Determination of [Mg2+]i – an update on the use of Mg2+-selective electrodes

Since their invention, ion-selective microelectrodes have become an indispensable tool for investigations of intracellular ion regulation and transport. While highly selective sensors for all major intracellular monovalent ions have been available for decades, the development of sensors for divalent cations seems to have presented more difficulties. As ion-selective microelectrodes typically have time-constants in the range of 0.5 to several seconds they turned out to be inapt for the investigation of intracellular Ca²⁺. The development of sensors for Mg²⁺-selective electrodes has made its most striking progress only over the past few years. While the first Mg²⁺ sensor, ETH 1117, was barely able to detect physiological Mg²⁺ concentrations in the presence of other mono- and divalent cations, the newest sensors allow measurements in the micromolar range. When used in macroelectrodes, the most recent developments, ETH 5506 and ETH 5504, have even been reported to do so in the presence of millimolar Ca²⁺ concentrations. Although there is still room for improvement to make these sensors applicable in microelectrodes, some preliminary data look extremely promising and indicate that a new era for Mg²⁺-selective microelectrodes is about to start.     

GEF-mediated GDP/GTP exchange by monomeric GTPases: A regulatory role for Mg2+?

GTPases share highly conserved guanine nucleotide-binding domains and fulfill diverse functions through a common molecular switch. An inactive GDP-bound protein is turned on by a guanine nucleotide exchange factor (GEF) that catalyzes exchange of GTP for GDP, but unfortunately little is known about the mechanism of GEF action. A common mechanism for GDP/GTP exchange can be envisioned wherein GEFs activate monomeric GTPases through transient disruption of Mg²⁺ coordination in the nucleotide-binding pocket while stabilizing a nucleotide-free (and cation-free) conformation. After guanine nucleotide exchange, Mg²⁺ coordination is restored to complete the conformational switch to the active GTP-bound state. Evidence in the literature highlighting an important regulatory role for Mg²⁺ in the mechanism of GEF-mediated GDP/GTP exchange by monomeric GTPases is summarized. BioEssays 20 :516–521, 1998. © 1998 John Wiley & Sons, Inc.     

Mg2+浓度对细胞融合效果的影响

目的:细胞融合是细胞生物学中一种常用的技术,有着广泛的应用,如单克隆抗体制备,核质研究,疫苗研发等.其中,聚乙二醇(PEG)化学融合是最为常用的一种细胞融合技术,影响PEG化学细胞融合效果的因素有很多,但是对一些具体因素的研究的不是很全面.本文旨在为了更全面的了解PEG诱导的化学细胞融合的影响因素,优化融合条件,以此扩大PEG化学融合应用范围.方法:以鸡血血红细胞为材料,通过调节已有的Hanks融合液中镁离子浓度,比较各实验组以及对照组的细胞融合率,探究了Mg2+浓度对细胞融合效果的影响,确定了为提高细胞融合效率应使用的Mg2+浓度区间.结果:可以在原有的Hanks配方的基础上,调节Mg2+浓度至10 mmol/L-20 mmol/L这个范围,细胞融合率较大.结论:Mg2+对细胞融合有一定影响,通过调节Mg2+浓度至上述合适区间可以达到较高的细胞融合率,从而为PEG化学融合提供了一种优化方案.     

Chick brain glutamine synthetase and Mn2+−Mg2+ interactions

Glutamine synthetase (GS) from the chick brain was purified to apparent homogeneity by ammonium sulfate fractionation followed by affinity chromatography, electrofocusing and Sephadex G-150 chromatography. The purified enzyme showed a single band on sodium dodecyl sulfate analysis in polyacrylamide gel. By sedimentation equilibrium analysis and gel electrophoresis analysis, it was shown that the enzyme has a subunit molecular weight of 45,000 and a native molecular weight of 364,000, which is consistent with an octameric structure. Sedimentation analysis in the presence of Mg²⁺ revealed three different forms of macromolecules corresponding respectively to a monomer, a tetramer and an octamer. Among eight cations tested (Ca²⁺, Co²⁺, Fe²⁺, Li⁺, Mg²⁺, Mn²⁺, Ni²⁺, Zn²⁺) only Co²⁺, Mg²⁺ and Mn²⁺ supported GS activity; the order of activatory ability was Mg²⁺>Co²⁺>Mn²⁺. The maximum activating effect of Mn²⁺ occurs only within a very narrow range of concentration: with an excess of cation causing strong inhibition of GS activity. For each cation, maximal GS activity occurs at a defined cation/ATP ratio. A regulatory system in which Mn²⁺, modulates the Mg²⁺ dependent GS activity, is proposed; such cation interactions may be of significance in the intracellular control of glutamine synthesis.     

Mg2+对灰树花菌丝体生长的影响

研究了不同浓度的Mg^2 对灰树花菌丝体生长的影响,结果表明:2—3g/L的Mg^2 浓度对菌丝体生长有明显的促进作用。浓度过高,则抑制菌丝体生长。     

?-Adrenergic Stimulation Increases RyR2 Activity via Intracellular Ca2+ and Mg2+ Regulation

Here we investigate how ß-adrenergic stimulation of the heart alters regulation of ryanodine receptors (RyRs) by intracellular Ca²⁺ and Mg²⁺ and the role of these changes in SR Ca²⁺ release. RyRs were isolated from rat hearts, perfused in a Langendorff apparatus for 5 min and subject to 1 min perfusion with 1 µM isoproterenol or without (control) and snap frozen in liquid N₂ to capture their phosphorylation state. Western Blots show that RyR2 phosphorylation was increased by isoproterenol, confirming that RyR2 were subject to normal ß-adrenergic signaling. Under basal conditions, S2808 and S2814 had phosphorylation levels of 69% and 15%, respectively. These levels were increased to 83% and 60%, respectively, after 60 s of ß-adrenergic stimulation consistent with other reports that ß-adrenergic stimulation of the heart can phosphorylate RyRs at specific residues including S2808 and S2814 causing an increase in RyR activity. At cytoplasmic [Ca²⁺] <1 µM, ß-adrenergic stimulation increased luminal Ca²⁺ activation of single RyR channels, decreased luminal Mg²⁺ inhibition and decreased inhibition of RyRs by mM cytoplasmic Mg²⁺. At cytoplasmic [Ca²⁺] >1 µM, ß-adrenergic stimulation only decreased cytoplasmic Mg²⁺ and Ca²⁺ inhibition of RyRs. The K_a and maximum levels of cytoplasmic Ca²⁺ activation site were not affected by ß-adrenergic stimulation.Our RyR2 gating model was fitted to the single channel data. It predicted that in diastole, ß-adrenergic stimulation is mediated by 1) increasing the activating potency of Ca²⁺ binding to the luminal Ca²⁺ site and decreasing its affinity for luminal Mg²⁺ and 2) decreasing affinity of the low-affinity Ca²⁺/Mg²⁺ cytoplasmic inhibition site. However in systole, ß-adrenergic stimulation is mediated mainly by the latter.     

Ca2+、Mg2+对籼稻幼苗分化及生根的影响

以籼稻愈伤组织为材料,研究了Ca2+、Mg2+对愈伤组织分化成苗及其生根的影响.结果表明在一定的浓度范围内,Ca2+、Mg2+对籼稻愈伤组织芽分化有很好的促进作用.Ca2+浓度为6×103mol/L,Mg2+浓度为1.5 × 103mol/L时,分化效果较佳.而不同浓度的Ca2+、Mg2+对籼稻生根影响不明显,生根效果均较好.     

心肌缺血预处理后Ca2+*Mg2+-ATPase及SDH活性的变化

198 6年Ｍｕｒｒｙ等首次发现实验狗心肌在经历了短暂性缺血后产生对随后持续严重缺血再灌注的保护作用 ,并称此现象为“缺血预处理 (ｉｓｃｈｅｍｉｃｐｒｏｅｏｎｄｉｔｉｏｎｉｎｇ,ＩＰＣ)。ＩＰＣ现象的发现为心肌保护提供了一条新的途径。实验及临床研究均发现其可以限制心肌梗塞范围 ,增加心肌收缩力 ,降低再灌性心律失常 ,但心肌的这一内源性保护机制不清。有人认为ＩＰＣ的产生机制与纠正细胞内外的离子紊乱和心肌能量代谢有关。Ｃａ2 ·Ｍｇ2 ＡＴＰａｓｅ在维持细胞内外的正常离子浓度中起重要作用 ,琥珀酸脱氢酶 (ＳＤＨ)是…     

南海永暑礁腹足类Acteocina壳Mg/Ca 比值的环境意义

对南沙群岛永暑礁泻湖南永3井88个样品中的腹足类Acteocina作了多元素测试分析,着重研究了Mg／Ca比值在过去l700年的变化。Mg／Ca比值在柱深13．4—20．10cm,40．2—46．9cm,388．9—395．6cm,415．7—422．4cm,583．3—590．0cm显示了高值,高于平均比值约3倍。这表明泻湖水化学性质曾发生了显著的变化,尤其是盐度在这些层段明显地提高。Mg／Ca高比值较好地对应于氧同位素低值区,显示了一种气候趋暖状态下的盐度升高现象。泻湖可能处于一种与外界较为开放的格局,以至大洋洋水对泻湖的影响显著增强。但是,Mg／Ca低比值区占居较长的时间,可能暗示着晚全新世南沙群岛海平面在中全新世高海平面的背景下总体上趋于平稳下降的状态。环礁相对的封闭增强或降雨的影响增大等因素,造成了Mg／Ca比值的偏低。     

不同黄瓜品种幼苗对等渗Mg（NO3）2和NaCl胁迫的生理响应

以3个不同类型的黄瓜品种为试材,采用营养液培养方法,研究等渗Mg(NO3)2和Na Cl胁迫对黄瓜幼苗生长、叶片膜脂过氧化、抗氧化酶活性以及渗透调节物质的影响,采用隶属函数法对其耐盐性进行综合评价.结果表明:与对照相比,60、80 mmol·L-1Mg(NO3)2和等渗90、120 mmol·L-1Na Cl胁迫下,随盐浓度的增加,3种不同生态类型的黄瓜品种幼苗株高、茎粗、叶面积、地上部和地下部干鲜质量及抗氧化酶活性显著降低,盐浓度越高,受抑制程度越高,丙二醛含量显著升高、增幅变大,膜脂过氧化程度加重,其中‘SJ31-1’的生物量及超氧化物歧化酶(SOD)、过氧化物酶(POD)、过氧化氢酶(CAT)活性下降幅度及丙二醛含量上升幅度均小于其他品种.等渗浓度的Mg(NO3)2比Na Cl对黄瓜幼苗的抑制程度大,浓度越大差异越显著.脯氨酸、可溶性蛋白和可溶性糖含量变化存在基因型和盐类型的差异.盐胁迫后,‘SJ31-1’的脯氨酸含量增幅最大,‘鲁白19号’的可溶性糖含量增幅最大,‘新泰密刺’介于两者之间.Na Cl胁迫下,不同黄瓜品种渗透调节物质以可溶性糖和可溶性蛋白为主,而Mg(NO3)2胁迫下以脯氨酸和可溶性蛋白为主.不同黄瓜品种耐盐性的综合评价次序为‘SJ31-1’>‘新泰密刺’>‘鲁白19号’.     

α-adrenergic receptor regulation of Ca2+/Mg2+-ATPase in brain synaptic membranes

The effects of ₁ and ₂ receptor ligands on Ca²⁺/Mg²⁺-ATPase have been studied using synaptosomal plasma membranes isolated from rat brain cortex. Both phenylephrine and clonidine inhibited Ca²⁺/Mg²⁺-ATPase, in a concentration-dependent fashion. IC₅₀ values for half-maximal inhibition for phenylephrine and clonidine were 29 M and 18 M, respectively. The inhibitory effect of phenylephrine was reversed by the alpha antagonist prazosin while yohimbine and rauwolscine reversed the inhibition of enzyme activity by clonidine. The two antagonist subtypes were effective only against the respective agonist subtypes, demonstrating distinct subtype preferences. Analysis of the kinetics of enzyme inhibition indicate both agonists to be noncompetitive. Some evidence suggests that yohimbine may exhibit mixed agonist/antagonist properties which depend on [Ca²⁺]. The present study provides biochemical evidence to support auto receptor adrenergic receptor regulation of neurotransmitter release.     

植物Mg2+转运蛋白与相关基因及其功能的研究进展

镁离子是植物细胞中最丰富的二价阳离子.在植物的生长发育中起着重要的作用.对Mg2+独特的几何和化学性质,Mg2对植物细胞体内中动态平衡的影响,植物中Mg2+转运相关蛋白与相关基因及其功能的研究进展进行了综述.     

TXA2/PGI2与心血管疾病

血栓素(Thromboxane,TXA2)和前列环素(Prostacyclin,PGI2)均为花生四烯酸的代谢物,是前列腺素(Prostaglandins,PGs)中生物活性最强的一对。在正常情况下,二者在体内保持一定的平衡,相互拮抗、相互协调,共同维持血液循环畅通,与心血管疾病关系密切。本文即就其生物特性及与心血管病的关系等进行综述,对人们全面认识TXA2/PGI2具有一定的参考价值。     

Mg2+和SeO2-3对鸡胚软骨细胞受模拟微重力不良影响的拮抗

在回转模拟微重力条件下,研究了鸡胚负重软骨细胞骨架的微管系统和碱性磷酸酶活性两项指标的变化,以及1 mg/L亚硒酸钠和5 mmol/L Mg2+对这些指标的影响.流式细胞仪对微管含量的测定显示回转后微管蛋白含量的减少,说明微管系统受到不良影响.碱性磷酸酶活性比对照组明显降低,表明模拟微重力能降低软骨细胞的钙化能力.如果在回转前加入SeO2-3和Mg2+,发现SeO2-3可以在一定程度上拮抗模拟微重力引起的微管蛋白及碱性磷酸酶活性改变,而Mg2+基本上可以完全拮抗模拟微重力对这两项指标的不良影响.     

Synthesis and structural characterization of the molecular loop [cis-Mo2(N,N-di-p-anisylformamidinate)2]2(O2C-CHCCH-CO2)2

A new molecular loop composed of two quadruply bonded Mo₂(DAniF)₂ units (DAniF=N,N^′-di-p-anisylformamidinate) linked by two chiral allene-1,3-dicarboxylate anions has been prepared from the reaction of [cis-Mo₂(DAniF)₂(MeCN)₄](BF₄)₂ with the bis(tetraethylammonium) salt of allene-1,3-dicarboxylic acid. This compound, [cis-Mo₂(DAniF)₂]₂(O₂C-CHCCH-CO₂)₂ (1), has been characterized by X-ray crystallography and by ¹H NMR and UV-Vis spectroscopy. The molecule possesses a center of inversion and hence is meso. There is only weak electronic coupling between the two Mo₂ ⁴⁺ units as revealed by electrochemical measurements.     

Spliceosomal snRNAs: Mg(2+)-dependent chemistry at the catalytic core?

Since the discovery of self-splicing RNAs, it has been suspected that the snRNAs are the catalytic components of the spliceosome. Recent evidence supports both the catalytic potential of the spliceosomal snRNAs and their resemblance to elements of group II introns.     

The reactions of 2-hydroxypyridine ligands with Re2Cl4(μ-dppm)2 (dppm=Ph2PCH2PPh2) that lead to 2-pyridonate complexes

2-Hydroxypyridine (Hhp), 2-hydroxynicotinic acid (HnicOH) and 6-hydroxypicolinic acid (HpicOH) react with Re₂Cl₄(μ-dppm)₂ (dppm=Ph₂PCH₂PPh₂) to afford the complexes Re₂(η²-hp)Cl₃(μ-dppm)₂ (1), Re₂(η²-HnicO)Cl₃(μ-dppm)₂ (2) and Re₂(μ-picO)₂(μ-dppm)₂ (3). The identities of 1 and 2 have been established by single-crystal X-ray structure determinations (Re-Re distances of 2.2602(3) and 2.2539(3) Å, respectively) and they are shown to have unsymmetrical structures with staggered rotational geometries and trans, cis coordination of the pair of μ-dppm ligands. The crystal of 2 that was used in the structure determination was found to be of composition 2Re₂(η²-HnicO)Cl₃(μ-dppm)₂ · Re₂Cl₆(μ-dppm)₂ · 2.906CH₂Cl₂. The structure of Re₂Cl₆(μ-dppm)₂ in this crystal is compared with structures reported in the literature for other crystals that contain this edge-sharing bioctahedral dirhenium(III) complex.