An intracellular P2X receptor required for osmoregulation in Dictyostelium discoideum

P2X receptors are membrane ion channels gated by extracellular ATP that are found widely in vertebrates, but not previously in microbes. Here we identify a weakly related gene in the genome of the social amoeba Dictyostelium discoideum, and show, with the use of heterologous expression in human embryonic kidney cells, that it encodes a membrane ion channel activated by ATP (30-100 muM). Site-directed mutagenesis revealed essential conservation of structure-function relations with P2X receptors of higher organisms. The receptor was insensitive to the usual P2X antagonists but was blocked by nanomolar concentrations of Cu2+ ions. In D. discoideum, the receptor was found on intracellular membranes, with prominent localization to an osmoregulatory organelle, the contractile vacuole. Targeted disruption of the gene in D. discoideum resulted in cells that were unable to regulate cell volume in hypotonic conditions. Cell swelling in these mutant cells was accompanied by a marked inhibition of contractile vacuole emptying. These findings demonstrate a new functional role for P2X receptors on intracellular organelles, in this case in osmoregulation.     

Superoxide involvement in the bactericidal effects of negative air ions on Staphylococcus albus.

The physical nature of small air ions is well established and it is recognized that they can produce a variety of biological effects. However, in only a few instances have any underlying biochemical changes been detected. Theoretically, one can consider the hydrated superoxide radical anion (O2) (H2O)n with n congruent to 4-8 as a likely candidate for a biologically active species of negative air ion. The chemical and biological reactivity of superoxide is high and includes a leading role in bacterial killing caused by radiation, in which superoxide dismutase (SOD), an enzyme that catalyses the reaction: O2 + O2 +2H leads to H2O2 +O2 protected markedly. Other studies have also demonstrated the bactericidal effect of O2 (refs 9-11). Inasmuch as the bactericidal action of small negative air ions has been repeatedly confirmed, we decided to test for the involvement of O2 in this phenomenon by evaluating the protective effect of SOD. Our results show strong O2 involvement in negative air ion bacterial kill.     

Inhibition by dopamine of (Na(+)+K+)ATPase activity in neostriatal neurons through D1 and D2 dopamine receptor synergism

The (Na(+)+K+)ATPase, an integral membrane protein located in virtually all animal cells, couples the hydrolysis of ATP to the countertransport of Na+ and K+ ions across the plasma membrane. In neurons, a large portion of cellular energy is expended by this enzyme to maintain the ionic gradients that underlie resting and action potentials. Although neurotransmitter regulation of the enzyme in brain has been reported, such regulation has been characterized either as a nonspecific phenomenon or as an indirect effect of neurotransmitter-induced changes in ionic gradients. We report here that the neurotransmitter dopamine, through a synergistic effect on D1 and D2 receptors, inhibits the (Na(+)+K+)ATPase activity of isolated striatal neurons. Our data provide unequivocal evidence for regulation by a neurotransmitter of a neuronal ion pump. They also demonstrate that synergism between D1 and D2 receptors, which underlies many of the electrophysical and behavioural effects of dopamine in the mammalian brain, can occur on the same neuron. In addition, the results support the possibility that dopamine and other neurotransmitters can regulate neuronal excitability through the novel mechanism of pump inhibition.     

配聚物[Cd2（2,5-pdc）2（H2O）4]n的光电性能

采用水热合成法,以2,5-吡啶-二羧酸为配体,得到了Cd(Ⅱ)配聚物:[Cd2(2,5-pdc)2(H2O)4]n(2,5-H2pdc=2,5-吡啶-二羧酸).采用X射线单晶衍射确定了配聚物的晶体结构.配聚物的不对称单元为Cd2(2,5-pdc)2(H2O)4,其中两个不等效的金属Cd(Ⅱ)离子均为6配位.在配聚物晶体中,Cd(Ⅱ)离子之间通过pdc2-上的羧基O原子连接,形成了具有2D结构的配聚物,氢键进一步将其连接成3D超分子.采用表面光电压光谱(SPS)研究了配聚物的表面光电性能.结果表明,该配聚物在300~800nm范围内呈现出较强的光伏响应,表明他具有一定的光-电转换能力.对配聚物的UV-Vis-NIR吸收光谱、IR光谱进行了测定和指认,并将SPS谱与UV-Vis-NIR吸收光谱进行了关联.     

CaMBP—10调节生长素应答反应机理初探

前期研究发现ＣａＭＢＰ－１０参与植物细胞对生长素应答反应的调节，但调节机理有待阐明，本文表明ＣａＭＢＰ－１０是由于影响质膜Ｈ－ＡＴＰａｓｅ活性，进而影响了质子外泌和细胞伸长，并进一步证明，它对质膜Ｈ－ＡＴＰａｓｅ活性的调节是通过介导该酶磷酸化而实现的最终调节了细胞对激素的应答。     

Extracellular sodium regulates airway ciliary motility by inhibiting a P2X receptor.

The mucociliary system is responsible for clearing inhaled particles and pathogens from the airways. This important task is performed by the beating of cilia and the consequent movement of mucus from the lungs to the upper airways. Because ciliary motility is enhanced by elevated intracellular calcium concentrations, inhibition of calcium influx could lead to disease by jeopardizing mucociliary clearance. Several hormones and neurotransmitters stimulate ciliary motility, one of the most potent of which is extracellular ATP (ATP0), which acts by releasing calcium ions from internal stores and by activating calcium influx. Here we show that, in airway ciliated cells, extracellular sodium ions (Na+(0)) specifically and competitively inhibit an ATP0-gated channel that is permeable to calcium ions, and thereby attenuate ATP0-induced ciliary motility. Our finding points to a physiological role for Na+(0) in ciliary function, and indicates that mucociliary clearance might be improved in respiratory disorders such as chronic bronchitis and cystic fibrosis by decreasing the sodium concentration of the airway surface fluid in which the cilia are bathed.     

固氮鱼腥藻(Anabaena azotica Ley HB686)氮固定的能量和还原剂来源

某些外源碳水化合物提高固氮鱼腥藻的固氮能力.在光照和5%氧浓度条件下,分子氢促进固氮作用.光合抑制剂、呼吸链抑制剂和解偶联剂均抑制固氮酶活性,若同时加入葡萄糖,DCMU的抑制作用被解除,而对DBMIB和解偶联剂的作用影响甚微.固氮鱼腥藻固氮作用的还原剂与光合作用产生的碳化合物有关,能量主要由循环光合磷酸化供给.     

一种Tb（Ⅲ）配合物的合成、结构及发光性能研究

采用水热合成方法,以对硝基苯甲酸为配体,合成了1种具有1D链状结构的Tb（Ⅲ）配合物[Tb2（C7H4NO4）6（H2O）4.H2O]n,通过X-射线单晶衍射确定了该配合物的晶体结构.结构分析表明,该配合物属三斜晶系,P-1空间群,配合物的不对称单元中包含2个不等效的Tb（Ⅲ）离子,Tb1为8配位,Tb2为9配位.在晶体中,Tb（Ⅲ）离子被对硝基苯甲酸根连成1D链状结构,其中,对硝基苯甲酸根采取3种配位模式,即螯合双齿,桥联双齿,桥联三齿.而1D链之间又通过3种类型的O—H…O氢键被连成2D氢键网络结构.在室温下,测定了该配合物晶体粉末的IR（红外）、UV-Vis-NIR（紫外-可见-近红外）吸收光谱以及荧光激发和发射光谱.光物理研究表明,该配合物在可见光的激发下（λEx=488nm）,表现出较强的Tb（Ⅲ）的特征发射,这主要归功于配体的敏化作用.     

Conflict adaptation in the perception of emotional valence in a Stroop task

Interference effects are commonly observed when conflicts arise between task-relevant and task-irrelevant dimensions of stimuli. Compared with responses to congruent trials in which the two dimensions are compatible, responses to incongruent trials are usually slower and less accurate. Moreover, the performance in a given trial is affected by the nature of the preceding trial, in that the interference effect for the current incongruent trial is reduced when it follows an incongruent trial than when it follows a congruent one. This conflict adaptation effect has been generally ascribed to the functioning of the cognitive control system, in which higher controls are recruited after conflicts to further constrain the processing of the task-irrelevant dimension. However, due to its uniqueness in neural and cognitive processes, whether the perception of emotional valence shows the same conflict adaptation effect in the conflicting context is an open question. This study adopted a variant of the Stroop task in which the task-relevant dimension was the affective facial expression while the task-irrelevant dimension was the meaning of an emotional word superimposed on the face. Results suggest that the perception of emotional valence in the conflicting context can have aspects that are both similar and dissimilar to the control of conflict for non-emotional information. The capturing of attention by emotional information can alter the functioning of the cognitive control system.     

Conflict adaptation in the perception of emotional valence in a Stroop task

Interference effects are commonly observed when conflicts arise between task-relevant and task-irrelevant dimensions of stimuli. Compared with responses to congruent trials in which the two dimensions are compatible, responses to incongruent trials are usually slower and less accurate. Moreover, the performance in a given trial is affected by the nature of the preceding trial, in that the interference effect for the current incongruent trial is reduced when it follows an incongruent trial than when it follows a congruent one. This conflict adaptation effect has been generally ascribed to the functioning of the cognitive control system, in which higher controls are recruited after conflicts to further constrain the processing of the task-irrelevant dimension. However, due to its uniqueness in neural and cognitive processes, whether the perception of emotional valence shows the same conflict adaptation effect in the conflicting context is an open question. This study adopted a variant of the Stroop task in which the task-relevant dimension was the affective facial expression while the task-irrelevant dimension was the meaning of an emotional word superimposed on the face. Results suggest that the perception of emotional valence in the conflicting context can have aspects that are both similar and dissimilar to the control of conflict for non-emotional information. The capturing of attention by emotional information can alter the functioning of the cognitive control system.     

Substituted benzimidazoles inhibit gastric acid secretion by blocking (H+ + K+)ATPase

Studies both in vivo and in vitro have shown that substituted benzimidazoles inhibit the stimulation of acid secretion produced by dibutyryl cyclic AMP and histamine. Furthermore, the results differ from those produced by H2 antagonists and anticholinergic agents in that the inhibition is not competitive, and the site of action is intracellular and peripheral to that of dibutyryl cyclic AMP. To investigate the biochemical mechanism of action of substituted benzimidazoles, one such compound, H 149/94 (2-([2-(3-methyl)pyridyl-methyl]-sulphinyl)-5-methoxycarbonyl-6-methylbenzimidazol), has been tested either directly on an (H+ + K+)ATPase isolated from pig and human gastric mucosa or on the function of this enzyme in gastric glands isolated from rabbit and human gastric mucosa. (H+ + K+)ATPase, which has only been found at the secretory surface of the parietal cell, catalyses a one-to-one exchange of protons and potassium ions. It is possibly the proton pump within the gastric mucosa, and may thus be the terminal or one of the terminal steps of the acid secretory process. We show here that H 149/94 inhibits (H+ + K+)ATPase, which may explain its inhibitory action on acid secretion in vitro and in vivo. Because of the unique distribution and properties of the (H+ + K+)ATPase, the inhibitory action of H 149/94 on this enzyme may be a highly selective clinical means of suppressing the acid secretory process.     

ATM damage response and XLF repair factor are functionally redundant in joining DNA breaks

Classical non-homologous DNA end-joining (NHEJ) is a major mammalian DNA double-strand-break (DSB) repair pathway. Deficiencies for classical NHEJ factors, such as XRCC4, abrogate lymphocyte development, owing to a strict requirement for classical NHEJ to join V(D)J recombination DSB intermediates. The XRCC4-like factor (XLF; also called NHEJ1) is mutated in certain immunodeficient human patients and has been implicated in classical NHEJ; however, XLF-deficient mice have relatively normal lymphocyte development and their lymphocytes support normal V(D)J recombination. The ataxia telangiectasia-mutated protein (ATM) detects DSBs and activates DSB responses by phosphorylating substrates including histone H2AX. However, ATM deficiency causes only modest V(D)J recombination and lymphocyte developmental defects, and H2AX deficiency does not have a measurable impact on these processes. Here we show that XLF, ATM and H2AX all have fundamental roles in processing and joining DNA ends during V(D)J recombination, but that these roles have been masked by unanticipated functional redundancies. Thus, combined deficiency of ATM and XLF nearly blocks mouse lymphocyte development due to an inability to process and join chromosomal V(D)J recombination DSB intermediates. Combined XLF and ATM deficiency also severely impairs classical NHEJ, but not alternative end-joining, during IgH class switch recombination. Redundant ATM and XLF functions in classical NHEJ are mediated by ATM kinase activity and are not required for extra-chromosomal V(D)J recombination, indicating a role for chromatin-associated ATM substrates. Correspondingly, conditional H2AX inactivation in XLF-deficient pro-B lines leads to V(D)J recombination defects associated with marked degradation of unjoined V(D)J ends, revealing that H2AX has a role in this process.     

Multiple D2 dopamine receptors produced by alternative RNA splicing

Dopamine receptor belong to a large class of neurotransmitter and hormone receptors that are linked to their signal transduction pathways through guanine nucleotide binding regulatory proteins (G proteins). Pharmacological, biochemical and physiological criteria have been used to define two subcategories of dopamine receptors referred to as D1 and D2. D1 receptors activate adenylyl cyclase and are coupled with the Gs regulatory protein. By contrast, activation of D2 receptors results in various responses including inhibition of adenylyl cyclase, inhibition of phosphatidylinositol turnover, increase in K+ channel activity and inhibition of Ca2+ mobilization. The G protein(s) linking the D2 receptors to these responses have not been identified, although D2 receptors have been shown to both copurify and functionally reconstitute with both Gi and Go related proteins. The diversity of responses elicited by D2-receptor activation could reflect the existence of multiple D2 receptor subtypes, the identification of which is facilitated by the recent cloning of a complementary DNA encoding a rat D2 receptor. This receptor exhibits considerable amino-acid homology with other members of the G protein-coupled receptor superfamily. Here we report the identification and cloning of a cDNA encoding an RNA splice variant of the rat D2 receptor cDNA. This cDNA codes for a receptor isoform which is predominantly expressed in the brain and contains an additional 29 amino acids in the third cytoplasmic loop, a region believed to be involved in G protein coupling.     

H+对非洲爪蟾卵母细胞ATP-激活电流的调制作用

研究H^＋对非洲爪蟾卵母细胞内源性ATP受体的调制作用。采用双极电压钳技术记录卵母细胞膜ATP受体介导的电流。实验检测的细胞全部对ATP敏感，应用pH为7．4的ATP（10^-3mol／L）后引起一特征性电流，呈浓度依赖性。改用pH为6．5，6．0，5．5的ATP（10^-3mol／L）后，电流幅值明显减弱。结果表明，pH值降低，可抑制ATP诱导的卵母细胞膜电流。     

Apamin blocks certain neurotransmitter-induced increases in potassium permeability.

Apamin is a neurotoxic polypeptide of known structure isolated from bee venom. Shuba and coworkers have recently shown that it abolishes the hyperpolarising action of externally-applied ATP on visceral smooth muscle (guinea pig stomach and taenia coli) as well as the hyperpolarisation (inhibitory junction potential) that follows stimulation of the non-adrenergic inhibitory nerve supply to these tissues. As it has been proposed that ATP is the neurotransmitter involved in the latter response, Vladimirova and Shuba tentatively concluded that apamin is a specific postsynaptic blocking agent of this non-adrenergic, possibly 'purinergic', inhibition. We have confirmed the important observation that nanomolar concentrations of apamin reduce inhibition by ATP and by non-adrenergic nerve stimulation, but further experiments suggest that, rather than acting as a specific blocker of ATP receptors, apamin inhibits the increase in potassium permeability caused by a number of agents, including ATP.     

Dopamine activation of the arachidonic acid cascade as a basis for D1/D2 receptor synergism

Understanding the actions of the neurotransmitter dopamine in the brain is important in view of its roles in neuropsychiatric illnesses. Dopamine D1 receptors, which stimulate both adenylyl cyclase and phospholipase C, and D2 receptors, which inhibit them, can nevertheless act synergistically to produce many electrophysiological and behavioral responses. Because this functional synergism can occur at the level of single neurons, another, as yet unidentified, signalling pathway activated by dopamine has been hypothesized. We report here that in Chinese hamster ovary (CHO) cells transfected with the D2 receptor complementary DNA, D2 agonists potently enhanced arachidonic acid release, provided that such release has been initiated by stimulating constitutive purinergic receptors or by increasing intracellular Ca2+. In CHO cells expressed D1 receptors, D1 agonists exert no such effect. When D1 and D2 receptors are coexpressed, however, activation of both subtypes results in a marked synergistic potentiation of arachidonic acid release. The numerous actions of arachidonic acid and its metabolites in neuronal signal transduction suggest that facilitation of its release may be implicated in dopaminergic responses, such as feedback inhibition mediated by D2 autoreceptors, and may constitute a molecular basis for D1/D2 receptor synergism.     

A novel receptor-operated Ca2+-permeable channel activated by ATP in smooth muscle

Receptor-operated Ca2+ entry has been proposed as a signalling mechanism in many cells. Receptor-operated Ca2+ channels (ROCs) were first postulated in smooth muscle by Bolton, van Breemen and Somlyo and Somlyo, but recordings of directly ligand-gated Ca2+ current are lacking. Here we describe receptor-operated Ca2+ current evoked in arterial smooth muscle cells by ATP, a sympathetic neurotransmitter. ATP activates channels with approximately 3:1 selectivity for Ca2+ over Na+ at near-physiological concentrations and with a unitary conductance of approximately 5 pS in 110 mM Ca2+ or Ba2+. The channels can be opened even at very negative potentials and resist inhibition by cadmium or nifedipine, unlike voltage-gated Ca2+ channels; they are not blocked by Mg2+, unlike NMDA (N-methyl-D-aspartate)-activated channels; they are directly activated by ligand, without involvement of readily diffusible second messengers, unlike cation channels in neutrophils and T lymphocytes. Thus, the ATP-activated channels provide a distinct mechanism for excitatory synaptic current and Ca2+ entry in smooth muscle.     

Control of Ca2+ in rod outer segment disks by light and cyclic GMP

Photons absorbed in vertebrate rods and cones probably cause electrochemical changes at the photoreceptor plasma membrane by changing the cytoplasmic concentration of a diffusible transmitter substance, reducing the Na+ current flowing into the outer segment of the cell in the dark, to produce the observed membrane hyperpolarization that is the initial excitatory response. Cyclic GMP has been proposed as the transmitter because a light-activated cyclic GMP phosphodiesterase (PDE) has been found in rod disk membranes and because intracellularly injected cyclic GMP reduces rod membrane potentials. Free Ca2+ has also been proposed because increasing external [Ca2+] quickly and reversibly reduces the dark current and divalent cationophores increase the Ca2+ sensitivity. Ca2+ efflux from rod outer segments (ROS) of intact retinas occurs simultaneously with light responses. Vesicles prepared from ROS disk membranes become more permeable on illumination, releasing trapped ions or molecules, but intact outer segment disks have not previously been found to store sufficient Ca2+ in darkness and to release enough in light to meet the theoretical requirements for control of the dark current by varying cytoplasmic Ca2+ (refs 14-18). We now report experiments that show the required Ca2+ storage and release from rod disk membranes suspended in media containing high-energy phosphate esters and electrolytes approximating the cytoplasmic composition of live rod cells. Cyclic GMP stimulates Ca2+ uptake by ROS disks in such media.     

小鼠肝癌H_(22)克隆细胞株H2D8与其原瘤株武汉H_(22)的基本特性比较研究

用细胞克隆的方法获得武汉大学典型培养物保藏中心保存的小鼠肝癌H2 2 瘤株 (武汉H2 2 )的克隆细胞株H2D8。比较武汉H2 2 及H2D8对血清的依赖性、致瘤性、病理特征和对环磷酰胺 (CTX)的敏感性。结果发现H2D8细胞株对血清的依赖性 ,和对小鼠致瘤性及肿瘤病理学特性与武汉H2 2 细胞无明显差异 ;H2D8细胞对CTX治疗的敏感性更高。说明H2D8克隆株在体外培养、致瘤性和病理特征方面能保持原瘤株的细胞特性 ;在化疗敏感性方面优于原代细胞