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Sample records for membrane sodium transport

  1. Membrane potential and conductance during transport of sodium, potassium and rubidium in frog muscle.

    PubMed

    Adrian, R H; Slayman, C L

    1966-06-01

    explained on the basis of a fall of the potassium or rubidium concentration in a region of the extracellular space immediately external to the membrane. It is argued that certain characteristics of the hyperpolarization make it difficult to explain the hyperpolarization on this basis alone, though some part of it may be due to extracellular depletion of either potassium or rubidium.The main conclusion is that the sodium pump is capable of transferring electric charge across the membrane in which it is operating, but that, in a given time, the net charge transferred is less than the charge on the sodium ions that the pump has transported, by an amount that corresponds to the charge on the potassium or rubidium ions chemically transported by the pump.

  2. Membrane potential and conductance during transport of sodium, potassium and rubidium in frog muscle

    PubMed Central

    Adrian, R. H.; Slayman, C. L.

    1966-01-01

    on the basis of a fall of the potassium or rubidium concentration in a region of the extracellular space immediately external to the membrane. It is argued that certain characteristics of the hyperpolarization make it difficult to explain the hyperpolarization on this basis alone, though some part of it may be due to extracellular depletion of either potassium or rubidium. The main conclusion is that the sodium pump is capable of transferring electric charge across the membrane in which it is operating, but that, in a given time, the net charge transferred is less than the charge on the sodium ions that the pump has transported, by an amount that corresponds to the charge on the potassium or rubidium ions chemically transported by the pump. PMID:5912216

  3. Allosteric Mechanisms of Molecular Machines at the Membrane: Transport by Sodium-Coupled Symporters.

    PubMed

    LeVine, Michael V; Cuendet, Michel A; Khelashvili, George; Weinstein, Harel

    2016-06-08

    Solute transport across cell membranes is ubiquitous in biology as an essential physiological process. Secondary active transporters couple the unfavorable process of solute transport against its concentration gradient to the energetically favorable transport of one or several ions. The study of such transporters over several decades indicates that their function involves complex allosteric mechanisms that are progressively being revealed in atomistic detail. We focus on two well-characterized sodium-coupled symporters: the bacterial amino acid transporter LeuT, which is the prototype for the "gated pore" mechanism in the mammalian synaptic monoamine transporters, and the archaeal GltPh, which is the prototype for the "elevator" mechanism in the mammalian excitatory amino acid transporters. We present the evidence for the role of allostery in the context of a quantitative formalism that can reconcile biochemical and biophysical data and thereby connects directly to recent insights into the molecular structure and dynamics of these proteins. We demonstrate that, while the structures and mechanisms of these transporters are very different, the available data suggest a common role of specific models of allostery in their functions. We argue that such allosteric mechanisms appear essential not only for sodium-coupled symport in general but also for the function of other types of molecular machines in the membrane.

  4. Aldosterone induction of electrogenic sodium transport in the apical membrane vesicles of rat distal colon

    SciTech Connect

    Rajendran, V.M.; Kashgarian, M.; Binder, H.J. )

    1989-11-05

    Na-H exchange is present in apical membrane vesicles (AMV) isolated from distal colon of normal rats. Because in intact tissue aldosterone both induces amiloride-sensitive electrogenic sodium transport and inhibits electroneutral sodium absorption, these studies with AMV were designed to establish the effect of aldosterone on sodium transport. An outward-directed proton gradient stimulated 22Na uptake in AMV isolated from distal colon of normal and dietary sodium depleted (with elevated aldosterone levels) experimental rats. Unlike normal AMV, proton gradient-dependent 22Na uptake in experimental AMV was inhibited when uptake was measured under voltage-clamped conditions. 10 microM amiloride inhibited the initial rate of proton gradient-dependent 22Na uptake in AMV of normal and experimental rats by 30 and 75%, respectively. In contrast, 1 mM amiloride produced comparable inhibition (90 and 80%) of 22Na uptake in normal and experimental AMV. Intravesicular-negative potential stimulated 22Na uptake in experimental but not in normal AMV. This increase was inhibited by 90% by 10 microM amiloride. An analogue of amiloride, 5-(N-ethylisopropyl) amiloride (1 microM), a potent inhibitor of electroneutral Na-H exchange in AMV of normal rat distal colon, did not alter potassium diffusion potential-dependent 22Na uptake. Increasing sodium concentration saturated proton gradient-dependent 22Na uptake in normal AMV. However, in experimental AMV, 22Na uptake stimulated by both proton gradient and potassium diffusion potential did not saturate as a function of increasing sodium concentration. We conclude from these results that an electrically sensitive conductive channel, not electroneutral Na-H exchange, mediates 22Na uptake in AMV isolated from the distal colon of aldosterone rats.

  5. Analysis of Porphyra membrane transporters demonstrates gene transfer among photosynthetic eukaryotes and numerous sodium-coupled transport systems.

    PubMed

    Chan, Cheong Xin; Zäuner, Simone; Wheeler, Glen; Grossman, Arthur R; Prochnik, Simon E; Blouin, Nicolas A; Zhuang, Yunyun; Benning, Christoph; Berg, Gry Mine; Yarish, Charles; Eriksen, Renée L; Klein, Anita S; Lin, Senjie; Levine, Ira; Brawley, Susan H; Bhattacharya, Debashish

    2012-04-01

    Membrane transporters play a central role in many cellular processes that rely on the movement of ions and organic molecules between the environment and the cell, and between cellular compartments. Transporters have been well characterized in plants and green algae, but little is known about transporters or their evolutionary histories in the red algae. Here we examined 482 expressed sequence tag contigs that encode putative membrane transporters in the economically important red seaweed Porphyra (Bangiophyceae, Rhodophyta). These contigs are part of a comprehensive transcriptome dataset from Porphyra umbilicalis and Porphyra purpurea. Using phylogenomics, we identified 30 trees that support the expected monophyly of red and green algae/plants (i.e. the Plantae hypothesis) and 19 expressed sequence tag contigs that show evidence of endosymbiotic/horizontal gene transfer involving stramenopiles. The majority (77%) of analyzed contigs encode transporters with unresolved phylogenies, demonstrating the difficulty in resolving the evolutionary history of genes. We observed molecular features of many sodium-coupled transport systems in marine algae, and the potential for coregulation of Porphyra transporter genes that are associated with fatty acid biosynthesis and intracellular lipid trafficking. Although both the tissue-specific and subcellular locations of the encoded proteins require further investigation, our study provides red algal gene candidates associated with transport functions and novel insights into the biology and evolution of these transporters.

  6. Sodium-dependent methyl 1-thio-beta-D-galactopyranoside transport in membrane vesicles isolated from Salmonella typhimurium.

    PubMed

    Tokuda, H; Kaback, H R

    1977-05-17

    Membrane vesicles isolated from Salmonella typhimurium G-30 grown in the presence of melibiose catalyze methyl 1-thio-beta-D-galactopyranoside (TMG) transport in the presence of sodium or lithium, as shown initially with intact cells by Stock and Roseman (Stock, J., and Roseman, S. (1971), Biochem. Biophys. Res. Commun. 44, 132). TMG-dependent sodium uptake is also observed, but only when a potassium diffusion potential (interior negative) is induced across the vesicle membrane. Cation-dependent TMG accumulation varies with the electrochemical gradient of protons generated as a result of D-lactate oxidation, and the vesicles catalyze D-lactate-dependent sodium efflux in a manner which is consistent with the operation of a proton-sodium exchange mechanism. Although the stoichiometry between sodium and TMG appears to be 1:1 when transport is induced by a potassium diffusion potential, evidence is presented which indicates that the relationship may exceed unity under certain conditions. The results are explained in terms of a model in which TMG-sodium (lithium) symport is driven by an electrochemical gradient of protons which functions to maintain a low intravesicular sodium or lithium concentration through proton--sodium (lithium) antiport.

  7. Effects of cell volume changes on membrane ionic permeabilities and sodium transport in frog skin (Rana ridibunda).

    PubMed Central

    Costa, P M; Fernandes, P L; Ferreira, H G; Ferreira, K T; Giraldez, F

    1987-01-01

    dilution of the serosal bath. Cells repolarized when exposed to low-osmolality solutions after being in the absence of serosal chloride or sodium. The repolarization ran in parallel with the restoration of the short-circuit current and the potassium selectivity of the serosal membrane. 6. The results show that the effects produced by the removal of sodium or chloride ions from the serosal bathing solution are most probably mediated by a reduction in cell volume. Cell volume changes would lead to changes in the serosal membrane selectivity to potassium and thus to changes in cell membrane potential and sodium transport.(ABSTRACT TRUNCATED AT 400 WORDS) PMID:2451735

  8. Light-dependent delta pH and membrane potential changes in halobacterial vesicles coupled to sodium transport

    SciTech Connect

    Kamo, N.; Racanelli, T.; Packer, L.

    1982-01-01

    Bacteriorhodopsin and Halorhodopsin present in Halobacterium halobium strains have been investigated in relation to Na/sup +//H/sup +/ exchange in isolated cell envelope vesicles. Upon illumination, these retinal proteins result in extrusion of sodium ions by either an electrogenic Na/sup +//Ha/sup +/ antiporter and/or a direct sodium pump. Since a molecular characterization of these mechanism(s) of sodium extrusion has not yet been realized, it was of interest to measure directly the light- and sodium-dependent changes in delta pH and membrane potential under nearly identical conditions in S9 and R1mR cell membrane vesicles to gain information on the relation of these retinal proteins to sodium extrusion. These activities were evaluated in terms of their dependence on light intensity, and on the inhibitory effect of chemical modifiers of carboxyl groups (carbodiimides); electroneutral exchanges (monensin and triphenyltin); digitoxin and some analogues; and phloretin. Under most of the conditions and treatments employed, light- and sodium-dependent delta pH led to similar effects in both membrane vesicle types. Hence, it is concluded that the delta pH and delta psi which arise from sodium transport occur by either a single mechanism or by one which shares common features.

  9. Plant nutrition 1: membrane transport and energetics, potassium nutrition, and sodium toxicity.

    PubMed

    2014-09-01

    In this first of three lessons spanning the topic of Plant Nutrition, we examine primarily the energetics and mechanisms of nutrient uptake and transport. These processes are particularly well illustrated by an examination of the essential nutrient potassium (K), and the closely related element sodium (Na). We also examine the challenges associated with providing plants with sufficient K to support vigorous growth, and the detrimental effects of sodium accumulation in soils. Finally, we examine efforts to improve the salinity tolerance of crop plants.

  10. Modulation of glycosylation and transport of viral membrane glycoproteins by a sodium ionophore

    PubMed Central

    1983-01-01

    Analysis of viral glycoprotein expression on surfaces of monensin- treated cells using a fluorescence-activated cell sorter (FACS) demonstrated that the sodium ionophore completely inhibited the appearance of the vesicular stomatitis virus (VSV) G protein on (Madin- Darby canine kidney) MDCK cell surfaces. In contrast, the expression of the influenza virus hemagglutinin (HA) glycoprotein on the surfaces of MDCK cells was observed to occur at high levels, and the time course of its appearance was not altered by the ionophore. Viral protein synthesis was not inhibited by monensin in either VSV- or influenza virus-infected cells. However, the electrophoretic mobilities of viral glycoproteins were altered, and analysis of pronase-derived glycopeptides by gel filtration indicated that the addition of sialic acid residues to the VSV G protein was impaired in monensin-treated cells. Reduced incorporation of fucose and galactose into influenza virus HA was observed in the presence of the ionophore, but the incompletely processed HA protein was cleaved, transported to the cell surface, and incorporated into budding virus particles. In contrast to the differential effects of monensin on VSV and influenza virus replication previously observed in monolayer cultures of MDCK cells, yields of both viruses were found to be significantly reduced by high concentrations of monensin in suspension cultures, indicating that cellular architecture may play a role in determining the sensitivity of virus replication to the drug. Nigericin, an ionophore that facilitates transport of potassium ions across membranes, blocked the replication of both influenza virus and VSV in MDCK cell monolayers, indicating that the ion specificity of ionophores influences their effect on the replication of enveloped viruses. PMID:6309867

  11. Reconstitution of the renal brush-border membrane sodium/phosphate co-transporter.

    PubMed Central

    Vachon, V; Delisle, M C; Laprade, R; Béliveau, R

    1991-01-01

    A simple and rapid procedure was developed for the reconstitution of Na(+)-dependent phosphate-transport activity from bovine kidney brush-border membranes. The phosphate transporter appears to be particularly sensitive to extraction conditions. To prevent its inactivation, the phosphate carrier was solubilized in a buffer containing its substrates, Na+ and phosphate, CHAPS, dithiothreitol, brush-border membrane lipids and glycerol. The uptake of phosphate by reconstituted vesicles was strongly stimulated by the presence of a transmembrane Na+ gradient. This stimulation was abolished when the Na+ gradient was dissipated by monensin. The affinity of the carrier for phosphate was similar in proteoliposomes and in brush-border membrane vesicles (apparent Kt = 40 microM). The transporter was also stimulated by the presence of a high concentration of phosphate on the trans side of the membrane. The reconstituted transport activity was inhibited by arsenate, a known inhibitor of phosphate transport. However, the bovine phosphate carrier, intact or reconstituted, was much less sensitive to inhibition by phosphonoformic and phosphonoacetic acids than were those of other species studied so far. SDS/PAGE revealed that only a small number of brush-border membrane proteins were incorporated into the proteoliposomes. This reconstitution procedure should be useful for the purification and identification of the carrier protein. Images Fig. 5. PMID:1832858

  12. Indirect coupling of urate and p-aminohippurate transport to sodium in human brush-border membrane vesicles.

    PubMed

    Roch-Ramel, F; Guisan, B; Schild, L

    1996-01-01

    [14C]urate and p-[14C]aminohippurate (PAH) uptake by human brush-border membrane vesicles (BBMV) were measured in the presence of an inwardly oriented sodium gradient. No direct sodium cotransport was observed. Indirect [14C]urate coupling to sodium transport was demonstrated by cis-stimulation of [14C]urate with nicotinate or pyrazinoate (PZA) in the extravesicular medium but not by adding lactate, alpha-ketoglutarate, or beta-hydroxybutyrate. Indirect sodium coupling of [14C]PAH uptake was observed only when alpha-ketoglutarate was added to the extravesicular medium, a mechanism similar to that of basolateral membranes. The ability for PZA (and nicotinate) to cis-stimulate urate uptake was correlated with a high apparent affinity for the urate/anion exchanger. In urate-loaded vesicles, for identical medium concentrations, [14C]PZA uptake via the urateanion exchanger was 10 times higher than [14C]lactate uptake. Such high PZA affinity for the urate exchanger, working in parallel with PZA sodium cotransport can account for the stimulation of urate reabsorption by PZA in vivo.

  13. Role of rat sodium/phosphate cotransporters in the cell membrane transport of arsenate

    SciTech Connect

    Villa-Bellosta, Ricardo Sorribas, Victor

    2008-10-01

    Inorganic arsenate (As{sup V}) is a common contaminant of underground water. Following oral exposure, it is assumed that As{sup V} is distributed and crosses cell membranes through inorganic phosphate (Pi) transporters. We have tested this hypothesis by studying the inhibition of rat Na/Pi cotransporters by As{sup V} in Xenopus laevis oocytes and in several rat tissues. The ubiquitously expressed type III Pi transporters (PiT-1 and PiT-2) showed a low affinity for As{sup V} (K{sub i} {approx} 3.8 mM), similar to the Pi transport system in aortic vascular smooth muscle cells (K{sub i} 1.5 mM). The type II renal isoforms, NaPi-IIa and NaPi-IIc, were also poorly inhibited by As{sup V} (K{sub i} {approx} 1 mM), similar to the Pi transport from kidney cortex brush-border membrane (BBM) vesicles. Conversely, the high-affinity intestinal transporter, NaPi-IIb, was very efficiently inhibited with a K{sub i} of 51 {mu}M, similar to the Pi transport from intestinal BBM vesicles. Taking into account the 1.1 mM Pi in blood and renal ultrafiltrate, and the nanomolar range of As{sup V} exposures, we have determined that the contribution by Na/Pi cotransporters to As{sup V} membrane transport is negligible, given that 10-15 mM As{sup V} would be necessary in these fluids to be significantly transported. Intestinal transport is an exception, because Pi competition is weak, thereby considering that its concentration in lumen mainly depends on low Pi levels from ingested fresh water, and because As{sup V} very efficiently inhibits Pi intestinal transport. Our data agree with current toxicokinetic knowledge, and they explain the asymmetric excretion of trivalent and pentavalent arsenic species into bile and urine.

  14. Role of rat sodium/phosphate cotransporters in the cell membrane transport of arsenate.

    PubMed

    Villa-Bellosta, Ricardo; Sorribas, Víctor

    2008-10-01

    Inorganic arsenate (As(V)) is a common contaminant of underground water. Following oral exposure, it is assumed that As(V) is distributed and crosses cell membranes through inorganic phosphate (Pi) transporters. We have tested this hypothesis by studying the inhibition of rat Na/Pi cotransporters by As(V) in Xenopus laevis oocytes and in several rat tissues. The ubiquitously expressed type III Pi transporters (PiT-1 and PiT-2) showed a low affinity for As(V) (K(i) approximately 3.8 mM), similar to the Pi transport system in aortic vascular smooth muscle cells (K(i) 1.5 mM). The type II renal isoforms, NaPi-IIa and NaPi-IIc, were also poorly inhibited by As(V) (K(i) approximately 1 mM), similar to the Pi transport from kidney cortex brush-border membrane (BBM) vesicles. Conversely, the high-affinity intestinal transporter, NaPi-IIb, was very efficiently inhibited with a K(i) of 51 microM, similar to the Pi transport from intestinal BBM vesicles. Taking into account the 1.1 mM Pi in blood and renal ultrafiltrate, and the nanomolar range of As(V) exposures, we have determined that the contribution by Na/Pi cotransporters to As(V) membrane transport is negligible, given that 10-15 mM As(V) would be necessary in these fluids to be significantly transported. Intestinal transport is an exception, because Pi competition is weak, thereby considering that its concentration in lumen mainly depends on low Pi levels from ingested fresh water, and because As(V) very efficiently inhibits Pi intestinal transport. Our data agree with current toxicokinetic knowledge, and they explain the asymmetric excretion of trivalent and pentavalent arsenic species into bile and urine.

  15. Membrane Na+-pyrophosphatases can transport protons at low sodium concentrations.

    PubMed

    Luoto, Heidi H; Nordbo, Erika; Baykov, Alexander A; Lahti, Reijo; Malinen, Anssi M

    2013-12-06

    Membrane-bound Na(+)-pyrophosphatase (Na(+)-PPase), working in parallel with the corresponding ATP-energized pumps, catalyzes active Na(+) transport in bacteria and archaea. Each ~75-kDa subunit of homodimeric Na(+)-PPase forms an unusual funnel-like structure with a catalytic site in the cytoplasmic part and a hydrophilic gated channel in the membrane. Here, we show that at subphysiological Na(+) concentrations (<5 mM), the Na(+)-PPases of Chlorobium limicola, four other bacteria, and one archaeon additionally exhibit an H(+)-pumping activity in inverted membrane vesicles prepared from recombinant Escherichia coli strains. H(+) accumulation in vesicles was measured with fluorescent pH indicators. At pH 6.2-8.2, H(+) transport activity was high at 0.1 mM Na(+) but decreased progressively with increasing Na(+) concentrations until virtually disappearing at 5 mM Na(+). In contrast, (22)Na(+) transport activity changed little over a Na(+) concentration range of 0.05-10 mM. Conservative substitutions of gate Glu(242) and nearby Ser(243) and Asn(677) residues reduced the catalytic and transport functions of the enzyme but did not affect the Na(+) dependence of H(+) transport, whereas a Lys(681) substitution abolished H(+) (but not Na(+)) transport. All four substitutions markedly decreased PPase affinity for the activating Na(+) ion. These results are interpreted in terms of a model that assumes the presence of two Na(+)-binding sites in the channel: one associated with the gate and controlling all enzyme activities and the other located at a distance and controlling only H(+) transport activity. The inherent H(+) transport activity of Na(+)-PPase provides a rationale for its easy evolution toward specific H(+) transport.

  16. L-Carnitine transport in human placental brush-border membranes is mediated by the sodium-dependent organic cation transporter OCTN2.

    PubMed

    Lahjouji, Karim; Elimrani, Ihsan; Lafond, Julie; Leduc, Line; Qureshi, Ijaz A; Mitchell, Grant A

    2004-08-01

    Maternofetal transport of l-carnitine, a molecule that shuttles long-chain fatty acids to the mitochondria for oxidation, is thought to be important in preparing the fetus for its lipid-rich postnatal milk diet. Using brush-border membrane (BBM) vesicles from human term placentas, we showed that l-carnitine uptake was sodium and temperature dependent, showed high affinity for carnitine (apparent K(m) = 11.09 +/- 1.32 microM; V(max) = 41.75 +/- 0.94 pmol.mg protein(-1).min(-1)), and was unchanged over the pH range from 5.5 to 8.5. l-Carnitine uptake was inhibited in BBM vesicles by valproate, verapamil, tetraethylammonium, and pyrilamine and by structural analogs of l-carnitine, including d-carnitine, acetyl-d,l-carnitine, and propionyl-, butyryl-, octanoyl-, isovaleryl-, and palmitoyl-l-carnitine. Western blot analysis revealed that OCTN2, a high-affinity, Na(+)-dependent carnitine transporter, was present in placental BBM but not in isolated basal plasma membrane vesicles. The reported properties of OCTN2 resemble those observed for l-carnitine uptake in placental BBM vesicles, suggesting that OCTN2 may mediate most maternofetal carnitine transport in humans.

  17. Changes in sodium pool and kinetics of sodium transport in frog skin produced by amiloride

    PubMed Central

    Salako, L. A.; Smith, A. J.

    1970-01-01

    1. Amiloride produces a decrease in size of the active sodium transport pool of isolated frog skin. 2. Rate coefficients for sodium movement into and out of the transporting cells across the outside membrane are decreased by amiloride. The rate coefficient for sodium extrusion across the inside membrane is not significantly affected. 3. In the presence and in the absence of amiloride, the relation of sodium transport to outside sodium concentration exhibits similar saturation kinetics but amiloride reduces sodium transport rate at every sodium concentration of the outside solution. 4. Labelling of skin with 14C-amiloride from the outside solution is significantly greater than labelling with 14C-inulin. 5. The results of these studies suggest that amiloride reacts with sites on the outside membrane of the transporting cells as a result of which the rate of sodium movement across this membrane is diminished. PMID:5420148

  18. Sulphate-ion/sodium-ion co-transport by brush-border membrane vesicles isolated from rat kidney cortex

    PubMed Central

    Lücke, Heinrich; Stange, Gertraud; Murer, Heini

    1979-01-01

    Uptake of SO42− into brush-border membrane vesicles isolated from rat kindey cortex by a Ca2+-precipitation method was investigated by using a rapid-filtration technique. Uptake of SO42− by the vesicles was osmotically sensitive and represented transport into an intra-vesicular space. Transport of SO42− by brush-border membranes was stimulated in the presence of Na+, compared with the presence of K+ or other univalent cations. A typical `overshoot' phenomenon was observed in the presence of an NaCl gradient (100mm-Na+ outside/zero mm-Na+ inside). Radioactive-SO42− exchange was faster in the presence of Na+ than in the presence of K+. Addition of gramicidin-D, an ionophore for univalent cations, decreased the Na+-gradient-driven SO42− uptake. SO42− uptake was only saturable in the presence of Na+. Counter-transport of Na+-dependent SO42− transport was shown with MoO42− and S2O32−, but not with PO42−. Changing the electrical potential difference across the vesicle membrane by establishing different diffusion potentials (anion replacement; K+ gradient±valinomycin) was not able to alter Na+-dependent SO42− uptake. The experiments indicate the presence of an electroneutral Na+/SO42−-co-transport system in brush-border membrane vesicles isolated from rat kidney cortex. PMID:91368

  19. Electrolytic process to produce sodium hypochlorite using sodium ion conductive ceramic membranes

    DOEpatents

    Balagopal, Shekar; Malhotra, Vinod; Pendleton, Justin; Reid, Kathy Jo

    2012-09-18

    An electrochemical process for the production of sodium hypochlorite is disclosed. The process may potentially be used to produce sodium hypochlorite from seawater or low purity un-softened or NaCl-based salt solutions. The process utilizes a sodium ion conductive ceramic membrane, such as membranes based on NASICON-type materials, in an electrolytic cell. In the process, water is reduced at a cathode to form hydroxyl ions and hydrogen gas. Chloride ions from a sodium chloride solution are oxidized in the anolyte compartment to produce chlorine gas which reacts with water to produce hypochlorous and hydrochloric acid. Sodium ions are transported from the anolyte compartment to the catholyte compartment across the sodium ion conductive ceramic membrane. Sodium hydroxide is transported from the catholyte compartment to the anolyte compartment to produce sodium hypochlorite within the anolyte compartment.

  20. Formaldehyde impairs transepithelial sodium transport

    PubMed Central

    Cui, Yong; Li, Huiming; Wu, Sihui; Zhao, Runzhen; Du, Deyi; Ding, Yan; Nie, Hongguang; Ji, Hong-Long

    2016-01-01

    Unsaturated oxidative formaldehyde is a noxious aldehyde in cigarette smoke that causes edematous acute lung injury. However, the mechanistic effects of formaldehyde on lung fluid transport are still poorly understood. We examined how formaldehyde regulates human epithelial sodium channels (ENaC) in H441 and expressed in Xenopus oocytes and exposed mice in vivo. Our results showed that formaldehyde reduced mouse transalveolar fluid clearance in vivo. Formaldehyde caused a dose-dependent inhibition of amiloride-sensitive short-circuit Na+ currents in H441 monolayers and of αβγ-ENaC channel activity in oocytes. α-ENaC protein was reduced, whereas phosphorylation of the extracellular regulated protein kinases 1 and 2 (ERK1/2) increased significantly post exposure. Moreover, both α- and γ-ENaC transcripts were down-regulated. Reactive oxygen species (ROS) was elevated significantly by formaldehyde in addition to markedly augmented membrane permeability of oocytes. These data suggest that formaldehyde contributes to edematous acute lung injury by reducing transalveolar Na+ transport, through decreased ENaC activity and enhanced membrane depolarization, and by elevating ROS production over long-term exposure. PMID:27762337

  1. Mechanism of basolateral membrane H+/OH-/HCO-3 transport in the rat proximal convoluted tubule. A sodium-coupled electrogenic process

    PubMed Central

    1985-01-01

    In order to examine the mechanism of basolateral membrane H+/OH-/HCO-3 transport, a method was developed for the measurement of cell pH in the vivo doubly microperfused rat proximal convoluted tubule. A pH- sensitive fluorescein derivative, (2',7')-bis(carboxyethyl)-(5,6)- carboxyfluorescein, was loaded into cells and relative changes in fluorescence at two excitation wavelengths were followed. Calibration was accomplished using nigericin with high extracellular potassium concentrations. When luminal and peritubular fluids were pH 7.32, cell pH was 7.14 +/- 0.01. Decreasing peritubular pH from 7.32 to 6.63 caused cell pH to decrease from 7.16 +/- 0.02 to 6.90 +/- 0.03. This effect occurred at an initial rate of 2.4 +/- 0.3 pH units/min, and was inhibited by 0.5 mM SITS. Lowering the peritubular sodium concentration from 147 to 25 meq/liter caused cell pH to decrease from 7.20 +/- 0.03 to 6.99 +/- 0.01. The effect of peritubular sodium concentration on cell pH was inhibited by 0.5 mM SITS, but was unaffected by 1 mM amiloride. In addition, when peritubular pH was decreased in the total absence of luminal and peritubular sodium, the rate of cell acidification was 0.2 +/- 0.1 pH units/min, a greater than 90% decrease from that in the presence of sodium. Cell depolarization achieved by increasing the peritubular potassium concentration caused cell pH to increase, an effect that was blocked by peritubular barium or luminal and peritubular sodium removal. Lowering the peritubular chloride concentration from 128 to 0 meq/liter did not affect cell pH. These results suggest the existence of an electrogenic, sodium-coupled H+/OH- /HCO-3 transport mechanism on the basolateral membrane of the rat proximal convoluted tubule. PMID:2999293

  2. Sodium-dependent nitrate transport at the plasma membrane of leaf cells of the marine higher plant Zostera marina L.

    PubMed

    García-Sánchez, M J; Jaime, M P; Ramos, A; Sanders, D; Fernández, J A

    2000-03-01

    NO(3)(-) is present at micromolar concentrations in seawater and must be absorbed by marine plants against a steep electrochemical potential difference across the plasma membrane. We studied NO(3)(-) transport in the marine angiosperm Zostera marina L. to address the question of how NO(3)(-) uptake is energized. Electrophysiological studies demonstrated that micromolar concentrations of NO(3)(-) induced depolarizations of the plasma membrane of leaf cells. Depolarizations showed saturation kinetics (K(m) = 2.31 +/- 0.78 microM NO(3)(-)) and were enhanced in alkaline conditions. The addition of NO(3)(-) did not affect the membrane potential in the absence of Na(+), but depolarizations were restored when Na(+) was resupplied. NO(3)(-)-induced depolarizations at increasing Na(+) concentrations showed saturation kinetics (K(m) = 0.72 +/- 0.18 mM Na(+)). Monensin, an ionophore that dissipates the Na(+) electrochemical potential, inhibited NO(3)(-)-evoked depolarizations by 85%, and NO(3)(-) uptake (measured by depletion from the external medium) was stimulated by Na(+) ions and by light. Our results strongly suggest that NO(3)(-) uptake in Z. marina is mediated by a high-affinity Na(+)-symport system, which is described here (for the first time to our knowledge) in an angiosperm. Coupling the uptake of NO(3)(-) to that of Na(+) enables the steep inwardly-directed electrochemical potential for Na(+) to drive net accumulation of NO(3)(-) within leaf cells.

  3. Uphill transport membrane electrodes

    SciTech Connect

    Uto, M.; Yoshida, H.; Sugawara, M.; Umezawa, Y.

    1986-07-01

    A new membrane electrode was constructed in which carrier-mediated uphill transport of analytes is incorporated. The electrode can boost selectively virtual concentration of specific analytes by uphill transport against their concentration gradient across a built-in liquid membrane into its inner filling solution, whose volume is purposely made very small. Cd(II), UO/sub 2//sup 2 +/, and Cu(II) ion uphill transport membrane electrodes constructed here as illustrative examples utilize three different types of input energies, i.e., complexation, concentration gradient, and redox, respectively, for uphill transport of each analyte. Voltammetric detections were demonstrated for Cd(II) and UO/sub 2//sup 2 +/ ion uphill transport electrodes, and a potentiometric detection for a Cu(II) ion uphill transport membrane electrode is also described in terms of fundamental behaviors and a possible use for a new type of electrochemical sensor.

  4. Sodium chloride transport across the chicken coprodeum. Basic characteristics and dependence on sodium chloride intake

    PubMed Central

    Choshniak, I.; Munck, B. G.; Skadhauge, E.

    1977-01-01

    1. The transport characteristics of the chicken coprodeum have been examined in vitro using the isolated mucosa. The short-circuit current (Isc), the transepithelial electrical potential difference (p.d.), the unidirectional transmural fluxes (Jms, Jsm) of sodium and chloride measured in the short-circuited state, and the unidirectional influx of sodium and chloride across the brush border membrane measured under open-circuit conditions have been studied. The effect of the sodium chloride contents of the diet on these parameters have been investigated. 2. The isolated mucosa depends functionally on the presence of glucose in the incubation media. This dependence reflects the need of glucose as a fuel. There is no indication of coupling between transport of sugars and sodium across the brush border membrane. For preparations from chickens on a low sodium diet a very high and stable Isc can quantitatively be accounted for by the net transport of sodium. Influx of sodium across the brush border membrane is not significantly different from the net flux of sodium. By feeding the chickens a high sodium diet the Isc is reduced by more than 95%, the net transport of sodium is abolished, and the transepithelial electrical conductance is reduced by more than 50%. 3. Both unidirectional transepithelial fluxes of chloride, and the serosa to mucosa flux of sodium appear to proceed through a paracellular shunt. 4. Under the conditions of the low sodium diet the paracellular pathway appears to be anion selective. Whereas, under the conditions of the high sodium regimen the paracellular route appears to be cation selective. After adaptation to a high sodium diet the influx of sodium across the brush border membrane is only moderately reduced. Consequently the decisive event in the adaptation must be localized elsewhere. PMID:926000

  5. Co-overexpressing a plasma membrane and a vacuolar membrane sodium/proton antiporter significantly improves salt tolerance in transgenic Arabidopsis plants.

    USDA-ARS?s Scientific Manuscript database

    The Arabidopsis gene AtNHX1 encodes a vacuolar membrane bound sodium/proton (Sodium/Hydrogen) antiporter that transports sodium into the vacuole and exports hydrogen into the cytoplasm. The Arabidopsis gene SOS1 encodes a plasma membrane bound sodium/hydrogen antiporter that exports sodium to the ex...

  6. Membrane Transport Phenomena (MTP)

    NASA Technical Reports Server (NTRS)

    Mason, Larry W.

    1997-01-01

    The third semi-annual period of the MTP project has been involved with performing experiments using the Membrane Transport Apparatus (MTA), development of analysis techniques for the experiment results, analytical modeling of the osmotic transport phenomena, and completion of a DC-9 microgravity flight to test candidate fluid cell geometries. Preparations were also made for the MTP Science Concept Review (SCR), held on 13 June 1997 at Lockheed Martin Astronautics in Denver. These activities are detailed in the report.

  7. Hydrogen transport membranes

    DOEpatents

    Mundschau, Michael V.

    2005-05-31

    Composite hydrogen transport membranes, which are used for extraction of hydrogen from gas mixtures are provided. Methods are described for supporting metals and metal alloys which have high hydrogen permeability, but which are either too thin to be self supporting, too weak to resist differential pressures across the membrane, or which become embrittled by hydrogen. Support materials are chosen to be lattice matched to the metals and metal alloys. Preferred metals with high permeability for hydrogen include vanadium, niobium, tantalum, zirconium, palladium, and alloys thereof. Hydrogen-permeable membranes include those in which the pores of a porous support matrix are blocked by hydrogen-permeable metals and metal alloys, those in which the pores of a porous metal matrix are blocked with materials which make the membrane impervious to gases other than hydrogen, and cermets fabricated by sintering powders of metals with powders of lattice-matched ceramic.

  8. Current-voltage relations of sodium-coupled sugar transport across the apical membrane of Necturus small intestine.

    PubMed

    Lapointe, J Y; Hudson, R L; Schultz, S G

    1986-01-01

    The current-voltage (I-V) relations of the rheogenic Na-sugar cotransport mechanism at the apical membrane of Necturus small intestine were determined from the relations between the electrical potential difference across the apical membrane, psi mc, and that across the entire epithelium, psi ms, when the latter was varied over the range +/- 200 mV, under steady conditions in the presence of galactose and after the current across the apical membrane carried by the cotransporter, ImSNa, is blocked by the addition of phloridzin to the mucosal solution. ImSNa was found to be strongly dependent upon psi mc over the range -50 mV less than psi mc less than EmSNa where EmSNa is the "zero current" or "reversal" potential. Over the range of values of psi mc encountered under physiological conditions the cotransporter may be modeled as a conductance in series with an electromotive force so that ImSNa = gmSNa (EmSNa - psi mc) where gmSNa is the contribution of this mechanism to the conductance of the apical membrane and is "near constant." In several instances ImSNa "saturated" at large hyperpolarizing or depolarizing values of psi mc. The values of EmSNa determined in the presence of 1, 5, and 15 mM galactose strongly suggest that if the Na-galactose cotransporters are kinetically homogeneous, the stoichiometry of this coupled process is unity. Finally, the shapes of the observed I-V relations are consistent with the predictions of a simple kinetic model which conforms with current notions regarding the mechanico-kinetic properties of this cotransport process.

  9. OXYGEN TRANSPORT CERAMIC MEMBRANES

    SciTech Connect

    Dr. Sukumar Bandopadhyay; Dr. Nagendra Nagabhushana

    2002-07-01

    In the present quarter, oxygen transport perovskite ceramic membranes are evaluated for strength and fracture in oxygen gradient conditions. Oxygen gradients are created in tubular membranes by insulating the inner surface from the reducing environment by platinum foils. Fracture in these test conditions is observed to have a gradient in trans and inter-granular fracture as opposed to pure trans-granular fracture observed in homogeneous conditions. Fracture gradients are reasoned to be due to oxygen gradient set up in the membrane, variation in stoichiometry across the thickness and due to varying decomposition of the parent perovskite. The studies are useful in predicting fracture criterion in actual reactor conditions and in understanding the initial evolution of fracture processes.

  10. Lifetime of Sodium Beta-Alumina Membranes in Molten Sodium Hydroxide

    DTIC Science & Technology

    2008-07-01

    Report 3. DATES COVERED (From – To) 1 April 2007 – 01 April 2008 4. TITLE AND SUBTITLE Lifetime of Sodium Beta-alumina Membranes in Molten Sodium ...ABSTRACT Summary: Sodium metal can be made by electrolysis of molten sodium hydroxide in sodium beta-alumina membrane electrolysis cells...However, there are some uncertainties about the lifetime of the sodium beta-alumina membranes in contact with molten sodium hydroxide. The main objective

  11. Angiotensin 2 directly increases rabbit renal brush-border membrane sodium transport: Presence of local signal transduction system

    SciTech Connect

    Morduchowicz, G.A.; Sheikh-Hamad, D.; Dwyer, B.E.; Stern, N.; Jo, O.D.; Yanagawa, N. )

    1991-05-01

    In the present study, the authors have examined the direct actions of angiotensin II (AII) in rabbit renal brush border membrane (BBM) where binding sites for AII exist. Addition of AII (10(-11)-10(-7) M) was found to stimulate 22Na+ uptake by the isolated BBM vesicles directly. All did not affect the Na(+)-dependent BBM glucose uptake, and the effect of AII on BBM 22Na+ uptake was inhibited by amiloride, suggesting the involvement of Na+/H+ exchange mechanism. BBM proton permeability as assessed by acridine orange quenching was not affected by AII, indicating the direct effect of AII on Na+/H+ antiport system. In search of the signal transduction mechanism, it was found that AII activated BBM phospholipase A2 (PLA) and that BBM contains a 42-kDa guanine nucleotide-binding regulatory protein (G-protein) that underwent pertussis toxin (PTX)-catalyzed ADP-ribosylation. Addition of GTP potentiated, while GDP-beta S or PTX abolished, the effects of AII on BBM PLA and 22Na+ uptake, suggesting the involvement of G-protein in AII's actions. On the other hand, inhibition of PLA by mepacrine prevented AII's effect on BBM 22Na+ uptake, and activation of PLA by mellitin or addition of arachidonic acid similarly enhanced BBM 22Na+ uptake, suggesting the role of PLA activation in mediating AII's effect on BBM 22Na+ uptake. In summary, results of the present study show a direct stimulatory effect of AII on BBM Na+/H+ antiport system, and suggest the presence of a local signal transduction system involving G-protein mediated PLA activation.

  12. NMR studies of cation transport across membranes

    SciTech Connect

    Shochet, N.R.

    1985-01-01

    /sup 23/Na NMR Studies of cation transport across membranes were conducted both on model and biological membranes. Two ionophores, the carrier monensin and the channel-former gramicidin, were chosen to induce cation transport in large unilamellar phosphatidylcholine vesicles. The distinction between the NMR signals arising from the two sides of the membrane was achieved by the addition of an anionic paramagnetic shift reagent to the outer solution. The kinetics of the cation transport across the membrane was observed simultaneously monitoring the changes in the /sup 23/Na NMR signals of both compartments. Two mathematical models were developed for the estimation of the transport parameters of the monensin- and gramicidin-induced cation transport. The models were able to fit the experimental data very well. A new method for the estimation of the volume trapped inside the vesicles was developed. The method uses the relative areas of the intra- and extravesicular NMR signals arising from a suspension of vesicles bathed in the same medium they contain, as a measure for the relative volumes of these compartments. Sodium transport across biological membranes was studied by /sup 23/ NMR, using suspensions of cultured nerve cells. The sodium influx through voltage-gated channels was studied using the channel modifier batrachotoxin in combination with scorpion toxin.

  13. OXYGEN TRANSPORT CERAMIC MEMBRANES

    SciTech Connect

    Dr. Sukumar Bandopadhyay; Dr. Nagendra Nagabhushana

    2003-01-01

    In the present quarter, the possibility of using a more complex interfacial engineering approach to the development of reliable and stable oxygen transport perovskite ceramic membranes/metal seals is discussed. Experiments are presented and ceramic/metal interactions are characterized. Crack growth and fracture toughness of the membrane in the reducing conditions are also discussed. Future work regarding this approach is proposed are evaluated for strength and fracture in oxygen gradient conditions. Oxygen gradients are created in tubular membranes by insulating the inner surface from the reducing environment by platinum foils. Fracture in these test conditions is observed to have a gradient in trans and inter-granular fracture as opposed to pure trans-granular fracture observed in homogeneous conditions. Fracture gradients are reasoned to be due to oxygen gradient set up in the membrane, variation in stoichiometry across the thickness and due to varying decomposition of the parent perovskite. The studies are useful in predicting fracture criterion in actual reactor conditions and in understanding the initial evolution of fracture processes.

  14. OXYGEN TRANSPORT CERAMIC MEMBRANES

    SciTech Connect

    Dr. Sukumar Bandopadhyay; Dr. Nagendra Nagabhushana

    2003-01-01

    In the present quarter, experiments are presented on ceramic/metal interactions of Zirconia/Ni-B-Si system and with a thin Ti coating deposited on zirconia surface. Processing of perovskites of LSC, LSF and LSCF composition for evaluation of mechanical properties as a function of environment are begun. The studies are to be in parallel with LSFCO composition to characterize the segregation of cations and slow crack growth in environmental conditions. La{sub 1-x}Sr{sub x}FeO{sub 3-d} has also been characterized for paramagnetic ordering at room temperature and the evolution of magnetic moments as a function of temperature are investigated. Investigation on the thermodynamic properties of the membrane materials are continued to develop a complete model for the membrane transport.

  15. OXYGEN TRANSPORT CERAMIC MEMBRANES

    SciTech Connect

    Dr. Sukumar Bandopadhyay; Dr. Nagendra Nagabhushana

    2001-12-01

    Conversion of natural gas to liquid fuels and chemicals is a major goal for the Nation as it enters the 21st Century. Technically robust and economically viable processes are needed to capture the value of the vast reserves of natural gas on Alaska's North Slope, and wean the Nation from dependence on foreign petroleum sources. Technologies that are emerging to fulfill this need are all based syngas as an intermediate. Syngas (a mixture of hydrogen and carbon monoxide) is a fundamental building block from which chemicals and fuels can be derived. Lower cost syngas translates directly into more cost-competitive fuels and chemicals. The currently practiced commercial technology for making syngas is either steam methane reforming (SMR) or a two-step process involving cryogenic oxygen separation followed by natural gas partial oxidation (POX). These high-energy, capital-intensive processes do not always produce syngas at a cost that makes its derivatives competitive with current petroleum-based fuels and chemicals. This project has the following 6 main tasks: Task 1--Design, fabricate and evaluate ceramic to metal seals based on graded ceramic powder/metal braze joints. Task 2--Evaluate the effect of defect configuration on ceramic membrane conductivity and long term chemical and structural stability. Task 3--Determine materials mechanical properties under conditions of high temperatures and reactive atmospheres. Task 4--Evaluate phase stability and thermal expansion of candidate perovskite membranes and develop techniques to support these materials on porous metal structures. Task 5--Assess the microstructure of membrane materials to evaluate the effects of vacancy-impurity association, defect clusters, and vacancy-dopant association on the membrane performance and stability. Task 6--Measure kinetics of oxygen uptake and transport in ceramic membrane materials under commercially relevant conditions using isotope labeling techniques.

  16. Oxygen Transport Ceramic Membranes

    SciTech Connect

    S. Bandopadhyay; N. Nagabhushana; T. Nithyanantham; X.-D Zhou; Y-W. Sin; H.U. Anderson; Alan Jacobson; C.A. Mims

    2005-02-01

    under air separation mode (small gradient) were completed on the membrane of LSCrF-2828 at 900 C. Low pO{sub 2} atmospheres based on with CO-CO{sub 2} mixtures have also been admitted to the delivery side of the LSCrF-2828 membrane to produce the gradients which exist under syngas generation conditions. The CO-CO{sub 2} mixtures have normal isotopic {sup 18}O abundances. The evolution of {sup 18}O on the delivery side in these experiments after an {sup 18}O pulse on the air side reveals a wealth of information about the oxygen transport processes.

  17. Membrane Transport Phenomena (MTP)

    NASA Technical Reports Server (NTRS)

    Mason, Larry W.

    1997-01-01

    The activities during the fourth semi-annual period of the MTP project have involved the completion of the Science Concept Review (SCR) presentation and peer review, continuation of analyses for the mass transfer coefficients measured from MTA experiment data, and development of the second generation (MTP-II) instrument. The SCR panel members were generated several recommendations for the MTP project recommendations are : Table 1 Summary of Primary SCR Panel Recommendations (1) Continue and refine development of mass transfer coefficient analyses (2) Refine and upgrade analytical modeling associated with the MTP experiment. (3) Increase resolution of measurements in proximity of the membrane interface. (4) Shift emphasis to measurement of coupled transport effects (i.e., development of MTP phase II experiment concept).

  18. Oxygen Transport Ceramic Membranes

    SciTech Connect

    S. Bandopadhyay; N. Nagabhushana; X.-D Zhou; Q. Cai; J. Yang; W.B. Yelon; W.J. James; H.U. Anderson; Alan Jacobson; C.A. Mims

    2004-05-01

    The present quarterly report describes some of the investigations on the structural properties of dense OTM bars provided by Praxair and studies on newer composition of Ti doped LSF. In this report, in situ neutron diffraction was used to characterize the chemical and structural properties of La{sub 0.2}Sr{sub 0.8}Fe{sub 0.55}Ti{sub 0.45}O{sub 3-{delta}} (here after as L2SF55T) specimen, which was subject to measurements of neutron diffraction from room temperature to 900 C. It was found that space group of R3c yielded a better refinement than a cubic structure of Pm3m. Oxygen occupancy was nearly 3 in the region from room temperature to 700 C, above which the occupancy decreased due to oxygen loss. Dense OTM bars provided by Praxair were loaded to fracture at varying stress rates. Studies were done at room temperature in air and at 1000 C in a specified environment to evaluate slow crack growth behavior. The X-Ray data and fracture mechanisms points to non-equilibrium decomposition of the LSFCO OTM membrane. The non-equilibrium conditions could probably be due to the nature of the applied stress field (stressing rates) and leads to transition in crystal structures and increased kinetics of decomposition. The formations of a Brownmillerite or Sr2Fe2O5 type structures, which are orthorhombic are attributed to the ordering of oxygen vacancies. The cubic to orthorhombic transitions leads to 2.6% increase in strains and thus residual stresses generated could influence the fracture behavior of the OTM membrane. Continued investigations on the thermodynamic properties (stability and phase-separation behavior) and total conductivity of prototype membrane materials were carried out. The data are needed together with the kinetic information to develop a complete model for the membrane transport. Previously characterization, stoichiometry and conductivity measurements for samples of La{sub 0.2}Sr{sub 0.8}Fe{sub 0.55}Ti{sub 0.45}O{sub 3-{delta}} were reported. In this report

  19. Oxygen Transport Ceramic Membranes

    SciTech Connect

    S. Bandopadhyay; N. Nagabhushana; Thomas W. Eagar; Harold R. Larson; Raymundo Arroyave; X.-D Zhou; Y.-W. Shin; H.U. Anderson; Nigel Browning; Alan Jacobson; C.A. Mims

    2003-11-01

    The present quarterly report describes some of the initial studies on newer compositions and also includes newer approaches to address various materials issues such as in metal-ceramic sealing. The current quarter's research has also focused on developing a comprehensive reliability model for predicting the structural behavior of the membranes in realistic conditions. In parallel to industry provided compositions, models membranes have been evaluated in varying environment. Of importance is the behavior of flaws and generation of new flaws aiding in fracture. Fracture mechanics parameters such as crack tip stresses are generated to characterize the influence of environment. Room temperature slow crack growth studies have also been initiated in industry provided compositions. The electrical conductivity and defect chemistry of an A site deficient compound (La{sub 0.55}Sr{sub 0.35}FeO{sub 3}) was studied. A higher conductivity was observed for La{sub 0.55}Sr{sub 0.35}FeO{sub 3} than that of La{sub 0.60}Sr{sub 0.40}FeO{sub 3} and La{sub 0.80}Sr{sub 0.20}FeO{sub 3}. Defect chemistry analysis showed that it was primarily contributed by a higher carrier concentration in La{sub 0.55}Sr{sub 0.35}FeO{sub 3}. Moreover, the ability for oxygen vacancy generation is much higher in La{sub 0.55}Sr{sub 0.35}FeO{sub 3} as well, which indicates a lower bonding strength between Fe-O and a possible higher catalytic activity for La{sub 0.55}Sr{sub 0.35}FeO{sub 3}. The program continued to investigate the thermodynamic properties (stability and phase separation behavior) and total conductivity of prototype membrane materials. The data are needed together with the kinetic information to develop a complete model for the membrane transport. Previous report listed initial measurements on a sample of La{sub 0.2}Sr{sub 0.8}Fe{sub 0.55}Ti{sub 0.45}O{sub 3-x} prepared in-house by Praxair. Subsequently, a second sample of powder from a larger batch of sample were characterized and compared with

  20. Identification of Transporters Involved in Beraprost Sodium Transport In Vitro.

    PubMed

    Oshida, Keiyu; Shimamura, Masahiro; Seya, Kazuhiro; Ando, Akihiro; Miyamoto, Yohei

    2017-02-01

    Beraprost sodium (BPS) is a chemically stable and orally active prostacyclin analog that is used in the treatment of chronic arterial occlusive disease since 1992 and primary pulmonary hypertension since 1999 in Japan. Multiple-drug therapy is common in clinical practice, and BPS is co-administered with other drugs. Membrane transporters are known to markedly affect pharmacokinetics, safety and efficacy, and many transporter-based drug-drug interactions have been recently reported. However, information on the transporters involved in the pharmacokinetics of BPS is limited. First of all, we have examined 11 transporters, ABCB1 (P-glycoprotein: P-gp), ABCG2 (breast cancer resistance protein: BCRP), SLC22A6 (organic anion transporter 1: OAT1), SLC22A8 (organic anion transporter 3: OAT3), SLCO1B1 (organic anion transporting polypeptide 1B1: OATP1B1), SLCO1B3 (organic anion transporting polypeptide 1B3: OATP1B3), SLCO2B1 (organic anion transporting polypeptide 2B1: OATP2B1), SLC22A1 (organic cation transporter 1: OCT1), SLC22A2 (organic cation transporter 2: OCT2), ABCB11 (bile-salt export pump: BSEP), and ABCC2 (multidrug resistance associated protein 2: MRP2) to clarify which of them would be candidates that might recognize BPS as their substrate in transporter-expressing LLC-PK1, S2, and HEK293 cells as well as in membrane vesicles. Furthermore, we determined whether the transport of BPS was inhibited by the typical inhibitors of each transporter, i.e., verapamil for P-gp, Ko143 for BCRP, probenecid for OAT3, rifampicin for OATP1B1 and OATP1B3, cyclosporine for BSEP, and sulfobromophthalein (BSP) for MRP2. The results obtained showed that P-gp, BCRP, OAT3, OATP1B1, OATP1B3, BSEP and MRP2 might be candidates for BPS transporters. From the further evaluation with the typical inhibitors of each transporter, it was confirmed that BPS is a substrate for P-gp, BCRP, OAT3, OATP1B1, OATP1B3 and MRP2, because the typical inhibitor, cyclosporine, had no effects on BPS

  1. Polarity and membrane transport in osteoclasts.

    PubMed

    Baron, R

    1989-01-01

    The osteoclast is a highly polarized non-epithelial cell. The apical pole of the cell is determined by the cell's attachment to the extracellular matrix. This attachment forms the sealing zone, delimiting the subosteoclastic bone resorbing compartment. The apical membrane of the cell forms the ruffled-border, which contains some specific membrane proteins and a proton pump ATPase, which acidifies the apical compartment. Newly synthesized lysosomal enzymes are vectorially transported into this apical compartment bound to mannose-6-phosphate receptors. The basolateral membrane is highly enriched in sodium pumps with beta and alpha 1 subunits. Associated with the acidification process is the carbonic anhydrase found in the cytoplasm and membrane-associated and a bicarbonate-chloride exchanger in the membrane.2 These features put the osteoclast in the same functional category as the kidney tubule intercalated cell and the gastric oxyntic cell, both of epithelial origin, which secrete acid in a polarized fashion.

  2. Oxygen Transport Membranes

    SciTech Connect

    S. Bandopadhyay

    2008-08-30

    The focus of this research was to develop new membrane materials by synthesizing different compounds and determining their defect structures, crystallographic structures and electrical properties. In addition to measuring electrical conductivity, oxygen vacancy concentration was also evaluated using thermogravimetry, Neutron diffraction and Moessbauer Spectroscopy. The reducing conditions (CO{sub 2}/CO/H{sub 2} gas mixtures with steam) as encountered in a reactor environment can be expected to have significant influence on the mechanical properties of the oxides membranes. Various La based materials with and without Ti were selected as candidate membrane materials for OTM. The maximum electrical conductivity of LSF in air as a function of temperature was achieved at < 600 C and depends on the concentration of Sr (acceptor dopant). Oxygen occupancy in LSF was estimated using Neutron diffractometry and Moessbauer Spectroscopy by measuring magnetic moment changes depending on the Fe{sup 3+} and Fe{sup 4+} ratio. After extensive studies of candidate materials, lanthanum ferrites (LSF and LSFT) were selected as the favored materials for the oxygen transport membrane (OTM). LSF is a very good material for an OTM because of its high electronic and oxygen ionic conductivity if long term stability and mechanical strength are improved. LSFT not only exhibits p-type behavior in the high oxygen activity regime, but also has n-type conduction in reducing atmospheres. Higher concentrations of oxygen vacancies in the low oxygen activity regime may improve the performance of LSFT as an OTM. The hole concentration is related to the difference in the acceptor and donor concentration by the relation p = [Sr'{sub La}]-[Ti{sm_bullet}{sub Fe}]. The chemical formulation predicts that the hole concentration is, p = 0.8-0.45 or 0.35. Experimental measurements indicated that p is about {approx} 0.35. The activation energy of conduction is 0.2 eV which implies that LSCF conducts via the

  3. Oxygen Transport Ceramic Membranes

    SciTech Connect

    S. Bandopadhyay; T. Nithyanantham; X.-D Zhou; Y-W. Sin; H.U. Anderson; Alan Jacobson; C.A. Mims

    2005-05-01

    been admitted to the delivery side of the LSCrF-2828 membrane to produce the gradients which exist under syngas generation conditions. The CO-CO{sub 2} mixtures have normal isotopic {sup 18}O abundances. The evolution of {sup 18}O on the delivery side in these experiments after an {sup 18}O pulse on the air side reveals a wealth of information about the oxygen transport processes.

  4. Influence of sodium concentration on changes of membrane capacitance associated with the electrogenic ion transport by the Na,K-ATPase.

    PubMed

    Sokolov, V S; Stukolov, S M; Darmostuk, A S; Apell, H J

    1998-01-01

    Electrogenic ion transport by the Na,K-ATPase was investigated in a model system of protein-containing membrane fragments adsorbed to a lipid bilayer. Transient Na+ currents were induced by photorelease of ATP from inactive caged ATP. This process was accompanied by a capacitance change of the membrane system. Two methods were applied to measure capacitances in the frequency range 1 to 6000 Hz. The frequency dependent capacitance increment, delta C, was of sigmoidal shape and decreased at high frequencies. The midpoint frequency, f0, depended on the ionic strength of the buffer. At 150 mM NaCl f0 was about 200 Hz and decreased to 12 Hz at high ionic strength (1 M). At low frequencies (f < f0) the capacitance increment became frequency independent. It was, however, dependent on Na+ concentration and on the membrane potential which was generated by the charge transferred. A simple model is presented to analyze the experimental data quantitatively as a function of two parameters, the capacitance of the adsorbed membrane fragments, Cp, and the potential of maximum capacitance increment, psi 0. Below 5 mM Na+ a negative capacitance change was detected which may be assigned to electrogenic Na+ binding to cytoplasmic sites. It could be shown that the results obtained by experiments with the presented alternating current method contain the information which is determined by current-relaxation experiments with cell membranes.

  5. Oxygen Transport Ceramic Membranes

    SciTech Connect

    S. Bandopadhyay; N. Nagabhushana; X.-D Zhou; Q. Cai; J. Yang; W.B. Yelon; W.J. James; H.U. Anderson; Alan Jacobson; C.A. Mims

    2004-10-01

    The present quarterly report describes some of the investigations on the structural properties of dense OTM bars provided by Praxair and studies on newer composition of Ti doped LSF. In this report, Moessbauer spectroscopy was used to study the local environmentals of LSFT with various level of oxygen deficiency. Ionic valence state, magnetic interaction and influence of Ti on superexchange are discussed Stable crack growth studies on Dense OTM bars provided by Praxair were done at elevated temperature, pressure and elevated conditions. Post-fracture X-ray data of the OTM fractured at 1000 C in environment were refined by FullProf code and results indicate a distortion of the parent cubic perovskite to orthorhombic structure with reduced symmetry. TGA-DTA studies on the post-fracture samples also indicated residual effect arising from the thermal and stress history of the samples. An electrochemical cell has been designed and built for measurements of the Seebeck coefficient as a function of temperature and pressure. The initial measurements on La{sub 0.2}Sr{sub 0.8}Fe{sub 0.55}Ti{sub 0.45}O{sub 3-{delta}} are reported. Neutron diffraction measurements of the same composition are in agreement with both the stoichiometry and the kinetic behavior observed in coulometric titration measurements. A series of isotope transients under air separation mode (small gradient) were completed on the membrane of LSCrF-2828 at 900 C. Low pO{sub 2} atmospheres based on with CO-CO{sub 2} mixtures have also been admitted to the delivery side of the LSCrF-2828 membrane to produce the gradients which exist under syngas generation conditions. The COCO{sub 2} mixtures have normal isotopic {sup 18}O abundances. The evolution of {sup 18}O on the delivery side in these experiments after an {sup 18}O pulse on the air side reveals a wealth of information about the oxygen transport processes.

  6. [The sodium-potassium-chloride cotransport of the cell membrane].

    PubMed

    Urazaev, A Kh

    1998-01-01

    Discovery and active exploration of the furosemid-sensitive derived-active co-transport of sodium-potassium-chlorine ions took place in the end of 1970-es-1980-es. This transportation mechanism was discovered in various types of cells, both of plant and of animal origin. This review describes properties of the transportation process, which was most comprehensive explored in experiments with erythrocytes, epithelium cells and muscles. The review covers the following properties: anion and cation selectivity of the chlorine transportation, its sensitivity to the specific blocking agents (furocemid, bumetanid, etc.), stoichiometry of the transportation process, etc. For energy source, the chlorine transportation is based on transmembrane electrochemical gradient for sodium ions. The article provides the most recent results of investigation of the chemical nature of the molecule of the chlorine membrane transport. Based on various studies, the molecule of this protein weighs from 120 to 200 kD, includes about 1200 amino acid residua, and forms long cytoplasmatic NH2 and COOH-termini. The gene encoding the amino acid sequence has been cloned. The article discusses the issues of regulation of the chlorine transportation. Humoral control of intensity of the chlorine transportation has been mostly studied in experiments with plain muscles, the issues related to nervous regulation--with only skeleton muscle fibers. The article provides specific data on the mechanisms of the above types of the physiological regulation of active chlorine transportation. In general, the humoral factors, which increase the intracellular concentration of cAMF stimulate chlorine transportation. On the contrary, the hormones, which increase concentration of cGMF in cytoplasm reduce its activity in plain muscles. The discussion of the mechanisms of the nervous controls of the chlorine transportation in the skeleton muscles includes the original results of the author. These results indicate that the

  7. Nanoengineered membranes for controlled transport

    SciTech Connect

    Doktycz, Mitchel J; Simpson, Michael L; McKnight, Timothy E; Melechko, Anatoli V; Lowndes, Douglas H; Guillorn, Michael A; Merkulov, Vladimir I

    2010-01-05

    A nanoengineered membrane for controlling material transport (e.g., molecular transport) is disclosed. The membrane includes a substrate, a cover definining a material transport channel between the substrate and the cover, and a plurality of fibers positioned in the channel and connected to an extending away from a surface of the substrate. The fibers are aligned perpendicular to the surface of the substrate, and have a width of 100 nanometers or less. The diffusion limits for material transport are controlled by the separation of the fibers. In one embodiment, chemical derivitization of carbon fibers may be undertaken to further affect the diffusion limits or affect selective permeability or facilitated transport. For example, a coating can be applied to at least a portion of the fibers. In another embodiment, individually addressable carbon nanofibers can be integrated with the membrane to provide an electrical driving force for material transport.

  8. Membrane Transport Phenomena (MTP)

    NASA Technical Reports Server (NTRS)

    Mason, Larry W.

    1996-01-01

    The development of the seal between the membrane and the Fluid Optical Cells (FOC) has been a high priority activity. This seal occurs at an interface in the instrument where three key functions must be realized: (1) physical membrane support, (2) fluid sealing, and (3) unobscured optical transmission.

  9. Oxygen Transport Ceramic Membranes

    SciTech Connect

    S. Bandopadhyay; N. Nagabhushana; X.-D Zhou; Q. Cai; J. Yang; W.B. Yelon; W.J. James; H.U. Anderson; Alan Jacobson; C.A. Mims

    2004-05-01

    the LSCrF-2828 membrane to produce the gradients which exist under syngas generation conditions. The CO-CO{sub 2} mixtures have normal isotopic {sup 18}O abundances. The evolution of {sup 18}O on the delivery side in these experiments after an {sup 18}O pulse on the air side reveals a wealth of information about the oxygen transport processes.

  10. Respiration and sodium transport in rabbit urinary bladder.

    PubMed

    Silverthorn, S U; Eaton, D C

    1982-07-28

    Respiration of rabbit urinary bladder was measured in free-floating pieces and in short-circuited pieces mounted in an Ussing chamber. Ouabain, amiloride, and potassium-free saline inhibited respiration approx. 20%; sodium-free saline depressed respiration approx. 40-50%. The coupling ratio between respiration and transport in short-circuited tissues was about two sodium ions per molecule O2. Chloride-free saline depressed mean oxygen consumption 21% in free-floating tissue pieces; 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (SITS) and furosemide had no effect. The effect of chloride-free saline in short-circuited tissues was variable; in tissues with low transport rates, respiration was stimulated about 21% while in tissue with high transport rates respiration was reduced about 24%. Nystatin and monensin, both of which markedly increase the conductance of cell membranes with a concomitant increase in sodium entry, stimulated respiration. These data indicate that 50-60% of the total oxygen consumption is not influenced by sodium, 20-25% is linked to (Na+ +K+)-ATPase transport, while the remaining 25-30% is sodium-dependent but not ouabain-inhibitable.

  11. Physiological evidence for a sodium-dependent high-affinity phosphate and nitrate transport at the plasma membrane of leaf and root cells of Zostera marina L.

    PubMed

    Rubio, L; Linares-Rueda, A; García-Sánchez, M J; Fernández, J A

    2005-02-01

    Zostera marina L. is an angiosperm that grows in a medium in which inorganic phosphate (P(i)) and nitrate (NO(3)(-)) are present in micromolar concentrations and must be absorbed against a steep electrochemical potential gradient. The operation of a Na(+)-dependent NO(3)(-) transport was previously demonstrated in leaf cells of this plant, suggesting that other Na(+)-coupled systems could mediate the uptake of anions. To address this question, P(i) transport was studied in leaves and roots of Z. marina, as well as NO(3)(-) uptake in roots. Electrophysiological studies demonstrated that micromolar concentrations of P(i) induced depolarizations of the plasma membrane of root cells. However, this effect was not observed in leaf cells. P(i)-induced depolarizations showed Michaelis-Menten kinetics (K(m)=1.5+/-0.6 microM P(i); D(max)=7.8+/-0.8 mV), and were not observed in the absence of Na(+). However, depolarizations were restored when Na(+) was resupplied. NO(3)(-) additions also evoked depolarizations of the plasma membrane of root cells only in the presence of Na(+). Both NO(3)(-)- and P(i)-induced depolarizations were accompanied by an increase in cytoplasmic Na(+) activity, detected by Na(+)-sensitive microelectrodes. P(i) net uptake (measured in depletion experiments) was stimulated by Na(+). These results strongly suggest that P(i) uptake in roots of Z. marina is mediated by a high-affinity Na(+)-dependent transport system. Both NO(3)(-) and P(i) transport systems exploit the steep inwardly directed electrochemical potential gradient for Na(+), considering the low cytoplasmic Na(+) activity (10.7+/-3.3 mM Na(+)) and the high external Na(+) concentration (500 mM Na(+)).

  12. Sodium-Dependent Nitrate Transport at the Plasma Membrane of Leaf Cells of the Marine Higher Plant Zostera marina L.1

    PubMed Central

    García-Sánchez, María J.; Jaime, M. Paz; Ramos, Alberto; Sanders, Dale; Fernández, José A.

    2000-01-01

    NO3− is present at micromolar concentrations in seawater and must be absorbed by marine plants against a steep electrochemical potential difference across the plasma membrane. We studied NO3− transport in the marine angiosperm Zostera marina L. to address the question of how NO3− uptake is energized. Electrophysiological studies demonstrated that micromolar concentrations of NO3− induced depolarizations of the plasma membrane of leaf cells. Depolarizations showed saturation kinetics (Km = 2.31 ± 0.78 μm NO3−) and were enhanced in alkaline conditions. The addition of NO3− did not affect the membrane potential in the absence of Na+, but depolarizations were restored when Na+ was resupplied. NO3−-induced depolarizations at increasing Na+ concentrations showed saturation kinetics (Km = 0.72 ± 0.18 mm Na+). Monensin, an ionophore that dissipates the Na+ electrochemical potential, inhibited NO3−-evoked depolarizations by 85%, and NO3− uptake (measured by depletion from the external medium) was stimulated by Na+ ions and by light. Our results strongly suggest that NO3− uptake in Z. marina is mediated by a high-affinity Na+-symport system, which is described here (for the first time to our knowledge) in an angiosperm. Coupling the uptake of NO3− to that of Na+ enables the steep inwardly-directed electrochemical potential for Na+ to drive net accumulation of NO3− within leaf cells. PMID:10712552

  13. Oxygen Transport Ceramic Membranes

    SciTech Connect

    S. Bandopadhyay; T. Nithyanantham; X.-D Zhou; Y-W. Sin; H.U. Anderson; Alan Jacobson; C.A. Mims

    2005-11-01

    The present quarterly report describes some of the investigations on the structural properties of dense OTM bars provided by Praxair and studies on newer composition of Ti doped LSF. In the current research, the electrical conductivity and Seebeck coefficient were measured as a function of temperature in air. Based on these measurements, the charge carrier concentration, net acceptor dopant concentration, activation energy of conduction and mobility were estimated. The studies on the fracture toughness of the LSFT and dual phase membranes at room temperature have been completed and reported previously. The membranes that are exposed to high temperatures at an inert and a reactive atmosphere undergo many structural and chemical changes which affects the mechanical properties. To study the effect of temperature on the membranes when exposed to an inert environment, the membranes (LAFT and Dual phase) were heat treated at 1000 C in air and N{sub 2} atmosphere and hardness and fracture toughness of the membranes were studied after the treatment. The indentation method was used to find the fracture toughness and the effect of the heat treatment on the mechanical properties of the membranes. Further results on the investigation of the origin of the slow kinetics on reduction of ferrites have been obtained. The slow kinetics appears to be related to a non-equilibrium reduction pathway that initially results in the formation of iron particles. At long times, equilibrium can be reestablished with recovery of the perovskite phase. 2-D modeling of oxygen movement has been undertaken in order to fit isotope data. The model will serve to study ''frozen'' profiles in patterned or composite membranes.

  14. Oxygen Transport Ceramic Membranes

    SciTech Connect

    S. Bandopadhyay; T. Nithyanantham; X.-D Zhou; Y-W. Sin; H.U. Anderson; Alan Jacobson; C.A. Mims

    2006-05-01

    In this quarter a systematic analysis on the decomposition behavior of the OTM membranes at air and nitrogen were initiated to understand the structural and stoichiometric changes associated with elevated temperatures. Evaluation of the flexural strengths using 4-point bend test was also started for the dual phase membranes. Initial results on the synthesis of dual phase composite materials have been obtained. The measurements have focused on the compatibility of mixed conductors with the pure ionic conductors yttria stabilized zirconia (YSZ) and gadolinium doped ceria (GDC). The initial results obtained for three different mixed conductors suggest that (GDC) is the better choice. A new membrane permeation system has been designed and tested and sintering studies of biphasic systems are in progress.

  15. OXYGEN TRANSPORT CERAMIC MEMBRANES

    SciTech Connect

    Dr. Sukumar Bandopadhyay; Dr. Nagendra Nagabhushana

    2001-02-01

    This is the fifth quarterly report on a new study to develop a ceramic membrane/metal joint. Results of wetting experiments on commercially available Nickel based brazing alloys on perovskite surfaces are described. Additionally, experimental and numerical investigations on the strength of concentric ceramic/metal joints are presented.

  16. Composite oxygen transport membrane

    DOEpatents

    Christie, Gervase Maxwell; Lane, Jonathan A.

    2016-11-15

    A method of producing a composite oxygen ion membrane and a composite oxygen ion membrane in which a porous fuel oxidation layer and a dense separation layer and optionally, a porous surface exchange layer are formed on a porous support from mixtures of (Ln.sub.1-xA.sub.x).sub.wCr.sub.1-yB.sub.yO.sub.3-.delta. and a doped zirconia. In the porous fuel oxidation layer and the optional porous surface exchange layer, A is Calcium and in the dense separation layer A is not Calcium and, preferably is Strontium. Preferred materials are (La.sub.0.8Ca.sub.0.2).sub.0.95Cr.sub.0.5Mn.sub.0.5O.sub.3-.delta. for the porous fuel oxidation and optional porous surface exchange layers and (La.sub.0.8Sr.sub.0.2).sub.0.95Cr.sub.0.5Fe.sub.0.5O.sub.3-.delta. for the dense separation layer. The use of such materials allows the membrane to sintered in air and without the use of pore formers to reduce membrane manufacturing costs. The use of materials, as described herein, for forming the porous layers have application for forming any type of porous structure, such as a catalyst support.

  17. Composite oxygen transport membrane

    DOEpatents

    Christie, Gervase Maxwell; Lane, Jonathan A.

    2014-08-05

    A method of producing a composite oxygen ion membrane and a composite oxygen ion membrane in which a porous fuel oxidation layer and a dense separation layer and optionally, a porous surface exchange layer are formed on a porous support from mixtures of (Ln.sub.1-xA.sub.x).sub.wCr.sub.1-yB.sub.yO.sub.3-.delta. and a doped zirconia. In the porous fuel oxidation layer and the optional porous surface exchange layer, A is Calcium and in the dense separation layer A is not Calcium and, preferably is Strontium. Preferred materials are (La.sub.0.8Ca.sub.0.2).sub.0.95Cr.sub.0.5Mn.sub.0.5O.sub.3-.delta. for the porous fuel oxidation and optional porous surface exchange layers and (La.sub.0.8Sr.sub.0.2).sub.0.95Cr.sub.0.5Fe.sub.0.5O.sub.3-.delta. for the dense separation layer. The use of such materials allows the membrane to sintered in air and without the use of pore formers to reduce membrane manufacturing costs. The use of materials, as described herein, for forming the porous layers have application for forming any type of porous structure, such as a catalyst support.

  18. OXYGEN TRANSPORT CERAMIC MEMBRANES

    SciTech Connect

    Dr. Sukumar Bandopadhyay; Dr. Nagendra Nagabhushana

    2000-07-01

    This is the fourth quarterly report on a new study to develop a ceramic membrane/metal joint. The first experiments using the La-Sr-Fe-O ceramic are reported. Some of the analysis performed on the samples obtained are commented upon. A set of experiments to characterize the mechanical strength and thermal fatigue properties of the joints has been designed and begun. Finite element models of joints used to model residual stresses are described.

  19. Facilitative plasma membrane transporters function during ER transit

    PubMed Central

    Takanaga, Hitomi; Frommer, Wolf B.

    2010-01-01

    Although biochemical studies suggested a high permeability of the endoplasmic reticulum (ER) membrane for small molecules, proteomics identified few specialized ER transporters. To test functionality of transporters during ER passage, we tested whether glucose transporters (GLUTs, SGLTs) destined for the plasma membrane are active during ER transit. HepG2 cells were characterized by low-affinity ER transport activity, suggesting that ER uptake is protein mediated. The much-reduced capacity of HEK293T cells to take up glucose across the plasma membrane correlated with low ER transport. Ectopic expression of GLUT1, -2, -4, or -9 induced GLUT isoform-specific ER transport activity in HEK293T cells. In contrast, the Na+-glucose cotransporter SGLT1 mediated efficient plasma membrane glucose transport but no detectable ER uptake, probably because of lack of a sufficient sodium gradient across the ER membrane. In conclusion, we demonstrate that GLUTs are sufficient for mediating ER glucose transport en route to the plasma membrane. Because of the low volume of the ER, trace amounts of these uniporters contribute to ER solute import during ER transit, while uniporters and cation-coupled transporters carry out export from the ER, together potentially explaining the low selectivity of ER transport. Expression levels and residence time of transporters in the ER, as well as their coupling mechanisms, could be key determinants of ER permeability.—Takanaga, H., Frommer, W. B. Facilitative plasma membrane transporters function during ER transit. PMID:20354141

  20. Carrier facilitated transport through membranes

    SciTech Connect

    Kaper, H.G.; Leaf, G.K.; Matkowsky, B.J.

    1980-06-01

    Facilitated transport is a process whereby the diffusion of a solute across a membrane is chemically enhanced. In this report an analysis is given of a facilitated transport system involving a volatile species A which reacts with a nonvolatile carrier species B to form the nonvolatile product AB. The species A is transported across the membrane by ordinary diffusion, as well as by the diffusion of the product AB. It is assumed that the reaction rates are large, so the reactions are confined mostly to thin boundary layers near the surfaces of the membrane. The method of matched asymptotic expansions is used to derive the asymptotic solution of the nonlinear boundary value problem governing equilibrium. The effect of various parameters on the facilitation factor is analyzed in detail.

  1. Oxygen Transport Ceramic Membranes

    SciTech Connect

    S. Bandopadhyay; T. Nithyanantham; X.-D Zhou; Y-W. Sin; H.U. Anderson; Alan Jacobson; C.A. Mims

    2005-02-01

    The present quarterly report describes some of the investigations on the structural properties of dense OTM bars provided by Praxair and studies on newer composition of Ti doped LSF. The in situ electrical conductivity and Seebeck coefficient measurements were made on LSFT at 1000 and 1200 C over the oxygen activity range from air to 10{sup -15} atm. The electrical conductivity measurements exhibited a p to n type transition at an oxygen activity of 1 x 10{sup -10} at 1000 C and 1 x 10{sup -6} at 1200 C. Thermogravimetric studies were also carried out over the same oxygen activities and temperatures. Based on the results of these measurements, the chemical and mechanical stability range of LSFT were determined and defect structure was established. The studies on the fracture toughness of the LSFT and dual phase membranes exposed to air and N{sub 2} at 1000 C was done and the XRD and SEM analysis of the specimens were carried out to understand the structural and microstructural changes. The membranes that are exposed to high temperatures at an inert and a reactive atmosphere undergo many structural and chemical changes which affect the mechanical properties. A complete transformation of fracture behavior was observed in the N{sub 2} treated LSFT samples. Further results to investigate the origin of the slow kinetics on reduction of ferrites have been obtained. The slow kinetics appear to be related to a non-equilibrium reduction pathway that initially results in the formation of iron particles. At long times, equilibrium can be reestablished with recovery of the perovskite phase. Recent results on transient kinetic data are presented. The 2-D modeling of oxygen movement has been undertaken in order to fit isotope data. The model is used to study ''frozen'' profiles in patterned or composite membranes.

  2. Oxygen Transport Ceramic Membranes

    SciTech Connect

    S. Bandopadhyay; T. Nithyanantham; X.-D Zhou; Y-W. Sin; H.U. Anderson; Alan Jacobson; C.A. Mims

    2005-08-01

    The present quarterly report describes some of the investigations on the structural properties of dense OTM bars provided by Praxair and studies on newer composition of Ti doped LSF. In the previous research, the reference point of oxygen occupancy was determined and verified. In the current research, the oxygen occupancy was investigated at 1200 C as a function of oxygen activity and compared with that at 1000 C. The cause of bumps at about 200 C was also investigated by using different heating and cooling rates during TGA. The fracture toughness of LSFT and dual phase membranes at room temperature is an important mechanical property. Vicker's indentation method was used to evaluate this toughness. Through this technique, a K{sub Ic} (Mode-I Fracture Toughness) value is attained by means of semi-empirical correlations between the indentation load and the length of the cracks emanating from the corresponding Vickers indentation impression. In the present investigation, crack propagation behavior was extensively analyzed in order to understand the strengthening mechanisms involved in the non-transforming La based ceramic composites. Cracks were generated using Vicker's indenter and used to identify and evaluate the toughening mechanisms involved. Preliminary results of an electron microscopy study of the origin of the slow kinetics on reduction of ferrites have been obtained. The slow kinetics appear to be related to a non-equilibrium reduction pathway that initially results in the formation of iron particles. At long times, equilibrium can be reestablished with recovery of the perovskite phase. Modeling of the isotopic transients on operating membranes (LSCrF-2828 at 900 C) and a ''frozen'' isotope profile have been analyzed in conjunction with a 1-D model to reveal the gradient in oxygen diffusivity through the membrane under conditions of high chemical gradients.

  3. Composite oxygen transport membrane

    DOEpatents

    Lu, Zigui; Plonczak, Pawel J.; Lane, Jonathan A.

    2016-11-08

    A method is described of producing a composite oxygen ion membrane and a composite oxygen ion membrane in which a porous fuel oxidation layer and a dense separation layer and optionally, a porous surface exchange layer are formed on a porous support from mixtures of (Ln.sub.1-xA.sub.x).sub.wCr.sub.1-yB.sub.yO.sub.3-.delta. and a doped zirconia. Preferred materials are (La.sub.0.8Sr.sub.0.2).sub.0.95Cr.sub.0.7Fe.sub.0.3O.sub.3-.delta. for the porous fuel oxidation layer, (La.sub.0.8Sr.sub.0.2).sub.0.95Cr.sub.0.5Fe.sub.0.5O.sub.3-.delta. for the dense separation layer, and (La.sub.0.8Sr.sub.0.2).sub.0.95Cr.sub.0.3Fe.sub.0.7O.sub.3-.delta. for the porous surface exchange layer. Firing the said fuel activation and separation layers in nitrogen atmosphere unexpectedly allows the separation layer to sinter into a fully densified mass.

  4. Membranes, mechanics, and intracellular transport

    NASA Astrophysics Data System (ADS)

    Parthasarathy, Raghuveer

    2012-10-01

    Cellular membranes are remarkable materials -- self-assembled, flexible, two-dimensional fluids. Understanding how proteins manipulate membrane curvature is crucial to understanding the transport of cargo in cells, yet the mechanical activities of trafficking proteins remain poorly understood. Using an optical-trap based assay involving dynamic deformation of biomimetic membranes, we have examined the behavior of Sar1, a key component of the COPII family of transport proteins. We find that Sar1 from yeast (S. cerevisiae) lowers membrane rigidity by up to 100% as a function of its concentration, thereby lowering the energetic cost of membrane deformation. Human Sar1 proteins can also lower the mechanical rigidity of the membranes to which they bind. However, unlike the yeast proteins, the rigidity is not a monotonically decreasing function of concentration but rather shows increased rigidity and decreased mobility at high concentrations that implies interactions between proteins. In addition to describing this study of membrane mechanics, I'll also discuss some topics relevant to a range of biophysical investigations, such as the insights provided by imaging methods and open questions in the dynamics of multicellular systems.

  5. Oxygen Transport Ceramic Membranes

    SciTech Connect

    S. Bandopadhyay; T. Nithyanantham

    2006-12-31

    Ti doping on La{sub 1-x}Sr{sub x}FeO{sub 3-{delta}} (LSF) tends to increase the oxygen equilibration kinetics of LSF in lower oxygen activity environment because of the high valence state of Ti. However, the addition of Ti decreases the total conductivity because the acceptor ([Sr{prime}{sub La}]) is compensated by the donor ([Ti{sub Fe}{sup {sm_bullet}}]) which decreases the carrier concentration. The properties of La{sub 0.2}Sr{sub 0.8}Fe{sub 1-x}Ti{sub x}O{sub 3-{delta}} (LSFT, x = 0.45) have been experimentally and theoretically investigated to elucidate (1) the dependence of oxygen occupancy and electrochemical properties on temperature and oxygen activity by thermogravimetric analysis (TGA) and (2) the electrical conductivity and carrier concentration by Seebeck coefficient and electrical measurements. In the present study, dual phase (La{sub 0.2}Sr{sub 0.8}Fe{sub 0.6}Ti{sub 0.4}O{sub 3-{delta}}/Ce{sub 0.9}Gd{sub 0.1}O{sub 2-{delta}}) membranes have been evaluated for structural properties such as hardness, fracture toughness and flexural strength. The effect of high temperature and slightly reducing atmosphere on the structural properties of the membranes was studied. The flexural strength of the membrane decreases upon exposure to slightly reducing conditions at 1000 C. The as-received and post-fractured membranes were characterized using XRD, SEM and TG-DTA to understand the fracture mechanisms. Changes in structural properties of the composite were sought to be correlated with the physiochemical features of the two-phases. We have reviewed the electrical conductivity data and stoichiometry data for La{sub 0.2}Sr{sub 0.8}Cr{sub 0.2}Fe{sub 0.8}O{sub 3-{delta}} some of which was reported previously. Electrical conductivity data for La{sub 0.2}Sr{sub 0.8}Cr{sub 0.2}Fe{sub 0.8}O{sub 3-{delta}} (LSCrF) were obtained in the temperature range, 752 {approx} 1055 C and in the pO{sub 2} range, 10{sup -18} {approx} 0.5 atm. The slope of the plot of log {sigma} vs

  6. Oxygen Transport Ceramic Membranes

    SciTech Connect

    S. Bandopadhyay; T. Nithyanantham

    2006-06-30

    A non-agglomerated and nanocrystalline-sized powder was successfully produced using ethylene glycol nitrate methods. The LSFT powder prepared using this method exhibits well dispersed and nano-sized particles about 100-200 nm. The density of LSFT sintered at 1300 C was about 90% of the theoretical density at which is 100 C less than that of the previous LSFT which was sintered at 1400 C. The sample sintered at 1400 C exhibited the evidence of a liquid phase at the grain boundaries and 2nd phase formation which probably caused low mechanical stability. The electrical conductivity and Seebeck coefficient were measured as a function of temperature. The LSFT-CGO specimens were cut from the as sintered bars and used for the evaluation of Mechanical Properties after polishing. The effect of strain rate on the flexural strength of the LSFT-CGO test specimens was studied. Three strain rates 6, 60 and 600 {micro}m/ min were chosen for this study. It is observed from the results that with increasing cross head speed the membrane takes higher loads to fail. A reduction in the strength of the membrane was observed at 1000 C in N{sub 2}. Two different routes were investigated to synthesis GDC using either formate or carbonate precursors. The precursor and CGO particle morphologies were examined by scanning electron microscopy. The thermal decomposition behaviors of Ce(Gd)(HCOO){sub 3} and Ce(Gd)(CO{sub 3})(OH) were determined by thermogravimetric analysis (TGA) at a rate of 3 C/min in air. The X-ray powder diffraction patterns of the precursor and CGO were collected and nitrogen adsorption isotherms were measured. Conductivity measurements were made by AC impedance spectroscopy on sintered disks in air using platinum electrodes.

  7. Carbon dioxide transport through membranes.

    PubMed

    Missner, Andreas; Kügler, Philipp; Saparov, Sapar M; Sommer, Klaus; Mathai, John C; Zeidel, Mark L; Pohl, Peter

    2008-09-12

    Several membrane channels, like aquaporin-1 (AQP1) and the RhAG protein of the rhesus complex, were hypothesized to be of physiological relevance for CO(2) transport. However, the underlying assumption that the lipid matrix imposes a significant barrier to CO(2) diffusion was never confirmed experimentally. Here we have monitored transmembrane CO(2) flux (J(CO2)) by imposing a CO(2) concentration gradient across planar lipid bilayers and detecting the resulting small pH shift in the immediate membrane vicinity. An analytical model, which accounts for the presence of both carbonic anhydrase and buffer molecules, was fitted to the experimental pH profiles using inverse problems techniques. At pH 7.4, the model revealed that J(CO2) was entirely rate-limited by near-membrane unstirred layers (USL), which act as diffusional barriers in series with the membrane. Membrane tightening by sphingomyelin and cholesterol did not alter J(CO2) confirming that membrane resistance was comparatively small. In contrast, a pH-induced shift of the CO(2) hydration-dehydration equilibrium resulted in a relative membrane contribution of about 15% to the total resistance (pH 9.6). Under these conditions, a membrane CO(2) permeability (3.2 +/- 1.6 cm/s) was estimated. It indicates that cellular CO(2) uptake (pH 7.4) is always USL-limited, because the USL size always exceeds 1 mum. Consequently, facilitation of CO(2) transport by AQP1, RhAG, or any other protein is highly unlikely. The conclusion was confirmed by the observation that CO(2) permeability of epithelial cell monolayers was always the same whether AQP1 was overexpressed in both the apical and basolateral membranes or not.

  8. Oxygen Transport Ceramic Membranes

    SciTech Connect

    S. Bandopadhyay; N. Nagabhushana; X.-D Zhou; W.B. Yelon; H.U. Anderson; Alan Jacobson; C.A. Mims

    2004-02-01

    The present quarterly report describes some of the investigations on the structural properties of dense OTM bars provided by Praxair and initial studies on newer composition of Ti doped LSF. Dense OTM bars provided by Praxair were loaded to fracture at varying stress rates. Studies were done at room temperature in air and at 1000 C in a specified environment to evaluate slow crack growth behavior. In addition, studies were also begun to obtain reliable estimates of fracture toughness and stable crack growth in specific environments. Newer composition of Ti doped LSF membranes were characterized by neutron diffraction analysis. Quench studies indicated an apparent correlation between the unit cell volume and oxygen occupancy. The studies however, indicated an anomaly of increasing Fe/Ti ratio with change in heat treatment. Ti doped LSF was also characterized for stoichiometry as a function of temp and pO{sub 2}. The non stoichiometry parameter {delta} was observed to increase almost linearly on lowering pO{sub 2} until a ideal stoichiometric composition of {delta} = 0.175 was approached.

  9. Highly Stable Sodium Batteries Enabled by Functional Ionic Polymer Membranes.

    PubMed

    Wei, Shuya; Choudhury, Snehashis; Xu, Jun; Nath, Pooja; Tu, Zhengyuan; Archer, Lynden A

    2017-01-23

    A sodium metal anode protected by an ion-rich polymeric membrane exhibits enhanced stability and high-Columbic efficiency cycling. Formed in situ via electropolymerization of functional imidazolium-type ionic liquid monomers, the polymer membrane protects the metal against parasitic reactions with electrolyte and, for fundamental reasons, inhibits dendrite formation and growth. The effectiveness of the membrane is demonstrated using direct visualization of sodium electrodeposition.

  10. The role of membranes and transport in the salt tolerance of halobacteria. [Halobacterium halobium

    SciTech Connect

    Lanyi, J.K.

    1986-01-01

    In halobacteria two light-driven membrane pumps have been investigated: bacteriorhodopsin, which extrudes protons from the cell, and halorhodopsin, a recently discovered translocator for sodium ions. Bacteriorhodopsin and halorhodopsin are retinal proteins, and upon illumination of these pigments, a series of photochemical intermediates are produced which relax within 10 to 20 msec, and in an unknown way are coupled to the vectorial uptake and release of protons or sodium ions, respectively. There is reason to believe that the main pathway of sodium transport is not halorhodopsin, however. Rapid sodium extrusion from halobacterial cells is via a sodium/proton antiporter, which, by exchanging sodium ions for protons across the membrane will utilize the energy of the proton gradient to drive sodium transport. As far as it is known, such exchange is a more widespread mechanism for sodium transport in procaryotes, but primary pumps for sodium do exist in mammalian cells, and have been suggested to operate in plants as well. 50 refs.

  11. Facilitative plasma membrane transporters function during ER transit.

    PubMed

    Takanaga, Hitomi; Frommer, Wolf B

    2010-08-01

    Although biochemical studies suggested a high permeability of the endoplasmic reticulum (ER) membrane for small molecules, proteomics identified few specialized ER transporters. To test functionality of transporters during ER passage, we tested whether glucose transporters (GLUTs, SGLTs) destined for the plasma membrane are active during ER transit. HepG2 cells were characterized by low-affinity ER transport activity, suggesting that ER uptake is protein mediated. The much-reduced capacity of HEK293T cells to take up glucose across the plasma membrane correlated with low ER transport. Ectopic expression of GLUT1, -2, -4, or -9 induced GLUT isoform-specific ER transport activity in HEK293T cells. In contrast, the Na(+)-glucose cotransporter SGLT1 mediated efficient plasma membrane glucose transport but no detectable ER uptake, probably because of lack of a sufficient sodium gradient across the ER membrane. In conclusion, we demonstrate that GLUTs are sufficient for mediating ER glucose transport en route to the plasma membrane. Because of the low volume of the ER, trace amounts of these uniporters contribute to ER solute import during ER transit, while uniporters and cation-coupled transporters carry out export from the ER, together potentially explaining the low selectivity of ER transport. Expression levels and residence time of transporters in the ER, as well as their coupling mechanisms, could be key determinants of ER permeability.

  12. Modulation of glucose transporters in rat diaphragm by sodium tungstate.

    PubMed

    Girón, M D; Caballero, J J; Vargas, A M; Suárez, M D; Guinovart, J J; Salto, R

    2003-05-08

    Oral administration of sodium tungstate is an effective treatment for diabetes in animal models. We examined the effects of 6 weeks of oral administration of tungstate on glucose transporters (GLUT) in streptozotocin-induced diabetic rat diaphragm. Diabetes decreased GLUT4 expression while tungstate treatment normalized not only GLUT4 protein but also GLUT4 mRNA in the diabetic rats. Furthermore, treatment increased GLUT4 protein in plasma and internal membranes, suggesting a stimulation of its translocation to the plasma membrane. Tungstate had no effect on healthy animals. There were no differences in the total amount of GLUT1 transporter in any group. We conclude that the normoglycemic effect of tungstate may be partly due to a normalization of the levels and subcellular localization of GLUT4, which should result in an increase in muscle glucose uptake.

  13. Calcium reduces the sodium permeability of luminal membrane vesicles from toad bladder. Studies using a fast-reaction apparatus

    SciTech Connect

    Chase, H.S. Jr.; Al-Awqati, Q.

    1983-05-01

    Regulation of the sodium permeability of the luminal membrane is the major mechanism by which the net rate of sodium transport across tight epithelia is varied. Previous evidence has suggested that the permeability of the luminal membrane might be regulated by changes in intracellular sodium or calcium activities. To test this directly, we isolated a fraction of the plasma membrane from the toad urinary bladder, which contains a fast, amiloride-sensitive sodium flux with characteristics similar to those of the native luminal membrane. Using a flow-quench apparatus to measure the initial rate of sodium efflux from these vesicles in the millisecond time range, we have demonstrated that the isotope exchange permeability of these vesicles is very sensitive to calcium. Calcium reduces the sodium permeability, and the half-maximal inhibitory concentration is 0.5 microM, well within the range of calcium activity found in cells. Also, the permeability of the luminal membrane vesicles is little affected by the ambient sodium concentration. These results, when taken together with studies on whole tissue, suggest that cell calcium may be an important regulator of transepithelial sodium transport by its effect on luminal sodium permeability. The effect of cell sodium on permeability may be mediated by calcium rather than by sodium itself.

  14. Modulating molecular and nanoparticle transport in flexible polydimethylsiloxane membranes

    PubMed Central

    Jiao, Kexin; Graham, Chase L.; Wolff, Justin

    2012-01-01

    The ability to fabricate flexible filtration membranes that can selectively separate particles of different sizes is of considerable interest. In this article, we describe a facile, reproducible and simple one-step method to produce pores in polydimethylsiloxane (PDMS) membranes. We embedded micron-sized NaHCO3 particles in 50 micron thick PDMS films. After curing, the membranes were immersed in concentrated HCl acid. Pores were generated in the membrane by the evolution of CO2 gas from the reaction of NaHCO3 and HCl. High resolution Scanning Electron Microscope images clearly reveal the presence of openings on the surface and the cross-section of the membranes. Fluorescence and back-scattered electron imaging of porous PDMS membrane with embedded gold nanoparticles and comparison with non-porous PDMS membranes provided unambiguous evidence of pores in the membrane. Transport studies of molecular fluoresceinate ions, ions (sodium and chloride) and 240 nm polystyrene nanoparticles through these membranes demonstrate passable pores and existence of channels within the body of the membrane. Mechanically stretching the porous PDMS membrane and comparing the flow rates of fluoresceinate ions and the polystyrene beads through the stretched and unstretched membranes allowed a direct proof of the modulation of transport rate in the membranes. We show that stretching the membranes by 10% increases the flow rate of fluorescein molecules by 2.8 times and by a factor of approximately ~40% for the polystyrene nanoparticles. PMID:22942529

  15. [Sodium ion transportation system and its possible mechanisms in bacteria].

    PubMed

    Yang, Li-Fu; Zhao, Bai-Suo; Yang, Su-Sheng

    2007-12-01

    Sodium ion with high concentration is toxic to living cells, and microorganisms adapt to the environment containing high concentration of salt by the strategies of salt-in-cytoplasm and compatible solutes. The Na+ extrusion system plays important roles in maintaining cytoplasmic Na+ homeostasis and pH level in microbial cells. Two possible mechanisms of Na+ circulation across the cytoplasmic membrane have been proposed, namely primary Na+ pump and secondary Na+/H+ antiporter. Primary sodium pumps coupled the extrusion of Na+ to respiration, and the activity of which was insensitive to uncoupler CCCP ( carbonyl-cyanide m-chlorophenylhydrazone). There were two types of secondary Na+/H+ antiporters-encoding genes designated single gene and multiple subunits, respectively. The types of transportation systems for Na+, possible mechanisms of Na+ extrusion, and projects for further study in bacteria are reviewed.

  16. Membrane transporters in drug development

    PubMed Central

    2011-01-01

    Membrane transporters can be major determinants of the pharmacokinetic, safety and efficacy profiles of drugs. This presents several key questions for drug development, including which transporters are clinically important in drug absorption and disposition, and which in vitro methods are suitable for studying drug interactions with these transporters. In addition, what criteria should trigger follow-up clinical studies, and which clinical studies should be conducted if needed. In this article, we provide the recommendations of the International Transporter Consortium on these issues, and present decision trees that are intended to help guide clinical studies on the currently recognized most important drug transporter interactions. The recommendations are generally intended to support clinical development and filing of a new drug application. Overall, it is advised that the timing of transporter investigations should be driven by efficacy, safety and clinical trial enrolment questions (for example, exclusion and inclusion criteria), as well as a need for further understanding of the absorption, distribution, metabolism and excretion properties of the drug molecule, and information required for drug labeling. PMID:20190787

  17. Electrophysiological characterization of membrane transport proteins.

    PubMed

    Grewer, Christof; Gameiro, Armanda; Mager, Thomas; Fendler, Klaus

    2013-01-01

    Active transport in biological membranes has been traditionally studied using a variety of biochemical and biophysical techniques, including electrophysiology. This review focuses on aspects of electrophysiological methods that make them particularly suited for the investigation of transporter function. Two major approaches to electrical recording of transporter activity are discussed: (a) artificial planar lipid membranes, such as the black lipid membrane and solid supported membrane, which are useful for studies on bacterial transporters and transporters of intracellular compartments, and (b) patch clamp and voltage clamp techniques, which investigate transporters in native cellular membranes. The analytical power of these methods is highlighted by several examples of mechanistic studies of specific membrane proteins, including cytochrome c oxidase, NhaA Na(+)/H(+) exchanger, ClC-7 H(+)/Cl(-) exchanger, glutamate transporters, and neutral amino acid transporters. These examples reveal the wealth of mechanistic information that can be obtained when electrophysiological methods are used in combination with rapid perturbation approaches.

  18. Urea transport through composite polyallylamine membranes

    NASA Technical Reports Server (NTRS)

    Ballou, E. V.; Kubo, L. Y.; Spitze, L. A.; Wydeven, T.; Clark, J. A.

    1977-01-01

    Polyallylamine composite reverse osmosis membranes were prepared by plasma polymerization and deposition onto small-pored cellulose acetate/cellulose nitrate films. The polyallylamine coated the porous substrate with a thin uniform polymer film which exhibited water permeability and urea rejection, of interest because of the potential application of reverse osmosis to urine purification in closed environmental systems. The flux of C-14 labeled urea was studied under the influence of osmotic gradients provided by sodium chloride solutions. The urea flux was found to be enhanced by an osmotic pressure gradient in the same direction and diminished, but not prevented, by an opposing osmotic pressure gradient. Consideration is given to the mechanism of the urea transport, as well as to the influence of concentration polarization on the experimental results. The minimization of coupled flow in pores of a critical size range is apparently necessary to improve urea rejection.

  19. Urea transport through composite polyallylamine membranes

    NASA Technical Reports Server (NTRS)

    Ballou, E. V.; Kubo, L. Y.; Spitze, L. A.; Wydeven, T.; Clark, J. A.

    1977-01-01

    Polyallylamine composite reverse osmosis membranes were prepared by plasma polymerization and deposition onto small-pored cellulose acetate/cellulose nitrate films. The polyallylamine coated the porous substrate with a thin uniform polymer film which exhibited water permeability and urea rejection, of interest because of the potential application of reverse osmosis to urine purification in closed environmental systems. The flux of C-14 labeled urea was studied under the influence of osmotic gradients provided by sodium chloride solutions. The urea flux was found to be enhanced by an osmotic pressure gradient in the same direction and diminished, but not prevented, by an opposing osmotic pressure gradient. Consideration is given to the mechanism of the urea transport, as well as to the influence of concentration polarization on the experimental results. The minimization of coupled flow in pores of a critical size range is apparently necessary to improve urea rejection.

  20. Ionic requirements of proximal tubular sodium transport. II. Hydrogen ion.

    PubMed

    Green, R; Giebisch, G

    1975-11-01

    Simultaneous perfusion to proximal convoluted tubules and peritubular capillaries was used to study the effects of different perfusion fluids on sodium reabsorption and hydrogen secretion, which was calculated as bicarbonate reabsorption and titratable acid. Results show that sodium reabsorption was not tightly coupled to hydrogen secretion. Bicarbonate stimulates both sodium reabsorption and hydrogen secretion, but Tris stimulates only sodium reabsorption. Imposing an adverse chloride gradient across the proximal tubule (C1- peritubular greater than C1- luminal) decreased sodium reabsorption but did not diminish hydrogen secretion. Diamox inhibited both net sodium and hydrogen transport. It is concluded that there is not firm linkage between sodium reabsorption and hydrogen secretion and that bicarbonate probably stimulates sodium transport by a number of mechanisms, including an effect on the sodium transport unrelated to its ability to increase hydrogen ion secretion.

  1. Pyrithione and 8-hydroxyquinolines transport lead across erythrocyte membranes.

    PubMed

    Lind, Stuart E; Park, Jong Sung; Drexler, John W

    2009-09-01

    Acute and chronic lead poisoning remains a significant health problem. Although chelating agents can bind to plasma lead, they cannot cross cell membranes where the total body lead burden resides, and are thus inefficient at reducing the total body lead burden. Recently, calcium and sodium ionophores have been shown to transport lead across cell membranes providing a novel method for reducing total body lead stores. We recently found that clioquinol, an 8-hydroxyquinoline derivative, can act as a zinc ionophore. We postulated that zinc ionophores might also be able to transport lead across biological membranes. To study this, we loaded lead in vitro into human erythrocytes and then studied the ability of zinc ionophores to transport lead into the extracellular space, where it was trapped with a lead chelator. Using inductively coupled plasma mass spectrometry (ICP-MS), we found that several 8-hydroxyquinoline derivatives, as well as the zinc and sodium salts of pyrithione (N-hydroxypyridine-2-thione), reduced erythrocyte lead content. The water-soluble compound, sodium pyrithione, was able to reduce lead in citrated whole blood, without partitioning into the erythrocytes. These results indicate that two classes of zinc ionophores can transport lead across a biological membrane, and they confirm that these ionophores are not cation-specific. Lead ionophores may prove useful in mobilizing lead into the extracellular space, thereby improving the efficacy of chelation therapy, in vivo or ex vivo.

  2. The plasma membrane sodium-hydrogen exchanger and its role in physiological and pathophysiological processes.

    PubMed

    Mahnensmith, R L; Aronson, P S

    1985-06-01

    The plasma membranes of most if not all vertebrate cells contain a transport system that mediates the transmembrane exchange of sodium for hydrogen. The kinetic properties of this transport system include a 1:1 stoichiometry, affinity for lithium and ammonium ion in addition to sodium and hydrogen, the ability to function in multiple 1:1 exchange modes involving these four cations, sensitivity to inhibition by amiloride and its analogues, and allosteric regulation by intracellular protons. The plasma membrane sodium-hydrogen exchanger plays a physiological role in the regulation of intracellular pH, the control of cell growth and proliferation, stimulus-response coupling in white cells and platelets, the metabolic response to hormones such as insulin and glucocorticoids, the regulation of cell volume, and the transepithelial absorption and secretion of sodium, hydrogen, bicarbonate and chloride ions, and organic anions. Preliminary evidence raises the possibility that the sodium-hydrogen exchanger may play a pathophysiological role in such diverse conditions as renal acid-base disorders, essential hypertension, cancer, and tissue or organ hypertrophy. Thus, future research on cellular acid-base homeostasis in general, and on plasma membrane sodium-hydrogen exchange in particular, will enhance our understanding of a great variety of physiological and pathophysiological processes.

  3. Iontophoretic Transport Across a Multiple Membrane System

    PubMed Central

    MOLOKHIA, SARAH A.; ZHANG, YANHUI; HIGUCHI, WILLIAM I.; LI, S. KEVIN

    2008-01-01

    The objective of the present study was to investigate the iontophoretic transport behavior across multiple membranes of different barrier properties. Spectra/Por® (SP) and Ionac membranes were the synthetic membranes and sclera was the biomembrane in this model study. The barrier properties of SP membranes were determined individually in passive and iontophoresis transport experiments with tetraethylammonium ion (TEA), chloride ion (Cl), and mannitol as the model permeants. Passive and iontophoretic transport experiments were then conducted with an assembly of SP membranes. The contribution of electroosmosis to iontophoresis was assessed using the mannitol data. Model analysis was performed to study the contribution of diffusion and electromigration to electrotransport across the multiple membrane system. The effects of membrane barrier thickness upon ion-exchange membrane-enhanced iontophoresis were examined with Ionac, SP, and sclera. The present study shows that iontophoretic transport of TEA across the membrane system was related to the thicknesses and permeability coefficients of the membranes and the electromobilities of the permeant across the individual membranes in the assembly. Model analysis suggests significant contribution of diffusion within the membranes across the membrane system, and this mechanism is relatively independent of the current density applied across the system in iontophoresis dominant transport. PMID:17990310

  4. Catalyst containing oxygen transport membrane

    DOEpatents

    Lane, Jonathan A.; Wilson, Jamie R.; Christie, Gervase Maxwell; Petigny, Nathalie; Sarantopoulos, Christos

    2017-02-07

    A composite oxygen transport membrane having a dense layer, a porous support layer and an intermediate porous layer located between the dense layer and the porous support layer. Both the dense layer and the intermediate porous layer are formed from an ionic conductive material to conduct oxygen ions and an electrically conductive material to conduct electrons. The porous support layer has a high permeability, high porosity, and a microstructure exhibiting substantially uniform pore size distribution as a result of using PMMA pore forming materials or a bi-modal particle size distribution of the porous support layer materials. Catalyst particles selected to promote oxidation of a combustible substance are located in the intermediate porous layer and in the porous support adjacent to the intermediate porous layer. The catalyst particles can be formed by wicking a solution of catalyst precursors through the porous support toward the intermediate porous layer.

  5. Catalyst containing oxygen transport membrane

    DOEpatents

    Christie, Gervase Maxwell; Wilson, Jamie Robyn; van Hassel, Bart Antonie

    2012-12-04

    A composite oxygen transport membrane having a dense layer, a porous support layer and an intermediate porous layer located between the dense layer and the porous support layer. Both the dense layer and the intermediate porous layer are formed from an ionic conductive material to conduct oxygen ions and an electrically conductive material to conduct electrons. The porous support layer has a high permeability, high porosity, and a high average pore diameter and the intermediate porous layer has a lower permeability and lower pore diameter than the porous support layer. Catalyst particles selected to promote oxidation of a combustible substance are located in the intermediate porous layer and in the porous support adjacent to the intermediate porous layer. The catalyst particles can be formed by wicking a solution of catalyst precursors through the porous support toward the intermediate porous layer.

  6. Electrogenic sodium/bicarbonate cotransport in rabbit renal cortical basolateral membrane vesicles.

    PubMed Central

    Akiba, T; Alpern, R J; Eveloff, J; Calamina, J; Warnock, D G

    1986-01-01

    The present studies examined the mechanism of bicarbonate transport across basolateral membrane vesicles prepared from rabbit renal cortex. Isotopic sodium uptake was stimulated by bicarbonate when compared with gluconate (2.5 nmol/mg protein per 5 s versus 1.4 nmol/mg protein per 5 s), and this process was inhibited by disulfonic stilbenes. Imposition of an interior-positive potassium diffusion potential further stimulated isotopic sodium uptake to 3.4 nmol/mg protein per 5 s, an effect that occurred only in the presence of bicarbonate and was blocked by disulfonic stilbenes. Kinetic analysis of the rate of bicarbonate-dependent sodium uptake as a function of sodium concentration revealed saturable stimulation with a Vmax of 2.7 nmol/mg protein per 2 s and a Km of 10.4 mM. The effect of bicarbonate concentration on bicarbonate-dependent sodium uptake was more complex. The present results demonstrate an electrogenic (negatively charged) sodium/bicarbonate cotransporter in basolateral membrane vesicles from the rabbit renal cortex. The electrogenicity implies a stoichiometry of at least two bicarbonate ions for each sodium ion. PMID:3782468

  7. Analysis of the sodium recirculation theory of solute-coupled water transport in small intestine

    PubMed Central

    Larsen, Erik Hviid; Sørensen, Jakob Balslev; Sørensen, Jens Nørkær

    2002-01-01

    Our previous mathematical model of solute-coupled water transport through the intestinal epithelium is extended for dealing with electrolytes rather than electroneutral solutes. A 3Na+–2K+ pump in the lateral membranes provides the energy-requiring step for driving transjunctional and translateral flows of water across the epithelium with recirculation of the diffusible ions maintained by a 1Na+-1K+–2Cl− cotransporter in the plasma membrane facing the serosal compartment. With intracellular non-diffusible anions and compliant plasma membranes, the model describes the dependence on membrane permeabilities and pump constants of fluxes of water and electrolytes, volumes and ion concentrations of cell and lateral intercellular space (lis), and membrane potentials and conductances. Simulating physiological bioelectrical features together with cellular and paracellular fluxes of the sodium ion, computations predict that the concentration differences between lis and bathing solutions are small for all three ions. Nevertheless, the diffusion fluxes of the ions out of lis significantly exceed their mass transports. It is concluded that isotonic transport requires recirculation of all three ions. The computed sodium recirculation flux that is required for isotonic transport corresponds to that estimated in experiments on toad small intestine. This result is shown to be robust and independent of whether the apical entrance mechanism for the sodium ion is a channel, a SGLT1 transporter driving inward uphill water flux, or an electroneutral Na+–K+–2Cl− cotransporter. PMID:12096047

  8. Sodium and potassium conductance changes during a membrane action potential.

    PubMed

    Bezanilla, F; Rojas, E; Taylor, R E

    1970-12-01

    1. A method for turning a membrane potential control system on and off in less than 10 musec is described. This method was used to record membrane currents in perfused giant axons from Dosidicus gigas and Loligo forbesi after turning on the voltage clamp system at various times during the course of a membrane action potential.2. The membrane current measured just after the capacity charging transient was found to have an almost linear relation to the controlled membrane potential.3. The total membrane conductance taken from these current-voltage curves was found to have a time course during the action potential similar to that found by Cole & Curtis (1939).4. The instantaneous current voltage curves were linear enough to make it possible to obtain a good estimate of the individual sodium and potassium channel conductances, either algebraically or by clamping to the sodium, or potassium, reversal potentials. Good general agreement was obtained with the predictions of the Hodgkin-Huxley equations.5. We consider these results to constitute the first direct experimental demonstration of the conductance changes to sodium and potassium during the course of an action potential.

  9. Sodium and potassium conductance changes during a membrane action potential

    PubMed Central

    Bezanilla, Francisco; Rojas, Eduardo; Taylor, Robert E.

    1970-01-01

    1. A method for turning a membrane potential control system on and off in less than 10 μsec is described. This method was used to record membrane currents in perfused giant axons from Dosidicus gigas and Loligo forbesi after turning on the voltage clamp system at various times during the course of a membrane action potential. 2. The membrane current measured just after the capacity charging transient was found to have an almost linear relation to the controlled membrane potential. 3. The total membrane conductance taken from these current—voltage curves was found to have a time course during the action potential similar to that found by Cole & Curtis (1939). 4. The instantaneous current voltage curves were linear enough to make it possible to obtain a good estimate of the individual sodium and potassium channel conductances, either algebraically or by clamping to the sodium, or potassium, reversal potentials. Good general agreement was obtained with the predictions of the Hodgkin—Huxley equations. 5. We consider these results to constitute the first direct experimental demonstration of the conductance changes to sodium and potassium during the course of an action potential. PMID:5505231

  10. Coupling Substrate and Ion Binding to Extracellular Gate of a Sodium-Dependent Aspartate Transporter

    SciTech Connect

    Boudker,O.; Ryan, R.; Yernool, D.; Shimamoto, K.; Gouaux, E.

    2007-01-01

    Secondary transporters are integral membrane proteins that catalyze the movement of substrate molecules across the lipid bilayer by coupling substrate transport to one or more ion gradients, thereby providing a mechanism for the concentrative uptake of substrates. Here we describe crystallographic and thermodynamic studies of Glt{sub Ph}, a sodium (Na{sup +})-coupled aspartate transporter, defining sites for aspartate, two sodium ions and D,L-threo-{beta}-benzyloxyaspartate, an inhibitor. We further show that helical hairpin 2 is the extracellular gate that controls access of substrate and ions to the internal binding sites. At least two sodium ions bind in close proximity to the substrate and these sodium-binding sites, together with the sodium-binding sites in another sodium-coupled transporter, LeuT, define an unwound {alpha}-helix as the central element of the ion-binding motif, a motif well suited to the binding of sodium and to participation in conformational changes that accompany ion binding and unbinding during the transport cycle.

  11. Ion transport membrane module and vessel system

    DOEpatents

    Stein, VanEric Edward [Allentown, PA; Carolan, Michael Francis [Allentown, PA; Chen, Christopher M [Allentown, PA; Armstrong, Phillip Andrew [Orefield, PA; Wahle, Harold W [North Canton, OH; Ohrn, Theodore R [Alliance, OH; Kneidel, Kurt E [Alliance, OH; Rackers, Keith Gerard [Louisville, OH; Blake, James Erik [Uniontown, OH; Nataraj, Shankar [Allentown, PA; van Doorn, Rene Hendrik Elias; Wilson, Merrill Anderson [West Jordan, UT

    2008-02-26

    An ion transport membrane system comprising (a) a pressure vessel having an interior, an exterior, an inlet, and an outlet; (b) a plurality of planar ion transport membrane modules disposed in the interior of the pressure vessel and arranged in series, each membrane module comprising mixed metal oxide ceramic material and having an interior region and an exterior region, wherein any inlet and any outlet of the pressure vessel are in flow communication with exterior regions of the membrane modules; and (c) one or more gas manifolds in flow communication with interior regions of the membrane modules and with the exterior of the pressure vessel.The ion transport membrane system may be utilized in a gas separation device to recover oxygen from an oxygen-containing gas or as an oxidation reactor to oxidize compounds in a feed gas stream by oxygen permeated through the mixed metal oxide ceramic material of the membrane modules.

  12. Ion transport membrane module and vessel system

    DOEpatents

    Stein, VanEric Edward [Allentown, PA; Carolan, Michael Francis [Allentown, PA; Chen, Christopher M [Allentown, PA; Armstrong, Phillip Andrew [Orefield, PA; Wahle, Harold W [North Canton, OH; Ohrn, Theodore R [Alliance, OH; Kneidel, Kurt E [Alliance, OH; Rackers, Keith Gerard [Louisville, OH; Blake, James Erik [Uniontown, OH; Nataraj, Shankar [Allentown, PA; Van Doorn, Rene Hendrik Elias; Wilson, Merrill Anderson [West Jordan, UT

    2012-02-14

    An ion transport membrane system comprising (a) a pressure vessel having an interior, an exterior, an inlet, and an outlet; (b) a plurality of planar ion transport membrane modules disposed in the interior of the pressure vessel and arranged in series, each membrane module comprising mixed metal oxide ceramic material and having an interior region and an exterior region, wherein any inlet and any outlet of the pressure vessel are in flow communication with exterior regions of the membrane modules; and (c) one or more gas manifolds in flow communication with interior regions of the membrane modules and with the exterior of the pressure vessel. The ion transport membrane system may be utilized in a gas separation device to recover oxygen from an oxygen-containing gas or as an oxidation reactor to oxidize compounds in a feed gas stream by oxygen permeated through the mixed metal oxide ceramic material of the membrane modules.

  13. Ion transport membrane module and vessel system

    DOEpatents

    Stein, VanEric Edward; Carolan, Michael Francis; Chen, Christopher M.; Armstrong, Phillip Andrew; Wahle, Harold W.; Ohrn, Theodore R.; Kneidel, Kurt E.; Rackers, Keith Gerard; Blake, James Erik; Nataraj, Shankar; van Doorn, Rene Hendrik Elias; Wilson, Merrill Anderson

    2007-02-20

    An ion transport membrane system comprising (a) a pressure vessel having an interior, an exterior, an inlet, and an outlet; (b) a plurality of planar ion transport membrane modules disposed in the interior of the pressure vessel and arranged in series, each membrane module comprising mixed metal oxide ceramic material and having an interior region and an exterior region, wherein any inlet and any outlet of the pressure vessel are in flow communication with exterior regions of the membrane modules; and (c) one or more gas manifolds in flow communication with interior regions of the membrane modules and with the exterior of the pressure vessel. The ion transport membrane system may be utilized in a gas separation device to recover oxygen from an oxygen-containing gas or as an oxidation reactor to oxidize compounds in a feed gas stream by oxygen permeated through the mixed metal oxide ceramic material of the membrane modules.

  14. Ion transport membrane module and vessel system

    DOEpatents

    Stein, VanEric Edward; Carolan, Michael Francis; Chen, Christopher M.; Armstrong, Phillip Andrew; Wahle, Harold W.; Ohrn, Theodore R.; Kneidel, Kurt E.; Rackers, Keith Gerard; Blake, James Erik; Nataraj, Shankar; van Doorn, Rene Hendrik Elias; Wilson, Merrill Anderson

    2008-02-26

    An ion transport membrane system comprising (a) a pressure vessel having an interior, an exterior, an inlet, and an outlet; (b) a plurality of planar ion transport membrane modules disposed in the interior of the pressure vessel and arranged in series, each membrane module comprising mixed metal oxide ceramic material and having an interior region and an exterior region, wherein any inlet and any outlet of the pressure vessel are in flow communication with exterior regions of the membrane modules; and (c) one or more gas manifolds in flow communication with interior regions of the membrane modules and with the exterior of the pressure vessel.The ion transport membrane system may be utilized in a gas separation device to recover oxygen from an oxygen-containing gas or as an oxidation reactor to oxidize compounds in a feed gas stream by oxygen permeated through the mixed metal oxide ceramic material of the membrane modules.

  15. Membrane transport of several ions during peritoneal dialysis: mathematical modeling.

    PubMed

    Galach, Magda; Waniewski, Jacek

    2012-09-01

    Peritoneal dialysis utilizes a complex mass exchange device created by natural permselective membranes of the visceral and abdominal muscle tissues. In mathematical modeling of solute transport during peritoneal dialysis, each solute is typically considered as a neutral, independent particle. However, such mathematical models cannot predict transport parameters for small ions. Therefore, the impact of the electrostatic interactions between ions on the estimated transport parameters needs to be investigated. In this study, transport of sodium, chloride, and a third ion through a permselective membrane with characteristics of the peritoneal transport barrier was described using two models: a model with the Nernst-Planck (NP) equations for a set of interacting ions and a model with combined diffusive and convective transport of each ion separately (DC). Transport parameters for the NP model were calculated using the pore theory, while the parameters for the DC model were estimated by fitting the model to the predictions from the NP model. Solute concentration profiles in the membrane obtained by computer simulations based on these two models were similar, whereas the transport parameters (diffusive mass transport parameters and sieving coefficients) were generally different. The presence of the third ion could substantially modify the values of diffusive mass parameter for sodium and chloride ions estimated using the DC model compared with those predicted by NP. The extent of this modification depended on the molecular mass and concentration of the third ion, and the rate of volumetric flow. Closed formulas for the transport parameters of the DC model in terms of the NP model parameters, ion concentration profiles in the membrane, and volumetric flow across the membrane were derived. Their reliable approximations, which include only boundary ion concentrations instead of spatial intramembrane concentration profiles, were formulated. The precision of this approximation

  16. Characterization and isolation of a light driven sodium pump from membranes of Halobacterium halobium. Final technical progress report

    SciTech Connect

    MacDonald, R.E.

    1982-01-01

    We investigated three aspects of the light driven sodium pump (halorhodopsin, which appear to be crucial to our understanding of the mechanisms employed by Halobacterium halobium and to further investigate this unique system of energy conservation. We characterized the molecular mechanisms of transmembrane sodium transport in vesicles from H. halobium with particular reference to the mechanism of couplins of light energy to net sodium translocation. We develop procedures and techniques for extracting the components of the light driven sodium pump from membranes and incorporating them into artificial membrane systems. We examine the mechanism of conversion of bacteriorhodopsin from an active to an inactive form in membrane vesicles and to relate this alternative state of this pigment to the presence of the light driven sodium pump.

  17. Fluid transport by active elastic membranes

    NASA Astrophysics Data System (ADS)

    Evans, Arthur A.; Lauga, Eric

    2011-09-01

    A flexible membrane deforming its shape in time can self-propel in a viscous fluid. Alternatively, if the membrane is anchored, its deformation will lead to fluid transport. Past work in this area focused on situations where the deformation kinematics of the membrane were prescribed. Here we consider models where the deformation of the membrane is not prescribed, but instead the membrane is internally forced. Both the time-varying membrane shape and the resulting fluid motion result then from a balance between prescribed internal active stresses, internal passive resistance, and external viscous stresses. We introduce two specific models for such active internal forcing: one where a distribution of active bending moments is prescribed, and one where active inclusions exert normal stresses on the membrane by pumping fluid through it. In each case, we asymptotically calculate the membrane shape and the fluid transport velocities for small forcing amplitudes, and recover our results using scaling analysis.

  18. Membrane Transporters: Structure, Function and Targets for Drug Design

    NASA Astrophysics Data System (ADS)

    Ravna, Aina W.; Sager, Georg; Dahl, Svein G.; Sylte, Ingebrigt

    Current therapeutic drugs act on four main types of molecular targets: enzymes, receptors, ion channels and transporters, among which a major part (60-70%) are membrane proteins. This review discusses the molecular structures and potential impact of membrane transporter proteins on new drug discovery. The three-dimensional (3D) molecular structure of a protein contains information about the active site and possible ligand binding, and about evolutionary relationships within the protein family. Transporters have a recognition site for a particular substrate, which may be used as a target for drugs inhibiting the transporter or acting as a false substrate. Three groups of transporters have particular interest as drug targets: the major facilitator superfamily, which includes almost 4000 different proteins transporting sugars, polyols, drugs, neurotransmitters, metabolites, amino acids, peptides, organic and inorganic anions and many other substrates; the ATP-binding cassette superfamily, which plays an important role in multidrug resistance in cancer chemotherapy; and the neurotransmitter:sodium symporter family, which includes the molecular targets for some of the most widely used psychotropic drugs. Recent technical advances have increased the number of known 3D structures of membrane transporters, and demonstrated that they form a divergent group of proteins with large conformational flexibility which facilitates transport of the substrate.

  19. Ionic transport properties of template-synthesized gold nanotube membranes

    NASA Astrophysics Data System (ADS)

    Gao, Peng

    Ionic transport in nanotubes exhibits unique properties due to the strong interactions between ions and the nanotube surface. The main objective of my research is to explore and regulate the ionic transport in gold nanotube membranes. Chapter 1 overviews a versatile method of fabricating nanostructured materials, called the template synthesis. Important parameters of the template synthesis are introduced such as templates and deposition methods. The template synthesis method is used to prepare membranes used in this dissertation. Chapter 2 describes a method to increase the ionic conductivity in membranes containing gold nanotubes with small diameter (4 nm). The gold nanotube membrane is prepared by the electroless plating of gold in a commercially available polycarbonate membrane. Voltages are applied to the gold nanotube membrane and fixed charges are injected on the gold nanotube walls. We show that ionic conductivity of the gold nanotube membrane can be enhanced in aqueous potassium chloride (KCl) solution at negative applied voltages. When the most negative voltage (-0.8 V vs. Ag/AgCl) is applied to the membrane, the ionic conductivity of the solution inside the gold nanotube (94 mS.cm-1) is comparable to that of 1 M aqueous KCl, over two orders of magnitude higher than that of the 0.01 M KCl contacting the membrane. Chapter 3 explores another important transport property of the gold nanotube membrane -- ion permselectivity. When the permselective membrane separates two electrolyte solutions at different concentrations, a membrane potential is developed and measured by the potentiometric method. Surface charge density and the ion mobilities are estimated by fitting the experimental data with a pre-existing model. The surface charge density of the gold nanotube membrane in this research is estimated to be 2 muC/cm2. Chapter 4 describes voltage-controlled ionic transport in a gold/polypyrrole membrane doped with sodium dodecylbenzene sulfonate (DBS). Polypyrrole

  20. Hydrogen Peroxide and Sodium Transport in the Lung and Kidney

    PubMed Central

    Shlyonsky, V.; Boom, A.; Mies, F.

    2016-01-01

    Renal and lung epithelial cells are exposed to some significant concentrations of H2O2. In urine it may reach 100 μM, while in the epithelial lining fluid in the lung it is estimated to be in micromolar to tens-micromolar range. Hydrogen peroxide has a stimulatory action on the epithelial sodium channel (ENaC) single-channel activity. It also increases stability of the channel at the membrane and slows down the transcription of the ENaC subunits. The expression and the activity of the channel may be inhibited in some other, likely higher, oxidative states of the cell. This review discusses the role and the origin of H2O2 in the lung and kidney. Concentration-dependent effects of hydrogen peroxide on ENaC and the mechanisms of its action have been summarized. This review also describes outlooks for future investigations linking oxidative stress, epithelial sodium transport, and lung and kidney function. PMID:27073804

  1. Regulation of Sodium Transport in the Inner Ear

    PubMed Central

    Kim, Sung Huhn; Marcus, Daniel C.

    2011-01-01

    Na+ concentrations in endolymph must be controlled to maintain hair cell function since the transduction channels of hair cells are cation-permeable, but not K+-selective. Flooding or fluctuations of the hair cell cytosol with Na+ would be expected to lead to cellular dysfunction, hearing loss and vertigo. This review briefly describes cellular mechanisms known to be responsible for Na+homeostasis in each compartment of the inner ear, including the cochlea, saccule, semicircular canals and endolymphatic sac. The influx of Na+into endolymph of each of the organs is likely via passive diffusion, but these pathways have not yet been identified or characterized. Na+ absorption is controlled by gate -keeper channels in the apical (endolymphatic) membrane of the transporting cells. Highly Na+-selective epithelial sodium channels (ENaC) control absorption by Reissner’s membrane, saccular extramacular epithelium, semicircular canal duct epithelium and endolymphatic sac. ENaC activity is controlled by a number of signal pathways, but most notably by genomic regulation of channel numbers in the membrane via glucocorticoid signaling. Nonselective cation channels in the apical membrane of outer sulcus epithelial cells and vestibular transitional cells mediate Na+ and parasensory K+ absorption. The K+-mediated transduction current in hair cells is also accompanied by a Na+ flux since the transduction channels are nonselective cation channels. Cation absorption by all of these cells is regulated by extracellular ATP via apical nonselective cation channels (P2X receptors). The heterogeneous population of epithelial cells in the endolymphatic sac is thought to have multiple absorptive pathways for Na+ with regulatory pathways that include glucocorticoids and purinergic agonists. PMID:21620939

  2. Regulation of sodium transport in the inner ear.

    PubMed

    Kim, Sung Huhn; Marcus, Daniel C

    2011-10-01

    Na(+) concentrations in endolymph must be controlled to maintain hair cell function since the transduction channels of hair cells are cation-permeable, but not K(+)-selective. Flooding or fluctuations of the hair cell cytosol with Na(+) would be expected to lead to cellular dysfunction, hearing loss and vertigo. This review briefly describes cellular mechanisms known to be responsible for Na(+) homeostasis in each compartment of the inner ear, including the cochlea, saccule, semicircular canals and endolymphatic sac. The influx of Na(+) into endolymph of each of the organs is likely via passive diffusion, but these pathways have not yet been identified or characterized. Na(+) absorption is controlled by gate-keeper channels in the apical (endolymphatic) membrane of the transporting cells. Highly Na(+)-selective epithelial sodium channels (ENaCs) control absorption by Reissner's membrane, saccular extramacular epithelium, semicircular canal duct epithelium and endolymphatic sac. ENaC activity is controlled by a number of signal pathways, but most notably by genomic regulation of channel numbers in the membrane via glucocorticoid signaling. Non-selective cation channels in the apical membrane of outer sulcus epithelial cells and vestibular transitional cells mediate Na(+) and parasensory K(+) absorption. The K(+)-mediated transduction current in hair cells is also accompanied by a Na(+) flux since the transduction channels are non-selective cation channels. Cation absorption by all of these cells is regulated by extracellular ATP via apical non-selective cation channels (P2X receptors). The heterogeneous population of epithelial cells in the endolymphatic sac is thought to have multiple absorptive pathways for Na(+) with regulatory pathways that include glucocorticoids and purinergic agonists. Copyright © 2011 Elsevier B.V. All rights reserved.

  3. Ceramic oxygen transport membrane array reactor and reforming method

    DOEpatents

    Kelly, Sean M.; Christie, Gervase Maxwell; Robinson, Charles; Wilson, Jamie R.; Gonzalez, Javier E.; Doraswami, Uttam R.

    2016-11-08

    The invention relates to a commercially viable modular ceramic oxygen transport membrane reforming reactor configured using repeating assemblies of oxygen transport membrane tubes and catalytic reforming reactors.

  4. Liners for ion transport membrane systems

    DOEpatents

    Carolan, Michael Francis; Miller, Christopher Francis

    2010-08-10

    Ion transport membrane system comprising (a) a pressure vessel comprising an interior, an exterior, an inlet, an inlet conduit, an outlet, and an outlet conduit; (b) a plurality of planar ion transport membrane modules disposed in the interior of the pressure vessel and arranged in series, each membrane module comprising mixed metal oxide ceramic material and having an interior region and an exterior region, wherein the inlet and the outlet of the pressure vessel are in flow communication with exterior regions of the membrane modules; (c) a gas manifold having an interior surface wherein the gas manifold is in flow communication with the interior region of each of the planar ion transport membrane modules and with the exterior of the pressure vessel; and (d) a liner disposed within any of the inlet conduit, the outlet conduit, and the interior surface of the gas manifold.

  5. The coupled movements of sodium and chloride across the basolateral membrane of frog skin epithelium.

    PubMed Central

    Fernandes, P L; Ferreira, H G; Ferreira, K T

    1989-01-01

    1. When frog skin epithelium was exposed to a chloride-free solution bathing the basolateral side of the frog skin preparation the short-circuit current fell and there was a simultaneous loss of chloride and water from its cells. This effect was partially blocked by furosemide when this drug was added to the basolateral bathing solution. 2. Under control conditions and when added to the solution bathing the basolateral side of the preparation furosemide had no effect on the ion and water contents of the frog skin epithelium. 3. Furosemide but not SITS (4-acetamide-4'-isothiocyanate-stilbene-2,2'-disulphonic acid) or amiloride blocked the recovery of short-circuit current and the reuptake of chloride and water by preparations pre-incubated with chloride-free solution on the basolateral side. The recovery of the short-circuit current was also blocked by the replacement of basolateral potassium by sodium. 4. The effect on the short-circuit current of graded replacements by impermeant ions of sodium or chloride did not show saturation for concentrations of these ions up to their control values. 5. Replacement of basolateral potassium by sodium inhibited the short-circuit current and the recovery observed when potassium was reintroduced in the basolateral bathing solution was blocked by furosemide. 6. The replacement of basolateral sodium or chloride by impermeant ions induced an immediate fall in the intracellular concentrations of both sodium and chloride suggesting that the transport system coupling the movements of the two ions across the basolateral membrane is operative under control conditions. 7. It is proposed that the coupled movements of sodium and chloride across the basolateral membrane of the frog skin epithelium are mediated by a sodium-potassium-2 chloride co-transport system which under control conditions is very near equilibrium. PMID:2607456

  6. Dopamine and Angiotensin Type 2 Receptors Cooperatively Inhibit Sodium Transport in Human Renal Proximal Tubule Cells

    PubMed Central

    Gildea, John J.; Wang, Xiaoli; Shah, Neema; Tran, Hanh; Spinosa, Michael; Van Sciver, Robert; Sasaki, Midori; Yatabe, Junichi; Carey, Robert M.; Jose, Pedro A.; Felder, Robin A.

    2012-01-01

    Little is known regarding how the kidney shifts from a sodium and water reclaiming state (antinatriuresis) to a state where sodium and water are eliminated (natriuresis). In human renal proximal tubule cells (RPTCs), sodium reabsorption is decreased by the dopamine D1-like receptors (D1R/D5R) and the angiotensin type 2 receptor (AT2R), while the angiotensin type 1 receptor increases sodium reabsorption. Aberrant control of these opposing systems is thought to lead to sodium retention and subsequently hypertension. We show that D1R/D5R stimulation increased plasma membrane AT2R 4-fold via a D1R-mediated, cAMP-coupled, and PP2A-dependent specific signaling pathway. D1R/D5R stimulation also reduced the ability of angiotensin II to stimulate phospho-ERK, an effect that was partially reversed by an AT2R antagonist. Fenoldopam did not increase AT2R recruitment in RPTCs with D1Rs uncoupled from adenylyl cyclase, suggesting a role of cAMP in mediating these events. D1Rs and AT2Rs heterodimerized and cooperatively increased cAMP and cGMP production, PP2A activation, sodium-potassium-ATPase internalization and sodium transport inhibition. These studies shed new light on the regulation of renal sodium transport by the dopaminergic and angiotensin systems and potential new therapeutic targets for selectively treating hypertension. PMID:22710646

  7. Dopamine and angiotensin type 2 receptors cooperatively inhibit sodium transport in human renal proximal tubule cells.

    PubMed

    Gildea, John J; Wang, Xiaoli; Shah, Neema; Tran, Hanh; Spinosa, Michael; Van Sciver, Robert; Sasaki, Midori; Yatabe, Junichi; Carey, Robert M; Jose, Pedro A; Felder, Robin A

    2012-08-01

    Little is known regarding how the kidney shifts from a sodium and water reclaiming state (antinatriuresis) to a state where sodium and water are eliminated (natriuresis). In human renal proximal tubule cells, sodium reabsorption is decreased by the dopamine D(1)-like receptors (D(1)R/D(5)R) and the angiotensin type 2 receptor (AT(2)R), whereas the angiotensin type 1 receptor increases sodium reabsorption. Aberrant control of these opposing systems is thought to lead to sodium retention and, subsequently, hypertension. We show that D(1)R/D(5)R stimulation increased plasma membrane AT(2)R 4-fold via a D(1)R-mediated, cAMP-coupled, and protein phosphatase 2A-dependent specific signaling pathway. D(1)R/D(5)R stimulation also reduced the ability of angiotensin II to stimulate phospho-extracellular signal-regulated kinase, an effect that was partially reversed by an AT(2)R antagonist. Fenoldopam did not increase AT(2)R recruitment in renal proximal tubule cells with D(1)Rs uncoupled from adenylyl cyclase, suggesting a role of cAMP in mediating these events. D(1)Rs and AT(2)Rs heterodimerized and cooperatively increased cAMP and cGMP production, protein phosphatase 2A activation, sodium-potassium-ATPase internalization, and sodium transport inhibition. These studies shed new light on the regulation of renal sodium transport by the dopaminergic and angiotensin systems and potential new therapeutic targets for selectively treating hypertension.

  8. Transport Properties of Cation Exchange Membranes in the Presence of Ether Compounds in Electrodialysis.

    PubMed

    Sata; Tanimoto; Kawamura; Matsusaki

    1999-11-15

    Ether compounds such as ethylene glycols with different molecular weights and crown ethers have good affinity to the cation exchange membranes, sulfonated styrene-divinylbenzene membrane (sodium ion form) and perfluorocarbon sodium sulfonate membrane. The impregnated amount of ethylene glycols in the membranes was higher than the water content of the membranes. After the ether compounds had been impregnated in the cation exchange membranes, electrodialysis of mixed salt solutions (1:1 mixture of alkaline earth metal ions or potassium ions and sodium ions) was carried out in the presence of the compounds to observe the change in permselectivity between two cations. Though current efficiency did not change in the presence of the compounds, transport numbers of alkaline earth metal ions relative to sodium ions decreased. Namely, sodium ions permeated through the membrane more selectively than alkaline earth metal ions. This is due mainly to a decrease in the mobility of alkaline earth metal ions in the membrane phase and partially to a decrease in the ion exchange equilibrium constant of alkaline earth metal ions to sodium ions with the membrane. This originates from the difference in ion-dipole interaction between cations and ether groups. The transport number of potassium ions relative to sodium ions also decreased in the presence of the compounds. In particular, the permeation of potassium ions relative to sodium ions remarkably decreased in the presence of 18-crown-6 in the membrane and in the solution due to the formation of a strong complex between potassium ions and 18-crown-6. Copyright 1999 Academic Press.

  9. A Markov State-based Quantitative Kinetic Model of Sodium Release from the Dopamine Transporter

    PubMed Central

    Razavi, Asghar M.; Khelashvili, George; Weinstein, Harel

    2017-01-01

    The dopamine transporter (DAT) belongs to the neurotransmitter:sodium symporter (NSS) family of membrane proteins that are responsible for reuptake of neurotransmitters from the synaptic cleft to terminate a neuronal signal and enable subsequent neurotransmitter release from the presynaptic neuron. The release of one sodium ion from the crystallographically determined sodium binding site Na2 had been identified as an initial step in the transport cycle which prepares the transporter for substrate translocation by stabilizing an inward-open conformation. We have constructed Markov State Models (MSMs) from extensive molecular dynamics simulations of human DAT (hDAT) to explore the mechanism of this sodium release. Our results quantify the release process triggered by hydration of the Na2 site that occurs concomitantly with a conformational transition from an outward-facing to an inward-facing state of the transporter. The kinetics of the release process are computed from the MSM, and transition path theory is used to identify the most probable sodium release pathways. An intermediate state is discovered on the sodium release pathway, and the results reveal the importance of various modes of interaction of the N-terminus of hDAT in controlling the pathways of release. PMID:28059145

  10. A Markov State-based Quantitative Kinetic Model of Sodium Release from the Dopamine Transporter

    NASA Astrophysics Data System (ADS)

    Razavi, Asghar M.; Khelashvili, George; Weinstein, Harel

    2017-01-01

    The dopamine transporter (DAT) belongs to the neurotransmitter:sodium symporter (NSS) family of membrane proteins that are responsible for reuptake of neurotransmitters from the synaptic cleft to terminate a neuronal signal and enable subsequent neurotransmitter release from the presynaptic neuron. The release of one sodium ion from the crystallographically determined sodium binding site Na2 had been identified as an initial step in the transport cycle which prepares the transporter for substrate translocation by stabilizing an inward-open conformation. We have constructed Markov State Models (MSMs) from extensive molecular dynamics simulations of human DAT (hDAT) to explore the mechanism of this sodium release. Our results quantify the release process triggered by hydration of the Na2 site that occurs concomitantly with a conformational transition from an outward-facing to an inward-facing state of the transporter. The kinetics of the release process are computed from the MSM, and transition path theory is used to identify the most probable sodium release pathways. An intermediate state is discovered on the sodium release pathway, and the results reveal the importance of various modes of interaction of the N-terminus of hDAT in controlling the pathways of release.

  11. Are Sodium Transporters in Urinary Exosomes Reliable Markers of Tubular Sodium Reabsorption in Hypertensive Patients?

    PubMed Central

    Esteva-Font, Cristina; Wang, Xiaoyan; Ars, Elisabet; Guillén-Gómez, Elena; Sans, Laia; González Saavedra, Isabel; Torres, Ferran; Torra, Roser; Masilamani, Shyama; Ballarín, José Aurelio; Fernández-Llama, Patricia

    2010-01-01

    Background Altered renal sodium handling has a major pathogenic role in salt-sensitive hypertension. Renal sodium transporters are present in urinary exosomes. We hypothesized that sodium transporters would be excreted into the urine in different amounts in response to sodium intake in salt-sensitive versus salt-resistant patients. Methods Urinary exosomes were isolated by ultracentrifugation, and their content of Na-K-2Cl cotransporter (NKCC2) and Na-Cl cotransporter (NCC) was analyzed by immunoblotting. Animal studies: NKCC2 and NCC excretion was measured in 2 rat models to test whether changes in sodium transporter excretion are indicative of regulated changes in the kidney tissue. Human studies: in hypertensive patients (n = 41), we investigated: (1) a possible correlation between sodium reabsorption and urinary exosomal excretion of sodium transporters, and (2) the profile of sodium transporter excretion related to blood pressure (BP) changes with salt intake. A 24-hour ambulatory BP monitoring and a 24-hour urine collection were performed after 1 week on a low- and 1 week on a high-salt diet. Results Animal studies: urinary NKCC2 and NCC excretion rates correlated well with their abundance in the kidney. Human studies:6 patients (15%) were classified as salt sensitive. The NKCC2 and NCC abundance did not decrease after the high-salt period, when the urinary sodium reabsorption decreased from 99.7 to 99.0%. In addition, the changes in BP with salt intake were not associated with a specific profile of exosomal excretion. Conclusions Our results do not support the idea that excretion levels of NKCC2 and NCC via urinary exosomes are markers of tubular sodium reabsorption in hypertensive patients. PMID:20068364

  12. Gas transport across hyperthin membranes.

    PubMed

    Wang, Minghui; Janout, Vaclav; Regen, Steven L

    2013-12-17

    The use of organic polymeric membranes to separate gaseous mixtures provides an attractive alternative to other methods such as selective adsorption and cryogenic distillation. The primary advantages of membrane-based separations are their relative energy efficiency and lower costs. Because the flux of a gas across a membrane is inversely proportional to the membrane's thickness, this method relies on fabricating membranes that are as thin as possible. However, as researchers have tried to produce "hyperthin" membranes (less than 100 nm), these membranes often form defects and lose their permeation selectivity. In this Account, we review some of the progress in our laboratories at Lehigh University to create hyperthin membranes with high permeation selectivities. We focus special attention on gaseous permeants that are relevant for the production of clean energy (H2 and CO2 formed from CH4) and the reduction of global warming (CO2 and N2, the major components of flue gas). Our studies make extensive use of Langmuir-Blodgett (LB) methods and porous surfactants derived from calix[6]arenes. We specially designed each surfactant to form cohesive monolayers and multilayers, and we introduced a "gluing" technique, where we cross-link porous surfactants containing quaternary ammonium groups ionically with polymeric counterions. Using ellipsometry, atomic force microscopy, X-ray photoelectron spectroscopy, monolayer isotherm, surface viscosity, and permeation measurements, we have characterized these hyperthin films. While molecular sieving appears to make a significant contribution to the permeation selectivity of some of these membranes, solution-diffusion pathways predominate. We also describe initial studies in which we formed hyperthin films from poly(ethylene glycol)-based polyelectrolytes using layer-by-layer deposition (LbL) methods. We have found remarkably high H2/CO2 and CO2/N2 permeation selectivities with these LB- and LbL-based hyperthin membranes. These

  13. Sulfate transport in Penicillium chrysogenum plasma membranes.

    PubMed Central

    Hillenga, D J; Versantvoort, H J; Driessen, A J; Konings, W N

    1996-01-01

    Transport studies with Penicillium chrysogenum plasma membranes fused with cytochrome c oxidase liposomes demonstrate that sulfate uptake is driven by the transmembrane pH gradient and not by the transmembrane electrical potential. Ca2+ and other divalent cations are not required. It is concluded that the sulfate transport system catalyzes the symport of two protons with one sulfate anion. PMID:8682803

  14. Membrane Transport in Isolated Vesicles from Sugarbeet Taproot 1

    PubMed Central

    Briskin, Donald P.; Thornley, W. Robert; Wyse, Roger E.

    1985-01-01

    Sealed membrane vesicles were isolated from homogenates of sugarbeet (Beta vulgaris L.) taproot by a combination of differential centrifugation, extraction with KI, and dextran gradient centrifugation. Relative to the KI-extracted microsomes, the content of plasma membranes, mitochondrial membranes, and Golgi membranes was much reduced in the final vesicle fraction. A component of ATPase activity that was inhibited by nitrate co-enriched with the capacity of the vesicles to form a steady state pH gradient during the purification procedure. This suggests that the nitrate-sensitive ATPase may be involved in driving H+-transport, and this is consistent with the observation that H+-transport, in the final vesicle fraction was inhibited by nitrate. Proton transport in the sugarbeet vesicles was substrate specific for ATP, insensitive to sodium vanadate and oligomycin but was inhibited by diethylstilbestrol and N,N′-dicyclohexylcarbodiimide. The formation of a pH gradient in the vesicles was enhanced by halide ions in the sequence I− > Br− > Cl− while F− was inhibitory. These stimulatory effects occur from both a direct stimulation of the ATPase by anions and a reduction in the vesicle membrane potential. In the presence of Cl−, alkali cations reduce the pH gradient relative to that observed with bis-tris-propane, possibly by H+/alkali cation exchange. Based upon the properties of the H+-transporting vesicles, it is proposed that they are most likely derived from the tonoplast so that this vesicle preparation would represent a convenient system for studying the mechanism of transport at this membrane boundary. PMID:16664342

  15. Swelling assisted photografting of itaconic acid onto sodium alginate membranes

    NASA Astrophysics Data System (ADS)

    Taşkın, Gülşen; Şanlı, Oya; Asman, Gülsen

    2011-09-01

    Grafting of itaconic acid (IA) was achieved onto sodium alginate (NaAlg) membranes by using UV-radiation. Process was performed under nitrogen atmosphere and benzophenone (BP) was used as a photoinitiator. Membranes were preswelled before the polymerization process and ethanol was determined as the best swelling agent among the studied solvents. The effect of polymerization time, initiator and monomer concentrations on the grafting efficiency were investigated. The best conditions for optimum grafting were obtained with IA concentration of 1.0 M, a BP concentration of 0.1 M and a reaction time of 4 h at 25 °C. Under these conditions grafting efficiency for NaAlg-g-IA membranes was found to be 14% (w/w). To obtain further increase in grafting efficiency membranes were also preswelled in IA and BP solutions and polymerization was carried out at different temperatures after UV polymerization. Grafted membranes were characterized by using Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). Effect of grafting on membrane properties such as intrinsic viscosity and swelling percentage were also determined.

  16. The alternating access mechanism of transport as observed in the sodium-hydantoin transporter Mhp1

    PubMed Central

    Weyand, Simone; Shimamura, Tatsuro; Beckstein, Oliver; Sansom, Mark S. P.; Iwata, So; Henderson, Peter J. F.; Cameron, Alexander D.

    2011-01-01

    Secondary active transporters move molecules across cell membranes by coupling this process to the energetically favourable downhill movement of ions or protons along an electrochemical gradient. They function by the alternating access model of transport in which, through conformational changes, the substrate binding site alternately faces either side of the membrane. Owing to the difficulties in obtaining the crystal structure of a single transporter in different conformational states, relatively little structural information is known to explain how this process occurs. Here, the structure of the sodium-benzylhydantoin transporter, Mhp1, from Microbacterium liquefaciens, has been determined in three conformational states; from this a mechanism is proposed for switching from the outward-facing open conformation through an occluded structure to the inward-facing open state. PMID:21169684

  17. Sodium Ion Production, Acceleration and Transport in Mercury's Magnetosphere

    NASA Astrophysics Data System (ADS)

    Perkins, D. J.; Schriver, D.; Travnicek, P. M.; Hellinger, P.; Richard, R. L.; Raines, J. M.

    2016-12-01

    Observations made by the MESSENGER spacecraft in orbit around Mercury have shown that sodium ions can form a significant portion of the plasma population in the magnetosphere, in particular in the dayside cusp and the nightside magnetotail plasma sheet. The sodium ions, as well as other heavy ions observed in and around Mercury, are of planetary origin and can be created by a number of different processes, including photo stimulated desorption (PSD), electron stimulated desorption (ESD), solar wind sputtering (SWS) and micro-meteorite impact vaporization (MIV). For all of these possible source mechanisms, sodium ions are born cold, with eV energies at most, yet when the sodium ions are observed in Mercury's magnetosphere they tend to have much higher energies, i.e., 10-10000 eV. Using global kinetic simulations, the origin, acceleration, transport and loss of sodium ions is examined for the different source mechanisms. In general it is found that PSD is a major contributor of sodium ions with energies of order 10-100 eV to the dayside regions of Mercury's magnetosphere, while ESD-created sodium ions generally gain higher energies (1-10 keV) and tend primarily to populate the magnetotail plasma sheet. The acceleration mechanisms and general transport properties of sodium ions will be discussed along with comparisons with MESSENGER observations.

  18. Understanding transport in model water desalination membranes

    NASA Astrophysics Data System (ADS)

    Chan, Edwin

    Polyamide based thin film composites represent the the state-of-the-art nanofiltration and reverse osmosis membranes used in water desalination. The performance of these membranes is enabled by the ultrathin (~100 nm) crosslinked polyamide film in facilitating the selective transport of water over salt ions. While these materials have been refined over the last several decades, understanding the relationships between polyamide structure and membrane performance remains a challenge because of the complex and heterogeneous nature of the polyamide film. In this contribution, we present our approach to addressing this challenge by studying the transport properties of model polyamide membranes synthesized via molecular layer-by-layer (mLbL) assembly. First, we demonstrate that mLbL can successfully construct polyamide membranes with well-defined nanoscale thickness and roughness using a variety of monomer formulations. Next, we present measurement tools for characterizing the network structure and transport of these model polyamide membranes. Specifically, we used X-ray and neutron scattering techniques to characterize their structure as well as a recently-developed indentation based poromechanics approach to extrapolate their water diffusion coefficient. Finally, we illustrate how these measurements can provide insight into the original problem by linking the key polyamide network properties, i.e. water-polyamide interaction parameter and characteristic network mesh size, to the membrane performance.

  19. Polyene antibiotic that inhibits membrane transport proteins.

    PubMed

    te Welscher, Yvonne Maria; van Leeuwen, Martin Richard; de Kruijff, Ben; Dijksterhuis, Jan; Breukink, Eefjan

    2012-07-10

    The limited therapeutic arsenal and the increase in reports of fungal resistance to multiple antifungal agents have made fungal infections a major therapeutic challenge. The polyene antibiotics are the only group of antifungal antibiotics that directly target the plasma membrane via a specific interaction with the main fungal sterol, ergosterol, often resulting in membrane permeabilization. In contrast to other polyene antibiotics that form pores in the membrane, the mode of action of natamycin has remained obscure but is not related to membrane permeabilization. Here, we demonstrate that natamycin inhibits growth of yeasts and fungi via the immediate inhibition of amino acid and glucose transport across the plasma membrane. This is attributable to ergosterol-specific and reversible inhibition of membrane transport proteins. It is proposed that ergosterol-dependent inhibition of membrane proteins is a general mode of action of all the polyene antibiotics, of which some have been shown additionally to permeabilize the plasma membrane. Our results imply that sterol-protein interactions are fundamentally important for protein function even for those proteins that are not known to reside in sterol-rich domains.

  20. Bidirectional diffusion of ammonium and sodium cations in forward osmosis: role of membrane active layer surface chemistry and charge.

    PubMed

    Lu, Xinglin; Boo, Chanhee; Ma, Jun; Elimelech, Menachem

    2014-12-16

    Systematic fundamental understanding of mass transport in osmosis-driven membrane processes is important for further development of this emerging technology. In this work, we investigate the role of membrane surface chemistry and charge on bidirectional solute diffusion in forward osmosis (FO). In particular, bidirectional diffusion of ammonium (NH4(+)) and sodium (Na(+)) is examined using FO membranes with different materials and surface charge characteristics. Using an ammonium bicarbonate (NH4HCO3) draw solution, we observe dramatically enhanced cation fluxes with sodium chloride feed solution compared to that with deionized water feed solution for thin-film composite (TFC) FO membrane. However, the bidirectional diffusion of cations does not change, regardless of the type of feed solution, for cellulose triacetate (CTA) FO membrane. We relate this phenomenon to the membrane fixed surface charge by employing different feed solution pH to foster different protonation conditions for the carboxyl groups on the TFC membrane surface. Membrane surface modification is also carried out with the TFC membrane using ethylenediamine to alter carboxyl groups into amine groups. The modified TFC membrane, with less negatively charged groups, exhibits a significant decrease in the bidirectional diffusion of cations under the same conditions employed with the pristine TFC membrane. Based on our experimental observations, we propose Donnan dialysis as a mechanism responsible for enhanced bidirectional diffusion of cations in TFC membranes.

  1. Paracellular epithelial sodium transport maximizes energy efficiency in the kidney

    PubMed Central

    Pei, Lei; Nguyen, Mien T.X.; Kamat, Nikhil; Magenheimer, Lynn; Zhuo, Min; Li, Jiahua; McDonough, Alicia A.; Fields, Timothy A.; Welch, William J.; Yu, Alan S.L.

    2016-01-01

    Efficient oxygen utilization in the kidney may be supported by paracellular epithelial transport, a form of passive diffusion that is driven by preexisting transepithelial electrochemical gradients. Claudins are tight-junction transmembrane proteins that act as paracellular ion channels in epithelial cells. In the proximal tubule (PT) of the kidney, claudin-2 mediates paracellular sodium reabsorption. Here, we used murine models to investigate the role of claudin-2 in maintaining energy efficiency in the kidney. We found that claudin-2–null mice conserve sodium to the same extent as WT mice, even during profound dietary sodium depletion, as a result of the upregulation of transcellular Na-K-2Cl transport activity in the thick ascending limb of Henle. We hypothesized that shifting sodium transport to transcellular pathways would lead to increased whole-kidney oxygen consumption. Indeed, compared with control animals, oxygen consumption in the kidneys of claudin-2–null mice was markedly increased, resulting in medullary hypoxia. Furthermore, tubular injury in kidneys subjected to bilateral renal ischemia-reperfusion injury was more severe in the absence of claudin-2. Our results indicate that paracellular transport in the PT is required for efficient utilization of oxygen in the service of sodium transport. We speculate that paracellular permeability may have evolved as a general strategy in epithelial tissues to maximize energy efficiency. PMID:27214555

  2. Thermodynamic and transport properties of sodium liquid and vapor

    SciTech Connect

    Fink, J.K.; Leibowitz, L.

    1995-01-01

    Data have been reviewed to obtain thermodynamically consistent equations for thermodynamic and transport properties of saturated sodium liquid and vapor. Recently published Russian recommendations and results of equation of state calculations on thermophysical properties of sodium have been included in this critical assessment. Thermodynamic properties of sodium liquid and vapor that have been assessed include: enthalpy, heat capacity at constant pressure, heat capacity at constant volume, vapor pressure, boiling point, enthalpy of vaporization, density, thermal expansion, adiabatic and isothermal compressibility, speed of sound, critical parameters, and surface tension. Transport properties of liquid sodium that have been assessed include: viscosity and thermal conductivity. For each property, recommended values and their uncertainties are graphed and tabulated as functions of temperature. Detailed discussions of the analyses and determinations of the recommended equations include comparisons with recommendations given in other assessments and explanations of consistency requirements. The rationale and methods used in determining the uncertainties in the recommended values are also discussed.

  3. Actinide transport across cell membranes.

    PubMed

    Bulman, R A; Griffin, R J

    1980-01-01

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

  4. Apical membrane sodium and chloride entry during osmotic swelling of renal (A6) epithelial cells.

    PubMed

    Crowe, W E; Ehrenfeld, J; Brochiero, E; Wills, N K

    1995-03-01

    To assess the role of chloride in cell volume and sodium transport regulation, we measured cell height changes (CH), transepithelial chloride and sodium fluxes, and intracellular chloride content during challenge with hyposmotic solutions under open circuit (OC) conditions. CH maximally increased following hyposmotic challenge within approximately 5 minutes. The change in CH was smaller under short circuit (SC) conditions or following replacement of chloride in the mucosal solution by gluconate or cyclamate (Cl(-)-freem). When corrected for the osmotically inactive cell volume (30 +/- 2%), delta CH for controls (OC) were greater than predicted for an ideal osmometer. In contrast, delta CH for Cl(-)-freem or SC conditions were similar to that predicted for an ideal osmometer. Na+ and Cl- mucosa-to-serosa fluxes increased following hyposmotic challenge. Chloride fluxes increased maximally within 5 min, then decreased. In contrast, the Na+ flux increased slowly and reached a steady state after approximately 25 min. Under isosmotic conditions, exposure to Cl(-)-freem solutions led to decreases in the transepithelial conductance, Na+ flux, and CH. Chloride permeabilities in the apical and basolateral membranes were detected using the fluorescent intracellular chloride indicator MQAE. The results indicate that during osmotic swelling, the entry of both sodium and chloride is increased. The time courses of these increases differ, suggesting distinct mechanisms for the osmotic regulation of these apical membrane transport processes.

  5. Conical nanopore membranes. Preparation and transport properties.

    PubMed

    Li, Naichao; Yu, Shufang; Harrell, C Chad; Martin, Charles R

    2004-04-01

    We have been investigating applications of nanopore membranes in analytical chemistry-specifically in membrane-based bioseparations, in electroanalytical chemistry, and in the development of new approaches to biosensor design. Membranes that have conically shaped pores (as opposed to the more conventional cylindrical shape) may offer some advantages for these applications. We describe here a simple plasma-etch method that converts cylindrical nanopores in track-etched polymeric membranes into conically shaped pores. This method allows for control of the shape of the resulting conical nanopores. For example, the plasma-etched pores may be cylindrical through most of the membrane thickness blossoming into cones at one face of the membrane (trumpet-shaped), or they may be nearly perfect cones. The key advantage of the conical pore shape is a dramatic enhancement in the rate of transport through the membrane, relative to an analogous cylindrical pore membrane. We demonstrate this here by measuring the ionic resistances of the plasma-etched conical pore membranes.

  6. Biomolecular Transport through Hemofiltration Membranes

    PubMed Central

    Datta, Subhra; Fissell, William H.; Roy, Shuvo

    2009-01-01

    A theoretical model for filtration of large solutes through a pore in the presence of transmembrane pressures, applied/induced electric fields, and dissimilar interactions at the pore entrance and exit is developed to characterize and predict the experimental performance of a hemofiltration membrane with nanometer scale pores designed for a proposed implantable Renal Assist Device (RAD). The model reveals that the sieving characteristics of the membrane can be improved by applying an external electric field, and ensuring a smaller ratio of the pore-feed and pore-permeate equilibrium partitioning coefficients when diffusion is present. The model is then customized to study the sieving characteristics for both charged and uncharged solutes in the slit-shaped nanopores of the hemofiltration device for the RAD. The effect of streaming potential or induced fields are found to be negligible under representative operating conditions. Experimental data on the sieving coefficient of bovine serum albumin, carbonic anhydrase and thyroglobulin are reported and compared with the theoretical predictions. Both steric and electrostatic partitioning are considered and the comparison suggests that in general electrostatic effects are present in the filtration of proteins though some data, particularly those recorded in a strongly hypertonic solution (10×PBS), show better agreement with the steric partitioning theory. PMID:19184436

  7. SLC5 Sodium-Anion Cotransporters and Renal Urate Transport

    NASA Astrophysics Data System (ADS)

    Mount, David B.; Kwon, Charles Y.; Plata, Consuelo; Romero, Michael F.; Zandi-Nejad, Kambiz

    2007-04-01

    Renal urate transport plays a key role in determining the concentration of circulating uric acid. The reabsorption of filtered urate by the renal proximal tubule appears to require apical sodium-dependent anion transport and the apical URAT1 urate-anion exchanger, in that sodium-dependent transport of lactate, ketoacids, nicotinate, and pyrazinoate (PZA) increases the intracellular concentration of substrates for the subsequent exchange with luminal urate. We have identified SLC5A8 and SLC5A12 as candidates for the sodium-anion cotransporter that collaborates with URAT1. Both transporters function as sodium-dependent nicotinate/monocarboxylate/PZA transporters. Localization studies reveal serial co-expression of these transporters with URAT1, with Slc5a12 in the early proximal tubule and Slc5a8 in S2 and S3 segments. Renal urate excretion is conceivably affected by changes in the activity of SLC5A8, SLC5A12, and/or URAT1, with implications for the pathogenesis of hyperuricemia, nephrolithiasis, and related disorders.

  8. Regulation & Development of Membrane Transport Processes.

    DTIC Science & Technology

    1985-05-15

    conducted studies on the regulation of a variety of trans- port processes as a function of cell cycle, growth phase, malignant transfor- mation, hormone ...fertilization of ideas. The contributions dealt with regulatory processes evoked by two kinds of stim- uli: (1) external stimuli, such as hormones or...Mineralocorticoid Regulation of Sodium and Potassium Transport by the Cortical Collecting Duct 89 Bruce M. Koeppen and Gerhard H. Giebisch 6. Hormonal Regulation of

  9. [Effect of padan on active sodium transport in the epithelium of isolated frog skin].

    PubMed

    Kontek, M; Pogorzelska, H; Knapowski, J

    1984-01-01

    The effects of " Padan " (hydrochloride of 1.3-di/ carbomylothio /-2-N-dimethylamino/propane/ upon transport capabilities of plasmatic membrane have been checked. The experiment was performed on isolated skin of Rana temporaria frogs. Assessment of transporting activity of membrane in relation to sodium ion involved a method developed by Ussing with so called "short-circuit" technique. The effects of the pesticide on the external and internal surface of the frog's skin have been examined, final concentrations of the compound being 3.4 X 10(-6) M to 3.4 X 10(-3) M. The results indicate that " Padan ", whether administered to the external or internal surface of the membrane, decreases the value of membrane potential and short-circuit current, which is indicative of membrane transport inhibition. The effect varies with pesticide concentration in the medium, though it is statistically significant only in concentration 3.4 X 10(-3) M. On the other hand, membrane resistance usually gets increased as the compound concentration in the medium increases. The results indicate that cellular membrane should be considered while explaining the mechanism of toxic effects of " Padan " upon organism.

  10. Sodium recirculation and isotonic transport in toad small intestine.

    PubMed

    Nedergaard, S; Larsen, E H; Ussing, H H

    1999-04-01

    + fluxes, is compatible with convective flow of the two alkali metal ions through the same population of water-filled pores. With a new set of equations, the fraction of the sodium flux passing the basement membrane barrier of the lateral space that is recirculated through the cellular compartment is estimated. This fraction was, on average, 0.72 +/- 0.03 (N = 5). It is concluded that isotonicity of the transportate can be maintained by producing a hypertonic fluid emerging from the lateral space combined with reuptake of salt via the cells.

  11. Angiotensin I conversion to angiotensin II stimulates cortical collecting duct sodium transport.

    PubMed

    Komlosi, Peter; Fuson, Amanda L; Fintha, Attila; Peti-Peterdi, János; Rosivall, Laszlo; Warnock, David G; Bell, Phillip Darwin

    2003-08-01

    Angiotensin (Ang) II directly stimulates epithelial sodium channel activity in the rabbit cortical collecting duct. Because Ang I and converting enzyme analogues might be present in the distal nephron, this raises the possibility of intraluminal generation of Ang II. Conversion of Ang I to Ang II was monitored by Ang II-dependent changes in intracellular sodium concentration as a reflection of sodium transport across the apical membrane. This involved imaging-based fluorescence microscopy with sodium-binding benzofuran isophthalate in isolated, perfused, cortical collecting-duct segments from rabbit kidney. Principal and intercalated cells were differentiated by rhodamine-conjugated peanut lectin. Control principal cell intracellular sodium concentration, during perfusion with 25 mmol/L NaCl and zero sodium in the bath plus monensin (10(-5) mol/L) averaged 5.8+/-0.14 mmol/L (n=156). The increase in intracellular sodium concentration, when luminal NaCl was increased from 25 to 150 mmol/L, was elevated by 3.5-fold in the presence of intraluminal Ang I (10(-6) mol/L). Also, the effects of Ang I on sodium transport were not significantly different from the effects of Ang II (10(-9) mol/L). Ang I was used in micromolar concentrations to ensure that there was sufficient substrate available for conversion to Ang II. Inhibition of the angiotensin-converting enzyme with captopril reduced the stimulatory effect of Ang I. These results suggest that intraluminal conversion of Ang I to Ang II can occur in the cortical collecting duct, resulting in enhanced apical sodium entry.

  12. Role of intracellular membranes in transcellular calcium transport

    SciTech Connect

    Coleman, J.R.; Young, L.B.; Wade, P.C.

    1981-01-01

    Models can be tested through the use of various agents that affect different portions of the overall mechanism. The calcium ionophore A23187 can be used to increase the rate of calcium entry through the brush border, effectively removing diffusion through the brush border as a rate-limiting step. It would be expected that treatment with A23187 would thus increase the overall rate of calcium transcellular transport. In contrast, chlorpromazine has been shown to inhibit in vitro calcium uptake by Golgi membranes. Consequently if the model is correct, treatment with A23187 and chlorpromazine would tend to raise the cytoplasmic calcium concentration, since the Golgi membrane uptake mechanism would be inhibited, and calcium would accumulate in mitochondria with little or no increase in transcellular transport. Finally, Golgi membranes have been shown to release calcium in response to ATP. Sodium azide inhibits ATP generation and calcium uptake by mitochondria. Thus, treatment with A23187 and soidum azide should cause accumulation of calcium in the Golgi membranes, if the proposed model is correct. The purpose of this investigation was to use coordinated electron probe x-ray microanalysis and transmission electron microscopy to test the response of the intestinal absorptive cells to the agents mentioned.

  13. Membrane Assembly and Ion Transport Ability of a Fluorinated Nanopore

    PubMed Central

    Godbout, Raphaël; Légaré, Sébastien; Auger, Maud; Carpentier, Claudia; Otis, François; Auger, Michèle; Lagüe, Patrick; Voyer, Normand

    2016-01-01

    A novel 21-residue peptide incorporating six fluorinated amino acids was prepared. It was designed to fold into an amphiphilic alpha helical structure of nanoscale length with one hydrophobic face and one fluorinated face. The formation of a fluorous interface serves as the main vector for the formation of a superstructure in a bilayer membrane. Fluorescence assays showed this ion channel's ability to facilitate the translocation of alkali metal ions through a phospholipid membrane, with selectivity for sodium ions. Computational studies showed that a tetramer structure is the most probable and stable supramolecular assembly for the active ion channel structure. The results illustrate the possibility of exploiting multiple Fδ-:M+ interactions for ion transport and using fluorous interfaces to create functional nanostructures. PMID:27835700

  14. Membrane Assembly and Ion Transport Ability of a Fluorinated Nanopore.

    PubMed

    Godbout, Raphaël; Légaré, Sébastien; Auger, Maud; Carpentier, Claudia; Otis, François; Auger, Michèle; Lagüe, Patrick; Voyer, Normand

    2016-01-01

    A novel 21-residue peptide incorporating six fluorinated amino acids was prepared. It was designed to fold into an amphiphilic alpha helical structure of nanoscale length with one hydrophobic face and one fluorinated face. The formation of a fluorous interface serves as the main vector for the formation of a superstructure in a bilayer membrane. Fluorescence assays showed this ion channel's ability to facilitate the translocation of alkali metal ions through a phospholipid membrane, with selectivity for sodium ions. Computational studies showed that a tetramer structure is the most probable and stable supramolecular assembly for the active ion channel structure. The results illustrate the possibility of exploiting multiple Fδ-:M+ interactions for ion transport and using fluorous interfaces to create functional nanostructures.

  15. Interactive effects of ethanol and silver on sodium transport across toad skin

    SciTech Connect

    Gerencser, G.A.; Loo, S.Y.; Cornette, K.M.

    1984-05-01

    Both ethanol and silver ions have been shown to affect ion transport across various epithelia. This investigation was principally undertaken to further define mechanisms of silver ions and ethanol, and their possible interactions, on sodium transport across toad skin. Isolated toad skin, mounted between identical oxygenated amphibian bicarbonate Ringer solutions, maintained stable transepithelial potential differences (serosa positive) and short-circuit currents for several hours at 25/sup 0/C. It was observed that (1) ethanol inhibited the active transcellular component of sodium absorption and this effect was reversible; (2) inhibition of sodium transport by ethanol was directly proportional to the applied concentration; (3) pretreatment with silver ions prevented any ethanol effects; and (4) pretreatment with ethanol prevented any silver ion effects. It was concluded from these results that ethanol induced its inhibitory effects on membrane phospholipids thereby perturbing the function of a sulfhydryl ligant, while silver ion or silver chloride complex binding to this ligand would maintain its function in sodium transport despite the presence of ethanol.

  16. Advanced Hydrogen Transport Membrane for Coal Gasification

    SciTech Connect

    Schwartz, Joseph; Porter, Jason; Patki, Neil; Kelley, Madison; Stanislowski, Josh; Tolbert, Scott; Way, J. Douglas; Makuch, David

    2015-12-23

    A pilot-scale hydrogen transport membrane (HTM) separator was built that incorporated 98 membranes that were each 24 inches long. This separator used an advanced design to minimize the impact of concentration polarization and separated over 1000 scfh of hydrogen from a hydrogen-nitrogen feed of 5000 scfh that contained 30% hydrogen. This mixture was chosen because it was representative of the hydrogen concentration expected in coal gasification. When tested with an operating gasifier, the hydrogen concentration was lower and contaminants in the syngas adversely impacted membrane performance. All 98 membranes survived the test, but flux was lower than expected. Improved ceramic substrates were produced that have small surface pores to enable membrane production and large pores in the bulk of the substrate to allow high flux. Pd-Au was chosen as the membrane alloy because of its resistance to sulfur contamination and good flux. Processes were developed to produce a large quantity of long membranes for use in the demonstration test.

  17. Thermodynamics of sodium dodecyl sulfate partitioning into lipid membranes.

    PubMed

    Tan, Anmin; Ziegler, André; Steinbauer, Bernhard; Seelig, Joachim

    2002-09-01

    The partition equilibria of sodium dodecyl sulfate (SDS) and lithium dodecyl sulfate between water and bilayer membranes were investigated with isothermal titration calorimetry and spectroscopic methods (light scattering, (31)P-nuclear magnetic resonance) in the temperature range of 28 degrees C to 56 degrees C. The partitioning of the dodecyl sulfate anion (DS(-)) into the bilayer membrane is energetically favored by an exothermic partition enthalpy of Delta H(O)(D) = -6.0 kcal/mol at 28 degrees C. This is in contrast to nonionic detergents where Delta H(O)(D) is usually positive. The partition enthalpy decreases linearly with increasing temperature and the molar heat capacity is Delta C(O)(P) = -50 +/- 3 cal mol(-1) K(-1). The partition isotherm is nonlinear if the bound detergent is plotted versus the free detergent concentration in bulk solution. This is caused by the electrostatic repulsion between the DS(-) ions inserted into the membrane and those free in solution near the membrane surface. The surface concentration of DS(-) immediately above the plane of binding was hence calculated with the Gouy-Chapman theory, and a strictly linear relationship was obtained between the surface concentration and the extent of DS(-) partitioning. The surface partition constant K describes the chemical equilibrium in the absence of electrostatic effects. For the SDS-membrane equilibrium K was found to be 1.2 x 10(4) M(-1) to 6 x 10(4) M(-1) for the various systems and conditions investigated, very similar to data available for nonionic detergents of the same chain length. The membrane-micelle phase diagram was also studied. Complete membrane solubilization requires a ratio of 2.2 mol SDS bound per mole of total lipid at 56 degrees C. The corresponding equilibrium concentration of SDS free in solution is C (sat)(D,F) approximately 1.7 mM and is slightly below the critical micelles concentration (CMC) = 2.1 mM (at 56 degrees C and 0.11 M buffer). Membrane saturation occurs at

  18. Effect of Polyvnylpyrrolidone (PVP) in Binary Solution on the Performance of Polyethersulfone Hollow Fibre Membrane for Sodium Chloride Separation

    NASA Astrophysics Data System (ADS)

    Bolong, N.; Ismail, A. F.; Salim, M. R.

    2010-03-01

    In membrane preparation, phase inversion is a versatile technique that allow polymer to be transformed from liquid to a solid state in a controlled manner. The preparation and process involves many factors and parameters specifically in fabricating hollow fibre membrane. In this study, dope solution factor in the process of fabricating hollow fibre membrane were explored. The effects of polymer concentration and polyvinylpyrrolidone (PVP) as additive in the dope solution on the morphology and separation performance were found able to produced high porous membranes, well interconnected pores and surface properties. Employing polyethersulfone (PES) as polymer, hollow fibre membranes were fabricated using N-methyl-2-pyrrolidone (NMP) as solvent and using water as the external coagulant. Finally the fabricated ultrafiltration membranes were characterized and evaluated based on solute transport concentration (sodium chloride) and pure water permeation properties.

  19. Ceramic oxygen transport membrane array reactor and reforming method

    SciTech Connect

    Kelly, Sean M.; Christie, Gervase Maxwell; Rosen, Lee J.; Robinson, Charles; Wilson, Jamie R.; Gonzalez, Javier E.; Doraswami, Uttam R.

    2016-09-27

    A commercially viable modular ceramic oxygen transport membrane reforming reactor for producing a synthesis gas that improves the thermal coupling of reactively-driven oxygen transport membrane tubes and catalyst reforming tubes required to efficiently and effectively produce synthesis gas.

  20. Cyclosporin A reduces canalicular membrane fluidity and regulates transporter function in rats.

    PubMed Central

    Yasumiba, S; Tazuma, S; Ochi, H; Chayama, K; Kajiyama, G

    2001-01-01

    Changes of the biliary canalicular membrane lipid content can affect membrane fluidity and biliary lipid secretion in rats. The immunosuppressant cyclosporin A is known to cause intrahepatic cholestasis. This study investigated whether cyclosporin A influenced canalicular membrane fluidity by altering membrane phospholipids or transporter expression. In male Sprague-Dawley rats, a bile-duct cannula was inserted to collect bile, and sodium taurocholate was infused (100 nmol/min per 100 g) for 60 min. During steady-state taurocholate infusion, cyclosporin A (20 mg/kg) or vehicle was injected intravenously and then bile was collected for 80 min. After killing the rats, canalicular membrane vesicles were prepared. Expression of canalicular membrane transporters was assessed by Western blotting and canalicular membrane vesicle fluidity was estimated by fluorescence polarization. Cyclosporin A reduced biliary lipid secretion along with a disproportionate reduction of lipids relative to bile acids. Cyclosporin A significantly decreased canalicular membrane fluidity along with an increase of the cholesterol/phospholipid molar ratio. Only expression of the transporter P-glycoprotein was increased by cyclosporin A. Because canalicular membrane transporter expression was largely unchanged by cyclosporin A despite a marked decrease of biliary lipid secretion, transporter activity may partly depend upon canalicular membrane fluidity. PMID:11237863

  1. 65Zn2+ transport by lobster hepato-pancreatic baso-lateral membrane vesicles.

    PubMed

    Capo, J A; Mandal, P K; Eyyunni, S; Ahearn, G A

    2005-01-01

    The lobster (Homarus americanus) hepato-pancreatic epithelial baso-lateral cell membrane possesses three transport proteins that transfer calcium between the cytoplasm and hemolymph: an ATP-dependent calcium ATPase, a sodium-calcium exchanger, and a verapamil-sensitive cation channel. We used standard centrifugation methods to prepare purified hepato-pancreatic baso-lateral membrane vesicles and a rapid filtration procedure to investigate whether (65)Zn(2+) transfer across this epithelial cell border occurs by any of these previously described transporters for calcium. Baso-lateral membrane vesicles were osmotically reactive and exhibited a time course of uptake that was linear for 10-15 s and approached equilibrium by 120 s. In the absence of sodium, (65)Zn(2+) influx was a hyperbolic function of external zinc concentration and followed the Michaelis-Menten equation for carrier transport. This carrier transport was stimulated by the addition of 150 microM ATP (increase in K(m) and J(max)) and inhibited by the simultaneous presence of 150 micromol l(-1) ATP+250 micromol l(-1) vanadate (decrease in both K(m) and J(max)). In the absence of ATP, (65)Zn(2+) influx was a sigmoidal function of preloaded vesicular sodium concentration (0, 5, 10, 20, 30, 45, and 75 mmol l(-1)) and exhibited a Hill Coefficient of 4.03+/-1.14, consistent with the exchange of 3 Na(+)/1Zn(2+). Using Dixon analysis, calcium was shown to be a competitive inhibitor of baso-lateral membrane vesicle (65)Zn(2+) influx by both the ATP-dependent (K(i)=205 nmol l(-1) Ca(2+)) and sodium-dependent (K(i)=2.47 micromol l(-1) Ca(2+)) transport processes. These results suggest that zinc transport across the lobster hepato-pancreatic baso-lateral membrane largely occurred by the ATP-dependent calcium ATPase and sodium-calcium exchanger carrier proteins.

  2. RING finger protein 121 facilitates the degradation and membrane localization of voltage-gated sodium channels.

    PubMed

    Ogino, Kazutoyo; Low, Sean E; Yamada, Kenta; Saint-Amant, Louis; Zhou, Weibin; Muto, Akira; Asakawa, Kazuhide; Nakai, Junichi; Kawakami, Koichi; Kuwada, John Y; Hirata, Hiromi

    2015-03-03

    Following their synthesis in the endoplasmic reticulum (ER), voltage-gated sodium channels (NaV) are transported to the membranes of excitable cells, where they often cluster, such as at the axon initial segment of neurons. Although the mechanisms by which NaV channels form and maintain clusters have been extensively examined, the processes that govern their transport and degradation have received less attention. Our entry into the study of these processes began with the isolation of a new allele of the zebrafish mutant alligator, which we found to be caused by mutations in the gene encoding really interesting new gene (RING) finger protein 121 (RNF121), an E3-ubiquitin ligase present in the ER and cis-Golgi compartments. Here we demonstrate that RNF121 facilitates two opposing fates of NaV channels: (i) ubiquitin-mediated proteasome degradation and (ii) membrane localization when coexpressed with auxiliary NaVβ subunits. Collectively, these results indicate that RNF121 participates in the quality control of NaV channels during their synthesis and subsequent transport to the membrane.

  3. Solute rejection by porous glass membranes. I - Hyperfiltration of sodium chloride and urea feed solutions.

    NASA Technical Reports Server (NTRS)

    Ballou, E. V.; Wydeven, T.; Leban, M. I.

    1971-01-01

    Hyperfiltration of sodium chloride and urea was studied with porous glass membranes in closed-end capillary form, to determine the effect of pressure, temperature, and concentration variations, and lifetime rejection and flux characteristics. Rejection data for sodium chloride were consistent with the functioning of the porous glass as a low-capacity ion-exchange membrane.

  4. Phylogenetic profiles of all membrane transport proteins

    PubMed Central

    Weiner, January; Kooij, Taco W.A.

    2016-01-01

    In order to combat the on-going malaria epidemic, discovery of new drug targets remains vital. Proteins that are essential to survival and specific to malaria parasites are key candidates. To survive within host cells, the parasites need to acquire nutrients and dispose of waste products across multiple membranes. Additionally, like all eukaryotes, they must redistribute ions and organic molecules between their various internal membrane bound compartments. Membrane transport proteins mediate all of these processes and are considered important mediators of drug resistance as well as drug targets in their own right. Recently, using advanced experimental genetic approaches and streamlined life cycle profiling, we generated a large collection of Plasmodium berghei gene deletion mutants and assigned essential gene functions, highlighting potential targets for prophylactic, therapeutic, and transmission-blocking anti-malarial drugs. Here, we present a comprehensive orthology assignment of all Plasmodium falciparum putative membrane transport proteins and provide a detailed overview of the associated essential gene functions obtained through experimental genetics studies in human and murine model parasites. Furthermore, we discuss the phylogeny of selected potential drug targets identified in our functional screen. We extensively discuss the results in the context of the functional assignments obtained using gene targeting available to date. PMID:28357319

  5. Membrane lipids and sodium pumps of cattle and crocodiles: an experimental test of the membrane pacemaker theory of metabolism.

    PubMed

    Wu, B J; Hulbert, A J; Storlien, L H; Else, P L

    2004-09-01

    The influence of membrane lipid composition on the molecular activity of a major membrane protein (the sodium pump) was examined as a test of the membrane pacemaker theory of metabolism. Microsomal membranes from the kidneys of cattle (Bos taurus) and crocodiles (Crocodylus porosus) were found to possess similar sodium pump concentrations, but cattle membranes showed a four- to fivefold higher enzyme (Na(+)-K(+)-ATPase) activity when measured at 37 degrees C. The molecular activity of the sodium pumps (ATP/min) from both species was fully recoverable when delipidated pumps were reconstituted with membrane from the original source (same species). The results of experiments involving species membrane crossovers showed cattle sodium pump molecular activity to progressively decrease from 3,245 to 1,953 (P < 0.005) to 1,031 (P < 0.003) ATP/min when subjected to two cycles of delipidation and reconstitution with crocodile membrane as a lipid source. In contrast, the molecular activity of crocodile sodium pumps progressively increased from 729 to 908 (P < 0.01) to 1,476 (P = 0.01) ATP/min when subjected to two cycles of delipidation and reconstitution with cattle membrane as a lipid source. The lipid composition of the two membrane preparations showed similar levels of saturated ( approximately 31-34%) and monounsaturated ( approximately 23-25%) fatty acids. Cattle membrane had fourfold more n-3 polyunsaturated fatty acids (11.2 vs. 2.9%) but had a reduced n-6 polyunsaturate content (29 vs. 43%). The results support the membrane pacemaker theory of metabolism and suggest membrane lipids and their polyunsaturates play a significant role in determining the molecular activity of the sodium pump.

  6. Icodextrin peritoneal transport in vitro: effect of sodium deoxycholate, glucose, and methylglyoxal.

    PubMed

    Szary, Beata; Grzelak, Teresa; Czyzewska, Krystyna

    2007-02-01

    The aim of the in vitro studies was to examine the effect of sodium deoxycholate, glucose, and methylglyoxal on icodextrin peritoneal transfer. The rabbit peritoneum in a modified Ussing chamber was an experimental model. Transport and morphometric analyses were performed. In the first of them, the icodextrin (7.5 g/dL) diffusion from the mesothelial to the interstitial side of the membrane, expressed as a diffusive permeability coefficient (P), was evaluated in the control stage, after chemical modification of the membrane using sodium deoxycholate (104 mg/dL), after the addition of glucose (1.8 g/dL) and methylglyoxal (1 mg/dL), in the separate experimental series. In the second morphometric studies, the thickness and transverse cross-section surface area of native tissue, in 75 min of experiment and after application of sodium deoxycholate, were investigated. In the control conditions, the rate of glucose polymer passage remained constant. A mean value of P +/- SD was 0.194 +/- 0.126 (x10(-4), cm/s) during 120 min of the study. The transfer of icodextrin was enhanced by 224% after 3 min of incubation of the peritoneum with sodium deoxycholate. The introduction of glucose into the circulating medium with icodextrin caused the increase of P values for glucose polymer by 94% during 60 min. In the same conditions, the usage of methylglyoxal did not change transport parameters. Both thickness and transverse cross-section surface area of the native tissue in 75 min of the study did not differ. It was 4.87 microm and 12.50 x 10(2) microm(2) for the mesothelial layer, and 63.83 microm and 208.10 x 10(2) microm(2) for the whole peritoneal membrane. The application of sodium deoxycholate caused the decrease of mesothelium thickness by 20% but the increase of thickness and transverse cross-section surface area of the peritoneum by 37% in comparison with 75 min of experiment. In conclusion, sodium deoxycholate and glucose, but not methylglyoxal, intensify peritoneal

  7. Radiation inactivation studies on the rabbit kidney sodium-dependent glucose transporter.

    PubMed

    Takahashi, M; Malathi, P; Preiser, H; Jung, C Y

    1985-09-05

    Rabbit kidney cortical brush-border membrane vesicles were irradiated in the frozen state with increasing doses of high energy electrons from a Van de Graaff generator. Sodium-dependent D-glucose and L-alanine transport showed a simple exponential loss of activity with increasing radiation dosage. Target size calculation based on these data gives estimates of 1.0 X 10(6) daltons for the glucose transporter and 1.2 X 10(6) daltons for the alanine transporter. A highly purified glucose transport protein extracted from rabbit kidney cortex was similarly irradiated both before and after reconstitution into liposomes. The target size of this purified glucose transporter was 343,000 daltons, based on inactivation of transport. The intensity of the major 165,000-dalton sodium dodecyl sulfate-gel electrophoresis band of this preparation was decreased by radiation. The decrease in staining intensity was dose-dependent, yielding a target size of 298,000 daltons, in situ. We propose that the purified glucose transporter reconstituted into liposomes is a tetramer comprised of 85,000-dalton subunits.

  8. Liver X receptor-activating ligands modulate renal and intestinal sodium-phosphate transporters.

    PubMed

    Caldas, Yupanqui A; Giral, Hector; Cortázar, Michael A; Sutherland, Eileen; Okamura, Kayo; Blaine, Judith; Sorribas, Victor; Koepsell, Hermann; Levi, Moshe

    2011-09-01

    Cholesterol is pumped out of the cells in different tissues, including the vasculature, intestine, liver, and kidney, by the ATP-binding cassette transporters. Ligands that activate the liver X receptor (LXR) modulate this efflux. Here we determined the effects of LXR agonists on the regulation of phosphate transporters. Phosphate homeostasis is regulated by the coordinated action of the intestinal and renal sodium-phosphate (NaPi) transporters, and the loss of this regulation causes hyperphosphatemia. Mice treated with DMHCA or TO901317, two LXR agonists that prevent atherosclerosis in ApoE or LDLR knockout mice, significantly decreased the activity of intestinal and kidney proximal tubular brush border membrane sodium gradient-dependent phosphate uptake, decreased serum phosphate, and increased urine phosphate excretion. The effects of DMHCA were due to a significant decrease in the abundance of the intestinal and renal NaPi transport proteins. The same effect was also found in opossum kidney cells in culture after treatment with either agonist. There was increased nuclear expression of the endogenous LXR receptor, a reduction in NaPi4 protein abundance (the main type II NaPi transporter in the opossum cells), and a reduction in NaPi co-transport activity. Thus, LXR agonists modulate intestinal and renal NaPi transporters and, in turn, serum phosphate levels.

  9. Coupled binding mechanism of three sodium ions and aspartate in the glutamate transporter homologue GltTk

    PubMed Central

    Guskov, Albert; Jensen, Sonja; Faustino, Ignacio; Marrink, Siewert J.; Slotboom, Dirk Jan

    2016-01-01

    Glutamate transporters catalyse the thermodynamically unfavourable transport of anionic amino acids across the cell membrane by coupling it to the downhill transport of cations. This coupling mechanism is still poorly understood, in part because the available crystal structures of these transporters are of relatively low resolution. Here we solve crystal structures of the archaeal transporter GltTk in the presence and absence of aspartate and use molecular dynamics simulations and binding assays to show how strict coupling between the binding of three sodium ions and aspartate takes place. PMID:27830699

  10. Sucrose transport by the alkaliphilic, thermophilic Bacillus sp. strain TA2.A1 is dependent on a sodium gradient.

    PubMed

    Peddie, C J; Cook, G M; Morgan, H W

    2000-10-01

    An alkaliphilic Bacillus designated strain TA2.A1, isolated from a thermal spring in Te Aroha, New Zealand, grew optimally at pH 9.2 and 70 degrees C. Sodium chloride (>5mM) was an obligate requirement for the growth of strain TA2.A1 on sucrose, and growth on sucrose was inhibited by monensin, an ionophore that collapses the sodium gradient (ApNa+) across the cell membrane. Sucrose transport by strain TA2.A1 was sodium dependent and was inhibited by monensin. The Kt for sucrose transport was 33 microM and the Eadie-Hofstee plot was linear, suggesting one high-affinity uptake system for sucrose. The affinity for sodium was low (0.5 mM), and the Hill plot had a slope of 1.6, suggesting that sodium binding was noncooperative and that the sucrose transporter had more than one binding site for sodium. Based on these results, Bacillus strain TA2.A1 uses a sodium gradient for sucrose uptake, in addition to the sodium-dependent glutamate uptake system reported previously.

  11. Synaptic uptake and beyond: the sodium- and chloride-dependent neurotransmitter transporter family SLC6.

    PubMed

    Chen, Nian-Hang; Reith, Maarten E A; Quick, Michael W

    2004-02-01

    The SLC6 family is a diverse set of transporters that mediate solute translocation across cell plasma membranes by coupling solute transport to the cotransport of sodium and chloride down their electrochemical gradients. These transporters probably have 12 transmembrane domains, with cytoplasmic N- and C-terminal tails, and at least some may function as homo-oligomers. Family members include the transporters for the inhibitory neurotransmitters GABA and glycine, the aminergic transmitters norepinephrine, serotonin, and dopamine, the osmolytes betaine and taurine, the amino acid proline, and the metabolic compound creatine. In addition, this family includes a system B(0+) cationic and neutral amino acid transporter, and two transporters for which the solutes are unknown. In general, SLC6 transporters act to regulate the level of extracellular solute concentrations. In the central and the peripheral nervous system, these transporters can regulate signaling among neurons, are the sites of action of various drugs of abuse, and naturally occurring mutations in several of these proteins are associated with a variety of neurological disorders. For example, transgenic animals lacking specific aminergic transporters show profoundly disturbed behavioral phenotypes and probably represent excellent systems for investigating psychiatric disease. SLC6 transporters are also found in many non-neural tissues, including kidney, intestine, and testis, consistent with their diverse physiological roles. Transporters in this family represent attractive therapeutic targets because they are subject to multiple forms of regulation by many different signaling cascades, and because a number of pharmacological agents have been identified that act specifically on these proteins.

  12. Structural Insights into the Transport Mechanism of the Human Sodium-dependent Lysophosphatidylcholine Transporter MFSD2A.

    PubMed

    Quek, Debra Q Y; Nguyen, Long N; Fan, Hao; Silver, David L

    2016-04-29

    Major facilitator superfamily domain containing 2A (MFSD2A) was recently characterized as a sodium-dependent lysophosphatidylcholine transporter expressed at the blood-brain barrier endothelium. It is the primary route for importation of docosohexaenoic acid and other long-chain fatty acids into fetal and adult brain and is essential for mouse and human brain growth and function. Remarkably, MFSD2A is the first identified major facilitator superfamily member that uniquely transports lipids, implying that MFSD2A harbors unique structural features and transport mechanism. Here, we present three three-dimensional structural models of human MFSD2A derived by homology modeling using MelB- and LacY-based crystal structures and refined by biochemical analysis. All models revealed 12 transmembrane helices and connecting loops and represented the partially outward-open, outward-partially occluded, and inward-open states of the transport cycle. In addition to a conserved sodium-binding site, three unique structural features were identified as follows: a phosphate headgroup binding site, a hydrophobic cleft to accommodate a hydrophobic hydrocarbon tail, and three sets of ionic locks that stabilize the outward-open conformation. Ligand docking studies and biochemical assays identified Lys-436 as a key residue for transport. It is seen forming a salt bridge with the negative charge on the phosphate headgroup. Importantly, MFSD2A transported structurally related acylcarnitines but not a lysolipid without a negative charge, demonstrating the necessity of a negatively charged headgroup interaction with Lys-436 for transport. These findings support a novel transport mechanism by which lysophosphatidylcholines are "flipped" within the transporter cavity by pivoting about Lys-436 leading to net transport from the outer to the inner leaflet of the plasma membrane.

  13. Structural Insights into the Transport Mechanism of the Human Sodium-dependent Lysophosphatidylcholine Transporter MFSD2A*♦

    PubMed Central

    Quek, Debra Q. Y.; Nguyen, Long N.; Fan, Hao; Silver, David L.

    2016-01-01

    Major facilitator superfamily domain containing 2A (MFSD2A) was recently characterized as a sodium-dependent lysophosphatidylcholine transporter expressed at the blood-brain barrier endothelium. It is the primary route for importation of docosohexaenoic acid and other long-chain fatty acids into fetal and adult brain and is essential for mouse and human brain growth and function. Remarkably, MFSD2A is the first identified major facilitator superfamily member that uniquely transports lipids, implying that MFSD2A harbors unique structural features and transport mechanism. Here, we present three three-dimensional structural models of human MFSD2A derived by homology modeling using MelB- and LacY-based crystal structures and refined by biochemical analysis. All models revealed 12 transmembrane helices and connecting loops and represented the partially outward-open, outward-partially occluded, and inward-open states of the transport cycle. In addition to a conserved sodium-binding site, three unique structural features were identified as follows: a phosphate headgroup binding site, a hydrophobic cleft to accommodate a hydrophobic hydrocarbon tail, and three sets of ionic locks that stabilize the outward-open conformation. Ligand docking studies and biochemical assays identified Lys-436 as a key residue for transport. It is seen forming a salt bridge with the negative charge on the phosphate headgroup. Importantly, MFSD2A transported structurally related acylcarnitines but not a lysolipid without a negative charge, demonstrating the necessity of a negatively charged headgroup interaction with Lys-436 for transport. These findings support a novel transport mechanism by which lysophosphatidylcholines are “flipped” within the transporter cavity by pivoting about Lys-436 leading to net transport from the outer to the inner leaflet of the plasma membrane. PMID:26945070

  14. Functional characterisation of human SGLT-5 as a novel kidney-specific sodium-dependent sugar transporter.

    PubMed

    Grempler, Rolf; Augustin, Robert; Froehner, Stefanie; Hildebrandt, Tobias; Simon, Eric; Mark, Michael; Eickelmann, Peter

    2012-02-03

    Sodium glucose cotransporters (SGLT) actively catalyse carbohydrate transport across cellular membranes. Six of the 12 known SGLT family members have the capacity to bind and/or transport monosaccharides (SGLT-1 to 6); of these, all but SGLT-5 have been characterised. Here we demonstrate that human SGLT-5 is exclusively expressed in the kidney. Four splice variants were detected and the most abundant SGLT-5-mRNA was functionally characterised. SGLT-5 mediates sodium-dependent [(14)C]-α-methyl-D-glucose (AMG) transport that can be inhibited by mannose, fructose, glucose, and galactose. Uptake studies using demonstrated high capacity transport for mannose and fructose and, to a lesser extent, glucose, AMG, and galactose. SGLT-5 mediated mannose, fructose and AMG transport was weakly (μM potency) inhibited by SGLT-2 inhibitors. In summary, we have characterised SGLT-5 as a kidney mannose transporter. Further studies are warranted to explore the physiological role of SGLT-5.

  15. The contribution of the sodium-calcium exchanger (NCX) and plasma membrane Ca(2+) ATPase (PMCA) to cerebellar synapse function.

    PubMed

    Roome, Chris J; Empson, Ruth M

    2013-01-01

    The cerebellum, a part of the brain critically involved in motor learning and sensory adaptation, expresses high levels of the sodium-calcium exchanger (NCX) and the plasma membrane calcium ATPase (PMCA). Both these transporters control calcium dynamics at a variety of synapses, and here, we draw upon the available literature to discuss how NCX and PMCA work together to shape pre-synaptic calcium dynamics at cerebellar synapses.

  16. Prenatal programming of rat cortical collecting tubule sodium transport.

    PubMed

    Cheng, Chih-Jen; Lozano, German; Baum, Michel

    2012-03-15

    Prenatal insults have been shown to lead to elevated blood pressure in offspring when they are studied as adults. Prenatal administration of dexamethasone and dietary protein deprivation have demonstrated that there is an increase in transporter abundance for a number of nephron segments but not the subunits of the epithelial sodium channel (ENaC) in the cortical collecting duct. Recent studies have shown that aldosterone is elevated in offspring of protein-deprived mothers when studied as adults, but the physiological importance of the increase in serum aldosterone is unknown. As an indirect measure of ENaC activity, we compared the natriuretic response to benzamil in offspring of mothers who ate a low-protein diet (6%) with those who ate a normal diet (20%) for the last half of pregnancy. The natriuretic response to benzamil was greater in the 6% group (821.1 ± 161.0 μmol/24 h) compared with the 20% group (279.1 ± 137.0 μmol/24 h), consistent with greater ENaC activity in vivo (P < 0.05). In this study, we also directly studied cortical collecting tubule function from adult rats using in vitro microperfusion. There was no difference in basal or vasopressin-stimulated osmotic water permeability. However, while cortical collecting ducts of adult offspring whose mothers ate a 20% protein diet had no sodium transport (-1.9 ± 3.1 pmol·mm(-1)·min(-1)), the offspring of rats that ate a 6% protein diet during the last half of pregnancy had a net sodium flux of 10.7 ± 2.6 pmol·mm(-1)·min(-1) (P = 0.01) in tubules perfused in vitro. Sodium transport was measured using ion-selective electrodes, a novel technique allowing measurement of sodium in nanoliter quantities of fluid. Thus we directly demonstrate that there is prenatal programming of cortical collecting duct sodium transport.

  17. Molecular and functional analysis of SDCT2, a novel rat sodium-dependent dicarboxylate transporter

    PubMed Central

    Chen, Xiangmei; Tsukaguchi, Hiroyasu; Chen, Xing-Zhen; Berger, Urs V.; Hediger, Matthias A.

    1999-01-01

    Kidney proximal tubule cells take up Krebs cycle intermediates for metabolic purposes and for secretion of organic anions through dicarboxylate/organic anion exchange. Alteration in reabsorption of citrate is closely related to renal stone formation. The presence of distinct types of sodium-coupled dicarboxylate transporters has been postulated on either side of the polarized epithelial membrane in the kidney proximal tubule. Using a PCR-based approach, we isolated a novel member of the sodium-dependent dicarboxylate/sulfate transporter called SDCT2. SDCT2 is a 600–amino acid residue protein that has 47–48% amino acid identity to SDCT1 and NaDC-1, previously identified in kidney and intestine. Northern analysis gave a single band of 3.3 kb for SDCT2 in kidney, liver, and brain. In situ hybridization revealed that SDCT2 is prominently expressed in kidney proximal tubule S3 segments and in perivenous hepatocytes, consistent with the sites of high-affinity dicarboxylate transport identified based on vesicle studies. A signal was also detected in the meningeal layers of the brain. SDCT2 expressed in Xenopus oocytes mediated sodium-dependent transport of di- and tricarboxylates with substrate preference for succinate rather than citrate, but excluding monocarboxylates. SDCT2, unlike SDCT1, displayed a unique pH dependence for succinate transport (optimal pH 7.5–8.5) and showed a high affinity for dimethylsuccinate, two features characteristic of basolateral transport. These data help to interpret the mechanisms of renal citrate transport, their alteration in pathophysiological conditions, and their role in the elimination of organic anions and therapeutic drugs. PMID:10207168

  18. Natriuretic Hormones, Endogenous Ouabain, and Related Sodium Transport Inhibitors

    PubMed Central

    Hamlyn, John M.

    2014-01-01

    The work of deWardener and colleagues stimulated longstanding interest in natriuretic hormones (NHs). In addition to the atrial peptides (APs), the circulation contains unidentified physiologically relevant NHs. One NH is controlled by the central nervous system (CNS) and likely secreted by the pituitary. Its circulating activity is modulated by salt intake and the prevailing sodium concentration of the blood and intracerebroventricular fluid, and contributes to postprandial and dehydration natriuresis. The other NH, mobilized by atrial stretch, promotes natriuresis by increasing the production of intrarenal dopamine and/or nitric oxide (NO). Both NHs have short (<35 min) circulating half lives, depress renotubular sodium transport, and neither requires the renal nerves. The search for NHs led to endogenous cardiotonic steroids (CTS) including ouabain-, digoxin-, and bufadienolide-like materials. These CTS, given acutely in high nanomole to micromole amounts into the general or renal circulations, inhibit sodium pumps and are natriuretic. Among these CTS, only bufalin is cleared sufficiently rapidly to qualify for an NH-like role. Ouabain-like CTS are cleared slowly, and when given chronically in low daily nanomole amounts, promote sodium retention, augment arterial myogenic tone, reduce renal blood flow and glomerular filtration, suppress NO in the renal vasa recta, and increase sympathetic nerve activity and blood pressure. Moreover, lowering total body sodium raises circulating endogenous ouabain. Thus, ouabain-like CTS have physiological actions that, like aldosterone, support renal sodium retention and blood pressure. In conclusion, the mammalian circulation contains two non-AP NHs. Identification of the CNS NH should be a priority. PMID:25520702

  19. Molecular mechanisms for proton transport in membranes.

    PubMed Central

    Nagle, J F; Morowitz, H J

    1978-01-01

    Likely mechanisms for proton transport through biomembranes are explored. The fundamental structural element is assumed to be continuous chains of hydrogen bonds formed from the protein side groups, and a molecular example is presented. From studies in ice, such chains are predicted to have low impedance and can function as proton wires. In addition, conformational changes in the protein may be linked to the proton conduction. If this possibility is allowed, a simple proton pump can be described that can be reversed into a molecular motor driven by an electrochemical potential across the membrane. PMID:272644

  20. Membrane ion transport in non-excitable tissues.

    PubMed

    Nehrke, Keith

    2014-12-23

    The facilitated movement of ions across cell membranes can be characterized as occurring through active (ATP-dependent), secondary active (coupled), or passive transport processes. Each of these processes is mediated by a diverse group of membrane proteins. Over the past fifteen years, studies of membrane transport in C. elegans have benefited from the fact that worms are anatomically simple, easily and economically cultured, and genetically tractable. These experimental advantages have been instrumental in defining how membrane transport processes contribute to whole organism physiology. The focus of this review is to survey the recent advances in our understanding of membrane transport that have arisen from integrative physiological approaches in the nematode C. elegans.

  1. [Sodium-dependent inorganic phosphate transporters and biomineralization].

    PubMed

    Tatsumi, Sawako; Fujii, Osamu; Miyagawa, Atsumi; Miyamoto, Kenichi

    2014-02-01

    Phosphate (Pi), one of most abundant anions in living organisms, plays a crucial role in biomineralization. An adequate plasma Pi concentration is required to maintain the calcium × phosphate ion product within a range sufficient for physiological bone mineralization, but an increase in the calcium × phosphate product in extracellular fluids above a certain threshold can predispose to extraskeletal calcification. Membrane transport systems for Pi transport are key elements in maintaining homeostasis of Pi in organisms. Members of two families of solute carrier (SLC) proteins (SLC20 and SLC34) act as Na⁺ -dependent, secondary-active cotransporters to transport Pi across cell membranes in mammals. This review summarizes the role of SLC20 and SCL34 proteins on biomineralization.

  2. Role of sodium ion in transport of folic acid in the small intestine

    SciTech Connect

    Zimmerman, J.; Selhub, J.; Rosenberg, I.H.

    1986-08-01

    The effect of sodium on folate transport across the intestinal luminal membrane was analyzed using two techniques: the influx chamber and isoalted brush-border membrane vesicles. Preincubation of tissue in Na -free medium did not have a consistent effect on folic acid influx provided that Na was present in the test solution. Replacement of Na in the test solution by choline resulted in a significant reduction of folic acid influx. However, when intestinal sheets that had been equilibrated in Na -free solution were exposed to test solutions containing either Na , Li , K , Rb , Cs , Tris , or guanidinium as main cations, folic acid influx was not significantly decreased. Concentration-dependence studies showed that replacement of Na by Rb did not affect the saturable mechanism of folate transport. Rather, a decrease in nonsaturable folic acid uptake accounted for the slightly reduced influx observed in the presence of Rb . Experiments with brush-border membrane vesicles revealed that methotrexate uptake was significantly higher in the presence of external Na than in the presence of K , but was not different from uptake in the presence of K plus valinomycin. These data suggest that 1) the saturable component of folate transport is not Na dependent, and 2) nonsaturable transport of folic acid across the luminal membrane occurs in part through a conductive pathway that involves a negatively charged species of folate and a cation whose membrane permeability affects the rate of folate transport. The importance of Na in this process in vivo derives from the fact that Na is the most permeant cation available at the absorptive site in the small intestine.

  3. The crystal structure of a sodium galactose transporter reveals mechanistic insights into Na[superscript +]/sugar symport

    SciTech Connect

    Faham, S.; Watanabe, A.; Besserer, G.M.; Cascio, D.; Specht, A.; Hirayama, B.A.; Wright, E.M.; Abramson, J.

    2009-08-27

    Membrane transporters that use energy stored in sodium gradients to drive nutrients into cells constitute a major class of proteins. We report the crystal structure of a member of the solute sodium symporters (SSS), the Vibrio parahaemolyticus sodium/galactose symporter (vSGLT). The -3.0 angstrom structure contains 14 transmembrane (TM) helices in an inward-facing conformation with a core structure of inverted repeats of 5 TM helices (TM2 to TM6 and TM7 to TM11). Galactose is bound in the center of the core, occluded from the outside solutions by hydrophobic residues. Surprisingly, the architecture of the core is similar to that of the leucine transporter (LeuT) from a different gene family. Modeling the outward-facing conformation based on the LeuT structure, in conjunction with biophysical data, provides insight into structural rearrangements for active transport.

  4. Glycosylation of Sodium/Iodide Symporter (NIS) Regulates Its Membrane Translocation and Radioiodine Uptake

    PubMed Central

    Chung, Taemoon; Youn, Hyewon; Yeom, Chan Joo; Kang, Keon Wook; Chung, June-Key

    2015-01-01

    Purpose Human sodium/iodide symporter (hNIS) protein is a membrane glycoprotein that transports iodide ions into thyroid cells. The function of this membrane protein is closely regulated by post-translational glycosylation. In this study, we measured glycosylation-mediated changes in subcellular location of hNIS and its function of iodine uptake. Methods HeLa cells were stably transfected with hNIS/tdTomato fusion gene in order to monitor the expression of hNIS. Cellular localization of hNIS was visualized by confocal microscopy of the red fluorescence of tdTomato. The expression of hNIS was evaluated by RT-PCR and immunoblot analysis. Functional activity of hNIS was estimated by radioiodine uptake. Cyclic AMP (cAMP) and tunicamycin were used to stimulate and inhibit glycosylation, respectively. In vivo images were obtained using a Maestro fluorescence imaging system. Results cAMP-mediated Glycosylation of NIS resulted in increased expression of hNIS, stimulating membrane translocation, and enhanced radioiodine uptake. In contrast, inhibition of glycosylation by treatment with tunicamycin dramatically reduced membrane translocation of intracellular hNIS, resulting in reduced radioiodine uptake. In addition, our hNIS/tdTomato fusion reporter successfully visualized cAMP-induced hNIS expression in xenografted tumors from mouse model. Conclusions These findings clearly reveal that the membrane localization of hNIS and its function of iodine uptake are glycosylation-dependent, as our results highlight enhancement of NIS expression and glycosylation with subsequent membrane localization after cAMP treatment. Therefore, enhancing functional NIS by the increasing level of glycosylation may be suggested as a promising therapeutic strategy for cancer patients who show refractory response to conventional radioiodine treatment. PMID:26599396

  5. Modulation of sulfate renal transport by alterations in cell membrane fluidity.

    PubMed

    Lee, H J; Balasubramanian, S V; Murer, H; Biber, J; Morris, M E

    1999-10-01

    Changes in membrane fluidity have been shown to alter the sodium-dependent renal transport of glucose and phosphate; however, this has not been examined for sodium/sulfate cotransport in the renal proximal tubule. Sodium/sulfate cotransport regulates the homeostasis of sulfate in mammals. The objective of this study was to investigate the influence of alterations of membrane fluidity on sodium-coupled sulfate transport in the Madin-Darby canine kidney cells, which have been stably transfected with sodium/sulfate cotransporter (NaSi-1) cDNA (MDCK-Si). Preincubation of cells with 0. 2 mM cholesterol significantly decreased the V(max) for sodium/sulfate cotransport (13.69 +/- 1.11 vs 10.15 +/- 1.17 nmol/mg protein/5 min, mean +/- SD, n = 4, p < 0.01) with no significant alteration in K(m). The addition of benzyl alcohol (20 mM) to cells increased the V(max) of sulfate uptake by 20% (11.97 +/- 0.91 vs 14. 35 +/- 0.56 nmol/mg protein/5 min, mean +/- SD, n = 3, p < 0.05) with no significant change in K(m). Membrane fluidity, as measured by the fluorescence polarization of 1,6-diphenyl 1,3,5-hexatriene (DPH), was significantly increased in MDCK-Si cells treated with 20 mM benzyl alcohol and decreased in the cells preincubated with 0.2 mM cholesterol, compared with control cells. Our results suggest that alterations in membrane fluidity that may occur as a result of disease states, aging, and pregnancy may play an important role in the modulation of renal sodium/sulfate cotransport.

  6. Osmotic water transport through carbon nanotube membranes

    PubMed Central

    Kalra, Amrit; Garde, Shekhar; Hummer, Gerhard

    2003-01-01

    We use molecular dynamics simulations to study osmotically driven transport of water molecules through hexagonally packed carbon nanotube membranes. Our simulation setup comprises two such semipermeable membranes separating compartments of pure water and salt solution. The osmotic force drives water flow from the pure-water to the salt-solution compartment. Monitoring the flow at molecular resolution reveals several distinct features of nanoscale flows. In particular, thermal fluctuations become significant at the nanoscopic length scales, and as a result, the flow is stochastic in nature. Further, the flow appears frictionless and is limited primarily by the barriers at the entry and exit of the nanotube pore. The observed flow rates are high (5.8 water molecules per nanosecond and nanotube), comparable to those through the transmembrane protein aquaporin-1, and are practically independent of the length of the nanotube, in contrast to predictions of macroscopic hydrodynamics. All of these distinct characteristics of nanoscopic water flow can be modeled quantitatively by a 1D continuous-time random walk. At long times, the pure-water compartment is drained, and the net flow of water is interrupted by the formation of structured solvation layers of water sandwiched between two nanotube membranes. Structural and thermodynamic aspects of confined water monolayers are studied. PMID:12878724

  7. A sodium/proton antiporter in chromaffin-granule membranes.

    PubMed Central

    Haigh, J R; Phillips, J H

    1989-01-01

    Chromaffin granules, the secretory vesicles of the adrenal medulla, have a Na+/H+ exchange activity in their membranes which brings their proton gradient into equilibrium with a Na+ gradient. This explains why Na+ is mildly inhibitory to amine transport (which is driven by the H+ gradient) The activity can be demonstrated by using accumulation of 22Na+ in response to a pH gradient that is either imposed by diluting membrane 'ghosts' into alkaline media, or generated by ATP hydrolysis. It can also be monitored indirectly by fluorescence measurements in which the pH inside 'ghost' is monitored by quenching of a fluorescent weak base. This method has been used to monitor Na+ entry into acid-loaded 'ghosts' of H+ entry into methylamine accumulation. The exchanger appears to be reversible and non-electrogenic, with a stoichiometry of 1:1. Using an indirect assay we measured an apparent Km for Na+ of 4.7 mM, and a Ki for amiloride, a competitive inhibitor, of 0.26 mM. Direct assays using 22Na+ suggested a higher Km. Ethylisopropylamiloride was not inhibitory. PMID:2539089

  8. Assessing the effects of sodium hypochlorite exposure on the characteristics of PVDF based membranes.

    PubMed

    Abdullah, Syed Z; Bérubé, Pierre R

    2013-09-15

    Sodium hypochlorite is commonly used as a cleaning agent to remove adsorbed foulants from PVDF based micro/ultra filtration membranes in water and wastewater treatment applications. Although effective for fouling control, extended sodium hypochlorite exposure can affect the physical/chemical characteristics and hinder the treatment performance of these membranes. To assess these effects, PVDF based membranes were exposed to sodium hypochlorite at different concentrations for varying periods of time, and the physical/chemical characteristics of the virgin and sodium hypochlorite exposed membranes were compared. The membranes were characterized based on chemical composition (FTIR and NMR), mechanical strength (yield strength), surface hydrophilicity (contact angle), pore size and porosity (scanning electron microscopy and challenge test), and membrane resistance (clean water permeation test). The results indicated that exposure dose and concentration of the sodium hypochlorite used have significant influence on the membrane characteristics. The impact of sodium hypochlorite exposure on the parameters investigated could be most accurately and consistently correlated to an exposure dose relationship of the form C(n)t (where, C = concentration and t = exposure time) rather than the Ct relationship commonly used to define the extent of exposure to cleaning agents. For all the parameters investigated, the power coefficient n was less than 1 indicating that time had a greater impact on the changes than did the concentration of the sodium hypochlorite. The results suggest that the use of sodium hypochlorite for chemical cleaning, at concentrations that are higher than those typically used for chemical cleaning would have less of an effect on the characteristics of the membrane materials. Changes in the characteristics were attributed to the oxidation of the hydrophilic additives (HA) present in blended PVDF membranes.

  9. Mechanism of organic anion transport across the apical membrane of choroid plexus.

    PubMed

    Pritchard, J B; Sweet, D H; Miller, D S; Walden, R

    1999-11-19

    The mechanism and membrane localization of choroid plexus (CP) organic anion transport were determined in apical (or brush border) membrane vesicles isolated from bovine choroid plexus and in intact CP tissue from cow and rat. Brush border membrane vesicles were enriched in Na(+),K(+)-ATPase (20-fold; an apical marker in CP) and demonstrated specific, sodium-coupled transport of proline, glucose, and glutarate. Vesicular uptake of the anionic herbicide 2, 4-dichlorophenoxyacetic acid (2,4-D) was markedly stimulated by an inward sodium gradient but only in the presence of glutarate, indicating the presence of apical dicarboxylate/organic anion exchange. Consistent with this interpretation, an imposed outward glutarate gradient stimulated 2,4-D uptake in the absence of sodium. Under both conditions, uptake was dramatically slowed and overshoot was abolished by probenecid. Likewise, apical accumulation of 2,4-D by intact bovine choroid plexus tissue in vitro was stimulated by external glutarate in the presence of sodium. Glutarate stimulation was abolished by 5 mM LiCl. Identical findings were obtained using rat CP tissue, which showed both sodium/glutarate-stimulated 2,4-D (tissue/medium (T/M) approximately 8) and p-aminohippurate (T/M = 2) transport. Finally, since the renal exchanger (rROAT1) has been cloned in rat kidney, a rROAT1-green fluorescent protein construct was used to analyze exchanger distribution directly in transiently transfected rat CP. As predicted by the functional studies, the fluorescently tagged transporter was seen in apical but not basolateral membranes of the CP.

  10. Salt splitting of sodium-dominated radioactive waste using ceramic membranes

    SciTech Connect

    Hollenberg, G.W.; Carlson, C.D.; Virkar, A.; Joshi, A.

    1994-08-01

    The potential for salt splitting of sodium dominated radioactive wastes by use of a ceramic membrane is reviewed. The technical basis for considering this processing technology is derived from the technology developed for battery and chlor-alkali chemical industry. Specific comparisons are made with the commercial organic membranes which are the standard in nonradioactive salt splitting. Two features of ceramic membranes are expected to be especially attractive: high tolerance to gamma irradiation and high selectivity between sodium and other ions. The objective of the salt splitting process is to separate nonradioactive sodium from contaminated sodium salts prior to other pretreatment processes in order to: (1) concentrate the waste in order to reduce the volume of subsequent additives and capacity of equipment, (2) decrease the pH of the waste in preparation for further processing, and (3) provide sodium with very low radioactivity levels for caustic washing of sludge or low level and mixed waste vitrification.

  11. Comparative molecular biological analysis of membrane transport genes in organisms

    PubMed Central

    Nagata, Toshifumi; Iizumi, Shigemi; Satoh, Kouji

    2008-01-01

    Comparative analyses of membrane transport genes revealed many differences in the features of transport homeostasis in eight diverse organisms, ranging from bacteria to animals and plants. In bacteria, membrane-transport systems depend mainly on single genes encoding proteins involved in an ATP-dependent pump and secondary transport proteins that use H+ as a co-transport molecule. Animals are especially divergent in their channel genes, and plants have larger numbers of P-type ATPase and secondary active transporters than do other organisms. The secondary transporter genes have diverged evolutionarily in both animals and plants for different co-transporter molecules. Animals use Na+ ions for the formation of concentration gradients across plasma membranes, dependent on secondary active transporters and on membrane voltages that in turn are dependent on ion transport regulation systems. Plants use H+ ions pooled in vacuoles and the apoplast to transport various substances; these proton gradients are also dependent on secondary active transporters. We also compared the numbers of membrane transporter genes in Arabidopsis and rice. Although many transporter genes are similar in these plants, Arabidopsis has a more diverse array of genes for multi-efflux transport and for response to stress signals, and rice has more secondary transporter genes for carbohydrate and nutrient transport. Electronic supplementary material The online version of this article (doi:10.1007/s11103-007-9287-z) contains supplementary material, which is available to authorized users. PMID:18293089

  12. The Effects of Altered Membrane Cholesterol Levels on Sodium Pump Activity in Subclinical Hypothyroidism

    PubMed Central

    2017-01-01

    Background Metabolic dysfunctions characteristic of overt hypothyroidism (OH) start at the early stage of subclinical hypothyroidism (SCH). Na+/K+-ATPase (the sodium pump) is a transmembrane enzyme that plays a vital role in cellular activities in combination with membrane lipids. We evaluated the effects of early changes in thyroid hormone and membrane cholesterol on sodium pump activity in SCH and OH patients. Methods In 32 SCH patients, 35 OH patients, and 34 euthyroid patients, sodium pump activity and cholesterol levels in red blood cell membranes were measured. Serum thyroxine (T4) and thyroid stimulating hormone (TSH) levels were measured using enzyme-linked immunosorbent assays. Differences in their mean values were analysed using post hoc analysis of variance. We assessed the dependence of the sodium pump on other metabolites by multiple regression analysis. Results Sodium pump activity and membrane cholesterol were lower in both hypothyroid groups than in control group, OH group exhibiting lower values than SCH group. In SCH group, sodium pump activity showed a significant direct dependence on membrane cholesterol with an inverse relationship with serum TSH levels. In OH group, sodium pump activity depended directly on membrane cholesterol and serum T4 levels. No dependence on serum cholesterol was observed in either case. Conclusion Despite the presence of elevated serum cholesterol in hypothyroidism, membrane cholesterol contributed significantly to maintain sodium pump activity in the cells. A critical reduction in membrane cholesterol levels heralds compromised enzyme activity, even in the early stage of hypothyroidism, and this can be predicted by elevated TSH levels alone, without any evident clinical manifestations. PMID:28256112

  13. [Inhibition of the sodium inactivation of the nodal membrane by anemonia sulcata toxin II].

    PubMed

    Bergman, C; Dubois, J M; Rojas, E; Rathmayer, W

    1976-05-31

    A neurotoxin (ATX-II) extracted from the tentacles of Anemonia sulcata has been found to interact with the sodium channel of the nodal membrane in myelinated nerve fibres from Rana esculenta. If externally applied at low concentration (Kd = 20 muM), it reduces considerably the rate of inactivation of the sodium conductance without affecting the activation. At such concentrations, the potassium conductance is not affected. If internally applied ATX-II does not affect the membrane conductance.

  14. Single molecule imaging of conformational dynamics in sodium-coupled transporters

    NASA Astrophysics Data System (ADS)

    Terry, Daniel S.

    Neurotransmitter:sodium symporter (NSS) proteins remove neurotransmitters released into the synapse through a transport process driven by the physiological sodium ion (Na+) gradient. NSSs for dopamine, noradrenaline, and serotonin are targeted by the psychostimulants cocaine and amphetamines, as well as by antidepressants. The crystal structure of LeuT, a prokaryotic NSS homologue, revealed the NSS molecular architecture and has been the basis for extensive structural, biochemical, and computational investigations of the mechanism of transporter proteins with a LeuT-like fold. In this dissertation, the conformational states sampled by LeuT are explored using single-molecule fluorescence resonance energy transfer imaging methods, with special focus on the motions of transmembrane helix 1a that lead to inward release of substrate. We also explored how dynamics are modulated by substrate, Na+, and protons to produce efficient transport. These advances represent a first of a kind study of the dynamics of an integral membrane protein at a truly single-molecule scale. Advances in instrumentation, analysis tools, and organic fluorophores were all required to achieve these goals, and such advances are also described. While these experiments were performed with detergent-solubilized protein, preliminary work suggests that imaging of LeuT in proteoliposomes is feasible and a fluorescence sensor assay could be used to simultaneously detect conformational dynamics and transport function.

  15. Fabrication of catalyzed ion transport membrane systems

    DOEpatents

    Carolan, Michael Francis; Kibby, Charles Leonard

    2013-06-04

    Process for fabricating a catalyzed ion transport membrane (ITM). In one embodiment, an uncatalyzed ITM is (a) contacted with a non-reducing gaseous stream while heating to a temperature and for a time period sufficient to provide an ITM possessing anion mobility; (b) contacted with a reducing gaseous stream for a time period sufficient to provide an ITM having anion mobility and essentially constant oxygen stoichiometry; (c) cooled while contacting the ITM with the reducing gaseous stream to provide an ITM having essentially constant oxygen stoichiometry and no anion mobility; and (d) treated by applying catalyst to at least one of (1) a porous mixed conducting multicomponent metallic oxide (MCMO) layer contiguous with a first side of a dense layer of MCMO and (2) a second side of the dense MCMO layer. In another embodiment, these steps are carried out in the alternative order of (a), (d), (b), and (c).

  16. Sodium/proton antiporters in the mitochondrial inner membrane.

    PubMed

    Garlid, K D

    1988-01-01

    the effects of the Na+,K+-ATPase. Nevertheless, a sound design principle would be followed if the cell, like mitochondria, were to regulate volume by governing a passive back-flow process rather than an active transport process. In conclusion, it seems premature to conclude that plasma membranes contain only one type of Na+/H+ antiporter. Nor does it seem likely that there is an unlimited variety of such transporters. I propose as a working hypothesis that antiporters from both mitochondria and plasmalemma may be separated into two classes: Na+-selective and non-Na+-selective.(ABSTRACT TRUNCATED AT 400 WORDS)

  17. Development of a label-free assay for sodium-dependent phosphate transporter NaPi-IIb.

    PubMed

    Wong, Soo-Hang; Gao, Alice; Ward, Sabrina; Henley, Charles; Lee, Paul H

    2012-07-01

    The most widely used assay format for characterizing plasma membrane transporter activity measures accumulation of radiolabeled substrates in tissues or cells expressing the transporters. This assay format had limitations and disadvantages; therefore, there was an unmet need for development of a homogeneous, nonradioactive assay for membrane transporter proteins. In this report, the authors describe the development of a label-free homogeneous assay for the sodium-dependent phosphate transporter NaPi-IIb using the Epic system. The addition of phosphate stimulated a dynamic mass redistribution (DMR) profile unique to cells expressing NaPi-IIb but not on parental cells. This DMR profile was phosphate specific because sulfate or buffer alone did not elicit the same response. Furthermore, the DMR response observed was phosphate and sodium dependent, with Km values in the micromolar and millimolar range, respectively. A known NaPi-IIb noncompetitive inhibitor was shown to completely inhibit the phosphate-stimulated DMR response, suggesting that this observed DMR response is an NaPi-IIb-mediated cellular event. The results demonstrate that a novel label-free assay was developed for studying transporter-mediated cellular activity, and this DMR assay platform could be applicable to other membrane transporter proteins.

  18. Biomimetic polyesters and their role in ion transport across cell membranes.

    PubMed

    Jedliński, Z; Kurcok, P; Adamus, G; Juzwa, M

    2000-01-01

    Syntheses of biomimetic low-molecular weight poly-(R)-3-hydroxybutanoate mediated by three types of supramolecular catalysts are presented. The utility of these synthetic polyesters for preparation of artificial channels in phospholipid bilayers capable of sodium and calcium ion transport across cell membranes, is discussed. Further studies on possible applications of these bio-polymers for manufacturing drugs of prolonged activity are under way.

  19. Active sodium transport and the electrophysiology of rabbit colon.

    PubMed

    Schultz, S G; Frizzell, R A; Nellans, H N

    1977-05-12

    The electrophysiologic properties of rabbit colonic epithelial cells were investigated employing microelectrode techniques. Under open-circuit conditions, the transepithelial electrical potential difference (PD) averaged 20 mV, serosa positive, and the intracellular electrical potential (psimc) averaged -32 mV, cell interior negative with respect to the mucosal solution; under short-circuit conditions, psimc averaged -46 mV. The addition of amiloride to the mucosal solution abolishes the transepithelial PD and active Na transport, and psimc is hyperpolarized to an average value of -53 mV. These results indicate that Na entry into the mucosal cell is a conductive process which, normally, depolarized psimc. The data obtained were interpreted using a double-membrane equivalent electrical circuit model of the "active Na transport pathway" involving two voltage-independent electromotive forces (emf's) and two voltage-independent resistances arrayed in series. Our observations are consistent with the notions that: (a) The emf's and resistances across the mucosal and baso-lateral membranes are determined predominantly by the emf (64 mV) and resistance of the Na entry process and the emf (53 mV) and resistance of the process responsible for active Na extrusion across the baso-lateral membranes: that is, the electrophysiological properties of the cell appear to be determined solely by the properties and processes responsible for transcellular active Na transport. The emf of the Na entry process is consistent with the notion that the Na activity in the intracellular transport pool is approximately one-tenth that in the mucosal solution or about 14 mM. (b) In the presence of amiloride, the transcellular conductance is essentially abolished and the total tissue conductance is the result of ionic diffusion through paracellular pathways. (c) The negative intracellular potential (with respect to the mucosal solution) is due primarily to the presence of a low resistance

  20. Carbonized-leaf Membrane with Anisotropic Surfaces for Sodium-ion Battery.

    PubMed

    Li, Hongbian; Shen, Fei; Luo, Wei; Dai, Jiaqi; Han, Xiaogang; Chen, Yanan; Yao, Yonggang; Zhu, Hongli; Fu, Kun; Hitz, Emily; Hu, Liangbing

    2016-01-27

    A simple one-step thermal pyrolysis route has been developed to prepare carbon membrane from a natural leaf. The carbonized leaf membrane possesses anisotropic surfaces and internal hierarchical porosity, exhibiting a high specific capacity of 360 mAh/g and a high initial Coulombic efficiency of 74.8% as a binder-free, current-collector-free anode for rechargeable sodium ion batteries. Moreover, large-area carbon membranes with low contact resistance are fabricated by simply stacking and carbonizing leaves, a promising strategy toward large-scale sodium-ion battery developments.

  1. Transport through liquid membranes containing omeprazole and lansoprazole.

    PubMed

    Nagappa, A N; Pandi, P V; Mishra, P K; Girish, Rahul K; Shanmukh, I

    2002-12-01

    Omeprazole and lansoprazole, the therapeutically important drugs belonging to proton pump inhibitor category are extensively used in the treatment of gastric ulcers. Transport through liquid membranes generated by these drugs in lecithin-cholesterol mixture in series with a supporting membrane has been studied. The data obtained show the formation of liquid membrane in series with the supporting membrane. Transport of cations, chloride and bicarbonate ions in the presence liquid membranes generated by omeprazole and lanzoprazole indicate the modification in the permeability of various permeants.

  2. Analytical Applications of Transport Through Bulk Liquid Membranes.

    PubMed

    Diaconu, Ioana; Ruse, Elena; Aboul-Enein, Hassan Y; Bunaciu, Andrei A

    2016-07-03

    This review discusses the results of research in the use of bulk liquid membranes in separation processes and preconcentration for analytical purposes. It includes some theoretical aspects, definitions, types of liquid membranes, and transport mechanism, as well as advantages of using liquid membranes in laboratory studies. These concepts are necessary to understand fundamental principles of liquid membrane transport. Due to the multiple advantages of liquid membranes several studies present analytical applications of the transport through liquid membranes in separation or preconcentration processes of metallic cations and some organic compounds, such as phenol and phenolic derivatives, organic acids, amino acids, carbohydrates, and drugs. This review presents coupled techniques such as separation through the liquid membrane coupled with flow injection analysis.

  3. Control of membrane thermal transport supporting superconducting detetctor development.

    SciTech Connect

    Yefremenko, V.; Wang, G.; Novosad, V.; Datesman, A. M.; Pearson, J. E.; Divan, R.; Chang, C. L.; Downes, T. P.; McMahon, J.; Bleem, L.; Crites, A. T.; Meyer, S. S.; Carlstrom, J. E.; Univ. of Chicago

    2009-06-01

    Because thermal transport determines the dynamic and static operation of bolometric detectors, control of the thermal conductance is critical for the implementation of detectors utilizing superconducting Transition Edge Sensors (TESs). For this reason, we have examined the use of partially perforated membranes for thermal management. This technique preserves the physical integrity of the membrane, and therefore maintains the mechanical robustness of the detector. This paper describes investigations of the thermal transport in trenched membranes.

  4. ATP-dependent calcium transport across basal plasma membranes of human placental trophoblast

    SciTech Connect

    Fisher, G.J.; Kelley, L.K.; Smith, C.H.

    1987-01-01

    As a first step in understanding the cellular basis of maternal-fetal calcium transfer, the authors examined the characteristics of calcium uptake by a highly purified preparation of the syncytiotrophoblast basal (fetal facing) plasma membrane. In the presence of nanomolar concentrations of free calcium, basal membranes demonstrated substantial ATP-dependent calcium uptake. This uptake required magnesium, was not significantly affected by Na/sup +/ or K/sup +/ (50 mM), or sodium azide (10 mM). Intravesicular calcium was rapidly and completely released by the calcium ionophore rapidly and completely released by the calcium ionophore A23187. Calcium transport was significantly stimulated by the calcium-dependent regulatory protein calmodulin. Placental membrane fractions enriched in endoplasmic reticulum (ER) and mitochondria also demonstrated ATP-dependent calcium uptake. In contrast to basal membrane, mitochondrial calcium uptake was completely inhibited by azide. The rate of calcium uptake was completely inhibited by azide. The rate of calcium uptake by the ER was only 20% of that of basal membranes. They conclude that the placental basal plasma membrane possesses a high-affinity calcium transport system similar to that found in plasma membranes of a variety of cell types. This transporter is situated to permit it to function in vivo in maternal-fetal calcium transfer.

  5. Nanostructured silicon membranes for control of molecular transport

    PubMed Central

    Srijanto, Bernadeta R.; Retterer, Scott T.; Fowlkes, Jason D.; Doktycz, Mitchel J.

    2010-01-01

    A membrane that allows selective transport of molecular species requires precise engineering on the nanoscale. Membrane permeability can be tuned by controlling the physical structure and surface chemistry of the pores. Here, a combination of electron beam and optical lithography, along with cryogenic deep reactive ion etching, has been used to fabricate silicon membranes that are physically robust, have uniform pore sizes, and are directly integrated into a microfluidic network. Additional reductions in pore size were achieved using plasma enhanced chemical vapor deposition and atomic layer deposition of silicon dioxide to coat membrane surfaces. Cross sectioning of the membranes using focused ion beam milling was used to determine the physical shape of the membrane pores before and after coating. Functional characterization of the membranes was performed by using quantitative fluorescence microscopy to document the transport of molecular species across the membrane. PMID:24932436

  6. Functional expression of sodium-glucose transporters in cancer

    PubMed Central

    Scafoglio, Claudio; Hirayama, Bruce A.; Kepe, Vladimir; Liu, Jie; Ghezzi, Chiara; Satyamurthy, Nagichettiar; Moatamed, Neda A.; Huang, Jiaoti; Koepsell, Hermann; Barrio, Jorge R.; Wright, Ernest M.

    2015-01-01

    Glucose is a major metabolic substrate required for cancer cell survival and growth. It is mainly imported into cells by facilitated glucose transporters (GLUTs). Here we demonstrate the importance of another glucose import system, the sodium-dependent glucose transporters (SGLTs), in pancreatic and prostate adenocarcinomas, and investigate their role in cancer cell survival. Three experimental approaches were used: (i) immunohistochemical mapping of SGLT1 and SGLT2 distribution in tumors; (ii) measurement of glucose uptake in fresh isolated tumors using an SGLT-specific radioactive glucose analog, α-methyl-4-deoxy-4-[18F]fluoro-d-glucopyranoside (Me4FDG), which is not transported by GLUTs; and (iii) measurement of in vivo SGLT activity in mouse models of pancreatic and prostate cancer using Me4FDG-PET imaging. We found that SGLT2 is functionally expressed in pancreatic and prostate adenocarcinomas, and provide evidence that SGLT2 inhibitors block glucose uptake and reduce tumor growth and survival in a xenograft model of pancreatic cancer. We suggest that Me4FDG-PET imaging may be used to diagnose and stage pancreatic and prostate cancers, and that SGLT2 inhibitors, currently in use for treating diabetes, may be useful for cancer therapy. PMID:26170283

  7. Ionic transport in lipid bilayer membranes.

    PubMed Central

    Bordi, F; Cametti, C; Naglieri, A

    1998-01-01

    The current-voltage relationships of model bilayer membranes have been measured in various phospholipid systems, under the influence of both a gradient of potential and an ionic concentration, in order to describe the ion translocation through hydrated transient defects (water channels) across the bilayer formed because of lipid structure fluctuations and induced by temperature. The results have been analyzed in the light of a statistical rate theory for the transport process across a lipid bilayer, recently proposed by Skinner et al. (1993). In order to take into account the observed I-V curves and in particular the deviation from an ohmic behavior observed at high potential values, the original model has been modified, and a new version has been proposed by introducing an additional kinetic process. In this way, a very good agreement with the experimental values has been obtained for all of the systems we have investigated (dimyristoylphosphatidyl ethanolamine bilayers and mixed systems composed by dimyristoylphosphatidyl ethanolamine/dimyristoylphosphatidylcholine mixtures and dimyristoylphosphatidyl ethanolamine/phosphatidic acid dipalmitoyl mixtures). The rate constants governing the reactions at the bilayer interfaces have been evaluated for K+ and Cl- ions, as a function of temperature, from 5 to 35 degrees C and bulk ionic concentrations from 0.02 to 0.2 M. Finally, a comparison between the original model of Skinner and the modified version is presented, and the advantages of this new formulation are briefly discussed. PMID:9512032

  8. Phenylalanine transport in guinea pig jejunum. A general mechanism for organic solute and sodium cotransport.

    PubMed

    Alvarado, F; Lherminier, M

    1982-08-01

    1. Sodium-dependent phenylalanine transport by guinea pig jejunum exhibits apparently pure K-type activation kinetics where Vmaxs is constant but KT decreases as [Na+] increases. At 0, 3 and 6 mM sodium, however, the results deviate from the expected hyperbolic kinetics and give a plateau. 2. This finding is interpreted in terms of the hypothesis that the outer face of the brush border membrane contains enough Na+ to support amino acid and Na+ cotransport at essentially maximal rates, even after preincubation of the tissues in vitro for several minutes in sodium-free buffers. 3. Sodium could move dynamically into this region from tissue stores and across the paracellular pathway. Passage of NaCl directly across the brush border also seems possible by reversal of the (neutral) Na+ and Cl- cotransport system. 4. To reconcile contradictory observations obtained in different laboratories, either with intact-epithelium preparations or with isolated brush border membrane vesicles, we include a theoretical analysis of the kinetics of organic solute and Na+ cotransport. For simplicity, this analysis is limited to cases of 1/2 stoichiometry and to neutral organic solutes such as sugars and monoamino-monocarboxylic amino acids. 5. Cotransport is explained in terms of a general, allosteric mechanism involving one site for S and another for Na+. There is no preferential order for binding, but only the ternary complex S-carrier-Na+ can translocate at quantitatively significant rates (obligatory activation kinetics). Since Na+ crosses the membrane as the free cation, under physiological conditions (inside-negative membrane potential) it will move towards its position of electrical equilibrium, hence unidirectionally. This explains why, with intact-tissue preparations, solute influx exhibits Michaelis-Menten kinetics. 6. By definition, cotransport kinetics are mixed type and involve effects on both KT and Vmaxs. Macroscopic deviations from this expected behaviour can be explained

  9. Development of Human Membrane Transporters: Drug Disposition and Pharmacogenetics.

    PubMed

    Mooij, Miriam G; Nies, Anne T; Knibbe, Catherijne A J; Schaeffeler, Elke; Tibboel, Dick; Schwab, Matthias; de Wildt, Saskia N

    2016-05-01

    Membrane transporters play an essential role in the transport of endogenous and exogenous compounds, and consequently they mediate the uptake, distribution, and excretion of many drugs. The clinical relevance of transporters in drug disposition and their effect in adults have been shown in drug-drug interaction and pharmacogenomic studies. Little is known, however, about the ontogeny of human membrane transporters and their roles in pediatric pharmacotherapy. As they are involved in the transport of endogenous substrates, growth and development may be important determinants of their expression and activity. This review presents an overview of our current knowledge on human membrane transporters in pediatric drug disposition and effect. Existing pharmacokinetic and pharmacogenetic data on membrane substrate drugs frequently used in children are presented and related, where possible, to existing ex vivo data, providing a basis for developmental patterns for individual human membrane transporters. As data for individual transporters are currently still scarce, there is a striking information gap regarding the role of human membrane transporters in drug therapy in children.

  10. Membranes for nanometer-scale mass fast transport

    DOEpatents

    Bakajin, Olgica [San Leandro, CA; Holt, Jason [Berkeley, CA; Noy, Aleksandr [Belmont, CA; Park, Hyung Gyu [Oakland, CA

    2011-10-18

    Nanoporous membranes comprising single walled, double walled, and multiwalled carbon nanotubes embedded in a matrix material were fabricated for fluid mechanics and mass transfer studies on the nanometer scale and commercial applications. Average pore size can be 2 nm to 20 nm, or seven nm or less, or two nanometers or less. The membrane can be free of large voids spanning the membrane such that transport of material such as gas or liquid occurs exclusively through the tubes. Fast fluid, vapor, and liquid transport are observed. Versatile micromachining methods can be used for membrane fabrication. A single chip can comprise multiple membranes. These membranes are a robust platform for the study of confined molecular transport, with applications in liquid and gas separations and chemical sensing including desalination, dialysis, and fabric formation.

  11. Ion transport controlled by nanoparticle-functionalized membranes.

    PubMed

    Barry, Edward; McBride, Sean P; Jaeger, Heinrich M; Lin, Xiao-Min

    2014-12-17

    From proton exchange membranes in fuel cells to ion channels in biological membranes, the well-specified control of ionic interactions in confined geometries profoundly influences the transport and selectivity of porous materials. Here we outline a versatile new approach to control a membrane's electrostatic interactions with ions by depositing ligand-coated nanoparticles around the pore entrances. Leveraging the flexibility and control by which ligated nanoparticles can be synthesized, we demonstrate how ligand terminal groups such as methyl, carboxyl and amine can be used to tune the membrane charge density and control ion transport. Further functionality, exploiting the ligands as binding sites, is demonstrated for sulfonate groups resulting in an enhancement of the membrane charge density. We then extend these results to smaller dimensions by systematically varying the underlying pore diameter. As a whole, these results outline a previously unexplored method for the nanoparticle functionalization of membranes using ligated nanoparticles to control ion transport.

  12. Sodium/proton antiport in brush-border-membrane vesicles isolated from rat small intestine and kidney.

    PubMed

    Murer, H; Hopfer, U; Kinne, R

    1976-03-15

    Studies on proton and Na+ transport by isolated intestinal and renal brush-border-membrane vesicles were carried out to test for the presence of an Na+/H+-exchange system. Proton transport was evaluated as proton transfer from the intravesicular space to the incubation medium by monitoring pH changes in the membrane suspension induced by sudden addition of cations. Na+ transport was determined as Na+ uptake into the vesicles by filtration technique. A sudden addition of sodium salts (but not choline) to the membrane suspension provokes an acidification of the incubation medium which is abolished by the addition of 0.5% Triton X-100. Pretreatment of the membranes with Triton X-100 prevents the acidification. The acidification is also not observed if the [K+] and proton conductance of the membranes have been increased by the simultaneous addition of valinomycin and carbonyl cyanide p-trifluoromethoxyphenylhydrazone to the K+-rich incubation medium. Either valinomycin or carbonyl cyanide p-trifluoromethoxyphenylhydrazone when added alone do not alter the response of the membranes to the addition of Na+. Na+ uptake by brush-border microvilli is enhanced in the presence of a proton gradient directed from the intravesicular space to the incubation medium. Under these conditions a transient accumulation of Na+ inside the vesicles is observed. It is concluded that intestinal and renal brush-border membranes contain a NA+/H+ antiport system which catalyses an electroneutral exchange of Na+ against protons and consequently can produce a proton gradient in the presence of a concentration difference for Na+. This system might be involved in the active proton secretion of the small intestine and the proximal tubule of the kidney.

  13. Low temperature thermal transport in partially perforated silicon nitride membranes.

    SciTech Connect

    Yefremenko, V.; Wang, G.; Novosad, V.; Datesman, A.; Pearson, J.; Divan, R.; Chang, C. L.; Downes, T. P.; Mcmahon, J. J.; Bleem, L. E.; Crites, A. T.; Meyer, S. S.; Carlstrom, J. E.; Univ. of Chicago

    2009-05-04

    The thermal transport in partially trenched silicon nitride membranes has been studied in the temperature range from 0.3 to 0.6 K, with the transition edge sensor (TES), the sole source of membrane heating. The test configuration consisted of Mo/Au TESs lithographically defined on silicon nitride membranes 1 {micro}m thick and 6 mm{sup 2} in size. Trenches with variable depth were incorporated between the TES and the silicon frame in order to manage the thermal transport. It was shown that sharp features in the membrane surface, such as trenches, significantly impede the modes of phonon transport. A nonlinear dependence of thermal resistance on trench depth was observed. Partial perforation of silicon nitride membranes to control thermal transport could be useful in fabricating mechanically robust detector devices.

  14. Sodium pump molecular activity and membrane lipid composition in two disparate ectotherms, and comparison with endotherms.

    PubMed

    Turner, Nigel; Hulbert, A J; Else, Paul L

    2005-02-01

    Previous research has shown that the lower sodium pump molecular activity observed in tissues of ectotherms compared to endotherms, is largely related to the lower levels of polyunsaturates and higher levels of monounsaturates found in the cell membranes of ectotherms. Marine-based ectotherms, however, have very polyunsaturated membranes, and in the current study, we measured molecular activity and membrane lipid composition in tissues of two disparate ectothermic species, the octopus (Octopus vulgaris) and the bearded dragon lizard (Pogona vitticeps), to determine whether the high level of membrane polyunsaturation generally observed in marine-based ectotherms is associated with an increased sodium pump molecular activity relative to other ectotherms. Phospholipids from all tissues of the octopus were highly polyunsaturated and contained high concentrations of the omega-3 polyunsaturate, docosahexaenoic acid (22:6 (n-3)). In contrast, phospholipids from bearded dragon tissues contained higher proportions of monounsaturates and lower proportions of polyunsaturates. Sodium pump molecular activity was only moderately elevated in tissues of the octopus compared to the bearded dragon, despite the much greater level of polyunsaturation in octopus membranes. When the current data were combined with data for the ectothermic cane toad, a significant (P = 0.003) correlation was observed between sodium pump molecular activity and the content of 22:6 (n-3) in the surrounding membrane. These results are discussed in relation to recent work which shows a similar relationship in endotherms.

  15. Effects of electrolytes on ion transport in Chitosan membranes

    NASA Astrophysics Data System (ADS)

    Rupiasih, N. N.

    2016-11-01

    Recently, charged polymer membranes are widely used for water purification applications involving control of water and ion transport, such as reverse osmosis and electrodialysis. In this study, we have explored the effects of electrolyte solutions on ion transport properties of chitosan synthetic membranes via concentration gradient driven transport. Also, the water uptake of those membranes, before (control) as well used membranes have studied. The membrane used was chitosan membrane 2%. The electrolyte solutions used were HCl, KCl, CaCl2, MgCl2 and AlCl3, with various concentrations of 0.1 mM, 1 mM, 10 mM, 100 mM and 1000 mM. Ion transport experiments were carried out in a cell membrane model which composed of two compartments and the potential difference of membrane was measured using Ag/AgCl calomel electrodes. Those measurements were conducted at ambient temperature 28.8 °C. The results showed that the current density (J) increased with increased in concentration gradient of solution. The current density was higher in electrolyte solution which has higher molar conductivity than those of a solution with a small molar conductivity. Meanwhile the current density was smaller in electrolyte solution which has larger Stokes radii than those of a solution with small Stokes radii. Except membrane which has been used in HCl solution, the water uptakes of the used membranes were greater than the control membrane. These results can develop and validate a common framework to interpret data of concentration gradient driven transport in chitosan synthetic membranes and to use it to design of membranes with improved performance.

  16. Silymarin protects plasma membrane and acrosome integrity in sperm treated with sodium arsenite.

    PubMed

    Eskandari, Farzaneh; Momeni, Hamid Reza

    2016-01-01

    Exposure to arsenic is associated with impairment of male reproductive function by inducing oxidative stress. Silymarin with an antioxidant property scavenges free radicals. The aim of this study was to investigate if silymarin can prevent the adverse effects of sodium arsenite on ram sperm plasma membrane and acrosome integrity. Ram epidydimal spermatozoa were divided into five groups: spermatozoa at 0 hr, spermatozoa at 180 min (control), spermatozoa treated with silymarin (20 μM) + sodium arsenite (10 μM) for 180 min, spermatozoa treated with sodium arsenite (10 μM) for 180 min and spermatozoa treated with silymarin (20 μM) for 180 min. Double staining of Hoechst and propidium iodide was performed to evaluate sperm plasma membrane integrity, whereas comassie brilliant blue staining was used to assess acrosome integrity. Plasma membrane (p< 0.001) and acrosome integrity (p< 0.05) of the spermatozoa were significantly reduced in sodium arsenite group compared to the control. In silymarin + sodium arsenite group, silymarin was able to significantly (p< 0.001) ameliorate the adverse effects of sodium arsenite on these sperm parameters compared to sodium arsenite group. The incubation of sperm for 180 min (control group) showed a significant (p< 0.001) decrease in acrosome integrity compared to the spermatozoa at 0 hour. The application of silymarin alone for 180 min could also significantly (p< 0.05) increase sperm acrosome integrity compared to the control. Silymarin as a potent antioxidant could compensate the adverse effects of sodium arsenite on the ram sperm plasma membrane and acrosome integrity.

  17. Feed gas contaminant removal in ion transport membrane systems

    DOEpatents

    Underwood, Richard Paul [Allentown, PA; Makitka, III, Alexander; Carolan, Michael Francis [Allentown, PA

    2012-04-03

    An oxygen ion transport membrane process wherein a heated oxygen-containing gas having one or more contaminants is contacted with a reactive solid material to remove the one or more contaminants. The reactive solid material is provided as a deposit on a support. The one or more contaminant compounds in the heated oxygen-containing gas react with the reactive solid material. The contaminant-depleted oxygen-containing gas is contacted with a membrane, and oxygen is transported through the membrane to provide transported oxygen.

  18. Electrophoretic Transport of Biomolecules through Carbon Nanotube Membranes

    PubMed Central

    Sun, Xinghua; Su, Xin; Wu, Ji; Hinds, Bruce J.

    2013-01-01

    Electrophoretic transport of proteins across electrochemically oxidized multi-walled carbon nanotube (MWCNT) membranes has been investigated. Small charged protein, lysozyme, was successfully pumped across MWCNT membranes by electric field while rejecting larger bovine serum albumin (BSA). Transport of the lysozome was reduced by a factor of about 30 in comparison to bulk mobility and consistent with prediction for hindered transport. Mobilities between 0.33-1.4×10-9 m2/V-s were observed and are approximately 10 fold faster than comparable ordered nanoporous membranes and are consistent with continuum models. For mixtures of BSA and lysozyme, complete rejection of BSA is seen with electrophoretic separations PMID:21338104

  19. The Sodium Glucose Cotransporter SGLT1 Is an Extremely Efficient Facilitator of Passive Water Transport.

    PubMed

    Erokhova, Liudmila; Horner, Andreas; Ollinger, Nicole; Siligan, Christine; Pohl, Peter

    2016-04-29

    The small intestine is void of aquaporins adept at facilitating vectorial water transport, and yet it reabsorbs ∼8 liters of fluid daily. Implications of the sodium glucose cotransporter SGLT1 in either pumping water or passively channeling water contrast with its reported water transporting capacity, which lags behind that of aquaporin-1 by 3 orders of magnitude. Here we overexpressed SGLT1 in MDCK cell monolayers and reconstituted the purified transporter into proteoliposomes. We observed the rate of osmotic proteoliposome deflation by light scattering. Fluorescence correlation spectroscopy served to assess (i) SGLT1 abundance in both vesicles and plasma membranes and (ii) flow-mediated dilution of an aqueous dye adjacent to the cell monolayer. Calculation of the unitary water channel permeability, pf, yielded similar values for cell and proteoliposome experiments. Neither the absence of glucose or Na(+), nor the lack of membrane voltage in vesicles, nor the directionality of water flow grossly altered pf Such weak dependence on protein conformation indicates that a water-impermeable occluded state (glucose and Na(+) in their binding pockets) lasts for only a minor fraction of the transport cycle or, alternatively, that occlusion of the substrate does not render the transporter water-impermeable as was suggested by computational studies of the bacterial homologue vSGLT. Although the similarity between the pf values of SGLT1 and aquaporin-1 makes a transcellular pathway plausible, it renders water pumping physiologically negligible because the passive flux would be orders of magnitude larger. © 2016 by The American Society for Biochemistry and Molecular Biology, Inc.

  20. Reduction of thrombogenicity of PVC-based sodium selective membrane electrodes using heparin-modified chitosan.

    PubMed

    Badr, Ibrahim H A; Gouda, M; Abdel-Sattar, R; Sayour, Hossam E M

    2014-01-01

    Heparin-modified chitosan (H-chitosan) membrane was utilized to enhance biocompatibility of sodium selective membrane electrode based on the highly thrombogenic polyvinyl chloride (PVC). Sodium ion sensing film was prepared using PVC, sodium ionophore-X, potassium tetrakis(chlorophenyl)-borate, and o-nitrophenyloctylether. The PVC-based sensing film was sandwiched to chitosan or H-chitosan to prevent platelet adhesion on the surface of PVC. Potentiometric response characteristics of PVC-chitosan and PVC-H-chitosan membrane electrodes were found to be comparable to that of a control PVC based sodium-selective electrode. This indicates that chitosan and H-chitosan layers do not alter the response behaviour of the PVC-based sensing film. Biocompatibility of H-chitosan was confirmed by in vitro platelet adhesion study. The platelet adhesion investigations indicated that H-chitosan film is less thrombogenic compared to PVC, which could result in enhancement of biocompatibility of sodium selective membrane electrodes based on PVC, while maintaining the overall electrochemical performance of the PVC-based sensing film.

  1. Thermodynamics of Ionic Transport through Functionalized Membranes

    NASA Astrophysics Data System (ADS)

    Rathee, Vikramjit; Qu, Siyi; Dilenschneider, Theodore; Phillip, William A.; Whitmer, Jonathan K.

    Through microphase separation of block copolymers, highly porous solid membranes may be assembled. Further functionalization with amine and sulfonic acid groups has demonstrated promise in exquisitely controlling the flux of charged species, and in particular multivalent ions. Using coarse-grained molecular simulations, we explore the essential thermodynamics underlying salt rejection in charge-functionalized membranes, and develop a model capable of linking the performance of these membranes to their molecular character through free energy calculations.

  2. Light-induced modification of plant plasma membrane ion transport.

    PubMed

    Marten, I; Deeken, R; Hedrich, R; Roelfsema, M R G

    2010-09-01

    Light is not only the driving force for electron and ion transport in the thylakoid membrane, but also regulates ion transport in various other membranes of plant cells. Light-dependent changes in ion transport at the plasma membrane and associated membrane potential changes have been studied intensively over the last century. These studies, with various species and cell types, revealed that apart from regulation by chloroplasts, plasma membrane transport can be controlled by phytochromes, phototropins or channel rhodopsins. In this review, we compare light-dependent plasma membrane responses of unicellular algae (Eremosphaera and Chlamydomonas), with those of a multicellular alga (Chara), liverworts (Conocephalum), mosses (Physcomitrella) and several angiosperm cell types. Light-dependent plasma membrane responses of Eremosphaera and Chara are characterised by the dominant role of K(+) channels during membrane potential changes. In most other species, the Ca(2+)-dependent activation of plasma membrane anion channels represents a general light-triggered event. Cell type-specific responses are likely to have evolved by modification of this general response or through the development of additional light-dependent signalling pathways. Future research to elucidate these light-activated signalling chains is likely to benefit from the recent identification of S-type anion channel genes and proteins capable of regulating these channels.

  3. Grafted functional groups on expanded tetrafluoroethylene (ePTFE) support for fuel cell and water transport membranes

    DOEpatents

    Fuller, Timothy J.; Jiang, Ruichun

    2017-01-24

    A method for forming a modified solid polymer includes a step of contacting a solid fluorinated polymer with a sodium sodium-naphthalenide solution to form a treated fluorinated solid polymer. The treated fluorinated solid polymer is contacted with carbon dioxide, sulfur dioxide, or sulfur trioxide to form a solid grafted fluorinated polymer. Characteristically, the grafted fluorinated polymer includes appended CO.sub.2H or SO.sub.2H or SO.sub.3H groups. The solid grafted fluorinated polymer is advantageously incorporated into a fuel cell as part of the ion-conducting membrane or a water transport membrane in a humidifier.

  4. Structural insights into the transport of small molecules across membranes

    PubMed Central

    Noinaj, Nicholas; Buchanan, Susan K.

    2014-01-01

    While hydrophobic small molecules often can freely permeate a lipid bilayer, ions and other polar molecules cannot and require transporters to mediate their transport. Recently, a number of important structures have been reported which have advanced our understanding of how membrane protein transporters function to transport small molecules. Structures of TbpA/B and HmuUV provided new insight into iron uptake by pathogenic bacteria while the structures of NarK, ASBT, and VcINDY revealed molecular details about the transport of nitrate, bile acids and dicarboxylates, respectively. The structure of the folate ECF transporter indicated that the S component likely undergoes a large conformational shift to mediate folate transport, while the cellulose synthase/transporter contains an elongated translocation pore for passage through the inner membrane. PMID:24681594

  5. Interfacial Water-Transport Effects in Proton-Exchange Membranes

    SciTech Connect

    Kienitz, Brian; Yamada, Haruhiko; Nonoyama, Nobuaki; Weber, Adam

    2009-11-19

    It is well known that the proton-exchange membrane is perhaps the most critical component of a polymer-electrolyte fuel cell. Typical membranes, such as Nafion(R), require hydration to conduct efficiently and are instrumental in cell water management. Recently, evidence has been shown that these membranes might have different interfacial morphology and transport properties than in the bulk. In this paper, experimental data combined with theoretical simulations will be presented that explore the existence and impact of interfacial resistance on water transport for Nafion(R) 21x membranes. A mass-transfer coefficient for the interfacial resistance is calculated from experimental data using different permeation cells. This coefficient is shown to depend exponentially on relative humidity or water activity. The interfacial resistance does not seem to exist for liquid/membrane or membrane/membrane interfaces. The effect of the interfacial resistance is to flatten the water-content profiles within the membrane during operation. Under typical operating conditions, the resistance is on par with the water-transport resistance of the bulk membrane. Thus, the interfacial resistance can be dominant especially in thin, dry membranes and can affect overall fuel-cell performance.

  6. Computational modelling of amino acid exchange and facilitated transport in placental membrane vesicles.

    PubMed

    Panitchob, N; Widdows, K L; Crocker, I P; Hanson, M A; Johnstone, E D; Please, C P; Sibley, C P; Glazier, J D; Lewis, R M; Sengers, B G

    2015-01-21

    Placental amino acid transport is required for fetal development and impaired transport has been associated with poor fetal growth. It is well known that placental amino acid transport is mediated by a broad array of specific membrane transporters with overlapping substrate specificity. However, it is not fully understood how these transporters function, both individually and as an integrated system. We propose that mathematical modelling could help in further elucidating the underlying mechanisms of how these transporters mediate placental amino acid transport. The aim of this work is to model the sodium independent transport of serine, which has been assumed to follow an obligatory exchange mechanism. However, previous amino acid uptake experiments in human placental microvillous plasma membrane vesicles have persistently produced results that are seemingly incompatible with such a mechanism; i.e. transport has been observed under zero-trans conditions, in the absence of internal substrates inside the vesicles to drive exchange. This observation raises two alternative hypotheses; (i) either exchange is not fully obligatory, or (ii) exchange is indeed obligatory, but an unforeseen initial concentration of amino acid substrate is present within the vesicle which could drive exchange. To investigate these possibilities, a mathematical model for tracer uptake was developed based on carrier mediated transport, which can represent either facilitated diffusion or obligatory exchange (also referred to as uniport and antiport mechanisms, respectively). In vitro measurements of serine uptake by placental microvillous membrane vesicles were carried out and the model applied to interpret the results based on the measured apparent Michaelis-Menten parameters Km and Vmax. In addition, based on model predictions, a new time series experiment was implemented to distinguish the hypothesised transporter mechanisms. Analysis of the results indicated the presence of a facilitated

  7. Calcium-Mediated Regulation of Proton-Coupled Sodium Transport - Final Report

    SciTech Connect

    Schumaker, Karen S

    2013-10-24

    The long-term goal of our experiments was to understand mechanisms that regulate energy coupling by ion currents in plants. Activities of living organisms require chemical, mechanical, osmotic or electrical work, the energy for which is supplied by metabolism. Adenosine triphosphate (ATP) has long been recognized as the universal energy currency, with metabolism supporting the synthesis of ATP and the hydrolysis of ATP being used for the subsequent work. However, ATP is not the only energy currency in living organisms. A second and very different energy currency links metabolism to work by the movement of ions passing from one side of a membrane to the other. These ion currents play a major role in energy capture and they support a range of physiological processes from the active transport of nutrients to the spatial control of growth and development. In Arabidopsis thaliana (Arabidopsis), the activity of a plasma membrane Na+/H+ exchanger, SALT OVERLY SENSITIVE1 (SOS1), is essential for regulation of sodium ion homeostasis during plant growth in saline conditions. Mutations in SOS1 result in severely reduced seedling growth in the presence of salt compared to the growth of wild type. SOS1 is a secondary active transporter coupling movement of sodium ions out of the cell using energy stored in the transplasma membrane proton gradient, thereby preventing the build-up of toxic levels of sodium in the cytosol. SOS1 is regulated by complexes containing the SOS2 and CALCINEURIN B-LIKE10 (CBL10) or SOS3 proteins. CBL10 and SOS3 (also identified as CBL4) encode EF-hand calcium sensors that interact physically with and activate SOS2, a serine/threonine protein kinase. The CBL10/SOS2 or SOS3/SOS2 complexes then activate SOS1 Na+/H+ exchange activity. We completed our studies to understand how SOS1 activity is regulated. Specifically, we asked: (1) how does CBL10 regulate SOS1 activity? (2) What role do two putative CBL10-interacting proteins play in SOS1 regulation? (3) Are

  8. Ion transport controlled by nanoparticle-functionalized membranes

    NASA Astrophysics Data System (ADS)

    Barry, Edward; McBride, Sean P.; Jaeger, Heinrich M.; Lin, Xiao-Min

    2014-12-01

    From proton exchange membranes in fuel cells to ion channels in biological membranes, the well-specified control of ionic interactions in confined geometries profoundly influences the transport and selectivity of porous materials. Here we outline a versatile new approach to control a membrane’s electrostatic interactions with ions by depositing ligand-coated nanoparticles around the pore entrances. Leveraging the flexibility and control by which ligated nanoparticles can be synthesized, we demonstrate how ligand terminal groups such as methyl, carboxyl and amine can be used to tune the membrane charge density and control ion transport. Further functionality, exploiting the ligands as binding sites, is demonstrated for sulfonate groups resulting in an enhancement of the membrane charge density. We then extend these results to smaller dimensions by systematically varying the underlying pore diameter. As a whole, these results outline a previously unexplored method for the nanoparticle functionalization of membranes using ligated nanoparticles to control ion transport.

  9. Mechanism Exploration of Ion Transport in Nanocomposite Cation Exchange Membranes.

    PubMed

    Tong, Xin; Zhang, Bopeng; Fan, Yilin; Chen, Yongsheng

    2017-04-19

    The origin of property enhancement of nanocomposite ion exchange membranes (IEMs) is far from being fully understood. By combining experimental work and computational modeling analysis, we could determine the influence of nanomaterials on the ion transport properties of nanocomposite cation exchange membranes (CEMs). We synthesized and characterized a series of nanocomposite CEMs by using SPPO as polymer materials and silica nanoparticles (NPs) (unsulfonated or sulfonated) as nanomaterials. We found that with the increase of NP loading, measured CEM permselectivity and swelling degree first increased and then decreased. We also found the ion exchange capacity (IEC) and ionic resistance of nanocomposite CEMs tend to be the same, regardless what type of NPs are incorporated into the membrane. Modeling analysis suggests that the change of membrane properties is related to the change in membrane microstructure. With the addition of silica NPs, membrane porosity (volume fraction of intergel phase) increases so that membranes can absorb more water. Also, volume fraction of sulfonated polymer segments increases, which can allow membranes to retain more counterions, causing membrane IEC to increase. By calculating the effective ion diffusion coefficients and membrane tortuosity factors of all the silica-NP-based CEMs synthesized in this study, along with nanocomposite CEMs from previous studies, we conclude that membrane ion transport efficiency tends to increase with the incorporation of nanomaterials. In addition, this paper presents a simulation model, which explains how the membrane property changes upon nanomaterial aggregation; the simulation results are in good agreement with the experimental data. Simulation results indicate that membrane properties are related to nanomaterial number concentration in the membrane matrices; thus, a plateau is reached for membrane ion diffusion coefficients due to the severe influence of aggregation on the increase of nanomaterial

  10. Transport of Ions Across the Inner Envelope Membrane of Chloroplasts

    SciTech Connect

    McCarty, R. E.

    2004-06-02

    The technical report outlines the results of nine years of research on how ions cross the inner envelope membrane of chloroplasts. The ions include protons, nitrite, calcium and ferrous iron. Bicarbonate transport was also studied.

  11. The Role of Potassium in Active Transport of Sodium by the Toad Bladder

    PubMed Central

    Essig, Alvin; Leaf, Alexander

    1963-01-01

    Studies were carried out on the isolated urinary bladder of the toad, Bufo marinus, in order to explain the dependence of active sodium transport on the presence of potassium, in the serosal medium. Attempts to obtain evidence for coupled sodium-potassium transport by the serosal pump were unsuccessful; no relation between sodium transport and uptake of K42 from the serosal medium was demonstrable. Rather, the predominant effect of serosal potassium appeared to be operative at the mucosal permeability barrier, influencing the permeability of this surface to sodium. The mucosal effects of serosal potassium were correlated with effects on cellular cation content. When sodium Ringer's solution was used as serosal medium, removal of potassium resulted in significant decrease in tissue potassium content, commensurate increase in tissue sodium content, and marked depression of mucosal permeability and sodium transport. When choline replaced sodium in the serosal medium, removal of potassium resulted in only slight alterations of tissue electrolyte content, and effects on mucosal permeability and sodium transport were minimal. PMID:19873552

  12. Performance of cellulose acetate butyrate membranes in hyperfiltration of sodium chloride and urea feed solution

    NASA Technical Reports Server (NTRS)

    Wydeven, T.; Leban, M.

    1973-01-01

    Cellulose acetate butyrate (CAB) membranes are shown to give high salt and urea rejection with water flux of about 3 gallons/sq ft per day at 600 psig. Membranes prepared from a formulation containing glyoxal show a significant increase in flux and decrease in salt and urea rejection with drying time. Zero drying time gives maximum urea and salt rejection and is therefore most suitable for hyperfiltration of sodium chloride and urea feed solution.

  13. Performance of cellulose acetate butyrate membranes in hyperfiltration of sodium chloride and urea feed solution

    NASA Technical Reports Server (NTRS)

    Wydeven, T.; Leban, M.

    1973-01-01

    Cellulose acetate butyrate (CAB) membranes are shown to give high salt and urea rejection with water flux of about 3 gallons/sq ft per day at 600 psig. Membranes prepared from a formulation containing glyoxal show a significant increase in flux and decrease in salt and urea rejection with drying time. Zero drying time gives maximum urea and salt rejection and is therefore most suitable for hyperfiltration of sodium chloride and urea feed solution.

  14. Characteristics of (+)-catechin and (-)-epicatechin transport across pig intestinal brush border membranes.

    PubMed

    Starp, Christiane; Alteheld, Birgit; Stehle, Peter

    2006-01-01

    (+)-Catechin and (-)-epicatechin are considered as disease preventive flavan-3-ols of foods like fruits, beverages and chocolate. We investigated mechanisms and kinetics of (+)-catechin and (-)-epicatechin uptake employing a validated in vitro model with isolated pig brush border membrane vesicles. Vesicles were isolated from pig small intestine employing the divalent cation method. Characterization (marker enzymes, electron microscopy) confirmed their purity and function. Transport studies with (+)-catechin and (-)-epicatechin under predefined conditions [presence/absence of sodium, pH gradient, temperature (8-37 degrees C), various initial substrate concentrations (2-20 mmol/l)] revealed a measurable transport (HPLC analyses) across the brush border membrane for both substrates. Catechin transport was stimulated by an outwardly directed H(+) gradient (pH(i) 5.5/pH(o) 7.5). The presence of an inwardly directed Na(+) gradient did not result in a transient overshoot in (+)-catechin and (-)-epicatechin uptake. At 37 degrees C, subtraction of diffusion from the total transport rate showed saturation kinetics. Our in vitro study indicate that both (+)-catechin and (-)-epicatechin are transported across the basolateral membrane using a dual transport system consisting of free diffusion (dominant at low concentrations) and carrier-mediated facilitated diffusion.

  15. Comparative Transport Activity of Intact Cells, Membrane Vesicles, and Mesosomes of Bacillus licheniformis

    PubMed Central

    MacLeod, Robert A.; Thurman, Paul; Rogers, H. J.

    1973-01-01

    Sodium ion was shown to stimulate strongly the transport of l-glutamic acid into cells of Bacillus licheniformis 6346 His−. Lithium ion had a slight capacity to replace Na+ in this capacity, but K+ was without effect. Three of five amino acids tested. l-glutamic acid, l-aspartic acid, and l-alanine, were concentrated against a gradient in the cells. Intracellular pools of these amino acids were extractable with 5% trichloroacetic acid. Pools of l-histidine and l-lysine could not be detected. No evidence of active transport of lysine into cells could be detected, and histidine was taken up in the absence of chloramphenicol but not in its presence. The uptake of glutamic acid by membrane vesicle preparations was strongly stimulated by reduced nicotinamide adenine dinucleotide (NADH) and to a lesser extent by succinate. The presence of phenazine methosulfate increased uptake in the presence of succinate. Either l- or d-lactate and adenosine triphosphate were without effect. None of these compounds stimulated the uptake of glutamic acid by mesosomes, although some mesosome preparations contained separable membrane which was very active. NADH strongly stimulated the uptake of aspartic acid and alanine by membrane vesicles but had only a slight effect on the uptake of histidine and lysine. No evidence of active transport of any of the amino acids into mesosomes could be detected either in the presence or absence of NADH. NADH stimulation of the uptake of glutamic acid by membrane vesicles was destroyed by exposure to light of 360 nm; this inactivation was reversible by vitamin K2(5) or K2(10). Sodium ion stimulated transport of glutamic acid by membrane vesicles. PMID:4347247

  16. Size- and charge-selective transport of aromatic compounds across polyelectrolyte multilayer membranes

    NASA Astrophysics Data System (ADS)

    Jin, Wanqin; Toutianoush, Ali; Tieke, Bernd

    2005-06-01

    The transport of various neutral and charged aromatic compounds across poly(diallyl dimethylammonium chloride)/poly(sodium styrenesulfonate) (PDADMA/PSS) and poly(allylamine hydrochloride)/poly(sodium styrenesulfonate) (PAH/PSS) multilayer membranes was investigated. The solutes were phenol (Ph), hydroquinone (1,4-BD), naphthalene (Np), pyrene (Py), triphenylene (Tp), alkali metal salts of benzene sulfonate (Bs), naphthalene 2-sulfonate (Ns), methyl orange (MO), and isomeric benzene disulfonates (1,2-, 1,3-BDS). For the neutral compounds, a size-selective transport was found, the transport being controlled by the pore size of the membrane and the size of the aromatic solute. The sieving effect from the membranes was so pronounced that mean pore sizes of 0.82 ± 0.09 and 0.67 ± 0.04 nm could be determined for PDADMA/PSS and PAH/PSS, respectively. Size exclusion leads to separation factors α(Ph/Py) ≈ 13 and α(Ph/Np) ≈ 28 using PDADMA/PSS and PAH/PSS membranes, respectively. For charged aromatic compounds, the transport is both size- and charge-selective. The charge-selectivity is based on Donnan rejection of permeating ions from the equally charged parts of the membrane, the rejection for dianions being much stronger than for monoanions comparable with the rejection of mono- and divalent inorganic ions. While size-based separation across PAH/PSS is only moderate (α(Bs/Ns) ≈ 4), the charge-based separation is high (α(Bs/1,3-BDS) ≈ 65).

  17. Cortisol-sensitive urea transport across the gill basolateral membrane of the gulf toadfish (Opsanus beta).

    PubMed

    Rodela, Tamara M; Gilmour, Kathleen M; Walsh, Patrick J; McDonald, M Danielle

    2009-08-01

    Gulf toadfish (Opsanus beta) use a unique pulsatile urea excretion mechanism that allows urea to be voided in large pulses via the periodic insertion or activation of a branchial urea transporter. The precise cellular and subcellular location of the facilitated diffusion mechanism(s) remains unclear. An in vitro basolateral membrane vesicle (BLMV) preparation was used to test the hypothesis that urea movement across the gill basolateral membrane occurs through a cortisol-sensitive carrier-mediated mechanism. Toadfish BLMVs demonstrated two components of urea uptake: a linear element at high external urea concentrations, and a phloretin-sensitive saturable constituent (K(m) = 0.24 mmol/l; V(max) = 6.95 micromol x mg protein(-1) x h(-1)) at low urea concentrations (<1 mmol/l). BLMV urea transport in toadfish was unaffected by in vitro treatment with ouabain, N-ethylmaleimide, or the absence of sodium, conditions that are known to inhibit sodium-coupled and proton-coupled urea transport in vertebrates. Transport kinetics were temperature sensitive with a Q(10) > 2, further suggestive of carrier-mediated processes. Our data provide evidence that a basolateral urea facilitated transporter accelerates the movement of urea between the plasma and gills to enable the pulsatile excretion of urea. Furthermore, in vivo infusion of cortisol caused a significant 4.3-fold reduction in BLMV urea transport capacity in lab-crowded fish, suggesting that cortisol inhibits the recruitment of urea transporters to the basolateral membrane, which may ultimately affect the size of the urea pulse event in gulf toadfish.

  18. Transport Activity of the Sodium Bicarbonate Cotransporter NBCe1 Is Enhanced by Different Isoforms of Carbonic Anhydrase

    PubMed Central

    Schueler, Christina; Becker, Holger M.; McKenna, Robert; Deitmer, Joachim W.

    2011-01-01

    Transport metabolons have been discussed between carbonic anhydrase II (CAII) and several membrane transporters. We have now studied different CA isoforms, expressed in Xenopus oocytes alone and together with the electrogenic sodium bicarbonate cotransporter 1 (NBCe1), to determine their catalytic activity and their ability to enhance NBCe1 transport activity. pH measurements in intact oocytes indicated similar activity of CAI, CAII and CAIII, while in vitro CAIII had no measurable activity and CAI only 30% of the activity of CAII. All three CA isoforms increased transport activity of NBCe1, as measured by the transport current and the rate of intracellular sodium rise in oocytes. Two CAII mutants, altered in their intramolecular proton pathway, CAII-H64A and CAII-Y7F, showed significant catalytic activity and also enhanced NBCe1 transport activity. The effect of CAI, CAII, and CAII mutants on NBCe1 activity could be reversed by blocking CA activity with ethoxyzolamide (EZA, 10 µM), while the effect of the less EZA-sensitive CAIII was not reversed. Our results indicate that different CA isoforms and mutants, even if they show little enzymatic activity in vitro, may display significant catalytic activity in intact cells, and that the ability of CA to enhance NBCe1 transport appears to depend primarily on its catalytic activity. PMID:22076132

  19. Sodium-calcium ion exchange in cardiac membrane vesicles.

    PubMed Central

    Reeves, J P; Sutko, J L

    1979-01-01

    Membrane vesicles isolated from rabbit ventricular tissue rapidly accumulated Ca2+ when an outwardly directed Na+ gradient was formed across the vesicle membrane. Vesicles loaded internally with K+ showed only 10% of the Ca2+ uptake activity observed with Na+-loaded vesicles. Dissipation of the Na+ gradient with the monovalent cation exchange ionophores nigericin or narasin caused a rapid decline in Ca2+ uptake activity. The Ca2+-ionophore A23187 inhibited Ca2+ uptake by Na+-loaded vesicles and enhanced the rate of Ca2+ loss from the vesicles after uptake. Efflux of preaccumulated Ca2+ from the vesicles was stimulated 30-fold by the presence of 50 mM Na+ in the external medium. Na+-dependent uptake and efflux of Ca2+ were both inhibited by La3+. The results indicate that cardiac membrane vesicles exhibit Na+-Ca2+ exchange activity. Fractionation of the vesicles by density gradient centrifugation revealed a close correspondence between Na+-Ca2+ exchange activity and specific ouabain-binding activity among the various fractions. This relationship suggests that the observed Na+-Ca2+ exchange activity derives from the sarcolemmal membranes within the vesicle preparation. PMID:284383

  20. Change of ruminal sodium transport in sheep during dietary adaptation.

    PubMed

    Etschmann, Benjamin; Suplie, Annabelle; Martens, Holger

    2009-02-01

    Rumen adaptation plays an important role in the productive cycle of dairy cattle. In this study, the time course of functional rumen epithelium adaptation after a change from hay feeding (ad libitum) to a mixed hay/concentrate diet was monitored by measuring Na+ transport rates in Ussing chamber experiments. A total of 18 sheep were subjected to different periods of mixed hay/concentrate feeding ranging from 0 weeks (control; hay ad libitum) to 12 weeks (800 g hay plus 800 g concentrate per day in two equal portions). For each animal, the net absorption of sodium was measured following the mixed hay/concentrate feeding period. Net Na transport, Jnet, significantly rose from 2.15 +/- 0.43 (control) to 3.73 +/- 1.02 microeq x cm(-2) x h(-1) after one week of mixed hay/ concentrate diet, reached peak levels of 4.55 +/- 0.50 microEq x cm(-2) x h(-1) after four weeks and levelled out at 3.92 +/- 0.36 microeq x cm(-2) x h(-1) after 12 weeks of mixed feeding. Thus, 73% of functional adaptation occurred during the first week after diet change. This is in apparent contrast to findings that morphological adaptation takes approximately six weeks to reach peak levels. Hence, early functional adaptation to a mixed hay/concentrate diet is characterised by enhanced Na absorption rates per epithelial cell. Absorption rates are likely to be further enhanced by proliferative effects on the rumen epithelium (number and size of papillae) when concentrate diets are fed over longer periods of time. Early functional adaptation without surface area enlargement of the rumen epithelium appears to be the first step in coping with altered fermentation rates following diet change.

  1. Role of plasma membrane transporters in muscle metabolism.

    PubMed Central

    Zorzano, A; Fandos, C; Palacín, M

    2000-01-01

    Muscle plays a major role in metabolism. Thus it is a major glucose-utilizing tissue in the absorptive state, and changes in muscle insulin-stimulated glucose uptake alter whole-body glucose disposal. In some conditions, muscle preferentially uses lipid substrates, such as fatty acids or ketone bodies. Furthermore, muscle is the main reservoir of amino acids and protein. The activity of many different plasma membrane transporters, such as glucose carriers and transporters of carnitine, creatine and amino acids, play a crucial role in muscle metabolism by catalysing the influx or the efflux of substrates across the cell surface. In some cases, the membrane transport process is subjected to intense regulatory control and may become a potential pharmacological target, as is the case with the glucose transporter GLUT4. The goal of this review is the molecular characterization of muscle membrane transporter proteins, as well as the analysis of their possible regulatory role. PMID:10903126

  2. Preparation and characterization of chitosan nanopores membranes for the transport of drugs.

    PubMed

    Li, Xingyi; Nan, Kaihui; Chen, Hao; Xu, Yu

    2011-11-28

    In this paper, a novel chitosan nanopores membrane was developed by selective dissolution of its composition. Polyethylene glycol (PEG) as the porogen was selected to generate the nanopores structure of chitosan membrane. As the observation with scanning electron microscopy (SEM), we could find that the PEG content was greatly influenced on the structure of chitosan membrane. As the PEG content was larger than 50%, the chitosan nanopores membrane could successfully developed. Differential scanning calorimeter (DSC) measurement revealed that the PEG component could not be completely dissolved from the membrane and there was presence the possible interaction (hydrogen bond) between two components. Water adsorption test suggested that the obtained membranes have the great capacity of water adsorption ranging from 162.4 ± 22.5% to 321.5 ± 6.5%. In vitro degradation experiment showed that the obtained chitosan membranes have good biodegradability in the lysozyme solution. The permeability test was performed with two model drugs: vitamin B12 (non-ionic water-soluble drug) and sodium sulfamerazine (ionic water-soluble drug). And the results showed that these two drugs have significant differences in the permeability, indicating that chitosan nanopores membranes can potentially be used to the transport of drugs with controlled diffusion manner. Copyright © 2011 Elsevier B.V. All rights reserved.

  3. Transport proteins of the plant plasma membrane

    NASA Technical Reports Server (NTRS)

    Assmann, S. M.; Haubrick, L. L.; Evans, M. L. (Principal Investigator)

    1996-01-01

    Recently developed molecular and genetic approaches have enabled the identification and functional characterization of novel genes encoding ion channels, ion carriers, and water channels of the plant plasma membrane.

  4. Transport proteins of the plant plasma membrane

    NASA Technical Reports Server (NTRS)

    Assmann, S. M.; Haubrick, L. L.; Evans, M. L. (Principal Investigator)

    1996-01-01

    Recently developed molecular and genetic approaches have enabled the identification and functional characterization of novel genes encoding ion channels, ion carriers, and water channels of the plant plasma membrane.

  5. Development of active-transport membrane devices

    SciTech Connect

    Laciak, D.V.

    1994-07-01

    This report introduces the concept of Air Products` AT membranes for the separation of NH{sub 3} and CO{sub 2} from process gas streams and presents results from the first year fabrication concept development studies.

  6. Mitochondrial ascorbic acid transport is mediated by a low-affinity form of the sodium-coupled ascorbic acid transporter-2.

    PubMed

    Muñoz-Montesino, Carola; Roa, Francisco J; Peña, Eduardo; González, Mauricio; Sotomayor, Kirsty; Inostroza, Eveling; Muñoz, Carolina A; González, Iván; Maldonado, Mafalda; Soliz, Carlos; Reyes, Alejandro M; Vera, Juan Carlos; Rivas, Coralia I

    2014-05-01

    Despite the fundamental importance of the redox metabolism of mitochondria under normal and pathological conditions, our knowledge regarding the transport of vitamin C across mitochondrial membranes remains far from complete. We report here that human HEK-293 cells express a mitochondrial low-affinity ascorbic acid transporter that molecularly corresponds to SVCT2, a member of the sodium-coupled ascorbic acid transporter family 2. The transporter SVCT1 is absent from HEK-293 cells. Confocal colocalization experiments with anti-SVCT2 and anti-organelle protein markers revealed that most of the SVCT2 immunoreactivity was associated with mitochondria, with minor colocalization at the endoplasmic reticulum and very low immunoreactivity at the plasma membrane. Immunoblotting of proteins extracted from highly purified mitochondrial fractions confirmed that SVCT2 protein was associated with mitochondria, and transport analysis revealed a sigmoidal ascorbic acid concentration curve with an apparent ascorbic acid transport Km of 0.6mM. Use of SVCT2 siRNA for silencing SVCT2 expression produced a major decrease in mitochondrial SVCT2 immunoreactivity, and immunoblotting revealed decreased SVCT2 protein expression by approximately 75%. Most importantly, the decreased protein expression was accompanied by a concomitant decrease in the mitochondrial ascorbic acid transport rate. Further studies using HEK-293 cells overexpressing SVCT2 at the plasma membrane revealed that the altered kinetic properties of mitochondrial SVCT2 are due to the ionic intracellular microenvironment (low in sodium and high in potassium), with potassium acting as a concentration-dependent inhibitor of SVCT2. We discarded the participation of two glucose transporters previously described as mitochondrial dehydroascorbic acid transporters; GLUT1 is absent from mitochondria and GLUT10 is not expressed in HEK-293 cells. Overall, our data indicate that intracellular SVCT2 is localized in mitochondria, is

  7. Changes in erythrocyte sodium, sodium transport and /sup 3/H ouabain binding capacity during digoxin administration in the pig

    SciTech Connect

    Whittaker, J.; Hawkins, M.; Swaminathan, R.

    1983-02-14

    Time course of the changes in erthrocyte sodium content, sodium transport, /sup 3/H ouabain binding capacity and Na/sup +/, K/sup +/-ATPase activity were measured for 14 weeks, in 6 young pigs treated with digoxin and in 6 control pigs. After one week of treatment the erythrocyte sodium content increased from 5.4 mmol/kg cells and the efflux rate constant of sodium decreased. With prolonged treatment the erythrocyte sodium content returned to normal and the /sup 3/H ouabain binding capacity increased by week 5. The plasma digoxin concentration decreased from 1.1 ng/ml at week 5 to 0.6 ng/ml at week 8 probably due to the decline in dose (..mu..g/kg) of digoxin with age. The efflux rate constant of sodium and Na/sup +/, K/sup +/-ATPase activity were higher towards the end of treatment. It is concluded that with prolonged administration of digoxin there is an increase in erythrocyte sodium pump units.

  8. Electrolyte transport in distal colon of sodium-depleted rats: Effect of sodium repletion

    SciTech Connect

    Turnamian, S.G.; Binder, H.J. )

    1988-09-01

    Dietary sodium depletion increases plasma aldosterone level and, as a result, induces amiloride-sensitive electrogenic sodium absorption and electrogenic potassium secretion and stimulates Na{sup +}-K{sup +}-ATPase activity in rat distal colon, while inhibiting electroneutral sodium chloride absorption. To assess the events that occur as the aldosterone-stimulated colon reverts to normal, unidirectional {sup 22}Na and {sup 36}Cl fluxes were measured under voltage-clamp conditions across isolated distal colonic mucosa of rats that were initially dietary sodium depleted for 7 days and then sodium repleted for varying periods of time before the study. Within 8 h of dietary sodium repletion, plasma aldosterone level and Na{sup +}-K{sup +}-ATPase activity declined to normal, amiloride-sensitive electrogenic sodium absorption decreased by >90%, and active electrogenic potassium secretion also decreased markedly. In contrast, electroneutral sodium chloride absorption did not completely return to levels seen in normal animals until {approximately}64-68 h. These results demonstrate that maintenance of electrogenic sodium absorption and potassium secretion are directly dependent on elevated plasma aldosterone levels. The inhibition of electroneutral sodium absorption, although initiated by excess aldosterone, persists after normalization of the plasma aldosterone level, thereby implying that the inhibition is dependent on additional factor(s).

  9. gamma. -Aminobutyric acid transport in reconstituted preparations from rat brain: coupled sodium and chloride fluxes

    SciTech Connect

    Keynan, S.; Kanner, B.I.

    1988-01-12

    Transport of ..gamma..-aminobutyric acid (GABA) is electrogenic and completely depends on the presence of both sodium and chloride ions. These ions appear to be cotransported with ..gamma..-aminobutyric acid through its transporter. Using proteoliposomes into which a partially purified ..gamma..-aminobutyric acid transporter preparation was reconstituted. The authors have been able-for the first time-to provide direct evidence for sodium- and chloride-coupled ..gamma..-aminobutyric acid transport. This has been done by measuring the fluxes of /sup 22/Na/sup +/, /sup 36/Cl/sup -/, and (/sup 3/H)GABA. These fluxes have the following characteristics: There are components of the net fluxes of sodium and chloride that are ..gamma..-aminobutyric acid dependent. The sodium flux is chloride dependent. The chloride flux is sodium dependent. Thus, the ..gamma..-aminobutyric acid dependent sodium and chloride fluxes appear to be catalyzed by the transporter. Using these fluxes they have attempted to determine the stoichiometry of the process. They measured the initial rate of sodium-dependent ..gamma..-aminobutyric acid fluxes and that of ..gamma..-aminobutyric acid dependent sodium fluxes. Similarly, they measured the stoichiometry between chloride and ..gamma..-aminobutyric acid. The half-maximal effect obtained when the ..gamma..-aminobutyric acid concentration dependence of Cl/sup -/ and Na/sup +/ transport is determined is much higher than the known K/sub m/ of this system. Reexamination of the kinetics of ..gamma..-aminobutyric acid transport reveals that there are two transport systems for it. The sodium, chloride, and ..gamma..-aminobutyric acid fluxes probably originate from the low-affinity transporter.

  10. Structure-Functional Basis of Ion Transport in Sodium-Calcium Exchanger (NCX) Proteins.

    PubMed

    Giladi, Moshe; Shor, Reut; Lisnyansky, Michal; Khananshvili, Daniel

    2016-11-22

    The membrane-bound sodium-calcium exchanger (NCX) proteins shape Ca(2+) homeostasis in many cell types, thus participating in a wide range of physiological and pathological processes. Determination of the crystal structure of an archaeal NCX (NCX_Mj) paved the way for a thorough and systematic investigation of ion transport mechanisms in NCX proteins. Here, we review the data gathered from the X-ray crystallography, molecular dynamics simulations, hydrogen-deuterium exchange mass-spectrometry (HDX-MS), and ion-flux analyses of mutants. Strikingly, the apo NCX_Mj protein exhibits characteristic patterns in the local backbone dynamics at particular helix segments, thereby possessing characteristic HDX profiles, suggesting structure-dynamic preorganization (geometric arrangements of catalytic residues before the transition state) of conserved α₁ and α₂ repeats at ion-coordinating residues involved in transport activities. Moreover, dynamic preorganization of local structural entities in the apo protein predefines the status of ion-occlusion and transition states, even though Na⁺ or Ca(2+) binding modifies the preceding backbone dynamics nearby functionally important residues. Future challenges include resolving the structural-dynamic determinants governing the ion selectivity, functional asymmetry and ion-induced alternating access. Taking into account the structural similarities of NCX_Mj with the other proteins belonging to the Ca(2+)/cation exchanger superfamily, the recent findings can significantly improve our understanding of ion transport mechanisms in NCX and similar proteins.

  11. Transport of heptafluorostearate across model membranes. Membrane transport of long-chain fatty acid anions I.

    PubMed

    Schmider, W; Fahr, A; Blum, H E; Kurz, G

    2000-05-01

    Heptafluorostearic acid, an isogeometric derivative of stearic acid, has a pK(a) value of about 0.5. To evaluate the suitability of heptafluorostearate as model compound for anions of long-chain fatty acids in membrane transport, monolayer and liposome studies were performed with lipid mixtures containing phospholipids;-cholesterol-heptafluorostearate or stearate (100:40:20 molar ratios). Transfer of heptafluorostearate and stearate from liposomes to bovine serum albumin (BSA) was followed by measuring the intrinsic fluorescence of BSA. The percentage of heptafluorostearate, equivalent to the amount placed in their outer monolayer, transferred from liposomes (120;-130 nm diameter) to BSA was 55.7 +/- 3.7% within 10 min at 25 degrees C and 55 +/- 2% within 5 min at 37 degrees C. Slow transfer of 22.7 +/- 2.5% of heptafluorostearate at 25 degrees C followed with a half-life of 2.3 +/- 0.4 h and of 20 +/- 4% at 37 degrees C with a half-life of 0.9 +/- 0.1 h until the final equilibrium distributions between BSA and liposomes were reached, 79 +/- 6% to 21 +/- 5% at 25 degrees C and 75 +/- 5% to 25 +/- 4% at 37 degrees C. The pseudounimolecular rate constants for flip-flop of heptafluorostearate equal k(FF,25) = 0.24 +/- 0.05 h(-) and k(FF,37) = 0.6 +/- 0.1 h(-), respectively. By comparison, transfer of stearate required only 3 min to reach equilibrium distribution. The difference between heptafluorostearate and stearate may be explained by a rapid flip-flop movement of the un-ionized fatty acids which exist in different concentrations in accordance with their pK(a) values. Half-life of flip-flop of heptafluorostearate makes it suitable to study mediated membrane transport of long-chain fatty acid anions.

  12. Hydroxide Solvation and Transport in Anion Exchange Membranes

    SciTech Connect

    Chen, Chen; Tse, Ying-Lung Steve; Lindberg, Gerrick E.; Knight, Chris; Voth, Gregory A.

    2016-01-27

    Understanding hydroxide solvation and transport in anion exchange membranes (AEMs) can provide important insight into the design principles of these new membranes. To accurately model hydroxide solvation and transport, we developed a new multiscale reactive molecular dynamics model for hydroxide in aqueous solution, which was then subsequently modified for an AEM material. With this model, we investigated the hydroxide solvation structure and transport mechanism in the membrane. We found that a relatively even separation of the rigid side chains produces a continuous overlapping region for hydroxide transport that is made up of the first hydration shell of the tethered cationic groups. Our results show that hydroxide has a significant preference for this overlapping region, transporting through it and between the AEM side chains with substantial contributions from both vehicular (standard diffusion) and Grotthuss (proton hopping) mechanisms. Comparison of the AEM with common proton exchange membranes (PEMs) showed that the excess charge is less delocalized in the AEM than the PEMs, which is correlated with a higher free energy barrier for proton transfer reactions. The vehicular mechanism also contributes considerably more than the Grotthuss mechanism for hydroxide transport in the AEM, while our previous studies of PEM systems showed a larger contribution from the Grotthuss mechanism than the vehicular mechanism for proton transport. The activation energy barrier for hydroxide diffusion in the AEM is greater than that for proton diffusion in PEMs, implying a more significant enhancement of ion transport in the AEM at elevated temperatures.

  13. Hydroxide Solvation and Transport in Anion Exchange Membranes.

    PubMed

    Chen, Chen; Tse, Ying-Lung Steve; Lindberg, Gerrick E; Knight, Chris; Voth, Gregory A

    2016-01-27

    Understanding hydroxide solvation and transport in anion exchange membranes (AEMs) can provide important insight into the design principles of these new membranes. To accurately model hydroxide solvation and transport, we developed a new multiscale reactive molecular dynamics model for hydroxide in aqueous solution, which was then subsequently modified for an AEM material. With this model, we investigated the hydroxide solvation structure and transport mechanism in the membrane. We found that a relatively even separation of the rigid side chains produces a continuous overlapping region for hydroxide transport that is made up of the first hydration shell of the tethered cationic groups. Our results show that hydroxide has a significant preference for this overlapping region, transporting through it and between the AEM side chains with substantial contributions from both vehicular (standard diffusion) and Grotthuss (proton hopping) mechanisms. Comparison of the AEM with common proton exchange membranes (PEMs) showed that the excess charge is less delocalized in the AEM than the PEMs, which is correlated with a higher free energy barrier for proton transfer reactions. The vehicular mechanism also contributes considerably more than the Grotthuss mechanism for hydroxide transport in the AEM, while our previous studies of PEM systems showed a larger contribution from the Grotthuss mechanism than the vehicular mechanism for proton transport. The activation energy barrier for hydroxide diffusion in the AEM is greater than that for proton diffusion in PEMs, implying a more significant enhancement of ion transport in the AEM at elevated temperatures.

  14. Energetics of Anaerobic Sodium Transport by the Fresh Water Turtle Bladder

    PubMed Central

    Klahr, Saulo; Bricker, Neal S.

    1965-01-01

    Certain of the metabolic events associated with anaerobic sodium transport by the isolated bladder of the fresh water turtle have been investigated. The data suggest that energy for this transport arises from glycolysis and that endogenous glycogen was the major and perhaps the sole source of substrate. The rate of anaerobic glycolysis, as determined by lactate formation, correlates well with the rate as determined by glycogen utilization. Using lactate formation as the index of anaerobic glycolysis, a linear relationship was observed between glycolysis and net anaerobic sodium transport. In the absence of sodium transport, glycolysis decreased by approximately 45 per cent. Tissue ATP concentrations were maintained at about the same level under anaerobic as under aerobic conditions. Finally if it is assumed that in the conversion of glycogen to lactate anaerobically, 3 moles of ATP are generated per mole of glucose residue, an average of over 15 equivalents of sodium were transported for every mole of ATP generated. PMID:14324976

  15. Phosphate transport in membrane vesicles from Escherichia coli.

    PubMed

    Konings, W N; Rosenberg, H

    1978-04-04

    Escherichia coli strain AN710 possesses only the PIT system for phosphate transport. Membrane vesicles from this strain, which contain phosphate internally, perform exchange and active transport of phosphate. The energy for active transport is supplied by the respiratory chain with ascorbate phenazine methosulphate as electron donor. To a lesser extent also the oxidation of D-lactate energizes phosphate transport; the oxidation of succinate is only marginally effective. Phosphate transport is driven by the proton-motive force and in particular by the pH gradient across the membrane. This view is supported by the observation that phosphate transport is stimulated by valinomycin, inhibited by nigericin and abolished by the uncoupler carbonyl cyanide m-chlorophenylhydrazone. Neither inhibitor affects phosphate exchange. The phosphate analogue arsenate inhibits both the exchange reaction and active transport. Both processes are stimulated by K+ and Mg2+, the highest activities being observed with both ions present. Membrane vesicles have also been isolated from Escherichia coli K10, a strain which possesses only a functional PST phosphate transport system. These vesicles perform neither exchange nor active transport of phosphate, although active transport of amino acids is observed in the presence of ascorbate-phenazine methosulphate or D-lactate.

  16. Simulating and Modeling Transport Through Atomically Thin Membranes

    NASA Astrophysics Data System (ADS)

    Ostrowski, Joseph; Eaves, Joel

    2014-03-01

    The world is running out of clean portable water. The efficacy of water desalination technologies using porous materials is a balance between membrane selectivity and solute throughput. These properties are just starting to be understood on the nanoscale, but in the limit of atomically thin membranes it is unclear whether one can apply typical continuous time random walk models. Depending on the size of the pore and thickness of the membrane, mass transport can range from single stochastic passage events to continuous flow describable by the usual hydrodynamic equations. We present a study of mass transport through membranes of various pore geometries using reverse nonequilibrium simulations, and analyze transport rates using stochastic master equations.

  17. Phospholipid flippases: building asymmetric membranes and transport vesicles.

    PubMed

    Sebastian, Tessy T; Baldridge, Ryan D; Xu, Peng; Graham, Todd R

    2012-08-01

    Phospholipid flippases in the type IV P-type ATPase family (P4-ATPases) are essential components of the Golgi, plasma membrane and endosomal system that play critical roles in membrane biogenesis. These pumps flip phospholipid across the bilayer to create an asymmetric membrane structure with substrate phospholipids, such as phosphatidylserine and phosphatidylethanolamine, enriched within the cytosolic leaflet. The P4-ATPases also help form transport vesicles that bud from Golgi and endosomal membranes, thereby impacting the sorting and localization of many different proteins in the secretory and endocytic pathways. At the organismal level, P4-ATPase deficiencies are linked to liver disease, obesity, diabetes, hearing loss, neurological deficits, immune deficiency and reduced fertility. Here, we review the biochemical, cellular and physiological functions of P4-ATPases, with an emphasis on their roles in vesicle-mediated protein transport. This article is part of a Special Issue entitled Lipids and Vesicular Transport. Copyright © 2011 Elsevier B.V. All rights reserved.

  18. Protein phosphorylation and sodium conductance in nerve membrane.

    PubMed Central

    Schoffeniels, E; Dandrifosse, G

    1980-01-01

    High molecular weight proteins extracted from the walking nerves of the shore crab (Carcinus maenas) exhibit a cycle of phosphorylation-dephosphorylation that is influenced by neurotropic compounds and inorganic ions. The net phosphorylation state of the proteins is increased in the presence of K+ ions and decreased with Na+ ions. In the absence of Mg2+ there is no phosphorylation. Ca2+ ions at low concentrations are necessary for optimal phosphorylation. At high concentration (above 0.1 mM), Ca2+ ions are inhibitory. Neurotropic compounds generally inhibit the phosphorylation process. More specifically, tetrodotoxin and veratridine, depending on the ionic composition of the medium, have opposite effects on the phosphorylation process, a result in agreement with their known physiological action. It is suggested that the high molecular weight components thus identified are part of the sodium permeation sites and that the conductance state of those sites is controlled by a phosphorylation process. Images PMID:6928680

  19. Water and Molecular Transport across Nanopores in Monolayer Graphene Membranes

    NASA Astrophysics Data System (ADS)

    Jang, Doojoon; O'Hern, Sean; Kidambi, Piran; Boutilier, Michael; Song, Yi; Idrobo, Juan-Carlos; Kong, Jing; Laoui, Tahar; Karnik, Rohit

    2015-11-01

    Graphene's atomic thickness and high tensile strength allow it to outstand as backbone material for next-generation high flux separation membrane. Molecular dynamics simulations predicted that a single-layer graphene membrane could exhibit high permeability and selectivity for water over ions/molecules, qualifying as novel water desalination membranes. However, experimental investigation of water and molecular transport across graphene nanopores had remained barely explored due to the presence of intrinsic defects and tears in graphene. We introduce two-step methods to seal leakage across centimeter scale single-layer graphene membranes create sub-nanometer pores using ion irradiation and oxidative etching. Pore creation parameters were varied to explore the effects of created pore structures on water and molecular transport driven by forward osmosis. The results demonstrate the potential of nanoporous graphene as a reliable platform for high flux nanofiltration membranes.

  20. Effects of sodium hypochlorite exposure mode on PES/PVP ultrafiltration membrane degradation.

    PubMed

    Causserand, Christel; Pellegrin, Bastien; Rouch, Jean-Christophe

    2015-11-15

    Drinking water production plants using membrane filtration processes report membrane failure issues. According to the literature, membrane degradation is often induced by exposure to sodium hypochlorite, an oxidant widely used during in-place cleanings. The present study focused on quantifying the effect of membrane exposure mode to hypochlorite on properties modifications of a PES/PVP ultrafiltration membrane widely used for drinking water production. For this purpose effects of sodium hypochlorite concentration, contact duration and exposure mode (static or dynamic) were investigated. The pH of the hypochlorite solution was set to 8 as it was demonstrated in numerous previous works that the pH range 7-8 leads to the most severe modification in the membrane characteristics. Membrane degradation was monitored at molecular scale by attenuated total reflectance infrared spectroscopy and at macroscopic scale by pure water permeability and elongation at break measurements. The results obtained in static (soaking) and dynamic (filtration and filtration/backwashing cycles) hypochlorite exposure modes indicated that PES/PVP membrane degradation progress was predominantly governed by hypochlorite oxidation rate. In the tested conditions, mechanical stress (pressure differentials) did not significantly contribute to membrane ageing. The correlation between molecular and macroscopic characterizations demonstrated that PVP degradation is responsible for the membrane integrity loss. A linear relationship between the loss of ductility of the membrane and the progress of the PVP degradation was obtained whatever the exposure mode. Thanks to experiments conducted at various hypochlorite concentrations and exposure durations, the hypochlorite dose parameter (hypochlorite concentration times contact time), widely used in the literature, was demonstrated to be inappropriate to describe the degradation rate: the hypochlorite concentration impact was shown to be dominating the

  1. Hijacking membrane transporters for arsenic phytoextraction

    PubMed Central

    LeBlanc, Melissa S.; McKinney, Elizabeth C.; Meagher, Richard B.; Smith, Aaron P.

    2012-01-01

    Arsenic is a toxic metalloid and recognized carcinogen. Arsenate and arsenite are the most common arsenic species available for uptake by plants. As an inorganic phosphate (Pi) analog, arsenate is acquired by plant roots through endogenous Pi transport systems. Inside the cell, arsenate is reduced to the thiol-reactive form arsenite. Glutathione (GSH)-conjugates of arsenite may be extruded from the cell or sequestered in vacuoles by members of the ATP-binding cassette (ABC) family of transporters. In the present study we sought to enhance both plant arsenic uptake through Pi transporter overexpression, and plant arsenic tolerance through ABC transporter overexpression. We demonstrate that Arabidopsis thaliana plants overexpressing the high-affinity Pi transporter family members, AtPht1;1 or AtPht1;7, are hypersensitive to arsenate due to increased arsenate uptake. These plants do not exhibit increased sensitivity to arsenite. Co-overexpression of the yeast ABC transporter YCF1 in combination with AtPht1;1 or AtPht1;7 suppresses the arsenate-sensitive phenotype while further enhancing arsenic uptake. Taken together, our results support an arsenic transport mechanism in which arsenate uptake is increased through Pi transporter overexpression, and arsenic tolerance is enhanced through YCF1-mediated vacuolar sequestration. This work substantiates the viability of coupling enhanced uptake and vacuolar sequestration as a means for developing a prototypical engineered arsenic hyperaccumulator. PMID:23108027

  2. Phosphate transport by rat intestinal basolateral-membrane vesicles.

    PubMed Central

    Ghishan, F K; Kikuchi, K; Arab, N

    1987-01-01

    The characteristics of phosphate transport across intestinal basolateral membranes of the rat were determined by using enriched preparations in which uphill Na+-dependent D-glucose transport could not be demonstrated, but ATP-dependent Ca2+ transport was present. Phosphate transport was saturable, Na+-dependent and exhibited Michaelis-Menten kinetics. Vmax. was 51.1 +/- 4.2 pmol/10 s per mg of protein and Km was 14 +/- 3.9 microM. The transport process was electroneutral. Tracer-exchange experiments and counter-transport studies confirmed the presence of a Na+-Pi carrier at the basolateral membrane. The presence of inside-positive membrane potential did not enhance phosphate uptake, indicating that the Na+ effect is secondary to the presence of the Na+-Pi carrier rather than an induction of positive membrane potential. The stoichiometry of this carrier at pH 7.4 was 2 Na+:1 phosphate, as shown by direct studies utilizing the static-head method. These studies are the first to determine the presence of a phosphate carrier at the basolateral membrane. PMID:3663094

  3. A novel method to quantify H+-ATPase-dependent Na+ transport across plasma membrane vesicles.

    PubMed

    Yang, Yongqing; Hu, Lei; Chen, Xuemei; Ottow, Eric A; Polle, Andrea; Jiang, Xiangning

    2007-09-01

    To prevent sodium toxicity in plants, Na(+) is excluded from the cytosol to the apoplast or the vacuole by Na(+)/H(+) antiporters. The secondary active transport of Na(+) to apoplast against its electrochemical gradient is driven by plasma membrane H(+)-ATPases that hydrolyze ATP and pump H(+) across the plasma membrane. Current methods to determine Na(+) flux rely either on the use of Na-isotopes ((22)Na) which require special working permission or sophisticated equipment or on indirect methods estimating changes in the H(+) gradient due to H(+)-ATPase in the presence or absence of Na(+) by pH-sensitive probes. To date, there are no methods that can directly quantify H(+)-ATPase-dependent Na(+) transport in plasma membrane vesicles. We developed a method to measure bidirectional H(+)-ATPase-dependent Na(+) transport in isolated membrane vesicle systems using atomic absorption spectrometry (AAS). The experiments were performed using plasma membrane-enriched vesicles isolated by aqueous two-phase partitioning from leaves of Populus tomentosa. Since most of the plasma membrane vesicles have a sealed right-side-out orientation after repeated aqueous two-phase partitioning, the ATP-binding sites of H(+)-ATPases are exposed towards inner side. Leaky vesicles were preloaded with Na(+) sealed for the study of H(+)-ATPase-dependent Na(+) transport. Our data implicate that Na(+) movement across vesicle membranes is highly dependent on H(+)-ATPase activity requiring ATP and Mg(2+) and displays optimum rates of 2.50 microM Na(+) mg(-1) membrane protein min(-1) at pH 6.5 and 25 degrees C. In this study, for the first time, we establish new protocols for the preparation of sealed preloaded right-side-out vesicles for the study of H(+)-ATPase-dependent Na(+) transport. The results demonstrate that the Na(+) content of various types of plasma membrane vesicle can be directly quantified by AAS, and the results measured using AAS method were consistent with those determined by the

  4. Selective transport of monoamine neurotransmitters by human plasma membrane monoamine transporter and organic cation transporter 3.

    PubMed

    Duan, Haichuan; Wang, Joanne

    2010-12-01

    The plasma membrane monoamine transporter (PMAT) and organic cation transporter 3 (OCT3) are the two most prominent low-affinity, high-capacity (i.e., uptake(2)) transporters for endogenous biogenic amines. Using the Flp-in system, we expressed human PMAT (hPMAT) and human OCT3 (hOCT3) at similar levels in human embryonic kidney 293 cells. Parallel and detailed kinetics analysis revealed distinct and seemingly complementary patterns for the two transporters in transporting monoamine neurotransmitters. hPMAT is highly selective toward serotonin (5-HT) and dopamine, with the rank order of transport efficiency (V(max)/K(m)) being: dopamine, 5-HT ≫ histamine, norepinephrine, epinephrine. The substrate preference of hPMAT toward these amines is substantially driven by large (up to 15-fold) distinctions in its apparent binding affinities (K(m)). In contrast, hOCT3 is less selective than hPMAT toward the monoamines, and the V(max)/K(m) rank order for hOCT3 is: histamine > norepinephrine, epinephrine > dopamine >5-HT. It is noteworthy that hOCT3 demonstrated comparable (≤2-fold difference) K(m) toward all amines, and distinctions in V(max) played an important role in determining its differential transport efficiency toward the monoamines. Real-time reverse transcription-polymerase chain reaction revealed that hPMAT is expressed at much higher levels than hOCT3 in most human brain areas, whereas hOCT3 is selectively and highly expressed in adrenal gland and skeletal muscle. Our results suggest that hOCT3 represents a major uptake(2) transporter for histamine, epinephrine, and norepinephrine. hPMAT, on the other hand, is a major uptake(2) transporter for 5-HT and dopamine and may play a more important role in transporting these two neurotransmitters in the central nervous system.

  5. A 22-year experience in global transport extracorporeal membrane oxygenation.

    PubMed

    Coppola, Christopher P; Tyree, Melissa; Larry, Karen; DiGeronimo, Robert

    2008-01-01

    Transport extracorporeal membrane oxygenation (ECMO) is currently available at 12 centers. We report a 22-year experience from the only facility providing global transport ECMO. Indications for transport ECMO include lack of ECMO services, inability to transport conventionally, inability to wean from cardiopulmonary bypass, extracorporeal cardiopulmonary resuscitation, and need to move a patient on ECMO for specialized services such as organ transplantation. Retrospective database review of children undergoing inhouse and transport ECMO from 1985 to 2007. Sixty-eight children underwent transport ECMO. Fifty-six were transported on ECMO into our facility. The remaining 12 were moved between 2 outside locations. Ground vehicles and fixed-wing aircraft were used. Distance transported was 8 to 7500 miles (13-12070 km), mean 1380 miles (2220 km). There were 116 inhouse ECMO runs. No child died during transport. Survival to discharge after transport ECMO was 65% (44/68) and, for inhouse ECMO, was 70% (81/116). Transport ECMO is feasible and effective, with survival rates comparable to inhouse ECMO. We have used transport ECMO to help children at non-ECMO centers with pulmonary failure who have not improved with inhaled nitric oxide and high-frequency ventilation. We have also transported a child after extracorporeal cardiopulmonary resuscitation, which may represent an emerging indication for transport ECMO. Transport ECMO often is the only option for children too unstable for conventional transport or those already on ECMO and requiring a specialized service at another facility, such as organ transplantation.

  6. Roles and Transport of Sodium and Potassium in Plants.

    PubMed

    Nieves-Cordones, Manuel; Al Shiblawi, Fouad Razzaq; Sentenac, Hervé

    2016-01-01

    The two alkali cations Na(+) and K(+) have similar relative abundances in the earth crust but display very different distributions in the biosphere. In all living organisms, K(+) is the major inorganic cation in the cytoplasm, where its concentration (ca. 0.1 M) is usually several times higher than that of Na(+). Accumulation of Na(+) at high concentrations in the cytoplasm results in deleterious effects on cell metabolism, e.g., on photosynthetic activity in plants. Thus, Na(+) is compartmentalized outside the cytoplasm. In plants, it can be accumulated at high concentrations in vacuoles, where it is used as osmoticum. Na(+) is not an essential element in most plants, except in some halophytes. On the other hand, it can be a beneficial element, by replacing K(+) as vacuolar osmoticum for instance. In contrast, K(+) is an essential element. It is involved in electrical neutralization of inorganic and organic anions and macromolecules, pH homeostasis, control of membrane electrical potential, and the regulation of cell osmotic pressure. Through the latter function in plants, it plays a role in turgor-driven cell and organ movements. It is also involved in the activation of enzymes, protein synthesis, cell metabolism, and photosynthesis. Thus, plant growth requires large quantities of K(+) ions that are taken up by roots from the soil solution, and then distributed throughout the plant. The availability of K(+) ions in the soil solution, slowly released by soil particles and clays, is often limiting for optimal growth in most natural ecosystems. In contrast, due to natural salinity or irrigation with poor quality water, detrimental Na(+) concentrations, toxic for all crop species, are present in many soils, representing 6 % to 10 % of the earth's land area. Three families of ion channels (Shaker, TPK/KCO, and TPC) and 3 families of transporters (HAK, HKT, and CPA) have been identified so far as contributing to K(+) and Na(+) transport across the plasmalemma and

  7. Surface expression of sodium channels and transporters in rat kidney: effects of dietary sodium.

    PubMed

    Frindt, Gustavo; Palmer, Lawrence G

    2009-11-01

    The abundance of Na transport proteins in the luminal membrane of the rat kidney was assessed using in situ biotinylation and immunoblotting. When animals were fed an Na-deficient diet for 1 wk, the amounts of epithelial Na channel (ENaC) beta-subunit (beta-ENaC) and gamma-subunit (gamma-ENaC) and Na-Cl cotransporter (NCC) protein in the surface fraction increased relative to controls by 1.9-, 3.5-, and 1.5-fold, respectively. The amounts of the luminal Na/H exchanger (NHE3) and the luminal Na-K-2Cl cotransporter (NKCC2) did not change significantly. The increases in ENaC subunits were mimicked by administration of aldosterone for 1 wk, but the increase in NCC was not. When the animals were fed a high-Na (5% NaCl) diet for 1 wk, the surface expression of beta-ENaC increased by 50%, whereas that of the other membrane proteins did not change, relative to controls. The biochemical parameter most strongly affected by dietary Na was the abundance of the 65-kDa cleaved form of gamma-ENaC at the surface. This increased by 8.5-fold with Na depletion and decreased by 40% with Na loading. The overall 14-fold change reflected regulation of the total abundance of the subunit as well as the fraction of the subunit protein in the cleaved form. We conclude that cleavage of gamma-ENaC and its expression at the apical surface play a major role in the regulation of renal Na reabsorption.

  8. Effect of chaotropic anions on the sodium transport by the Na,K-ATPase.

    PubMed

    Ayuyan, Artem G; Sokolov, Valerij S; Lenz, Alexander A; Apell, Hans-Jürgen

    2006-02-01

    The effect of choline iodide, bromide and chloride on the kinetics of the electrogenic sodium transport by the Na,K-ATPase was investigated in a model system of ATPase-containing membrane fragments adsorbed on the lipid bilayer membrane. The kinetic parameters of Na(+) transport were determined from short circuit currents after fast release of ATP from its caged precursor. The falling phase of the current transients could be fitted by a single exponential with the time constant, tau (2). Its temperature dependence allowed an estimation of the activation energy of the rate-limiting reaction step, the conformation transition E(1)/E(2). Choline iodide and bromide caused a decrease of the activation energy as well as the overall rate of the process expressed as the pre-exponential factor A of the Arrhenius equation. If choline iodide or bromide were present on the cytoplasmic and extracellular sides of the protein, the temperature dependent changes were more pronounced than when present on the cytoplasmic side only. These results can be explained by an effect of the anions on water structure on the extracellular surface of the protein, where a deep access channel connects the ion-binding sites with the solution. Chloride ions also caused a deceleration of the electrogenic transport, however, in contrast to iodide or bromide, they did not affect the activation energy, and were more effective when added on the cytoplasmic side. This effect can be explained by asymmetric screening of the negative surface charges which leads to a transmembrane electric potential that modifies the ion transfer.

  9. Light-induced DELTApH and DELTApsi in halobacterial vesicles related to sodium transport

    SciTech Connect

    Kamo, N.; Racanclli, T.; Packer, L.

    1986-01-01

    Membranes of Halobacterium halobium contain two retinoproteins, baceteriorhodopsin (BR/sub 568nm/) and halorhodopsin (HR/sub 588nm/). We have investigated the light- and sodium-dependent activities in vesicles from the HR containing R/sub 1/mR strain, and the BR + HR containing S/sub 9/ strain to study energy conversion and ion flow mechanisms. Simultaneous ..delta..pH and ..delta..psi measurements have been made with electrodes. In R/sub 1/mR vesicles, -..delta..psi and H/sup +/ uptake occurs in NaCl but not in KCl medium. In S/sub 9/ vesicles, net H/sup +/ extrusion is reduced at high light intensity in NaCl but not KCl medium. Such results indicate Na/sup +//H/sup +/ exchange in vesicles from both strains. As S/sub 9/ contains BR + HR, it is unclear whether the Na/sup +/ extrusion is due to a Na/sup +//H/sup +/ antiporter and/or HR which has been proposed to be a light driven Na/sup +/ pump. To evaluate these concepts for Na/sup +/ transport, the light intensity dependence and action of several membrane transport active agents have been compared. Digitoxin, electro-neutral exchangers (triphenyltin and monensin), and phloretin yielded similar results for HR (R/sub 1/mR) and HR + BR (S/sub 9/) vesicles. Moreover treatment of vesicles with carboxyl reacting reagents inhibited Na/sup +/ dependent activity in both types of vesicles. Thus, common mechanisms of Na/sup +/ transport are indicated in S/sub 9/ and R/sub 1/mR vesicles. 22 refs., 9 figs., 1 tab.

  10. Alterations in plasma membrane promote overexpression and increase of sodium influx through epithelial sodium channel in hypertensive platelets.

    PubMed

    Cerecedo, D; Martínez-Vieyra, Ivette; Sosa-Peinado, Alejandro; Cornejo-Garrido, Jorge; Ordaz-Pichardo, Cynthia; Benítez-Cardoza, Claudia

    2016-08-01

    Platelets are small, anucleated cell fragments that activate in response to a wide variety of stimuli, triggering a complex series of intracellular pathways leading to a hemostatic thrombus formation at vascular injury sites. However, in essential hypertension, platelet activation contributes to causing myocardial infarction and ischemic stroke. Reported abnormalities in platelet functions, such as platelet hyperactivity and hyperaggregability to several agonists, contribute to the pathogenesis and complications of thrombotic events associated with hypertension. Platelet membrane lipid composition and fluidity are determining for protein site accessibility, structural arrangement of platelet surface, and response to appropriate stimuli. The present study aimed to demonstrate whether structural and biochemical abnormalities in lipid membrane composition and fluidity characteristic of platelets from hypertensive patients influence the expression of the Epithelial Sodium Channel (ENaC), fundamental for sodium influx during collagen activation. Wb, cytometry and quantitative Reverse Transcription-Polymerase Chain Reaction (qRT-PCR) assays demonstrated ENaC overexpression in platelets from hypertensive subjects and in relation to control subjects. Additionally, our results strongly suggest a key role of β-dystroglycan as a scaffold for the organization of ENaC and associated proteins. Understanding of the mechanisms of platelet alterations in hypertension should provide valuable information for the pathophysiology of hypertension. Copyright © 2016 Elsevier B.V. All rights reserved.

  11. Sodium channels in membrane vesicles from cultured toad bladder cells

    SciTech Connect

    Asher, C.; Moran, A.; Rossier, B.C.; Garty, H. Ben Gurion Univ., Beer-Sheva Institut de Pharmacologie de l'Universite de Lausanne )

    1988-04-01

    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.

  12. Current topics in membranes and transport

    SciTech Connect

    Kleinzeller, A.

    1987-01-01

    This book contains 10 chapters. Some of the chapter titles are: Expression of the Oxytocin and Vasopressin Genes; Steroid Effects on Excitable Membranes: The Secretory Vesicle in Processing and Secretion of Neuropeptides: and Steroid Hormone Influences on Cyclic AMP-Generating Systems.

  13. Gating effects in Halobacterium halobium membrane transport

    NASA Technical Reports Server (NTRS)

    Lanyi, J. K.; Silverman, M. P.

    1979-01-01

    The transport of Na(+) via an H(+)/Na(+) antiporter and of aspartate and serine via Na(+)/amino acid symport systems was studied in Halobacterium halobium cell envelope vesicles. Gradients for H(+) were produced by illuminating the bacteriorhodopsin-containing vesicles at different light intensities, and the rate and extent of Na(+) transport were followed as functions of the electrochemical potential difference for protons. The coupling of Na(+) and H(+) gradients suggested a translocation stoichiometry of 2H(+)/Na(+) for the antiporter. The rate of Na(+) transport increases steeply above a critical transmembrane electrochemical proton gradient, and since the electrical and the chemical potentials of H(+) at this threshold point vary with the experimental conditions, while the sum of these potentials is constant, it was concluded that the gating of the Na(+) transport is caused by the total electrochemical gradient.

  14. Gating effects in Halobacterium halobium membrane transport

    NASA Technical Reports Server (NTRS)

    Lanyi, J. K.; Silverman, M. P.

    1979-01-01

    The transport of Na(+) via an H(+)/Na(+) antiporter and of aspartate and serine via Na(+)/amino acid symport systems was studied in Halobacterium halobium cell envelope vesicles. Gradients for H(+) were produced by illuminating the bacteriorhodopsin-containing vesicles at different light intensities, and the rate and extent of Na(+) transport were followed as functions of the electrochemical potential difference for protons. The coupling of Na(+) and H(+) gradients suggested a translocation stoichiometry of 2H(+)/Na(+) for the antiporter. The rate of Na(+) transport increases steeply above a critical transmembrane electrochemical proton gradient, and since the electrical and the chemical potentials of H(+) at this threshold point vary with the experimental conditions, while the sum of these potentials is constant, it was concluded that the gating of the Na(+) transport is caused by the total electrochemical gradient.

  15. Single Molecule Imaging of Conformational Dynamics in Sodium-Coupled Transporters

    ERIC Educational Resources Information Center

    Terry, Daniel S.

    2013-01-01

    Neurotransmitter:sodium symporter (NSS) proteins remove neurotransmitters released into the synapse through a transport process driven by the physiological sodium ion (Na[superscript +]) gradient. NSSs for dopamine, noradrenaline, and serotonin are targeted by the psychostimulants cocaine and amphetamines, as well as by antidepressants. The…

  16. Single Molecule Imaging of Conformational Dynamics in Sodium-Coupled Transporters

    ERIC Educational Resources Information Center

    Terry, Daniel S.

    2013-01-01

    Neurotransmitter:sodium symporter (NSS) proteins remove neurotransmitters released into the synapse through a transport process driven by the physiological sodium ion (Na[superscript +]) gradient. NSSs for dopamine, noradrenaline, and serotonin are targeted by the psychostimulants cocaine and amphetamines, as well as by antidepressants. The…

  17. Natural polyphenols: Influence on membrane transporters

    PubMed Central

    Hussain, Saad Abdulrahman; Sulaiman, Amal Ajaweed; Alhaddad, Hasan; Alhadidi, Qasim

    2016-01-01

    Accumulated evidence has focused on the use of natural polyphenolic compounds as nutraceuticals since they showed a wide range of bioactivities and exhibited protection against variety of age-related disorders. Polyphenols have variable potencies to interact, and hence alter the activities of various transporter proteins, many of them classified as anion transporting polypeptide-binding cassette transporters like multidrug resistance protein and p-glycoprotein. Some of the efflux transporters are, generally, linked with anticancer and antiviral drug resistance; in this context, polyphenols may be beneficial in modulating drug resistance by increasing the efficacy of anticancer and antiviral drugs. In addition, these effects were implicated to explain the influence of dietary polyphenols on drug efficacy as result of food-drug interactions. However, limited data are available about the influence of these components on uptake transporters. Therefore, the objective of this article is to review the potential efficacies of polyphenols in modulating the functional integrity of uptake transporter proteins, including those terminated the effect of neurotransmitters, and their possible influence in neuropharmacology. PMID:27069731

  18. Chloroplast membrane transport: interplay of prokaryotic and eukaryotic traits.

    PubMed

    Vothknecht, Ute C; Soll, Jürgen

    2005-07-18

    Chloroplasts are specific plant organelles of prokaryotic origin. They are separated from the surrounding cell by a double membrane, which represents an effective barrier for the transport of metabolites and proteins. Specific transporters in the inner envelope membrane have been described, which facilitate the exchange of metabolites. In contrast, the outer envelope has been viewed for a long time as a molecular sieve that offers a mere size constriction to the passage of molecules. This view has been challenged lately, and a number of specific and regulated pore proteins of the outer envelope (OEPs) have been identified. These pores seem to have originated by adaptation of outer membrane proteins of the cyanobacterial ancestor of the chloroplast. In a similar fashion, the transport of proteins across the two envelope membranes is achieved by two hetero-oligomeric protein complexes called Toc (translocon in the outer envelope of chloroplasts) and Tic (translocon in the inner envelope of chloroplasts). The phylogenetic provenance of the translocon components is less clear, but at least the channel protein of the Toc translocon is of cyanobacterial origin. Characteristic of cyanobacteria and chloroplasts is furthermore a specialized internal membrane system, the thylakoids, on which the components of the photosynthetic machinery are located. Despite the importance of this membrane, very little is known about its phylogenetic origin or the manner of its synthesis. Vipp1 appears to be a ubiquitous component of thylakoid formation, while in chloroplasts of land plants, additionally a vesicle transport system of eukaryotic origin might be involved in this process.

  19. Novel macrocyclic carriers for proton-coupled liquid membrane transport

    SciTech Connect

    Lamb, J.D.

    1991-06-10

    The objective of our research program is to elucidate the chemical principles which are responsible for the cation selectivity and permeability of liquid membranes containing macrocyclic carriers. Several new macrocyclic carriers were synthesized during the last three year period, including selenium-containing macrocycles, new crown-4 structures, and several new crown structures containing nitrogen based heterocycles as substituents in the principal macrocyclic ring. The cation binding properties of these macrocycles were investigated by potentiometric titration, calorimetric titration, solvent extraction, and NMR techniques. In addition, hydrophobic macrocycles were incorporated into dual hollow fiber membrane systems to investigate their membrane performance, especially in the proton-coupled transport mode. It was found that the dual hollow fiber system maintains the cation selectivity and permeability of supported liquid membranes, while enhancing membrane stability. The diffusion limited transport model was expanded to account for membrane solvent effects. Furthermore, Eu{sup 2+} transport was found to be similar to that of strontium and much higher than that of the lanthanides, in supported liquid membrane systems.

  20. Chloride ion transport into pig jejunal brush-border membrane vesicles.

    PubMed Central

    Forsyth, G W; Gabriel, S E

    1988-01-01

    1. This study was carried out to determine the types and activities of carrier proteins which transport the chloride ion in pig jejunal brush-border membranes, with an emphasis on studying the properties of chloride conductance activity in vesicles prepared from these membranes. 2. Sodium-chloride co-transport activity was not detected in this tissue. A sodium-proton antiport with typical amiloride sensitivity was present. An anion exchanger linking chloride to hydroxyl or bicarbonate ions was also found in the pig jejunal brush-border membrane vesicles. 3. Chloride conductance activity in this system was specifically dependent on the buffering agents used for vesicle preparation. Conductance activity could not be demonstrated in vesicles prepared in imidazolium acetate or in HEPES-Tris buffers. HEPES-tetramethylammonium buffering of vesicles in the chloride uptake system produced a significant conductance response to a potassium gradient plus valinomycin. 4. Chloride conductance showed saturable kinetics with respect to substrate concentration, with a Michaelis-Menten constant (Km) of approximately 116 mM and a maximum velocity (Vmax) of 132 nmol (mg protein)-1 min-1. 5. Preliminary screening of potential inhibitors of chloride conductance showed only minimal inhibitor effects of SITS (4-acetamido-4'-isothiocyanostilbene-2,2'-sulphonic acid), anthracene-9-carboxylate, N-phenylanthranilate and piretanide. 6. The conductance activity in pig jejunal vesicles appears to have stringent buffer requirements, and to be relatively insensitive to the effects of reported conductance inhibitors. PMID:2466986

  1. Dehydration of dioxane by pervaporation using filled blend membranes of polyvinyl alcohol and sodium alginate.

    PubMed

    Kuila, Sunil Baran; Ray, Samit Kumar

    2014-01-30

    Pervaporation membranes were made by solution blending of polyvinyl alcohol (PVA) and sodium alginate (SA). Accordingly, five different blends with PVA:SA weight ratio of 75:25, 50:50, 25:75, 20:80 and 10:90 designated as PS1, PS2, PS3, PS4 and PS5, respectively, were prepared. Each of these blends was crosslinked with 2, 4 and 6 wt% glutaraldehyde and the resulting fifteen (5 × 3) membranes were used for pervaporative separation of 90 wt% dioxane in water. The membranes made from PS4 and PS5 were not stable during pervaporation experiments. Among the stable membranes PS3 membrane crosslinked with 2 wt% glutaraldehyde showed the best results for flux and selectivity. Thus, it was filled with nano size sodium montmorillonite filler and used for separation of dioxane-water mixtures over the entire concentration range of 80-99.5 wt% dioxane in water. The membranes were also characterized by mechanical properties, FTIR, SEM, DTA-TGA and XRD.

  2. Ferrous Ion Transport across Chloroplast Inner Envelope Membranes1

    PubMed Central

    Shingles, Richard; North, Marisa; McCarty, Richard E.

    2002-01-01

    The initial rate of Fe2+ movement across the inner envelope membrane of pea (Pisum sativum) chloroplasts was directly measured by stopped-flow spectrofluorometry using membrane vesicles loaded with the Fe2+-sensitive fluorophore, Phen Green SK. The rate of Fe2+ transport was rapid, coming to equilibrium within 3s. The maximal rate and concentration dependence of Fe2+ transport in predominantly right-side-out vesicles were nearly equivalent to those measured in largely inside-out vesicles. Fe2+ transport was stimulated by an inwardly directed electrochemical proton gradient across right-side-out vesicles, an effect that was diminished by the addition of valinomycin in the presence of K+. Fe2+ transport was inhibited by Zn2+, in a competitive manner, as well as by Cu2+ and Mn2+. These results indicate that inward-directed Fe2+ transport across the chloroplast inner envelope occurs by a potential-stimulated uniport mechanism. PMID:11891257

  3. Hydrogen transport membranes for dehydrogenation reactions

    DOEpatents

    Balachandran,; Uthamalingam, [Hinsdale, IL

    2008-02-12

    A method of converting C.sub.2 and/or higher alkanes to olefins by contacting a feedstock containing C.sub.2 and/or higher alkanes with a first surface of a metal composite membrane of a sintered homogenous mixture of an Al oxide or stabilized or partially stabilized Zr oxide ceramic powder and a metal powder of one or more of Pd, Nb, V, Zr, Ta and/or alloys or mixtures thereof. The alkanes dehydrogenate to olefins by contact with the first surface with substantially only atomic hydrogen from the dehydrogenation of the alkanes passing through the metal composite membrane. Apparatus for effecting the conversion and separation is also disclosed.

  4. MECHANISM OF GLUCOSE TRANSPORT ACROSS THE YEAST CELL MEMBRANE

    PubMed Central

    Cirillo, Vincent P.

    1962-01-01

    Cirillo, Vincent P. (Seton Hall College of Medicine and Dentistry, Jersey City, N.J.). Mechanism of glucose transport across the yeast cell membrane. J. Bacteriol. 84:485–491. 1962.—The kinetics of d-glucose and l-sorbose transport was studied in Saccharomyces cerevisiae inhibited with iodoacetic acid under nitrogen to prevent glucose metabolism. d-Glucose was found to compete with l-sorbose for a common membrane transport system with an apparent affinity greater than 25 times that of sorbose. A comparison of the net rate of glucose and sorbose transport at 50 and 500 mm external concentration showed that glucose transport is greater than that of sorbose from the lower concentration, but sorbose transport is greater than glucose at the higher concentration. This reversal of transport rate of two sugars with markedly different affinities is predicted by the membrane carrier theory. A further prediction of carrier theory was confirmed by the demonstration that the rate of glucose transport into fructose-loaded cells is greater than into unloaded cells. PMID:14021412

  5. Modification of erythrocyte membrane proteins, enzymes and transport mechanisms in chronic alcoholics: an in vivo and in vitro study.

    PubMed

    Maturu, Paramahamsa; Vaddi, Damodara Reddy; Pannuru, Padmavathi; Nallanchakravarthula, Varadacharyulu

    2013-01-01

    The aim of the study was to elucidate the molecular mechanisms underlying the alcohol perturbation leading to deleterious effects on erythrocyte membrane transport in chronic alcoholics. Membrane bound enzyme activities such as Na(+), K(+)-ATPase, Ca(2+),Mg(2+)-ATPase and acetylcholine esterase and membrane transport analysis by in vitro and erythrocyte membrane profile analysis in controls and chronic alcoholic red cells were analyzed. It was observed that decreased Na(+), K(+)-ATPase enzyme activity and increased activities of Ca(2+),Mg(2+)-ATPase and acetylcholine esterase in chronic alcoholics compared to controls. The in vitro studies of erythrocytes suggested that there is an increased uptake of glucose through chronic alcoholic red cells. However, glucose utilization by chronic alcoholic red cells was decreased. An increased sensitivity of ouabain for its binding site on Na(+), K(+)-ATPase in chronic alcoholic erythrocyte membrane was evident from this study. Though there appears to be an increased Na(+) influx in chronic alcoholic cells, the status of Na(+) transport is not altered much. However, ouabain caused slight disturbances in the transport of sodium, similar disturbances in the potassium transport resulting in much accumulation of potassium in red cells. It was concluded that chronic alcohol consumption modified certain membrane bound proteins, enzymes and transport mechanisms in chronic alcoholics.

  6. Structure and Water Transport in Nafion Nanocomposite Membranes

    NASA Astrophysics Data System (ADS)

    Davis, Eric; Page, Kirt

    2014-03-01

    Perfluorinated ionomers, specifically Nafion, are the most widely used ion exchange membranes for vanadium redox flow battery applications, where an understanding of the relationship between membrane structure and transport of water/ions is critical to battery performance. In this study, the structure of Nafion/SiO2 nanocomposite membranes, synthesized using sol-gel chemistry, as well as cast directly from Nafion/SiO2 nanoparticle dispersions, was measured using both small-angle neutron scattering (SANS) and ultra-small-angle neutron scattering (USANS). Through contrast match studies of the SiO2 nanoparticles, direct information on the change in the structure of the Nafion membranes and the ion-transport channels within was obtained, where differences in membrane structure was observed between the solution-cast membranes and the membranes synthesized using sol-gel chemistry. Additionally, water sorption and diffusion in these Nafion/SiO2 nanocomposite membranes were measured using in situ time-resolved Fourier transform infrared-attenuated total reflectance (FTIR-ATR) spectroscopy and dynamic vapor sorption (DVS).

  7. Free energy landscapes of sodium ions bound to DMPC-cholesterol membrane surfaces at infinite dilution.

    PubMed

    Yang, Jing; Bonomi, Massimiliano; Calero, Carles; Martí, Jordi

    2016-04-07

    Exploring the free energy landscapes of metal cations on phospholipid membrane surfaces is important for the understanding of chemical and biological processes in cellular environments. Using metadynamics simulations we have performed systematic free energy calculations of sodium cations bound to DMPC phospholipid membranes with cholesterol concentration varying between 0% (cholesterol-free) and 50% (cholesterol-rich) at infinite dilution. The resulting free energy landscapes reveal the competition between binding of sodium to water and to lipid head groups. Moreover, the binding competitiveness of lipid head groups is diminished by cholesterol contents. As cholesterol concentration increases, the ionic affinity to membranes decreases. When cholesterol concentration is greater than 30%, the ionic binding is significantly reduced, which coincides with the phase transition point of DMPC-cholesterol membranes from a liquid-disordered phase to a liquid-ordered phase. We have also evaluated the contributions of different lipid head groups to the binding free energy separately. The DMPC's carbonyl group is the most favorable binding site for sodium, followed by DMPC's phosphate group and then the hydroxyl group of cholesterol.

  8. A dileucine motif is involved in plasma membrane expression and endocytosis of rat sodium taurocholate cotransporting polypeptide (Ntcp).

    PubMed

    Stross, Claudia; Kluge, Stefanie; Weissenberger, Katrin; Winands, Elisabeth; Häussinger, Dieter; Kubitz, Ralf

    2013-11-15

    The sodium taurocholate cotransporting polypeptide (Ntcp) is the major uptake transporter for bile salts into liver parenchymal cells, and PKC-mediated endocytosis was shown to regulate the number of Ntcp molecules at the plasma membrane. In this study, mechanisms of Ntcp internalization were analyzed by flow cytometry, immunofluorescence, and Western blot analyses in HepG2 cells. PKC activation induced endocytosis of Ntcp from the plasma membrane by ~30%. Endocytosis of Ntcp was clathrin dependent and was followed by lysosomal degradation. A dileucine motif located in the third intracellular loop of Ntcp was essential for endocytosis but also for processing and plasma membrane targeting, suggesting a dual function of this motif for intracellular trafficking of Ntcp. Mutation of two of five potential phosphorylation sites surrounding the dileucine motif (Thr225 and Ser226) inhibited PKC-mediated endocytosis. In conclusion, we could identify a motif, which is critical for Ntcp plasma membrane localization. Endocytic retrieval protects hepatocytes from elevated bile salt concentrations and is of special interest, because NTCP has been identified as a receptor for the hepatitis B and D virus.

  9. Selective Fusion of Heterogeneous Classifiers for Predicting Substrates of Membrane Transporters.

    PubMed

    Shaikh, Naeem; Sharma, Mahesh; Garg, Prabha

    2017-03-27

    Membrane transporters play a crucial role in determining fate of administered drugs in a biological system. Early identification of plausible transporters for a drug molecule can provide insights into its therapeutic, pharmacokinetic, and toxicological profiles. In the present study, predictive models for classifying small molecules into substrates and nonsubstrates of various pharmaceutically important membrane transporters were developed using quantitative structure-activity relationship (QSAR) and proteochemometric (PCM) approaches. For this purpose, 4575 substrate interactions for these transporters were collected from the Metabolism and Transport Database (Metrabase) and the literature. The transporters selected for this study include (i) six efflux transporters, viz., breast cancer resistance protein (BCRP/ABCG2), P-glycoprotein (P-gp/MDR1), and multidrug resistance proteins (MRP1, MRP2, MRP3, and MRP4), and (ii) seven influx transporters, viz., organic cation transporter (OCT1/SO22A1), peptide transporter (PEPT1/SO15A1), apical sodium-bile acid transporter (ASBT/NTCP2), and organic anion transporting peptides (OATP1A2/SO1A2, OATP1B/SO1B1, OATP1B3/SO1B3, and OATP2B1/SO2B1). Various types of descriptors and machine learning methods (classifiers) were evaluated for the development of robust predictive models. Additionally, ensemble models were developed by bagging of homogeneous classifiers and selective fusion of heterogeneous classifiers. It was observed that the latter approach improves the accuracy of substrate/nonsubstrate prediction for transporters (average correct classification rate of more than 0.80 for external validation). Moreover, structural fragments important in determining the substrate specificity across the various transporters were identified. To demonstrate these fragments on the query molecule, contour maps were generated. The prediction efficacy of the developed models was illustrated by a good correlation between the reported logBB value

  10. Mass Transport through Nanostructured Membranes: Towards a Predictive Tool

    PubMed Central

    Darvishmanesh, Siavash; Van der Bruggen, Bart

    2016-01-01

    This study proposes a new mechanism to understand the transport of solvents through nanostructured membranes from a fundamental point of view. The findings are used to develop readily applicable mathematical models to predict solvent fluxes and solute rejections through solvent resistant membranes used for nanofiltration. The new model was developed based on a pore-flow type of transport. New parameters found to be of fundamental importance were introduced to the equation, i.e., the affinity of the solute and the solvent for the membrane expressed as the hydrogen-bonding contribution of the solubility parameter for the solute, solvent and membrane. A graphical map was constructed to predict the solute rejection based on the hydrogen-bonding contribution of the solubility parameter. The model was evaluated with performance data from the literature. Both the solvent flux and the solute rejection calculated with the new approach were similar to values reported in the literature. PMID:27918434

  11. Phospholipid flippases: building asymmetric membranes and transport vesicles

    PubMed Central

    Sebastian, Tessy T.; Baldridge, Ryan D.; Xu, Peng; Graham, Todd R.

    2012-01-01

    Phospholipid flippases in the type IV P-type ATPase family (P4-ATPases) are essential components of the Golgi, plasma membrane and endosomal system that play critical roles in membrane biogenesis. These pumps flip phospholipid across the bilayer to create an asymmetric membrane structure with substrate phospholipids, such as phosphatidylserine and phosphatidylethanolamine, enriched within the cytosolic leaflet. The P4-ATPases also help form transport vesicles that bud from Golgi and endosomal membranes, thereby impacting the sorting and localization of many different proteins in the secretory and endocytic pathways. At the organismal level, P4-ATPase deficiencies are linked to liver disease, obesity, diabetes, hearing loss, neurological deficits, immune deficiency and reduced fertility. Here, we review the biochemical, cellular and physiological functions of P4-ATPases, with an emphasis on their roles in vesicle-mediated protein transport. PMID:22234261

  12. Transport analysis of hollow fiber gas separation membranes

    SciTech Connect

    Singh, V.; Rhinehart, R.R.; Narayan, R.S.; Tock, R.W.

    1995-12-01

    Membrane technology is extensively used for industrial gas separation. A steady-state model for gas permeation by hollow membrane fibers is developed for a multicomponent ideal gas system in countercurrent flow. Gas phase diffusion is shown to dominate transport in the substrate making local bore concentration, not diffusing species flux fraction, the appropriate measure of permeate activity for this experimental system. The model is able to predict the experimental trends in a O{sub 2}/N{sub 2}/polysulfone system.

  13. Membranes with functionalized carbon nanotube pores for selective transport

    DOEpatents

    Bakajin, Olgica; Noy, Aleksandr; Fornasiero, Francesco; Park, Hyung Gyu; Holt, Jason K; Kim, Sangil

    2015-01-27

    Provided herein composition and methods for nanoporous membranes comprising single walled, double walled, or multi-walled carbon nanotubes embedded in a matrix material. Average pore size of the carbon nanotube can be 6 nm or less. These membranes are a robust platform for the study of confined molecular transport, with applications in liquid and gas separations and chemical sensing including desalination, dialysis, and fabric formation.

  14. Membrane transporter proteins: a challenge for CNS drug development

    PubMed Central

    Girardin, François

    2006-01-01

    Drug transporters are membrane proteins present in various tissues such as the lymphocytes, intestine, liver, kidney, testis, placenta, and central nervous system. These transporters play a significant role in drug absorption and distribution to organic systems, particularly if the organs are protected by blood-organ barriers, such as the blood-brain barrier or the maternal-fetal barrier. In contrast to neurotransmitters and receptor-coupled transporters or other modes of interneuronal transmission, drug transporters are not directly involved in specific neuronal functions, but provide global protection to the central nervous system. The lack of capillary fenestration, the low pinocytic activity, and the tight junctions between brain capillary and choroid plexus endothelial cells represent further gatekeepers limiting the entrance of endogenous and exogenous compounds into the central nervous system. Drug transport is a result of the concerted action of efflux and influx pumps (transporters) located both in the basolateral and apical membranes of brain capillary and choroid plexus endothelial cells. By regulating efflux and influx of endogenous or exogenous substances, the blood-brain barrier and, to a lesser extent, the blood-cerebrospinal barrier in the ventricles, represents the main interface between the central nervous system and the blood, ie, the rest of the body. As drug distribution to organs is dependent on the affinity of a substrate for a specific transport system, membrane transporter proteins are increasingly recognized as a key determinant of drug disposition. Many drug transporters are members of the adenosine triphosphate (ATP)-binding cassette (ABC) transporter superfamily or the solute-linked carrier (SLC) class. The multidrug resistance protein MDR1 (ABCB1), also called P-glycoprotein, the multidrug resistance-associated proteins MRP1 (ABCC1) and MRP2 (ABCC2), and the breast cancer-resistance protein BCRP (ABCG2) are ATP-dependent efflux

  15. Calixarene-Mediated Liquid-Membrane Transport of Choline Conjugates.

    PubMed

    Adhikari, Birendra Babu; Fujii, Ayu; Schramm, Michael P

    2014-05-01

    A series of supramolecular calixarenes efficiently transport distinct molecular species through a liquid membrane when attached to a receptor-complementary choline handle. Calix-[6]arene hexacarboxylic acid was highly effective at transporting different target molecules against a pH gradient. Both carboxylic- and phosphonic-acid-functionalized calix[4]arenes effect transport without requiring a pH or ion gradient. NMR binding studies, two-phase solvent extraction, and three-phase transport experiments reveal the necessary and subtle parameters to effect the transport of molecules attached to a choline "handle". On the other hand, rescorin[4]arene cavitands, which have similar guest recognition profiles, did not transport guest molecules. These developments reveal new approaches towards attempting synthetic-receptor-mediated selective small-molecule transport in vesicular and cellular systems.

  16. Chloride transport and the actions of nedocromil sodium and cromolyn sodium in asthma.

    PubMed

    Alton, E W; Norris, A A

    1996-11-01

    Nedocromil sodium has been shown to be capable of inhibiting chloride ion flux in mast cells, epithelial cells, and neurons. This feature may explain how it can prevent responses such as mast-cell degranulation, the effects of osmolarity changes in the airways, and neuronal activation. This mechanism may also provide a unifying hypothesis to explain the effects of nedocromil sodium on a range of cell types involved in asthma, such as sensory and efferent neurons and cells involved in inflammation.

  17. The maltose ABC transporter: action of membrane lipids on the transporter stability, coupling and ATPase activity.

    PubMed

    Bao, Huan; Dalal, Kush; Wang, Victor; Rouiller, Isabelle; Duong, Franck

    2013-08-01

    The coupling between ATP hydrolysis and substrate transport remains a key question in the understanding of ABC-mediated transport. We show using the MalFGK2 complex reconstituted into nanodiscs, that membrane lipids participate directly to the coupling reaction by stabilizing the transporter in a low energy conformation. When surrounded by short acyl chain phospholipids, the transporter is unstable and hydrolyzes large amounts of ATP without inducing maltose. The presence of long acyl chain phospholipids stabilizes the conformational dynamics of the transporter, reduces its ATPase activity and restores dependence on maltose. Membrane lipids therefore play an essential allosteric function, they restrict the transporter ATPase activity to increase coupling to the substrate. In support to the notion, we show that increasing the conformational dynamics of MalFGK2 with mutations in MalF increases the transporter ATPase activity but decreases the maltose transport efficiency.

  18. Survey of the transport properties of sodium superionic conductor materials for use in sodium batteries

    NASA Astrophysics Data System (ADS)

    Guin, M.; Tietz, F.

    2015-01-01

    One important issue in future scenarios predominantly using renewable energy sources is the electrochemical storage of electricity in batteries. Among all rechargeable battery technologies, Li-ion cells have the largest energy density and output voltage today, but they have yet to be optimized in terms of capacity, safety and cost for use as stationary systems. Recently, sodium batteries have been attracting attention again because of the abundant availability of Na. However, much work is still required in the field of sodium batteries in order to mature this technology. Sodium superionic conductor (NASICON) materials are a thoroughly studied class of solid electrolytes. In this study, their crystal structure, compositional diversity and ionic conductivity are surveyed and analysed in order to correlate the lattice parameters and specific crystal structure data with sodium conductivity and activation energy using as much data sets as possible. Approximately 110 compositions with the general formula Na 1 + 2 w + x - y + zMw(II) Mx(III) My(V) M2- w - x - y (IV) (SiO4)z(PO4) 3 - z were included in the data collection to determine an optimal size for the M cations. In addition, the impact of the amount of Na per formula unit on the conductivity and the substitution of P with Si are discussed. An extensive study of the size of the structural bottleneck for sodium conduction (formed by triangles of oxygen ions) was carried out to validate the influence of this geometrical parameter on sodium conductivity.

  19. RAB-10-Dependent Membrane Transport Is Required for Dendrite Arborization

    PubMed Central

    Zou, Wei; Yadav, Smita; DeVault, Laura; Jan, Yuh Nung; Sherwood, David R.

    2015-01-01

    Formation of elaborately branched dendrites is necessary for the proper input and connectivity of many sensory neurons. Previous studies have revealed that dendritic growth relies heavily on ER-to-Golgi transport, Golgi outposts and endocytic recycling. How new membrane and associated cargo is delivered from the secretory and endosomal compartments to sites of active dendritic growth, however, remains unknown. Using a candidate-based genetic screen in C. elegans, we have identified the small GTPase RAB-10 as a key regulator of membrane trafficking during dendrite morphogenesis. Loss of rab-10 severely reduced proximal dendritic arborization in the multi-dendritic PVD neuron. RAB-10 acts cell-autonomously in the PVD neuron and localizes to the Golgi and early endosomes. Loss of function mutations of the exocyst complex components exoc-8 and sec-8, which regulate tethering, docking and fusion of transport vesicles at the plasma membrane, also caused proximal dendritic arborization defects and led to the accumulation of intracellular RAB-10 vesicles. In rab-10 and exoc-8 mutants, the trans-membrane proteins DMA-1 and HPO-30, which promote PVD dendrite stabilization and branching, no longer localized strongly to the proximal dendritic membranes and instead were sequestered within intracellular vesicles. Together these results suggest a crucial role for the Rab10 GTPase and the exocyst complex in controlling membrane transport from the secretory and/or endosomal compartments that is required for dendritic growth. PMID:26394140

  20. RAB-10-Dependent Membrane Transport Is Required for Dendrite Arborization.

    PubMed

    Zou, Wei; Yadav, Smita; DeVault, Laura; Nung Jan, Yuh; Sherwood, David R

    2015-01-01

    Formation of elaborately branched dendrites is necessary for the proper input and connectivity of many sensory neurons. Previous studies have revealed that dendritic growth relies heavily on ER-to-Golgi transport, Golgi outposts and endocytic recycling. How new membrane and associated cargo is delivered from the secretory and endosomal compartments to sites of active dendritic growth, however, remains unknown. Using a candidate-based genetic screen in C. elegans, we have identified the small GTPase RAB-10 as a key regulator of membrane trafficking during dendrite morphogenesis. Loss of rab-10 severely reduced proximal dendritic arborization in the multi-dendritic PVD neuron. RAB-10 acts cell-autonomously in the PVD neuron and localizes to the Golgi and early endosomes. Loss of function mutations of the exocyst complex components exoc-8 and sec-8, which regulate tethering, docking and fusion of transport vesicles at the plasma membrane, also caused proximal dendritic arborization defects and led to the accumulation of intracellular RAB-10 vesicles. In rab-10 and exoc-8 mutants, the trans-membrane proteins DMA-1 and HPO-30, which promote PVD dendrite stabilization and branching, no longer localized strongly to the proximal dendritic membranes and instead were sequestered within intracellular vesicles. Together these results suggest a crucial role for the Rab10 GTPase and the exocyst complex in controlling membrane transport from the secretory and/or endosomal compartments that is required for dendritic growth.

  1. Requirement for Coenzyme Q in Plasma Membrane Electron Transport

    NASA Astrophysics Data System (ADS)

    Sun, I. L.; Sun, E. E.; Crane, F. L.; Morre, D. J.; Lindgren, A.; Low, H.

    1992-12-01

    Coenzyme Q is required in the electron transport system of rat hepatocyte and human erythrocyte plasma membranes. Extraction of coenzyme Q from the membrane decreases NADH dehydrogenase and NADH:oxygen oxidoreductase activity. Addition of coenzyme Q to the extracted membrane restores the activity. Partial restoration of activity is also found with α-tocopherylquinone, but not with vitamin K_1. Analogs of coenzyme Q inhibit NADH dehydrogenase and oxidase activity and the inhibition is reversed by added coenzyme Q. Ferricyanide reduction by transmembrane electron transport from HeLa cells is inhibited by coenzyme Q analogs and restored with added coenzyme Q10. Reduction of external ferricyanide and diferric transferrin by HeLa cells is accompanied by proton release from the cells. Inhibition of the reduction by coenzyme Q analogs also inhibits the proton release, and coenzyme Q10 restores the proton release activity. Trans-plasma membrane electron transport stimulates growth of serum-deficient cells, and added coenzyme Q10 increases growth of HeLa (human adenocarcinoma) and BALB/3T3 (mouse fibroblast) cells. The evidence is consistent with a function for coenzyme Q in a trans-plasma membrane electron transport system which influences cell growth.

  2. Does hindered transport theory apply to desalination membranes?

    PubMed

    Dražević, Emil; Košutić, Krešimir; Kolev, Vesselin; Freger, Viatcheslav

    2014-10-07

    As reverse osmosis (RO) and nanofiltration polyamide membranes become increasingly used for water purification, prediction of pollutant transport is required for membrane development and process engineering. Many popular models use hindered transport theory (HTT), which considers a spherical solute moving through an array of fluid-filled rigid cylindrical pores. Experiments and molecular dynamic simulations, however, reveal that polyamide membranes have a distinctly different structure of a "molecular sponge", a network of randomly connected voids widely distributed in size. In view of this disagreement, this study critically examined the validity of HTT by directly measuring diffusivities of several alcohols within a polyamide film of commercial RO membrane using attenuated total reflection-FTIR. It is found that measured diffusivities deviate from HTT predictions by as much as 2-3 orders of magnitude. This result indicates that HTT does not adequately describe solute transport in desalination membranes. As a more adequate alternative, the concept of random resistor networks is suggested, with resistances described by models of activated transport in "soft" polymers without a sharp size cutoff and with a proper address of solute partitioning.

  3. Transport in nanoporous carbon membranes: Experiments and analysis

    SciTech Connect

    Acharya, M.; Foley, H.C.

    2000-05-01

    Single-component permeances of six gases were measured on three different supported nanoporous carbon membranes prepared by spray coating and pyrolysis of poly(furfuryl alcohol) on porous stainless-steel disks. Global activation energies were regressed from data collected as a function of temperature. Permeances and global activation energies were correlated to molecular size, assuming that entropic affects dominated the transport. The permeance was best correlated to the minimum projected area of the molecule computed from first principles. The free-energy barriers to transport within the membranes were derived from the temperature dependence of the permeance data, after accounting for porosity differences between the membranes and differences in molecular adsorption. Using transition-state theory and an entropic model derived, the free energy, enthalpy, and entropic barriers to transport within the membrane were examined as a function of molecular size. Computed on the basis of size, the entropic component of this barrier did not account for the large differences in the transition-state free energies. However, when these entropic barrier values were used to compute the enthalpic portion of the barrier free energies, the minimum projected area of each molecule correlated strongly. Furthermore, these enthalpic components of the barriers were fitted nicely by the Everett-Powl mean field potential, using only the pore size as the adjustable parameter. These results shed light on the underlying mechanism by which shape-selective transport takes place in the NPC membranes and small molecules are separated.

  4. Stability properties of elementary dynamic models of membrane transport.

    PubMed

    Hernández, Julio A

    2003-01-01

    Living cells are characterized by their capacity to maintain a stable steady state. For instance, cells are able to conserve their volume, internal ionic composition and electrical potential difference across the plasma membrane within values compatible with the overall cell functions. The dynamics of these cellular variables is described by complex integrated models of membrane transport. Some clues for the understanding of the processes involved in global cellular homeostasis may be obtained by the study of the local stability properties of some partial cellular processes. As an example of this approach, I perform, in this study, the neighborhood stability analysis of some elementary integrated models of membrane transport. In essence, the models describe the rate of change of the intracellular concentration of a ligand subject to active and passive transport across the plasma membrane of an ideal cell. The ligand can be ionic or nonionic, and it can affect the cell volume or the plasma membrane potential. The fundamental finding of this study is that, within the physiological range, the steady states are asymptotically stable. This basic property is a necessary consequence of the general forms of the expressions employed to describe the active and passive fluxes of the transported ligand.

  5. Vasopressin regulation of sodium transport in the distal nephron and collecting duct.

    PubMed

    Kortenoeven, M L A; Pedersen, N B; Rosenbaek, L L; Fenton, R A

    2015-08-15

    Arginine vasopressin (AVP) is released from the posterior pituitary gland during states of hyperosmolality or hypovolemia. AVP is a peptide hormone, with antidiuretic and antinatriuretic properties. It allows the kidneys to increase body water retention predominantly by increasing the cell surface expression of aquaporin water channels in the collecting duct alongside increasing the osmotic driving forces for water reabsorption. The antinatriuretic effects of AVP are mediated by the regulation of sodium transport throughout the distal nephron, from the thick ascending limb through to the collecting duct, which in turn partially facilitates osmotic movement of water. In this review, we will discuss the regulatory role of AVP in sodium transport and summarize the effects of AVP on various molecular targets, including the sodium-potassium-chloride cotransporter NKCC2, the thiazide-sensitive sodium-chloride cotransporter NCC, and the epithelial sodium channel ENaC.

  6. Continuous Modeling of Calcium Transport Through Biological Membranes

    NASA Astrophysics Data System (ADS)

    Jasielec, J. J.; Filipek, R.; Szyszkiewicz, K.; Sokalski, T.; Lewenstam, A.

    2016-08-01

    In this work an approach to the modeling of the biological membranes where a membrane is treated as a continuous medium is presented. The Nernst-Planck-Poisson model including Poisson equation for electric potential is used to describe transport of ions in the mitochondrial membrane—the interface which joins mitochondrial matrix with cellular cytosis. The transport of calcium ions is considered. Concentration of calcium inside the mitochondrion is not known accurately because different analytical methods give dramatically different results. We explain mathematically these differences assuming the complexing reaction inside mitochondrion and the existence of the calcium set-point (concentration of calcium in cytosis below which calcium stops entering the mitochondrion).

  7. Computer Simulations of Ion Transport in Polymer Electrolyte Membranes.

    PubMed

    Mogurampelly, Santosh; Borodin, Oleg; Ganesan, Venkat

    2016-06-07

    Understanding the mechanisms and optimizing ion transport in polymer membranes have been the subject of active research for more than three decades. We present an overview of the progress and challenges involved with the modeling and simulation aspects of the ion transport properties of polymer membranes. We are concerned mainly with atomistic and coarser level simulation studies and discuss some salient work in the context of pure binary and single ion conducting polymer electrolytes, polymer nanocomposites, block copolymers, and ionic liquid-based hybrid electrolytes. We conclude with an outlook highlighting future directions.

  8. Electroosmosis in Membranes: Effects of Unstirred Layers and Transport Numbers

    PubMed Central

    Barry, P. H.; Hope, A. B.

    1969-01-01

    When a current is passed through a membrane system, differences in transport numbers between the membrane and the adjacent solutions will, in general, result in depletion and enhancement of concentrations at the membrane-solution interfaces. This will be balanced by diffusion back into the bulk solution, diffusion of solute back across the membrane itself, and osmosis resulting from these local concentration gradients. The two main results of such a phenomenon are (1) that there is a current-induced volume flow, which may be mistaken for electroosmosis, and (2) that there will generally develop transient changes in potential difference (PD) across membranes during and after the passage of current through them. PMID:5786317

  9. Features of ion transport in perfluorinated ion-exchange membranes

    SciTech Connect

    Timashev, S.F.

    1986-02-01

    The conditions for functioning for various systems and devices electrolyzers for ''chlorate'' electrolysis, current sources, etc.) with perfluorinated ion-exchange membranes and septums are determined to a considerable degree by the physicochemical properties of the perfluorinated materials. In this work, on the basis of concepts developed in streaming theory as to the topology of the ''infinite clusters'' (ICs), the author defines more precisely the form of the preexponential dependence of ion transport coefficients and draws conclusions on the character of heat evolution in a perfluorinated membrane when an electric current is passed through the membrane.

  10. Method of making a hydrogen transport membrane, and article

    DOEpatents

    Schwartz, Joseph M.; Corpus, Joseph M.; Lim, Hankwon

    2015-07-21

    The present invention relates to a method of manufacturing a hydrogen transport membrane and the composite article itself. More specifically, the invention relates to producing a membrane substrate, wherein the ceramic substrate is coated with a metal oxide slurry, thereby eliminating the need for an activation step prior to plating the ceramic membrane through an electroless plating process. The invention also relates to modifying the pore size and porosity of the substrate by oxidation or reduction of the particles deposited by the metal oxide slurry.

  11. Capacitance-Voltage Measurement of Transporting Function at Cell Membrane

    NASA Astrophysics Data System (ADS)

    Sakata, Toshiya; Miyahara, Yuji

    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.

  12. Increased sodium plus potassium adenosine triphosphatase activity in erythrocyte membranes in Huntington's disease.

    PubMed

    Butterfield, D A; Oeswein, J Q; Prunty, M E; Hisle, K C; Markesbery, W R

    1978-07-01

    Dopa-decarboxylase, acetylcholinesterase, sodium plus potassium stimulated adenosine triphosphatase (Na+ + K+-ATPase), and membrane-bound protein kinase were compared in the erythrocytes of patients with Huntington's disease and normal controls. All these enzymes also exist in the basal ganglia. The Na+ +K+-ATPase level was elevated (p less than 0.05) in Huntington's disease, while no significant changes were observed in the other enzymes. This finding is consistent with the concept that Huntington's disease is associated with a general membrane abnormality.

  13. Sodium

    MedlinePlus

    Table salt is a combination of two minerals - sodium and chloride Your body needs some sodium to work properly. It helps with the function ... in your body. Your kidneys control how much sodium is in your body. If you have too ...

  14. SPAK isoforms and OSR1 regulate sodium-chloride co-transporters in a nephron-specific manner.

    PubMed

    Grimm, P Richard; Taneja, Tarvinder K; Liu, Jie; Coleman, Richard; Chen, Yang-Yi; Delpire, Eric; Wade, James B; Welling, Paul A

    2012-11-02

    STE20/SPS-1-related proline-alanine-rich protein kinase (SPAK) and oxidative stress-related kinase (OSR1) activate the potassium-dependent sodium-chloride co-transporter, NKCC2, and thiazide-sensitive sodium-chloride cotransporter, NCC, in vitro, and both co-localize with a kinase regulatory molecule, Cab39/MO25α, at the apical membrane of the thick ascending limb (TAL) and distal convoluted tubule (DCT). Yet genetic ablation of SPAK in mice causes a selective loss of NCC function, whereas NKCC2 becomes hyperphosphorylated. Here, we explore the underlying mechanisms in wild-type and SPAK-null mice. Unlike in the DCT, OSR1 remains at the TAL apical membrane of KO mice where it is accompanied by an increase in the active, phosphorylated form of AMP-activated kinase. We found an alterative SPAK isoform (putative SPAK2 form), which modestly inhibits co-transporter activity in vitro, is more abundant in the medulla than the cortex. Thus, enhanced NKCC2 phosphorylation in the SPAK knock-out may be explained by removal of inhibitory SPAK2, sustained activity of OSR1, and activation of other kinases. By contrast, the OSR1/SPAK/M025α signaling apparatus is disrupted in the DCT. OSR1 becomes largely inactive and displaced from M025α and NCC at the apical membrane, and redistributes to dense punctate structures, containing WNK1, within the cytoplasm. These changes are paralleled by a decrease in NCC phosphorylation and a decrease in the mass of the distal convoluted tubule, exclusive to DCT1. As a result of the dependent nature of OSR1 on SPAK in the DCT, NCC is unable to be activated. Consequently, SPAK(-/-) mice are highly sensitive to dietary salt restriction, displaying prolonged negative sodium balance and hypotension.

  15. SPAK Isoforms and OSR1 Regulate Sodium-Chloride Co-transporters in a Nephron-specific Manner*

    PubMed Central

    Grimm, P. Richard; Taneja, Tarvinder K.; Liu, Jie; Coleman, Richard; Chen, Yang-Yi; Delpire, Eric; Wade, James B.; Welling, Paul A.

    2012-01-01

    STE20/SPS-1-related proline-alanine-rich protein kinase (SPAK) and oxidative stress-related kinase (OSR1) activate the potassium-dependent sodium-chloride co-transporter, NKCC2, and thiazide-sensitive sodium-chloride cotransporter, NCC, in vitro, and both co-localize with a kinase regulatory molecule, Cab39/MO25α, at the apical membrane of the thick ascending limb (TAL) and distal convoluted tubule (DCT). Yet genetic ablation of SPAK in mice causes a selective loss of NCC function, whereas NKCC2 becomes hyperphosphorylated. Here, we explore the underlying mechanisms in wild-type and SPAK-null mice. Unlike in the DCT, OSR1 remains at the TAL apical membrane of KO mice where it is accompanied by an increase in the active, phosphorylated form of AMP-activated kinase. We found an alterative SPAK isoform (putative SPAK2 form), which modestly inhibits co-transporter activity in vitro, is more abundant in the medulla than the cortex. Thus, enhanced NKCC2 phosphorylation in the SPAK knock-out may be explained by removal of inhibitory SPAK2, sustained activity of OSR1, and activation of other kinases. By contrast, the OSR1/SPAK/M025α signaling apparatus is disrupted in the DCT. OSR1 becomes largely inactive and displaced from M025α and NCC at the apical membrane, and redistributes to dense punctate structures, containing WNK1, within the cytoplasm. These changes are paralleled by a decrease in NCC phosphorylation and a decrease in the mass of the distal convoluted tubule, exclusive to DCT1. As a result of the dependent nature of OSR1 on SPAK in the DCT, NCC is unable to be activated. Consequently, SPAK−/− mice are highly sensitive to dietary salt restriction, displaying prolonged negative sodium balance and hypotension. PMID:22977235

  16. Effect of N-bromoacetamide on single sodium channel currents in excised membrane patches

    PubMed Central

    1982-01-01

    We have studied the effect of N-bromoacetamide (NBA) on the behavior of single sodium channel currents in excised patches of rat myotube membrane at 10 degree C. Inward sodium currents were activated by voltage steps from holding potentials of about -100 mV to test potentials of -40 mV. The cytoplasmic-face solution was isotonic CsF. Application of NBA or pronase to the cytoplasmic face of the membrane irreversibly removed sodium channel inactivation, as determined by averaged single-channel records. Teh lifetime of the open channel at - 40 mV was increased about 10-fold by NBA treatment without affecting the amplitude of single-channel currents. A binomial analysis was used both before and after treatment to determine the number of channels within the excised patch. NBA was shown to have little effect on activation kinetics, as determined by an examination of both the rising phase of averaged currents and measurements f the delay between the start of the pulse and the first channel opening. Our data support a kinetic model of sodium channel activation in which the rate constant leading back from the open state to the last closed state is slower than expected from a strict Hodgkin-Huxley model. The data also suggest that the normal open-channel lifetime is primarily determined by the inactivation process in the voltage range we have examined. PMID:6281357

  17. Effect of N-bromoacetamide on single sodium channel currents in excised membrane patches.

    PubMed

    Patlak, J; Horn, R

    1982-03-01

    We have studied the effect of N-bromoacetamide (NBA) on the behavior of single sodium channel currents in excised patches of rat myotube membrane at 10 degree C. Inward sodium currents were activated by voltage steps from holding potentials of about -100 mV to test potentials of -40 mV. The cytoplasmic-face solution was isotonic CsF. Application of NBA or pronase to the cytoplasmic face of the membrane irreversibly removed sodium channel inactivation, as determined by averaged single-channel records. Teh lifetime of the open channel at -40 mV was increased about 10-fold by NBA treatment without affecting the amplitude of single-channel currents. A binomial analysis was used both before and after treatment to determine the number of channels within the excised patch. NBA was shown to have little effect on activation kinetics, as determined by an examination of both the rising phase of averaged currents and measurements f the delay between the start of the pulse and the first channel opening. Our data support a kinetic model of sodium channel activation in which the rate constant leading back from the open state to the last closed state is slower than expected from a strict Hodgkin-Huxley model. The data also suggest that the normal open-channel lifetime is primarily determined by the inactivation process in the voltage range we have examined.

  18. Energetics of alanine, lysine, and proline transport in cytoplasmic membranes of the polyphosphate-accumulating Acinetobacter johnsonii strain 210A.

    PubMed Central

    Van Veen, H W; Abee, T; Kleefsman, A W; Melgers, B; Kortstee, G J; Konings, W N; Zehnder, A J

    1994-01-01

    Amino acid transport in right-side-out membrane vesicles of Acinetobacter johnsonii 210A was studied. L-Alanine, L-lysine, and L-proline were actively transported when a proton motive force of -76 mV was generated by the oxidation of glucose via the membrane-bound glucose dehydrogenase. Kinetic analysis of amino acid uptake at concentrations of up to 80 microM revealed the presence of a single transport system for each of these amino acids with a Kt of less than 4 microM. The mode of energy coupling to solute uptake was analyzed by imposition of artificial ion diffusion gradients. The uptake of alanine and lysine was driven by a membrane potential and a transmembrane pH gradient. In contrast, the uptake of proline was driven by a membrane potential and a transmembrane chemical gradient of sodium ions. The mechanistic stoichiometry for the solute and the coupling ion was close to unity for all three amino acids. The Na+ dependence of the proline carrier was studied in greater detail. Membrane potential-driven uptake of proline was stimulated by Na+, with a half-maximal Na+ concentration of 26 microM. At Na+ concentrations above 250 microM, proline uptake was strongly inhibited. Generation of a sodium motive force and maintenance of a low internal Na+ concentration are most likely mediated by a sodium/proton antiporter, the presence of which was suggested by the Na(+)-dependent alkalinization of the intravesicular pH in inside-out membrane vesicles. The results show that both H+ and Na+ can function as coupling ions in amino acid transport in Acinetobacter spp. PMID:8169217

  19. Evidence for Bidirectional Endocannabinoid Transport across Cell Membranes*

    PubMed Central

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

    2012-01-01

    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 μm 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 μm) and OMDM-2 (5 μm), 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

  20. Does Membrane Thickness Affect the Transport of Selective Ions Mediated by Ionophores in Synthetic Membranes?

    PubMed

    Lomora, Mihai; Dinu, Ionel Adrian; Itel, Fabian; Rigo, Serena; Spulber, Mariana; Palivan, Cornelia G

    2015-08-31

    Biomimetic polymer nanocompartments (polymersomes) with preserved architecture and ion-selective membrane permeability represent cutting-edge mimics of cellular compartmentalization. Here it is studied whether the membrane thickness affects the functionality of ionophores in respect to the transport of Ca(2+) ions in synthetic membranes of polymersomes, which are up to 2.6 times thicker than lipid membranes (5 nm). Selective permeability toward calcium ions is achieved by proper insertion of ionomycin, and demonstrated by using specific fluorescence markers encapsulated in their inner cavities. Preservation of polymersome architecture is shown by a combination of light scattering, transmission electron microscopy, and fluorescence spectroscopy. By using a combination of stopped-flow and fluorescence spectroscopy, it is shown that ionomycin can function and transport calcium ions across polymer membranes with thicknesses in the range 10.7-13.4 nm (7.1-8.9 times larger than the size of the ionophore). Thicker membranes induce a decrease in transport, but do not block it due to the intrinsic flexibility of these synthetic membranes. The design of ion selective biomimetic nanocompartments represents a new path toward the development of cellular ion nanosensors and nano-reactors, in which calcium sensitive biomacromolecules can be triggered for specific biological functions. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  1. Improvement of a sample preparation method assisted by sodium deoxycholate for mass-spectrometry-based shotgun membrane proteomics.

    PubMed

    Lin, Yong; Lin, Haiyan; Liu, Zhonghua; Wang, Kunbo; Yan, Yujun

    2014-11-01

    In current shotgun-proteomics-based biological discovery, the identification of membrane proteins is a challenge. This is especially true for integral membrane proteins due to their highly hydrophobic nature and low abundance. Thus, much effort has been directed at sample preparation strategies such as use of detergents, chaotropes, and organic solvents. We previously described a sample preparation method for shotgun membrane proteomics, the sodium deoxycholate assisted method, which cleverly circumvents many of the challenges associated with traditional sample preparation methods. However, the method is associated with significant sample loss due to the slightly weaker extraction/solubilization ability of sodium deoxycholate when it is used at relatively low concentrations such as 1%. Hence, we present an enhanced sodium deoxycholate sample preparation strategy that first uses a high concentration of sodium deoxycholate (5%) to lyse membranes and extract/solubilize hydrophobic membrane proteins, and then dilutes the detergent to 1% for a more efficient digestion. We then applied the improved method to shotgun analysis of proteins from rat liver membrane enriched fraction. Compared with other representative sample preparation strategies including our previous sodium deoxycholate assisted method, the enhanced sodium deoxycholate method exhibited superior sensitivity, coverage, and reliability for the identification of membrane proteins particularly those with high hydrophobicity and/or multiple transmembrane domains. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  2. Electrochemical control of ion transport through a mesoporous carbon membrane

    SciTech Connect

    Surwade, Sumedh P; Chai, Songhai; Choi, Jai-Pil; Wang, Xiqing; Lee, Jeseung; Vlassiouk, Ivan V; Mahurin, Shannon Mark; Dai, Sheng

    2014-01-01

    The transport of fluids through nanometer scale channels typically on the order of 1 -100 nm often exhibit unique properties compared to the bulk fluid. These phenomena occur because the channel dimensions and molecular size become comparable to the range of several important forces including electrostatic and van der Waals forces. Small changes in properties such as the electric double layer or surface charge can significantly affect molecular transport through the channels. Based on these emerging properties, a variety of nanofluidic devices such as nanofluidic transistors, nanofluidic diodes or lab-on-a-chip devices have been developed3-7 with a diverse range of applications including water purification, biomolecular sensing, DNA separation, and rectified ion transport. Nanofluidic devices are typically fabricated using expensive lithography techniques or sacrificial templates. Here we report a carbon-based, three-dimensional nanofluidic transport membrane that enables gated, or on/off, control of the transport of organic molecular species and metal ions using an applied electrical potential. In the absence of an applied potential, both cationic and anionic molecules freely diffuse across the membrane via a concentration gradient. However, when an electrochemical potential is applied, the transport of ions through the membrane is inhibited.

  3. Membrane transporter engineering in industrial biotechnology and whole cell biocatalysis.

    PubMed

    Kell, Douglas B; Swainston, Neil; Pir, Pınar; Oliver, Stephen G

    2015-04-01

    Because they mainly do not involve chemical changes, membrane transporters have been a Cinderella subject in the biotechnology of small molecule production, but this is a serious oversight. Influx transporters contribute significantly to the flux towards product, and efflux transporters ensure the accumulation of product in the much greater extracellular space of fermentors. Programmes for improving biotechnological processes might therefore give greater consideration to transporters than may have been commonplace. Strategies for identifying important transporters include expression profiling, genome-wide knockout studies, stress-based selection, and the use of inhibitors. In addition, modern methods of directed evolution and synthetic biology, especially those effecting changes in energy coupling, offer huge opportunities for increasing the flux towards extracellular product formation by transporter engineering. Copyright © 2015 The Authors. Published by Elsevier Ltd.. All rights reserved.

  4. Host-microbe interactions via membrane transport systems.

    PubMed

    Konishi, Hiroaki; Fujiya, Mikihiro; Kohgo, Yutaka

    2015-04-01

    Living organisms take in essential molecules and get rid of wastes effectively through the selective transport of materials. Especially in the digestive tract, advanced transport systems are indispensable for the absorption of nutrients and elimination of waste products. These transport pathways control physiological functions by modulating the ionic environment inside and outside the cells. Moreover, recent studies have shown the importance of the expression of trafficking-related molecules and the population of gut microbiota. We found that the molecules secreted from microorganisms are imported into the cells via transporters or endocytosis and that they activate cell survival pathways of intestinal epithelial cells. These findings indicate that the interactions between the gut microbiota and host cells are mediated, at least partly, by the membrane transport systems. In addition, it is well known that the breakdown of transport systems induces various diseases. This review highlights the significance of the transport systems as the pathogenic molecules and therapeutic targets in gastrointestinal disorders. For example, abnormal expression of the genes encoding membrane transport-related molecules is frequently involved in digestive diseases, such as colorectal cancer and inflammatory bowel disease. We herein review the significance of these molecules as pathogenic and therapeutic targets for digestive diseases.

  5. Facilitated transport of small molecules and ions for energy-efficient membranes.

    PubMed

    Li, Yifan; Wang, Shaofei; He, Guangwei; Wu, Hong; Pan, Fusheng; Jiang, Zhongyi

    2015-01-07

    In nature, the biological membrane can selectively transport essential small molecules/ions through facilitated diffusion via carrier proteins. Intrigued by this phenomenon and principle, membrane researchers have successfully employed synthetic carriers and carrier-mediated reversible reactions to enhance the separation performance of synthetic membranes. However, the existing facilitated transport membranes as well as the relevant facilitated transport theories have scarcely been comprehensively reviewed in the literature. This tutorial review primarily covers the two aspects of facilitated transport theories: carrier-mediated transport mechanisms and facilitated transport chemistries, including the design and fabrication of facilitated transport membranes. The applications of facilitated transport membranes in energy-intensive membrane processes (gas separation, pervaporation, and proton exchange membrane fuel cells) have also been discussed. Hopefully, this review will provide guidelines for the future research and development of facilitated transport membranes with high energy efficiency.

  6. Comparison of the antiangiogenic effects of heparin sodium, enoxaparin sodium, and tinzaparin sodium by using chorioallantoic membrane assay.

    PubMed

    Katrancioglu, Nurkay; Karahan, Oguz; Kilic, Ahmet Turhan; Altun, Ahmet; Katrancioglu, Ozgur; Polat, Zubeyde Akin

    2012-04-01

    Unfractionated heparin (UFH) and low molecular weight heparins have been used as anticoagulation agents in cardiovascular clinics for decades. However, these molecules also have potent antiangiogenic effects. Whereas, angiogenesis may be the most crucial determinant of the prognosis of cardiovascular diseases, and except some special situation, antiangiogenic effect is not desirable in the most of the cardiovascular disease. In this study, we aimed to compare the antiangiogenic potency of UFH, enoxaparin, and tinzaparin. The antiangiogenic efficacies of UFH, enoxaparin, and tinzaparin were examined in vivo by using the chick chorioallantoic membrane (CAM) model. Twenty fertilized eggs were used for each studied drug. Drug solutions were prepared in 10 and 1 IU/10 μl concentrations. Decreases in the density of the capillaries were assessed and scored. All three drugs showed antiangiogenic effects on the chick CAM at the 10 IU/10 μl concentration. However, the antiangiogenic score of the UFH was significantly higher than that of enoxaparin and tinzaparin at 1 and 10 IU/10 μl concentrations. UFH had stronger and antiangiogenic potential than enoxaparin and tinzaparin. However, tinzaparin showed dose-dependent antiangiogenic effects. We think that an anticoagulant molecule with a less and dose-dependent antiangiogenic effect, as in the case of tinzaparin, may be more desirable in case of cardiovascular disease related with insufficient angiogenesis.

  7. The transport along membrane nanotubes driven by the spontaneous curvature of membrane components.

    PubMed

    Kabaso, Doron; Bobrovska, Nataliya; Góźdź, Wojciech; Gongadze, Ekaterina; Kralj-Iglič, Veronika; Zorec, Robert; Iglič, Aleš

    2012-10-01

    Intercellular membrane nanotubes (ICNs) serve as a very specific transport system between neighboring cells. The underlying mechanisms responsible for the transport of membrane components and vesicular dilations along the ICNs are not clearly understood. The present study investigated the spatial distribution of anisotropic membrane components of tubular shapes and isotropic membrane components of spherical shapes. Experimental results revealed the preferential distribution of CTB (cholera toxin B)-GM1 complexes mainly on the spherical cell membrane, and cholesterol-sphingomyelin at the membrane leading edge and ICNs. In agreement with previous studies, we here propose that the spatial distribution of CTB-GM1 complexes and cholesterol-sphingomyelin rafts were due to their isotropic and anisotropic shapes, respectively. To elucidate the relationship between a membrane component shape and its spatial distribution, a two-component computational model was constructed. The minimization of the membrane bending (free) energy revealed the enrichment of the anisotropic component along the ICN and the isotropic component in the parent cell membrane, which was due to the curvature mismatch between the ICN curvature and the spontaneous curvature of the isotropic component. The equations of motion, derived from the differentiation of the membrane free energy, revealed a curvature-dependent flux of the isotropic component and a curvature-dependent force exerted on a vesicular dilation along the ICN. Finally, the effects of possible changes in the orientational ordering of the anisotropic component attendant to the transport of the vesicular dilation were discussed with connection to the propagation of electrical and chemical signals. Copyright © 2012 Elsevier B.V. All rights reserved.

  8. Molecular level water and solute transport in reverse osmosis membranes

    NASA Astrophysics Data System (ADS)

    Lueptow, Richard M.; Shen, Meng; Keten, Sinan

    2015-11-01

    The water permeability and rejection characteristics of six solutes, methanol, ethanol, 2-propanol, urea, Na+, and Cl-, were studied for a polymeric reverse osmosis (RO) membrane using non-equilibrium molecular dynamics simulations. Results indicate that water flux increases with an increasing fraction of percolated free volume in the membrane polymer structure. Solute molecules display Brownian motion and hop from pore to pore as they pass through the membrane. The solute rejection depends on both the size of the solute molecule and the chemical interaction of the solute with water and the membrane. When the open spaces in the polymeric structure are such that solutes have to shed at least one water molecule from their solvation shell to pass through the membrane molecular structure, the water-solute pair interaction energy governs solute rejection. Organic solutes more easily shed water molecules than ions to more readily pass through the membrane. Hydrogen-bonding sites for molecules like urea also lead to a higher rejection. These findings underline the importance of the solute's solvation shell and solute-water-membrane chemistry in solute transport and rejection in RO membranes. Funded by the Institute for Sustainability and Energy at Northwestern with computing resources from XSEDE (NSF grant ACI-1053575).

  9. Prism-patterned Nafion membrane for enhanced water transport in polymer electrolyte membrane fuel cell

    NASA Astrophysics Data System (ADS)

    Kim, Sang Moon; Kang, Yun Sik; Ahn, Chiyeong; Jang, Segeun; Kim, Minhyoung; Sung, Yung-Eun; Yoo, Sung Jong; Choi, Mansoo

    2016-06-01

    Here, we report a simple and effective strategy to enhance the performance of the polymer electrolyte membrane fuel cell by imprinting prism-patterned arrays onto the Nafion membrane, which provides three combined effects directly related to the device performance. First, a locally thinned membrane via imprinted micro prism-structures lead to reduced membrane resistance, which is confirmed by electrochemical impedance spectroscopy. Second, increments of the geometrical surface area of the prism-patterned Nafion membrane compared to a flat membrane result in the increase in the electrochemical active surface area. Third, the vertically asymmetric geometry of prism structures in the cathode catalyst layer lead to enhanced water transport, which is confirmed by oxygen gain calculation. To explain the enhanced water transport, we propose a simple theoretical model on removal of water droplets existing in the asymmetric catalyst layer. These three combined effects achieved via incorporating prism patterned arrays into the Nafion membrane effectively enhance the performance of the polymer electrolyte membrane fuel cell.

  10. Transmembrane transport of peptidoglycan precursors across model and bacterial membranes.

    PubMed

    van Dam, Vincent; Sijbrandi, Robert; Kol, Matthijs; Swiezewska, Ewa; de Kruijff, Ben; Breukink, Eefjan

    2007-05-01

    Translocation of the peptidoglycan precursor Lipid II across the cytoplasmic membrane is a key step in bacterial cell wall synthesis, but hardly understood. Using NBD-labelled Lipid II, we showed by fluorescence and TLC assays that Lipid II transport does not occur spontaneously and is not induced by the presence of single spanning helical transmembrane peptides that facilitate transbilayer movement of membrane phospholipids. MurG catalysed synthesis of Lipid II from Lipid I in lipid vesicles also did not result in membrane translocation of Lipid II. These findings demonstrate that a specialized protein machinery is needed for transmembrane movement of Lipid II. In line with this, we could demonstrate Lipid II translocation in isolated Escherichia coli inner membrane vesicles and this transport could be uncoupled from the synthesis of Lipid II at low temperatures. The transport process appeared to be independent from an energy source (ATP or proton motive force). Additionally, our studies indicate that translocation of Lipid II is coupled to transglycosylation activity on the periplasmic side of the inner membrane.

  11. Theory for reactive solute transport through clay membrane barriers

    NASA Astrophysics Data System (ADS)

    Malusis, Michael A.; Shackelford, Charles D.

    2002-12-01

    The theoretical development for one-dimensional, coupled migration of solutes with different ionic mobilities through clay soils that behave as ion-restrictive membranes, referred to as clay membrane barriers (CMBs), is presented. The transport formulation is based on principles of irreversible thermodynamics and accounts explicitly for coupling effects of hyperfiltration (ultrafiltration) and chemico-osmotic counter-advection associated with clay membrane behavior in the absence of electrical current. Since, by definition, no solute can enter a "perfect" or "ideal" membrane, the concept of an implicit coupling effect, such that the effective salt-diffusion coefficient, Ds* approaches zero as the chemico-osmotic efficiency coefficient, ω approaches unity is introduced. The theoretical development also illustrates that, even in the absence of membrane behavior, traditional advective-dispersive transport theory based on a constant value of Ds* for the solutes may not be appropriate for simulating transient transport in reactive (ion exchanging) systems. This potential limitation is illustrated through simulations for solute mass flux involving the migration of a binary salt solution (KCl) through a clay barrier with exchange sites saturated with a single exchangeable cation (e.g., Na +) that enters the pore solution upon ion exchange with the salt cation (K +).

  12. Mechanism of action of anions on the electron transport chain in thylakoid membranes of higher plants.

    PubMed

    Singh-Rawal, Pooja; Zsiros, Ottó; Bharti, Sudhakar; Garab, Gyozo; Jajoo, Anjana

    2011-04-01

    With an aim to improve our understanding of the mechanisms behind specific anion effects in biological membranes, we have studied the effects of sodium salts of anions of varying valency in thylakoid membranes. Rates of electron transport of PS II and PS I, 77K fluorescence emission and excitation spectra, cyclic electron flow around PS I and circular dichroism (CD) spectra were measured in thylakoid membranes in order to elucidate a general mechanism of action of inorganic anions on photosynthetic electron transport chain. Re-distribution of absorbed excitation energy has been observed as a signature effect of inorganic anions. In the presence of anions, such as nitrite, sulphate and phosphate, distribution of absorbed excitation energy was found to be more in favor of Photosystem I (PS I). The amount of energy distributed towards PS I depended on the valency of the anion. In this paper, we propose for the first time that energy re-distribution and its valence dependence may not be the effect of anions per se. The entry of negative charge (anion) is accompanied by influx of positive charge (protons) to maintain a balance of charge across the thylakoid membranes. As reflected by the CD spectra, the observed energy re-distribution could be a result of structural rearrangements of the protein complexes of PS II caused by changes in the ionic environment of the thylakoid lumen.

  13. Effect of barium ion on p-aminohippurate transport in basolateral membrane vesicles isolated from rat kidney cortex.

    PubMed

    Hori, M; Gemba, M

    1985-06-01

    To clarify the cause of the stimulation of p-aminohippurate (PAH) accumulation in rat kidney cortical slices by barium, an experiment was carried out with basolateral membrane vesicles isolated from rat kidney cortex. The effect of barium on PAH uptake by the membrane vesicles was compared with that of verapamil which also stimulated PAH accumulation in the slices. The enzyme marker for basolateral membrane, (Na+ + K+)- ATPase, was enriched 15-fold and the brushborder enzyme marker, alkaline phosphatase, was 1.3-fold in our membrane preparation. Contamination in this preparation by lysosomes, mitochondria and cytosol was also low but that by endoplasmic reticulum was slightly high as judged by the enzyme markers. PAH uptake by the membrane vesicles possessed the usual characteristics, i.e., sodium-dependence and probenecid-sensitivity. PAH uptake by the membrane vesicles was enhanced by barium, but not by verapamil. On the other hand, barium did not affect tetraethylammonium (TEA) uptake by the vesicles, and verapamil strongly inhibited it. Manganese also stimulated PAH uptake to the same extent as did barium, but calcium and strontium did not affect the uptake. Barium did not act on sodium transport in the membrane vesicles. An 'anion-sensitively transported lipophilic cation', triphenylmethylphosphonium iodide (TPMP), uptake was depressed by barium. These results suggest that barium stimulates selectively PAH uptake in basolateral membrane vesicles. Its stimulatory action may contribute at least partly to an increase in PAH accumulation in rat kidney cortical slices by this ion and may prove useful in an analysis of the mechanism of PAH transport system in renal basolateral membranes.

  14. Using membrane transporters to improve crops for sustainable food production

    USDA-ARS?s Scientific Manuscript database

    With the global population predicted to grow by at least 25% by 2050, the need for sustainable production of nutritious foods is critical for human and environmental well-being. Recent advances show that specialized plant membrane transporters can be utilized to enhance yields of staple crops, incre...

  15. Understanding the transport processes in polymer electrolyte membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Cheah, May Jean

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

  16. Interleukin-17A Regulates Renal Sodium Transporters and Renal Injury in Angiotensin II-Induced Hypertension.

    PubMed

    Norlander, Allison E; Saleh, Mohamed A; Kamat, Nikhil V; Ko, Benjamin; Gnecco, Juan; Zhu, Linjue; Dale, Bethany L; Iwakura, Yoichiro; Hoover, Robert S; McDonough, Alicia A; Madhur, Meena S

    2016-07-01

    Angiotensin II-induced hypertension is associated with an increase in T-cell production of interleukin-17A (IL-17A). Recently, we reported that IL-17A(-/-) mice exhibit blunted hypertension, preserved natriuresis in response to a saline challenge, and decreased renal sodium hydrogen exchanger 3 expression after 2 weeks of angiotensin II infusion compared with wild-type mice. In the current study, we performed renal transporter profiling in mice deficient in IL-17A or the related isoform, IL-17F, after 4 weeks of Ang II infusion, the time when the blood pressure reduction in IL-17A(-/-) mice is most prominent. Deficiency of IL-17A abolished the activation of distal tubule transporters, specifically the sodium-chloride cotransporter and the epithelial sodium channel and protected mice from glomerular and tubular injury. In human proximal tubule (HK-2) cells, IL-17A increased sodium hydrogen exchanger 3 expression through a serum and glucocorticoid-regulated kinase 1-dependent pathway. In mouse distal convoluted tubule cells, IL-17A increased sodium-chloride cotransporter activity in a serum and glucocorticoid-regulated kinase 1/Nedd4-2-dependent pathway. In both cell types, acute treatment with IL-17A induced phosphorylation of serum and glucocorticoid-regulated kinase 1 at serine 78, and treatment with a serum and glucocorticoid-regulated kinase 1 inhibitor blocked the effects of IL-17A on sodium hydrogen exchanger 3 and sodium-chloride cotransporter. Interestingly, both HK-2 and mouse distal convoluted tubule 15 cells produce endogenous IL-17A. IL17F had little or no effect on blood pressure or renal sodium transporter abundance. These studies provide a mechanistic link by which IL-17A modulates renal sodium transport and suggest that IL-17A inhibition may improve renal function in hypertension and other autoimmune disorders. © 2016 American Heart Association, Inc.

  17. Feed gas contaminant control in ion transport membrane systems

    DOEpatents

    Carolan, Michael Francis; Minford, Eric; Waldron, William Emil

    2009-07-07

    Ion transport membrane oxidation system comprising an enclosure having an interior and an interior surface, inlet piping having an internal surface and adapted to introduce a heated feed gas into the interior of the enclosure, and outlet piping adapted to withdraw a product gas from the interior of the enclosure; one or more planar ion transport membrane modules disposed in the interior of the enclosure, each membrane module comprising mixed metal oxide material; and a preheater adapted to heat a feed gas to provide the heated feed gas to the inlet piping, wherein the preheater comprises an interior surface. Any of the interior surfaces of the enclosure, the inlet piping, and the preheater may be lined with a copper-containing metal lining. Alternatively, any of the interior surfaces of the inlet piping and the preheater may be lined with a copper-containing metal lining and the enclosure may comprise copper.

  18. Multicomponent Transport through Realistic Zeolite Membranes: Characterization & Transport in Nanoporous Networks

    SciTech Connect

    William C. Conner

    2007-08-02

    These research studies focused on the characterization and transport for porous solids which comprise both microporosity and mesoporosity. Such materials represent membranes made from zeolites as well as for many new nanoporous solids. Several analytical sorption techniques were developed and evaluated by which these multi-dimensional porous solids could be quantitatively characterized. Notably an approach by which intact membranes could be studied was developed and applied to plate-like and tubular supported zeolitic membranes. Transport processes were studied experimentally and theoretically based on the characterization studies.

  19. Volumetric Deformation of Live Cells Induced by Pressure-Activated Cross-Membrane Ion Transport

    NASA Astrophysics Data System (ADS)

    Hui, T. H.; Zhou, Z. L.; Qian, J.; Lin, Y.; Ngan, A. H. W.; Gao, H.

    2014-09-01

    In this work, we developed a method that allows precise control over changes in the size of a cell via hydrostatic pressure changes in the medium. Specifically, we show that a sudden increase, or reduction, in the surrounding pressure, in the physiologically relevant range, triggers cross-membrane fluxes of sodium and potassium ions in leukemia cell lines K562 and HL60, resulting in reversible volumetric deformation with a characteristic time of around 30 min. Interestingly, healthy leukocytes do not respond to pressure shocks, suggesting that the cancer cells may have evolved the ability to adapt to pressure changes in their microenvironment. A model is also proposed to explain the observed cell deformation, which highlights how the apparent viscoelastic response of cells is governed by the microscopic cross-membrane transport.

  20. Mechanistic equations for membrane transport of multicomponent solutions.

    PubMed

    Suchanek, G

    2006-03-01

    In the present article, mechanistic equations for membrane transport of N + 1-component solutions have been derived. The major specific investigation result is the introduction - for ternary solutions - of two diffusion coefficients omega(d1) and omega(d2) for solutes, as well as two cross coefficients omega(d12) and omega(d21) for these solutes. The latter parameters may be treated as coefficients of interdiffusion. The expansion of the description of substance transport to include the N + 1-component solutions does not formulate any additional physical phenomena other than those which are formulated by the transport equations for three-component solutions.

  1. Atrial Natriuretic Peptide Stimulates Dopamine Tubular Transport by Organic Cation Transporters: A Novel Mechanism to Enhance Renal Sodium Excretion

    PubMed Central

    Kouyoumdzian, Nicolás M.; Rukavina Mikusic, Natalia L.; Kravetz, María C.; Lee, Brenda M.; Carranza, Andrea; Del Mauro, Julieta S.; Pandolfo, Marcela; Gironacci, Mariela M.; Gorzalczany, Susana; Toblli, Jorge E.; Fernández, Belisario E.

    2016-01-01

    The aim of this study was to demonstrate the effects of atrial natriuretic peptide (ANP) on organic cation transporters (OCTs) expression and activity, and its consequences on dopamine urinary levels, Na+, K+-ATPase activity and renal function. Male Sprague Dawley rats were infused with isotonic saline solution during 120 minutes and randomized in nine different groups: control, pargyline plus tolcapone (P+T), ANP, dopamine (DA), D-22, DA+D-22, ANP+D-22, ANP+DA and ANP+DA+D-22. Renal functional parameters were determined and urinary dopamine concentration was quantified by HPLC. Expression of OCTs and D1-receptor in membrane preparations from renal cortex tissues were determined by western blot and Na+, K+-ATPase activity was determined using in vitro enzyme assay. 3H-DA renal uptake was determined in vitro. Compared to P+T group, ANP and dopamine infusion increased diuresis, urinary sodium and dopamine excretion significantly. These effects were more pronounced in ANP+DA group and reversed by OCTs blockade by D-22, demonstrating that OCTs are implied in ANP stimulated-DA uptake and transport in renal tissues. The activity of Na+, K+-ATPase exhibited a similar fashion when it was measured in the same experimental groups. Although OCTs and D1-receptor protein expression were not modified by ANP, OCTs-dependent-dopamine tubular uptake was increased by ANP through activation of NPR-A receptor and protein kinase G as signaling pathway. This effect was reflected by an increase in urinary dopamine excretion, natriuresis, diuresis and decreased Na+, K+-ATPase activity. OCTs represent a novel target that links the activity of ANP and dopamine together in a common mechanism to enhance their natriuretic and diuretic effects. PMID:27392042

  2. Nanocapillary Membrane Devices: A Study in Electrokinetic Transport Phenomena

    NASA Astrophysics Data System (ADS)

    Schiffbauer, Jarrod

    There is considerable interest in developing micro-total analysis systems, also known as lab-on-a-chip devices, for applications in chemical and biological analysis. These devices often employ electrokinetic transport phenomena to move, mix, concentrate and separate dissolved species. The details of these phenomena in micro- and nanometer scale geometries are not fully understood; consequently, the basic principles of device operation are often unclear. For example, nanocapillary membranes (NCM) and other nanometer-sized passages can exhibit charge-selectivity and rectification effects similar to those observed in biological membranes. This dissertation addresses several issues related to ion transport in these membranes. Leading-order 1D steady-state models for diffusion-layer modulated transport through non-ideal membranes are used to study ionic rectification in geometrically asymmetric devices. These models provide qualitative explanations of the operation of a variety of fluidic rectifiers and experimentally observed hysteresis effects. By taking the first steps in the full boundary-layer analysis of the model, it is shown that non-ideal membranes do not maintain local electro-neutrality under passage of electric current. This is in contrast to the usual assumption of membrane local electro-neutrality, but is compatible with the existence of the non-equilibrium macroscopic space charge known to appear in the flanking electrolyte and the requirement of overall charge conservation. Lastly, the problem of electrokinetic instability due to non-equilibrium electro-osmotic slip is considered for the case of an electrolyte-membrane interface inside a 2D channel.

  3. Human membrane transporter database: a Web-accessible relational database for drug transport studies and pharmacogenomics.

    PubMed

    Yan, Q; Sadée, W

    2000-01-01

    The human genome contains numerous genes that encode membrane transporters and related proteins. For drug discovery, development, and targeting, one needs to know which transporters play a role in drug disposition and effects. Moreover, genetic polymorphisms in human membrane transporters may contribute to interindividual differences in the response to drugs. Pharmacogenetics, and, on a genome-wide basis, pharmacogenomics, address the effect of genetic variants on an individual's response to drugs and xenobiotics. However, our knowledge of the relevant transporters is limited at present. To facilitate the study of drug transporters on a broad scale, including the use of microarray technology, we have constructed a human membrane transporter database (HMTD). Even though it is still largely incomplete, the database contains information on more than 250 human membrane transporters, such as sequence, gene family, structure, function, substrate, tissue distribution, and genetic disorders associated with transporter polymorphisms. Readers are invited to submit additional data. Implemented as a relational database, HMTD supports complex biological queries. Accessible through a Web browser user interface via Common Gateway Interface (CGI) and Java Database Connection (JDBC), HMTD also provides useful links and references, allowing interactive searching and downloading of data. Taking advantage of the features of an electronic journal, this paper serves as an interactive tutorial for using the database, which we expect to develop into a research tool.

  4. Relationship between sodium-dependent phosphate transporter (NaPi-IIc) function and cellular vacuole formation in opossum kidney cells.

    PubMed

    Shiozaki, Yuji; Segawa, Hiroko; Ohnishi, Saori; Ohi, Akiko; Ito, Mikiko; Kaneko, Ichiro; Kido, Shinsuke; Tatsumi, Sawako; Miyamoto, Ken-ichi

    2015-01-01

    NaPi-IIc/SLC34A3 is a sodium-dependent inorganic phosphate (Pi) transporter in the renal proximal tubules and its mutations cause hereditary hypophosphatemic rickets with hypercalciuria (HHRH). In the present study, we created a specific antibody for opossum SLC34A3, NaPi-IIc (oNaPi-IIc), and analyzed its localization and regulation in opossum kidney cells (a tissue culture model of proximal tubular cells). Immunoreactive oNaPi-IIc protein levels increased during the proliferative phase and decreased during differentiation. Moreover, stimulating cell growth upregulated oNaPi-IIc protein levels, whereas suppressing cell proliferation downregulated oNaPi-IIc protein levels. Immunocytochemistry revealed that endogenous and exogenous oNaPi-IIc proteins localized at the protrusion of the plasma membrane, which is a phosphatidylinositol 4,5-bisphosphate (PIP2) rich-membrane, and at the intracellular vacuolar membrane. Exogenous NaPi-IIc also induced cellular vacuoles and localized in the plasma membrane. The ability to form vacuoles is specific to electroneutral NaPi-IIc, and not electrogenic NaPi-IIa or NaPi-IIb. In addition, mutations of NaPi-IIc (S138F and R468W) in HHRH did not cause cellular PIP2-rich vacuoles. In conclusion, our data anticipate that NaPi-IIc may regulate PIP2 production at the plasma membrane and cellular vesicle formation.

  5. Structure and Function of Thyroid Hormone Plasma Membrane Transporters

    PubMed Central

    Schweizer, Ulrich; Johannes, Jörg; Bayer, Dorothea; Braun, Doreen

    2014-01-01

    Thyroid hormones (TH) cross the plasma membrane with the help of transporter proteins. As charged amino acid derivatives, TH cannot simply diffuse across a lipid bilayer membrane, despite their notorious hydrophobicity. The identification of monocarboxylate transporter 8 (MCT8, SLC16A2) as a specific and very active TH transporter paved the way to the finding that mutations in the MCT8 gene cause a syndrome of psychomotor retardation in humans. The purpose of this review is to introduce the current model of transmembrane transport and highlight the diversity of TH transmembrane transporters. The interactions of TH with plasma transfer proteins, T3 receptors, and deiodinase are summarized. It is shown that proteins may bind TH owing to their hydrophobic character in hydrophobic cavities and/or by specific polar interaction with the phenolic hydroxyl, the aminopropionic acid moiety, and by weak polar interactions with the iodine atoms. These findings are compared with our understanding of how TH transporters interact with substrate. The presumed effects of mutations in MCT8 on protein folding and transport function are explained in light of the available homology model. PMID:25538896

  6. Structure and function of thyroid hormone plasma membrane transporters.

    PubMed

    Schweizer, Ulrich; Johannes, Jörg; Bayer, Dorothea; Braun, Doreen

    2014-09-01

    Thyroid hormones (TH) cross the plasma membrane with the help of transporter proteins. As charged amino acid derivatives, TH cannot simply diffuse across a lipid bilayer membrane, despite their notorious hydrophobicity. The identification of monocarboxylate transporter 8 (MCT8, SLC16A2) as a specific and very active TH transporter paved the way to the finding that mutations in the MCT8 gene cause a syndrome of psychomotor retardation in humans. The purpose of this review is to introduce the current model of transmembrane transport and highlight the diversity of TH transmembrane transporters. The interactions of TH with plasma transfer proteins, T3 receptors, and deiodinase are summarized. It is shown that proteins may bind TH owing to their hydrophobic character in hydrophobic cavities and/or by specific polar interaction with the phenolic hydroxyl, the aminopropionic acid moiety, and by weak polar interactions with the iodine atoms. These findings are compared with our understanding of how TH transporters interact with substrate. The presumed effects of mutations in MCT8 on protein folding and transport function are explained in light of the available homology model.

  7. Centrifuge-induced hypergravity and glutamate efflux by reversal of high-affinity, sodium-dependent transporters from rat brain synaptosomes.

    NASA Astrophysics Data System (ADS)

    Borisova, T.; Himmelreich, N.

    Glutamate uptake by high affinity sodium-dependent glutamate transporters is essential for termination of the synaptic transmission. Glutamate transporters may also contribute to an increase in extracellular glutamate. Glutamate efflux can occur by reversal of the sodium-dependent glutamate transporters during ATP depletion and dissipation of the sodium gradient across the cell membrane. Depolarization-induced calcium independent release of neurotransmitter from synaptosomal cytosolic pool is Na+-dependent and due to reverse of the neurotransmitter transporters also. We used monovalent organic cations N-methyl-D-glucamine (NMDG) to replace extracellular sodium, suggesting that the reducing of Na+ elucidate further the mechanism underlying Ca2+-independent glutamate release. A reduction in extracellular sodium would facilitate reversal of sodium-dependent transporters with extrusion of glutamate. We have compared the basal release of glutamate in Ca2+-free Na+-supplemented and NMDG-supplemented medium in control and after exposure of animals to long-arm centrifuge-induced hypergravity (ten G, during one hour). Replacement of sodium by NMDG enhanced basal level of neurotransmitter. The value of basal level increased to 110± 4% and 140± 2% in the medium with NMDG in comparison with Na+ under the control and hypergravity conditions, respectively. It is likely to reflect the enhancement of the neurotransmitter level in cytosolic pool. Thermodynamic considerations show that the extracellular level of a amino acid neurotransmitter, such as glutamate, that can be generated by transporter reversal are directly proportional to the intracellular concentration of the intracellular concentration of amino acid. KCl-stimulated glutamate release from cytosolic pool increased not statistically after hypergravity loading. We examined the effects of transporter inhibitors DL-threo-beta-benzyloxyaspartate ( DL-TBOA) on the release to elucidate whether reverse transport via the

  8. Barriers to superfast water transport in carbon nanotube membranes.

    PubMed

    Walther, Jens H; Ritos, Konstantinos; Cruz-Chu, Eduardo R; Megaridis, Constantine M; Koumoutsakos, Petros

    2013-05-08

    Carbon nanotube (CNT) membranes hold the promise of extraordinary fast water transport for applications such as energy efficient filtration and molecular level drug delivery. However, experiments and computations have reported flow rate enhancements over continuum hydrodynamics that contradict each other by orders of magnitude. We perform large scale molecular dynamics simulations emulating for the first time the micrometer thick CNTs membranes used in experiments. We find transport enhancement rates that are length dependent due to entrance and exit losses but asymptote to 2 orders of magnitude over the continuum predictions. These rates are far below those reported experimentally. The results suggest that the reported superfast water transport rates cannot be attributed to interactions of water with pristine CNTs alone.

  9. Membrane potential shapes regulation of dopamine transporter trafficking at the plasma membrane

    PubMed Central

    Richardson, Ben D.; Saha, Kaustuv; Krout, Danielle; Cabrera, Elizabeth; Felts, Bruce; Henry, L. Keith; Swant, Jarod; Zou, Mu-Fa; Newman, Amy Hauck; Khoshbouei, Habibeh

    2016-01-01

    The dopaminergic system is essential for cognitive processes, including reward, attention and motor control. In addition to DA release and availability of synaptic DA receptors, timing and magnitude of DA neurotransmission depend on extracellular DA-level regulation by the dopamine transporter (DAT), the membrane expression and trafficking of which are highly dynamic. Data presented here from real-time TIRF (TIRFM) and confocal microscopy coupled with surface biotinylation and electrophysiology suggest that changes in the membrane potential alone, a universal yet dynamic cellular property, rapidly alter trafficking of DAT to and from the surface membrane. Broadly, these findings suggest that cell-surface DAT levels are sensitive to membrane potential changes, which can rapidly drive DAT internalization from and insertion into the cell membrane, thus having an impact on the capacity for DAT to regulate extracellular DA levels. PMID:26804245

  10. Facilitated transport membrane hybrid systems for olefin purification

    SciTech Connect

    Davis, J.C.; Valus, R.J.; Eshraghi, R.; Velikoff, A.E.

    1993-01-01

    A new membrane system has been developed by BP for refinery and chemical plant olefin purification and recovery. This facilitated transport system, coupled with distillation, offers lower capital and operating costs than conventional distillation alone. Initial results on lab scale hollow fiber devices indicate membrane flux ranging from 8.75 {times} 10{sup {minus}6} to 8 {times} 10{sup {minus}5} m{sup 3}/m{sup 2}/sec (2.5 to 23 scfd/ft{sub 2}) and selectivities from 150 to 300. Pilot plant experiments on propylene/propane and ethylene purge gas recovery over three to six months duration show membrane stability and product purity of 98.5% or greater using refinery grade propylene feed. Hybrid system optimization data for membranes and distillation indicate that using a side draw from the distillation tower provides advantages in terms of membrane area, purity of feed to the membrane, and low per-pass recovery coupled with high overall propylene recovery. Membrane performance data under various conditions are also presented. In addition to performance data, economic evaluation and energy savings are discussed.

  11. A novel strategy for the treatment of diabetes mellitus - sodium glucose co-transport inhibitors.

    PubMed

    Niazi, Asfandyar Khan; Niazi, Saad Hameed

    2010-12-01

    Diabetes is one of the most common chronic diseases, affecting almost 3 million in Canada alone and is characterized by increased blood glucose levels. Treatment varies from lifestyle changes to oral anti-diabetics and/or insulin. Sodium glucose co-transport inhibitors may offer promising treatment for patients suffering from diabetes. The inhibitors act by increasing the loss of glucose in urine by decreasing the reabsorption of glucose from the proximal tubules of nephrons. The aim of this review was to assess the efficacy of sodium glucose co-transport inhibitors in the treatment of diabetes as well as any adverse effects. Databases such as MEDLINE, COCHRANE and EMBASE were systematically searched for literature on the efficacy of sodium glucose co-transport inhibitors in improving the glycemic control of patients with diabetes. Research showed that sodium glucose co-transport inhibitors significantly decreased blood glucose levels by increasing glucosuria. Due to the diuretic effects of these inhibitors, diabetic patients who were suffering from hypertension showed a decrease in blood pressure. The caloric loss associated with these inhibitors resulted in weight loss as well. The most common adverse effect seen in patients on these medications was mycotic infection of the urinary or genital tract. Sodium glucose co-transport inhibitors may be an effective line of treatment for diabetes. Although short-term research has shown these drugs to be safe and well-tolerated, studies should be conducted to assess the long-term effects of these drugs.

  12. Direct influence of the sodium pump on the membrane potential of vomeronasal chemoreceptor neurones in frog.

    PubMed Central

    Trotier, D; Døving, K B

    1996-01-01

    1. Whole-cell measurements were made from microvillous receptor neurones isolated from the frog vomeronasal organ. We examined the mechanisms that determined the value of the resting membrane potential. 2. Cells recorded in Ringer solution containing 4 mM K+ showed a resting membrane potential of -88 +/- 20 mV (mean +/- 1 S.D., n = 56). Sixty-six per cent of the cells had stable resting potentials more negative than the calculated equilibrium potentials for K+ (EK, -82 mV) indicating the presence of a hyperpolarizing outward pump current. 3. Cells recorded with an intracellular solution containing Na+ instead of K+, to set EK at 0 mV, presented stable membrane potentials in the range -65 to -119 mV when bathed in a normal Ringer solution. 4. Ouabain, a specific inhibitor of the Na+,K(+)-ATPase, blocked the outward sodium pump current (Ip) and depolarized the membrane. 5. The sodium pump current, measured as the current blocked by 0.5 mM dihydro-ouabain, was linearly related to the membrane potential in the range -60 to -120 mV. The reversal potential measured with a calculated free energy of ATP hydrolysis of -36.2 kJ mol-1 was estimated to be -143 mV. 6. Reduction of the external K+ concentration to 0 mM depolarized the membrane to less than -40 mV. Voltage-clamp observations in this condition indicated a reduction of Ip. Ouabain added to the bath reduced the blocking effect of low external K+. The addition of external K+ activated Ip and induced a rapid hyperpolarization of the cell membrane. 7. At membrane potentials more negative than -80 mV, an inward rectifying depolarizing current characterized as Ih was activated. When Ih was blocked by 5 mM external Cs+ the resting membrane potential increased. 8. These data indicate that the membrane potential of the vomeronasal receptor neurones is not generated by a passive diffusion of K+ ions but by the hyperpolarizing current created by the Na+,K(+)-ATPase. We propose that the resting potential is set by a balance

  13. Pervaporation dehydration of ethanol by hyaluronic acid/sodium alginate two-active-layer composite membranes.

    PubMed

    Gao, Chengyun; Zhang, Minhua; Ding, Jianwu; Pan, Fusheng; Jiang, Zhongyi; Li, Yifan; Zhao, Jing

    2014-01-01

    The composite membranes with two-active-layer (a capping layer and an inner layer) were prepared by sequential spin-coatings of hyaluronic acid (HA) and sodium alginate (NaAlg) on the polyacrylonitrile (PAN) support layer. The SEM showed a mutilayer structure and a distinct interface between the HA layer and the NaAlg layer. The coating sequence of two-active-layer had an obvious influence on the pervaporation dehydration performance of membranes. When the operation temperature was 80 °C and water concentration in feed was 10 wt.%, the permeate fluxes of HA/Alg/PAN membrane and Alg/HA/PAN membrane were similar, whereas the separation factor were 1130 and 527, respectively. It was found that the capping layer with higher hydrophilicity and water retention capacity, and the inner layer with higher permselectivity could increase the separation performance of the composite membranes. Meanwhile, effects of operation temperature and water concentration in feed on pervaporation performance as well as membrane properties were studied.

  14. Transport Properties of Water and Sodium Dodecyl Sulfate (Postprint)

    DTIC Science & Technology

    2013-08-01

    the diffusion of SDS in water. We carry out classical molecular dynamics (MD) simulations [31], where the individual atoms are approximated by spheres... Molecular Dynamics Simulations ,” J. Chem. Phys., 108, pp. 4739–4755. [34] Guillot, J., 2002, “A Reappraisal of What We Have Learnt During Three Deca- des...Berkowitz, M. L., Perera, L., and Forbes, M. D. E., 2002, “ Molecular Dynamics Simulation of Sodium Dodecyl Sulfate Micelle in Water: Micellar

  15. Transposome mutagenesis of an integral membrane transporter in Corynebacterium matruchotii.

    PubMed

    Wang, Cindy; Hayes, Barry; Vestling, Martha M; Takayama, Kuni

    2006-02-17

    A transposon-5 insertion library of Corynebacterium matruchotii ATCC14266 was generated and screened for mutants with altered corynomycolic acid content. One of these designated 319 mutants showed an interruption of a gene encoding an integral membrane protein. MALDI mass spectra of trehalose monocorynomycolate (TMCM), trehalose dicorynomycolate, and methyl corynomycolates derived from cell wall arabinogalactan-corynomycolate showed that these lipids from the mutant contained a lower amount of short-chain (C24 to C34) and much greater amount of long-chain (primarily C(36:2)) corynomycolic acids than the wild type. An analysis of mRNA demonstrated that the integral membrane protein and ATP-binding cassette transporter are transcriptionally coupled. These results suggested that the proteins/enzymes encoded by the membrane transporter gene locus preferably move short-chain corynomycolic acids from the cytoplasm across the membrane bilayer to the periplasmic space where the synthesis of TMCM is thought to occur. This is the first evidence linking corynomycolic acid to a transporter gene locus.

  16. Transport Mechanisms of Carnosine in SKPT Cells: Contribution of Apical and Basolateral Membrane Transporters

    PubMed Central

    Jappar, Dilara; Hu, Yongjun; Keep, Richard F.; Smith, David E.

    2010-01-01

    Purpose The aim of this study was to investigate the transport properties of carnosine in kidney using SKPT cell cultures as a model of proximal tubular transport, and to isolate the functional activities of renal apical and basolateral transporters in this process. Methods The membrane transport kinetics of 10 µM [3H]carnosine was studied in SKPT cells as a function of time, pH, potential inhibitors and substrate concentration. A cellular compartment model was constructed in which the influx, efflux and transepithelial clearances of carnosine were determined. Peptide transporter expression was probed by RT-PCR. Results Carnosine uptake was 15-fold greater from the apical than basolateral surface of SKPT cells. However, the apical-to-basolateral transepithelial transport of carnosine was severely rate-limited by its cellular efflux across the basolateral membrane. The high-affinity, proton-dependence, concentration-dependence and inhibitor specificity of carnosine supports the contention that PEPT2 is responsible for its apical uptake. In contrast, the basolateral transporter is saturable, inhibited by PEPT2 substrates but non-concentrative, thereby, suggesting a facilitative carrier. Conclusions Carnosine is expected to have a substantial cellular accumulation in kidney but minimal tubular reabsorption in blood because of its high influx clearance across apical membranes by PEPT2 and very low efflux clearance across basolateral membranes. PMID:18820998

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

    NASA Astrophysics Data System (ADS)

    Siu, Ana Rosa

    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

  18. Millimeter microwave effect on ion transport across lipid bilayer membranes.

    PubMed

    Alekseev, S I; Ziskin, M C

    1995-01-01

    The effects of millimeter microwaves in the frequency range of 54-76 GHz on capacitance and conductance of lipid bilayer membranes (BLM) were studied. Some of the membranes were modified by gramicidin A and amphotericin B or by tetraphenylboron anions (TPhB-). The millimeter microwaves were pulse-modulated (PW) at repetition rates ranging from 1 to 100 pps, PW at 1000 pps, or unmodulated continuous waves (CW). The maximum output power at the waveguide outlet was 20 mW. It was found that CW irradiation decreased the unmodified BLM capacitance by 1.2% +/- 0.5%. At the same time, membrane current induced by TPhB- transport increased by 5% +/- 1%. The changes in conductance of ionic channels formed by gramicidin A and amphotericin B were small (0.6% +/- 0.4%). No "resonance-like" effects of mm-wave irradiation on membrane capacitance, ionic channel currents, or TPhB- transport were detected. All changes in membrane capacitance and currents were independent of the modulation employed and were equivalent to heating by approximately 1.1 degrees C.

  19. Cholesterol transport through lysosome-peroxisome membrane contacts.

    PubMed

    Chu, Bei-Bei; Liao, Ya-Cheng; Qi, Wei; Xie, Chang; Du, Ximing; Wang, Jiang; Yang, Hongyuan; Miao, Hong-Hua; Li, Bo-Liang; Song, Bao-Liang

    2015-04-09

    Cholesterol is dynamically transported among organelles, which is essential for multiple cellular functions. However, the mechanism underlying intracellular cholesterol transport has remained largely unknown. We established an amphotericin B-based assay enabling a genome-wide shRNA screen for delayed LDL-cholesterol transport and identified 341 hits with particular enrichment of peroxisome genes, suggesting a previously unappreciated pathway for cholesterol transport. We show dynamic membrane contacts between peroxisome and lysosome, which are mediated by lysosomal Synaptotagmin VII binding to the lipid PI(4,5)P2 on peroxisomal membrane. LDL-cholesterol enhances such contacts, and cholesterol is transported from lysosome to peroxisome. Disruption of critical peroxisome genes leads to cholesterol accumulation in lysosome. Together, these findings reveal an unexpected role of peroxisome in intracellular cholesterol transport. We further demonstrate massive cholesterol accumulation in human patient cells and mouse model of peroxisomal disorders, suggesting a contribution of abnormal cholesterol accumulation to these diseases. Copyright © 2015 Elsevier Inc. All rights reserved.

  20. TonB-dependent outer membrane transport: going for Baroque?

    PubMed

    Wiener, Michael C

    2005-08-01

    The import of essential organometallic micronutrients (such as iron-siderophores and vitamin B(12)) across the outer membrane of Gram-negative bacteria proceeds via TonB-dependent outer membrane transporters (TBDTs). The TBDT couples to the TonB protein, which is part of a multiprotein complex in the plasma (inner) membrane. Five crystal structures of TBDTs illustrate clearly the architecture of the protein in energy-independent substrate-free and substrate-bound states. In each of the TBDT structures, an N-terminal hatch (or plug or cork) domain occludes the lumen of a 22-stranded beta barrel. The manner by which substrate passes through the transporter (the "hatch-barrel problem") is currently unknown. Solution NMR and X-ray crystallographic structures of various TonB domains indicate a striking structural plasticity of this protein. Thermodynamic, biochemical and bacteriological studies of TonB and TBDTs indicate further that existing structures do not yet capture critical energy-dependent and in vivo conformations of the transport cycle. The reconciliation of structural and non-structural experimental data, and the unambiguous experimental elucidation of a detailed molecular mechanism of transport are current challenges for this field.

  1. Function and evolution of channels and transporters in photosynthetic membranes.

    PubMed

    Pfeil, Bernard E; Schoefs, Benoît; Spetea, Cornelia

    2014-03-01

    Chloroplasts from land plants and algae originated from an endosymbiotic event, most likely involving an ancestral photoautotrophic prokaryote related to cyanobacteria. Both chloroplasts and cyanobacteria have thylakoid membranes, harboring pigment-protein complexes that perform the light-dependent reactions of oxygenic photosynthesis. The composition, function and regulation of these complexes have thus far been the major topics in thylakoid membrane research. For many decades, we have also accumulated biochemical and electrophysiological evidence for the existence of solute transthylakoid transport activities that affect photosynthesis. However, research dedicated to molecular identification of the responsible proteins has only recently emerged with the explosion of genomic information. Here we review the current knowledge about channels and transporters from the thylakoid membrane of Arabidopsis thaliana and of the cyanobacterium Synechocystis sp. PCC 6803. No homologues of these proteins have been characterized in algae, although similar sequences could be recognized in many of the available sequenced genomes. Based on phylogenetic analyses, we hypothesize a host origin for most of the so far identified Arabidopsis thylakoid channels and transporters. Additionally, the shift from a non-thylakoid to a thylakoid location appears to have occurred at different times for different transport proteins. We propose that closer control of and provision for the thylakoid by products of the host genome has been an ongoing process, rather than a one-step event. Some of the proteins recruited to serve in the thylakoid may have been the result of the increased specialization of its pigment-protein composition and organization in green plants.

  2. Calcium transport by rat duodenal villus and crypt basolateral membranes

    SciTech Connect

    Walters, J.R.F.; Weiser, M.M.

    1987-02-01

    Rat duodenal cells were isolated sequentially to give fractions enriched for villus and crypt cells. From each of these fractions, basolateral-enriched membrane vesicles were prepared and ATP-dependent calcium uptake was studied. Calcium uptake was sensitive to temperature, was inhibited by vanadate and by A23187, and was lower in vitamin D-deficient animals. In normal animals, (UVCa)-transport was approximately twofold greater in villus-tip than in crypt cell-fraction basolateral membranes though the affinity of the uptake for calcium was similar (K/sub m/ = 0.3 M). In vitamin D-deficient animals, the crypt-to-villus gradient was reduced, and in all fractions, calcium transport was similar to or lower than that in the crypts of normal animals. Six hours after vitamin D-deficient animals were repleted with 1,25-dihydroxycholecalciferol, a significant increase in calcium transport by everted gut sacs was present; however, basolateral calcium transport was significantly increased in only the mid-villus fractions, and no change was seen in the villus-tip fractions. Thus vitamin D appears necessary for the development of increased basolateral membrane calcium pump activity in duodenal villus cells, but not all cells in vitamin D-deficient rats are able to respond to 1,25-dihydroxycholecalciferol.

  3. Mechanism of electrodialytic ion transport through solvent extraction membranes

    SciTech Connect

    Moskvin, L.N.; Shmatko, A.G.; Krasnoperov, V.M.

    1987-02-01

    The authors construct a mathematical model for electrodialysis and solvent extraction via an ion-selective ion exchange membrane and accounts for the electrochemical, ion exchange, and diffusional behavior of the processes including their dependence on component concentration and current and voltage. The model is tested against experimental data for the electrodialytic transport of anionic platinum complexes of chlorides from hydrochloric acid solution through tributylphosphate membranes. The platinum concentration in the aqueous solution was determined by gamma spectroscopy obtained via platinum 191 as a radiotracer.

  4. Metabolic evidence that serosal sodium does not recycle through the active transepithelial transport pathway of toad bladder.

    PubMed

    Canessa, M; Labarca, P; Leaf, A

    1976-12-25

    The possibility that sodium from the serosal bathing medium "back diffuses" into the active sodium transport pool within the mucosal epithelial cell of the isolated toad bladder was examined by determining the effect on the metabolism of the tissue of removing sodium from the serosal medium. It was expected that if recycling of serosal sodium did occur through the active transepithelial transport pathway of the isolated toad bladder, removal of sodium from the serosal medium would reduce the rate of CO2 production by the tissue and enhance of stoichiometric ratio of sodium ions transported across the bladder per molecula of sodium transport dependent CO2 produced simultaneously by the bladder (JNa/JCO2). The data revealed no significant change in this ratio (17.19 with serosal sodium and 16.13 after replacing serosal sodium with choline). Further, when transepithelial sodium transport was inhibited (a) by adding amiloride to the mucosal medium, or (b) by removing sodium from the mucosal medium, subsequent removal of sodium from the serosal medium, or (c) addition of ouabain failed to depress the basal rate of CO2 production by the bladder [(a)rate of basal, nontransport related, CO2 production (JbCO2) equals 1.54 +/- 0.52 with serosal sodium and 1.54 +/- 0.37 without serosal sodium; (b) Jb CO2 equals 2.18 +/- 0.21 with serosal sodium and 2.09 +/- 0.21 without serosal sodium; (c) 1.14 +/- 0.26 without ouabain and 1.13 +/- 0.25 with ouabain; unite of JbCO2 are nmoles mg d.w.-1 min-1]. The results support the hypothesis that little, if any, recycling of serosal sodium occurs in the total bladder.

  5. Selective separation of sodium ions from a mixture with phenylalanine by Donnan dialysis with a profiled sulfogroup cation exchange membrane

    NASA Astrophysics Data System (ADS)

    Vasil'eva, V. I.; Goleva, E. A.

    2013-11-01

    The possibility of separating ions of metal from a mixture with ampholyte (an amino acid) by Donnan dialysis with an MK-40 sulfogroup cation exchange membrane is demonstrated. Conditions ensuring the selectivity and intensity of the mass transfer of sodium ions from a mixture with bipolar phenylalanine ions into a diffusate containing hydrochloric acid through a cation exchange membrane are found.

  6. Mechanism of unassisted ion transport across membrane bilayers

    NASA Technical Reports Server (NTRS)

    Wilson, M. A.; Pohorille, A.

    1996-01-01

    To establish how charged species move from water to the nonpolar membrane interior and to determine the energetic and structural effects accompanying this process, we performed molecular dynamics simulations of the transport of Na+ and Cl- across a lipid bilayer located between two water lamellae. The total length of molecular dynamics trajectories generated for each ion was 10 ns. Our simulations demonstrate that permeation of ions into the membrane is accompanied by the formation of deep, asymmetric thinning defects in the bilayer, whereby polar lipid head groups and water penetrate the nonpolar membrane interior. Once the ion crosses the midplane of the bilayer the deformation "switches sides"; the initial defect slowly relaxes, and a defect forms in the outgoing side of the bilayer. As a result, the ion remains well solvated during the process; the total number of oxygen atoms from water and lipid head groups in the first solvation shell remains constant. A similar membrane deformation is formed when the ion is instantaneously inserted into the interior of the bilayer. The formation of defects considerably lowers the free energy barrier to transfer of the ion across the bilayer and, consequently, increases the permeabilities of the membrane to ions, compared to the rigid, planar structure, by approximately 14 orders of magnitude. Our results have implications for drug delivery using liposomes and peptide insertion into membranes.

  7. Mechanism of unassisted ion transport across membrane bilayers

    NASA Technical Reports Server (NTRS)

    Wilson, M. A.; Pohorille, A.

    1996-01-01

    To establish how charged species move from water to the nonpolar membrane interior and to determine the energetic and structural effects accompanying this process, we performed molecular dynamics simulations of the transport of Na+ and Cl- across a lipid bilayer located between two water lamellae. The total length of molecular dynamics trajectories generated for each ion was 10 ns. Our simulations demonstrate that permeation of ions into the membrane is accompanied by the formation of deep, asymmetric thinning defects in the bilayer, whereby polar lipid head groups and water penetrate the nonpolar membrane interior. Once the ion crosses the midplane of the bilayer the deformation "switches sides"; the initial defect slowly relaxes, and a defect forms in the outgoing side of the bilayer. As a result, the ion remains well solvated during the process; the total number of oxygen atoms from water and lipid head groups in the first solvation shell remains constant. A similar membrane deformation is formed when the ion is instantaneously inserted into the interior of the bilayer. The formation of defects considerably lowers the free energy barrier to transfer of the ion across the bilayer and, consequently, increases the permeabilities of the membrane to ions, compared to the rigid, planar structure, by approximately 14 orders of magnitude. Our results have implications for drug delivery using liposomes and peptide insertion into membranes.

  8. Membranous nephropathy with renal salt wasting: role of neurohumoral factors in sodium retention.

    PubMed

    Hommos, Musab; Sinkey, Christine; Haynes, William G; Dixon, Bradley S

    2012-09-01

    The role of neurohumoral factors in the sodium retention of nephrotic syndrome is controversial. We report a case with abrupt onset of severe nephrotic-range proteinuria and hypoalbuminemia due to membranous glomerulonephritis that was associated with renal salt wasting and hypovolemia without edema. Further evaluation showed hypoaldosteronism, hyporeninemia, and primary autonomic failure principally affecting the sympathetic nervous system, determined by the Valsalva maneuver. Administration of exogenous mineralocorticoid and oral salt caused edema and accelerated hypertension. The severe hypoaldosteronism likely was due to use of the angiotensin-converting enzyme inhibitor lisinopril, and it improved after this drug treatment was discontinued. The nephrotic proteinuria resolved after treatment with cyclosporine and prednisone, but the primary autonomic failure with hyporeninemic hypoaldosteronism persisted. The case shows that intratubular factors activated by nephrotic proteinuria are not sufficient to produce sodium retention in the absence of aldosterone and an intact sympathetic nervous system. Copyright © 2012 National Kidney Foundation, Inc. All rights reserved.

  9. Effects of spatial variation in membrane diffusibility and solubility on the lateral transport of membrane components.

    PubMed Central

    Eisinger, J; Halperin, B I

    1986-01-01

    There exist many examples of membrane components (e.g. receptors) accumulating in special domains of cell membranes. We analyze how certain variations in lateral diffusibility and solubility of the membrane would increase the efficiency of transport to these regions. A theorem is derived to show that the mean-time-of capture, tc, for particles diffusing to a trap from an annular region surrounding it, is intermediate to the tc values that correspond to the minimum and maximum diffusion coefficients that obtain in this region. An analytical solution for tc as a function of the gradient of diffusivity surrounding a trap is derived for circular geometry. Since local diffusion coefficients can be increased dramatically by reducing the concentration of intra-membrane particles and/or allowing them to form aggregates, such mechanisms could greatly enhance the diffusion-limited transport of particular membrane components to a trap (e.g. coated pit). If the trap is surrounded by an annular region in which the probe particles' partition function is increased, say, by the local segregation of certain phospholipids, tc is shown to vary inversely with the logarithm of the relative partition function. We provide some conjectural examples to illustrate the magnitude of the effects which heterogeneities in diffusibility and solubility may have in biological membranes. PMID:3756302

  10. Co-overexpressing a Plasma Membrane and a Vacuolar Membrane Sodium/Proton Antiporter Significantly Improves Salt Tolerance in Transgenic Arabidopsis Plants.

    PubMed

    Pehlivan, Necla; Sun, Li; Jarrett, Philip; Yang, Xiaojie; Mishra, Neelam; Chen, Lin; Kadioglu, Asim; Shen, Guoxin; Zhang, Hong

    2016-05-01

    The Arabidopsis gene AtNHX1 encodes a vacuolar membrane-bound sodium/proton (Na(+)/H(+)) antiporter that transports Na(+) into the vacuole and exports H(+) into the cytoplasm. The Arabidopsis gene SOS1 encodes a plasma membrane-bound Na(+)/H(+) antiporter that exports Na(+) to the extracellular space and imports H(+) into the plant cell. Plants rely on these enzymes either to keep Na(+) out of the cell or to sequester Na(+) into vacuoles to avoid the toxic level of Na(+) in the cytoplasm. Overexpression of AtNHX1 or SOS1 could improve salt tolerance in transgenic plants, but the improved salt tolerance is limited. NaCl at concentration >200 mM would kill AtNHX1-overexpressing or SOS1-overexpressing plants. Here it is shown that co-overexpressing AtNHX1 and SOS1 could further improve salt tolerance in transgenic Arabidopsis plants, making transgenic Arabidopsis able to tolerate up to 250 mM NaCl treatment. Furthermore, co-overexpression of AtNHX1 and SOS1 could significantly reduce yield loss caused by the combined stresses of heat and salt, confirming the hypothesis that stacked overexpression of two genes could substantially improve tolerance against multiple stresses. This research serves as a proof of concept for improving salt tolerance in other plants including crops. © The Author 2016. Published by Oxford University Press on behalf of Japanese Society of Plant Physiologists.

  11. Co-overexpressing a Plasma Membrane and a Vacuolar Membrane Sodium/Proton Antiporter Significantly Improves Salt Tolerance in Transgenic Arabidopsis Plants

    PubMed Central

    Pehlivan, Necla; Sun, Li; Jarrett, Philip; Yang, Xiaojie; Mishra, Neelam; Chen, Lin; Kadioglu, Asim; Shen, Guoxin; Zhang, Hong

    2016-01-01

    The Arabidopsis gene AtNHX1 encodes a vacuolar membrane-bound sodium/proton (Na+/H+) antiporter that transports Na+ into the vacuole and exports H+ into the cytoplasm. The Arabidopsis gene SOS1 encodes a plasma membrane-bound Na+/H+ antiporter that exports Na+ to the extracellular space and imports H+ into the plant cell. Plants rely on these enzymes either to keep Na+ out of the cell or to sequester Na+ into vacuoles to avoid the toxic level of Na+ in the cytoplasm. Overexpression of AtNHX1 or SOS1 could improve salt tolerance in transgenic plants, but the improved salt tolerance is limited. NaCl at concentration >200 mM would kill AtNHX1-overexpressing or SOS1-overexpressing plants. Here it is shown that co-overexpressing AtNHX1 and SOS1 could further improve salt tolerance in transgenic Arabidopsis plants, making transgenic Arabidopsis able to tolerate up to 250 mM NaCl treatment. Furthermore, co-overexpression of AtNHX1 and SOS1 could significantly reduce yield loss caused by the combined stresses of heat and salt, confirming the hypothesis that stacked overexpression of two genes could substantially improve tolerance against multiple stresses. This research serves as a proof of concept for improving salt tolerance in other plants including crops. PMID:26985021

  12. Sodium influx through cerebral sodium-glucose transporter type 1 exacerbates the development of cerebral ischemic neuronal damage.

    PubMed

    Yamazaki, Yui; Harada, Shinichi; Wada, Tetsuyuki; Hagiwara, Teruki; Yoshida, Shigeru; Tokuyama, Shogo

    2017-03-15

    We recently reported that cerebral sodium-glucose transporter type 1 (SGLT-1) plays a role in exacerbation of cerebral ischemia. However, the mechanism by which cerebral SGLT-1 acts remains unclear. Here we demonstrated that sodium influx through cerebral SGLT-1 exacerbates cerebral ischemic neuronal damage. SGLT-specific sodium ion influx was induced using α-methyl-D-glucopyranoside (α-MG). Intracellular sodium concentrations in primary cortical neurons were estimated using sodium-binding benzofuran isophthalate fluorescence. SGLT-1 knockdown in primary cortical neurons and mice was achieved using SGLT-1 siRNA. The survival rates of primary cultured cortical neurons were assessed using biochemical assays 1 day after treatment. Middle cerebral artery occlusion (MCAO) was used to generate a focal cerebral ischemic model in SGLT-1 knockdown mice. The change in fasting blood glucose levels, infarction development, and behavioral abnormalities were assessed 1 day after MCAO. Treatment with 200mM α-MG induced a continuous increase in the intracellular sodium concentration, and this increase was normalized after α-MG removal. Neuronal SGLT-1 knockdown had no effect on 100µM H2O2-induced neuronal cell death; however, the knockdown prevented the neuronal cell death induced by 17.5mM glucose and the co-treatment of 100µM H2O2/8.75mM glucose. Neuronal SGLT-1 knockdown also suppressed the cell death induced by α-MG alone and the co-treatment of 100µM H2O2/0.01mM α-MG. Our in vivo results showed that the exacerbation of cerebral ischemic neuronal damage induced by the intracerebroventricular administration of 5.0µg α-MG/mouse was ameliorated in cerebral SGLT-1 knockdown mice. Thus, sodium influx through cerebral SGLT-1 may exacerbate cerebral ischemia-induced neuronal damage. Copyright © 2017 Elsevier B.V. All rights reserved.

  13. Method and system for producing hydrogen using sodium ion separation membranes

    SciTech Connect

    Bingham, Dennis N; Klingler, Kerry M; Turner, Terry D; Wilding, Bruce M; Frost, Lyman

    2013-05-21

    A method of producing hydrogen from sodium hydroxide and water is disclosed. The method comprises separating sodium from a first aqueous sodium hydroxide stream in a sodium ion separator, feeding the sodium produced in the sodium ion separator to a sodium reactor, reacting the sodium in the sodium reactor with water, and producing a second aqueous sodium hydroxide stream and hydrogen. The method may also comprise reusing the second aqueous sodium hydroxide stream by combining the second aqueous sodium hydroxide stream with the first aqueous sodium hydroxide stream. A system of producing hydrogen is also disclosed.

  14. Microbial responses to membrane cleaning using sodium hypochlorite in membrane bioreactors: Cell integrity, key enzymes and intracellular reactive oxygen species.

    PubMed

    Han, Xiaomeng; Wang, Zhiwei; Wang, Xueye; Zheng, Xiang; Ma, Jinxing; Wu, Zhichao

    2016-01-01

    Sodium hypochlorite (NaClO) is a commonly used reagent for membrane cleaning in membrane bioreactors (MBRs), while it, being a kind of disinfectant (oxidant), may impair viability of microbes or even totally inactivate them upon its diffusion into mixed liquor during membrane cleaning. In this study, we systematically examine the effects of NaClO on microorganisms in terms of microbial cell integrity, metabolism behaviours (key enzymes), and intracellular reactive oxygen species (ROS) under various NaClO concentrations. Different proportions of microbial cells in activated sludge were damaged within several minutes dependent on NaClO dosages (5-50 mg/g-SS), and correspondingly organic matters were released to bulk solution. Inhibition of key enzymes involved in organic matter biodegradation, nitrification and denitrification was observed in the presence of NaClO above 1 mg/g-SS, and thus organic matter and nitrogen removal efficiencies were decreased. It was also demonstrated that intracellular ROS production was increased with the NaClO dosage higher than 1 mg/g-SS, which likely induced further damage to microbial cells.

  15. Arsenate transport by sodium/phosphate cotransporter type IIb

    SciTech Connect

    Villa-Bellosta, Ricardo; Sorribas, Victor

    2010-08-15

    Arsenic is a metalloid that causes the dysfunction of critical enzymes, oxidative stress, and malignancies. In recent years several transporters of As{sup III} have been identified, including aquaglyceroporins (AQP) and multidrug resistance proteins (MRP). As{sup V} transport, however, has not been sufficiently studied because it has been assumed that arsenate is taken up by mammalian cells through inorganic phosphate (Pi) transporters. In this paper we have analyzed the role of Pi transporters in the uptake of arsenate by directly using {sup 73}As{sup V} as a radiotracer in phosphate transporter-expressing Xenopus laevis oocytes. The affinities of Pi transporters for H{sub 3}AsO{sub 4} were lower than the affinities for Pi. NaPiIIa, NaPiIIc, Pit1, and Pit2 showed a K{sub m} for arsenate that was > 1 mM (i.e., at least ten times lower than the affinities for Pi). The NaPiIIb isoform showed the highest affinity for As{sup V} in mouse (57 {mu}M), rat (51 {mu}M), and human (9.7 {mu}M), which are very similar to the affinities for Pi. Therefore, NaPiIIb can have a prominent role in the toxicokinetics of arsenic following oral exposure to freshwater or food contaminated with As{sup V}.

  16. Glutaraldehyde fixation of sodium transport in dog red blood cells

    SciTech Connect

    Parker, J.C.

    1984-11-01

    The large increase in passive Na flux that occurs when dog red blood cells are caused to shrink is amiloride sensitive and inhibited when Cl is replaced by nitrate or thiocyanate. Activation and deactivation of this transport pathway by manipulation of cell volume is reversible. Brief treatment of the cells with 0.01-0.03% glutaraldehyde can cause the shrinkage-activated transporter to become irreversibly activated or inactivated, depending on the volume of the cells at the time of glutaraldehyde exposure. Thus, if glutaraldehyde is applied when the cells are shrunken, the amiloride-sensitive Na transporter is activated and remains so regardless of subsequent alterations in cell volume. If the fixative is applied to swollen cells, no amount of subsequent shrinkage will turn on the Na pathway. In its fixed state, the activated transporter is fully amiloride sensitive, but it is no longer inhibited when Cl is replaced by thiocyanate. The action of glutaraldehyde thus allows one to dissect the response to cell shrinkage into two phases. Activation of the pathway is affected by anions and is not prevented by amiloride. Once activated and fixed, the anion requirement disappears. Amiloride inhibits movement of Na through the activated transporter. These experiments demonstrate how a chemical cross-linking agent may be used to study the functional properties of a regulable transport pathway.

  17. Membrane permeability as a cause of transport defects in experimental Fanconi syndrome. A new hypothesis.

    PubMed Central

    Bergeron, M; Dubord, L; Hausser, C; Schwab, C

    1976-01-01

    The injection of sodium maleate (200-400 mg/kg) into rats produces aminoaciduria along with glycosuria and phosphaturia, resembling the Fanconi syndrome. This experimental model was studied by means of microinjections into proximal convoluted tubules of the kidney, stop-flow diuresis, and microperfusion of single nephrons. Our results show that, in maleate-treated rats, competition between amino acids or related structures (L-proline, L-OH-proline, and glycine) possesses the same characteristics, and net influx of amino acids appear normal at the proximal nephron. Data obtained by classical stop-flow techniques and single nephron microperfusions also indicate a normal entry of labeled amino acids (L-lysine, glycine, L-valine, L-proline, L-cystine), and 3-0-methyl-D-[3H]glucose and [32P]phosphate from the luminal side of the proximal tubule cell. However, the efflux of molecules from the cell appears enhanced throughout the proximal and distal tubule; molecules that exit at this site are excreted directly into the urine. Our results suggest that the phosphaturia, aminoaciduria, and glycosuria of the experimental Fanconi syndrome can be explained by a modification of the cell membrane permeability (increased efflux) at distal sites of the nephron rather than by a modification of the membrane transport (decreased influx) at the proximal sites, as is currently accepted. Our data also stress the importance of efflux phenomena in membrane transport. PMID:1262464

  18. Renal phosphate transport: inhomogeneity of local proximal transport rates and sodium dependence.

    PubMed

    Baumann, K; de Rouffignac, C; Roinel, N; Rumrich, G; Ullrich, K J

    1975-01-01

    The standing droplet method has been used in combination with the peritibular perfusion of blood capillaries to determine the build up of transtubular concentration differences of phosphate (Piota) in the renal proximal convoluted tubule of parathyroidectomized rats. Electron probe analysis was used to estimate Piota. At zero time both the intraluminal and the contraluminal Piota concentration was 2 mM. The time dependent decrease of the intraluminal Piota concentration was approximately 4 times faster in the early than in the late proximal convoluted tubule. After 45 sec an intraluminal steady state concentration of 0.20 mM Piota was achieved in the early part. In the late part the intraluminal Piota concentration approached a steady statevalue of 0.54 mM at 123 sec. When sodium free solutions were used the intaluminal Piota concentration increased to 2.22 mM in the earlier and to 2.76 mM in the late part. The data indicate that in the proximal convoluted tubule 1. the rate of phosphate reabsorption is greater in the early part than in the later part, and 2. phospate reabsorption might occur as co-transport with Na+ ions.

  19. Carboxylic Acids Plasma Membrane Transporters in Saccharomyces cerevisiae.

    PubMed

    Casal, Margarida; Queirós, Odília; Talaia, Gabriel; Ribas, David; Paiva, Sandra

    2016-01-01

    This chapter covers the functionally characterized plasma membrane carboxylic acids transporters Jen1, Ady2, Fps1 and Pdr12 in the yeast Saccharomyces cerevisiae, addressing also their homologues in other microorganisms, as filamentous fungi and bacteria. Carboxylic acids can either be transported into the cells, to be used as nutrients, or extruded in response to acid stress conditions. The secondary active transporters Jen1 and Ady2 can mediate the uptake of the anionic form of these substrates by a H(+)-symport mechanism. The undissociated form of carboxylic acids is lipid-soluble, crossing the plasma membrane by simple diffusion. Furthermore, acetic acid can also be transported by facilitated diffusion via Fps1 channel. At the cytoplasmic physiological pH, the anionic form of the acid prevails and it can be exported by the Pdr12 pump. This review will highlight the mechanisms involving carboxylic acids transporters, and the way they operate according to the yeast cell response to environmental changes, as carbon source availability, extracellular pH and acid stress conditions.

  20. Transport Across Chloroplast Membranes: Optimizing Photosynthesis for Adverse Environmental Conditions.

    PubMed

    Pottosin, Igor; Shabala, Sergey

    2016-03-07

    Chloroplasts are central to solar light harvesting and photosynthesis. Optimal chloroplast functioning is vitally dependent on a very intensive traffic of metabolites and ions between the cytosol and stroma, and should be attuned for adverse environmental conditions. This is achieved by an orchestrated regulation of a variety of transport systems located at chloroplast membranes such as porines, solute channels, ion-specific cation and anion channels, and various primary and secondary active transport systems. In this review we describe the molecular nature and functional properties of the inner and outer envelope and thylakoid membrane channels and transporters. We then discuss how their orchestrated regulation affects thylakoid structure, electron transport and excitation energy transfer, proton-motive force partition, ion homeostasis, stromal pH regulation, and volume regulation. We link the activity of key cation and anion transport systems with stress-specific signaling processes in chloroplasts, and discuss how these signals interact with the signals generated in other organelles to optimize the cell performance, with a special emphasis on Ca(2+) and reactive oxygen species signaling. Copyright © 2016 The Author. Published by Elsevier Inc. All rights reserved.

  1. Ballistic electron transport in structured suspended semiconductor membranes

    SciTech Connect

    Pogosov, A. G.; Budantsev, M. V.; Zhdanov, E. Yu.; Pokhabov, D. A.

    2013-12-04

    We study ballistic electron transport in freely suspended AlAs/GaAs microstructures containing a high mobility two-dimensional electron gas with square lattice of antidots. We found that the magnetoresistance of the samples demonstrates commensurability oscillations both for the case of non-suspended and suspended devices. The temperature dependence of the commensurability oscillations is similar for both cases. However, the critical dc current, that suppresses these oscillations, in suspended samples is three times lower than in non-suspended ones. The observed phenomenon can be explained by peculiarities of the heat transport in membranes.

  2. Membrane transporters and drought resistance – a complex issue

    PubMed Central

    Jarzyniak, Karolina M.; Jasiński, Michał

    2014-01-01

    Land plants have evolved complex adaptation strategies to survive changes in water status in the environment. Understanding the molecular nature of such adaptive changes allows the development of rapid innovations to improve crop performance. Plant membrane transport systems play a significant role when adjusting to water scarcity. Here we put proteins participating in transmembrane allocations of various molecules in the context of stomatal, cuticular, and root responses, representing a part of the drought resistance strategy. Their role in the transport of signaling molecules, ions or osmolytes is summarized and the challenge of the forthcoming research, resulting from the recent discoveries, is highlighted. PMID:25538721

  3. An efficient strategy for small-scale screening and production of archaeal membrane transport proteins in Escherichia coli.

    PubMed

    Ma, Pikyee; Varela, Filipa; Magoch, Malgorzata; Silva, Ana Rita; Rosário, Ana Lúcia; Brito, José; Oliveira, Tânia Filipa; Nogly, Przemyslaw; Pessanha, Miguel; Stelter, Meike; Kletzin, Arnulf; Henderson, Peter J F; Archer, Margarida

    2013-01-01

    Membrane proteins play a key role in many fundamental cellular processes such as transport of nutrients, sensing of environmental signals and energy transduction, and account for over 50% of all known drug targets. Despite their importance, structural and functional characterisation of membrane proteins still remains a challenge, partially due to the difficulties in recombinant expression and purification. Therefore the need for development of efficient methods for heterologous production is essential. Fifteen integral membrane transport proteins from Archaea were selected as test targets, chosen to represent two superfamilies widespread in all organisms known as the Major Facilitator Superfamily (MFS) and the 5-Helix Inverted Repeat Transporter superfamily (5HIRT). These proteins typically have eleven to twelve predicted transmembrane helices and are putative transporters for sugar, metabolite, nucleobase, vitamin or neurotransmitter. They include a wide range of examples from the following families: Metabolite-H(+)-symporter; Sugar Porter; Nucleobase-Cation-Symporter-1; Nucleobase-Cation-Symporter-2; and neurotransmitter-sodium-symporter. Overproduction of transporters was evaluated with three vectors (pTTQ18, pET52b, pWarf) and two Escherichia coli strains (BL21 Star and C43 (DE3)). Thirteen transporter genes were successfully expressed; only two did not express in any of the tested vector-strain combinations. Initial trials showed that seven transporters could be purified and six of these yielded quantities of ≥ 0.4 mg per litre suitable for functional and structural studies. Size-exclusion chromatography confirmed that two purified transporters were almost homogeneous while four others were shown to be non-aggregating, indicating that they are ready for up-scale production and crystallisation trials. Here, we describe an efficient strategy for heterologous production of membrane transport proteins in E. coli. Small-volume cultures (10 mL) produced sufficient

  4. Isothermal titration calorimetry of ion-coupled membrane transporters.

    PubMed

    Boudker, Olga; Oh, SeCheol

    2015-04-01

    Binding of ligands, ranging from proteins to ions, to membrane proteins is associated with absorption or release of heat that can be detected by isothermal titration calorimetry (ITC). Such measurements not only provide binding affinities but also afford direct access to thermodynamic parameters of binding--enthalpy, entropy and heat capacity. These parameters can be interpreted in a structural context, allow discrimination between different binding mechanisms and guide drug design. In this review, we introduce advantages and limitations of ITC as a methodology to study molecular interactions of membrane proteins. We further describe case studies where ITC was used to analyze thermodynamic linkage between ions and substrates in ion-coupled transporters. Similar type of linkage analysis will likely be applicable to a wide range of transporters, channels, and receptors.

  5. OCTN3 is a mammalian peroxisomal membrane carnitine transporter

    SciTech Connect

    Lamhonwah, Anne-Marie; Ackerley, Cameron A.; Tilups, Aina; Edwards, Vernon D.; Wanders, Ronald J.; Tein, Ingrid . E-mail: ingrid.tein@sickkids.ca

    2005-12-30

    Carnitine is a zwitterion essential for the {beta}-oxidation of fatty acids. The role of the carnitine system is to maintain homeostasis in the acyl-CoA pools of the cell, keeping the acyl-CoA/CoA pool constant even under conditions of very high acyl-CoA turnover, thereby providing cells with a critical source of free CoA. Carnitine derivatives can be moved across intracellular barriers providing a shuttle mechanism between mitochondria, peroxisomes, and microsomes. We now demonstrate expression and colocalization of mOctn3, the intermediate-affinity carnitine transporter (K {sub m} 20 {mu}M), and catalase in murine liver peroxisomes by TEM using immunogold labelled anti-mOctn3 and anti-catalase antibodies. We further demonstrate expression of hOCTN3 in control human cultured skin fibroblasts both by Western blotting and immunostaining analysis using our specific anti-mOctn3 antibody. In contrast with two peroxisomal biogenesis disorders, we show reduced expression of hOCTN3 in human PEX 1 deficient Zellweger fibroblasts in which the uptake of peroxisomal matrix enzymes is impaired but the biosynthesis of peroxisomal membrane proteins is normal, versus a complete absence of hOCTN3 in human PEX 19 deficient Zellweger fibroblasts in which both the uptake of peroxisomal matrix enzymes as well as peroxisomal membranes are deficient. This supports the localization of hOCTN3 to the peroxisomal membrane. Given the impermeability of the peroxisomal membrane and the key role of carnitine in the transport of different chain-shortened products out of peroxisomes, there appears to be a critical need for the intermediate-affinity carnitine/organic cation transporter, OCTN3, on peroxisomal membranes now shown to be expressed in both human and murine peroxisomes. This Octn3 localization is in keeping with the essential role of carnitine in peroxisomal lipid metabolism.

  6. Using membrane transporters to improve crops for sustainable food production.

    PubMed

    Schroeder, Julian I; Delhaize, Emmanuel; Frommer, Wolf B; Guerinot, Mary Lou; Harrison, Maria J; Herrera-Estrella, Luis; Horie, Tomoaki; Kochian, Leon V; Munns, Rana; Nishizawa, Naoko K; Tsay, Yi-Fang; Sanders, Dale

    2013-05-02

    With the global population predicted to grow by at least 25 per cent by 2050, the need for sustainable production of nutritious foods is critical for human and environmental health. Recent advances show that specialized plant membrane transporters can be used to enhance yields of staple crops, increase nutrient content and increase resistance to key stresses, including salinity, pathogens and aluminium toxicity, which in turn could expand available arable land.

  7. Using membrane transporters to improve crops for sustainable food production

    PubMed Central

    Schroeder, Julian I.; Delhaize, Emmanuel; Frommer, Wolf B.; Guerinot, Mary Lou; Harrison, Maria J.; Herrera-Estrella, Luis; Horie, Tomoaki; Kochian, Leon V.; Munns, Rana; Nishizawa, Naoko K.; Tsay, Yi-Fang; Sanders, Dale

    2013-01-01

    With the global population predicted to grow by at least 25 per cent by 2050, the need for sustainable production of nutritious foods is critical for human and environmental health. Recent advances show that specialized plant membrane transporters can be used to enhance yields of staple crops, increase nutrient content and increase resistance to key stresses, including salinity, pathogens and aluminium toxicity, which in turn could expand available arable land. PMID:23636397

  8. Barium, TEA and sodium sensitive potassium channels are present in the human placental syncytiotrophoblast apical membrane.

    PubMed

    Díaz, P; Vallejos, C; Guerrero, I; Riquelme, G

    2008-10-01

    The human placental syncytiotrophoblast (hSTB) is a polarized epithelial structure, without paracellular routes, forming the main barrier for materno-fetal exchange. There is ample evidence suggesting the presence of potassium (K(+)) channels in the placental apical membrane; which could contribute to membrane potential and volume regulation. We have therefore examined the K(+) currents of isolated apical membranes from human term placenta using electrophysiological methods: reconstitution of ion channels from apical membranes into giant liposomes (single channel recordings, patch clamp method) or their functional transplantation into Xenopus laevis oocytes (total currents recording, voltage clamp method). Single channel recording experiments show the presence of K(+) channels in the hSTB microvillous membrane sensitive to Tetraethylammonium (TEA) and Barium (Ba(+2)). Patch current activity was diminished 50% and 70% by 20 mmol/L TEA and 5 mmol/L Ba(+2) respectively. The more frequent conductance was approximately 73pS, however several levels of current were detected suggesting the presence of more than one type of K(+) channel. In addition, sodium (Na(+)) sensitivity was detected in the patch current thus, over 10 mmol/L Na(+) reduced the seal current to 38%. These results were corroborated by the total current experiments where the K(+) current elicited in injected oocytes with apical purified membrane was blocked by Ba(+2) and TEA. The total current was also affected by Na(+), becoming larger when a Na(+)-free solution was used. Our results show the existence of at least two types of Ba(+2)-sensitive K(+) channels including a TEA sensitive sub-population, and some of them Na(+) sensitive K(+) channels. These channels could be the conductive pathways proposed previously for this cation in placental hSTB. Our novel contribution has been to successfully obtain K(+) channel recordings in systems suitable for electrophysiological studies of isolated apical membranes.

  9. Plasma membrane microdomains regulate turnover of transport proteins in yeast

    PubMed Central

    Grossmann, Guido; Malinsky, Jan; Stahlschmidt, Wiebke; Loibl, Martin; Weig-Meckl, Ina; Frommer, Wolf B.; Opekarová, Miroslava; Tanner, Widmar

    2008-01-01

    In this study, we investigate whether the stable segregation of proteins and lipids within the yeast plasma membrane serves a particular biological function. We show that 21 proteins cluster within or associate with the ergosterol-rich membrane compartment of Can1 (MCC). However, proteins of the endocytic machinery are excluded from MCC. In a screen, we identified 28 genes affecting MCC appearance and found that genes involved in lipid biosynthesis and vesicle transport are significantly overrepresented. Deletion of Pil1, a component of eisosomes, or of Nce102, an integral membrane protein of MCC, results in the dissipation of all MCC markers. These deletion mutants also show accelerated endocytosis of MCC-resident permeases Can1 and Fur4. Our data suggest that release from MCC makes these proteins accessible to the endocytic machinery. Addition of arginine to wild-type cells leads to a similar redistribution and increased turnover of Can1. Thus, MCC represents a protective area within the plasma membrane to control turnover of transport proteins. PMID:19064668

  10. Active transport of calcium in Neurospora plasma membrane vesicles.

    PubMed Central

    Stroobant, P; Scarborough, G A

    1979-01-01

    Functionally inverted plasma membrane vesicles isolated from the eukaryotic microorganism Neurospora crassa catalyze Mg2+/ATP-dependent Ca2+ uptake. Inhibitors induced efflux studies and isotope-exchange experiments indicate that the Ca2+ is accumulated inside the vesicles against a concentration gradient of about 40-fold, and that the majority of the transported Ca2+ is present essentially in free solution. Comparisons of Mg2+/ATP-driven 45Ca2+ uptake and [14C]SCN-uptake with respect to the Mg2+/ATP concentration dependence, the effects of inhibitors, and the nucleotide and divalent cation specificities indicate that the energy for Ca2+ accumulation is derived from ATP hydrolysis catalyzed by the electrogenic plasma membrane ATPase. Energized Ca2+ uptake is stimulated by the permeant anion SCN- to a degree that varies reciprocally with the ability of this anion to dissipate the membrane potential, and is inhibited by K+ in the presence of nigericin. All of these data point to the conclusion that the active transport of Ca2+ across the Neurospora plasma membrane takes place via a Ca2+/H+ antiporter, which functions to pump Ca2+ out of the intact cell. PMID:40223

  11. An Integrated Field-Effect Microdevice for Monitoring Membrane Transport in Xenopus laevis Oocytes via Lateral Proton Diffusion

    PubMed Central

    Schaffhauser, Daniel Felix; Patti, Monica; Goda, Tatsuro; Miyahara, Yuji; Forster, Ian Cameron; Dittrich, Petra Stephanie

    2012-01-01

    An integrated microdevice for measuring proton-dependent membrane activity at the surface of Xenopus laevis oocytes is presented. By establishing a stable contact between the oocyte vitelline membrane and an ion-sensitive field-effect (ISFET) sensor inside a microperfusion channel, changes in surface pH that are hypothesized to result from facilitated proton lateral diffusion along the membrane were detected. The solute diffusion barrier created between the sensor and the active membrane area allowed detection of surface proton concentration free from interference of solutes in bulk solution. The proposed sensor mechanism was verified by heterologously expressing membrane transport proteins and recording changes in surface pH during application of the specific substrates. Experiments conducted on two families of phosphate-sodium cotransporters (SLC20 & SLC34) demonstrated that it is possible to detect phosphate transport for both electrogenic and electroneutral isoforms and distinguish between transport of different phosphate species. Furthermore, the transport activity of the proton/amino acid cotransporter PAT1 assayed using conventional whole cell electrophysiology correlated well with changes in surface pH, confirming the ability of the system to detect activity proportional to expression level. PMID:22792166

  12. Selective Lysosomal Transporter Degradation by Organelle Membrane Fusion.

    PubMed

    McNally, Erin Kate; Karim, Mahmoud Abdul; Brett, Christopher Leonard

    2017-01-23

    Lysosomes rely on their resident transporter proteins to return products of catabolism to the cell for reuse and for cellular signaling, metal storage, and maintaining the lumenal environment. Despite their importance, little is known about the lifetime of these transporters or how they are regulated. Using Saccharomyces cerevisiae as a model, we discovered a new pathway intrinsic to homotypic lysosome membrane fusion that is responsible for their degradation. Transporter proteins are selectively sorted by the docking machinery into an area between apposing lysosome membranes, which is internalized and degraded by lumenal hydrolases upon organelle fusion. These proteins have diverse lifetimes that are regulated in response to protein misfolding, changing substrate levels, or TOR activation. Analogous to endocytosis for controlling surface protein levels, the "intralumenal fragment pathway" is critical for lysosome membrane remodeling required for organelle function in the context of cellular protein quality control, ion homeostasis, and metabolism. Copyright © 2017 Elsevier Inc. All rights reserved.

  13. Membrane Transport in Isolated Vesicles from Sugarbeet Taproot

    PubMed Central

    Giannini, John L.; Miller, Gene W.; Briskin, Donald P.

    1987-01-01

    The effects of fluoride on the tonoplast type ATPase and transport activities associated with sealed membrane vesicles isolated from sugarbeet (Beta vulgaris L.) storage tissue were examined. This anion had two distinct effects upon the proton-pumping vesicles. When ATP hydrolysis was measured in the presence of gramicidin D, significant inhibition (approximately 50%) only occurred when the fluoride concentration approached 50 millimolar. In contrast, the same degree of inhibition of proton transport occurred when the fluoride concentration was about 24 millimolar. Effects on proton pumping at this concentration of fluoride could be attributed to an inhibition of chloride movement which serves to dissipate the vesicle membrane potential. Valinomycin could partially restore ATPase activity in sealed vesicles which were inhibited by fluoride and this restoration occurred with a reduction in the membrane potential. Fluoride demonstrated a competitive interaction with chloride-stimulation of proton transport and inhibited the uptake of radioactive chloride into sealed vesicles. When the vesicles were allowed to develop a pH gradient in the absence of KCl, and KCl was subsequently added, fluoride reduced enhancement of the existing pH gradient by KCl. The results are consistent with a chloride carrier that is inhibited by fluoride. PMID:16665312

  14. Sum frequency generation studies of membrane transport phenomena

    SciTech Connect

    Dyer, R.B.; Shreve, A.P.

    1998-11-01

    This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). The objective of this work is to study the transport of protons and ions across biological membranes, one of the most fundamental processes in living organisms, critical for energy transduction in respiration and photosynthesis and for a wide variety of cellular signal transduction events. Membrane protein structure and function, in particular proton and ion pumping are poorly understood. The authors have developed sum frequency generation (SFG) spectroscopy for the study of membrane phenomena, a nonlinear spectroscopic technique that is uniquely sensitive to interfaces and with demonstrated structural specificity. They have used SFG and conventional vibrational spectroscopic approaches to study proton transport processes in cytochrome c oxidase. A key finding has been the identification of vibrational modes associated with proton labile groups, including a glutamic acid near the redox active binuclear center and structural waters. These groups are sensitive to the ligation and redox states of the metal centers and hence are ideal candidates for coupling redox energy to proton transport processes.

  15. What role for membranes in determining the higher sodium pump molecular activity of mammals compared to ectotherms?

    PubMed

    Else, P L; Wu, B J

    1999-07-01

    The major body organs of mammals have sodium pumps that turn over energy (ATP) three to four times faster than those of ectotherms, at the same temperature. To examine if membranes play a role in these differences in molecular activity, membrane cross-over experiments were performed using two representative species, Rattus norvegicus and Bufo marinus. Microsomal membrane of kidney and brain displayed characteristic molecular activity differences (three- to four-fold) between the species. These molecular activity differences could be removed by delipidation. Pre-existing molecular activities and differences could be restored when reconstituted with original membrane. Using the same reconstitution method, species membrane cross-over experiments resulted in toad sodium pumps in rat membrane significantly increasing (approximately 30-40%) and rat sodium pumps in toad membrane significantly decreasing (approximately 40%) activities in both kidney and brain. Analysis of membrane composition showed reduced cholesterol content and differences in the fatty acids of phospholipids with higher overall unsaturation in the mammal. The scope for membranes to determine protein performance and its broader implications for metabolism are discussed.

  16. Temperature effect on transport performance by inorganic nanofiltration membranes

    SciTech Connect

    Tsuru, Toshinori; Izumi, Shuhei; Yoshioka, Tomohisa; Asaeda, Masashi

    2000-03-01

    The effect of temperature on nanofiltration performance was examined using three inorganic membranes with a molecular-weight cutoff of approximately 200, 600, and 2,000, respectively. The inorganic porous membranes were prepared from silica-zirconia colloidal sols and used in nanofiltration experiments for neutral solutes over a temperature range of 20 to 60 C. The rejection of solutes decreased with an increase in temperature for the membranes, while the permeate volume flux increased. Three transport coefficients--reflection coefficient, solute permeability, and water permeability--were obtained using the Spiegler-Kedem equation, which accounts for the contribution of convection and diffusion to solute flux. As a result, the reflection coefficient corresponding to the fraction of solutes reflected by the membrane in convective flow was almost constant, irrespective of experimental temperature. The dependency was larger for larger solutes and membranes with smaller pore diameters. Therefore, the hindered diffusion of solutes through micropores was indicative of an activated process. Moreover, pure water permeability, after correction for the temperature effect on viscosity, also increased with experimental temperature.

  17. Use of inside-out chloroplast thylakoid membrane vesicles for studying electron transport and membrane structure

    SciTech Connect

    Atta-Asafo-Adjei, E.

    1987-01-01

    Inside-out and right-side-out thylakoid vesicles were isolated from spinach chloroplasts by aqueous-polymer two-phase partitioning following mechanical fragmentation of thylakoid membranes by Yeda press treatment. Externally added plastocyanin stimulated the whole-chain and PSI electron transport rates in the inside-out thylakoid vesicles by about 500 and 350%, respectively, compared to about 50% stimulation for both assays in the fraction enriched in right-side-out vesicles. The electron transport between PSII and PSI in inside-out thylakoid vesicles appears to be interrupted due to plastocyanin release from the thylakoids by the Yeda press treatment, but it was restored by externally added plastocyanin. Acetic anhydride chemical modification and uncoupler-induced proton release from dark-adapted membranes are probes for detecting the sequested proton domains in thylakoid membranes. Both assays were used to find out if inside-out membranes retain metastable, localized proton binding domains. Treatment of dark-maintained inside-out thylakoid membrane vesicles with ({sup 3}H)acetic anhydride showed no uncoupler-induced increase in acetylation of the 33, 24, and 18 kDa polypeptides of the oxygen-evolving-complex, indicating complete loss of the implicated proton domains in these polypeptides. The various steps in the inside-out preparation were studied to discern which steps(s) leads to the loss of the metastable domain proton pool.

  18. Investigation of ionic transport in sodium scandium phosphate (NSP) and related compounds

    NASA Astrophysics Data System (ADS)

    Bhat, Kaustubh; Blügel, Stefan; Lustfeld, Hans

    Sodium ionic conductors offer significant advantages for application in large scale energy storage systems. In this study, we investigate the different pathways available for sodium ion conduction in NSP and calculate energy barriers for ionic transport using Density Functional Theory (DFT) and the Nudged Elastic Band Method. We identify the structural parameters that reduce the energy barrier, by calculating the influence of positive and negative external pressure on the energy barrier. Lattice strain can be introduced by cation or anion substitution within the NASICON structure. We substitute the scandium atom with other trivalent atoms such as aluminium and yttrium, and calculate the resulting energy barriers. Sodium thiophosphate (Na3PS4) has previously shown about two orders of magnitude higher ionic conductivity than sodium phosphate (Na3PO4). We investigate the effect of substituting oxygen with sulphur in NSP. We acknowledge discussions with our experimental colleagues F. Tietz and M. Guin toward this work

  19. Protective effect of silymarin on viability, motility and mitochondrial membrane potential of ram sperm treated with sodium arsenite

    PubMed Central

    Eskandari, Farzaneh; Momeni, Hamid Reza

    2016-01-01

    Background: Sodium arsenite can impair male reproductive function by inducing oxidative stress. Silymarin is known as a potent antioxidant. Objective: This study was performed to investigate if silymarin can prevent the adverse effect of sodium arsenite on ram sperm viability, motility and mitochondrial membrane potential. Materials and Methods: Epidydimal spermatozoa obtained from ram were divided into five groups: 1) Spermatozoa at 0 hr, 2) spermatozoa at 180 min (control), 3) spermatozoa treated with sodium arsenite (10 μM) for 180 min, 4) spermatozoa treated with silymarin (20 μM) + sodium arsenite (10 μM) for 180 min and 5) spermatozoa treated with silymarin (20 μM) for 180 min. MTT assay and Rhodamine 123 staining were used to assess sperm viability and mitochondrial membrane potential respectively. Sperm motility was performed according to World Health Organization (WHO) guidelines. Results: Viability (p<0.01), nonprogressive motility (p<0.001) and intact mitochondrial membrane potential (p<0.001) of the spermatozoa were significantly decreased in sodium arsenite treated group compared to control group. In silymarin + sodium arsenite group, silymarin could significantly reverse the adverse effect of sodium arsenite on these sperm parameters compared to sodium arsenite group (p<0.001). In addition, the application of silymarin alone for 180 minutes could significantly increase progressively motile sperm (p<0.001) and decrease non motile sperm (p<0.01) compared to the control. Conclusion: Silymarin could compensate the adverse effect of sodium arsenite on viability, nonprogressive motility and mitochondrial membrane potential of ram sperm. PMID:27525323

  20. Mechanism of exaggerated natriuresis in hypertensive man: impaired sodium transport in the loop of henle

    PubMed Central

    Buckalew, Vardaman M.; Puschett, Jules B.; Kintzel, James E.; Goldberg, Martin

    1969-01-01

    To evaluate the effects of saline loading on distal sodium reabsorption in hypertensive man, studies were performed during both water deprivation and water diuresis in eight hypertensive subjects, and the results were compared to data obtained from similar studies in normal subjects. All hypertensive patients exhibited an enhanced excretion of filtered sodium (CNa/CIn) at any level of distal delivery of sodium compared to normal controls. Free water reabsorption (TcH2O) during hypertonic saline loading was quantitatively abnormal in the hypertensives at high levels of osmolar clearance (COsm), and also the curve of TcH2O vs. COsm leveled off above a COsm of 18 ml/min per 1.73 m2 in the hypertensive group in contrast to the normal controls in whom TcH2O showed no evidence of achieving an upper limit. Sodium depletion exaggerated the abnormality in TcH2O in hypertensives, and resulted in a positive free water clearance (CH2O) during hydropenia. During hypotonic saline loading in water diuresis, changes in free water clearance per 100 ml of glomerular filtrate (CH2O/CIn) were less at any given increment in urine flow per 100 ml of glomerular filtrate (V/CIn) in the hypertensives compared to normal controls (P < 0.001). This abnormality in CH2O/CIn in the hypertensives in conjunction with the defect in TcH2O observed during hydropenia indicates that sodium reabsorption in the loop of Henle was abnormal at any given rate of distal delivery of sodium in hypertension. Furthermore, these abnormalities in TcH2O and CH2O coincided temporally with the development of the exaggerated natriuresis. Although the distal defect in sodium transport, in large part, accounted for the augmented natriuresis in hypertension, evidence was present also for enhanced rejection of sodium in the proximal tubule during saline loading in the hypertensives. Additional studies utilizing acetazolamide which increases distal delivery of sodium without extracellular fluid volume expansion showed only

  1. Plasma membrane-localized transporter for aluminum in rice

    PubMed Central

    Xia, Jixing; Yamaji, Naoki; Kasai, Tomonari; Ma, Jian Feng

    2010-01-01

    Aluminum (Al) is the most abundant metal in the Earth's crust, but its trivalent ionic form is highly toxic to all organisms at low concentrations. How Al enters cells has not been elucidated in any organisms. Herein, we report a transporter, Nrat1 (Nramp aluminum transporter 1), specific for trivalent Al ion in rice. Nrat1 belongs to the Nramp (natural resistance-associated macrophage protein) family, but shares a low similarity with other Nramp members. When expressed in yeast, Nrat1 transports trivalent Al ion, but not other divalent ions, such as manganese, iron, and cadmium, or the Al–citrate complex. Nrat1 is localized at the plasma membranes of all cells of root tips except epidermal cells. Knockout of Nrat1 resulted in decreased Al uptake, increased Al binding to cell wall, and enhanced Al sensitivity, but did not affect the tolerance to other metals. Expression of Nrat1 is up-regulated by Al in the roots and regulated by a C2H2 zinc finger transcription factor (ART1). We therefore concluded that Nrat1 is a plasma membrane-localized transporter for trivalent Al, which is required for a prior step of final Al detoxification through sequestration of Al into vacuoles. PMID:20937890

  2. Plasma membrane-localized transporter for aluminum in rice.

    PubMed

    Xia, Jixing; Yamaji, Naoki; Kasai, Tomonari; Ma, Jian Feng

    2010-10-26

    Aluminum (Al) is the most abundant metal in the Earth's crust, but its trivalent ionic form is highly toxic to all organisms at low concentrations. How Al enters cells has not been elucidated in any organisms. Herein, we report a transporter, Nrat1 (Nramp aluminum transporter 1), specific for trivalent Al ion in rice. Nrat1 belongs to the Nramp (natural resistance-associated macrophage protein) family, but shares a low similarity with other Nramp members. When expressed in yeast, Nrat1 transports trivalent Al ion, but not other divalent ions, such as manganese, iron, and cadmium, or the Al-citrate complex. Nrat1 is localized at the plasma membranes of all cells of root tips except epidermal cells. Knockout of Nrat1 resulted in decreased Al uptake, increased Al binding to cell wall, and enhanced Al sensitivity, but did not affect the tolerance to other metals. Expression of Nrat1 is up-regulated by Al in the roots and regulated by a C2H2 zinc finger transcription factor (ART1). We therefore concluded that Nrat1 is a plasma membrane-localized transporter for trivalent Al, which is required for a prior step of final Al detoxification through sequestration of Al into vacuoles.

  3. YTPdb: a wiki database of yeast membrane transporters.

    PubMed

    Brohée, Sylvain; Barriot, Roland; Moreau, Yves; André, Bruno

    2010-10-01

    Membrane transporters constitute one of the largest functional categories of proteins in all organisms. In the yeast Saccharomyces cerevisiae, this represents about 300 proteins ( approximately 5% of the proteome). We here present the Yeast Transport Protein database (YTPdb), a user-friendly collaborative resource dedicated to the precise classification and annotation of yeast transporters. YTPdb exploits an evolution of the MediaWiki web engine used for popular collaborative databases like Wikipedia, allowing every registered user to edit the data in a user-friendly manner. Proteins in YTPdb are classified on the basis of functional criteria such as subcellular location or their substrate compounds. These classifications are hierarchical, allowing queries to be performed at various levels, from highly specific (e.g. ammonium as a substrate or the vacuole as a location) to broader (e.g. cation as a substrate or inner membranes as location). Other resources accessible for each transporter via YTPdb include post-translational modifications, K(m) values, a permanently updated bibliography, and a hierarchical classification into families. The YTPdb concept can be extrapolated to other organisms and could even be applied for other functional categories of proteins. YTPdb is accessible at http://homes.esat.kuleuven.be/ytpdb/.

  4. Core Transmembrane Domain 6 Plays a Pivotal Role in the Transport Cycle of the Sodium/Proline Symporter PutP.

    PubMed

    Bracher, Susanne; Schmidt, Claudia C; Dittmer, Sophie I; Jung, Heinrich

    2016-12-09

    Crystal structures of transporters with a LeuT-type structural fold assign core transmembrane domain 6 (TM6') a central role in substrate binding and translocation. Here, the function of TM6' in the sodium/proline symporter PutP, a member of the solute/sodium symporter family, was investigated. A complete scan of TM6' identified eight amino acids as particularly important for PutP function. Of these residues, Tyr-248, His-253, and Arg-257 impact sodium binding, whereas Arg-257 and Ala-260 may participate in interactions leading to closure of the inner gate. Furthermore, the previous suggestion of an involvement of Trp-244, Tyr-248, and Pro-252 in proline binding is further supported. In addition, substitution of Gly-245, Gly-247, and Gly-250 affects the amount of PutP in the membrane. A Cys accessibility analysis suggests an involvement of the inner half of TM6' in the formation of a hydrophilic pathway that is open to the inside in the absence of ligands and closed in the presence of sodium and proline. In conclusion, the results demonstrate that TM6' plays a central role in substrate binding and release on the inner side of the membrane also in PutP and extend the knowledge on functionally relevant amino acids in transporters with a LeuT-type structural fold.

  5. Multicomponent transport in membranes for redox flow batteries

    NASA Astrophysics Data System (ADS)

    Monroe, Charles

    2015-03-01

    Redox flow batteries (RFBs) incorporate separator membranes, which ideally prevent mixing of electrochemically active species while permitting crossover of inactive supporting ions. Understanding crossover and membrane selectivity may require multicomponent transport models that account for solute/solute interactions within the membrane, as well as solute/membrane interactions. Application of the Onsager-Stefan-Maxwell formalism allows one to account for all the dissipative phenomena that may accompany component fluxes through RFB membranes. The magnitudes of dissipative interactions (diffusional drag forces) are quantified by matching experimentally established concentration transients with theory. Such transients can be measured non-invasively using DC conductometry, but the accuracy of this method requires precise characterization of the bulk RFB electrolytes. Aqueous solutions containing both vanadyl sulfate (VOSO4) and sulfuric acid (H2SO4) are relevant to RFB technology. One of the first precise characterizations of aqueous vanadyl sulfate has been implemented and will be reported. To assess the viability of a separator for vanadium RFB applications with cell-level simulations, it is critical to understand the tendencies of various classes of membranes to absorb (uptake) active species, and to know the relative rates of active-species and supporting-electrolyte diffusion. It is also of practical interest to investigate the simultaneous diffusion of active species and supports, because interactions between solutes may ultimately affect the charge efficiency and power efficiency of the RFB system as a whole. A novel implementation of Barnes's classical model of dialysis-cell diffusion [Physics 5:1 (1934) 4-8] is developed to measure the binary diffusion coefficients and sorption equilibria for single solutes (VOSO4 or H2SO4) in porous membranes and cation-exchange membranes. With the binary diffusion and uptake measurement in hand, a computer simulation that

  6. Numerical modeling transport phenomena in proton exchange membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Suh, DongMyung

    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

  7. Flexible oligocholate foldamers as membrane transporters and their guest-dependent transport mechanism.

    PubMed

    Zhang, Shiyong; Zhao, Yan

    2012-01-14

    Dimeric, trimeric, and tetrameric oligocholates with flexible 4-aminobutyroyl spacers caused the efflux of hydrophilic molecules such as carboxyfluorescein (CF) and glucose from POPC/POPG liposomes. Transport was greatly suppressed across higher-melting DPPC membranes. Lipid-mixing assays and dynamic light scattering (DLS) indicated that the liposomes were intact during the transport. Kinetic analysis supported the involvement of monomeric species in the rate-limiting step of CF transport, consistent with a carrier-based mechanism. Glucose transport, on the other hand, displayed a highly unusual zero-order dependence on the oligocholate concentration at low loading of the transporter. Different selectivity was observed in the oligocholate transporters depending on the guest involved.

  8. [Conus venoms: a source of toxins which interact with membrane- potential-dependent sodium channels].

    PubMed

    Le Gall, F; Favreau, P; Benoit, E; Richard, G; Molgó, J

    1999-01-01

    Marine snails of the genus Conus, as they are carnivorous predators, have a venom apparatus used to capture their prey. The toxins contained in the venoms of Conidae, called conotoxins, are of a particular high degree of diversity and represent powerful tools in the neuroscience field. Indeed, these toxins specifically bind with a high affinity to receptors and ionic channels. Therefore, they provide original pharmacological tools which receive increasing investigation both to identify and study some functions of the nervous systems and to characterize new types and closely related subtypes of receptors or ionic channels. The voltage-gated sodium channel, because of its fundamental role in cell membrane excitability, is the specific target of a large number of animal and vegetal toxins. Actually, at least seven toxin receptor sites have been identified on this channel-protein. These toxins, and in particular conotoxins, are used to precise the role of different types and/or closely related subtypes of sodium channels in the peripheral and central nervous systems. The focus of the present review is to summarize our current knowledge of the consequences of physiological interactions between different conotoxin families and sodium channels.

  9. The plasma membrane transport systems and adaptation to salinity.

    PubMed

    Mansour, Mohamed Magdy F

    2014-11-15

    Salt stress represents one of the environmental challenges that drastically affect plant growth and yield. Evidence suggests that glycophytes and halophytes have a salt tolerance mechanisms working at the cellular level, and the plasma membrane (PM) is believed to be one facet of the cellular mechanisms. The responses of the PM transport proteins to salinity in contrasting species/cultivars were discussed. The review provides a comprehensive overview of the recent advances describing the crucial roles that the PM transport systems have in plant adaptation to salt. Several lines of evidence were presented to demonstrate the correlation between the PM transport proteins and adaptation of plants to high salinity. How alterations in these transport systems of the PM allow plants to cope with the salt stress was also addressed. Although inconsistencies exist in some of the information related to the responses of the PM transport proteins to salinity in different species/cultivars, their key roles in adaptation of plants to high salinity is obvious and evident, and cannot be precluded. Despite the promising results, detailed investigations at the cellular/molecular level are needed in some issues of the PM transport systems in response to salinity to further evaluate their implication in salt tolerance.

  10. Modular structure of sodium-coupled bicarbonate transporters.

    PubMed

    Boron, Walter F; Chen, Liming; Parker, Mark D

    2009-06-01

    Mammalian genomes contain 10 SLC4 genes that, between them, encode three Cl-HCO(3) exchangers, five Na(+)-coupled HCO(3) transporters (NCBTs), one reported borate transporter, and what is reported to be a fourth Cl-HCO(3) exchanger. The NCBTs are expressed throughout the body and play important roles in maintaining intracellular and whole-body pH, as well as contributing to transepithelial transport processes. The importance of NCBTs is underscored by the genetic association of dysfunctional NCBT genes with blindness, deafness, epilepsy, hypertension and metal retardation. Key to understanding the action and regulation of NCBTs is an appreciation of the diversity of NCBT gene products. The transmembrane domains of human NCBT paralogs are 50-84% identical to each other at the amino acid level, and are capable of a diverse range of actions, including electrogenic Na/HCO(3) cotransport (i.e. NBCe1 and NBCe2) and electroneutral Na/HCO(3) cotransport (i.e. NBCn1 and NBCn2), as well as Na(+)-dependent Cl-HCO(3) exchange (i.e. NDCBE). Furthermore, by the use of alternative promoters and alternative-splicing events, individual SLC4 genes have the potential to generate multiple splice variants (as many as 16 in the case of NBCn1), each of which could have unique temporal and spatial patterns of distribution, unitary transporter activity (i.e. flux mediated by one molecule), array of protein-binding partners, and complement of regulatory stimuli. In the first section of this review, we summarize our present knowledge of the function and distribution of mammalian NCBTs and their multiple variants. In the second section of this review we consider the molecular consequences of NCBT variation.

  11. Proton transport and the water environment in nafion fuel cell membranes and AOT reverse micelles.

    PubMed

    Spry, D B; Goun, A; Glusac, K; Moilanen, David E; Fayer, M D

    2007-07-04

    The properties of confined water and diffusive proton-transfer kinetics in the nanoscopic water channels of Nafion fuel cell membranes at various hydration levels are compared to water in a series of well-characterized AOT reverse micelles with known water nanopool sizes using the photoacid pyranine as a molecular probe. The side chains of Nafion are terminated by sulfonate groups with sodium counterions that are arrayed along the water channels. AOT has sulfonate head groups with sodium counterions that form the interface with the reverse micelle's water nanopool. The extent of excited-state deprotonation is observed by steady-state fluorescence measurements. Proton-transfer kinetics and orientational relaxation are measured by time-dependent fluorescence using time-correlated single photon counting. The time dependence of deprotonation is related to diffusive proton transport away from the photoacid. The fluorescence reflecting the long time scale proton transport has an approximately t-0.8 power law decay in contrast to bulk water, which has a t-3/2 power law. For a given hydration level of Nafion, the excited-state proton transfer and the orientational relaxation are similar to those observed for a related size AOT water nanopool. The effective size of the Nafion water channels at various hydration levels are estimated by the known size of the AOT reverse micelles that display the corresponding proton-transfer kinetics and orientational relaxation.

  12. Degradation of poly(ether sulfone)/polyvinylpyrrolidone membranes by sodium hypochlorite: insight from advanced electrokinetic characterizations.

    PubMed

    Hanafi, Yamina; Szymczyk, Anthony; Rabiller-Baudry, Murielle; Baddari, Kamel

    2014-11-18

    Poly(ether sulfone) (PES)/polyvinylpyrrolidone (PVP) membranes are widely used in various industrial fields such as drinking water production and in the dairy industry. However, the use of oxidants to sanitize the processing equipment is known to impair the integrity and lifespan of polymer membranes. In this work we showed how thorough electrokinetic measurements can provide essential information regarding the mechanism of degradation of PES/PVP membranes by sodium hypochlorite. Tangential streaming current measurements were performed with ultrafiltration and nanofiltration PES/PVP membranes for various aging times. The electrokinetic characterization of membranes was complemented by FTIR-ATR spectroscopy. Results confirmed that sodium hypochlorite induces the degradation of both PES and PVP. This latter is easily oxidized by sodium hypochlorite, which leads to an increase in the negative charge density of the membrane due to the formation of carboxylic acid groups. The PVP was also found to be partly released from the membrane with aging time. Thanks to the advanced electrokinetic characterization implemented in this work it was possible for the first time to demonstrate that two different mechanisms are involved in the degradation of PES. Phenol groups were first formed as a result of the oxidation of PES aromatic rings by substitution of hydrogen by hydroxyl radicals. For more severe aging conditions, this membrane degradation mechanism was followed by the formation of sulfonic acid functions, thus indicating a second degradation process through scission of PES chains.

  13. Regulation of membrane excitability: a convergence on voltage-gated sodium conductance.

    PubMed

    Lin, Wei-Hsiang; Baines, Richard A

    2015-02-01

    The voltage-gated sodium channel (Nav) plays a key role in regulation of neuronal excitability. Aberrant regulation of Nav expression and/or function can result in an imbalance in neuronal activity which can progress to epilepsy. Regulation of Nav activity is achieved by coordination of a multitude of mechanisms including RNA alternative splicing and translational repression. Understanding of these regulatory mechanisms is complicated by extensive genetic redundancy: the mammalian genome encodes ten Navs. By contrast, the genome of the fruitfly, Drosophila melanogaster, contains just one Nav homologue, encoded by paralytic (DmNa v ). Analysis of splicing in DmNa v shows variants exhibit distinct gating properties including varying magnitudes of persistent sodium current (INaP). Splicing by Pasilla, an identified RNA splicing factor, alters INaP magnitude as part of an activity-dependent mechanism. Enhanced INaP promotes membrane hyperexcitability that is associated with seizure-like behaviour in Drosophila. Nova-2, a mammalian Pasilla homologue, has also been linked to splicing of Navs and, moreover, mouse gene knockouts display seizure-like behaviour.Expression level of Navs is also regulated through a mechanism of translational repression in both flies and mammals. The translational repressor Pumilio (Pum) can bind to Na v transcripts and repress the normal process of translation, thus regulating sodium current (INa) density in neurons. Pum2-deficient mice exhibit spontaneous EEG abnormalities. Taken together, aberrant regulation of Nav function and/or expression is often epileptogenic. As such, a better understanding of regulation of membrane excitability through RNA alternative splicing and translational repression of Navs should provide new leads to treat epilepsy.

  14. Bioinformatic Analyses of Integral Membrane Transport Proteins Encoded Within the Genome of the Planctomycetes species, Rhodopirellula baltica

    PubMed Central

    Paparoditis, Philipp; Vastermark, Ake; Le, Andrew J.; Fuerst, John A.; Saier, Milton H.

    2013-01-01

    Rhodopirellula baltica (R. baltica) is a Planctomycete, known to have intracellular membranes. Because of its unusual cell structure and ecological significance, we have conducted comprehensive analyses of its transmembrane transport proteins. The complete proteome of R. baltica was screened against the Transporter Classification Database (TCDB) to identify recognizable integral membrane transport proteins. 342 proteins were identified with a high degree of confidence, and these fell into several different classes. R. baltica encodes in its genome channels (12%), secondary carriers (33%), and primary active transport proteins (41%) in addition to classes represented in smaller numbers. Relative to most non-marine bacteria, R. baltica possesses a larger number of sodium-dependent symporters but fewer proton-dependent symporters, and it has dimethylsulfoxide (DMSO) and trimethyl-amine-oxide (TMAO) reductases, consistent with its Na+-rich marine environment. R. baltica also possesses a Na+-translocating NADH:quinone dehydrogenase (Na+-NDH), a Na+ efflux decarboxylase, two Na+-exporting ABC pumps, two Na+-translocating F-type ATPases, two Na+:H+ antiporters and two K+:H+ antiporters. Flagellar motility probably depends on the sodium electrochemical gradient. Surprisingly, R. baltica also has a complete set of H+-translocating electron transport complexes similar to those present in β-proteobacteria and eukaryotic mitochondria. The transport proteins identified proved to be typical of the bacterial domain with little or no indication of the presence of eukaryotic-type transporters. However, novel functionally uncharacterized multispanning membrane proteins were identified, some of which are found only in Rhodopirellula species, but others of which are widely distributed in bacteria. The analyses lead to predictions regarding the physiology, ecology and evolution of R. baltica. PMID:23969110

  15. Clay and pillard clay membranes: Synthesis, characterization and transport properties

    NASA Astrophysics Data System (ADS)

    Vercauteren, Sven

    In this work, the preparation and characterization of ceramic multilayer membranes with an Alsb2Osb3-pillared montmorillonite (Al-PILC) and a Laponite separating layer have been studied. Al-PILC is a pillared clay prepared by intercalation of polyoxo cations of aluminium between the montmorillonite clay sheets, followed by a thermal treatment (400sp°C) to obtain rigid oxide pillars. The free spacing between the clay plates is about 0.8 nm. Laponite is a synthetic clay with a pore structure formed by the stacking of very small clay plates. To deposit an Al-PILC top layer on a macro- or mesoporous aluminiumoxide support membrane, two preparation routes were considered. According to the standard preparation route of a pillared clay, the easiest way is to use a suspension of clay mixed with the pillaring solution in which the support membrane is dipped. However, it is not possible to deposit uniform and crack-free top layers in this way because of the formation of unstable suspensions. A second preparation route is based on an indirect pillaring procedure. By dipping a support membrane in a stable clay suspension, a thin clay film is deposited in a first step. Pillaring is achieved via immersion of the supported clay film in the pillaring solution in a second step. After a washing procedure, the membrane is dried and calcined at 400sp°C. Laponite membranes were simply prepared by dipping a support membrane in a suspension of this synthetic clay in water. Afterwards a drying at room temperature and a calcination at 400 ar 500sp°C is performed. Both membrane types were tested for gas separation and pervaporation purposes. Transport of permanent gases (He, N2) occurs by means of Knudsen diffusion. Diffusion is kinetically controlled and for a binary mixture, the maximum separation factor is determined by the difference in molecular weight of both components. From pervaporation experiments with water/alcohol mixtures it was found that Al-PILC membranes can be used for

  16. Myosin VI is required for targeted membrane transport during cytokinesis.

    PubMed

    Arden, Susan D; Puri, Claudia; Au, Josephine Sui-Yan; Kendrick-Jones, John; Buss, Folma

    2007-12-01

    Myosin VI plays important roles in endocytic and exocytic membrane-trafficking pathways in cells. Because recent work has highlighted the importance of targeted membrane transport during cytokinesis, we investigated whether myosin VI plays a role in this process during cell division. In dividing cells, myosin VI undergoes dramatic changes in localization: in prophase, myosin VI is recruited to the spindle poles; and in cytokinesis, myosin VI is targeted to the walls of the ingressing cleavage furrow, with a dramatic concentration in the midbody region. Furthermore, myosin VI is present on vesicles moving into and out of the cytoplasmic bridge connecting the two daughter cells. Inhibition of myosin VI activity by small interfering RNA (siRNA)-mediated knockdown or by overexpression of dominant-negative myosin VI tail leads to a delay in metaphase progression and a defect in cytokinesis. GAIP-interacting protein COOH terminus (GIPC), a myosin VI binding partner, is associated with the function(s) of myosin VI in dividing cells. Loss of GIPC in siRNA knockdown cells results in a more than fourfold increase in the number of multinucleated cells. Our results suggest that myosin VI has novel functions in mitosis and that it plays an essential role in targeted membrane transport during cytokinesis.

  17. Myosin VI Is Required for Targeted Membrane Transport during Cytokinesis

    PubMed Central

    Arden, Susan D.; Puri, Claudia; Au, Josephine Sui-Yan; Kendrick-Jones, John

    2007-01-01

    Myosin VI plays important roles in endocytic and exocytic membrane-trafficking pathways in cells. Because recent work has highlighted the importance of targeted membrane transport during cytokinesis, we investigated whether myosin VI plays a role in this process during cell division. In dividing cells, myosin VI undergoes dramatic changes in localization: in prophase, myosin VI is recruited to the spindle poles; and in cytokinesis, myosin VI is targeted to the walls of the ingressing cleavage furrow, with a dramatic concentration in the midbody region. Furthermore, myosin VI is present on vesicles moving into and out of the cytoplasmic bridge connecting the two daughter cells. Inhibition of myosin VI activity by small interfering RNA (siRNA)-mediated knockdown or by overexpression of dominant-negative myosin VI tail leads to a delay in metaphase progression and a defect in cytokinesis. GAIP-interacting protein COOH terminus (GIPC), a myosin VI binding partner, is associated with the function(s) of myosin VI in dividing cells. Loss of GIPC in siRNA knockdown cells results in a more than fourfold increase in the number of multinucleated cells. Our results suggest that myosin VI has novel functions in mitosis and that it plays an essential role in targeted membrane transport during cytokinesis. PMID:17881731

  18. Carotenoid binding to proteins: Modeling pigment transport to lipid membranes.

    PubMed

    Reszczynska, Emilia; Welc, Renata; Grudzinski, Wojciech; Trebacz, Kazimierz; Gruszecki, Wieslaw I

    2015-10-15

    Carotenoid pigments play numerous important physiological functions in human organism. Very special is a role of lutein and zeaxanthin in the retina of an eye and in particular in its central part, the macula lutea. In the retina, carotenoids can be directly present in the lipid phase of the membranes or remain bound to the protein-pigment complexes. In this work we address a problem of binding of carotenoids to proteins and possible role of such structures in pigment transport to lipid membranes. Interaction of three carotenoids, beta-carotene, lutein and zeaxanthin with two proteins: bovine serum albumin and glutathione S-transferase (GST) was investigated with application of molecular spectroscopy techniques: UV-Vis absorption, circular dichroism and Fourier transform infrared spectroscopy (FTIR). Interaction of pigment-protein complexes with model lipid bilayers formed with egg yolk phosphatidylcholine was investigated with application of FTIR, Raman imaging of liposomes and electrophysiological technique, in the planar lipid bilayer models. The results show that in all the cases of protein and pigment studied, carotenoids bind to protein and that the complexes formed can interact with membranes. This means that protein-carotenoid complexes are capable of playing physiological role in pigment transport to biomembranes.

  19. Transport properties of tomato fruit tonoplast membrane vesicles

    SciTech Connect

    Oleski, N.; Joyce, D.; Osteryoung, K.; Bennett, A.B.

    1986-04-01

    To study the role of the tonoplast in tomato fruit development, methods were developed to isolate sealed tonoplast membrane vesicles. Low density (approx. 1.23 g/cc) membrane vesicles they found to possess a NO/sub 3//sup -/-sensitive H/sup +/-translocating ATPase. The properties of this H/sup +/-ATPase are similar to those described for other tonoplast H/sup +/-ATPases. ATP-dependent Ca/sup + +/ transport into the vesicles proceeded by two mechanisms, one operative at low Ca/sup + +/ concentrations (1 ..mu..M) and inhibited by vanadate, and the other operative at high Ca/sup + +/ concentrations (10 ..mu..M) and inhibited by NO/sub 3//sup -/. Their present results indicate that the high affinity (vanadate-sensitive) Ca/sup + +/ transporter resides in E.R. membrane that contaminates the tonoplast preparation. Citrate uptake in tonoplast vesicles is stimulated by ATP and inhibited by NO/sub 3//sup -/ suggesting that citrate uptake is driven indirectly by the H/sup +/-ATPase. The substrate for sugar uptake is UDP-glucose resulting in the appearance of sucrose inside the tonoplast vesicle. No evidence for ATP stimulation of glucose, fructose, or sucrose uptake was observed.

  20. Cellular Transport and Membrane Dynamics of the Glycine Receptor

    PubMed Central

    Dumoulin, Andrea; Triller, Antoine; Kneussel, Matthias

    2009-01-01

    Regulation of synaptic transmission is essential to tune individual-to-network neuronal activity. One way to modulate synaptic strength is to regulate neurotransmitter receptor numbers at postsynaptic sites. This can be achieved either through plasma membrane insertion of receptors derived from intracellular vesicle pools, a process depending on active cytoskeleton transport, or through surface membrane removal via endocytosis. In parallel, lateral diffusion events along the plasma membrane allow the exchange of receptor molecules between synaptic and extrasynaptic compartments, contributing to synaptic strength regulation. In recent years, results obtained from several groups studying glycine receptor (GlyR) trafficking and dynamics shed light on the regulation of synaptic GlyR density. Here, we review (i) proteins and mechanisms involved in GlyR cytoskeletal transport, (ii) the diffusion dynamics of GlyR and of its scaffolding protein gephyrin that control receptor numbers, and its relationship with synaptic plasticity, and (iii) adaptative changes in GlyR diffusion in response to global activity modifications, as a homeostatic mechanism. PMID:20161805

  1. Interactions of connexins with other membrane channels and transporters

    PubMed Central

    Chanson, Marc; Kotsias, Basilio A.; Peracchia, Camillo; O’Grady, Scott M.

    2009-01-01

    Cell-to-cell communication through gap junctions exists in most animal cells and is essential for many important biological processes including rapid transmission of electric signals to coordinate contraction of cardiac and smooth muscle, the intercellular propagation of Ca2+ waves and synchronization of physiological processes between adjacent cells within a tissue. Recent studies have shown that connexins can have either direct or indirect interactions with other plasma membrane ion channels or membrane transport proteins with important functional consequences. For example, in tissues most severely affected by cystic fibrosis, activation of the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) has been shown to influence connexin function. Moreover, a direct interaction between Cx45.6 and the Major Intrinsic Protein/AQP0 in lens appears to influence the process of cell differentiation whereas interactions between aquaporin 4 (AQP4) and Cx43 in mouse astrocytes may coordinate the intercellular movement of ions and water between astrocytes. In this review, we discuss evidence supporting interactions between connexins and membrane channels/transporters including CFTR, aquaporins, ionotropic glutamate receptors, and between pannexin1, another class of putative gap-junction-forming proteins, and Kvβ3, a regulatory β-subunit of voltage gated potassium channels. Although the precise molecular nature of these interactions has yet to be defined, their consequences may be critical for normal tissue homeostasis. PMID:17475311

  2. A novel strategy for the treatment of diabetes mellitus - sodium glucose co-transport inhibitors

    PubMed Central

    Niazi, Asfandyar Khan; Niazi, Saad Hameed

    2010-01-01

    Background: Diabetes is one of the most common chronic diseases, affecting almost 3 million in Canada alone and is characterized by increased blood glucose levels. Treatment varies from lifestyle changes to oral anti-diabetics and/or insulin. Sodium glucose co-transport inhibitors may offer promising treatment for patients suffering from diabetes. The inhibitors act by increasing the loss of glucose in urine by decreasing the reabsorption of glucose from the proximal tubules of nephrons. Aims: The aim of this review was to assess the efficacy of sodium glucose co-transport inhibitors in the treatment of diabetes as well as any adverse effects. Materials and Methods: Databases such as MEDLINE, COCHRANE and EMBASE were systematically searched for literature on the efficacy of sodium glucose co-transport inhibitors in improving the glycemic control of patients with diabetes. Results: Research showed that sodium glucose co-transport inhibitors significantly decreased blood glucose levels by increasing glucosuria. Due to the diuretic effects of these inhibitors, diabetic patients who were suffering from hypertension showed a decrease in blood pressure. The caloric loss associated with these inhibitors resulted in weight loss as well. The most common adverse effect seen in patients on these medications was mycotic infection of the urinary or genital tract. Conclusion: Sodium glucose co-transport inhibitors may be an effective line of treatment for diabetes. Although short-term research has shown these drugs to be safe and well-tolerated, studies should be conducted to assess the long-term effects of these drugs. PMID:22558567

  3. Effects of changes in membrane sodium flux on virulence gene expression in Vibrio cholerae

    PubMed Central

    Häse, Claudia C.; Mekalanos, John J.

    1999-01-01

    The expression of several virulence factors of Vibrio cholerae is coordinately regulated by the ToxT molecule and the membrane proteins TcpP/H and ToxR/S, which are required for toxT transcription. To identify proteins that negatively affect toxT transcription, we screened transposon mutants of V. cholerae carrying a chromosomally integrated toxT∷lacZ reporter construct for darker blue colonies on media containing 5-bromo-4-chlor-3-indolyl β-d galactoside (X-gal). Two mutants had transposon insertions in a region homologous to the nqr gene cluster of Vibrio alginolyticus, encoding a sodium-translocating NADH–ubiquinone oxidoreductase (NQR). In V. alginolyticus, NQR is a respiration-linked Na+ extrusion pump generating a sodium motive force that can be used for solute import, ATP synthesis, and flagella rotation. Inhibition of NQR enzyme function in V. cholerae by the specific inhibitor 2-n-heptyl-4-hydroxyquinoline N-oxide (HQNO) resulted in elevated toxT∷lacZ activity. Increased toxT∷lacZ expression in an nqr mutant strain compared with the parental strain was observed when the TcpP/H molecules alone were strongly expressed, suggesting that the negative effect of the NQR complex on toxT transcription is mediated through TcpP/H. However, the ability of the TcpP/H proteins to activate the toxT∷lacZ reporter construct was greatly diminished in the presence of high NaCl concentrations in the growth medium. The flagellar motor of V. cholerae appears to be driven by a sodium motive force, and modulation of flagella rotation by inhibitory drugs, high media viscosity, or specific mutations resulted in increases of toxT∷lacZ expression. Thus, the regulation of the main virulence factors of V. cholerae appears to be modulated by endogenous and exogenous sodium levels in a complex way. PMID:10077658

  4. Electrogenicity of phosphate transport by renal brush-border membranes.

    PubMed Central

    Béliveau, R; Ibnoul-Khatib, H

    1988-01-01

    Phosphate uptake by rat renal brush-border membrane vesicles was studied under experimental conditions where transmembrane electrical potential (delta psi) could be manipulated. Experiments were performed under initial rate conditions to avoid complications associated with the dissipation of ion gradients. First, phosphate uptake was shown to be strongly affected by the nature of Na+ co-anions, the highest rates of uptake being observed with 100 mM-NaSCN (1.010 +/- 0.086 pmol/5 s per micrograms of protein) and the lowest with 50 mM-Na2SO4 (0.331 +/- 0.046 pmol/5 s per micrograms of protein). Anion substitution studies showed that potency of the effect of the co-anions was in the order thiocyanate greater than nitrate greater than chloride greater than isethionate greater than gluconate greater than sulphate, which correlates with the known permeability of the membrane to these anions and thus to the generation of transmembrane electrical potentials of decreasing magnitude (inside negative). The stimulation by ion-diffusion-induced potential was observed from pH 6.5 to 8.5, indicating that the transport of both monovalent and divalent phosphate was affected. In addition, inside-negative membrane potentials were generated by valinomycin-induced diffusion of K+ from K+-loaded vesicles and showed a 57% stimulation of phosphate uptake, at pH 7.5. Similar experiments with H+-loaded vesicles, in the presence of carbonyl cyanide m-chlorophenylhydrazone gave a 50% stimulation compared with controls. Inside-positive membrane potentials were also induced by reversal of the K+ gradient (outside greater than inside) in the presence of valinomycin and gave 58% inhibition of phosphate uptake. The membrane-potential dependency of phosphate uptake was finally analysed under thermodynamic equilibrium, and a stimulation by inside-negative potential was observed. The transport of phosphate was thus driven against a concentration gradient by a membrane potential, implicating the net

  5. Sodium-glucose co-transporter 2 inhibitors: from apple tree to 'Sweet Pee'.

    PubMed

    Hardman, Timothy C; Rutherford, Peter; Dubrey, Simon W; Wierzbicki, Anthony S

    2010-01-01

    The sodium-glucose co-transporter 2 (SGLT2), located in the plasma membrane of cells lining the proximal tubule, facilitates the reabsorbtion of glucose in the kidney. Inhibition of SGLT2 has the potential to reduce blood glucose and represents an opportune target for managing blood glucose. By promoting the excretion of glucose, SGLT2 inhibitors are the first anti-diabetic treatment to target the removal rather than the metabolic redirection of glucose. Their mechanism of action is independent of that of endogenous insulin status and thus provides a means of managing plasma glucose irrespective of a patient's glycaemic status or treatments being used in combination. Several candidate SGLT2 inhibitors based on the core glucoside structure of phlorizin are currently being developed, of which, the metabolically more stable aromatic and heteroaromatic C-glucosides have demonstrated the most promising preclinical and clinical data. The inhibition of SGLT2 by messenger antisense technology is also being investigated. Current indications suggest that short-term benefits, in terms of HbA1(c) reductions, are modest and it remains to be seen whether encouraging exogenous glucose disposal will result in long term patient benefits in terms of returning metabolic balance or even weight loss. Indications are that clinical efficacy will be greater with molecules based on an O-glucoside structure. Concerns have been raised over the safety of these agents, particularly a possible predisposition to urinary tract infections, but these concerns have yet to be confirmed in clinical studies. Clinical development programs will need to establish those patients most likely to benefit from inhibition of SGLT2.

  6. Free Energy Wells and Barriers to Ion Transport Across Membranes

    NASA Astrophysics Data System (ADS)

    Rempe, Susan

    2014-03-01

    The flow of ions across cellular membranes is essential to many biological processes. Ion transport is also important in synthetic materials used as battery electrolytes. Transport often involves specific ions and fast conduction. To achieve those properties, ion conduction pathways must solvate specific ions by just the ``right amount.'' The right amount of solvation avoids ion traps due to deep free energy wells, and avoids ion block due to high free energy barriers. Ion channel proteins in cellular membranes demonstrate this subtle balance in solvation of specific ions. Using ab initio molecular simulations, we have interrogated the link between binding site structure and ion solvation free energies in biological ion binding sites. Our results emphasize the surprisingly important role of the environment that surrounds ion-binding sites for fast transport of specific ions. We acknowledge support from Sandia's LDRD program. Sandia National Labs is a multi-program laboratory operated by Sandia Corp., a wholly owned subsidiary of Lockheed Martin Corp., for the US DOE's NNSA under contract DE-AC04-94AL85000.

  7. Amiloride transport in rabbit renal brush-border membrane vesicles

    SciTech Connect

    Wright, S.H.; Wunz, T.M.

    1989-03-01

    Rabbit renal brush-border membrane vesicles (BBMV) were used to study amiloride transport across the luminal membrane of proximal tubular cells. An outwardly directed H+ gradient (pHi 6.0; pHo 7.5) stimulated 8 microM (/sup 14/C)-amiloride uptake into BBMV and supported a transient active accumulation of substrate consistent with the presence of an amiloride-H+ exchange process. Uptake was inhibited, in the presence or absence of a pH gradient, by 1 mM unlabeled amiloride or 20 mM tetraethylammonium (TEA). Amiloride transport was not directly affected by the presence of 100 mM Na+ in the extravesicular medium, suggesting that Na-H exchange did not mediate amiloride flux. Amiloride transport was a saturable process with a maximal flux (under pH gradient conditions) of 3 nmol.mg-1.min-1 and an apparent Kt of 8 microM. TEA acted as a competitive inhibitor of this process with an apparent Ki of approximately 80 microM, similar to the Kt of TEA transport via the TEA-H+ exchanger. Likewise, amiloride acted as a competitive inhibitor of TEA uptake with an apparent Ki of approximately 11 microM. Preloading BBMV with 1-2 mM TEA stimulated the rate of amiloride uptake and supported a transient active accumulation of amiloride. We conclude that amiloride and TEA are transported by a common pathway in BBMV, which involves a carrier-mediated exchange with H+ and which may play a role in the tubular secretion of these compounds.

  8. Renal sodium transport in renin-deficient Dahl salt-sensitive rats.

    PubMed

    Pavlov, Tengis S; Levchenko, Vladislav; Ilatovskaya, Daria V; Moreno, Carol; Staruschenko, Alexander

    2016-07-01

    The Dahl salt-sensitive rat is a well-established model of salt-sensitive hypertension. The goal of this study was to assess the expression and activity of renal sodium channels and transporters in the renin-deficient salt-sensitive rat. Renin knockout (Ren(-/-)) rats created on the salt-sensitive rat background were used to investigate the role of renin in the regulation of ion transport in salt-sensitive hypertension. Western blotting and patch-clamp analyses were utilized to assess the expression level and activity of Na(+) transporters. It has been described previously that Ren(-/-) rats exhibit severe kidney underdevelopment, polyuria, and lower body weight and blood pressure compared to their wild-type littermates. Here we found that renin deficiency led to decreased expression of sodium-hydrogen antiporter (NHE3), the Na(+)/H(+) exchanger involved in Na(+) absorption in the proximal tubules, but did not affect the expression of Na-K-Cl cotransporter (NKCC2), the main transporter in the loop of Henle. In the distal nephron, the expression of sodium chloride cotransporter (NCC) was lower in Ren(-/-) rats. Single-channel patch clamp analysis detected decreased ENaC activity in Ren(-/-) rats which was mediated via changes in the channel open probability. These data illustrate that renin deficiency leads to significant dysregulation of ion transporters. © The Author(s) 2016.

  9. Apical membrane permeability and kinetic properties of the sodium pump in rabbit urinary bladder.

    PubMed Central

    Lewis, S A; Wills, N K

    1983-01-01

    Previous studies have shown that aldosterone stimulates the rate of Na+ transport across the rabbit urinary bladder epithelium by increasing the apical membrane permeability to Na+. Paradoxically, ion-sensitive and conventional micro-electrode measurements demonstrated that intracellular Na+ activity aiNa+ was essentially unchanged by aldosterone, i.e. aiNa+ was constant regardless of the rate of Na+ transport. The present study was designed to resolve this apparent contradiction. The effects of elevated, endogenous aldosterone levels produced by low-Na+ diet (Lewis & Diamond, 1976) on urinary bladder Na+ transport were investigated in vitro using Ussing-type chambers and intracellular conventional and ion-sensitive microelectrodes. Apical membrane selectivity and kinetics of the Na+ pump were assessed as a function of hormone stimulation. The aldosterone-stimulated increase in Na+ transport was accounted for by increases in both the relative selective permeability of the apical membrane to Na+ and an increase in its absolute Na+ permeability. The kinetics of the Na+ pump were evaluated electrically by loading the cells with Na+ (monitored with Na+-sensitive micro-electrodes) or alternatively by manipulating serosal solution K+ concentration and measuring changes in the basolateral membrane electromotive forces and resistance. From these measurements the current generated by the pump was calculated as a function of intracellular Na+ or extracellular K+. The kinetics of the pump were not altered by aldosterone. A model of highly co-operative binding estimated Km for Na+ as 14.2 mM and 2.3 mM for K+. Hill coefficients for these ions were 2.8 and 1.8, respectively, consistent with a pump stoichiometry of 3 Na+ to 2 K+. The kinetic properties of the Na-K pump indicate that physiological levels of aiNa+ are poised at the foot of a step kinetic curve which energetically favours Na+ extrusion. PMID:6312027

  10. Quantized Water Transport: Ideal Desalination through Graphyne-4 Membrane

    NASA Astrophysics Data System (ADS)

    Zhu, Chongqin; Li, Hui; Zeng, Xiao Cheng; Wang, E. G.; Meng, Sheng

    2013-11-01

    Graphyne sheet exhibits promising potential for nanoscale desalination to achieve both high water permeability and salt rejection rate. Extensive molecular dynamics simulations on pore-size effects suggest that γ-graphyne-4, with 4 acetylene bonds between two adjacent phenyl rings, has the best performance with 100% salt rejection and an unprecedented water permeability, to our knowledge, of ~13 L/cm2/day/MPa, 3 orders of magnitude higher than prevailing commercial membranes based on reverse osmosis, and ~10 times higher than the state-of-the-art nanoporous graphene. Strikingly, water permeability across graphyne exhibits unexpected nonlinear dependence on the pore size. This counter-intuitive behavior is attributed to the quantized nature of water flow at the nanoscale, which has wide implications in controlling nanoscale water transport and designing highly effective membranes.

  11. Quantized Water Transport: Ideal Desalination through Graphyne-4 Membrane

    PubMed Central

    Zhu, Chongqin; Li, Hui; Zeng, Xiao Cheng; Wang, E. G.; Meng, Sheng

    2013-01-01

    Graphyne sheet exhibits promising potential for nanoscale desalination to achieve both high water permeability and salt rejection rate. Extensive molecular dynamics simulations on pore-size effects suggest that γ-graphyne-4, with 4 acetylene bonds between two adjacent phenyl rings, has the best performance with 100% salt rejection and an unprecedented water permeability, to our knowledge, of ~13 L/cm2/day/MPa, 3 orders of magnitude higher than prevailing commercial membranes based on reverse osmosis, and ~10 times higher than the state-of-the-art nanoporous graphene. Strikingly, water permeability across graphyne exhibits unexpected nonlinear dependence on the pore size. This counter-intuitive behavior is attributed to the quantized nature of water flow at the nanoscale, which has wide implications in controlling nanoscale water transport and designing highly effective membranes. PMID:24196437

  12. Study of transport through an electro responsive polymer membrane

    NASA Astrophysics Data System (ADS)

    Das, D.; Datta, A.; Contractor, A. Q.

    2015-02-01

    Conducting polymers have been used widely for development of several electronic, sensing devices because of its electro active nature. In the present work porous polycarbonate (PC) support was coated with a thin gold layer. An electrochemically synthesized polyaniline (PANI) film was deposited on gold coated PC and characterisation was done by field emission gun scanning electron microscopy (FEG-SEM), transmission electron microscopy (TEM) and atomic force microscopy (AFM). For measuring the concentration of potassium ion (K+) inductively coupled plasma atomic emission spectrometry (ICP-AES) was used. Potassium ion transport across PANI membrane at various potential showed the gradual opening of the coiled PANI. In this work an effort has been given to picture the situation in the membrane electrolyte junction on application of potential.

  13. A new mechanism for membrane iron transport in Pseudomonas aeruginosa.

    PubMed

    Schalk, I J; Abdallah, M A; Pattus, F

    2002-08-01

    Various biochemical and biophysical studies have demonstrated the existence of a novel iron-uptake mechanism in Pseudomonas aeruginosa, different from that generally described for ferrichrome and ferric-enterobactin in Escherichia coli. This new iron-uptake mechanism involves all the proteins generally reported to be involved in the uptake of ferric-siderophore complexes in Gram-negative bacteria (i.e. the outer membrane receptor, periplasmic binding protein and ATP-binding-cassette transporter), but differs in the behaviour of the siderophore. One of the key features of this process is the binding of iron-free pyoverdin to the outer membrane receptor FpvA in conditions of iron deficiency.

  14. Supramolecular functional assemblies: dynamic membrane transporters and peptide nanotubular composites.

    PubMed

    Fuertes, Alberto; Juanes, Marisa; Granja, Juan R; Montenegro, Javier

    2017-07-11

    The fabrication of functional molecular devices constitutes one of the most important current challenges for chemical sciences. The complex processes accomplished by living systems continuously demand the assistance of non-covalent interactions between molecular building blocks. Additionally, these building blocks (proteins, membranes, nucleotides) are also constituted by self-assembled structures. Therefore, supramolecular chemistry is the discipline required to understand the properties of the minimal self-assembled building blocks of living systems and to develop new functional smart materials. In the first part of this feature article, we highlight selected examples of the preparation of supramolecular membrane transporters with special emphasis on the application of dynamic covalent bonds. In the second section of the paper we review recent breakthroughs in the preparation of peptide nanotube hybrids with functional applications. The development of these devices constitutes an exciting process from where we can learn how to understand and manipulate supramolecular functional assemblies.

  15. Sodium and chloride transport in the large intestine of potassium-loaded rats

    SciTech Connect

    Budinger, M.E.; Foster, E.S.; Hayslett, J.P.; Binder, H.J.

    1986-08-01

    Increased dietary potassium (potassium loading) induces several adaptive changes in colonic function, including increased potential dependent potassium secretion, active potassium secretion, and Na-K-ATPase activity, but does not alter net sodium absorption in vivo. To establish whether potassium loading stimulates active sodium transport, unidirectional, net sodium, and chloride fluxes were determined under voltage-clamp conditions across isolated rat distal colonic mucosa. In normal animals net sodium flux (J/sub net/sup Na/), net chloride flux (J/sub net/sub Cl/) and short-circuit current (I/sub sc/) were 6.1 +/- 1.1, 8.4 +/-1.0, and 0.7 +/- 0.1 eq h cm S, respectively; potassium loading significantly increased J/sub net/sup Na/ and I/sup sc/ by 4.9 +/- 1.4 and 3.5 +/- 0.7 eq h cm S, respectively, without changing J/sub net/sup Na/ and I/sub sc/ produced by potassium loading. In Cl-free Ringer solution in normal animals J/sub net/sup Na was reduced to 0.6 +/- 0.3 eq h cm S. Potassium loading produced identical increases in J/sub net/sup Na/ and I/sub sc/, which were also completely inhibited by 0.1 mM amiloride. These studies establish that potassium loading induces amiloride-sensitive electrogenic sodium absorption without affecting electroneutral sodium-chloride absorption.

  16. Effects of Replacement of External Sodium Chloride with Sucrose on Membrane Currents of the Squid Giant Axon

    PubMed Central

    Adelman, William J.; Taylor, Robert E.

    1964-01-01

    It was observed that a reduction of the sodium chloride concentration in the external solution bathing a squid giant axon by replacement with sucrose resulted in marked decreases in the peak inward and steady-state outward currents through the axon membrane following a step decrease in membrane potential. These effects are quantitatively acounted for by the increase in series resistance resulting from the decreased conductivity of the sea water and the assumption that the sodium current obeys a relation of the form I = k1C1 - k2C2 where C1, C2 are internal and external ion activities and k1, k2 are independent of concentration. It is concluded that the potassium ion current is independent of the sodium concentration. That the inward current is carried by sodium ions has been confirmed. The electrical potential (or barrier height) profile in the membrane which drives sodium ions appears to be independent of sodium ion concentration or current. A specific effect of the sucrose on hyperpolarizing currents was observed and noted but not investigated in detail. PMID:14232131

  17. Epidermal growth factor-mediated proliferation and sodium transport in normal and PKD epithelial cells

    PubMed Central

    Zheleznova, Nadezhda N.; Wilson, Patricia D.; Staruschenko, Alexander

    2010-01-01

    Members of the epidermal growth factor (EGF)-family bind to ErbB (EGFR)-family receptors which play an important role in the regulation of various fundamental cell processes including cell proliferation and differentiation. The normal rodent kidney has been shown to express at least three members of the ErbB receptor family and is a major site of EGF ligand synthesis. Polycystic kidney disease (PKD) is a group of diseases caused by mutations in single genes and is characterized by enlarged kidneys due to the formation of multiple cysts in both kidneys. Tubule cells proliferate, causing segmental dilation, in association with the abnormal deposition of several proteins. One of the first abnormalities described in cell biological studies of PKD pathogenesis was the abnormal mislocalization of the EGFR in cyst lining epithelial cells. The kidney collecting duct (CD) is predominantly an absorptive epithelium where electrogenic Na+ entry is mediated by the epithelial Na+ channel (ENaC). ENaC-mediated sodium absorption represents an important ion transport pathway in the CD that might be involved in the development of PKD. A role for EGF in the regulation of ENaC-mediated sodium absorption has been proposed. However, several investigations have reported contradictory results indicating opposite effects of EGF and its related factors on ENaC activity and sodium transport. Recent advances in understanding how proteins in the EGF-family regulate the proliferation and sodium transport in normal and PKD epithelial cells are discussed here. PMID:20959142

  18. Resolution of parameters in the equivalent electrical circuit of the sodium transport mechanism across toad skin.

    PubMed

    Isaacson, L C

    1977-01-28

    In amphibian epithelia, amiloride reduces net sodium transport by hindering the entry of sodium to the active transport mechanism, that is, by increasing the series resistance (Rser). Theoretically, therefore, analysis of amiloride-induced changes in potential differences and short-circuit current should yield numerical estimates of all the parameters in the equivalent electrical circuit of the sodium transport mechanism. The concept has been explored by analysis of such changes in toad skins (Xenopus laevis) bathed in hypotonic sulphate Ringer's, after exposure to varying doses of amiloride, or to amphotericin, dinitrophenol or Pitressin. The estimated values of Rser, of the electromotive force of the sodium pump (ENa), and of the shunt resistance (Rsh) were independent of the dose of amiloride employed. Skins bathed in hypotonic sulphate Ringer's exhibited a progressive rise in ENa. Amphotericin produced a fall in Rser, while dinitrophenol caused a fall in ENa; washout of the drugs reversed these effects. Pitressin produced a fall in both Rser and Rsh, with a rise in ENa. These results are in accord with earlier suggestions regarding the site(s) of action of these agents.

  19. Mechanisms of calcium transport in human colonic basolateral membrane vesicles.

    PubMed

    Saksena, Seema; Ammar, Mohammad S; Tyagi, Sangeeta; Elsharydah, Ahmed; Gill, Ravinder K; Ramaswamy, Krishnamurthy; Dudeja, Pradeep K

    2002-10-01

    Human colon has been suggested to play an important role in calcium absorption especially after extensive disease or resection of the small intestine. We have previously demonstrated the presence of a carrier-mediated calcium uptake mechanism in the human colonic luminal membrane vesicles. Current studies were, therefore, undertaken to investigate the mechanism(s) of calcium exit across the basolateral membrane domain of the human colon. Human colonic basolateral membrane vesicles (BLMVs) were isolated and purified from mucosal scrapings of organ donor colons, utilizing a technique developed in our laboratory. 45Ca uptake was measured by a rapid filtration technique. 45Ca uptake represented transport into the intravesicular space as evidenced by an osmolarity study and by the demonstration of Ca2' efflux from calcium preloaded vesicles by Ca2+ ionophore A23187. Calcium uptake was stimulated by Mg2+ ATP. The kinetic parameters for ATP-dependent Ca2+ uptake revealed saturation kinetics with Michaelis constant (Km) of 0.22 +/- 0.04 microM and a maximum rate of uptake (Vmax) of 0.38 +/- 0.12 nmol/mg protein/min. The Km of ATP concentration required for half maximal Ca2+ uptake was 0.39 +/- 0.04 mM. ATP-stimulated calcium uptake into these vesicles was further stimulated in the presence of calmodulin and was inhibited by calmodulin antagonist, trifluoperazine. Uptake of 45Ca into BLMVs was markedly inhibited by cis-Na+ but was significantly stimulated by trans-Na+ (40-50% stimulation). Our results demonstrate the presence of a Mg2+/ATP-dependent calmodulin-regulated Ca2+ transport system and a Na+-Ca2+ exchange process in the human colonic basolateral membranes.

  20. Immobilization of sodium alginate sulfates on polysulfone ultrafiltration membranes for selective adsorption of low-density lipoprotein.

    PubMed

    Wang, Wei; Huang, Xiao-Jun; Cao, Jian-Da; Lan, Ping; Wu, Wen

    2014-01-01

    A novel method for the immobilization of sodium alginate sulfates (SAS) on polysulfone (PSu) ultrafiltration membranes to achieve selective adsorption of low-density lipoprotein (LDL) was developed, which involved the photoinduced graft polymerization of acrylamide on the membrane and the Hofmann rearrangement reaction of grafted acrylamide followed by chemical binding of SAS with glutaraldehyde. The surface modification processes were confirmed by attenuated total reflectance Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy characterization. Zeta potential and water contact angle measurements were performed to investigate the surface charge and wettability of the membranes. An enzyme-linked immunosorbent assay was used to measure the binding of LDL on plain and modified PSu membranes. It was found that the PSu membrane immobilized with sodium alginate sulfates (PSu-SAS) greatly enhanced the selective adsorption of LDL from protein solutions and the absorbed LDL could be easily eluted with sodium chloride solution, indicating a specific and reversible binding of LDL to SAS, mainly driven by electrostatic forces. Furthermore, the PSu-SAS membrane showed good blood compatibility as examined by platelet adhesion. The results suggest that the PSu-SAS membranes are promising for application in simultaneous hemodialysis and LDL apheresis therapy.

  1. Characterization of transport of calcium by microsomal membranes from roots maize

    SciTech Connect

    Vaughan, M.A.

    1985-01-01

    This study investigates calcium transport by membranes of roots of maize isolated by differential centrifugation. The preparation was determined to be enriched in plasma membrane using market enzyme and electron microscopy. Using the /sup 45/Ca filtration technique and liquid scintillation counting, vesicular calcium uptake was shown to be stimulated by added calmodulin and specific for and dependent on ATP. Conditions for maximal calcium accumulation were found to be 30 min incubation in the presence of 5 mM ATP, 5 mM MgCl/sub 2/, 50 ..mu..M CaCl/sub 2/, at 23/sup 0/C, and at pH 6.5. Calcium uptake was inhibited by the ionophores A23187, X-537A, and ionomycin. Sodium fluoride, ruthenium red, and p-chloromercuribenzoate completely inhibited transport: diamide and vanadate produced slight inhibition; caffeine, caffeic acid, oligomycin, and ouabain produced little or no inhibition. Chlorpromazine, W7, trifluoperazine, and R 24 571 inhibit calcium uptake irrespective of added calmodulin, while W5 showed little effect on uptake. Verapamil, nifedipine, cinnarizine, flunarizine, lidoflazine, and diltiazem decreased calcium uptake by 17%-50%. Electron microscopic localization of calcium by pyroantimonate showed vesicles incubated with calmodulin and ATP showed the greatest amount of precipitate. These results suggest that these vesicles accumulate calcium in an ATP-dependent, calmodulin-stimulated manner.

  2. Intrinsic limitations of spin transport in 2D membranes

    NASA Astrophysics Data System (ADS)

    Song, Yang

    2014-03-01

    Two dimensional membranes have become the playground for both theorists and experimentalists due to their unique intrinsic properties emerged from simple lattice structures. They are the new focus of spintronic applications. Therefore, it is important that we have a clear view of the relaxation processes in spin transport, limited by their intrinsic and symmetry structures. In this talk, we present our findings by systematically applying group theory to the coupling of phonons and transport carriers in spin-dependent scattering. Scattering by phonon is amplified in 2D membranes due to its unique and populous flexural mode. Opposite spin coupling by one flexural phonon is allowed by symmetry, unlike the momentum scattering by higher-order two flexural phonons. Furthermore, we specifically discuss the ultrafast electron spin relaxation in single-layer transition metal dichalcogenides (SL-TMDs). The additional factor stems from the decoupling of tiny conduction band spin splitting and the large spin scattering constant. The former results from conduction band orbital orientation, while the latter comes from inter-band coupling and reflects the atomic SOC strength. We will present that the essential use of group theory (invariant quantities) elucidates various spin-dependent selection rules of electron/hole-phonon interaction, within and between all relevant band-valley edges. Multiple potential applications of the derived results can be explored in transport problems, such as the strain effects, spin Gunn effect, hot exciton dynamics, and the scattering angle and spin anisotropy dependence. We compare different 2D membranes (graphene, SL-TMD, silicene and germanene) from general consideration of the lattice and band-edge symmetries. This work is supported by NRI-NSF, NSF, and DTRA Contracts No. DMR-1124601, No. ECCS-1231570, and No. HDTRA1-13-1-0013, respectively.

  3. Synthesis and characterization of polymer electrolyte membranes with controlled ion transport properties

    NASA Astrophysics Data System (ADS)

    Xu, Kui

    2011-12-01

    conductivity at the same order of magnitude as Nafion. This unique transport feature gave rise to exceedingly higher electrochemical selectivity in relation to Nafion. The selectivity characteristics have been rationalized based on the formation of restrained ionic domains and the state of the absorbed water within the membranes. A series of new Nafion-based composite membranes were prepared via an in situ sol-gel reaction of 3-(trihydroxylsilyl) propane-1-sulfonic acid and solution casting method. The morphological structure, ion-exchange capacity, water uptake, proton conductivity, and methanol permeability of the resulting composite membranes were extensively investigated as functions of the content of sulfopropylated polysilsesquioxane filler, temperature, and relative humidity. Unlike the conventional Nafion/silica composites, the prepared membranes exhibit an increased water uptake and associated enhancement in proton conductivity compared to unmodified Nafion. In particular, considerably high proton conductivities at 80 and 120 °C under 30% relative humidity were demonstrated in the composite membranes, which are over 2 times greater than that of Nafion. In addition to a remarkable improvement in proton conductivity, the composite membranes displayed lower methanol permeability and superior electrochemical selectivity in comparison to the pure Nafion membrane. A versatile and facile synthetic approach was developed for the preparation of a family of new ionomers with rigid aromatic backbones and pendant perfluorinated sulfonic acid groups. Variation in the chemical composition and structure of the new aromatic ionomers were performed to optimize PEM properties and fuel cell performance. The ionomers prepared from condensation polymerization of Sodium 1,1,2,2-tetrafluoro-2-(2',3',5',6'-tetrafluoro-phenoxy)- ethane sulfonate and bisphenol monomers, e.g. hydroquinone, 4,4'-biphenol, or their mixture with appropriate ratio, exhibited comparable or greater proton

  4. Ionic charge transport between blockages: Sodium cation conduction in freshly excised bulk brain tissue

    SciTech Connect

    Emin, David; Akhtari, Massoud; Ellingson, B. M.; Mathern, G. W.

    2015-08-15

    We analyze the transient-dc and frequency-dependent electrical conductivities between blocking electrodes. We extend this analysis to measurements of ions’ transport in freshly excised bulk samples of human brain tissue whose complex cellular structure produces blockages. The associated ionic charge-carrier density and diffusivity are consistent with local values for sodium cations determined non-invasively in brain tissue by MRI (NMR) and diffusion-MRI (spin-echo NMR). The characteristic separation between blockages, about 450 microns, is very much shorter than that found for sodium-doped gel proxies for brain tissue, >1 cm.

  5. Ammonium across a Selective Polymer Inclusion Membrane: Characterization, Transport, and Selectivity.

    PubMed

    Casadellà, Anna; Schaetzle, Olivier; Loos, Katja

    2016-05-01

    The recovery of ammonium from urine requires distinguishing and excluding sodium and potassium. A polymer inclusion membrane selective for ammonium is developed using an ionophore based on pyrazole substituted benzene. The interactions of the components are studied, as well as their effect on transport and selectivity. Spectroscopic and thermogravimetric measurements show no extensive physical interactions of the components, and that the plasticizer reduces the intermolecular forces (rigidity) of the membrane. The ionophore turns the membrane more rigid, although it increases its swelling degree and therefore the affinity of cations. A ratio of plasticizer (DEHP) and polymer (PVC) of 1:3 in mass gives the highest ammonium flux. Tested contents of ionophore (2 and 5 wt%) show that the higher the content of the ionophore, the fastest the flux is (7.5 × 10(-3) mmol cm(-2) h(-1) ). Selectivity of NH4 (+) over Na(+) and over K(+) is reduced from 13.07 to 9.33 and from 14.15 to 9.57 correspondingly.

  6. Membrane fouling by sodium alginate in high salinity conditions to simulate biofouling during seawater desalination.

    PubMed

    Charfi, Amine; Jang, Hoseok; Kim, Jeonghwan

    2017-02-21

    This study aims to better understand biofouling by algal organic matters (AOM) during seawater pretreatment by microfiltration (MF). To simulate AOM biofouling, sodium alginate (SA) solutions with three different concentrations (2, 20 and 50ppm) were filtered in dead-end mode with MF membrane. A modelling approach with blocking laws was used to identify the fouling mechanisms behind flux decline with time. The effect of SA concentration and cations such as Na(+) (0.6M) and Ca(2+) (0.015M) addition to SA solution on fouling mechanisms was studied. While for low SA concentration (2ppm), fouling occurs within two phases: a pore constriction phase followed by cake formation phase, for high SA concentration (50ppm), fouling occurs within only one phase controlled by cake formation. The addition of Na(+) (0.6M) or Ca(2+) (0.015M) to SA solution mitigates membrane fouling, however, the addition of both cations enhances fouling by formation of dense cake layer on membrane.

  7. Intracellular sodium ion activity and sodium transport in rabbit urinary bladder.

    PubMed Central

    Eaton, D C

    1981-01-01

    1. Intracellular potentials and the intracellular activities of Na+ and K+ were examined using conventional and ion-selective micro-electrodes. 2. In animals on a normal diet, the intracellular Na+ activity was 8.6 +/- 2.9 mM (mean +/- S.D.) with a mean short-circuit current of 2.8 +/- 0.9 microA/cm2. 3. In animals on a low-Na+ diet, the intracellular Na+ activity was 18.5 +/- 9.9 mM with a short-circuit current of 4.5 +/- 1.3 microA/cm2 (mean +/- S.D.). 4. There was a correlation between short-circuit current and intracellular Na+ activity which could be fitted by a saturating hyperbolic relationship. 5. Treatment of the issue with ouabain and amiloride produced an increase and a decrease, respectively, in the intracellular Na+ activity. 6. Treatment with aldosterone produced a large increase in short-circuit current with a substantial increase in intracellular Na+ activity. 7. Intracellular Na+ activity does not seem to affect apical membrane permeability directly. PMID:7320880

  8. FOOD VACUOLE MEMBRANE GROWTH WITH MICROTUBULE-ASSOCIATED MEMBRANE TRANSPORT IN PARAMECIUM

    PubMed Central

    Allen, Richard D.

    1974-01-01

    Evidence from a morphological study of the oral apparatus of Paramecium caudatum using electron microscope techniques have shown the existence of an elaborate structural system which is apparently designed to recycle digestive-vacuole membrane. Disk-shaped vesicles are filtered out of the cytoplasm by a group of microtubular ribbons. The vesicles, after being transported to the cytostome-cytopharynx region in association with these ribbons, accumulate next to the cytopharynx before they become fused with the cytopharyngeal membrane. This fusion allows the nascent food vacuole to grow and increase its membrane surface area. The morphology of this cytostome-cytopharynx region is described in detail and illustrated with a three-dimensional drawing of a portion of this region and a clay sculpture of the oral apparatus of Paramecium. Evidence from the literature for the transformation of food vacuole membrane into disk-shaped vesicles both from condensing food vacuoles in the endoplasm and from egested food vacuoles at the cytoproct is presented. This transformation would complete a system of digestive vacuole membrane recycling. PMID:4373478

  9. Surfactant and temperature effects on paraben transport through silicone membranes.

    PubMed

    Waters, Laura J; Dennis, Laura; Bibi, Aisha; Mitchell, John C

    2013-08-01

    This study investigates the effects of two surfactants (one anionic and one non-ionic) and controlled modifications in temperature (298-323K) on the permeation of two structurally similar compounds through a silicone membrane using a Franz diffusion cell system. In all cases the presence of an anionic surfactant, namely sodium dodecyl sulphate (SDS), reduced the permeation of both compounds (methylparaben and ethylparaben) over a period of 24h. The degree of permeation reduction was proportional to the concentration of surfactant with a maximum effect observed, with an average reduction of approximately 50%, at the highest surfactant concentration of 20mM. Differences were seen around the critical micelle concentration (CMC) of SDS implying the effect was partially connected with the favoured formation of micelles. In contrast, the presence of non-ionic surfactant (Brij 35) had no effect on the permeation of methylparaben or ethylparaben at any of the concentrations investigated, both above and below the CMC of the surfactant. From these findings the authors conclude that the specific effects of SDS are a consequence of ionic surfactant-silicone interactions retarding the movement of paraben through the membrane through indirect modifications to the surface of the membrane. As expected, an increase in experimental temperature appeared to enhance the permeation of both model compounds, a finding that is in agreement with previously reported data. Interestingly, in the majority of cases this effect was optimum at the second highest temperature studied (45°C) which suggests that permeation is a temperature-dependent phenomenon.

  10. Slow DNA Transport through Nanopores in Hafnium Oxide Membranes

    PubMed Central

    Bell, David C.; Cohen-Karni, Tzahi; Rosenstein, Jacob K.; Wanunu, Meni

    2016-01-01

    We present a study of double- and single-stranded DNA transport through nanopores fabricated in ultrathin (2–7 nm thick) free-standing hafnium oxide (HfO2) membranes. The high chemical stability of ultrathin HfO2 enables long-lived experiments with <2 nm diameter pores that last several hours, in which we observe >50 000 DNA translocations with no detectable pore expansion. Mean DNA velocities are slower than velocities through comparable silicon nitride pores, providing evidence that HfO2 nanopores have favorable physicochemical interactions with nucleic acids that can be leveraged to slow down DNA in a nanopore. PMID:24083444

  11. Slow DNA transport through nanopores in hafnium oxide membranes.

    PubMed

    Larkin, Joseph; Henley, Robert; Bell, David C; Cohen-Karni, Tzahi; Rosenstein, Jacob K; Wanunu, Meni

    2013-11-26

    We present a study of double- and single-stranded DNA transport through nanopores fabricated in ultrathin (2-7 nm thick) freestanding hafnium oxide (HfO2) membranes. The high chemical stability of ultrathin HfO2 enables long-lived experiments with <2 nm diameter pores that last several hours, in which we observe >50 000 DNA translocations with no detectable pore expansion. Mean DNA velocities are slower than velocities through comparable silicon nitride pores, providing evidence that HfO2 nanopores have favorable physicochemical interactions with nucleic acids that can be leveraged to slow down DNA in a nanopore.

  12. Novel macrocyclic carriers for proton-coupled liquid membrane transport

    SciTech Connect

    Lamb, J.D.; Bradshaw, J.S.; Izatt, R.M.

    1992-07-01

    A number of new macrocyclic ligands was prepared for transport studies. The cryptands were prpepared (18-40% yield) by a new metal carbonate-catalyzed one-step method from 1 mole oligoethyleneoxy diamine and 2 moles diahlide derivative of oligoethylene glycol. Bis-crown ethers were also isolated in 17-30% yields. Cage compounds were also prepared; they interact with various metal ions and protons. Back extraction and dual module hollow fiber membrane separation experiments were used to study the cation selectivity of new ligands, including crown thioethers. An isothermal flow calorimeter is being constructed for studies of macrocycle-cation reactions. 3 figs, 2 tabs.

  13. Protein Mediators of Sterol Transport Across Intestinal Brush Border Membrane

    PubMed Central

    Brown, J. Mark; Yu, Liqing

    2012-01-01

    Dysregulation of cholesterol balance contributes significantly to atherosclerotic cardiovascular disease (ASCVD), the leading cause of death in the United States. The intestine has the unique capability to act as a gatekeeper for entry of cholesterol into the body, and inhibition of intestinal cholesterol absorption is now widely regarded as an attractive non-statin therapeutic strategy for ASCVD prevention. In this chapter we discuss the current state of knowledge regarding sterol transport across the intestinal brush border membrane. The purpose of this work is to summarize substantial progress made in the last decade in regards to protein-mediated sterol trafficking, and to discuss this in the context of human disease. PMID:20213550

  14. Membrane vesicles: A simplified system for studying auxin transport

    SciTech Connect

    Goldsmith, M.H.M.

    1989-01-01

    Indoleacetic acid (IAA), the auxin responsible for regulation of growth, is transported polarly in plants. Several different models have been suggested to account for IAA transport by cells and its accumulation by membrane vesicles. One model sees diffusion of IAA driven by a pH gradient. The anion of a lipophilic weak acid like IAA or butyrate accumulates in an alkaline compartment in accord with the size of the pH gradient The accumulation of IAA may be diminished by the permeability of its lipophilic anion. This anion leak may be blocked by NPA. With anion efflux blocked, a gradient of two pH units would support an IAA accumulation of less than 50-fold at equilibrium (2) Another model sees diffusion of IAA in parallel with a saturable symport (IAA[sup [minus

  15. Amiloride-sensitive sodium transport in lamprey red blood cells: evidence for two distinct transport pathways.

    PubMed

    Gusev, G P; Ivanova, T I

    2004-12-01

    To determine Na+/H+ exchange in lamprey erythrocyte membranes, the cells were acidified to pH(i) 6.0 using the K+/H+ ionophore nigericin. Incubation of acidified erythrocytes in a NaCl medium at pH 8.0 caused a considerable rise in 22Na+ influx and H+ efflux during the first 1 min of exposure. In addition, exposure of acidified red cells to NaCl medium was associated with rapid elevation of intracellular Na+ content. The acid-induced changes in Na+ influx and H+ efflux were almost completely inhibited by amiloride and dimethylamiloride. In native lamprey erythrocytes, amiloride-sensitive Na+ influx progressively increased as the osmolality of incubation medium was increased by addition of 100, 200, or 300 mmol/l sucrose. Unexpectedly, the hypertonic stress induced a small, yet statistically significant decrease in intracellular Na+ content in these cells. The reduction in the cellular Na+ content increased with hypertonicity of the medium. The acid- and shrinkage-induced Na+ influxes were inhibited by both amiloride and 5-(N-ethyl-N-isopropyl)-amiloride (EIPA) in a dose-dependent manner. For both blockers, the half-maximal inhibitory values (IC50) were much greater for the shrinkage-induced (44 and 15 micromol/l for amiloride and EIPA, respectively) than for the acid-induced Na+ influx (5.1 and 3.3 micromol/l, respectively). The data obtained are the first demonstration of the presence of a Na+/H+ exchanger with high activity in acidified (pH(i) 6.0) lamprey red blood cells (on average, 512 +/- 56 mmol/l cells/h, n = 13). The amiloride-sensitive Na+ influxes produced by hypertonic cell shrinkage and acid load are likely to be mediated by distinct ion transporters in these cells.

  16. Osteoblast protects osteoclast devoid of sodium-dependent vitamin C transporters from oxidative cytotoxicity of ascorbic acid.

    PubMed

    Takarada, Takeshi; Hinoi, Eiichi; Kambe, Yuki; Sahara, Koichi; Kurokawa, Shintaro; Takahata, Yoshifumi; Yoneda, Yukio

    2007-12-01

    The view that ascorbic acid indirectly benefits osteoclastogenesis through expression of receptor activator of nuclear factor-kappaB (NF-kappaB) ligand (RANKL) by osteoblasts is prevailing. In this study, we have examined the direct effect of ascorbic acid on osteoclastogenesis in cultured mouse osteoclasts differentiated from bone marrow precursors. The absence of alkaline phosphatase and osteoblastic marker genes validated the usefulness of isolation procedures. Sustained exposure to ascorbic acid, but not to dehydroascorbic acid, significantly reduced the number of multinucleated cells positive to tartrate-resistant acid phosphatase (TRAP) staining. In cultured osteoclasts, mRNA expression was seen for glucose transporter-1 involved in membrane transport of dehydroascorbic acid, but not for sodium-dependent vitamin C transporters-1 and -2 that are both responsible for the transport of ascorbic acid. The inhibition by ascorbic acid was completely prevented by catalase, while ascorbic acid or hydrogen peroxide drastically increased the number of cells stained with propidium iodide and the generation of reactive oxygen species, in addition to inducing mitochondrial membrane depolarization in cultured osteoclasts. In pre-osteoclastic cell line RAW264.7 cells, ascorbic acid similarly inhibited the formation of TRAP-positive multinucleated cells, with a significant decrease in RANKL-induced NF-kappaB transactivation. Moreover, co-culture with osteoblastic MC3T3-E1 cells significantly prevented the ascorbic acid-induced decrease in the number of TRAP-positive multinucleated cells in RAW264.7 cells. These results suggest that ascorbic acid may play a dual repulsive role in osteoclastogenesis toward bone remodeling through the direct cytotoxicity mediated by oxidative stress to osteoclasts, in addition to the indirect trophism mediated by RANKL from osteoblasts.

  17. Chlorotrifluoroethylcysteine interaction with rabbit proximal tubule cell basolateral membrane organic anion transport and apical membrane amino acid transport.

    PubMed

    Groves, C E; Morales, M N

    1999-11-01

    The interaction of the cysteine conjugate S-(1-chloro-1,2,2, -trifluoroethyl)-L-cysteine (CTFC) with organic anion and amino acid transport in the basolateral and apical membranes was examined with rabbit renal proximal tubule suspensions and primary cultures of rabbit renal proximal tubule cells. The apparent K(i) for CTFC inhibition of the 1-min uptake of [(3)H]p-aminohippurate in tubule suspensions was 105+/-3 microM and suggests that CTFC interacts with basolateral organic anion transport. Also, the addition of 1 mM CTFC decreased the secretion and intracellular accumulation of fluorescein by approximately 70 to 75%. The addition of 1 mM CTFC to the apical compartment decreased the reabsorption and intracellular accumulation of the amino acid [(3)H]phenylalanine by approximately 60 to 70%. Similar to CTFC, saturating concentrations of the organic anion [(3)H]p-aminohippurate and the amino acid phenylalanine reduced by approximately 75% fluorescein secretion and [(3)H]phenylalanine reabsorption, respectively, by approximately 60 to 70%. Thus, the cysteine conjugate CTFC appears to be a potent inhibitor of basolateral organic anion and apical amino acid transepithelial transport. In contrast to its effects on apical phenylalanine uptake, CTFC had no effect on the basal uptake of [(3)H]phenylalanine by primary cultures. The presence of CTFC in the external bath did trans-stimulate the efflux of fluorescein and [(3)H]phenylalanine across the basal and apical membrane in tubule suspensions or primary cultures, respectively, grown on plastic. Collectively, these data demonstrate that CTFC interacts with, and is transported by, two anatomically and functionally distinct transporters, the basolateral organic anion and apical neutral amino acid pathways, in the rabbit renal proximal tubule cell.

  18. Large-scale preparation of plasma membrane vesicles from PC-12 pheochromocytoma cells and their use in noradrenaline transport studies.

    PubMed

    Harder, R; Bönisch, H

    1984-08-08

    Plasma membranes were isolated from rat pheochromocytoma cells (PC-12) grown in spinner culture. The rapid and simple isolation procedure consisted of a differential and isopycnic centrifugation (in a linear sucrose gradient) with the aid of a high capacity fixed angle rotor equipped with siliconized centrifuge tubes. The isolated membranes were closed and osmotically active vesicles (about 0.3 micron in diameter) with a mean intravesicular water space of 1.84 microliters/mg protein. In the presence of an inward gradient of sodium chloride and an outward gradient of potassium, [3H]noradrenaline (50 nM) was taken up and accumulated 550-fold (at 31 degrees C). The uptake and accumulation of [3H]noradrenaline was temperature-sensitive and inhibited by the tricyclic antidepressant desipramine. Membrane vesicles isolated from PC-12 cells represent a useful model for the investigation of the molecular mechanism of the neuronal noradrenaline transport system.

  19. Sulfate transport in apical membrane vesicles isolated from tracheal epithelium

    SciTech Connect

    Elgavish, A.; DiBona, D.R.; Norton, P.; Meezan, E.

    1987-09-01

    Sulfate uptake in apical membrane vesicles isolated from bovine tracheal epithelium is shown to occur into an osmotically sensitive intravesicular space, via a carrier-mediated system. This conclusion is based on three lines of evidence: 1) saturation kinetics: 2) substrate specificity; and 3) inhibition by the anion transport inhibitors SITS and DIDS. The affinity of the transport system is highest in low ionic strength media and decreases in the presence of gluconate. Chloride appears to cis-inhibit sulfate uptake and to trans-stimulate sulfate efflux. Cis-inhibition and trans-stimulation studies with a variety of anions indicate that this exchange system may be shared by HCO/sub 3//sup -/, S/sub 2/O/sub 3//sup 2 -/, SeO/sub 4//sup 2 -/, and MoO/sub 4//sup 2 -/ but not by H/sub 2/PO/sub 4//sup -/ or HAsO/sub 4//sup 2/. Studies indicate that protons may play two distinct roles in sulfate transport in this system. These studies show that the carrier-mediated system can function in the absence of chloride. The overshoot observed in the presence of a proton gradient indicates that under those conditions the mechanism of transport may be a SO/sub 4//sup 2 -/-OH/sup -/ exchange.

  20. Membrane fractionation processes for removing 90% to 95% of the lactose and sodium from skim milk and for preparing lactose and sodium-reduced skim milk.

    PubMed

    Morr, C V; Brandon, S C

    2008-11-01

    Pilot-scale microfiltration (MF), microfiltration-diafiltration (MDF), ultrafiltration (UF), ultrafiltration-diafiltration (UDF), and nanofilration (NF) membrane fractionation processes were designed and evaluated for removing 90% to 95% of the lactose and sodium from skim milk. The study was designed to evaluate several membrane fractionation schemes as a function of: (1) membrane types with and without diafiltration; (2) fractionation process temperatures ranging from 17 to 45 degrees C; (3) sources of commercial drinking water used as diafiltrant; and (4) final mass concentration ratios (MCR) ranging from about 2 to 5. MF and MDF membranes provided highest flux values, but were unsatisfactory because they failed to retain all of the whey proteins. UDF fractionation processes removed more than 90% to 95% of the lactose and sodium from skim milk. NF permeate prepared from UDF cumulative permeate contained sodium and other mineral concentrations that would make them unsuitable for use as a diafiltrant for UDF applications. A method was devised for preparing simulated milk permeate (SMP) formulated with calcium, magnesium, and potassium hydroxides, and phosphoric and citric acids for use as UDF diafiltrant or for preparing lactose and sodium reduced skim milk (L-RSM). MF retentates with MCR values of 4.7 to 5.0 exhibited extremely poor frozen storage stabilities of less than 1 wk at -20 degrees C, whereas MCR 1.77 to 2.95 MDF and UDF retentates and skim milk control exhibited frozen storage stabilities of more than 16 wk. L-RSM exhibited a whiter appearance and a lower viscosity than skim milk, lacked natural milk flavor, and exhibited a metallic off-flavor.

  1. The sodium pump. Its molecular properties and mechanics of ion transport.

    PubMed

    Scheiner-Bobis, Georgios

    2002-05-01

    The sodium pump (Na(+)/K(+)-ATPase; sodium- and potassium-activated adenosine 5'-triphosphatase; EC 3.6.1.37) has been under investigation for more than four decades. During this time, the knowledge about the structure and properties of the enzyme has increased to such an extent that specialized groups have formed within this field that focus on specific aspects of the active ion transport catalyzed by this enzyme. Taking this into account, this review, while somewhat speculative, is an attempt to summarize the information regarding the enzymology of the sodium pump with the hope of providing to interested readers from outside the field a concentrated overview and to readers from related fields a guide in their search for gathering specific information concerning the structure, function, and enzymology of this enzyme.

  2. FACTORS WHICH MODIFY THE EFFECT OF SODIUM AND POTASSIUM ON BACTERIAL CELL MEMBRANES.

    PubMed

    HENNEMAN, D H; UMBREIT, W W

    1964-06-01

    Henneman, Dorothy H. (Rutgers, The State University, New Brunswick, N.J.), and W. W. Umbreit. Factors which modify the effect of sodium and potassium on bacterial cell membranes. J. Bacteriol. 87:1266-1273. 1964.-Suspensions of Escherichia coli B, when placed in 0.2 to 0.5 m solutions of NaCl, KCl, or LiCl, show an increased turbidity. With NaCl, this increased turbidity is stable with time; with KCl and LiCl, it is gradually lost. The stability to NaCl with time is due to substances removable from the cell by incubation in phosphate buffer; these materials exist in water washings from such phosphate-incubated cells.

  3. Primary sodium plasma membrane ATPases in salt-tolerant algae: facts and fictions.

    PubMed

    Gimmler, H

    2000-07-01

    For thermodynamic reasons algae growing in media of both high salinity and high alkalinity require active export of sodium. However, experimental evidence for an active Na+-dependent cycle was scarce until recently, in contrast to the situation in marine bacteria (including cyanobacteria), fungi and animals. However, a review of literature reveals that some progress has been made in this respect, recently: data demonstrate that at least in two marine algae, Tetraselmis (Platymonas) viridis and Heterosigma akashiwo (syn. Olisthodiscus luteus), active Na+-export is carried out by means of a plasma membrane localized Na+-pump (apparent molecular mass 100-140 kDa). Biochemical characteristics of this vanadate-sensitive, but ouabain-resistant primary P-type Na+-ATPase are described and compared with the corresponding properties of Na+-ATPase from prokaryotes and animals. Alternative mechanisms for Na+-pumping are discussed.

  4. Molecular Structure and Transport Dynamics in Perfluoro Sulfonyl Imide Membranes

    SciTech Connect

    Idupulapati, Nagesh B.; Devanathan, Ramaswami; Dupuis, Michel

    2011-05-25

    We report a detailed and comprehensive analysis of the nanostructure, transport dynamics of water and hydronium and water percolation in hydrated perfluoro sulfonyl imides (PFSI), a polymer considered for proton transport in PEM fuel cells, using classical molecular dynamics simulations. The dynamical changes are related to the changes in the membrane nanostructure. Water network percolation threshold, the level at which a consistent spanning water network starts to develop in the membrane, lies between hydration level (λ) 6 and 7. The higher acidity of the sulfonyl imide acid group of PFSI compared to Nafion reported in our earlier ab initio study, translates into more free hydronium ions at low hydration levels. Nevertheless, the calculated diffusion coefficients of the H3O+ ions and H2O molecules as a function the hydration level were observed to be almost the same as that of Nafion, indicating similar conductivity and consistent with the experimental observations. This research was performed in part using the Molecular Science Computing Facility in the William R. Wiley Environmental Molecular Sciences Laboratory, a U.S. Department of Energy (DOE) national scientific user facility located at the Pacific Northwest National Laboratory (PNNL). This work was supported by the US Department of Energy Basic Energy Sciences' Chemical Sciences, Geosciences & Biosciences Division. Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy.

  5. Molecular structure and transport dynamics in perfluoro sulfonyl imide membranes.

    PubMed

    Idupulapati, Nagesh; Devanathan, Ram; Dupuis, Michel

    2011-06-15

    We report a detailed and comprehensive analysis from classical molecular dynamics simulations of the nanostructure of a model of hydrated perfluoro sulfonyl imide (PFSI) membrane, a polymeric system of interest as a proton conductor in polymer electrolyte membrane fuel cells. We also report on the transport dynamics of water and hydronium ions, and water network percolation in this system. We find that the water network percolation threshold for PFSI, i.e. the threshold at which a consistent spanning water network starts to develop in the membrane, is found to occur between hydration levels (λ) 6 and 7. The higher acidity of the sulfonyl imide acid group of PFSI compared to the sulfonic acid group in Nafion, as computationally characterized in our earlier ab initio study (Idupulapati et al 2010 J. Phys. Chem. A 114 6904-12), results in a larger fraction of 'free' hydronium ions at low hydration levels in PFSI compared to Nafion. However, the calculated diffusion coefficients of the H(3)O(+) ions and H(2)O molecules as a function the hydration level are observed to be almost the same as that of Nafion, indicating similar conductivity and consistent with experimental data.

  6. Components of the plasma membrane of growing axons. III. Saxitoxin binding to sodium channels

    PubMed Central

    1984-01-01

    The density of sodium channels was measured in growing and mature axons of the olfactory nerve of the bullfrog, using as a probe the drug saxitoxin (STX). The toxin binds to control nerves from adult animals in a saturable manner with a dissociation constant of approximately 23 nM at 4 degrees C and a capacity of 72 fmol/mg wet weight, equivalent to about five sites per square micrometer of axolemma. In growing nerves, obtained from adult frogs 4-5 wk following removal of the original nerve, the STX-binding capacity per wet weight of tissue is markedly reduced, to approximately 25% of control values, and appears to decrease in the proximodistal direction. STX-binding data, expressed as STX/mg wet weight, was converted to STX/micron 2 of axolemma using stereologically derived values of membrane area per milligram wet weight of nerve. The axolemmal content (area/mg wet weight) of all regions of growing nerve is substantially decreased compared to controls, but increases in the proximodistal direction by 60%. These changes in axolemmal area result in calculated STX receptor densities (per unit axolemmal area) which, in distal regions, are approximately at the level of the mature nerve and, in proximal regions, are actually increased above controls by 50 to 70%. Upon comparing the axolemmal density of intramembrane particles, reported in the companion paper, with the calculated density of STX receptors in both mature and growing nerves, we find a correlation between STX receptors and intramembrane particles with diameters of 11.5-14.0 nm. The growing axon's gradient of sodium channels and the shift from this gradient to a uniform distribution in the mature axon suggest (a) that sodium channels are inserted into the perikaryal plasmalemma and diffuse from there into the growing axolemma, and (b) that the axolemma undergoes functional maturation during growth. PMID:6325471

  7. Sodium Lauryl Sulfate Stimulates the Generation of Reactive Oxygen Species through Interactions with Cell Membranes.

    PubMed

    Mizutani, Taeko; Mori, Ryota; Hirayama, Misaki; Sagawa, Yuki; Shimizu, Kenji; Okano, Yuri; Masaki, Hitoshi

    2016-12-01

    Sodium lauryl sulfate (SLS), a representative anionic surfactant, is well-known to induce rough skin following single or multiple topical applications. The mechanism by which SLS induces rough skin is thought to result from the disruption of skin moisture function consisting of NMF and epidermal lipids. However, a recent study demonstrated that topically applied SLS easily penetrates into the living cell layers of the epidermis, which suggests that physiological alterations of keratinocytes might cause the SLS-induced rough skin. This study was conducted to clarify the effects of SLS on keratinocytes to demonstrate the contribution of SLS to the induction of rough skin. In addition, the potentials of other widely used anionic surfactants to induce rough skin were evaluated. HaCaT keratinocytes treated with SLS had increased levels of intracellular ROS and IL-1α secretion. Application of SLS on the surface of a reconstructed epidermal equivalent also showed the increased generation of ROS. Further, SLS-treated cells showed an increase of intracellular calpain activity associated with the increase of intracellular Ca(2+) concentration. The increase of intracellular ROS was abolished by the addition of BAPTA-AM, a specific chelator of Ca(2+). In addition, IL-1α also stimulated ROS generation by HaCaT keratinocytes. An ESR spin-labeling study demonstrated that SLS increased the fluidity of membranes of liposomes and cells. Together, those results indicate that SLS initially interacts with cell membranes, which results in the elevation of intracellular Ca(2+) influx. Ca(2+) stimulates the secretion of IL-1α due to the activation of calpain, and also increases ROS generation. IL-1α also stimulates ROS generation by HaCaT keratinocytes. We conclude from these results that the elevation of intracellular ROS levels is one of the causes of SLS-induced rough skin. Finally, among the other anionic surfactants tested, sodium lauryl phosphate has less potential to induce

  8. Calcium and proton transport in membrane vesicles from barley roots

    SciTech Connect

    DuPont, F.M.; Windle, J.J. ); Bush, D.S.; Jones, R.L. )

    1990-09-01

    Ca{sup 2+} uptake by membrane fractions from barley (Hordeum vulgare L. cv CM72) roots was characterized. Uptake of {sup 45}Ca{sup 2+} was measured in membrane vesicles obtained from continuous and discontinuous sucrose gradients. A single, large peak of Ca{sup 2+} uptake coincided with the peak of proton transport by the tonoplast H{sup +}-ATPase. Depending on the concentration of Ca{sup 2+} in the assay, Ca{sup 2+} uptake was inhibited 50 to 75% by those combinations of ionophores and solutes that eliminated the pH gradient and membrane potential. However, 25 to 50% of the Ca{sup 2+} uptake in the tonoplast-enriched fraction was not sensitive to ionophores but was inhibited by vanadate. The results suggest that {sup 45}Ca uptake was driven by the low affinity, high capacity tonoplast Ca{sup 2+}/nH{sup +} antiporter and also by a high affinity, lower capacity Ca{sup 2+}-ATPase. The Ca{sup 2+}-ATPase may be associated with tonoplast, Golgi or contaminating vesicles of unknown origin. No Ca{sup 2+} transport was specifically associated with the distinct peak of endoplasmic reticulum that was identified by NADH cytochrome c reductase, choline phosphotransferase, and dolichol-P-mannosyl synthase activities. A small shoulder of Ca{sup 2+} uptake in the plasma membrane region of the gradient was inhibited by vanadate and erythrosin B and may represent the activity of a separate plasma membrane Ca{sup 2+}-ATPase. Vesicle volumes were estimated using electron spin resonance techniques, and intravesicular Ca{sup 2+} concentrations were estimated to be as high as 5 millimolar. ATP-driven uptake of Ca{sup 2+} created 800- to 2,000-fold concentration gradients within minutes. Problems in interpreting the effects of Ca{sup 2+} on ATP-generated pH gradients are discussed and the suggestion is made that Ca{sup 2+} dissipates pH gradients by a different mechanism than is responsible for Ca{sup 2+} uptake into tonoplast vesicles.

  9. Electrical resistance and transport numbers of ion-exchange membranes used in electrodialytic soil remediation

    SciTech Connect

    Hansen, H.K.; Ottosen, L.M.; Villumsen, A.

    1999-08-01

    Electrodialytic soil remediation is a recently developed method to decontaminate heavy metal polluted soil using ion-exchange membranes. In this method one side of the ion-exchange membrane is in direct contact with the polluted soil. It is of great importance to known if this contact with the soil causes damage to the membrane. This work presents the result of transport number and electrical resistance measurements done on four sets of ion-exchange membranes (Ionics, Inc CR67 HMR412 cation-exchange membranes and Ionics, Inc AR204 SXZR anion-exchange membranes), which have been used in four different electrodialytic soil remediation experiments. The experiments showed that after the use in electrodialytic soil remediation, the ion-exchange membranes had transport numbers in the same magnitude as new membranes. The electrical resistance for six membranes did not differ from that of new membranes, whereas two membranes showed a slightly increased resistance.

  10. Sodium laurate, a novel protease- and mass spectrometry-compatible detergent for mass spectrometry-based membrane proteomics.

    PubMed

    Lin, Yong; Huo, Linju; Liu, Zhonghua; Li, Jianglin; Liu, Yi; He, Quanze; Wang, Xianchun; Liang, Songping

    2013-01-01

    The hydrophobic nature of most membrane proteins severely complicates their extraction, proteolysis and identification. Although detergents can be used to enhance the solubility of the membrane proteins, it is often difficult for a detergent not only to have a strong ability to extract membrane proteins, but also to be compatible with the subsequent proteolysis and mass spectrometric analysis. In this study, we made evaluation on a novel application of sodium laurate (SL) to the shotgun analysis of membrane proteomes. SL was found not only to lyse the membranes and solubilize membrane proteins as efficiently as SDS, but also to be well compatible with trypsin and chymotrypsin. Furthermore, SL could be efficiently removed by phase transfer method from samples after acidification, thus ensuring not to interfere with the subsequent CapLC-MS/MS analysis of the proteolytic peptides of proteins. When SL was applied to assist the digestion and identification of a standard protein mixture containing bacteriorhodoposin and the proteins in rat liver plasma membrane-enriched fractions, it was found that, compared with other two representative enzyme- and MS-compatible detergents RapiGest SF (RGS) and sodium deoxycholate (SDC), SL exhibited obvious superiority in the identification of membrane proteins particularly those with high hydrophobicity and/or multiple transmembrane domains.

  11. Towards Co-evolution of Membrane Transport and Metabolism

    NASA Technical Reports Server (NTRS)

    Wei, Chenyu; Pohorille, Andrzej

    2014-01-01

    Protocellular boundaries were inextricably connected to the metabolism they encapsulated: to be inheritable, early metabolism must have led to an increased rate of growth and division of vesicles and, similarly, transport through vesicle boundaries must have supported the evolution of metabolism. Even though explaining how this coupling emerged and evolved in the absence of the complex machinery of modern cells is one of the key issues in studies on the origin of life, little is known about the biochemical and biophysical processes that might have been involved. This gap in our knowledge is a major impediment in efforts to construct scenarios for the origin of life and laboratory models of protocells. A combination of experimental and computational studies carried out by us and our collaborators is aimed at helping to close this gap. Properties of membranes might have contributed to the selection of RNA as an early biopolymer. A kinetic mechanism was proposed (Sacerdote & Szostak, 2005) in which ribose was supplied more quickly than other aldopentoses to primordial cells for preferential incorporation of ribonucleotides into nucleic acids. This proposal is based on a finding that ribose permeates membranes an order of magnitude faster than its diastereomers, arabinose and xylose. Our computer simulations, which yield permeation rates in excellent agreement with experiment, and kinetic modeling explain this phenomenon in terms of inter- and intramolecular interactions involving exocyclic hydroxyl groups attached to carbon atoms of the pyranose ring (Wei and Pohorille, 2009). They also constrain scenarios for the formation of the earliest nucleic acids (Wei and Pohorille, 2013). In one scenario, sugars permeate protocellular walls and subsequently are used to synthesize nucleic acids inside protocells. As long as this process proceeds at the rate faster than 6x10(exp -3)/s, ribose derivatives will be available for synthesis easier than their diastereomers. If

  12. K⁺-dependent ³H-D-glucose transport by hepatopancreatic brush border membrane vesicles of a marine shrimp.

    PubMed

    Obi, Ijeoma E; Sterling, Kenneth M; Ahearn, Gregory A

    2013-01-01

    The effects of sodium, potassium, sugar inhibitors, and membrane potential on ³H-D-glucose uptake by hepatopancreatic epithelial brush border membrane vesicles (BBMV) of the Atlantic marine shrimp, Litopenaeus setiferus, were investigated. Brush border membrane vesicles were prepared using a MgCl₂/EGTA precipitation method and uptake experiments were conducted using a high speed filtration technique. ³H-D-Glucose uptake was stimulated by both sodium and potassium and these transport rates were almost doubled in the presence of an inside-negative-induced membrane potential. Kinetics of ³H-D-glucose influx were hyperbolic functions of both external Na⁺ or K⁺, and an induced membrane potential increased influx J(max) and lowered K(m) in both salts. ³H-D-Glucose influx versus [glucose] in both Na⁺ or K⁺ media also displayed Michaelis-Menten properties that were only slightly affected by induced membrane potential. Phloridzin was a poor inhibitor of 0.5 mM ³H-D-glucose influx, requiring at least 5 mM in NaCl and 10 mM in KCl to significantly reduce hexose transport. Several sugars (D-galactose, α-methyl-D-gluco-pyranoside, unlabeled D-glucose, D-fructose, and D-mannose) were used at 75 mM as potential inhibitors of 0.1 mM ³H-D-glucose influx. Only unlabeled D-glucose, D-fructose, and D-mannose significantly (p < 0.05) reduced labeled glucose transport. An additional experiment using increasing concentrations of D-mannose (0, 10, 25, 75, and 100 mM) showed this hexose to be an effective inhibitor of 0.1 mM ³H-D-glucose uptake at concentrations of 75 mM and higher. As a whole these results suggest that ³H-D-glucose transport by hepatopancreatic BBMV occurs by a carrier system that is able to use both Na⁺ and K⁺ as drivers, is enhanced by membrane potential, is relatively refractory to phloridzin, and is only inhibited by itself, D-fructose, and D-mannose. These properties are similar to those exhibited by the mammalian SLC5A9/SGLT4 transporter

  13. ATP-dependent transport of bile acid intermediates across rat liver peroxisomal membranes.

    PubMed

    Une, Mizuho; Iguchi, Yusuke; Sakamoto, Tomoko; Tomita, Takashi; Suzuki, Yasuyuki; Morita, Masashi; Imanaka, Tsuneo

    2003-08-01

    The bile acid intermediate 3alpha,7alpha,12alpha-trihydroxy-5beta-cholestanoic acid (THCA) is converted to cholic acid exclusively in peroxisomes by the oxidative cleavage of the side chain. To investigate the mechanism by which the biosynthetic intermediates of bile acids are transported into peroxisomes, we incubated THCA or its CoA ester (THC-CoA) with isolated intact rat liver peroxisomes and analyzed their oxidation products, cholic acid and 3alpha,7alpha,12alpha-trihydroxy-5beta-cholest-24-enoic acid. The oxidation of both THCA and THC-CoA was dependent on incubation time and peroxisomal proteins, and was stimulated by ATP. THC-CoA was efficiently oxidized to cholic acid and 3alpha,7alpha,12alpha-trihydroxy-5beta-cholest-24-enoic acid as compared with THCA, suggesting that THC-CoA is the preferred substrate for transport into peroxisomes. The oxidation of THC-CoA was significantly inhibited by sodium azide, verapamile, and N-ethylmaleimide. Furthermore, the stimulatory effect of ATP on the oxidation was not replaced by GTP or AMP. In addition, the ATP-dependent oxidation of THC-CoA was markedly inhibited by pretreatment of peroxisomes with proteinase K when peroxisomal matrix proteins were not degraded. These results suggest that an ATP-dependent transport system for THC-CoA exists on peroxisomal membranes.

  14. Polymer electrolyte membranes from fluorinated polyisoprene-block-sulfonated polystyrene: Membrane structure and transport properties

    SciTech Connect

    Sodeye, Akinbode; Huang, Tianzi; Gido, Samuel; Mays, Jimmy

    2011-01-01

    With a view to optimizing morphology and ultimately properties, membranes have been cast from relatively inexpensive block copolymer ionomers of fluorinated polyisoprene-block-sulfonated polystyrene (FISS) with various sulfonation levels, in both the acid form and the cesium neutralized form. The morphology of these membranes was characterized by transmission electron microscopy and ultra-small angle X-ray scattering, as well as water uptake, proton conductivity and methanol permeability within the temperature range from 20 to 60 C. Random phase separated morphologies were obtained for all samples except the cesium sample with 50 mol% sulfonation. The transport properties increased with increasing degree of sulfonation and temperature for all samples. The acid form samples absorbed more water than the cesium samples with a maximum swelling of 595% recorded at 60 C for the acid sample having 50 mol% sulfonation. Methanol permeability for the latter sample was more than an order of magnitude less than for Nafion 112 but so was the proton conductivity within the plane of the membrane at 20 C. Across the plane of the membrane this sample had half the conductivity of Nafion 112 at 60 C.

  15. Riboflavin transport by rabbit renal basolateral membrane vesicles.

    PubMed

    Yanagawa, N; Jo, O D; Said, H M

    1998-12-09

    The present study examined riboflavin (RF) uptake by isolated rabbit renal basolateral membrane (BLM). RF uptake was linear during the initial 10 seconds and leveled off thereafter with longer incubation. Studies on RF uptake as a function of incubation medium osmolarity indicated that the BLM RF uptake was the results of transport (approximately 45%) into the intravesicular space as well as binding (approximately 55%) to membrane surfaces. The RF binding to BLM was Na+-dependent so that replacement of Na+ by other cations eliminated the binding component of RF uptake. The process of BLM RF uptake was saturable as a function of substrate concentration and was significantly inhibited by cis-addition of its structural analogs, lumiflavin and lumichrome, indicating the involvement of a carrier-mediated process. The BLM RF uptake was affected by changes in extravesicular pH so that, as compared to pH 7.5, RF uptake was lower at pH 6.5 and higher at pH 8.5. The effect of extravesicular pH persisted when the transmembrane H+ gradient was dissipated by FCCP, indicating the direct effect of pH on BLM RF uptake. The BLM RF uptake was not affected by alterations of the transmembrane electrical potential, induced by either the presence of anions with different membrane permeability (Cl-=NO-3>SO-4>gluconate-) or using nigericin (10 microg/mg protein) with an outwardly or inwardly directed transmembrane K+ gradient. The BLM RF uptake was, however, inhibited by probenecid and p-aminohippurate, and was enhanced by trans-RF. In summary, these results demonstrate the existence of a Na+-dependent BLM binding of RF and a membrane-associated carrier system for RF uptake by renal BLM.

  16. Purification and Identification of a Plasma Membrane Associated Electron Transport Protein from Maize (Zea mays L.) Roots

    PubMed Central

    Luster, Douglas G.; Buckhout, Thomas J.

    1989-01-01

    Plasma membranes isolated from three-day-old maize (Zea mays L.) roots by aqueous two-phase partitioning were used as starting material for the purification of a novel electron transport enzyme. The detergent-solubilized enzyme was purified by dyeligand affinity chromatography on Cibacron blue 3G-A-agarose. Elution was achieved with a gradient of 0 to 30 micromolar NADH. The purified protein fraction exhibited a single 27 kilodalton silver nitrate-stained band on sodium dodecyl sulfate polyacrylamide gel electrophoretograms. Staining intensity correlated with the enzyme activity profile when analyzed in affinity chromatography column fractions. The enzyme was capable of accepting electrons from NADPH or NADH to reduce either ferricyanide, juglone, duroquinone, or cytochrome c, but did not transfer electrons to ascorbate free-radical or nitrate. The high degree of purity of plasma membranes used as starting material as well as the demonstrated insensitivity to mitochondrial electron transport inhibitors confirmed the plasma membrane origin of this enzyme. The purified reductase was stimulated upon prolonged incubation with flavin mononucleotide suggesting that the enzyme may be a flavoprotein. Established effectors of plasma membrane electron transport systems had little effect on the purified enzyme, with the exception of the sulfhydryl inhibitor p-chloromercuriphenyl-sulfonate, which was a strong inhibitor of ferricyanide reducing activity. Images Figure 1 PMID:16667103

  17. Transport of lithium across the lamprey (Lampetra fluviatilis) erythrocyte membrane.

    PubMed

    Gusev, Gennadii P; Agalakova, Natalia I; Ivanova, Tatiana I

    2008-12-01

    Lithium, capable of replacing Na+ in various membrane transport processes, was used to investigate Na+ transport pathways across the lamprey erythrocytes membrane. The values of Li+ influxes have ranged from 8 to 24 mmol/l cells/h. Intracellular accumulation of Li+ was associated with loss of cellular Na+, the value of which was less than the value of Li+ influx. Both Li+ influx and Na+ efflux were partially inhibited by amiloride. The amiloride-sensitive Li+ influx was considerably stimulated by hyperosmotic cell shrinkage. The treatment of lamprey erythrocytes with blockers of protein phosphatases (fluoride and cantharidin) also resulted in a considerable increase in Li+ accumulation within the cells. No significant difference was observed between the values of Li+ and Na+ (22Na) influxes measured in red cells incubated simultaneously in isotonic LiCl and NaCl media (9.2 +/- 2.1 and 7.8 +/- 1.3 mmol/l cells/h, respectively). In hypo- and hypertonic media, however, the rate of Na+ influx in lamprey erythrocytes was approximately twice higher as compared to the rate of Li+ influx, what was determined by the difference in the amiloride-sensitive components. In acidified lamprey erythrocytes (intracellular pH 6.0) Li+ and Na+ influxes were considerably increased due to activation of amiloride-sensitive Na+/H+ (Li+/H+) exchange mechanism, although the activity of Na+/H+ exchange was much greater than that of Li+/H+ exchange. The data obtained confirm the hypothesis on the presence of two amiloride-sensitive systems of Na+ transport in the lamprey red blood cells.

  18. Modeling bidirectional transport of quantum dot nanoparticles in membrane nanotubes.

    PubMed

    Kuznetsov, A V

    2011-08-01

    This paper develops a model of transport of quantum dot (QD) nanoparticles in membrane nanotubes (MNTs). It is assumed that QDs are transported inside intracellular organelles (called here nanoparticle-loaded vesicles, NLVs) that are propelled by either kinesin or dynein molecular motors while moving on microtubules (MTs). A vesicle may have both types of motors attached to it, but the motors are assumed to work in a cooperative fashion, meaning that at a given time the vesicle is moved by either kinesin or dynein motors. The motors are assumed not to work against each other, when one type of motors is pulling the vesicle, the other type is inactive. From time to time the motors may switch their roles: passive motors can become active motors and vice versa, resulting in the change of the vesicle's direction of motion. It is further assumed that QDs can escape NLVs and become free QDs, which are then transported by diffusion. Free QDs can be internalized by NLVs. The effects of two possible types of MT orientation in MNTs are investigated: when all MTs have a uniform polarity orientation, with their plus-ends directed toward one of the cells connected by an MNT, and when MTs have a mixed polarity orientation, with half of MTs having their plus-ends directed toward one of the cells and the other half having their plus-ends directed toward the other cell. Computational results are presented for three cases. The first case is when organelles are as likely to be transported by kinesin motors as by dynein motors. The second case is when organelles are more likely to be transported by kinesin motors than by dynein motors, and the third case is when NLVs do not associate with dynein motors at all. Copyright © 2011 Elsevier Inc. All rights reserved.

  19. Brownian dynamics study of ion transport in the vestibule of membrane channels.

    PubMed

    Li, S C; Hoyles, M; Kuyucak, S; Chung, S H

    1998-01-01

    Brownian dynamics simulations have been carried out to study the transport of ions in a vestibular geometry, which offers a more realistic shape for membrane channels than cylindrical tubes. Specifically, we consider a torus-shaped channel, for which the analytical solution of Poisson's equation is possible. The system is composed of the toroidal channel, with length and radius of the constricted region of 80 A and 4 A, respectively, and two reservoirs containing 50 sodium ions and 50 chloride ions. The positions of each of these ions executing Brownian motion under the influence of a stochastic force and a systematic electric force are determined at discrete time steps of 50 fs for up to 2.5 ns. All of the systematic forces acting on an ion due to the other ions, an external electric field, fixed charges in the channel protein, and the image charges induced at the water-protein boundary are explicitly included in the calculations. We find that the repulsive dielectric force arising from the induced surface charges plays a dominant role in channel dynamics. It expels an ion from the vestibule when it is deliberately put in it. Even in the presence of an applied electric potential of 100 mV, an ion cannot overcome this repulsive force and permeate the channel. Only when dipoles of a favorable orientation are placed along the sides of the transmembrane segment can an ion traverse the channel under the influence of a membrane potential. When the strength of the dipoles is further increased, an ion becomes detained in a potential well, and the driving force provided by the applied field is not sufficient to drive the ion out of the well. The trajectory of an ion navigating across the channel mostly remains close to the central axis of the pore lumen. Finally, we discuss the implications of these findings for the transport of ions across the membrane.

  20. Molecular characterization of the first aromatic nutrient transporter from the sodium neurotransmitter symporter family.

    PubMed

    Meleshkevitch, Ella A; Assis-Nascimento, Poincyane; Popova, Lyudmila B; Miller, Melissa M; Kohn, Andrea B; Phung, Elizabeth N; Mandal, Anita; Harvey, William R; Boudko, Dmitri Y

    2006-08-01

    Nutrient amino acid transporters (NATs, subfamily of sodium neurotransmitter symporter family SNF, a.k.a. SLC6) represent a set of phylogenetically and functionally related transport proteins, which perform intracellular absorption of neutral, predominantly essential amino acids. Functions of NATs appear to be critical for the development and survival in organisms. However, mechanisms of specific and synergetic action of various NAT members in the amino acid transport network are virtually unexplored. A new transporter, agNAT8, was cloned from the malaria vector mosquito Anopheles gambiae (SS). Upon heterologous expression in Xenopus oocytes it performs high-capacity, sodium-coupled (2:1) uptake of nutrients with a strong preference for aromatic catechol-branched substrates, especially phenylalanine and its derivatives tyrosine and L-DOPA, but not catecholamines. It represents a previously unknown SNF phenotype, and also appears to be the first sodium-dependent B(0) type transporter with a narrow selectivity for essential precursors of catecholamine synthesis pathways. It is strongly and specifically transcribed in absorptive and secretory parts of the larval alimentary canal and specific populations of central and peripheral neurons of visual-, chemo- and mechano-sensory afferents. We have identified a new SNF transporter with previously unknown phenotype and showed its important role in the accumulation and redistribution of aromatic substrates. Our results strongly suggest that agNAT8 is an important, if not the major, provider of an essential catechol group in the synthesis of catecholamines for neurochemical signaling as well as ecdysozoan melanization and sclerotization pathways, which may include cuticle hardening/coloring, wound curing, oogenesis, immune responses and melanization of pathogens.

  1. ATP-dependent cadmium transport by the cadA cadmium resistance determinant in everted membrane vesicles of Bacillus subtilis.

    PubMed Central

    Tsai, K J; Yoon, K P; Lynn, A R

    1992-01-01

    Resistance to cadmium conferred by the staphylococcal plasmid pI258 occurs by means of energy-dependent efflux, resulting in decreased intracellular accumulation of cadmium. Recent sequence information suggested that efflux is mediated by a P-type ATPase. The cadA gene was previously expressed in Bacillus subtilis, conferring resistance to cadmium. Everted membrane vesicles were prepared from B. subtilis cells harboring either a plasmid containing the cadA system or the vector plasmid alone. 109Cd2+ transport into the everted membranes was measured in the presence of various energy sources. Cadmium transport was detected only in the presence of ATP as an energy source. The production of an electrochemical proton gradient (delta mu H+) by using NADH or phenazine methosulfate plus ascorbate was not able to drive transport. Reagents which dissipate delta pH abolished calcium transport due to the Ca2+/H+ antiporter but only partially inhibited cadmium transport. Inhibition of transport by the antibiotic bafilomycin A1 occurred at concentrations comparable to those which inhibit P-type ATPases. A band corresponding to the cadA gene product was identified on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and antibodies to the protein were prepared. Images PMID:1530844

  2. Effects of Hypotonic Saline Loading in Hydrated Dog: Evidence for a Saline-induced Limit on Distal Tubular Sodium Transport*

    PubMed Central

    Stein, Richard M.; Abramson, Ruth G.; Kahn, Thomas; Levitt, Marvin F.

    1967-01-01

    We performed studies on dogs under hydrated conditions, utilizing the rate of free water formation (CH2O) as an index of the rate of distal tubular sodium transport. Since CH2O could be progressively increased with no evidence of a maximal rate during loading with hypotonic (2.5%) mannitol, it was concluded that there is no limit on distal tubular sodium transport during mannitol loading. In contrast, during hypotonic (0.45%) saline loading CH2O rose initially, but as urine flow (V) exceeded 25% of the filtered load CH2O attained maximal levels (up to 20% of the filtered load) and remained stable as V increased to 50% of the filtered load. It was concluded that saline loading progressively inhibits proximal sodium reabsorption. Initially, the distal tubule absorbes a large fraction of the proximal rejectate and sodium excretion rises slightly. Eventually, an alteration in distal sodium transport appears which culminates in a maximal rate or transport limit. This distal transport limit provoked by saline loading could not be characterized by a classical Tm as seen with glucose and does not seem to be consequent to high rates of flow through the distal tubule. Regardless of the precise nature of this limit, the major increment in sodium excretion develops during saline loading only after saline alters the capacity of the distal tubule to transport sodium. PMID:6027084

  3. Malnutrition causes a reduction in alveolar epithelial sodium and chloride transport which predisposes to death from lung injury.

    PubMed

    Eisenhut, Michael

    2007-01-01

    All forms of malnutrition have been associated with increased severity of pneumonia, an increased pneumonia associated mortality and an increased risk of pulmonary fluid overload. Malnutrition was found to be associated with increased sweat sodium and chloride concentrations. A reduction of systemic sodium and chloride transport reflected in sweat sodium and chloride levels has been linked to increased severity of pulmonary edema in children with septicemia. Malnutrition causes a reduction in alveolar epithelial sodium and chloride transport which predisposes to death from lung injury. SUPPORTING EVIDENCE FOR THE HYPOTHESIS: Malnutrition caused reduced pulmonary fluid clearance in the rat model. Amiloride insensitive pulmonary fluid clearance in malnourished rats was reduced. The reduction in fluid clearance was reversible by beta agonists which increases epithelial sodium and chloride transport. Reduction of alveolar ion and fluid transport capacity explains the predisposition to death from pulmonary edema associated with intravenous fluids and blood transfusions in inpatients with malnutrition. Reduced alveolar epithelial ion transport impairs absorption of intra-alveolar inflammatory exudate in pneumonia leading to a increased severity of respiratory compromise and increased mortality. MEANS TO TEST THE HYPOTHESIS: Nasal potential difference measurements could compare airway epithelial sodium and chloride transport in patients with and without malnutrition and malnutrition associated lung disease. Sweat sodium and chloride concentrations could be compared in patients with and without respiratory disease associated with malnutrition and correlated with the severity of respiratory compromise.

  4. Constraints imposed by the membrane selectively guide the alternating access dynamics of the glutamate transporter GltPh.

    PubMed

    Lezon, Timothy R; Bahar, Ivet

    2012-03-21

    Substrate transport in sodium-coupled amino acid symporters involves a large-scale conformational change that shifts the access to the substrate-binding site from one side of the membrane to the other. The structural change is particularly substantial and entails a unique piston-like quaternary rearrangement in glutamate transporters, as evidenced by the difference between the outward-facing and inward-facing structures resolved for the archaeal aspartate transporter Glt(Ph). These structural changes occur over time and length scales that extend beyond the reach of current fully atomic models, but are regularly explored with the use of elastic network models (ENMs). Despite their success with other membrane proteins, ENM-based approaches for exploring the collective dynamics of Glt(Ph) have fallen short of providing a plausible mechanism. This deficiency is attributed here to the anisotropic constraints imposed by the membrane, which are not incorporated into conventional ENMs. Here we employ two novel (to our knowledge) ENMs to demonstrate that one can largely capture the experimentally observed structural change using only the few lowest-energy modes of motion that are intrinsically accessible to the transporter, provided that the surrounding lipid molecules are incorporated into the ENM. The presence of the membrane reduces the overall energy of the transition compared with conventional models, showing that the membrane not only guides the selected mechanism but also acts as a facilitator. Finally, we show that the dynamics of Glt(Ph) is biased toward transitions of individual subunits of the trimer rather than cooperative transitions of all three subunits simultaneously, suggesting a mechanism of transport that exploits the intrinsic dynamics of individual subunits. Our software is available online at http://www.membranm.csb.pitt.edu. Copyright © 2012 Biophysical Society. Published by Elsevier Inc. All rights reserved.

  5. Study of skin and mucous membrane disorders among workers engaged in the sodium dichromate manufacturing industry and chrome plating industry.

    PubMed

    Singhal, Vijay Kumar; Deswal, Balbir Singh; Singh, Bachu Narayan

    2015-01-01

    Inhalation of dusts and fumes arising during the manufacture of sodium dichromate from chrome ore, chromic acid mist emitted during electroplating, and skin contact with chromate produce hazards to workers. (1) To elucidate the prevalence of skin and mucous membrane disorders among the workers engaged in the sodium dichromate manufacturing industry and chrome plating industry. (2) To know the relationship of prevalence with the duration of exposure to chrome mist, dust, and fumes. A cross-sectional study was conducted among all the workers engaged in sodium dichromate manufacturing and chrome plating from several industries situated near the Delhi-Haryana border in the districts of Faridabad and Sonepat of Haryana, India from January 01, 2014 to December 31, 2014. All the workers available from the concerned industries for the study were interviewed and medically examined after obtaining their informed consent. A total of 130 workers comprising 66 workers from the sodium dichromate manufacturing industry and 64 workers from the chrome plating industry were examined on a pretested schedule. Descriptive statistical methods (proportions, relative risk, and Chi-square test of significance with P value analyzed using Epi Info version 7). All the workers were found to be males and of the adult age group. Out of the total examined, 69.69% and 56.22% of the workers had disorders of the nasal mucous membrane in the sodium dichromate manufacturing industry and the chrome plating industry, respectively. 42.42% and 28.22% of the workers had perforation of the nasal septum in the sodium dichromate manufacturing industry and chrome plating industry, respectively. 6.06% and 3.12% workers had skin ulcers in the sodium dichromate manufacturing industry and chrome plating industry, respectively. Nas