Transmembrane segments of syntaxin line the fusion pore of Ca2+-triggered exocytosis

The fusion pore of regulated exocytosis is a channel that connects and spans the vesicle and plasma membranes. The molecular composition of this important intermediate structure of exocytosis is unknown. Here, we found that mutations of some residues within the transmembrane segment of syntaxin (Syx), a plasma membrane protein essential for exocytosis, altered neurotransmitter flux through fusion pores and altered pore conductance. The residues that influenced fusion-pore flux lay along one face of an alpha-helical model. Thus, the fusion pore is formed at least in part by a circular arrangement of 5 to 8 Syx transmembrane segments in the plasma membrane.     

Emerging roles of presynaptic proteins in Ca++-triggered exocytosis

The twinning of techniques from biophysics and molecular biology has led to remarkable progress in understanding the molecular mechanisms of synaptic transmission. Here we review the current picture of Ca++-triggered exocytosis, which has emerged from studies of a simple cellular model, the adrenal chromaffin cell. We discuss the molecular players that have been assigned a specific role in a particular step of this process and give a brief outlook on what these insights might tell us about mechanisms of short-term plasticity at classical synapses.     

Control of fusion pore dynamics during exocytosis by Munc18

Intracellular membrane fusion is mediated by the SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) proteins. All vesicle transport steps also have an essential requirement for a member of the Sec1 protein family, including the neuronal Munc18-1 (also known as nSec1) in regulated exocytosis. Here, in adrenal chromaffin cells, we expressed a Munc18 mutant with reduced affinity for syntaxin, which specifically modified the kinetics of single-granule exocytotic release events, consistent with an acceleration of fusion pore expansion. Thus, Munc18 functions in a late stage in the fusion process, where its dissociation from syntaxin determines the kinetics of postfusion events.     

Reconstitution of Ca2+-regulated membrane fusion by synaptotagmin and SNAREs

We investigated the effect of synaptotagmin I on membrane fusion mediated by neuronal SNARE proteins, SNAP-25, syntaxin, and synaptobrevin, which were reconstituted into vesicles. In the presence of Ca2+, the cytoplasmic domain of synaptotagmin I (syt) strongly stimulated membrane fusion when synaptobrevin densities were similar to those found in native synaptic vesicles. The Ca2+ dependence of syt-stimulated fusion was modulated by changes in lipid composition of the vesicles and by a truncation that mimics cleavage of SNAP-25 by botulinum neurotoxin A. Stimulation of fusion was abolished by disrupting the Ca2+-binding activity, or by severing the tandem C2 domains, of syt. Thus, syt and SNAREs are likely to represent the minimal protein complement for Ca2+-triggered exocytosis.     

Ca2+抑制红掌佛焰苞季节性“绿耳”的生理效应

为抑制海南地区红掌季节性佛焰苞耳部变绿(俗称“绿耳”)的发生,以盆栽品种‘大哥大’(‘Dakota')为试验材料,研究不同Ca2+浓度处理对红掌佛焰苞季节性“绿耳”的生理效应.结果表明:随着Ca2+处理浓度增加,佛焰苞的“绿耳”发生率降低,且耳部色相a*值和彩度C*值均显著提高,佛焰苞中总花青素苷含量显著增加,叶绿素含量显著降低.增施Ca2+还有利于促进佛焰苞中可溶性糖和可溶性蛋白的积累.综合以上研究结果可知,从7月份开始增施浓度在8～10 mmol/L范围内的Ca2+,可使佛焰苞“绿耳”现象得到较好的改善.     

G protein betagamma subunit-mediated presynaptic inhibition: regulation of exocytotic fusion downstream of Ca2+ entry

The nervous system can modulate neurotransmitter release by neurotransmitter activation of heterotrimeric GTP-binding protein (G protein)-coupled receptors. We found that microinjection of G protein betagamma subunits (Gbetagamma) mimics serotonin's inhibitory effect on neurotransmission. Release of free Gbetagamma was critical for this effect because a Gbetagamma scavenger blocked serotonin's effect. Gbetagamma had no effect on fast, action potential-evoked intracellular Ca2+ release that triggered neurotransmission. Inhibition of neurotransmitter release by serotonin was still seen after blockade of all classical Gbetagamma effector pathways. Thus, Gbetagamma blocked neurotransmitter release downstream of Ca2+ entry and may directly target the exocytotic fusion machinery at the presynaptic terminal.     

植物Ca2+信号的研究进展

在植物的生长发育过程中,为了适应环境,调节自身代谢和生长,需要对各种外界环境刺激以及植物内部生理信息做出反应,因此,植物产生了自己的信号系统。Ca2 作为一种信号分子在植物细胞信号系统中起着举足轻重的作用。针对国内外对植物Ca2 信号的研究情况,综述了Ca2 信号的产生、Ca2 信号参与的各种植物生理过程、Ca2 信号的检测以及其研究的最新进展。     

铁·镁·钙元素对白腐真菌生长及降解石油的影响

[目的]探讨黄孢原毛平革菌的生长及对石油的降解能力的优化条件。[方法]选用白腐真菌的典型菌种——黄孢原毛平革菌作为降解菌,研究其生长及对石油的降解性能,以不同浓度的Fe、Mg、Ca元素作为研究对象,在筛选单因素最佳水平的基础上,设计L9(33)正交表进行正交试验,对各因素的重要性及其最优水平进行分析。[结果]单因素试验表明,体系中添加Fe、Mg、Ca元素对白腐真菌的生长及其对石油的降解能力有较大的影响。正交试验结果表明,3种元素对P.C.菌降解石油的影响大小依次为Fe2+Ca2+Mg2+;溶液中铁、镁、钙元素的最佳组合为0.008 g/L的Fe2+、0.8 g/L的Mg2+、1.5 g/L的Ca2+,该条件下10 d后白腐真菌对石油的降解率为70.9%。[结论]该研究为探索白腐真菌的生长及其对石油降解能力的优化提供了科学依据。     

Cu2+、Mn2+、Mg2+胁迫对小麦种子发芽状况的影响

采用不同浓度Cu^2 、Mn^2 、Mg^2 胁迫，研究其对小麦种子发芽状况的影响。结果表明：≥0．1％浓度的Cu^2 胁迫对小麦种子发芽影响最大，导致小麦叶片呈黄绿色，苗矮小，根系衰退，发芽势和发芽率大幅度降低，不正常幼苗和未发芽种子数增加。≥0．1％浓度的Mn^2 胁迫对小麦种子发芽产生负面影响，幼苗新生叶尖全部枯黄，叶片相对较短，根系生长受抑制。≥0．5％浓度的Mn^2 胁迫对小麦种子发芽产生较明显影响。≤0．5％浓度的Mg^2 胁迫对小麦种子发芽的影响较小，与对照差异不明显。     

钙对蕹菜产量及生理生化指标的影响

采用水培方法,研究了不同钙离子浓度对蕹菜产量及生理生化的影响.结果表明:随着钙离子浓度的增加,蕹菜产量相应增加,当超过蕹菜生长所需的临界值时,其产量随着钙离子浓度的增加反而降低,钙离子浓度为80mg/L时,黑子蕹产量最高,达197.47 g.随着钙离子浓度的增加,3个品种蕹菜中超氧化物歧化酶活性和过氧化氢酶的活性都呈现先升高后下降的趋势,在0～80 mg/L钙离子范围内,2种酶活性随着钙离子浓度的增加而升高,在80～200 mg/L范围内,2种酶活性都随着钙离子浓度的增加而降低.相同钙离子浓度处理,3个品种中黑子蕹的净光合速率最高.     

Comment on "HST2 mediates SIR2-independent life-span extension by calorie restriction"

Calorie restriction (CR) increases life span in yeast independently of Sir2. Lamming et al. (Reports, 16 September 2005, p. 1861) recently proposed that Sir2-independent life-span extension by CR is mediated by the Sir2 paralogs Hst1 and Hst2. Contradictory to this, we find that CR greatly increases life span in cells lacking Sir2, Hst1, and Hst2, which suggests that CR is not mediated by Sir2, Hst2, or Hst1.     

The Role of Extracellular Ca2+Influx, Intracellular Ca2+ Release and Calmodulin in Mouse Egg Fertilization

The effects of various Ca^2 -modifying drugs on moue egg fertilization were studied.Ca^2 chelator,ethylen glycol-bis-(2-aminoethyl)-tetracetic acid(EGTA),and calmodulin(CaM) antagonist,trifluoperzaine (TFP),inhibited fertilization in a dose-dependent manner,whild Ca^2 channel bolcker,verspamil,did not have any effect.When intracellular Ca^2 release was blocked by 8-(N,N-diethylamino) octy 1-3,4,5-trimethoxy-benzonate(TME-8) or the Ca^2 oscillations were inhibited by an inhibitor of endoplasmic reticulum Ca^2 -At-Pase,thapsigargin,the second polar body emission and pronuclear formation were significantly decreased.In contrast,inhibition of intracellular Ca^2 release via bolckage of inositol 1,4,5-triphosphate (IP3) production by neomycin or lithium did not affect fertilization.The results sugest that both extracellular influx,intracellular Ca^2 release and CaM activation are required for mormal fertilization.However,extracellular influx through voltage-gated Ca^2 channel and intracellular release induced by IP3 and not the only pathways for producing Ca^2 transients in moue eggs.     

肉鸡腹水综合征患鸡肺脏组织钙沉积和Ca2＋-ATPase活性变化

肺动脉收缩和重塑在肉鸡AS发生过程中起着重要作用.本实验经采用右心导管法研究发现AS患鸡PASP 、PADP和mPAP极显著高于对照组(P <0.01).同时,采用焦锑酸钾沉淀法、电镜酶细胞化学法研究AS患鸡肺脏组织Ca2+和Ca2+-ATPase活性变化,发现AS患鸡肺脏组织中钙沉积量显著增多,且Ca2+-ATPase的电子密度颗粒显著减少或缺失.表明AS患鸡具有明显的肺动脉高压,其可能与肺脏组织,特别是肺动脉平滑肌细胞钙处理能力异常导致的钙离子浓度升高和肌浆网Ca2+-ATPase酶活性降低有关.     

Na+,K+,Mg2+,Ca2+浓度对嗜盐放线菌生长的影响

通过研究近30株嗜盐或耐盐放线菌在不同浓度的Na^＋，K^＋，M^2＋，Ca^2＋条件下的生长范围，发现耐盐放线菌对Na^＋，K^＋，M^2＋有广泛的适应性。只有少数耐盐放线菌能在较底浓度的CaCl2条件下生长；多数嗜盐放线菌生长所需的Na^＋可被K^＋，Mg^2＋所替代，而不能被Ca^2＋所替代，少数嗜盐放线菌的生长离不开Na^＋，对Na^＋有高度的专一性。因此，提出自然环境中是否也存在类似的专嗜K^＋或专嗜Mg^2＋的嗜盐放线菌的推测。     

Comment on "Reconstructing the origin of Andaman islanders"

On the basis of mitochondrial DNA sequence analyses, Thangaraj et al. (Brevia, 13 May 2005, p. 996) proposed that Andaman islanders descended from the first humans to migrate out of Africa. We identified mitochondrial DNA from two northeast Indian Rajbanshi individuals that shares three specific mutations with the M31a lineage observed in the Great Andamanese, which suggests that the predecessor of haplogroup M31 originated on the Indian subcontinent.     

Comment on "Saturation of the southern ocean CO2 sink due to recent climate change"

Unlike Le Quéré et al. (Reports, 22 June 2007, p. 1735), we do not find a saturating Southern Ocean carbon sink due to recent climate change. In our ocean model, observed wind forcing causes reduced carbon uptake, but heat and freshwater flux forcing cause increased uptake. Our inversions of atmospheric carbon dioxide show that the Southern Ocean sink trend is dependent on network choice.     

植物体内钙离子的感受器类型及功能研究

阐述了Ca2 信号的产生与特点,Ca2 的感受器CaM(钙调蛋白),CDPK(钙依赖性蛋白激酶)以及CBL(钙调磷酸酶B类似蛋白)的结构与生理功能。     

缺氧对肉鸡心肌细胞内游离Ca2+浓度的影响

 【目的】检测缺氧对肉鸡心肌细胞内Ca2+浓度的影响，阐明缺氧对心肌细胞影响的机制。【方法】利用体外细胞培养技术，以Fluo-3/AM为Ca2+指示剂，用LSCM检测缺氧对体外培养的肉鸡心肌细胞内游离Ca2+浓度的影响。【结果】与常氧组比较缺氧显著引起心肌细胞内游离Ca2+升高（常氧99.3±13.1；缺氧129.4±24.3,P<0.01）,钙通道拮抗剂Verapamil（Ver）和Nifedipine（Nif）可显著抑制缺氧引起的游离Ca2+升高（缺氧＋Ver 100.9±28.2,缺氧＋Nif 107.6±27.7）。【结论】缺氧能够增强心肌细胞的游离Ca2+跨膜转运导致细胞内Ca2+浓度升高，Ca2+通道拮抗剂能够减弱缺氧引起的心肌细胞膜上Ca2+的跨膜转运。