Articles de revues : « Calcium cations divalents »

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Hess, P., J. B. Lansman et R. W. Tsien. « Calcium channel selectivity for divalent and monovalent cations. Voltage and concentration dependence of single channel current in ventricular heart cells. » Journal of General Physiology 88, n^o 3 (1 septembre 1986) : 293–319. http://dx.doi.org/10.1085/jgp.88.3.293.

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Single channel and whole cell recordings were used to study ion permeation through Ca channels in isolated ventricular heart cells of guinea pigs. We evaluated the permeability to various divalent and monovalent cations in two ways, by measuring either unitary current amplitude or reversal potential (Erev). According to whole cell measurements of Erev, the relative permeability sequence is Ca2+ greater than Sr2+ greater than Ba2+ for divalent ions; Mg2+ is not measurably permeant. Monovalent ions follow the sequence Li+ greater than Na+ greater than K+ greater than Cs+, and are much less permeant than the divalents. These whole cell measurements were supported by single channel recordings, which showed clear outward currents through single Ca channels at strong depolarizations, similar values of Erev, and similar inflections in the current-voltage relation near Erev. Information from Erev measurements stands in contrast to estimates of open channel flux or single channel conductance, which give the sequence Na+ (85 pS) greater than Li+ (45 pS) greater than Ba2+ (20 pS) greater than Ca2+ (9 pS) near 0 mV with 110-150 mM charge carrier. Thus, ions with a higher permeability, judged by Erev, have lower ion transfer rates. In another comparison, whole cell Na currents through Ca channels are halved by less than 2 microM [Ca]o, but greater than 10 mM [Ca]o is required to produce half-maximal unitary Ca current. All of these observations seem consistent with a recent hypothesis for the mechanism of Ca channel permeation, which proposes that: ions pass through the pore in single file, interacting with multiple binding sites along the way; selectivity is largely determined by ion affinity to the binding sites rather than by exclusion by a selectivity filter; occupancy by only one Ca ion is sufficient to block the pore's high conductance for monovalent ions like Na+; rapid permeation by Ca ions depends upon double occupancy, which only becomes significant at millimolar [Ca]o, because of electrostatic repulsion or some other interaction between ions; and once double occupancy occurs, the ion-ion interaction helps promote a quick exit of Ca ions from the pore into the cell.

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Kamgaing, Théophile. « Précipitation de carbonates de cations divalents dans les systèmes lacustres : intérêt, état des connaissances des mécanismes et suggestions (Revue critique de la littérature) ». Revue des sciences de l’eau 28, n^o 2 (7 juillet 2015) : 81–102. http://dx.doi.org/10.7202/1032292ar.

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Les carbonates de fer, de manganèse, de calcium et de magnésium précipités en solution des lacs sont documentés. Indicateurs de climat et de variation des caractéristiques chimiques des lacs, ils sont de plus en plus recherchés dans les sédiments. Souvent incomplets, les mécanismes de leur précipitation dans la colonne d’eau du lac et dans les eaux interstitielles sont reprécisés dans cette étude. D’après la littérature, la sidérite et la rhodochrosite précipitent en milieu réducteur saturé de carbonate de fer et de carbonate de manganèse respectivement. Ces prévisions sont confirmées dans cette étude, le potentiel redox étant un paramètre déterminant pour la précipitation du carbonate de fer. Toutefois, la littérature ne décrit pas suffisamment l’origine (géochimique ou biologique) des éléments constitutifs des solides carbonatés lacustres, encore moins les phénomènes qui stabilisent ces derniers ou les rendent vulnérables (dissolution). Cette étude apporte plus de précisions à l’endogènèse de ces carbonates, l’origine de leurs éléments constitutifs étant prise en compte. Elle montre que le caractère de l’eau (agressif ou incrustant) pourrait avoir un impact considérable sur le devenir de ces carbonates. Ainsi un dégazage forcé d’un lac rendrait ses eaux incrustantes, caractère idéal pour la précipitation des carbonates, mais néfaste à la stabilité des strates qui changent de composition après précipitation d’espèces chimiques. Par conséquent, tout projet de dégazage de lac devrait prendre en considération ce paramètre (caractère de l’eau) dans sa conception, sa mise en oeuvre et son exploitation.

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Momoshima, N., et E. A. Bondietti. « Cation binding in wood : applications to understanding historical changes in divalent cation availability to red spruce ». Canadian Journal of Forest Research 20, n^o 12 (1 décembre 1990) : 1840–49. http://dx.doi.org/10.1139/x90-247.

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The ion exchange characteristics of red spruce (Picearubens Sarg.) bolewood were investigated to understand factors that control divalent cation and H+ concentrations in tracheid cell walls. Vertical concentration measurements of selected cations along the stem demonstrated that the alkaline earths showed the expected chromatographic fractionation, while other cations showed variable patterns relative to calcium. The concentration of cation binding sites (pectates) decreased in a predictable manner from the pith towards the cambium as a function of radius, not chronological age, explaining why in red spruce calcium concentrations are usually highest in the oldest wood. Red spruce wood from Maine and Tennessee had divalent base saturations of about 60 to 65% before the mid-1900s; however, divalent base saturations increased to about 75 to 80% in the mid-1900s, after which they decreased. Wood pH values were highest when divalent base saturation was highest. Calcium and potassium equilibration experiments were conducted, and the results were used to parameterize the Donnan model of cation exchange to understand why base saturation in woody tissues changes in different time periods. Increased divalent cation concentrations in red spruce wood formed during the 1940s to the 1970s are explainable by small increases in both sap pH and divalent cation concentrations and may be the signal of cation mobilization following increasing mineral acid anion deposition from the atmosphere.

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Yoder, C. H., N. T. Landes, L. K. Tran, A. K. Smith et J. D. Pasteris. « The relative stabilities of A- and B-type carbonate substitution in apatites synthesized in aqueous solution ». Mineralogical Magazine 80, n^o 6 (octobre 2016) : 977–83. http://dx.doi.org/10.1180/minmag.2016.080.035.

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AbstractCarbonated calcium apatites doped with a monovalent cation (Li+, Na+, or K+) or a divalent cation (Mg2+ or Zn2+) were prepared in aqueous solution and analysed by powder X-ray diffraction, inductively coupled plasma atomic emission spectroscopy and infrared spectroscopy. The hypothesis that the location of carbonate in the apatite structure, either in place of hydroxide ions in the c-axis channels (A-type substitution) or in place of phosphate (B-type substitution), is affected by the solution energetics of the cation (specifically its enthalpy of hydration) was strengthened by the observation of larger amounts of Atype carbonate in apatites containing the monovalent cations in aqueous solution. It is shown that cations with low negative enthalpies of hydration favour A-type substitution, whereas cations with higher negative hydration enthalpies, such as divalent cations (Mg2+, Zn2+), favour B-type substitution.

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D’Elia, John A., et Larry A. Weinrauch. « Role of Divalent Cations in Infections in Host–Pathogen Interaction ». International Journal of Molecular Sciences 25, n^o 18 (10 septembre 2024) : 9775. http://dx.doi.org/10.3390/ijms25189775.

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With increasing numbers of patients worldwide diagnosed with diabetes mellitus, renal disease, and iatrogenic immune deficiencies, an increased understanding of the role of electrolyte interactions in mitigating pathogen virulence is necessary. The levels of divalent cations affect host susceptibility and pathogen survival in persons with relative immune insufficiency. For instance, when host cellular levels of calcium are high compared to magnesium, this relationship contributes to insulin resistance and triples the risk of clinical tuberculosis. The movement of divalent cations within intracellular spaces contributes to the host defense, causing apoptosis or autophagy of the pathogen. The control of divalent cation flow is dependent in part upon the mammalian natural resistance-associated macrophage protein (NRAMP) in the host. Survival of pathogens such as M tuberculosis within the bronchoalveolar macrophage is also dependent upon NRAMP. Pathogens evolve mutations to control the movement of calcium through external and internal channels. The host NRAMP as a metal transporter competes for divalent cations with the pathogen NRAMP in M tuberculosis (whether in latent, dormant, or active phase). This review paper summarizes mechanisms of pathogen offense and patient defense using inflow and efflux through divalent cation channels under the influence of parathyroid hormone vitamin D and calcitonin.

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Silverman, Harold, James W. McNeil et Thomas H. Dietz. « Interaction of trace metals Zn, Cd, and Mn, with Ca concretions in the gills of freshwater unionid mussels ». Canadian Journal of Zoology 65, n^o 4 (1 avril 1987) : 828–32. http://dx.doi.org/10.1139/z87-131.

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The interaction of Zn, Mn, and Cd with Ca concretions in the gills of unionid mussels was investigated. Raising blood levels of these ions to twice their normal values for a week does not result in significant deposition of these metals into gill concretions. The interaction of Zn with the concretions was examined in more detail both in vivo and in vitro. Isolated concretions bind Zn as rapidly as Ca. However short-term in vivo labelling studies using radiolabeled Zn and Ca verify that Zn is not added to concretions while Ca is being rapidly accumulated. These studies demonstrate that calcium concretions from the gills of unionid mussels do not indiscriminately bind divalent cations, but precisely regulate the species of divalent cation incorporated. This is further evidenced by the lack of relationship between blood or pond water cation levels and the levels of specific cations found in the concretions. Since the concretions are mobilized during the reproductive period, and serve as a source of glochidial calcium, it would be disadvantageous for these concretions to bind divalent cations for detoxification purposes.

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Bondietti, E. A., N. Momoshima, W. C. Shortle et K. T. Smith. « A historical perspective on divalent cation trends in red spruce stemwood and the hypothetical relationship to acidic deposition ». Canadian Journal of Forest Research 20, n^o 12 (1 décembre 1990) : 1850–58. http://dx.doi.org/10.1139/x90-248.

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Anomalies in the radial concentration trends of Ca2+, Mg2+, and other divalent cations in the stemwood of red spruce (Picearubens Sarg.) occurred in trees grown in New England, Tennessee, and North Carolina. These anomalies may be assumed to result from changes in sap chemistry. These inferred changes in sap chemistry were the expected result of changes of divalent cation availability in forest soils. The patterns of these anomalies may be interpreted as a signal of a regional mobilization of cations in the rooting zone of red spruce. The anomalous increase in divalent cations present in wood formed in the mid-1900s is coincident both with rapid increases in SOx and NOx deposition in eastern North America and with increases in radial growth increment. The anomalous decrease in divalent cations in wood formed in the late-1900s is coincident with declines in radial increment. Comparisons with divalent cation trends in eastern hemlock (Tsugacanadensis (L.) Carr.), Fraser fir (Abiesfraseri (Pursh) Poir.), and yellow birch (Betulaalleghaniensis Britt. = B. lutea Michx.) suggested that these anomalies were not restricted to red spruce. Radial concentration trends of 90Sr introduced to the environment through radioactive fallout during the 1950s and 1960s were used to investigate the physiology of these divalent cation concentration anomalies. The distributions of 90Sr were also used to estimate the turnover rates for the nutritionally available pools of alkaline earths such as calcium.

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Rokitskaya, Tatyana I., Alexander M. Arutyunyan, Ljudmila S. Khailova, Alisa D. Kataeva, Alexander M. Firsov, Elena A. Kotova et Yuri N. Antonenko. « Usnic Acid-Mediated Exchange of Protons for Divalent Metal Cations across Lipid Membranes : Relevance to Mitochondrial Uncoupling ». International Journal of Molecular Sciences 23, n^o 24 (19 décembre 2022) : 16203. http://dx.doi.org/10.3390/ijms232416203.

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Usnic acid (UA), a unique lichen metabolite, is a protonophoric uncoupler of oxidative phosphorylation, widely known as a weight-loss dietary supplement. In contrast to conventional proton-shuttling mitochondrial uncouplers, UA was found to carry protons across lipid membranes via the induction of an electrogenic proton exchange for calcium or magnesium cations. Here, we evaluated the ability of various divalent metal cations to stimulate a proton transport through both planar and vesicular bilayer lipid membranes by measuring the transmembrane electrical current and fluorescence-detected pH gradient dissipation in pyranine-loaded liposomes, respectively. Thus, we obtained the following selectivity series of calcium, magnesium, zinc, manganese and copper cations: Zn2+ > Mn2+ > Mg2+ > Ca2+ >> Cu2+. Remarkably, Cu2+ appeared to suppress the UA-mediated proton transport in both lipid membrane systems. The data on the divalent metal cation/proton exchange were supported by circular dichroism spectroscopy of UA in the presence of the corresponding cations.

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Marshall, Wayne E., Lynda H. Wartelle et Danny E. Akin. « Flax shive as a source of activated carbon for metals remediation ». BioResources 2, n^o 1 (23 février 2007) : 82–90. http://dx.doi.org/10.15376/biores.2.1.82-90.

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Flax shive constitutes about 70% of the flax stem and has limited use. Because shive is a lignocellulosic by-product, it can potentially be pyrolyzed and activated to produce an activated carbon. The objective of this study was to create an activated carbon from flax shive by chemical activation in order to achieve significant binding of selected divalent cations (cadmium, calcium, copper, magnesium, nickel, zinc). Shive carbons activated by exposure to phosphoric acid and com-pressed air showed greater binding of cadmium, copper, nickel or zinc than a sulfuric acid-activated flax shive carbon reported in the literature and a commercial, wood-based carbon. Uptake of calcium from a drinking water sample by the shive carbon was similar to commercial drinking water filters that contained cation exchange resins. Magnesium removal by the shive carbon was greater than a commercial drinking water filtration carbon but less than for filters containing cation exchange resins. The results indicate that chemically activated flax shive carbon shows considerable promise as a component in industrial and residential water filtration systems for removal of divalent cations.

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Almatrafi, Roua, Saeed Banawas et Mahfuzur R. Sarker. « Divalent Cation Signaling in Clostridium perfringens Spore Germination ». Microorganisms 11, n^o 3 (26 février 2023) : 591. http://dx.doi.org/10.3390/microorganisms11030591.

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Spore germination plays an essential role in the pathogenesis of Clostridium perfringens-associated food poisoning. Germination is initiated when bacterial spores sense various stimuli, including chemicals and enzymes. A previous study showed that dipicolinic acid (DPA) chelated with calcium (Ca-DPA) significantly stimulated spore germination in C. perfringens. However, whether Ca2+ or DPA alone can induce germination is unknown. Therefore, we aimed to evaluate the possible roles of Ca2+ and other divalent cations present in the spore core, such as Mn2+ and Mg2+, in C. perfringens spore germination. Our study demonstrated that (i) Ca-DPA, but not DPA alone, induced C. perfringens spore germination, suggesting that Ca2+ might play a signaling role; (ii) all tested calcium salts induced spore germination, indicating that Ca2+ is critical for germination; (iii) the spore-specific divalent cations Mn2+ and Mg2+, but not Zn2+, induced spore germination, suggesting that spore core-specific divalent cations are involved in C. perfringens spore germination; and (iv) endogenous Ca2+ and Mg2+ are not required for induction of C. perfringens spore germination, whereas exogenous and partly endogenous Mn2+ are required. Collectively, our results suggest that exogenous spore core-specific divalent cation signals are more important than endogenous signals for the induction of spore germination.

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Lee, Hye Kyung, Lian Liu et Keith S. Elmslie. « Effect of High Ba2+ on Norepinephrine-Induced Inhibition of N-Type Calcium Current in Bullfrog Sympathetic Neurons ». Journal of Neurophysiology 83, n^o 2 (1 février 2000) : 791–95. http://dx.doi.org/10.1152/jn.2000.83.2.791.

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The voltage-dependent inhibition of N-type calcium current by neurotransmitters is the best-understood example of neuronal calcium channel inhibition. One of the mechanisms by which this pathway is thought to inhibit the calcium current is by reducing the permeation of divalent cations through the channel. In this study one prediction of this hypothesis was examined, that high concentrations of divalent cations reduce the maximum neurotransmitter-induced inhibition. Norepinephrine (NE)-induced inhibition was compared in external solutions containing either 2 or 100 mM Ba2+. Initially, NE dose-response curves were generated by averaging data from many neurons, and it was found that the relationship was right shifted in the high-Ba2+ external solution without an effect on maximum inhibition. The IC50 was 0.6 and 3 μM in 2 and 100 mM Ba2+, respectively. This shift was verified by comparing the effect of NE on single neurons exposed to both 2 and 100 mM Ba2+. The inhibition induced by 1 μM NE was reduced in 100 mM Ba2+ compared with that in 2 mM Ba2+. However, the response to 100 μM NE was identical between high and low Ba2+. Thus, divalent cations appear to act as a competitive inhibitor of NE binding, which likely results from these ions' interacting with negatively charged amino acids that are important for catecholamine binding to adrenergic receptors. Because the maximum inhibition induced by NE was similar in low and high Ba2+, the effect of inhibition on single N-type calcium channels was not altered by the divalent cation concentration.

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Padigi, Prasanna, Neal Kuperman, Joseph James Thiebes, Gary Goncher, David Evans et Raj Solanki. « Calcium Cobalt Hexacyanoferrate Cathodes for Rechargeable Divalent Ion Batteries ». Journal of New Materials for Electrochemical Systems 19, n^o 2 (1 juillet 2016) : 057–64. http://dx.doi.org/10.14447/jnmes.v19i2.231.

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Calcium cobalt hexacyanoferrate (CaCoHCF) was synthesized and tested as a cathode material for rechargeable batteries, using divalent cations (Mg2+, Ca2+, Ba2+). CaCoHCF demonstrated reversible specific capacity and coulombic efficiency (in parentheses) of 45.49 mAh/g (99.18%) for Mg2+, 55.04 mAh/g (99.2%) for Ca2+, and 44.09 mAh/g (99.42%) for Ba2+, at a current density of 25 mA/g. Of the three ions, Ca2+ resulted in the highest absolute specific capacity as well as high specific capacity utilization. The cathodes were also subjected to rate capability measurements using current densities of 50 mA/g (30 cycles) and 0.1 A/g (100 cycles). Upon addition of 2 mL water to the non-aqueous electrolyte, the fraction of theoretical specific capacity increased to 0.55 for Mg2+, 94.8% for Ca2+, and 95.53% forBa2+. This increase has been interpreted as the ability of the cathode material to intercalate and de-intercalate more ions due to the electrostatic shielding provided by water molecules between the host lattice and the guest cations. An empirical relationship between the cation size and specific capacity utilization is presented.Calcium cobalt hexacyanoferrate (CaCoHCF) was synthesized and tested as a cathode material for rechargeable batteries, using divalent cations (Mg2+, Ca2+, Ba2+). CaCoHCF demonstrated reversible specific capacity and coulombic efficiency (in parentheses) of 45.49 mAh/g (99.18%) for Mg2+, 55.04 mAh/g (99.2%) for Ca2+, and 44.09 mAh/g (99.42%) for Ba2+, at a current density of 25 mA/g. Of the three ions, Ca2+ resulted in highest absolute specific capacity as well as high specific capacity utilization. The cathodes were also subjected to rate capability measurements using current densities of 50 mA/g (30 cycles) and 0.1 A/g (100 cycles). Upon addition of 2 mL water to the non-aqueous electrolyte, the fraction of theoretical specific capacity increased to 0.55 for Mg2+, 94.8% for Ca2+, and 95.53% forBa2+. This increase has been interpreted as the ability of the cathode material to intercalate and de-intercalate more ions due to the electrostatic shielding provided by water molecules between the host lattice and the guest cations. An empirical relationship between the cation size and specific capacity utilization is presented.

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Pérez, José Francisco, Marie-Christine Ruiz, María Elena Chemello et Fabián Michelangeli. « Characterization of a Membrane Calcium Pathway Induced by Rotavirus Infection in Cultured Cells ». Journal of Virology 73, n^o 3 (1 mars 1999) : 2481–90. http://dx.doi.org/10.1128/jvi.73.3.2481-2490.1999.

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ABSTRACT Some viruses induce changes in membrane permeability during infection. We have shown previously that the porcine strain of rotavirus, OSU, induced an increase in the permeability to Na+, K+, and Ca2+ during replication in MA104 cells. In this work, we have characterized the divalent cation entry pathway by measuring intracellular Ca2+ in fura-2-loaded MA104 and HT29 cells in suspension. The permeability to Ca2+ and other cations was evaluated by the change of the intracellular concentration following an extracellular cation pulse. Rotavirus infection induced an increase in permeability to Ca2+, Ba2+, Sr2+, Mn2+, and Co2+. The rate of cation entry decreased over time as the intracellular concentration increased during the first 20 s. This indicates that regulatory mechanisms, including channel inactivation, are triggered. La3+ did not enter the cell and blocked the entry of the divalent cations in a dose-dependent manner. Metoxyverapamil (D600), a blocker of L-type voltage-gated channels, partially inhibited the entry of Ca2+ in virus-infected MA104 and HT29 cells. The results suggest that rotavirus infection of cultured cells activates a cation channel rather than nonspecific permeation through the plasma membrane. This activation involves the synthesis of viral proteins through mechanisms yet unknown. The increase in intracellular Ca2+induced by the activation of this channel may be related to the increase in cytoplasmic and endoplasmic reticulum Ca2+pools required for virus maturation and cell death.

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Shanthi, Rangasamy. « Inhibition and Activation of Humoral Phenoloxidase and Their Effect on Divalent Cations in the Hemolymph of Freshwater Prawn Macrobrachium rosenbergii (De Man, 1879) ». International Journal of Zoology and Animal Biology 6, n^o 6 (2023) : 1–13. http://dx.doi.org/10.23880/izab-16000540.

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The aim of the present study is to examine phenoloxidase (PO), a copper-containing enzyme that plays a crucial role in the immune responses of arthropods, especially crustaceans and insects. However, PO activity is present in the plasma of the hemolymph without pathogenic infections. Here we report the PO activity in the plasma of M. rosenbergii was spectrophotometrically studied. The phenylthiourea (PTU) inhibition of PO activity was found to be the highest at a 10 mM concentration. The determination of PO activity was also highest activated by trypsin (2 mg.ml-1), detergents like sodium dodecyl sulphate (SDS; 8 mg.ml-1) and laminarin (4 mg.ml-1) enzyme expression. The effect of divalent cations on PO activity like sodium chloride (100 mM), calcium chloride, magnesium chloride, manganese chloride, and potassium chloride (10 mM) affected the activation of PO activity in trypsin, SDS, and laminarin. However, these divalent cations only slightly affected PTU inhibition of PO activity. In addition to calcium chloride, the PO activity with trypsin and laminarin is more or less the same as with control, but a great enhancement was found in SDS, which indicates that the combination of SDS with calcium chloride is required for increasing the PO activity in M. rosenbergii. The concentration of ethylenediaminetetraacetic acid (EDTA) of 1–10 mM has the maximum inhibition in PTU and activation of trypsin, SDS, and laminarin, which indicates that EDTA is a divalent cation chelator that affects the PO activity in M. rosenbergii. Hence, an attempt has been made to optimize the conditions for inhibitor, activators, divalent cations, EDTA sensitivity, and phenoloxidase activity in the plasma of the freshwater prawn M. rosenbergii.

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Man, Ernest, Dimitrios Lamprou, Claire Easdon, Iain McLellan, Humphrey H. P. Yiu et Clare Hoskins. « Exploration of Dual Ionic Cross-Linked Alginate Hydrogels Via Cations of Varying Valences towards Wound Healing ». Polymers 14, n^o 23 (29 novembre 2022) : 5192. http://dx.doi.org/10.3390/polym14235192.

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This study explored the synergistic effects of simultaneously using calcium and gallium cations in the cross-linking of alginate, detailing its effects on the characteristics of alginate compared to its single cation counterparts. The primary goal is to determine if there are any synergistic effects associated with the utilisation of multiple multivalent cations in polymer cross-linking and whether or not it could therefore be used in pharmaceutical applications such as wound healing. Given the fact divalent and trivalent cations have never been utilised together for cross-linking, an explanation for the mode of binding that occurs between the alginate and the cations during the cross-linking process and how it may affect the future applications of the polymer has been investigated. The calcium gallium alginate polymers were able to retain the antibacterial effects of gallium within the confines of the polymer matrix, possessing superior rheological properties, 6 times that of pure calcium and pure gallium, coupled with an improved swelling capacity that is 4 times higher than that of gallium alginate.

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Verdoucq, Lionel, Alexandre Grondin et Christophe Maurel. « Structure–function analysis of plant aquaporin AtPIP2;1 gating by divalent cations and protons ». Biochemical Journal 415, n^o 3 (15 octobre 2008) : 409–16. http://dx.doi.org/10.1042/bj20080275.

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Water channel proteins, AQPs (aquaporins), of the PIP (plasma membrane intrinsic protein) subfamily, provide a means for fine and quick adjustments of the plant water status. A molecular model for gating of PIPs by cytosolic protons (H+) and divalent cations was derived from the atomic structure of spinach SoPIP2;1 (Spinacia oleracea PIP2;1) in an open- and a closed-pore conformation. In the present study, we produced the Arabidopsis AtPIP2;1 (Arabidopsis thaliana PIP2;1) homologue in Pichia pastoris, either WT (wild-type) or mutations at residues supposedly involved in gating. Stopped-flow spectrophotometric measurements showed that, upon reconstitution in proteoliposomes, all forms function as water channels. The first functional evidence for a direct gating of PIPs by divalent (bivalent) cations was obtained. In particular, cadmium and manganese were identified, in addition to calcium (Ca2+) and H+ as potent inhibitors of WT AtPIP2;1. Our results further show that His199, the previously identified site for H+ sensing, but also N-terminal located Glu31, and to a lesser extent Asp28, are involved in both divalent-cation- and H+-mediated gating. In contrast, mutation of Arg124 rendered AtPIP2;1 largely insensitive to Ca2+ while remaining fully sensitive to H+. The role of these residues in binding divalent cations and/or stabilizing the open or closed pore conformations is discussed.

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Chan, A. F., et V. J. Kremesec. « Cation Exchange in Porous Media With Broad-Equivalent-Weight Sulfonate Micellar Fluids ». Society of Petroleum Engineers Journal 25, n^o 04 (1 août 1985) : 580–86. http://dx.doi.org/10.2118/12126-pa.

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Abstract This paper describes experimental and theoretical studies of cation exchange in porous media with micellar fluids formulated using a broad-equivalent-weight (BEW) sulfonate. The sulfonates can be described as composed of two pseudocomponents a quasi-monosulfonate (the oil-moving pseudo components a quasi-monosulfonate (the oil-moving component) and a quasi-disulfonate (the sulfonate-solubilizing component). With this description and a mass-action model for cation exchange between the micelles, clays, and solution, a match between computer model predictions and results of laboratory single-phase flow tests in Berea sandstone was carried out. The assumptions required are reviewed and independent experimental results presented. With these assumptions and parameter values determined from the Berea history match, satisfactory predictions of divalent cation concentrations in field core experiments have been made. The good predictive capability of this model allows initial screening and development of micellar formulations for specific reservoir applications to be conducted at appropriate hardness levels. Introduction It is well known that the oil recovery performance of a micellar fluid is strongly affected by salinity and hardness (calcium and magnesium divalent cations). This is because they have strong effects on the phase behavior and interfacial tension (IFT) of the surfactant/oil/brine system. It is also well known that the hardness and salinity of the micellar fluid can change significantly as a result of cation exchange and dissolution as the micellar fluid propagates through the reservoir. Since a knowledge of the in-situ levels of salinity and hardness is of primary importance in the screening and development of micellar fluids for field applications, an adequate prediction is necessary. Cation exchange between a brine and the clays within a reservoir rock occurs if the injected fluids have a salinity and hardness different from that of the in-place fluids. Smith, Griffith, and Hill and Lake have studied this problem and have shown the significance of the cation-exchange capacity (CEC) of the clays and the selectivity of the cation species with the clays. The clay selectivity is a measure of the preference of the clay for monovalent vs. divalent cations; for a given brine, smaller values indicate a higher fraction of the clays complexed by the divalent cations. Further, Hill and Lake concluded that the law of mass action is the best model with which to describe the process. Smith, and Hill and Lake, also showed that calcium and magnesium ions have the same selectivity with the clays vs. sodium, and hence they can be treated as a single ionic species. Hill and Lake extended their study to systems containing surfactants. They found that cation exchange in the presence of a surfactant system was complicated by interaction between surfactant and divalent cations. To describe the levels of hardness measured in the presence of surfactant micelles, they postulated the formation of a divalent-cation/surfactant complex and modeled the phenomenon with a mass-action isotherm. Gupta provided phenomenon with a mass-action isotherm. Gupta provided additional data supporting the formation of such a complex. Hirasaki and Lawson proposed a Donnan equilibrium model to describe the association of sodium and calcium with the micelles, and they estimated selectivity values from the resulting expressions. Hirasaki has incorporated a mass-action model, surfactant adsorption, and electroneutrality conditions with the mass balances neglecting dispersion to obtain a description of cation exchange during single-phase-flow in porous media. He has solved the system of equations using a method-of-characteristics approach and has been able to describe the experiments of Hill and Lake and Gupta showing good agreement between experiment and theory. The model is limited to one surfactant species and two cations-one monovalent and one divalent. The surfactant system used by Gupta closely conforms to these limitations. The micellar system used by Hill and Lake, however, was composed of two petroleum sulfonates and sodium alkyl ethoxysulfate (Neodol 25–3S). Nevertheless, Hirasaki assumed the surfactant mixture to be acting as a single surfactant species. This paper deals with the cation exchange that occurs during the propagation of a micellar system containing BEW sulfonate. The objective is to history-match limited tests in Berea cores and then to use the understanding gained and parameter values obtained to predict hardness concentrations in field cores over a wide range of micellar compositions. To correlate the Berea data and to extrapolate to other conditions, the approach of Hirasaki is desirable because of its simplicity. However, the complex composition of the BEW sulfonate micellar system, as well as a desire to include an adsorption isotherm and dispersion-important for small slug processes-precluded the straightforward use of the equations and the solution that he put forward. SPEJ P. 580

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Abdalla, Mohamed Mahmoud, Osama Sayed, Christie Ying Kei Lung, Vidhyashree Rajasekar et Cynthia Kar Yung Yiu. « Applications of Bioactive Strontium Compounds in Dentistry ». Journal of Functional Biomaterials 15, n^o 8 (31 juillet 2024) : 216. http://dx.doi.org/10.3390/jfb15080216.

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Divalent cations have captured the interest of researchers in biomedical and dental fields due to their beneficial effects on bone formation. These metallic elements are similar to trace elements found in human bone. Strontium is a divalent cation commonly found in various biomaterials. Since strontium has a radius similar to calcium, it has been used to replace calcium in many calcium-containing biomaterials. Strontium has the ability to inhibit bone resorption and increase bone deposition, making it useful in the treatment of osteoporosis. Strontium has also been used as a radiopacifier in dentistry and has been incorporated into a variety of dental materials to improve their radiopacity. Furthermore, strontium has been shown to improve the antimicrobial and mechanical properties of dental materials, promote enamel remineralization, alleviate dentin hypersensitivity, and enhance dentin regeneration. The objective of this review is to provide a comprehensive review of the applications of strontium in dentistry.

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Kurczewska, Joanna, Grzegorz Schroeder et Urszula Narkiewicz. « Copper removal by carbon nanomaterials bearing cyclam-functionalized silica ». Open Chemistry 8, n^o 2 (1 avril 2010) : 341–46. http://dx.doi.org/10.2478/s11532-009-0131-y.

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AbstractThe synthesis of metal (Fe, Co, Ni)-encapsulated carbon nanomaterials coated with cyclam-bonded silica has been described. The organic layer was identified by Fourier transform infrared spectroscopy and elemental analysis. The functionalized magnetic nanomaterials were employed to extract the divalent cations: copper, calcium, cobalt, manganese and nickel from aqueous solutions. Their adsorption capacities were studied by the batch procedure. The concentration of cations extracted was determined by inductively coupled plasma mass spectrometry. Influence of different parameters viz. pH, amount of the compound studied, contact time, on the cation extraction was investigated. Under optimum conditions copper extraction was significantly more efficient when compared with other coexisting ions.

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JAIN, Renu K., Wen Tzu CHANG, Chitta GEETHA, Paul B. M. JOYCE et Sven-Ulrik GORR. « In vitro aggregation of the regulated secretory protein chromogranin A ». Biochemical Journal 368, n^o 2 (1 décembre 2002) : 605–10. http://dx.doi.org/10.1042/bj20021195.

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Aggregation chaperones, consisting of secretory proteins that contain a hexa-histidine epitope tag, enhance the calcium-induced aggregation of regulated secretory proteins and their sorting to secretory granules. The goal of this study was to gain a better understanding of this unusual aggregation mechanism. Hexa-histidine-epitope-tagged secreted alkaline phosphatase, an aggregation chaperone, enhanced the in vitro aggregation of chromogranin A in the presence of calcium, but not in the presence of magnesium or other divalent cations. As an exception, chromogranin was completely aggregated by zinc, even in the absence of the aggregation chaperone. In addition, fluorescence spectroscopy of the aggregation reaction mixture showed an increase in fluorescence intensity consistent with the formation of protein aggregates. The calcium-induced aggregation of chromogranin A was completely inhibited by 0.2% Triton X-100, suggesting that it involves hydrophobic interactions. In contrast, the detergent did not affect chaperone-enhanced aggregation, suggesting that this aggregation does not depend on hydrophobic interactions. EDTA-treated chaperone did not enhance chromogranin A aggregation, indicating that divalent cations are necessary for chaperone action. Although the structure of the aggregation chaperone was not important, the size of the chaperone was. Thus the free His-hexapeptide could not substitute for the aggregation chaperone. Based on these results, we propose that the hexa-histidine tag, in the context of a polypeptide, acts as a divalent cation-dependent nucleation site for chromogranin A aggregation.

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Robinson, John J. « Selective metal ion binding at the calcium-binding sites of the sea urchin extraembryonic coat protein hyalin ». Biochemistry and Cell Biology 67, n^o 11-12 (1 novembre 1989) : 808–12. http://dx.doi.org/10.1139/o89-119.

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The interaction of metal ions with the sea urchin extraembryonic coat protein hyalin was investigated. Hyalin, immobilized on nitrocellulose membrane, bound Ca2+ and this interaction was disrupted by ruthenium red and selective metal ions. The divalent cations Cd2+ and Mn2+, when present at a concentration of 30 μM, displaced hyalin-bound Ca2+. In competition assays, 1 mM Cd2+ or 3 mM Mn2+ were effective competitors with Ca2+ for binding to hyalin. Cobalt, at a concentration of 30 μM, was unable to displace protein-bound Ca2+, but was effective in competition assays at a concentration of at least 10 mM. Magnesium and the monovalent cation Cs+ were unable to disrupt Ca2+–hyalin interaction. Interestingly, Cd2+, Mn2+, and Co2+ mimicked the biological effects of Ca2+ on the hyalin self-association reaction. These results clearly demonstrate that the Ca2+-binding sites on hyalin can selectively accommodate other divalent cations in a biologically active configuration.Key words: calcium, metal ion, binding, hyalin.

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Mishra, Sujata R., et Surendra Chandra Sabat. « Effect of Magnesium and Calcium Ions on the Photoelectron Transport Activity of Low-Salt Suspended Hydrilla verticillata Thylakoids : Possible Sites of Cation Interaction ». Zeitschrift für Naturforschung C 53, n^o 9-10 (1 octobre 1998) : 849–56. http://dx.doi.org/10.1515/znc-1998-9-1011.

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Stimulatory effect of divalent cations like calcium (Ca2+) and magnesium (Mg2+) was investigated on electron transport activity of divalent cation deficient low-salt suspended (LS) thylakoid preparation from a submerged aquatic angiosperm, Hydrilla verticillata. Both the cations stimulated electron transport activity of LS-suspended thylakoids having an intact water oxidation complex. But in hydroxylamine (NH2OH) - or alkaline Tris - washed thylakoid preparations (with the water oxidation enzyme impaired), only Ca2+ dependent stimulation of electron transport activity was found. The apparent Km of Ca2+ dependent stimulation of electron flow from H2O (endogenous) or from artificial electron donor (exogenous) to dichlorophenol indophenol (acceptor) was found to be identical. Calcium supported stimulation of electron transport activity in NH2OH - or Tris - washed thylakoids was electron donor selective, i.e., Ca2+ ion was only effective in electron flow with diphenylcarbazide but not with NH2OH as electron donor to photosystem II. A magnesium effect was observed in thylakoids having an intact water oxidation complex and the ion became unacceptable in NH2OH - or Tris - washed thylakoids. Indirect experimental evidences have been presented to suggest that Mg2+ interacts with the water oxidation complex, while the Ca2+ interaction is localized betw een Yz and reaction center of photosystem II.

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Choi, Y. G., et T. H. Chung. « Effects of humus soil on the settling and dewatering characteristics of activated sludge ». Water Science and Technology 42, n^o 9 (1 novembre 2000) : 127–34. http://dx.doi.org/10.2166/wst.2000.0187.

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Effects of humus soil on the settling and dewatering characteristics of the activated sludge were investigated. Addition of the humus soil improved the sedimentation characteristics of the activated sludge remarkably. The initial lag phase was diminished and the zone settling velocity increased as the humus soil dosage increased. For estimation of the chemical effect of the humus soil on sludge settling, cation mixtures equivalent to the cations leaching from the humus soil were added and only the chemical effect was examined. The physical effect was then isolated by subtracting the chemical effect. The chemical effect on sludge settling was about30∼50% of the equivalent humus soil powder dosage and the physical effect was more important in improvement of the sludge settling properties. Dewatering characteristics of the activated sludge were dependent on both the concentration and distribution of the cations leaching from the humus soil. Divalent cations, calcium and magnesium from the humus soil decreased the bound water content of the sludge, which in turn increased floc density and cake solids content. However, excess sodium ion increased the SRF (specific resistance to filtration) slightly. Addition of humus soil to thickened activated sludge improved the dewatering properties, which could be well explained by the effect of the cations leaching. The SRF showed a good trend with the monovalent to divalent cation (M/D) ratio, which could be utilized as a useful tool for evaluation of the sludge dewatering characteristics.

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Xiong, Zhi-Gang, et J. F. MacDonald. « Sensing of extracellular calcium by neurones ». Canadian Journal of Physiology and Pharmacology 77, n^o 9 (10 octobre 1999) : 715–21. http://dx.doi.org/10.1139/y99-077.

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Transient changes in the intracellular concentration of Ca2+ provide a major signal for the regulation of many ion channels and enzymes in central neurones. In contrast, changes in extracellular Ca2+ are thought to play little or no signaling role. However, concentrations of extracellular calcium in the central nervous system do change dramatically during intense physiological and pathological stimulation, and recent studies have identified a number of membrane proteins that can sense and respond to changes in extracellular Ca2+. These include the recently cloned Ca2+-sensing receptor, hemi-gap-junction channels, and a potential Ca2+-sensing cation channel. Lowering extracellular Ca2+ strongly depolarizes and excites cultured hippocampal neurones. The excitation can be detected with decreases from physiological concentrations of as little as 100 µM. The depolarization results from activation of a nonselective cation current, which is sensitive to block by divalent and polyvalent cations. In outside-out patches, lowering Ca2+ induces a single-channel current with a conductance of 36 pS. Activation of this cation channel, in response to decreases in extracellular Ca2+, likely plays a key role in a positive feedback system of excessive neuronal depolarization, which accompanies intense excitatory activity in the hippocampus.Key words: nonselective cation channel, calcium-sensing receptor, calcium-sensing channel, hemi-gap channels, extracellular calcium.

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Weidman, P. J., E. S. Kay et B. M. Shapiro. « Assembly of the sea urchin fertilization membrane : isolation of proteoliaisin, a calcium-dependent ovoperoxidase binding protein. » Journal of Cell Biology 100, n^o 3 (1 mars 1985) : 938–46. http://dx.doi.org/10.1083/jcb.100.3.938.

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Fertilization of the sea urchin egg is accompanied by the assembly of an extracellular glycoprotein coat, the fertilization membrane. Assembly of the fertilization membrane involves exocytosis of egg cortical granules, divalent cation-mediated association of exudate proteins with the egg glycocalyx (the vitelline layer), and cross-linking of the assembled structure by ovoperoxidase, a fertilization membrane component derived from the cortical granules. We have identified and isolated a new protein, which we call proteoliaisin, that appears to be responsible for inserting ovoperoxidase into the fertilization membrane. Proteoliaisin is a 250,000-Mr protein that binds ovoperoxidase in a Ca2+-dependent manner, with half-maximal binding at 50 microM Ca2+. Other divalent cations are less effective (Ba2+, Mn2+, and Sr2+) or ineffective (Mg2+ and Cd2+) in mediating the binding interaction. Binding is optimal over the physiological pH range of fertilization membrane assembly (pH 5.5-7.5). Both proteoliaisin and ovoperoxidase are found in isolated, uncross-linked fertilization membranes. We have identified several macromolecular aggregates that are released from uncross-linked fertilization membranes after dilution into divalent cation-free buffer. One of these is an ovoperoxidase-proteoliaisin complex that is further disrupted only upon the addition of EGTA. These results suggest that a Ca2+-stabilized complex of ovoperoxidase and proteoliaisin forms one structural subunit of the fertilization membrane.

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Hebert, S. C., E. M. Brown et H. W. Harris. « Role of the Ca(2+)-sensing receptor in divalent mineral ion homeostasis. » Journal of Experimental Biology 200, n^o 2 (1 janvier 1997) : 295–302. http://dx.doi.org/10.1242/jeb.200.2.295.

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The divalent mineral cations Ca2+ and Mg2+ play many and diverse roles both in the function of cells and in extracellular processes. The metabolism of these cations is a complex process involving the coordinated function of several organ systems and endocrine glands. A recently cloned G-protein-coupled receptor responds to extracellular calcium concentration (Ca2+0-sensing receptor, CaSR) and mediates several of the known effects of Ca2+0 on parathyroid and renal function. The CaSR, which is also expressed in a number of other tissues including thyroidal C-cells, brain and gastrointestinal tract, may function as a Ca2+0 sensor in these tissues as well. Thus, Ca2+0 is a first messenger (or hormone) which, via CaSR-mediated activation of second messenger systems (e.g. phospholipases C and A2, cyclic AMP) leads to altered function of these cells. Several mutations in the human CaSR gene have been identified and shown to cause three inherited diseases of calcium homeostasis, clearly implicating the CaSR as an important component of the homeostatic mechanism for divalent mineral ions. Ca2+ and Mg2+ losses from the body are regulated by altering the urinary excretion of these divalent cations. The localization of the CaSR transcripts and protein in the kidney not only provides a basis for a direct Ca2+0 (or Mg2+0)-mediated regulation of Ca2+ (and Mg2+) excretion but also suggests a functional link between divalent mineral and water metabolism. In the kidney, the thick ascending limb of Henle (TAL) plays crucial roles in regulating both divalent mineral reabsorption and urine concentration. Recent studies have suggested models whereby extracellular Ca2+, via the CaSR expressed in the TAL as well as in the collecting duct system, modulates both Ca2+ 0 and Mg2+ 0 as well as water reabsorbtion. When taken together, these studies suggest that the CaSR not only provides the primary mechanism for Ca2+ 0-mediated regulation of parathyroid hormone secretion from parathyroid glands but also for direct modulation of renal divalent mineral excretion and urinary concentrating ability. These latter functions may furnish a mechanism for integrating and balancing water and divalent cation losses that minimizes the risk of urinary tract stone formation. This mechanism can explain hypercalcemia-mediated polyuria (diabetes insipidus).

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Miranda, Pablo, Teresa Giraldez et Miguel Holmgren. « Interactions of divalent cations with calcium binding sites of BK channels reveal independent motions within the gating ring ». Proceedings of the National Academy of Sciences 113, n^o 49 (21 novembre 2016) : 14055–60. http://dx.doi.org/10.1073/pnas.1611415113.

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Large-conductance voltage- and calcium-activated K+ (BK) channels are key physiological players in muscle, nerve, and endocrine function by integrating intracellular Ca2+ and membrane voltage signals. The open probability of BK channels is regulated by the intracellular concentration of divalent cations sensed by a large structure in the BK channel called the “gating ring,” which is formed by four tandems of regulator of conductance for K+ (RCK1 and RCK2) domains. In contrast to Ca2+ that binds to both RCK domains, Mg2+, Cd2+, or Ba2+ interact preferentially with either one or the other. Interaction of cations with their binding sites causes molecular rearrangements of the gating ring, but how these motions occur remains elusive. We have assessed the separate contributions of each RCK domain to the cation-induced gating-ring structural rearrangements, using patch-clamp fluorometry. Here we show that Mg2+ and Ba2+ selectively induce structural movement of the RCK2 domain, whereas Cd2+ causes motions of RCK1, in all cases substantially smaller than those elicited by Ca2+. By combining divalent species interacting with unique sites, we demonstrate that RCK1 and RCK2 domains move independently when their specific binding sites are occupied. Moreover, binding of chemically distinct cations to both RCK domains is additive, emulating the effect of fully occupied Ca2+ binding sites.

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Byerly, L., P. B. Chase et J. R. Stimers. « Permeation and interaction of divalent cations in calcium channels of snail neurons. » Journal of General Physiology 85, n^o 4 (1 avril 1985) : 491–518. http://dx.doi.org/10.1085/jgp.85.4.491.

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We have studied the current-carrying ability and blocking action of various divalent cations in the Ca channel of Lymnaea stagnalis neurons. Changing the concentration or species of the permeant divalent cation shifts the voltage dependence of activation of the Ca channel current in a manner that is consistent with the action of the divalent cation on an external surface potential. Increasing the concentration of the permeant cation from 1 to 30 mM produces a twofold increase in the maximum Ca current and a fourfold increase in the maximum Ba current; the maximum Ba current is twice the size of the maximum Ca current for 10 mM bulk concentration. Correcting for the changing surface potential seen by the gating mechanism, the current-concentration relation is almost linear for Ba2+, and shows only moderate saturation for Ca2+; also, Ca2+, Ba2+, and Sr2+ are found to pass through the channel almost equally well. These conclusions are obtained for either of two assumptions: that the mouth of the channel sees (a) all or (b) none of the surface potential seen by the gating mechanism. Cd2+ blocks Lymnaea and Helix Ca channels at concentrations 200 times smaller than those required for Co2+ or Ni2+. Ca2+ competes with Cd2+ for the blocking site; Ba2+ binds less strongly than Ca2+ to this site. Mixtures of Ca2+ and Ba2+ produce an anomalous mole fraction effect on the Ca channel current. After correction for the changing surface potential (using either assumption), the anomalous mole fraction effect is even more prominent, which suggests that Ba2+ blocks Ca current more than Ca2+ blocks Ba current.

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Chang, Haiqing, Teng Liu, Qiping He, Duo Li, John Crittenden et Baicang Liu. « Removal of calcium and magnesium ions from shale gas flowback water by chemically activated zeolite ». Water Science and Technology 76, n^o 3 (20 avril 2017) : 575–83. http://dx.doi.org/10.2166/wst.2017.237.

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Shale gas has become a new sweet spot of global oil and gas exploration, and the large amount of flowback water produced during shale gas extraction is attracting increased attention. Internal recycling of flowback water for future hydraulic fracturing is currently the most effective, and it is necessary to decrease the content of divalent cations for eliminating scaling and maintaining effectiveness of friction reducer. Zeolite has been widely used as a sorbent to remove cations from wastewater. This work was carried out to investigate the effects of zeolite type, zeolite form, activation chemical, activation condition, and sorption condition on removal of Ca2+ and Mg2+ from shale gas flowback water. Results showed that low removal of Ca2+ and Mg2+ was found for raw zeolite 4A and zeolite 13X, and the efficiency of the mixture of both zeolites was slightly higher. Compared with the raw zeolites, the zeolites after activation using NaOH and NaCl greatly improved the sorption performance, and there was no significant difference between dynamic activation and static activation. Dynamic sorption outperformed static sorption, the difference exceeding 40% and 7–70% for removal of Ca2+ and Mg2+, respectively. Moreover, powdered zeolites outperformed granulated zeolites in divalent cation removal.

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Kim, Andrew Y., Huanghe Yang, Tovo David, Jason Tien, Shaun R. Coughlin, Yuh Nung Jan et Lily Jan. « TMEM16F Ion Channel Regulates Calcium-Dependent PS Exposure, Hemostasis, and Thrombosis ». Blood 120, n^o 21 (16 novembre 2012) : 1111. http://dx.doi.org/10.1182/blood.v120.21.1111.1111.

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Abstract Abstract 1111 Collapse of membrane lipid asymmetry is a hallmark of blood coagulation. TMEM16F of the TMEM16 family that includes TMEM16A/B Ca2+-activated Cl− channels (CaCCs) is linked to Scott Syndrome with deficient Ca2+-dependent lipid scrambling. We generated TMEM16F-knockout mice that exhibit bleeding defects associated with platelet deficiency in Ca2+-dependent phosphatidylserine exposure and procoagulant activity, and lack a Ca2+-activated cation current in the platelet precursor megakaryocytes. TMEM16F channels permeate both monovalent and divalent cations including Ca2+, and exhibit synergistic gating by Ca2+ and voltage. We further pinpointed a residue in the putative pore region important for the cation versus anion selectivity of TMEM16F-SCAN and TMEM16A-CaCC channels. This study thus identifies a novel Ca2+-activated channel permeable to Ca2+ and critical for Ca2+-dependent scramblase activity. Disclosures: No relevant conflicts of interest to declare.

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González-Lozano, Katia Jamileth, Elva Teresa Aréchiga-Carvajal, Zacarías Jiménez-Salas, Debany Marlen Valdez-Rodríguez, Claudia Geraldine León-Ramírez, José Ruiz-Herrera, Juan Manuel Adame-Rodríguez, Manuel López-Cabanillas-Lomelí et Eduardo Campos-Góngora. « Identification and Characterization of Dmct : A Cation Transporter in Yarrowia lipolytica Involved in Metal Tolerance ». Journal of Fungi 9, n^o 6 (23 mai 2023) : 600. http://dx.doi.org/10.3390/jof9060600.

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Yarrowia lipolytica is a dimorphic fungus used as a model organism to investigate diverse biotechnological and biological processes, such as cell differentiation, heterologous protein production, and bioremediation strategies. However, little is known about the biological processes responsible for cation concentration homeostasis. Metals play pivotal roles in critical biochemical processes, and some are toxic at unbalanced intracellular concentrations. Membrane transport proteins control intracellular cation concentrations. Analysis of the Y. lipolytica genome revealed a characteristic functional domain of the cation efflux protein family, i.e., YALI0F19734g, which encodes YALI0F19734p (a putative Yl-Dmct protein), which is related to divalent metal cation tolerance. We report the in silico analysis of the putative Yl-Dmct protein’s characteristics and the phenotypic response to divalent cations (Ca2+, Cu2+, Fe2+, and Zn2+) in the presence of mutant strains, Δdmct and Rdmct, constructed by deletion and reinsertion of the DMCT gene, respectively. The absence of the Yl-Dmct protein induces cellular and growth rate changes, as well as dimorphism differences, when calcium, copper, iron, and zinc are added to the cultured medium. Interestingly, the parental and mutant strains were able to internalize the ions. Our results suggest that the protein encoded by the DMCT gene is involved in cell development and cation homeostasis in Y. lipolytica.

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Dvoreckaya, Aleksandra, Lyubov' Anikanova, Tat'yana Sudzilovskaya, Zoya Malysheva et Nikolay Dvoretsky. « Electrical conductivity of potassium polyferrite doped with doubly charged cations ». From Chemistry Towards Technology Step-By-Step 5, n^o 2 (24 juin 2024) : 140–46. http://dx.doi.org/10.52957/2782-1900-2024-5-2-140-146.

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To clarify the charge compensation mechanism and the way of alloying additives placement, the authors synthesised samples of potassium βʺ-polyferrites with a wide range of mole fraction of introduced doubly charged cations. For these samples, the authors measured the electronic conductivity, cationic conductivity, and performed X-ray diffraction (XRD) analysis. The authors identified the charge compensation mechanism in potassium β″-polyferrite when doped with divalent ions of calcium, strontium, magnesium, and zinc. The charge compensation mechanisms differ depending on the radius of the introduced doubly charged ion. The results of cationic conductivity measurements of potassium β″-polyferrites show the mobility reduction of large calcium and strontium cations of potassium ions. Such additives are quite promising for improving the mechanical strength and thermal stability of the catalyst granules. They also increase the chemical stability of the contact granules. Corrosion resistance of pellets is a critical parameter. It determines the period of effective functioning of the catalyst. The data on electronic conductivity allow one to conclude that the introduction of Mg2+, Zn2+ cations sharply reduces the electron exchange in the structure of potassium β″-polyferrite. This should inevitably cause deactivation of the catalyst, while Ca2+ and Sr2+ ions do not reduce the electron transfer rate. Moreover, using the proposed approach will intensify the research process.

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García-Sánchez, Almudena, Elena García-Pérez, David Dubbeldam, Rajamani Krishna et Sofía Calero. « A Simulation Study of Alkanes in Linde Type A Zeolites ». Adsorption Science & ; Technology 25, n^o 6 (juillet 2007) : 417–27. http://dx.doi.org/10.1260/026361707783908274.

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Monte Carlo simulations were performed to study the adsorption and diffusion of small hydrocarbons in Linde Type A zeolites as a function of their calcium/sodium ratio. The diffusion studies were focused on methane whereas the adsorption simulations were performed from methane up to pentane. The results obtained showed that an increase in the number of cations in the structure (exchange of univalent sodium ions by divalent calcium ions) led to an increase in the adsorption of linear alkanes at low and medium pressure, but caused a decrease in adsorption at the highest pressures. An increase in the amount of cations favours molecular attraction and hence results in lower mobility. At higher cation loading the ions block the windows interconnecting the LTA cages, leading to a further decrease in diffusion. Methane self-diffusion coefficients obtained from our simulations were twice as high for the Linde Type 5A zeolite as for the Linde Type 4A zeolite. These results are consistent with previous experimental studies and provide a molecular picture of the influence of the zeolite type, the amount of cations contained and their location in the structure.

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Barbagallo, Mario, Lawrence M. Resnick, R. Ernest Sosa, Mary Lou Corbett et John H. Laragh. « Renal divalent cation excretion in secondary hypertension ». Clinical Science 83, n^o 5 (1 novembre 1992) : 561–65. http://dx.doi.org/10.1042/cs0830561.

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1. To determine whether abnormal renal calcium excretion is unique to primary genetic hypertension, blood pressure and 24 h urinary excretion of calcium, magnesium, sodium and creatinine were measured in deoxycorticosterone—saline and two-kidney, one-clip Goldblatt hypertensive rats and in their respective controls on low (0.2%) and high (1.8%) dietary calcium intakes. 2. Calcium supplementation lowered blood pressure (P<0.05) in deoxycorticosterone—saline rats and in control saline-loaded rats, raised blood pressure in two-kidney, one clip rats, and had no effect in sham-operated control rats. 3. On both diets, calcium excretion was higher in hypertensive than in normotensive rats. The high calcium diet increased urinary calcium excretion in all rats, but the changes in urinary calcium excretion closely paralleled the diet-induced changes in blood pressure. Thus, urinary calcium excretion in deoxycorticosterone—saline animals, in whom calcium lowered blood pressure the most, rose the least (107%). Urinary calcium excretion rose the most in two-kidney, one-clip animals (1113%), whose blood pressure also rose the most. 4. Urinary magnesium excretion was also abnormal in hypertensive rats compared with normotensive rats, falling on the high compared with the low calcium diet in normotensive rats, but not in either hypertensive strain. Furthermore, urinary magnesium excretion was closely linked to urinary calcium excretion in saline-loaded control rats (r = 0.78; P = 0.008), but was dissociated from urinary calcium excretion in deoxycorticosterone—saline rats (r = 0.02; not significant). 5. We conclude (a) that the renal handling of both calcium and magnesium is altered in secondary hypertension, and (b) that dietary calcium supplementation may have different effects on blood pressure in different forms of hypertensive disease. We hypothesize that elevated blood pressure per se may be responsible for the exaggerated calciuresis of hypertension.

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Haynes, L. W. « Permeation and block by internal and external divalent cations of the catfish cone photoreceptor cGMP-gated channel. » Journal of General Physiology 106, n^o 3 (1 septembre 1995) : 507–23. http://dx.doi.org/10.1085/jgp.106.3.507.

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The ability of the divalent cations calcium, magnesium, and barium to permeate through the cGMP-gated channel of catfish cone outer segments was examined by measuring permeability and conductance ratios under biionic conditions and by measuring their ability to block current carried by sodium when presented on the cytoplasmic or extracellular side of the channel. Current carried by divalent cations in the absence of monovalent cations showed the typical rectification pattern observed from these channels under physiological conditions (an exponential increase in current at both positive and negative voltages). With calcium as the reference ion, the relative permeabilities were Ca > Ba > Mg, and the chord conductance ratios at +50 mV were in the order of Ca approximately Mg > Ba. With external sodium as the reference ion, the relative permeabilities were Ca > Mg > Ba > Na with chord conductance ratios at +30 mV in the order of Na > Ca = Mg > Ba. The ability of divalent cations presented on the intracellular side to block the sodium current was in the order Ca > Mg > Ba at +30 mV and Ca > Ba > Mg at -30 mV. Block by external divalent cations was also investigated. The current-voltage relations showed block by internal divalent cations reveal no anomalous mole fraction behavior, suggesting little ion-ion interaction within the pore. An Eyring rate theory model with two barriers and a single binding site is sufficient to explain both these observations and those for monovalent cations, predicting a single-channel conductance under physiological conditions of 2 pS and an inward current at -30 mV carried by 82% Na, 5% Mg, and 13% Ca.

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Smith, J. S., T. Imagawa, J. Ma, M. Fill, K. P. Campbell et R. Coronado. « Purified ryanodine receptor from rabbit skeletal muscle is the calcium-release channel of sarcoplasmic reticulum. » Journal of General Physiology 92, n^o 1 (1 juillet 1988) : 1–26. http://dx.doi.org/10.1085/jgp.92.1.1.

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The ryanodine receptor of rabbit skeletal muscle sarcoplasmic reticulum was purified as a single 450,000-dalton polypeptide from CHAPS-solubilized triads using immunoaffinity chromatography. The purified receptor had a [3H]ryanodine-binding capacity (Bmax) of 490 pmol/mg and a binding affinity (Kd) of 7.0 nM. Using planar bilayer recording techniques, we show that the purified receptor forms cationic channels selective for divalent ions. Ryanodine receptor channels were identical to the Ca-release channels described in native sarcoplasmic reticulum using the same techniques. In the present work, four criteria were used to establish this identity: (a) activation of channels by micromolar Ca and millimolar ATP and inhibition by micromolar ruthenium red, (b) a main channel conductance of 110 +/- 10 pS in 54 mM trans Ca, (c) a long-term open state of lower unitary conductance induced by ryanodine concentrations as low as 20 nM, and (d) a permeability ratio PCa/PTris approximately equal to 14. In addition, we show that the purified ryanodine receptor channel displays a saturable conductance in both monovalent and divalent cation solutions (gamma max for K and Ca = 1 nS and 172 pS, respectively). In the absence of Ca, channels had a broad selectivity for monovalent cations, but in the presence of Ca, they were selectively permeable to Ca against K by a permeability ratio PCa/PK approximately equal to 6. Receptor channels displayed several equivalent conductance levels, which suggest an oligomeric pore structure. We conclude that the 450,000-dalton polypeptide ryanodine receptor is the Ca-release channel of the sarcoplasmic reticulum and is the target site of ruthenium red and ryanodine.

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Brommundt, G., et F. Kavaler. « La3+, Mn2+, and Ni2+ effects on Ca2+ pump and on Na+-Ca2+ exchange in bullfrog ventricle ». American Journal of Physiology-Cell Physiology 253, n^o 1 (1 juillet 1987) : C45—C51. http://dx.doi.org/10.1152/ajpcell.1987.253.1.c45.

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45Ca washout from ventricles of the bullfrog was followed through an automated technique previously described. Lanthanum decreased the fractional rate of loss of 45Ca (by 67% at the saturating concentration, 1 mM, for this effect of the trivalent cation). In contrast, both manganous and nickel ions decreased the fractional rate of loss of 45Ca in 21 of the 30 ventricles studied. In the remainder of the experiments these ions increased this rate. This augmentation of the rate of 45Ca efflux by manganese and nickel could be converted consistently to an inhibition by experimental maneuvers known to increase the intracellular concentration of sodium-potassium-free washout solution, dihydroouabain. These results are consistent with the hypothesis that manganese and nickel increase 45Ca efflux through a process of sarcolemmal manganese-calcium (or nickel-calcium) exchange, operating through the sodium-calcium exchanger. Support for this interpretation was obtained in the further observation that the rate of loss of radioactive nickel from 63Ni-loaded ventricles was monotonically related to the extracellular concentration of calcium. Thus the augmenting effect of the divalent cations on 45Ca efflux appears to be mediated by the sodium-calcium exchanger. That the inhibitory effect arises from an action of the cations on the ATP-dependent component of 45Ca efflux is indicated by the fact that it disappears after vigorous ATP depletion in the presence of cyanide and 2-deoxy-D-glucose.

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Friedman, M. E., G. Suarez-Kurtz, G. J. Kaczorowski, G. M. Katz et J. P. Reuben. « Two calcium currents in a smooth muscle cell line ». American Journal of Physiology-Heart and Circulatory Physiology 250, n^o 4 (1 avril 1986) : H699—H703. http://dx.doi.org/10.1152/ajpheart.1986.250.4.h699.

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Membrane currents in small cells of a smooth muscle cell line (A10) derived from embryonic rat thoracic aorta were monitored by the patch electrode whole-cell voltage clamp technique. Three currents, two divalent cation currents, and a Ca2+-activated K+ current have been observed. The latter is readily abolished pharmacologically, allowing the characterization of the divalent cation currents. With a holding potential of -50 mV, a single divalent current, which inactivates slowly, is elicited on depolarization of the membrane potential to values positive to ca. -10 mV. The second divalent cation current is only observed when the holding potential is negative to -55 mV and the membrane is pulsed to values positive to ca. -35 mV. This current is rapidly inactivating, peaking in approximately 5 ms and decaying with a t1/2 of ca. 15 ms at 0 mV when conveyed by Ba2+. The rapidly inactivating divalent cation current is depressed by substitution of Ba2+ for Ca2+ in the bathing solution and is highly insensitive to organic Ca2+ channel blockers. The slowly inactivating channel has more typical characteristics of Ca2+ channels; it is more permeable to Ba2+ than to Ca2+ and is sensitive to modulation by dihydropyridines. These data demonstrate the presence of two distinctly different Ca2+ channels in A10 cells.

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Banke, T. G., S. R. Chaplan et A. D. Wickenden. « Dynamic changes in the TRPA1 selectivity filter lead to progressive but reversible pore dilation ». American Journal of Physiology-Cell Physiology 298, n^o 6 (juin 2010) : C1457—C1468. http://dx.doi.org/10.1152/ajpcell.00489.2009.

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TRPA1 is a nonselective cation channel belonging to the transient receptor potential (TRP) family that is expressed in peripheral sensory neurons and may play important roles in pain perception and inflammation. We found that agonist stimulation of TRPA1, along with other members of the TRP family (TRPV1–4 and TRPM8), can induce the appearance of a large pore permeable to large organic cations such as Yo-Pro (YP) and N-methyl-d-glucamine, in an agonist and divalent cation-dependent manner. YP uptake was not inhibited by a panel of putative gap junction/pannexin blockers, suggesting that gap junction proteins are not required in this process. Our data suggest that changes in the TRP channel selectivity filter itself result in a progressive but reversible pore dilation process, a process that is under strong regulation by external calcium ions. Our data suggest that calcium plays a novel role in setting the amount of time TRPA1 channels spend in a dilated state providing a mechanism that may limit sensory neuron activation by painful or irritating substances.

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Jay, Eleanor E., Phillip M. Mallinson, Shirley K. Fong, Brian L. Metcalfe et Robin W. Grimes. « Divalent cation diffusion in calcium fluorapatite ». Journal of Materials Science 46, n^o 23 (12 juillet 2011) : 7459–65. http://dx.doi.org/10.1007/s10853-011-5712-4.

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Makarova, Anastasiya O., Svetlana R. Derkach, Tahar Khair, Mariia A. Kazantseva, Yuriy F. Zuev et Olga S. Zueva. « Ion-Induced Polysaccharide Gelation : Peculiarities of Alginate Egg-Box Association with Different Divalent Cations ». Polymers 15, n^o 5 (28 février 2023) : 1243. http://dx.doi.org/10.3390/polym15051243.

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Structural aspects of polysaccharide hydrogels based on sodium alginate and divalent cations Ba2+, Ca2+, Sr2+, Cu2+, Zn2+, Ni2+ and Mn2+ was studied using data on hydrogel elemental composition and combinatorial analysis of the primary structure of alginate chains. It was shown that the elemental composition of hydrogels in the form of freezing dried microspheres gives information on the structure of junction zones in the polysaccharide hydrogel network, the degree of filling of egg-box cells by cations, the type and magnitude of the interaction of cations with alginate chains, the most preferred types of alginate egg-box cells for cation binding and the nature of alginate dimers binding in junction zones. It was ascertained that metal–alginate complexes have more complicated organization than was previously desired. It was revealed that in metal–alginate hydrogels, the number of cations of various metals per C12 block may be less than the limiting theoretical value equal to 1 for completely filled cells. In the case of alkaline earth metals and zinc, this number is equal to 0.3 for calcium, 0.6 for barium and zinc and 0.65–0.7 for strontium. We have determined that in the presence of transition metals copper, nickel and manganese, a structure similar to an egg-box is formed with completely filled cells. It was determined that in nickel–alginate and copper–alginate microspheres, the cross-linking of alginate chains and formation of ordered egg-box structures with completely filled cells are carried out by hydrated metal complexes with complicated composition. It was found that an additional characteristic of complex formation with manganese cations is the partial destruction of alginate chains. It has been established that the existence of unequal binding sites of metal ions with alginate chains can lead to the appearance of ordered secondary structures due to the physical sorption of metal ions and their compounds from the environment. It was shown that hydrogels based on calcium alginate are most promising for absorbent engineering in environmental and other modern technologies.

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G, Asha, Jyothi A. Natikar et Shrabani Mohanty. « Role of Divalent Cations in Pathophysiology of Essential Hypertension ». Galore International Journal of Health Sciences and Research 6, n^o 3 (1 juillet 2021) : 7–15. http://dx.doi.org/10.52403/gijhsr.20210702.

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Introduction: Essential hypertension (EHTN) accounts for 95% of all cases of hypertension affecting approximately one billion individuals worldwide. Alteration in trace elements like calcium and magnesium can be helpful in knowing the elemental involvement in the pathophysiology of EHTN and its associated complications. Aims and Objectives: To estimate serum levels of calcium and magnesium in patients of EHTN and compare it with normotensive healthy subjects. To find the correlation of serum levels of calcium and magnesium with systolic blood pressure (SBP) and diastolic blood pressure (DBP) in patients of EHTN. Materials and Methods: The study was conducted in 100 subjects, out of which 50 were essential hypertensive patients (cases) and 50 were normotensive healthy subjects (controls), within the age group of 25-65 years. Serum calcium and magnesium were measured by using the auto analyzer Beckman Coulter DXC 600. The results were analysed by using students ‘t’ test and pearson’s correlation. Results: Our study found a significantly (p<0.001**) increased levels of serum calcium and significantly (p<0.001**) decreased levels of serum magnesium in cases as compared to controls. Our study also revealed a significant positive correlation between serum calcium with SBP (r= 0.842, p<0.001**) and DBP (r= 0.403, p= 0.004**); and a significant negative correlation between serum magnesium with SBP (r= -0.805, p<0.001**) and DBP (r=-0.395, p=0.005**) among essential hypertensives. Keywords: EHTN-Essential hypertension, HTN-Hypertension, SBP-Systolic blood pressure, DBP-Diastolic blood pressure, BP-Blood pressure.

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Park, Haesun, et Deahyun Kim. « First-Principles Study of Layered Electrode Materials for Multivalent Batteries ». ECS Meeting Abstracts MA2024-02, n^o 9 (22 novembre 2024) : 1299. https://doi.org/10.1149/ma2024-0291299mtgabs.

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Energy storage systems that efficiently shuttle multivalent cations such as calcium (Ca) or magnesium (Mg) have been increasingly spotlighted due to their potential for achieving high energy density at a lower cost. The advancement of these multivalent energy storage systems necessitates the exploration and development of electrode materials that not only offer high capacity but also ensure the reversible accommodation of multivalent cations. Recent studies on monovalent alkaline ions such as potassium and sodium, which exhibit a similar ionic radius to calcium, have demonstrated their capability for reversible intercalation into inorganic compounds with layered structures. This notable finding suggests a strong potential for the successful intercalation of divalent ions in analogous structures, thereby enhancing the versatility and efficiency of these energy storage systems. In this context, we have employed first-principles calculations to systematically investigate and reveal that layered structures are conducive to topotactic intercalation of Ca or Mg, attributes characterized by favorable phase stability, electrochemical performance, cation mobility, and transition metal redox behavior. These layered materials, through our detailed computational analysis, show promise for the next generation of high-performance, cost-effective multivalent energy storage systems.

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Smiles, D. E., et C. J. Smith. « A survey of the cation content of piggery effluents and some consequences of their use to irrigate soils ». Soil Research 42, n^o 2 (2004) : 231. http://dx.doi.org/10.1071/sr03059.

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Piggery effluent contains high concentrations of potassium, and its repeated irrigation raises soil exchangeable potassium to levels, relative to divalent cations, that may degrade soil structure. We surveyed 6 big piggeries extending from south-eastern Queensland on a self-mulching Vertosol, to an Arenic Rudosol in south-eastern South Australia. We sampled effluent used for irrigation and also soil profiles to permit 'fenceline' comparisons between soils that had and had not been irrigated. The major water-soluble cations sodium (Na+), potassium (K+), calcium (Ca2+), and magnesium (Mg2+) were measured in the effluent and the soil saturation extracts, and also their exchangeable forms on air-dried soil samples. Ammonium-nitrogen (NH4+-N) was also assayed. The effluents were similar, with pH values between 7.5 and 8 together with very high water-soluble NH4-N, lower values for K+ and Na+, and quite low concentrations of Ca2+ and Mg2+. Cation concentrations varied across effluents; sodium and potassium adsorption ratios (SAR and KAR) were relatively constant but smaller than an ammonium adsorption ratio (Am-AR), which we conceive to estimate the influence of NH4+-N relative to the divalent cations in the effluent. Exchangeable K+ ratios in all profiles that had been irrigated were greater than their non-irrigated partners, as were the KAR values in their saturation extracts. Despite high concentrations of NH4+-N and high values of Am-AR in the effluents, there was no evidence of exchangeable NH4+ in the soils when sampled, which, we presume, is rapidly taken up by plants or oxidised. We present data that support a useful relationship between total cation content and effluent and the soil saturation extract electrical conductivity (EC), We also observed a modest increase in the EC of the saturation extract of irrigated soils. Farm records were insufficient to permit material balance calculations.

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Nagorna, V. F., et T. A. Kulish. « Magnesium at physiological pregnancy and at its complications ». REPRODUCTIVE ENDOCRINOLOGY, n^o 69 (29 septembre 2023) : 41–52. http://dx.doi.org/10.18370/2309-4117.2023.69.41-52.

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Sources of literature on the role of the trace element magnesium and the assosiation with calcium in physiological processes in the body of reproductive aged women and pregnant women, the importance of its main functions and role in preventing the main pregnancy complications were analyzed. Magnesium is the fourth most important extracellular cation after sodium, potassium and calcium and the second intracellular cation in importance after potassium. Many researchers have proven the participation of magnesium in almost everyone important functions in the body. Magnesium performs the following functions which are closely interconnected: metabolic, energetic, enzymatic, cardiovascular, antithrombotic, vascular, neuroprotective, structural, is an antagonist of calcium and an agonist of NMDA receptors. Magnesium realizes its functions in close interaction with cations of sodium, potassium and calcium. It acts as a calcium antagonist. It should be noted attention to the understanding of the interaction of divalent cations-competitors of magnesium and calcium. Calcium has complex influences on interaction of magnesium with blood proteins, reduces its concentration, which can affect physiological processes during pregnancy and in non-pregnant women. Today, magnesium is used only for prevention and treatment of eclampsia, in which anticonvulsants are commonly used ineffective. It can be assumed that different convulsive states have different intracellularly or extracellularly magnesium concentration is important in the pathogenesis and occurrence of eclampsia. Determination of magnesium concentration never was indicated in the recommendations for the management of preeclampsia. Magnesium use is insufficiently substantiated in cases of uterus contraction activity in any conditions (threat of abortion, premature birth) and prevention of pathological blood clot formation (as causes of multiple complications of pregnancy), neuroprotective effect on a child. The role of magnesium in the production of steroid hormones has been proven. However, this effect remains unrealized in obstetrics and gynecology practice. Data from literature sources given in the article help justify the use of magnesium and analyze its interaction with calcium during pregnancy.

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Smedley, Martin J., et Martin Stanisstreet. « Calcium and neurulation in mammalian embryos ». Development 89, n^o 1 (1 octobre 1985) : 1–14. http://dx.doi.org/10.1242/dev.89.1.1.

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The role of calcium in neurulation in rat embryos has been studied. Rat embryos at 10·4 days of gestation, when the cephalic neural folds have elevated but not fused, have been cultured in various media, and the effects of these media on the morphology of the cephalic neural folds have been observed by scanning and transmission electron microscopy. Embryos cultured in serum containing EDTA or EGTA, or in saline without divalent cations exhibit opening, then folding back (‘collapse’) of the cephalic neural folds. The neural cells lose their elongated shape and become rounded. Older embryos in which the cephalic neural folds have already fused do not show collapse of the neural tube. Culture of 10·4-day rat embryos with elevated but unfused cephalic neural folds in calcium- and magnesium-free saline to which either calcium or magnesium has been restored shows that calcium is the divalent cation which is essential for the maintenance of the elevated neural folds. In the presence of calcium, lanthanum, which competes for calcium sites, causes opening but not collapse of the elevated cephalic neural folds. Embryos treated with trypsin show dissociation of the lateral (non-neural) ectoderm but the neural folds remain elevated. If embryos in which the cephalic neural folds have been caused to collapse are further cultured in serum the folds re-elevate, although normal neural tube morphology is not completely regained. The possible implications of these observations to the understanding of the cellular mechanisms of normal neurulation, and of neural tube malformations are discussed.

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Alli, Yani Faozani. « THE EFFECT OF ELECTROLYTES ON POLYMER VISCOSITY FOR EFFECTIVENESS OF POLYMER INJECTION ». Scientific Contributions Oil and Gas 42, n^o 2 (6 août 2020) : 59–63. http://dx.doi.org/10.29017/scog.42.2.386.

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The use of polymer for tertiary oil recovery has been known to be important as viscosity modifier to increase sweep efficiency of water flood and chemical flood. The most common polymer used for chemical flood is hydrolyzed polyacrylamide (HPAM) that owing large number of charges along the polymer chains. However, formation water as dissolution water contain high electrolytes that has a great effect on polymer viscosity, as well as responsible to generate the efficiency of polymer flooding. In this study, the effect of electrolytes from saline and cation divalent to the viscosity of polymer was investigated. Three studied polymers were dissolved in various concentration of saline and cation divalent by analyzing the compatibility, viscosity, and the filtration ratio of polymers. The results showed that the presence of electrolytes in every concentration of water did not impact the compatibility and filtration ratio of polymers. Whereas, the addition of sodium chloride as saline ionic and calcium chloride as cationic divalent were both reducing the viscosity of polymers. The lower viscosity of polymer related to the ability of polymer to expand the hydrodynamic which limited by the neutralization of internal repulsion of the electrolytes.

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Kučerka, N., E. Dushanov, Kt Kholmurodov, J. Katsaras et D. Uhríková. « Cation-containing lipid membranes – experiment and md simulations ». European Pharmaceutical Journal 64, n^o 2 (27 novembre 2017) : 9–14. http://dx.doi.org/10.1515/afpuc-2016-0018.

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AbstractUsing small angle neutron diffraction and molecular dynamics simulations we studied the interactions between calcium (Ca2+) or zinc (Zn2+) cations, and oriented gel phase dipalmitoyl-phosphatidylcholine (DPPC) bilayers. For both cations studied at ~1:7 divalent metal ion to lipid molar ratio (Me2+:DPPC), bilayer thickness increased. Simulation results helped reveal subtle differences in the effects of the two cations on gel phase membranes.

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Dufner, Matthias M., Philipp Kirchhoff, Christine Remy, Patricia Hafner, Markus K. Müller, Sam X. Cheng, Lie-Qi Tang, Steven C. Hebert, John P. Geibel et Carsten A. Wagner. « The calcium-sensing receptor acts as a modulator of gastric acid secretion in freshly isolated human gastric glands ». American Journal of Physiology-Gastrointestinal and Liver Physiology 289, n^o 6 (décembre 2005) : G1084—G1090. http://dx.doi.org/10.1152/ajpgi.00571.2004.

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Gastric acid secretion is activated by two distinct pathways: a neuronal pathway via the vagus nerve and release of acetylcholine and an endocrine pathway involving gastrin and histamine. Recently, we demonstrated that activation of H+-K+-ATPase activity in parietal cells in freshly isolated rat gastric glands is modulated by the calcium-sensing receptor (CaSR). Here, we investigated if the CaSR is functionally expressed in freshly isolated gastric glands from human patients undergoing surgery and if the CaSR is influencing histamine-induced activation of H+-K+-ATPase activity. In tissue samples obtained from patients, immunohistochemistry demonstrated the expression in parietal cells of both subunits of gastric H+-K+-ATPase and the CaSR. Functional experiments using the pH-sensitive dye 2′,7′-bis-(2-carboxyethyl)-5-(and 6)-carboxyfluorescein and measurement of intracellular pH changes allowed us to estimate the activity of H+-K+-ATPase in single freshly isolated human gastric glands. Under control conditions, H+-K+-ATPase activity was stimulated by histamine (100 μM) and inhibited by omeprazole (100 μM). Reduction of the extracellular divalent cation concentration (0 Mg2+, 100 μM Ca2+) inactivated the CaSR and reduced histamine-induced activation of H+-K+-ATPase activity. In contrast, activation of the CaSR with the trivalent cation Gd3+ caused activation of omeprazole-sensitive H+-K+-ATPase activity even in the absence of histamine and under conditions of low extracellular divalent cations. This stimulation was not due to release of histamine from neighbouring enterochromaffin-like cells as the stimulation persisted in the presence of the H2 receptor antagonist cimetidine (100 μM). Furthermore, intracellular calcium measurements with fura-2 and fluo-4 showed that activation of the CaSR by Gd3+ led to a sustained increase in intracellular Ca2+ even under conditions of low extracellular divalent cations. These experiments demonstrate the presence of a functional CaSR in the human stomach and show that this receptor may modulate the activity of acid-secreting H+-K+-ATPase in parietal cells. Furthermore, our results show the viability of freshly isolated human gastric glands and may allow the use of this preparation for experiments investigating the physiological regulation and properties of human gastric glands in vitro.

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Kamioka, H., K. Sumitani, K. Tagami, Y. Miki, K. Terai, Y. Hakeda, M. Kumegawa et T. Kawata. « Divalent Cations Elevate Cytosolic Calcium of Chick Osteocytes ». Biochemical and Biophysical Research Communications 204, n^o 2 (octobre 1994) : 519–24. http://dx.doi.org/10.1006/bbrc.1994.2490.

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