The Ca 2+ pumps and the Na + / Ca 2+ exchangers

The Ca 2+ ATPases or Ca 2+ pumps transport Ca 2+ ions out of the cytosol, by using the energy stored in ATP. The Na + / Ca 2+ exchanger uses the chemical energy of the Na + gradient (the Na + concentration is much higher outside than inside the cell) to remove Ca 2+ from the cytosol. Ca 2+ pumps are found in the plasma membrane and in the endoplasmic reticulum of the cells. The pumps are probably present in the membrane of other organelles, but little experimental information is available on this matter. The Na + / Ca 2+ exchangers are located on the plasma membrane. A Na + / Ca 2+ exchanger was found in the mitochondria, but very little is known on its structure and sequence. These transporters control the Ca 2+ concentration in the cytosol and are vital to prevent Ca 2+ overload of the cells. Their activity is controlled by different mechanisms, that are still under investigation. A number of the possible isoforms for both types of proteins has been detected.© Kluwer Academic Publishers     

Calcium in fungi

Abstract. Recently much experimental evidence has accumulated concerning intracellular calcium and its fundamental role as a regulator in eukaryotic cells. The literature relating to Ca²⁺ in fungi is large and diverse and this paper draws together the available information and discusses the particular functions of the ion in this group of organisms.
Uptake mechanisms in fungi are considered with special reference to the effect of Ca²⁺ on permeability and the systems responsible for transport of ions, sugars and amino acids. Discussion of the subcellular locations and distribution of Ca²⁺ is accompanied by a critique of methodology used in determination of subcellular sites of Ca²⁺ in fungi. The role of Ca²⁺ in morphogenesis in fungi is considered with particular reference to selected groups.     

NaHCO3胁迫下星星草根中Ca2＋与Ca2＋-ATPase的超微细胞化学定位

利用焦锑酸盐和磷酸铅沉淀技术分别对NaHCO3胁迫条件下星星草（Puccinellia tenuiflora）根中Ca2＋和Ca2＋-ATPase进行超微细胞化学定位研究,旨在进一步探讨Ca2＋在NaHCO3胁迫诱导胞内信号转导过程中的作用,以及Ca2＋-ATPase活性定位变化与NaHCO3胁迫下星星草抗盐碱能力的关系。结果表明：在正常状态下,根毛区细胞质内Ca2＋较少,主要位于质膜附近和液泡中,Ca2＋-ATPase主要定位于质膜和液泡膜,有一定活性。在0.448%NaHCO3胁迫下,根毛区细胞质中Ca2＋增多,液泡中Ca2＋减少,且主要集中于液泡膜附近,质膜和液泡膜Ca2＋-ATPase活性明显升高。在1.054%NaHCO3胁迫下,细胞质中分布的Ca2＋增多,而液泡中Ca2＋极少,Ca2＋-ATPase活性也降低。以上结果表明,Ca2＋亚细胞定位和Ca2＋-ATPase活性变化在星星草响应NaHCO3胁迫的信号传递过程中具有重要作用。     

影响玉米根中K+、Na+离子向地上部输送的因素（简报）

培养液中含有 1mmol·L-1K 、Na 离子的玉米根运往木质部渗出液中的K /Na 比最大 ;低温不影响渗出液中的K /Na 比 ,但极大地减少了根部向地上部输送的K 、Na 总量 ;钙的加入可以大大提高渗出液中的K /Na 比 ,减少由根部向地上部输送的Na 量。     

大鼠海马CA1区锥体细胞上一种 Ca2+依赖性KATP通道

KATP通道在细胞的新陈代谢与膜兴奋性的耦联中起重要作用.采用膜片钳的内面向外式记录方法,在成年大鼠海马CA1区锥体细胞上记录到一种被胞浆侧ATP和甲糖宁(tolbutamide,一种KATP通道阻断剂)抑制的Ca2+依赖性钾离子通道.在细胞膜内外的K+浓度均为140 mmol/L时,通道的电导为(204±21) pS,翻转电位为(3.57±1.13) mV,通道无整流性.通道开放概率及ATP对通道的抑制作用均呈现电压依赖性.该KATP通道与以往报道的"经典"KATP通道有显著不同,其活动受膜电位、胞内Ca2+和ATP三重调节,表明这是一种新型的KATP通道.上述结果表明在海马神经元上至少有两种性质不同的KATP通道,提示神经元可能通过不同性质的KATP通道感受细胞内的代谢状态,进而调节细胞膜的兴奋性.     

外源Ca2+对高温强光胁迫下滨梅幼苗的保护效应

以10 mmol/L CaCl2溶液处理滨梅幼苗叶片后,置于培养箱于(40±2)℃高温、光照强度(1 200±50)μmol·m-2·s-1下培养,定期测定有关生理生化指标,以探讨外源Ca2+对高温强光胁迫下滨梅幼苗的保护效应.结果显示:(1)与蒸馏水处理组相比,Ca2+处理使高温强光胁迫下滨梅幼苗叶片的脯氨酸含量显著升高,可溶性糖含量变化不明显,根系活力小幅降低;Ca2+处理有效抑制了高温强光下膜透性的加大,提高和保护了Ca2+-ATPase的活性.(2)采用Ca2+螯合剂EGTA或钙调素拮抗剂TFP对滨梅幼苗叶片同法处理并同条件胁迫时,与Ca2+处理相比,滨梅幼苗的脯氨酸、可溶性糖含量、Ca2+-ATPase活性和根系活力均明显下降,膜透性加大.研究表明,Ca2+处理能提高滨梅幼苗对高温强光的耐受性;Ca2+信号系统参与了胁迫过程中的渗透物质和Ca2+-ATPase活性等的调节.     

Kinetic Characterization of Ca2+ Transport in Synaptic Membranes

Lysed synaptosomal membranes were prepared from brain cortices of HA/ICR Swiss mice, and the ATP-stimulated Ca2+ uptake, Ca2+-stimulated Mg2+-dependent ATPase activity, and the Ca2+-stimulated acyl phosphorylation of these membranes were studied. The Km values for free calcium concentrations ([Ca2+]f) for these processes were 0.50 microM, 0.40 microM, and 0.31 microM, respectively. Two kinetically distinct binding sites for ATP were observed for the ATP-stimulated Ca2+ uptake and the Ca2+-stimulated Mg2+-ATPase activity. The high-affinity Km values for ATP for these two processes were 16.3 microM and 28 microM, respectively. These results indicate that the processes studied operate in similar physiological concentration ranges for the substrates [Ca2+]f and ATP under identical assay conditions and, further, that these processes may be functionally coupled in the membrane.     

Capacitative calcium influx in human epithelial breast cancer and non-tumorigenic cells occurs through Ca2+ entry pathways with different permeabilities to divalent cations

The operation of capacitative Ca(2+) entry (CCE) in human breast cancer (SKBR3) and non-tumorigenic (HBL100) cell lines was investigated as an alternative Ca(2+) entry route in these cells. Ca(2+) readdition after thapsigargin-induced store depletion showed activation of CCE in both cell lines. SKBR3 cells exhibited retarded store depletion and CCE decay kinetics compared to the non-tumorigenic HBL100 cells, suggesting alterations in Ca(2+) homeostasis. CCE was also highly permeable to Mn(2+) and to a lesser extent to Sr(2+), but not to Ba(2+). In HBL100 cells, CCE is contributed (30%) by a Ca(2+)/Mn(2+) permeable route insensitive to low (1 microM) Gd(3+) and a Ca(2+)/Sr(2+)/Mn(2+) permeable non-selective pathway (70%) sensitive to 1 microM Gd(3+). In SKBR3 cells, the relative contribution to CCE of both routes was opposite to that in non-tumorigenic cells.     

微电极芯片系统中酵母细胞电穿孔的实验研究

采用自主研制的微电极芯片系统,研究电脉冲参数及Ca2+对酵母细胞穿孔率的影响.发现酵母细胞穿孔率随着脉冲电压、脉冲持续时间、脉冲个数的增大而升高,且电穿孔具有累积效应,在脉冲电压40 V、脉冲持续时间10 μs、脉冲个数8个的条件下,穿孔率达到83%.此外,研究了钙离子对酵母细胞穿孔率的影响,一定浓度的Ca2+能提高酵母细胞穿孔率,当Ca2+浓度为0.1 mmol/L时,穿孔率可达到89%;Ca2+浓度过高会降低酵母细胞的穿孔率甚至会抑制穿孔的发生,并从机理方面对其进行了初步探讨,为进一步研究电穿孔机制提供有益参考.     

水稻非花粉型细胞质雄性不育系及其保持系花药发育过程中Ca2+的分布变化

钙在高等植物中被称为第二信使,与植物的有性生殖有关。为了研究水稻（Oryza sativa L.）花药中钙的定位与花粉败育的关系,利用焦锑酸钾沉淀法研究了非花粉型细胞质雄性不育系G37A及其保持系G37B花药的发育过程及其细胞中Ca^2＋ 的分布变化。研究发现,在2个材料间花药中钙的分布存在大量差异。G37B的可育花药在花粉母细胞时期及二分体时期,很少看到有Ca^2＋的沉积;而在单核花粉时期,Ca^2＋沉积急速地增加,主要定位在绒毡层细胞、花粉外壁外层及乌氏体的表面;随后花药壁上沉积的Ca^2＋减少而花粉的外壁外层仍然有很多Ca^2＋沉积物。相反,G37A的不育花药在花粉母细胞时期和二分体时期有大量的Ca^2＋沉积在小孢子母细胞和花药壁,中间层和绒毡层特别多。在二分体时期之后,不育花药的Ca^2＋沉积减少,特别是绒毡层内切向质膜附近的Ca^2＋几乎消失。但是同时期的可育花药中,有大量的Ca^2＋沉积在绒毡层。不育花药的Ca^2＋沉积在开花几天后消失。根据研究结果推测在不育花药发育早期中更多的钙离子与花粉败育有一定的关系。     

木本植物季节性休眠的分子机制

季节性休眠是多年生木本植物在生态和进化上的一种"权衡"机制,也是植物界多样性生存策略的组成部分.木本植物的休眠反应首先是Ca2+作为信号物质诱导CO/FT基因的表达,进而引起与休眠相关的DAM基因的表达;而低温可以诱导休眠的发生,冷诱导表达的基因CBF和COR在休眠期间也有表达;而与逆境相关的蛋白如脱水蛋白、抗冻蛋白、热激蛋白和热稳定蛋白等也与休眠反应有密切的关系.本文就与木本植物季节性休眠相关的分子机制进行了综述.     

Ca2+调节1,4,5-三磷酸肌醇受体活性的温度依赖性及其构象基础

分离纯化了牛小脑1,4,5-三磷酸肌醇(IP3)受体,并将其重建到脂质体中,无论4℃还是25℃Ca2+对未重建的IP3受体结合IP3活性都没有影响;而Ca2+对重建的IP3受体的影响则与温度有关.4℃时脂蛋白体外侧Ca2+([Ca2+].)不影响IP3受体与IP3结合,而25℃时[Ca2+].从0上升到100 nmol/L时IP3结合活力逐步增加,但[Ca2+].继续增加会使IP3结合迅速下降,并最终导致完全被抑制.构象测定表明,在4℃时,[Ca2+].并不影响重建IP3受体的整体构象,在25℃时,10μmol/L的[Ca2+].对重建IP3受体的整体构象、膜结构域和胞质结构域构象的影响显著不同于100 nmol/L的[Ca2+].     

组胺受体家族新成员:组胺H4受体

组胺H4受体是最近在基因库内筛选寻找新的G蛋白偶联受体时发现的,其cDNA序列与组胺H1、H2受体的同源性很低,与组胺H3受体有很高的同源性。很多组胺受体的配体与组胺H4受体有亲和性,但该受体表现出独特的药理学性质。组胺H4受体激动后可影响细胞内Ca^2 浓度和cAMP的生成,推测其与Gi或Go蛋白相偶联。组胺H4受体主要分布于骨髓、肺、脾脏、小肠和中枢,可能与机体的免疫反应和精神活动有关。     

Update on vascular endothelial Ca(2+) signalling: A tale of ion channels, pumps and transporters

A monolayer of endothelial cells (ECs) lines the lumen of blood vessels and forms a multifunctional transducing organ that mediates a plethora of cardiovascular processes. The activation of ECs from as state of quiescence is, therefore, regarded among the early events leading to the onset and progression of potentially lethal diseases, such as hypertension, myocardial infarction, brain stroke, and tumor. Intracellular Ca2+ signals have long been know to play a central role in the complex network of signaling pathways regulating the endothelial functions. Notably, recent work has outlined how any change in the pattern of expression of endothelial channels, transporters and pumps involved in the modulation of intracellular Ca2+ levels may dramatically affect whole body homeostasis. Vascular ECs may react to both mechanical and chemical stimuli by generating a variety of intracellular Ca2+ signals, ranging from brief, localized Ca2+ pulses to prolonged Ca2+ oscillations engulfing the whole cytoplasm. The well-defined spatiotemporal profile of the subcellular Ca2+ signals elicited in ECs by specific extracellular inputs depends on the interaction between Ca2+ releasing channels, which arelocated both on the plasma membrane and in a number of intracellular organelles, and Ca2+ removing systems. The present article aims to summarize both the past and recent literature in the field to provide a clear-cut picture of our current knowledge on the molecular nature and the role played by the components of the Ca2+ machinery in vascular ECs under both physiological and pathological conditions.     

Acute effect of beta amyloid on synchronized spontaneous Ca2+ oscillations in cultured hippocampal networks

The effects of beta amyloid (Abeta) on cytoplasmic Ca(2+) ([Ca(2+)](c)) have been studied extensively, but the current literature on this aspect is confusing. We reported that 20 microM Abeta(25-35) significantly inhibited the synchronized spontaneous cytoplasmic Ca(2+) transients immediately after application, whereas it had little effect on the baseline [Ca(2+)](c) concentration in neurons. Abeta(1-42) had a similar effect on the Ca(2+) transients as Abeta(25-35), while it increased baseline [Ca(2+)](c) concentration gradually. However, Abeta(1-40) had little effect on either Ca(2+) transients or baseline [Ca(2+)](c). Such differential effects of Abeta on Ca(2+) signals might explain, at least partially, the confusing observations from the previous studies and provide important therapeutic implications for preventing or reversing early neuron damage in Alzheimer's disease.     

Modulation of the low affinity Ca2+-binding sites of skeletal muscle and blood platelets Ca2+-ATPase by nordihydroguaiaretic acid

The antioxidant nordihydroguaiaretic acid (NDGA) inhibited the different sarco/endoplasmic reticulum Ca2+-ATPase isoforms found in skeletal muscle and blood platelets. For the sarcoplasmic reticulum, but not for the blood platelets Ca2+-ATPase, the concentration of NDGA needed for half-maximal inhibition was found to vary depending on the substrate used and its concentration in the assay medium. The phosphorylation of the sarcoplasmic reticulum Ca2+-ATPase by ATP and by Pi were both inhibited by NDGA. In leaky vesicles, measurements of the ATP Pi exchange showed that NDGA increases the affinity for Ca2+ of the E2 conformation of the enzyme, which has low affinity for Ca2+. The effects of NDGA on the Ca2+-ATPase were not reverted by the reducing agent dithiothreitol nor by the lipid-soluble antioxidant butylated hydroxytoluene.     

rhlL-6影响巨噬细胞内钙离子浓度和空间分布

使用重组人白细胞介素刺小鼠腹腔巨噬细胞,应用荧光分光光度计和激光扫描共焦显微镜检测胞浆内游离钙离子的时空分布。静息状态巨噬细胞Ｃａ＾２＋浓度１０＾－８,－１０＾７ｍｏｏ／Ｌ,加入１００ｕ／ｍｌｒｈＩＬ－６后,未见作用。     

Ca2+-Regulating mechanisms that modulate bull sperm capacitation and acrosomal exocytosis as determined by chlortetracycline analysis

We have used chlortetracycline (CTC) analysis to investigate mechanisms that may play important roles during bull sperm capacitation in a culture medium (containing glucose, heparin, and caffeine) known to promote capacitation and fertilization in vitro. In initial experiments employing the Ca²⁺ ionophore A23187, we identified three discrete CTC patterns so similar to those described for mouse and human sperm that we have employed the same nomenclature: “F,” characteristic of uncapacitated, acrosome-intact cells; “B,” characteristic of capacitated, acrosome-intact, cells; “AR,” characteristic of capacitated, acrosome-reacted cells. Over a 60-min period, A23187 stimulated significant increases in B and AR pattern cells, with concomitant decreases in F pattern cells, suggesting a very rapid transition from the uncapacitated to the capacitated state and then on to exocytosis. Without ionophore, significant changes in the proportions of F and B pattern cells were also observed, but the maximum responses required 4 hr; the proportion of AR cells was consistently ～ 15% throughout, indicating a low incidence of spontaneous acrosome loss. Analysis of cells in media with altered composition indicated that the inclusion of either heparin or caffeine significantly promoted capacitation to about the same extent, but together, heparin plus caffeine had an even more stimulatory effect. Despite this, none of these treatments triggered acrosome loss above the levels seen in media lacking these constituents. In the presence of caffeine, with or without heparin, the inclusion of glucose had little effect on responses, but in the presence of heparin there were fewer B cells. In the presence of either quercetin, a Ca-ATPase inhibitor used at 50–200 μM, or W-7, a calmodulin antagonist used at 5–125 μM, capacitation per se was accelerated, as evidenced by significant decreases in F and significant increases in B pattern cells; only the highest concentration of each caused significant increases in AR cells. In addition, 25 and 125 μM W-7 markedly stimulated motility, both quantitatively and qualitatively. Finally the Na⁺ ionophore monensin at 500 μM significantly accelerated both capacitation and acrosomal exocytosis. The addition of the dihydropyridine calcium channel blocker nifedipine at 10 nM, just prior to monensin, did not inhibit capacitation (F to B transition) but blocked acrosomal exocytosis (B to AR transition). We suggest that Ca²⁺ is required for functional changes in bull sperm, with a Ca²⁺-ATPase modulating intracellular Ca²⁺ during capacitation and calcium channels controlling the Ca²⁺ influx required for acrosomal exocytosis. © 1995 Wiley-Liss, Inc.     

Calmodulin Stimulation of Ca2+-Dependent ATP Hydrolysis and ATP-Dependent Ca2+ Transport in Synaptic Membranes

We report here characterization of calmodulin-stimulated Ca2+ transport activities in synaptic plasma membranes (SPM). The calcium transport activity consists of a Ca2+-stimulated, Mg2+-dependent ATP hydrolysis coupled with ATP-dependent Ca2+ uptake into membraneous sacs on the cytosolic face of the synaptosomal membrane. These transport activities have been found in synaptosomal subfractions to be located primarily in SPM-1 and SPM-2. Both Ca2+-ATPase and ATP-dependent Ca2+ uptake require calmodulin for maximal activity (KCm for ATPase = 60 nM; KCm for uptake = 50 nM). In the reconstituted membrane system, KCa was found to be 0.8 microM for Ca2+-ATPase and 0.4 microM for Ca2+ uptake. These results demonstrate for the first time the calmodulin requirements for the Ca2+ pump in SPM when Ca2+ ATPase and Ca2+ uptake are assayed under functionally coupled conditions. They suggest that calmodulin association with the membrane calcium pump is regulated by the level of free Ca2+ in the cytoplasm. The activation by calmodulin, in turn, regulates the cytosolic Ca2+ levels in a feedback process. These studies expand the calmodulin hypothesis of synaptic transmission to include activation of a high-affinity Ca2+ + Mg2+ ATPase as a regulator for cytosolic Ca2+.     

Calcium fluxes at plasmalemma and tonoplast

Abstract. An account is given of the characterization of calcium fluxes across plasmalemma and tonoplast membranes of root cortical cells, using compartmental analysis. Some of the assumptions associated with the method are discussed. Recent evidence regarding the concentration of free Ca²⁺ in plant cells, and the mechanisms driving active calcium transport across cell membranes, is reviewed. It is proposed that the evidence from whole cell studies and work at the molecular level is mutually supportive, and some speculation is ventured about the general pattern of calcium transport in higher plant cells.