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Potassium Ions (potassium + ion)
Selected AbstractsAdsorption Behavior of Potassium Ion on Planting MaterialsCHINESE JOURNAL OF CHEMISTRY, Issue 9 2007Dechprasitthichokea Paunpassanan Abstract Characterization of planting materials used as adsorbent has been studied in order to compare potassium ion adsorption on two types of planting materials, which are a fired planting material (FPM) made from a mixture of 4 kinds of wastes (bottom ash, flue gas desulfurization (FGD) gypsum, paddy soil and sawdust) formed and fired at 850 °C and the commercial planting material called "hydroball" (HDB) bought from Jatujak market, Bangkok. The physical characteristics of both types of planting materials indicate that the FPM has a larger specific surface area than the HDB. The factors affecting potassium adsorption on both the planting materials such as an equilibration time and some solid/solution ratios were investigated. The suitable equilibration time for the adsorption to reach an equilibrium on the FPM and HDB is one and two hours, respectively. The highest amounts of potassium ion adsorbed on both the planting materials were obtained when the solid/solution ratio was 1:15. The adsorption behavior on both the planting materials tends to correspond with the Freundlich isotherm. [source] Model-Based Analysis of Potassium Removal During HemodialysisARTIFICIAL ORGANS, Issue 10 2009Andrea Ciandrini Abstract Potassium ion (K+) kinetics in intra- and extracellular compartments during dialysis was studied by means of a double-pool computer model, which included potassium-dependent active transport (Na-K-ATPase pump) in 38 patients undergoing chronic hemodialysis. Each patient was treated for 2 weeks with a constant K+ dialysate concentration (K+CONST therapy) and afterward for 2 weeks with a time-varying (profiled) K+ dialysate concentration (K+PROF therapy). The two therapies induced different levels of K+ plasma concentration (K+CONST: 3.71 ± 0.88 mmol/L vs. K+PROF: 3.97 ± 0.64 mmol/L, time-averaged values, P < 0.01). The computer model was tuned to accurately fit plasmatic K+ measured in the course and 1 h after K+CONST and K+PROF therapies and was then used to simulate the kinetics of intra- and extracellular K+. Model-based analysis showed that almost all the K+ removal in the first 90 min of dialysis was derived from the extracellular compartment. The different K+ time course in the dialysate and the consequently different Na-K pump activity resulted in a different sharing of removed potassium mass at the end of dialysis: 56% ± 17% from the extracellular compartment in K+PROF versus 41% ± 14% in K+CONST. At the end of both therapies, the K+ distribution was largely unbalanced, and, in the next 3 h, K+ continued to flow in the extracellular space (about 24 mmol). After rebalancing, about 80% of the K+ mass that was removed derived from the intracellular compartment. In conclusion, the Na-K pump plays a major role in K+ apportionment between extracellular and intracellular compartments, and potassium dialysate concentration strongly influences pump activity. [source] Structure, phase transitions and ionic conductivity of K3NdSi6O15·xH2O.ACTA CRYSTALLOGRAPHICA SECTION B, Issue 3 2000-K3NdSi6O15·2H2O, its polymorphs Hydrothermally grown crystals of ,-K3NdSi6O15·2H2O, potassium neodymium silicate, have been studied by single-crystal X-ray methods. The compound crystallizes in space group Pbam, contains four formula units per unit cell and has lattice constants a = 16.008,(2), b = 15.004,(2) and c = 7.2794,(7),Å, giving a calculated density of 2.683,Mg,m,3. Refinement was carried out with 2161 independent structure factors to a residual, R(F), of 0.0528 [wR(F2) = 0.1562] using anisotropic temperature factors for all atoms other than those associated with water molecules. The structure is based on highly corrugated (Si2O52,), layers which can be generated by the condensation of xonotlite-like ribbons, which can, in turn, be generated by the condensation of wollastonite-like chains. The silicate layers are connected by Nd octahedra to form a three-dimensional framework. Potassium ions and water molecules are located in interstitial sites within this framework, in particular, within channels that extend along [001]. Aging of as-grown crystals at room temperature for periods of six months or more results in an ordering phenomenon that causes the length of the c axis to double. In addition, two phase transitions were found to occur upon heating. The high-temperature transformations, investigated by differential scanning calorimetry, thermal gravimetric analysis and high-temperature X-ray diffraction, are reversible, suggesting displacive transformations in which the layers remain intact. Conductivity measurements along all three crystallographic axes showed the conductivity to be greatest along [001] and further suggest that the channels present in the room-temperature structure are preserved at high temperatures so as to serve as pathways for easy ion transport. Ion-exchange experiments revealed that silver can readily be incorporated into the structure. [source] The Dependence of the Sensitivity and Reliability of Contactless Conductivity Detection on the Wall Thickness of Electrophoretic Fused-Silica CapillariesELECTROANALYSIS, Issue 3-5 2009Petr T Abstract A contactless conductivity detector (C4D) performance has been tested on a simple capillary electrophoretic separation in a standard fused-silica capillary with an external diameter of 360,,m and in a thin-walled capillary (an external diameter of 150,,m); the internal diameters of the two capillaries were identical, equal to 75,,m. Potassium and sodium ions have been separated in a morpholinoethanesulfonic acid/histidine background electrolyte (MES/His), over a wide range of its concentrations (0,100,mM). At low MES/His concentrations, the C4D response, obtained from the height of the potassium peak, is by 100 to 200 per cent higher for the thin-walled capillary and the calibration dependences are linear, in contrast to the thick-walled capillary. These differences between the two capillaries decrease with increasing MES/His concentration, the C4D response in the thin-walled capillary is then higher by mere 20 per cent and the calibration dependences are linear in both the capillaries. The highest sensitivities have been obtained at a MES/His concentration of 50,mM, with LOD values for potassium ion of 2.0 and 2.6,,M, in the thin- and thick-walled capillaries, respectively. The signal-to-noise ratios and the plate counts are generally similar for the two capillaries. It follows from the results that special thin-walled capillaries can be advantageous when background electrolytes with very low conductivities must be employed. [source] On-column conductivity detection in capillary-chip electrophoresisELECTROPHORESIS, Issue 24 2007Zhi-Yong Wu Professor Abstract On-column conductivity detection in capillary-chip electrophoresis was achieved by actively coupling the high electric field with two sensing electrodes connected to the main capillary channel through two side detection channels. The principle of this concept was demonstrated by using a glass chip with a separation channel incorporating two double-Ts. One double-T was used for sample introduction, and the other for detection. The two electrophoresis electrodes apply the high voltage and provide the current, and the two sensing electrodes connected to the separation channel through the second double-T and probe a potential difference. This potential difference is directly related to the local resistance or the conductivity of the solution defined by the two side channels on the main separation channel. A detection limit of 15,,M (600,ppb or 900,fg) was achieved for potassium ion in a 2,mM Tris-HCl buffer (pH,8.7) with a linear range of 2 orders of magnitude without any stacking. The proposed detection method avoids integrating the sensing electrodes directly within the separation channel and prevents any direct contact of the electrodes with the sample. The baseline signal can also be used for online monitoring of the electric field strength and electroosmosis mobility characterization in the separation channel. [source] Sensitive detection of phosphopeptides by matrix-assisted laser desorption/ionization mass spectrometry: use of alkylphosphonic acids as matrix additivesRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 8 2008Hiroki Kuyama Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) has been one of the most powerful tools for analyzing protein phosphorylation. However, it is frequently difficult to detect phosphopeptides with high sensitivity by MALDI-MS. In our investigation of matrix/matrix-additive substances for improving the phosphopeptide ion response in MALDI-MS, we found that the addition of low-concentration alkylphosphonic acid to the matrix/analyte solution significantly enhanced the signal of phosphopeptides. In this study, the combination of methanediphosphonic acid and 2,5-dihydroxybenzoic acid gave the best results. In addition to enhancing the signal of the phosphopeptides, alkylphosphonic acid almost completely eliminated the signals of sodium and potassium ion adducts. We report herein sensitive detection of phosphopeptides by MALDI-MS with the use of alkylphosphonic acids as matrix additives. Copyright © 2008 John Wiley & Sons, Ltd. [source] Structure of Staphylococcus aureus guanylate monophosphate kinaseACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 10 2006Kamel El Omari Nucleotide monophosphate kinases (NMPKs) are potential antimicrobial drug targets owing to their role in supplying DNA and RNA precursors. The present work reports the crystal structure of Staphylococcus aureus guanylate monophosphate kinase (SaGMK) at 1.9,Å resolution. The structure shows that unlike most GMKs SaGMK is dimeric, confirming the role of the extended C-terminus in dimer formation as first observed for Escherichia coli GMK (EcGMK). One of the two SaGMK dimers within the crystal asymmetric unit has two monomers in different conformations: an open form with a bound sulfate ion (mimicking the ,-phosphate of ATP) and a closed form with bound GMP and sulfate ion. GMP-induced domain movements in SaGMK can thus be defined by comparison of these conformational states. Like other GMKs, the binding of GMP firstly triggers a partial closure of the enzyme, diminishing the distance between the GMP-binding and ATP-binding sites. In addition, the closed structure shows the presence of a potassium ion in contact with the guanine ring of GMP. The potassium ion appears to form an integral part of the GMP-binding site, as the Tyr36 side chain has significantly moved to form a metal ion,ligand coordination involving the lone pair of the side-chain O atom. The potassium-binding site might also be exploited in the design of novel inhibitors. [source] A Combined ESI- and MALDI-MS(/MS) Study of Peripherally Persulfonylated Dendrimers: False Negative Results by MALDI-MS and Analysis of Defects,CHEMISTRY - A EUROPEAN JOURNAL, Issue 19 2005Thorsten Felder Dipl.-Chem. Abstract Mass spectrometry, in particular MALDI-MS, has often been used as a valuable means to characterize dendritic molecules with respect to their molecular masses. Also, it is a valuable tool for analyzing potential defects in their structure which result from incomplete synthetic steps. This article presents a comparison of ESI and MALDI mass spectrometric experiments on dendrimers persulfonylated at their periphery. While the ESI mass spectra easily permit impurities and defects to be identified and thus provide evidence for sample purity, reactions with acidic matrices occur during the MALDI process. The resulting defects are identical to those expected from incomplete substitution. Thus, in these cases, MALDI-MS yields false negative results. With mass-selected, ESI-generated ions, collision experiments were performed in an FT-ICR mass spectrometer cell to provide detailed insight into the fragmentation patterns of the various dendrimers. Different fragmentation patterns are observed depending on the exact structure of the dendrimer. Also, the nature of the charge is important. The fragmentation reactions for protonated species differ much from those binding a sodium or potassium ion. These differences can be traced back to different sites for binding H+ versus Na+ or K+. Tandem MS experiments on mass-selected dendrimer ions with defects can be used to distinguish different types of defects. A concise structural assignment can thus be made on the basis of these experiments. Even mixtures of two isobaric defect variants with the same elemental composition can be identified. Massenspektrometrie, insbesondere MALDI-MS wurde oft als wertvolle Analysenmethode für die Charakterisierung von Dendrimeren hinsichtlich ihrer Molekülmasse, aber auch hinsichtlich einer Analyse potentieller Strukturdefekte eingesetzt, die aus unvollständig verlaufenden Synthesestufen resultieren. In diesem Artikel berichten wir über einen Vergleich von ESI- und MALDI-massenspektrometrischen Experimenten mit an ihrer Peripherie persulfonylierten Dendrimeren. Während die ESI-Massenspektren eine einfache Identifizierung von Verunreinigungen und Defekten erlauben und damit eine Reinheitskontrolle ermöglichen, laufen während der Ionisierung mittels MALDI Reaktionen mit sauren Matrices ab, die genau solche Defekte erzeugen, wie man sie aus einer unvollständigen Synthese erwarten würde. MALDI-MS führt hier also zu einem falsch-negativen Ergebnis. Mit massenselektierten Ionen aus der Electrospray-Ionisierung wurden Stoßexperimente in einer FT-ICR-Zelle durchgeführt, um einen detaillierten Einblick in das Fragmentierungsmuster der verschiedenen Dendrimere zu erhalten. Man beobachtet unterschiedliche Fragmentierungsmuster in Abhängigkeit von der genauen Struktur der Dendrimere. Auch die Art der Ladung ist wichtig, da die Fragmentierungswege der protonierten Dendrimere sich deutlich von denen ihrer Na+ - und K+ -Addukte unterscheiden. Diese Unterschiede können auf unterschiedliche Bindungsstellen für H+gegenüber Na+oder K+zurückgeführt werden. Tandem MS-Experimente mit massenselektierten, strukturdefekten Dendrimer-Ionen erlauben eine genaue Unterscheidung verschiedener Typen von Defekten. Sie können daher für eine detaillierte Strukturaufklärung verwendet werden. Sogar Mischungen zweier isobarer Defektvarianten mit gleicher Elementarzusammensetzung werden zuverlässig identifiziert. [source] Adsorption Behavior of Potassium Ion on Planting MaterialsCHINESE JOURNAL OF CHEMISTRY, Issue 9 2007Dechprasitthichokea Paunpassanan Abstract Characterization of planting materials used as adsorbent has been studied in order to compare potassium ion adsorption on two types of planting materials, which are a fired planting material (FPM) made from a mixture of 4 kinds of wastes (bottom ash, flue gas desulfurization (FGD) gypsum, paddy soil and sawdust) formed and fired at 850 °C and the commercial planting material called "hydroball" (HDB) bought from Jatujak market, Bangkok. The physical characteristics of both types of planting materials indicate that the FPM has a larger specific surface area than the HDB. The factors affecting potassium adsorption on both the planting materials such as an equilibration time and some solid/solution ratios were investigated. The suitable equilibration time for the adsorption to reach an equilibrium on the FPM and HDB is one and two hours, respectively. The highest amounts of potassium ion adsorbed on both the planting materials were obtained when the solid/solution ratio was 1:15. The adsorption behavior on both the planting materials tends to correspond with the Freundlich isotherm. [source] Contribution of endothelium-derived hyperpolarizing factors to the regulation of vascular tone in humansFUNDAMENTAL & CLINICAL PHARMACOLOGY, Issue 4 2008Jeremy Bellien Abstract Endothelium plays a crucial role in the regulation of cardiovascular homeostasis through the release of vasoactive factors. Besides nitric oxide (NO) and prostacyclin, increasing evidences show that endothelium-derived hyperpolarizing factors (EDHF) participate in the control of vasomotor tone through the activation of calcium-activated potassium channels. In humans, the role of EDHF has been demonstrated in various vascular beds including coronary, peripheral, skin and venous vessels. The mechanisms of EDHF-type relaxations identified in humans involved the release by the endothelium of hydrogen peroxide, epoxyeicosatrienoic acids (EETs), potassium ions and electronical communication through the gap junctions. The role of EETs could be particularly important because, in addition contributing to the maintenance of the basal tone and endothelium-dependent dilation of conduit arteries, these factors share many vascular protective properties of NO. The alteration of which might be involved in the physiopathology of cardiovascular diseases. The evolution of EDHF availability in human pathology is currently under investigation with some results demonstrating an increase in EDHF release to compensate the loss of NO synthesis and to maintain the endothelial vasomotor function whereas others reported a parallel decrease in NO and EDHF-mediated relaxations. Thus, the modulation of EDHF activity emerges as a new pharmacological target and some existing therapies in particular those affecting the renin,angiotensin system have already been shown to improve endothelial function through hyperpolarizing mechanisms. In this context, the development of new specific pharmacological agents especially those increasing EETs availability may help to prevent endothelial dysfunction and therefore enhance cardiovascular protection in patients. [source] Diamond Transistor Array for Extracellular Recording From Electrogenic CellsADVANCED FUNCTIONAL MATERIALS, Issue 18 2009Markus Dankerl Abstract The transduction of electric signals from cells to electronic devices is mandatory for medical applications such as neuroprostheses and fundamental research on communication in neuronal networks. Here, the use of diamond with its advantages for biological applications as a new material for biohybrid devices for the detection of cell signals is investigated. Using the surface conductivity of hydrogen-terminated single-crystalline diamond substrates, arrays of solution-gate field-effect transistors were fabricated. The characterization of the transistors reveals a good stability in electrolyte solutions for at least 7 days. On these devices, cardiomyocyte-like HL-1 cells as well as human embryonic kidney cells (HEK293), which were stably transfected with potassium channels, are cultured. Both types of cells show healthy growth and good adhesion to the substrate. The diamond transistors are used to detect electrical signals from both types of cells by recording the extracellular potential. For the HL-1 cells, the shape of action potentials can be resolved and the propagation of the signal across the cell layer is visible. Potassium currents of HEK293 cells are activated with the patch-clamp technique in voltage-clamp mode and simultaneously measured with the field-effect transistors. The ion sensitivity of the diamond surface enables the detection of released potassium ions accumulated in the cleft between transistor and cell. [source] New enzymatic assay for serum urea nitrogen using urea amidolyaseJOURNAL OF CLINICAL LABORATORY ANALYSIS, Issue 2 2003Shigeki Kimura Abstract We established an enzymatic assay for measurement of serum urea nitrogen using urea amidolyase (EC 3.5.1.45) from yeast species. The method is based on hydrolysis of urea by the enzyme. In this assay, we eliminated endogenous ammonium ion by use of glutamate dehydrogenase (EC 1.4.1.4). Then in the presence of urea amido-lyase, ATP, bicarbonate, magnesium, and potassium ions, ammonium ion was produced proportionally to urea concentration in serum. The concentra-tion of ammonium ion formed was determined by adding GLDH to produce NADP+ in the presence of 2-oxoglutarate and NADPH. We then monitored the change of absorbance at 340 nm. The inhibitory effect of calcium ion on this assay was eliminated by adding glyco-letherdiamine-N, N, N,, N,-tetraacetic acid to the reaction system. The with-in-assay coefficient of variations (CVs) of the present method were 1.80,3.76% (n = 10) at 2.8,19.0 mmol/L, respectively. The day-to-day CVs were 2.23,4.59%. Analytical recovery was 92,115%. The presence of ascorbic acid, bilirubin, hemoglobin, lipemic material, ammo-nium ion, or calcium ion did not affect this assay system. The correlation be-tween values obtained with the present method (y) and those by another enzy-matic method (x) was 0.997 (y = 1.02x , 0.10 mmol/L, Sy/x = 0.841, n = 100), with a mean difference of ,0.18 ± 0.86 mmol/L [(values by reference method , that of present method) ± SD] using the Bland-Altman technique. J. Clin. Lab. Anal. 17:52,56, 2003. © 2003 Wiley-Liss, Inc. [source] Imbalance of plasma membrane ion leak and pump relationship as a new aetiological basis of certain disease statesJOURNAL OF INTERNAL MEDICINE, Issue 6 2003G. Ronquist Abstract. The basis for life is the ability of the cell to maintain ion gradients across biological membranes. Such gradients are created by specific membrane-bound ion pumps [adenosine triphosphatases (ATPases)]. According to physicochemical rules passive forces equilibrate (dissipate) ion gradients. The cholesterol/phospholipid ratio of the membrane and the degree of saturation of phospholipid fatty acids are important factors for membrane molecular order and herewith a determinant of the degree of non-specific membrane leakiness. Other operative principles, i.e. specific ion channels can be opened and closed according to mechanisms that are specific to the cell. Certain compounds called ionophores can be integrated in the plasma membrane and permit specific inorganic ions to pass. Irrespective of which mechanism ions leak across the plasma membrane the homeostasis may be kept by increasing ion pumping (ATPase activity) in an attempt to restore the physiological ion gradient. The energy source for this work seems to be glycolytically derived ATP formation. Thus an increase in ion pumping is reflected by increased ATP hydrolysis and rate of glycolysis. This can be measured as an accumulation of breakdown products of ATP and end-products of anaerobic glycolysis (lactate). In certain disease entities, the balance between ATP formation and ion pumping may be disordered resulting in a decrease in inter alia (i.a.) cellular energy charge, and an increase in lactate formation and catabolites of adenylates. Cardiac syndrome X is proposed to be due to an excessive leakage of potassium ions, leading to electrocardiographic (ECG) changes, abnormal Tl-scintigraphy of the heart and anginal pain (induced by adenosine). Cocksackie B3 infections, a common agent in myocarditis might also induce an ionophore-like effect. Moreover, Alzheimer's disease is characterized by the formation of extracellular amyloid deposits in the brain of patients. Perturbation of cellular membranes by the amyloid peptide during the development of Alzheimer's disease is one of several mechanisms proposed to account for the toxicity of this peptide on neuronal membranes. We have studied the effects of the peptide and fragments thereof on 45Ca2+ -uptake in human erythrocytes and the energetic consequences. Treatment of erythrocytes with the ,1,40 peptide, results in qualitatively similar nucleotide pattern and decrease of energy charge as the treatment with Ca2+ -ionophore A23187. Finally, in recent studies we have revealed and published in this journal that a rare condition, Tarui's disease or glycogenosis type VII, primarily associated with a defect M-subunit of phosphofructokinase, demonstrates as a cophenomenon an increased leak of Ca2+ into erythrocytes. [source] Determination of the activity of H+ ions within and beyond the pH meter rangeAICHE JOURNAL, Issue 12 2001Eva Rodil This work confirms that the activities of individual ions measured with ion-selective electrodes are physically meaningful. The individual activities of the Cl,, Na+ and K+ ions in single-electrolyte aqueous solutions of HCl, NaOH and KOH were measured at 298.2 K in the range from 0 to 2 molal. In the pH range from 1 to 13, the pH values calculated from the measured activities of the ions are in good agreement with the values obtained with a pH probe. In agreement with previous results for potassium ions, and opposite to the behavior of other cations in 1:1 electrolyte solutions, the K+ and the H+ ions were found to have smaller activities than their conjugate anions. The experimental activity coefficients of the ions were correlated with the Khoshkbarchi-Vera equation and with the New Hydration Theory, and compared with the predictions given by the Pitzer theory. [source] Characterization of the complex formation of 1,6-anhydro-,-maltotriose with potassium using 1H and 39K NMR spectroscopyMAGNETIC RESONANCE IN CHEMISTRY, Issue 11 2009Takayuki Kato Abstract The 1H and 39K longitudinal relaxation times (T1) and 1H diffusion coefficients were measured to investigate the complex formation of 1,6-anhydro-,-maltotriose and potassium ions. Although the 1H- T1 values of H3,, H5,, H1, and H4, decreased in the presence of potassium ions, 1H chemical shifts and 1H diffusion coefficients did not show significant changes. The long-range coupling constants of 3JC,H around the glycosyl bonds did not show significant changes either. In the measurements of 39K spectra, the 39K signal obviously broadened and the 39K- T1 values decreased in the presence of 1,6-anhydro-,-maltotriose, indicating the complex formation of 1,6-anhydro-,-maltotriose and potassium ions. These results indicate that the conformation and molecular volume were unaffected in the complex formation. Copyright © 2009 John Wiley & Sons, Ltd. [source] Developmental changes in myoendothelial gap junction mediated vasodilator activity in the rat saphenous arteryTHE JOURNAL OF PHYSIOLOGY, Issue 3 2004Shaun L. Sandow A role for myoendothelial gap junctions (MEGJs) has been proposed in the action of the vasodilator endothelium-derived hyperpolarizing factor (EDHF). EDHF activity varies in disease and during ageing, but little is known of the role of EDHF during development when, in many organ systems, gap junctions are up-regulated. The aims of the present study were therefore to determine whether an up-regulation of heterocellular gap junctional coupling occurs during arterial development and whether this change is reflected functionally through an increased action of EDHF. Results demonstrated that in the saphenous artery of juvenile WKY rats, MEGJs were abundant and application of acetylcholine (ACh) evoked EDHF-mediated hyperpolarization and relaxation in the presence of N, -nitro- l -arginine methyl ester (L-NAME) and indomethacin to inhibit nitric oxide and prostaglandins, respectively. Responses were blocked by a combination of charybdotoxin plus apamin, or 1-[(2-chlorophenyl)diphenylmethyl]-1H-pyrazole (TRAM-34) plus apamin, or by blockade of gap junctions with the connexin (Cx)-mimetic peptides, 43Gap26, 40Gap27 and 37,43Gap27. On the other hand, we found no evidence for the involvement of the putative chemical mediators of EDHF, eicosanoids, L-NAME-insensitive nitric oxide, hydrogen peroxide or potassium ions, since 14,15-epoxyeicosa-5(Z)-enoic acid (14,15-EEZE), hydroxocobalamin, catalase or barium and ouabain were without effect. In contrast, in the adult saphenous artery, MEGJs were rare, EDHF-mediated relaxation was absent and hyperpolarizations were small and unstable. The present study demonstrates that MEGJs and EDHF are up-regulated during arterial development. Furthermore, the data show for the first time that this developmentally regulated EDHF is dependent on direct electrotonic coupling via MEGJs. [source] Cs6Nb4Se22 and K12Nb6Se35.3: two new compounds containing the M4Q22 building blockACTA CRYSTALLOGRAPHICA SECTION C, Issue 7 2010Jason W. Krizan The title compounds, namely hexacaesium tetraniobium docosaselenide and dodecapotassium hexaniobium pentatriacontaselenide, were formed from their respective alkali chalcogenide reactive flux and niobium metal. Both compounds fall into the larger family of solid-state compounds that contain the M2Q11 building block (M = Nb, Ta; Q = Se, S), where the metal chalcogenide forms dimers of face-shared pentagonal bipyramids. Cs6Nb4Se22 contains two Nb2Se11 building blocks linked by an Se,Se bond to form isolated Nb4Se22 tetrameric building blocks surrounded by caesium ions. K12Nb6Se35.3 contains similar Nb4Se22 tetramers that are linked by an Se,Se,Se unit to an Nb2Se11 dimer to form one-dimensional anionic chains surrounded by potassium ions. Further crystallographic studies of K12Nb6Se35.3 demonstrate a new M2Se12 building block because of disorder between an Se2, site (85%) and an (Se,Se)2, unit (15%). The subtle differences between the structures are discussed. [source] The centrosymmetric metal metaborate KCdB3O6ACTA CRYSTALLOGRAPHICA SECTION C, Issue 7 2009Shifeng Jin The title compound, potassium cadmium metaborate, crystallizes in a monoclinic cell, featuring infinite one-dimensional CdO5 chains and trigonal planar B atoms in hexagonal B3O6 metaborate ions. The trigonal bipyramidal CdO5 chains and metaborate ions are interlinked to form a three-dimensional framework, creating channels running parallel to the [10] direction in which the potassium ions reside. [source] A pseudo-merohedrally twinned rare-earth sulfate: K6[Ce(HSO4)2(SO4)4]·H2O, a novel structure typeACTA CRYSTALLOGRAPHICA SECTION C, Issue 4 2007Vratislav Langer A novel structure type of an acidic rare-earth sulfate, hexapotassium cerium dihydrogensulfate tetrasulfate monohydrate, is reported. The crystal is twinned, mimicking tetragonal symmetry. The CeIV atom is nine-coordinate, connecting to one corner-sharing and four edge-sharing sulfate groups. One of the potassium ions is disordered over two general positions. The compound is unique as it contains rare-earth monomers, [Ce(HSO4)(SO4)4]5,. The structure is composed of these monomers, water molecules, discrete hydrogensulfate ions and potassium ions held together by ionic interactions. There are two types of alternating layers in the structure, with compositions [K4Ce(HSO4)(SO4)4], and [K2(HSO4)(H2O)]+. [source] The X-ray structure of Salmonella typhimurium uridine nucleoside phosphorylase complexed with 2,2,-anhydrouridine, phosphate and potassium ions at 1.86,Å resolutionACTA CRYSTALLOGRAPHICA SECTION D, Issue 1 2010Alexander A. Lashkov Uridine nucleoside phosphorylase is an important drug target for the development of anti-infective and antitumour agents. The X-ray crystal structure of Salmonella typhimurium uridine nucleoside phosphorylase (StUPh) complexed with its inhibitor 2,2,-anhydrouridine, phosphate and potassium ions has been solved and refined at 1.86,Å resolution (Rcryst = 17.6%, Rfree = 20.6%). The complex of human uridine phosphorylase I (HUPhI) with 2,2,-anhydrouridine was modelled using a computational approach. The model allowed the identification of atomic groups in 2,2,-anhydrouridine that might improve the interaction of future inhibitors with StUPh and HUPhI. [source] Purification, crystallization and structure determination of native GroEL from Escherichia coli lacking bound potassium ionsACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 6 2007Philip D. Kiser GroEL is a member of the ATP-dependent chaperonin family that promotes the proper folding of many cytosolic bacterial proteins. The structures of GroEL in a variety of different states have been determined using X-ray crystallography and cryo-electron microscopy. In this study, a 3.02,Å crystal structure of the native GroEL complex from Escherichia coli is presented. The complex was purified and crystallized in the absence of potassium ions, which allowed evaluation of the structural changes that may occur in response to cognate potassium-ion binding by comparison to the previously determined wild-type GroEL structure (PDB code 1xck), in which potassium ions were observed in all 14 subunits. In general, the structure is similar to the previously determined wild-type GroEL crystal structure with some differences in regard to temperature-factor distribution. [source] Calcium-activated potassium channels and endothelial dysfunction: therapeutic options?BRITISH JOURNAL OF PHARMACOLOGY, Issue 4 2009Michel Félétou The three subtypes of calcium-activated potassium channels (KCa) of large, intermediate and small conductance (BKCa, IKCa and SKCa) are present in the vascular wall. In healthy arteries, BKCa channels are preferentially expressed in vascular smooth muscle cells, while IKCa and SKCa are preferentially located in endothelial cells. The activation of endothelial IKCa and SKCa contributes to nitric oxide (NO) generation and is required to elicit endothelium-dependent hyperpolarizations. In the latter responses, the hyperpolarization of the smooth muscle cells is evoked either via electrical coupling through myo-endothelial gap junctions or by potassium ions, which by accumulating in the intercellular space activate the inwardly rectifying potassium channel Kir2.1 and/or the Na+/K+ -ATPase. Additionally, endothelium-derived factors such as cytochrome P450-derived epoxyeicosatrienoic acids and under some circumstances NO, prostacyclin, lipoxygenase products and hydrogen peroxide (H2O2) hyperpolarize and relax the underlying smooth muscle cells by activating BKCa. In contrast, cytochrome P450-derived 20-hydroxyeicosatetraenoic acid and various endothelium-derived contracting factors inhibit BKCa. Aging and cardiovascular diseases are associated with endothelial dysfunctions that can involve a decrease in NO bioavailability, alterations of EDHF-mediated responses and/or enhanced production of endothelium-derived contracting factors. Because potassium channels are involved in these endothelium-dependent responses, activation of endothelial and/or smooth muscle KCa could prevent the occurrence of endothelial dysfunction. Therefore, direct activators of these potassium channels or compounds that regulate their activity or their expression may be of some therapeutic interest. Conversely, blockers of IKCa may prevent restenosis and that of BKCa channels sepsis-dependent hypotension. Mandarin translation of abstract [source] The Na-K-ATPase is a target for an EDHF displaying characteristics similar to potassium ions in the porcine renal interlobar arteryBRITISH JOURNAL OF PHARMACOLOGY, Issue 5 2002Eckhart Büssemaker The present study was performed to determine the characteristics of the endothelium-derived hyperpolarizing factor (EDHF) that mediates the nitric oxide (NO)- and prostacyclin (PGI2)-independent hyperpolarization and relaxation of porcine renal interlobar arteries. Bradykinin-induced changes in isometric force or smooth muscle membrane potential were assessed in rings of porcine renal interlobar artery preconstricted with the thromboxane analogue U46619 in the continuous presence of N, -nitro- L -arginine and diclofenac to inhibit NO synthases and cyclo-oxygenases. Inhibition of NO- and PGI2 -production induced a rightward shift in the concentration-relaxation curve to bradykinin without affecting maximal relaxation. EDHF-mediated relaxation was abolished by a depolarizing concentration of KCl (40 mM) as well as by a combination of charybdotoxin and apamin (each 100 nM), two inhibitors of calcium-dependent K+ (K+Ca) channels. Charybdotoxin and apamin also reduced the bradykinin-induced, EDHF-mediated hyperpolarization of smooth muscle cells from 13.7±1.3 mV to 5.7±1.2 mV. In addition to the ubiquitous ,1 subunit of the Na-K-ATPase, the interlobar artery expressed the , subunit as well as the ouabain-sensitive ,2, ,3 subunits. A low concentration of ouabain (100 nM) abolished the EDHF-mediated relaxation and reduced the bradykinin-induced hyperpolarization of smooth muscle cells (13.6±2.8 mV versus 5.20±1.39 mV in the absence and presence of ouabain). Chelation of K+, using cryptate 2.2.2., inhibited EDHF-mediated relaxation, without affecting NO-mediated responses. Elevating extracellular KCl (from 4 to 14 mM) elicited a transient, ouabain-sensitive hyperpolarization and relaxation that was endothelium-independent and insensitive to charybdotoxin and apamin. These results indicate that in the renal interlobar artery, EDHF-mediated responses display the pharmacological characteristics of K+ ions released from endothelial K+Ca channels. Smooth muscle cell hyperpolarization and relaxation appear to be dependent on the activation of highly ouabain-sensitive subunits of the Na-K-ATPase. British Journal of Pharmacology (2002) 137, 647,654. doi:10.1038/sj.bjp.0704919 [source] 3251: From elementary concept in animal models to new frontiers in humans: neurovascular coupling in the ocular circulationACTA OPHTHALMOLOGICA, Issue 2010C RIVA Purpose The retina and optic nerve, both optically accessible components of the central nervous system, are ideally suited for the investigation of the intrinsic physiological process by which blood ,ow, metabolism and neural activity are tightly coupled (Roy and Sherrington. 1890). Methods Using various techniques in the cat and human eye, the changes in blood flow in the retina and optic nerve in response to increased neural activity by flicker stimulation have been determined. The effect of varying the stimulus parameters, such as flicker modulation depth, frequency, luminance and red-green color ratio, on the blood flow response was investigated. Putative mediators of the activity-induced flow changes and the relationship between activity, blood flow and metabolic changes were assessed. Results Visual stimulation with flicker increases rapidly and markedly both retinal and optic nerve blood ,ows (functional hyperemia). Moreover, the data reveal unequivocally the presence, under specific conditions of flicker, of a neurovascular/neurometabolic coupling in these tissues, partly mediated by local potassium ions and nitric oxide production. Furthermore, the activity-induced hyperemia is altered during a number of physiological and pharmacological interventions and in some pathologic conditions. Conclusion Flicker stimulation of the retina offers a new and powerful means to modulate blood flow and investigate the neurovascular coupling in the neural eye tissues. Exploration of this activity-induced hyperemia and the mechanism(s) underlying the neurovascular coupling will lead to an increased understanding of the pathophysiology of various ocular diseases. [source] | |||||||||||||||||||||||||||||||