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1
Canadell, i. Sala David. "Potassium starvation responses in yeast highlight novel potassium-related functions." Doctoral thesis, Universitat Autònoma de Barcelona, 2015. http://hdl.handle.net/10803/298180.
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Mantenir la homeòstasis de cations és essencial per la supervivència dels éssers vius, i en especial pels organismes unicel·lulars. El llevat Saccharomyces cerevisiae s’ha utilitzat al llarg dels anys com un organisme model per l’estudi del conjunt de processos que controlen els nivells intracel·lulars de cations. El potassi és el principal catió intracel·lular del llevat i està involucrat en diversos processos de la fisiologia d'aquest organisme. Per aquest motiu la seva homeòstasis està minuciosament controlada per un seguit de transportadors que permeten la seva captació, distribució intracel·lular i eliminació de la cèl·lula i per un conjunt de proteïnes reguladores d’aquests processos. Encara que es té constància de la rellevància del potassi en el llevat, les seves dianes específiques i les bases moleculars d’algunes de les seves funcions són poc conegudes.
En aquest treball, mitjançant aproximacions d’eliminació del potassi del medi de cultiu, s’han pogut determinar els mecanismes d’algunes de les funcions conegudes del potassi i descobrir-ne de noves. S’ha demostrat que la manca de potassi provoca profundes alteracions en el perfil transcripcional del llevat. Entre elles destaquen l’accentuada repressió del gens que codifiquen proteïnes ribosomals i elements necessaris per la síntesi del ribosoma, dotant d’explicació molecular al ja conegut bloqueig en la síntesi de proteïnes provocat per la manca de potassi. L’eliminació del potassi del medi també provoca una caiguda dels nivells dels aminoàcids cisteïna i metionina que condueix a una activació del gens relacionats amb el metabolisme del sulfat i la síntesi d’aminoàcids sulfurats. Igualment, la privació del potassi comporta una acumulació d’espècies reactives de l’oxigen que produeixen un estat d’estrès oxidatiu a la cèl·lula. Aquesta respon amb l’activació transcripcional dels gens necessaris per combatre l’estrès oxidatiu, eliminar els oxidants i retornar la cèl·lula a un correcte estat redox. El llevat creixent en un medi sense potassi i en presència d’amoni acumula grans quantitats d’amoni a l’interior cel·lular a través del transportador de potassi Trk1 aprofitant la similitud química d’ambdós cations. Aquesta acumulació d’amoni activa vies per la seva fixació i eliminació en forma d’aminoàcids com és la via retrograda mitocondrial. L’eliminació del potassi del medi atura la proliferació cel·lular. Els nostres resultats han demostrat que aquesta aturada podria ser deguda a la disminució de les ciclines i d’elements reguladors de la formació dels anells de septines que afecten la progressió del cicle cel·lular.
El potassi també l’hem relacionat amb la homeòstasi d’un nutrient essencial com és el fosfat. L’absència de potassi o la pertorbació de la entrada normal d’aquest catió indueix els gens involucrats en la obtenció i mobilització del fosfat, d’igual manera com ho faria la depleció o limitació del fosfat. En aquetes condicions, la resposta transcripcional d’aquets gens està regulada pels diferents elements que composen la via PHO. L’afectació en l’obtenció del potassi impacte en la normal homeòstasis del fosfat provocant la mobilització de les reserves emmagatzemades en forma de polifosfats. La limitació del potassi, però, no modifica els nivells de fosfat lliure intracel·lular però sí que provoca una caiguda del nivells d’ATP i d’ADP, que podrien ser el senyal d’activació de la via PHO. A més, la pertorbació de la homeòstasis del potassi afecta el creixement dels llevats en medis amb baixos nivells de fosfat.
El conjunt de dades obtingudes en aquest treball ha permès descobrir nous vincles entre la homeòstasis del potassi i diversos processos cel·lulars, a més de la connexió d’aquest catió amb la homeòstasis de nutrients com el nitrogen, el sulfat i el fosfat.<br>The maintenance of cation homeostasis is essential for the survival of all living organisms and especially for microorganisms. The yeast Saccharomyces cerevisiae has been used over the years as a model organism for study the processes that control intracellular cation levels. Potassium is the major intracellular cation in yeast and it has been associated with various relevant cellular processes. For this reason, potassium homeostasis is tightly controlled by several transporters, that allow the cation uptake, intracellular traffic and efflux, and by a set of proteins regulating these processes. In spite of the importance of potassium for yeast physiology, not all relevant functional potassium-related targets have been identified.
In this work, potassium starvation conditions are used to determine the mechanisms of some of the known potassium functions and to discover new ones. We show that lack of potassium causes major alterations in the transcriptional profile of yeast cells. These transcriptional changes include the marked repression of genes encoding ribosomal proteins and elements necessary for the synthesis and assembly of ribosomes, providing the molecular basis for previously observed halt in protein synthesis caused by potassium deprivation. The elimination of potassium from the medium also causes a drop in cysteine and methionine levels which lead to transcriptional activation of genes related to metabolism of sulfate and biosynthesis of sulfur-contain amino acids. Similarly, cells deprived for potassium accumulate reactive oxygen species which results in oxidative stress. Concomitantly, cells trigger the transcriptional activation of genes necessary to combat oxidative stress, eliminate oxidants and return cells to the proper redox state. Yeast cells growing on ammonium as nitrogen source but lacking potassium accumulate large amounts of intracellular ammonium, which is transported through Trk1 taking advantage of the chemical similarity of both cations. Ammonium accumulation activates the retrograde mitochondrial pathway, resulting in detoxification of ammonium by its integration into amino acids. The complete removal of potassium from the medium leads to growth arrest. Our results show that this arrest could be due to the decrease in cyclins levels and in proteins involved in the assembly of septin rings, elements that are necessary for cell cycle progression.
We also have related potassium to the homeostasis of other essential nutrients such as phosphate. Depletion of potassium from the medium or disturbance of normal potassium uptake induces genes involved in the acquisition and release of phosphate, as it is usually observed in a situation of phosphate starvation. Under these conditions, the transcription of PHO-controlled genes is activated by different regulatory elements of the PHO pathway. Situations that impact on normal potassium homeostasis also cause mobilization of the phosphate reserves stored in form of polyphosphates. Potassium restrictions, however, does not alter the levels of intracellular free phosphate but it causes a drop in the levels of ATP and ADP, which could be the signal for the activation of the PHO pathway. In addition, on media with low levels of phosphate, disruption of normal potassium homeostasis effects yeast growth.
The results obtained in this work have been crucial to uncover new links between potassium homeostasis and many important cellular processes, in particular establishing the link between the homeostasis of this cation with that of other essential nutrients such as nitrogen, sulfate, and phosphate.
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Young, Bradford Kenneth Guertal Elizabeth A. "Potassium movement and uptake as affected by potassium source and placement." Auburn, Ala, 2009. http://hdl.handle.net/10415/1575.
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Bailey, Matthew Alexander. "Studies in renal cation transport in potassium replete and potassium-depleted rats." Thesis, Imperial College London, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.264703.
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Alfaro, Marta Andrea. "Potassium balances in grassland systems : does nitrogen affect potassium cycling and leaching?" Thesis, University of Reading, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.252256.
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Lee, Kai-lok. "The contribution of KATP channels to potassium release into the interstitial space during skeletal muscle contractions /." View the Table of Contents & Abstract, 2007. http://sunzi.lib.hku.hk/hkuto/record/B38347647.
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Salomon, Eva. "Availability of potassium to clover and grass from soils with different potassium fertilization histories /." Uppsala : Swedish Univ. of Agricultural Sciences (Sveriges lantbruksuniv.), 1999. http://epsilon.slu.se/avh/1999/91-576-5459-X.pdf.
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Stansfield, Phillip James. "Molecular modelling of potassium channels." Thesis, University of Leicester, 2007. http://hdl.handle.net/2381/29963.
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This study uses the structural coordinates of the determined K+ channels to create comparative models of three diverse members of this family, with the aim of enabling a better understanding of the function of these channels. The K+ channel of primary interest is the hERG K+ channel. The pharmacology of this channel is of considerable interest as serendipitous block of K+ conduction pore may result in cardiac arrest. A set of known antagonists have been docked into novel comparative models of hERG to propose how these drugs interact with the channel. The models have also been subjected to molecular dynamics simulations to investigate the drug binding in more detail and to gain a structural understanding of two critical biophysical properties of this channel: activation and inactivation. Additionally, ancillary domains of the channel have been modelled to provide a tool for interpreting detailed structure-function relationships for the hERG channel. The second channel investigated is the TASK-1 channel. Comparative models of this channel have been created to evaluate mutations that alter selectivity and pH sensitivity. The final K+ channel studied is the Kir2.1 channel. A fundamental property of this channel is its block by polyamines, which prevents the efflux of K+. Comparative models have been created, with a series of polyamine analogues docked into the membrane and cytoplasmic pore regions of this channel. Overall, this study has illuminated the structural basis of several biophysical properties that are intrinsic to normal K+ channel function.
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Chan, Brenda Kit Ching. "Reaction of potassium with carbons." Thesis, University of Newcastle Upon Tyne, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.316091.
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Viriyatum, Rawee Boyd Claude E. "Potassium fertilization of bluegill ponds." Auburn, Ala., 2009. http://hdl.handle.net/10415/1940.
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Podesta, M. de. "Helicon wave studies in potassium." Thesis, University of Sussex, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.370431.
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Karnik, Rucha. "Trafficking motifs in potassium channels." Thesis, University of Leeds, 2010. http://etheses.whiterose.ac.uk/1364/.
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The pancreatic ATP-sensitive potassium (KATP) channels couple glucose metabolism to excitability of the pancreatic β-cells to regulate insulin secretion. The channel subunits, Kir6.2 and SUR1, are encoded by the KCNJ11 and ABCC8 genes respectively. Genetic polymorphisms in these genes, which reduce channel activity, cause congenital hyperinsulinism (CHI) characterized by insulin hyper-secretion and hypoglycemia. The hERG (human ether-a-go-go related gene) potassium channels,encoded by the KCNH2 gene, contribute to the rapidly activating delayed rectifier K+ current (IKr), which is responsible for rapid repolarisation of the cardiac action potential. Decreased hERG channel function causes the Long QT syndrome 2 (LQTS2) and life threatening cardiac arrhythmias. Several mutations in these two clinically important potassium ion channels alter their surface density leading to disease. Therefore, it is of fundamental importance to investigate the trafficking mechanisms that regulate the surface density of these channels. Techniques in cell biology, molecular biology and biochemistry were employed to identify the molecular basis of Sar1-GTPase dependent ER exit of the KATP and hERG channels in COPII vesicles. Blocking the cargo binding sites on the Sec24 protein of the COPII coat with membrane-permeable synthetic peptides prevented ER exit of both these channels. While the diacidic 280DLE282 sequence on the Kir6.2 subunit of KATP channels was found to be the ER exit motif required for entry of the channels into COPII vesicles at the ER exit sites, such a motif was found to be absent on hERG Cterminus. Further, endocytic trafficking mechanism of hERG channels was studied in recombinant (HEK MSRII and HeLa) and native (neonatal rat cardiac myocytes) systems using cell biological and pharmacological tools. hERG channels were found to be internalised by a dynamin-independent, raft-mediated, and ARF6-dependent pathway. A prolonged block of this pathway revealed that the channels could also undergo internalisation by an alternate dynamin-mediated pathway. Internalised hERG channels were found to recycle back to the cell surface and undergo lysosomal degradation. Degradation of the channels was enhanced when Rab11a-GTPase function was disrupted leading to reduced surface density indicating that recycling is crucial to maintain cell surface density of the channels. Thus this study investigated and compared the previously unknown mechanisms of biosynthetic and endosomal trafficking of the KATP and hERG potassium channels with a conclusion that these processes play an important role in maintaining surface density and thereby in the function of these channels in physiological and patho-physiological conditions.
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Alexander, Sian. "Modulation of voltage-gated potassium channels: a pathophysiological mechanism of potassium channel antibodies in limbic encephalitis?" Thesis, University of Oxford, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.487139.
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Limbic encephalitis (LE) is a central nervous system disorder that is characterised by memory impairments, confusion, agitation and seizures, and associated with hyperintense lesions of the medial temporal lobe, seen with MRI. Anti-voltage-gated potassium channel (VOKC) antibodies have been been detected in the plasma of a subset of LE patients using a 125I-a-dendrotoxin (a-DTX) radioimmunoprecipitation assay, suggesting that the likely antigens are VOKC Kv1.l, 1.2 and 1.6 subunits. Symptoms of the disease improve markedly with immunosuppression, correlating with similarly dramatic falls in the titre of anti-VOKC antibodies, thus implicating anti-VOKC antibodies in the pathogenesis of LE. Circumstantial evidence from studies of inherited channelopathies and animal models of reduced VOKC activity suggests that VOKC dysfunction may contribute to the pathogenesis of LE. This thesis addresses whether anti-VOKC antibodies (i) bind to a-DTX-sensitive subunits and (ii) affect VOKC function. Immunofluorescence data show that binding of LE patient IgO to the surface of primary neurons and Kvl-expressing HEK-293/HEKTSA cells could not be detected with indirect immunofluorescence. Comparison of intracellular labelling with patient and control IgO showed that no additional labelling could be detected with LE patient IgO. Electrophysiological data show first, that a-DTXsensitive currents could not be reliably isolated from primary cultured hippocampal neurons; second, that NMT or LE samples did not affect VOKCs expressed by neuroblastoma-l cells; third, that none of the LE samples affected potassium currents in Kvl-transfected HEK-293 cells. These data suggest that 'anti-VOKC' antibodies may not bind directly to Kv1.111.2/1.6 homomers, or to a range of Kv1.I/1.2/1.6 subunit-containing heteromers in transfected cells. The findings instead suggest that 'anti-VOKC' antibodies in LE patient plasma may bind to a Kvl-associated protein that contributes to a-DTX-sensitive complexes in the radioimmunoprecipitation assay, but is absent from Kv1.111.2/1.6-transfected cells. Future work to characterise whether another antigen is bound by LE patient anti-VOKC antibodies will be important in determining how these antibodies contribute to the pathogenesis of LE.
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Hess, Tanja Maria. "Potassium-free and potassium-containing electrolytes affect plasma ions and acid-base status of endurance horses." Diss., Virginia Tech, 2005. http://hdl.handle.net/10919/26163.
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Effects of potassium supplementation were evaluated in four studies in endurance horses during races and treadmill exercise. In the first and second studies a potassium-free experimental formula was compared to potassium rich commercial formulas. The first study showed that supplementation increased plasma [K+], and that the extra sodium in the potassium-free experimental formulas helped to attenuate acidosis at the end of the ride. In the second study supplementation also increased plasma [K+], however speeds were lower and no increases were observed in plasma concentrations during the race. Supplementation of potassium during recovery helped to restore plasma [K+]. Higher plasma [Ca++] was found in horses supplied with experimental feeds, due to a lower dietary cation anion balance (DCAB). Three eliminated horses had heart rate arrhythmias and labile heart rates accompanied with higher plasma [K+] and lower [Ca++] than finishers. Also horses supplied with the experimental sodium-rich formula were less dehydrated than the ones receiving commercial formulas. The third study involved an 80 km endurance exercise test on the treadmill, and plasma [K+] was affected by potassium supplementation during exercise and recovery. The supply of potassium caused higher plasma [K+] helping to restore body stores. Also chloride supply in the electrolyte formulas maintained plasma [Cl-] levels during exercise and affected plasma concentrations during recovery. The fourth study showed that potassium supply affects plasma concentration, but also increases lactate production and glucose during sub-maximal exercise. A potassium-free electrolyte supply caused higher plasma [Ca++] during exercise. Higher sodium supply in the potassium-free electrolytes improved hydration during exercise. These studies show that potassium should supplemented after exercise and but not be done during exercise because of the risk of increased neuromuscular excitability.<br>Ph. D.
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Ait, Houssa Abdelhadi. "Contribution à l'étude du potassium dans les sols marocains échantillonnage, normes d'interprétation, étude du potassium échangeable." Grenoble 2 : ANRT, 1986. http://catalogue.bnf.fr/ark:/12148/cb375953692.
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Pikros, Léon. "Elaboration d'un sel industriel, le chlorure de potassium : adaptation d'un procédé industriel aux nouvelles contraintes technico-économiques." Mulhouse, 1999. http://www.theses.fr/1999MULH0589.
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L'optimisation de la production industrielle de KCl à partir de sel minier examine successivement : - 1) les aspects liés à la production de sels purs. - 2) les aspects liés aux adjuvants destinés à en éviter la prise en masse. - 3) les aspects liés à la diversification de la production, (assurance qualité, nouvelles formulations en fonction du marché. ). La première partie concerne l'optimisation de l'unité de production de sels purs. Après avoir développé des moyens de mesure appropriés, il a été possible de modéliser l'appareillage existant : un dissolveur, un cristalliseur et un filtre à bande. L'optimisation consécutive a permis une importante amélioration du cristalliseur en évitant la formation de plaques de sel sur les éléments réfrigérants Au niveau du filtre à bande, les bilans de matière ont permis de localiser les pertes de saumure, réduisant de 50% les pertes totales en sel. La deuxième partie traite des produits anti-mottants. Une étude critique des techniques analytiques existantes (spectrophotométrie infrarouge, ultraviolette, la résonance magnétique nucléaire, le dosage du carbone total) en ont permis de mettre au point une analyse fiable dans la matrice saline. Il a ainsi été possible de comprendre comment ils se fixent aux interfaces et de déterminer l'efficacité relative des agents destinés à les éliminer des sels où ils ne pouvaient être tolérés. Une troisième partie traite des travaux visant à assurer la diversification des produits : l'obtention d'un sel exempt de traces de vanadium a nécessité le développement d'une nouvelle technique analytique d'absorption atomique en four graphite avec prétraitement superficiel ; l'adaptation des produits aux normes de la pharmacopée européenne a fait l'objet d'une étude analytique spécifique ; enfin, l'élaboration d'un produit à usage alimentaire constitué d'un mélange quaternaire chlorure du potassium/glycine/chlorure de magnésium/ eau a été abordée. Son diagramme de phases partiel a été élaboré, ce qui a permis de préciser les domaines d'existence et les cinétiques d'évolution des états métastables des différentes phases susceptibles d'exister dans un produit commercial à température ambiante.
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Dewachter, Pascale. "Inhibiteurs calciques, activateurs potassiques et bronchospasme expérimental à l'histamine." Nancy 1, 1995. http://docnum.univ-lorraine.fr/public/SCD_T_1995_0459_DEWACHTER.pdf.
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Syeda, Ruhma. "Potassium channels in droplet interface bilayers." Thesis, University of Oxford, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.669989.
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Hodge, J. J. L. "Shaw potassium channel genes in Drosophila." Thesis, University of Cambridge, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.604121.
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Potassium (K<SUP>+</SUP>) channels shape the electrical activities of cells by changing the frequency and duration of action potentials and by setting the resting potential. The huge diversity of K<SUP>+</SUP> channels is conserved across species and is thought to be required to uniquely customise both the active excitable and passive properties of different cell types. When this study began, <I>Drosophila</I> voltage-gated K<SUP>+</SUP> currents were thought to be encoded by the four cloned members of this family <I>Shaker, Shab, Shaw </I>and <I>Shal</I>. Mutant analysis had only been performed with <I>Shaker</I>. In order to investigate the <I>in vivo</I> function of another member of the family, a number of methods of making <I>Shaw</I> mutants were used. A more accurate genomic structure and location of <I>Shaw</I> was determined, and I attempted to identify <I>P</I>-element inserts in <I>Shaw.</I> However all the candidate inserts identified were located too far from <I>Shaw</I> to be of practical use for generating mutations affecting <I>Shaw</I>. A dominant negative strategy to remove Shaw function was therefore performed. PCR mutagenesis was used to generate both epitope-tagged full-length and truncated mutant versions of <I>Shaw</I>. Additional control constructs were also made: a full-length wildtype <I>Shaw </I>and a dominant negative version of <I>Shaker</I>. Transgenic lines were generated containing the constructs whose expression was GAL4 inducible. Expression of mutant <I>Shaw</I>, using a number of GAL4 lines, caused an ether-sensitive leg-shaking phenotype.
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Miller, B. A. "Potassium channels in cultured locust muscle." Thesis, University of Nottingham, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.384270.
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Walker, David James. "Potassium compartmentation in barley root cells." Thesis, University of Nottingham, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.319644.
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Smith, Ruth Deborah. "Potassium intake, growth and energy metabolism." Thesis, University of Southampton, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.295704.
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Craighead, Anthea N. "Taxonomic variation of plant potassium concentrations." Thesis, University of Cambridge, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.444740.
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Marshall, Peter R. "Potassium promotion of nickel alumina catalysts." Thesis, University of Edinburgh, 1994. http://hdl.handle.net/1842/12572.
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The chemical and physical effects of potassium promotion on prepared nickel-alumina catalysts have been examined using "<I>in-situ</I>" Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS), Temperature Programmed studies and X-ray Powder Diffraction (XRPD). Various preparative methods were explored to obtain catalyst samples with a high metallic surface area. A sequential precipitation technique was employed, yielding a highly loaded nickel alumina catalyst (56 %wt Ni) with the hydrotalcite structure, typical of other industrial catalysts. Subsequent potassium promotion of this initial catalyst was achieved by impregnation. X.R.P.D. studies showed no observable changes in the bulk structure of the catalyst at room temperature or during calcination with low loadings of potassium (≤ 1 %wt). However, at higher loadings, potassium carbonate/oxide peaks became apparent but there was no indication of any other potassium derivatives. The presence of potassium both inhibited the reduction of the catalyst and brought about a reduction of the nickel surface area in the final reduced catalyst. Infrared studies showed definite changes in the surface chemistry of the catalyst with potassium promotion. Adsorption of carbon monoxide showed a downward shift in the wavenumber of the characteristic bands together with an apparent change in the relative proportions of the different carbon monoxide adsorbed species. Temperature dependent adsorption studies further indicated the formation of an activated species which was increasingly stable as a function of potassium promotion. The same species was observed in analogous carbon dioxide experiments. The effect of potassium on the infrared spectra from adsorbed ethene, propene and but-1-ene was more subtle.
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Rasol, Hepa. "Influence of Potassium on Gasification Performance." Thesis, Högskolan i Borås, Akademin för textil, teknik och ekonomi, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:hb:diva-10350.
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To release energy from chemically stored energy in the biomass was the new investigation in recent years. Utilizing of biomass for this purpose occur in two different ways, directly by burning (combustion) the biomass and indirectly by pyrolysis process which will convert the biomass to three main products, bio- tar, bio- char and synthetic gas. Biomass contains different amount of inorganic compound, especially alkali metals which causes some diverse impacts on combustion, pyrolysis and gasification process such as corrosion, agglomeration and fouling problems. This project aims to investigate the effect of K2CO3 on the pyrolysis and gasification processes of three different types of fuel; wood pellets, forest residue pellets and synthetic waste pellets at three different temperatures, 750 °C, 850 °C and 900 °C respectively. The purpose of this work to study and clarify the influence of K2CO3 on char yield, tar yield and tar compositions and the gasification rate and the reactivity of different fuels char. The pyrolysis process was carried out in a fluidized bed reactor during 2 minutes and the products were tar, char and synthetic gas. In this project interested in char and tar only. Char yield calculated and the results shows the char yield increase with increasing of [K2CO3]. While the tar analysis carried on GC- MS instrument at HB to study the tar yield and compositions. The results showed that potassium carbonate has not so much effect on tar yield and its composition. The last part was gasified the char in TGA with steam and CO2 as oxidizing media to study the influence of [K2CO3] on gasification rate and the reactivity of char samples at different temperatures. The result showed the [K2CO3] has inhibitory effect on gasification rate and the reactivity.
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Andrew, S. C. "Potassium homeostasis during intracellular Chlamydia development." Thesis, University College London (University of London), 2014. http://discovery.ucl.ac.uk/1430699/.
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Chlamydia trachomatis is an obligate intracellular bacterium, which is the leading cause of acquired blindness and the most prevalent bacterial sexually transmitted infection worldwide. Chlamydiae exist in two distinct forms. The infectious spore-like elementary bodies (EBs) that invade host cells differentiate into non-infectious reticulate bodies (RBs) that replicate intracellularly within a modified membrane-bound vacuole called the inclusion. Under stress, Chlamydiae can enter a persistent state, in which aberrant bodies (ABs) with reduced metabolic activity are formed. Surprisingly little is known about the mechanisms employed by the bacteria to maintain and manipulate their environment within host cells. This thesis investigates the role of inorganic ions in sustaining the inclusion throughout the Chlamydia infection cycle. Potassium starvation of intracellular RBs either after specific ionophore treatment or inhibition of inward rectifying cellular potassium channels induced the formation of ABs, which no longer differentiated into infectious EBs. These data demonstrate an essential role for potassium during C.trachomatis replication. Analysis of live RBs, using a potassium sensitive fluorescent probe, illustrated that potassium is actively scavenged from the host cell. Furthermore, when bacteria undergo RB-EB differentiation accumulated potassium is released prior to inclusion lysis. Experimentally reducing potassium ion concentration at this stage caused cells to expel bacteria in bursts. This event is distinct from previously described extrusion mechanisms, where either the inclusion is released intact or the host cell is lysed. These data show that RBs actively accumulate potassium during replication, with starvation leading to persistence. Loss of potassium ions during re-differentiation into EBs suggests that potassium efflux has a role in triggering inclusion lysis or bacteria exit from the host cell.
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Zheng, Jingfeng. "Designing Ionic Polymers for Potassium Batteries." The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu155508012993124.
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Mitchell, William D. "Polarization Reversal in Potassium Titanyl Phosphate." Wright State University / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=wright1194982327.
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Wegrzyn, Margaret. "Sodium potassium niobate based piezoelectric ceramics." Thesis, University of Manchester, 2012. https://www.research.manchester.ac.uk/portal/en/theses/sodium-potassium-niobate-based-piezoelectric-ceramics(8f2d3804-5012-4562-8bb0-2b325b754d13).html.
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NKN doped samples, (100-x)NKN-xSBN (0 ≤ x ≤ 10) were produced using the conventional mixed oxide route with 0.45 wt% Fe2O3 sintering aid (xSBNF). After 20-24 hours mixing, samples were calcined at 850°C and sintered at 1100–1140°C (± 180°C/hour) for 4 hours. By XRD 4 mol% SBN was found to be the solubility limit for single phase structure. By SEM, second phases were visible when 2 ≤ x ≤ 4; their structure was subsequently shown to be tungsten bronze type (TBT). 2-4 SBNF samples were high density, over 96% theoretical. For x = 0, TC = 457°C, TO-T = 234°C, Pr = 22 μC/cm2 and EC = 16.5 kV/cm. TC was found to decrease by 14.7°C and TO-T by 9.0°C per 1 mol% addition SBN. 2SBNF was the optimal formulation in terms of microstructure and electrical properties, with average grain size 3 μm, Pr = 25 μC/cm2 and EC = 8.8 kV/cm, ρ = 4.7 kΩm and Q = 1.16 eV. This material comprised approximately 90% orthorhombic and 10% tetragonal phases coexisting. Pseudo-cubic lattice parameters are a’ = c’ = 3.947180 Å, and b’ = 3.999996 Å for orthorhombic phase; the tetragonal has a’ = c’ = 3.989798 Å, and b’ = 3.975777 Å.Synchrotron XRD studies were undertaken as a function of temperature on 99.5NKN-0.5CuO + 0.6 wt% Nb2O5 solid and powder samples. The data were Rietveld refined. The solid sample underwent two polymorphic phase transitions at 300°C and 515°C; the latter was between two tetragonal phases: lattice parameters for the tetragonal phase (300-520°C) were a’ = c’ = 4.99557 Å, and b’ = 4.0363 Å; high temperature tetragonal (>500°C) exhibited a’ = c’ = 4.9519 Å, and b’ = 4.4941 Å. The powder sample of the same formulation exhibited more, smaller transformations. It was only orthorhombic at temperatures <140°C with a’ = c’ = 4.10680 Å, and b’ = 4.02620 Å. Above 140°C both orthorhombic and tetragonal phases were present. Another significant transformation occurred at 360°C where the structural unit cell parameters changed significantly. Parameter lengths are provided. P-E data was characterised by Pr = 19.9 μC/cm2 and EC = 13.5 kV/cm. Synchrotron X-ray diffraction analysis of 94 NKN-6LiTaO3 showed that tetragonal phase was present at 20-390°C, although an orthorhombic phase was identified at 20-200°C and again at 340-390°C just before the cubic transition temperature at 390°C. This is a new observation for NKN. A new and simple method for tape casting was developed to reduce powder wastage, enabling thick films of 50 μm to be cast. The reactive templated grain growth (RTGG) method was employed to orient 95NKN-5LiNbO3 and 94NKN-6LiNbO3 samples; CuO was utilised as a sintering aid. Pre-cursor BNN and NN template particles were produced using the molten salt synthesis (MSS) method, using a salt to oxide ratio of 1:1. Resulting NN particles were 15 μm wide and 0.5 μm thick. Eight layered 6LN + 0.4 wt% tapes produced using 10 wt% template particles resulted in 210 μm thick tapes with 67% orientation when sintered at 1150°C. Resulting properties include TC = 440ºC and TO-T = 70ºC, 25 kΩ resistance and capacitance 21.6 pF.
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Unrah, B. L., J. C. Silvertooth, D. M. Hendricks, and J. E. Malcuit. "Potassium Fertility of Several Arizona Soils." College of Agriculture, University of Arizona (Tucson, AZ), 1993. http://hdl.handle.net/10150/209581.
Full textAbstract:
Potassium (K) fertility requirements for cotton ( Gossypium spp) have been a matter of concern due to increasing interest and emphasis on fiber quality and numerous reports of K deficiencies in various cotton producing regions. To address this matter appropriately, a thorough understanding of the chemical, physical, and mineralogical composition of the soils in question is in order. Soil samples were collected from ten sites across southern Arizona that are representative of the common agricultural soils of the region. At all locations soils were sampled to a depth of 120 cm in 30 cm increments. All soils were characterized with respect to chemical composition by the following parameters: exchangeable K, total K, cation exchange capacity and particle size analysis. With the exception of one soil (a soil not commonly employed in cotton production), none of the chemically characterized soils contained less than 150 mg K kg⁻¹ of extractable K in the surface 90 cm of soil. All of the soils contained K- bearing mica and none of the soils contained any K- fixing vermiculite. From the initial chemical and mineralogical information, K fertilization is not likely for similar situations in Arizona. Further research is under way to quantify the K-fixing ability of each soil in this survey and additional field studies are also being conducted to evaluate K fertilization in both Upland (G. hirsutum L.) and Pima (G. barbadense L.) cotton.
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Hovorkova, Zuzana. "Monitoring of patients prescribed potassium supplements." Thesis, Uppsala universitet, Institutionen för farmaceutisk biovetenskap, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-389654.
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Monitoring of patients prescribed potassium supplements Zuzana Hovorkova Degree Project 30 hp, Pharmacotherapy Department of Pharmaceutical Biosciences/Division of Pharmacokinetics and Drug Therapy Supervisor: Linden Ashfield, Examiner: Margareta Hammarlund-Udenaes Introduction: In Northern Ireland, clinical technicians have been supporting pharmacist in their work in over five decades. From initially having mainly administrative tasks, the role of pharmacy technicians has progressed to more clinical activities. Following recent incidents caused by inadequate monitoring of potassium blood levels it was suggested pharmacy technicians could be utilized to improve patient care. Aim: Aim of this project was to ensure the appropriate monitoring and compliance with treatment guidelines for patients prescribed potassium supplements by extending the role of pharmacy technicians at Antrim Area Hospital. Methods: Training for extending the roles of clinical technicians was developed, following the structure of a regional training programme. Literature search was made to find appropriate background about the subject of interest. Data about monitoring of potassium levels in the relevant patients was collected. Daily monitoring of these patients before and after the change was implemented were compared. Results: Clinical technicians contribution to monitoring of patients prescribed potassium replacement therapy improved guidelines compliance from 66.6 % to 90 % (x2-test, p = 0.028). Percentage of successful treatment raised from 66 % to 89.7 % (x2-test, p = 0.028). Conclusion: By extending roles of the clinical technicians, better and appropriate monitoring of patients prescribed potassium supplements can be reached. In future, roles of the pharmacy technicians could be extended further, thus releasing pharmacists time to expand their role, leading to a more cost- effective system and ensuring medicines optimization.
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Widman, Lars. "Skeletal muscle potassium and magnesium in diuretic treated patients : effects of potassium - sparing diuretics of magnesium supplementation." Doctoral thesis, Umeå universitet, Medicin, 1988. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-100556.
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Lee, Mun Ching. "Regulation of voltage-gated potassium (Kv) and two-pore domain potassium (K2P) channels implicated in pulmonary hypertension." Thesis, University of Kent, 2018. https://kar.kent.ac.uk/67654/.
Full textAbstract:
Background: Kv2.1 and TASK-1 channels are two main contributors of K+ currents in pulmonary artery smooth muscle cells (PASMC). Dysregulation of these channels has been implicated in the pathogenesis of pulmonary hypertension (PH). This thesis aims to delve deeper into the implications of the regulation of Kv2.1 by Kv9.3 in PH. Another subject of interest would be whether NADPH oxidase type 4 (Nox4), one of the major reactive oxygen species (ROS) producers in the PASMC, modulates Kv2.1, Kv9.3, and TASK-1 channels. The effects of several redox agents are also investigated as potential modulators of Kv2.1, Kv9.3, and TASK-1. In addition, this thesis also examined the effect of a Kv2-channel blocker, stromatoxin, on Kv2.1 and Kv9.3. Finally, since amphoterin-induced gene and open reading frame (AMIGO) proteins have recently been shown as novel Kv2.1-interacting partners, their effects on Kv2.1 and/or Kv9.3 are also explored in this study. Experimental approach: Whole-cell patch clamp electrophysiology was used to measure currents of the ion channels expressed in modified tsA-201 cells, in the absence and presence of Nox4 AMIGO and other regulatory molecules. Immunohistochemistry was deployed to visualize the distribution of Kv2.1 and Kv9.3 proteins in the rat lungs and hearts. Key results and Conclusions: This study supports the findings that Kv9.3 regulates Kv2.1 by increasing the current amplitude, shifting the activation threshold to a more negative voltage range, and prolonging the slow component of time constant of deactivation. These effects could be beneficial in PH as this would mean cells could be brought back to its resting membrane potential faster and the transduction of the next action potential can be delayed. Kv2.1 and Kv9.3 have also been detected at the endothelium and PASMC in rat lungs and hearts, further substantiating the claim that these channels are potential players in regulating PH. AMIGO1 and AMIGO2 proteins are confirmed as regulators of Kv2.1 and Kv9.3 proteins. Nox4 does not regulate Kv2.1, Kv9.3, and TASK-1 channels expressed in tsA-201 cells. While hydrogen peroxide (H2O2) does not have any effect on Kv2.1 and Kv9.3, it abolished the current reduction effect of AMIGO2 on Kv2.1/Kv9.3. Other redox agents used in this study such as dithiothreitol (DTT), 5,5'-dithiobis-(2-nitrobenzoic acid) (DTNB), and chloramine T (Ch-T) are not modulators of these channels expressed in tsA-201 cells. The lack of effect from Nox4 and these redox agents could suggest that the redox regulation of different Nox subunit/Kv channels combination varies for different cell types due to the different regulatory proteins present in different heterologous expression systems. As with the case of H2O2 and AMIGO2, it is likely that the regulatory proteins, which could facilitate the hypoxia-sensing properties of Nox4 and the effects of the redox agents on the ion channels, are missing in our heterologous expression system, compared with other host cells.
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Biswas, Sumitra Bose. "Impact of mineralogy on potassium dynamics and retention behavior in Bangladesh soils used in rice cropping systems." Texas A&M University, 2008. http://hdl.handle.net/1969.1/85972.
Full textAbstract:
The combination of rising population and increasing food demand has placed
tremendous pressure on the soil resource in Bangladesh, especially floodplain soils
where rice may be grown year round. Although these floodplain soils contain minerals
high in potassium (K) such as micas, K deficiency in rice paddy soils is increasing
throughout Bangladesh. Harvesting of straw from fields exacerbates the removal of
nutrients including K, and intensive cropping with unbalanced fertilizer has resulted in
depletion of "readily available" K in large areas.
Five representative floodplain soils in rice production were sampled by horizon
to determine physical, chemical and mineralogical properties, assess soil K, investigate
plant available K, and understand impacts of redox on K fixation and release.
Total and nonexchangeable K were determined using concentrated hydrogen
fluoride (HF) digestion and 1.0 M HNO3 digestion, respectively, along with NH4OAcextractable
K. Cation exchange capacity under both oxidized and reduced conditions
was determined. Assessment of adsorption and release of K as a function of redox was done in conjunction with seven different concentrations of potassium chloride (KCl)
solution and three different soils.
Significant amounts of K were present in all fractions of silts and clays.
Potassium concentration was greatest in the coarse clay fraction. High HNO3-
extractable K suggested that much of the K in soils was from mica interlayers. Acidic
soils contained less K in all fractions than the less weathered, calcareous soils. The clay
fractions exhibited mostly mica, vermiculite, smectite and kaolinite. The cation
exchange capacity (CEC) of reduced soils was less under oxidized condition, due to
collapse of the interlayer in response to increased layer charge upon structural Fe
reduction.
The adsorption of K was greater for calcareous soils under both oxidized and
reduced conditions than for the acidic soils. Less native K was extracted under oxidized
conditions than under reduced conditions. Less adsorption under reduced conditions may
be due to an increase in solution Fe2+ which can compete with K+ for exchange sites on
clays.
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Choi, Eun Kyung. "Regulation of KCNQ1 potassium channel trafficking and gating by KCNE1 and KCNE3 /." Access full-text from WCMC, 2009. http://proquest.umi.com/pqdweb?did=1692648191&sid=1&Fmt=2&clientId=8424&RQT=309&VName=PQD.
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Matz, Jason D. "Correction of potassium deficiency in soybean and corn production in southeast Kansas." Thesis, Kansas State University, 2012. http://hdl.handle.net/2097/13415.
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Master of Science<br>Department of Agronomy<br>David B. Mengel<br>Over the last decade low (< 130 mg kg -1) soil test potassium (K) levels and increased crop K deficiency have become a major concern in the clay-pan soils of southeast Kansas. The use of more intense crop rotations and the increased production of high K extracting crops (e.g.
soybeans (Glycine max L.)) has significantly increased K removal from these soils. In addition, the traditional use of the nutrient sufficiency-based fertilizer recommendations has resulted in K application rates being substantially lower than removal rates. Because of these practices, many soils that had naturally elevated K availability 25 years ago have declined in K content. More troubling is the extreme yearly variation of soil test exchangeable K levels reported in the region,
which has many producers and consultants concerned about proper K management.
This study was initiated to examine the extent of K soil test variation and to determine if
the variability is impacting plant K availability by analyzing soybean leaf K content and crop
yield. A major objective of our research is to identify the mechanism(s) driving these changes in soil test K levels and K availability to crops during the growing season. The long-term goal is to be able to design a soil sampling system and develop alternative K fertilizer recommendation
strategies that could alleviate K deficiency impacts on crop yield. Evaluation of different K
fertilizer application practices including rate of application and broadcast or surface band
methods of application were studied as tools to correct soybean K deficiency. The direct and
residual impacts of K fertilization and placement were also evaluated on corn (Zea mays L.)
grown in the rotation with the soybeans.
Results observed from this research showed that monthly soil samples taken during three
crop years at multiple locations have ammonium acetate exchangeable K levels that indeed
change dramatically. The data we collected together with data accumulated by farmers and crop consultants showed significant fluctuation in exchangeable K levels of up to 50% on a yearly and even on a monthly basis. Levels seem to demonstrate seasonal changes: higher in the spring months and then decline in the summer and fall. Potassium soil test levels also appear to follow a similar trend as monthly precipitation and soil moisture status. During wet months soil levels tend to increase and then decline during drier months, however, this is not a perfect relationship and other factors are likely to be involved in regulating soil test K levels. No clear effect of K fertilization or method of placement on soybean or corn yields was observed during the study. However, soybean leaf samples revealed that on very low (< 90 mg kg -1) soil test sites surface band applied fertilizer increased leaf K concentrations compared to broadcasted applications. Furthermore, the corn study revealed no distinct difference between using a split annual or biannual fertilizer application system.
Maintaining soil test K levels above 130 mg kg
-1 using a spring soil test appears to be a
successful strategy for avoiding K deficiency. Traditionally most soil sampling occurs in late
summer or fall when soil conditions are dry. Our data has demonstrated that during this period
one should expect to encounter low soil test results that may not be true indicators of soil K
levels during the spring planting months. With that said, spring soil sampling can be difficult to do in a timely fashion due to weather, as well as potential labor restrictions. Another critical point is to not switch back and forth between spring and fall sampling dates. Staying consistent with your sample timing will minimize the seasonal variability that is frequently experienced. Additionally, adopting a build and maintain fertilizer recommendation philosophy rather than a nutrient sufficiency-based recommendation approach is a better nutrient budgeting method to avoid having removal rates exceeding nutrient additions. The best K management proposal would be to consider using a build and maintain approach in combination with basing fertilizer rates on spring soil test K levels.
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Lafond-Puyo, Martine. "Les hypokaliémies iatrogènes." Bordeaux 2, 1992. http://www.theses.fr/1992BOR2P098.
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Sherstov, Ivan V. "Matter wave interferences of potassium molecules and the influence of collisions with potassium atoms in the ground state." [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=981904947.
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Zhang, Hailin. "ATP-sensitive potassium channels and their modulation by nucleotides and potassium channel openers in vascular smooth muscle cells." Thesis, St George's, University of London, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.309744.
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Genies, Laure. "Etude des transporteurs impliqués dans l’absorption racinaire et la translocation aux parties aériennes du césium chez Arabidopsis thaliana." Thesis, Aix-Marseille, 2017. http://www.theses.fr/2017AIXM0022.
Full textAbstract:
Le 134Cs et le 137Cs, isotopes radioactifs du césium relâchés entre autres à la suite des accidents de Tchernobyl et Fukushima, sont des sources de préoccupations majeures pour la sécurité sanitaire et la protection des écosystèmes. La contamination des plantes est liée en partie à leur capacité à absorber le césium présent dans la solution du sol via des transporteurs. Le césium emprunte en effet, au moins en partie, le système de transport potassique sans disposer de transporteurs qui lui sont spécifiques. Il existe une grande diversité de transporteurs potassiques et la part du flux total qu’ils prennent en charge dépend du niveau de potassium fourni à la plante. Nous avons fait varier ce niveau et étudié son impact sur l’absorption et la distribution du césium dans la plante. Outre les phénomènes de compétition existant entre les deux éléments, le type de transporteurs dominant à un niveau de potassium donné a également une influence sur le transport du césium. Nous avons ainsi pu mettre en évidence des familles de transporteurs potassiques ayant de plus fortes chances d’être impliquées dans le transport de césium. Ainsi, les résultats produits pendant cette thèse mettent en évidence le rôle in planta du transporteur KUP9, jusque-là peu étudié, dans les flux de césium chez Arabidopsis thaliana. Nous n’observons pas de modifications de l’absorption du potassium chez les mutants invalidés sur ce transporteur : il serait donc possible de le manipuler pour moduler l’absorption de césium sans que la nutrition potassique ne soit altérée<br>134Cs and 137Cs, two radioactive isotopes unintentionally released after the Chernobyl and the Fukushima accidents, are of major concern for ecosystems protection and human health. Plants contamination is due to their ability to absorb cesium from the soil solution via transporters. Indeed, cesium which is supposed to have no role in plants can pass through potassium transporters. Proteins involved in potassium transport are diverse and the part of fluxes covered by each of them depends on the level of potassium supplied to the plant. We tested the effects of this level on uptake and distribution of cesium into the plant. Beside competition between the two elements, transporters which are dominant for a given potassium supply condition modify the cesium transport. Making the link between these modifications and knowledge on identity and properties of potassium transporters, we highlighted candidates with high potential for cesium transport. Hence, results produced during my thesis demonstrate in planta the role of KUP9 transporter, which has received little attention so far, in cesium fluxes in Arabidopsis thaliana. Changing in potassium uptake has not been observed in mutant lines disrupted in this KUP9 transporter suggesting interestingly that it could be possible to modulate cesium uptake without alteration of potassium nutrition
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Rudbeck, Maria. "Potassium(I) in water from Theoretical Calculations." Thesis, Uppsala University, Department of Mathematics, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-121236.
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Bennett, Aline Miriam. "Potential for potassium recovery as K-struvite." Thesis, University of British Columbia, 2015. http://hdl.handle.net/2429/54296.
Full textAbstract:
Crystallization of NH₄-struvite (MgNH₄PO4:6H₂O) pellets has proven to be a successful method of recovering nitrogen and phosphorus from wastewaters. Thus far, little work has been done on potassium recovery since it is not considered a water pollutant, nor do we face potassium shortages. However, potassium is an essential plant macronutrient and we are seeing worldwide imbalances in nutrient and fertilizer use, as well as a need for a slow release potassium fertilizer. Development of a full complement NPK fertilizer with NH₄-struvite and K-struvite components may have great potential. Given this, research into potassium recovery through crystallization of K-struvite (MgKPO₄: 6H₂O) is relevant and complements previous work done with NH₄-struvite.
The goals of this research were to develop fundamental understanding of K-struvite formation as the first step to recovering potassium, and eventually produce a full complement NPK slow-release fertilizer from wastewaters. This required the determination of new solubility product values for K-struvite at different temperatures, followed by bench-scale experiments to assess K-struvite synthesis under various solution conditions. A model to simulate each batch experiment and to predict optimal supersaturation conditions for K-struvite precipitation was developed using PHREEQC, aqueous equilibrium modelling software. Finally, initial experiments in the UBC fluidized bed reactor (UBC-FBR) were undertaken to assess the pelletization potential of K-struvite.
New solubility product values for K-struvite indicate that it is less soluble than previously reported, and the values determined at 10, 25 and 35°C fit the Van’t Hoff model. Optimal Mg:K:P molar ratio for synthesis of pure K-struvite was found to be approximately 3:50:1 in a wastewater matrix with pH 8, P-PO₄ concentration of 8 mM and a Mg:P ratio of 3:1. These concentrations were used in the UBC-FBR to assess the pelletization potential of K-struvite. These initial reactor runs were inconclusive due to an inability to stabilize the reactor without seeding. It would be recommended to seed the reactor during start-up in order to be able to compare process performance with the NH₄-struvite crystallization process in the UBC-FBR.
This study showed that formation of pure K-struvite is possible given the right supersaturation conditions in solution, requiring high potassium concentrations.<br>Applied Science, Faculty of<br>Civil Engineering, Department of<br>Graduate
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Sobek, Joanna Amanda. "Atomic force microscopy studies of potassium channels." Thesis, University of Oxford, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.669955.
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Ellis, Lee David. "Potassium channel control of neuronal frequency response." Thesis, McGill University, 2007. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=103381.
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The processing of sensory signals is an important, yet complex task in which a system must extract behaviorally relevant stimulus patterns from a vast array of sensory cues. When a neuron within a major sensory area is presented with a stimulus, one of the important characteristics used to distinguish between types of input is frequency. Often sensory neurons are tuned to narrow stimulus frequency ranges and are thus charged with the processing of subtypes of sensory signals. The weakly electric fish Apteronotus lepthorhynchus senses it's environment through modulations of a self-generated electric field. Two main types of sensory signals can be distinguished based on their frequency patterns. Prey stimuli cause low frequency perturbations of the electric field, while communication signals often result in high frequency signals. Pyramidal neurons in the electrosensory lateral line lobe (ELL) encode the low frequency signals with bursts, while the high frequency signals are relayed with single spikes. This thesis describes how a pyramidal neuron's response patterns can be tuned to specific frequencies by the expression of distinct classes of potassium channels.<br>I have cloned 3 small conductance (SK) calcium activated potassium channels from cDNA libraries created from the brain of Apteronotus. I have subsequently localized the AptSK channels throughout the brain using both in situ hybridization (AptSK1, 2 & 3) and immunohistochemical (AptSK1 & 2) techniques. The 3 channels showed distinct expression patterns, with the AptSK1 & 2 channels showing a partially overlapping expression pattern, while AptSK3 appears to be expressed in unique areas of the brain. In the ELL AptSK1 & 2 show a partially overlapping expression pattern, appearing in similar pyramidal neurons. However, their distribution within individual cell is unique, with AptSK1 showing a dendritic localization, while AptSK2 is primarily somatic. We have demonstrated that the unique expression pattern of the somatic AptSK2 channel in the ELL coincides with the functional SK currents evaluated through in vitro electrophysiology. Further we have shown that neurons that encode low frequencies do not possess functional SK channels. It thus appears that the presence of the AptSK2 channel subtype can predispose a neuron to respond to specific types of sensory signals.<br>In an attempt to evaluate if second messengers could modify the AptSK control of frequency tuning I investigated the consequences of muscarinic acetylcholine receptor (mAChR) activation on a pyramidal neurons response patterns. While it had been shown in vivo that mAChR activation increased a pyramidal neuron's response to low frequencies, I have found that this was not due to a decrease in AptSK current, but rather appears to be the result of a down-regulation of an A-type potassium channel.<br>Taken together the studies that comprise this thesis show how the selective expression of a single potassium channel subtype can control a sensory neurons response to specific environmental cues. The secondary modulation of the A-type current highlights the potential for a second messenger to control a neuron's sensory response through the down-regulation of constitutively expressed potassium current.
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Andres-Enguix, Isabelle. "TASK potassium channels and their anesthetic sensitivity." Thesis, Imperial College London, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.444148.
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Clarke, Catherine Elizabeth. "Characterisation of two pore domain potassium channels." Thesis, Imperial College London, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.408808.
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Capener, Charlotte E. "Modelling and simulation studies of potassium channels." Thesis, University of Oxford, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.249241.
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Khan, Asif Iqbal. "Potassium transport in human red blood cells." Thesis, University of Oxford, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.342545.
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Cockcroft, Christopher John. "Expression and Characterisation of Chimeric Potassium Channels." Thesis, University of Leeds, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.494113.
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Bethell, H. W. L. "Potassium, acidosis and ventricular repolarisation during ischaemia." Thesis, University of Cambridge, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.596607.
Full textAbstract:
In the first section the relative severity of the insult produced by low-flow ischaemia was established through a series of experiments monitoring the change in intracellular pH, high energy phosphates and LVDP during zero-flow, low flow (7.5% of the control flow rate) and moderate flow ischaemia (30% of the control flow rate). This established that in terms of mechanical performance and bioenergetic status reducing the flow to 7.5% of the control flow rate produced a significant ischaemic insult. Separate experiments showed that low-flow ischaemia caused action potential duration (APD) shortening which could be prevented by the K<SUB>ATP</SUB> channel inhibitor glibenclamide, so implicating the K<SUB>ATP</SUB> channel in the shortening process. In the second section it was established that low-flow ischaemia caused an early increase in <SUP>86</SUP>Rb efflux which was maximal during the phase of APD shortening. Once again glibenclamide abolished APD shortening but only reduced the degree of <SUP>86</SUP>Rb efflux. In the third section the effects of respiratory and metabolic acidosis, both known modulators of channel function, on the APD were investigated to establish whether they caused K<SUB>ATP</SUB> channel activation in isolation in whole heart. In conclusion, this study has demonstrated that in whole heart low-flow ischaemia causes potassium efflux as a result of K<SUB>ATP</SUB> channel activation, with the subsequent APD shortening. Intracellular acidosis and increased intracellular lactate, both known modulators of channel function in isolated patches, cause activation of the channel in isolation in whole heart but their main effect is to cause APD lengthening. Hence, these metabolic changes during ischaemia may serve to reduce overall APD shortening.
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Zhang, Nan. "Phases and Structures of Sodium Potassium Niobate." Thesis, University of Oxford, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.526133.
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