers (nms) is disclosed. The membranes are useful in fuel cells or any device which requires hydrogen to be separated from carbon monoxide.

Sandi-Tapia, Giselle; Carrado Gregar, Kathleen; Kizilel, Riza

2010-06-08

208

Gangliosides asymmetrically alter the membrane order in cultured PC12 cells  

Microsoft Academic Search

Exogenous gangliosides readily associate with the cell membranes and produce marked effects on cell growth and differentiation. We have studied the effect of bovine brain gangliosides (BBG) on the membrane dynamics of intact cells. The structural and dynamic changes in the cell membrane were monitored by the fluorescence probes DPH, TMA-DPH and laurdan. Incorporation of BBG into the cell membrane

B. Ravichandra; Preeti G. Joshi

1999-01-01

209

Thermodynamic and fluid properties of cells, tissues and membranes  

NASA Astrophysics Data System (ADS)

This dissertation studies cellular rearrangements in tissues and attempts to establish the role of physical properties of cells, tissues and membranes in several biological phenomena. Using experiments and statistical mechanical modeling, we study cell sorting, tissue engulfment, single cell motion and membrane fluctuations. When cells of two different types are mixed together, they sort out, with the less cohesive tissue surrounding the more cohesive one. This sorting out resembles the phase separation of a mixture of immiscible liquids. We have measured the rate of sorting in tissues and compared it with a cellular automaton based model of cell aggregates. We have also established that cell sorting agrees well with the theory for phase separating fluids. Engulfment is the spreading of one type of tissue over the surface of another tissue placed adjacent to it. Differences in adhesion cause an imbalance of surface tension forces which drives tissue spreading. We have quantitatively studied engulfment between different tissue types and compared the experimental rate with results from computer simulations and a liquid model. Our results suggest that simple physical principles can model tissue motion. Studying the motion of single cells in aggregates is important to understanding the overall pattern formation in tissues. We characterized cell motion in different types of adhesive aggregates to elucidate the role of adhesion in cell motion. We also observed that the cells exhibited a novel type of statistics including correlations and collective motion. Membrane deformations of cells played a negligible role in large scale cell motion. Our results indicate the importance of correlated motion for cells to move long distances in tissues. At the single cell level, tension of the cell membrane and intracellular membrane can play an important role in cell shape changes, regulation of cell motility and membrane dynamics. We used optical tweezers to measure the membrane tension of tubulo-vesicular networks obtained from Golgi and Endoplasmic Reticulum (ER) membranes within cells. As expected on the basis of some previous experiments, the ER has a higher membrane tension than the Golgi.

Upadhyaya, Arpita

2000-10-01

210

Layer-by-layer cell membrane assembly  

NASA Astrophysics Data System (ADS)

Eukaryotic subcellular membrane systems, such as the nuclear envelope or endoplasmic reticulum, present a rich array of architecturally and compositionally complex supramolecular targets that are as yet inaccessible. Here we describe layer-by-layer phospholipid membrane assembly on microfluidic droplets, a route to structures with defined compositional asymmetry and lamellarity. Starting with phospholipid-stabilized water-in-oil droplets trapped in a static droplet array, lipid monolayer deposition proceeds as oil/water-phase boundaries pass over the droplets. Unilamellar vesicles assembled layer-by-layer support functional insertion both of purified and of in situ expressed membrane proteins. Synthesis and chemical probing of asymmetric unilamellar and double-bilayer vesicles demonstrate the programmability of both membrane lamellarity and lipid-leaflet composition during assembly. The immobilized vesicle arrays are a pragmatic experimental platform for biophysical studies of membranes and their associated proteins, particularly complexes that assemble and function in multilamellar contexts in vivo.

Matosevic, Sandro; Paegel, Brian M.

2013-11-01

211

Membrane organization and cell fusion during mating in fission yeast requires multipass membrane protein Prm1.  

PubMed

The involvement of Schizosaccharomyces pombe prm1(+) in cell fusion during mating and its relationship with other genes required for this process have been addressed. S. pombe prm1? mutant exhibits an almost complete blockade in cell fusion and an abnormal distribution of the plasma membrane and cell wall in the area of cell-cell interaction. The distribution of cellular envelopes is similar to that described for mutants devoid of the Fig1-related claudin-like Dni proteins; however, prm1(+) and the dni(+) genes act in different subpathways. Time-lapse analyses show that in the wild-type S. pombe strain, the distribution of phosphatidylserine in the cytoplasmic leaflet of the plasma membrane undergoes some modification before an opening is observed in the cross wall at the cell-cell contact region. In the prm1? mutant, this membrane modification does not take place, and the cross wall between the mating partners is not extensively degraded; plasma membrane forms invaginations and fingers that sometimes collapse/retract and that are sometimes strengthened by the synthesis of cell-wall material. Neither prm1? nor prm1? dni? zygotes lyse after cell-cell contact in medium containing and lacking calcium. Response to drugs that inhibit lipid synthesis or interfere with lipids is different in wild-type, prm1?, and dni1? strains, suggesting that membrane structure/organization/dynamics is different in all these strains and that Prm1p and the Dni proteins exert some functions required to guarantee correct membrane organization that are critical for cell fusion. PMID:24514900

Curto, M-Ángeles; Sharifmoghadam, Mohammad Reza; Calpena, Eduardo; De León, Nagore; Hoya, Marta; Doncel, Cristina; Leatherwood, Janet; Valdivieso, M-Henar

2014-04-01

212

Research Resource: Monitoring Endoplasmic Reticulum Membrane Integrity in ?-Cells at the Single-Cell Level  

PubMed Central

Endoplasmic reticulum (ER) membrane integrity is an emerging target for human chronic diseases associated with ER stress. Despite the underlying importance of compromised ER membrane integrity in disease states, the entire process leading to ER membrane permeabilization and cell death is still not clear due to technical limitations. Here we describe a novel method for monitoring ER membrane integrity at the single-cell level in real time. Using a ?-cell line expressing ER-targeted redox sensitive green fluorescent protein, we could identify a ?-cell population undergoing ER membrane permeabilization induced by palmitate and could monitor cell fate and ER stress of these cells at the single-cell level. Our method could be used to develop a novel therapeutic modality targeting the ER membrane for ER-associated disorders, including ?-cell death in diabetes, neurodegeneration, and Wolfram syndrome. PMID:25584413

Kanekura, Kohsuke; Ou, Jianhong; Hara, Takashi; Zhu, Lihua J.

2015-01-01

213

Low Crossover Polymer Electrolyte Membranes for Direct Methanol Fuel Cells  

NASA Technical Reports Server (NTRS)

Direct Methanol Fuel Cells (DMFC's) using polymer electrolyte membranes are promising power sources for portable and vehicular applications. State of the art technology using Nafion(R) 117 membranes (Dupont) are limited by high methanol permeability and cost, resulting in reduced fuel cell efficiencies and impractical commercialization. Therefore, much research in the fuel cell field is focused on the preparation and testing of low crossover and cost efficient polymer electrolyte membranes. The University of Southern California in cooperation with the Jet Propulsion Laboratory is focused on development of such materials. Interpenetrating polymer networks are an effective method used to blend polymer systems without forming chemical links. They provide the ability to modify physical and chemical properties of polymers by optimizing blend compositions. We have developed a novel interpenetrating polymer network based on poly (vinyl - difluoride)/cross-linked polystyrenesulfonic acid polymer composites (PVDF PSSA). Sulfonation of polystyrene accounts for protonic conductivity while the non-polar, PVDF backbone provides structural integrity in addition to methanol rejection. Precursor materials were prepared and analyzed to characterize membrane crystallinity, stability and degree of interpenetration. USC JPL PVDF-PSSA membranes were also characterized to determine methanol permeability, protonic conductivity and sulfur distribution. Membranes were fabricated into membrane electrode assemblies (MEA) and tested for single cell performance. Tests include cell performance over a wide range of temperatures (20 C - 90 C) and cathode conditions (ambient Air/O2). Methanol crossover values are measured in situ using an in-line CO2 analyzer.

Prakash, G. K. Surya; Smart, Marshall; Atti, Anthony R.; Olah, George A.; Narayanan, S. R.; Valdez, T.; Surampudi, S.

1996-01-01

214

Actin-propelled Invasive Membrane Protrusions Promote Fusogenic Protein Engagement During Cell-Cell Fusion  

PubMed Central

Cell-cell fusion is critical for the conception, development and physiology of multicellular organisms. Although cellular fusogenic proteins and the actin cytoskeleton are implicated in cell-cell fusion, whether and how they coordinate to promote plasma membrane fusion remain unclear. Here, we reconstituted a high-efficiency, inducible cell-fusion culture system in the normally non-fusing Drosophila S2R+ cells. Both fusogenic proteins and actin cytoskeletal rearrangements were necessary for cell fusion, and, in combination, were sufficient to impart fusion competence. Localized actin polymerization triggered by specific cell-cell or cell-matrix adhesion molecules propelled invasive cell membrane protrusions, which, in turn, promoted fusogenic protein engagement and plasma membrane fusion. This de novo cell-fusion culture system reveals a general role for actin-propelled invasive membrane protrusions in driving fusogenic protein engagement during cell-cell fusion. PMID:23470732

Shilagardi, Khurts; Li, Shuo; Luo, Fengbao; Marikar, Faiz; Duan, Rui; Jin, Peng; Kim, Ji Hoon; Murnen, Katherine; Chen, Elizabeth H.

2013-01-01

215

Decreasing Outer Hair Cell Membrane Cholesterol Increases Cochlear Electromechanics  

NASA Astrophysics Data System (ADS)

The effect of decreasing membrane cholesterol on the mechanical response of the cochlea to acoustic and/or electrical stimulation was monitored using laser interferometry. In contrast to pharmacological interventions that typically decrease cochlear electromechanics, reducing membrane cholesterol increased the response. The electromechanical response in untreated preparations was asymmetric with greater displacements in response to positive currents and cholesterol depletion increased the asymmetry. The results confirm that outer hair cell electromotility is enhanced by low membrane cholesterol. The asymmetry of the response indicates the outer hair cell resting membrane potential is hyperpolarized relative to the voltage of maximum gain for the outer hair cell voltage-displacement function. The magnitude of the response increase suggests a non-uniform distribution of cholesterol along the lateral wall of normal adult outer hair cells.

Brownell, William E.; Jacob, Stefan; Hakizimana, Pierre; Ulfendahl, Mats; Fridberger, Anders

2011-11-01

216

Interferometric tomography of fuel cells for monitoring membrane water content  

E-print Network

We have developed a system that uses two 1D interferometric phase projections for reconstruction of 2D water content changes over time in situ in a proton exchange membrane (PEM) fuel cell system. By modifying the filtered ...

Waller, Laura

217

A composite electrolyte membrane containing high-content sulfonated carbon spheres for proton exchange membrane fuel cells  

Microsoft Academic Search

Sulfonated carbon spheres (SCS) were employed with perfluorinated ionomers as a binder to make proton-conducting electrolyte membranes for polymer electrolyte membrane fuel cells (PEMFC). Hot-pressing produced a symmetric, thin membrane with SCS particles concentrated in the center of the membrane. Relative to Nafion, the SCS materials showed higher density of sulfonic acid groups and increased water retention capacity of the

Younggeun choi; Youngkwon Kim; Kyung Yeon Kang; Jae Sung Lee

2011-01-01

218

Membrane-electrode assemblies for electrochemical cells  

DOEpatents

A combination, unitary, membrane and electrode assembly with a solid polymer electrolyte membrane, and first and second electrodes at least partially embedded in opposed surfaces of the membrane. The electrodes each comprise a respective group of finely divided carbon particles, very finely divided catalytic particles supported on internal and external surfaces of the carbon particles and a proton conductive material intermingled with the catalytic and carbon particles. A first group of finely divided carbon particles forming the first electrode has greater water attraction and retention properties, and is more hydrophilic than a second group of carbon particles forming the second electrode. In a preferred method, the membrane electrode assembly of the invention is prepared by forming a slurry of proton conductive material and at least one group of the carbon and catalyst particles. The slurry is applied to the opposed surfaces of the membrane and heated while being pressed to the membrane for a time and at a temperature and compressive load sufficient to embed at least a portion of the particles into the membrane.

Swathirajan, Sundararajan (Troy, MI); Mikhail, Youssef M. (Sterling Heights, MI)

1993-01-01

219

Adaptation of yeast cell membranes to ethanol  

SciTech Connect

A highly ethanol-tolerant Saccharomyces wine strain is able, after growth in the presence of ethanol, to efficiently improve the ethanol tolerance of its membrane. A less-tolerant Saccharomyces laboratory strain, however, is unable to adapt its membrane to ethanol. Furthermore, after growth in the presence of ethanol, the membrane of the latter strain becomes increasingly sensitive, although this is a reversible process. Reversion to a higher tolerance occurs only after the addition of an energy source and does not take place in the presence of cycloheximide.

Jimenez, J.; Benitez, T.

1987-05-01

220

Blend Concepts for Fuel Cell Membranes  

Microsoft Academic Search

\\u000a Differently cross-linked blend membranes were prepared from commercial arylene main-chain polymers from the classes of poly(ether-ketones)\\u000a and poly(ethersulfones) modified with sulfonate groups, sulfinate cross-linking groups and basic N-groups. The following membrane\\u000a types have been prepared: (a) van-der Waals\\/dipole-dipole blends by mixing a polysulfonate with unmodified PSU. This membrane\\u000a type showed a heterogeneous morphology, leading to extreme swelling and even dissolution

Jochen Kerres

2009-01-01

221

Membrane–wall attachments in plasmolysed plant cells  

Microsoft Academic Search

Summary. Field emission scanning electron microscopy of plasmolysed Tradescantia virginiana leaf epidermal cells gave novel insights into the three-dimensional architecture of Hechtian strands, Hechtian reticulum, and the inner surface of the cell wall without the need for extraction. At high magnification, we observed fibres that pin the plasma membrane to the cell wall after plasmolysis. Treatment with cellulase caused these

I. Lang; D. A. Barton; R. L. Overall

2004-01-01

222

Cell-free system for synthesizing membrane proteins cell free method for synthesizing membrane proteins  

DOEpatents

The invention provides an in vitro method for producing proteins, membrane proteins, membrane-associated proteins, and soluble proteins that interact with membrane-associated proteins for assembly into an oligomeric complex or that require association with a membrane for proper folding. The method comprises, supplying intracytoplasmic membranes from organisms; modifying protein composition of intracytoplasmic membranes from organism by modifying DNA to delete genes encoding functions of the organism not associated with the formation of the intracytoplasmic membranes; generating appropriate DNA or RNA templates that encode the target protein; and mixing the intracytoplasmic membranes with the template and a transcription/translation-competent cellular extract to cause simultaneous production of the membrane proteins and encapsulation of the membrane proteins within the intracytoplasmic membranes.

Laible, Philip D; Hanson, Deborah K

2013-06-04

223

Surface-Enhanced Raman Spectroscopy of the Endothelial Cell Membrane  

PubMed Central

We applied surface-enhanced Raman spectroscopy (SERS) to cationic gold-labeled endothelial cells to derive SERS-enhanced spectra of the bimolecular makeup of the plasma membrane. A two-step protocol with cationic charged gold nanoparticles followed by silver-intensification to generate silver nanoparticles on the cell surface was employed. This protocol of post-labelling silver-intensification facilitates the collection of SERS-enhanced spectra from the cell membrane without contribution from conjugated antibodies or other molecules. This approach generated a 100-fold SERS-enhancement of the spectral signal. The SERS spectra exhibited many vibrational peaks that can be assigned to components of the cell membrane. We were able to carry out spectral mapping using some of the enhanced wavenumbers. Significantly, the spectral maps suggest the distribution of some membrane components are was not evenly distributed over the cells plasma membrane. These results provide some possible evidence for the existence of lipid rafts in the plasma membrane and show that SERS has great potential for the study and characterization of cell surfaces. PMID:25188340

Fogarty, Simon W.; Patel, Imran I.; Martin, Francis L.; Fullwood, Nigel J.

2014-01-01

224

Protein diffusion in plant cell plasma membranes: the cell-wall corral  

PubMed Central

Studying protein diffusion informs us about how proteins interact with their environment. Work on protein diffusion over the last several decades has illustrated the complex nature of biological lipid bilayers. The plasma membrane contains an array of membrane-spanning proteins or proteins with peripheral membrane associations. Maintenance of plasma membrane microstructure can be via physical features that provide intrinsic ordering such as lipid microdomains, or from membrane-associated structures such as the cytoskeleton. Recent evidence indicates, that in the case of plant cells, the cell wall seems to be a major player in maintaining plasma membrane microstructure. This interconnection / interaction between cell-wall and plasma membrane proteins most likely plays an important role in signal transduction, cell growth, and cell physiological responses to the environment. PMID:24381579

Martinière, Alexandre; Runions, John

2013-01-01

225

Fractionation of Tetrahymena ciliary membranes with triton X-114 and the identification of a ciliary membrane ATPase  

E-print Network

Cilia were isolated from Tetrahymena thermophila, extracted with Triton X-114, and the detergent-soluble membrane + matrix proteins separated into Triton X-114 aqueous and detergent phases. The aqueous phase polypeptides include a high molecular...

Dentler, William L., Jr

1988-12-01

226

A life-like virtual cell membrane using discrete automata.  

PubMed

A framework is presented that captures the discrete and probabilistic nature of molecular transport and reaction kinetics found in a living cell as well as formally representing the spatial distribution of these phenomena. This particle or agent-based approach is computationally robust and complements established methods. Namely it provides a higher level of spatial resolution than formulations based on ordinary differential equations (ODE) while offering significant advantages in computational efficiency over molecular dynamics (MD). Using this framework, a model cell membrane has been constructed with discrete particle agents that respond to local component interactions that resemble flocking or herding behavioural cues in animals. Results from simulation experiments are presented where this model cell exhibits many of the characteristic behaviours associated with its biological counterpart such as lateral diffusion, response to osmotic pressure gradients, membrane growth and cell division. Lateral diffusion rates and estimates for the membrane modulus of elasticity derived from these simple experiments fall well within a biologically relevant range of values. More importantly, these estimates were obtained by applying a simple qualitative tuning of the model membrane. Membrane growth was simulated by injecting precursor molecules into the proto-cell at different rates and produced a variety of morphologies ranging from a single large cell to a cluster of cells. The computational scalability of this methodology has been tested and results from benchmarking experiments indicate that real-time simulation of a complete bacterial cell will be possible within 10 years. PMID:15972012

Broderick, Gordon; Ru'aini, Melania; Chan, Eugene; Ellison, Michael J

2005-01-01

227

Fractions  

NSDL National Science Digital Library

This is an accessible, easy-to-read book introducing fractions. It can be downloaded in PowerPoint, Impress, and Flash formats. For struggling or non-readers the book can be read aloud in a variety of voices. All of the books on the Tar Heel Reader site can be used with the Intellikeys keyboard with a custom overlay, a touch screen, and/or 1-3 switches. The text and background colors can be modified for students with visual impairments.

K. Cowley

2011-05-09

228

Regular structures in membranes. I. Membranes in the endocytic complex of ileal epithelial cells.  

PubMed

An "apical endocytic complex" in the ileal lining cells of suckling rats is described. The complex consists of a continuous network of membrane-limited tubules which originate as invaginations of the apical plasma membrane at the base of the microvilli, some associated vesicles, and a giant vacuole. The lumenal surface of this tubular network of membranes and associated vesicles is covered with a regular repeating particulate structure. The repeating unit is an approximately 7.5-nm diameter particle which has a distinct subunit structure composed of possibly nine smaller particles each approximately 3 nm in diameter. The approximately 7.5-nm diameter particles are joined together with a center-to-center separation of approximately 15 nm to form long rows. These linear aggregates, when arranged laterally, give rise to several square and oblique two-dimensional lattice arrangements of the particles which cover the surface of the membrane. Whether a square or oblique lattice is generated depends on the center-to-center separation of the rows and on the relative displacement of the particles in adjacent rows. Four membrane faces are revealed by fracturing frozen membranes of the apical tubules and vesicles: two complementary inner membrane faces exposed by the fracturing process and the lumenal and cytoplasmic membrane surfaces revealed by etching. The outer membrane face reveals a distinct array of membrane particles. This array also sometimes can be seen on the outer (B) fracture face and is sometimes faintly visible on the inner (A) fracture face. Combined data from sectioned, negatively stained, and freeze-etched preparations indicate that this regular particulate structure is a specialization that is primarily localized in the outer half of the membrane mainly in the outer leaflet. PMID:4854072

Knutton, S; Limbrick, A R; Robertson, J D

1974-09-01

229

Phosphatidylserine Membrane Translocation in Human Spermatozoa: Topography in Membrane Domains and Relation to Cell Vitality  

Microsoft Academic Search

The complex structure of the human spermatozoa membrane comprises five topographic domains. Transmembrane asymmetry of the\\u000a distribution of phospholipids including phosphatidylserine (PS) is considered a marker of cell activity. The objective of\\u000a the study was to determine which cytomembrane domains of human spermatozoa are involved in PS membrane translocation and to\\u000a identify the possible relationship of PS translocation with spermatozoa

Malgorzata Kotwicka; Magdalena Jendraszak; Piotr Jedrzejczak

2011-01-01

230

Anhydrous Proton-Conducting Membranes for Fuel Cells  

NASA Technical Reports Server (NTRS)

Polymeric electrolyte membranes that do not depend on water for conduction of protons are undergoing development for use in fuel cells. Prior polymeric electrolyte fuel-cell membranes (e.g., those that contain perfluorosulfonic acid) depend on water and must be limited to operation below a temperature of 125 C because they retain water poorly at higher temperatures. In contrast, the present developmental anhydrous membranes are expected to function well at temperatures up to 200 C. The developmental membranes exploit a hopping-and-reorganization proton- conduction process that can occur in the solid state in organic amine salts and is similar to a proton-conduction process in a liquid. This process was studied during the 1970s, but until now, there has been no report of exploiting organic amine salts for proton conduction in fuel cells.

Narayanan, Sekharipuram; Yen, Shiao-Pin S.

2005-01-01

231

PVDF/PVIm polymer blend films for fuel cell membranes  

NASA Astrophysics Data System (ADS)

We report the preparation and characterization of binary blend films of poly(vinylidene fluoride) (PVDF) and poly(1-ethyl-3-vinylimidazolium trifluoromethylsulfonimide) (PVIm+TFSI-). The potential utility of such materials in proton exchange membrane fuel cells is of particular interest. Thin PVDF/ PVIm+TFSI- films were fabricated from solutions of dimethly formamide by doctor blading. The nature of the PVDF crystalline polymorph and degree of crystallinity was evaluated as a function of the volume fraction of imidazolium polymer and thermal treatment. The morphology, thermal and mechanical characteristics of the blend films was studied by wide angle X-ray diffraction, thermogravimetry, calorimetry, and Fourier transform infrared spectroscopy. In these materials, conditions such as choice of solvent, drying conditions, and thermal treatment affect the crystal phase, crystallite size, and degree of crystallinity of PVDF as well as the distribution of PVIm+TFSI-. The beta phase of PVDF crystals dominates in as-cast films, while the alpha phase is observed after cooling from the melt. PVDF imparts mechanical strength and chemical stability to the composite films, and because of its high crystal melting point (Tm > 160 C), serves to improve the high temperature stability of resulting films.

Huang, Wenwen; Zhao, Meng; Yang, Fan; Farovitch, Lorne; Haghighi, Parisa; Macisco, Leonard; Swob, Tyler; Smith, Thomas; Cebe, Peggy

2012-02-01

232

Controlled bacterial lysis for electron tomography of native cell membranes.  

PubMed

Cryo-electron tomography (cryoET) has become a powerful tool for direct visualization of 3D structures of native biological specimens at molecular resolution, but its application is limited to thin specimens (<300 nm). Recently, vitreous sectioning and cryoFIB milling technologies were developed to physically reduce the specimen thickness; however, cryoET analysis of membrane protein complexes within native cell membranes remains a great challenge. Here, we use phage ?X174 lysis gene E to rapidly produce native, intact, bacterial cell membranes for high resolution cryoET. We characterized E gene-induced cell lysis using FIB/SEM and cryoEM and showed that the bacteria cytoplasm was largely depleted through spot lesion, producing ghosts with the cell membranes intact. We further demonstrated the utility of E-gene-induced lysis for cryoET using the bacterial chemotaxis receptor signaling complex array. The described method should have a broad application for structural and functional studies of native, intact cell membranes and membrane protein complexes. PMID:25456413

Fu, Xiaofeng; Himes, Benjamin A; Ke, Danxia; Rice, William J; Ning, Jiying; Zhang, Peijun

2014-12-01

233

Membrane Targeting of P-type ATPases in Plant Cells  

SciTech Connect

How membrane proteins are targeted to specific subcellular locations is a very complex and poorly understood area of research. Our long-term goal is to use P-type ATPases (ion pumps), in a model plant system Arabidopsis, as a paradigm to understand how members of a family of closely related membrane proteins can be targeted to different subcellular locations. The research is divided into two specific aims. The first aim is focused on determining the targeting destination of all 10 ACA-type calcium pumps (Arabidopsis Calcium ATPase) in Arabidopsis. ACAs represent a plant specific-subfamily of plasma membrane-type calcium pumps. In contrast to animals, the plant homologs have been found in multiple membrane systems, including the ER (ACA2), tonoplast (ACA4) and plasma membrane (ACA8). Their high degree of similarity provides a unique opportunity to use a comparative approach to delineate the membrane specific targeting information for each pump. One hypothesis to be tested is that an endomembrane located ACA can be re-directed to the plasma membrane by including targeting information from a plasma membrane isoform, ACA8. Our approach is to engineer domain swaps between pumps and monitor the targeting of chimeric proteins in plant cells using a Green Fluorescence Protein (GFP) as a tag. The second aim is to test the hypothesis that heterologous transporters can be engineered into plants and targeted to the plasma membrane by fusing them to a plasma membrane proton pump. As a test case we are evaluating the targeting properties of fusions made between a yeast sodium/proton exchanger (Sod2) and a proton pump (AHA2). This fusion may potentially lead to a new strategy for engineering salt resistant plants. Together these aims are designed to provide fundamental insights into the biogenesis and function of plant cell membrane systems.

Jeffrey F. Harper, Ph.D.

2004-06-30

234

MG53 nucleates assembly of cell membrane repair machinery  

PubMed Central

Dynamic membrane repair and remodelling is an elemental process that maintains cell integrity and mediates efficient cellular function. Here we report that MG53, a muscle-specific tripartite motif family protein (TRIM72), is a component of the sarcolemmal membrane-repair machinery. MG53 interacts with phosphatidylserine to associate with intracellular vesicles that traffic to and fuse with sarcolemmal membranes. Mice null for MG53 show progressive myopathy and reduced exercise capability, associated with defective membrane-repair capacity. Injury of the sarcolemmal membrane leads to entry of the extracellular oxidative environment and MG53 oligomerization, resulting in recruitment of MG53-containing vesicles to the injury site. After vesicle translocation, entry of extracellular Ca2+ facilitates vesicle fusion to reseal the membrane. Our data indicate that intracellular vesicle translocation and Ca2+-dependent membrane fusion are distinct steps involved in the repair of membrane damage and that MG53 may initiate the assembly of the membrane repair machinery in an oxidation-dependent manner. PMID:19043407

Cai, Chuanxi; Masumiya, Haruko; Weisleder, Noah; Matsuda, Noriyuki; Nishi, Miyuki; Hwang, Moonsun; Ko, Jae-Kyun; Lin, Peihui; Thornton, Angela; Zhao, Xiaoli; Pan, Zui; Komazaki, Shinji; Brotto, Marco; Takeshima, Hiroshi; Ma, Jianjie

2010-01-01

235

A new class of partially fluorinated fuel cell membranes  

SciTech Connect

A series of differently crosslinked FEP-g-polystyrene proton exchange membranes has been synthesized by the pre-irradiation grafting method. Divinylbenzene (DVB) and/or triallyl cyanurate (TAC) were used as crosslinkers in the membranes. It was found, that the physical properties of the membranes, such as water-uptake and specific resistance are strongly influenced by the nature of the crosslinker. Generally it can be stated, that DVB decreases water-uptake and increases specific resistance, on the other hand TAC increases swelling and decreases specific resistance to values as low as 5.0 {Omega}cm at 60 C. The membranes were tested in H{sub 2}/O{sub 2} fuel cells for stability and performance. It was found, that thick (170 {mu}m) DBV crosslinked membranes showed stable operation for 1,400 hours at temperatures up to 80 C. The highest power density in the fuel cell was found for the DVB and TAC double crosslinked membrane, it exceeded the value of a cell with a Nafion{reg_sign} 117 membrane by more than 60%.

Buechi, F.N.; Gupta, B.; Halim, J.; Haas, O.; Scherer, G.G. [Paul Scherrer Inst., Villigen-PSI (Switzerland)

1994-12-31

236

Electroosmotic flow through polymer electrolyte membranes in PEM fuel cells  

NASA Astrophysics Data System (ADS)

Water management is critically important for polymer electrolyte membrane fuel cells (PEMFC), and is complicated by the electroosmotic flow of water from anode to cathode through the polymer electrolyte membrane. In this study, electroosmotic flow in polymer electrolyte membranes is modeled incorporating the electrokinetic effect, and key parameters affecting the PEM fuel cell performance are identified. The governing Poisson-Boltzmann and the Navier-Stokes equations were solved numerically for a single membrane pore to determine the electroosmotic flow through the membrane over a wide range of geometrical and operating conditions. It was found that the electroosmotic drag coefficient, K, increases with the pore diameter. The membrane thickness has a significant effect on the electroosmotic flow. At constant cell voltage, the electroosmotic flow through thicker membranes (e.g. Nafion 117) is reduced because of the reduced electric field strength. The pressure difference required to stop electroosmotic flow is very large due to the extremely small pore diameters. In the presence of sulphuric acid, numerical results have revealed that the electroosmotic flow increases with the acid concentration.

Karimi, G.; Li, X.

237

A review of polymer electrolyte membranes for direct methanol fuel cells  

Microsoft Academic Search

This review describes the polymer electrolyte membranes (PEM) that are both under development and commercialized for direct methanol fuel cells (DMFC). Unlike the membranes for hydrogen fuelled PEM fuel cells, among which perfluorosulfonic acid based membranes show complete domination, the membranes for DMFC have numerous variations, each has its advantages and disadvantages. No single membrane is emerging as absolutely superior

Vladimir Neburchilov; Jonathan Martin; Haijiang Wang; Jiujun Zhang

2007-01-01

238

The enriched fraction of Elephantopus scaber Triggers apoptosis and inhibits multi-drug resistance transporters in human epithelial cancer cells  

PubMed Central

Background: Medicinal plants have played an important role in the development of clinically useful anticancer agents. Elephantopus scaber (Asteraceae) (ES) is widely used in Indian traditional system of medicine for the treatment of various ailments including cancer. Objective: To investigate anticancer effects of ES in human epithelial cancer cells. Materials and Methods: Cytotoxicity of ethanolic extract of ES (ES-ET) and its fractions, such as ES Petroleum ether fraction (ES-PET), ES Dichloromethane fraction (ES DCM), n Butyl alcohol fraction (ES-BT), and ES-Rest (ES-R) were assessed in human epithelial cancer cell lines using sulforhodamine B (SRB) assay. Acridine orange/ethidium bromide assay and Hoechst 33342 assays were used to gauge induction of apoptosis. Cell cycle analysis and micronuclei assay were used to assess cell cycle specific pharmacological effects and drug induced genotoxicty. Further, the ability of ES to inhibit multi drug resistant (MDR) transporters (ABC-B1 and ABC-G2) was determined by Rhodamine (Rho) and Mitoxantrone (MXR) efflux assays. Results: The enriched fraction of ES (ES DCM) possessed dose-dependent potent cytotoxicity in human epithelial cancer cells. Further, treatment of cancer cells (HeLa, A549, MCF-7, and Caco-2) with ES DCM showed hall mark properties of apoptosis (membrane blebbing, nuclear condensation etc.). Similarly, ES DCM caused enhanced sub G0 content and micronuclei formation indicating the induction of apoptosis and drug induced genotoxicity in cancer cells, respectively. Interestingly, ES DCM inhibited MDR transporters (ABC B1 and ABC G2) in cancer cells. Conclusion: The enriched fraction of ES imparted cytotoxic effects, triggered apoptosis, induced genotoxicity, and inhibited MDR transporters in human epithelial cancer cells. Thus, ES appears to be potential anticancer agent.

Beeran, Asmy Appadath; Maliyakkal, Naseer; Rao, Chamallamudi Mallikarjuna; Udupa, Nayanabhirama

2015-01-01

239

Enantiomeric fraction determination of 2-arylpropionic acids in a package plant membrane bioreactor.  

PubMed

Enantiomeric compositions of three 2-arylpropionic acid (2-APA) drugs, ibuprofen, naproxen, and ketoprofen, were monitored in a membrane bioreactor (MBR) treating municipal effluent in a small rural town in Australia. Specific enantiomers were determined as amide diastereomers using the chiral derivatizing reagent, (R)-1-phenylethylamine (PEA), followed by gas chromatography-tandem mass spectrometry (GC-MS/MS). The six individual enantiomers were quantified by isotope dilution and the enantiomeric fractions (EFs) were determined. Over four separate sampling events, ibuprofen EF ranged from 0.88 to 0.94 (median 0.93) in the influent and 0.38 to 0.40 (median 0.39) in the effluent. However, no significant change in ketoprofen EF was observed, with influent EFs of 0.56-0.60 (median 0.58) and effluent EFs 0.54-0.68 (median 0.56). This is the first report of enantiospecific analysis of ketoprofen in municipal wastewater and it is not yet clear why such different behavior was observed compared to ibuprofen. Naproxen EF was consistently measured at 0.99 in the influent and ranged from 0.86 to 0.94 (median 0.91) in the effluent. This study demonstrates that EF is a relatively stable parameter and does not fluctuate according to concentration or other short-term variables introduced by sampling limitations. The enantiospecific analysis of chiral chemicals presents a promising approach to elucidate a more thorough understanding of biological treatment processes and a potential tool for monitoring the performance of key biological pathways. PMID:23620266

Hashim, Nor H; Stuetz, Richard M; Khan, Stuart J

2013-05-01

240

A statistical mechanical model of cell membrane ion channels in electric fields: The mean-field approximation  

NASA Astrophysics Data System (ADS)

A statistical mechanical model of cell membrane ion channels is proposed which incorporates interactions between ion channels and external electric fields. The model provides a physical explanation of trans-membrane ion transport. Under a mean-field approximation, the maximum fractions of open potassium and sodium channels are obtained by solving a self-consistent nonlinear algebraic equation. Using known parameters for the squid giant axon, the model gives excellent agreement with experimental measurements for potassium and sodium trans-membrane conductance. The numerical results imply that the chemical potential of open channels and the interaction energy between channels are well above the thermal noise.

Yang, Y. S.; Thompson, C. J.; Anderson, V.; Wood, A. W.

241

Separation of membranes by flotation centrifugation for in vitro synthesis of plant cell wall polysaccharides  

Microsoft Academic Search

Summary Membranes from etiolated maize seedlings were isolated using sucrose gradients for in vitro studies of polysaccharide synthesis. Following downward centrifugation, flotation centrifugation improved the purity of membrane fractions, in particular the Golgi apparatus. Based on naphthylphthalamic acid binding to plasma membrane and inosine-5'-diphosphatase activity in Golgi apparatus, flotation centrifugation removed about 70% of the plasma membrane which cosedimented with

D. M. Gibeaut; N. C. Carpita

1990-01-01

242

Effects of Extracellular Calcium on Cell Membrane Resealing during Sonoporation  

NASA Astrophysics Data System (ADS)

Sonoporation has been exploited as a novel strategy for intracellular drug and gene delivery. In sonoporation, ultrasound application generates transient pores or openings in the cell membrane that allow entry of extracellular agents normally not permeable to the cell membrane. In order to improve the sonoporation outcome, we seek to obtain improved understanding of the sonoporation mechanism and investigate the factors affecting sonoporation process. We established a voltage clamp technique for real time measurement of sonoporation at single cell level using Xenopus oocytes as a model system. As both cell survival and intracellular delivery efficiency of drug or genes depend on the sonoporation dynamic process, and Calcium plays important roles in cellular processes, we focus on studying of the effect of extracellular Calcium concentration on the formation, extension, and resealing of membrane pores in sonoporation. We obtained experimental results demonstrating that the cell membrane reseals in the order of seconds in the presence of physiological level of extracellular [Ca]. We measured the resealing as function of extracellular [Ca] (0-1.8mM) and observed that the resealing rate decreases as extracellular [Ca] decreases from normal physiological level. No resealing was demonstrated when 1mM EGTA was added in the extracellular medium to chelate the [Ca] extracellularly. Our experimental findings suggest that extracellular Calcium plays an important role in controlling membrane resealing in sonoporation and thus the sonoporation outcome such as cell survival and delivery efficiency.

Zhou, Yun; Cui, Jianmin; Deng, Cheri X.

2006-05-01

243

Isolated primary squamous cell carcinoma of the tympanic membrane  

PubMed Central

INTRODUCTION Primary squamous cell carcinoma (SCC) of the tympanic membrane is exceptionally rare. We describe the history, investigation and management of this disease. PRESENTATION OF CASE A 68-year-old woman presented with a three month history of intermittent otorrhoea and external ear canal (EAC) pruritus. Otoscopy revealed a polypoidal granular nodule, confined to the posterior aspect of the tympanic membrane. Examination under anaesthesia (EUA) confirmed that the lesion was confined to the tympanic membrane, with a surrounding rim of normal drum. Biopsies were consistent with well differentiated SCC. DISCUSSION Following discussion at multi-disciplinary team meeting for treatment planning, the patient underwent lateral temporal bone resection with ipsilateral superficial parotidectomy and selective neck dissection. Post-operative histology confirmed an SCC confined to the tympanic membrane. CONCLUSION SCC of the tympanic membrane is an extremely rare condition. As with early temporal bone SCC, surgical resection with adjacent structure clearance remains the primary treatment modality. PMID:23123413

Wijaya, Clifton; Leonard, David S.; Kinsella, John B.; McShane, Donald P.

2012-01-01

244

Nonlinear electro-mechanobiological behavior of cell membrane during electroporation  

NASA Astrophysics Data System (ADS)

A nonlinear electroporation (EP) model is proposed to study the electro-mechanobiological behavior of cell membrane during EP, by taking the nonlinear large deformation of the membrane into account. The proposed model predicts the critical transmembrane potential and the activation energy for EP, the equilibrium pore size, and the resealing process of the pore. Single-cell EP experiments using a micro EP chip were conducted on chicken red blood cells at different temperatures to determine the activation energy and the critical transmembrane potential for EP. The experimental results are in good agreement with the theoretical predictions.

Deng, Peigang; Lee, Yi-Kuen; Lin, Ran; Zhang, Tong-Yi

2012-07-01

245

Fuel cell electrolyte membrane with basic polymer  

DOEpatents

The present invention is an electrolyte membrane comprising an acid and a basic polymer, where the acid is a low-volatile acid that is fluorinated and is either oligomeric or non-polymeric, and where the basic polymer is protonated by the acid and is stable to hydrolysis.

Larson, James M. (Saint Paul, MN); Pham, Phat T. (Little Canada, MN); Frey, Matthew H. (Cottage Grove, MN); Hamrock, Steven J. (Stillwater, MN); Haugen, Gregory M. (Edina, MN); Lamanna, William M. (Stillwater, MN)

2010-11-23

246

Fuel cell electrolyte membrane with basic polymer  

DOEpatents

The present invention is an electrolyte membrane comprising an acid and a basic polymer, where the acid is a low-volatile acid that is fluorinated and is either oligomeric or non-polymeric, and where the basic polymer is protonated by the acid and is stable to hydrolysis.

Larson, James M.; Pham, Phat T.; Frey, Matthew H.; Hamrock, Steven J.; Haugen, Gregory M.; Lamanna, William M.

2012-12-04

247

Molecular Cell Misfolded Membrane Proteins Are Specifically  

E-print Network

Domain of the Hrd1p Ubiquitin Ligase Brian K. Sato,1 Daniel Schulz,1 Phong H. Do,1 and Randolph Y in trans with the active C-terminal region (Gardner et al., 2000). The multispanning Hrd1p membrane domain

Hampton, Randy

248

A review of the performance and analysis of proton exchange membrane fuel cell membrane electrode assemblies  

NASA Astrophysics Data System (ADS)

This study describes a performance review of several membrane electrode assemblies (MEAs) for proton exchange membrane fuel cells (PEMFC). First, different methods for preparing catalyst-coated membranes (CCMs) and gas diffusion electrodes (GDEs) are presented to show that the power density of the CCMs method is approximately 18% better than that obtained by using GDEs. Second, different thickness membranes and a self-fabricated membrane are discussed. The self-fabricated membrane used a PTFE microporous membrane as a backing structure and was impregnated with Nafion for reinforcement. Third, we compared the performance differences of four different amounts of platinum loaded in Nafion-bonded CCMs to prove that more platinum loading can produce better performance linearly at a platinum loading from 0.1 to 0.4 mg cm-2. Fourth, a water storage zone was created on the surface of the GDL. The voltage-time curve shows that the voltage is maintained at 0.650 V ± 0.015 V over more than 300 h while supplying with dry hydrogen and oxygen. Fifth, a matched 250 ?m silicon gasket was used to test the performance of a standard MEA with different torques of 5-30 Kgf cm, and the performance differences are within 10%.

Liu, Chao-Yang; Sung, Chia-Chi

2012-12-01

249

Towards fuel cell membranes with improved lifetime: Aquivion® Perfluorosulfonic Acid membranes containing immobilized radical scavengers  

NASA Astrophysics Data System (ADS)

A facile synthesis, based on a wet impregnation technique and a thermal treatment, of a novel silica-supported cerium-oxide-based radical scavenger bearing sulfonic acid functionalities is presented. This material is loaded as a filler in ePTFE reinforced membranes (called R79-02S) prepared starting from Aquivion® Perfluoro-Sulfonic Acid (PFSA) dispersions. The aim is to mitigate the peroxy radicals attack to the polymeric membrane under fuel cell operating conditions. These membranes show much longer (7 times more) life-time in Accelerated Stress Tests (AST) and reduced fluoride release (about one half) in Fenton's tests than the radical scavenger-free membrane without any loss in electrochemical performance. Scavenger-free Aquivion® PFSA-based membrane durability is about 200 h in AST whereas the same membrane containing the newly developed radical scavenger exceeds 1400 h. These results confirm the stability of the modified membranes and the excellent activity of the composite scavenger in mitigating the polymer electrolyte degradation.

D'Urso, C.; Oldani, C.; Baglio, V.; Merlo, L.; Aricò, A. S.

2014-12-01

250

Membrane Transport and Ca 2+ Oscillations in Guard Cells  

Microsoft Academic Search

Since the 1980s, work on ion transport and the control of guard cell ion channels has provided a wealth of information that is still unparalleled in plant biology, driven primarily by electrophysiological studies and, more recently, by molecular genetics and cell biology. We know now sufficient detail of all of the major transport pathways at the plasma membrane to encapsulate

Michael R. Blatt; Carlos Garcia-Mata; Sergei Sokolovski

251

Stimulation of Erythrocyte Cell Membrane Scrambling by Methyldopa  

Microsoft Academic Search

Methyldopa is used for treatment of hypertension in pregnancy. Side effects of methyldopa include anemia, which could result from decreased formation or accelerated death of circulating erythrocytes. Several drugs cause anemia by triggering of suicidal erythrocyte death or eryptosis, which is characterized by cell shrinkage and cell membrane scrambling, the latter leading to phosphatidylserine exposure at the erythrocyte surface. Stimulators

Hasan Mahmud; Michael Föller; Florian Lang

2008-01-01

252

Investigation of oxygen gain in polymer electrolyte membrane fuel cells  

Microsoft Academic Search

The polymer electrolyte membrane fuel cell (PEMFC) faces an efficiency loss, so called “oxygen gain”, when the cathode gas is changed from oxygen to air due to the reduced oxygen partial pressure. To reduce the oxygen gain of a PEMFC, performance and oxygen gain of the single cells were evaluated as a function of carbon support, Pt content in the

M. Prasanna; H. Y. Ha; E. A. Cho; S.-A. Hong; I.-H. Oh

2004-01-01

253

Membrane-particle interactions in an asymmetric flow field flow fractionation channel studied with titanium dioxide nanoparticles.  

PubMed

Asymmetric flow field flow fractionation operated in a multidetector approach (A4F-MDA) is a powerful tool to perform size-classified nanoparticle analysis. Recently several publications mentioned insufficient recovery rates and even retention time shifts attributed to unspecific membrane-particle interactions. One hypothesis to explain this phenomenon is based on the surface charge (zeta-potential) of the membrane material and the particle. In this study, we investigated in how far the ?-potential of A4F membrane and particles would determine the outcome of A4F in terms of feasibility, separation efficiency, retention time, and recovery rate, or whether other factors such as membrane morphology and particle size were equally important. We systematically studied the influence of the ?-potential on the interactions between the most commonly used A4F membrane materials and two representative types of titanium dioxide nanoparticles (TiO2 NP). Furthermore the effect of different carrier media and additional surfactants on the surface charge of membranes and particles was investigated and the influence of the particle size and the particle concentration on the recovery rate was evaluated. We found that the eligibility of an A4F method can be predicted based on the ?-potential of the NPs and the A4F membrane. Furthermore knowing the ?-potential allows to tuning the separation efficiency of an A4F method. On the other hand we observed significant shifts in retention time for different membrane materials that impede the determination of particle size based on the classical A4F theory. These shifts cannot be attributed to the ?-potential. Also the ?-potential does not account for varying recovery rates of different particle types, instead the particle size seems to be the limiting factor. Therefore, the proper characterization of a polydisperse sample remains a challenge. PMID:24556173

Bendixen, Nina; Losert, Sabrina; Adlhart, Christian; Lattuada, Marco; Ulrich, Andrea

2014-03-21

254

Anion selective membrane. [ion exchange resins and ion exchange membrane electrolytes for electrolytic cells  

NASA Technical Reports Server (NTRS)

Experimental anion permselective membranes were prepared and tested for their suitability as cell separators in a chemical redox power storage system being developed at NASA-Lewis Research Center. The goals of long-term (1000 hr) oxidative and thermal stability at 80 C in FeCl3 and CrCl3 electrolytes were met by most of the weak base and strong base amino exchange groups considered in the program. Good stability is exhibited by several of the membrane substrate resins. These are 'styrene' divinylbenzene copolymer and PVC film. At least four membrane systems produce strong flexible films with electrochemical properties (resistivity, cation transfer) superior to those of the 103QZL, the most promising commercial membrane. The physical and chemical properties of the resins are listed.

Alexander, S. S.; Geoffroy, R. R.; Hodgdon, R. B.

1975-01-01

255

Composite polymer membranes for proton exchange membrane fuel cells operating at elevated temperatures and reduced humidities  

NASA Astrophysics Data System (ADS)

Proton Exchange Membrane Fuel Cells (PEMFCs) are the leading candidate in the fuel cell technology due to the high power density, solid electrolyte, and low operational temperature. However, PEMFCs operating in the normal temperature range (60-80°C) face problems including poor carbon monoxide tolerance and heat rejection. The poisoning effect can be significantly relieved by operating the fuel cell at elevated temperature, which also improves the heat rejection and electrochemical kinetics. Low relative humidity (RH) operation is also desirable to simplify the reactant humidification system. However, at elevated temperatures, reduced RH PEMFC performance is seriously impaired due to irreversible water loss from presently employed state-of-the-art polymer membrane, Nafion. This thesis focuses on developing polymer electrolyte membranes with high water retention ability for operation in elevated temperature (110-150°C), reduced humidity (˜50%RH) PEMFCs. One approach is to alter Nafion by adding inorganic particles such as TiO2, SiO2, Zr(HPO 4)2, etc. While the presence of these materials in Nafion has proven beneficial, a reduction or no improvement in the PEMFC performance of Nafion/TiO2 and Nafion/Zr(HPO4)2 membranes is observed with reduced particle sizes or increased particle loadings in Nafion. It is concluded that the PEMFC performance enhancement associated with addition of these inorganic particles was not due to the particle hydrophilicity. Rather, the particle, partially located in the hydrophobic region of the membrane, benefits the cell performance by altering the membrane structure. Water transport properties of some Nafion composite membranes were investigated by NMR methods including pulsed field gradient spin echo diffusion, spin-lattice relaxation, and spectral measurements. Compared to unmodified Nafion, composite membranes materials exhibit longer longitudinal relaxation time constant T1. In addition to the Nafion material, sulfonated styrene-ethylene/butylene-styrene triblock copolymer (sSEBS) was investigated as an alternate membrane candidate. sSEBS was modified through introduction of polymer crosslinks using benzephenone as a photoinitiator and addition of a titania co-phase. A photocrosslinked membrane initially containing 15% benzophenone and 3% titania laminated with a 10 mum Nafion layer was found to produce the best PEMFC performance (120°C, 50%RH).

Zhang, Tao

256

Computational fluid dynamics modeling of proton exchange membrane fuel cells  

Microsoft Academic Search

A transient, multi-dimensional model has been developed to simulate proton exchange membrane (PEM) fuel cells. The model accounts simultaneously for electrochemical kinetics, current distribution, hydrodynamics and multi-component transport. A single set of conservation equations valid for flow channels, gas-diffusion electrodes, catalyst layers and the membrane region are developed and numerically solved using a finite-volume-based computational fluid dynamics (CFD) technique. The

SUKKEE UM; C.-Y. Wang; KEN S. CHEN

2000-01-01

257

Nuclear magnetic resonance of polymer electrolyte membrane fuel cells.  

PubMed

In this review, the contribution of NMR spectroscopy to the development of the proton exchange membrane fuel cell (PEMFC) is discussed, with particular emphasis on its use in the characterization of structure and transport in proton exchange membranes (PEMs). Owing to copious amount of information available, results of the past decade will be the main focal point. In addition, its use as a screening tool for the PEM materials will be discussed. PMID:20648522

Suarez, Sophia; Greenbaum, Steve

2010-12-01

258

Differential proliferative responses of cultured Schwann cells to axolemma- and myelin-enriched fractions. I. Biochemical studies  

PubMed Central

Cultured rat Schwann cells were treated for 72 h with axolemma- and myelin-enriched fractions prepared from rat brainstem. [3H]Thymidine was added to the cultures 48 h before the termination of the experiment. Although, both fractions produced a dose-dependent uptake of label into Schwann cells, the shape of the dose response curves and rates at which [3H]thymidine was incorporated were different. The axolemma-enriched fraction produced a sigmoid dose response curve with a Hill coefficient of 2.05. The dose response curve for myelin rose sharply and saturated at a level that was approximately 50% of the maximal response observed with axolemma. Schwann cells that had been treated with axolemma exhibited little change in the rate of [3H]thymidine incorporation from 36-72 h after the addition of the membranes. In contrast, Schwann cells accumulated label three times faster during the 48-72-h period following the addition of myelin to the cultures when compared with the rate during the preceding 12-h interval. Furthermore, the mitogenic activity of the myelin-enriched fraction was decreased by the addition of ammonium chloride, a lysosomal inhibitor, whereas the activity of the axolemmal fraction was not impaired. PMID:6501427

1984-01-01

259

Theory of proton exchange membranes fuel cells and the testing of performance characteristics of polymer electrolyte membranes  

E-print Network

Proton exchange membrane (PEM) fuel cells hold great promise as source of power. A hydrogen and oxygen PEM fuel is a simple fuel cell that can be theoretically characterized. The performance of a PEM fuel cell can be ...

Cruz-Gonzalez, Tizoc, 1982-

2004-01-01

260

Ultrafiltration by a compacted clay membrane. I - Oxygen and hydrogen isotopic fractionation. II - Sodium ion exclusion at various ionic strengths.  

NASA Technical Reports Server (NTRS)

Laboratory experiments were carried out to determine the magnitude of the isotopic fractionation of distilled water and of 0.01N NaCl forced to flow at ambient temperature under a hydraulic pressure drop of 100 bars across a montmorillonite disk compacted to a porosity of 35% by a pressure of 330 bars. The ultrafiltrates in both experiments were depleted in D by 2.5% and in O-18 by 0.8% relative to the residual solution. No additional isotopic fractionation due to a salt-filtering mechanism was observed at NaCl concentrations up to 0.01N. Adsorption is most likely the principal mechanism which produces isotopic fractionation, but molecular diffusion may play a minor role. The results suggest that oxygen and hydrogen isotopic fractionation of ground water during passage through compacted clayey sediments should be a common occurrence, in accord with published interpretations of isotopic data from the Illinois and Alberta basins. It is shown how it is possible to proceed from the ion exchange capacity of clay minerals and, by means of the Donnan membrane equilibrium concept and the Teorell-Meyer-Siever theory, develop a theory to explain why and to what extent ultrafiltration occurs when solutions of known concentration are forced to flow through a clay membrane.

Coplen, T. B.; Hanshaw, B. B.

1973-01-01

261

Understanding the transport processes in polymer electrolyte membrane fuel cells  

NASA Astrophysics Data System (ADS)

Polymer electrolyte membrane (PEM) fuel cells are energy conversion devices suitable for automotive, stationary and portable applications. An engineering challenge that is hindering the widespread use of PEM fuel cells is the water management issue, where either a lack of water (resulting in membrane dehydration) or an excess accumulation of liquid water (resulting in fuel cell flooding) critically reduces the PEM fuel cell performance. The water management issue is addressed by this dissertation through the study of three transport processes occurring in PEM fuel cells. Water transport within the membrane is a combination of water diffusion down the water activity gradient and the dragging of water molecules by protons when there is a proton current, in a phenomenon termed electro-osmotic drag, EOD. The impact of water diffusion and EOD on the water flux across the membrane is reduced due to water transport resistance at the vapor/membrane interface. The redistribution of water inside the membrane by EOD causes an overall increase in the membrane resistance that regulates the current and thus EOD, thereby preventing membrane dehydration. Liquid water transport in the PEM fuel cell flow channel was examined at different gas flow regimes. At low gas Reynolds numbers, drops transitioned into slugs that are subsequently pushed out of the flow channel by the gas flow. The slug volume is dependent on the geometric shape, the surface wettability and the orientation (with respect to gravity) of the flow channel. The differential pressure required for slug motion primarily depends on the interfacial forces acting along the contact lines at the front and the back of the slug. At high gas Reynolds number, water is removed as a film or as drops depending on the flow channel surface wettability. The shape of growing drops at low and high Reynolds number can be described by a simple interfacial energy minimization model. Under flooding conditions, the fuel cell local current can be significantly reduced due to diffusional limitation of the transport of gaseous reactants through inerts such as water vapor and nitrogen gas. A non-uniform current distribution across the membrane electrode assembly can cause pinhole formation and ultimately, fuel cell failure.

Cheah, May Jean

262

Mast Cell Synapses and Exosomes: Membrane Contacts for Information Exchange  

PubMed Central

In addition to their central role in allergy, mast cells are involved in a wide variety of cellular interactions during homeostasis and disease. In this review, we discuss the ability of mast cells to extend their mechanisms for intercellular communication beyond the release of soluble mediators. These include formation of mast cell synapses on antigen presenting surfaces, as well as cell–cell contacts with dendritic cells and T cells. Release of membrane bound exosomes also provide for the transfer of antigen, mast cell proteins, and RNA to other leukocytes. With the recognition of the extended role mast cells have during immune modulation, further investigation of the processes in which mast cells are involved is necessary. This reopens mast cell research to exciting possibilities, demonstrating it to be an immunological frontier. PMID:22566928

Carroll-Portillo, Amanda; Surviladze, Zurab; Cambi, Alessandra; Lidke, Diane S.; Wilson, Bridget S.

2012-01-01

263

Tension of red blood cell membrane in simple shear flow.  

PubMed

When a red blood cell (RBC) is subjected to an external flow, it is deformed by the hydrodynamic forces acting on its membrane. The resulting elastic tensions in the membrane play a key role in mechanotransduction and govern its rupture in the case of hemolysis. In this study, we analyze the motion and deformation of an RBC in a simple shear flow and the resulting elastic tensions on the membrane. The large deformation of the red blood cell is modelled by coupling a finite element method to solve the membrane mechanics and a boundary element method to solve the flows of the internal and external liquids. Depending on the capillary number Ca, ratio of the viscous to elastic forces, we observe three kinds of RBC motion: tumbling at low Ca, swinging at larger Ca, and breathing at the transitions. In the swinging regime, the region of the high principal tensions periodically oscillates, whereas that of the high isotropic tensions is almost unchanged. Due to the strain-hardening property of the membrane, the deformation is limited but the membrane tension increases monotonically with the capillary number. We have quantitatively compared our numerical results with former experimental results. It indicates that a membrane isotropic tension O(10{-6} N/m) is high enough for molecular release from RBCs and that the typical maximum membrane principal tension for haemolysis would be O(10{-4} N/m). These findings are useful to clarify not only the membrane rupture but also the mechanotransduction of RBCs. PMID:23214889

Omori, T; Ishikawa, T; Barthès-Biesel, D; Salsac, A-V; Imai, Y; Yamaguchi, T

2012-11-01

264

Plasma membrane reorganization induced by tumor promoters in an epithelial cell line  

SciTech Connect

The effects of phorbol ester tumor promoters on the lateral diffusion in plasma membrane lipid environments were examined by the technique of fluorescence recovery after photobleaching. To this end, the probe collarein, a fluorescent lipid analog that has the property of exclusive localization in the plasma membrane, was synthesized. Measured decreases in three parameters [percentage of fluorescence bleached (30%), percentage of recovery (52%), and half-time for recovery (52%)] connoted the appearance of an immobile fraction upon exposure to tumor promoters. These data are consistent with lipid reorganization in response to a reorganization of the intra- and perimembranous macromolecular scaffolding upon the interaction of cells with tumor promoters. The idea of induced reorganization is supported by experiments in which cell shape change, brought about by either exposure to cytochalasin B or growth on matrices of collagen, fibronectin, or laminin, resulted in values in the fluorescence recovery after photobleaching technique similar to those with active phorbol esters.

PACKARD, BEVERLY S.; SAXTON, MICHAEL J.; BISSELL, MINA J.; KLEIN, MELVIN P.

1984-01-01

265

Basement membranes and artificial substrates in cell transplantation  

Microsoft Academic Search

This article will concentrate largely on the current developments in the area of cell transplantations presented at the 1st Workshop for Cell Transplantation in Age-related Macular Degeneration. In particular, this brief review will address our current understanding of the role of cell–matrix interactions by covering the pathobiology of normal ageing Bruch’s membrane; some of the problems faced at the time

Carl Sheridan; Rachel Williams; Ian Grierson

2004-01-01

266

Of microbes and membranes: pathogenic subversion of host cell processes.  

PubMed

A recent gathering of researchers at the EMBO conference "At the joint edge of Cellular Microbiology and Cell Biology" was aimed at melding ideas from both scientific fields to advance our understanding of infectious diseases at the cellular level. Work presented at this meeting highlighted how pathogens exploit host cell membrane processes to their advantage and also revealed fundamental signaling and trafficking mechanisms of eukaryotic cells. PMID:19064252

Celli, Jean; Knodler, Leigh A

2008-12-11

267

Polymer-zeolite nanocomposite membranes for proton exchange membrane fuel cells  

NASA Astrophysics Data System (ADS)

Proton exchange membrane fuel cells (PEMFCs) have recently received a great deal of attention for their potential as compact, high efficiency power sources for portable, distributed generation, and transportation applications. Unfortunately, current proton exchange membrane (PEM) technology hinders fuel cell performance by limiting fuel cell operation temperature and methanol feed concentration in direct methanol fuel cells (DMFCs). Nafion-zeolite nanocomposite membranes that take advantage of the hydrophilicity, selectivity, and proton conductivity of zeolite nanocrystals have been developed to address these problems. All known zeolite topologies were evaluated as potential additives to Nafion proton exchange membranes. Zeolites Y and beta were determined to have great potential as additives due to their low framework density, three dimensional pore structure, and high hydrophilicity. Zeolite Y nanocrystal syntheses were optimized to enhance yield and produce smaller crystal size. Significant improvement of the acid stability of the zeolite Y nanocrystals was not achieved with both ammonium hexafluorosilicate treatments and direct high silica nanocrystal synthesis. However, control of zeolite Y nanocrystal framework Si/Al ratio was demonstrated in the range of SiO2/Al2O3 = 4.38 to 5.84 by manipulating the tetramethylammonium structure directing agent hydroxide content. Zeolite beta nanocrystals were investigated due to their inherent high silica content and high acid stability. Zeolite beta nanocrystals were hydrothermally synthesized with and without phenethyl (called PE-BEA and BEA respectively) organic functional groups. Sulfonic acid functionalized zeolite beta (SAPE-BEA) was generated by treating the PE-BEA nanocrystals with a concentrated sulfuric acid post synthesis treatment. SAPE-BEA samples demonstrated proton conductivities up to 0.01 S/cm at room temperature under water-saturated conditions using a newly developed characterization technique. With optimization, acid functionalized zeolite materials could possibly perform as competent stand-alone proton conducting materials with the proper engineering. BEA and SAPE-BEA zeolite nanocrystals mixed with suspensions of Nafion were cast into nanocomposite membranes. DMFC membrane electrode assemblies (MEAs) prepared with a 2.5wt% SAPE-BEA nanocomposite membrane delivered twice the peak power of a MEA with a commercial Nafion 117 membrane. Membrane performance improvements of this magnitude could ultimately lead to DMFC cost and size reductions that make the technology commercially viable for a variety of applications.

Holmberg, Brett Anderson

2005-07-01

268

Effects of chronic kidney disease on blood cells membrane properties.  

PubMed

Chronic kidney disease (CKD) is progressive loss of renal function associated among others with increased intracellular calcium concentration. The purpose of this study was to identify the effects of CKD on cell membrane properties such as human red blood cell Ca(2+) ATPase activity, lymphocyte plasma membrane P2X(7) receptor expression and function. This could help us in elucidating the origin of increased calcium concentration in blood cells. We found out Ca(2+) ATPase activity is decreased in early stage CKD patients resulting in altered calcium removal from cytoplasm. By means of flow cytometry we assessed that P2X(7) receptor expression on lymphocyte membrane is 1.5 fold increased for CKD patients. Moreover, we detected an increased uptake of ethidium bromide through this receptor in CKD at basal conditions. It means CKD lymphocyte membranes contain more receptors which are more permeable thus allowing increased calcium influx from extracellular milieu. Finally, we can state alterations in blood cell membranes are closely linked to CKD and may be responsible for intracellular calcium accumulation. PMID:22425286

Kaderjakova, Z; Lajdova, I; Horvathova, M; Morvova, M; Sikurova, L

2012-10-01

269

Nuclear Membrane Dynamics and Reassembly in Living Cells: Targeting of an Inner Nuclear Membrane Protein in Interphase and Mitosis  

Microsoft Academic Search

The mechanisms of localization and reten- tion of membrane proteins in the inner nuclear mem- brane and the fate of this membrane system during mi- tosis were studied in living cells using the inner nuclear membrane protein, lamin B receptor, fused to green fluorescent protein (LBR-GFP). Photobleaching tech- niques revealed the majority of LBR-GFP to be com- pletely immobilized in

Jan Ellenberg; Eric D. Siggia; Jorge E. Moreira; Carolyn L. Smith; John F. Presley; Howard J. Worman; Jennifer Lippincott-Schwartz

1997-01-01

270

The role of cell membranes in the regulation of lignification in pine cells  

NASA Technical Reports Server (NTRS)

The identity of pine cell membranes bearing PAL enzyme activity, the isolation of a plasma membrane preparation from pine cells for testing as a regulatory barrier in lignification, and the measurement of the geopotential effect in pine stems are presented. A model to describe and predict the interaction of gravity and lignification of higher plants was developed.

Hendrix, D. L.

1978-01-01

271

Immunologically Induced Alterations of Airway Smooth Muscle Cell Membrane  

NASA Astrophysics Data System (ADS)

Active and passive sensitization, both in vivo and in vitro, caused significant hyperpolarization of airway smooth muscle cell preparations isolated from guinea pigs. An increase in the contribution of the electrogenic Na+ pump to the resting membrane potential was responsible for this change. Hyperpolarization, as induced by passive sensitization, was not prevented by agents that inhibit specific mediators of anaphylaxis but was abolished when serum from sensitized animals was heated. The heat-sensitive serum factor, presumably reaginic antibodies, appears to be responsible for the membrane hyperpolarization of airway smooth muscle cells after sensitization.

Souhrada, M.; Souhrada, J. F.

1984-08-01

272

Lactic acid fermentation in cell-recycle membrane bioreactor.  

PubMed

Traditional lactic acid fermentation suffers from low productivity and low product purity. Cell-recycle fermentation has become one of the methods to obtain high cell density, which results in higher productivity. Lactic acid fermentation was investigated in a cell-recycle membrane bioreactor at higher substrate concentrations of 100 and 120 g/dm3. A maximum cell density of 145 g/dm3 and a maximum productivity of 34 g/(dm3.h) were achieved in cell-recycle fermentation. In spite of complete consumption of substrate, there was a continuous increase in cell density in cell-recycle fermentation. Control of cell density in cell-recycle fermentation was attempted by cell bleeding and reduction in yeast extract concentration. PMID:16484726

Choudhury, B; Swaminathan, T

2006-02-01

273

Membrane with internal passages to permit fluid flow and an electrochemical cell containing the same  

NASA Technical Reports Server (NTRS)

The invention provides an improved proton exchange membrane for use in electrochemical cells having internal passages parallel to the membrane surface, an apparatus and process for making the membrane, membrane and electrode assemblies fabricated using the membrane, and the application of the membrane and electrode assemblies to a variety of devices, both electrochemical and otherwise. The passages in the membrane extend from one edge of the membrane to another and allow fluid flow through the membrane and give access directly to the membrane for purposes of hydration.

Cisar, Alan J. (Inventor); Gonzalez-Martin, Anuncia (Inventor); Hitchens, G. Duncan (Inventor); Murphy, Oliver J. (Inventor)

1997-01-01

274

PROTEIN STRUCTURE: Pumping Iron Through Cell Membranes  

NSDL National Science Digital Library

Access to the article is free, however registration and sign-in are required. Despite their importance in various cellular functions, the three-dimensional structure at atomic resolution has been determined for only a few membrane proteins. In his Perspective, Braun discusses results reported in the same issue by Ferguson et al. in which the crystal structure of FhuA, an iron transporter protein, has been determined at high resolution. This and related proteins may be the general model for a large class of iron-transporting molecules.

Volkmar Braun (Universität Tüebingen; Department of Mikrobiologie/Membranphysiologie)

1998-12-18

275

Membrane-assisted isoelectric focusing device as a micropreparative fractionator for two-dimensional shotgun proteomics.  

PubMed

Recently, we introduced an online multijunction capillary isoelectric focusing (OMJ-CIEF) fractionator to fractionate proteins and peptides in electrospray-friendly solution. In this follow-up study, the original configuration of the fractionator was modified to improve the resolving power and reproducibility of separation. The major improvements include stabilization of the electrical current through the device using a voltage divider and stepwise elution of peptide zones in conjunction with the repeated refocusing of remaining peptides. Also, a novel algorithm was developed to calculate more accurately the pI values of peptides identified from experimental data. The standard deviation of calculated pI values for unmodified peptides from the theoretically predicted pI values was on average 0.21 pH units, which is more accurate than in standard-resolution gel-based methods. In order to characterize the analytical performance of the improved device, it was applied for the pI fractionation of yeast proteome digest into 18 fractions, with the collected fractions being analyzed by reverse-phase liquid chromatography coupled with tandem mass spectrometry. Approximately 37% of 20047 identified peptides were detected in only one fraction and 27% - in two fractions. On average, every peptide was found in 2.4 fractions. These results strongly indicate the suitability of the improved device as a first dimension of separation in multidimensional shotgun proteomics analysis, with a potential for fully automated workflow. PMID:24824042

Pirmoradian, Mohammad; Zhang, Bo; Chingin, Konstantin; Astorga-Wells, Juan; Zubarev, Roman A

2014-06-17

276

Excess membrane synthesis drives a primitive mode of cell proliferation.  

PubMed

The peptidoglycan cell wall is a hallmark of the bacterial subkingdom. Surprisingly, many modern bacteria retain the ability to switch into a wall-free state called the L-form. L-form proliferation is remarkable in being independent of the normally essential FtsZ-based division machinery and in occurring by membrane blebbing and tubulation. We show that mutations leading to excess membrane synthesis are sufficient to drive L-form division in Bacillus subtilis. Artificially increasing the cell surface area to volume ratio in wild-type protoplasts generates similar shape changes and cell division. Our findings show that simple biophysical processes could have supported efficient cell proliferation during the evolution of early cells and provide an extant biological model for studying this problem. PMID:23452849

Mercier, Romain; Kawai, Yoshikazu; Errington, Jeff

2013-02-28

277

The structure of the membrane systems in a novel muscle cell modified for heat production  

PubMed Central

A thermogenic organ, modified from an eye muscle, warms the brain and eyes of several oceanic fish. The extraocular muscles associated with thermogenesis are composed of modified muscle cells that are structurally distinct from all other types of muscle previously described. In "heater" cells, contractile filaments are virtually absent and the cell volume is packed with mitochondria and smooth membranes. Freeze-fracture studies and negative staining of microsomal fractions treated with vanadate indicate that most of the membrane system of heater cells has a high Ca2+-ATPase density and is equivalent to skeletal muscle sarcoplasmic reticulum (SR). High voltage electron micrographs of heater cells infiltrated with the Golgi stain demonstrate that the cells also have an extensive transverse tubule system with a complicated three-dimensional structure. Junctional regions between transverse tubules and SR occur in the heater cell and contain feet protein. Activation of thermogenesis in heater cells may occur through the same protein components involved in excitation- contraction coupling and appears to be associated with the ATP- dependent cycling of calcium at the SR. PMID:3417775

1988-01-01

278

Time courses of mammalian cell electropermeabilization observed by millisecond imaging of membrane property changes during the pulse.  

PubMed Central

Time courses of electropermeabilization were analyzed during the electric field application using a rapid fluorescent imaging system. Exchanges of calcium ions through electropermeabilized membrane of Chinese hamster ovary cells were found to be asymmetrical. Entry of calcium ions during a millisecond pulse occurred on the anode-facing cell hemisphere. Entry through the region facing the cathode was observed only after the pulse. Leakage of intracellular calcium ions from electropermeabilized cell in low-calcium content medium was observed only from the anode-facing side. The exchanges during the pulse were mostly due to diffusion-driven processes, i.e., governed by the concentration gradient. Interaction of propidium iodide, a dye sensitive to the structural alteration of membrane, with cell membrane was asymmetrical during electropermeabilization. Localized enhancement of the dye fluorescence was observed during and after the pulsation on the cell surface. Specific staining of a limited anode-facing part of the membrane was observed as soon as the pulse was applied. The membrane fluorescence level increased during and immediately after the pulse whereas the geometry of the staining was unchanged. The membrane regions stained by propidium iodide were the same as those where calcium exchanges occurred. The fraction of the membrane on which structural alterations occurred was defined by the field strength. The density of defects was governed by the pulse duration. Electropermeabilization is a localized but asymmetrical process. The membrane defects are created unequally on the two cell sides during the pulse, implying a vectorial effect of the electric field on the membrane. PMID:10096909

Gabriel, B; Teissié, J

1999-01-01

279

Binding of white spot syndrome virus to Artemia sp. cell membranes.  

PubMed

Using differential velocity centrifugation, cell membranes of Artemia sp. were prepared, and their binding to white spot syndrome virus (WSSV) was analyzed in vitro. The results indicated that WSSV can specifically bind to Artemia cell membranes, and that WSSV receptor very likely existed in this membrane, which suggested that Artemia sp. may be a reservoir of WSSV. This study investigated the specific WSSV binding site by performing competitive inhibition experiments using shrimp gill cell membranes to bind WSSV to Artemia cell membranes. The results showed that shrimp gill cell membranes had a distinct inhibition effect on the specific binding of Artemia cell membranes to WSSV. Thus, potentially similar WSSV receptors or binding sites existed on Artemia sp. cell membranes and shrimp gill cell membranes. Taken together, these findings may provide experimental basis for the development of an effective approach to controlling WSSV, and theoretical basis for the study of WSSV receptors. PMID:23711885

Feng, Shuying; Li, Guangda; Feng, Wenpo; Huang, Jie

2013-10-01

280

Evidence for Bidirectional Endocannabinoid Transport across Cell Membranes*  

PubMed Central

Despite extensive research on the trafficking of anandamide (AEA) across cell membranes, little is known about the membrane transport of other endocannabinoids, such as 2-arachidonoylglycerol (2-AG). Previous studies have provided data both in favor and against a cell membrane carrier-mediated transport of endocannabinoids, using different methodological approaches. Because AEA and 2-AG undergo rapid and almost complete intracellular hydrolysis, we employed a combination of radioligand assays and absolute quantification of cellular and extracellular endocannabinoid levels. In human U937 leukemia cells, 100 nm AEA and 1 ?m 2-AG were taken up through a fast and saturable process, reaching a plateau after 5 min. Employing differential pharmacological blockage of endocannabinoid uptake, breakdown, and interaction with intracellular binding proteins, we show that eicosanoid endocannabinoids harboring an arachidonoyl chain compete for a common membrane target that regulates their transport, whereas other N-acylethanolamines did not interfere with AEA and 2-AG uptake. By combining fatty acid amide hydrolase or monoacyl glycerol lipase inhibitors with hydrolase-inactive concentrations of the AEA transport inhibitors UCM707 (1 ?m) and OMDM-2 (5 ?m), a functional synergism on cellular AEA and 2-AG uptake was observed. Intriguingly, structurally unrelated AEA uptake inhibitors also blocked the cellular release of AEA and 2-AG. We show, for the first time, that UCM707 and OMDM-2 inhibit the bidirectional movement of AEA and 2-AG across cell membranes. Our findings suggest that a putative endocannabinoid cell membrane transporter controls the cellular AEA and 2-AG trafficking and metabolism. PMID:22879589

Chicca, Andrea; Marazzi, Janine; Nicolussi, Simon; Gertsch, Jürg

2012-01-01

281

New High-Temperature Membranes Developed for Proton Exchange Membrane Fuel Cells  

NASA Technical Reports Server (NTRS)

Fuel cells are receiving a considerable amount of attention for potential use in a variety of areas, including the automotive industry, commercial power generation, and personal electronics. Research at the NASA Glenn Research Center has focused on the development of fuel cells for use in aerospace power systems for aircraft, unmanned air vehicles, and space transportation systems. These applications require fuel cells with higher power densities and better durability than what is required for nonaerospace uses. In addition, membrane cost is a concern for any fuel cell application. The most widely used membrane materials for proton exchange membrane (PEM) fuel cells are based on sulfonated perfluorinated polyethers, typically Nafion 117, Flemion, or Aciplex. However, these polymers are costly and do not function well at temperatures above 80 C. At higher temperatures, conventional membrane materials dry out and lose their ability to conduct protons, essential for the operation of the fuel cell. Increasing the operating temperature of PEM fuel cells from 80 to 120 C would significantly increase their power densities and enhance their durability by reducing the susceptibility of the electrode catalysts to carbon monoxide poisoning. Glenn's Polymers Branch has focused on developing new, low-cost membranes that can operate at these higher temperatures. A new series of organically modified siloxane (ORMOSIL) polymers were synthesized for use as membrane materials in a high-temperature PEM fuel cell. These polymers have an organic portion that can allow protons to transport through the polymer film and a cross-linked silica network that gives the polymers dimensional stability. These flexible xerogel polymer films are thermally stable, with decomposition onset as high as 380 C. Two types of proton-conducting ORMOSIL films have been produced: (1) NASA-A, which can coordinate many highly acid inorganic salts that facilitate proton conduction and (2) NASA-B, which has been produced and which incorporates strongly acidic (proton donating) functional groups into the polymer backbone. Both of these polymer films have demonstrated significantly higher proton conductivity than Nafion at elevated temperatures and low relative humidities. An added advantage is that these polymers are very inexpensive to produce because their starting materials are commodity chemicals that are commercially available in large volumes.

Kinder, James D.

2004-01-01

282

Purification and characterization of a CMP-sialic:LcOse4Cer sialyltransferase from human colorectal carcinoma cell membranes  

SciTech Connect

Purified lactotetraosylceramide (Gal beta 1----3GlcNAc beta 1----3Gal beta 1----4Glc1-Cer) was tested for its ability to accept (14C)sialic acid from CMP-(14C)sialic into monosialoganglioside fractions in the presence of membrane fractions purified from human colorectal carcinoma cells (SW1116). Membrane fractions were isolated by three different methods: sucrose density centrifugation, CMP-agarose gel column chromatography, and LcOse4 gel chromatography. We optimized the incubation conditions for detergent dependency (taurocholate), pH (6.3), and acceptor concentration. The sialyltransferase activity was dependent on membrane protein and linear for time up to at least 4 h. The LcOse4 affinity chromatography of the crude microsomal membrane pellet from these cells yielded a membrane fraction that was 136-fold enriched in LcOse4 acceptor specific activity compared to cell homogenates. The apparent Km for the sialyltransferase activity with LcOse4Cer acceptor in the presence of affinity-purified membranes was 20 microM and the Vmax was 7 pmol h-1 (100 micrograms of protein)-1. Acceptor capabilities of other core structures were 5-20-fold lower: LcOse4Cer much greater than GgOse4Cer greater than nLcOse4Cer much greater than GbOse4Cer. The enzymatic activity was purified further (900-fold) by a combination of LcOse4 and CMP affinity gels. SDS-PAGE electrophoresis of this material showed a major set of closely migrating bands of Mr 58,000-54,000 compared to authentic proteins, as well as a minor band at 27,000. We analyzed picomole quantities of the radioactive product by convenient controlled short-term hydrolyses with an endoglycoceramidase and sialidases (from four different sources) in comparison to sialylated tetrasaccharides of known structure.

Liepkans, V.; Jolif, A.; Larson, G.

1988-11-15

283

Crucial role for membrane fluidity in proliferation of primitive cells.  

PubMed

The cell wall is a defining structural feature of the bacterial subkingdom. However, most bacteria are capable of mutating into a cell-wall-deficient "L-form" state, requiring remarkable physiological and structural adaptations. L-forms proliferate by an unusual membrane deformation and scission process that is independent of the conserved and normally essential FtsZ based division machinery, and which may provide a model for the replication of primitive cells. Candidate gene screening revealed no requirement for the cytoskeletal systems that might actively drive membrane deformation or scission. Instead, we uncovered a crucial role for branched-chain fatty acid (BCFA) synthesis. BCFA-deficient mutants grow and undergo pulsating shape changes, but membrane scission fails, abolishing the separation of progeny cells. The failure in scission is associated with a reduction in membrane fluidity. The results identify a step in L-form proliferation and demonstrate that purely biophysical processes may have been sufficient for proliferation of primitive cells. PMID:22832271

Mercier, Romain; Domínguez-Cuevas, Patricia; Errington, Jeff

2012-05-31

284

Multimodal method for cell membrane extraction in hepatic histological images.  

PubMed

A multimodal method, which uses different kinds of imaging methods, was applied to extract cell membranes in microscopic images of hematoxylin and eosin-stained hepatic histological sections. Cell membrane extraction in hepatic histological images is difficult because the color difference between the cell membrane and the cytoplasm is small in bright-field images. Three kinds of imaging methods, bright-field, dark-field, and phase-contrast imaging, were used because they are readily available for general pathologists. These imaging methods can be switched easily by revolving a combined condenser with the same phase-contrast objective lens. Therefore, little additional time and cost are needed for this approach. Experimental results show the effectiveness of this approach. The correct rate was improved by using additional color information obtained by dark-field and phase-contrast images compared to conventional bright-field images. The best correct rate was obtained when color information of all three images was used. A graphical user interface to calculate the N/C ratio was developed by combining cell membrane extraction with conventional cell nucleus extraction. PMID:21097099

Matsushita, Nobumitsu; Takahashi, Masanobu; Nakano, Masayuki

2010-01-01

285

The development of PTFE\\/Nafion\\/TEOS membranes for application in moderate and high temperature proton exchange membrane fuel cells  

Microsoft Academic Search

PTFE\\/Nafion (PN) and PTFE\\/Nafion\\/TEOS (PNS) membranes were fabricated for the application of moderate and high temperature proton exchange membrane fuel cells (PEMFCs), respectively. Membrane electrode assemblies (MEAs) were fabricated by PTFE\\/Nafion (and PTFE\\/Nafion\\/TEOS) membranes with commercially available low and high temperature gas diffusion electrodes (GDEs). The effects of relative humidity, operation temperature, and back pressure on the performance and durability

Guo-Bin Jung; Feng-Bor Weng; Chao-Chun Peng; Ting-Chu Jao

2011-01-01

286

Autophagy modulates cell migration and ?1 integrin membrane recycling  

PubMed Central

Cell migration is dependent on a series of integrated cellular events including the membrane recycling of the extracellular matrix receptor integrins. In this paper, we investigate the role of autophagy in regulating cell migration. In a wound-healing assay, we observed that autophagy was reduced in cells at the leading edge than in cells located rearward. These differences in autophagy were correlated with the robustness of MTOR activity. The spatial difference in the accumulation of autophagic structures was not detected in rapamycin-treated cells, which had less migration capacity than untreated cells. In contrast, the knockdown of the autophagic protein ATG7 stimulated cell migration of HeLa cells. Accordingly, atg3?/? and atg5?/? MEFs have greater cell migration properties than their wild-type counterparts. Stimulation of autophagy increased the co-localization of ?1 integrin-containing vesicles with LC3-stained autophagic vacuoles. Moreover, inhibition of autophagy slowed down the lysosomal degradation of internalized ?1 integrins and promoted its membrane recycling. From these findings, we conclude that autophagy regulates cell migration, a central mechanism in cell development, angiogenesis, and tumor progression, by mitigating the cell surface expression of ?1 integrins. PMID:24036548

Tuloup-Minguez, Véronique; Hamaï, Ahmed; Greffard, Anne; Nicolas, Valérie; Codogno, Patrice; Botti, Joëlle

2013-01-01

287

Membrane and MEA Development in Polymer Electrolyte Fuel Cells  

NASA Astrophysics Data System (ADS)

The polymer electrolyte fuel cell (PEFC) is based on Nafion polymer membranes operating at a temperature of 80°C. The main characteristics (structure and properties) and problems of Nafion-based PEFC technology are discussed. The primary drawbacks of Nafion membranes are poor conductivity at low relative humidities (and consequently at temperatures >100°C and ambient pressure) and large crossover of methanol in direct methanol fuel cell (DMFC) applications. These drawbacks have prompted an extensive effort to improve the properties of Nafion and identify alternate materials to replace Nafion. Polymer electrolyte membranes (PEMs) are classified in modified Nafion, membranes based on functionalized non-fluorinated backbones and acid-base polymer systems. Perhaps the most widely employed approach is the addition of inorganic additives to Nafion membranes to yield organic/inorganic composite membranes. Four major types of inorganic additives that have been studied (zirconium phosphates, heteropolyacids, metal hydrogen sulfates, and metal oxides) are reviewed in the following. DMFC and H2/O2 (air) cells based on modified Nafion membranes have been successfully operated at temperatures up to 120°C under ambient pressure and up to 150°C under 3-5 atm. Membranes based on functionalized non-fluorinated backbones are potentially promising for high-temperature operation. High conductivities have been obtained at temperatures up to 180°C. The final category of polymeric PEMs comprises non-functionalized polymers with basic character doped with proton-conducting acids such as phosphoric acid. The advanced features include high CO tolerance and thermal management. The advances made in the fabrication of electrodes for PEM fuel cells from the PTFE-bound catalyst layers of almost 20 years ago to the present technology are briefly discussed. There are two widely employed electrode designs: (1) PTFE-bound, and (2) thin-film electrodes. Emerging methods include those featuring catalyst layers formed with electrodeposition and vacuum deposition (sputtering). The thin-film electrodes have significantly increased performance and reduced the level of platinum loading required. Thin sputtered layers have shown promise for low catalyst loading with adequate performance. Electrodeposition methods are briefly discussed. Finally, the relationship between MEA processing and the durability of the membrane/electrode interface and hence the fuel cell as a whole is presented.

Trogadas, Panagiotis; Ramani, Vijay

288

The formin FMNL3 assembles plasma membrane protrusions that participate in cell–cell adhesion  

PubMed Central

FMNL3 is a vertebrate-specific formin protein previously shown to play a role in angiogenesis and cell migration. Here we define the cellular localization of endogenous FMNL3, the dynamics of GFP-tagged FMNL3 during cell migration, and the effects of FMNL3 suppression in mammalian culture cells. The majority of FMNL3 localizes in a punctate pattern, with >95% of these puncta being indistinguishable from the plasma membrane by fluorescence microscopy. A small number of dynamic cytoplasmic FMNL3 patches also exist, which enrich near cell–cell contact sites and fuse with the plasma membrane at these sites. These cytoplasmic puncta appear to be part of larger membranes of endocytic origin. On the plasma membrane, FMNL3 enriches particularly in filopodia and membrane ruffles and at nascent cell–cell adhesions. FMNL3-containing filopodia occur both at the cell–substratum interface and at cell–cell contacts, with the latter being 10-fold more stable. FMNL3 suppression by siRNA has two major effects: decrease in filopodia and compromised cell–cell adhesion in cells migrating as a sheet. Overall our results suggest that FMNL3 functions in assembly of actin-based protrusions that are specialized for cell–cell adhesion. PMID:25428984

Gauvin, Timothy J.; Young, Lorna E.; Higgs, Henry N.

2015-01-01

289

Fractionation of whey protein hydrolysates using charged UF\\/NF membranes  

Microsoft Academic Search

The possibility to separate peptides from a tryptic hydrolysates of whey proteins with charged UF\\/NF membranes has been investigated. A total hydrolysate (TH) was prepared by tryptic hydrolysis of a commercial whey protein isolate followed by UF-treatment using a 10kDa MWCO in order to remove the enzyme and non-hydrolyzed material from the reaction mixture. Firstly, five different membrane materials were

Y. Pouliot; M. C. Wijers; S. F. Gauthier; L. Nadeau

1999-01-01

290

Changes in Band 3 oligomeric state precede cell membrane phospholipid loss during blood bank storage of red blood cells  

PubMed Central

BACKGROUND Lipid loss in the form of vesicles contributes to the red blood cell (RBC) storage lesion, and this loss of lipid is correlated with changes in membrane protein function. Sensitive spectroscopic techniques were used to measure changes in Band 3 oligomeric state during storage of RBCs, compared to metabolic changes and phospholipid loss. The aim of the study was to determine whether changes in the macromolecular organization of membrane proteins occur before, coincident with, or after lipid loss during RBC storage. STUDY DESIGN AND METHODS Five RBC units were collected from normal volunteers and stored under standard blood bank conditions, and both metabolic changes and lipid loss were measured by multiple assays. Band 3 oligomeric state was assessed by time-resolved phosphorescence anisotropy and fluorescence resonance energy transfer of eosin-5-maleimide–labeled RBC ghosts. RESULTS Extracellular pH decreased and extracellular potassium increased rapidly during cold storage of blood. Band 3 on the RBC membrane exhibited a shift from small to large oligomers early in the storage period and before detectable loss of phospholipid from the RBC membrane. The immobilized fraction of Band 3, that which is tethered to the cytoskeletal network via spectrin and ankyrin, did not change during cold storage. CONCLUSION Our results demonstrate that changes in the macromolecular organization of membrane proteins on the RBC occur early in storage, and these changes may induce phospholipid loss, irreversible morphologic changes, and loss of function during RBC storage. PMID:19389033

Karon, Brad S.; Hoyer, James D.; Stubbs, James R.; Thomas, David D.

2013-01-01

291

Hostile Takeover by Plasmodium: Reorganization of Parasite and Host Cell Membranes during Liver Stage  

E-print Network

Hostile Takeover by Plasmodium: Reorganization of Parasite and Host Cell Membranes during Liver of Cell Biology, University of Bern, Bern, Switzerland Abstract The protozoan parasite Plasmodium the membrane of these merosomes was derived from the parasite membrane, the parasitophorous vacuole membrane

Arnold, Jonathan

292

THE FLUIDITY OF CHINESE HAMSTER OVARY CELL AND BULL SPERM MEMBRANES AFTER CHOLESTEROL ADDITION  

Technology Transfer Automated Retrieval System (TEKTRAN)

Cell plasma membrane fluidity is affected by membrane lipid and protein composition as well as temperature. Altering the cholesterol content of a membrane can change membrane fluidity at different temperatures and this may affect cell survival during cryopreservation. In these experiments, we exami...

293

Durable, Low-cost, Improved Fuel Cell Membranes  

SciTech Connect

The development of low cost, durable membranes and membranes electrode assemblies (MEAs) that operate under reduced relative humidity (RH) conditions remain a critical challenge for the successful introduction of fuel cells into mass markets. It was the goal of the team lead by Arkema, Inc. to address these shortages. Thus, this project addresses the following technical barriers from the fuel cells section of the Hydrogen Fuel Cells and Infrastructure Technologies Program Multi-Year Research, Development and Demonstration Plan: (A) Durability (B) Cost Arkema’s approach consisted of using blends of polyvinylidenefluoride (PVDF) and proprietary sulfonated polyelectrolytes. In the traditional approach to polyelectrolytes for proton exchange membranes (PEM), all the required properties are “packaged” in one macromolecule. The properties of interest include proton conductivity, mechanical properties, durability, and water/gas transport. This is the case, for example, for perfluorosulfonic acid-containing (PFSA) membranes. However, the cost of these materials is high, largely due to the complexity and the number of steps involved in their synthesis. In addition, they suffer other shortcomings such as mediocre mechanical properties and insufficient durability for some applications. The strength and originality of Arkema’s approach lies in the decoupling of ion conductivity from the other requirements. Kynar® PVDF provides an exceptional combination of properties that make it ideally suited for a membrane matrix (Kynar® is a registered trademark of Arkema Inc.). It exhibits outstanding chemical resistance in highly oxidative and acidic environments. In work with a prior grant, a membrane known as M41 was developed by Arkema. M41 had many of the properties needed for a high performance PEM, but had a significant deficiency in conductivity at low RH. In the first phase of this work, the processing parameters of M41 were explored as a means to increase its proton conductivity. Optimizing the processing of M41 was found to increase its proton conductivity by almost an order of magnitude at 50% RH. Characterization of the membrane morphology with Karren More at Oak Ridge National Laboratory showed that the membrane morphology was complex. This technology platform was dubbed M43 and was used as a baseline in the majority of the work on the project. Although its performance was superior to M41, M43 still showed proton conductivity an order of magnitude lower than that of a PFSA membrane at 50% RH. The MEA performance of M43 could be increased by reducing the thickness from 1 to 0.6 mils. However, the performance of the thinner M43 still did not match that of a PFSA membrane.

Chris Roger; David Mountz; Wensheng He; Tao Zhang

2011-03-17

294

Electrospun fiber membranes enable proliferation of genetically modified cells  

PubMed Central

Polycaprolactone (PCL) and its blended composites (chitosan, gelatin, and lecithin) are well-established biomaterials that can enrich cell growth and enable tissue engineering. However, their application in the recovery and proliferation of genetically modified cells has not been studied. In the study reported here, we fabricated PCL-biomaterial blended fiber membranes, characterized them using physicochemical techniques, and used them as templates for the growth of genetically modified HCT116-19 colon cancer cells. Our data show that the blended polymers are highly miscible and form homogenous electrospun fiber membranes of uniform texture. The aligned PCL nanofibers support robust cell growth, yielding a 2.5-fold higher proliferation rate than cells plated on standard plastic plate surfaces. PCL-lecithin fiber membranes yielded a 2.7-fold higher rate of proliferation, while PCL-chitosan supported a more modest growth rate (1.5-fold higher). Surprisingly, PCL-gelatin did not enhance cell proliferation when compared to the rate of cell growth on plastic surfaces. PMID:23467983

Borjigin, Mandula; Eskridge, Chris; Niamat, Rohina; Strouse, Bryan; Bialk, Pawel; Kmiec, Eric B

2013-01-01

295

Electrospun fiber membranes enable proliferation of genetically modified cells.  

PubMed

Polycaprolactone (PCL) and its blended composites (chitosan, gelatin, and lecithin) are well-established biomaterials that can enrich cell growth and enable tissue engineering. However, their application in the recovery and proliferation of genetically modified cells has not been studied. In the study reported here, we fabricated PCL-biomaterial blended fiber membranes, characterized them using physicochemical techniques, and used them as templates for the growth of genetically modified HCT116-19 colon cancer cells. Our data show that the blended polymers are highly miscible and form homogenous electrospun fiber membranes of uniform texture. The aligned PCL nanofibers support robust cell growth, yielding a 2.5-fold higher proliferation rate than cells plated on standard plastic plate surfaces. PCL-lecithin fiber membranes yielded a 2.7-fold higher rate of proliferation, while PCL-chitosan supported a more modest growth rate (1.5-fold higher). Surprisingly, PCL-gelatin did not enhance cell proliferation when compared to the rate of cell growth on plastic surfaces. PMID:23467983

Borjigin, Mandula; Eskridge, Chris; Niamat, Rohina; Strouse, Bryan; Bialk, Pawel; Kmiec, Eric B

2013-01-01

296

Characteristics of high-water-uptake activated carbon/Nafion hybrid membranes for proton exchange membrane fuel cells  

NASA Astrophysics Data System (ADS)

A cost-effective and high-throughput method for producing high-water-uptake membranes is developed by combining high-porosity and superior-surface-area activated carbon with Nafion. The resultant activated carbon/Nafion hybrid composite exhibits high water uptake and an improved proton conductivity, which can be exploited in a proton exchange membrane fuel cell (PEMFC). This hybrid membrane displays a superior performance to that of the commercial Nafion 211 when used in fuel-cell measurements. Electrochemical impedance spectroscopy (EIS) is used to simulate the changes in resistance during the operation of the fuel cells and conclusively explains the improved performance of the composite membranes.

Chien, Hung-Chung; Tsai, Li-Duan; Lai, Chien-Ming; Lin, Jiunn-Nan; Zhu, Chao-Yuan; Chang, Feng-Chih

2013-03-01

297

Interaction of Dendritic Polymers with Synthetic Lipid and Cell Membranes  

NASA Astrophysics Data System (ADS)

Polyamidoamine (PAMAM) dendrimers are promising candidates for the development of nanoscale therapeutic transport agents. Here we present studies on dendrimer-membrane interactions leading to a better understanding of possible uptake mechanisms into cells. Using synthetic lipid and natural cell membranes as model systems it is shown that the effect of PAMAM dendrimers on a membrane strongly depends on the dendrimer generation, architecture and chemical properties of the branch end groups. Atomic force microscopy data indicates that generation 7 dendrimers have the ability to form small ( 10-100 nm) holes in a lipid bilayer. When dendrimers with otherwise identical chemical properties are arranged in a covalently linked cluster, no hole formation occurs. Dendrimer-lipid micelle formation is proposed and investigated as a possible mechanism for this behavior. Smaller dendrimers (generation 5) have a greatly reduced ability to remove lipid molecules from a bilayer. In addition to the size of the dendrimer, the charge of the branch end groups plays a significant role for dendrimer-membrane interactions. These results agree well with biological studies using cultured cells and point to a new mechanism of specific targeting and uptake into cells.

Mecke, Almut; Hong, Seungpyo; Bielinska, Anna U.; Banaszak Holl, Mark M.; Orr, Bradford G.; Baker, James R., Jr.

2004-03-01

298

Membrane electrolytic cell for minimizing hypochlorite and chlorate formation  

Microsoft Academic Search

An electrolytic cell for the electrolysis of an alkali metal chloride brine is comprised of an anode compartment and a cathode compartment separated by a cation exchange membrane. The anode is comprised of an unflattened expanded structure of a valve metal selected from the group consisting of titanium, tantalum, niobium, and alloys thereof. At least one side of the anode

D. L. Fair; D. D. Justice; K. E. Woodard Jr

1985-01-01

299

Nonminimum-Phase Phenomenon of PEM Fuel Cell Membrane  

E-print Network

. In this paper, stack cooling water replaces the exhaust gas as the source to warm and humidify the dry inlet gas 48109-2125 A membrane-based humidifier that uses cooling water of a fuel cell system to humidify and thus are not as practical as those using cooling water. In this paper, the model developed in Ref. 2

Peng, Huei

300

Applications of proton exchange membrane fuel cell systems  

Microsoft Academic Search

Proton exchange membrane fuel cells (PEMFCs) have recently passed the test or demonstration phase and have partially reached the commercialization stage due to the impressive worldwide research effort. Despite the currently promising achievements and the plausible prospects of PEMFCs, there are many challenges remaining that need to be overcome before PEMFCs can successfully and economically substitute for the various traditional

Jung-Ho Wee

2007-01-01

301

Basolateral membrane K+ channels in renal epithelial cells  

PubMed Central

The major function of epithelial tissues is to maintain proper ion, solute, and water homeostasis. The tubule of the renal nephron has an amazingly simple structure, lined by epithelial cells, yet the segments (i.e., proximal tubule vs. collecting duct) of the nephron have unique transport functions. The functional differences are because epithelial cells are polarized and thus possess different patterns (distributions) of membrane transport proteins in the apical and basolateral membranes of the cell. K+ channels play critical roles in normal physiology. Over 90 different genes for K+ channels have been identified in the human genome. Epithelial K+ channels can be located within either or both the apical and basolateral membranes of the cell. One of the primary functions of basolateral K+ channels is to recycle K+ across the basolateral membrane for proper function of the Na+-K+-ATPase, among other functions. Mutations of these channels can cause significant disease. The focus of this review is to provide an overview of the basolateral K+ channels of the nephron, providing potential physiological functions and pathophysiology of these channels, where appropriate. We have taken a “K+ channel gene family” approach in presenting the representative basolateral K+ channels of the nephron. The basolateral K+ channels of the renal epithelia are represented by members of the KCNK, KCNJ, KCNQ, KCNE, and SLO gene families. PMID:22338089

Devor, Daniel C.

2012-01-01

302

CAPSTONE SENIOR DESIGN - SUPRAMOLECULAR PROTON EXCHANGE MEMBRANES FOR FUEL CELLS  

EPA Science Inventory

In order to assume a leading role in the burgeoning hydrogen economy, new infrastructure will be required for fuel cell manufacturing and R&D capabilities. The objective of this proposal is the development of a new generation of advanced proton exchange membrane (PEM) technol...

303

Sulfonated Nanoplates in Proton Conducting Membranes for Fuel Cells  

SciTech Connect

Surface-functionalized nanoplates are synthesized by anchoring sulfonic acid containing siloxanes on zirconium phosphate, and in turn blended with Nafion to fabricate proton conducting membranes. The effects of these sulfonated nanoplates on proton conduction, hydro-characteristics and fuel cell performance are reported.

Chen, W.F.; Ni’mah, H.; Yu-Cheng Shen, Y.-C.; Kuo, P.-L.

2011-09-29

304

Duration of ultrasound bubbles enhanced cell membrane permeability  

Microsoft Academic Search

Purpose: Ultrasound (US) has shown the ability to modulate the cell membrane permeability in a process known as sonoporation. In addition, the sonoporation process has been proven to be amplified when US is associated with contrast microbubbles. The purpose of this study is to quantify the duration of the sonoporation process for external molecules with different sizes. Method: monolayers of

Annemieke van Wamel; Ayache Bouakaz; Nico de Jong

2003-01-01

305

Lipid Signalling Dynamics at the ?-cell Plasma Membrane.  

PubMed

Pancreatic ?-cells are clustered in islets of Langerhans and secrete insulin in response to increased concentrations of circulating glucose. Insulin in turn acts on liver, muscle and fat tissue to store energy and normalize the blood glucose level. Inappropriate insulin release may lead to impaired glucose tolerance and diabetes. In addition to glucose, other nutrients, neural stimuli and hormonal stimuli control insulin secretion. Many of these signals are perceived at the plasma membrane, which is also the site where insulin granules undergo exocytosis. Therefore, it is not surprising that membrane lipids play an important role in the regulation of insulin secretion. ?-cells release insulin in a pulsatile fashion. Signalling lipids integrate the nutrient and neurohormonal inputs to fine-tune, shape and co-ordinate the pulsatility. An important group of signalling lipids are phosphoinositides and their downstream messengers. This MiniReview will discuss new insights into lipid signalling dynamics in ?-cells obtained from live-cell imaging experiments with fluorescent translocation biosensors. The plasma membrane concentration of several phosphoinositides and of their downstream messengers changes rapidly upon nutrient or neurohormonal stimulation. Glucose induces the most complex spatio-temporal patterns, typically involving oscillations of messenger concentrations, which sometimes are locally restricted. The tightly controlled levels of lipid messengers can mediate specific binding of downstream effectors to the plasma membrane, contributing to the appropriate regulation of insulin secretion. PMID:25529872

Wuttke, Anne

2015-04-01

306

Alternative Sources of Adult Stem Cells: Human Amniotic Membrane  

NASA Astrophysics Data System (ADS)

Human amniotic membrane is a highly promising cell source for tissue engineering. The cells thereof, human amniotic epithelial cells (hAEC) and human amniotic mesenchymal stromal cells (hAMSC), may be immunoprivileged, they represent an early developmental status, and their application is ethically uncontroversial. Cell banking strategies may use freshly isolated cells or involve in vitro expansion to increase cell numbers. Therefore, we have thoroughly characterized the effect of in vitro cultivation on both phenotype and differentiation potential of hAEC. Moreover, we present different strategies to improve expansion including replacement of animal-derived supplements by human platelet products or the introduction of the catalytic subunit of human telomerase to extend the in vitro lifespan of amniotic cells. Characterization of the resulting cultures includes phenotype, growth characteristics, and differentiation potential, as well as immunogenic and immunomodulatory properties.

Wolbank, Susanne; van Griensven, Martijn; Grillari-Voglauer, Regina; Peterbauer-Scherb, Anja

307

Development of new membrane materials for direct methanol fuel cells  

Microsoft Academic Search

Development of new membrane materials for direct methanol fuel cells\\u000aDirect methanol fuel cells (DMFCs) can convert the chemical energy of a fuel directly into electrical energy with high efficiency and low emission of pollutants. DMFCs can be used as the power sources to portable electronic devices like laptop computers, cellular phones and, to a less degree, vehicular applications. \\u000aIn

Mustafa Hakan Yildirim

2009-01-01

308

Performance of proton exchange membrane fuel cells at elevated temperature  

Microsoft Academic Search

The polarization curves of a single PEMFC having a Nafion membrane fed with H2\\/O2 with relative humidity (RH) of 35%, 70% and 100% were measured at cell temperatures ranging from 65°C to 120°C at back pressures of 0atm and 1atm, respectively. Measured results showed that the best cell performance at 0.6V operated within 65–120°C at zero back pressure was 1000mAcm?2

Jin-Cherng Shyu; Kan-Lin Hsueh; Fanghei Tsau

2011-01-01

309

Effect of acetaminophen on the membrane anchoring of Na+, K+ATPase of rat renal cortical cells.  

PubMed

In previous works we reported that the administration of a toxic dose of acetaminophen (APAP) induces acute renal failure (ARF) and promotes changes on Na(+), K(+)ATPase distribution in renal proximal plasma membranes. In the present work, we analyzed if APAP could promote the dissociation of Na(+), K(+)ATPase from its membrane anchorage. The participation of calpain activation was also evaluated. We analyzed the Triton X-100 extractability of Na(+), K(+)ATPase in freshly isolated cortical cell suspensions incubated with different APAP concentrations (0.1, 1, 10 and 100 mM). Both alpha(1) and beta(1) subunits were studied by Western blot. APAP promoted the increment of both subunits abundance in the Triton-soluble fraction. Calpain activation was detected in the membrane fractions of cells incubated with APAP. Incubation with APAP 0.1, 1 and 10 mM did not promote an increment in LDH release compared with controls, while APAP 100 mM promoted an increased LDH release. Our results show that incubation of proximal cells with sublethal and lethal APAP concentrations promotes the detachment of Na(+), K(+)ATPase from its membrane anchoring. Inhibition of calpain activation by SJA 7029 protected against APAP-induced membrane damage but not against APAP-induced increase of the Triton X-100 extractability of Na(+), K(+)ATPase. PMID:15949700

Trumper, Laura; Coux, Gabriela; Monasterolo, Liliana A; Molinas, Sara; García, Verónica M C; Elías, M Mónica

2005-06-10

310

In vitro synthesis of cellulose II from a cytoplasmic membrane fraction of Acetobacter xylinum.  

PubMed

The cytoplasmic and outer membranes of Acetobacter xylinum (ATCC 53582) were isolated by discontinuous sucrose density ultracentrifugation. Both lysozyme (EC 3.2.1.17) and trypsin (EC 3.4.21.4) were required for efficient crude membrane separation. Primary dehydrogenases and NADH oxidase were used as cytoplasmic membrane markers, and 2-keto-3-deoxyoctulosonic acid was used to identify the outer membranes. Cellulose synthetase (UDP-glucose:1,4-beta-D-glucan 4-beta-D-glucosyltransferase; EC 2.4.1.12) activity was assayed as the conversion of radioactivity from UDP-[(14)C]glucose into an alkali-insoluble beta-1,4-D-[(14)C]glucan. This activity was predominantly found in the cytoplasmic membrane. The cellulose nature of the product was demonstrated by (i) enzymatic hydrolysis followed by TLC, (ii) methylation analysis followed by TLC, and (iii) GC/MS. Further, the weight-average and number-average degree of polymerization of the in vitro product, determined by high-performance gel permeation chromatography, were 4820 and 5270, respectively. In addition, x-ray diffraction analysis indicated that the in vitro product is cellulose II, which is in contrast to the in vivo product-namely, cellulose I. PMID:16593877

Bureau, T E; Brown, R M

1987-10-01

311

In vitro synthesis of cellulose II from a cytoplasmic membrane fraction of Acetobacter xylinum  

PubMed Central

The cytoplasmic and outer membranes of Acetobacter xylinum (ATCC 53582) were isolated by discontinuous sucrose density ultracentrifugation. Both lysozyme (EC 3.2.1.17) and trypsin (EC 3.4.21.4) were required for efficient crude membrane separation. Primary dehydrogenases and NADH oxidase were used as cytoplasmic membrane markers, and 2-keto-3-deoxyoctulosonic acid was used to identify the outer membranes. Cellulose synthetase (UDP-glucose:1,4-?-D-glucan 4-?-D-glucosyltransferase; EC 2.4.1.12) activity was assayed as the conversion of radioactivity from UDP-[14C]glucose into an alkali-insoluble ?-1,4-D-[14C]glucan. This activity was predominantly found in the cytoplasmic membrane. The cellulose nature of the product was demonstrated by (i) enzymatic hydrolysis followed by TLC, (ii) methylation analysis followed by TLC, and (iii) GC/MS. Further, the weight-average and number-average degree of polymerization of the in vitro product, determined by high-performance gel permeation chromatography, were 4820 and 5270, respectively. In addition, x-ray diffraction analysis indicated that the in vitro product is cellulose II, which is in contrast to the in vivo product—namely, cellulose I. Images PMID:16593877

Bureau, Thomas E.; Brown, R. Malcolm

1987-01-01

312

Cholesterol-mediated membrane surface area dynamics in neuroendocrine cells.  

PubMed

How cholesterol, a key membrane constituent, affects membrane surface area dynamics in secretory cells is unclear. Using methyl-beta-cyclodextrin (MbetaCD) to deplete cholesterol, we imaged melanotrophs from male Wistar rats in real-time and monitored membrane capacitance (C(m)), fluctuations of which reflect exocytosis and endocytosis. Treatment with MbetaCD reduced cellular cholesterol and caused a dose-dependent attenuation of the Ca(2+)-evoked increase in C(m) (IC50 = 5.3 mM) vs. untreated cells. Cytosol dialysis of MbetaCD enhanced the attenuation of C(m) increase (IC50 = 3.3 mM), suggesting cholesterol depletion at intracellular membrane sites was involved in attenuating exocytosis. Acute extracellular application of MbetaCD resulted in an immediate C(m) decline, which correlated well with the cellular surface area decrease, indicating the involvement of cholesterol in the regulation of membrane surface area dynamics. This decline in C(m) was three-fold slower than MbetaCD-mediated fluorescent cholesterol decay, implying that exocytosis is the likely physiological means for plasma membrane cholesterol replenishment. MbetaCD had no effect on the specific C(m) and the blockade of endocytosis by Dyngo 4a, confirmed by inhibition of dextran uptake, also had no effect on the time-course of MbetaCD-induced C(m) decline. Thus acute exposure to MbetaCD evokes a C(m) decline linked to the removal of membrane cholesterol, which cannot be compensated for by exocytosis. We propose that the primary contribution of cholesterol to surface area dynamics is via its role in regulated exocytosis. PMID:24046863

Rituper, Bostjan; Chowdhury, Helena Haque; Jorgacevski, Jernej; Coorssen, Jens R; Kreft, Marko; Zorec, Robert

2013-07-01

313

Probing cell membrane dynamics using plasmon coupling microscopy  

NASA Astrophysics Data System (ADS)

The plasma membrane of mammalian cells is depicted as a two-dimensional hybrid material which is compartmentalized into submicron-sized domains. These membrane domains play a pivotal role in cellular signaling processes due to selective recruitment of specific cell surface receptors. The structural dynamics of the membrane domains and their exact biological functions are, however, still unclear, partially due to the wave nature of light, which limits the optical resolution in the visible light to approximately 400 nm in conventional optical microscopy. Here, we provide a non-fluorescence based approach for monitoring distance changes on subdiffraction limit length scales in a conventional far-field optical microscope. This approach, which is referred to as plasmon coupling microscopy (PCM), utilizes the distance dependent near-field coupling between noble metal nanoparticle (NP) labels to resolve close contacts on the length scale of approximately one NP diameter. We firstly utilize this PCM strategy to resolve interparticle separations during individual encounters of gold NP labeled fibronectin-integrin complexes in living HeLa cells. We then further refine this ratiometric detection methodology by augmenting it with a polarization-sensitive detection, which enables simultaneous monitoring of the distance and conformation changes in NP dimers and clusters. We apply this polarization resolved PCM approach to characterize the structural lateral heterogeneity of cell membranes on sub-micron length scales. Finally, we demonstrate that PCM can provide quantitative information about the structural dynamics of individual epidermal growth factor receptor (ErbB1)-enriched membrane domains in living cells.

Rong, Guoxin

314

Ultrafiltration by a compacted clay membrane-I. Oxygen and hydrogen isotopic fractionation  

USGS Publications Warehouse

Laboratory experiments were carried out to determine the magnitude of the isotopic fractionation of distilled water and of 0.01 N NaCl forced to flow at ambient temperature under a hydraulic pressure drop of 100 bars across a montmorillonite disc compacted to a porosity of 35 per cent by a pressure of 330 bars. The ultrafiltrates in both experiments were depleted in D by 2.5%. and in O18 by 0.8%. relative to the residual solution. No additional isotopic fractionation due to a salt filtering mechanism was observed at NaCl concentrations up to 0.01 N. Adsorption is most likely the principal mechanism which produces isotopic fractionation, but molecular diffusion may play a minor role. The results suggest that oxygen and hydrogen isotopic fractionation of ground water during passage through compacted clayey sediments should be a common occurrence, in accord with published interpretations of isotopic data from the Illinois and Alberta basins. ?? 1973.

Coplen, T.B.; Hanshaw, B.B.

1973-01-01

315

The Membrane Environment Can Promote or Suppress Bistability in Cell Signaling Networks  

E-print Network

Many key biochemical reactions that mediate signal transduction in cells occur at the cell membrane, yet how the two-dimensional membrane environment influences the collective behavior of signaling networks is poorly ...

Abel, Steven M.

316

Development of Thin Film Membrane Assemblies with Novel Nanostructured Electrocatalyst for Next Generation Fuel Cells  

E-print Network

. Background Recent advances have made proton exchange membrane fuel cells (PEMFC) a leading alternative-air fuel cell based on Nafion- related membranes is a potential technology but sourcing the hydrogen

Popov, Branko N.

317

Chemical Imaging of the Cell Membrane by NanoSIMS  

SciTech Connect

The existence of lipid microdomains and their role in cell membrane organization are currently topics of great interest and controversy. The cell membrane is composed of a lipid bilayer with embedded proteins that can flow along the two-dimensional surface defined by the membrane. Microdomains, known as lipid rafts, are believed to play a central role in organizing this fluid system, enabling the cell membrane to carry out essential cellular processes, including protein recruitment and signal transduction. Lipid rafts are also implicated in cell invasion by pathogens, as in the case of the HIV. Therefore, understanding the role of lipid rafts in cell membrane organization not only has broad scientific implications, but also has practical implications for medical therapies. One of the major limitations on lipid organization research has been the inability to directly analyze lipid composition without introducing artifacts and at the relevant length-scales of tens to hundreds of nanometers. Fluorescence microscopy is widely used due to its sensitivity and specificity to the labeled species, but only the labeled components can be observed, fluorophores can alter the behavior of the lipids they label, and the length scales relevant to imaging cell membrane domains are between that probed by fluorescence resonance energy transfer (FRET) imaging (<10 nm) and the diffraction limit of light. Topographical features can be imaged on this length scale by atomic force microscopy (AFM), but the chemical composition of the observed structures cannot be determined. Immuno-labeling can be used to study the distribution of membrane proteins at high resolution, but not lipid composition. We are using imaging mass spectrometry by secondary ion mass spectrometry (SIMS) in concert with other high resolution imaging methods to overcome these limitations. The experimental approach of this project is to combine molecule-specific stable isotope labeling with high-resolution SIMS using a Cameca NanoSIMS 50 to probe membrane organization and test microdomain hypotheses. The NanoSIMS is an imaging secondary ion mass spectrometer with an unprecedented combination of spatial resolution, sensitivity and mass specificity. It has 50 nm lateral resolution and is capable of detecting 1 in 20 nitrogen atoms while excluding near-neighbor isobaric interferences. The tightly focused cesium ion beam is rastered across the sample to produce simultaneous, quantitative digital images of up to five different masses. By labeling each specific components of a membrane with a unique rare stable isotope or element and mapping the location of the labels with the NanoSIMS, the location of the each labeled component can be determined and quantified. This new approach to membrane composition analysis allows molecular interactions of biological membranes to be probed at length-scales relevant to lipid rafts (10s to 100s of nm) that were not previously possible. Results from our most recent experiments analyzing whole cells will be presented.

Weber, P K; Kraft, M L; Frisz, J F; Carpenter, K J; Hutcheon, I D

2010-02-23

318

Mesoscopic simulation of cell membrane damage, morphology change and rupture by nonionic surfactants.  

PubMed Central

A new simulation method, dissipative particle dynamics, is applied to model biological membranes. In this method, several atoms are united into a single simulation particle. The solubility and compressibility of the various liquid components are reproduced by the simulation model. When applied to a bilayer of phosphatidylethanolamine, the membrane structure obtained matches quantitatively with full atomistic simulations and with experiments reported in the literature. The method is applied to investigate the cause of cell death when bacteria are exposed to nonionic surfactants. Mixed bilayers of lipid and nonionic surfactant were studied, and the diffusion of water through the bilayer was monitored. Small transient holes are seen to appear at 40% mole-fraction C(9)E(8), which become permanent holes between 60 and 70% surfactant. When C(12)E(6) is applied, permanent holes only arise at 90% mole-fraction surfactant. Some simulations have been carried out to determine the rupture properties of mixed bilayers of phosphatidylethanolamine and C(12)E(6). These simulations indicate that the area of a pure lipid bilayer can be increased by a factor 2. The inclusion of surfactant considerably reduces both the extensibility and the maximum stress that the bilayer can withstand. This may explain why dividing cells are more at risk than static cells. PMID:11463621

Groot, R D; Rabone, K L

2001-01-01

319

Synthesis and characterization of Nafion/TiO2 nanocomposite membrane for proton exchange membrane fuel cell.  

PubMed

In this study, the syntheses and characterizations of Nafion/TiO2 membranes for a proton exchange membrane fuel cell (PEMFC) were investigated. Porous TiO2 powders were synthesized using the sol-gel method; with Nafion/TiO2 nanocomposite membranes prepared using the casting method. An X-ray diffraction analysis demonstrated that the synthesized TiO2 had an anatase structure. The specific surface areas of the TiO2 and Nafion/TiO2 nanocomposite membrane were found to be 115.97 and 33.91 m2/g using a nitrogen adsorption analyzer. The energy dispersive spectra analysis indicated that the TiO2 particles were uniformly distributed in the nanocomposite membrane. The membrane electrode assembly prepared from the Nafion/TiO2 nanocomposite membrane gave the best PEMFC performance compared to the Nafion/P-25 and Nafion membranes. PMID:22103220

Kim, Tae Young; Cho, Sung Yong

2011-08-01

320

Novel phosphoric acid doped polybenzimidazole membranes for fuel cells  

NASA Astrophysics Data System (ADS)

Acid doped polybenzimidazole (PBIRTM, called mPBI in this thesis) membranes are applied as electrolytes in high temperature polymer electrolyte membrane fuel cells (PEMFCs). Several series of homopolymers and copolymers with high I.V. were synthesized in PPA solution. A novel membrane fabrication and acid doping process, called the PPA process, was developed by casting the polymer-polyphosphoric acid (PPA) solution directly after polymerization without isolation or redissolution of the polymers. The PPA absorbed moisture from the atmosphere and hydrolyzed to phosphoric acid, which induced a sol-gel transition and produced a high acid doped PBI membrane. A water spray method was developed to make an acid doped ABPBI membrane by spraying water or dilute phosphoric acid onto the cast solution directly. This process induced film formation for ABPBI, but washed out most of the phosphoric acid dopant. A more rigid pPBI homopolymer was synthesized in PPA solution with high inherent viscosity (2˜3 dL/g). Acid doped pPBI membranes showed high acid doping level (pPBI·69H3PO4) and high conductivity (0.24 S/cm at 160°C). Fuel cells based on pPBI/PA showed good performance at various conditions. For example, a fuel cell based on pPBI/PA showed a maximum power density of 0.92 W/cm2 at 160°C and ambient pressure (H2/O2). The degradation rate of the cell potential was -21 mV/1,000 hours and -35 mV/1,000 hours at 160°C and 180°C, respectively in continuous testing. Fuel cells also showed good performance and tolerance to carbon monoxide poisoning when operated at temperatures higher than 120°C. The voltage drop was only 31 mV (from 0.657 V to 0.626 V at 0.3 A/cm2) when reformate gas (40.0% H2, 0.2% CO, 19.0% CO2, 40.8% N2) was used instead of pure hydrogen at one atmosphere pressure and 160°C. The structure-property relationships were investigated on the homopolymers and copolymers with different rigidities in the main chain. It is found that para-oriented structures greatly improved the mechanical properties, retained more acid in the membrane and showed higher fuel cell performance.

Zhang, Haifeng

321

Human T cell crosstalk is induced by tumor membrane transfer.  

PubMed

Trogocytosis is a contact-dependent unidirectional transfer of membrane fragments between immune effector cells and their targets, initially detected in T cells following interaction with professional antigen presenting cells (APC). Previously, we have demonstrated that trogocytosis also takes place between melanoma-specific cytotoxic T lymphocytes (CTLs) and their cognate tumors. In the present study, we took this finding a step further, focusing on the ability of melanoma membrane-imprinted CD8+ T cells to act as APCs (CD8+T-APCs). We demonstrate that, following trogocytosis, CD8+T-APCs directly present a variety of melanoma derived peptides to fraternal T cells with the same TCR specificity or to T cells with different TCRs. The resulting T cell-T cell immune synapse leads to (1) Activation of effector CTLs, as determined by proliferation, cytokine secretion and degranulation; (2) Fratricide (killing) of CD8+T-APCs by the activated CTLs. Thus, trogocytosis enables cross-reactivity among CD8+ T cells with interchanging roles of effectors and APCs. This dual function of tumor-reactive CTLs may hint at their ability to amplify or restrict reactivity against the tumor and participate in modulation of the anti-cancer immune response. PMID:25671577

Uzana, Ronny; Eisenberg, Galit; Merims, Sharon; Frankenburg, Shoshana; Pato, Aviad; Yefenof, Eitan; Engelstein, Roni; Peretz, Tamar; Machlenkin, Arthur; Lotem, Michal

2015-01-01

322

Block copolymers for alkaline fuel cell membrane materials  

NASA Astrophysics Data System (ADS)

Alkaline fuel cells (AFCs) using anion exchange membranes (AEMs) as electrolyte have recently received considerable attention. AFCs offer some advantages over proton exchange membrane fuel cells, including the potential of non-noble metal (e.g. nickel, silver) catalyst on the cathode, which can dramatically lower the fuel cell cost. The main drawback of traditional AFCs is the use of liquid electrolyte (e.g. aqueous potassium hydroxide), which can result in the formation of carbonate precipitates by reaction with carbon dioxide. AEMs with tethered cations can overcome the precipitates formed in traditional AFCs. Our current research focuses on developing different polymer systems (blend, block, grafted, and crosslinked polymers) in order to understand alkaline fuel cell membrane in many aspects and design optimized anion exchange membranes with better alkaline stability, mechanical integrity and ionic conductivity. A number of distinct materials have been produced and characterized. A polymer blend system comprised of poly(vinylbenzyl chloride)-b-polystyrene (PVBC-b-PS) diblock copolymer, prepared by nitroxide mediated polymerization (NMP), with poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) or brominated PPO was studied for conversion into a blend membrane for AEM. The formation of a miscible blend matrix improved mechanical properties while maintaining high ionic conductivity through formation of phase separated ionic domains. Using anionic polymerization, a polyethylene based block copolymer was designed where the polyethylene-based block copolymer formed bicontinuous morphological structures to enhance the hydroxide conductivity (up to 94 mS/cm at 80 °C) while excellent mechanical properties (strain up to 205%) of the polyethylene block copolymer membrane was observed. A polymer system was designed and characterized with monomethoxy polyethylene glycol (mPEG) as a hydrophilic polymer grafted through substitution of pendent benzyl chloride groups of a PVBC-b-PS. The incorporation of the hydrophilic polymer allows for an investigation of the effect of hydration on ionic conductivity, resulting in the increase in membrane water affinity, enhancement of conductivity and reduced dependence of conductivity on relative humidity. A study of crosslinking of block copolymers was done wherein the crosslinking occurs in the non-matrix phase in order to maintain mechanical properties. The formation of a cationic crosslinked structure improves the mechanical integrity of the membrane in water while showing little deleterious effect on ionic conductivity and mechanical properties.

Li, Yifan

323

Influence of water and membrane microstructure on the transport properties of proton exchange membrane fuel cells  

NASA Astrophysics Data System (ADS)

Proton transport in proton exchange membranes (PEMs) depends on interaction between water and acid groups covalently bound to the polymer. Although the presence of water is important in maintaining the PEM's functions, a thorough understanding of this topic is still lacking. The objective of this work is to provide a better understanding of how the nature water, confined to ionic domains of the polymer, influences the membrane's ability to transport protons, methanol and water. Understanding this topic will facilitate development of new materials with favorable transport properties for fuel cells use. Five classes of polymer membranes were used in this work: polyacrylonitrile-graft-poly(styrenesulfonic) acid (PAN-g-macPSSA); poly(vinylidene difluoride) irradiation-graft-poly(styrenesulfonic) acid (PVDF-g-PSSA); poly(ethylenetetrafluoroethylene) irradiation-graft-poly(styrenesulfonic) acid (ETFE-gPSSA); PVDF-g-PSSA with hydroxyethylmethacrylate (HEMA); and perfluorosulfonic acid membrane (Nafion). The nature of water within the polymers (freezable versus non-freezable states) was measured by systematically freezing samples, and observing the temperature at which water freezes and the amount of heat released in the process. Freezing water-swollen membranes resulted in a 4-fold decrease in the proton conductivity of the PEM. Activation energies of proton transport before and after freezing were ˜ 0.15 eV and 0.5 eV, consistent with proton transport through liquid water and bound water, respectively. Reducing the content of water in membrane samples decreased the amount of freezable and non-freezable water. Calorimetric measurements of membranes in various degrees of hydration showed that water molecules became non-freezable when lambda, (water molecules per sulfonic acid group) was less than ˜14. Proton conduction through membranes containing only non-freezable water was demonstrated to be feasible. Diffusion experiments showed that the permeability of methanol decreased when the content of free water in the membranes decreased. Variation in permeability trends observed for the different polymer classes of the same content of free water was explained on the basis of tortuosity and interaction of methanol within the ionic network. Finally, a novel set of polymers containing non-ionic hydrophilic segments were examined for enhanced water transport in order to see if such domains might offset the flux of water due to electro-osmosis.

Siu, Ana Rosa

324

FtsL, an Essential Cytoplasmic Membrane Protein Involved in Cell Division in Escherichia coli  

PubMed Central

We have identified a gene involved in bacterial cell division, located immediately upstream of the ftsI gene in the min 2 region of the Escherichia coli chromosome. This gene, which we named ftsL, was detected through characterization of TnphoA insertions in a plasmid containing this chromosomal region. TnphoA topological analysis and fractionation of alkaline phosphatase fusion proteins indicated that the ftsL gene product is a 13.6-kDa cytoplasmic membrane protein with a cytoplasmic amino terminus, a single membrane-spanning segment, and a periplasmic carboxy terminus. The ftsL gene is essential for cell growth and division. A null mutation in ftsL resulted in inhibition of cell division, formation of long, nonseptate filaments, ultimate cessation of growth, and lysis. Under certain growth conditions, depletion of FtsL or expression of the largest ftsL-phoA fusion produced a variety of cell morphologies, including Y-shaped bacteria, indicating a possible general weakening of the cell wall. The FtsL protein is estimated to be present at about 20 to 40 copies per cell. The periplasmic domain of the protein displays a sequence with features characteristic of leucine zippers, which are involved in protein dimerization. Images PMID:1332942

Guzman, Luz-Maria; Barondess, James J.; Beckwith, Jon

1992-01-01

325

Regulation of nitrite transport in red blood cells by hemoglobin oxygen fractional saturation  

PubMed Central

Allosteric regulation of nitrite reduction by deoxyhemoglobin has been proposed to mediate nitric oxide (NO) formation during hypoxia. Nitrite is predominantly an anion at physiological pH, raising questions about the mechanism by which it enters the red blood cell (RBC) and whether this is regulated and coupled to deoxyhemoglobin-mediated reduction. We tested the hypothesis that nitrite transport by RBCs is regulated by fractional saturation. Using human RBCs, nitrite consumption was faster at lower fractional saturations, consistent with faster reactions with deoxyheme. A membrane-based regulation was suggested by slower nitrite consumption with intact versus lysed RBCs. Interestingly, upon nitrite addition, intracellular nitrite concentrations attained a steady state that, despite increased rates of consumption, did not change with decreasing oxygen tensions, suggesting a deoxygenation-sensitive step that either increases nitrite import or decreases the rate of nitrite export. A role for anion exchanger (AE)-1 in the control of nitrite export was suggested by increased intracellular nitrite concentrations in RBCs treated with DIDS. Moreover, deoxygenation decreased steady-state levels of intracellular nitrite in AE-1-inhibited RBCs. Based on these data, we propose a model in which deoxyhemoglobin binding to AE-1 inhibits nitrite export under low oxygen tensions allowing for the coupling between deoxygenation and nitrite reduction to NO along the arterial-to-venous gradient. PMID:19286940

Vitturi, Dario A.; Teng, Xinjun; Toledo, José C.; Matalon, Sadis; Lancaster, Jack R.; Patel, Rakesh P.

2009-01-01

326

Amniotic membrane-derived cells inhibit proliferation of cancer cell lines by inducing cell cycle arrest  

PubMed Central

Cells derived from the amniotic foetal membrane of human term placenta have drawn particular attention mainly for their plasticity and immunological properties, which render them interesting for stem-cell research and cell-based therapeutic applications. In particular, we have previously demonstrated that amniotic mesenchymal tissue cells (AMTC) inhibit lymphocyte proliferation in vitro and suppress the generation and maturation of monocyte-derived dendritic cells. Here, we show that AMTC also significantly reduce the proliferation of cancer cell lines of haematopoietic and non-haematopoietic origin, in both cell–cell contact and transwell co-cultures, therefore suggesting the involvement of yet-unknown inhibitory soluble factor(s) in this ‘cell growth restraint’. Importantly, we provide evidence that the anti-proliferative effect of AMTC is associated with induction of cell cycle arrest in G0/G1 phase. Gene expression analyses demonstrate that AMTC can down-regulate cancer cells' mRNA expression of genes associated with cell cycle progression, such as cyclins (cyclin D2, cyclin E1, cyclin H) and cyclin-dependent kinase (CDK4, CDK6 and CDK2), whilst they up-regulate cell cycle negative regulator such as p15 and p21, consistent with a block in G0/G1 phase with no progression to S phase. Taken together, these findings warrant further studies to investigate the applicability of these cells for controlling cancer cell proliferation in vivo. PMID:22260183

Magatti, Marta; Munari, Silvia; Vertua, Elsa; Parolini, Ornella

2012-01-01

327

A polybenzimidazole/ionic-liquid-graphite-oxide composite membrane for high temperature polymer electrolyte membrane fuel cells  

NASA Astrophysics Data System (ADS)

Graphite oxide is successfully functionalised by 3-aminopropyltriethoxysilane ionic liquid and used as a filler material in a polybenzimidazole (PBI) membrane for high temperature proton exchange membrane fuel cells. The ionic-liquid-graphite-oxide/polybenzimidazole (ILGO/PBI) composite membrane exhibits an appropriate level of proton conductivity when imbibed with phosphoric acid at low phosphoric acid loading, which promotes its use in fuel cells by avoiding acid leakage and materials corrosion. The ionic conductivities of the ILGO/PBI membranes at 175 °C are 0.035 S cm-1 and 0.025 S cm-1 at per repeat units of 3.5 and 2.0, respectively. The fuel cell performance of ILGO/PBI membranes exhibits a maximum power density of 320 mW cm-2 at 175 °C, which is higher than that of a pristine PBI membrane.

Xu, Chenxi; Liu, Xiaoteng; Cheng, Jigui; Scott, Keith

2015-01-01

328

Use the force: Membrane tension as an organizer of cell shape and motility  

PubMed Central

Many cell phenomena that involve shape changes are affected by the intrinsic deformability of the plasma membrane. Far from being a passive participant, the plasma membrane is now known to physically, as well as biochemically, influence cell processes ranging from vesicle trafficking to actin assembly. Here we review current understanding of how changes in plasma membrane tension regulate cell shape and movement as well as how cells sense plasma membrane tension. PMID:23122885

Diz-Muñoz, Alba; Fletcher, Daniel A.; Weiner, Orion D.

2012-01-01

329

Cell Component Accelerated Stress Test and Polarization Curve Protocols for Polymer Electrolyte Membrane Fuel Cells  

NSDL National Science Digital Library

This document contains test protocols to determine the performance and durability of fuel cell components such as electrocatalysts and supports, membranes, and membrane electrode assemblies (MEAs). These protocols were established with the intent to be used as a common industry standard when assessing durability of different polymer electrolyte membranes (PEM) in fuel cells for automotive applications and to be compared against DOE and FreedomCar targets. The resulting data may also help to model the performance of the fuel cell under variable load conditions and the effects of ageing on performance.

2013-10-28

330

Translocation of an Aib-containing peptide through cell membranes.  

PubMed

The biophysical characteristics and channel-forming activity of peptaibols inserted into artificial membranes have been studied over the last 30 years. However, to our knowledge, no studies have addressed directly their behavior in living cells. In this work, a novel strategy has been employed to precisely assess the living cell membrane-penetrating activity of a fluorescein-labeled Aib (alpha-aminoisobutyric acid)-containing peptide derived from a peptaibol, trichorovin-XIIa (TV-XIIa). We have demonstrated for the first time that the peptide containing an unusual amino acid residue, Aib, is taken up by cells via a non endocytic pathway. The replacement of Aib in the TV-XIIa sequence with Ala inhibits the cellular uptake. PMID:18565748

Wada, Shun-ichi; Hitora, Yasunari; Tanaka, Reiko; Urata, Hidehito

2008-07-15

331

Stimulation of erythrocyte cell membrane scrambling by nystatin.  

PubMed

The antifungal ionophore nystatin dissipates the Na(+) and K(+) gradients across the cell membrane, leading to cellular gain of Na(+) and cellular loss of K(+) . The increase of cellular Na(+) concentration may result in Ca(2+) accumulation in exchange for Na(+) . Increase of cytosolic Ca(2+) activity ([Ca(2+) ]i ) and loss of cellular K(+) foster apoptosis-like suicidal erythrocyte death or eryptosis, which is characterised by cell shrinkage and cell membrane scrambling leading to phosphatidylserine exposure at the erythrocyte surface. The present study explored whether nystatin stimulates eryptosis. Cell volume was estimated from forward scatter (FSC), phosphatidylserine exposure from annexin V binding and [Ca(2+) ]i from Fluo3-fluorescence in flow cytometry. A 48-hr exposure to nystatin (15 ?g/ml) was followed by a significant increase of [Ca(2+) ]i , a significant increase of annexin V binding and a significant decrease of FSC. The annexin V binding after nystatin treatment was significantly blunted in the nominal absence of extracellular Ca(2+) . Partial replacement of extracellular Na(+) with extracellular K(+) blunted the nystatin-induced erythrocyte shrinkage but increased [Ca(2+) ]i and annexin V binding. Nystatin triggers cell membrane scrambling, an effect at least partially due to entry of extracellular Ca(2+) . PMID:24894380

Malik, Abaid; Bissinger, Rosi; Jilani, Kashif; Lang, Florian

2015-01-01

332

Stem cell differentiation increases membrane-actin adhesion regulating cell blebability, migration and mechanics  

PubMed Central

This study examines how differentiation of human mesenchymal stem cells regulates the interaction between the cell membrane and the actin cortex controlling cell behavior. Micropipette aspiration was used to measure the pressure required for membrane-cortex detachment which increased from 0.15?kPa in stem cells to 0.71?kPa following chondrogenic differentiation. This effect was associated with reduced susceptibility to mechanical and osmotic bleb formation, reduced migration and an increase in cell modulus. Theoretical modelling of bleb formation demonstrated that the increased stiffness of differentiated cells was due to the increased membrane-cortex adhesion. Differentiated cells exhibited greater F-actin density and slower actin remodelling. Differentiated cells also expressed greater levels of the membrane-cortex ezrin, radixin, moeisin (ERM) linker proteins which was responsible for the reduced blebability, as confirmed by transfection of stem cells with dominant active ezrin-T567D-GFP. This study demonstrates that stem cells have an inherently weak membrane-cortex adhesion which increases blebability thereby regulating cell migration and stiffness. PMID:25471686

Sliogeryte, Kristina; Thorpe, Stephen D.; Lee, David A.; Botto, Lorenzo; Knight, Martin M.

2014-01-01

333

Creating Transient Cell Membrane Pores Using a Standard Inkjet Printer  

PubMed Central

Bioprinting has a wide range of applications and significance, including tissue engineering, direct cell application therapies, and biosensor microfabrication.1-10 Recently, thermal inkjet printing has also been used for gene transfection.8,9 The thermal inkjet printing process was shown to temporarily disrupt the cell membranes without affecting cell viability. The transient pores in the membrane can be used to introduce molecules, which would otherwise be too large to pass through the membrane, into the cell cytoplasm.8,9,11 The application being demonstrated here is the use of thermal inkjet printing for the incorporation of fluorescently labeled g-actin monomers into cells. The advantage of using thermal ink-jet printing to inject molecules into cells is that the technique is relatively benign to cells.8, 12 Cell viability after printing has been shown to be similar to standard cell plating methods1,8. In addition, inkjet printing can process thousands of cells in minutes, which is much faster than manual microinjection. The pores created by printing have been shown to close within about two hours. However, there is a limit to the size of the pore created (~10 nm) with this printing technique, which limits the technique to injecting cells with small proteins and/or particles. 8,9,11 A standard HP DeskJet 500 printer was modified to allow for cell printing.3, 5, 8 The cover of the printer was removed and the paper feed mechanism was bypassed using a mechanical lever. A stage was created to allow for placement of microscope slides and coverslips directly under the print head. Ink cartridges were opened, the ink was removed and they were cleaned prior to use with cells. The printing pattern was created using standard drawing software, which then controlled the printer through a simple print command. 3T3 fibroblasts were grown to confluence, trypsinized, and then resuspended into phosphate buffered saline with soluble fluorescently labeled g-actin monomers. The cell suspension was pipetted into the ink cartridge and lines of cells were printed onto glass microscope cover slips. The live cells were imaged using fluorescence microscopy and actin was found throughout the cytoplasm. Incorporation of fluorescent actin into the cell allows for imaging of short-time cytoskeletal dynamics and is useful for a wide range of applications.13-15 PMID:22453577

Owczarczak, Alexander B.; Shuford, Stephen O.; Wood, Scott T.; Deitch, Sandra; Dean, Delphine

2012-01-01

334

Research Paper New uorescent probes for the measurement of cell membrane  

E-print Network

Research Paper New £uorescent probes for the measurement of cell membrane viscosity Mark A: The modification of molecular rotors towards increased cell membrane association provides a new research tool cells in patients with Alzheimer's disease [11,12]. Increased membrane vis- cosity is also associated

Theodorakis, Emmanuel

335

Three steps in the anode reaction of the polymer electrolyte membrane fuel cell. Effect of CO  

E-print Network

Three steps in the anode reaction of the polymer electrolyte membrane fuel cell. Effect of CO Anne in the polymer electrolyte membrane fuel cell (PEMFC) using electrochemical impedance spectroscopy (EIS mechanism 1. Introduction In the polymer electrolyte membrane fuel cell (PEMFC), the largest overpotential

Kjelstrup, Signe

336

Vaccinia Virus Interactions with the Cell Membrane Studied by New Chromatic Vesicle and Cell Sensor Assays  

Microsoft Academic Search

The potential danger of cross-species viral infection points to the significance of understanding the contri- butions of nonspecific membrane interactions with the viral envelope compared to receptor-mediated uptake as a factor in virus internalization and infection. We present a detailed investigation of the interactions of vaccinia virus particles with lipid bilayers and with epithelial cell membranes using newly developed chromatic

Z. Orynbayeva; S. Kolusheva; N. Groysman; N. Gavrielov; L. Lobel; R. Jelinek

2007-01-01

337

Fractional Proliferation: A method to deconvolve cell population dynamics from single-cell data  

PubMed Central

We present an integrated method that exploits extended time-lapse automated imaging to quantify dynamics of cell proliferation. Cell counts are fit with a Quiescence-Growth model that estimates rates of cell division, entry into quiescence and death. The model is constrained with rates extracted experimentally from the behavior of tracked single cells over time. We visualize the output of the analysis in Fractional Proliferation graphs, which deconvolve dynamic proliferative responses to perturbations into the relative contributions of dividing, quiescent (non-dividing) and dead cells. The method reveals that the response of “oncogene-addicted” human cancer cells to tyrosine kinase inhibitors is a composite of altered rates of division, death and entry into quiescence, challenging the notion that such cells simply ‘die’ in response to oncogene-targeted therapy. PMID:22886092

Tyson, Darren R.; Garbett, Shawn P.; Frick, Peter L.; Quaranta, Vito

2012-01-01

338

Rapid determination of membrane transport parameters in adherent cells.  

PubMed

Reported here is a new method that permits rapid (approximately 5 s) determinations of membrane transport phenomena in cells grown in monolayers at the base of 17-mm glass scintillation vials. The method is convenient, cost effective and requires no special apparatus. Initial uptake rates, steady-state and free substrate levels are demonstrated in ZR-75-1 breast cancer and Chinese hamster ovary cell lines using methotrexate, a model agent transported by the reduced folate carrier. The technique should be applicable to the study of the transport properties in a broad range of substrates and cells in monolayer culture. PMID:10818699

Sharif, K A; Goldman, I D

2000-05-01

339

Xanthine oxidase-catalyzed crosslinking of cell membrane proteins.  

PubMed

Isolated erythrocyte membranes exposed to protease-free xanthine oxidase plus xanthine and ferric iron undergo lipid peroxidation and protein crosslinking (appearance of high molecular weight aggregates on sodium dodecyl sulfate (SDS) gel electrophoresis). Spectrin is more susceptible to crosslinking than the other polypeptides. Thiol-reducible bonds (disulfides) as well as nonreducible bonds are generated, the former type relatively rapidly (detected within 10-20 min) and the latter type more slowly (usually detected after 1 h). Reducible crosslinking is inhibited by catalase, but not by superoxide dismutase, desferrioxamine, butylated hydroxyltoluene, and mannitol; whereas nonreducible crosslinking, like free radical lipid peroxidation, is inhibited by all of these agents except mannitol. Zinc(II) also inhibits lipid peroxidation, but stimulates disulfide bond formation to the virtual exclusion of all other crosslinking. Our results indicate that disulfide formation is dependent on H2O2, but not O2- or iron. However, O2-, H2O2, and iron are all required for lipid peroxidation and nondisulfide crosslinking, suggesting the intermediacy of OH generated via the iron-catalyzed Haber-Weiss reaction. The possible role of malonaldehyde (MDA, a by-product of lipid peroxidation) in the latter type of crosslinking was examined. Solubilized samples of xanthine/xanthine oxidase-treated membranes showed a strong visible fluorescence (emission maximum 450 nm; excitation 390 nm). This resembled the fluorescence of membranes treated with authentic MDA, which forms conjugated imine linkages between amino groups. Fluorescence scanning of SDS gels from MDA-treated membranes showed a strong signal coincident with crosslinked proteins and also one in the low molecular weight, nonprotein region, suggestive of aminolipid conjugates. Similar scanning on xanthine/xanthine oxidase-reacted membranes indicated that all fluorescence is associated with the lipid fraction. Thus, nonreducible protein crosslinks in this system do not appear to be of the MDA-derived, Schiff base type. PMID:3800391

Girotti, A W; Thomas, J P; Jordan, J E

1986-12-01

340

Membrane tether formation from outer hair cells with optical tweezers.  

PubMed Central

Optical tweezers were used to characterize the mechanical properties of the outer hair cell (OHC) plasma membrane by pulling tethers with 4.5-microm polystyrene beads. Tether formation force and tether force were measured in static and dynamic conditions. A greater force was required for tether formations from OHC lateral wall (499 +/- 152 pN) than from OHC basal end (142 +/- 49 pN). The difference in the force required to pull tethers is consistent with an extensive cytoskeletal framework associated with the lateral wall known as the cortical lattice. The apparent plasma membrane stiffness, estimated under the static conditions by measuring tether force at different tether length, was 3.71 pN/microm for OHC lateral wall and 4.57 pN/microm for OHC basal end. The effective membrane viscosity was measured by pulling tethers at different rates while continuously recording the tether force, and estimated in the range of 2.39 to 5.25 pN x s/microm. The viscous force most likely results from the viscous interactions between plasma membrane lipids and the OHC cortical lattice and/or integral membrane proteins. The information these studies provide on the mechanical properties of the OHC lateral wall is important for understanding the mechanism of OHC electromotility. PMID:11867454

Li, Zhiwei; Anvari, Bahman; Takashima, Masayoshi; Brecht, Peter; Torres, Jorge H; Brownell, William E

2002-01-01

341

BIOCHEMISTRY: Signaling Across the Cell Membrane  

NSDL National Science Digital Library

Access to the article is free, however registration and sign-in are required. Structural and functional studies shed light on how G protein-coupled receptors sense external stimuli. G protein-coupled receptors (GPCRs)--the largest and most diverse group of tranmembrane receptors--occur in nearly every eukaryotic cell and can sense photons, cations, small molecules, peptides, and proteins (1, 2). Two research articles in this issue (4, 5) and a recent article in Nature (6) report important steps towards understanding how GPCRs operate.

Rama Ranganathan (University of Texas Southwestern Medical Center; Green Center for Systems Biology and Department of Pharmacology)

2007-11-23

342

Comparison of cell membrane water permeability in monolayers and suspensions.  

PubMed

We previously measured the membrane water permeability of monolayers and suspensions of MIN6 mouse insulinoma cells at room temperature, and found that water transport was faster in monolayers. Here, we compare water transport kinetics in monolayers and suspensions over a range of temperatures for two different cell types, MIN6 cells and bovine pulmonary artery endothelial cells (BPAEC). At room temperature the results for BPAEC and MIN6 cells were similar, with approximately 2-fold faster water transport in monolayers than suspensions. The activation energy for water transport (Ea) was estimated from Arrhenius plots of the water permeability data. The values of Ea for monolayers and suspensions of MIN6 cells were not significantly different. However, the activation energy was significantly lower for BPAEC monolayers (Ea = 49 +/- 2 kJ per mol) than suspensions (Ea = 70 +/- 4 kJ per mol). Predictions of water transport during cryopreservation revealed substantial differences in supercooling between monolayers and suspensions. PMID:22576122

Higgins, Adam Z; Karlsson, Jens O M

2012-01-01

343

Anaerobic digestion of the organic fraction of municipal solid waste in a two-stage membrane process.  

PubMed

A batch of the Organic Fraction of Municipal Solid Waste (OFMSW) was treated in a two-step process with effluent recirculation comprising a novel hydrolytic reactor (HR) followed by a Submerged Anaerobic Membrane Bioreactor (SAMBR) operating at a stable permeate flux of 5.6 L/m(2) hr (LMH). A soluble COD removal higher than 95% was obtained from the SAMBR. The soluble COD as well as the Total Suspended Solids (TSS) did not build up due to efficient hydrolysis inside the SAMBR, and no VFA accumulation occurred due to the complete retention of methanogens by the membrane as well as the formation of syntrophic associations. Because of the microfiltration membrane in the second reactor a stabilized leachate was obtained from the very first days of the treatment and the highly stable process enabled shorter treatment periods compared to traditional leach bed processes. This experiment showed that the recycle of the stabilised leachate does not lead to a build up of SCOD. Size exclusion chromatography analysis confirmed that high molecular weight compounds were completely degraded and did not appear in the SAMBR permeate, and that low molecular weight fulvic-like and medium MW material were present in the permeate of the SAMBR but their concentration remained stable with time. PMID:19844043

Trzcinski, A P; Stuckey, D C

2009-01-01

344

Nafion/silane nanocomposite membranes for high temperature polymer electrolyte membrane fuel cell.  

PubMed

The polymer electrolyte membrane fuel cell (PEMFC) has been studied actively for both potable and stationary applications because it can offer high power density and be used only hydrogen and oxygen as environment-friendly fuels. Nafion which is widely used has mechanical and chemical stabilities as well as high conductivity. However, there is a drawback that it can be useless at high temperatures (> or = 90 degrees C) because proton conducting mechanism cannot work above 100 degrees C due to dehydration of membrane. Therefore, PEMFC should be operated for long-term at high temperatures continuously. In this study, we developed nanocomposite membrane using stable properties of Nafion and phosphonic acid groups which made proton conducting mechanism without water. 3-Aminopropyl triethoxysilane (APTES) was used to replace sulfonic acid groups of Nafion and then its aminopropyl group was chemically modified to phosphonic acid groups. The nanocomposite membrane showed very high conductivity (approximately 0.02 S/cm at 110 degrees C, <30% RH). PMID:22121602

Ghi, Lee Jin; Park, Na Ri; Kim, Moon Sung; Rhee, Hee Woo

2011-07-01

345

hERG ion channel pharmacology: cell membrane liposomes in porous-supported lipid bilayers compared with whole-cell patch-clamping.  

PubMed

The purpose of this study was to obtain functional hERG ion channel protein for use in a non-cell-based ion channel assay. hERG was expressed in Sf9 insect cells. Attempts to solubilise the hERG protein from Sf9 insect cell membranes using non-ionic detergents (NP40 and DDM) were not successful. We therefore generated liposomes from the unpurified membrane fraction and incorporated these into porous Teflon-supported bilayer lipid membranes. Macroscopic potassium currents (1 nA) were recorded that approximated those in whole-cell patch-clamping, but the channels were bidirectional in the bilayer lipid membrane (BLM). Currents were partially inhibited by the hERG blockers E4031, verapamil, and clofilium, indicating that the protein of interest is present at high levels in the BLM relative to endogenous channels. Cell liposomes produced from Sf9 insect cell membranes expressing voltage-gated sodium channels also gave current responses that were activated by veratridine and inhibited by saxitoxin. These results demonstrate that purification of the ion channel of interest is not always necessary for liposomes used in macro-current BLM systems. PMID:22936309

Zhang, Yanli; Phung, Thai; Dunlop, James; Dalziel, Julie

2012-11-01

346

Membrane associated qualitative differences in cell ultrastructure of chemically and high pressure cryofixed plant cells.  

PubMed

Membrane contrast can sometimes be poor in biological samples after high pressure freezing (HPF) and freeze substitution (FS). The addition of water to the FS-medium has been shown to improve membrane contrast in animal tissue and yeast. In the present study we tested the effects of 1% and 5% water added to the FS-medium (2% osmium with 0.2% uranyl acetate in anhydrous acetone) on the quality and visibility of membranes in high pressure frozen leaf samples of Cucurbita pepo L. plants and compared them to chemically fixed cells (3% glutaraldehyde post-fixed with 1% osmium tetroxide). The addition of water to the FS-medium drastically decreased the amounts of well preserved cells and did not significantly improve the quality nor visibility of membranes. In samples that were freeze substituted in FS-media containing 1% and 5% water the width of thylakoid membranes was found to be significantly increased of about 20% and the perinuclear space was up to 76% wider in comparison to what was found in samples which were freeze substituted without water. No differences were found in the thickness of membranes between chemically and cryofixed cells that were freeze substituted in the FS-medium without water. Nevertheless, in chemically fixed cells the intrathylakoidal space was about 120% wider than in cryofixed cells that were freeze substituted with or without water. The present results demonstrate that the addition of water to the FS-medium does not improve membrane contrast but changes the width of thylakoid membranes and the perinuclear space in the present plant material. The addition of water to the FS-medium is therefore not as essential for improved membrane contrast in the investigated plant samples as it was observed in cells of animal tissues and yeast cells. PMID:17270463

Zechmann, Bernd; Müller, Maria; Zellnig, Günther

2007-06-01

347

Fluconazole treatment hyperpolarizes the plasma membrane of Candida cells.  

PubMed

Five pathogenic Candida species were compared in terms of their osmotolerance, tolerance to toxic sodium and lithium cations, and resistance to fluconazole. The species not only differed, in general, in their tolerance to high osmotic pressure (C. albicans and C. parapsilosis being the most osmotolerant) but exhibited distinct sensitivities to toxic sodium and lithium cations, with C. parapsilosis and C. tropicalis being very tolerant but C. krusei and C. dubliniensis sensitive to LiCl. The treatment of both fluconazole-susceptible (C. albicans and C. parapsilosis) and fluconazole-resistant (C. dubliniensis, C. krusei and C. tropicalis) growing cells with subinhibitory concentrations of fluconazole resulted in substantially elevated intracellular Na(+) levels. Using a diS-C3(3) assay, for the first time, to monitor the relative membrane potential (??) of Candida cells, we show that the fluconazole treatment of growing cells of all five species results in a substantial hyperpolarization of their plasma membranes, which is responsible for an increased non-specific transport of toxic alkali metal cations and other cationic drugs (e.g., hygromycin B). Thus, the combination of relatively low doses of fluconazole and drugs, whose import into the tested Candida strains is driven by the cell membrane potential, might be especially potent in terms of its ability to inhibit the growth of or even kill various Candida species. PMID:23547882

Elicharova, Hana; Sychrova, Hana

2013-11-01

348

Sequential CD34 cell fractionation by magnetophoresis in a magnetic dipole flow sorter  

PubMed Central

Cell separation and fractionation based on fluorescent and magnetic labeling procedures are common tools in contemporary research. These techniques rely on binding of fluorophores or magnetic particles conjugated to antibodies to target cells. Cell surface marker expression levels within cell populations vary with progression through the cell cycle. In an earlier work we showed the reproducible magnetic fractionation (single pass) of the Jurkat cell line based on the population distribution of CD45 surface marker expression. Here we present a study on magnetic fractionation of a stem and progenitor cell (SPC) population using the established acute myelogenous leukemia cell line KG-1a as a cell model. The cells express a CD34 cell surface marker associated with the hematopoietic progenitor cell activity and the progenitor cell lineage commitment (related to the CD34 marker expression level). The CD34 expression level is approximately an order of magnitude lower than that of the CD45 marker, which required further improvements of the magnetic fractionation apparatus. The cells were immuno-magnetically labeled using a sandwich of anti CD34 antibody-phycoerythrin (PE) conjugate and anti PE magnetic nanobead and fractionated into eight components using a continuous flow dipole magnetophoresis apparatus. The CD34 marker expression distribution between sorted fractions was measured by quantitative PE flow cytometry (using QuantiBRITE™ PE calibration beads), and it was shown to be correlated with the cell magnetophoretic mobility distribution. A flow outlet addressing scheme based on the concept of the transport lamina thickness was used to control cell distribution between the eight outlet ports. The fractional cell distributions showed good agreement with numerical simulations of the fractionation based on the cell magnetophoretic mobility distribution in the unsorted sample. PMID:20024182

Schneider, Thomas; Karl, Stephan; Moore, Lee R.; Chalmers, Jeffrey J.; Williams, P. Stephen; Zborowski, Maciej

2010-01-01

349

Tetraspanins regulate the protrusive activities of cell membrane  

SciTech Connect

Highlights: Black-Right-Pointing-Pointer Tetraspanins regulate microvillus formation. Black-Right-Pointing-Pointer Tetraspanin CD81 promotes microvillus formation. Black-Right-Pointing-Pointer Tetraspanin CD82 inhibits microvillus formation. Black-Right-Pointing-Pointer Based on this study, we extrapolated a general cellular mechanism for tetraspanins. Black-Right-Pointing-Pointer Tetraspanins engage various functions by regulating membrane protrusion morphogenesis. -- Abstract: Tetraspanins have gained increased attention due to their functional versatility. But the universal cellular mechanism that governs such versatility remains unknown. Herein we present the evidence that tetraspanins CD81 and CD82 regulate the formation and/or development of cell membrane protrusions. We analyzed the ultrastructure of the cells in which a tetraspanin is either overexpressed or ablated using transmission electron microscopy. The numbers of microvilli on the cell surface were counted, and the radii of microvillar tips and the lengths of microvilli were measured. We found that tetraspanin CD81 promotes the microvillus formation and/or extension while tetraspanin CD82 inhibits these events. In addition, CD81 enhances the outward bending of the plasma membrane while CD82 inhibits it. We also found that CD81 and CD82 proteins are localized at microvilli using immunofluorescence. CD82 regulates microvillus morphogenesis likely by altering the plasma membrane curvature and/or the cortical actin cytoskeletal organization. We predict that membrane protrusions embody a common morphological phenotype and cellular mechanism for, at least some if not all, tetraspanins. The differential effects of tetraspanins on microvilli likely lead to the functional diversification of tetraspanins and appear to correlate with their functional propensity.

Bari, Rafijul [Cancer Center and Department of Medicine, University of Tennessee, Memphis, TN (United States)] [Cancer Center and Department of Medicine, University of Tennessee, Memphis, TN (United States); Guo, Qiusha [Cancer Center and Department of Medicine, University of Tennessee, Memphis, TN (United States) [Cancer Center and Department of Medicine, University of Tennessee, Memphis, TN (United States); Zhongnan Hospital, Wuhan University, Wuhan (China); Xia, Bing [Zhongnan Hospital, Wuhan University, Wuhan (China)] [Zhongnan Hospital, Wuhan University, Wuhan (China); Zhang, Yanhui H. [Cancer Center and Department of Medicine, University of Tennessee, Memphis, TN (United States)] [Cancer Center and Department of Medicine, University of Tennessee, Memphis, TN (United States); Giesert, Eldon E. [Department of Ophthalmology, University of Tennessee, Memphis, TN (United States)] [Department of Ophthalmology, University of Tennessee, Memphis, TN (United States); Levy, Shoshana [Department of Medicine, Stanford University, Palo Alto, CA (United States)] [Department of Medicine, Stanford University, Palo Alto, CA (United States); Zheng, Jie J. [Department of Structural Biology, St. Jude Children's Research Hospital, Memphis, TN (United States)] [Department of Structural Biology, St. Jude Children's Research Hospital, Memphis, TN (United States); Zhang, Xin A., E-mail: xzhang@uthsc.edu [Cancer Center and Department of Medicine, University of Tennessee, Memphis, TN (United States)

2011-12-02

350

Low copy numbers of DC-SIGN in cell membrane microdomains: implications for structure and function.  

PubMed

Presently, there are few estimates of the number of molecules occupying membrane domains. Using a total internal reflection fluorescence microscopy (TIRFM) imaging approach, based on comparing the intensities of fluorescently labeled microdomains with those of single fluorophores, we measured the occupancy of DC-SIGN, a C-type lectin, in membrane microdomains. DC-SIGN or its mutants were labeled with primary monoclonal antibodies (mAbs) in either dendritic cells (DCs) or NIH3T3 cells, or expressed as GFP fusions in NIH3T3 cells. The number of DC-SIGN molecules per microdomain ranges from only a few to over 20, while microdomain dimensions range from the diffraction limit to > 1 µm. The largest fraction of microdomains, appearing at the diffraction limit, in either immature DCs or 3 T3 cells contains only 4-8 molecules of DC-SIGN, consistent with our preliminary super-resolution Blink microscopy estimates. We further show that these small assemblies are sufficient to bind and efficiently internalize a small (? 50 nm) pathogen, dengue virus, leading to infection of host cells. PMID:24313910

Liu, Ping; Wang, Xiang; Itano, Michelle S; Neumann, Aaron K; de Silva, Aravinda M; Jacobson, Ken; Thompson, Nancy L

2014-02-01

351

CLN3 Loss Disturbs Membrane Microdomain Properties and Protein Transport in Brain Endothelial Cells  

PubMed Central

Juvenile neuronal ceroid lipofuscinosis (JNCL) is a fatal childhood-onset neurodegenerative disorder caused by mutations in ceroid lipofuscinosis neuronal-3 (CLN3), a hydrophobic transmembrane protein of unresolved function. Previous studies indicate blood–brain barrier (BBB) defects in JNCL, and our earlier report showed prominent Cln3 expression in mouse brain endothelium. Here we find that CLN3 is necessary for normal trafficking of the microdomain-associated proteins caveolin-1, syntaxin-6, and multidrug resistance protein 1 (MDR1) in brain endothelial cells. Correspondingly, CLN3-null cells have reduced caveolae, and impaired caveolae- and MDR1-related functions including endocytosis, drug efflux, and cell volume regulation. We also detected an abnormal blood–brain barrier response to osmotic stress in vivo. Evaluation of the plasma membrane with fluorescent sphingolipid probes suggests microdomain destabilization and enhanced fluidity in CLN3-null cells. In further work we found that application of the glycosphingolipid lactosylceramide to CLN3-deficient cells rescues protein transport and caveolar endocytosis. Last, we show that CLN3 localizes to the trans-Golgi network (TGN) and partitions with buoyant microdomain fractions. We propose that CLN3 facilitates TGN-to-plasma membrane transport of microdomain-associated proteins. Insult to this pathway may underlie BBB dysfunction and contribute to JNCL pathogenesis. PMID:24227717

Tecedor, Luis; Stein, Colleen S.; Schultz, Mark L.; Farwanah, Hany; Sandhoff, Konrad

2013-01-01

352

The hydroxyflavone, fisetin, suppresses mast cell activation induced by interaction with activated T cell membranes  

PubMed Central

Background and purpose: Cell-to-cell interactions between mast cells and activated T cells are increasingly recognized as a possible mechanism in the aetiology of allergic or non-allergic inflammatory disorders. To determine the anti-allergic effect of fisetin, we examined the ability of fisetin to suppress activation of the human mast cell line, HMC-1, induced by activated Jurkat T cell membranes. Experimental approach: HMC-1 cells were incubated with or without fisetin for 15 min and then co-cultured with Jurkat T cell membranes activated by phorbol-12-myristate 13-acetate for 16 h. We determined gene expression in activated HMC-1 cells by DNA microarray and quantitative reverse transcription (RT)-PCR analysis. We also examined activation of the transcription factor NF-?B and MAP kinases (MAPKs) in activated HMC-1 cells. Key results: Fisetin suppresses cell spreading and gene expression in HMC-1 cells stimulated by activated T cell membranes. Additionally, we show that these stimulated HMC-1 cells expressed granzyme B. The stimulatory interaction also induced activation of NF-?B and MAPKs; these activations were suppressed by fisetin. Fisetin also reduced the amount of cell surface antigen CD40 and intercellular adhesion molecule-1 (ICAM-1) on activated HMC-1 cells. Conclusions and implications: Fisetin suppressed activation of HMC-1 cells by activated T cell membranes by interfering with cell-to-cell interaction and inhibiting the activity of NF-?B and MAPKs and thereby suppressing gene expression. Fisetin may protect against the progression of inflammatory diseases by limiting interactions between mast cells and activated T cells. PMID:19702784

Nagai, K; Takahashi, Y; Mikami, I; Fukusima, T; Oike, H; Kobori, M

2009-01-01

353

The Toxoplasma gondii rhoptry protein ROP 2 is inserted into the parasitophorous vacuole membrane, surrounding the intracellular parasite, and is exposed to the host cell cytoplasm  

PubMed Central

The origin of the vacuole membrane surrounding the intracellular protozoan parasite Toxoplasma gondii is not known. Although unique secretory organelles, the rhoptries, discharge during invasion of the host cell and may contribute to the formation of this parasitophorous vacuole membrane (PVM), no direct evidence for this hypothesis exists. Using a novel approach we have determined that parasite-encoded proteins are present in the PVM, exposed to the host cell cytoplasm. In infected cells incubated with streptolysin-O or low concentrations of digitonin, the host cell plasma membrane was selectively permeabilized without significantly affecting the integrity of the PVM. Antisera prepared against whole parasites or a parasite fraction enriched in rhoptries and dense granules reacted with the PVM in these permeabilized cells, indicating that parasite-encoded antigens were exposed on the cytoplasmic side of the PVM. Parasite antigens responsible for this staining of the PVM were identified by fractionating total parasite proteins by SDS-PAGE and velocity sedimentation, and then affinity purifying "fraction-specific" antibodies from the crude antisera. Proteins responsible for the PVM- staining, identified with fraction-specific antibodies, cofractionated with known rhoptry proteins. The gene encoding one of the rhoptry proteins, ROP 2, was cloned and sequenced, predicting and integral membrane protein. Antibodies specific for ROP 2 reacted with the intact PVM. These results provide the first direct evidence that rhoptry contents participate in the formation of the PVM of T. gondii and suggest a possible role of ROP 2 in parasite-host cell interactions. PMID:7962077

1994-01-01

354

Fractionation and characterization of cellular membranes from root tips of garden cress ( Lepidium sativum L.)  

Microsoft Academic Search

The first step in the gravitropic reaction chain, i.e. perception, is known to occur in the statenchyma of the root cap. Because of the importance of the root tip in graviperception, a procedure has been developed to isolate root tips from garden cress (Lepidium sativum L.). The root tip fraction contains the tissues of the root cap plus the lower

Thomas J. Buckhout; Liane Heyder-Caspers; Andreas Sievers

1982-01-01

355

Ultrafiltration by a compacted clay membrane--I. Oxygen and hydrogen isotopic fractionation  

Microsoft Academic Search

Laboratory experiments were carried out to determine the magnitude of the isotopic fractionation of distilled water and of 0.01 N NaCl forced to flow at ambient temperature under a hydraulic pressure drop of 100 bars across a montmorillonite disc compacted to a porosity of 35 per cent by a pressure of 330 bars. The ultrafiltrates in both experiments were depleted

Tyler B. Coplen; Bruce B. Hanshaw

1973-01-01

356

Thyroid hormone cell membrane transport defect.  

PubMed

In the last few years, many studies have pinpointed the crucial role of thyroid hormone (TH) transporters for TH action in human target cells. The importance was better documented by the phenotype observed in patients harboring mutations of the monocarboxylate transporter 8 (MCT8) gene immediately linked to Allan-Herndon-Dudley syndrome, in which severe neurological findings are associated with abnormal TH levels. The hereditary pattern of MCT8 mutations is X chromosome linked, with males presenting a homogeneous neurological psychomotor phenotype and mental retardation associated with low serum thyroxine and elevated triiodothyronine levels. The mechanism of disease is still obscure, and the physiopathology as well as the existent therapeutic options need to be discussed in order to improve the clinical management. PMID:25231447

Ramos, Helton Estrela

2014-01-01

357

Nafion\\/PTFE composite membranes for fuel cell applications  

Microsoft Academic Search

Porous polytetrafluoroethylene (PTFE) membranes were used as support material for Nafion®\\/PTFE composite membranes. The composite membranes were synthesized by impregnating porous PTFE membranes with a self-made Nafion solution. The resulting composite membranes were mechanically durable and quite thin relative to traditional perfluorosulfonated ionomer membranes (PFSI); we expect the composite membranes to be of low resistance and cost. In this study,

Fuqiang Liu; Baolian Yi; Danmin Xing; Jingrong Yu; Huamin Zhang

2003-01-01

358

Neuroprotective properties of Loranthus parasiticus aqueous fraction against oxidative stress-induced damage in NG108-15 cells.  

PubMed

Loranthus parasiticus, a Chinese folk medicine, has been widely used for the treatment of brain diseases, particularly in southwest China. Hence, the present neuroprotection model was designed to investigate its neuroprotective properties against H(2)O(2)-induced oxidative stress in NG108-15 cells. L. parasiticus aqueous fraction (LPAF), which was selected in the present study, had proved to be the most active fraction among the other tested extracts and fractions in our previous screening. The restoration of depleted intracellular glutathione (GSH), a major endogenous antioxidant, by LPAF was observed after H(2)O(2) insult. Pretreatment with LPAF substantially reduced the production of intracellular reactive oxygen species generated from H(2)O(2). Apoptotic features such as externalization of phosphatidylserine and disruption of mitochondrial membrane potential were significantly attenuated by LPAF. In addition, cell cycle analysis revealed a prominent decrease in the H(2)O(2)-induced sub-G(1) population by LPAF. Moreover, apoptotic morphological analysis by DAPI nuclear staining demonstrated that NG108-15 cells treated with H(2)O(2) exhibited apoptotic features, while such changes were greatly reduced in cells pretreated with LPAF. Taken together, these findings confirmed that LPAF exerts marked neuroprotective activity, which raises the possibility of potential therapeutic application of LPAF for managing oxidative stress-related neurological disorders and supports the traditional use of L. parasiticus in treating brain-related diseases. PMID:22318341

Wong, Daniel Zin Hua; Kadir, Habsah Abdul; Lee, Choy Long; Goh, Bey Hing

2012-07-01

359

Translocation of cell-penetrating peptides across the plasma membrane is controlled by cholesterol and microenvironment created by membranous proteins.  

PubMed

Despite the extensive research in the field of CPPs' cell entry the exact mechanisms underlying their cellular uptake and the role of involved cell surface molecules in the internalization process have remained controversial. The present study focused on the interactions between CPPs and plasma membrane compounds using giant plasma membrane vesicles (GPMVs). GPMVs have shown to be a suitable model to study the translocation of CPPs across the plasma membrane in conditions lacking endocytosis. Our results show that higher cholesterol content and tighter packing of membrane predominantly reduce the accumulation of transportan, TP10 and model amphipathic peptide (MAP) in vesicles, indicating that the internalization of CPPs takes place preferentially via the more dynamic membrane regions. The partial digestion of membrane proteins from GPMVs' surface, on the other hand, drastically reduced the accumulation of nona-arginine and Tat peptide into vesicles, suggesting that proteins play a crucial role in the uptake of arginine-rich CPPs. PMID:25016968

Pae, Janely; Säälik, Pille; Liivamägi, Laura; Lubenets, Dmitri; Arukuusk, Piret; Langel, Ülo; Pooga, Margus

2014-10-28

360

A comparative study of water uptake by and transport through ionomeric fuel cell membranes  

SciTech Connect

Water uptake and transport parameters measured at 30 C for several available perfluorosulfonic acid membranes are compared. The water sorption characteristics, diffusion coefficient of water, electroosmotic drag, and protonic conductivity were determined for Nafion 117, Membrane C, and Dow XUS 13204.10 developmental fuel cell membrane. The diffusion coefficient and conductivity of each of these membranes were determined as functions of membrane water content. Experimental determination of transport parameters, enables one to compare membranes without the skewing effects of extensive features such as membrane thickness which contributes in a nonlinear fashion to performance in polymer electrolyte fuel cells.

Zawodzinski, T.A.Jr.; Springer, T.E.; Davey, J.; Jestel, R.; Lopez, C.; Valerio, J.; Gottesfeld, S. (Los Alamos National Lab., NM (United States). Electronics Materials and Device Research)

1993-07-01

361

Properties of electrophoretic fractions of human embryonic kidney cells separated on space shuttle flight STS-8  

NASA Technical Reports Server (NTRS)

Suspensions of cultured primary human embryonic kidney cells were subjected to continuous flow electrophoresis on Space Shuttle flight STS-8. The objectives of the experiments were to obtain electrophoretically separated fractions of the original cell populations and to test these fractions for the amount and kind of urokinase (a kidney plasminogen activator that is used medically for digesting blood clots), the morphologies of cells in the individual fractions, and their cellular electrophoretic mobilities after separation and subsequent proliferation. Individual fractions were successfully cultured after return from orbit, and they were found to differ substantially from one another and from the starting sample with respect to all of these properties.

Morrison, D. R.; Lewis, M. L.; Barlow, G. H.; Todd, P. W.; Kunze, M. E.; Sarnoff, B. E.; Li, Z. K.

1985-01-01

362

Lysosomotropic agents: impact on lysosomal membrane permeabilization and cell death.  

PubMed

Lysosomes are acidic organelles essential for degradation, signalling and cell homoeostasis. In addition, they play a key role in cell death. Permeabilization of the lysosomal membrane and release of hydrolytic enzymes to the cytosol accompanies apoptosis signalling in several systems. The regulatory mechanism of lysosomal stability is, however, poorly understood. Lipophilic or amphiphilic compounds with a basic moiety will become protonated and trapped within lysosomes, and such lysosomotropic behaviour is also found in many pharmacological drugs. The natural sphingolipid sphingosine exhibits lysosomotropic detergent ability and is an endogenous candidate for controlling lysosomal membrane permeabilization. The lysosomotropic properties of certain detergents might be of use in lysosome-targeting anticancer drugs and drug delivery system in the future. The present review summarizes the current knowledge on the targeting and permeabilizing properties of lysosomotropic detergents from a cellular and physicochemical perspective. PMID:25233432

Villamil Giraldo, Ana M; Appelqvist, Hanna; Ederth, Thomas; Öllinger, Karin

2014-10-01

363

Airborne elements, cell membranes, and chlorophyll in transplanted lichens  

SciTech Connect

The objective of the present study was to test the concentration of airborne mineral elements in the lichen Ramalina lacera (with.) J.R. Laund. in comparison with its physiological status. Thalli of Ramalina lacera were collected in a remote unpolluted site and transplanted in a polluted region for 10 mo. An analysis of 20 elements in addition to an analysis of the status of cell membranes and the integrity of chlorophyll was performed after this period of transplantation. The lichen manifested a great potential for the accumulation of Pb, V, Ni, Zn, and Cu. Potassium and P were found to leach out. High concentrations of Ni, Mg, and B coincided with damage caused to cell membranes. The integrity of chlorophyll correlated with the concentration of K and correlated inversely with the concentration of Cr, Fe, Mn, Ni, Pb, and B.

Garty, J.; Cohen, Y.; Kloog, N. [Tel Aviv Univ. (Israel)

1998-07-01

364

Novel proton exchange membrane for high temperature fuel cells  

SciTech Connect

This research effort sought to demonstrate that combining select phosphonic acid additives with Nafion could improve Nafion's high temperature electrochemical performance. A 1:1 mixture of the additive with Nafion, resulted in a film that demonstrated 30% higher conductivity than a phosphoric acid equilibrated Nafion control at 175 C. This improvement to the high temperature conductivity of the proton exchange membrane Nafion is without precedent. In addition, thermal analysis data of the test films suggested that the additives did not compromise the thermal stability of Nafion. The results suggest that the improved Nafion proton exchange membranes could offer superior electrochemical performance, but would retain the same degree of thermal stability as Nafion. This research could eventually lead to portable fuel cells that could oxidize unrefined hydrocarbon fuels, resulting in wider proliferation of fuel cells for portable power.

Bhamidipati, M.; Lazaro, E.; Lyons, F.; Morris, R.S.

1998-07-01

365

A comparative study of water uptake by and transport through ionomeric fuel cell membranes  

Microsoft Academic Search

Water uptake and transport parameters measured at 30 C for several available perfluorosulfonic acid membranes are compared. The water sorption characteristics, diffusion coefficient of water, electroosmotic drag, and protonic conductivity were determined for Nafion 117, Membrane C, and Dow XUS 13204.10 developmental fuel cell membrane. The diffusion coefficient and conductivity of each of these membranes were determined as functions of

Thomas A. Zawodzinski; T. E. Springer; J. Davey; R. Jestel; C. Lopez; J. Valerio; S. Gottesfeld

1993-01-01

366

Role of Amphipathic Helix of a Herpesviral Protein in Membrane Deformation and T Cell Receptor Downregulation  

Microsoft Academic Search

Lipid rafts are membrane microdomains that function as platforms for signal transduction and membrane trafficking. Tyrosine kinase interacting protein (Tip) of T lymphotropic Herpesvirus saimiri (HVS) is targeted to lipid rafts in T cells and downregulates TCR and CD4 surface expression. Here, we report that the membrane-proximal amphipathic helix preceding Tip's transmembrane (TM) domain mediates lipid raft localization and membrane

Chan-Ki Min; Sun-Young Bang; Bon-A Cho; Yun-Hui Choi; Jae-Seong Yang; Sun-Hwa Lee; Seung-Yong Seong; Ki Woo Kim; Sanguk Kim; Jae Ung Jung; Myung-Sik Choi; Ik-Sang Kim; Nam-Hyuk Cho

2008-01-01

367

Separation of Adenosine Triphosphatase of HK and LK Sheep Red Cell Membranes by Density Gradient Centrifugation  

Microsoft Academic Search

Membrane fragments from high potassium (HK) and low potas- sium (LK) sheep red cells were separated by density gradient centrifugation. Three preparations were studied: (1) HK membranes sonicated for 20 min- utes, (2) HK membranes sonicated for 3 minutes, and (3) LK membranes sonicated for 3 minutes. The adenosine triphosphatase (ATPase) activity in the maximally disrupted preparation (1) was not

D. C. Tosteson; P. COOK; R. BLOUNT

1965-01-01

368

Simulation for water management in membranes for polymer electrolyte fuel cells  

Microsoft Academic Search

Water management in membranes for polymer electrolyte fuel cells during their operational conditions is considered theoretically. Using a linear transport equation based on the diffusion of water and the electroosmotic drag, analytical solutions for water concentration profiles in the membrane are obtained from which membrane resistance overvoltage and other characteristic values are calculated. Specific parameters of the membranes such as

Tatsuhiro Okada; Gang Xie; Morten Meeg

1998-01-01

369

Effect of growth and sodium butyrate on brush border membrane-associated hydrolases in human colorectal cancer cell lines.  

PubMed

The activities of brush border membrane-associated hydrolases such as alkaline phosphatase (Alkpase), aminopeptidase, dipeptidyl aminopeptidase IV (DAP-IV), sucrase, lactase, and trehalase were studied in 14 different human colorectal cancer cell lines. The effect of sodium butyrate, a known differentiating agent, and cell growth on the activities of these enzymes was also examined. All 14 cell lines exhibited brush border membrane enzyme activities, and in general, the activity of Alkpase, aminopeptidase, and DAP-IV was much higher than the disaccharidases. However, the specific enzyme activities varied among different cell lines. The induction of Alkpase activity by sodium butyrate occurred in most of the 14 cell lines (2- to 123-fold), while induction of the other enzyme activities was observed in several (1.5- to 3.5-fold). In some instances, butyrate caused a decrease in enzyme activity. There was no statistically significant correlation between the induction of Alkpase activity and that of other enzyme activities by sodium butyrate. Levels of aminopeptidase and DAP-IV activity were found to be dependent on cell density and increased 3- to 4-fold by the tenth day in most of the cell lines. Sodium butyrate altered the subcellular distribution pattern of the disaccharidases, causing a significant increase in activity associated with the soluble (cytoplasmic) fraction. Other enzymes such as Alkpase and DAP-IV continued to be predominantly associated with the membrane fraction in butyrate-treated cells. These data suggest that brush border membrane hydrolase activity and the effect of sodium butyrate may provide useful information regarding the differentiation of human colorectal cancer cells. PMID:4005836

Chung, Y S; Song, I S; Erickson, R H; Sleisenger, M H; Kim, Y S

1985-07-01

370

Membrane potential measurements across a human fat cell using ZnO nanorods  

NASA Astrophysics Data System (ADS)

A ZnO nanorod probe was employed to determine the resting membrane potential of a human fat cell. The distribution of protons associated with the cell versus the extracellular distribution is proportional to changes in membrane potential. The membrane potential determines the concentration gradient of the protons with dominant permeability according to the Nernst equation. A ZnO nanorod probe was successfully used to find the resting membrane potential for a human fat cell: 34 ± 2.6 mV.

Al-Hilli, S.; Willander, M.

2009-04-01

371

Do heavy ions cause microlesions in cell membranes?  

NASA Technical Reports Server (NTRS)

The microlesion question is investigated by monitoring the electrical potential difference across the endothelium of rat corneas in vitro before, during, and after irradiation. When the corneas were exposed to 1 Gy of Fe-56 ions (450 and 600 MeV/a.m.u.), no effect was detected on this parameter. These results suggest that direct physical damage to cell membranes, as predicted by the microlesion theory, does not take place.

Koniarek, Jan P.; Worgul, Basil V.

1992-01-01

372

Microfluidics analysis of red blood cell membrane viscoelasticity.  

PubMed

In this work, a microfluidic system to investigate the flow behavior of red blood cells in a microcirculation-mimicking network of PDMS microchannels with thickness comparable to cell size is presented. We provide the first quantitative description of cell velocity and shape as a function of the applied pressure drop in such devices. Based on these results, a novel methodology to measure cell membrane viscoelastic properties in converging/diverging flow is developed, and the results are in good agreement with data from the literature. In particular, in the diverging channel the effect of RBC surface viscosity is dominant with respect to shear elasticity. Possible applications include measurements of cell deformability in pathological samples, where reliable methods are still lacking. PMID:21076756

Tomaiuolo, Giovanna; Barra, Mario; Preziosi, Valentina; Cassinese, Antonio; Rotoli, Bruno; Guido, Stefano

2011-02-01

373

Amniotic membrane transplantation for partial limbal stem cell deficiency  

PubMed Central

AIM—To examine the efficacy, safety, and long term outcomes of amniotic membrane transplantation for corneal surface reconstruction in cases of partial limbal stem cell deficiency.?METHODS—17 eyes of 15 patients with partial limbal stem cell deficiency underwent superficial keratectomy of the conjunctivalised corneal surface followed by amniotic membrane transplantation. Cases were followed up for at least a year.?RESULTS—All eyes exhibited a stable, intact corneal epithelial surface after a mean follow up period of 25.8 months with no eyes developing recurrent erosion or persistent epithelial defect. The mean time to re-epithelialisation was 22.8 days. Overall improvement in visual acuity was observed in 92.9% of 14 eyes with visual potential. Of those, five eyes gained six or more lines, two eyes gained between four and five lines, six eyes gained between one and three lines, and one eye lost three lines of Snellen acuity. Pain and photophobia were abolished in 86% of cases and substantially reduced in 14%, with all eyes exhibiting decreased vascularisation and inflammation at final follow up.?CONCLUSIONS—Amniotic membrane transplantation appears to be a safe and effective method of restoring a stable corneal epithelium for cases of partial limbal stem cell deficiency and can be considered as an alternative to limbal autograft or allograft.?? PMID:11316719

Anderson, D.; Ellies, P.; Pires, R.; Tseng, S.

2001-01-01

374

Identification of Proteins from a Cell Wall Fraction of the Diatom Thalassiosira pseudonana  

Microsoft Academic Search

Diatoms are unicellular eucaryotic algae with cell walls containing silica, intricately and ornately structured on the nanometer scale. Overall silica structure is formed by expansion and molding of the membrane-bound silica deposition vesicle. Although molecular details of silica polymerization are being clarified, we have limited insight into molecular components of the silica deposition vesi- cle, particularly of membrane-associated proteins that

Luciano G. Frigeri; Timothy R. Radabaugh; Paul A. Haynes; Mark Hildebrand

375

Development of Nanoparticles Incorporating a Novel Liposomal Membrane Destabilization Peptide for Efficient Release of Cargos into Cancer Cells  

PubMed Central

In anti-cancer therapy mediated by a nanoparticle-based drug delivery system (DDS), overall efficacy depends on the release efficiency of cargos from the nanoparticles in the cancer cells as well as the specificity of delivery to tumor tissue. However, conventional liposome-based DDS have no mechanism for specifically releasing the encapsulated cargos inside the cancer cells. To overcome this barrier, we developed nanoparticles containing a novel liposomal membrane destabilization peptide (LMDP) that can destabilize membranes by cleavage with intramembranous proteases on/in cancer cells. Calcein encapsulated in liposomes modified with LMDP (LMDP-lipo) was effectively released in the presence of a membrane fraction containing an LMDP-cleavable protease. The release was inhibited by a protease inhibitor, suggesting that LMDP-lipo could effectively release its cargo into cells in response to a cancer-specific protease. Moreover, when LMDP-lipo contained fusogenic lipids, the release of cargo was accelerated, suggesting that the fusion of LMDP-lipo with cellular membranes was the initial step in the intracellular delivery. Time-lapse microscopic observations showed that the release of cargo from LMDP-lipo occurred immediately after association of LMDP-lipo with target cells. Consequently, LMDP-lipo could be a useful nanoparticle capable of effective release of cargos specifically into targeted cancer cells. PMID:25343714

Ohgita, Takashi; Kogure, Kentaro

2014-01-01

376

[Plasma membrane focal defects in structurally normal cells].  

PubMed

The technique of perfusion fixation through the rat kidney vasculature was modified to ensure the highest possible level of cell preservation close to that under in vivo conditions. Electron microscopic analysis of the tissue specimens treated in such a way revealed local defects of the plasma membrane in a number of cells than that otherwise looked normal. These findings together with the evidence for reparability of such defects and some data on the purely artificial nature of certain alterations should be taken into consideration in order to avoid misinterpretations while diagnosing the biopsy specimens. PMID:20131509

Nevorotin, A I; Khokhlov, S E; Borisova, E A; Sipovski?, V G; Chefu, S G

2009-01-01

377

Estrogen-induced membrane alterations and growth associated with proteinase activity in endometrial cells  

PubMed Central

Endometrial cells isolated from uteri of ovariectomized rats were treated in vitro with 1 X 10(-9) M estradiol-17 beta (E2beta) to analyze early changes in membrane properties during hormone-induced growth. After 30-min exposure to E2beta at 22 degrees C, cells exhibited an enhanced capacity to bind erythrocytes (hemadsorption) in the presence of concanavalin A (Con A) to 237% of the level in paired controls. Fluorescence microscopy revealted that approximately 25% of cells exposed to E2beta, but not estradiol-17 alpha (E2alpha), showed a redistribution into polar clusters of Con A-binding sites that were dispersed in random patches at the external surfaces of control cells. These hormore-induced membrane alterations were abolished by prior treatment of cells with inhibitors of thiol proteinase activity of the cathepsin B1 (CB1) type, such as leupeptin and iodoacetate. Leupeptin at 4.5 X 10(-7) M also reduced the affinity of [3H]E2beta binding to intact cells but did not influence specific binding of the hormone to macromolecular components of cytosol. A pronounced increase in the availability of endogenous CB1, But not of alkaline phosphatase, succinate, or lactate dehydrogenase, in the extracellular media was elicited within 30 min after E2beta treatment. In cells cultured in chemically defined medium for up to 48 h, E2beta, but not E2alpha, enhanced cell proliferation and stimulated [3H]thymidine incorporation into macromolecular form. These E2beta-induced effects were abolished by prior treatment of cells with liposome-entrapped leupeptin at a final concentration of 7 X 10(-8) M. The net rate of intercellular adhesion among endometrial cells was also enhanced by E2beta. This hormonal response was diminished by prior exposure to leupeptin. Fractionation of cells by selection for adhesiveness due to E2beta exposure for 30 min yielded a subpopulation of rapidly dividing cells which surpassed their less adhesive counterparts in cathepsin secretion and in Con A-mediated hemadsorption. These results indicate that leupeptin-sensitive proteinase activity may contribute to membrane and growth modifications elicited by E2beta treatment in endometrial cells. PMID:457777

1979-01-01

378

Correlation of cell membrane dynamics and cell motility  

E-print Network

Abstract Background Essential events of cell development and homeostasis are revealed by the associated changes of cell morphology and therefore have been widely used as a key indicator of physiological states and molecular ...

Veronika, Merlin

379

Intact transmembrane isoforms of the neural cell adhesion molecule are released from the plasma membrane.  

PubMed Central

Three soluble neural cell adhesion molecule (NCAM) polypeptide classes of M(r) values 190,000 (NCAM-s1), 135,000 (NCAM-s2) and 115,000-110,000 (NCAM-s3) have been demonstrated in rat brain and cerebrospinal fluid [Krog, Olsen, Dalseg, Roth and Bock (1992) J. Neurochem. 59, 838-847]. NCAM-s3 is known to arise from released glycosylphosphatidylinositol (GPI)-linked NCAM [He, Finne and Goridis (1987) J. Cell. Biol. 105, 2489-2500] as well as from extracellularly cleaved transmembrane NCAM isoforms [Nybroe, Linnemann and Bock (1989) J. Neurochem. 53, 1372-1378]. In this study the origin of NCAM-s1 and NCAM-s2 and the function of soluble NCAM forms were investigated. It was shown that all three soluble forms could be released from brain membranes with M(r) values identical to the three major membrane-associated forms: the large transmembrane 190,000-M(r) form (NCAM-A), the smaller transmembrane 135,000-M(r) form (NCAM-B) and the GPI-anchored 115,000-110,000-M(r) form (NCAM-C). A polyclonal antibody, directed against transmembrane and cytoplasmic epitopes common to NCAM-A and NCAM-B, was shown to react with NCAM-s1 and NCAM-s2. Furthermore, NCAM-B was shown to be shed in a presumably intact soluble form from membranes of cells transfected with this isoform. Thus, NCAM-s1 and NCAM-s2 probably represent intact released transmembrane NCAM-A and NCAM-B. The soluble transmembrane forms are likely to exist in vivo, as NCAM-s1 and NCAM-s2 were readily demonstrated in cerebrospinal fluid. By density-gradient centrifugation it was shown that shed transmembrane NCAM-B was present in fractions of high, as well as low, density, indicating that a fraction of the shed NCAM is associated with minor plasma membrane fragments. Finally, it was shown that isolated soluble NCAM inhibited cell binding to an immobilized NCAM substratum, attributing a pivotal role to soluble NCAM in vivo as a modulator of NCAM-mediated cell behaviour. Images Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 PMID:8240299

Olsen, M; Krog, L; Edvardsen, K; Skovgaard, L T; Bock, E

1993-01-01

380

Quantitative proteomics of the Neisseria gonorrhoeae cell envelope and membrane vesicles for the discovery of potential therapeutic targets.  

PubMed

Neisseria gonorrhoeae (GC) is a human-specific pathogen, and the agent of a sexually transmitted disease, gonorrhea. There is a critical need for new approaches to study and treat GC infections because of the growing threat of multidrug-resistant isolates and the lack of a vaccine. Despite the implied role of the GC cell envelope and membrane vesicles in colonization and infection of human tissues and cell lines, comprehensive studies have not been undertaken to elucidate their constituents. Accordingly, in pursuit of novel molecular therapeutic targets, we have applied isobaric tagging for absolute quantification coupled with liquid chromatography and mass spectrometry for proteome quantitative analyses. Mining the proteome of cell envelopes and native membrane vesicles revealed 533 and 168 common proteins, respectively, in analyzed GC strains FA1090, F62, MS11, and 1291. A total of 22 differentially abundant proteins were discovered including previously unknown proteins. Among those proteins that displayed similar abundance in four GC strains, 34 were found in both cell envelopes and membrane vesicles fractions. Focusing on one of them, a homolog of an outer membrane protein LptD, we demonstrated that its depletion caused loss of GC viability. In addition, we selected for initial characterization six predicted outer membrane proteins with unknown function, which were identified as ubiquitous in the cell envelopes derived from examined GC isolates. These studies entitled a construction of deletion mutants and analyses of their resistance to different chemical probes. Loss of NGO1985, in particular, resulted in dramatically decreased GC viability upon treatment with detergents, polymyxin B, and chloramphenicol, suggesting that this protein functions in the maintenance of the cell envelope permeability barrier. Together, these findings underscore the concept that the cell envelope and membrane vesicles contain crucial, yet under-explored determinants of GC physiology, which may represent promising targets for designing new therapeutic interventions. PMID:24607996

Zielke, Ryszard A; Wierzbicki, Igor H; Weber, Jacob V; Gafken, Philip R; Sikora, Aleksandra E

2014-05-01

381

The effect of unsaturated fatty acids on membrane composition and signal transduction in HT-29 human colon cancer cells.  

PubMed

The objective of the present study was to investigate the effect of membrane fatty acid (FA) composition on the activity of phospholipase C (PLC) in HT-29 human colon cancer cells. The membrane FA composition was altered by supplementing cultured cells with FAs of different composition. The FAs were stearic acid (18:0; SA), gamma linolenic acid (18:3 omega 6; gamma LnA); alpha linolenic acid (18:3 omega 3; alpha LnA;); eicosapentaenoic acid (20:5 omega 3; EPA) and docosahexaenoic acid (22:6 omega 3; DHA). The fatty acids were supplemented as a FA/BSA complex. Cells supplemented with SA served as the control. Tumor growth was followed by counting the number of cells in culture. The results indicate that polyunsaturated fatty acid (PUFA) supplementation had no consistent effect on tumor growth from 1 day to another throughout the 15 days of growth. The fatty acid composition of membranes indicates that cells incorporated and modified the supplemented fatty acids by desaturation, elongation and retroconversion. The unsaturation index (UI) of membranes of cells supplemented with EPA and DHA was higher than other groups. PLC activity; measured in the absence of GTP gamma(S) in the assay mixture; was not influenced by membrane FA modification. However, in the presence of GTP gamma(S) PLC of cells supplemented with 18:3(omega 6) was the lowest among the groups. It has been shown that 18:3(omega 6) accumulated the most in the phosphatidylethanolamine (PE) fraction. There was a negative correlation between the activity of PLC in the presence of G protein activation and PE 18:3 (omega 6) content without affecting UI. It was concluded that G protein may be sensitive to the level of 18:3(omega 6) content and not to the general fluidity of the membranes. PMID:8950205

Awad, A B; Young, A L; Fink, C S

1996-11-12

382

Relationship Between the Membrane Envelope of Rhizobial Bacteroids and the Plasma Membrane of the Host Cell as Demonstrated by Histochemical Localization of Adenyl Cyclase  

PubMed Central

By using adenyl cyclase as a marker enzyme, the relationship between the membrane envelope of the bacteroids of rhizobia and the plasma membrane of the host cell was demonstrated histochemically. Electron-dense deposits were found on the outer surface of the plasma membrane of the host cell and on the inner surface of the membrane envelopes of the bacteroids, but not in vacuole membranes, endoplasmic reticula, Golgi apparatus, and mitochondrial membranes. The results suggest that the membrane envelopes of the bacteroids are closely related to the host plasma membrane, and that entry of the bacteroids into the cytoplasm is in a manner similar to endocytosis. Images PMID:4854087

Tu, J. C.

1974-01-01

383

Membrane Compartmentalization in Southeast Asian Ovalocytosis Red Blood Cells  

PubMed Central

Summary Red blood cells (RBCs) from individuals with Southeast Asian ovalocytosis (SAO) contain a mutant band 3 protein that causes the formation of unique linear oligomers in the RBC membrane. We used single-particle tracking to measure the lateral diffusion of individual glycophorin C (GPC), band 3, and CD58 proteins in membranes of intact SAO RBCs and normal RBCs (nRBCs). GPC, an integral protein that binds with high affinity to the RBC membrane skeleton, showed oscillatory motion within confinement areas that were smaller in SAO RBCs than in nRBCs. The additional confinement in SAO RBCs could be due to membrane stiffening associated with the SAO phenotype. Band 3 in both SAO RBCs and nRBCs also showed confined motion over short times (ms) and distances (nm), and the area of confinement was smaller in SAO RBCs than in nRBCs. These data presumably reflect the constraints imposed by band 3 oligomerization. Similarly, the glycosylphosphatidylinositol-linked protein CD58 showed loosely confined diffusion in nRBCs and a substantially higher degree of confinement in SAO RBCs. Restricted protein mobility could contribute to the altered adherence of parasite-infected RBCs to vascular endothelium that is thought to protect individuals with SAO from severe manifestations of malaria. PMID:21793815

Mirchev, Rossen; Lam, Alexander; Golan, David E.

2011-01-01

384

Better Proton-Conducting Polymers for Fuel-Cell Membranes  

NASA Technical Reports Server (NTRS)

Polyoxyphenylene triazole sulfonic acid has been proposed as a basis for development of improved proton-conducting polymeric materials for solid-electrolyte membranes in hydrogen/air fuel cells. Heretofore, the proton-conducting membrane materials of choice have been exemplified by a family of perfluorosulfonic acid-based polymers (Nafion7 or equivalent). These materials are suitable for operation in the temperature of 75 to 85 C, but in order to reduce the sizes and/or increase the energy-conversion efficiencies of fuel-cell systems, it would be desirable to increase temperatures to as high as 120 C for transportation applications, and to as high as 180 C for stationary applications. However, at 120 C and at relative humidity values below 50 percent, the loss of water from perfluorosulfonic acid-based polymer membranes results in fuel-cell power densities too low to be of practical value. Therefore, membrane electrolyte materials that have usefully high proton conductivity in the temperature range of 180 C at low relative humidity and that do not rely on water for proton conduction at 180 C would be desirable. The proposed polyoxyphenylene triazole sulfonic acid-based materials have been conjectured to have these desirable properties. These materials would be free of volatile or mobile acid constituents. The generic molecular structure of these materials is intended to exploit the fact, demonstrated in previous research, that materials that contain ionizable acid and base groups covalently attached to thermally stable polymer backbones exhibit proton conduction even in the anhydrous state.

Narayan, Sri; Reddy, Prakash

2012-01-01

385

Non-Fluorinated Polymer Materials for Proton Exchange Membrane Fuel Cells  

Microsoft Academic Search

The past 10 years have witnessed a tremendous acceleration in research devoted to non-fluorinated polymer membranes, both as competitive alternatives to commercial perfluorosulfonic acid membranes operating in the same temperature range and with the objective of extending the range of operation of polymer fuel cells toward those more generally occupied by phosphoric acid fuel cells. Important requirements are adequate membrane

Jacques Roziere; Deborah J. Jones

2003-01-01

386

Water free proton conducting membranes based on poly-4-vinylpyridinebisulfate for fuel cells  

NASA Technical Reports Server (NTRS)

Disclosed are methods for forming a water-free electrolyte membrane useful in fuel cells. Also provided is a water-free electrolyte membrane comprising a quaternized amine salt including poly-4-vinylpyridinebisulfate, a poly-4-vinylpyridinebisulfate silica composite, and a combination thereof and a fuel cell comprising the membrane.

Narayanan, Sekharipuram R. (Inventor); Yen, Shiao-Pin S. (Inventor)

2007-01-01

387

HIV Fusion Peptide Penetrates, Disorders, and Softens T-Cell Membrane Mimics  

E-print Network

HIV Fusion Peptide Penetrates, Disorders, and Softens T-Cell Membrane Mimics Stephanie Tristram of N-terminal gp41 fusion peptide (FP) of human immunodeficiency virus type 1 (HIV-1) with model membranes in order to elucidate how FP leads to fusion of HIV and T-cell membranes. FP constructs were (i

Weliky, David

388

Cytoplasmic phospholipase A2 translocates to membrane fraction in human neutrophils activated by stimuli that phosphorylate mitogen-activated protein kinase.  

PubMed Central

The addition of the chemotactic peptide formylmethionylleucylphenylalanine (fMet-Leu-Phe) to human neutrophils pretreated with the cytokine granulocyte/macrophage colony-stimulating factor (GM-CSF) results in a 10-fold enhanced activity of phospholipase A2, measured as the release of arachidonic acid. It is found that GM-CSF increases the tyrosine phosphorylation, enhances the activity of a mitogen-activated protein kinase, and greatly potentiates the fMet-Leu-Phe-induced tyrosine phosphorylation and enhanced activity of this kinase. Stimuli that increase the tyrosine phosphorylation, enhance the activity of the mitogen-activated protein kinase, and cause a rise in the intracellular concentration of free calcium increase the amount of phospholipase A2 associated with the plasma membrane. This increase corresponds to a decrease in the amount found in the cytosol. Whereas GM-CSF alone produces only a small increase in the amount of phospholipase A2 associated with the membrane, it potentiates greatly the fMet-Leu-Phe-induced increase. The total amount (whole cell) of phospholipase A2, as measured by immunoblotting using anti-phospholipase A2 antibody, does not change upon stimulation of human neutrophils with GM-CSF, fMet-Leu-Phe, or both. In addition, the band that corresponds to phospholipase A2 is shifted upward in membrane isolated from neutrophils stimulated with fMet-Leu-Phe, suggesting that the enzyme has been altered, possibly phosphorylated, though not on tyrosine residues. A working hypothesis is presented. Briefly, stimulation of human neutrophils with GM-CSF, in the absence of an additional stimulus, increases the tyrosine phosphorylation and activation of a mitogen-activated protein kinase, which in turn phosphorylates and activates cytoplasmic phospholipase A2. In the presence of an increased intracellular concentration of free calcium the phospholipase A2 is translocated to the plasma membrane where its substrate is located. GM-CSF also potentiates greatly the fMet-Leu-Phe-induced tyrosine phosphorylation and activation of a mitogen-activated protein kinase and, since fMet-Leu-Phe causes an intracellular calcium rise, the amount of the phospholipase A2 that is associated with the membrane fraction. Images PMID:7512725

Durstin, M; Durstin, S; Molski, T F; Becker, E L; Sha'afi, R I

1994-01-01

389

NREL Develops Technique to Measure Membrane Thickness and Defects in Polymer Electrode Membrane Fuel Cells (Fact Sheet)  

SciTech Connect

This fact sheet describes NREL's accomplishments in fuel cell membrane electrode assembly research and development. Work was performed by the Hydrogen Technologies and Systems Center and the National Center for Photovoltaics.

Not Available

2010-11-01

390

A C-Terminal Domain Targets the Pseudomonas aeruginosa Cytotoxin ExoU to the Plasma Membrane of Host Cells  

PubMed Central

ExoU, a phospholipase injected into host cells by the type III secretion system of Pseudomonas aeruginosa, leads to rapid cytolytic cell death. Although the importance of ExoU in infection is well established, the mechanism by which this toxin kills host cells is less clear. To gain insight into how ExoU causes cell death, we examined its subcellular localization following transfection or type III secretion/translocation into HeLa cells. Although rapid cell lysis precluded visualization of wild-type ExoU by fluorescence microscopy, catalytically inactive toxin was readily detected at the periphery of HeLa cells. Biochemical analysis confirmed that ExoU was targeted to the membrane fraction of transfected cells. Visualization of ExoU peptides fused with green fluorescent protein indicated that the domain responsible for this targeting was in the C terminus of ExoU, between residues 550 and 687. Localization to the plasma membrane occurred within 1 h of expression, which is consistent with the kinetics of cytotoxicity. Together, these results indicate that a domain between residues 550 and 687 of ExoU targets this toxin to the plasma membrane, a process that may be important in cytotoxicity. PMID:16622190

Rabin, Shira D. P.; Veesenmeyer, Jeffrey L.; Bieging, Kathryn T.; Hauser, Alan R.

2006-01-01

391

Process for recycling components of a PEM fuel cell membrane electrode assembly  

DOEpatents

The membrane electrode assembly (MEA) of a PEM fuel cell can be recycled by contacting the MEA with a lower alkyl alcohol solvent which separates the membrane from the anode and cathode layers of the assembly. The resulting solution containing both the polymer membrane and supported noble metal catalysts can be heated under mild conditions to disperse the polymer membrane as particles and the supported noble metal catalysts and polymer membrane particles separated by known filtration means.

Shore, Lawrence (Edison, NJ)

2012-02-28

392

Noncontact microsurgery of cell membranes using femtosecond laser pulses for optoinjection of specified substances into cells  

SciTech Connect

IR femtosecond laser pulses were used for microsurgery of a cell membrane aimed at local and short-duration change in its permeability and injection of specified extracellular substances into the cells. The possibility of noncontact laser delivery of the propidium iodide fluorescent dye and the pEGFP plasmid, encoding the green fluorescent protein, into the cells with preservation of the cell viability was demonstrated. (extreme light fields and their applications)

Il'ina, I V; Ovchinnikov, A V; Chefonov, O V; Sitnikov, D S; Agranat, Mikhail B; Mikaelyan, A S

2013-04-30

393

Aluminum and temperature alteration of cell membrane permeability of Quercus rubra  

SciTech Connect

Al toxicity is the major factor limiting plant growth in acid soils. This report extends research on Al-induced changes in membrane behavior of intact root cortex cells of Northern red oak (Quercus rubra). Membrane permeability was determined by the plasmometric method for individual intact cells at temperatures from 2 or 4 to 35 C. Al (0.37 millimolar) significantly increased membrane permeability to urea and monoethyl urea and decreased permeability to water. Al significantly altered the activation energy required to transport water (+ 32%), urea (+ 9%), and monoethyl urea ({minus}7%) across cell membranes. Above 9 C, Al increased the lipid partiality of the cell membranes; below 7 C, Al decreased it. Al narrowed by 6 C the temperature range over which plasmolysis occurred without membrane damage. These changes in membrane behavior are explainable if Al reduced membrane lipid fluidity and kink frequency and increases packing density and the occurrence of straight lipid chains.

Junping Chen; Sucoff, E.I.; Stadelmann, E.J. (Univ. of Minnesota, St. Paul (United States))

1991-06-01

394

Direct liquid-feed fuel cell with membrane electrolyte and manufacturing thereof  

NASA Technical Reports Server (NTRS)

An improved direct liquid-feed fuel cell having a solid membrane electrolyte for electrochemical reactions of an organic fuel. Improvements in interfacing of the catalyst layer and the membrane and activating catalyst materials are disclosed.

Narayanan, Sekharipuram (Inventor); Surampudi, Subbarao (Inventor); Halpert, Gerald (Inventor)

1999-01-01

395

Nafion\\/Silicon oxide composite membrane for high temperature proton exchange membrane fuel cell  

Microsoft Academic Search

Nafion\\/Silicon oxide composite membranes were produced via in situ sol-gel reaction of tetraethylorthosilicate (TEOS) in Nafion membranes. The physicochemical properties of the membranes were\\u000a studied by FT-IR,TG-DSC and tensile strength. The results show that the silicon oxide is compatible with the Nafion membrane\\u000a and the thermo stability of Nafion\\/Silicon oxide composite membrane is higher than that of Nafion membrane. Furthermore,

Jun Yu; Mu Pan; Runzhang Yuan

2007-01-01

396

Saccadic Burst Cell Membrane Dysfunction Is Responsible for Saccadic Oscillations  

PubMed Central

Saccadic oscillations threaten clear vision by causing image motion on the retina. They are either purely horizontal (ocular flutter) or multidimensional (opsoclonus). We propose that ion channel dysfunction in the burst cell membrane is the underlying abnormality. We have tested this hypothesis by simulating a neuromimetic computational model of the burst neurons. This biologically realistic model mimics the physiologic properties and anatomic connections in the brainstem saccade generator. A rebound firing after sustained inhibition, called post-inhibitory rebound (PIR), and reciprocal inhibition between premotor saccadic burst neurons are the key features of this conceptual scheme. PIR and reciprocal inhibition make the circuits that generate the saccadic burst inherently unstable and can lead to oscillations unless stabilized by external inhibition. Our simulations suggest that alterations in membrane properties that lead to an increase in PIR, a reduction in external glycinergic inhibition, or both can cause saccadic oscillations. PMID:19145136

Shaikh, Aasef G.; Ramat, Stefano; Optican, Lance M.; Miura, Kenichiro; Leigh, R. John; Zee, David S.

2009-01-01

397

From cells to computers: computing with membranes (P systems).  

PubMed

The aim of this paper is to introduce to the reader the main ideas of computing with membranes, a recent branch of (theoretical) molecular computing. In short, in a cell-like system, multisets of objects evolve according to given rules in the compartments defined by a membrane structure and compute natural numbers as the result of halting sequences of transitions. The model is parallel, nondeterministic. Many variants have already been considered and many problems about them were investigated. We present here some of these variants, focusing on two central classes of results: (1) characterizations of the recursively enumerable sets of numbers and (2) possibilities to solve NP-complete problems in polynomial--even linear--time (of course, by making use of an exponential space). The results are given without proofs. An almost complete bibliography of the domain, at the middle of October 2000, is also provided. PMID:11311465

P?un, G

2001-03-01

398

Biofilm productivity and concomitant cell autolysis in a membrane bioreactor.  

PubMed

Phanerochaete chrysoporium morphology and manganese peroxidase (MnP) productivity was characterised in a scalable, modularised 1145 cm(3) membrane gradostat reactor in response to switching between an enhanced production medium and a nutrient limited feed (50% C and N reduction). Irrespective of the feed composition used nutrients permeating from the lumen of the ultrafiltration membrane matrix established nutrient gradients across the immobilised biofilm with distinct primary, stationary and decline growth phases observed. Severe nutrient C and N limitation did not change the cyclic nature of enzyme production (MnP(max) = 189.5 U l(-1)) but did reduce the overall bioreactor efficiency from 32 to 22 U l(-1) day(-1). Stress induced secondary metabolism resulted in concomitant cell autolysis causing biomass loss and increased operational flux after 20 days in the 33 day bioreactor operation cycle. PMID:20972820

Govender, S

2011-02-01

399

A Simple Alkaline Method for Decellularizing Human Amniotic Membrane for Cell Culture  

PubMed Central

Human amniotic membrane is a standard substratum used to culture limbal epithelial stem cells for transplantation to patients with limbal stem cell deficiency. Various methods were developed to decellularize amniotic membrane, because denuded membrane is poorly immunogenic and better supports repopulation by dissociated limbal epithelial cells. Amniotic membrane denuding usually involves treatment with EDTA and/or proteolytic enzymes; in many cases additional mechanical scraping is required. Although ensuring limbal cell proliferation, these methods are not standardized, require relatively long treatment times and can result in membrane damage. We propose to use 0.5 M NaOH to reliably remove amniotic cells from the membrane. This method was used before to lyse cells for DNA isolation and radioactivity counting. Gently rubbing a cotton swab soaked in NaOH over the epithelial side of amniotic membrane leads to nearly complete and easy removal of adherent cells in less than a minute. The denuded membrane is subsequently washed in a neutral buffer. Cell removal was more thorough and uniform than with EDTA, or EDTA plus mechanical scraping with an electric toothbrush, or n-heptanol plus EDTA treatment. NaOH-denuded amniotic membrane did not show any perforations compared with mechanical or thermolysin denuding, and showed excellent preservation of immunoreactivity for major basement membrane components including laminin ?2, ?1-?3 chains, ?1/?2 and ?6 type IV collagen chains, fibronectin, nidogen-2, and perlecan. Sodium hydroxide treatment was efficient with fresh or cryopreserved (10% dimethyl sulfoxide or 50% glycerol) amniotic membrane. The latter method is a common way of membrane storage for subsequent grafting in the European Union. NaOH-denuded amniotic membrane supported growth of human limbal epithelial cells, immortalized corneal epithelial cells, and induced pluripotent stem cells. This simple, fast and reliable method can be used to standardize decellularized amniotic membrane preparations for expansion of limbal stem cells in vitro before transplantation to patients. PMID:24236148

Saghizadeh, Mehrnoosh; Winkler, Michael A.; Kramerov, Andrei A.; Hemmati, David M.; Ghiam, Chantelle A.; Dimitrijevich, Slobodan D.; Sareen, Dhruv; Ornelas, Loren; Ghiasi, Homayon; Brunken, William J.; Maguen, Ezra; Rabinowitz, Yaron S.; Svendsen, Clive N.; Jirsova, Katerina; Ljubimov, Alexander V.

2013-01-01

400

Thermoase-Derived Flaxseed Protein Hydrolysates and Membrane Ultrafiltration Peptide Fractions Have Systolic Blood Pressure-Lowering Effects in Spontaneously Hypertensive Rats  

PubMed Central

Thermoase-digested flaxseed protein hydrolysate (FPH) samples and ultrafiltration membrane-separated peptide fractions were initially evaluated for in vitro inhibition of angiotensin I-converting enzyme (ACE) and renin activities. The two most active FPH samples and their corresponding peptide fractions were subsequently tested for in vivo antihypertensive activity in spontaneously hypertensive rats (SHR). The FPH produced with 3% thermoase digestion showed the highest ACE- and renin-inhibitory activities. Whereas membrane ultrafiltration resulted in significant (p < 0.05) increases in ACE inhibition by the <1 and 1–3 kDa peptides, only a marginal improvement in renin-inhibitory activity was observed for virtually all the samples after membrane ultrafiltration. The FPH samples and membrane fractions were also effective in lowering systolic blood pressure (SBP) in SHR with the largest effect occurring after oral administration (200 mg/kg body weight) of the 1–3 kDa peptide fraction of the 2.5% FPH and the 3–5 kDa fraction of the 3% FPH. Such potent SBP-lowering capacity indicates the potential of flaxseed protein-derived bioactive peptides as ingredients for the formulation of antihypertensive functional foods and nutraceuticals. PMID:25302619

Nwachukwu, Ifeanyi D.; Girgih, Abraham T.; Malomo, Sunday A.; Onuh, John O.; Aluko, Rotimi E.

2014-01-01

401

160 C PROTON EXCHANGE MEMBRANE (PEM) FUEL CELL SYSTEM DEVELOPMENT  

SciTech Connect

The objectives of this program were: (a) to develop and demonstrate a new polymer electrolyte membrane fuel cell (PEMFC) system that operates up to 160 C temperatures and at ambient pressures for stationary power applications, and (b) to determine if the GTI-molded composite graphite bipolar separator plate could provide long term operational stability at 160 C or higher. There are many reasons that fuel cell research has been receiving much attention. Fuel cells represent environmentally friendly and efficient sources of electrical power generation that could use a variety of fuel sources. The Gas Technology Institute (GTI), formerly Institute of Gas Technology (IGT), is focused on distributed energy stationary power generation systems. Currently the preferred method for hydrogen production for stationary power systems is conversion of natural gas, which has a vast distribution system in place. However, in the conversion of natural gas into a hydrogen-rich fuel, traces of carbon monoxide are produced. Carbon monoxide present in the fuel gas will in time cumulatively poison, or passivate the active platinum catalysts used in the anodes of PEMFC's operating at temperatures of 60 to 80 C. Various fuel processors have incorporated systems to reduce the carbon monoxide to levels below 10 ppm, but these require additional catalytic section(s) with sensors and controls for effective carbon monoxide control. These CO cleanup systems must also function especially well during transient load operation where CO can spike 300% or more. One way to circumvent the carbon monoxide problem is to operate the fuel cell at a higher temperature where carbon monoxide cannot easily adsorb onto the catalyst and poison it. Commercially available polymer membranes such as Nafion{trademark} are not capable of operation at temperatures sufficiently high to prevent this. Hence this project investigated a new polymer membrane alternative to Nafion{trademark} that is capable of operation at temperatures up to 160 C.

L.G. Marianowski

2001-12-21

402

Elastic thickness compressibilty of the red cell membrane.  

PubMed Central

We have used an ultrasensitive force probe and optical interferometry to examine the thickness compressibility of the red cell membrane in situ. Pushed into the centers of washed-white red cell ghosts lying on a coverglass, the height of the microsphere-probe tip relative to its closest approach on the adjacent glass surface revealed the apparent material thickness, which began at approximately 90 nm per membrane upon detection of contact (force approximately 1-2 pN). With further impingement, the apparent thickness per membrane diminished over a soft compliant regime that spanned approximately 40 nm and stiffened on approach to approximately 50 nm under forces of approximately 100 pN. The same force-thickness response was obtained on recompression after retraction of the probe, which demonstrated elastic recoverability. Scaled by circumferences of the microspheres, the forces yielded energies of compression per area which exhibited an inverse distance dependence resembling that expected for flexible polymers. Attributed to the spectrin component of the membrane cytoskeleton, the energy density only reached one thermal energy unit (k(B)T) per spectrin tetramer near maximum compression. Hence, we hypothesized that the soft compliant regime probed in the experiments represented the compressibility of the outer region of spectrin loops and that the stiff regime < 50 nm was the response of a compact mesh of spectrin backed by a hardcore structure. To evaluate this hypothesis, we used a random flight theory for the entropic elasticity of polymer loops to model the spectrin network. We also examined the possibility that additional steric repulsion and apparent thickening could arise from membrane thermal-bending excitations. Fixing the energy scale to k(B)T/spectrin tetramer, the combined elastic response of a network of ideal polymer loops plus the membrane steric interaction correlated well with the measured dependence of energy density on distance for a statistical segment length of approximately 5 nm for spectrin (i.e., free chain end-to-end length of approximately 29 nm) and a hardcore limit of approximately 30 nm for underlying structure. PMID:11509359

Heinrich, V; Ritchie, K; Mohandas, N; Evans, E

2001-01-01

403

High temperature polymers for proton exchange membrane fuel cells  

NASA Astrophysics Data System (ADS)

Novel proton exchange membranes (PEMs) were investigated that show potential for operating at higher temperatures in both direct methanol (DMFC) and H 2/air PEM fuel cells. The need for thermally stable polymers immediately suggests the possibility of heterocyclic polymers bearing appropriate ion conducting sites. Accordingly, monomers and random disulfonated poly(arylene ether) copolymers containing either naphthalimide, benzoxazole or benzimidazole moieties were synthesized via direct copolymerization. The ion exchange capacity (IEC) was varied by simply changing the ratio of disulfonated monomer to nonsulfonated monomer in the copolymerization step. Water uptake and proton conductivity of cast membranes increased with IEC. The water uptake of these heterocyclic copolymers was lower than that of comparable disulfonated poly(arylene ether) systems, which is a desirable improvement for PEMs. Membrane electrode assemblies were prepared and the initial fuel cell performance of the disulfonated polyimide and polybenzoxazole (PBO) copolymers was very promising at 80°C compared to the state-of-the-art PEM (NafionRTM); nevertheless these membranes became brittle under operating conditions. Several series of poly(arylene ether)s based on disodium-3,3'-disulfonate-4,4 '-dichlorodiphenylsulfone (S-DCDPS) and a benzimidazole-containing bisphenol were synthesized and afforded copolymers with enhanced stability. Selected properties of these membranes were compared to separately prepared miscible blends of disulfonated poly(arylene ether sulfone) copolymers and polybenzimidazole (PBI). Complexation of the sulfonic acid groups with the PBI structure reduced water swelling and proton conductivity. The enhanced proton conductivity of NafionRTM membranes has been proposed to be due to the aggregation of the highly acidic side-chain sulfonic acid sites to form ion channels. A series of side-chain sulfonated poly(arylene ether sulfone) copolymers based on methoxyhydroquinone was synthesized in order to investigate this possible advantage and to couple this with the excellent hydrolytic stability of poly(arylene ether)s. The methoxy groups were deprotected to afford reactive phenolic sites and nucleophilic substitution reactions with functional aryl sulfonates were used to prepare simple aryl or highly acidic fluorinated sulfonated copolymers. The proton conductivity and water sorption of the resulting copolymers increased with the ion exchange capacity, but changing the acidity of the sulfonic acid had no apparent effect.

Einsla, Brian Russel

404

Triggering of erythrocyte cell membrane scrambling by salinomycin.  

PubMed

Salinomycin, a polyether ionophore antibiotic effective against a variety of pathogens, has been shown to trigger apoptosis of cancer cells and cancer stem cells. The substance is thus considered for the treatment of malignancy. Salinomycin compromises tumour cell survival at least in part by interference with mitochondrial function. Erythrocytes lack mitochondria but may undergo apoptosis-like suicidal cell death or eryptosis, which is characterized by scrambling of the cell membrane with phosphatidylserine exposure at the erythrocyte surface. Signalling involved in the triggering of eryptosis includes activation of oxidant-sensitive Ca(2+) permeable cation channels with subsequent increase in cytosolic Ca(2+) activity ([Ca(2+)]i). This study explored whether salinomycin stimulates eryptosis. Phosphatidylserine-exposing erythrocytes were identified by measurement of annexin-V binding, cell volume was estimated from forward scatter, haemolysis determined from haemoglobin release, [Ca(2+)]i quantified utilizing Fluo3-fluorescence and oxidative stress from 2',7' dichlorodihydrofluorescein diacetate (DCFDA) fluorescence in flow cytometry. A 48-hr exposure to salinomycin (5-100 nM) was followed by a significant increase in Fluo3-fluorescence, DCFDA fluorescence and annexin-V binding, as well as a significant decrease in forward scatter (at 5-10 nM, but not at 50 and 100 nM). The annexin-V binding after salinomycin treatment was significantly blunted but not abrogated in the nominal absence of extracellular Ca(2+) or in the presence of antioxidant n-acetyl cysteine (1 mM). Salinomycin triggers cell membrane scrambling, an effect at least partially due to oxidative stress and entry of extracellular Ca(2+). PMID:24717091

Bissinger, Rosi; Malik, Abaid; Jilani, Kashif; Lang, Florian

2014-11-01

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