Home About us Contact
|
Home About us Contact | ||
|
|
||
Mg2+
Kinds of Mg2+ Terms modified by Mg2+ Selected AbstractsGrowth and characterization of pure and doped nonlinear optical l-arginine acetate single crystalsCRYSTAL RESEARCH AND TECHNOLOGY, Issue 10 2007M. Gulam Mohamed Abstract Single crystals of organic nonlinear optical material of pure, Cu2+ and Mg2+ doped L-arginine acetate (LAA) were successfully grown by slow evaporation method at room temperature. The UV-Vis-NIR spectra of pure and doped LAA indicate that these crystals possess a wide optical transmission window from 240-1600 nm. Non-linear optical studies reveal that the SHG efficiency of LAA is nearly three times that of KDP. The dielectric response of the samples was studied in the frequency region 100 Hz to 2 MHz and the influence of Cu2+ and Mg2+ substitution on the dielectric behaviour had been investigated. Photoconductivity study proves that both pure and Cu2+ and Mg2+ doped LAA crystal exhibit positive photoconductivity. It is evident from the Vickers hardness study that the hardness of the crystal decreases with increasing load both for pure and doped samples. ESR studies confirmed the incorporation of Cu2+ into LAA and the value of g-factor was found to be 2.1654. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Influence of Mg/Er co-doping on the principal laser parameters of LiNbO3 crystalsCRYSTAL RESEARCH AND TECHNOLOGY, Issue 7 2007Liang Sun Abstract Mg: Er: LiNbO3 crystals were grown by the Czochralski technique with various concentrations of MgO = 2 mol%, 4 mol%, 6 mol% and the fixed concentration of Er2O3= 1 mol% in the melt, and the 8 mol%Mg: 1 mol%Er: LiNbO3 crystal was fabricated by the Czochralski technique with special technology process. The crystals were treated by polarization, reduction and oxidation. The segregation coefficients of Mg2+ and Er3+ in Mg: Er: LiNbO3 crystals were measured by X-ray fluorescence spectrograph, as well as the crystal's defect structure and optical properties were analyzed by the UV-Vis, IR and fluorescent spectroscopy. The pump wavelength and the surge wavelength were determined. Using m-line method tested optical damage resistance of those crystals, the results show that photodamage threshold of Mg: Er: LiNbO3 crystals are higher than that of Er: LiNbO3 crystal, and the oxidation treat could enhance the photodamage resistant ability of crystals while the reduction treat could depress the ability. The optical damage resistance of 8 mol%Mg: 1 mol%Er: LiNbO3 crystal was the strongest among the samples, which was two orders magnitude higher than that of 1 mol%Er: LiNbO3 crystal. The dependence of the optical properties on defect structure of Mg: Er: LiNbO3 crystals was discussed. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] The influence of metallic substitution on the physical properties of manganese mercury thiyocyanate crystalsCRYSTAL RESEARCH AND TECHNOLOGY, Issue 3 2007G. P. Joseph Abstract Good optical grade single crystals of pure, Cd2+ and Mg2+ doped Manganese Mercury Thiyocyanate (MMTC) crystals are grown by slow solvent evaporation technique at room temperature. Single crystal XRD studies reveal that the incorporation of metallic dopants has not changed the structure of the parent crystal. The SHG efficiencies of the pure and doped samples of MMTC are measured by Kurtz Perry powder method and the results are compared with urea. It is evident from microhardness study that the presence of dopants has increased the mechanical strength of MMTC crystal. The TG/DTG studies confirm that the thermal decomposition temperatures of pure (353°C), Mg2+ doped (363°C) and Cd2+ doped (365°C) MMTC are relatively high when compared to other NLO crystals of the same family. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Survival of mammalian B104 cells following neurite transection at different locations depends on somal Ca2+ concentrationDEVELOPMENTAL NEUROBIOLOGY, Issue 2 2004Soonmoon Yoo Abstract We report that cell survival after neurite transection in a mammalian neuronal model (cultured B104 cells) critically depends on somal [Ca2+]i, a novel result that reconciles separate long-standing observations that somal survival decreases with more-proximal axonal transections and that increased somal Ca2+ is cytotoxic. Using fluorescence microscopy, we demonstrate that extracellular Ca2+ at the site of plasmalemmal transection is necessary to form a plasmalemmal barrier, and that other divalent ions (Ba2+, Mg2+) do not play a major role. We also show that extracellular Ca2+, rather than injury per se, initiates the formation of a plasmalemmal barrier and that a transient increase in somal [Ca2+]i significantly decreases the percentage of cells that survive neurite transection. Furthermore, we show that the increased somal [Ca2+]i and decreased cell survival following proximal transections are not due to less frequent or slower plasmalemmal sealing or Ca2+ entry through plasmalemmal Na+ and Ca2+ channels. Rather, the increased somal [Ca2+]i and lethality of proximal neurite injuries may be due to the decreased path length/increased diameter for Ca2+ entering the transection site to reach the soma. A ryanodine block of Ca2+ release from internal stores before transection has no effect on cell survival; however, a ryanodine- or thapsigargin-induced buildup of somal [Ca2+]i before transection markedly reduces cell survival, suggesting a minor involvement of Ca2+ -induced release from internal stores. Finally, we show that cell survival following proximal injuries can be enhanced by increasing intracellular Ca2+ buffering capacity with BAPTA to prevent the increase in somal [Ca2+]i. © 2004 Wiley Periodicals, Inc. J Neurobiol 60: 137,153, 2004 [source] Dynamics of P2X7 receptor pore dilation: Pharmacological and functional consequencesDRUG DEVELOPMENT RESEARCH, Issue 2-3 2001I.P. Chessell Abstract The biophysical and functional properties of the human P2X7 receptor, expressed recombinantly in HEK-293 cells or natively in THP-1 pro-monocytic cells, were investigated in the context of pore dilation and externalisation of mature interleukin 1, (IL1,). In HEK-293 cells, the agonist 2,- and 3,-O-(4-benzoylbenzoyl)-ATP (BzATP) caused concentration-dependent inward currents (EC50 59 ,M) and with prolonged application this agonist caused a gradual increase in inward current culminating in a plateau. This increase in current was associated with pore dilation, determined by intracellular accumulation of YO-PRO-1. BzATP displayed increased potency at the pore-dilated form of the P2X7 receptor (EC50 17 ,M), and positive correlations between apparent receptor density and speed of pore dilation were observed. A monoclonal antibody selectively blocked current mediated by the naïve receptor, while currents through pore-dilated receptors were not significantly affected, which together suggest a conformational change at the level of the receptor during the dilation event. The release of mature IL1, from THP-1 cells was independent of P2X7 -mediated cell lysis, as determined by study of lactate dehydrogenase release. Moreover, using conditions designed to minimise pore dilation (using buffers containing 2 mM Ca2+ and 1 mM Mg2+), BzATP caused significant release of IL1,, but without concomitant YO-PRO-1 accumulation, indicating pore dilation is not required for IL1, release. In addition, short (4-min) incubation of THP-1 cells with BzATP (terminated by enzymatic degradation of BzATP using apyrase) resulted in significant quantities of IL1, release some 60 min later, suggesting commitment of cells to release IL1, can be triggered with only brief receptor ligation. These findings suggest that receptor expression and ligation time are critical factors for selecting multiple functional states of P2X7. Drug Dev. Res. 53:60,65, 2001. © 2001 Wiley-Liss, Inc. [source] A Cobalt Film Electrode for Nitrite Determination in Natural WaterELECTROANALYSIS, Issue 24 2007Koïkoï Soropogui Abstract In this study a cobalt film electrodeposited on a copper disk (Ø=3.1,mm) was tested as electrode to measure nitrite ions in raw water. This electrode was able to determine the nitrite ions concentration in nondeaerated synthetic media and in natural water. The electrode reached a detection limit of 0.2,,mol L,1 and has a linear concentration range of 0.4 to 2,,mol L,1 NO2,. The influence of several ions such as NO3,, Cl,, SO42,, Mg2+, HCO3, and NH4+ was also tested. The electrode was used to determine the concentration of nitrite ions in a real sample. [source] Silver(I)-Selective PVC Membrane Potentiometric Sensor Based on a Recently Synthesized Calix[4]areneELECTROANALYSIS, Issue 10 2006Ayça Demirel Abstract A new PVC membrane potentiometric sensor for Ag(I) ion based on a recently synthesized calix[4]arene compound of 5,11,17,23-tetra- tert -butyl-25,27-dihydroxy-calix[4]arene-thiacrown-4 is developed. The electrode exhibits a Nernstian response for Ag(I) ions over a wide concentration range (1.0×10,2,1.0×10,6 M) with a slope of 53.8±1.6,mV per decade. It has a relatively fast response time (5,10,s) and can be used for at least 2 months without any considerable divergence in potentials. The proposed electrode shows high selectivity towards Ag+ ions over Pb2+, Cd2+, Co2+, Zn2+, Cu2+, Ni2+, Sr2+, Mg2+, Ca2+, Li+, K+, Na+, NH4+ ions and can be used in a pH range of 2,6. Only interference of Hg2+ is found. It is successfully used as an indicator electrode in potentiometric titration of a mixture of chloride, bromide and iodide ions. [source] Analysis of Simulated Martian Regolith Using an Array of Ion Selective ElectrodesELECTROANALYSIS, Issue 15-16 2005Stefan Abstract A prototype miniature array of polymer membrane and solid state ion selective electrodes was developed for the purpose of performing an in-situ analysis of the soluble ionic species in Martian regolith (soil). The array contains a total of 27 electrodes for K+, Na+, Ca2+, Mg2+, NH, Ba2+, NO, Cl,, and Li+, each in triplicate. Barium electrodes were used to indirectly monitor sulfate through precipitation by the addition of barium chloride while the lithium electrodes served as a reference for the array by having a constant lithium concentration as a background for all solutions. The array was tested with several types of simulants, soils, and sawdust from a Mars meteorite, all with varying salt content, meant to approximate the various hypotheses regarding the ionic composition of the Martian soil. The activities of anions and cations determined with the array were compared to ion chromatography data. [source] A Bis-Oxime Derivative of Diaza-18-Crown-6 as an Ionophore for Silver IonELECTROANALYSIS, Issue 11 2005Michael Abstract A new pendant-arm derivative of diaza-18-crown-6, containing two oxime donor groups, has been synthesized and incorporated into a polyvinyl chloride (PVC) membrane ion-selective electrode. The electrode shows selectivity for Ag+ ion, with a near Nernstian response. Pb2+, Cu2+, Hg2+, and Tl+ are major interfering ions, with Cd2+ having minor interference. The electrode shows no potentiometric response for the ions Mg2+, Al3+, K+, Ca2+, Ni2+, Fe3+, and La3+, and is responsive to H+ at pH<6. [source] Interaction study of a lysozyme-binding aptamer with mono- and divalent cations by ACEELECTROPHORESIS, Issue 3 2010Marie Girardot Abstract Binding between an aptamer and its target is highly dependent on the conformation of the aptamer molecule, this latter seeming to be affected by a variety of cations. As only a few studies have reported on the interactions of monovalent or divalent cations with aptamers, we describe herein the use of ACE in its mobility shift format for investigating interactions between various monovalent (Na+, K+, Cs+) or divalent (Mg2+, Ca2+, Ba2+) cations and a 30-mer lysozyme-binding aptamer. This study was performed in BGEs of different natures (phosphate and MOPS buffers) and ionic strengths. First, the effective charges of the aptamer in 30,mM ionic strength phosphate and MOPS (pH 7.0) were estimated to be 7.4 and 3.6, respectively. Then, corrections for ionic strength and counterion condensation effects were performed for all studies. The effective mobility shift was attributed not only to these effects, but also to a possible interaction with the buffer components (binary or ternary complexes) as well as possible conformational changes of the aptamer. Finally, apparent binding constants were calculated for divalent cations with mathematical linearization methods, and the influence of the nature of the BGE was evidenced. [source] Electrophoretic behaviors of human hepatoma HepG2 cellsELECTROPHORESIS, Issue 9 2009Jyh-Ping Hsu Abstract The electrophoretic mobility of HepG2 cells was measured and a charge-regulated model was proposed to simulate the results obtained. Here, a cell was simulated by a rigid core and an ion-penetrable membrane layer containing both acidic and basic functional groups. The influences of the key parameters, including the pH, the ionic strength, the thickness of the membrane layer of a cell, the density and the dissociation constant of the dissociable functional groups in the membrane layer, and the binding constant of divalent cations on the electrophoretic mobility of a cell were investigated. In particular, the role of the buffer used in the experiment was discussed; this effect was neglected in almost all the relevant theoretical analyses in the literature. We showed that the binding ability of divalent cations to the dissociated functional groups in the membrane layer of a cell ranks as Ca2+>Mg2+>hexamethonium. [source] Response of the charophyte Nitellopsis obtusa to heavy metals at the cellular, cell membrane, and enzyme levelsENVIRONMENTAL TOXICOLOGY, Issue 3 2002Levonas Manusad, ianas Abstract The responses of the freshwater macroalga Nitellopsis obtusa to heavy metal (HM) salts of Hg, Cd, Co, Cu, Cr, and Ni were assessed at different levels: whole-cell mortality (96-h LC50), in vivo cell membrane (45-min depolarization of resting potential, EC50), and enzyme in plasma membrane preparations (K+, Mg2+ -specific H+ -ATPase inhibition, IC50). To measure ATPase activity, a novel procedure for isolation of plasma membrane,enriched vesicles from charophyte cells was developed. The short-term ATPase inhibition assay (IC50 from 6.0 × 10,7 to 4.6 × 10,4 M) was slightly more sensitive than the cell mortality test (LC50 from 1.1 × 10,6 to 2.6 × 10,3 M), and the electrophysiological test with the end point of 45-min depolarization of resting potential was characterized by less sensitivity for HMs (EC50 from 1.1 × 10,4 to 2.2 × 10,2 M). The variability of IC50 values assessed for HMs in the ATPase assays was close to that of LC50 values in the mortality tests (CVs from 33.5 to 83.5 and from 12.4% to 57.7%, respectively), whereas the EC50 values in the electrophysiological tests were characterized by CVs generally below 30%. All three end points identified two separate HM groups according to their toxicity to N. obtusa: Co, Ni, and Cr comprised a group of less toxic metals, whereas Hg, Cu, and Cd comprised a group of more toxic metals. However, the adverse effects within each group were discriminated differently. For example, the maximum difference between the highest and lowest LC50 for the group of less toxic metals in the long-term mortality test was approximately 60% of the response range, whereas the corresponding difference in IC50 values in the ATPase assay was 30%. In contrast, the LC50 values of the more toxic metals occupied only 10% of the response range, whereas the IC50 values were spread over 70%. Further investigation should be done of the underlying mechanism or mechanisms responsible for the observed differences in the dynamic range of a particular end point of the groups of toxicants of varying strength. © 2002 Wiley Periodicals, Inc. Environ Toxicol 17: 275,283, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/tox.10058 [source] Molecular modeling of metal complexation by a fluoroquinolone antibioticENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 11 2008Ludmilla Aristilde Abstract An understanding of the factors controlling the chemodynamics of fluoroquinolone antibiotics in different environmental matrices is a necessary prerequisite to the assessment of their potential impact on nontarget organisms in soils and receiving waters. Of particular interest are the complexes formed between fluoroquinolones and metal cations, which are believed to be important in the mechanism of sequestration of the antibiotic by minerals and natural organic matter. The structures of these complexes have not been fully resolved by conventional spectroscopy; therefore, molecular simulations may provide useful complementary insights. We present results from apparently the first molecular dynamics simulations of a widely used fluoroquinolone antibiotic, ciprofloxacin (Cipro), in aqueous complexes with five metal cations typically found in soils and surface waters: Ca2+, Mg2+, Fe2+, Na+, and K+. The interatomic potential functions employed in the simulations were validated by comparison with available structural data for solid-phase Cipro-hexahydrate and for the metal cations in aqueous solution. Although no comprehensive structural data on the aqueous complexes appear to be available, properties of the metal complexes predicted by our simulations agree with available data for solid-phase metal,Cipro complexes. Our results indicate that the ionic potential of the metal cation controls the stability of the complex formed and that the hydration number of the metal cation in aqueous solution determines its coordination number with O atoms in the metal,Cipro complex. In respect to environmental chemodynamics, our results imply that Cipro will form two configurations of bidendate chelates with metal centers on exposed surfaces of mineral oxides, water-bridged surface complexes with exchangeable cations in clay mineral interlayers, and cation-bridged complexes with functional groups in natural organic matter. [source] The effect of food rations on tissue-specific copper accumulation patterns of sublethal waterborne exposure in Cyprinus carpioENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 7 2007Shodja Hashemi Abstract Common carp (Cyprinus carpio) were fed to two different food rations, 0.5% body weight (low ration [LR]) and 5% body weight (high ration [HR]), and were exposed to sublethal (1 ,M) copper levels for 28 d in softened Antwerp (Belgium) city tap water (Ca2+, 79.3 mg/L; Mg2+, 7.4 mg/L; Na+, 27.8 mg/L; pH 7.5,8.0). Copper accumulations in the liver, gills, kidney, anterior intestine, posterior intestine, and muscle were determined. Copper accumulation in the gills, liver, and kidney of LR fish was significantly higher than in HR fish. The only time copper uptake in HR fish was significantly higher than in LR fish was in the posterior intestine after two weeks of exposure. No difference was found between the two rations in the anterior intestine. Copper accumulation in the liver of both feeding treatments occurred in a time-dependent manner and did not reach steady state in any treatment. On the contrary, copper concentration in the gills reached a steady state for both HR and LR fish within the first week of exposure. No copper accumulation was found in muscle tissues of either treatment. Copper concentration dropped to control levels in all tissues, except liver tissue, two weeks after the exposure ended. Our studies indicated that copper uptake was influenced by the food ration in carp. The difference in copper accumulation probably is related to the amount of dietary NaCl and different rates of metallothionein synthesis. Low food availability provides less Na+ influx and leads to increased brachial uptake of Na+ and copper. In addition, it has been shown that starved animals show increased levels of metallothionein, possibly causing higher copper accumulation. [source] Plasma membrane surface potential (,pm) as a determinant of ion bioavailability: A critical analysis of new and published toxicological studies and a simplified method for the computation of plant ,pmENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 12 2006Thomas B. Kinraide Abstract Plasma membranes (PMs) are negatively charged, and this creates a negative PM surface electrical potential ,PM) that is also controlled by the ionic composition of the bathing medium. The ,PM controls the distribution of ions between the PM surface and the medium so that negative potentials increase the surface activity of cations and decrease the surface activity of anions. All cations reduce the negativity of ,PM, and these common ions are effective in the following order: Al3+ > H+ > Cu2+ > Ca2+ , Mg2+ > Na+ , K+. These ions, especially H+, Ca2+, and Mg2+, are known to reduce the uptake and biotic effectiveness of cations and to have the opposite effects on anions. Toxicologists commonly interpret the interactions between toxic cations (commonly metals) and ameliorative cations (commonly H+, Ca2+, and Mg2+) as competitions for binding sites at a PM surface ligand. The ,PM is rarely considered in this biotic ligand model, which incorporates the free ion activity model. The thesis of this article is that ,PM effects are likely to be more important to bioavailability than site-specific competition. Furthermore, ,PM effects could give the false appearance of competition even when it does not occur. The electrostatic approach can account for the bioavailability of anions, whereas the biotic ligand model cannot, and it can account for interactions among cations when competition does not occur. Finally, a simplified procedure is presented for the computation of ,PM for plants, and the possible use of ,PM in a general assessment of the bioavailability of ions is considered. [source] Variations of chemical compositions in coarse aerosols and fine aerosols in two successive episodesENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 8 2006Chung-Yih Kuo Abstract Particulate matter with diameters less than 2.5 ,m (PM2.5) and ranging between 10 to 2.5 ,m (PM10-2.5) were simultaneously collected at four air-quality monitoring stations in the Taichung area of central Taiwan during the period of February 12 to 22, 2004. Two different types of PM10 episodes, a nonlocal dust-storm episode and a local episode, were observed in the present study. High concentrations of coarse aerosols occurred during the dust-storm episode, whereas high concentrations of fine aerosols were present during the local episode. Relatively high levels of Na+, Mg2+, Ca2+, and Cl, in coarse aerosols were observed during the dust-storm episode. Very high concentrations of secondary aerosols (NH+4, SO2,4, and NO,3) in fine aerosols were observed during the local episode. The nitrate ion demonstrated the greatest increase in the ratios of ionic species to PM2.5 and ionic species to PM10-2.5 during the local episode. Significantly high ratios (0.444) of NO,3 to NO2 in fine aerosols were present during the local episode, indicating that the relatively high formation rate of NO,3 was one of the important factors leading to the increase of the NO,3 to PM2.5 ratio during the local episode. Results also showed that an abundant quantity of fine ammonium nitrate was formed during the local episode, and chloride depletion probably was the major pathway to form coarse NaNO3 during this episode. [source] ,9 -Tetrahydrocannabivarin suppresses in vitro epileptiform and in vivo seizure activity in adult ratsEPILEPSIA, Issue 8 2010Andrew J. Hill Summary Purpose:, We assessed the anticonvulsant potential of the phytocannabinoid ,9 -tetrahydrocannabivarin (,9 -THCV) by investigating its effects in an in vitro piriform cortex (PC) brain slice model of epileptiform activity, on cannabinoid CB1 receptor radioligand-binding assays and in a generalized seizure model in rats. Methods:, ,9 -THCV was applied before (10 ,m,9 -THCV) or during (10,50 ,m,9 -THCV) epileptiform activity induced by Mg2+ -free extracellular media in adult rat PC slices and measured using multielectrode array (MEA) extracellular electrophysiologic techniques. The actions of ,9 -THCV on CB1 receptors were examined using [3H]SR141716A competition binding and [35S]GTP,S assays in rat cortical membranes. Effects of ,9 -THCV (0.025,2.5 mg/kg) on pentylenetetrazole (PTZ),induced seizures in adult rats were also assessed. Results:, After induction of stable spontaneous epileptiform activity, acute ,9 -THCV application (,20 ,m) significantly reduced burst complex incidence and the amplitude and frequency of paroxysmal depolarizing shifts (PDSs). Furthermore, slices pretreated with 10 ,m,9 -THCV prior to induction of epileptiform activity exhibited significantly reduced burst complex incidence and PDS peak amplitude. In radioligand-binding experiments, ,9 -THCV acted as a CB1 receptor ligand, displacing 0.5 nm [3H]SR141716A with a Ki,290 nm, but exerted no agonist stimulation of [35S]GTP,S binding. In PTZ-induced seizures in vivo, 0.25 mg/kg ,9 -THCV significantly reduced seizure incidence. Discussion:, These data demonstrate that ,9 -THCV exerts antiepileptiform and anticonvulsant properties, actions that are consistent with a CB1 receptor,mediated mechanism and suggest possible therapeutic application in the treatment of pathophysiologic hyperexcitability states. [source] Neocortical Potassium Currents Are Enhanced by the Antiepileptic Drug LamotrigineEPILEPSIA, Issue 7 2002Cristina Zona Summary: ,Purpose: We used field-potential recordings in slices of rat cerebral cortex along with whole-cell patch recordings from rat neocortical cells in culture to test the hypothesis that the antiepileptic drug (AED) lamotrigine (LTG) modulates K+ -mediated, hyperpolarizing currents. Methods: Extracellular field-potential recordings were performed in neocortical slices obtained from Wistar rats aged 25,50 days. Rat neocortical neurons in culture were subjected to the whole-cell mode of voltage clamping under experimental conditions designed to study voltage-gated K+ currents. Results: In the in vitro slice preparation, LTG (100,400 ,M) reduced and/or abolished epileptiform discharges induced by 4-aminopyridine (4AP, 100 ,M; n = 10), at doses that were significantly higher than those required to affect epileptiform activity recorded in Mg2+ -free medium (n = 8). We also discovered that in cultured cortical cells, LTG (100,500 ,M; n = 13) increased a transient, 4AP-sensitive, outward current elicited by depolarizing commands in medium containing voltage-gated Ca2+ and Na+ channel antagonists. Moreover, we did not observe any change in a late, tetraethylammonium-sensitive outward current. Conclusions: Our data indicate that LTG, in addition to the well-known reduction of voltage-gated Na+ currents, potentiates 4AP-sensitive, K+ -mediated hyperpolarizing conductances in cortical neurons. This mechanism of action contributes to the anticonvulsant effects exerted by LTG in experimental models of epileptiform discharge, and presumably in clinical practice. [source] Comparison of Intrinsic Optical Signals Associated with Low Mg2+, and 4-Aminopyridine,Induced Seizure-Like Events Reveals Characteristic Features in Adult Rat Limbic SystemEPILEPSIA, Issue 6 2000Katharina Buchheim Summary: Purpose: To analyze the intrinsic optical signal change associated with seizure-like events in two frequently used in vitro models,the low-Mg2+ and the 4-aminopyridine (4-AP) models,and to monitor regions of onset and spread patterns of these discharges by using imaging of intrinsic optical signals (IOS). Methods: Combined hippocampal,entorhinal,cortex slices of adult rats were exposed to two different treatments: lowering extracellular Mg2+ concentrations or application of 100 ,M 4-AP. The electrographic features of the discharges were monitored using extracellular microelectrodes. Optical imaging was achieved by infrared transillumination of the slice and analysis of changes in light transmission using a subtraction approach. The electrographic features were compared with the optical changes. Regions of onset and spread patterns were analyzed in relevant anatomic regions of the slice. Results: Both lowering extracellular Mg2+ concentrations and application of 4-AP induced seizure-like events. The relative duration of the intrinsic optical signal change associated with seizure-like events in the low-Mg2+ model was significantly longer compared with that seen with those occurring in the 4-AP model, although duration of field potentials did not differ significantly in the two models. Seizure-like events of the low-Mg2+ model originated predominantly in the entorhinal cortex, with subsequent propagation toward the subiculum and neocortical structures. In contrast, no consistent region of onset or spread patterns were seen in the 4-AP model, indicating that the seizure initiation is not confined to a particular region in this model. Conclusions: We conclude that different forms of spontaneous epileptiform activity are associated with characteristic optical signal changes and that optical imaging represents an excellent method to assess regions of seizure onset and spread patterns. [source] Single-Electron-Transfer Reactions of ,-Diimine dpp-BIAN and Its Magnesium Complex (dpp-BIAN)2,Mg2+(THF)3EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 4 2006Igor L. Fedushkin Abstract The reactions of (dpp-BIAN)Mg(THF)3 (1) {dpp-BIAN = 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene} with ethyl halides EtX (X = Cl, Br, I) in hexane proceed by single-electron transfer (SET) from the metal complex to the organic halide. Complexes [(dpp-BIAN)(Et)]MgX(THF)n [X = Cl, n = 0 (2); X = Br, n = 2 (3); X = I, n = 1 (4)] are the products of ethyl transfer to an imine carbon atom of a coordinated diimine ligand. The compound [(dpp-BIAN)(Et)]MgBr (3a) was obtained from the reaction of free dpp-BIAN with ethylmagnesiumbromide in hexane. In this case SET from the Grignard reagent to the neutral diimine takes place. Compounds 2,4 and 3a were isolated as crystals and characterized by 1H NMR spectroscopy. The molecular structure of 3 was determined by single-crystal X-ray analysis. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Towards Understanding of the Selective Precipitation of Alkali Metal Cations in Presence of Dipicrylamine AnionEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 11 2005Suresh Eringathodi Abstract Dipicrylamine anion (DPA,) precipitates out [K(DPA)] with high selectivity from salt bitterns containing Na+, K+, and Mg2+, whereas the same ligand shows poor selectivity towards K+ , and much higher selectivity towards Cs+ , in studies conducted with a mixture of K+, Rb+, and Cs+. Their single-crystal structures reveal that the K+ and Rb+ salts have similar layered structures, with 8 oxygen atoms from seven DPA, anions encapsulating the metal cation, whereas the Cs+ salt possesses a channel-like structure with the metal ion encapsulated by ten oxygen atoms from six DPA,. The conformation of DPA, in the [Cs(DPA)] single crystal matches closely that of DPA in crystalline state. M···O and intermolecular C,H···O interactions together stabilize the structures. The 133Cs NMR spectrum of the poorly soluble [Cs(DPA)] shows an upfield shift of the peak with respect to CsCl as a result of the interaction with the oxygen atoms of DPA,, whereas 23Na NMR spectrum of the highly soluble [Na(DPA)] shows no such upfield shift compared to NaCl. Powder XRD patterns of bulk [M(DPA)] (M = K+, Rb+, and Cs+) precipitates show that these are similar to the patterns obtained by simulation of the single-crystal X-ray data. The selectivity of precipitation correlates qualitatively with the size and hydration enthalpies of the ions. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Oxidation of oleuropein studied by EPR and spectrophotometryEUROPEAN JOURNAL OF LIPID SCIENCE AND TECHNOLOGY, Issue 2 2008Evaggelia D. Tzika Abstract The autoxidation at alkaline pH and enzymatic oxidation by mushroom tyrosinase of oleuropein, the dominant biophenol present in the fruits and leaves of Olea europea, was followed by both electron paramagnetic resonance (EPR) and absorption spectroscopy. For comparison, the same oxidation processes were applied to 4-methylcatechol, a simple polyphenol present in olive mill wastewaters. EPR spectra of stable o -semiquinone radicals produced during autoxidation at pH,12 and short-lived o -semiquinone free radicals produced during autoxidation at pH,9.0 or tyrosinase action and stabilized by chelation with a diamagnetic metal ion (Mg2+) were recorded for both polyphenols, and the corresponding hyperfine splitting constants were determined. The UV-Vis spectral characteristics of the oxidation of polyphenols were highly dependent on the type of polyphenol, oxidant type and the pH of the reaction. The kinetic behavior of tyrosinase in the presence of oleuropein and 4-methylcatechol was followed by recording spectral changes at 400,nm (absorption maximum) over time. The tysosinase activity with oleuropein showed a pronounced pH optimum at pH,6.5 and a minor one around pH,8. From the data analysis of the initial rate at pH,6.5, the kinetic parameters Km = 0.34,±,0.03,mM and Vmax = 0.029,±,0.002 ,A400,min,1 were determined for oleuropein. [source] Sodium/bicarbonate cotransporter NBCn1/slc4a7 increases cytotoxicity in magnesium depletion in primary cultures of hippocampal neuronsEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 3 2009Deborah S. Cooper Abstract Growing evidence suggests that pharmacological inhibition of Na/H exchange and Na/HCO3 transport provides protection against damage or injury in cardiac ischemia. In this study, we examined the contribution of the sodium/bicarbonate cotransporter NBCn1 (slc4a7) to cytotoxicity in cultured hippocampal neurons of rats. In neurons exposed to extracellular pH (pHo) ranging from 6.2 to 8.3, NBCn1 protein expression increased by fivefold at pH < 6.5 compared to the expression at pHo 7.4. At pHo 6.5, the intracellular pH of neurons was ,1 unit lower than that at pH 7.4. Immunochemistry showed a marked increase in NBCn1 immunofluorescence in plasma membranes and cytosol of the soma as well as in dendrites, at pHo 6.5. NBCn1 expression also increased by 40% in a prolonged Mg2+ -free incubation at normal pHo. Knockdown of NBCn1 in neurons had negligible effect on cell viability. The effect of NBCn1 knockdown on cytotoxicity was then determined by exposing neurons to 0.5 mm glutamate for 10 min and measuring lactate dehydrogenase (LDH) release from neurons. Compared to normal incubation (pHo 7.2 for 6 h) after glutamate exposure, acidic incubation (pHo 6.3 for 6 h) reduced cytotoxicity by 75% for control neurons and 78% for NBCn1-knockdown neurons. Thus, both controls and knockdown neurons showed acidic protection from cytotoxicity. However, in Mg2+ -free incubation after glutamate exposure, NBCn1 knockdown progressively attenuated cytotoxicity. This attenuation was unaffected by acidic preincubation before glutamate exposure. We conclude that NBCn1 has a dynamic upregulation in low pHo and Mg2+ depletion. NBCn1 is not required for acidic protection, but increases cytotoxicity in Mg2+ -free conditions. [source] Small-conductance Cl, channels contribute to volume regulation and phagocytosis in microgliaEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 8 2007Guillaume Ducharme Abstract The shape and volume of microglia (brain immune cells) change when they activate during brain inflammation and become migratory and phagocytic. Swollen rat microglia express a large Cl, current (IClswell), whose biophysical properties and functional roles are poorly understood and whose molecular identity is unknown. We constructed a fingerprint of useful biophysical properties for comparison with IClswell in other cell types and with cloned Cl, channels. The microglial IClswell was rapidly activated by cell swelling but not by voltage, and showed no time-dependence during voltage-clamp steps. Like IClswell in many cell types, the halide selectivity sequence was I, > Br, > Cl, > F,. However, it differed in lacking inactivation, even at +100 mV with high extracellular Mg2+, and in having a much lower single-channel conductance: 1,3 pS. Based on these fundamental differences, the microglia channel is apparently a different gene product than the more common intermediate-conductance IClswell. Microglia express several candidate genes, with relative mRNA expression levels of: CLIC1 > ClC3 > ICln , ClC2 > Best2 > Best1 , Best3 > Best4. Using a pharmacological toolbox, we show that all drugs that reduced the microglia current (NPPB, IAA-94, flufenamic acid and DIOA) increased the resting cell volume in isotonic solution and inhibited the regulatory volume decrease that followed cell swelling in hypotonic solution. Both channel blockers tested (NPPB and flufenamic acid) dose-dependently inhibited microglia phagocytosis of E. coli bacteria. Because IClswell is involved in microglia functions that involve shape and volume changes, it is potentially important for controlling their ability to migrate to damage sites and phagocytose dead cells and debris. [source] Differential responses to NMDA receptor activation in rat hippocampal interneurons and pyramidal cells may underlie enhanced pyramidal cell vulnerabilityEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 12 2005E. Avignone Abstract Hippocampal interneurons are generally more resistant than pyramidal cells to excitotoxic insults. Because NMDA receptors play a crucial role in neurodegeneration, we have compared the response to exogenous NMDA in CA1 pyramidal cells and interneurons of the stratum oriens using combined whole-cell patch-clamp recording and ratiometric Ca2+ imaging. In voltage-clamp, current-clamp or in nominally Mg2+ -free medium, NMDA (10 µm; 3,5 min exposure in the presence of tetrodotoxin) induced a markedly larger inward current and Ca2+ rise in pyramidal cells than in interneurons. Pyramidal cells also showed a more pronounced voltage dependence in their response to NMDA. We hypothesized that this enhanced response to NMDA receptor activation in pyramidal cells could underlie their increased vulnerability to excitotoxicity. Using loss of dye as an indicator of degenerative membrane disruption, interneurons tolerated continuous exposure to a high concentration of NMDA (30 µm) for longer periods than pyramidal cells. This acute neurodegeneration in pyramidal cells was independent of intracellular Ca2+, because high intracellular BAPTA (20 mm) did not prolong survival time. Thus, a plausible explanation for the enhanced sensitivity of pyramidal neurons to excitotoxic insults associated with cerebral ischemia is their greater response to NMDA receptor activation, which may reflect differences in NMDA receptor expression and/or subunit composition. [source] Mechanisms of ATP action on motor nerve terminals at the frog neuromuscular junctionEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 5 2005S. Grishin Abstract We have shown previously that ATP inhibits transmitter release at the neuromuscular junction through the action on metabotropic P2Y receptors coupled to specific second messenger cascades. In the present study we recorded K+ or Ca2+ currents in motor nerve endings or blocked K+ or Ca2+ channels in order to explore the nature of downstream presynaptic effectors. Endplate currents were presynaptically depressed by ATP. Blockers of Ca2+ -activated K+ -channels, such as iberiotoxin, apamin or tetraethylammonium, did not change the depressant action of ATP. By contrast, K+ channel blocker 4-aminopyridine (4-AP) and raised extracellular Ca2+ attenuated the effect of ATP. However, these effects of 4-AP and high Ca2+ were reversed by Mg2+, suggesting Ca2+ -dependence of the ATP action. Ba2+ promoted the depressant action of ATP as did glibenclamide, a blocker of ATP-sensitive K+ channels, or mild depolarization produced by 7.5 mm K+. None of the K+ channel blockers affected the depressant action of adenosine. Focal recording revealed that neither ATP nor adenosine affected the fast K+ currents of the motor nerve endings. However, unlike adenosine, ATP or UTP, an agonist of P2Y receptors, reversibly reduced the presynaptic Ca2+ -current. This effect was abolished by suramin, an antagonist of P2 receptors. Depressant effect of ATP on the endplate and Ca2+ -currents was mimicked by arachidonate, which precluded the action of ATP. ATP reduced acetylcholine release triggered by ionomycin or sucrose, suggesting inhibition of release machinery. Thus, the presynaptic depressant action of ATP is mediated by inhibition of Ca2+ channels and by mechanism acting downstream of Ca2+ entry. [source] Descending respiratory polysynaptic inputs to cervical and thoracic motoneurons diminish during early postnatal maturation in rat spinal cordEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 3 2005Laurent Juvin Abstract Isolated brainstem-spinal cord preparations were used to explore the coexistence of a direct and an indirect descending drive from the brainstem respiratory centre to cervical and thoracic respiratory motoneurons in the neonatal Sprague,Dawley rat. Polysynaptic spinal relay pathways from the respiratory centre were suppressed by selectively perfusing the cord with mephenesin (1 mm) or a solution enriched with Ca2+ and Mg2+. At birth, both direct and spinally relayed pathways are functional and contribute equally to the global descending respiratory drive. However, during the first postnatal week, significant maturational changes appear in the way the respiratory centre controls its target respiratory motoneurons in the cervical and thoracic spinal cord, with the direct respiratory drive becoming progressively predominant with maturation (from 50% to around 75% of the global descending command). The relative contributions of the monosynaptic and the polysynaptic spinal pathways may therefore have important implications for effective respiratory control during early postnatal development. [source] AMPA/kainate and NMDA-like glutamate receptors at the chromatophore neuromuscular junction of the squid: role in synaptic transmission and skin patterningEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 3 2003Pedro A. Lima Abstract Glutamate receptor types were examined at the chromatophore synapses of the squids Alloteuthis subulata and Loligo vulgaris, where nerve-induced muscle contraction causes chromatophore expansion. Immunoblotting with antibody raised against a squid AMPA receptor (sGluR) demonstrated that AMPA/kainate receptors are present in squid skin. Application of l -glutamate evoked chromatophore muscle contractions in both ventral and dorsal skins, while NMDA was only active on a subpopulation of dorsal chromatophores. In dorsal skin, neurotransmission was partly blocked by either AMPA/kainate receptor antagonists (CNQX and DNQX) or NMDA receptor antagonists (AP-5 and MK-801) or completely blocked by simultaneous application of both classes of antagonists. In isolated muscle fibres, ionophoretic application of l -glutamate evoked fast inward CNQX- and DNQX-sensitive currents with reversal potentials around +14 mV and a high conductance to Na+. In fibres from dorsal skin only, a slower outward glutamate-sensitive current appeared at positive holding potentials. At negative potentials, currents were potentiated by glycine or by removing external Mg2+ and were blocked by AP-5 and MK-801. Glutamate caused a fast, followed by a slow, transient increase in cytoplasmic Ca2+. The slow component was increased in amplitude and duration by glycine or by lowering external Mg2+ and decreased by AP-5 and MK-801. In cells from ventral skin, no ,NMDA-like responses' were detected. Thus, while AMPA/kainate receptors mediated fast excitatory synaptic transmission and rapid colour change over the whole skin, activation of both AMPA/kainate and NMDA-like receptors in a subpopulation of dorsal chromatophores prolonged the postsynaptically evoked Ca2+ elevation causing temporally extended colour displays with behavioural significance. [source] Dopaminergic signalling in the rodent neonatal suprachiasmatic nucleus identifies a role for protein kinase A and mitogen-activated protein kinase in circadian entrainmentEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 2 2002Irina L. Schurov Abstract The circadian clock of the suprachiasmatic nuclei (SCN) of perinatal rodents is entrained by maternally derived cues. The SCN of neonatal Syrian hamsters express high-affinity D1 dopamine receptors, and the circadian activity,rest cycle of pups can be entrained by maternal injection of dopaminergic agonists. The present study sought to characterize the intracellular pathways mediating dopaminergic signalling in neonatal rodent SCN. Both dopamine and the D1 agonist SKF81297 caused a dose-dependent increase in phosphorylation of the transcriptional regulator Ca2+/cyclic AMP response element (CRE) binding protein (CREB) in suprachiasmatic GABA-immunoreactive (-IR) neurons held in primary culture. The D1 antagonist SCH23390 blocked this effect. Dopaminergic induction of pCREB-IR in GABA-IR neurons was also blocked by a protein kinase A (PKA) inhibitor, 5,24, and by the MAPK inhibitor, PD98059, whereas KN-62, an inhibitor of Ca2+/calmodulin-dependent (CAM) kinase II/IV was ineffective. Treatment with NMDA increased the level of intracellular Ca2+ in the cultured primary SCN neurons in Mg2+ -free medium, but SKF81297 did not. Blockade of CaM kinase II/IV with KN-62 inhibited glutamatergic induction of pCREB-IR in GABA-IR neurons, whereas 5,24 was ineffective, confirming the independent action of Ca2+ - and cAMP-mediated inputs on pCREB. SKF81297 caused an increase in pERK-IR in SCN cells, and this was blocked by 5,24, indicative of activation of MAPK via D1/cAMP. These results demonstrate that dopaminergic signalling in the neonatal SCN is mediated via the D1-dependent activation of PKA and MAPK, and that this is independent of the glutamatergic regulation via Ca2+ and CaM kinase II/IV responsible for entrainment to the light/dark cycle. [source] Differential sensitivity of medium- and large-sized striatal neurons to NMDA but not kainate receptor activation in the ratEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 10 2001Carlos Cepeda Abstract Infrared videomicroscopy and differential interference contrast optics were used to identify medium- and large-sized neurons in striatal slices from young rats. Whole-cell patch-clamp recordings were obtained to compare membrane currents evoked by application of N -methyl- d -aspartate (NMDA) and kainate. Inward currents and current densities induced by NMDA were significantly smaller in large- than in medium-sized striatal neurons. The negative slope conductance for NMDA currents was greater in medium- than in large-sized neurons and more depolarization was required to remove the Mg2+ blockade. In contrast, currents induced by kainate were significantly greater in large-sized neurons whilst current densities were approximately equal in both cell types. Spontaneous excitatory postsynaptic currents occurred frequently in medium-sized neurons but were relatively infrequent in large-sized neurons. Excitatory postsynaptic currents evoked by electrical stimulation were smaller in large- than in medium-sized neurons. A final set of experiments assessed a functional consequence of the differential sensitivity of medium- and large-sized neurons to NMDA. Cell swelling was used to examine changes in somatic area in both neuronal types after prolonged application of NMDA or kainate. NMDA produced a time-dependent increase in somatic area in medium-sized neurons whilst it produced only minimal changes in large interneurons. In contrast, application of kainate produced significant swelling in both medium- and large-sized cells. We hypothesize that reduced sensitivity to NMDA may be due to variations in receptor subunit composition and/or the relative density of receptors in the two cell types. These findings help define the conditions that put neurons at risk for excitotoxic damage in neurological disorders. [source] | ||||||||||||||||||||||||||||||||||||||||||||||||||||