ACTA PHYSIOLOGICA, Issue 2 2010
M. Kristensen
Abstract Potassium (K+) displacement in skeletal muscle may be an important factor in the development of muscle fatigue during intense exercise. It has been shown in vitro that an increase in the extracellular K+ concentration ([K+]e) to values higher than approx. 10 mm significantly reduce force development in unfatigued skeletal muscle. Several in vivo studies have shown that [K+]e increases progressively with increasing work intensity, reaching values higher than 10 mm. This increase in [K+]e is expected to be even higher in the transverse (T)-tubules than the concentration reached in the interstitium. Besides the voltage-sensitive K+ (Kv) channels that generate the action potential (AP) it is suggested that the big-conductance Ca2+ -dependent K+ (KCa1.1) channel contributes significantly to the K+ release into the T-tubules. Also the ATP-dependent K+ (KATP) channel participates, but is suggested primarily to participate in K+ release to the interstitium. Because there is restricted diffusion of K+ to the interstitium, K+ released to the T-tubules during AP propagation will be removed primarily by reuptake mediated by transport proteins located in the T-tubule membrane. The most important protein that mediates K+ reuptake in the T-tubules is the Na+,K+ -ATPase ,2 dimers, but a significant contribution of the strong inward rectifier K+ (Kir2.1) channel is also suggested. The Na+, K+, 2Cl, 1 (NKCC1) cotransporter also participates in K+ reuptake but probably mainly from the interstitium. The relative content of the different K+ -transporting proteins differs in oxidative and glycolytic muscles, and might explain the different [K+]e tolerance observed. [source]

Protein kinase A modulates A-type potassium currents of larval zebrafish (Danio rerio) white muscle fibres

ACTA PHYSIOLOGICA, Issue 2 2009
C. A. Coutts
Abstract Aims:, Potassium (K+) channels are involved in regulating cell excitability and action potential shape. To our knowledge, very little is known about the modulation of A-type K+ currents in skeletal muscle fibres. Therefore, we sought to determine whether K+ currents of zebrafish white skeletal muscle were modulated by protein kinase A (PKA). Methods:, Pharmacology and whole-cell patch clamp were used to examine A-type K+ currents and action potentials associated with zebrafish white skeletal muscle fibres. Results:, Activation of PKA by a combination of forskolin + 3-isobutyl-1-methylxanthine (Fsk + IBMX) decreased the peak current density by ,60% and altered the inactivation kinetics of A-type K+ currents. The specific PKA inhibitor H-89 partially blocked the Fsk + IBMX-induced reduction in peak current density, but had no effect on the change in decay kinetics. Fsk + IBMX treatment did not shift the activation curve, but it significantly reduced the slope factor of activation. Activation of PKA by Fsk + IBMX resulted in a negative shift in the V50 of inactivation. H-89 prevented all Fsk + IBMX-induced changes in the steady-state properties of K+ currents. Application of Fsk + IBMX increased action potential amplitude, but had no significant effect on action potential threshold, half width or recovery rate, when fibres were depolarized with single pulses, paired pulses or with high-frequency stimuli. Conclusion:, PKA modulates the A-type K+ current in zebrafish skeletal muscle and affects action potential properties. Our results provide new insights into the role of A-type K+ channels in muscle physiology. [source]

Experimental frost weathering of sandstone by various combinations of salts

EARTH SURFACE PROCESSES AND LANDFORMS, Issue 8 2001
R. B. G. Williams
Abstract Weathering experiments are reported combining frost and a range of salts that occur naturally on rock faces in western and central Europe. Potassium and ammonium alums enhanced frost weathering quite considerably, both singly and in combination, though they were less potent than halite, the destructiveness of which, at sub-zero temperatures, was again confirmed. By contrast, alunogen and gypsum had little or no effect on rates of frost weathering either singly or in combination. Combining halite and gypsum produced breakdown that was intermediate between that of the two salts individually, as did the combination of gypsum and potassium alum. Breakdown in solutions of ammonium alum and gypsum, and in a combination of potassium and ammonium alum with gypsum, caused greater breakdown over 25 cycles of freeze,thaw than was recorded with the salts singly. The results extend the range of salts known to enhance frost weathering, and show that it is difficult to predict the aggressiveness of combinations of salts by experimenting with each salt separately. Copyright © 2001 John Wiley & Sons, Ltd. [source]

The Dependence of the Sensitivity and Reliability of Contactless Conductivity Detection on the Wall Thickness of Electrophoretic Fused-Silica Capillaries

ELECTROANALYSIS, Issue 3-5 2009
Petr 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]

Neocortical Microenvironment in Patients with Intractable Epilepsy: Potassium and Chloride Concentrations

EPILEPSIA, Issue 2 2006
Ali Gorji
Summary:,Purpose: The regulation of extracellular ion concentrations plays an important role in neuronal function and epileptogenesis. Despite the many studies into the mechanisms of epileptogenesis in human experimental models, no data are available regarding the fluctuations of extracellular potassium ([K+]o) and chloride ([Cl,]o) concentrations, which could underlie seizure susceptibility in human chronically epileptic tissues in vivo. Methods: By using cerebral microdialysis during surgical resection of epileptic foci, the basic [K+]o and [Cl,]o as well as their changes after epicortical electric stimulation were studied in samples of dialysates obtained from 11 patients by ion-selective microelectrodes. Results: The mean basal values of [K+]o and [Cl,]o in all patients were 3.83 ± 0.08 mM and 122.9 ± 2.6 mM, respectively. However, significant differences were observed in the basal levels of both [K+]o and [Cl,]o between different patients. Statistically, no correlation was found between basal [K+]o or [Cl,]o and electrocorticogram (ECoG) spike activity, but in one patient, dramatically lowered baseline [Cl,]o was accompanied by enhanced ECoG spike activity. Application of epicortical electrical stimulation increased [K+]o but not [Cl,]o in all cases. According to the velocity as well as spatial distribution of [K+]o reduction to the prestimulation levels, three different types of responses were observed: slow decline, fast decline, and slow and fast declines at adjacent sites. Conclusions: These data may represent abnormalities in ion homeostasis of the epileptic brain. [source]

Isostructural Potassium and Thallium Salts of Sterically Crowded Thio- and Selenophenols: A Structural and Computational Study

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 36 2008
Denis Bubrin
Abstract Because of their similar cationic radii, potassium and thallium(I) compounds are usually regarded as closely related. Homologous molecular species containing either K+ or Tl+ are very rare, however. We have synthesized potassium and thallium salts MEAr* [M, E = K, S (2a); K, Se (2b); Tl, S (3a); Tl, Se (3b); Ar* = 2,6-Trip2C6H3, Trip = 2,4,6- iPr3C6H2] derived from terphenyl-substituted thio- and selenophenols. In the solid-state structures of dimeric 2a, 2b, 3a, and 3b additional metal-,n,,-arene interactions to the flanking arms of the terphenyl substituents of different hapticity n are observed. Remarkably, the homologous potassium and thallium complexes 2b and 3b crystallize in isomorphous cells. For 2a, 3a, and model complexes of the composition METph (Tph = C6H4 -2-Trip) the nature of the M,E and M···C(arene) bonding was studied by density functional theory calculations.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source]

Potassium cycling and losses in grassland systems: a review

GRASS & FORAGE SCIENCE, Issue 3 2005
M. Kayser
Abstract Cycling of potassium in grassland systems has received relatively little attention in research and practice in recent years. Balanced nutrient systems require consideration of nutrients other than nitrogen (N). Potassium (K) is needed in large amounts and is closely related to N nutrition. In intensive dairy farming, surpluses of K arise from the input of concentrates and fertilizer and are returned to the grassland and may lead to increasing K content in the soil. Organic farming, on the other hand, is characterized by limitations in input of nutrient sources and quantities. Leaching of K from grassland is usually low, but high levels of available soil K, high K input from fertilizer or at urine patches lead to increasing losses. High K inputs have a negative influence on Mg and Ca uptake by plants and can cause accelerated leaching of these cations. High levels of K have been associated with inducing nutrition-related dairy cow health problems such as milk fever (hypocalcaemia) and grass tetany (hypomagnesaemia). This review gives an overview of the cycling of potassium and related cations in grassland systems especially with regard to leaching losses and identifies limitations to knowledge. [source]

Effect of acetate-free biofiltration with a potassium-profiled dialysate on the control of cardiac arrhythmias in patients at risk: A pilot study

HEMODIALYSIS INTERNATIONAL, Issue 1 2008
Rosa I. MUÑOZ
Abstract Cardiac arrhythmias are a frequent event in chronic hemodialysis patients. The aim of this study was to evaluate the efficacy and safety of acetate-free hemofiltration with potassium-profiled dialysate (AFB-K) dialysis compared with constant potassium acetate-free biofiltration (AFB). Twelve patients (mean age 79 years) affected by cardiac arrhythmias or at a high risk for arrhythmia (advanced age, hypertension, left ventricular hypertrophy, heart valve disease, coronary artery disease, diabetes, paroxysmal atrial fibrillation) participated in a single-center, sequential cohort study. All were treated with hemodialysis 3 times per week, using constant potassium AFB for the first 3 weeks, followed by an AFB-K dialysate for the subsequent 3 weeks. The hemofilter, duration of dialysis, and electrolyte concentration were the same in both treatments. Both AFB-K and constant potassium AFB dialytic techniques were safe and well tolerated. The results of biochemical tests were similar, except for serum potassium levels after 2 hr of dialysis, which were significantly higher in the AFB-K group (4.0 mmol/L) than in the constant potassium AFB group (3.6 mmol/L) (p<0.001). All cardiac variables improved during AFB-K dialysis. There was a significant reduction of postdialysis QT intervals corrected for heart rate in the AFB-K group (448.8 ms) compared with the constant potassium AFB group (456.8 ms) (p=0.039). The severity and mean number of ventricular extasystoles also decreased (163.5 vs. 444.5/24 hr). Potassium profiling during hemodialysis treatment may be beneficial for patients with arrhythmias or at those risk of arrhythmias, particularly those with predialysis hyperkalemia. [source]

Potassium Carbonate-Catalyzed Reactions of Salicylic Aldehydes with Allenic Ketones and Esters: an Effective Way to Synthesize Functionalized 2H -Chromenes

ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 7-8 2006
Min Shi
Abstract Potassium carbonate-catalyzed reactions of salicylic aldehydes with 3-methylpenta-3,4-dien-2-one, 3-benzylpenta-3,4-dien-2-one or ethyl 2-methylbuta-2,3-dienoate gave the corresponding functionalized 2H -1-chromenes in good to excellent yields and good stereoselectivities in some cases in DMSO at 120,°C within 1,h, respectively. [source]

Nitrogen, Phosphorus, Potassium, Magnesium and Calcium Removal by Brown Midrib Sorghum Sudangrass in the Northeastern USA

JOURNAL OF AGRONOMY AND CROP SCIENCE, Issue 6 2006
Q. M. Ketterings
Abstract For the long-term sustainability of the dairy industry in the Northeastern USA, manure nutrient application rates should not exceed crop nutrient removal once above-optimum soil fertility levels are reached. Dairy producers have shown a growing interest in brown midrib (BMR) forage sorghum (Sorghum bicolor (L.) Moench.) × sudangrass (Sorghum sudanense Piper) hybrids (S × S) as a more environmentally sound alternative to maize (Zea mays L.) but data on S × S nutrient removal rates are scant. Our objectives were to determine N, P, K, Ca and Mg removal with harvest as impacted by N application rate, using six N rate studies in New York. One of the six sites had a recent manure history. Although site-to-site differences existed, N application tended to decrease P and K and increase N, Ca and Mg concentrations in BMR S × S forage. Nutrient removal and yield were highly correlated for all sites except one location that showed a K deficiency. The crop removed large amounts of P and K in the manured site, suggesting that BMR S × S is an excellent scavenger of these nutrients. If manure is applied mid-season, forage K levels are likely too high for feeding to non-lactating cows. [source]

THE COMPOSITION OF TWO SPANISH PEPPER VARIETIES (FRESNO DE LA VEGA AND BENAVENTE-LOS VALLES) IN DIFFERENT RIPENING STAGES

JOURNAL OF FOOD QUALITY, Issue 6 2008
ANA BERNARDO
ABSTRACT The chemical composition of two traditional varieties of Spanish peppers, "Fresno de la Vega" and "Benavente-Los Valles" harvested in the provinces of León and Zamora, respectively, at different ripening stages (green mature, breaker and red) were evaluated. Herein we report the global composition, mineral and trace element contents, and the most relevant physicochemical parameters of each variety of pepper collected in 2 consecutive years. Both pepper varieties showed a similar chemical composition, except in vitamin C content, which resulted to be about 70% higher in Fresno de la Vega peppers. Red ripe fruits were high in total carbohydrates, fructose, glucose, sucrose, fat (64.5, 29.14, 25.57, 2.94, 1.79/100 g dry weight, respectively) and total soluble solids (6.83°Brix). Ascorbic acid content also increased progressively during ripening, reaching a mean value of 1.81 mg/100 g dry weight for Fresno de la Vega peppers. Potassium was the most abundant of the analyzed elements in the all samples, followed by phosphorus, magnesium, calcium and sodium. The order of the levels of the trace elements was iron > manganese > zinc > copper. PRACTICAL APPLICATIONS This report underscores the potential value of two traditional varieties of Spanish peppers and provides information on their composition during ripening to decide the proper harvesting time, which can be useful in the food industry. [source]

The Effects of Boiling and Leaching on the Content of Potassium and Other Minerals in Potatoes

JOURNAL OF FOOD SCIENCE, Issue 5 2008
P.C. Bethke
ABSTRACT:, The white potato (Solanum tuberosum L.) is a valuable source of potassium in the human diet. While most consumers benefit from high levels of potassium in potato tubers, individuals with compromised kidney function must minimize their potassium intake. This study was undertaken to determine the effects of leaching and boiling on levels of potassium and other minerals in potato tubers. Leaching alone did not significantly reduce levels of potassium or other minerals in tubers. Boiling tuber cubes and shredded tubers decreased potassium levels by 50% and 75%, respectively. Reductions in mineral amounts following boiling were observed for phosphorus, magnesium, sulfur, zinc, manganese, and iron. There was no difference between the leaching and boiling treatment and the boiling treatment. In addition, mineral levels in tubers of 6 North American potato cultivars are reported. Significant differences in mineral levels were detected among cultivars, but they were too small to be nutritionally important. Individuals wishing to maximize the mineral nutrition benefits of consuming potatoes should boil them whole or bake, roast, or microwave them. Those who must reduce potassium uptake should boil small pieces before consuming them. [source]

Effects of Whey Permeate-Based Medium on the Proximate Composition of Lentinus edodes in the Submerged Culture

JOURNAL OF FOOD SCIENCE, Issue 6 2006
Xiaojun Jeffrey Wu
ABSTRACT:, Biomass production, crude water-soluble polysaccharide (WSP), ash content, mineral profile, and crude protein content were determined for Lentinus edodes mycelia grown on whey permeate (WP)-based medium with lactose content of 4.5% or defined synthetic medium, and harvested after 5, 10, 15, or 20 d of fermentation at 25 °C. Harvesting time and the type of media interact to alter the chemical content of mycelia. Mycelia grown in WP had greater (P < 0.05) WSP and ash than mycelia grown in the synthetic media. A maximum production of WSP was obtained on the 10th day (4.1 × 102± 71 mg WSP/g dried mycelia) from mycelia grown on the WP-based media. Mycelia grown on WP harvested on the 20th day had the highest value in ash content (18 ± 3%). Potassium was found to be the main constituent in the ash of mushroom mycelia, which was followed by phosphorus, sodium, calcium, and magnesium. A steady increase of ash content was only noted in mycelia grown on WP. The calcium content of WP-grown mycelia was at least 10 times higher compared to mycelia grown in the control media regardless the harvesting time. Data in this research suggested that WP was more favorable than the synthetic media in the production of WSP, which is traditionally known for their medicinal value in L. edodes. [source]

Some cesium and potassium salts increase the water permeability of astomatous isolated plant cuticles

JOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 1 2007
Salem Elshatshat
Abstract Salts were applied as aqueous solution to the outer surfaces of astomatous isolated cuticles, and the water was allowed to evaporate. Effects of salt residues on the surfaces of cuticles on water permeability of cuticles were measured at 25°C. A surface dose of 0.2 mol m,2 Cs2CO3 and K2CO3 increased the water permeability of pear leaf cuticles by factors of 9.9 and 3.9, respectively. Na2CO3 was barely effective, and Li2CO3 as well as (NH4)2CO3 had no influence on water permeability. Potassium applied as sulfate, nitrate, or chloride had no effect on the water permeability of pear leaf cuticles, while K+ salts of weak acids (0.2 mol m,2) were effective, as they increased water permeability by factors of 5.4 (K+ -acetate), 3.9 (K2CO3), and 2.0 (K2HPO4), respectively. Sensitivity of Idesia polycarpa leaf cuticles to treatment with K2CO3 at 0.2 mol m,2 was greatest as water permeability was increased 35-fold, while the water permeability of cuticles from other species tested (astomatous leaf cuticles from Hedera helix, Citrus aurantium, Prunus laurocerasus, Pyrus communis, and Populus canescens; fruit cuticles from Capsicum annuum and Lycopersicon esculentum) increased only by factors ranging from 1.7 to 3.9. Data are discussed in relation to swelling and ion-exchange properties of cuticles. [source]

Fabrication of Structural Leucite Glass,Ceramics from Potassium-Based Geopolymer Precursors

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2010
Ning Xie
Leucite glass,ceramics were fabricated by cold isostatically pressing K2O·Al2O3·4SiO2·11H2O geopolymer powders into pellets followed by firing at 950°,1200°C, every 50°C in air. Leucite formation was observed in specimens heat treated to ,1000°C. The relative density, Vickers hardness, fracture toughness, and biaxial flexural strength of sintered samples ranged approximately 96%,98%, 767,865 kg/mm2, 0.94,2.36 MPa·m1/2, and 90,140 MPa, respectively. The toughness and biaxial flexure strength increased with the firing temperature, while the density and hardness were relatively constant. Scanning electron microscopic and transmission electron microscopic analysis revealed that the sintered geopolymer formed leucite crystals and a compositionally variable glassy phase. Samples heated to 1200°C attained the highest biaxial flexure strength and toughness. This higher strength is believed to arise from an optimum in density, leucite content, and crystal size distribution. [source]

The Chemical Interaction of Silver,Palladium Alloy Electrodes with Bismuth-Based Piezomaterials

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2010
Denis Schuetz
Multilayer technology relies heavily on the chemical compatibility of metal and ceramic. This work focuses on the ceramic,electrode interaction between 92Bi0.5Na0.5TiO3,6 BaTiO3,2K0.5Na0.5NbO3 [(Bi0.46Na0.47Ba0.06K0.01)(Nb0.02Ti0.98)O3], a promising actuator material and forerunner to an emerging class of lead-free actuator materials, and a silver,palladium alloy for inner electrodes, the only currently viable material for the firing temperatures necessary (1100°C). Of special concern was the high content of bismuth in the ceramic since prior investigations suggest that Bi2O3 (as well as various bismuth titanates) used as a fluxor in electroceramics are prone to forming the intermediate-phase bismuth palladate (Bi2PdO4), which can lead to poor contacting and delamination of multilayer stacks. Remarkably, no evidence of bismuth palladate formation could be found. However, the phase relations of the bulk ceramic have proven to be quite complex. Potassium was being drained out of the bulk ceramic either constituting the secondary phase K4Na2(TiO3)3 in unmodified experiments or evaporating and being replaced by silver in samples in contact with Ag. Mechanisms for the formation of these phases or the lack thereof are proposed. These findings were obtained by XRD, TG-DSC, and SEM with EDX, and LA-ICPMS. [source]

Adsorption of Magnesium by Bottom Soils in Inland Brackish Water Shrimp Ponds in Alabama

JOURNAL OF THE WORLD AQUACULTURE SOCIETY, Issue 4 2010
Harvey J. Pine
Low-salinity (2.0,9.0 g/L) well waters used for inland culture of marine shrimp in Alabama are imbalanced with respect to ionic composition. Inputs of potassium (muriate of potash) and potassium-magnesium sulfate (Kmag®) fertilizers are used to correct these imbalances. Potassium is lost in overflow and intentional discharge, seepage, and through adsorption by bottom soils by exchangeable and non-exchangeable processes. This study was initiated to determine if bottom soils removed magnesium in the same manner as potassium. Laboratory soil,water mesocosms revealed that soils strongly adsorbed magnesium. The rate of adsorption tended to decline over time, indicating establishment of the equilibrium. Magnesium losses for the three soils ranged from 1405 to 1713 mg/tank (average = 1568 mg/tank). The cation exchange capacity (CEC) of the soils varied from 10.4 to 44.0 cmolc/kg (average = 24.6cmolc/kg). The decline in magnesium increased with higher soil CEC. In another trial, repeated exposures of soils to solutions of 40 mg Mg2+/L failed to saturate exchange sites, but rather maintained equilibrium with other base cations on soil adsorption sites. Dissolved sulfate resulting from additions of magnesium with magnesium sulfate heptahydrate (MgSO4·7H2O) was also monitored. Although difficulties of analysis occurred, sulfate was not adsorbed appreciably by the soils. [source]

Potassium and ammonium hydrogen phthalates KHC6H4(COO)2 and (NH4)HC6H4(COO)2 , new organic crystals for Raman laser converters with large frequency shift

LASER PHYSICS LETTERS, Issue 7 2009
A.A. Kaminskii
Abstract Raman-induced many-phonons Stokes and anti-Stokes generation in a orthorhombic crystals KHC6H4(COO)2 and (NH4)HC6H4(COO)2 under picosecond pumping has been observed. All recorded nonlinear lasing lines in the visible and near-IR regions are identified and attributed to the ,(3) -promoting vibration modes of these orthorhombic phthalates. (© 2009 by Astro Ltd., Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA) [source]

Culturing in vitro produced blastocysts in sequential media promotes ES cell derivation

MOLECULAR REPRODUCTION & DEVELOPMENT, Issue 8 2006
J. Liu
Abstract Embryonic stem (ES) cell lines are routinely derived from in vivo produced blastocysts. We investigated the efficiency of ES cells derivation from in vitro produced blastocysts either in monoculture or sequential culture. Zygotes from hybrid F1 B6D2 mice were cultured in vitro to the blastocyst stage in Potassium (K+) simplex optimised medium (KSOM) throughout or in KSOM and switched to COOK blastocyst medium on day 3 (KSOM,CBM). Blastocysts were explanted on a feeder layer of mitomycin C-inactivated murine embryonic fibroblasts (MEF) in TX-WES medium for ES cell derivation. Sequential KSOM,CBM resulted in improved blastocyst formation compared to KSOM monoculture. ES cells were obtained from 32.1% of explanted blastocsyts cultured in KSOM,CBM versus18.4% in KSOM alone. ES cell lines were characterized by morphology, expression of SSEA-1, Oct-4 and alkaline phosphatase activity, and normal karyotype. These results indicate that in vitro culture systems to produce blastocysts can influence the efficiency of ES cell line derivation. Mol. Reprod. Dev. 1017,1021, 2006. © 2006 Wiley-Liss, Inc. [source]

Cellular mechanisms of potassium transport in plants

PHYSIOLOGIA PLANTARUM, Issue 4 2008
Dev T. Britto
Potassium (K+) is the most abundant ion in the plant cell and is required for a wide array of functions, ranging from the maintenance of electrical potential gradients across cell membranes, to the generation of turgor, to the activation of numerous enzymes. The majority of these functions depend more or less directly upon the activities and regulation of membrane-bound K+ transport proteins, operating over a wide range of K+ concentrations. Here, we review the physiological aspects of potassium transport systems in the plasma membrane, re-examining fundamental problems in the field such as the distinctions between high- and low-affinity transport systems, the interactions between K+ and other ions such as NH4+ and Na+, the regulation of cellular K+ pools, the generation of electrical potentials and the problems involved in measurement of unidirectional K+ fluxes. We place these discussions in the context of recent discoveries in the molecular biology of K+ acquisition and produce an overview of gene families encoding K+ transporters. [source]

Electrophysiological characterization of pathways for K+ uptake into growing and non-growing leaf cells of barley

PLANT CELL & ENVIRONMENT, Issue 12 2009
VADIM VOLKOV
ABSTRACT Potassium is a major osmolyte used by plant cells. The accumulation rates of K+ in cells may limit the rate of expansion. In the present study, we investigated the involvement of ion channels in K+ uptake using patch clamp technique. Ion currents were quantified in protoplasts of the elongation and emerged blade zone of the developing leaf 3 of barley (Hordeum vulgare L.). A time-dependent inward-rectifying K+ -selective current was observed almost exclusively in elongation zone protoplasts. The current showed characteristics typical of Shaker-type channels. Instantaneous inward current was highest in the epidermis of the emerged blade and selective for Na+ over K+. Selectivity disappeared, and currents decreased or remained the same, depending on tissue, in response to salt treatment. Net accumulation rates of K+ in cells calculated from patch clamp current,voltage curves exceeded rates calculated from membrane potential and K+ concentrations of cells measured in planta by factor 2.5,2.7 at physiological apoplastic K+ concentrations (10,100 mm). It is concluded that under these conditions, K+ accumulation in growing barley leaf cells is not limited by transport properties of cells. Under saline conditions, down-regulation of voltage-independent channels may reduce the capacity for growth-related K+ accumulation. [source]

Potassium diperiodatonickelate-initiated graft copolymerization of methyl acrylate onto organophilic montmorillonite

POLYMERS FOR ADVANCED TECHNOLOGIES, Issue 8 2008
Kuilin Deng
Abstract Using potassium diperiodatonickelate (Ni (IV)) as an efficient initiator, the graft copolymerization of methyl acrylate (MA) onto organophilic montmorillonite (OMMT) was successfully performed in an alkaline medium. Three grafting parameters were systematically evaluated as functions of the temperature, the initiator concentration, reaction time, pH value, and the ratio of MA to OMMT substrate. The structure of the titled graft copolymers (OMMT- g -PMA) were confirmed by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), differential scanning calorimetry (DSC), and thermo-gravimetric analysis (TGA). It was found that Ni (IV) was a highly efficient initiator for graft copolymerization of the MA onto OMMT, i.e., grafting efficiency is as high as 95% and grafting percentage can be facilely controlled within 700% in this study. In addition, the highest grafting efficiency and grafting percentage were obtained when temperature adopted was over 40°C and pH was about 10.3. A single-electron-transfer mechanism was proposed to illustrate the formation of radicals and the initiation reaction. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Bimodal role of conventional protein kinase C in insulin secretion from rat pancreatic , cells

THE JOURNAL OF PHYSIOLOGY, Issue 1 2004
Hui Zhang
The present study was conducted to evaluate the role of conventional protein kinase C (PKC) in calcium-evoked insulin secretion. In rat , cells transfected with green fluorescent protein-tagged PKC-, (PKC-,,EGFP), a depolarizing concentration of potassium induced transient elevation of cytoplasmic free calcium ([Ca2+]c), which was accompanied by transient translocation of PKC-,,EGFP from the cytosol to the plasma membrane. Potassium also induced transient translocation of PKC-,,EGFP, the C1 domain of PKC-, and PKC-,,GFP. A high concentration of glucose induced repetitive elevation of [Ca2+]c and repetitive translocation of PKC-,,EGFP. Diazoxide completely blocked both elevation of [Ca2+]c and translocation of PKC-,,EGFP. We then studied the role of conventional PKC in calcium-evoked insulin secretion using rat islets. When islets were incubated for 10 min with high potassium, Gö-6976, an inhibitor of conventional PKC, and PKC-, pseudosubstrate fused to antennapedia peptide (Antp-PKC19,31) increased potassium induced secretion. Similarly, insulin release induced by high glucose for 10 min was enhanced by Gö-6976 and Antp-PKC19,31. However, when islets were stimulated for 60 min with high glucose, both Gö-6976 and Antp-PKC19,31 reduced glucose-induced insulin secretion. Similar results were obtained by transfection of dominant-negative PKC-, using adenovirus vector. Taken together, PKC-, is activated when cells are depolarized by a high concentration of potassium or glucose. Conventional PKC is inhibitory on depolarization-induced insulin secretion per se, but it also augments glucose-induced secretion. [source]

Supramolecular Chemistry on a Cluster Surface: Fixation/Complexation of Potassium and Ammonium Ions with Crown-Ether-Like Rings,

ANGEWANDTE CHEMIE, Issue 32 2009
Achim Müller Prof.
Gemeinsam und doch getrennt: Auf einer hochnucleophilen Clusteroberfläche lassen sich Ammonium- und Kaliumionen selektiv komplexieren und trennen. Sechs {Mo4VKO6}-Ringe mit einer Kronenether-artigen Funktionalität (siehe Bild; Mo,blau, V,grün, K,violett, O,rot) in den Löchern des untersuchten Clusterkomplexes fixieren sechs Ammoniumionen (N,orange, H,gelb). [source]

Potassium channels Kv1.3 and Kv1.5 are expressed on blood-derived dendritic cells in the central nervous system

ANNALS OF NEUROLOGY, Issue 1 2006
Katherine M. Mullen AB
Objective Potassium (K+) channels on immune cells have gained attention recently as promising targets of therapy for immune-mediated neurological diseases such as multiple sclerosis (MS). We examined K+ channels on dendritic cells (DCs), which infiltrate the brain in MS and may impact disease course. Methods We identified K+ channels on blood-derived DCs by whole-cell patch-clamp analysis, confirmed by immunofluorescent staining. We also stained K+ channels in brain sections from MS patients and control subjects. To test functionality, we blocked Kv1.3 and Kv1.5 in stimulated DCs with pharmacological blockers or with an inducible dominant-negative Kv1.x adenovirus construct and analyzed changes in costimulatory molecule upregulation. Results Electrophysiological analysis of DCs showed an inward-rectifying K+ current early after stimulation, replaced by a mix of voltage-gated Kv1.3- and Kv1.5-like channels at later stages of maturation. Kv1.3 and Kv1.5 were also highly expressed on DCs infiltrating MS brain tissue. Of note, we found that CD83, CD80, CD86, CD40, and interleukin-12 upregulation were significantly impaired on Kv1.3 and Kv1.5 blockade. Interpretation These data support a functional role of Kv1.5 and Kv1.3 on activated human DCs and further define the mechanisms by which K+ channel blockade may act to suppress immune-mediated neurological diseases. Ann Neurol 2006 [source]

Organocatalytic synthesis of cyanohydrin trimethylsilyl ethers by potassium 4-benzylpiperidinedithiocarbamate under solvent-free conditions

APPLIED ORGANOMETALLIC CHEMISTRY, Issue 3 2010
Mohammad G. Dekamin
Abstract Potassium 4-benzylpiperidinedithiocarbamate was found to be an efficient organocatalyst for facile addition of trimethylsilyl cyanide to a wide variety of aldehydes and ketones to afford corresponding cyanohydrin trimethylsilyl ethers in high to quantitative yields. The reaction proceeded smoothly by employing 2.0 mol% PBPDC loading under mild conditions at room temperature within a very short reaction time. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Nutrient limitation in species-rich Calthion grasslands in relation to opportunities for restoration in a peat meadow landscape

APPLIED VEGETATION SCIENCE, Issue 3 2010
B.P. Van de Riet
Abstract Questions: Which nutrient(s) limit(s) vegetation productivity in Calthion grasslands? Is phosphorus release a bottleneck for restoration of species-rich Calthion grasslands on rewetted dairy meadows? Location: Three species-rich Calthion grasslands in the Western Peat District in the Netherlands. Methods: We conducted a field fertilization experiment with nitrogen (N), phosphorus (P) and potassium (K) in three existing Calthion grasslands to evaluate the potential for restoration on rewetted dairy meadows. Responses of above-ground biomass, tissue nutrient concentrations and nutrient ratios were determined after 2 yr of fertilization. Results: Biomass increased with fertilization with N-only and K-only but did not react to P-only additions. Comparisons of tissue nutrient concentrations and nutrient ratios also gave indications of N and K limitation. Conclusions: The strong P release expected after rewetting should not necessarily interfere with restoration of Calthion communities on rewetted dairy meadows. It is concluded that for successful restoration management measures should focus on reducing N and/or K availability. Potassium might be an overlooked bottleneck in the restoration of species-rich grasslands. [source]

Potassium bis(4,5-dimercapto-1,3-dithiole-2-thionato)nickelate 1,4,7,10,13,16-hexaoxa-2,3:11,12-dibenzocyclooctadeca-2,11-diene propanone solvate

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 11 2001
Kozo Shitagami
In the title compound, K[Ni(C3S5)2]·C20H24O6·C3H6O, K+ is incorporated in the cavity of the 1,4,7,10,13,16-hexaoxa-2,3:11,12-dibenzocyclooctadeca-2,11-diene (DB18c6) molecule and is coordinated by the six DB18c6 O atoms and the propanone O atom. Two {K+(DB18c6)[(CH3)2CO]} units form a dimer which is aligned in a one-dimensional manner along the a axis through a face-to-face interaction between the benzene rings of neighboring DB18c6 molecules. [Ni(dmit)2], anions are also aligned along the a axis through side-by-side S,S interactions. [source]

ChemInform Abstract: Supramolecular Chemistry on a Cluster Surface: Fixation/Complexation of Potassium and Ammonium Ions with Crown-Ether-Like Rings.

CHEMINFORM, Issue 41 2009
Achim Mueller
Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]

ChemInform Abstract: Regioselective Palladium-Catalyzed Prenylation of CH Acids in the Presence of Diamidophosphite Ligands and Potassium Carbonate.

CHEMINFORM, Issue 35 2009
Andrei A. Vasil'ev
Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]

Potassium

Selected Abstracts

Potassium-transporting proteins in skeletal muscle: cellular location and fibre-type differences