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1

Protein profiling of sickle cell versus control RBC core membrane skeletons by ICAT technology and tandem mass spectrometry  

Microsoft Academic Search

A proteomic approach using a cleavable ICAT reagent and nano-LC ESI tandem mass spectrometry was used to perform protein profiling\\u000a of core RBC membrane skeleton proteins between sickle cell patients (SS) and controls (AA), and determine the efficacy of\\u000a this technology. The data was validated through Peptide\\/Protein Prophet and protein ratios were calculated through ASAPratio.\\u000a Through an ANOVA test, it

Jose Chou; Pankaj K. Choudhary; Steven R. Goodman

2006-01-01

2

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

3

Autoantibodies against mouse bromelain-modified RBC are specifically inhibited by a common membrane phospholipid, phosphatidylcholine.  

PubMed Central

Sera from mice injected 4 days earlier with lipopolysaccharide lysed mouse RBC treated with bromelain (brom). This lytic activity was totally inhibited by including phosphatidylcholine at final concentrations of about 2 micrograms/ml, or more, in the lytic mixtures. In contrast, the lytic activity of antibodies against rat RBC was not inhibited, even at concentrations of phosphatidylcholine up to 2.5 mg/ml. Various components of the phosphatidylcholine molecule, and other lipids including the closely-related molecule dipalmitoyl phosphatidyl-dimethyl-ethanolamine which is identical to dipalmitoyl phosphatidylcholine, except for the absence of a CH2 group on the polar head group, did not inhibit lysis by the autoantibodies. Autoantibodies against mouse brom RBC, but not antibodies against rat RBC, bound to, and could be eluted from, phosphatidylcholine molecules attached to an insoluble matrix. Liposomes of phosphatidylcholine prepared in the presence of phosphatidic acid or phosphatidylinositol did not inhibit the lysis of mouse brom RBC by autoantibodies to the same extent as liposomes of only phosphatidylcholine. This suggests that phosphatidylcholine is recognized by the autoantibodies only if presented in a certain configuration. We suggest that the function of these autoantibodies may be to facilitate the removal of membrane-damaged cells from the body. Such cells may arise by the process of ageing, or because of the effects of infectious agents such as viruses. PMID:4007927

Cox, K O; Hardy, S J

1985-01-01

4

Laser diffractometer of RBC suspension  

Microsoft Academic Search

The original optical diagnostic device for measuring the RBC membrane permeability and RBC charge is considered in this message. A blood microsample drips in the mixer filled with a solution of NaCl. The resultant RBC suspension trickles down the pipe into the drain vessel. The flat thin cell is fitted into the pipe. The optical channel consists of He-Ne laser

Igor Z. Nemtsev

1996-01-01

5

Spectrin Folding versus Unfolding Reactions and RBC Membrane Stiffness  

PubMed Central

Spectrin (Sp), a key component of the erythrocyte membrane, is routinely stretched to near its fully folded contour length during cell deformations. Such dynamic loading may induce domain unfolding as suggested by recent experiments. Herein we develop a model to describe the folding/unfolding of spectrin during equilibrium or nonequilibrium extensions. In both cases, our model indicates that there exists a critical extension beyond which unfolding occurs. We further deploy this model, together with a three-dimensional model of the junctional complex in the erythrocyte membrane, to explore the effect of Sp unfolding on the membrane's mechanical properties, and on the thermal fluctuation of membrane-attached beads. At large deformations our results show a distinctive strain-induced unstiffening behavior, manifested in the slow decrease of the shear modulus, and accompanied by an increase in bead fluctuation. Bead fluctuation is also found to be influenced by mode switching, a phenomenon predicted by our three-dimensional model. The amount of stiffness reduction, however, is modest compared with that reported in experiments. A possible explanation for the discrepancy is the occurrence of spectrin head-to-head disassociation which is also included within our modeling framework and used to analyze bead motion as observed via experiment. PMID:18065469

Zhu, Qiang; Asaro, Robert J.

2008-01-01

6

RBC count  

MedlinePLUS

... cor pulmonale ) Dehydration (such as from severe diarrhea) Kidney tumor (renal cell carcinoma) Low blood oxygen level (hypoxia) ... marrow failure (for example, from radiation, toxins, or tumor) ... disease) RBC destruction ( hemolysis ) due to transfusion, blood ...

7

Red Blood Cell Membrane-Cloaked Nanoparticles For Drug Delivery  

NASA Astrophysics Data System (ADS)

Herein we describe the development of the Red Blood Cell coated nanoparticle, RBC-NP. Purified natural erythrocyte membrane is used to coat drug-loaded poly(lacticco-glycolic acid) (PLGA). Synthetic PLGA co-polymer is biocompatible and biodegradable and has already received US FDA approval for drug-delivery and diagnostics. This work looks specifically at the retention of immunosuppressive proteins on RBC-NPs, right-sidedness of natural RBC membranes interfacing with synthetic polymer nanoparticles, sustained and retarded drug release of RBC-NPs as well as further surface modification of RBC-NPs for increased targeting of model cancer cell lines.

Carpenter, Cody Westcott

8

RBC urine test  

MedlinePLUS

Red blood cells in urine; Hematuria test; Urine - red blood cells ... A normal result is 4 RBC/HPF (red blood cells per high power field) or less when the sample is examined under a microscope. The example above is a common measurement ...

9

The cellular antioxidant activity in red blood cells (CAA-RBC): A new approach to bioavailability and synergy of phytochemicals and botanical extracts  

Microsoft Academic Search

In the present work, human red blood cells (RBC) were used to determine cellular antioxidant activity (CAA-RBC) of pure phytochemicals and botanical extracts, with the aim to predict their bioavailability.Amongst the pure flavonoids, isorhamnetin, tamarixetin, myricetin, and kaempferol showed the highest activity in the CAA-RBC assay; whereas, with the “chemical” oxygen radical absorbance capacity (ORAC) assay, the compounds that showed

Manuela Blasa; Donato Angelino; Lorenzo Gennari; Paolino Ninfali

2011-01-01

10

Light scattering of human red blood cells during metabolic remodeling of membrane  

E-print Network

We present the light scattering properties of individual human red blood cells (RBCs). We show that both the RBC static and dynamic scattering signals are altered by adenosine 5’-triphosphate (ATP)-driven membrane metabolic ...

Park, YongKeun

11

RBC indices  

MedlinePLUS

... corpuscular hemoglobin concentration (MCHC); Mean corpuscular volume (MCV); Red blood cell indices ... and hemoglobin. The MCV reflects the size of red blood cells. The MCH and MCHC reflect the ...

12

Transformation of membrane nanosurface of red blood cells under hemin action  

NASA Astrophysics Data System (ADS)

Hemin is the product of hemoglobin oxidation. Some diseases may lead to a formation of hemin. The accumulation of hemin causes destruction of red blood cells (RBC) membranes. In this study the process of development of topological defects of RBC membranes within the size range from nanoscale to microscale levels is shown. The formation of the grain-like structures in the membrane (``grains'') with typical sizes of 120-200 nm was experimentally shown. The process of formation of ``grains'' was dependent on the hemin concentration and incubation time. The possible mechanism of membrane nanostructure alterations is proposed. The kinetic equations of formation and transformation of small and medium topological defects were analyzed. This research can be used to study the cell intoxication and analyze the action of various agents on RBC membranes.

Kozlova, Elena; Chernysh, Alexander; Moroz, Victor; Gudkova, Olga; Sergunova, Victoria; Kuzovlev, Artem

2014-08-01

13

Transformation of membrane nanosurface of red blood cells under hemin action  

PubMed Central

Hemin is the product of hemoglobin oxidation. Some diseases may lead to a formation of hemin. The accumulation of hemin causes destruction of red blood cells (RBC) membranes. In this study the process of development of topological defects of RBC membranes within the size range from nanoscale to microscale levels is shown. The formation of the grain-like structures in the membrane (“grains”) with typical sizes of 120–200?nm was experimentally shown. The process of formation of “grains” was dependent on the hemin concentration and incubation time. The possible mechanism of membrane nanostructure alterations is proposed. The kinetic equations of formation and transformation of small and medium topological defects were analyzed. This research can be used to study the cell intoxication and analyze the action of various agents on RBC membranes. PMID:25112597

Kozlova, Elena; Chernysh, Alexander; Moroz, Victor; Gudkova, Olga; Sergunova, Victoria; Kuzovlev, Artem

2014-01-01

14

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

15

Restoration of intracellular ATP production in banked red blood cells improves inducible ATP export and suppresses RBC-endothelial adhesion.  

PubMed

Transfusion of banked red blood cells (RBCs) has been associated with poor cardiovascular outcomes. Storage-induced alterations in RBC glycolytic flux, attenuated ATP export, and microvascular adhesion of transfused RBCs in vivo could contribute, but the underlying mechanisms have not been tested. We tested the novel hypothesis that improving deoxygenation-induced metabolic flux and the associated intracellular ATP generation in stored RBCs (sRBCs) results in an increased extracellular ATP export and suppresses microvascular adhesion of RBCs to endothelium in vivo following transfusion. We show deficient intracellular ATP production and ATP export by human sRBCs during deoxygenation (impairments ?42% and 49%, respectively). sRBC pretreatment with a solution containing glycolytic intermediate/purine/phosphate precursors (i.e., "PIPA") restored deoxygenation-induced intracellular ATP production and promoted extracellular ATP export (improvement ?120% and 50%, respectively). In a nude mouse model of transfusion, adhesion of human RBCs to the microvasculature in vivo was examined. Only 2% of fresh RBCs (fRBCs) transfused adhered to the vascular wall, compared with 16% of sRBCs transfused. PIPA pretreatment of sRBCs significantly reduced adhesion to just 5%. In hypoxia, adhesion of sRBCs transfused was significantly augmented (up to 21%), but not following transfusion of fRBCs or PIPA-treated sRBCs (3.5% or 6%). Enhancing the capacity for deoxygenation-induced glycolytic flux within sRBCs increases their ability to generate intracellular ATP, improves the inducible export of extracellular anti-adhesive ATP, and consequently suppresses adhesion of stored, transfused RBCs to the vascular wall in vivo. PMID:25305182

Kirby, Brett S; Hanna, Gabi; Hendargo, Hansford C; McMahon, Timothy J

2014-12-15

16

Electroporation of cell membranes.  

PubMed Central

Electric pulses of intensity in kilovolts per centimeter and of duration in microseconds to milliseconds cause a temporary loss of the semipermeability of cell membranes, thus leading to ion leakage, escape of metabolites, and increased uptake by cells of drugs, molecular probes, and DNA. A generally accepted term describing this phenomenon is "electroporation." Other effects of a high-intensity electric field on cell membranes include membrane fusions, bleb formation, cell lysis... etc. Electroporation and its related phenomena reflect the basic bioelectrochemistry of cell membranes and are thus important for the study of membrane structure and function. These phenomena also occur in such events as electric injury, electrocution, and cardiac procedures involving electric shocks. Electroporation has found applications in: (a) introduction of plasmids or foreign DNA into living cells for gene transfections, (b) fusion of cells to prepare heterokaryons, hybridoma, hybrid embryos... etc., (c) insertion of proteins into cell membranes, (d) improving drug delivery and hence effectiveness in chemotherapy of cancerous cells, (e) constructing animal model by fusing human cells with animal tissues, (f) activation of membrane transporters and enzymes, and (g) alteration of genetic expression in living cells. A brief review of mechanistic studies of electroporation is given. PMID:1912274

Tsong, T Y

1991-01-01

17

Red blood cell membrane and serum sialic acid in relation to erythrocyte sedimentation rate.  

PubMed

Sialic acid was determined in red blood cell (RBC) membrane and in serum, and correlated to erythrocyte sedimentation rate (ESR). For this purpose blood samples were obtained from 57 patients, regardless of their pathological condition, and divided into groups according to the ESR. 15 blood samples obtained from health individuals whose ESR was lower than 20 mm/h served as controls. Sialic acid was released from RBC membranes obtained by hemolysis, and from serum glycoproteins precipitated with ethanol by treatment with 0.1 N HCl at 80 degrees C for 1 h. The results showed the sialic acid contents of both membranes and serum to be higher in most of the groups with elevated ESR, as compared to the control group, although no quantitative correlation was noticed. Statistical evaluation showed highly significant differences between the group of pathological samples as a whole and the control group in the sialic acid content of both RBC membranes and sera. PMID:6779485

Levinsky, H; Rothman, G; Lapidot, M; Allalouf, D

1980-01-01

18

Effect of the natural state of an elastic cellular membrane on tank-treading and tumbling motions of a single red blood cell.  

PubMed

A two-dimensional computer simulation model was proposed for tank-treading and tumbling motions of an elastic biconcave red blood cell (RBC) under steady shear flow. The RBC model consisted of an outer cellular membrane and an inner fluid; the membrane's elastic properties were modeled by springs for stretch/compression and bending to consider the membrane's natural state in a practical manner. Membrane deformation was coupled with incompressible viscous flow of the inner and outer fluids of the RBC using a particle method. The proposed simulation model was capable of reproducing tank-treading and tumbling motions of an RBC along with rotational oscillation, which is the transition between the two motions. In simulations using the same initial RBC shape with different natural states of the RBC membrane, only tank-treading motion was exhibited in the case of a uniform natural state of the membrane, and a nonuniform natural state was necessary to generate the rotational oscillation and tumbling motion. Simulation results corresponded to published data from experimental and computational studies. In the range of simulation parameters considered, the relative membrane elastic force versus fluid viscous force was approximately 1 at the transition when the natural state nonuniformity was taken into account in estimating the membrane elastic force. A combination of natural state nonuniformity and elastic spring constant determined that change in the RBC deformation at the transition is that from a large compressive deformation to no deformation, such as rigid body. PMID:20365402

Tsubota, Ken-ichi; Wada, Shigeo

2010-01-01

19

Rheological properties of RBC in the microcirculation of mammalian skeletal muscle. [red blood cells  

NASA Technical Reports Server (NTRS)

In the investigation the established technique of direct microscopic viewing was combined with the use of a closed circuit television system and cinematography. The red cell flow patterns in all capillaries were found to be oscillatory with characteristic cycle frequencies and amplitudes for all concentrations of inspired oxygen greater than 8%. Generally, there was a transient decrease in mean flow rate with increasing severity of hypoxia, with a gradual return toward control values. Red cell flow patterns are discussed along with questions of red cell configuration.

Ehrenberg, M. H.

1974-01-01

20

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

21

Antigens Protected Functional Red Blood Cells By The Membrane Grafting Of Compact Hyperbranched Polyglycerols  

PubMed Central

Red blood cell (RBC) transfusion is vital for the treatment of a number of acute and chronic medical problems such as thalassemia major and sickle cell anemia 1-3. Due to the presence of multitude of antigens on the RBC surface (~308 known antigens 4), patients in the chronic blood transfusion therapy develop alloantibodies due to the miss match of minor antigens on transfused RBCs 4, 5. Grafting of hydrophilic polymers such as polyethylene glycol (PEG) and hyperbranched polyglycerol (HPG) forms an exclusion layer on RBC membrane that prevents the interaction of antibodies with surface antigens without affecting the passage of small molecules such as oxygen ,glucose, and ions3. At present no method is available for the generation of universal red blood donor cells in part because of the daunting challenge presented by the presence of large number of antigens (protein and carbohydrate based) on the RBC surface and the development of such methods will significantly improve transfusion safety, and dramatically improve the availability and use of RBCs. In this report, the experiments that are used to develop antigen protected functional RBCs by the membrane grafting of HPG and their characterization are presented. HPGs are highly biocompatible compact polymers 6, 7, and are expected to be located within the cell glycocalyx that surrounds the lipid membrane 8, 9 and mask RBC surface antigens10, 11. PMID:23328980

Chapanian, Rafi; Constantinescu, Iren; Brooks, Donald E.; Scott, Mark D.; Kizhakkedathu, Jayachandran

2013-01-01

22

Depletion of Omega3 Fatty Acid Levels in Red Blood Cell Membranes of Depressive Patients  

Microsoft Academic Search

Background: It has been hypothesized that depletion of cell membrane n3 polyunsaturated fatty acids (PUFA), particularly docosahexanoic acid (DHA), may be of etiological importance in depression.Methods: We measured the fatty acid composition of phospholipid in cell membranes from red blood cells (RBC) of 15 depressive patients and 15 healthy control subjects.Results: Depressive patients showed significant depletions of total n3 PUFA

Malcolm Peet; Brendan Murphy; Janet Shay; David Horrobin

1998-01-01

23

RBC deformability and amino acid concentrations after hypo-osmotic challenge may reflect chronic cell hydration status in healthy young men  

PubMed Central

Biomarkers of chronic cell hydration status are needed to determine whether chronic hyperosmotic stress increases chronic disease risk in population-representative samples. In vitro, cells adapt to chronic hyperosmotic stress by upregulating protein breakdown to counter the osmotic gradient with higher intracellular amino acid concentrations. If cells are subsequently exposed to hypo-osmotic conditions, the adaptation results in excess cell swelling and/or efflux of free amino acids. This study explored whether increased red blood cell (RBC) swelling and/or plasma or urine amino acid concentrations after hypo-osmotic challenge might be informative about relative chronic hyperosmotic stress in free-living men. Five healthy men (20–25 years) with baseline total water intake below 2 L/day participated in an 8-week clinical study: four 2-week periods in a U-shaped A-B-C-A design. Intake of drinking water was increased by +0.8 ± 0.3 L/day in period 2, and +1.5 ± 0.3 L/day in period 3, and returned to baseline intake (0.4 ± 0.2 L/day) in period 4. Each week, fasting blood and urine were collected after a 750 mL bolus of drinking water, following overnight water restriction. The periods of higher water intake were associated with significant decreases in RBC deformability (index of cell swelling), plasma histidine, urine arginine, and urine glutamic acid. After 4 weeks of higher water intake, four out of five participants had ½ maximal RBC deformability below 400 mmol/kg; plasma histidine below 100 ?mol/L; and/or undetectable urine arginine and urine glutamic acid concentrations. Work is warranted to pursue RBC deformability and amino acid concentrations after hypo-osmotic challenge as possible biomarkers of chronic cell hydration. PMID:24303184

Stookey, Jodi D; Klein, Alexis; Hamer, Janice; Chi, Christine; Higa, Annie; Ng, Vivian; Arieff, Allen; Kuypers, Frans A; Larkin, Sandra; Perrier, Erica; Lang, Florian

2013-01-01

24

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

25

IgG red blood cell autoantibodies in autoimmune hemolytic anemia bind to epitopes on red blood cell membrane band 3 glycoprotein  

SciTech Connect

Red blood cell (RBC) autoantibodies from patients with IgG warm-type autoimmune hemolytic anemia were labeled with iodine 125 and their RBC binding behavior characterized. Epitope-bearing RBC membrane polypeptides were identified after autoantibody immunoprecipitation of labeled membranes and immunoblotting. Immunoaffinity isolation of labeled membrane proteins with 12 different IgG hemolytic autoantibodies with protein A-agarose revealed a major polypeptide at Mr 95 to 110 kd, which coelectrophoresed on sodium dodecylsulfate-polyacrylamide gel electrophoresis with a membrane component isolated with sheep IgG anti-band 3. Immunoprecipitation studies with chymotrypsinized RBCs resulted in the recovery of two labeled membrane polypeptides with molecular weights characteristically resulting from the chymotryptic fragmentation of band 3. Immunoblotting with sheep IgG anti-band 3 of the immunoprecipitated polypeptides confirmed that hemolytic autoantibody binding led to recovery of band 3 or its fragments. Two 125I-labeled IgG hemolytic autoantibodies showed binding behavior consistent with epitope localization on band 3. The labeled RBC autoantibodies bound immunospecifically to all types of human RBC tested, including those of rare Rh type (Rh-null, D--) at a site density of approximately 10(6) per RBC. The 125I-IgG in two labeled autoantibodies was 84% and 92% adsorbable by human and higher nonhuman primate RBCs. Antigen-negative animal RBC bound less than 10%, consistent with immunospecific RBC binding. IgG-1 was the major subclass in five autoantibodies tested; one of six fixed complement; and autoantibody IgG appeared polyclonal by isoelectric focusing. We conclude that IgG eluted from RBCs of patients with autoimmune hemolytic anemia consists predominantly of a single totally RBC-adsorbable antibody population that binds to antigenic determinants on band 3.

Victoria, E.J.; Pierce, S.W.; Branks, M.J.; Masouredis, S.P. (Univ. of California, San Diego (USA))

1990-01-01

26

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

27

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

28

Relationships between membrane lipids and ion transport in red blood cells of Dahl rats.  

PubMed

Distinct changes of membrane lipid content could contribute to the abnormalities of ion transport that take part in the development of salt hypertension in Dahl rats. The relationships between lipid content and particular ion transport systems were studied in red blood cells (RBC) of Dahl rats kept on low- and high-salt diets for 5 weeks since weaning. Dahl salt-sensitive (SS/Jr) rats on high-salt diet had increased blood pressure, levels of plasma triacylglycerols and total plasma cholesterol compared to salt-resistant (SR/Jr) rats. Furthermore, RBC of SS/Jr rats differed from SR/Jr ones by increased content of total membrane phospholipids, but membrane cholesterol was not changed significantly. SS/Jr rats had higher RBC intracellular Na+ (Na(i)+) content and enhanced bumetanide-sensitive Rb+ uptake. RBC membrane content of cholesterol and phospholipids correlated positively with RBC Na(i)+ content, with the activity of Na+-K+ pump and Na+-K+-2Cl- cotransport and also with Rb+ leak. The content of phosphatidylserines plus phosphatidylinositols was positively associated with RBC Na(i)+ content, with the activity of Na+-K+ pump and Na+-K+-2Cl- cotransport and with Rb+ leak. The content of sphingomyelins was positively related to Na+-K+-2Cl- cotransport activity and negatively to ouabain-sensitive Rb+-K+ exchange. We can conclude that observed relationships between ion transport and the membrane content of cholesterol and/or sphingomyelins, which are known to regulate membrane fluidity, might participate in the pathogenesis of salt hypertension in Dahl rats. PMID:15936778

Vokurková, Martina; Nováková, Olga; Dobesová, Zdenka; Kunes, Jaroslav; Zicha, Josef

2005-08-12

29

Interaction of flavonoids with red blood cell membrane lipids and proteins: antioxidant and antihemolytic effects.  

PubMed

Plant flavonoids are emerging as potent therapeutic drugs effective against a wide range of free radical mediated diseases. Hence their interactions with cell membranes, which generally serve as targets for lipid peroxidation, are of enormous interest. Here we report in vitro studies, via absorption and fluorescence spectroscopy, on the effects of several flavonoids (namely fisetin, quercetin, chrysin, morin, and 3-hydroxyflavone, 3-HF) in goat RBC membranes. Owing to the presence of functionally relevant membrane protein components embedded in the lipid bilayer RBC ghosts provide a more realistic system for exploring drug actions in biomembranes than simpler membrane models like phosphatidylcholine liposomes used in our previous studies [e.g. B. Sengupta, A. Banerjee, P.K. Sengupta, FEBS Lett. 570 (2004) 77-81]. Here, we demonstrate that binding of the flavonoids to the RBC membranes significantly inhibits lipid peroxidation, and at the same time enhances their integrity against hypotonic lysis. Interestingly, the antioxidant and antihemolytic activities are found to be crucially dependent on the locations of the flavonoids in the membrane matrix as revealed by fluorescence studies. Furthermore, we observe that FRET (from membrane protein tryptophans to flavonoids) occurs with significant efficiency indicating that the flavonoid binding sites lie in close proximity to the tryptophan residues in the ghost membrane proteins. PMID:17239435

Chaudhuri, Sudip; Banerjee, Anwesha; Basu, Kaushik; Sengupta, Bidisa; Sengupta, Pradeep K

2007-06-01

30

Cell Membrane Structure and Function  

NSDL National Science Digital Library

Students learn about the different structures that comprise cell membranes, fulfilling part of the Research and Revise stages of the legacy cycle. They view online animations of cell membrane dynamics (links provided). Then they observe three teacher demonstrations that illustrate diffusion and osmosis concepts, as well as the effect of movement through a semi-permeable membrane using Lugol's solution.

Vu Bioengineering Ret Program

31

Two-dimensional strain-hardening membrane model for large deformation behavior of multiple red blood cells in high shear conditions  

PubMed Central

Background Computational modeling of Red Blood Cell (RBC) flow contributes to the fundamental understanding of microhemodynamics and microcirculation. In order to construct theoretical RBC models, experimental studies on single RBC mechanics have presented a material description for RBC membranes based on their membrane shear, bending and area moduli. These properties have been directly employed in 3D continuum models of RBCs but practical flow analysis with 3D models have been limited by their computationally expensive nature. As such, various researchers have employed 2D models to efficiently and qualitatively study microvessel flows. Currently, the representation of RBC dynamics using 2D models is a limited methodology that breaks down at high shear rates due to excessive and unrealistic stretching. Methods We propose a localized scaling of the 2D elastic moduli such that it increases with RBC local membrane strain, thereby accounting for effects such as the Poisson effect and membrane local area incompressibility lost in the 2D simplification. Validation of our 2D Large Deformation (2D-LD) RBC model was achieved by comparing the predicted RBC deformation against the 3D model from literature for the case of a single RBC in simple shear flow under various shear rates (dimensionless shear rate G?=?0.05, 0.1, 0.2, 0.5). The multi-cell flow of RBCs (38% Hematocrit) in a 20 ?m width microchannel under varying shear rates (50, 150, 150 s-1) was then simulated with our proposed model and the popularly-employed 2D neo-Hookean model in order to evaluate the efficacy of our proposed 2D-LD model. Results The validation set indicated similar RBC deformation for both the 2D-LD and the 3D models across the studied shear rates, highlighting the robustness of our model. The multi-cell simulation indicated that the 2D neo-Hookean model predicts noodle-like RBC shapes at high shear rates (G?=?0.5) whereas our 2D-LD model maintains sensible RBC deformations. Conclusion The ability of the 2D-LD model to limit RBC strain even at high shear rates enables this proposed model to be employed in practical simulations of high shear rate microfluidic flows such as blood separation channels. PMID:24885482

2014-01-01

32

Inhibition of membrane Na(+)-K+ Atpase of the brain, liver and RBC in rats administered di(2-ethyl hexyl) phthalate (DEHP) a plasticizer used in polyvinyl chloride (PVC) blood storage bags.  

PubMed

Significant amounts of di(2-ethylhexyl) phthalate (DEHP) leach out into blood stored in DEHP plasticized polyvinyl chloride (PVC) bags resulting in the exposure of recipients of blood transfusion to this compound. The aim of this study was to find out whether DEHP at these low levels has any effect on the activity of membrane Na(+)-K+ ATPase, since a decrease in this enzyme activity has been reported to take place in a number of disorders like neurodegenerative and psychiatric disorders, coronary artery disease and stroke, syndrome-X, tumours etc. DEHP was administered (ip) at a low dose of 750 microg/100 g body weight to rats and the activity of membrane Na(+)-K+ ATPase in liver, brain and RBC was estimated. Histopathology of brain, activity of HMG CoA reductase (a major rate limiting enzyme in the isoprenoid pathway of which digoxin, the physiological inhibitor of Na(+)-K+ ATPase is a product), intracellular concentration of Ca2+ and Mg2+ in RBC (which is altered as a result of inhibition of Na(+)-K+ ATPase) were also studied. (In the light of the observation of increase of intracellular Ca2+ load and intracellular depletion of Mg2+ when Na(+)-K+ ATPase is inhibited). Histopathology of brain revealed areas of degeneration in the rats administered DEHP. There was significant inhibition of membrane Na(+)-K+ ATPase in brain, liver and RBC. Intracellular Ca2+ increased in the RBC while intracellular Mg2+ decreased. However activity of hepatic HMG CoA reductase decreased. Activity of Na(+)-K+ ATPase and HMG CoA reductase, however returned to normal levels within 7 days of stopping administration of DEHP. The inhibition of membrane Na(+)-K+ ATPase activity by DEHP may indicate the possibility of predisposing recipients of transfusion of blood or hemodialysis to the various disorders mentioned above. However since this effect is reversed when DEHP administration is stopped, it may not be a serious problem in the case of a few transfusion; but in patients receiving repeated blood transfusion as in thalassemia patients or patients undergoing hemodialysis, possibility of this risk has to be considered. This inhibition is a direct effect of DEHP or its metabolites, since activity of HMG CoA reductase, (an enzyme which catalyses a major rate limiting step in the isoprenoid pathway by which digoxin, the physiological inhibitor of Na(+)-K+ ATPase is synthesized) showed a decrease. PMID:15248477

Dhanya, C R; Indu, A R; Deepadevi, K V; Kurup, P A

2003-08-01

33

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

34

Influence of moxaverine hydrochloride on membrane curvature and microsieve filterability of red cells after exposure to hyperosmolarity and lactacidosis.  

PubMed

Using a combination of novel techniques to assess quantitatively the shape and the filterability of red blood cells (RBC) after exposure to stress conditions (400 mosmol/l, lactacidosis, pH 6.8), the effects of 1-benzyl-3-ethyl-6,7-dimethoxy-isoquinoline hydrochloride (moxaverine-HCl, Kollateral) were tested. The shape of freely suspended RBC was quantified using the tangent count procedure. The filterability (microrheological performance) of leukocyte-free RBC suspensions was determined by computer-assisted conductometry using novel precision metal microsieves with uniform pore diameter of 4.2 micron. Moxaverine, when present in doses between 10(-5) und 10(-2) mol/l while the RBC are stressed, restored both the normal discoid red cell configuration and the microrheological performance when tested under low shear stresses. The data show that moxaverine, a papaverine derivative, hitherto considered as a classical vasodilator exerts protective effects on RBC membrane curvature and whole cell microrheological behavior (performance). The protective effects manifest themselves when the RBC's are exposed to abnormal biochemical conditions such as they might occur in poststenotic areas, where hypoxic ischemia is known to lead to a combination of hyperosmolarity and lactacidosis which modify the RBCs. PMID:3415714

Schmid-Schönbein, H; Schröder, S; Grebe, R; Artmann, G; Eschweiler, H; Teitel, P

1988-05-01

35

Fuel cell with ionization membrane  

NASA Technical Reports Server (NTRS)

A fuel cell is disclosed comprising an ionization membrane having at least one area through which gas is passed, and which ionizes the gas passing therethrough, and a cathode for receiving the ions generated by the ionization membrane. The ionization membrane may include one or more openings in the membrane with electrodes that are located closer than a mean free path of molecules within the gas to be ionized. Methods of manufacture are also provided.

Hartley, Frank T. (Inventor)

2007-01-01

36

A study of the dynamic properties of the human red blood cell membrane using quasi-elastic light-scattering spectroscopy.  

PubMed Central

A quasi-elastic light-scattering (QELS) microscope spectrometer was used to study the dynamic properties of the membrane/cytoskeleton of individual human red blood cells (RBCs). QELS is a spectroscopic technique that measures intensity fluctuations of laser light scattered from a sample. The intensity fluctuations were analyzed using power spectra and the intensity autocorrelation function, g(2)(tau), which was approximated with a single exponential. The value of the correlation time, Tcorr, was used for comparing results. Motion of the RBC membrane/cytoskeleton was previously identified as the source of the QELS signal from the RBC (R. B. Tishler and F. D. Carlson, 1987. Biophys. J. 51:993-997), and additional data supporting that conclusion are presented. Similar results were obtained from anucleate mammalian RBCs that have structures similar to that of the human RBC, but not for morphologically distinct, nucleated RBCs. The effect of altering the physical properties of the cytoplasm and the membrane/cytoskeleton was also studied. Osmotically increasing the cytoplasmic viscosity led to significant increases in Tcorr. Increasing the membrane cholesterol content and increasing the intracellular calcium content both led to decreased deformability of the human RBC. In both cases, the modified cells with decreased deformability showed an increase in Tcorr, demonstrating that QELS could measure biochemically induced changes of the membrane/cytoskeleton. Physiological changes were measured in studies of age-separated RBC populations which showed that Tcorr was increased in the older, less deformable cells. PMID:8312494

Tishler, R B; Carlson, F D

1993-01-01

37

Factors Influencing RBC Alloimmunization: Lessons Learned from Murine Models  

PubMed Central

Summary Red blood cell (RBC) alloimmunization may occur following transfusion or pregnancy/delivery. Although observational human studies have described the immunogenicity of RBC antigens and the clinical significance of RBC alloantibodies, studies of factors influencing RBC alloimmunization in humans are inherently limited by the large number of independent variables involved. This manuscript reviews data generated in murine models that utilize transgenic donor mice, which express RBC-specific model or authentic human blood group antigens. Transfusion of RBCs from such donors into nontransgenic but otherwise genetically identical recipient mice allows for the investigation of individual donor or recipient-specific variables that may impact RBC alloimmunization. Potential donor-related variables include methods of blood product collection, processing and storage, donor-specific characteristics, RBC antigen-specific factors, and others. Potential recipient-related variables include genetic factors (MHC/HLA type and polymorphisms of immunoregulatory genes), immune activation status, phenotype of regulatory immune cell subsets, immune cell functional characteristics, prior antigen exposures, and others. Although murine models are not perfect surrogates for human biology, these models generate phenomenological and mechanistic hypotheses of RBC alloimmunization and lay the groundwork for follow-up human studies. Long-term goals include improving transfusion safety and minimizing the morbidity/mortality associated with RBC alloimmunization.

Ryder, Alex B.; Zimring, James C.; Hendrickson, Jeanne E.

2014-01-01

38

Studying red blood cell agglutination by measuring membrane viscosity with optical tweezers  

NASA Astrophysics Data System (ADS)

The red blood cell (RBC) viscoelastic membrane contains proteins and glycoproteins embedded in a fluid lipid bilayer that are responsible for cell agglutination. Manipulating RBCs rouleaux with a double optical tweezers, we observed that the cells slide easily one over the others but are strongly connected by their edges. An explanation for this behavior could be the fact that when the cells slide one over the others, proteins are dragged through the membrane. It confers to the movement a viscous characteristic that is dependent of the velocity between the RBCs and justifies why is so easy to slide them apart. Therefore, in a first step of this work, by measuring the force as a function of the relative velocity between two cells, we confirmed this assumption and used this viscous characteristic of the RBC rouleaux to determine the apparent membrane viscosity of the cell. As this behavior is related to the proteins interactions, we can use the apparent membrane viscosity to obtain a better understanding about cell agglutination. Methods related to cell agglutination induced by antigen-antibody interactions are the basis of most of tests used in transfusion centers. Then, in a second step of this work, we measured the apparent membrane viscosity using antibodies. We observed that this methodology is sensitive to different kinds of bindings between RBCs. Better comprehension of the forces and bindings between RBCs could improve the sensibility and specificity of the hemagglutination reactions and also guides the development of new potentiator substances.

Fernandes, Heloise P.; Fontes, Adriana; de Thomaz, André A.; Barbosa, Luiz C.; Barjas-Castro, Maria L.; Cesar, Carlos L.

2007-09-01

39

The Molecules of the Cell Membrane.  

ERIC Educational Resources Information Center

Cell membrane molecules form a simple, two-dimensional liquid controlling what enters and leaves the cell. Discusses cell membrane molecular architecture, plasma membranes, epithelial cells, cycles of endocytosis and exocytosis, and other topics. Indicates that some cells internalize, then recycle, membrane area equivalent to their entire surface…

Bretscher, Mark S.

1985-01-01

40

Membrane Transport in Primitive Cells  

PubMed Central

Although model protocellular membranes consisting of monoacyl lipids are similar to membranes composed of contemporary diacyl lipids, they differ in at least one important aspect. Model protocellular membranes allow for the passage of polar solutes and thus can potentially support cell-to functions without the aid of transport machinery. The ability to transport polar molecules likely stems from increased lipid dynamics. Selectively permeable vesicle membranes composed of monoacyl lipids allow for many lifelike processes to emerge from a remarkably small set of molecules. PMID:20679338

Mansy, Sheref S.

2010-01-01

41

[Critical role of phosphatidylserine in hemolysis due to red blood cell enzyme/membrane defects].  

PubMed

The life span of human red blood cells (RBCs) is approximately for 120 days, and finally destroyed in reticuloendothelial systems. In pathological conditions, RBCs fall into premature death, i.e. hemolysis. Recent studies have unveiled that abnormal RBCs affected by either membrane disorders or enzyme deficiency as well as senescent RBCs shared the common feature, i.e. exposure of phosphatidylserine (PS) in the outer leaflet of the RBC membrane. Increased intracellular oxidative stress or enhanced calcium permeability impairs maintenance of phospholipid asymmetry, resulting in PS externalization. PS and other eat-me signals may contribute to recognition of abnormal RBC by macrophage. In this review, recent understanding of mechanisms underlying hemolysis are discussed. PMID:18330023

Kanno, Hitoshi

2008-03-01

42

Preliminary Evidence for Cell Membrane Amelioration in Children with Cystic Fibrosis by 5-MTHF and Vitamin B12 Supplementation: A Single Arm Trial  

PubMed Central

Background Cystic fibrosis (CF) is one of the most common fatal autosomal recessive disorders in the Caucasian population caused by mutations of gene for the cystic fibrosis transmembrane conductance regulator (CFTR). New experimental therapeutic strategies for CF propose a diet supplementation to affect the plasma membrane fluidity and to modulate amplified inflammatory response. The objective of this study was to evaluate the efficacy of 5-methyltetrahydrofolate (5-MTHF) and vitamin B12 supplementation for ameliorating cell plasma membrane features in pediatric patients with cystic fibrosis. Methodology and Principal Findings A single arm trial was conducted from April 2004 to March 2006 in an Italian CF care centre. 31 children with CF aged from 3 to 8 years old were enrolled. Exclusion criteria were diabetes, chronic infections of the airways and regular antibiotics intake. Children with CF were supplemented for 24 weeks with 5-methyltetrahydrofolate (5-MTHF, 7.5 mg /day) and vitamin B12 (0.5 mg/day). Red blood cells (RBCs) were used to investigate plasma membrane, since RBCs share lipid, protein composition and organization with other cell types. We evaluated RBCs membrane lipid composition, membrane protein oxidative damage, cation content, cation transport pathways, plasma and RBCs folate levels and plasma homocysteine levels at baseline and after 24 weeks of 5-MTHF and vitamin B12 supplementation. In CF children, 5-MTHF and vitamin B12 supplementation (i) increased plasma and RBC folate levels; (ii) decreased plasma homocysteine levels; (iii) modified RBC membrane phospholipid fatty acid composition; (iv) increased RBC K+ content; (v) reduced RBC membrane oxidative damage and HSP70 membrane association. Conclusion and Significance 5-MTHF and vitamin B12 supplementation might ameliorate RBC membrane features of children with CF. Trial Registration ClinicalTrials.gov NCT00730509 PMID:19277125

Scambi, Cinzia; De Franceschi, Lucia; Guarini, Patrizia; Poli, Fabio; Siciliano, Angela; Pattini, Patrizia; Biondani, Andrea; La Verde, Valentina; Bortolami, Oscar; Turrini, Francesco; Carta, Franco; D'Orazio, Ciro; Assael, Baroukh M.; Faccini, Giovanni; Bambara, Lisa M.

2009-01-01

43

Marathon Running Fails to Influence RBC Survival Rates in Iron-Replete Women.  

ERIC Educational Resources Information Center

This study used radiolabeling to measure red blood cell (RBC) survival rates in six iron-replete female marathon runners, and urinary tests were conducted to search for secondary evidence of RBC damage. The hypothesized RBC fragmentation was not disclosed. (Author/MT)

Steenkamp, Irene; And Others

1986-01-01

44

A gene phylogeny of the red algae (Rhodophyta) based on plastid rbcL.  

PubMed Central

A phylogeny for the Rhodophyta has been inferred by parsimony analysis of plastid rbcL sequences representing 81 species, 68 genera, 38 families, and 17 orders of red algae; rbcL encodes the large subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase. Levels of sequence divergence among species, genera, and families are high in red algae, typically much greater than those reported for flowering plants. The Rhodophyta traditionally consists of one class, Rhodophyceae, and two subclasses, Bangiophycidae and Florideophycidae. The Bangiophycidae with three orders (Porphyridiales, Compsopogonales, and Bangiales) appears to be polyphyletic, and the Florideophycidae with 17 orders is monophyletic in this study. The current classification of the Florideophycidae based on ultrastructure of pit connections is supported. With the exception of the Rhodogorgonales, which appears to be misplaced, orders with one or two pit-plug cap layers (Hildenbrandiales, Corallinales, Acrochaetiales, Palmanales, Batrachospermales, and Nemaliales) terminate long branches of basal position within Florideophycidae in the most parsimonious rbcL tree. Orders that lack typical cap layers but possess a cap membrane are resolved as a monophyletic clade sister to the Ahnfeltiales. The large order Gigartinales, which is distributed among five rbcL clades, is polyphyletic. Families that possess typical carrageenan in their cell walls are resolved as a terminal clade containing two family complexes centered around the Solieriaceae and Gigartinaceae. PMID:8041781

Freshwater, D W; Fredericq, S; Butler, B S; Hommersand, M H; Chase, M W

1994-01-01

45

Metabolic remodeling of the human red blood cell membrane  

E-print Network

The remarkable deformability of the human red blood cell (RBC) results from the coupled dynamic response of the phospholipid bilayer and the spectrin molecular network. Here we present quantitative connections between ...

Suresh, Subra

46

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

47

Role of the membrane in the formation of heme degradation products in red blood cells  

PubMed Central

Aims Red blood cells (RBCs) have an extensive antioxidant system designed to eliminate the formation of reactive oxygen species (ROS). Nevertheless, RBC oxidant stress has been demonstrated by the formation of a fluorescent heme degradation product (ex.321 nm, em 465 nm) both in vitro and in vivo. We investigated the possibility that the observed heme degradation results from ROS generated on the membrane surface that are relatively inaccessible to the cellular antioxidants. Main Methods Membrane and cytosol were separated by centrifugation and the fluorescence intensity and emission maximum was measured. The effect on the maximum emission of adding oxidized and reduced hemoglobin to the fluorescent product formed when hemin is degraded by H2O2 was studied. Key findings 90% of the fluorescent heme degradation products in hemolysates are found on the membrane. Furthermore, these products are not transferred from the cytosol to the membrane and must, therefore, be formed on the membrane. We also showed that the elevated level of heme degradation in HbCC cells that is attributed to increased oxidative stress was found on the membrane. Significance These results suggest that, although ROS generated in the cytosol are neutralized by antioxidant enzymes, H2O2 generated by the membrane bound hemoglobin is not accessible to the cytostolic antioxidants and reacts to generate fluorescent heme degradation products. The formation of H2O2 on the membrane surface can explain the release of ROS from the RBC to other tissues and ROS damage to the membrane that can alter red cell function and lead to the removal of RBCs from circulation by macrophages. PMID:19958781

Nagababu, Enika; Mohanty, Joy G.; Bhamidipaty, Surya; Ostera, Graciela R.; Rifkind, Joseph M.

2010-01-01

48

Dietary supplementation with docosahexanoic acid (DHA) increases red blood cell membrane flexibility in mice with sickle cell disease.  

PubMed

Humans and mice with sickle cell disease (SCD) have rigid red blood cells (RBCs). Omega-3 fatty acids, such as docosahexanoic acid (DHA), may influence RBC deformability via incorporation into the RBC membrane. In this study, sickle cell (SS) mice were fed natural ingredient rodent diets supplemented with 3% DHA (DHA diet) or a control diet matched in total fat (CTRL diet). After 8weeks of feeding, we examined the RBCs for: 1) stiffness, as measured by atomic force microscopy; 2) deformability, as measured by ektacytometry; and 3) percent irreversibly sickled RBCs on peripheral blood smears. Using atomic force microscopy, it is found that stiffness is increased and deformability decreased in RBCs from SS mice fed CTRL diet compared to wild-type mice. In contrast, RBCs from SS mice fed DHA diet had markedly decreased stiffness and increased deformability compared to RBCs from SS mice fed CTRL diet. Furthermore, examination of peripheral blood smears revealed less irreversibly sickled RBCs in SS mice fed DHA diet as compared to CTRL diet. In summary, our findings indicate that DHA supplementation improves RBC flexibility and reduces irreversibly sickled cells by 40% in SS mice. These results point to potential therapeutic benefits of dietary omega-3 fatty acids in SCD. PMID:25488613

Wandersee, Nancy J; Maciaszek, Jamie L; Giger, Katie M; Hanson, Madelyn S; Zheng, Suilan; Guo, YiHe; Mickelson, Barbara; Hillery, Cheryl A; Lykotrafitis, George; Low, Philip S; Hogg, Neil

2015-02-01

49

Redox Signaling Across Cell Membranes  

PubMed Central

Abstract Generation of reactive oxygen species (ROS) by plasma membrane–localized NADPH oxidase (Nox 2) is a major mechanism of cell signaling associated with activation of the enzyme by a variety of agonists. With activation, the integral membrane flavocytochrome of Nox 2 transfers an electron from intracellular NADPH to extracellular O2, generating superoxide anion (O2•?). The latter dismutes to H2O2 which can diffuse through aquaporin channels in the plasma membrane to elicit an intracellular signaling response. O2•? also can initiate intracellular signaling by penetration of the cell membrane through anion channels (Cl- channel-3, ClC-3). Endosomes containing Nox2 and ClC-3 (called signaling endosomes) are composed of internalized plasma membrane and generate O2•? in the endosomal lumen to initiate signaling at intracellular sites. Thus, cellular signaling by Nox2 is dependent on the transmembrane flux of ROS. The role of this pathway has only recently been described and will require additional investigation to appreciate its physiological significance fully. Antioxid. Redox Signal. 11, 1349–1356. PMID:19061438

2009-01-01

50

Thylakoid dismantling of damaged unfunctional chloroplasts modulates the Cab and RbcS gene expression in wheat leaves.  

PubMed

Thylakoid membrane dismantling and Lhcb and RbcS nuclear gene expression have been analysed in leaves of wheat plants grown in high fluence rate light and deprived of photoprotective carotenoids by treatments with the two bleaching herbicides, either norflurazon or amitrole. The Lhcb transcript was not detectable in cells of norflurazon-supplied leaves, having chloroplasts totally devoid of both inner membranes and pigments. In contrast, a substantial amount of Lhcb mRNA could be found in cells of amitrole-treated leaves, whose severely damaged organelles still contained few strikingly altered and photosynthetically unfunctional thylakoids, as well as chlorophyll traces. A possible relationship between chlorophyll synthesis and Lhcb expression, with the transcript level depending on the rate of pigment production in photodamaged chloroplasts is discussed. Also the RbcS expression was linked to the chloroplast membrane photodamage. However, a detectable level of transcript was still produced in norflurazon-treated cells, despite complete thylakoid demolition. Thus, the wheat cell behaviour had to be placed between that of species, such as maize, in which the RbcS expression is broken off in these conditions, and that of species, such as pea, in which it is slightly lowered. Interestingly, the dramatically photodamaged chloroplasts still maintained the ability to synthesize proteins and this allowed SSU and LSU Rubisco subunits to be found in the organelles of both norflurazon- and amitrole-treated plants. PMID:14975404

La Rocca, Nicoletta; Barbato, Roberto; Bonora, Angelo; Dalla Valle, Luisa; De Faveri, Stefania; Rascio, Nicoletta

2004-02-20

51

General coarse-grained red blood cell models: I. Mechanics  

E-print Network

We present a rigorous procedure to derive coarse-grained red blood cell (RBC) models, which lead to accurate mechanical properties of realistic RBCs. Based on a semi-analytic theory linear and non-linear elastic properties of the RBC membrane can be matched with those obtained in optical tweezers stretching experiments. In addition, we develop a nearly stress-free model which avoids a number of pitfalls of existing RBC models, such as non-biconcave equilibrium shape and dependence of RBC mechanical properties on the triangulation quality. The proposed RBC model is suitable for use in many existing numerical methods, such as Lattice Boltzmann, Multiparticle Collision Dynamics, Immersed Boundary, etc.

Dmitry A. Fedosov; Bruce Caswell; George E. Karniadakis

2009-05-01

52

Fuel-Cell Structure Prevents Membrane Drying  

NASA Technical Reports Server (NTRS)

Embossed plates direct flows of reactants and coolant. Membrane-type fuel-cell battery has improved reactant flow and heat removal. Compact, lightweight battery produces high current and power without drying of membranes.

Mcelroy, J.

1986-01-01

53

for drug-cell membrane interactions  

E-print Network

Since cell membranes are highly complex entities, there has been extensive interest in employing simple models to mimic biological cell membranes. Phospholipids are amphipatic molecules with long hydrophobic acyl chains and zwitterionic polar heads which are assembled into different types of molecular aggregates. The most relevant is the bilayer because of its relation with cell membranes. Among a large variety of relevant biological functions, the cell membrane acts as a diffusion barrier and protects the cell interior. Both structure and functions of the cell membrane are susceptible to alterations as a consequence of interactions with extrinsic chemical species such as therapeutic drugs. On the other hand, pharmacologic activity of a drug frequently involves an intial interaction with cell membranes even if they are not their final targets. With the aim to better

Mario Suwalsky

54

Dynamics of Interaction of RBC with optical tweezers  

NASA Astrophysics Data System (ADS)

It has recently been shown that a red blood cell (RBC) can be used as optically driven motor. The mechanism for rotation is however not fully understood. While the dependence on osmolarity of the buffer led us to conclude that the osmolarity dependent changes in shape of the cell are responsible for the observed rotation, role of ion gradients and folding of RBC to a rod shape has been invoked by Dharmadhikari et al to explain their observations. In this paper we report results of studies undertaken to understand the dynamics of a RBC when it is optically tweezed. The results obtained support our earlier conjecture that osmolarity dependent changes in shape of the cell are responsible for the observed rotation.

Mohanty, Samarendra K.; Mohanty, Khyati S.; Gupta, Pradeep Kumar

2005-06-01

55

Elastic behavior of a red blood cell with the membrane's nonuniform natural state: equilibrium shape, motion transition under shear flow, and elongation during tank-treading motion.  

PubMed

Direct numerical simulations of the mechanics of a single red blood cell (RBC) were performed by considering the nonuniform natural state of the elastic membrane. A RBC was modeled as an incompressible viscous fluid encapsulated by an elastic membrane. The in-plane shear and area dilatation deformations of the membrane were modeled by Skalak constitutive equation, while out-of-plane bending deformation was formulated by the spring model. The natural state of the membrane with respect to in-plane shear deformation was modeled as a sphere ([Formula: see text]), biconcave disk shape ([Formula: see text]) and their intermediate shapes ([Formula: see text]) with the nonuniformity parameter [Formula: see text], while the natural state with respect to out-of-plane bending deformation was modeled as a flat plane. According to the numerical simulations, at an experimentally measured in-plane shear modulus of [Formula: see text] and an out-of-plane bending rigidity of [Formula: see text] of the cell membrane, the following results were obtained. (i) The RBC shape at equilibrium was biconcave discoid for [Formula: see text] and cupped otherwise; (ii) the experimentally measured fluid shear stress at the transition between tumbling and tank-treading motions under shear flow was reproduced for [Formula: see text]; (iii) the elongation deformation of the RBC during tank-treading motion from the simulation was consistent with that from in vitro experiments, irrespective of the [Formula: see text] value. Based on our RBC modeling, the three phenomena (i), (ii), and (iii) were mechanically consistent for [Formula: see text]. The condition [Formula: see text] precludes a biconcave discoid shape at equilibrium (i); however, it gives appropriate fluid shear stress at the motion transition under shear flow (ii), suggesting that a combined effect of [Formula: see text] and the natural state with respect to out-of-plane bending deformation is necessary for understanding details of the RBC mechanics at equilibrium. Our numerical results demonstrate that moderate nonuniformity in a membrane's natural state with respect to in-plane shear deformation plays a key role in RBC mechanics. PMID:24104211

Tsubota, Ken-Ichi; Wada, Shigeo; Liu, Hao

2014-08-01

56

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.

2012-09-13

57

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

58

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

59

Advanced composite polymer electrolyte fuel cell membranes  

NASA Astrophysics Data System (ADS)

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 microns thick) are available. The combination of reinforcement and thinness provides high membrane, conductances (80 S/cm(exp 2) for a 12-micron 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, Mahlon S.; Zawodzinski, Thomas A.; Gottesfeld, Shimshon; Kolde, Jeffrey A.; Bahar, Bamdad

60

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

61

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

62

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

63

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

64

Live cell imaging of membrane / cytoskeleton interactions and membrane topology  

NASA Astrophysics Data System (ADS)

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.

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

2014-09-01

65

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

66

Demonstration of a natural antigalactosyl IgG antibody on thalassemic red blood cells.  

PubMed

A modified antiglobulin test, based on the high affinity between the Fc portion of the red blood cell (RBC) bound IgG and the Fc receptor on the myeloid cell K-562, was utilized for demonstration of immunoglobulins (Ig) on thalassemic RBC. Ig was found on the RBC of 73 out of 80 patients with thalassemia. The immunoglobulins on the thalassemic RBC belonged to the IgG subclass and were autoreactive. Elution studies utilizing various carbohydrates, or by thermal stripping, indicated that at least part of the IgG molecules found on the thalassemic RBC were specifically reactive with terminal galactosyl residues on the RBC membrane. IgG antibodies with similar reactivity were also demonstrated in normal human serum. These natural antigalactosyl IgG antibodies from normal sera could bind to IgG-depleted thalassemic RBC. Thalassemic RBC and normal senescent RBC were previously found to contain reduced amounts of membrane sialic acid (SA). It is suggested that the antigalactosyl IgG antibodies interact with newly exposed galactosyl residues underlying the sialic acid units. Such interaction may lead to the shortened lifespan of thalassemic RBC and may result in sequestration of senescent normal RBC by the reticuloendothelial system. PMID:6839023

Galili, U; Korkesh, A; Kahane, I; Rachmilewitz, E A

1983-06-01

67

Functional dynamics of cell surface membrane proteins  

NASA Astrophysics Data System (ADS)

Cell surface receptors are integral membrane proteins that receive external stimuli, and transmit signals across plasma membranes. In the conventional view of receptor activation, ligand binding to the extracellular side of the receptor induces conformational changes, which convert the structure of the receptor into an active conformation. However, recent NMR studies of cell surface membrane proteins have revealed that their structures are more dynamic than previously envisioned, and they fluctuate between multiple conformations in an equilibrium on various timescales. In addition, NMR analyses, along with biochemical and cell biological experiments indicated that such dynamical properties are critical for the proper functions of the receptors. In this review, we will describe several NMR studies that revealed direct linkage between the structural dynamics and the functions of the cell surface membrane proteins, such as G-protein coupled receptors (GPCRs), ion channels, membrane transporters, and cell adhesion molecules.

Nishida, Noritaka; Osawa, Masanori; Takeuchi, Koh; Imai, Shunsuke; Stampoulis, Pavlos; Kofuku, Yutaka; Ueda, Takumi; Shimada, Ichio

2014-04-01

68

Secretion machinery at the cell plasma membrane  

PubMed Central

Summary Secretion is a fundamental cellular process involving the regulated release of intracellular products from cells. Physiological functions such as neurotransmission, or the release of hormones and digestive enzymes, are all governed by cell secretion. Three critical activities occur at the cell plasma membrane to ensure secretion. Membrane-bound secretory vesicles dock, fuse, and expel their contents to the outside via specialized and permanent plasma membrane structures, called porosomes or fusion pores. In recent years, significant progress has been made in our understanding of these three key cellular activities required for cell secretion. The molecular machinery and mechanism involving them is summarized in this article. PMID:17764925

Jena, Bhanu P.

2007-01-01

69

Interaction of detergent sclerosants with cell membranes.  

PubMed

Commonly used detergent sclerosants including sodium tetradecyl sulphate (STS) and polidocanol (POL) are clinically used to induce endovascular fibrosis and vessel occlusion. They achieve this by lysing the endothelial lining of target vessels. These agents are surface active (surfactant) molecules that interfere with cell membranes. Surfactants have a striking similarity to the phospholipid molecules of the membrane lipid bilayer. By adsorbing at the cell membrane, surfactants disrupt the normal architecture of the lipid bilayer and reduce the surface tension. The outcome of this interaction is concentration dependent. At high enough concentrations, surfactants solubilise cell membranes resulting in cell lysis. At lower concentrations, these agents can induce a procoagulant negatively charged surface on the external aspect of the cell membrane. The interaction is also influenced by the ionic charge, molecular structure, pH and the chemical nature of the diluent (e.g. saline vs. water). The ionic charge of the surfactant molecule can influence the effect on plasma proteins and the protein contents of cell membranes. STS, an anionic detergent, denatures the tertiary complex of most proteins and in particular the clinically relevant clotting factors. By contrast, POL has no effect on proteins due to its non-ionic structure. These agents therefore exhibit remarkable differences in their interaction with lipid membranes, target cells and circulating proteins with potential implications in a range of clinical applications. PMID:24827732

Parsi, Kurosh

2014-05-14

70

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

71

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

72

Temporal sequence of major biochemical events during Blood Bank storage of packed red blood cells  

PubMed Central

Background. We used sensitive spectroscopic techniques to measure changes in Band 3 oligomeric state during storage of packed red blood cells (RBC); these changes were compared to metabolic changes, RBC morphology, cholesterol and membrane protein loss, phospholipid reorganisation of the RBC membrane, and peroxidation of membrane lipid. The aim of the study was to temporally sequence major biochemical events occurring during cold storage, in order to determine which changes may underlie the structural defects in stored RBC. Materials and methods. Fifteen RBC units were collected from normal volunteers and stored under standard blood bank conditions; both metabolic changes and lipid parameters were measured by multiple novel assays including a new mass spectrometric measurement of isoprostane (lipid peroxidation) and flow cytometric assessment of CD47 expression. Band 3 oligomeric state was assessed by time-resolved phosphorescence anisotropy, and RBC morphology by microscopy of glutaraldehyde-fixed RBC. Results. Extracellular pH decreased and extracellular potassium increased rapidly during cold storage. Band 3 on the RBC membrane aggregated into large oligomers early in the storage period and coincident with changes in RBC morphology. Membrane lipid changes, including loss of unesterified cholesterol, lipid peroxidation and expression of CD47, also changed early during the storage period. In contrast loss of acetylcholinesterase activity and haemolysis of RBC occurred late during storage. Discussion. Our results demonstrate that changes in the macromolecular organisation of membrane proteins on the RBC occur early in storage and suggest that lipid peroxidation and/or oxidative damage to the membrane are responsible for irreversible morphological changes and loss of function during red cell storage. PMID:22507860

Karon, Brad S.; van Buskirk, Camille M.; Jaben, Elizabeth A.; Hoyer, James D.; Thomas, David D.

2012-01-01

73

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

74

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

75

DYNAMIC MODELING PROTON EXCHANGE MEMBRANE FUEL CELL  

E-print Network

DYNAMIC MODELING PROTON EXCHANGE MEMBRANE FUEL CELL OVERVIEW Current/Completed Plug Power to garner SCAQMD funding for fuel cell testing GenCore system is sensitive to diluents · As built design stream to compensate for removal of EGR · Functionality of the modified GenCore Fuel Cell system

Mease, Kenneth D.

76

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

77

Activated Membrane Patches Guide Chemotactic Cell Motility  

PubMed Central

Many eukaryotic cells are able to crawl on surfaces and guide their motility based on environmental cues. These cues are interpreted by signaling systems which couple to cell mechanics; indeed membrane protrusions in crawling cells are often accompanied by activated membrane patches, which are localized areas of increased concentration of one or more signaling components. To determine how these patches are related to cell motion, we examine the spatial localization of RasGTP in chemotaxing Dictyostelium discoideum cells under conditions where the vertical extent of the cell was restricted. Quantitative analyses of the data reveal a high degree of spatial correlation between patches of activated Ras and membrane protrusions. Based on these findings, we formulate a model for amoeboid cell motion that consists of two coupled modules. The first module utilizes a recently developed two-component reaction diffusion model that generates transient and localized areas of elevated concentration of one of the components along the membrane. The activated patches determine the location of membrane protrusions (and overall cell motion) that are computed in the second module, which also takes into account the cortical tension and the availability of protrusion resources. We show that our model is able to produce realistic amoeboid-like motion and that our numerical results are consistent with experimentally observed pseudopod dynamics. Specifically, we show that the commonly observed splitting of pseudopods can result directly from the dynamics of the signaling patches. PMID:21738453

Hecht, Inbal; Skoge, Monica L.; Charest, Pascale G.; Ben-Jacob, Eshel; Firtel, Richard A.; Loomis, William F.; Levine, Herbert; Rappel, Wouter-Jan

2011-01-01

78

Protective effects of stem bark of Harungana madgascariensis on the red blood cell membrane  

PubMed Central

Background Anemia is a condition that has multiple origins. One such origin is the destruction of red blood cells’ (RBCs) membrane induced by free radicals. Treatment of anemia could therefore be enhanced by the use of free radicals’ scavengers potentially found in some medicinal plants. In this study, the protective effect of Harungana madagascariensis on the RBCs’ membrane physiology was investigated in vitro and in vivo. Methods In vitro hemolytic anemia was induced by incubation of fresh human RBCs with carbontetrachloride (CCl4) in Olive oil (Oo). Relaxation times of protons excited at 20 MHz (Carr-Purcell-Meiboom-Gill pulse sequence) in the absence or presence of paramagnetic Mn2+ ions (T2i for “extracellular” water and T2a for “intracellular” water, respectively) were determined at several temperatures (25–37°C) via Nuclear Magnetic Resonance (NMR) on a Bruker Minispec spectrometer. Water exchange times (Te) were consequently calculated using the Conlon-Outhred equation: 1/Te = (1/T2a) – (1/T2i). Morphological characteristics (mean cell volume, V, and cell surface area, A) were determined by photonic microscopy and the RBCs’ diffusional water permeability (Pd) was calculated as Pd = (1/Te)*(Va/A), where Va is the aqueous volume in the RBC and is about 0.7 of the cell volume (V). The activation energy of the diffusional process (Ea) for the respective temperature range was estimated using the Arrhenius modified equation k = A(T/T0)n*e-Ea/RT. Inhibition of the water diffusion induced by incubation with para-chloro-mercuribenzoic acid (PCMB) at 25, 30 and 37°C was calculated as I(%) = [(Pd control – Pd sample)/Pd control]*100. To investigate the protective influence of the extract on the RBC membrane, inhibition of the water permeability was evaluated on membranes pre-incubated with the Harungana madagascariensis extract. Male rats were used in in vivo investigations. Malondialdehyde (MDA) and cholesterol in the RBC membrane were estimated by induction of lipid peroxidation while the antioxidant properties of catalase (CAT) and superoxide dismutase (SOD) on the membrane were evaluated in regard to their antioxidant properties on the membrane. Results T2a significantly decreased at each temperature. Te results were higher in both RBCs and RBCs + extract groups incubated with PCMB compared to non-incubated controls, but differences were not statistically significant. A high percentage (73.81 ± 7.22) of RBCs pre-incubated with the extract presented the regular biconcave shape. Inhibition by PCMB of the RBCs’ membrane water permeability was increased at 30°C and decreased in the presence of extract (25°C and 37°C), while Ea decreased from 30.52 ± 1.3 KJ/mol to 25.49 ± 1.84 KJ/mol. Presence of the Harungana madagascariensis extract normalized the SOD and CAT activities as well as the MDA and membrane cholesterol concentrations altered by the CCl4-induced oxidative stress. Conclusion Harungana madagascariensis could protect the RBCs’ membrane through its antioxidative properties. PMID:23663227

2013-01-01

79

Nafion-sepiolite composite membranes for improved Proton Exchange Membrane Fuel Cell performance.  

E-print Network

1 Nafion®-sepiolite composite membranes for improved Proton Exchange Membrane Fuel Cell performance, characterized and integrated in Membrane-Electrodes Assembly to be tested in fuel cell operating conditions, mobile or stationary), Proton Exchange Membrane Fuel Cells (PEMFC) are amongst the most studied fuel

Boyer, Edmond

80

Fixed charge in the cell membrane  

PubMed Central

1. Focal electric field was generated by passing a current of 5 × 10-7 to 1 × 10-5 A from a micropipette into the culture medium. Movement of cells at a distance of 5-50 ? from the electrode tip was observed. In case of cells embedded in the culture only local deformation of the membrane was observed. 2. The cell species explored included neurones, glia, muscle fibres, connective cells, malignant cells and erythrocytes. All cells responded in a similar manner to the electric field, and the current required was in the same range. 3. Cells were attracted to a positive micropipette and repelled from a negative one: the only exception was observed in certain malignant cells which moved in the opposite direction. 4. Movement and membrane deformation could be obtained with electrodes filled with various concentrated and isotonic solutions. The composition of the culture medium also had no qualitative influence on these effects. 5. Metabolic poisons or rupture of the cell membrane had no effect on the movement. Isolated membrane fragments showed movement similar to that of intact cells. 6. The possibility of artifacts due to proximity of the focal electrode is considered. It is shown that electro-osmosis cannot account for the present observations. Some other artifacts are also excluded. 7. It is proposed that the most satisfactory way to account for the present observations is by a membrane carrying negative fixed charge of the order of 2·5 × 103 e.s.u./cm2. Some physiological consequences of presence of negative charge in the membrane are briefly discussed. ImagesFig. 1Fig. 2Fig. 3 PMID:6040152

Elul, R.

1967-01-01

81

Solar cell preparation in thin silicon membranes  

Microsoft Academic Search

Solar cells prepared in a thin (≈30 ?m) crystalline silicon membrane with a supporting frame allow an evaluation of the potential of c-Si thin film cells on cheap substrates. At the same time, lightweight and more radiation-hard solar cells may have direct applications in space. This paper studies the fabrication process of solar cells in ≈30 ?m thick p-Si epitaxial

M. Libezny; J. Poortmans; M. Caymax; G. Beaucame; W. Laureys; J. Nijs

1997-01-01

82

Oxidative insult in sheep red blood cells induced by T-butyl hydroperoxide: the roles of glutathione and glutathione peroxidase.  

PubMed

Three different types of red blood cells (RBC) were used: (i) RBC from sheep having genetically high GSH (ii) RBC from sheep with genetically low GSH and (iii) RBC from high-GSH sheep treated with CDNB to deplete GSH. Incubation of these RBC with t-butyl hydroperoxide (tBHP, 3 mM) for 10 min caused the formation of TBARS, oxidation of haemoglobin and degradation and aggregation of membrane proteins in RBC from low-GSH sheep and GSH-depleted RBC. By contrast, RBC from high-GSH sheep (normal RBC) did not show the degradation and aggregation of membrane proteins within the first 10 min. Dithiothreitol (DTT) was highly effective in preventing the tBHP-mediated oxidation of haemoglobin, the formation of TBARS and the degradation and aggregation of membrane proteins in both normal RBC and low-GSH RBC. However, DTT did not provide protection in GSH-depleted RBC or normal RBCs in the presence of 1.5 mM mercaptosuccinate (MCS), a potent inhibitor of GSH peroxidase (GSHPx). The ability of GSH to prevent the oxidation of haemoglobin and the degradation and aggregation of membrane proteins was abolished in the presence of MCS. These results indicate that the protective function of DTT involves a GSH-dependent mechanism. Both GSH and GSHPx play key roles in this enzymatic system. In the light of the complete protection of RBC against oxidation induced by tBHP in the presence of DTT or GSH, the GSH/GSHPx system appears to act directly as a tBHP scavenger. The activities of four well-known antioxidants, Butylated hydroxytoluene, ascorbate, alpha-tocopherol and desferrioxamine were also tested in this study to cast further light on the role of free radical scavenging in protection from tBHP mediated free radical insult. PMID:11234995

Zou, C G; Agar, N S; Jone, G L

2001-01-01

83

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

84

Erythrocyte membrane is an alternative coating to polyethylene glycol for prolonging the circulation lifetime of gold nanocages for photothermal therapy.  

PubMed

Gold nanocages (AuNCs), which have tunable near-infrared (NIR) absorption and intrinsically high photothermal conversion efficiency, have been actively investigated as photothermal conversion agents for photothermal therapy (PTT). The short blood circulation lifetime of AuNCs, however, limits their tumor uptake and thus in vivo applications. Here we show that such a limitation can be overcome by cloaking AuNCs with red blood cell (RBC) membranes, a natural stealth coating. The fusion of RBC membranes over AuNC surface does not alter the unique porous and hollow structures of AuNCs, and the resulting RBC-membrane-coated AuNCs (RBC-AuNCs) exhibit good colloidal stability. Upon NIR laser irradiation, the RBC-AuNCs demonstrate in vitro photothermal effects and selectively ablate cancerous cells within the irradiation zone as do the pristine biopolymer-stealth-coated AuNCs. Moreover, the RBC-AuNCs exhibit significantly enhanced in vivo blood retention and circulation lifetime compared to the biopolymer-stealth-coated counterparts, as demonstrated using a mouse model. With integrated advantages of photothermal effects from AuNCs and long blood circulation lifetime from RBCs, the RBC-AuNCs demonstrate drastically enhanced tumor uptake when administered systematically, and mice that received PPT cancer treatment modulated by RBC-AuNCs achieve 100% survival over a span of 45 days. Taken together, our results indicate that the long circulating RBC-AuNCs may facilitate the in vivo applications of AuNCs, and the RBC-membrane stealth coating technique may pave the way to improved efficacy of PPT modulated by noble metal nanoparticles. PMID:25286086

Piao, Ji-Gang; Wang, Limin; Gao, Feng; You, Ye-Zi; Xiong, Yujie; Yang, Lihua

2014-10-28

85

Nafion ® perfluorinated membranes in fuel cells  

Microsoft Academic Search

Increasing global energy requirements, localized power issues and the need for less environmental impact are now providing even more incentive to make fuel cells a reality. A number of technologies have been demonstrated to be feasible for generation of power from fuel cells over the last several years. Proton exchange membranes (PEM) have emerged as an essential factor in the

Shoibal Banerjee; Dennis E. Curtin

2004-01-01

86

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

E-print Network

Design and optimization of polymer electrolyte membrane (PEM) fuel cells M. Grujicic* , K electrolyte membrane (PEM) fuel cells; Design; Optimization; Robustness 1. Introduction A fuel cell.M. Chittajallu Department of Mechanical Engineering, Clemson University, 241 Engineering Innovation Building

Grujicic, Mica

87

Cell motility through plasma membrane blebbing  

PubMed Central

Plasma membrane blebs are dynamic cytoskeleton-regulated cell protrusions that have been implicated in apoptosis, cytokinesis, and cell movement. Influencing Rho–guanosine triphosphatase activities and subsequent actomyosin dynamics appears to constitute a core component for bleb formation. In this paper, we discuss recent evidence in support of a central role of nonapoptotic membrane blebbing for cell migration and cancer cell invasion as well as advances in our understanding of the underlying molecular mechanisms. Based on these studies, we propose that in a physiological context, bleb-associated cell motility reflects a cell's response to reduced substratum adhesion. The importance of blebbing as a functional protrusion is underscored by the existence of multiple molecular mechanisms that govern actin-mediated bleb retraction. PMID:18541702

Fackler, Oliver T.; Grosse, Robert

2008-01-01

88

Change dynamics of RBC morphology after injection glucose for diabetes by diffraction phase microscope  

NASA Astrophysics Data System (ADS)

Experimental setup of diffraction phase microscope (DPM) with double low-coherence lighting system is presented in the paper. Algorithm of interference picture processing and optical thickness, height, volume and mean cells volume (MCV) of RBC calculating is shown. We demonstrate results of experiments with blood smears and ability of the method to calculate 3D model of the biological cells shape. Investigation change dynamics of RBC morphology after injection glucose for diabetes by DPM is shown in the paper.

Talaykova, N. A.; Kalyanov, A. L.; Lychagov, V. V.; Ryabukho, V. P.; Malinova, L. I.

2013-11-01

89

Hereditary spherocytosis, elliptocytosis, and other red cell membrane disorders.  

PubMed

Hereditary spherocytosis and elliptocytosis are the two most common inherited red cell membrane disorders resulting from mutations in genes encoding various red cell membrane and skeletal proteins. Red cell membrane, a composite structure composed of lipid bilayer linked to spectrin-based membrane skeleton is responsible for the unique features of flexibility and mechanical stability of the cell. Defects in various proteins involved in linking the lipid bilayer to membrane skeleton result in loss in membrane cohesion leading to surface area loss and hereditary spherocytosis while defects in proteins involved in lateral interactions of the spectrin-based skeleton lead to decreased mechanical stability, membrane fragmentation and hereditary elliptocytosis. The disease severity is primarily dependent on the extent of membrane surface area loss. Both these diseases can be readily diagnosed by various laboratory approaches that include red blood cell cytology, flow cytometry, ektacytometry, electrophoresis of the red cell membrane proteins, and mutational analysis of gene encoding red cell membrane proteins. PMID:23664421

Da Costa, Lydie; Galimand, Julie; Fenneteau, Odile; Mohandas, Narla

2013-07-01

90

Use of mouse models to study the mechanisms and consequences of RBC clearance  

PubMed Central

Mice provide tractable animal models for studying the pathophysiology of various human disorders. This review discusses the use of mouse models for understanding red-blood-cell (RBC) clearance. These models provide important insights into the pathophysiology of various clinically relevant entities, such as autoimmune haemolytic anaemia, haemolytic transfusion reactions, other complications of RBC transfusions and immunomodulation by Rh immune globulin therapy. Mouse models of both antibody- and non-antibody-mediated RBC clearance are reviewed. Approaches for exploring unanswered questions in transfusion medicine using these models are also discussed. PMID:20345515

Hod, E. A.; Arinsburg, S. A.; Francis, R. O.; Hendrickson, J. E.; Zimring, J. C.; Spitalnik, S. L.

2013-01-01

91

Studies in erythropoiesis: the influence of the glycocalyx of the red cell membrane  

SciTech Connect

The possible existence of a correlation between the removal from the circulation of aged cells and the production of new RBCs was investigated. An erythropoietic influence was found to be associated with the glycocalyx of the erythrocyte membrane. The influencing factor, presumably a desialated glycopeptide, asialoglycophorin, appeared to be masked on the young RBC by an amino ketosugar, sialic acid. Ostensibly during the aging process, an increasing amount of sialic acid becomes removed from the membrane to expose the underlying erythropoietic message. Sialic acid was removed enzymatically in vitro from the membranes of erythrocytes by incubation with neuraminidase from Clostridium Perfringens. Erythropoietic activity was assayed by measuring iron-59 uptake after injection or transfusion of test material into exhypoxic mice. The amount of erythropoietic activity was found to be directly related to the number of desialated erythrocytes transfused and to the degree of desialation of the transfused erythrocytes. Asialoglycophorin was shown to be an erythrocyte stimulating factor following its isolation from the membrane and subsequent injection into test mice. Both mouse and human asialoglycophorin were found to be stimulatory.

Franco, M.W.

1980-01-01

92

Membrane fluidity sensoring microbial fuel cell.  

PubMed

A study has been performed to examine the effect of temperature and ethanolic stresses on the coulombic efficiency of a microbial fuel cell. The conventional-type fuel cell containing Gram-negative bacteria, Proteus vulgaris, was investigated as a model system. From current output measurements, it was found that the coulombic yields were altered by environmental stresses such as temperature shock or ethanol treatment to the bacteria. While high-temperature or ethanolic shock led to a remarkable decrement in coulombic output, the low-temperature shock induced a slight increase in microbial fuel cell efficiency. These results indicate that the membrane fluidity is affected considerably by environmental stress, which in turn affects the electron transfer process through the bacterial cell membrane to and from the electrode. This interpretation was confirmed by the cyclic voltammetric study of a mediator on an electrode surface modified with the lipids extracted from the membrane of P. vulgaris under the given stress. Markedly different electrochemical behaviors were observed depending on the environmental stress. A reciprocal relationship between coulomb output and the ratio of saturation/unsaturation of fatty acids has been observed. This is the first report, to our knowledge, that the structural adaptation of membrane fatty acids in response to the environmental shock can regulate the coulombic efficiency of a microbial fuel cell. PMID:12699828

Choi, Youngjin; Jung, Eunkyoung; Kim, Sunghyun; Jung, Seunho

2003-04-01

93

Particle method for computer simulation of red blood cell motion in blood flow.  

PubMed

A particle method for the computer simulation of blood flow was proposed to analyze the motion of a deformable red blood cell (RBC) in flowing blood plasma. The RBC and plasma were discretized by particles that have the characteristics of an elastic membrane and a viscous fluid, respectively. The membrane particles were connected to their neighboring membrane particles by springs, and the motion of the particles was determined on the basis of the minimum energy principle. The incompressible flow of plasma that was expressed by the motion of the fluid particles was determined by the moving-particle semi-implicit (MPS) method. The RBC motion and plasma flow were weakly coupled. The two-dimensional simulation of blood flow between parallel plates demonstrated the capability of the proposed method to express the blood flow phenomena observed in experiments, such as the downstream motion of the RBC and the deformation of the RBC into a parachute shape. PMID:16879895

Tsubota, Ken-ichi; Wada, Shigeo; Yamaguchi, Takami

2006-08-01

94

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

95

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

96

The Quality Assessment of Stored Red Blood Cells Probed Using Atomic-Force Microscopy  

PubMed Central

At the moment the suitability of stored red blood cells (sRBC) for transfusion is checked by routine methods such as haemoglobin estimation and the level of haemolysis. These methods cannot characterize directly the quality of the membranes of sRBC. The aim of this work is to assess the quality of sRBC based on such criteria as the membrane's stiffness and the size and the form of sRBC. Materials and Methods. We have investigated 5 series of dry cytosmears of the sRBC which had been kept in blood bank in a period from 1 to 35 days. After AFM imaging, in every specimen, 5 RBC were chosen at random; the diameter, the height, and the stiffness were measured on each of them. Results. The present study shows high increase of the mean values of YM and height of RBC after 35 days of storage and decrease of the mean values of their diameter. Conclusion. Statistically significant high increase of the mean values of YM indicates the decrease of the elasticity of the cells in the course of storing of the RBC. This parameter along with the morphological characteristics can be used as criterion for assessment of applicability of the sRBC for blood transfusion. PMID:25610651

Lamzin, I. M.; Khayrullin, R. M.

2014-01-01

97

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

98

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

99

Mitochondrial toxin betulinic acid induces in vitro eryptosis in human red blood cells through membrane permeabilization.  

PubMed

Betulinic acid (BA), a compound isolated from the bark of white birch (Betula pubescens), was reported to induce apoptosis in many types of cancer through mitochondrial dysfunction with low side effects in normal cells. Because of these features, BA is regarded as a potential anti-cancer agent. However, the effect of BA on the induction of cell death in human erythrocytes remains unknown. Given that BA is a mitochondrial toxin and mitochondria are the central cell death regulator, we hypothesized that BA is unable to elicit apoptosis (also known as eryptosis or erythroptosis) in human erythrocytes devoid of mitochondria. This study therefore tried to determine the in vitro effect of BA on the induction of eryptosis/erythroptosis. Contrary to our prediction, BA caused phosphatidylserine externalization, increase in cellular Ca(2+) ion concentration ([Ca(2+)]i) and eryptosis/erythroptosis in human erythrocytes with a lethal dose larger than that in cancer lines. Mechanistically, the rise of [Ca(2+)]i seems not to be the only key mediator in the BA-mediated eryptosis/erythroptosis because depletion of external Ca(2+) and use of Ca(2+) channels blockers could not eliminate the BA's effect. Also, BA was able to elicit discocyte-echinocyte transformation and release calcein from the RBC ghosts in a way similar to digitonin through membrane permeabilization. Collectively, we report here for the first time that BA induced eryptosis/erythroptosis in human erythrocytes through Ca(2+) loading and membrane permeabilization. PMID:24241250

Gao, Minghui; Lau, P M; Kong, S K

2014-03-01

100

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

101

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

102

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

103

Different activities of the reovirus FAST proteins and influenza hemagglutinin in cell-cell fusion assays and in response to membrane curvature agents  

SciTech Connect

The reovirus fusion-associated small transmembrane (FAST) proteins evolved to induce cell-cell, rather than virus-cell, membrane fusion. It is unclear whether the FAST protein fusion reaction proceeds in the same manner as the enveloped virus fusion proteins. We now show that fluorescence-based cell-cell and cell-RBC hemifusion assays are unsuited for detecting lipid mixing in the absence of content mixing during FAST protein-mediated membrane fusion. Furthermore, membrane curvature agents that inhibit hemifusion or promote pore formation mediated by influenza hemagglutinin had no effect on p14-induced cell-cell fusion, even under conditions of limiting p14 concentrations. Standard assays used to detect fusion intermediates induced by enveloped virus fusion proteins are therefore not applicable to the FAST proteins. These results suggest the possibility that the nature of the fusion intermediates or the mechanisms used to transit through the various stages of the fusion reaction may differ between these distinct classes of viral fusogens.

Clancy, Eileen K.; Barry, Chris; Ciechonska, Marta [Department of Microbiology and Immunology, Dalhousie University, Halifax, Nova Scotia, B3H 1X5 (Canada); Duncan, Roy, E-mail: roy.duncan@dal.c [Department of Microbiology and Immunology, Dalhousie University, Halifax, Nova Scotia, B3H 1X5 (Canada); Department of Pediatrics, Dalhousie University, Halifax, Nova Scotia, B3H 1X5 (Canada)

2010-02-05

104

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

105

Cell invasion through basement membranes: an anchor of understanding.  

PubMed

To metastasize, cancer cells must acquire the ability to breach several basement membrane barriers. Cell invasions through basement membranes also occur during normal development and immune system function, enabling organ formation and cell dispersal. The mechanisms that cells use to cross basement membranes in vivo remain elusive. In cancer and development, these invasions occur in complex and inaccessible environments, which are difficult to study in vivo. Anchor-cell invasion in Caenorhabditis elegans is a simple, visually and experimentally accessible model of basement membrane invasion that is beginning to reveal a network of cellular and molecular control mechanisms that regulate the fundamental cellular process of invasion through basement membranes. PMID:16580836

Sherwood, David R

2006-05-01

106

Solar cell preparation in thin silicon membranes  

SciTech Connect

Solar cells prepared in a thin ({approx} 30 {micro}m) crystalline silicon membrane with a supporting frame allow an evaluation of the potential of c-Si thin film cells on cheap substrates. In the same time, light-weight and more radiation-hard solar cells may have direct applications in space. This paper studies the fabrication process of solar cells in {approx} 30 {micro}m thick p-Si epitaxial layers, incorporating a p{sup +2}-Si etch-stop/back-surface field layer, using KOH etching. Wax, rubber and silicon nitride were tested as masking material during the etching. It was found that both wax and silicon nitride could be used as materials for masking of supporting frames for the solar cell thinning up to 30 {micro}m. However, silicon nitride does not reliably protect the frontside structure.

Libezny, M.; Poortmans, J.; Caymax, M.; Beaucarne, G.; Laureys, W.; Nijs, J. [IMEC, Leuven (Belgium)

1997-12-31

107

Lysosomal membrane permeabilization in cell death.  

PubMed

Mitochondrial outer membrane permeabilization (MOMP) constitutes one of the major checkpoint(s) of apoptotic and necrotic cell death. Recently, the permeabilization of yet another organelle, the lysosome, has been shown to initiate a cell death pathway, in specific circumstances. Lysosomal membrane permeabilization (LMP) causes the release of cathepsins and other hydrolases from the lysosomal lumen to the cytosol. LMP is induced by a plethora of distinct stimuli including reactive oxygen species, lysosomotropic compounds with detergent activity, as well as some endogenous cell death effectors such as Bax. LMP is a potentially lethal event because the ectopic presence of lysosomal proteases in the cytosol causes digestion of vital proteins and the activation of additional hydrolases including caspases. This latter process is usually mediated indirectly, through a cascade in which LMP causes the proteolytic activation of Bid (which is cleaved by the two lysosomal cathepsins B and D), which then induces MOMP, resulting in cytochrome c release and apoptosome-dependent caspase activation. However, massive LMP often results in cell death without caspase activation; this cell death may adopt a subapoptotic or necrotic appearance. The regulation of LMP is perturbed in cancer cells, suggesting that specific strategies for LMP induction might lead to novel therapeutic avenues. PMID:18955971

Boya, P; Kroemer, G

2008-10-27

108

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

109

ALTERNATIVE RBC (ROTATING BIOLOGICAL CONTACTOR) DESIGN - SECOND ORDER KINETICS  

EPA Science Inventory

This paper presents an alternative method for designing rotating biological contactors (RBC) for use as a secondary treatment operation. The method uses a combination of chemical kinetics, good engineering practice, operational simplicity, and cost effectiveness to design a RBC s...

110

Membrane Transport Chloride Transport Across Vesicle and Cell  

E-print Network

Membrane Transport Chloride Transport Across Vesicle and Cell Membranes by Steroid-Based Receptors-established that molecules which transport cations across cell membranes (cationophores) can have potent biological effects of biological activity. Indeed, chloride transporters have direct medical potential as treatments for cystic

Smith, Bradley D.

111

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

112

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

113

Micropatterning cells on permeable membrane filters.  

PubMed

Epithelium is abundantly present in the human body as it lines most major organs. Therefore, ensuring the proper function of epithelium is pivotal for successfully engineering whole organ replacements. An important characteristic of mature epithelium is apical-basal polarization which can be obtained using the air-liquid interface (ALI) culture system. Micropatterning is a widely used bioengineering strategy to spatially control the location and organization of cells on tissue culture substrates. Micropatterning is therefore an interesting method for generating patterned epithelium. Enabling micropatterning of epithelial cells however requires micropatterning methods that are designed to (i) be compatible with permeable membranes substrates and (ii) allow prolonged culture of patterned cells, both of which are required for appropriate epithelial apical-basal polarization. Here, we describe a number of methods we have developed for generating monoculture as well as coculture of epithelial cells that are compatible with ALI culture. PMID:24560510

Javaherian, Sahar; Paz, Ana C; McGuigan, Alison P

2014-01-01

114

Active organization of membrane constituents in living cells.  

PubMed

A search for organizing principles underlying molecular patterning at the cell surface and its regulation over different scales is necessary. This is important for understanding how the cell builds membrane bound organelles that emanate from it and for how the cell interacts with its physical and chemical milieu. This requires a broad framework to rationalize the mass of accumulated data about the spatial localization and dynamics of its constituents, and their physical and chemical environment. Lateral heterogeneities in the organization of membrane components of a living cell appear to be a hallmark of how a cell addresses sorting and signaling functions. Here we explore two classes of mechanisms of segregation of membrane components in the plasma membrane. We suggest that viewing the membrane as a passive, thermally equilibrated system is unlikely to provide an adequate framework to understand the mechanisms of membrane component segregation in vivo. Instead the surface of living cells behaves as an active membrane composite. PMID:24975942

Rao, Madan; Mayor, Satyajit

2014-08-01

115

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

116

Membrane rafts of the human red blood cell.  

PubMed

The cell type of election for the study of cell membranes, the mammalian non-nucleated erythrocyte, has been scarcely considered in the research of membrane rafts of the plasma membrane. However, detergent-resistant-membranes (DRM) were actually first described in human erythrocytes, as a fraction resisting solubilization by the nonionic detergent Triton X-100. These DRMs were insoluble entities of high density, easily pelleted by centrifugation, as opposed to the now accepted concept of lipid raft-like membrane fractions as material floating in low-density regions of sucrose gradients. The present article reviews the available literature on membrane rafts/DRMs in human erythrocytes from an historical point of view, describing the experiments that provided the solution to the above described discrepancy and suggesting possible avenue of research in the field of membrane rafts that, moving from the most studied model of living cell membrane, the erythrocyte's, could be relevant also for other cell types. PMID:24720522

Ciana, Annarita; Achilli, Cesare; Minetti, Giampaolo

2014-01-01

117

Measurement of the nonlinear elasticity of red blood cell membranes  

E-print Network

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 ...

Park, YongKeun

118

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

119

Polymer synthesis toward fuel cell membrane materials  

NASA Astrophysics Data System (ADS)

Fuel cells are a promising technology that will be part of the future energy landscape. New membranes for alkaline and proton exchange membrane fuel cells are needed to improve the performance, simplify the system, and reduce cost. Polymer chemistry can be applied to develop new polymers and to assemble polymers into improved membranes that need less water, have increased performance and are less expensive, thereby removing the deficiencies of current membranes. Nucleophilic aromatic substitution polymerization typically produces thermally stable engineering polymers that can be easily functionalized. New functional monomers were developed to explore new routes to novel functional polymers. Sulfonamides were discovered as new activating groups for polymerization of high molecular weight thermooxidatively stable materials with sulfonic acid latent functionality. While the sulfonamide functional polymers could be produced, the sulfonamide group proved to be too stable to convert into a sulfonic acid after reaction. The reactivity of 2-aminophenol was investigated to search for a new class of ion conducting polymer materials. Both the amine and the phenol groups are found to be reactive in a nucleophilic aromatic substitution, however not to the extent to allow the formation of high molecular weight polymer materials. Layer-by-layer films were assembled from aqueous solutions of poly(styrene sulfonate) and trimethylammonium functionalized poly(phenylene oxide). The deposition conditions were adjusted to increase the free charge carrier content, and chloride conductivites reached almost 30 mS/cm for the best films. Block and random poly(phenylene oxide) copolymers were produced from 2,6-dimethylphenol and 2,6-diphenylphenol and the methyl substituted repeat units were functionalized with trimethylammonium bromide. The block copolymers displayed bromide conductivities up to 26 mS/cm and outperformed the random copolymers, indicating that morphology has an effect on ion transport.

Rebeck, Nathaniel T.

120

Micropatterned porous membranes for combinatorial cell-based assays.  

PubMed

Here, we describe a protocol for producing micropatterned porous membranes which can be used for combinatorial cell-based assays. We use contact printing to pattern the surface of a porous filter membrane with a thin layer of polydimethylsiloxane (PDMS). This allows the porosity of the filter membrane to be altered at selected locations. Cells can be grown on one side of the filter membrane, while drugs and reagents can be deposited on the porous areas of the other side of the membrane. The reagents can diffuse through the pores of the membrane to the cells. The first part of the protocol describes how to design a stamp and use it to contact print PDMS. The second part describes how to create microprinted membranes for cell-based assays. The method is simple, highly customizable, can be performed at the bench, and can be used to perform combinatorial or time-dependent cell-based assays. PMID:24560509

Vulin, Clément; Evenou, Fanny; Di Meglio, Jean Marc; Hersen, Pascal

2014-01-01

121

Heinz body formation in red cell membrane disorders: its acceleration in membrane lipid abnormalities.  

PubMed

Abnormal Heinz body formation in the presence of acetylphenyl hydrazine was observed in some patients with red cell membrane abnormalities, such as hereditary red cell membrane high phosphatidyl choline haemolytic anaemia, congenital haemolytic anaemias of unknown origin, acquired hyperlipidaemia and paroxysmal nocturnal haemoglobinuria. No abnormality of haemoglobin composition or of oxidation-reduction activities was noted in 66 patients studied. No abnormal Heinz body formation was seen in hereditary spherocytosis, hereditary elliptocytosis or hereditary stomatocytosis with normal membrane lipids, but increased Heinz body formation was observed in some patients with red cell membrane lipid abnormalities. The extent of abnormal Heinz body formation inversely correlated with a decreased molar ratio of free cholesterol to phosphatidyl choline in these red cells. Heinz body formation, therefore, may be abnormal in some red cell membrane disorders, especially when membrane lipid abnormalities exist. PMID:4059856

Mannoji, M; Sugihra, T; Yawata, Y

1985-09-01

122

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... lias t:spl:cially proVt:1I ils vt:rsalilily in oruer lo tultill all reqUirements tor the conversion of an existing chlor alkali plant. The worldwide chlorine/causlic soda production has reached approximately 40 milhon tpv. The United States...

Lesker, K.

123

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

124

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

125

Guard cells undergo constitutive and pressure-driven membrane turnover  

Microsoft Academic Search

Summary.  During stomatal movement, guard cells undergo large and reversible changes in cell volume and consequently surface area. These\\u000a alterations in surface area require addition and removal of plasma membrane material. How this is achieved is largely unknown.\\u000a Here we summarize recent studies of membrane turnover in guard cells using electrophysiology and fluorescent imaging techniques.\\u000a The results implicate that membrane turnover

T. Meckel; A. C. Hurst; G. Thiel; U. Homann

2005-01-01

126

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

127

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

128

Measurement of red blood cell mechanics during morphological changes  

NASA Astrophysics Data System (ADS)

The human red blood cell (RBC) membrane, a fluid lipid bilayer tethered to an elastic 2D spectrin network, provides the principal control of the cell's morphology and mechanics. These properties, in turn, influence the ability of RBCs to transport oxygen in circulation. Current mechanical measurements of RBCs rely on external loads. Here we apply a Noncontact optical interferometric technique to quantify the thermal fluctuations of RBC membranes with 3 nm accuracy over a broad range of spatial and temporal frequencies. Combining this technique with a new mathematical model describing RBC membrane undulations, we measure the mechanical changes of RBCs as they undergo a transition from the normal discoid shape to the abnormal echinocyte and spherical shapes. These measurements indicate that, coincident with this morphological transition, there is a significant increase in the membrane's shear and bending moduli. This mechanical transition can alter cell circulation and impede oxygen delivery.

Popescu, Gabriel; Park, Yongkeun; Best, Catherine; Dasari, Ramachandra; Feld, Michael; Kuriabova, Tatiana; Henle, Mark; Levine, Alex

2010-03-01

129

Effect of Processing and Storage on RBC function in vivo  

PubMed Central

Red Blood Cell (RBC) transfusion is indicated to improve oxygen delivery to tissue, and for no other purpose. We have come to appreciate that donor RBCs are fundamentally altered during processing and storage, in a fashion that both impairs oxygen transport efficacy and introduces additional risk by perturbing both immune and coagulation systems. The protean biophysical and physiologic changes in RBC function arising from storage are termed the ‘storage lesion’; many have been understood for some time; for example, we know that the oxygen affinity of stored blood rises during the storage period1 and that intracellular allosteric regulators, notably 2,3-bisphosphoglyceric acid (DPG) and ATP, are depleted during storage. Our appreciation of other storage lesion features has emerged with improved understanding of coagulation, immune and vascular signaling systems. Herein we review key features of the ‘storage lesion’. Additionally, we call particular attention to the newly appreciated role of RBCs in regulating linkage between regional blood flow and regional O2 consumption by regulating the bioavailability of key vasoactive mediators in plasma, as well as discuss how processing and storage disturbs this key signaling function and impairs transfusion efficacy. PMID:22818545

Doctor, Allan; Spinella, Phil

2012-01-01

130

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

131

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

132

Sialoglycosylation of RBC in Visceral Leishmaniasis Leads to Enhanced Oxidative Stress, Calpain-Induced Fragmentation of Spectrin and Hemolysis  

PubMed Central

Visceral leishmaniasis (VL) caused by the intracellular parasite Leishmania donovani accounts for an estimated 12 million cases of human infection. It is almost always associated with anemia, which severely complicates the disease course. However, the pathological processes leading to anemia in VL have thus far not been adequately characterized to date. In studying the glycosylation patterns of peripheral blood cells we found that the red blood cells (RBC) of VL patients (RBCVL) express eight 9-O-acetylated sialoglycoproteins (9-O-AcSGPs) that are not detected in the RBC of healthy individuals (RBCN). At the same time, the patients had high titers of anti-9-O-AcSGP IgG antibodies in their sera. These two conditions appear to be linked and related to the anemic state of the patients, as exposure of RBCVL but not RBCN to anti-9-O-AcSGPs antibodies purified from patient sera triggered a series of responses. These included calcium influx via the P/Q-type but not L-type channels, activation of calpain I, proteolysis of spectrin, enhanced oxidative stress, lipid peroxidation, externalization of phosphatidyl serine with enhanced erythrophagocytosis, enhanced membrane fragility and, finally, hemolysis. Taken together, this study suggests that the enhanced hemolysis is linked to an impairment of membrane integrity in RBCVL which is mediated by ligand-specific interaction of surface 9-O-AcSGPs. This affords a potential explanation for the structural and functional features of RBCVL which are involved in the hemolysis related to the anemia which develops in VL patients. PMID:22860118

Samanta, Sajal; Ghoshal, Angana; Bhattacharya, Kaushik; Saha, Bibhuti; Walden, Peter; Mandal, Chitra

2012-01-01

133

Allogeneic Stimulation of Cytotoxic T Cells by Supported Planar Membranes  

NASA Astrophysics Data System (ADS)

Phospholipid vesicles containing the transmembrane protein H-2Kk spontaneously fuse to form planar membranes when incubated on treated glass surfaces. Pattern photobleaching of fluorescent lipid probes indicates that these planar membranes are continuous and that the lipids are as mobile as they are in conventional fluid bilayers or monolayers. H-2Kk molecules in these planar membranes are immobile. These membranes stimulate cytotoxic T lymphocytes when cultured with immune spleen cells. The response to H-2Kk in planar membranes is greatly enhanced by the addition of supernatant from concanavalin A-stimulated spleen cells, indicating that relatively little antigen processing or presentation by accessory cells occurs. Cytotoxic T cells induced by purified alloantigen are found to be as susceptible to antibody blockade as are effectors from conventional mixed lymphocyte culture, where the antibody is directed against a T-cell surface antigen reputed to strengthen target cell adhesion through an interaction independent of major histocompatibility antigens.

Brian, Adrienne A.; McConnell, Harden M.

1984-10-01

134

In vivo crossmatching with Tc-99m-RBC's and In-111-oxine-RBC's  

SciTech Connect

In vitro crossmatching techniques are often inadequate for patients who have received multiple prior transfusions. These patients usually have multiple antibodies to minor blood groups, not all of which are necessarily important to vivo. It becomes increasingly difficult to obtain appropriate units for transfusion, and often units are used with hopes that a minor group antibody will not be significantly active in vivo. If a transfusion reaction occurs, the unit is stopped. The authors have developed and successfully tested a method whereby 1.5 to 3c of potential donor RBC's are labeled with 25-50 ..mu..Ci of Tc-99m using the BNL kits. After injection, samples are drawn at 10, 20, 60, and 120 minutes and the RBC survival is measured. If it is desirable to test 2 units simultaneously, the authors use 400 ..mu..Ci Tc-99m to label an RBC aliquot of one unit and 25 ..mu..Ci In-111-oxine to label the other; both labeled aliquots are injected together. The method is simple and reliable. In addition to assessing compatibility, the authors may also estimate the % viability of transfused, compatible RBC's by starting with 400 ..mu..Ci of Tc-99m and multiplying % survival at 24 hours by 1.2. For 24 hr. survival measurements of IN-111-oxine-RBC's, 25 ..mu..Ci is adequate and no multiplication factor is necessary. The authors have performed 13 in vivo crossmatches, 4 of which were double, in 6 patients. One documented mild transfusion reaction occurred. There were no false positive or false negative results.

Marcus, C.S.; Myhre, B.A.; Angulo, M.C.; Salk, R.D.; Essex, C.E.

1984-01-01

135

Membrane assembly, electrochemical cell and electrolysis process using perfluorinated sandwich type membrane  

SciTech Connect

A membrane assembly which comprises a layer of perfluorinated polymer which has carboxylate functional groups, a layer of perfluorinated polymer which has ion exchange functional groups, and a water-containing or water-soluble stratum which lies between these two layers and joins them together, is described. Such a multilayered composite membrane is more simply made than conventional multilayered membranes having adherent layers, and provides for easy recovery of the component parts thereof. The membrane assembly is useful for separating the compartments of an electrochemical cell, especially a chloralkali cell.

Bissot, Th. C.; Grigsby, W. E.

1984-12-25

136

Inhibition of dendritic cell maturation by malaria is dose dependent and does not require Plasmodium falciparum erythrocyte membrane protein 1.  

PubMed

Red blood cells infected with Plasmodium falciparum (iRBCs) have been shown to modulate maturation of human monocyte-derived dendritic cells (DCs), interfering with their ability to activate T cells. Interaction between Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) and CD36 expressed by DCs is the proposed mechanism, but we show here that DC modulation does not require CD36 binding, PfEMP1, or contact between DCs and infected RBCs and depends on the iRBC dose. iRBCs expressing a PfEMP1 variant that binds chondroitin sulfate A (CSA) but not CD36 were phagocytosed, inhibited lipopolysaccharide (LPS)-induced phenotypic maturation and cytokine secretion, and abrogated the ability of DCs to stimulate allogeneic T-cell proliferation. CD36- and CSA-binding iRBCs showed comparable inhibition. P. falciparum lines rendered deficient in PfEMP1 expression by targeted gene knockout or knockdown also inhibited LPS-induced phenotypic maturation, and separation of DCs and iRBCs in transwells showed that inhibition was not contact dependent. Inhibition was observed at an iRBC:DC ratio of 100:1 but not at a ratio of 10:1. High doses of iRBCs were associated with apoptosis of DCs, which was not activation induced. Lower doses of iRBCs stimulated DC maturation sufficient to activate autologous T-cell proliferation. In conclusion, modulation of DC maturation by P. falciparum is dose dependent and does not require interaction between PfEMP1 and CD36. Inhibition and apoptosis of DCs by high-dose iRBCs may or may not be physiological. However, our observation that low-dose iRBCs initiate functional DC maturation warrants reevaluation and further investigation of DC interactions with blood-stage P. falciparum. PMID:17470539

Elliott, Salenna R; Spurck, Timothy P; Dodin, Joelle M; Maier, Alexander G; Voss, Till S; Yosaatmadja, Francisca; Payne, Paul D; McFadden, Geoffrey I; Cowman, Alan F; Rogerson, Stephen J; Schofield, Louis; Brown, Graham V

2007-07-01

137

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

138

Organic-Inorganic Membranes for Fuel Cell Application  

NASA Astrophysics Data System (ADS)

Organic-inorganic membranes are worldwide under investigation with the purpose of achieving reduced methanol crossover for direct methanol fuel cell (DMFC) and increasing the proton conductivity at temperatures higher than 100°C in hydrogen fuel cells. The advantages and disadvantages of these membranes are discussed here with membrane examples containing aerosol, layered silicates, and modified silica as passive fillers as well as zirconium phosphate and heteropolyacids as conductive fillers.

Nunes, Suzana Pereira

139

Toxic effects of Litsea elliptica Blume essential oil on red blood cells of Sprague-Dawley rats*  

PubMed Central

Litsea elliptica Blume leaves have been traditionally used as medicinal herbs because of its antimutagenicity, chemopreventative and insecticidal properties. In this study, the toxic effects of L. elliptica essential oil against Sprague-Dawley rat’s red blood cells (RBCs) were evaluated. L. elliptica essential oil was given by oral gavage 5 times per week for 3 treated groups in the doses of 125, 250, and 500 mg/(kg body weight), respectively, and the control group received distilled water. Full blood count, RBC osmotic fragility, RBC morphological changes, and RBC membrane lipid were analyzed 28 d after the treatment. Although L. elliptica essential oil administration had significantly different effects on hemoglobin (Hb), mean cell hemoglobin concentration (MCHC), mean cell volume (MCV), and mean cell hemoglobin (MCH) in the experimental groups as compared to the control group (P<0.05), the values were still within the normal range. L. elliptica induced morphological changes of RBC into the form of echinocyte. The percentage of echinocyte increased significantly among the treated groups in a dose-response manner (P<0.001). The concentrations of RBC membrane phospholipids and cholesterol of all treated groups were significantly lower than those of control group (P<0.001). However, the RBC membrane osmotic fragility and total proteins of RBC membrane findings did not differ significantly between control and treated groups (P>0.05). It is concluded that structural changes in the RBC membrane due to L. elliptica essential oil administration did not cause severe membrane damage. PMID:19882755

Taib, Izatus Shima; Budin, Siti Balkis; Siti Nor Ain, Seri Maseran; Mohamed, Jamaludin; Louis, Santhana Raj; Das, Srijit; Sallehudin, Sulaiman; Rajab, Nor Fadilah; Hidayatulfathi, Othman

2009-01-01

140

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

141

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

142

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

143

Temperature transitions of protein properties in human red blood cells.  

PubMed Central

Human red blood cells (RBC) undergo a sudden change from blocking to passing through 1.3 +/- 0.2-micrometer micropipettes at a transition temperature (Tc) of 36.4 degrees C. For resealed RBC ghosts this transition occurs at 28.3 degrees C (Tg). These findings are attributed to an elastomeric transition of hemoglobin from being gel-like to a fluid and to an elastomeric transition of membrane proteins such as spectrin. Spectrin shows a uniform distribution along the aspirated RBC tongue above Tg in contrast to the linear gradient below Tg. PMID:9826638

Artmann, G M; Kelemen, C; Porst, D; Büldt, G; Chien, S

1998-01-01

144

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

145

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.

146

Simulated Red Blood Cell Motion in Microvessel Bifurcations: Effects of Cell-Cell Interactions on Cell Partitioning  

PubMed Central

Partitioning of red blood cell (RBC) fluxes between the branches of a diverging microvessel bifurcation is generally not proportional to the flow rates, as RBCs preferentially enter the higher-flow branch. A two-dimensional model for RBC motion and deformation is used to investigate the effects of cell-cell mechanical interactions on RBC partitioning in bifurcations. The RBC membrane and cytoplasm are represented by sets of viscoelastic elements immersed in a low Reynolds number flow. Several types of two-cell interactions that can affect partitioning are found. In the most frequent interactions, a `trade-off' occurs, in which a cell entering one branch causes a following cell to enter the other branch. Other types of interactions include `herding,' where the leading cell is caused to enter the same branch as the following cell, and `following,' where the trailing cell is caused to enter the same branch as the leading cell. The combined effect of these cell-cell interactions is a tendency towards more uniform partitioning, which results from the trade-off effect but is reduced by the herding and following effects. With increasing hematocrit, the frequency of interactions increases, and more uniform partitioning results. This prediction is consistent with experimental observations on how hematocrit affects RBC partitioning. PMID:23555330

Barber, Jared O.; Restrepo, Juan M.; Secomb, Timothy W.

2013-01-01

147

Plasma dependent reduction in red blood cell aggregation after dextran sulfate low-density lipoprotein apheresis--implications for rheological studies.  

PubMed

Red blood cell (RBC) aggregation is increased in familial hypercholesterolemia, and is reduced significantly after low density lipoprotein (LDL) apheresis. The purpose of the present study was to clarify whether this reduction depends on changes in plasma composition, RBC membrane properties, or both. RBC aggregation was determined in a computerized cell flow-properties analyzer, before and after LDL apheresis. We compared RBC aggregation in autologous plasma with aggregation in a plasma-free standard solution (0.5% of dextran 500 kDa) to define the separate contributions of plasma and cellular properties to the observed RBC aggregation. RBC aggregation in autologous plasma was reduced by 35.5% after LDL apheresis (P=0.01) but was not significantly affected when measured in dextran 500. This suggests that LDL apheresis attenuated RBC aggregation by altering plasma composition rather than RBC membrane properties. These results are relevant to the understanding of hemorheological changes which follow therapeutic apheresis in hypercholesterolemic patients. PMID:16202011

Schechner, Vered; Ben-Ami, Ronen; Hershcovici, Tiberiu; Yedgar, Shaul; Beigel, Ytzhak; Shapira, Itzhak; Berliner, Shlomo; Barsthein, Gershon

2005-10-01

148

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

149

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

150

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

151

Phosphorylation and Activation of the Plasma Membrane Na+/H+ Exchanger (NHE1) during Osmotic Cell Shrinkage  

PubMed Central

The Na+/H+ Exchanger isoform 1 (NHE1) is a highly versatile, broadly distributed and precisely controlled transport protein that mediates volume and pH regulation in most cell types. NHE1 phosphorylation contributes to Na+/H+ exchange activity in response to phorbol esters, growth factors or protein phosphatase inhibitors, but has not been observed during activation by osmotic cell shrinkage (OCS). We examined the role of NHE1 phosphorylation during activation by OCS, using an ideal model system, the Amphiuma tridactylum red blood cell (atRBC). Na+/H+ exchange in atRBCs is mediated by an NHE1 homolog (atNHE1) that is 79% identical to human NHE1 at the amino acid level. NHE1 activity in atRBCs is exceptionally robust in that transport activity can increase more than 2 orders of magnitude from rest to full activation. Michaelis-Menten transport kinetics indicates that either OCS or treatment with the phosphatase inhibitor calyculin-A (CLA) increase Na+ transport capacity without affecting transport affinity (Km?=?44 mM) in atRBCs. CLA and OCS act non-additively to activate atNHE1, indicating convergent, phosphorylation-dependent signaling in atNHE1 activation. In situ 32P labeling and immunoprecipitation demonstrates that the net phosphorylation of atNHE1 is increased 4-fold during OCS coinciding with a more than 2-order increase in Na+ transport activity. This is the first reported evidence of increased NHE1 phosphorylation during OCS in any vertebrate cell type. Finally, liquid chromatography and mass spectrometry (LC-MS/MS) analysis of atNHE1 immunoprecipitated from atRBC membranes reveals 9 phosphorylated serine/threonine residues, suggesting that activation of atNHE1 involves multiple phosphorylation and/or dephosphorylation events. PMID:22216214

Rigor, Robert R.; Damoc, Catalina; Phinney, Brett S.; Cala, Peter M.

2011-01-01

152

RBC acetyl cholinesterase: A poor man's early diagnostic biomarker for familial alzheimer's and Parkinson's disease dementia  

PubMed Central

Objective: Analysis of red blood cell acetyl cholinesterase (AChE) in a familial Alzheimer's diseases (AD) Parkinson's disease dementia (PDD) and their first generation. Setting: General hospital, Mahad district, Raigad. Patients and Methods: Clinically diagnosed patients of AD and PDD and their asymptomatic relatives. Their blood was collected in EDTA tube and transferred to laboratory at Mumbai. Result: Median red blood cell (RBC) cholinesterase levels amongst PDD, their first generation asymptomatic relatives, familial AD, asymptomatic relatives of AD, healthy controls, farmers exposed to pesticides (positive control) and other neurological condition without dementia (hypertension with TIA 1, sub-dural hematoma 2, hypothyroid 1, non-familial unilateral parkinsonism without dementia 3, writers cramps 2, hyponitremia 1 and cerebral palsy with non-fluent aphasia 1). Median values of RBC AChE were 19086.78 U/L, 15666.05 U/L, 9013.11 U/L, 7806.19 U/L, 14334.57 U/L, 9785.05 U/L and 13162.60 U/L, respectively. As compared to controls, RBC AChE levels were statistically significant among PDD (P = 0.004) and significantly lowered among familial AD patients (P = 0.010), relatives of patients (P = 0.010). Interpretations: Below the normal RBC AChE level is a potential biomarker in asymptomatic relatives of familial AD patients. RBC AChE is raised than normal level in patients suffering from PDD, where AChE inhibitors are helpful. However, RBC AChE level below the normal where AChE inhibitor may not be effective. PMID:25552849

Bawaskar, Himmatrao Saluba; Bawaskar, Parag Himmatrao; Bawaskar, Pramodini Himmatrao

2015-01-01

153

Membranous basal cell adenoma arising in the eyelid  

PubMed Central

Basal cell adenoma (BCA) is a specific entity that lacks the myxochondroid stromal component of pleomorphic adenoma. Membranous basal cell adenoma is a rare variant of BCA, which is characteristic by abundant eosinophilicextracellular hyaline material deposited either inside or at the periphery of the epithelial islands. Herin we describe the first case of membranous BCA arising in the upper eyelid in a 38-year-old woman. A well-demarcated nodule arising in the eyelid was composed of isomorphic basaloid cells organized with a prominent basal cell layer and distinct basement membrane-like material. Immunohistochemically, S100 protein and p63 highlighted the basal aspect of the peripheral epithelial cells, while CK7 expressed on the luminal cells. A diagnosis of membranous basal cell adenoma of the eyelid was made. At follow-up for 2 years and 3 months later, there was no evidence of recurrence. Further pathological characteristics of this disease are discussed. PMID:25120843

Huang, Yong; Yang, Min; Ding, Jianhui

2014-01-01

154

Predicting dynamics and rheology of blood flow: A comparative study of multiscale and low-dimensional models of red blood cells  

SciTech Connect

In this work we compare the predictive capability of two mathematical models for red blood cells (RBCs) focusing on blood flow in capillaries and arterioles. Both RBC models as well as their corresponding blood flows are based on the dissipative particle dynamics (DPD) method, a coarse-grained molecular dynamics approach. The first model employs a multiscale description of the RBC (MS-RBC), with its membrane represented by hundreds or even thousands of DPD-particles connected by springs into a triangular network in combination with out-of-plane elastic bending resistance. Extra dissipation within the network accounts for membrane viscosity, while the characteristic biconcave RBC shape is achieved by imposition of constraints for constant membrane area and constant cell volume. The second model is based on a low-dimensional description (LD-RBC) constructed as a closed torus-like ring of only 10 large DPD colloidal particles. They are connected into a ring by worm-like chain (WLC) springs combined with bending resistance. The LD-RBC model can be fitted to represent the entire range of nonlinear elastic deformations as measured by optical-tweezers for healthy and for infected RBCs in malaria. MS-RBCs suspensions model the dynamics and rheology of blood flow accurately for any size vessel but this approach is computationally expensive above 100 microns. Surprisingly, the much more economical suspensions of LD-RBCs also capture the blood flow dynamics and rheology accurately except for vessels with sizes comparable to RBC diameter. In particular, the LD-RBC suspensions are shown to properly capture the experimental data for the apparent viscosity of blood and its cell-free layer (CFL) in tube flow. Taken together, these findings suggest a hierarchical approach in modeling blood flow in the arterial tree, whereby the MS-RBC model should be employed for capillaries and arterioles below 100 microns, the LD-RBC model for arterioles, and the continuum description for arteries.

Pan, Wenxiao; Fedosov, Dmitry A.; Caswell, Bruce; Karniadakis, George E.

2011-05-27

155

Modifications in Erythrocyte Membrane Zeta Potential by Plasmodium falciparum Infection  

PubMed Central

The zeta potential (ZP) is an electrochemical property of cell surfaces that is determined by the net electrical charge of molecules exposed at the surface of cell membranes. Membrane proteins contribute to the total net electrical charge of cell surfaces and can alter ZP through variation in their copy number and changes in their intermolecular interactions. Plasmodium falciparum extensively remodels its host red blood cell (RBC) membrane by placing ‘knob’-like structures at the cell surface. Using an electrophoretic mobility assay, we found that the mean ZP of human RBCs was ?15.7 mV. In RBCs infected with P. falciparum trophozoites (‘iRBCs’), the mean ZP was significantly lower (?14.6 mV, p<0.001). Removal of sialic acid from the cell surface by neuraminidase treatment significantly decreased the ZP of both RBCs (?6.06 mV) and iRBCs (?4.64 mV). Parasite-induced changes in ZP varied by P. falciparum clone and the presence of knobs on the iRBC surface. Variations in ZP values were accompanied by altered binding of iRBCs to human microvascular endothelial cells (MVECs). These data suggest that parasite-derived knob proteins contribute to the ZP of iRBCs, and that electrostatic and hydrophobic interactions between iRBC and MVEC membranes are involved in cytoadherence. PMID:22459624

Tokumasu, Fuyuki; Ostera, Graciela R.; Amaratunga, Chanaki; Fairhurst, Rick M.

2012-01-01

156

Systematic Design of Polymer Electrolyte Membranes for Fuel Cells Using a Pore-Filling Membrane Concept  

NASA Astrophysics Data System (ADS)

In this chapter, systematic membrane design and development using our pore-filling membrane concept is described. Pore-filling electrolyte membranes for use as electrolyte membranes for polymer electrolyte membrane fuel cells (PEMFCs) or direct methanol fuel cells (DMFCs) are described. The pores of a porous substrate are filled with a polymer electrolyte and the membrane swelling is suppressed by the substrate matrix. Proton conductivity is achieved through the impregnated electrolyte polymer. Fuel crossover is reduced by suppression of the electrolyte polymer swelling and mechanical strength is maintained by the substrate. Using this concept, high proton conductivity has been shown to exist with reduced membrane fuel crossover and good dimensional stability. In this chapter, high performance pore-filling electrolyte membranes and their DMFC or PEMFC performances are shown. To achieve a high energy density DMFC device, we must use a high concentration of methanol aqueous solution as the fuel and crossover must be reduced. The membrane also showed almost no dimensional change with variation in humidity. The DMFC and PEMFC performances are also described with several varieties of pore-filling membranes for each application.

Yamaguchi, Takeo

157

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

158

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

159

Proteomics and Phosphoproteomics Analysis of Human Lens Fiber Cell Membranes  

PubMed Central

Purpose. The human lens fiber cell insoluble membrane fraction contains important membrane proteins, cytoskeletal proteins, and cytosolic proteins that are strongly associated with the membrane. The purpose of this study was to characterize the lens fiber cell membrane proteome and phosphoproteome from human lenses. Methods. HPLC-mass spectrometry–based multidimensional protein identification technology (MudPIT), without or with phosphopeptide enrichment, was applied to study the proteome and phosphoproteome of lens fiber cell membranes, respectively. Results. In total, 951 proteins were identified, including 379 integral membrane and membrane-associated proteins. Enriched gene categories and pathways based on the proteomic analysis include carbohydrate metabolism (glycolysis/gluconeogenesis, pentose phosphate pathway, pyruvate metabolism), proteasome, cell-cell signaling and communication (GTP binding, gap junction, focal adhesion), glutathione metabolism, and actin regulation. The combination of TiO2 phosphopeptide enrichment and MudPIT analysis revealed 855 phosphorylation sites on 271 proteins, including 455 phosphorylation sites that have not been previously identified. PKA, PKC, CKII, p38MAPK, and RSK are predicted as the major kinases for phosphorylation on the sites identified in the human lens membrane fraction. Conclusions. The results presented herein significantly expand the characterized proteome and phosphoproteome of the human lens fiber cell and provide a valuable reference for future research in studies of lens development and disease. PMID:23349431

Wang, Zhen; Han, Jun; David, Larry L.; Schey, Kevin L.

2013-01-01

160

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

161

Single cell wound generates electric current circuit and cell membrane potential variations that requires calcium influx.  

PubMed

Breaching of the cell membrane is one of the earliest and most common causes of cell injury, tissue damage, and disease. If the compromise in cell membrane is not repaired quickly, irreversible cell damage, cell death and defective organ functions will result. It is therefore fundamentally important to efficiently repair damage to the cell membrane. While the molecular aspects of single cell wound healing are starting to be deciphered, its bio-physical counterpart has been poorly investigated. Using Xenopus laevis oocytes as a model for single cell wound healing, we describe the temporal and spatial dynamics of the wound electric current circuitry and the temporal dynamics of cell membrane potential variation. In addition, we show the role of calcium influx in controlling electric current circuitry and cell membrane potential variations. (i) Upon wounding a single cell: an inward electric current appears at the wound center while an outward electric current is observed at its sides, illustrating the wound electric current circuitry; the cell membrane is depolarized; calcium flows into the cell. (ii) During cell membrane re-sealing: the wound center current density is maintained for a few minutes before decreasing; the cell membrane gradually re-polarizes; calcium flow into the cell drops. (iii) In conclusion, calcium influx is required for the formation and maintenance of the wound electric current circuitry, for cell membrane re-polarization and for wound healing. PMID:24801267

Luxardi, Guillaume; Reid, Brian; Maillard, Pauline; Zhao, Min

2014-07-24

162

Development and characterization of proton conductive membranes and membrane electrode assemblies for fuel cells  

NASA Astrophysics Data System (ADS)

Polymer electrolyte membrane fuel cells (PEMFCs), including hydrogen fuel cells (PEMFCs) and direct methanol fuel cells (DMFCs), are considered as attractive electrical power sources. However, there are some technical obstacles that impede the commercialization of PEMFCs. For instance, in H 2-PEMFCs, carbon monoxide (CO) poisoning of the anode catalyst causes serious performance loss; in DMFCs, methanol crossover through the membrane reduces the overall fuel cell efficiency. This work focused on: (1) developing high performance membrane electrode assemblies (MEAs) and investigating their behavior at higher temperature H2-PEMFC with H2+CO as the fuel; (2) improving DMFCs efficiency by preparing low methanol crossover/good proton conductivity membranes based on NafionRTM matrix; (3) synthesizing and modifying low cost sulfonated hydrocarbon (SPEEK) membranes for both H2-PEMFCs and DMFCs applications. High performance membrane electrode assemblies (MEAs) with composite NafionRTM-TeflonRTM-Zr(HPO 4)2 membranes were prepared, optimized and characterized at higher temperature (> 100°C)/lower relative humidity (< 100% RH) condition, using H2 or H2+CO as the fuel. Effects of CO concentration, temperature, relative humidity to the CO poisoning on H 2-PEMFC were studied by applying various electrochemical techniques. The electrochemical oxidation mechanism of H2/CO in higher temperature PEMFC was investigated and simulated. Two type of membranes based on NafionRTM matrix were prepared: silica/NafionRTM membrane and palladium impregnated NafionRTM (Pd-NafionRTM) membrane. The composite silica/NafionRTM membrane was developed by in-situ sol-gel reaction followed by solution casting, while the Pd-NafionRTM was fabricated via a supercritical fluid CO2 (scCO 2) route. Reduced methanol crossover and enhanced efficiency was observed by applying each of the two membranes to DMFCs. In addition, the research demonstrated that scCO2 is a promising technique for modifying membranes or depositing nano-particle electrocatalysts onto electrolyte. Sulfonated poly(ether ether ketone) (SPEEK) was synthesized by a sulfonation reaction using poly(ether ether ketone) (PEEK). Multilayer structure SPEEK membranes with methanol barriers were fabricated and showed enhanced membrane stability in DMFCs. Improved MEA performance was obtained due to lower methanol crossover and the presence of a good membrane/electrode interface for facilitating proton transfer.

Jiang, Ruichun

163

Lipid-insertion enables targeting functionalization of erythrocyte membrane-cloaked nanoparticles.  

PubMed

RBC membrane-cloaked polymeric nanoparticles represent an emerging nanocarrier platform with extended circulation in vivo. A lipid-insertion method is employed to functionalize these nanoparticles without the need for direct chemical conjugation. Insertion of both folate and the nucleolin-targeting aptamer AS1411 shows receptor-specific targeting against model cancer cell lines. PMID:23907698

Fang, Ronnie H; Hu, Che-Ming J; Chen, Kevin N H; Luk, Brian T; Carpenter, Cody W; Gao, Weiwei; Li, Shulin; Zhang, Dong-Er; Lu, Weiyue; Zhang, Liangfang

2013-10-01

164

Lipid-insertion enables targeting functionalization of erythrocyte membrane-cloaked nanoparticles†  

PubMed Central

RBC membrane-cloaked polymeric nanoparticles represent an emerging nanocarrier platform with extended circulation in vivo. A lipid-insertion method is employed to functionalize these nanoparticles without the need for direct chemical conjugation. Insertion of both folate and the nucleolin-targeting aptamer AS1411 shows receptor-specific targeting against model cancer cell lines. PMID:23907698

Fang, Ronnie H.; Hu, Che-Ming J.; Chen, Kevin N. H.; Luk, Brian T.; Carpenter, Cody W.; Gao, Weiwei; Li, Shulin; Zhang, Dong-Er; Lu, Weiyue; Zhang, Liangfang

2013-01-01

165

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

166

Numerical and Experimental Study on the Development of Electric Sensor as for Measurement of Red Blood Cell Deformability in Microchannels  

PubMed Central

A microsensor that can continuously measure the deformability of a single red blood cell (RBC) in its microchannels using microelectrodes is described in this paper. The time series of the electric resistance is measured using an AC current vs. voltage method as the RBC passes between counter-electrode-type micro-membrane sensors attached to the bottom wall of the microchannel. The RBC is deformed by the shear flow created in the microchannel; the degree of deformation depends on the elastic modulus of the RBC. The resistance distribution, which is unique to the shape of the RBC, is analyzed to obtain the deformability of each cell. First, a numerical simulation of the electric field around the electrodes and RBC is carried out to evaluate the influences of the RBC height position, channel height, distance between the electrodes, electrode width, and RBC shape on the sensor sensitivity. Then, a microsensor was designed and fabricated on the basis of the numerical results. Resistance measurement was carried out using samples of normal RBCs and rigidified (Ca2+–A23186 treated) RBCs. Visualization measurement of the cells' behavior was carried out using a high-speed camera, and the results were compared with those obtained above to evaluate the performance of the sensor. PMID:23112616

Tatsumi, Kazuya; Katsumoto, Yoichi; Fujiwara, Ryoji; Nakabe, Kazuyoshi

2012-01-01

167

Time-Resolved Molecular Transport across Living Cell Membranes  

PubMed Central

It is shown that the nonlinear optical phenomenon known as second-harmonic generation can be used for label-free, time-resolved study of the transport of molecules through living cell membranes. The adsorption and transport of a 300-Da molecular-mass hydrophobic ion at the Escherichia coli membrane is observed. Remarkably, at low ion concentrations, the second-harmonic generation technique clearly exposes a multistep molecular transport process: Transport of the molecular ion across the outer and cytoplasmic membranes of the Gram-negative bacteria is recorded, in sequence, in time. Fitting of the data to a multiprocess kinematic model reveals that the transport of this hydrophobic ion through the outer membrane is much faster than through the cytoplasmic membrane, likely reflecting the effectiveness of ion transport porins. The observations illustrate an experimental means for studying the interactions of small molecules with cell membranes. PMID:23332066

Zeng, Jia; Eckenrode, Heather M.; Dounce, Susan M.; Dai, Hai-Lung

2013-01-01

168

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

169

Regulatory Aspects of Membrane Microdomain (Raft) Dynamics in Live Cells  

Microsoft Academic Search

Most vertebrate cells display a considerable microheterogeneity in their plasma membranes, often termed microdomain structure.\\u000a Some of these microdomains are enriched in glycosphingolipids and cholesterol and are resistant to solubilization with nonionic\\u000a detergents; they are therefore called detergent-insoluble-glycolipid enriched membrane (DIG) or glycosphingolipid enriched\\u000a membrane (GEM). These domains, also called “lipid rafts” (Simons and Ikonen, 1997), may form at the

János Matkó; János Szöll?si

170

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; Liang, Barbara

171

Organisation of B-cell receptors on the cell membrane.  

PubMed

B-cell receptors (BCRs) have been reported to organise into oligomeric clusters on the B-cell surface, and mutations, that are likely to interfere with such clustering, result in B-cell unresponsiveness. This has led to the suggestion that pre-formed BCR clusters may be crucial for B-cell signalling. However, neither the size nor the fraction of BCRs organised in such clusters have yet been determined in experiments. Hence, the authors use a statistical approach to predict the membrane organisation of BCRs, based on available experimental data. For physiological parameters, most BCRs will organise into supramolecular polymers that comprise about five receptors where the non-covalent interactions are mediated by the IgH transmembrane helix. A reduction in the density of IgM to 2-5% of the normal density, a characteristic of anergic MD4 B cells, strongly reduces IgM polymerisation, and it is suggested that impaired BCR clustering may be responsible for the unresponsiveness of anergic B cells. PMID:16986327

Iber, D; Gruhn, T

2006-09-01

172

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 cell devices revolves around the development and subsequent investigation of the perfluorinated inomeric membrane separator useful in proton-exchange membrane systems. Work is currently focusing on studying the effects of equivalent weight, thickness, water of hydration, pretreatment procedures, as well as the degree of water management required for a given membrane separator in the cell. The presentation will include details of certain aspects of the above as well as some of the requirements for high and low power generation.

Eisman, G. A.

1989-01-01

173

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

174

Direct measurements of membrane potential and membrane resistance of human red cells  

PubMed Central

1. In order to evaluate the membrane potentials calculated from the distribution of chloride ions in human red cells and plasma, it is desirable to have a direct measurement of the transmembrane potential of these cells. 2. A method has been devised for introducing a capillary micro-electrode into human red cells. The method allows simultaneous measurements of potential and membrane resistance with only one micro-electrode located in the cell. 3. Upon impalement of single cells in plasma, a scatter of membrane potentials and of resistance values was obtained. The potential drop never exceeded -14 mV and the maximum resistances were about 7 ?. cm2. Positive potentials were obtained on impalement of red cell aggregates. 4. Arguments are given to support the view that it is in these cells which suffer least damage from the impalement that maximum values of membrane potentials and resistances are observed. The errors caused by the change in the liquid junction during the impalement have been estimated. 5. As judged from this study, it seems permissible under normal conditions to calculate the membrane potential of the red cell from the chloride concentrations in plasma and in intracellular water. PMID:5649641

Lassen, U. V.; Sten-Knudsen, O.

1968-01-01

175

Membrane Protein Dynamics and Functional Implications in Mammalian Cells  

PubMed Central

The organization of the plasma membrane is both highly complex and highly dynamic. One manifestation of this dynamic complexity is the lateral mobility of proteins within the plane of the membrane, which is often an important determinant of intermolecular protein-binding interactions, downstream signal transduction, and local membrane mechanics. The mode of membrane protein mobility can range from random Brownian motion to immobility and from confined or restricted motion to actively directed motion. Several methods can be used to distinguish among the various modes of protein mobility, including fluorescence recovery after photobleaching, single-particle tracking, fluorescence correlation spectroscopy, and variations of these techniques. Here, we present both a brief overview of these methods and examples of their use to elucidate the dynamics of membrane proteins in mammalian cells—first in erythrocytes, then in erythroblasts and other cells in the hematopoietic lineage, and finally in non-hematopoietic cells. This multisystem analysis shows that the cytoskeleton frequently governs modes of membrane protein motion by stably anchoring the proteins through direct-binding interactions, by restricting protein diffusion through steric interactions, or by facilitating directed protein motion. Together, these studies have begun to delineate mechanisms by which membrane protein dynamics influence signaling sequelae and membrane mechanical properties, which, in turn, govern cell function. PMID:24210428

Alenghat, Francis J.; Golan, David E.

2014-01-01

176

Alkaline Membrane Fuel Cell System Break-Out Session  

E-print Network

on anode + Alkaline membrane on cathode ­ High temperature operation ­ KOH to capture carbonate · SystemAlkaline Membrane Fuel Cell Workshop System Break-Out Session Anil Trehan (CommScope) Huyen Dinh/stop cycles · Ordinary air operation at ambient temperature (CO2 scrubber part of system) #12;Medium Term Fuel

177

Prevalence and Specificity of RBC Alloantibodies in Indian Patients Attending a Tertiary Care Hospital  

PubMed Central

Background. Red blood cell (RBC) alloimmunization results from genetic disparity of RBC antigens between donor and recipients. Data about alloimmunization rate in general patient population is scarce especially from resource limited countries. We undertook this study to determine prevalence and specificity of RBC alloantibodies in patients admitted in various clinical specialties at a tertiary care hospital in North India. Methods. Antibody screening was carried out in 11,235 patients on automated QWALYS 3 platform (Diagast, Loos, France). Antibody identification was carried out with an 11-cell identification panel (ID-Diapanel, Diamed GmbH, Switzerland). Results. The overall incidence of RBC alloimmunization in transfused patients was 1.4% (157/11235), with anti-E being the most common specificity (36.3%), followed by anti-D (16%), anti-c (6.4%), anti-c + E (6.4%), anti-C + D (5.1%), and anti-K (4.5%). The highest incidence of alloimmunization was observed in hematology/oncology patients (1.9%), whereas in other specialties the range was 0.7–1%. Conclusion. As alloimmunization complicates the transfusion outcomes, authors recommend pretransfusion antibody screening and issue of Rh and Kell matched blood to patients who warrant high transfusion requirements in future. PMID:25386192

Zaman, Shamsuz; Chaurasia, Rahul; Chatterjee, Kabita; Thapliyal, Rakesh Mohan

2014-01-01

178

The fluidity of Chinese hamster ovary cell and bull sperm membranes after cholesterol addition  

Microsoft Academic Search

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 examined the effect that adding cholesterol to the membranes of Chinese hamster ovary cells (CHO) and bull sperm

P. H. Purdy; M. H. Fox; J. K. Graham

2005-01-01

179

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

180

Two novel approaches targeting cancer cell membrane for tumor therapy.  

PubMed

Disruption of normal cell function by chemicals, UV radiation or viruses can cause various cancer. Drugs that have been developed for cancer therapy bind to various targets to correct disorder cell behavior, repair damaged DNA or promote cell apoptosis. However, there is rare study that focuses on cancer cell membrane as target. We propose two approaches for achieving our goal. One is to use phospholipase A2 (PLA2) to cleave phospholipid heads of the bilayer of cancer cells. Because PLA2 has unique Ca(2+) catalytic site and the pH of healthy tissue cells should be slightly alkaline at 7.2-7.5, it can be easily protected by CO3(2-) in the form of PLA2-CaCO3. While PLA2-CaCO3 accumulate in cancer cells in the acidic microenvironment of which the pH is below 7, it could be converted to active state (PLA2-Ca(2+)) which can intensively damage the cancer cell membrane. The other one is to use both monoclonal antibodies and dimethylsulfoxide (DMSO). The internalization of targeted cancer cell antibodies could change the curvature of cell membrane from order state to disorder state, therefore strong detergent DMSO can destroy cancer cells at extreme low concentration. These two approaches present no harm for normal cells, therefore, drugs targeted cancer cell membrane might become a new and high effective clinical cancer therapy. PMID:23374423

Feng, Yingzhu; Wang, Bochu; Cao, Yang; He, Rui

2013-04-01

181

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

182

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

183

Apparatus measures swelling of membranes in electrochemical cells  

NASA Technical Reports Server (NTRS)

Apparatus consisting of a pressure plate unit, four springs of known spring constant and a micrometer measures the swelling and force exerted by the polymer membranes of alkaline electrochemical cells.

Hennigan, T. J.

1965-01-01

184

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

185

Fibronectin coating of oxygenator membranes enhances endothelial cell attachment  

PubMed Central

Background Extracorporeal membrane oxygenation (ECMO) can replace the lungs’ gas exchange capacity in refractory lung failure. However, its limited hemocompatibility, the activation of the coagulation and complement system as well as plasma leakage and protein deposition hamper mid- to long-term use and have constrained the development of an implantable lung assist device. In a tissue engineering approach, lining the blood contact surfaces of the ECMO device with endothelial cells might overcome these limitations. As a first step towards this aim, we hypothesized that coating the oxygenator’s gas exchange membrane with proteins might positively influence the attachment and proliferation of arterial endothelial cells. Methods Sheets of polypropylene (PP), polyoxymethylpentene (TPX) and polydimethylsiloxane (PDMS), typical material used for oxygenator gas exchange membranes, were coated with collagen, fibrinogen, gelatin or fibronectin. Tissue culture treated well plates served as controls. Endothelial cell attachment and proliferation were analyzed for a period of 4 days by microscopic examination and computer assisted cell counting. Results Endothelial cell seeding efficiency is within range of tissue culture treated controls for fibronectin treated surfaces only. Uncoated membranes as well as all other coatings lead to lower cell attachment. A confluent endothelial cell layer develops on fibronectin coated PDMS and the control surface only. Conclusions Fibronectin increases endothelial cells’ seeding efficiency on different oxygenator membrane material. PDMS coated with fibronectin shows sustained cell attachment for a period of four days in static culture conditions. PMID:23356939

2013-01-01

186

Adaptation of Yeast Cell Membranes to Ethanol  

PubMed Central

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. PMID:16347349

Jiménez, J.; Benítez, T.

1987-01-01

187

Numerical analysis of a red blood cell flowing through a thin micropore  

NASA Astrophysics Data System (ADS)

Red blood cell (RBC) deformability plays a key role in microcirculation, especially in vessels that have diameters even smaller than the nominal cell size. In this study, we numerically investigate the dynamics of an RBC in a thin micropore. The RBC is modeled as a capsule with a thin hyperelastic membrane. In a numerical simulation, we employ a boundary element method for fluid mechanics and a finite element method for membrane mechanics. The resulting RBC deformation towards the flow direction is suppressed considerably by increased cytoplasm viscosity, whereas the gap between the cell membrane and solid wall becomes smaller with higher cytoplasm viscosity. We also measure the transit time of the RBC and find that nondimensional transit time increases nonlinearly with respect to the viscosity ratio, whereas it is invariant to the capillary number. In conclusion, cytoplasmic viscosity plays a key role in the dynamics of an RBC in a thin pore. The results of this study will be useful for designing a microfluidic device to measure cytoplasmic viscosity.

Omori, Toshihiro; Hosaka, Haruki; Imai, Yohsuke; Yamaguchi, Takami; Ishikawa, Takuji

2014-01-01

188

Computational fluid dynamics modeling of polymer electrolyte membrane fuel cells  

Microsoft Academic Search

A detailed steady-state isothermal two-dimensional model of a proton exchange membrane fuel cell has been developed. A finite element method was used to solve this multi-component transport model coupled with flow in porous medium, charge balance, electrochemical kinetics, and a rigorous water balance in the membrane. The model-predicted fuel cell performance curves are compared with published experimental results and a

Galip H. Guvelioglu; Harvey G. Stenger

2005-01-01

189

Penetration of cell membranes and synthetic lipid bilayers by nanoprobes.  

PubMed

Nanoscale devices have been proposed as tools for measuring and controlling intracellular activity by providing electrical and/or chemical access to the cytosol. Unfortunately, nanostructures with diameters of 50-500 nm do not readily penetrate the cell membrane, and rationally optimizing nanoprobes for cell penetration requires real-time characterization methods that are capable of following the process of membrane penetration with nanometer resolution. Although extensive work has examined the rupture of supported synthetic lipid bilayers, little is known about the applicability of these model systems to living cell membranes with complex lipid compositions, cytoskeletal attachment, and membrane proteins. Here, we describe atomic force microscopy (AFM) membrane penetration experiments in two parallel systems: live HEK293 cells and stacks of synthetic lipid bilayers. By using the same probes in both systems, we were able to clearly identify membrane penetration in synthetic bilayers and compare these events with putative membrane penetration events in cells. We examined membrane penetration forces for three tip geometries and 18 chemical modifications of the probe surface, and in all cases the median forces required to penetrate cellular and synthetic lipid bilayers with nanoprobes were greater than 1 nN. The penetration force was sensitive to the probe's sharpness, but not its surface chemistry, and the force did not depend on cell surface or cytoskeletal properties, with cells and lipid stacks yielding similar forces. This systematic assessment of penetration under various mechanical and chemical conditions provides insights into nanoprobe-cell interactions and informs the design of future intracellular nanoprobes. PMID:25418094

Angle, Matthew R; Wang, Andrew; Thomas, Aman; Schaefer, Andreas T; Melosh, Nicholas A

2014-11-01

190

Basement Membrane Matrix (BME) has Multiple Uses with Stem Cells  

Microsoft Academic Search

The utilization of basement membrane matrix has helped to overcome many of the obstacles associated with stem cell research.\\u000a Initially, there were several problems with investigating stem cells, including difficult extraction from tissues, the need\\u000a for feeder layers, poor survival, minimal proliferation, limited differentiation in vitro, and inadequate survival when injected\\u000a or transplanted in vivo. Given that the basement membrane

Irina Arnaoutova; Jay George; Hynda K. Kleinman; Gabriel Benton

191

Cell membranes: The electromagnetic environment and cancer promotion  

Microsoft Academic Search

Use of weak electromagnetic fields to study the sequence and energetics of events that couple humoral stimuli from surface receptor sites to the cell interior has identified cell membranes as a primary site of interaction, with these low frequency fields. Field modulation of cell surface chemical events indicates a major amplification of initial weak triggers associated with binding of hormones,

W. R. Adey

1988-01-01

192

Evaluation of composite membranes for direct methanol fuel cells  

NASA Astrophysics Data System (ADS)

The performance of direct methanol fuel cells (DMFCs) can be significantly affected by the transport of methanol through the membrane, depolarising the cathode. In this paper, the literature on composite membranes that have been developed for reduction of methanol crossover in DMFCs is reviewed. While such membranes can be effective in reducing methanol permeability, this is usually combined with a reduction in proton conductivity. Measurements of methanol permeability and proton conductivity are relatively straightforward, and these parameters (or a membrane 'selectivity' based on the ratio between them) are often used to characterize DMFC membranes. However, we have carried out one-dimensional simulations of DMFC performance for a wide range of membrane properties, and the results indicate that DMFC performance is normally either limited by methanol permeability or proton conductivity. Thus use of a 'selectivity' is not appropriate for comparison of membrane materials, and results from the model can be used to compare different membranes. The results also show that Nafion ® 117 has an optimum thickness, where DMFC performance is equally limited by both methanol permeability and proton conductivity. The model also indicates that new composite membranes based on Nafion ® can only offer significant improvement in DMFC performance by enabling operation with increased methanol concentration in the fuel. A number of composite membrane materials that have been reported in the literature are shown to deliver significant reduction in DMFC performance due to reduced proton conductivity, although improved performance at high methanol concentration may be possible.

Li, X.; Roberts, E. P. L.; Holmes, S. M.

193

Membrane Composition Tunes the Outer Hair Cell Motor  

NASA Astrophysics Data System (ADS)

Cholesterol and docosahexaenoic acid (DHA), an ?-3 fatty acid, affect membrane mechanical properties in different ways and modulate the function of membrane proteins. We have probed the functional consequence of altering cholesterol and DHA levels in the membranes of OHCs and prestin expressing HEK cells. Large, dynamic and reversible changes in prestin-associated charge movement and OHC motor activity result from altering the concentration of membrane cholesterol. Increasing membrane cholesterol shifts the q/V function ~ 50 mV in the hyperpolarizing direction, possibly a response related to increases in membrane stiffness. The voltage shift is linearly related to total membrane cholesterol. Increasing cholesterol also decreases the total charge moved in a linear fashion. Decreasing membrane cholesterol shifts the q/V function ~ 50 mV in the depolarizing direction with little or no effect on the amount of charge moved. In vivo increases in membrane cholesterol transiently increase but ultimately lead to decreases in DPOAE. Docosahexaenoic acid shifts the q/V function in the hyperpolarizing direction < 15 mV and increases total charge moved. Tuning of cochlear function by membrane cholesterol contributes to the exquisite temporal and frequency processing of mammalian hearing by optimizing the cochlear amplifier.

Rajagopalan, L.; Sfondouris, J.; Oghalai, J. S.; Pereira, F. A.; Brownell, W. E.

2009-02-01

194

[Characteristics of thiamine triphosphatase from neural cells plasma membranes].  

PubMed

The kinetic parameters of the ThTP hydrolysis by synaptic plasma membranes isolated from rat brain were investigated. It was shown that the ThTPase reaction pH optimum was 7.4, the apparent K(m) was 52 microM and the apparent affinity constant for Mg2+ was 1.9 mM. The comparative analysis of the indicated parameters was done for the ThTPase activity of membrane bound (the data of present work and literature data) and cytosolic (literature data) proteins. The analysis allows us to suppose that thiamine-binding protein described earlier is the single ThTPase activity carrier in neural cells plasma membranes. It was shown that the active site of the enzyme that catalyzes the ThTP hydrolysis in neural cells plasma membranes is associated with the inside membrane surface. PMID:19877430

Sidorova, A A; Stepanenko, S P; Parkhomenko, Iu M

2009-01-01

195

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

SciTech Connect

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

196

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

197

Neuronal inhibition of astroglial cell proliferation is membrane mediated  

PubMed Central

Previously we have used a microwell tissue culture assay to show that early postnatal mouse cerebellar astroglia have a flattened morphology and proliferate rapidly when they are cultured in the absence of neurons, but develop specific cell-cell contacts and undergo morphological differentiation when they are co-cultured with purified granule neurons (Hatten, M. E., 1985, J. Cell Biol., 100:384-396). In these studies of cell binding between neurons and astroglia, measurement with light and fluorescence microscopy or with [35S]methionine-labeled cells indicated that the kinetics of the binding of the neurons to astroglial cells are rapid, occurring within 10 min of the addition of the neurons to the growing glia. 6 h after neuronal attachment, astroglial DNA synthesis decreases, as shown by a two- to fivefold decrease in [3H]thymidine incorporation, and glial growth ceases. No effects on astroglial cell growth were seen after adding medium conditioned by purified cerebellar neurons cultured in the absence of astroglia, by astroglia cultured in the absence of neurons, or by a mixed population of cerebellar cells. This result was unchanged when any of these media were concentrated up to 50-fold, or when neurons and astroglia were cultured in separate chambers with confluent medium. Two groups of experiments suggest that membrane- membrane interactions between granule neurons and astroglia control astroglial cell growth. First, neurons fixed with dilute amounts of paraformaldehyde (0.5%) bound to the astroglia with the same kinetics as did living cells, inhibited DNA synthesis, and arrested glial growth within hours. Second, a cell membrane preparation of highly purified granule neurons also bound rapidly to the glia, decreased [3H]thymidine incorporation two- to fivefold and inhibited astroglial cell growth. The rate of the decrease in glial growth depended on the concentration of the granule neural membrane preparation added. A similar membrane preparation from purified cerebellar astroglial cells, PC12 cells, 3T3 mouse fibroblasts, or PTK rat epithelial cells did not decrease astroglial cell growth rates. Living neurons were the only preparation that both inhibited glial DNA synthesis and induced the astroglial cells to transform from the flat, epithelial shapes they have when they are cultured without neurons to highly differentiated forms that resemble Bergmann glia or astrocytes seen in vivo. These results suggest that membrane-membrane interactions between neurons and astroglia inhibit astroglial proliferation in vitro, and raise the possibility that membrane elements involved in glial growth regulation include neuron-glial interaction molecules. PMID:3571332

1987-01-01

198

Decreased Fluidity of Red Cell Membrane Lipids in Abetalipoproteinemia  

PubMed Central

Acanthocytic red cells in patients with abetalipoproteinemia are morphologically similar to the red cells in spur cell anemia. Fluidity of membrane lipids is decreased in spur cells due to their excess cholesterol content. Acanthocyte membranes have an increased content of sphingomyelin and a decreased content of lecithin. To assess the effect of this abnormality of acanthocyte membrane lipid composition on membrane fluidity, we studied red cells from five patients with abetalipoproteinemia and four obligate heterozygote family members. Membrane fluidity was measured in terms of microviscosity (¯?) at 37°C, assessed by means of the fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene. It was increased from 3.2±0.1 poise in normals to 4.01-4.14 poise in acanthocytes. This was associated with an increase in the sphingomyelin/lecithin ratio from 0.84±0.08 in normals in 1.45-1.61 in acanthocytes. The ¯? of acanthocyte membranes was not influenced by the degree of vitamin E deficiency. Similar changes in ¯? were observed in liposomes prepared from red cell lipids. Heterozygotes had normal sphingomyelin/lecithin ratios and normal values for ¯?. The flow activation energy for viscosity, a measure of the degree of order in the hydrophobic portion of the membrane, was decreased from 8.3 kcal/mole in normal red cells to 7.2 kcal/mole in acanthocytes, indicating that acanthocyte membrane lipids are more ordered. Variations in the sphingomyelin/lecithin mole ratio of liposomes prepared from brain sphingomyelin and egg lecithin with equimolar cholesterol caused similar changes in both ¯? and activation energy. The deformability of acanthocytes, assessed by means of filtration through 3-?m filters, was decreased. These studies indicate that the increased sphingomyelin/lecithin ratio of acanthocytes is responsible for their decreased membrane fluidity. As in spur cells and in red cells enriched with cholesterol in vitro, this decrease in membrane fluidity occurs coincidentally with an abnormality in cell contour and an impairment in cell deformability. PMID:874076

Cooper, Richard A.; Durocher, John R.; Leslie, Mary H.

1977-01-01

199

?E-catenin regulates cell-cell adhesion and membrane blebbing during zebrafish epiboly  

PubMed Central

?E-catenin is an actin-binding protein associated with the E-cadherin-based adherens junction that regulates cell-cell adhesion. Recent studies identified additional E-cadherin-independent roles of ?E-catenin in regulating plasma membrane dynamics and cell migration. However, little is known about the roles of ?E-catenin in these different cellular processes in vivo during early vertebrate development. Here, we examined the functions of ?E-catenin in cell-cell adhesion, cell migration and plasma membrane dynamics during morphogenetic processes that drive epiboly in early Danio rerio (zebrafish) development. We show that depletion of ?E-catenin caused a defect in radial intercalation that was associated with decreased cell-cell adhesion, in a similar manner to E-cadherin depletion. Depletion of ?E-catenin also caused deep cells to have protracted plasma membrane blebbing, and a defect in plasma membrane recruitment of ERM proteins that are involved in controlling membrane-to-cortex attachment and membrane blebbing. Significantly, depletion of both E-cadherin and ?E-catenin suppressed plasma membrane blebbing. We suggest that during radial intercalation the activities of E-cadherin and ?E-catenin in the maintenance of membrane-to-cortex attachment are balanced, resulting in stabilization of cell-cell adhesion and suppression of membrane blebbing, thereby enabling proper radial intercalation. PMID:22190637

Schepis, Antonino; Sepich, Diane; Nelson, W. James

2012-01-01

200

Proton conducting membranes for high temperature fuel cells with solid state water free membranes  

NASA Technical Reports Server (NTRS)

A water free, proton conducting membrane for use in a fuel cell is fabricated as a highly conducting sheet of converted solid state organic amine salt, such as converted acid salt of triethylenediamine with two quaternized tertiary nitrogen atoms, combined with a nanoparticulate oxide and a stable binder combined with the converted solid state organic amine salt to form a polymeric electrolyte membrane. In one embodiment the membrane is derived from triethylenediamine sulfate, hydrogen phosphate or trifiate, an oxoanion with at least one ionizable hydrogen, organic tertiary amine bisulfate, polymeric quaternized amine bisulfate or phosphate, or polymeric organic compounds with quaternizable nitrogen combined with Nafion to form an intimate network with ionic interactions.

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

2006-01-01

201

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

202

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

203

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

204

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

205

An Adaptive Finite Element Method For The Modeling Of The Equilibrium Of Red Blood Cells  

E-print Network

An Adaptive Finite Element Method For The Modeling Of The Equilibrium Of Red Blood Cells Aymen with a the numerical modeling of an isolated red blood cell (RBC), and more generally of phospholipid membranes. We, Lagrange multipliers, Numerical methods, Vesicle, Red Blood Cell, Elastic bending energy, Canham

Saramito, Pierre

206

Imaging Cell Membrane Injury and Subcellular Processes Involved in Repair  

PubMed Central

The ability of injured cells to heal is a fundamental cellular process, but cellular and molecular mechanisms involved in healing injured cells are poorly understood. Here assays are described to monitor the ability and kinetics of healing of cultured cells following localized injury. The first protocol describes an end point based approach to simultaneously assess cell membrane repair ability of hundreds of cells. The second protocol describes a real time imaging approach to monitor the kinetics of cell membrane repair in individual cells following localized injury with a pulsed laser. As healing injured cells involves trafficking of specific proteins and subcellular compartments to the site of injury, the third protocol describes the use of above end point based approach to assess one such trafficking event (lysosomal exocytosis) in hundreds of cells injured simultaneously and the last protocol describes the use of pulsed laser injury together with TIRF microscopy to monitor the dynamics of individual subcellular compartments in injured cells at high spatial and temporal resolution. While the protocols here describe the use of these approaches to study the link between cell membrane repair and lysosomal exocytosis in cultured muscle cells, they can be applied as such for any other adherent cultured cell and subcellular compartment of choice. PMID:24686523

Defour, Aurelia; Sreetama, S. C.; Jaiswal, Jyoti K.

2014-01-01

207

Tight binding of proteins to membranes from older human cells.  

PubMed

The lens is an ideal model system for the study of macromolecular aging and its consequences for cellular function, since there is no turnover of lens fibre cells. To examine biochemical processes that take place in the lens and that may also occur in other long-lived cells, membranes were isolated from defined regions of human lenses that are synthesised at different times during life, and assayed for the presence of tightly bound cytosolic proteins using quantitative iTRAQ proteomics technology. A majority of lens beta crystallins and all gamma crystallins became increasingly membrane bound with age, however, the chaperone proteins alpha A and alpha B crystallin, as well as the thermally-stable protein, ?B2 crystallin, did not. Other proteins such as brain-associated signal protein 1 and paralemmin 1 became less tightly bound in the older regions of the lens. It is evident that protein-membrane interactions change significantly with age. Selected proteins that were formerly cytosolic become increasingly tightly bound to cell membranes with age and are not removed even by treatment with 7 M urea. It is likely that such processes reflect polypeptide denaturation over time and the untoward binding of proteins to membranes may alter membrane properties and contribute to impairment of communication between older cells. PMID:21181282

Truscott, Roger J W; Comte-Walters, Susana; Ablonczy, Zsolt; Schwacke, John H; Berry, Yoke; Korlimbinis, Anastasia; Friedrich, Michael G; Schey, Kevin L

2011-12-01

208

Prebiotic cell membranes that survive extreme environmental pressure conditions.  

PubMed

Attractive candidates for compartmentalizing prebiotic cells are membranes comprised of single-chain fatty acids. It is generally believed that life may have originated in the depth of the protoocean, that is, under high hydrostatic pressure conditions, but the structure and physical-chemical properties of prebiotic membranes under such conditions have not yet been explored. We report the temperature- and pressure-dependent properties of membranes composed of prebiotically highly-plausible lipids and demonstrate that prebiotic membranes could not only withstand extreme temperatures, but also serve as robust models of protocells operating in extreme pressure environments. We show that pressure not only increases the stability of vesicular systems but also limits their flexibility and permeability to solutes, while still keeping the membrane in an overall fluid-like and thus functional state. PMID:24953643

Kapoor, Shobhna; Berghaus, Melanie; Suladze, Saba; Prumbaum, Daniel; Grobelny, Sebastian; Degen, Patrick; Raunser, Stefan; Winter, Roland

2014-08-01

209

VIEW OF RBC (REFINED BICARBONATE) BUILDING LOOKING NORTHEAST. DEMOLITION IN ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

VIEW OF RBC (REFINED BICARBONATE) BUILDING LOOKING NORTHEAST. DEMOLITION IN PROGRESS. "ARM & HAMMER BAKING SODA WAS MADE HERE FOR OVER 50 YEARS AND THEN SHIPPED ACROSS THE STREET TO THE CHURCH & DWIGHT PLANT ON WILLIS AVE. (ON THE RIGHT IN THIS PHOTO). LAYING ON THE GROUND IN FRONT OF C&D BUILDING IS PART OF AN RBC DRYING TOWER. - Solvay Process Company, Refined Bicarbonate Building, Between Willis & Milton Avenues, Solvay, Onondaga County, NY

210

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

211

Light-sensitive membrane potentials in onion guard cells  

Microsoft Academic Search

INTRACELLULAR electrical recordings in onion guard cells show that they maintain a membrane potential difference (MPD), inside negative. The MPD is light-sensitive; cells subjected to short light and dark cycles depolarise in the dark and hyperpolarise in the light. The swiftness of the electrical changes makes them among the fastest known stomatal responses, suggesting a causal relationship between the reception

E. Zeiger; W. Moody; P. Hepler; F. VARELA

1977-01-01

212

Carbon monoxide poisoning of proton-exchange membrane fuel cells  

Microsoft Academic Search

The platinum-alloy catalyst used in proton-exchange membrane (PEM) fuel cell anodes is highly susceptible to carbon monoxide (CO) poisoning. CO reduces the catalyst activity by blocking active catalyst sites normally available for hydrogen chemisorption and dissociation. The reaction kinetics at the anode catalyst surface can be used to estimate the decrease in cell voltage due to various levels of CO

Aida Rodrigues; John C. Amphlett; Ronald F. Mann; Brant A. Peppley; Pierre R. Roberge

1997-01-01

213

Transient disruptions of aortic endothelial cell plasma membranes.  

PubMed Central

Cells of gut, skin, and muscle frequently suffer transient survivable plasma membrane disruptions ("wounds") under physiological conditions, but it is not known whether endothelial cells of the aorta, which are constantly exposed to hemodynamically generated mechanical forces, similarly are injured in vivo. We have used serum albumin as a molecular probe for identifying endothelial cells of the rat aorta that incurred and survived transient plasma membrane wounds in vivo. Such wounded endothelial cells were in fact observed in the aortas of all rats examined. However, the percentage of wounded cells in the total aortic endothelial population varied remarkably between individuals ranging from 1.4% to 17.9% with a mean of 6.5% (+/- 4.6% SD). Wounded endothelial cells were heterogeneously distributed, being found in distinct clusters often in the shape of streaks aligned with the long axis of the vessel, or in the shape of partial or complete rims surrounding bifurcation openings, such as the ostia of the intercostal arteries. Physical exercise (running) did not increase the frequency of aortic endothelial cell membrane wounding, nor did spontaneous hypertension. Surprisingly, 80% of mitotic endothelial cell figures were identified as wounded. This article identified a previously unrecognized form of endothelial cell injury, survivable disruptions of the plasma membrane, and shows that injury to the endothelial cells of the normal aorta is far more commonplace than previously suspected. Plasma membrane wounding of endothelial cells could be linked to the initiation of atherosclerosis. Images Figure 1 Figure 3 Figure 4 Figure 5 Figure 11 Figure 6 Figure 8 PMID:1466399

Yu, Q. C.; McNeil, P. L.

1992-01-01

214

Application of Dissipative Particle Dynamics to the Study of a Red Blood Cell in Simple Shear Flow  

NASA Astrophysics Data System (ADS)

The present work reports an attempt to apply the dissipative particle dynamics (DPD) method to study the dynamic behaviors of a red blood cell (RBC) in simple shear flow. The simulation system is discretized into four types of particles, namely wall particles, fluid particles, membrane particles and internal particles. The particle interaction is modeled by the DPD method, and the membrane particles are connected into a viscoelastic triangular network to represent the RBC membrane. As benchmarking tests, we simulate the deformation of a spherical capsule in shear flow and compare it with the past study, and also examine the effect of computational domain size. After that, we investigate the dynamics of a RBC in shear flow at different membrane shear and bending moduli. Our simulations reproduce the tank-treading, trembling and tumbling motions of the RBC at the shear modulus Es = 6, 60 and 600 ?N/m, respectively. Moreover, we find that the RBC undergoes a trembling motion when its bending modulus is large enough, where the obvious stretching and smoothing of the RBC occur alternately in shape.

Ye, Ting; Phan-Thien, Nhan; Khoo, Boo Cheong; Lim, Chwee Teck

2014-11-01

215

The protective effect of aqueous extracts of roselle (Hibiscus sabdariffa L. UKMR-2) against red blood cell membrane oxidative stress in rats with streptozotocin-induced diabetes  

PubMed Central

OBJECTIVES: The aim of this study was to investigate the protective effects of aqueous extracts of roselle (Hibiscus sabdariffa L. UKMR-2) against red blood cell (RBC) membrane oxidative stress in rats with streptozotocin-induced diabetes. METHODS: Forty male Sprague-Dawley rats weighing 230-250 g were randomly divided into four groups (n?=?10 rats each): control group (N), roselle-treated control group, diabetic group, and roselle-treated diabetic group. Roselle was administered by force-feeding with aqueous extracts of roselle (100 mg/kg body weight) for 28 days. RESULTS: The results demonstrated that the malondialdehyde levels of the red blood cell membranes in the diabetic group were significantly higher than the levels in the roselle-treated control and roselle-treated diabetic groups. The protein carbonyl level was significantly higher in the roselle-treated diabetic group than in the roselle-treated control group but lower than that in the diabetic group. A significant increase in the red blood cell membrane superoxide dismutase enzyme was found in roselle-treated diabetic rats compared with roselle-treated control rats and diabetic rats. The total protein level of the red blood cell membrane, osmotic fragility, and red blood cell morphology were maintained. CONCLUSION: The present study demonstrates that aqueous extracts of roselle possess a protective effect against red blood cell membrane oxidative stress in rats with streptozotocin-induced diabetes. These data suggest that roselle can be used as a natural antioxidative supplement in the prevention of oxidative damage in diabetic patients. PMID:24212844

Mohamed, Jamaludin; Shing, Saw Wuan; Md Idris, Muhd Hanis; Budin, Siti Balkis; Zainalabidin, Satirah

2013-01-01

216

Mechanical degradation of fuel cell membranes under fatigue fracture tests  

NASA Astrophysics Data System (ADS)

The effects of cyclic stresses on the fatigue and mechanical stability of perfluorosulfonic acid (PFSA) membranes are experimentally investigated under standard fuel cell conditions. The experiments are conducted ex-situ by subjecting membrane specimens to cyclic uniaxial tension at controlled temperature and relative humidity. The fatigue lifetime is measured in terms of the number of cycles until ultimate fracture. The results indicate that the membrane fatigue lifetime is a strong function of the applied stress, temperature, and relative humidity. The fatigue life increases exponentially with reduced stresses in all cases. The effect of temperature is found to be more significant than that of humidity, with reduced fatigue life at high temperatures. The maximum membrane strain at fracture is determined to decrease exponentially with increasing membrane lifetime. At a given fatigue life, a membrane exposed to fuel cell conditions is shown to accommodate more plastic strain before fracture than one exposed to room conditions. Overall, the proposed ex-situ membrane fatigue experiment can be utilized to benchmark the fatigue lifetime of new materials in a fraction of the time and cost associated with conventional in-situ accelerated stress testing methods.

M. H. Khorasany, Ramin; Sadeghi Alavijeh, Alireza; Kjeang, Erik; Wang, G. G.; Rajapakse, R. K. N. D.

2015-01-01

217

Phytosphingosine kills Candida albicans by disrupting its cell membrane.  

PubMed

The mechanism of action of phytosphingosine (PHS), a member of the sphingosine family which has candidacidal activity when added externally, was investigated. Previously, it has been reported that the fungicidal activity of PHS is based on the induction of caspase-independent apoptosis. In contrast, we found that addition of PHS causes a direct permeabilization of the plasma membrane of yeast, highlighted by the influx of the membrane probe propidium iodide, and the efflux of small molecules (i.e., adenine nucleotides) as well as large cellular constituents such as proteins. Freeze-fracture electron microscopy revealed that PHS treatment causes severe damage of the plasma membrane of the cell, which seems to have lost its integrity completely. We also found that PHS reverts the azide-induced insensitivity to histatin 5 (Hst5) of Candida albicans. In a previous study, we had found that the decreased sensitivity to Hst5 of energy-depleted cells is due to rigidification of the plasma membrane, which could be reverted by the membrane fluidizer benzyl alcohol. In line with the increased membrane permeabilization and ultrastructural damage, this reversal of the azide-induced insensitivity by PHS also points to a direct interaction between PHS and the cytoplasmic membrane of C. albicans. PMID:19919184

Veerman, Enno C I; Valentijn-Benz, Marianne; van't Hof, Wim; Nazmi, Kamran; van Marle, Jan; Amerongen, Arie V Nieuw

2010-01-01

218

Numerical modeling transport phenomena in proton exchange membrane fuel cells  

NASA Astrophysics Data System (ADS)

To study the coupled phenomena occurring in proton exchange membrane fuel cells, a two-phase, one-dimensional, non-isothermal model is developed in the chapter 1. The model includes water phase change, proton transport in the membrane and electro-osmotic effect. The thinnest, but most complex layer in the membrane electrode assembly, catalyst layer, is considered an interfacial boundary between the gas diffusion layer and the membrane. Mass and heat transfer and electro-chemical reaction through the catalyst layer are formulated into equations, which are applied to boundary conditions for the gas diffusion layer and the membrane. Detail accounts of the boundary equations and the numerical solving procedure used in this work are given. The polarization curve is calculated at different oxygen pressures and compared with the experimental results. When the operating condition is changed along the polarization curve, the change of physicochemical variables in the membrane electrode assembly is studied. In particular, the over-potential diagram presents the usage of the electrochemical energy at each layer of the membrane electrode assembly. Humidity in supplying gases is one of the most important factors to consider for improving the performance of PEMFE. Both high and low humidity conditions can result in a deteriorating cell performance. The effect of humidity on the cell performance is studied in the chapter 2. First, a numerical model based on computational fluid dynamics is developed. Second, the cell performances are simulated, when the relative humidity is changed from 0% to 100% in the anode and the cathode channel. The simulation results show how humidity in the reactant gases affects the water content distribution in the membrane, the over-potential at the catalyst layers and eventually the cell performance. In particular, the rapid enhancement in the cell performance caused by self-hydrating membrane is captured by the simulation. Fully humidifying either H2 in the anode or air in the cathode makes the membrane conductive enough for proton transfer. Water supplied more than that can hinder mass transfer of O2 and degrade the cell performance. At low output voltage, the limiting current density is increased by reducing the humidity at the cathode.

Suh, DongMyung

219

Nanodomain stabilization dynamics in plasma membranes of biological cells  

NASA Astrophysics Data System (ADS)

We discover that a synergistically amplifying role of stabilizing membrane proteins and continuous lipid recycling can explain the physics governing the stability, polydispersity, and dynamics of lipid raft domains in plasma membranes of biological cells. We establish the conjecture using a generalized order parameter based on theoretical formalism, endorsed by detailed scaling arguments and domain mapping. Quantitative agreements with morphological distributions of raft complexes, as obtained from Förster resonance energy transfer based visualization, support the present theoretical conjecture.

Das, Tamal; Maiti, Tapas K.; Chakraborty, Suman

2011-02-01

220

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

221

Influence of the phosphoric acid-doping level in a polybenzimidazole membrane on the cell performance of high-temperature proton exchange membrane fuel cells  

Microsoft Academic Search

The acid migration in phosphoric acid-doped polybenzimidazole (PBI) membrane high-temperature proton exchange membrane fuel cells (HT-PEMFC) during operation is experimentally evaluated to clarify the influence of the acid balance between the membrane and electrodes on cell performance. A method for controlling the amount of phosphoric acid doped in PBI membranes is investigated, and PBI membranes with various amounts of phosphoric

Yuka Oono; Atsuo Sounai; Michio Hori

2009-01-01

222

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

223

Cell volume and membrane stretch independently control K+ channel activity.  

PubMed

A number of potassium channels including members of the KCNQ family and the Ca(2+) activated IK and SK, but not BK, are strongly and reversibly regulated by small changes in cell volume. It has been argued that this general regulation is mediated through sensitivity to changes in membrane stretch. To test this hypothesis we have studied the regulation of KCNQ1 and BK channels after expression in Xenopus oocytes. Results from cell-attached patch clamp studies (approximately 50 microm(2) macropatches) in oocytes expressing BK channels demonstrate that the macroscopic volume-insensitive BK current increases with increasing negative hydrostatic pressure (suction) applied to the pipette. Thus, at a pipette pressure of -5.0 +/- 0.1 mmHg the increase amounted to 381 +/- 146% (mean +/- S.E.M., n = 6, P < 0.025). In contrast, in oocytes expressing the strongly volume-sensitive KCNQ1 channel, the current was not affected by membrane stretch. The results indicate that (1) activation of BK channels by local membrane stretch is not mimicked by membrane stress induced by cell swelling, and (2) activation of KCNQ1 channels by cell volume increase is not mediated by local tension in the cell membrane. We conclude that stretch and volume sensitivity can be considered two independent regulatory mechanisms. PMID:19289549

Hammami, Sofia; Willumsen, Niels J; Olsen, Hervør L; Morera, Francisco J; Latorre, Ramón; Klaerke, Dan A

2009-05-15

224

InVited Feature Article Water Dynamics and Proton Transfer in Nafion Fuel Cell Membranes  

E-print Network

InVited Feature Article Water Dynamics and Proton Transfer in Nafion Fuel Cell Membranes David E is the most widely used polyelectrolyte membrane in fuel cells. Ultrafast infrared spectroscopy of the O but has since become the most commonly used membrane separator in polymer electrolyte membrane fuel cells

Fayer, Michael D.

225

Fluorescence lifetime imaging (FLIM) of membrane markers in living cells  

NASA Astrophysics Data System (ADS)

An experimental setup for fluorescence lifetime imaging (FLIM) has been combined with total internal reflection fluorescence microscopy (TIRFM) in order to detect various membrane markers within living cells. The method is established using T47D human breast cancer cells transfected by a plasmid encoding for a membrane associated yellow fluorescent protein (EYFPmem). For further measurements the mitochondrial marker rhodamine 123 (R123) as well as the membrane marker laurdan are used. With increasing concentration R123 is accumulated outside the mitochondria, in particular within the plasma membrane, whereas mitochondrial fluorescence is quenched. Fluorescence lifetime of laurdan can be used to probe membrane dynamics, in particular the phase of membrane lipids. These lipids are in a rigid gel phase at temperatures around 24°C, whereas the gel phases and a liquid crystalline phase coexist at T >= 30°C. This phase pattern also depends on the age and the growth phase of the cells and may play a role in the uptake of pharmaceutical agents.

Schneckenburger, Herbert; Wagner, Michael; Kretzschmar, Martina; Strauss, Wolfgang S.; Sailer, Reinhard

2003-10-01

226

Neutrons for fuel cell membranes: Structure, sorption and transport properties  

NASA Astrophysics Data System (ADS)

A molecular level understanding of structure and transport properties in fuel cell ionomer membranes is essential for designing new electrolytes with improved performance. Scattering techniques are suited tools for this purpose. In particular, neutron scattering, which has been extensively used in hydrogen-containing systems, is well adapted to investigate water-dependent complex polymeric morphologies. We report Small-Angle Neutron Scattering (SANS) studies on different types of fuel cell polymers: perfluorinated, radiation-grafted and sulfonated polyphosphazene membranes. We show that contrast variation methods can be efficiently employed to provide new insights on membrane microstructure and reveal ionic condensation effects. Neutrons have been used also as non-intrusive diagnosis tool to probe water properties and distribution inside membranes. Recently, in-situ neutronography and SANS experiments on operating fuel cells have been reported. In-plane cartography of water distribution at the surface of bipolar plates and water profiles across membrane thickness have been obtained and studied as a function of operating conditions. The last section of the article is devoted to the use of Quasi-Elastic Neutron Scattering to study water dynamics at molecular scale. We show that analysis with an appropriate sophisticated diffusion model allows to extract diffusion coefficients, characteristic times and length-scales of molecular motions. This quantitative information is fruitfully integrated in multi-scale modelling and usefully compared with numerical simulations. QENS also permits to compare alternative polymers and relate dynamical properties to chemical composition and membrane nanostructure.

Lyonnard, S.; Gebel, G.

2012-11-01

227

Journal of Biomechanics 31 (1998) 151--156 A possible physical mechanism of red blood cell vesiculation obtained  

E-print Network

erythrocyte; Vesiculation; pH; Membrane skeleton 1. Introduction The human red blood cell (RBC) has resting shape of the red blood cells at physiological pH 7.4 is the discocyte. However, at alkaline pHK11--bilayer interactions at this pH. 1998 Elsevier Science Ltd. All rights reserved. Keywords: Cell biomechanics; Human

Iglic, Ales

228

Dielectrophoretic discrimination of bovine red blood cell starvation age by buffer selection and membrane cross-linking.  

PubMed

We report an interesting buffer electric relaxation time tuning technique, coupled with a glutaraldehyde cross-linking cell fixation reaction, which allows for sensitive dielectrophoretic analysis and discrimination of bovine red blood cell (bRBC) starvation age. The buffer composition is selected such that two easily accessible dielectrophoretic crossover frequencies (cof) exist. Low concentration glutaraldehyde fixation was observed to produce a threefold decrease in the higher cof with a comparable increase in the lower cof also witnessed. More importantly, increased glutaraldehyde fixation concentration significantly increased the higher cof by a factor found to be sensitive to the bRBC starvation age. PMID:19693401

Gordon, Jason E; Gagnon, Zachary; Chang, Hsueh-Chia

2007-01-01

229

Membrane potential genesis in Nitella cells, mitochondria, and thylakoids.  

PubMed

The resting membrane potential of Nitella cells shifts in parallel with the change in H+ equilibrium potential, but is not equal to the H+ equilibrium potential. The deviation of the membrane potential from the H+ equilibrium potential depends on the extrusion rate of H+ by the electrogenic H+-pump. The activity of the electrogenic H+-pump was formulated in terms of the change in the free energy of ATP hydrolysis. The deviation of membrane potential from the H+ equilibrium potential induces a passive H+ flow. The passive inward H+ current may be coupled with Cl- uptake. The coupling rate of H+,Cl- co-transport was discussed. The membrane potential of mitochondria was electrochemically formulated in terms of oxidation-reduction H2/H+ half-cells spontaneously formed at the inner and outer boundaries of each trans-membrane electron-conducting pathway. The membrane potential formed by a pair of H2/H+ redox cells is pH-sensitive in its nature, but deviates from the H+ equilibrium potential to an extent that depends on the logarithm of the ratio of H2 concentrations at the inner and outer boundaries. The membrane potential of thylakoids is considered to be primarily due to the electromotive force of photocells embedded in the thylakoid membrane, as far as the anode and cathode of each photocell are in contact with the inner and outer solutions, respectively. The light-induced electronic current yields oxygen at the inner boundary and causes an increase in the H2 pool at the outer boundary of the electron-conducting pathway, which has no shunting plastoquinone chain between these two boundaries. PMID:12920604

Kitasato, Hiroshi

2003-10-01

230

Electrophoresis of concanavalin A receptors along embryonic muscle cell membrane  

Microsoft Academic Search

Fluorescent concanavalin A (con A)-labelling showed that an electric field of 4 V cm-1 grossly redistributed con A receptors along the plasma membranes of living muscle cells within 4 h. This field produced a voltage drop of 12 mV across these 30 µm-wide cells. The movement of receptors was independent of cell metabolism and seemed to be electrophoretic in nature.

Mu-Ming Poo; Kenneth R. Robinson

1977-01-01

231

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

232

Water management in a single cell proton exchange membrane fuel cells with a serpentine flow field  

Microsoft Academic Search

Gas and water management is the key to achieving good performance from a polymer electrolyte membrane fuel cell (PEMFC) stack. Imbalance between production and evaporation rates can result in either flooding of the electrodes or membrane dehydration, both of which severely limit fuel cell performance. In the present study, a mathematical model was developed to evaluate moisture profiles of hydrogen

Nik Suhaimi Mat Hassan; Wan Ramli Wan Daud; Kamaruzzaman Sopian; Jaafar Sahari

2009-01-01

233

Boron Induces Hyperpolarization of Sunflower Root Cell Membranes and Increases Membrane Permeability to K+1  

PubMed Central

Although many studies have alluded to a role for boron (B) in membrane function, there is little evidence for a direct effect of B on the plasmalemma of higher plant cells. These studies were conducted to demonstrate, by electrophysiological techniques, a direct effect of B on the membrane potential (Em) of sunflower (Helianthus annuus [L.], cv Mammoth Grey Stripe) root tip cells and to determine if the response to B occurs rapidly enough to account for the previously observed effects of B on ion uptake. By inserting a glass microelectrode into an individual cell in the root tip, the Em of the cell was determined in basal salt medium (BSM), pH 6.0. The perfusion solution surrounding the root tissue was then changed to BSM + 50 micromolar H3BO3, pH 6.0. The exposure to B induced a significant plasmalemma hyperpolarization in sunflower root cells within 20 minutes. After just 3 minutes of exposure to B, the change in Em was already significantly different from the negligible change in Em observed over time in root cells never exposed to B. Membrane hyperpolarization could be caused by a stimulation of the proton pump or by a change in the conductance of one or more permeable ions. Since B has been shown to affect K+ uptake by plants, the electrophysiological techniques described above were used to determine if B has an effect on membrane permeability to K+, and could thereby lead to an increased diffusion potential. When sunflower root tips were pretreated in 50 micromolar B for 2 hours, cell membranes exhibited a significantly greater depolarization with each 10-fold increase in external [K+] than minus-B cells. Subsequent studies demonstrated that the depolarization due to increased external [K+] was also significantly greater when tissue was exposed to B at the same time as the 10-fold increase in [K+], indicating that the effect of B on K+ permeability was immediate. Analysis of sunflower root tips demonstrated that treatment in 50 micromolar B caused a significantly greater accumulation of K+ after 48 hours. The B-induced increase in K+ uptake may cause a subsequent stimulation of the H+-ATPase (proton pump) and lead to the observed hyperpolarization of root cell membranes. Alternatively, B may stimulate the proton pump, with the subsequent hyperpolarization resulting in an increased driving force for K+ influx. Images Figure 2 PMID:16667504

Schon, Mary K.; Novacky, Anton; Blevins, Dale G.

1990-01-01

234

Microstructured Electrolyte Membranes to Improve Fuel Cell Performance  

NASA Astrophysics Data System (ADS)

Fuel cells, with the advantages of high efficiency, low greenhouse gas emission, and long lifetime are a promising technology for both portable power and stationary power sources. The development of efficient electrolyte membranes with high ionic conductivity, good mechanical durability and dense structure at low cost remains a challenge to the commercialization of fuel cells. This thesis focuses on exploring novel composite polymer membranes and ceramic electrolytes with the microstructure engineered to improve performance in direct methanol fuel cells (DMFCs) and solid oxide fuel cells (SOFCs), respectively. Polymer/particle composite membranes hold promise to meet the demands of DMFCs at lower cost. The structure of composite membranes was controlled by aligning proton conducting particles across the membrane thickness under an applied electric field. The field-induced structural changes caused the membranes to display an enhanced water uptake, proton conductivity, and methanol permeability in comparison to membranes prepared without an applied field. Although both methanol permeability and proton conductivity are enhanced by the applied field, the permeability increase is relatively lower than the proton conductivity improvement, which results in enhanced proton/methanol selectivity and improved DMFC performance. Apatite ceramics are a new class of fast ion conductors being studied as alternative SOFC electrolytes in the intermediate temperature range. An electrochemical/hydrothermal deposition method was developed to grow fully dense apatite membranes containing well-developed crystals with c-axis alignment to promote ion conductivity. Hydroxyapatite seed crystals were first deposited onto a metal substrate electrochemically. Subsequent ion substitution during the hydrothermal growth process promoted the formation of dense, fully crystalline films with microstructure optimal for ion transport. The deposition parameters were systematically investigated, such as reactant type, reagent concentration, solution pH, and reaction time. Dense apatite films were formed on palladium substrates that can serve as intermediate temperature fuel cell anodes. The novel apatite membrane structure is promising for fuel cell applications, as well as in improving the biocompatibility of orthopedic implants when coated on stainless steel or titanium substrates.

Wei, Xue

235

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

236

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

237

Inorganic Nanoporous Membranes for Immunoisolated Cell-Based Drug Delivery  

PubMed Central

Materials advances enabled by nanotechnology have brought about promising approaches to improve the encapsulation mechanism for immunoisolated cell-based drug delivery. Cell-based drug delivery is a promising treatment for many diseases but has thus far achieved only limited clinical success. Treatment of insulin dependent diabetes mellitus (IDDM) by transplantation of pancreatic ?-cells represents the most anticipated application of cell-based drug delivery technology. This review outlines the challenges involved with maintaining transplanted cell viability and discusses how inorganic nanoporous membranes may be useful in achieving clinical success. PMID:20384222

Mendelsohn, Adam; Desai, Tejal

2014-01-01

238

Membrane glycoproteins involved in cell--substratum adhesion.  

PubMed Central

A combination of immunological and biochemical methods were used to identify surface membrane components involved in cell-substratum adhesion. Broad-spectrum antiserum, prepared against surface membranes from hamster cells, induced reversible rounding and detachment of hamster fibroblasts from a substratum in vitro. This phenomenon was inhibited by Nonidet P-40 extracts of hamster cells. Therefore, an antibody neutralization assay was developed to detect the presence of antigen during the fractionation of Nonidet P-40 extracts of cells. After two differential precipitation steps, anion exchange chromatography, and sequential lectin affinity chromatography, a fraction greatly enriched in ability to block antiserum-induced changes in cell adhesion and appearance was isolated. Analysis of this fraction by NaDodSO4/polyacrylamide gel electrophoresis revealed a highly restricted group of glycoproteins with Mr approximately 140,000. A lectin-purified glycoprotein fraction was used to raise a higher titer antiserum that was able to induce reversible rounding and detachment of cells from a substratum and, when immobilized on an antibody affinity column, was able to bind and release material capable of blocking antiserum-induced cell rounding. These methods have allowed us to focus attention on a restricted group of glycoproteins that are integral constituents of the surface membrane and which play some as yet undetermined role in the process of cell--substratum adhesion. Images PMID:6273845

Knudsen, K A; Rao, P E; Damsky, C H; Buck, C A

1981-01-01

239

Evidence for bidirectional endocannabinoid transport across cell membranes.  

PubMed

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

2012-10-01

240

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

241

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

242

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

243

Adaptive evolution of rbcL in Conocephalum (Hepaticae, bryophytes).  

PubMed

An excess of nonsynonymous substitutions over synonymous ones has been regarded as an important indicator of adaptive evolution or positive selection at the molecular level. We now report such a case for rbcL sequences among cryptic species in Conocephalum (Hepaticae, Bryophytes). This finding can be regarded as evidence of adaptive evolution in several cryptic species (especially in F and JN types) within the genus. Bryophytes are small land plants with simple morphology. We can therefore expect the existence of several biologically distinct units or cryptic species within each morphological species. In our previous study, we found three rbcL types in Asian Conocephalum japonicum (Thunb.) Grolle and also found evidence strongly suggesting that the three types are reproductively isolated cryptic species. Additionally, we examined rbcL sequence variation in six cryptic species of C. conicum (L.) Dumort. previously recognized by allozyme analyses. As a result, we were able to discriminate the six cryptic species based only on their rbcL sequences. We were able to show that rbcL sequence variation is also useful in finding cryptic species of C. conicum. PMID:19100313

Miwa, Hidetsugu; Odrzykoski, Ireneusz J; Matsui, Atsushi; Hasegawa, Masami; Akiyama, Hiroyuki; Jia, Yu; Sabirov, Renat; Takahashi, Hideki; Boufford, David E; Murakami, Noriaki

2009-07-15

244

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

PubMed

FMNL3 is a vertebrate-specific formin protein that has previously been 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 over 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, 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: a 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

2014-11-26

245

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

246

Extracellular Heme Uptake and the Challenges of Bacterial Cell Membranes  

PubMed Central

In bacteria, the fine balance of maintaining adequate iron levels while preventing the deleterious effects of excess iron has led to the evolution of sophisticated cellular mechanisms to obtain, store, and regulate iron. Iron uptake provides a significant challenge given its limited bioavailability and need to be transported across the bacterial cell wall and membranes. Pathogenic bacteria have circumvented the iron-availability issue by utilizing the hosts' heme-containing proteins as a source of iron. Once internalized, iron is liberated from the porphyrin enzymatically for cellular processes within the bacterial cell. Heme, a lipophilic and toxic molecule, poses a significant challenge in terms of transport given its chemical reactivity. As such, pathogenic bacteria have evolved sophisticated membrane transporters to coordinate, sequester, and transport heme. Recent advances in the biochemical and structural characterization of the membrane-bound heme transport proteins are discussed in the context of ligand coordination, protein–protein interaction, and heme transfer. PMID:23046657

Smith, Aaron D.; Wilks, Angela

2013-01-01

247

Oyxsterols induce membrane procoagulant activity in monocytic THP-1 cells.  

PubMed Central

Oxidized cholesterol compounds or oxysterols are thought to be potent membrane-destabilizing agents. Anionic phospholipids, chiefly phosphatidylserine, have a procoagulant potential due to their ability to favour the membrane assembly of the characteristic clotting enzyme complexes including the tissue factor-dependent initiating complex. However, in resting cells, phosphatidylserine is sequestered in the inner leaflet of the plasma membrane. When THP-1 monocytic cells were cultured in the presence of 7beta-hydroxycholesterol (7beta-OH) or 25-hydroxycholesterol (25-OH), prothrombinase, which reflects anionic phospholipid exposure and tissue factor (TF) procoagulant activities, increased in a time- and dose-dependent manner. 7beta-OH appeared 1.5- to 2-fold more potent than 25-OH. Interestingly, no effect of cholesterol itself could be detected on procoagulant activities. Nevertheless, no difference in TF activity could be detected between oxysterol-treated and control cells after disruption. TF antigen expression was the same in oxysterol-treated and control cells as shown by flow cytometry. In contrast, the use of labelled annexin V, a protein probe of anionic phospholipids, revealed an elevated number of cells with exposed phosphatidylserine. Because the latter also constitutes a signal for phagocyte recognition of apoptotic cells and fragments, and a proportion of cells displayed altered morphology with condensed chromatin and membrane blebs, analysis of DNA was performed and indicated apoptosis in oxysterol-treated cells. Hence, oxysterol-induced phosphatidylserine exposure and enhanced TF activity may results from apoptosis. These results suggest relationships between oxysterol and the amplification of coagulation reactions by monocytic cells resulting from induced phosphatidylserine exposure. PMID:8615754

Aupeix, K; Toti, F; Satta, N; Bischoff, P; Freyssinet, J M

1996-01-01

248

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

249

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

250

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

251

Lipids of rabies virus and BHK-21 cell membranes.  

PubMed Central

The lipid composition of highly purified Flury strain of rabies virus (HEP) propagated in BHK-21 cells in a chemically defined medium was observed to be 6.7% neutral lipids, 15.8% phospholipids, and 1.5% glycolipids. In the virion, phosphatidylethanolamine, phosphatidylcholine, and sphingomyelin were the most abundant phospholipids, accounting for 90% of the total, and the molar ratio of cholesterol to phospholipid was 0.48. Uninfected BHK-21 cell membranes were obtained by nitrogen cavitation techniques and separated by density gradient centrifugation, and the membranes were assayed for purity using 5'-nucleotidase, cytochrome oxidase, and reduced nicotinamide adenine dinucleotide phosphate diaphorase activities. Lipids of the plasma membrane were enriched in cholesterol, phosphatidylcholine, and phosphatidylethanolamine. In contrast, membranes of the endoplasmic reticulum were enriched in phosphatidylcholine, but contained smaller amounts of phosphatidylethanolamine and sphingomyelin. Comparison of the fatty acyl chains of virus and membranes from uninfected cells revealed the virion to have the lowest ratio of C18:1 to C18:0 (1.771), compared with values of about 3.0 for the plasma membrane and endoplasmic reticulum. Total polyenoic fatty acids were enriched in the plasma membrane, whereas the virus contained higher amounts of total saturates than either of the two membrane preparations. Analysis of the polar and neutral lipid fractions as well as the acyl chain analysis suggests the virion has a lipid composition that is intermiediate to that of the plasma membrane and endoplasmic reticulum and is consistent with the view that numerous viral particles are synthesized de novo by not utilizing a preexisting membrane template. From the ratio of cholesterol to phospholipid of 0.48, we calculated that 1.92 X 10(5) molecules of lipid would cover 4.14 X 10(4) nm2 in the form of a bilayer. Considerations of the molecular dimensions of the rabies envelope (total surface area, 5 X 10(4) nm2) as a bilayer suggest that some penetration of lipids by envelope proteins (M and G) is necessary. PMID:557573

Blough, H A; Tiffany, J M; Aaslestad, H G

1977-01-01

252

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

253

Facile and green assembly of nanocomposite membranes for fuel cells.  

PubMed

We report on a facile spray deposition method, which allows obtaining nanocomposite membranes for high-temperature polymer fuel cells characterized by high homogeneity and excellent proton conductivity. The proposed method is also green, as it requires much smaller amounts of solvents with respect to standard casting. PMID:25525903

Quartarone, Eliana; Villa, Davide Carlo; Angioni, Simone; Mustarelli, Piercarlo

2015-01-20

254

Alterations in cell membrane properties caused by perfluorinated compounds  

Microsoft Academic Search

The recent detection of perfluorinated compounds (PFCs) in wildlife from even remote locations has spurred interest in the environmental occurrence and effects of these chemicals. While the global distribution of PFCs is increasingly understood, there is still little information available on their effects on wildlife. The amphiphillic nature of PFCs suggests that their effects could be primarily on cell membranes.

Wen yue Hu; Paul D Jones; Wim DeCoen; Louis King; Pamela Fraker; John Newsted; John P Giesy

2003-01-01

255

Basolateral membrane K+ channels in renal epithelial cells.  

PubMed

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

Hamilton, Kirk L; Devor, Daniel C

2012-05-01

256

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

257

Carbon monoxide poisoning of proton exchange membrane fuel cells  

Microsoft Academic Search

SUMMARY Proton exchange membrane fuel cell (PEMFC) performance degrades when carbon monoxide (CO) is present in the fuel gas; this is referred to as CO poisoning. This paper investigates CO poisoning of PEMFCs by reviewing work on the electrochemistry of CO and hydrogen, the experimental performance of PEMFCs exhibiting CO poisoning, methods to mitigate CO poisoning and theoretical models of

J. J. Baschuk; Xianguo Li

2001-01-01

258

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...

259

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

260

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

261

Plasma membrane growth during the cell cycle: unsolved mysteries and recent progress  

PubMed Central

Growth of the plasma membrane is as fundamental to cell reproduction as DNA replication, chromosome segregation and ribosome biogenesis, yet little is known about the underlying mechanisms. Membrane growth during the cell cycle requires mechanisms that control the initiation, location, and extent of membrane growth, as well as mechanisms that coordinate membrane growth with cell cycle progression. Recent experiments have established links between membrane growth and core cell cycle regulators. Further analysis of these links will yield insights into conserved and fundamental mechanisms of cell growth. A better understanding of the post-Golgi pathways by which membrane growth occurs will be essential for future progress. PMID:23141634

McCusker, Derek; Kellogg, Douglas R.

2012-01-01

262

The nuclear membranes in hypertrophied human cardiac muscle cells.  

PubMed Central

Nuclear membranes of cardiac muscle cells were studied in 134 patients with cardiac hypertrophy of various causes. Abnormalities observed consisted of: a) increased foldings and convolutions; b) nuclear pseudoinclusions formed by cytoplasmic organelles protruding into saccular invaginations of the nuclear membranes, and c) intranuclear tubules. The increased foldings and convolutions of the nuclear membranes and the nuclear pseudoinclusions appear to result from synthesis of nuclear membranes in excess of that needed to accommodate the increase in nuclear volume which occurs in hypertrophy. Intranuclear tubules were found in 6 patients and consisted of tubular invaginations, 400 to 650 A in diameter, of the inner nuclear membranes into the nucleoplasm. Some of these tubules were straight and cylindrical, and were associated with a peripheral layer of marginated chromatin; others were not associated with chromatin, appeared coiled and followed irregular courses. Intranuclear tubules in cardiac muscle cells probably represent an extreme cellular response to the stimulus of hypertrophy. Images Fig 21 Fig 11 Fig 12 Fig 13 Fig 14 Fig 1 Fig 15 Fig 2 Figs 3 and 4 Fig 5 Fig 16 Fig 17 Fig 6 Fig 18 Fig 7 Fig 8 Fig 9 Fig 10 Fig 19 Fig 20 PMID:164122

Ferrans, V. J.; Jones, M.; Maron, B. J.; Roberts, W. C.

1975-01-01

263

Mechanical properties of stored red blood cells using optical tweezers  

NASA Astrophysics Data System (ADS)

We have developed a method for measuring the red blood cell (RBC) membrane overall elasticity ? by measuring the deformation of the cells when dragged at a constant velocity through a plasma fluid by an optical tweezers. The deformability of erythrocytes is a critical determinant of blood flow in the microcirculation. We tested our method and hydrodynamic models, which included the presence of two walls, by measuring the RBC deformation as a function of drag velocity and of the distance to the walls. The capability and sensitivity of this method can be evaluated by its application to a variety of studies, such as, the measurement of RBC elasticity of sickle cell anemia patients comparing homozygous (HbSS), including patients taking hydroxyrea (HU) and heterozygous (HbAS) with normal donors and the RBC elasticity measurement of gamma irradiated stored blood for transfusion to immunosupressed patients as a function of time and dose. These studies show that the technique has the sensitivity to discriminate heterozygous and homozygous sickle cell anemia patients from normal donors and even follow the course of HU treatment of Homozygous patients. The gamma irradiation studies show that there is no significant change in RBC elasticity over time for up to 14 days of storage, regardless of whether the unit was irradiated or not, but there was a huge change in the measured elasticity for the RBC units stored for more than 21 days after irradiation. These finds are important for the assessment of stored irradiated RBC viability for transfusion purposes because the present protocol consider 28 storage days after irradiation as the limit for the RBC usage.

Fontes, Adriana; Alexandre de Thomaz, Andre; de Ysasa Pozzo, Liliana; de Lourdes Barjas-Castro, Maria; Brandao, Marcelo M.; Saad, Sara T. O.; Barbosa, Luiz Carlos; Cesar, Carlos Lenz

2005-08-01

264

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

265

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

266

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

267

Human T Cell Crosstalk Is Induced by Tumor Membrane Transfer  

PubMed Central

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

2015-01-01

268

A Novel Unitized Regenerative Proton Exchange Membrane Fuel Cell  

NASA Technical Reports Server (NTRS)

A difficulty encountered in designing a unitized regenerative proton exchange membrane (PEM) fuel cell lies in the incompatibility of electrode structures and electrocatalyst materials optimized for either of the two functions (fuel cell or electrolyzer) with the needs of the other function. This difficulty is compounded in previous regenerative fuel cell designs by the fact that water, which is needed for proton conduction in the PEM during both modes of operation, is the reactant supplied to the anode in the electrolyzer mode of operation and the product formed at the cathode in the fuel cell mode. Drawbacks associated with existing regenerative fuel cells have been addressed. In a first innovation, electrodes function either as oxidation electrodes (hydrogen ionization or oxygen evolution) or as reduction electrodes (oxygen reduction or hydrogen evolution) in the fuel cell and electrolyzer modes, respectively. Control of liquid water within the regenerative fuel cell has been brought about by a second innovation. A novel PEM has been developed with internal channels that permit the direct access of water along the length of the membrane. Lateral diffusion of water along the polymer chains of the PEM provides the water needed at electrode/PEM interfaces. Fabrication of the novel single cell unitized regenerative fuel cell and results obtained on testing it are presented.

Murphy, O. J.; Cisar, A. J.; Gonzalez-Martin, A.; Salinas, C. E.; Simpson, S. F.

1996-01-01

269

Analysis of Membrane Topology of Prestin Expressing in CHO Cells  

NASA Astrophysics Data System (ADS)

Outer hair cell (OHC) motility is thought to be based on the voltage-dependent conformational changes of the motor protein prestin. However, little is known about its structure and function. In this study, the membrane topology of prestin was investigated by single molecule force spectroscopy using an atomic force microscope (AFM). The C-terminus of prestin was tagged with an Avi-tag and biotinylated. Prestin was then connected with a streptavidin-coated AFM cantilever via biotin-streptavidin binding. The prestin was pulled out from the plasma membrane by retracting the cantilever and force curves were obtained. Obtained force curves suggested the existence of 12 transmembrane domains of prestin.

Murakoshi, Michio; Kawase, Tomohiro; Kumano, Shun; Wada, Hiroshi

2011-11-01

270

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

271

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

272

Capacitance-Voltage Measurement of Transporting Function at Cell Membrane  

NASA Astrophysics Data System (ADS)

In this paper, we report the detection of transporting function at cell membrane using capacitance-voltage (CV) measurement. The detection principle of our devices is based on the field-effect of electrostatic interaction between charged species at cell membrane in solution and surface electrons in silicon crystal through the gate insulator of Si3N4/SiO2 thin double-layer. We designed an oocyte-based field-effect capacitor, on which a Xenopus laevis oocyte was fixed. The transporter of human organic anion transporting peptide C (hOATP-C) was expressed at oocyte membrane by induction of cRNA. The electrical phenomena such as ion or molecular charge flux at the interface between cell membrane and gate surface could be detected as the change of flat band voltage in CV characteristics. The flat band voltage shift decreased with incubation time after introduction of substrate into the oocyte-based field-effect capacitor. The electrical signal is due to the change of charge flux from the oocyte at the gate surface inspired by transporter-substrate binding. The platform based on the oocyte-based field-effect capacitor is suitable for a simple and non-invasive detection system in order to analyze function of transporters related to drug efficacy.

Sakata, Toshiya; Miyahara, Yuji

273

Mechanics of surface area regulation in cells examined with confined lipid membranes  

PubMed Central

Cells are wrapped in inelastic membranes, yet they can sustain large mechanical strains by regulating their area. The area regulation in cells is achieved either by membrane folding or by membrane exo- and endocytosis. These processes involve complex morphological transformations of the cell membrane, i.e., invagination, vesicle fusion, and fission, whose precise mechanisms are still under debate. Here we provide mechanistic insights into the area regulation of cell membranes, based on the previously neglected role of membrane confinement, as well as on the strain-induced membrane tension. Commonly, the membranes of mammalian and plant cells are not isolated, but rather they are adhered to an extracellular matrix, the cytoskeleton, and to other cell membranes. Using a lipid bilayer, coupled to an elastic sheet, we are able to demonstrate that, upon straining, the confined membrane is able to regulate passively its area. In particular, by stretching the elastic support, the bilayer laterally expands without rupture by fusing adhered lipid vesicles; upon compression, lipid tubes grow out of the membrane plane, thus reducing its area. These transformations are reversible, as we show using cycles of expansion and compression, and closely reproduce membrane processes found in cells during area regulation. Moreover, we demonstrate a new mechanism for the formation of lipid tubes in cells, which is driven by the membrane lateral compression and may therefore explain the various membrane tubules observed in shrinking cells. PMID:21562210

Staykova, Margarita; Holmes, Douglas P.; Read, Clarke; Stone, Howard A.

2011-01-01

274

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

275

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

276

New materials for polymer electrolyte membrane fuel cell current collectors  

NASA Astrophysics Data System (ADS)

Polymer Electrolyte Membrane Fuel cells for automotive applications need to have high power density, and be inexpensive and robust to compete effectively with the internal combustion engine. Development of membranes and new electrodes and catalysts have increased power significantly, but further improvements may be achieved by the use of new materials and construction techniques in the manufacture of the bipolar plates. To show this, a variety of materials have been fabricated into flow field plates, both metallic and graphitic, and single fuel cell tests were conducted to determine the performance of each material. Maximum power was obtained with materials which had lowest contact resistance and good electrical conductivity. The performance of the best material was characterised as a function of cell compression and flow field geometry.

Hentall, Philip L.; Lakeman, J. Barry; Mepsted, Gary O.; Adcock, Paul L.; Moore, Jon M.

277

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

278

Outer membrane proteins and cell surface structure of Selenomonas ruminantium.  

PubMed Central

The protein compositions of the membrane preparations from Selenomonas ruminantium grown in glucose or lactate medium were determined by sodium dodecyl sulfate- and two-dimensional (first, isoelectric focusing; second, sodium dodecyl sulfate) polyacrylamide slab gel electrophoresis. The outer membrane from both glucose- and lactate-grown cells contained two major proteins with apparent molecular weights of 42,000 and 40,000. These proteins existed as peptidoglycan-associated proteins in the outer membrane. The critical temperature at which they were dissociated completely into the monomeric subunits of 42,000 and 40,000 daltons was found to be 85 degrees C. The amount of each protein varied considerably depending upon the cultural conditions. The absence of the lipoprotein of Braun in S. ruminantium was suggested in our preceding paper (Y. Kamio, and H. Takahashi, J. Bacteriol. 141:888--898, 1980), and the possible absence of the protein components corresponding to the Braun lipoprotein in this strain was confirmed by electrophoretic analysis of the outer membrane and the lysozyme-treated peptidoglycan fractions. Examination of the cell surface of S. ruminantium by electron microscopy showed that the outer membrane formed a wrinkled surface with irregular blebs, some of which pinched off forming vesicles of various sizes. Rapid cell lysis occurred with the addition of a low level of lysozyme to the cell suspension. These findings led us to conclude that the physiological and morphological properties of this strain were similar to those of "deep rough" and mlp or lpo mutants of Escherichia coli K-12, respectively. Images PMID:7364720

Kamio, Y; Takahashi, H

1980-01-01

279

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

280

A novel RNA binding protein affects rbcL gene expression and is specific to bundle sheath chloroplasts in C4 plants  

PubMed Central

Background Plants that utilize the highly efficient C4 pathway of photosynthesis typically possess kranz-type leaf anatomy that consists of two morphologically and functionally distinct photosynthetic cell types, the bundle sheath (BS) and mesophyll (M) cells. These two cell types differentially express many genes that are required for C4 capability and function. In mature C4 leaves, the plastidic rbcL gene, encoding the large subunit of the primary CO2 fixation enzyme Rubisco, is expressed specifically within BS cells. Numerous studies have demonstrated that BS-specific rbcL gene expression is regulated predominantly at post-transcriptional levels, through the control of translation and mRNA stability. The identification of regulatory factors associated with C4 patterns of rbcL gene expression has been an elusive goal for many years. Results RLSB, encoded by the nuclear RLSB gene, is an S1-domain RNA binding protein purified from C4 chloroplasts based on its specific binding to plastid-encoded rbcL mRNA in vitro. Co-localized with LSU to chloroplasts, RLSB is highly conserved across many plant species. Most significantly, RLSB localizes specifically to leaf bundle sheath (BS) cells in C4 plants. Comparative analysis using maize (C4) and Arabidopsis (C3) reveals its tight association with rbcL gene expression in both plants. Reduced RLSB expression (through insertion mutation or RNA silencing, respectively) led to reductions in rbcL mRNA accumulation and LSU production. Additional developmental effects, such as virescent/yellow leaves, were likely associated with decreased photosynthetic function and disruption of associated signaling networks. Conclusions Reductions in RLSB expression, due to insertion mutation or gene silencing, are strictly correlated with reductions in rbcL gene expression in both maize and Arabidopsis. In both plants, accumulation of rbcL mRNA as well as synthesis of LSU protein were affected. These findings suggest that specific accumulation and binding of the RLSB binding protein to rbcL mRNA within BS chloroplasts may be one determinant leading to the characteristic cell type-specific localization of Rubisco in C4 plants. Evolutionary modification of RLSB expression, from a C3 “default” state to BS cell-specificity, could represent one mechanism by which rbcL expression has become restricted to only one cell type in C4 plants. PMID:24053212

2013-01-01

281

A novel unitized regenerative proton exchange membrane fuel cell  

NASA Technical Reports Server (NTRS)

A difficulty encountered in designing a unitized regenerative proton exchange membrane (PEM) fuel cell lies in the incompatibility of electrode structures and electrocatalyst materials optimized for either of the two functions (fuel cell or electrolyzer) with the needs of the other function. This difficulty is compounded in previous regenerative fuel cell designs by the fact that water, which is needed for proton conduction in the PEM during both modes of operation, is the reactant supplied to the anode in the electrolyzer mode of operation and the product formed at the cathode in the fuel cell mode. Drawbacks associated with existing regenerative fuel cells have been addressed in work performed at Lynntech. In a first innovation, electrodes function either as oxidation electrodes (hydrogen ionization or oxygen evolution) or as reduction electrodes (oxygen reduction or hydrogen evolution) in the fuel cell and electrolyzer modes, respectively. Control of liquid water within the regenerative fuel cell has been brought about by a second innovation. A novel PEM has been developed with internal channels that permit the direct access of water along the length of the membrane. Lateral diffusion of water along the polymer chains of the PEM provides the water needed at electrode/PEM interfaces. Fabrication of the novel unitized regenerative fuel cell and results obtained on testing it will be presented.

Murphy, O. J.; Cisar, A. J.; Gonzalez-Martin, A.; Salinas, C. E.; Simpson, S. F.

1995-01-01

282

A novel unitized regenerative proton exchange membrane fuel cell  

NASA Astrophysics Data System (ADS)

A difficulty encountered in designing a unitized regenerative proton exchange membrane (PEM) fuel cell lies in the incompatibility of electrode structures and electrocatalyst materials optimized for either of the two functions (fuel cell or electrolyzer) with the needs of the other function. This difficulty is compounded in previous regenerative fuel cell designs by the fact that water, which is needed for proton conduction in the PEM during both modes of operation, is the reactant supplied to the anode in the electrolyzer mode of operation and the product formed at the cathode in the fuel cell mode. Drawbacks associated with existing regenerative fuel cells have been addressed in work performed at Lynntech. In a first innovation, electrodes function either as oxidation electrodes (hydrogen ionization or oxygen evolution) or as reduction electrodes (oxygen reduction or hydrogen evolution) in the fuel cell and electrolyzer modes, respectively. Control of liquid water within the regenerative fuel cell has been brought about by a second innovation. A novel PEM has been developed with internal channels that permit the direct access of water along the length of the membrane. Lateral diffusion of water along the polymer chains of the PEM provides the water needed at electrode/PEM interfaces. Fabrication of the novel unitized regenerative fuel cell and results obtained on testing it will be presented.

Murphy, O. J.; Cisar, A. J.; Gonzalez-Martin, A.; Salinas, C. E.; Simpson, S. F.

1995-04-01

283

Sodium channels in membrane vesicles from cultured toad bladder cells  

SciTech Connect

Electrical potential-driven {sup 22}Na{sup +} fluxes were measured in membrane vesicles prepared from TBM-18(cl23) cells (a clone of the established cell line TB-M). Fifty to seventy percent of the tracer uptake in vesicles derived from cells that were cultivated on a porous support were blocked by the diuretic amiloride. The amiloride inhibition constant was <0.1 {mu}M, indicating that this flux is mediated by the apical Na{sup +}-specific channels. Vesicles prepared from cells that were not grown on a porous support exhibited much smaller amiloride-sensitive fluxes. Two Ca{sup 2+}-dependent processes that down-regulated the channel conductance and were previously identified in native epithelia were found in the cultured cells as well. Vesicles isolated from cells that were preincubated with 5 {times} 10{sup {minus}7} M aldosterone for 16-20 h exhibited higher amiloride-sensitive conductance than vesicles derived from control, steroid-depleted cells. Thus membrane derived from TBM-18(cl23) cells can be used to characterize the epithelial Na{sup +} channel and its hormonal regulation.

Asher, C.; Moran, A.; Rossier, B.C.; Garty, H. (Weizmann Institute of Science, Rehovot (Israel) Ben Gurion Univ., Beer-Sheva (Israel) Institut de Pharmacologie de l'Universite de Lausanne (Switzerland))

1988-04-01

284

Role of membrane phospholipids and glycolipids in the Vero cell surface receptor for rubella virus  

Microsoft Academic Search

Membrane receptors for rubella virus (RV) in Vero cells were studied by means of two different approaches: (i) by enzyme treatment of the whole cell membrane and (ii) by testing the ability of isolated plasma membrane molecules to compete with cells for virus binding. The replication of RV was studied with both indirect immunofluorescence assay and molecular hybridization techniques. Phospholipases

P. Mastromarino; L. Cioè; S. Rieti; N. Orsi

1990-01-01

285

Understanding external forces acting on cells control lipid membrane structure and dynamics  

E-print Network

Understanding external forces acting on cells control lipid membrane structure and dynamics to understanding how they regulate signaling at the cell surface. Structural features of lipid membranes. Butler's lab is to understand how external forces acting on cells control lipid membrane structure

Bjørnstad, Ottar Nordal

286

Osmotic Transport across Cell Membranes in Nondilute Solutions: A New Nondilute Solute Transport Equation  

Microsoft Academic Search

The fundamental physical mechanisms of water and solute transport across cell membranes have long been studied in the field of cell membrane biophysics. Cryobiology is a discipline that requires an understanding of osmotic transport across cell membranes under nondilute solution conditions, yet many of the currently-used transport formalisms make limiting dilute solution assumptions. While dilute solution assumptions are often appropriate

Heidi Y. Elmoazzen; Janet A. W. Elliott; Locksley E. McGann

2009-01-01

287

Adaptive evolution of rbcL in Conocephalum (Hepaticae, bryophytes)  

Microsoft Academic Search

An excess of nonsynonymous substitutions over synonymous ones has been regarded as an important indicator of adaptive evolution or positive selection at the molecular level. We now report such a case for rbcL sequences among cryptic species in Conocephalum (Hepaticae, Bryophytes). This finding can be regarded as evidence of adaptive evolution in several cryptic species (especially in F and JN

Hidetsugu Miwa; Ireneusz J. Odrzykoski; Atsushi Matsui; Masami Hasegawa; Hiroyuki Akiyama; Yu Jia; Renat Sabirov; Hideki Takahashi; David E. Boufford; Noriaki Murakami

2009-01-01

288

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

289

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

290

Membrane Domains Based on Ankyrin and Spectrin Associated with Cell–Cell Interactions  

PubMed Central

Nodes of Ranvier and axon initial segments of myelinated nerves, sites of cell–cell contact in early embryos and epithelial cells, and neuromuscular junctions of skeletal muscle all perform physiological functions that depend on clustering of functionally related but structurally diverse ion transporters and cell adhesion molecules within microdomains of the plasma membrane. These specialized cell surface domains appeared at different times in metazoan evolution, involve a variety of cell types, and are populated by distinct membrane-spanning proteins. Nevertheless, recent work has shown that these domains all share on their cytoplasmic surfaces a membrane skeleton comprised of members of the ankyrin and spectrin families. This review will summarize basic features of ankyrins and spectrins, and will discuss emerging evidence that these proteins are key players in a conserved mechanism responsible for assembly and maintenance of physiologically important domains on the surfaces of diverse cells. PMID:20457566

Bennett, Vann; Healy, Jane

2009-01-01

291

Imaging the cell membrane with surface plasmon resonance phase microscopy  

NASA Astrophysics Data System (ADS)

Molecular interactions occurring on or near cell membrane surfaces are expected to have different properties from those occurring in bulk solutions. In order to analyze molecular interactions between the cell membrane with biomolecules having no additional fluorescence labeling, a microscope based on the integration of surface plasmon resonance (SPR) and common-path phase-shift interferometry (PSI) techniques is developed and used to study the cell adhesion and migration on the biosurfaces. The surface plasmons are excited by light via the attenuated total reflection method. The common-path PSI technique has features of long-term stability, even when subjected to external disturbances. Hence, the developed SPR phase microscope meets the requirements of real-time kinetic imaging. The proposed common-path SPR-PSI microscope demonstrates a detection limit of 2x10 -7 refractive index unit and a long-term phase stability of 2.5x10 -4 ? root mean square over four hours. The developed microscope is successfully applied to the real-time observation the live cell membranes with thrombomodulin proteins.

He, R.-Y.; Su, Y.-D.; Chang, G.-L.; Chen, S.-J.

2006-08-01

292

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

293

Lipid translocation across the plasma membrane of mammalian cells.  

PubMed

The plasma membrane, which forms the physical barrier between the intra- and extracellular milieu, plays a pivotal role in the communication of cells with their environment. Exchanging metabolites, transferring signals and providing a platform for the assembly of multi-protein complexes are a few of the major functions of the plasma membrane, each of which requires participation of specific membrane proteins and/or lipids. It is therefore not surprising that the two leaflets of the membrane bilayer each have their specific lipid composition. Although membrane lipid asymmetry has been known for many years, the mechanisms for maintaining or regulating the transbilayer lipid distribution are still not completely understood. Three major players have been presented over the past years: (1) an inward-directed pump specific for phosphatidylserine and phosphatidylethanolamine, known as aminophospholipid translocase; (2) an outward-directed pump referred to as 'floppase' with little selectivity for the polar headgroup of the phospholipid, but whose actual participation in transport of endogenous lipids has not been well established; and (3) a lipid scramblase, which facilitates bi-directional migration across the bilayer of all phospholipid classes, independent of the polar headgroup. Whereas a concerted action of aminophospholipid translocase and floppase could, in principle, account for the maintenance of lipid asymmetry in quiescent cells, activation of the scramblase and concomitant inhibition of the aminophospholipid translocase causes a collapse of lipid asymmetry, manifested by exposure of phosphatidylserine on the cell surface. In this article, each of these transporters will be discussed, and their physiological importance will be illustrated by the Scott syndrome, a bleeding disorder caused by impaired lipid scrambling. Finally, phosphatidylserine exposure during apoptosis will be briefly discussed in relation to inhibition of translocase and simultaneous activation of scramblase. PMID:10446420

Bevers, E M; Comfurius, P; Dekkers, D W; Zwaal, R F

1999-08-18

294

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

295

Muscarinic receptor size on smooth muscle cells and membranes  

SciTech Connect

The loss of (/sup 3/H)quinuclidinyl benzilate ((/sup 3/H)QNB) binding following high-energy radiation was used to compare the muscarinic receptor size on single smooth muscle cells isolated by collagenase digestion from the canine stomach and on plasma membranes derived from intact gastric smooth muscle without exposure to exogenous proteolysis. Radiation inactivation of galactose oxidase (68 kdaltons), yeast alcohol dehydrogenase (160 kdaltons), and pyruvate kinase (224 kdaltons) activities were used as molecular-weight standards. Radiation inactivation of (/sup 3/H)QNB binding to rat brain membranes, which gave a target size of 86 kdaltons, served as an additional control. In isolated smooth muscle cells, the calculated size of the muscarinic receptor was 80 +/- 8 kdaltons. In contrast, in a smooth muscle enriched plasma membrane preparation, muscarinic receptor size was significantly smaller at 45 +/- 3 kdaltons. Larger molecular sizes were obtained either in the presence of protease inhibitors (62 +/- 4 kdaltons) or by using a crude membrane preparation of gastric smooth muscle 86 +/- 7 kdaltons).

Collins, S.M.; Jung, C.Y.; Grover, A.K.

1986-08-01

296

Membrane electrolytic cell for minimizing hypochlorite and chlorate formation  

SciTech Connect

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 has as the electrochemically active surface an electrodeposited layer of a valve metal oxide. A plurality of cracks traverse the electrodeposited layer and a coating of a platinum metal group oxide covers the electrodeposited layer and substantially fills the cracks. The cationic exchange membrane is comprised of a laminated structure having a first surface adapted to contact an anolyte in which the ion exchange groups are predominately sulfonic acid groups. The first surface is also in contact with the electrochemically active surface of the anode. A second surface of the cation exchange membrane, adapted to contact a catholyte, has ion exchange groups which are predominately carboxylic acid groups. The cathode positioned in the cathode compartment is spaced apart from the cation exchange membrane. The cell operates with both a low chlorine overvoltage and a low oxygen overvoltage. During electrolysis of alkali metal chloride brines, the formation of hypochlorite and chlorate ions is minimized and the alkali metal hydroxides produced have low chlorate concentrations and are suitable for use without further treatment in chlorate-sensitive applications. Spent brine treatment is simplified and at reduced costs.

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

1985-07-09

297

Cross-linked high conductive membranes based on water soluble ionomer for high performance proton exchange membrane fuel cells  

NASA Astrophysics Data System (ADS)

In this paper, a series of proton exchange membranes prepared by “Click Reaction” are reported. The cross-linked membranes are based on water soluble sulfonated poly (ether ether ketone) containing dipropenyl groups (SDPEEK-nE/nH). Compared with self-crosslinked membranes (SDPEEK-nS), this “Click” cross-linked membranes using 1,2-Ethanedithiol and 1,6-Hexanedithiol as the cross-linker exhibit extremely reduced water uptake and swelling ratio. The lowest proton conductivity at 80 °C of the “Click” cross-linked membranes reaches to 0.168 S cm-1, and the highest methanol permeability of the “Click” cross-linked SDPEEK-8E is only 4.13 × 10-7 cm2 s-1, which is 5 times lower than that of Nafion 117 membrane. All the results imply that the cross-linked membranes with novel thiol cross-linker are promising alternative material for fuel cell application.

Jiang, Hao; Guo, Xin; Zhang, Gang; Ni, Jing; Zhao, Chengji; Liu, Zhongguo; Zhang, Liyuan; Li, Mingyu; Xu, Shuai; Na, Hui

2013-11-01

298

Quantitative understanding of cell signaling: the importance of membrane organization.  

PubMed

Systems biology modeling of signal transduction pathways traditionally employs ordinary differential equations, deterministic models based on the assumptions of spatial homogeneity. However, this can be a poor approximation for certain aspects of signal transduction, especially its initial steps: the cell membrane exhibits significant spatial organization, with diffusion rates approximately two orders of magnitude slower than those in the cytosol. Thus, to unravel the complexities of signaling pathways, quantitative models must consider spatial organization as an important feature of cell signaling. Furthermore, spatial separation limits the number of molecules that can physically interact, requiring stochastic simulation methods that account for individual molecules. Herein, we discuss the need for mathematical models and experiments that appreciate the importance of spatial organization in the membrane. PMID:20829029

Radhakrishnan, Krishnan; Halász, Adám; Vlachos, Dion; Edwards, Jeremy S

2010-10-01

299

Morphology matters in immune cell chemotaxis: membrane asymmetry affects amplification  

NASA Astrophysics Data System (ADS)

A key mediator of eukaryotic chemotaxis is the asymmetric accumulation of phosphatidylinositol-3,4,5-triphosphate (PIP3) on the cell membrane. Recent work has focused on understanding how a shallow external gradient of chemoattractant leads to an amplified internal gradient of PIP3. In this paper we dissect what fraction of this amplification is derived biochemically by the signal transduction network and how much arises entirely from the effects of cell morphology. Here we identify and formalize the role of morphology in signal detection and demonstrate its effects through simulation and experiments. Our key result is that an asymmetric distribution of membrane accounts for approximately one-half of the measured amplification from ligand concentration to PIP3 production. We also show that the underlying biochemical network behaves as a linear amplifier in the micropipette assay.

Onsum, Matthew David; Wong, Kit; Herzmark, Paul; Bourne, Henry R.; Arkin, Adam Paul

2006-09-01

300

Development of structured polymer electrolyte membranes for fuel cell applications  

NASA Astrophysics Data System (ADS)

The objective of this research was to explore structure-property relationships to develop the understanding needed for introduction of superior PEM materials. Polymer electrolyte membranes based on sulfonated poly(ether ketone ketone) (SPEKK) were fabricated using N-methyl pyrrolidone as casting solvent. The membranes were characterized in terms of properties that were relevant to fuel cell applications, such as proton conductivity, methanol permeability, and swelling properties, among others. It was found in this study that the proton conductivity of neat SPEKK membranes could reach the conductivity of commercial membranes such as NafionRTM. However, when the conductivity of SPEKK was comparable to NafionRTM, the swelling of SPEKK in water was quite excessive. The swelling problem was remedied by modifying the microstructure of SPEKK using different techniques. One of them involved blending of lightly sulfonated PEKK with highly acidic particles (sulfonated crosslinked polystyrene-SXLPS). Low sulfonation level of SPEKK was used to reduce the swelling of the membrane in water and the role of the highly acidic particles was to enhance the proton conductivity of the membrane. Because of the residual crystallinity in SPEKK with low sulfonation levels (IEC < 1 meq/g), the composite membranes exhibited excellent dimensional stability in water at elevated temperatures (30-90 °C). Also, the resistance to swelling of these composite membranes in methanol-water mixtures was far better than NafionRTM, and so was the methanol permeability. Another technique explored was blending with non-conductive polymers (poly(ether imide) and poly(ether sulfone)) to act as mechanical reinforcement. It was found that miscibility behavior of the blends had a significant impact on the transport and swelling properties of these blends, which could be explained by the blend microstructure. The miscibility behavior was found to be strongly dependent on the sulfonation level of SPEKK. The conductivities of the blends were enhanced by as much as two orders of magnitude when the morphology was modified by electric field. The last approach was ionic crosslinking of the sulfonate groups in SPEKK using divalent cations, specifically barium ions. The crosslinking treatment has greatly improved the thermal stability of the membranes in both dry and wet conditions.

Gasa, Jeffrey

301

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

302

Nitrate reductase activity of plasma membranes from cultured carrot cells  

Microsoft Academic Search

Summary Cultured carrot cells (Daucus carota L.) reduced nitrate to nitrite at a slow rate (0.4 µmoles\\/g dry wt · h) without any additions to the reaction medium. This rate was doubled or tripled in presence of 100 µM NADH. Ethanol and other alcohols stimulated the basal rate 8–10-fold. Isolated carrot plasma membranes also reduced nitrate to nitrite at a

R. Barr; M. Böttger; F. L. Crane; D. J. Morré

1995-01-01

303

Stimulation of Erythrocyte Cell Membrane Scrambling by Mushroom Tyrosinase  

PubMed Central

Background: Mushroom tyrosinase, a copper containing enzyme, modifies growth and survival of tumor cells. Mushroom tyrosinase may foster apoptosis, an effect in part due to interference with mitochondrial function. Erythrocytes lack mitochondria but are able to undergo apoptosis-like suicidal cell death or eryptosis, which is characterized by cell shrinkage and cell membrane scrambling leading to phosphatidylserine-exposure at the erythrocyte surface. Signaling involved in the triggering of eryptosis include increase of cytosolic Ca2+-activity ([Ca2+]i) and activation of sphingomyelinase with subsequent formation of ceramide. The present study explored, whether tyrosinase stimulates eryptosis. Methods: Cell volume has been estimated from forward scatter, phosphatidylserine-exposure from annexin V binding, [Ca2+]i from Fluo3-fluorescence, and ceramide abundance from binding of fluorescent antibodies in flow cytometry. Results: A 24 h exposure to mushroom tyrosinase (7 U/mL) was followed by a significant increase of [Ca2+]i, a significant increase of ceramide abundance, and a significant increase of annexin-V-binding. The annexin-V-binding following tyrosinase treatment was significantly blunted but not abrogated in the nominal absence of extracellular Ca2+. Tyrosinase did not significantly modify forward scatter. Conclusions: Tyrosinase triggers cell membrane scrambling, an effect, at least partially, due to entry of extracellular Ca2+ and ceramide formation. PMID:24647148

Frauenfeld, Leonie; Alzoubi, Kousi; Abed, Majed; Lang, Florian

2014-01-01

304

Polymer Electrolyte Membrane (PEM) Fuel Cells Modeling and Optimization  

NASA Astrophysics Data System (ADS)

Performance of polymer electrolyte membrane (PEM) fuel cells is dependent on operating parameters and designing parameters. Operating parameters mainly include temperature, pressure, humidity and the flow rate of the inlet reactants. Designing parameters include reactants distributor patterns and dimensions, electrodes dimensions, and electrodes properties such as porosity, permeability and so on. This work aims to investigate the effects of various designing parameters on the performance of PEM fuel cells, and the optimum values will be determined under a given operating condition.A three-dimensional steady-state electrochemical mathematical model was established where the mass, fluid and thermal transport processes are considered as well as the electrochemical reaction. A Powell multivariable optimization algorithm will be applied to investigate the optimum values of designing parameters. The objective function is defined as the maximum potential of the electrolyte fluid phase at the membrane/cathode interface at a typical value of the cell voltage. The robustness of the optimum design of the fuel cell under different cell potentials will be investigated using a statistical sensitivity analysis. By comparing with the reference case, the results obtained here provide useful tools for a better design of fuel cells.

Zhang, Zhuqian; Wang, Xia; Shi, Zhongying; Zhang, Xinxin; Yu, Fan

2006-11-01

305

Dynamics of cell membrane passive depolarization: a phase portrait.  

PubMed

Does a persistent blockage of the ionic pumps bring cell membrane voltage to zero? This apparently trivial question of basic cellular Biology stirred up an intriguing problem of nonlinear dynamics. A 3-ion model based on continuity and charge conservation proves that membrane voltage actually sets on a negative value, meaning that chemical equilibrium is never reached, rather an inversion of the Na+ concentration gradient occurs, usually hours after the blockage of the pumps. Experimental tests carried out with PC12 cells incubated with Oubaine for a period of 24 hours show an increase of cytosolic Na+ of about 266 mM/l with respect to a control sample. The result is compatible with an inversion of the Na+ gradient, which eventually brings the membrane voltage to a negative value. Reactivation of the Na+-K+ pumps even after a prolonged period of blockage (late repolarization) should lead to repolarization and revival of the cell. In the 3D space of the ionic concentrations, the dynamics of passive depolarization reveals an intriguing topology, all trajectories being stacked in parallel planes, each set ending to a unique fixed point via an infinitely dense set of lines. The dynamics of repolarization has a different phase portrait, especially in the case of late repolarization. Thus, a sequence of depolarization- repolarization cycles may result in a path wandering in the phase space, or in a closed loop, depending on the timing of the sequence. PMID:17572986

Aiello, Gaetano L; Bignetti, Enrico; Casarino, Carlo; Sciacca, Ivan D; Scopelliti, Michelangelo; Venezia, Maurizio

2007-07-01

306

Proton electrolyte membrane properties and direct methanol fuel cell performance. II. Fuel cell performance and membrane properties effects  

NASA Astrophysics Data System (ADS)

In order to study the relationship between the properties of proton electrolyte membranes (PEMs), obtained through standard characterization methods, and the direct methanol fuel cell (DMFC) performance, inorganic-organic hybrid membranes, modified via in situ hydrolysis, were used in a membrane electrolyte assembly (MEA) for DMFC application. The membranes, the characterization of which was performed in the previous paper of this series, were based on sulfonated poly(ether ether ketone) (sPEEK) with a sulfonation degree (SD) of 87% and were loaded with different amounts of zirconium oxide (5.0, 7.5, 10.0, 12.5 wt.%). The standard characterization methods applied were impedance spectroscopy (proton conductivity), water uptake, and pervaporation (permeability to methanol). The MEAs were characterized investigating the DMFC current-voltage polarization curves, constant voltage current (CV, 35 mV), and open-circuit voltage (OCV). The fuel cell ohmic resistance (null phase angle impedance, NPAI) and CO 2 concentration in the cathode outlet were also measured. The characterization results show that the incorporation of the inorganic oxide in the polymer network decreases the DMFC current density for CV experiments, CO 2 concentration in the cathode outlet for both OCV and CV experiments and, finally, the maximum power density output. The opposite effect was verified in terms of the NPAI (ohmic resistance) for both OCV and CV experiments. A good agreement was found between the studied DMFC performance parameters and the characterization results evaluated by impedance spectroscopy, water uptake and pervaporation experiments.

Silva, V. S.; Schirmer, J.; Reissner, R.; Ruffmann, B.; Silva, H.; Mendes, A.; Madeira, L. M.; Nunes, S. P.

307

Quantitative analysis of cell surface membrane proteins using membrane-impermeable chemical probe coupled with 18O labeling  

PubMed Central

We report a mass spectrometry-based strategy for quantitative analysis of cell surface membrane proteome changes. The strategy includes enrichment of surface membrane proteins using a membrane-impermeable chemical probe followed by stable isotope 18O labeling and LC-MS analysis. We applied this strategy for enriching membrane proteins expressed by Shewanella oneidensis MR-1, a gram-negative bacterium with known metal-reduction capability via extracellular electron transfer between outer membrane proteins and extracellular electron receptors. LC/MS/MS analysis resulted in the identification of about 400 proteins with 79% of them being predicted to be membrane localized. Quantitative aspects of the membrane enrichment were shown by peptide level 16O and 18O labeling of proteins from wild-type and mutant cells (generated from deletion of a type II secretion protein, GspD) prior to LC-MS analysis. Using a chemical probe labeled pure protein as an internal standard for normalization, the quantitative data revealed reduced abundances in ?gspD mutant cells of many outer membrane proteins including the outer membrane c-cype cytochromes OmcA and MtrC, in agreement with previously investigation demonstrating that these proteins are substrates of the type II secretion system. PMID:20380418

Zhang, Haizhen; Brown, Roslyn N.; Qian, Wei-Jun; Monroe, Matthew E.; Purvine, Samuel O.; Moore, Ronald J.; Gritsenko, Marina A.; Shi, Liang; Romine, Margaret F; Fredrickson, James K.; Paša-Toli?, Ljiljana; Smith, Richard D.; Lipton, Mary S.

2010-01-01

308

Method for measuring the three-dimensional distribution of a fluorescent dye in a cell membrane  

NASA Astrophysics Data System (ADS)

This letter reports on a method for accurately determining the component distribution in a cell membrane over the entire cell surface. This method involves exciting a fluorescent-dyed cell membrane using evanescent light and scanning the entire cell surface by rotating the cell using a noncontact technique, namely, proximal two-beam optical tweezers. To position the cell membrane in the thin evanescent field, the authors designed an optical system capable of precisely positioning the focal position. Using this method, they were able to measure the surface distribution of glycoprotein labeled by lectin in a breast cancer cell membrane.

Yamamoto, Kazuya; Ishimaru, Ichirou; Fujii, Yoshiki; Yasokawa, Toshiki; Kuriyama, Shigeki; Masaki, Tsutomu; Takegawa, Kaoru; Tanaka, Naotaka

2007-01-01

309

Long-distance relationships: do membrane nanotubes regulate cell–cell communication and disease progression?  

PubMed Central

Metazoan cells rapidly exchange signals at tight cell–cell interfaces, including synapses and gap junctions. Advances in imaging recently exposed a third mode of intercellular cross-talk mediated by thin, actin-containing membrane extensions broadly known as “membrane” or “tunneling” nanotubes. An explosion of research suggests diverse functions for nanotubular superhighways, including cell–cell electrical coupling, calcium signaling, small-molecule exchange, and, remarkably, the transfer of bulky cargoes, including organelles or pathogenic agents. Despite great enthusiasm for all things nanotubular and their potential roles in cell signaling and pathogenesis, key questions remain regarding the mechanisms by which these structures regulate directional cell–cell exchange; how these linkages are formed and between which cells and, critically, whether nanotubes are as prevalent in vivo as they appear to be in the incubator. PMID:23580190

Sherer, Nathan M.

2013-01-01

310

Serum iron metabolism and erythropoiesis in patients with myelodysplastic syndrome not receiving RBC transfusions.  

PubMed

Dysregulation of hepcidin, a key iron regulating hormone, is important in the pathogenesis of iron overload in patients with myelodysplatic syndrome (MDS). However, most studies of hepcidin levels are complicated by concomitant RBC transfusions. To evaluate the relationship between iron metabolism and erythropoiesis, we measured serum levels of hepcidin, growth-differentiation factor-15 (GDF15) and other markers of erythropoiesis in 107 subjects with MDS not receiving RBC transfusions. Patients with MDS had significantly higher levels of hepcidin than normals. However, their hepcidin-ferritin ratio was markedly decreased compared to normals (P<0.001) and varied substantially between MDS subtypes (P=0.011). GDF15 levels positively correlated with percent of bone marrow erythroblasts (P<0.001), soluble transferrin receptor (sTfR) (P=0.018), and also with transferrin saturation (ISAT) (P=0.038). The hepcidin-ferritin ratio negatively correlated with serum erythropoietin (EPO) levels (P<0.001), and also with GDF15 levels (P=0.014). Colony forming cells (CFC) were evaluated in 70 subjects. Those with serum ferritin (SF) levels <500 ng/ml had significantly more BFU-E than subjects with SF ? 500 ng/L (P=0.007), but numbers of granulocyte/macrophage-colony-forming cells (CFU-GM) were similar (P=0.190). Our data indicate serum hepcidin levels are inappropriately low in patients MDS not receiving RBC transfusions. GDF15 levels correlated with low hepcidin levels and may contribute to iron overload in this setting. Iron overload may in turn suppress erythropoiesis by imparing the proliferative capacity of the erythroid progenitor cells. PMID:24598841

Cui, Rui; Gale, Robert Peter; Zhu, Guoqing; Xu, Zefeng; Qin, Tiejun; Zhang, Yue; Huang, Gang; Li, Bing; Fang, Liwei; Zhang, Hongli; Pan, Lijuan; Hu, Naibo; Qu, Shiqiang; Xiao, Zhijian

2014-05-01

311

A flexible portable proton exchange membrane fuel cell  

NASA Astrophysics Data System (ADS)

A flexible portable proton exchange membrane fuel cell (PEMFC) is developed with non-directional flexibility acquired through new carbon-fibre-made current collectors and a new cell structure. The performance of a pilot cell suffers no significant loss when bent to curvatures with various radii in multiple directions. It also compares well with a nonflexible cylindrical portable PEMFC composed of similar components. The new cell is made with a single cup-like flexible main body with the membrane glued to the inside rim. The current collector is composed of several bunches of carbon fibre, each with metal wires embedded in them. The soft and flexible fibres not only allow for close and evenly-distributed contact with the bent electrode, but also change the character of the contact so that a large compressional force is no longer required to acquire low contact resistance which is, above all, the key to the success of this flexible cell design. The metal wire provides the needed flexibility to cover large curved electrode areas. A wire spring is used to pressure the collector against the electrode while the main body bends.

Hsu, Fu-Kuang; Lee, Ming-San; Lin, Chi-Chang; Lin, Yu-Kuo; Hsu, Wei-Ting

2012-12-01

312

Mathematical and Computational Modeling of Polymer Exchange Membrane Fuel Cells  

NASA Astrophysics Data System (ADS)

In this thesis a comprehensive review of fuel cell modeling has been given and based on the review, a general mathematical fuel cell model has been developed in order to understand the physical phenomena governing the fuel cell behavior and in order to contribute to the efforts investigating the optimum performance at different operating conditions as well as with different physical parameters. The steady state, isothermal model presented here accounts for the combined effects of mass and species transfer, momentum conservation, electrical current distribution through the gas channels, the electrodes and the membrane, and the electrochemical kinetics of the reactions in the anode and cathode catalyst layers. One of the important features of the model is that it proposes a simpler modified pseudo-homogeneous/agglomerate catalyst layer model which takes the advantage of the simplicity of pseudo-homogenous modeling while taking into account the effects of the agglomerates in the catalyst layer by using experimental geometric parameters published. The computation of the general mathematical model can be accomplished in 3D, 2D and 1D with the proper assumptions. Mainly, there are two computational domains considered in this thesis. The first modeling domain is a 2D Membrane Electrode Assembly (MEA) model including the modified agglomerate/pseudo-homogeneous catalyst layer modeling with consistent treatment of water transport in the MEA while the second domain presents a 3D model with different flow filed designs: straight, stepped and tapered. COMSOL Multiphysics along with Batteries and Fuel Cell Module have been used for 2D & 3D model computations while ANSYS FLUENT PEMFC Module has been used for only 3D two-phase computation. Both models have been validated with experimental data. With 2D MEA model, the effects of temperature and water content of the membrane as well as the equivalent weight of the membrane on the performance have been addressed. 3D COMSOL simulation results showed that the fuel performance can be improved by using flow field designs alleviating the reactant depletion along the channels and supplying more uniform reactant distribution. Stepped flow field was found to show better performance when compared to straight and tapered ones. ANSYS FLUENT model is evaluated in terms of predicting the two phase flow in the fuel cell components. It is proposed that it is not capable of predicting the entire fuel cell polarization due to the lack of agglomerate catalyst layer modeling and well-established two-phase flow modeling. Along with the comprehensive modeling efforts, also an analytical model has been computed by using MathCAD and it is found that this simpler model is able to predict the performance in a general trend according to the experimental data obtained for a new novel membrane. Therefore, it can be used for robust prediction of the cell performance at different operating conditions such as temperature and pressure, and the electrochemical properties such as the catalyst loading, the exchange current density and the diffusion coefficients of the reactants. In addition to the modeling efforts, this thesis also presents a very comprehensive literature review on the models developed in the literature so far, the modeling efforts in fuel cell sandwich including membrane, catalyst layer and gas diffusion layer and fuel cell model properties. Moreover, a summary of possible directions of research in fuel cell analysis and computational modeling has been presented.

Ulusoy, Sehribani

313

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

314

77 FR 50487 - Application To Export Electric Energy; RBC Energy Services LP  

Federal Register 2010, 2011, 2012, 2013, 2014

...its application, RBC Energy states that neither it nor its affiliates ``owns, operates or controls any electric power transmission or distribution facilities in the United States.'' RBC Energy states and it is reasonable to presume,...

2012-08-21

315

40 CFR 35.2035 - Rotating biological contractor (RBC) replacement grants.  

Code of Federal Regulations, 2012 CFR

...Rotating biological contractor (RBC) replacement grants. 35.2035 Section 35.2035 Protection of Environment ENVIRONMENTAL PROTECTION...ASSISTANCE Grants for Construction of Treatment Works § 35.2035 Rotating biological contractor (RBC)...

2012-07-01

316

40 CFR 35.2035 - Rotating biological contractor (RBC) replacement grants.  

Code of Federal Regulations, 2011 CFR

...Rotating biological contractor (RBC) replacement grants. 35.2035 Section 35.2035 Protection of Environment ENVIRONMENTAL PROTECTION...ASSISTANCE Grants for Construction of Treatment Works § 35.2035 Rotating biological contractor (RBC)...

2011-07-01

317

40 CFR 35.2035 - Rotating biological contractor (RBC) replacement grants.  

Code of Federal Regulations, 2010 CFR

...Rotating biological contractor (RBC) replacement grants. 35.2035 Section 35.2035 Protection of Environment ENVIRONMENTAL PROTECTION...ASSISTANCE Grants for Construction of Treatment Works § 35.2035 Rotating biological contractor (RBC)...

2010-07-01

318

40 CFR 35.2035 - Rotating biological contractor (RBC) replacement grants.  

Code of Federal Regulations, 2014 CFR

...Rotating biological contractor (RBC) replacement grants. 35.2035 Section 35.2035 Protection of Environment ENVIRONMENTAL PROTECTION...ASSISTANCE Grants for Construction of Treatment Works § 35.2035 Rotating biological contractor (RBC)...

2014-07-01

319

40 CFR 35.2035 - Rotating biological contractor (RBC) replacement grants.  

Code of Federal Regulations, 2013 CFR

...Rotating biological contractor (RBC) replacement grants. 35.2035 Section 35.2035 Protection of Environment ENVIRONMENTAL PROTECTION...ASSISTANCE Grants for Construction of Treatment Works § 35.2035 Rotating biological contractor (RBC)...

2013-07-01

320

CR1-mediated ATP Release by Human Red Blood Cells Promotes CR1 Clustering and Modulates the Immune Transfer Process*  

PubMed Central

Humans and other higher primates are unique among mammals in using complement receptor 1 (CR1, CD35) on red blood cells (RBC) to ligate complement-tagged inflammatory particles (immune complexes, apoptotic/necrotic debris, and microbes) in the circulation for quiet transport to the sinusoids of spleen and liver where resident macrophages remove the particles, but allow the RBC to return unharmed to the circulation. This process is called immune-adherence clearance. In this study we found using luminometric- and fluorescence-based methods that ligation of CR1 on human RBC promotes ATP release. Our data show that CR1-mediated ATP release does not depend on Ca2+ or enzymes previously shown to mediate an increase in membrane deformability promoted by CR1 ligation. Furthermore, ATP release following CR1 ligation increases the mobility of the lipid fraction of RBC membranes, which in turn facilitates CR1 clustering, and thereby enhances the binding avidity of complement-opsonized particles to the RBC CR1. Finally, we have found that RBC-derived ATP has a stimulatory effect on phagocytosis of immune-adherent immune complexes. PMID:24022490

Melhorn, Mark I.; Brodsky, Abigail S.; Estanislau, Jessica; Khoory, Joseph A.; Illigens, Ben; Hamachi, Itaru; Kurishita, Yasutaka; Fraser, Andrew D.; Nicholson-Weller, Anne; Dolmatova, Elena; Duffy, Heather S.; Ghiran, Ionita C.

2013-01-01

321

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

322

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

323

Alloantibodies to a paternally derived RBC KEL antigen lead to hemolytic disease of the fetus/newborn in a murine model  

PubMed Central

Exposure to nonself red blood cell (RBC) antigens, either from transfusion or pregnancy, may result in alloimmunization and incompatible RBC clearance. First described as a pregnancy complication 80 years ago, hemolytic disease of the fetus and newborn (HDFN) is caused by alloimmunization to paternally derived RBC antigens. Despite the morbidity/mortality of HDFN, women at risk for RBC alloimmunization have few therapeutic options. Given that alloantibodies to antigens in the KEL family are among the most clinically significant, we developed a murine model with RBC-specific expression of the human KEL antigen to evaluate the impact of maternal/fetal KEL incompatibility. After exposure to fetal KEL RBCs during successive pregnancies with KEL-positive males, 21 of 21 wild-type female mice developed anti-KEL alloantibodies; intrauterine fetal anemia and/or demise occurred in a subset of KEL-positive pups born to wild type, but not agammaglobulinemic mothers. Similar to previous observations in humans, pregnancy-associated alloantibodies were detrimental in a transfusion setting, and transfusion-associated alloantibodies were detrimental in a pregnancy setting. This is the first pregnancy-associated HDFN model described to date, which will serve as a platform to develop targeted therapies to prevent and/or mitigate the dangers of RBC alloantibodies to fetuses and newborns. PMID:23801629

Stowell, Sean R.; Henry, Kate L.; Smith, Nicole H.; Hudson, Krystalyn E.; Halverson, Greg R.; Park, Jaekeun C.; Bennett, Ashley M.; Girard-Pierce, Kathryn R.; Arthur, C. Maridith; Bunting, Silvia T.; Zimring, James C.

2013-01-01

324

Alkaline direct alcohol fuel cells using an anion exchange membrane  

NASA Astrophysics Data System (ADS)

Alkaline direct alcohol fuel cells using an OH-form anion exchange membrane and polyhydric alcohols were studied. A high open circuit voltage of ca. 800 mV was obtained for a cell using Pt-Ru/C (anode) and Pt/C (cathode) at 323 K, which was about 100-200 mV higher than that for a DMFC using Nafion ®. The maximum power densities were in the order of ethylene glycol > glycerol > methanol > erythritol > xylitol. Silver catalysts were used as a cathode catalyst to fabricate alkaline fuel cells, since silver catalyst is almost inactive in the oxidation of polyhydric alcohols. Alkaline direct ethylene glycol fuel cells using silver as a cathode catalyst gave excellent performance because higher concentrations of fuel could be supplied to the anode.

Matsuoka, Koji; Iriyama, Yasutoshi; Abe, Takeshi; Matsuoka, Masao; Ogumi, Zempachi

325

Preparation of Highly Sulfonated Ultra-Thin Proton-Exchange Polymer Membranes for Proton Exchange Membrane Fuel Cells  

NASA Astrophysics Data System (ADS)

Sulfonated ultra-thin proton-exchange polymer membrane carrying pyridine groups was made from a plasma polymerization of styrene, 2-vinylpyridine, and trifluoromethanesulfonic acid by after-glow capacitively coupled discharge technique. Pyridine groups tethered to the polymer backbone acts as a medium through the basic nitrogen for transfer of protons between the sulfonic acid groups of proton exchange membrane. It shows that the method using present technology could effectively depress the degradation of monomers during the plasma polymerization. Spectroscopic analyses reveal that the obtained membranes are highly functionalized with proton exchange groups and have higher proton conductivity. Thus, the membranes are expected to be used in direct methanol fuel cells.

Jiang, Zhongqing; Meng, Yuedong; Jiang, Zhong-Jie; Shi, Yicai

326

ACME: Automated Cell Morphology Extractor for Comprehensive Reconstruction of Cell Membranes  

PubMed Central

The quantification of cell shape, cell migration, and cell rearrangements is important for addressing classical questions in developmental biology such as patterning and tissue morphogenesis. Time-lapse microscopic imaging of transgenic embryos expressing fluorescent reporters is the method of choice for tracking morphogenetic changes and establishing cell lineages and fate maps in vivo. However, the manual steps involved in curating thousands of putative cell segmentations have been a major bottleneck in the application of these technologies especially for cell membranes. Segmentation of cell membranes while more difficult than nuclear segmentation is necessary for quantifying the relations between changes in cell morphology and morphogenesis. We present a novel and fully automated method to first reconstruct membrane signals and then segment out cells from 3D membrane images even in dense tissues. The approach has three stages: 1) detection of local membrane planes, 2) voting to fill structural gaps, and 3) region segmentation. We demonstrate the superior performance of the algorithms quantitatively on time-lapse confocal and two-photon images of zebrafish neuroectoderm and paraxial mesoderm by comparing its results with those derived from human inspection. We also compared with synthetic microscopic images generated by simulating the process of imaging with fluorescent reporters under varying conditions of noise. Both the over-segmentation and under-segmentation percentages of our method are around 5%. The volume overlap of individual cells, compared to expert manual segmentation, is consistently over 84%. By using our software (ACME) to study somite formation, we were able to segment touching cells with high accuracy and reliably quantify changes in morphogenetic parameters such as cell shape and size, and the arrangement of epithelial and mesenchymal cells. Our software has been developed and tested on Windows, Mac, and Linux platforms and is available publicly under an open source BSD license (https://github.com/krm15/ACME). PMID:23236265

Mosaliganti, Kishore R.; Noche, Ramil R.; Xiong, Fengzhu; Swinburne, Ian A.; Megason, Sean G.

2012-01-01

327

Evolution of rbcL among Lathyrus and Kupicha's classification.  

PubMed

Phylogenetic relationships in the Lathyrus genus were examined using cpDNA data, particularly data attributed to the "barcode" rbcL gene to construct a possible evolutionary scenario. Plant barcoding can be used to differentiate between species within a genus and to conserve DNA within the same species. We assessed the phylogeny of 29 species of Lathyrus using maximum parsimony, maximum likelihood and unweighted pair-group method and arithmetic mean. The classifications did not agree with current morphological and basic Lathyrus classification. Lathyrus belinensis is a new species that was not described by Kupicha; according to rbcL analysis, the species belongs in the Lathyrus genus. Additionally, the genus Lathyrus has undergone a rapid population expansion as indicated by neutral selection indices. PMID:25366764

Marghali, S; Zitouna, N; Gharbi, M; Fadhlaoui, I; Trifi-Farah, N

2014-01-01

328

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

329

Molecular modeling of membrane responses to the adsorption of rotating nanoparticles: promoted cell uptake and mechanical membrane rupture.  

PubMed

Recently, a unique dynamic magnetic field was developed to induce the rotational movement of superparamagnetic iron oxide nanoparticles. This technique has been applied to remotely control both cellular internalization and apoptosis. Therefore, a thorough understanding of how a lipid membrane responds to the introduction of rotating NPs is quite important to promote the applications of this technique in a variety of biomedical area. Here, we performed Dissipative Particle Dynamics (DPD) simulations to systematically investigate the interaction mechanism between lipid membranes and rotating NPs. Two kinds of membrane responses are observed. One is the promoted cell uptake and the other is the mechanical membrane rupture. The promoting effect of NP rotation on the cell uptake is ascribed to the enhanced membrane monolayer protrusion, which can wrap the NP from the top side. Meanwhile, the rotating NP exerts a shearing force on the membrane. Accordingly, the membrane undergoes a local distortion around the NP. If the shearing force exceeds a critical value, the local membrane distortion develops into a mechanical rupture. A number of factors, like NP size, NP shape, ligand density and rotation speed, are critical in both of the above membrane responses. PMID:25388826

Yue, Tongtao; Zhang, Xianren; Huang, Fang

2015-01-21

330

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

331

Cancer cell detection based on the interaction between an anticancer drug and cell membrane components.  

PubMed

Simple and general cancer cell detection methods are required in point-of-care diagnostics. Herein, the interaction between an anticancer drug, daunomycin, and cancer cell membrane components has been studied using an aptamer probe immobilized on a conducting polymer-gold nanoparticle composite film through electrochemical and fluorescence methods and applied to the quantitative detection of cancer cells. The developed method differentiates between cancerous and noncancerous cells effectively. PMID:23296144

Chandra, Pranjal; Noh, Hui-Bog; Shim, Yoon-Bo

2013-03-01

332

Surface-enhanced Raman imaging of red blood cell membrane with highly uniform active substrates obtained using block copolymers self-assembly  

NASA Astrophysics Data System (ADS)

In this communication, we discuss the application of ordered, ultrahigh-density templates of nano-textured Ag-particles obtained by self-assembling of inorganic-containing polystyrene-block-poly(4-vinylpyridine) copolymer (PS-b-P4VP) micelles, for the spectroscopic surface-enhanced Raman imaging in-vitro of red blood cells (RBCs) and its capability to identify the vibrational fingerprint of the plasma membrane of the cell physisorbed to the SERS substrate. Hexagonal arrays of PS-b-P4VP micelles, with selective inclusion of Ag nanoparticles (NPs) in the polar core, prepared by in situ reduction of a suitable precursor, are obtained by polymer self-assembly upon fast solvent evaporation during spin coating on the supporting substrate. UV irradiation and/or plasma oxygen treatment remove the polymer matrix leaving immobilized nano-islands of Ag-NPs. Such a kind of SERS-active substrate consists of a reproducible and uniform twodimensional hexagonal array of silver clusters with a diameter ranging from 25 to 30 nm (single particles having typically diameters of 5 nm) and nano-island gap distances of the order of 5-8 nm on silicon and 15 nm on glass , while giving rise to high enhancement factors and addressing the issue of SERS reproducibility. The basic substrate supporting the plasmonic coating used in this work is either of silicon or glass. This last allows working in back scattering configuration permitting real time monitoring, via microscopy, of the RBCs on which Raman measurements are being carried out. The template is thus applied for surface-enhanced Raman analysis of the red blood cell (RBC) membrane in confocal micro-Raman configuration demonstrating to have SERS imaging potential thanks to the uniformity of the nano-textured substrate. The first experimental evidence of SERS imaging of a red blood cell membrane in-vitro is demonstrated.

Zito, Gianluigi; Malafronte, Anna; Dochshanov, Alden; Rusciano, Giulia; Auriemma, Finizia; Pesce, Giuseppe; De Rosa, Claudio; Sasso, Antonio

2013-05-01

333

Lysosomal membrane permeabilization induces cell death in human mast cells.  

PubMed

Mast cells (MC) have pathogenic roles in numerous disorders, and strategies that stabilize MC or induce MC apoptosis are therefore emerging as possible therapeutic regimens. A typical feature of MC is their high content of secretory lysosomes (granules), containing numerous components such as biogenic amines, cytokines, serglycin proteoglycan and proteases. Damage to the secretory lysosomes will thus lead to leakage of these compounds, including the proteases, into the cytosol, and this could potentially trigger apoptosis. Here, we evaluated whether MC are sensitive to cell death induced by secretory lysosome destabilization, induced by the lysosomotropic agent Leu-Leu-OMe (LLME). Human MC were sensitive to LLME-induced cell death. In contrast, fibroblasts and HEK-293 cells were largely resistant. As judged by Annexin V/propidium iodide staining, LLME caused apoptotic cell death, and this was supported by induction of caspase-3-like activity, detection of activated caspase-3 by immunoblot analysis and reduced cell death in the presence of a caspase inhibitor. In support of a role for serglycin in regulating LLME-induced cell death, the survival rate of various cell types correlated negatively with the level of serglycin expression. In summary, this study introduces the concept of using lysosomotropic agents to induce cell death of human MC. PMID:21645032

Melo, F R; Lundequist, A; Calounova, G; Wernersson, S; Pejler, G

2011-10-01

334

Membrane processes and biophysical characterization of living cells decorated with chromatic polydiacetylene vesicles  

E-print Network

permeation FRET Biomimetic chemistry 1. Introduction The plasma membrane constitutes the platformMembrane processes and biophysical characterization of living cells decorated with chromatic and Department of Chemistry, Ben Gurion University of the Negev, Beer Sheva 84105, Israel b Department

Jelinek, Raz

335

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

336

Cell Membrane Tethers Generate Mechanical Force in Response to Electrical Stimulation  

PubMed Central

Living cells maintain a huge transmembrane electric field across their membranes. This electric field exerts a force on the membrane because the membrane surfaces are highly charged. We have measured electromechanical force generation by cell membranes using optically trapped beads to detach the plasma membrane from the cytoskeleton and form long thin cylinders (tethers). Hyperpolarizing potentials increased and depolarizing potentials decreased the force required to pull a tether. The membrane tether force in response to sinusoidal voltage signals was a function of holding potential, tether diameter, and tether length. Membrane electromechanical force production can occur at speeds exceeding those of ATP-based protein motors. By harnessing the energy in the transmembrane electric field, cell membranes may contribute to processes as diverse as outer hair cell electromotility, ion channel gating, and transport. PMID:20682262

Brownell, William E.; Qian, Feng; Anvari, Bahman

2010-01-01

337

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

338

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

339

Carbon monoxide poisoning of proton-exchange membrane fuel cells  

SciTech Connect

The platinum-alloy catalyst used in proton-exchange membrane (PEM) fuel cell anodes is highly susceptible to carbon monoxide (CO) poisoning. CO reduces the catalyst activity by blocking active catalyst sites normally available for hydrogen chemisorption and dissociation. The reaction kinetics at the anode catalyst surface can be used to estimate the decrease in cell voltage due to various levels of CO contamination in the inlet fuel streams on PEM fuel cell performance have been reviewed and analyzed in an attempt to further understand the electrochemical properties of the CO adsorption process. A fuel cell performance model of bipolar, Nafion 117 PEM fuel cell stack has been developed which predicts equilibrium cell output voltage as a function of current density and partial pressure of CO. The model contains both empirical and mechanistic parameters and evolved from a steady-state electrochemical model for a PEM fuel cell fed with a CO-free anode gas. Reaction kinetics and equilibrium surface coverage have been incorporated into the electrochemical model to predict the decrease in fuel cell performance at equilibrium. The effects of CO were studied at various concentrations of CO in hydrogen as the anode feed gas. Literature data were used to develop the model parameters and the resulting model is used to compare the model-predicted voltages, with and without CO, to data found in the literature.

Rodrigues, A.; Amphlett, J.C.; Mann, R.F.; Peppley, B.A.; Roberge, P.R. [Royal Military Coll. of Canada, Kingston, Ontario (Canada). Dept. of Chemistry and Chemical Engineering

1997-12-31

340

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

341

Red Blood Cell Antibody Identification  

MedlinePLUS

... Antibody ID, RBC; RBC Ab ID Formal name: Red Blood Cell Antibody Identification Related tests: Direct Antiglobulin ... None The Test Sample What is being tested? Red blood cell antibodies are proteins produced by the ...

342

Novel nanofiber-based triple-layer proton exchange membranes for fuel cell applications  

NASA Astrophysics Data System (ADS)

New types of triple-layer membranes were fabricated using multi-step impregnation of Nafion in electrospun webs based on bead-free nanofibers of sulfonated poly(ether sulfone) (SPES). The results showed that the fabricated nanofiber-filled membrane owing to its reduced methanol permeability as well as sufficient proton conductivity and membrane selectivity can be used as a promising proton exchange membrane for direct methanol fuel cell (DMFC) applications. The single cell DMFC performance results revealed that the SPES nanofiber-based triple-layer membranes have higher electrochemical performance than commercial Nafion membranes.

Hasani-Sadrabadi, Mohammad Mahdi; Shabani, Iman; Soleimani, Masoud; Moaddel, Homayoun

2011-05-01

343

Characteristics of Subfreezing Operation of Polymer Electrolyte Membrane Fuel Cells  

NASA Astrophysics Data System (ADS)

Polymer Electrolyte Membrane (PEM) Fuel Cells are capable of high efficiency operation, and are free of NOx, SOx, and CO2 emissions when using hydrogen fuel, and ideally suited for use in transportation applications due to their high power density and low operating temperatures. However, under subfreezing conditions which may be encountered during winter seasons in some areas, product water will freeze within the membrane, cathode side catalyst layer and gas diffusion media, leading to voltage loss and operation failure. Experiments were undertaken in order to characterize the amount and location of water during fuel cell operation. First, in-situ neutron radiography was undertaken on the fuel cells at a normal operating temperature for various operating current densities, inlet relative humidities, and diffusion media hydrophobicities. It was found that more hydrophobic cathode microporous layer (MPL) or hydrophilic anode MPL may result in a larger amount of water transporting back to the anode. The water profiles along the channels were measured and the point of liquid water emergence, where two phase flow begins, was compared to previous models. Secondly, under subfreezing temperatures, neutron imaging showed that water ice product accumulates because of lack of a water removal mechanism. Water was observed under both the lands and channels, and increased almost linearly with time. It is found that most ice exists in the cathode side. With evidence from experimental observation, a cold start model was developed and explained, following existing approaches in the literature. Three stages of cold start are explained: membrane saturation, ice storage in catalyst layer pores, and then ice melting. The voltage losses due to temperature change, increased transport resistance, and reduced electrochemical surface area. The ionic conductivity of the membrane at subfreezing temperatures was modeled. Voltage evolution over time for isothermal cold starts was predicted and validated against experimental data. The ice coverage coefficient was shown to be a key variable in matching with experimental data. From model analysis, it appears that the coulombs of charge passed before operation failure is an important parameter characterizing PEM fuel cell cold start. To investigate the coulombs of charge and its determining factors, PEM fuel cells were constructed to measure the effects of membrane configuration (thickness and initial state), catalyst layer configuration (thickness and ionomer-carbon ratio), current density, and temperature on the quantity. It was found that subfreezing temperature, ionomer-catalyst ratio, and catalyst-layer thickness significantly affect the amount of charge transferred before operational failure, whereas the membrane thickness and initial hydration level have limited effect for the considered cases. In addition, degradation of the catalyst layer was observed and quantified. These results improve the fundamental understanding of characteristics of subfreezing operation and thus are valuable for automobile applications of PEM fuel cells. The model directly relates the material properties to voltage loss, and predicts voltage evolution, thus providing a way for material optimization and diagnostics. Additionally, insights into component design and operating conditions can be used to better optimize the fuel cell for cold start-up of the vehicle.

Mishler, Jeffrey Harris

344

Ionic Liquids and New Proton Exchange Membranes for Fuel Cells  

NASA Technical Reports Server (NTRS)

There is currently a great surge of activity in fuel cell research as laboratories across the world seek to take advantage of the high energy capacity provided by &el cells relative to those of other portable electrochemical power systems. Much of this activity is aimed at high temperature fie1 cells, and a vital component of such &el cells must be the availability of a high temperature stable proton-permeable membrane. NASA Glenn Research Center is greatly involved in developing this technology. Other approaches to the high temperature fuel cell involve the use of single- component or almost-single-component electrolytes that provide a path for protons through the cell. A heavily researched case is the phosphoric acid fuel cell, in which the electrolyte is almost pure phosphoric acid and the cathode reaction produces water directly. The phosphoric acid fie1 cell delivers an open circuit voltage of 0.9 V falling to about 0.7 V under operating conditions at 170 C. The proton transport mechanism is mainly vehicular in character according to the viscosity/conductance relation. Here we describe some Proton Transfer Ionic Liquids (PTILs) with low vapor pressure and high temperature stability that have conductivities of unprecedented magnitude for non-aqueous systems. The first requirement of an ionic liquid is that, contrary to experience with most liquids consisting of ions, it must have a melting point that is not much above room temperature. The limit commonly suggested is 100 C. PTILs constitute an interesting class of non-corrosive proton-exchange electrolyte, which can serve well in high temperature (T = 100 - 250 C) fuel cell applications. We will present cell performance data showing that the open circuit voltage output, and the performance of a simple H2(g)Pt/PTIL/Pt/O2(g) fuel cell may be superior to those of the equivalent phosphoric acid electrolyte fuel cell both at ambient temperature and temperatures up to and above 200 C. My work at NASA Glenn Research Center during this summer is to develop and characterize proton exchange membranes doped with ionic liquids. The main techniques used to characterize these materials are: Impedance Spectroscopy, NMR, DSC, TGA, DMA, IR, and SEM ...

Belieres, Jean-Philippe

2004-01-01

345

Live-cell subcellular measurement of cell stiffness using a microengineered stretchable micropost array membrane  

PubMed Central

Forces are increasingly recognized as major regulators of cell structure and function, and the mechanical properties of cells, such as cell stiffness, are essential to the mechanisms by which cells sense forces, transmit them to the cell interior or to other cells, and transduce them into chemical signals that impact a spectrum of cellular responses. Here we reported a new whole-cell cell stiffness measurement technique with a subcellular spatial resolution. This technique was based on a novel cell stretching device that allowed for quantitative control and real-time measurements of mechanical stimuli and cellular biomechanical responses. Our strategy involved a microfabricated array of silicone elastomeric microposts integrated onto a stretchable elastomeric membrane. Using a computer-controlled vacuum, this micropost array membrane (mPAM) was activated to apply equibiaxial cell stretching forces to adherent cells attached on the tops of the microposts. The micropost top positions before and after mPAM stretches were recorded using fluorescence microscopy and further utilized to quantify local cell stretching forces and cell area increments. A robust computation scheme was developed and implemented for subcellular quantifications of cell stiffness using the data of local cell stretching forces and cell area increments generated from mPAM cell stretch assays. Our cell stiffness studies using the mPAM revealed strong positive correlations among cell stiffness, cellular traction force, and cell spread area, and illustrated the important functional roles of actin polymerization and myosin II-mediated cytoskeleton contractility in regulating cell stiffness. Collectively, our work reported a new approach for whole-cell cell stiffness measurements with a subcellular spatial resolution, which would likely help explain the complex biomechanical functions and force-sensing mechanisms of cells and design better materials for cell and tissue engineering and other applications in vivo. PMID:22935822

Lam, Raymond H. W.; Weng, Shinuo; Lu, Wei; Fu, Jianping

2014-01-01

346

Evidence for Transfer of Membranes from Mesenchymal Stem Cells to HL-1 Cardiac Cells  

PubMed Central

This study examined the interaction of mouse bone marrow mesenchymal stem cells (MSC) with cardiac HL-1 cells during coculture by fluorescent dye labeling and then flow cytometry. MSC were layered onto confluent HL-1 cell cultures in a 1?:?4 ratio. MSC gained gap junction permeant calcein from HL-1 cells after 4 hours which was partially reduced by oleamide. After 20 hours, 99% MSC gained calcein, unaffected by oleamide. Double-labeling HL-1 cells with calcein and the membrane dye DiO resulted in transfer of both calcein and DiO to MSC. When HL-1 cells were labeled with calcein and MSC with DiO, MSC gained calcein while HL-1 cells gained DiO. Very little fusion was observed since more than 90% Sca-1 positive MSC gained DiO from HL-1 cells while less than 9% gained gap junction impermeant CMFDA after 20 hours with no Sca-1 transfer to HL-1 cells. Time dependent transfer of membrane DiD was observed from HL-1 cells to MSC (100%) and vice versa (50%) after 20 hours with more limited transfer of CMFDA. These results demonstrate that MSC and HL-1 cells exchange membrane components which may account for some of the beneficial effect of MSC in the heart after myocardial infarction. PMID:25295065

Boomsma, Robert A.; Geenen, David L.

2014-01-01

347

Effect of Some Proteins on the Yeast Cell Membrane  

PubMed Central

Yeast cells, Candida utilis, in water suspension and in the absence of electrolytes were found to be very sensitive to several proteins of moderate size, including ribonuclease, protamine, lysozyme, bovine serum albumin, cytochrome c, and myoglobin. Viability ceases rapidly, and ultraviolet-absorbing compounds (260 m?) and the amino acid pool are released into the medium. The ultraviolet-absorbing material appears to be the nucleotide and coenzyme fraction usually extracted by 0.2 n perchloric acid at low temperature. The ribonucleic acid fraction remains in the cell ghosts and can be released by ribonuclease. The enzymatic properties of some of these proteins have no relation to their damaging effect on the cell membrane. Poly-l-lysine shows the same activity. PMID:4294420

Yphantis, D. A.; Dainko, J. L.; Schlenk, F.

1967-01-01

348

Organized Living: From Cell Surfaces to Basement Membranes  

NSDL National Science Digital Library

Binding of extracellular matrix (ECM) proteins to integrin receptors initiates intracellular signaling events that are essential for the differentiation and survival of epithelial cells. However, the propagation and processing of these signals also depend on the cells acquiring an appropriate three-dimensional morphology and polarity after contact with the ECM. In fact, even if adhesion to the ECM is maintained but subsequent cellular organization and polarity are impaired, epithelial cells fail to fully differentiate and become susceptible to apoptotic stimuli. Studies using three-dimensional tissue culture models with reconstituted basement membranes not only demonstrate the central role of tissue organization for differentiation and survival, but also emphasize how acquiring this organized polarized phenotype can override a number of genetic changes that would otherwise disrupt normal tissue function.

Nancy J. Boudreau (University of California San Francisco; Department of Surgery REV)

2003-08-19

349

Percolation in a Proton Exchange Membrane Fuel Cell Catalyst Layer  

SciTech Connect

Water management in the catalyst layers of proton exchange membrane fuel cells (PEMFC) is confronted by two issues, flooding and dry out, both of which result in improper functioning of the fuel cell and lead to poor performance and degradation. At the present time, the data that has been reported about water percolation and wettability within a fuel cell catalyst layer is limited. A method and apparatus for measuring the percolation pressure in the catalyst layer has been developed based upon an experimental apparatus used to test water percolation in porous transport layers (PTL). The experimental setup uses a pseudo Hele-Shaw type testing where samples are compressed and a fluid is injected into the sample. Testing the samples gives percolation pressure plots which show trends in increasing percolation pressure with an increase in flow rate. A decrease in pressure was seen as percolation occurred in one sample, however the pressure only had a rising effect in the other sample.

Stacy, Stephen; Allen, Jeffrey

2012-07-01

350

Reusable, reversibly sealable parylene membranes for cell and protein patterning  

PubMed Central

The patterned deposition of cells and biomolecules on surfaces is a potentially useful tool for in vitro diagnostics, high-throughput screening, and tissue engineering. Here, we describe an inexpensive and potentially widely applicable micropatterning technique that uses reversible sealing of microfabricated parylene-C stencils on surfaces to enable surface patterning. Using these stencils it is possible to generate micropatterns and copatterns of proteins and cells, including NIH-3T3 fibroblasts, hepatocytes and embryonic stem cells. After patterning, the stencils can be removed from the surface, plasma treated to remove adsorbed proteins, and reused. A variety of hydrophobic surfaces including PDMS, polystyrene and acrylated glass were patterned using this approach. Furthermore, we demonstrated the reusability and mechanical integrity of the parylene membrane for at least 10 consecutive patterning processes. These parylene-C stencils are potentially scalable commercially and easily accessible for many biological and biomedical applications. PMID:17729252

Wright, Dylan; Rajalingam, Bimalraj; Karp, Jeffrey M.; Selvarasah, Selvapraba; Ling, Yibo; Yeh, Judy; Langer, Robert; Dokmeci, Mehmet R.; Khademhosseini, Ali

2010-01-01

351

Chimerism of buccal membrane cells in a monochorionic dizygotic twin.  

PubMed

No monochorionic dizygotic twins (MCDZTs) with cellular chimerism involving cells other than blood cells have been reported in the literature to date. Here we report a probable first case of MCDZTs with buccal cell chimerism. A 32-year-old woman conceived twins by in vitro fertilization by using 2 cryopreserved blastocysts that were transferred into her uterus. An ultrasound scan at 8 weeks' gestation showed signs indicative of monochorionic twins. A healthy boy and a healthy girl were born, showing no sexual ambiguity. Cytogenetic analyses and microsatellite studies demonstrated chimerism in blood cells of both twins. Notably, repeated fluorescence in situ hybridization and microsatellite studies revealed chimerism in buccal cells obtained from 1 of the twins. Although the mechanism through which buccal cell chimerism was generated remains to be elucidated, ectopic differentiation of chimeric hematopoietic cells that migrated to the buccal membrane or the cellular transfer between the 2 embryos at the early stage of development might be responsible for the phenomenon. This hypothesis raises an interesting issue regarding embryonic development and cellular differentiation into organs during fetal development. Given the possibility of cryptic chimerism in various organs including gonadal tissues in MCDZTs, close observation will be required to determine whether complications develop in the course of the patients' growth. PMID:24685957

Fumoto, Seiko; Hosoi, Kenichiro; Ohnishi, Hiroaki; Hoshina, Hiroaki; Yan, Kunimasa; Saji, Hiroh; Oka, Akira

2014-04-01

352

Lysosomal membrane permeabilization in cell death: Concepts and challenges.  

PubMed

Late endocytic compartments include late endosomes, lysosomes and hybrid organelles. In the acidic lumen, cargo material derived from endocytosed and phagocytosed extracellular material and autophagy-derived intracellular material is degraded. In the event of lysosomal membrane permeabilization (LMP), the function of endo/lysosomal compartment is affected and the luminal contents are released into the cytosol to various extents. LMP can be a result of osmotic lysis or direct membranolytic activity of the compounds that accumulate in the lumen of endo/lysosomes. In addition to several synthetic compounds, such as dipeptide methyl esters and lysosomotropic detergents, endogenous agents that can cause LMP include ROS and lipid metabolites such as sphingosine and phosphatidic acid. Depending on the cell type and the dose, LMP can initiate the lysosomal apoptotic pathway, pyroptosis or necrosis. LMP can also amplify cell death signaling that was initiated outside the endocytic compartment, and hamper cell recovery via autophagy. However, mechanisms that connect LMP with cell death signaling are poorly understood, with the exception of the proteolytic activation of Bid by aspartic cathepsin D and cysteine cathepsins. Determination of LMP in a cell model system is methodologically challenging. Even more difficult is to prove that LMP is the primary event leading to cell death. Nevertheless, LMP may prove to be a valuable approach in therapy, either as a trigger of cell death or as a mechanism of therapeutic drug release in the case of delivery systems that target the endocytic pathway. PMID:24984038

Repnik, Urška; Hafner ?esen, Maruša; Turk, Boris

2014-11-01

353

Mechanism of spontaneous inside-out vesiculation of red cell membranes  

PubMed Central

In certain conditions, human red cell membranes spontaneously form inside out vesicles within 20 min after hypotonic lysis. Study of the geometry of this process now reveals that, contrary to earlier views of vesiculation by endocytosis or by the mechanical shearing of cytoskeleton-depleted membrane, lysis generates a persistent membrane edge which spontaneously curls, cuts, and splices the membrane surface to form single or concentric vesicles. Analysis of the processes by which proteins may stabilize a free membrane edge led us to formulate a novel zip-type mechanism for membrane cutting-splicing and fusion even in the absence of free edges. Such protein-led membrane fusion represents an alternative to mechanisms of membrane fusion based on phospholipid interactions, and may prove relevant to processes of secretion, endocytosis, phagocytosis, and membrane recycling in many cell types. PMID:3384849

1988-01-01

354

Cooperative binding of Annexin A5 to phosphatidylserine on apoptotic cell membranes.  

PubMed

Healthy cells exhibit an asymmetric plasma membrane with phosphatidylserine (PS) located on the cytoplasmic leaflet of the plasma membrane bilayer. Annexin A5-FITC, a PS binding protein, is commonly used to evaluate apoptosis in flow cytometry. PS exposed by apoptotic cells serves as a major 'eat-me' signal for phagocytes. Although exposition of PS has been observed after alternative stimuli, no clearance of viable, PS exposing cells has been detected. Thus, besides PS exposure, membranes of viable and apoptotic cells might exhibit specific characteristics. Here, we show that Annexin A5 binds in a cooperative manner to different types of dead cells. Shrunken apoptotic cells thereby showed the highest Hill coefficient values. Contrarily, parafomaldehyde fixation of apoptotic cells completely abrogates the cooperativity effect seen with dead and dying cells. We tend to speculate that the cooperative binding of Annexin A5 to the membranes of apoptotic cells reflects higher fluidity of the exposed membranes facilitating PS clustering. PMID:24304966

Janko, Christina; Jeremic, Ivica; Biermann, Mona; Chaurio, Ricardo; Schorn, Christine; Muñoz, Luis E; Herrmann, Martin

2013-12-01

355

Effective Temperature of Red Blood Cell Membrane Fluctuations  

E-print Network

Biologically driven non-equilibrium fluctuations are often characterized by their non-Gaussianity or by an "effective temperature", which is frequency dependent and higher than the ambient temperature. We address these two measures theoretically by examining a randomly kicked "particle", with a variable number of kicking "motors", and show how these two indicators of non-equilibrium behavior can contradict. Our results are compared with new experiments on shape fluctuations of red-blood cell membranes, and demonstrate how the physical nature of the motors in this system can be revealed using these global measures of non-equilibrium.

Eyal Ben-Isaac; YongKeun Park; Gabriel Popescu; Frank L. H. Brown; Nir S. Gov; Yair Shokef

2011-05-04

356

Cytoskeleton confinement of red blood cell membrane fluctuations  

E-print Network

We analyze both the static and dynamic fluctuation spectrum of the red-blood cell in a unified manner, using a simple model of the composite membrane. In this model, the two-dimensional spectrin network that forms the cytoskeleton is treated as a rigid shell which is located at some constant average separation from the lipid bilayer. The cytoskeleton thereby confines both the static and dynamic fluctuations of the lipid bilayer. The predictions of the model account for the wavevector and frequency dependence of the experimental data. The observed amplitude of the thermal fluctuations is related to effects of ATP-driven fluctuations.

N. Gov; A. G. Zilman; S. Safran

2002-07-22

357

Grafted polyelectrolyte membranes for lithium batteries and fuel cells  

SciTech Connect

Polyelectrolyte materials have been developed for lithium battery systems in response to the severe problems due to salt concentration gradients that occur in composite electrodes (aka membrane-electrode assemblies). Comb branch polymer architectures are described which allow for grafting of appropriate anions on to the polymer and also for cross-linking to provide for appropriate mechanical properties. The interactions of the polymers with the electrode surfaces are critical for the performance of the system and some of the structural features that influence this will be described. Parallels with the fuel cell MEA structures exist and will also be discussed.

Kerr, John B.

2003-06-24

358

Probing red cell membrane cholesterol movement with cyclodextrin.  

PubMed Central

We probed the kinetics with which cholesterol moves across the human red cell bilayer and exits the membrane using methyl-beta-cyclodextrin as an acceptor. The fractional rate of cholesterol transfer (% s(-1)) was unprecedented, the half-time at 37 degrees C being ~1 s. The kinetics observed under typical conditions were independent of donor concentration and directly proportional to acceptor concentration. The rate of exit of membrane cholesterol fell hyperbolically to zero with increasing dilution. The energy of activation for cholesterol transfer was the same at high and low dilution; namely, 27-28 Kcal/mol. This behavior is not consistent with an exit pathway involving desorption followed by aqueous diffusion to acceptors nor with a simple one-step collision mechanism. Rather, it is that predicted for an activation-collision mechanism in which the reversible partial projection of cholesterol molecules out of the bilayer precedes their collisional capture by cyclodextrin. Because the entire membrane pool was transferred in a single first-order process under all conditions, we infer that the transbilayer diffusion (flip-flop) of cholesterol must have proceeded faster than its exit, i.e., with a half-time of <1 s at 37 degrees C. PMID:12324429

Steck, Theodore L; Ye, Jin; Lange, Yvonne

2002-01-01

359

Near-infrared femtosecond laser assisted cell membrane permeabilization  

NASA Astrophysics Data System (ADS)

The controlled delivery of membrane impermeable molecules into single living cells (micro-injection) is important for a variety of applications such genomics, proteomics or drug screening and testing. Recently, it has been demonstrated that opto-injection with tightly focused (˜300nm) femtosecond (fs) laser pulses at near-infrared (nir) wavelengths (700-1100nm) has the potential to create highly localized transient pores in single living cells with high cell survival rates and transfection efficiency. We have investigated the creation of transient pores in single living BAEC cells by focused fs nir laser pulses dependent on the incident laser intensity by dye uptake studies. Our experimental data agree very well with the experimentally and theoretically determined thresholds for laser-induced plasma formation and LIB. We observe that pore creation is observed for laser intensities of 4.0x10^12W/cm^2 and higher. For laser intensities above 3.3x10^13W/cm^2 BAEC cells are irreversibly destroyed. Within these two limits the pore size increases logarithmically with increasing laser intensity. This functional dependence is explained by considering the Gaussian intensity distribution across the laser focal spot. The physical understanding of the relationship between pore size and laser intensity allows the control of the number of molecules delivered into a cell per unit time through the control of the pore size.

Peng, Cheng; Palazzo, Robert; Wilke, Ingrid

2006-03-01

360

Mechanistic investigation of interactions between steroidal saponin digitonin and cell membrane models.  

PubMed

Digitonin is an amphiphilic steroidal saponin, a class of natural products that can bind to cholesterol and lyse cells. Despite the known cell membrane lysis activity, it remains unclear how it interacts with cell membranes. In the present work, the interaction mechanism between digitonin and cell membrane models has quantitatively been investigated using a combination of physical techniques. It has been demonstrated that digitonin molecules bind specifically to cholesterol in the membrane, resulting in the formation of cholesterol-digitonin complexes on the membrane surface by removing cholesterol from the membrane core. Changes in the mass density and the film mechanics caused by the digitonin were determined by using quartz crystal microbalance with dissipation (QCM-D), and the combination of X-ray reflectivity (XRR) and dual polarization interferometry (DPI) yielded the hydration level of the cholesterol-digitonin complexes. From differential scanning calorimetry (DSC) analysis, supporting evidence was obtained that cholesterol was removed from the membrane core. PMID:25412206

Frenkel, Nataliya; Makky, Ali; Sudji, Ikhwan Resmala; Wink, Michael; Tanaka, Motomu

2014-12-18

361

Prevention of complement activation on the homologous cell membrane of nucleated cells as well as erythrocytes.  

PubMed

A C3b receptor, a glycoprotein with a molecular weight of 205 kDa (gp205) on human erythrocytes (Ehu), has been claimed to restrict the activation of human complement via the alternative complement pathway (ACP), thereby inhibiting the activation of the ACP even on neuraminidase (Nase)-treated Ehu. However, the Nase-treated Ehu were sensitive to hemolysis by guinea pig complement via ACP activation, although the C3b receptors on Ehu can react with guinea pig C3b. Furthermore, HeLa cells which had no detectable C3b receptor did not became reactive with guinea pig ACP. On the contrary, Nase treatment of guinea pig erythrocytes (Egp) as well as guinea pig line 10 tumor cells, which have no detectable C3b receptor, could not make those cells reactive with the homologous guinea pig ACP although they became reactive with human and rabbit ACP. Similarly, rabbit E did not become reactive with the homologous rabbit ACP following Nase treatment. Nase-treated Egp preincubated with human serum in the presence of EDTA were also not lysed by guinea pig serum. Therefore the unreactiveness of Nase-treated cell membrane with homologous ACP was not merely due to the absence of antibody to cell membrane in the homologous serum. There may be a membrane inhibitor which preferentially interacts with homologous complement to circumvent undesirable complement activation on the homologous cell membrane. PMID:6221932

Okada, H; Tanaka, H; Okada, N

1983-04-01

362

Single-cell force spectroscopy as a technique to quantify human red blood cell adhesion to subendothelial laminin.  

PubMed

Single-cell force spectroscopy (SCFS), an atomic force microscopy (AFM)-based assay, enables quantitative study of cell adhesion while maintaining the native state of surface receptors in physiological conditions. Human healthy and pathological red blood cells (RBCs) express a large number of surface proteins which mediate cell-cell interactions, or cell adhesion to the extracellular matrix. In particular, RBCs adhere with high affinity to subendothelial matrix laminin via the basal cell adhesion molecule and Lutheran protein (BCAM/Lu). Here, we established SCFS as an in vitro technique to study human RBC adhesion at baseline and following biochemical treatment. Using blood obtained from healthy human subjects, we recorded adhesion forces from single RBCs attached to AFM cantilevers as the cell was pulled-off of substrates coated with laminin protein. We found that an increase in the overall cell adhesion measured via SCFS is correlated with an increase in the resultant total force measured on 1 µm(2) areas of the RBC membrane. Further, we showed that SCFS can detect significant changes in the adhesive response of RBCs to modulation of the cyclic adenosine monophosphate (cAMP) and protein kinase A (PKA) pathway. Lastly, we identified variability in the RBC adhesion force to laminin amongst the human subjects, suggesting that RBCs maintain diverse levels of active BCAM/Lu adhesion receptors. By using single-cell measurements, we established a powerful new method for the quantitative measurement of single RBC adhesion with specific receptor-mediated binding. PMID:25458578

Maciaszek, Jamie L; Partola, Kostyantyn; Zhang, Jing; Andemariam, Biree; Lykotrafitis, George

2014-12-18

363

Changes in Surface Area of Intact Guard Cells Are Correlated with Membrane Internalization  

Microsoft Academic Search

Guard cells must maintain the integrity of the plasma membrane as they undergo large, rapid changes in volume. It has been assumed that changes in volume are accompanied by changes in surface area, but mechanisms for regulating plasma membrane surface area have not been identified in intact guard cells, and the extent to which surface area of the guard cells

Joseph C. Shope; Daryll B. DeWald; Keith A. Mott

2003-01-01

364

Cationic Nanoparticles Induce Nanoscale Disruption in Living Cell Plasma Membranes Jiumei Chen,,  

E-print Network

nanoparticles that yield millimolar charge concentra- tions are acutely cytotoxic and lead to cell lysis.1Cationic Nanoparticles Induce Nanoscale Disruption in Living Cell Plasma Membranes Jiumei Chen recognized that cationic nanoparticles induce cell membrane permeability. Recently, it has been found

Tew, Gregory N.

365

Proton Exchange Membrane Fuel Cell degradation prediction based on Adaptive Neuro Fuzzy Inference Systems  

E-print Network

Proton Exchange Membrane Fuel Cell degradation prediction based on Adaptive Neuro Fuzzy Inference online XX XX XXXX Keywords: Proton Exchange Membrane fuel cell degradation, Prognostic and Health nominal operating condition of a PEM fuel cell stack. It proposes a methodology based on Adaptive Neuro

Paris-Sud XI, Université de

366

Control of the mass and energy dynamics of polybenzimidazole-membrane fuel cells  

E-print Network

Control of the mass and energy dynamics of polybenzimidazole-membrane fuel cells Federico Zenith-temperature proton- exchange-membrane fuel cell are investigated. For a particular configuration, three lumped the necessary conditions for the fuel-cell stack to operate. It is possible to control temperature by using only

Skogestad, Sigurd

367

Fluorescein transport properties across artificial lipid membranes, Caco-2 cell monolayers and rat jejunum  

Microsoft Academic Search

Membrane transport characteristics of a paracellular permeability marker fluorescein were evaluated using artificial membrane, Caco-2 cell monolayers and rat jejunum, all mounted in side-by-side diffusion cells. Modified Ringer buffers with varied pH values were applied as incubation salines on both sides of artificial membrane, cell culture monolayers or rat jejunum. Passive transport according to pH partition theory was determined using

Katja Berginc; Simon Žakelj; Lea Levstik; Darko Urši?; Albin Kristl

2007-01-01

368

Effects of La 3+ on inward K + channels at plasma membrane in guard cells  

Microsoft Academic Search

The effects of La3+ on inward K+ channels at plasma membrane in vicia guard cells are investigated using the whole-cell patch-clamp recording mode. It is\\u000a shown that La3+ on both sides of plasma membrane blocks inward K+ currents in a concentration-dependent manner, indicating that La3+ binding sites may exist on both sides of plasma membrane in guard cells in vicia.

Shaowu Xue; Pin Yang

2005-01-01

369

Live-cell imaging reveals periarbuscular membrane domains and organelle location in Medicago truncatula roots during arbuscular mycorrhizal symbiosis  

Microsoft Academic Search

In the arbuscular mycorrhizal symbiosis, the fungal symbiont colonizes root cortical cells, where it establishes differentiated hyphae called arbuscules. As each arbuscule develops, the cortical cell undergoes a transient reorganization and envelops the arbuscule in a novel symbiosis-specific membrane, called the periarbuscular membrane. The periarbuscular membrane, which is continuous with the plant plasma membrane of the cortical cell, is a

Nathan Pumplin; Maria J. Harrison

2009-01-01

370

Bending elasticities of model membranes: influences of temperature and sterol content.  

PubMed Central

Giant liposomes obtained by electroformation and observed by phase-contrast video microscopy show spontaneous deformations originating from Brownian motion that are characterized, in the case of quasispherical vesicles, by two parameters only, the membrane tension sigma and the bending elasticity k(c). For liposomes containing dimyristoyl phosphatidylcholine (DMPC) or a 10 mol% cholesterol/DMPC mixture, the mechanical property of the membrane, k(c), is shown to be temperature dependent on approaching the main (thermotropic) phase transition temperature T(m). In the case of DMPC/cholesterol bilayers, we also obtained evidence for a relation between the bending elasticity and the corresponding temperature/cholesterol molecular ratio phase diagram. Comparison of DMPC/cholesterol with DMPC/cholesterol sulfate bilayers at 30 degrees C containing 30% sterol ratio shows that k(c) is independent of the surface charge density of the bilayer. Finally, bending elasticities of red blood cell (RBC) total lipid extracts lead to a very low k(c) at 37 degrees C if we refer to DMPC/cholesterol bilayers. At 25 degrees C, the very low bending elasticity of a cholesterol-free RBC lipid extract seems to be related to a phase coexistence, as it can be observed by solid-state (31)P-NMR. At the same temperature, the cholesterol-containing RBC lipid extract membrane shows an increase in the bending constant comparable to the one observed for a high cholesterol ratio in DMPC membranes. Images FIGURE 1 FIGURE 7 PMID:9168037

Méléard, P; Gerbeaud, C; Pott, T; Fernandez-Puente, L; Bivas, I; Mitov, M D; Dufourcq, J; Bothorel, P

1997-01-01

371

Cell-Culture Reactor Having a Porous Organic Polymer Membrane  

NASA Technical Reports Server (NTRS)

A method for making a biocompatible polymer article using a uniform atomic oxygen treatment is disclosed. The substrate may be subsequently optionally grated with a compatibilizing compound. Compatibilizing compounds may include proteins, phosphory1choline groups, platelet adhesion preventing polymers, albumin adhesion promoters, and the like. The compatibilized substrate may also have a living cell layer adhered thereto. The atomic oxygen is preferably produced by a flowing afterglow microwave discharge, wherein the substrate resides in a sidearm out of the plasma. Also, methods for culturing cells for various purposes using the various membranes are disclosed as well. Also disclosed are porous organic polymers having a distributed pore chemistry (DPC) comprising hydrophilic and hydrophobic regions, and a method for making the DPC by exposing the polymer to atomic oxygen wherein the rate of hydrophilization is greater than the rate of mass loss.

Koontz, Steven L. (Inventor)

2000-01-01

372

Association rates of membrane-coupled cell adhesion molecules.  

PubMed

Thus far, understanding how the confined cellular environment affects the lifetime of bonds, as well as the extraction of complexation rates, has been a major challenge in studies of cell adhesion. Based on a theoretical description of the growth curves of adhesion domains, we present a new (to our knowledge) method to measure the association rate kon of ligand-receptor pairs incorporated into lipid membranes. As a proof of principle, we apply this method to several systems. We find that the kon for the interaction of biotin with neutravidin is larger than that for integrin binding to RGD or sialyl Lewis(x) to E-selectin. Furthermore, we find kon to be enhanced by membrane fluctuations that increase the probability for encounters between the binders. The opposite effect on kon could be attributed to the presence of repulsive polymers that mimic the glycocalyx, which points to two potential mechanisms for controlling the speed of protein complexation during the cell recognition process. PMID:25468354

Bihr, Timo; Fenz, Susanne; Sackmann, Erich; Merkel, Rudolf; Seifert, Udo; Sengupta, Kheya; Smith, Ana-Sun?ana

2014-12-01

373

Proliferation of Schwann cells induced by axolemmal and myelin membranes  

SciTech Connect

Purified Schwann Cells were cultured from neonatal rat sciatic nerve using a modification of the method of Brockes. Schwann cells and contaminating fibroblasts were unambiguously identified using fluorescent antibodies of 2'3' cyclic nucleotide 3'-phosphodiesterase and the thy 1.1 antigen respectively. The Schwann cells were quiescent unless challenged with mitogens. They proliferated rapidly in response to the soluble mitogen, cholera toxin, or to membrane fractions from rat CNS or PNS, prepared by the method of DeVries. Mitogenic activity was present in both axolemmal and myelin enriched fractions and promoted a 10-15 fold increase in the rate of /sup 3/H-thymidine uptake. The axolemmal mitogen was sensitive to heat (80/sup 0/C for 10 minutes), trypsin digestion (0.05% x 30 mins) or to treatment with endoglycosidase D, suggesting that it could be a glycoprotein. Fifty percent of the axolemmal mitogenic activity was solubilized in 1% octyl-glucoside. The solubilized material, however, was very unstable and further purification was not possible. The myelin associated mitogenic activity was markedly different. It was resistant to freeze thaw cycles, trypsin digestion of endoglycosidase treatment and the activity was actually enhanced by heating at 100/sup 0/C for two hours. It is proposed that the axolemmal activity is responsible for Schwann cell proliferation during development and that the myelin associated activity promotes Schwann cell proliferation during Wallerian degeneration.

Dinneen, M..

1985-01-01

374

DEVELOPMENT OF NOVEL ELECTROCATALYSTS FOR PROTON EXCHANGE MEMBRANE FUEL CELLS  

SciTech Connect

The Proton Exchange Membrane Fuel Cell (PEMFC) is one of the most promising power sources for stand-alone utility and electric vehicle applications. Platinum (Pt) Catalyst is used for both fuel and air electrodes in PEMFCs. However, carbon monoxide (CO) contamination of H{sub 2} greatly affects electro catalysts used at the anode of PEMFCs and decreases cell performance. The irreversible poisoning of the anode can occur even in CO concentrations as low as few parts per million (ppm). In this work, we have synthesized several novel elctrocatalysts (Pt/C, Pt/Ru/C, Pt/Mo/C, Pt/Ir and Pt/Ru/Mo) for PEMFCs. These catalysts have been tested for CO tolerance in the H{sub 2}/air fuel cell, using CO concentrations in the H{sub 2} fuel that varies from 10 to 100 ppm. The performance of the electrodes was evaluated by determining the cell potential against current density. The effects of catalyst composition and electrode film preparation method on the performance of PEM fuel cell were also studied. It was found that at 70 C and 3.5 atm pressure at the cathode, Pt-alloy catalyst (10 wt% Pt/Ru/C, 20 wt% Pt/Mo/C) were more CO tolerant than the 20 wt% Pt/C catalyst alone. It was also observed that spraying method was better than the brushing technique for the preparation of electrode film.

Shamsuddin Ilias

2002-06-11

375

High temperature proton exchange membranes based on polybenzimidazoles for fuel cells  

Microsoft Academic Search

To achieve high temperature operation of proton exchange membrane fuel cells (PEMFC), preferably under ambient pressure, acid–base polymer membranes represent an effective approach. The phosphoric acid-doped polybenzimidazole membrane seems so far the most successful system in the field. It has in recent years motivated extensive research activities with great progress. This treatise is devoted to updating the development, covering polymer

Qingfeng Li; Jens Oluf Jensen; Robert F. Savinell; Niels J. Bjerrum

2009-01-01

376

Hydrogen production using single-chamber membrane-free microbial electrolysis cells  

Microsoft Academic Search

Microbial electrohydrogenesis provides a new approach for hydrogen generation from renewable biomass. Membranes were used in all the reported microbial electrolysis cells (MECs) to separate the anode and cathode chambers. To reduce the potential losses associated with membrane and increase the energy recovery of this process, single-chamber membrane-free MECs were designed and used to investigate hydrogen production by one mixed

Hongqiang Hu; Yanzhen Fan; Hong Liu

2008-01-01

377

Direct deposit of catalyst on the membrane of direct feed fuel cells  

NASA Technical Reports Server (NTRS)

An improved direct liquid-feed fuel cell having a solid membrane electrolyte for electrochemical reactions of an organic fuel. Catalyst utilization and catalyst/membrane interface improvements are disclosed. Specifically, the catalyst layer is applied directly onto the membrane electrolyte.

Chun, William (Inventor); Narayanan, Sekharipuram R. (Inventor); Jeffries-Nakamura, Barbara (Inventor); Valdez, Thomas I. (Inventor); Linke, Juergen (Inventor)

2001-01-01

378

Membranes produced by PECVD technique for low temperature fuel cell applications  

E-print Network

and styrene. The chemical and physical structure of plasma membranes has been investigated using FTIR and SEM cells have especially focused on perfluorosulfonic acid membranes such as Nafion® (DuPont), Dow® (DOW Chemicals) or Flemion® (Asahi Glass) [5]. Although highly proton conductive, these membranes have several

Paris-Sud XI, Université de

379

Time-dependent mechanical behavior of proton exchange membrane fuel cell electrodes  

NASA Astrophysics Data System (ADS)

The electrodes used for Proton Exchange Membrane Fuel Cells (PEMFCs) are typically painted or sprayed onto the membrane during manufacturing, making it difficult to directly characterize their mechanical behavior as a stand-alone material. An experimental-numerical hybrid technique is devised to extract the electrode properties from the experimentally measured properties of Nafion® 211 membrane

Lu, Zongwen; Santare, Michael H.; Karlsson, Anette M.; Busby, F. Colin; Walsh, Peter

2014-01-01

380

Transport of Small Molecules Across Cell Membranes: Water Channels and Urea Transporters  

NSDL National Science Digital Library

How do small hydrophilic nonelectrolytes cross cell membranes? Which pathways are most important for small lipid insoluble molecules to cross cell membranes? These are questions that have been basic to membrane transport physiology for decades. More importantly, these are questions whose answers have changed significantly within the last 10 years. This review discusses the evidence that pathways other than the lipid bilayer itself exist for the transport across cell membranes of specific small hydrophilic nonelectrolytes. The description begins with briefly analyzing the relevance of well accepted basic mathematical models for transport for understanding the permeability of representative physiologically important molecules across actual cell membranes. Particular emphasis is placed on describing recently discovered proteins that facilitate the transport of some of the smallest physiologically important lipid-insoluble molecules, water, and urea. Evidence also exists for transport proteins that selectively enhance the transmembrane transport of other small lipid-insoluble molecules. Do nonselective pores for small molecules exist in cell membranes?

PhD Barbara E. Goodman (University of South Dakota School of Medicine Division of Basic Biomedical Sciences)

2002-09-01

381

Development of a living membrane comprising a functional human renal proximal tubule cell monolayer on polyethersulfone polymeric membrane.  

PubMed

The need for improved renal replacement therapies has stimulated innovative research for the development of a cell-based renal assist device. A key requirement for such a device is the formation of a "living membrane", consisting of a tight kidney cell monolayer with preserved functional organic ion transporters on a suitable artificial membrane surface. In this work, we applied a unique conditionally immortalized proximal tubule epithelial cell (ciPTEC) line with an optimized coating strategy on polyethersulfone (PES) membranes to develop a living membrane with a functional proximal tubule epithelial cell layer. PES membranes were coated with combinations of 3,4-dihydroxy-l-phenylalanine and human collagen IV (Coll IV). The optimal coating time and concentrations were determined to achieve retention of vital blood components while preserving high water transport and optimal ciPTEC adhesion. The ciPTEC monolayers obtained were examined through immunocytochemistry to detect zona occludens 1 tight junction proteins. Reproducible monolayers were formed when using a combination of 2mgml(-1) 3,4-dihydroxy-l-phenylalanine (4min coating, 1h dissolution) and 25?gml(-1) Coll IV (4min coating). The successful transport of (14)C-creatinine through the developed living membrane system was used as an indication for organic cation transporter functionality. The addition of metformin or cimetidine significantly reduced the creatinine transepithelial flux, indicating active creatinine uptake in ciPTECs, most likely mediated by the organic cation transporter, OCT2 (SLC22A2). In conclusion, this study shows the successful development of a living membrane consisting of a reproducible ciPTEC monolayer on PES membranes, an important step towards the development of a bioartificial kidney. PMID:25527093

Schophuizen, Carolien M S; De Napoli, Ilaria E; Jansen, Jitske; Teixeira, Sandra; Wilmer, Martijn J; Hoenderop, Joost G J; Van den Heuvel, Lambert P W; Masereeuw, Rosalinde; Stamatialis, Dimitrios

2015-03-01

382

Fluorescent molecular rotor for the study of membrane fluidity in endothelial cells under fluid shear stress  

NASA Astrophysics Data System (ADS)

Molecular rotors are fluorescent probes that change quantum yield with the viscosity of their environment. When integrated into the cell membrane, they can be used to probe viscosity changes of the membrane. Fluid shear stress is hypothesized to increase membrane fluidity in the membrane of endothelial cells, a change that leads to the activation of heterotrimetric G proteins, thus activating a signal transduction cascade. This hypothesis was examined using a molecular rotor, 9-dicyanovinyl-julolidine (DCVJ) as membrane probe. The principal response, a decease of fluorescence intensity caused by increased membrane fluidity, was obtained by adding a fluidity-increasing agent to the cells. In a parallel-plate flow chamber, a confluent layer of DCVJ-labeled human umbilical cord venous endothelial cells were exposed to different levels of fluid shear stress. With increased shear, a reduced fluorescence intensity was observed, indicating an increase of membrane fluidity. Step changes of fluid shear stress caused an approximately linear drop of fluorescence within 5 seconds, showing fast and almost full recovery after shear stopped. A linear relationship between shear stress and membrane fluidity changes was also observed. This study not only shows the suitability of the molecular rotor DCVJ as a membrane fluidity probe, but also provides evidence for the direct link between fluid shear stress and membrane fluidity, and suggests that the membrane is the primary flow mechanosensor of the cell.

Haidekker, Mark A.; Frangos, John A.

2000-04-01

383

1. Introduction 2. Red blood cell (RBC)-based  

E-print Network

-coated nanoparticles present a major breakthrough in drug deli- very technology and show great promise for clinical by the macrophages of the mononuclear phagocyte system (MPS). The advent of `stealth' nanoparticles has had a great

Zhang, Liangfang

384

Computational Estimates of Membrane Flow and Tension Gradient in Motile Cells  

PubMed Central

All parts of motile cells, including the plasma membrane, have to translocate in the direction of locomotion. Both directed intracellular membrane transport coupled with polarized endo- and exocytosis and fluid flow in the plane of the plasma membrane can contribute to this overall plasma membrane translocation. It remains unclear how strong a force is required to generate this flow. We numerically solve Stokes equations for the viscous membrane flow across a flat plasma membrane surface in the presence of transmembrane proteins attached to the cytoskeleton and find the membrane tension gradient associated with this flow. This gradient is sensitive to the size and density of the transmembrane proteins attached to the cytoskeleton and can become significant enough to slow down cell movement. We estimate the influence of intracellular membrane transport and actin growth and contraction on the tension gradient, and discuss possible ‘tank tread’ flow at ventral and dorsal surfaces. PMID:24465414

Fogelson, Ben; Mogilner, Alex

2014-01-01

385

Cell invasion through basement membrane: the anchor cell breaches the barrier.  

PubMed

Cell invasion through basement membrane (BM) is a specialized cellular behavior critical to many normal developmental events, immune surveillance, and cancer metastasis. A highly dynamic process, cell invasion involves a complex interplay between cell-intrinsic elements that promote the invasive phenotype, and cell-cell and cell-BM interactions that regulate the timing and targeting of BM transmigration. The intricate nature of these interactions has made it challenging to study cell invasion in vivo and model in vitro. Anchor cell invasion in Caenorhabditis elegans is emerging as an important experimental paradigm for comprehensive analysis of BM invasion, revealing the gene networks that specify invasive behavior and the interactions that occur at the cell-BM interface. PMID:21632231

Hagedorn, Elliott J; Sherwood, David R

2011-10-01

386

Lipid regulation of cell membrane structure and function  

Microsoft Academic Search

Recent studies of structure-function relationships in biological membranes have revealed fundamental con- cepts concerning the regulation of cellular membrane function by membrane lipids. Considerable progress has been made in understanding the roles played by two membrane lipids: cholesterol and phosphatidyl- ethanolamine. Cholesterol has been shown to regulate ion pumps, which in some cases show an absolute de- pendence on cholesterol

PHILIP L. YEAGLE

387

Water-Free Proton-Conducting Membranes for Fuel Cells  

NASA Technical Reports Server (NTRS)

Poly-4-vinylpyridinebisulfate (P4VPBS) is a polymeric salt that has shown promise as a water-free proton-conducting material (solid electrolyte) suitable for use in membrane/electrode assemblies in fuel cells. Heretofore, proton-conducting membranes in fuel cells have been made from perfluorinated ionomers that cannot conduct protons in the absence of water and, consequently, cannot function at temperatures >100 C. In addition, the stability of perfluorinated ionomers at temperatures >100 C is questionable. However, the performances of fuel cells of the power systems of which they are parts could be improved if operating temperatures could be raised above 140 C. What is needed to make this possible is a solid-electrolyte material, such as P4VPBS, that can be cast into membranes and that both retains proton conductivity and remains stable in the desired higher operating temperature range. A family of solid-electrolyte materials different from P4VPBS was described in Anhydrous Proton-Conducting Membranes for Fuel Cells (NPO-30493), NASA Tech Briefs, Vol. 29, No. 8 (August 2005), page 48. Those materials notably include polymeric quaternized amine salts. If molecules of such a polymeric salt could be endowed with flexible chain structures, it would be possible to overcome the deficiencies of simple organic amine salts that must melt before being able to conduct protons. However, no polymeric quaternized amine salts have yet shown to be useful in this respect. The present solid electrolyte is made by quaternizing the linear polymer poly- 4-vinylpyridine (P4VP) to obtain P4VPBS. It is important to start with P4VP having a molecular weight of 160,000 daltons because P4VPBS made from lower-molecular-weight P4VP yields brittle membranes. In an experimental synthesis, P4VP was dissolved in methanol and then reacted with an excess of sulfuric acid to precipitate P4VPBS. The precipitate was recovered, washed several times with methanol to remove traces of acid, and dried to a white granular solid. In another synthesis, nanoparticles of silica rich with surface hydroxyl groups were added to P4VP in methanol solution, which was then reacted with excess sulfuric acid to precipitate granules of a composite that most probably had the composition (P4VPBS)-SiO2-SiO(HSO4)2. The granular P4VPBS produced in the first-mentioned synthesis was dissolved in water to make a glue-like, turbid solution; the granular P4VPBS/silica composite produced in the second-mentioned synthesis was mixed with water to make a turbid, glue-like suspension. The proportions of polymer salt to water in such preparations can be varied; it was found that approximately equal parts of water and polymer salt yield a solution or suspension amenable to further processing.

Narayanan, Sekharipuram; Yen, Shiao-Pin

2007-01-01

388

DEVELOPMENT OF NOVEL ELECTROCATALYSTS FOR PROTON EXCHANGE MEMBRANE FUEL CELLS  

SciTech Connect

Fuel cells are electrochemical devices that convert the available chemical free energy directly into electrical energy, without going through heat exchange process. Of all different types of fuel cells, the Proton Exchange Membrane Fuel Cell (PEMFC) is one of the most promising power sources for stand-alone utility and electric vehicle applications. Platinum (Pt) Catalyst is used for both fuel and air electrodes in PEMFCs. However, carbon monoxide (CO) contamination of H{sub 2} greatly affects electro catalysts used at the anode of PEMFCs and decreases cell performance. The irreversible poisoning of the anode can occur even in CO concentrations as low as few parts per million (ppm). In this work, we have synthesized several novel elctrocatalysts (Pt/C, Pt/Ru/C, Pt/Mo/C, Pt/Ir and Pt/Ru/Mo) for PEMFCs. These catalysts have been tested for CO tolerance in the H{sub 2}/air fuel cell, using CO concentrations in the H{sub 2} fuel that varies from 10 to 100 ppm. The performance of the electrodes was evaluated by determining the cell potential against current density. The effects of catalyst composition and electrode film preparation method on the performance of PEM fuel cell were also studied. It was found that at 70 C and 3.5 atm pressure at the cathode, Pt-alloy catalyst (10 wt% Pt/Ru/C, 20 wt% Pt/Mo/C) were more CO tolerant than the 20 wt% Pt/C catalyst alone. It was also observed that spraying method was better than the brushing technique for the preparation of electrode film.

Shamsuddin Ilias

2003-04-24

389

Membrane Type 1 Matrix Metalloproteinase Regulates Cellular Invasiveness and Survival in Cutaneous Epidermal Cells  

Microsoft Academic Search

Membrane type 1 matrix metalloproteinase is a member of the membrane-anchored matrix metalloproteinase family and is involved in tissue remodeling events ranging from tumor invasion and angiogenesis to growth and development. We sought to clarify the role of membrane type 1 matrix metalloproteinase in cutaneous epidermal cells using anti-sense cDNA expression in human keratinocytes. Modulation of membrane type 1 matrix

Usha Nagavarapu; Kenneth Relloma; G. Scott Herron

2002-01-01

390

Visualization of the heterogeneous membrane distribution of sphingomyelin associated with cytokinesis, cell polarity, and sphingolipidosis.  

PubMed

Sphingomyelin (SM) is a major sphingolipid in mammalian cells and is reported to form specific lipid domains together with cholesterol. However, methods to examine the membrane distribution of SM are limited. We demonstrated in model membranes that fluorescent protein conjugates of 2 specific SM-binding toxins, lysenin (Lys) and equinatoxin II (EqtII), recognize different membrane distributions of SM; Lys exclusively binds clustered SM, whereas EqtII preferentially binds dispersed SM. Freeze-fracture immunoelectron microscopy showed that clustered but not dispersed SM formed lipid domains on the cell surface. Glycolipids and the membrane concentration of SM affect the SM distribution pattern on the plasma membrane. Using derivatives of Lys and EqtII as SM distribution-sensitive probes, we revealed the exclusive accumulation of SM clusters in the midbody at the time of cytokinesis. Interestingly, apical membranes of differentiated epithelial cells exhibited dispersed SM distribution, whereas SM was clustered in basolateral membranes. Clustered but not dispersed SM was absent from the cell surface of acid sphingomyelinase-deficient Niemann-Pick type A cells. These data suggest that both the SM content and membrane distribution are crucial for pathophysiological events bringing therapeutic perspective in the role of SM membrane distribution.-Makino, A., Abe, M., Murate, M., Inaba, T., Yilmaz, N., Hullin-Matsuda, F., Kishimoto, T., Schieber, N. L., Taguchi, T., Arai, H., Anderluh, G., Parton, R. G., Kobayashi, T. Visualization of the heterogeneous membrane distribution of sphingomyelin associated with cytokinesis, cell polarity, and sphingolipidosis. PMID:25389132

Makino, Asami; Abe, Mitsuhiro; Murate, Motohide; Inaba, Takehiko; Yilmaz, Neval; Hullin-Matsuda, Françoise; Kishimoto, Takuma; Schieber, Nicole L; Taguchi, Tomohiko; Arai, Hiroyuki; Anderluh, Gregor; Parton, Robert G; Kobayashi, Toshihide

2015-02-01

391

In situ single molecule imaging of cell membranes: linking basic nanotechniques to cell biology, immunology and medicine  

NASA Astrophysics Data System (ADS)

The cell membrane, which consists of a viscous phospholipid bilayer, different kinds of proteins and various nano/micrometer-sized domains, plays a very important role in ensuring the stability of the intracellular environment and the order of cellular signal transductions. Exploring the precise cell membrane structure and detailed functions of the biomolecules in a cell membrane would be helpful to understand the underlying mechanisms involved in cell membrane signal transductions, which could further benefit research into cell biology, immunology and medicine. The detection of membrane biomolecules at the single molecule level can provide some subtle information about the molecular structure and the functions of the cell membrane. In particular, information obtained about the molecular mechanisms and other information at the single molecule level are significantly different from that detected from a large amount of biomolecules at the large-scale through traditional techniques, and can thus provide a novel perspective for the study of cell membrane structures and functions. However, the precise investigations of membrane biomolecules prompts researchers to explore cell membranes at the single molecule level by the use of in situ imaging methods, as the exact conformation and functions of biomolecules are highly controlled by the native cellular environment. Recently, the in situ single molecule imaging of cell membranes has attracted increasing attention from cell biologists and immunologists. The size of biomolecules and their clusters on the cell surface are set at the nanoscale, which makes it mandatory to use high- and super-resolution imaging techniques to realize the in situ single molecule imaging of cell membranes. In the past few decades, some amazing imaging techniques and instruments with super resolution have been widely developed for molecule imaging, which can also be further employed for the in situ single molecule imaging of cell membranes. In this review, we attempt to summarize the characteristics of these advanced techniques for use in the in situ single molecule imaging of cell membranes. We believe that this work will help to promote the technological and methodological developments of super-resolution techniques for the single molecule imaging of cell membranes and help researchers better understand which technique is most suitable for their future exploring of membrane biomolecules; ultimately promoting further developments in cell biology, immunology and medicine.

Pi, Jiang; Jin, Hua; Yang, Fen; Chen, Zheng W.; Cai, Jiye

2014-10-01

392

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

393

Volume-sensitive chloride conductance in bovine chromaffin cell membrane.  

PubMed Central

1. Bovine chromaffin cells were inflated by pressure applied through a pipette or swollen during intracellular perfusion with hypertonic solutions. Effects of such procedures on electrical properties of the membrane were studied by a combination of the tight-seal whole-cell patch-clamp technique and Fura-2 fluorescence measurements of free intracellular calcium concentration ([Ca2+]i). 2. Application of air pressure (about +5 cmH2O or 490 Pa) through the patch pipette caused an increase in the cell volume and concomitant development of an inwardly directed transient current at the holding potential of -60 mV. The current gradually increased to a peak value and subsequently decayed almost to its initial level within 5-10 min. A short pulse of pressure (5-10 s) was sufficient to elicit the whole sequence of events. 3. Intracellular free Ca2+ ion concentration, [Ca2+]i, steeply increased at the beginning of the pressure pulse to about 0.2 microM and either stayed at this level or decayed back to the more usual value of approximately 0.1 microM. 4. Similar changes in the transmembrane current and [Ca2+]i were observed during intracellular perfusion of cells with hypertonic solutions (30-50 mosM difference relative to the bath solution) or during extracellular application of hypotonic solution. 5. Swelling of non-perfused cells by extracellular application of hyposmotic solution caused the appearance of inward currents in cell-attached membrane patches held at a fixed potential -30 mV relative to the cell's resting potential. The kinetics of the current resembled those of the whole-cell current. 6. Intracellular introduction of guanosine triphosphate (GTP, 300 microM) significantly prolonged the duration (from 62 +/- 10 s, n = 5, to 98 +/- 8 s, n = 4, when measured at the level of half-amplitude), while introduction of the non-hydrolysable analogue of guanosine diphosphate (GDP), guanosine 5'-O-(2-thiodiphosphate) (GDP beta S, 300 microM), decreased the maximal rate of increase (from 11.4 +/- 2.6 pA/s, n = 6, to 3.2 +/- 2.1 pA/s, n = 10) of the current activated by pressure. 7. Lowering of the intracellular free Ca2+ ion concentration by introduction of 10 mM-EGTA did not significantly affect the current amplitude or time course. However, a rapid increase in the [Ca2+]i to micromolar levels (by activation of the voltage-operated calcium channels during membrane depolarization) could terminate development of the current activated by pressure and cause its fast decay to zero-current level.(ABSTRACT TRUNCATED AT 400 WORDS) Images Fig. 5 PMID:1326043

Doroshenko, P; Neher, E

1992-01-01

394

Red blood cells serve as intravascular carriers of myeloperoxidase.  

PubMed

Myeloperoxidase (MPO) is a heme enzyme abundantly expressed in polymorphonuclear neutrophils. MPO is enzymatically capable of catalyzing the generation of reactive oxygen species (ROS) and the consumption of nitric oxide (NO). Thus MPO has both potent microbicidal and, upon binding to the vessel wall, pro-inflammatory properties. Interestingly, MPO - a highly cationic protein - has been shown to bind to both endothelial cells and leukocyte membranes. Given the anionic surface charge of red blood cells, we investigated binding of MPO to erythrocytes. Red blood cells (RBCs) derived from patients with elevated MPO plasma levels showed significantly higher amounts of MPO by flow cytometry and ELISA than healthy controls. Heparin-induced MPO-release from patient-derived RBCs was significantly increased compared to controls. Ex vivo experiments revealed dose and time dependency for MPO-RBC binding, and immunofluorescence staining as well as confocal microscopy localized MPO-RBC interaction to the erythrocyte plasma membrane. NO-consumption by RBC-membrane fragments (erythrocyte "ghosts") increased with incrementally greater concentrations of MPO during incubation, indicating preserved catalytic MPO activity. In vivo infusion of MPO-loaded RBCs into C57BL/6J mice increased local MPO tissue concentrations in liver, spleen, lung, and heart tissue as well as within the cardiac vasculature. Further, NO-dependent relaxation of aortic rings was altered by RBC bound-MPO and systemic vascular resistance significantly increased after infusion of MPO-loaded RBCs into mice. In summary, we find that MPO binds to RBC membranes in vitro and in vivo, is transported by RBCs to remote sites in mice, and affects endothelial function as well as systemic vascular resistance. RBCs may avidly bind circulating MPO, and act as carriers of this leukocyte-derived enzyme. PMID:24976018

Adam, Matti; Gajdova, Silvie; Kolarova, Hana; Kubala, Lukas; Lau, Denise; Geisler, Anne; Ravekes, Thorben; Rudolph, Volker; Tsao, Philip S; Blankenberg, Stefan; Baldus, Stephan; Klinke, Anna

2014-09-01

395

Annexin-A5 assembled into two-dimensional arrays promotes cell membrane repair  

PubMed Central

Eukaryotic cells possess a universal repair machinery that ensures rapid resealing of plasma membrane disruptions. Before resealing, the torn membrane is submitted to considerable tension, which functions to expand the disruption. Here we show that annexin-A5 (AnxA5), a protein that self-assembles into two-dimensional (2D) arrays on membranes upon Ca2+ activation, promotes membrane repair. Compared with wild-type mouse perivascular cells, AnxA5-null cells exhibit a severe membrane repair defect. Membrane repair in AnxA5-null cells is rescued by addition of AnxA5, which binds exclusively to disrupted membrane areas. In contrast, an AnxA5 mutant that lacks the ability of forming 2D arrays is unable to promote membrane repair. We propose that AnxA5 participates in a previously unrecognized step of the membrane repair process: triggered by the local influx of Ca2+, AnxA5 proteins bind to torn membrane edges and form a 2D array, which prevents wound expansion and promotes membrane resealing. PMID:21468022

Bouter, Anthony; Gounou, Céline; Bérat, Rémi; Tan, Sisareuth; Gallois, Bernard; Granier, Thierry; d'Estaintot, Béatrice Langlois; Pöschl, Ernst; Brachvogel, Bent; Brisson, Alain R.

2011-01-01

396

Changes in surface area of intact guard cells are correlated with membrane internalization.  

PubMed

Guard cells must maintain the integrity of the plasma membrane as they undergo large, rapid changes in volume. It has been assumed that changes in volume are accompanied by changes in surface area, but mechanisms for regulating plasma membrane surface area have not been identified in intact guard cells, and the extent to which surface area of the guard cells changes with volume has never been determined. The alternative hypothesis-that surface area remains approximately constant because of changes in shape-has not been investigated. To address these questions, we determined surface area for intact guard cells of Vicia faba as they underwent changes in volume in response to changes in the external osmotic potential. We also estimated membrane internalization for these cells. Epidermal peels were subjected to external solutions of varying osmotic potential to shrink and swell the guard cells. A membrane-specific fluorescent dye was used to identify the plasma membrane, and confocal microscopy was used to acquire a series of optical paradermal sections of the guard cell pair at each osmotic potential. Solid digital objects representing the guard cells were created from the membrane outlines identified in these paradermal sections, and surface area, volume, and various linear dimensions were determined for these solid objects. Surface area decreased by as much as 40% when external osmotic potential was increased from 0 to 1.5 MPa, and surface area varied linearly with volume. Membrane internalization was approximated by determining the amount of the fluorescence in the cell's interior. This value was shown to increase approximately linearly with decreases in the cell's surface area. The changes in surface area, volume, and membrane internalization were reversible when the guard cells were returned to a buffer solution with an osmotic potential of approximately zero. The data show that intact guard cells undergo changes in surface area that are too large to be accommodated by plasma membrane stretching and shrinkage and suggest that membrane is reversibly internalized to maintain cell integrity. PMID:14551331

Shope, Joseph C; DeWald, Daryll B; Mott, Keith A

2003-11-01

397

Six cell 'single cell' stack diagnostics and membrane electrode assembly evaluation  

SciTech Connect

Polymer electrolyte fuel cells are promising candidates as energy conversion devices in applications from portable power to stationary applications or electric vehicles. In order to achieve practical voltage, power and energy density, stacks are employed for almost all applications. Here, we present a six-cell 'single cell' stack in which individual cells can be isolated from the stack by current carrying leads found within each of the bipolar plates. The current carrying leads allow individual cells to be isolated from the rest of the stack, so that cells can either be tested together or independently. The design of the stack, utility for specific applications, including stack diagnostics and membrane electrode assembly (MEA) testing, and some experimental results, obtained using the stack, are presented. Special focus is given in this paper to the area of direct methanol fuel cell (DMFC) stacks, however the equipment and many of the experimental results presented are appropriate for other fuel cell systems.

Pivovar, B. S. (Bryan Scott); Le Scornet, F. (Francois); Eickes, C. (Christian); Zawodzinski, C. (Christine); Purdy, G. M. (Geraldine M.); Wilson, M. S. (Mahlon S.); Zelenay, P. (Piotr)

2002-01-01

398