Rapid mobilization of Ca2+ from rat insulinoma microsomes by inositol-1,4,5-trisphosphate

Several hormones and neurotransmitters raise the cytosolic free Ca2+ concentration by stimulating the influx of Ca2+ and/or by mobilizing stored Ca2+. However, the link between the agonist receptor on the cell surface and the organelle(s) from which Ca2+ is mobilized is unknown. One feature of the agonists that increase cytosolic Ca2+ is their rapid induction of phosphatidylinositol turnover and polyphosphoinositide hydrolysis; in some tissues this leads, within seconds, to a marked accumulation of the water-soluble products, inositol 1,4-bisphosphate ( Ins1 , 4P2 ) and inositol-1,4,5- trisphosphate ( Ins1 ,4, 5P3 ), suggesting that these might mediate Ca2+ mobilization from internal pools. Such an action of Ins1 ,4, 5P3 has recently been inferred from studies with permeabilized pancreatic acinar cells and hepatocytes. Here we show directly that Ins1 ,4, 5P3 rapidly releases Ca2+ from a microsomal fraction of rat insulinoma but not from mitochondria or secretory granules. Moreover, this response is transient and desensitizes the microsomes to subsequent Ins1 ,4, 5P3 additions. These results suggest that Ins1 ,4, 5P3 functions as a cellular messenger inducing early mobilization of Ca2+ from the endoplasmic reticulum.     

Ca2+ release induced by inositol 1,4,5-trisphosphate is a steady-state phenomenon controlled by luminal Ca2+ in permeabilized cells.

Low concentrations of inositol 1,4,5-trisphosphate (InsP3) evoke a very rapid mobilization of intracellular Ca2+ stores in many cell types, which can be followed by a further, much slower efflux. Two explanations have been suggested for this biphasic release. The first proposes that the Ca2+ stores vary in their sensitivity to InsP3, and each store releases either its entire contents or nothing (all-or-none release); the second proposes instead that the stores are uniformly sensitive to the effects of InsP3, but that they can release only a fraction of their Ca2+ before their sensitivity is somehow attenuated (steady-state release). Experiments using purified InsP3 receptor molecules reconstituted into lipid vesicles have shown heterogeneity of the receptors in their response to InsP3 under conditions in which the total Ca2+ level at both sides of the receptor is held constant. We now report that in permeabilized A7r5 smooth-muscle cells incubated in Ca(2+)-free medium, the amount of 45Ca2+ remaining in the stores after the rapid transient phase of release is independent of their initial Ca2+ levels, indicating that partially depleted stores are less sensitive to InsP3. Moreover, if the stores are reloaded with 40Ca2+ after the first stimulus, reapplication of the same low concentration of InsP3 will release further 45Ca2+. This recovery of InsP3 sensitivity is almost complete. Under these conditions, Ca2+ release must thus occur by a steady-state mechanism, in which the decreasing Ca2+ content of the stores slows down further release.     

Glucagon stimulates the cardiac Ca2+ current by activation of adenylyl cyclase and inhibition of phosphodiesterase

Glucagon exerts positive inotropic and chronotropic effects in the heart. Like its glycogenolytic effect in liver cells, the cardiac effects of glucagon are often correlated with adenylyl cyclase stimulation. Therefore, cyclic AMP-dependent phosphorylation of L-type Ca2+ channels might be involved in the inotropic effect of glucagon. There have been no reports, however, of the effects of glucagon on the cardiac Ca2+ current (ICa). Also, the physiological effects of glucagon could involve mechanisms other than stimulation of adenylyl cyclase. Here we show that glucagon enhances ICa in frog and rat ventricular myocytes. The effect of glucagon in rats resulted from a stimulation of adenylyl cyclase. In frogs, however, the effect of glucagon on ICa was smaller and occurred at a concentration tenfold lower than in rats, and adenylyl cyclase was not modified. In addition, cAMP potentiated the effect of glucagon on ICa in frog ventricle, which correlated with the observed inhibition by glucagon of low-Km cAMP phosphodiesterase activity. Therefore, this is an example of a hormone that affects cardiac function in a similar way to a variety of synthetic cardiotonic compounds, such as milrinone and Ro-20-1724. Inhibition of phosphodiesterase activity by glucagon may be essential in animals in which glucagon increases cardiac contractility but does not effectively stimulate adenylyl cyclase.     

Use of chlorotetracycline fluorescence to demonstrate Ca2+-induced release of Ca2+ from the sarcoplasmic reticulum of skinned cardiac cells.

It has been proposed that the trans-sarcolemmal influx of Ca2+ occurring during the plateau of the mammalian cardiac action potentials is insufficient in itself to activate the myofilaments, but can trigger a release of Ca2+ from the sarcoplasmic reticulum (SR) which is sufficient for activation. The demonstration of this Ca2+-induced release of Ca2+ relied entirely on experiments in which the tension developed by the myofilaments was used as a sensor of the changes of myoplasmic free Ca2+ concentration ([free Ca2+]) in segments of single cardiac cells from which the sarcolemma had been removed by microdissection (skinned cardiac cells). The small size of these preparations has previously prevented the use of more direct methods for the detection of myoplasmic Ca2+ movements. The present study is a direct demonstration of Ca2+-induced release of Ca2+ from the SR of skinned cardiac cells treated with chlorotetracycline (CTC), a fluorescent chelate probe which enables changes in the amount of Ca2+ bound to a variety of biological membranes or micelles to be monitored. The fluorescence increases when more Ca2+ is bound.     

Open structure of the Ca2+ gating ring in the high-conductance Ca2+-activated K+ channel

High-conductance voltage- and Ca(2+)-activated K(+) channels function in many physiological processes that link cell membrane voltage and intracellular Ca(2+) concentration, including neuronal electrical activity, skeletal and smooth muscle contraction, and hair cell tuning. Like other voltage-dependent K(+) channels, Ca(2+)-activated K(+) channels open when the cell membrane depolarizes, but in contrast to other voltage-dependent K(+) channels, they also open when intracellular Ca(2+) concentrations rise. Channel opening by Ca(2+) is made possible by a structure called the gating ring, which is located in the cytoplasm. Recent structural studies have defined the Ca(2+)-free, closed, conformation of the gating ring, but the Ca(2+)-bound, open, conformation is not yet known. Here we present the Ca(2+)-bound conformation of the gating ring. This structure shows how one layer of the gating ring, in response to the binding of Ca(2+), opens like the petals of a flower. The degree to which it opens explains how Ca(2+) binding can open the transmembrane pore. These findings present a molecular basis for Ca(2+) activation of K(+) channels and suggest new possibilities for targeting the gating ring to treat conditions such as asthma and hypertension.     

草酸铵试法鉴定Ca2+用NaNTU掩蔽Ag+和Hg2+

在实验的基础上，提出了用草酸铵试法签定钙时，用N—烯丙基—N’—(对苯磺酸钠)硫脲掩蔽Ag^ 和Hg^2 离子干扰，与传统的H2S沉淀消除的干扰的方法相比，具有操作筒便、条件易控制、无污染等优点．     

铈存在下导数光谱直接测定钬

稀土元素铈和钬与偶氮氯膦Ⅲ(CPAⅢ)在pH=1.30显色后,Ce-CPAIII和Ho-CPAIII的吸收光谱相互重叠,不能进行铈或钬的单独测定.实验发现,Ce-CPAIII的二阶导数光谱在λ=696.1 nm时基线上存在等吸收点,此时Ho-CPAIII的二阶导数具有一定值,可用于Ho的测定;Ce-CPAIII的四阶导数光谱在λ=690.7 nm时基线上存在等吸收点,此时Ho-CPAIII的四阶导数具有一定值,也可用于Ho的测定.据此,当Ce4 、Ho3 的配比在1:1~4:1范围内,Ho3 浓度在6.6×10-2μg/mL~2.3μg/mL范围内遵守比尔定律,测定Ho3 的工作曲线方程分别为:二阶,y=-2.168×10-5 6.930×10-5x(相关系数R=0.9991);四阶,y=-2.822×10-7 1.346×10-6x(R=0.9991).二阶、四阶导数光谱的回收率分别为108%~127%、103%~123%.     

3－苯基－4－芳酰基－1，2，4－三唑－5－巯基乙酸和－5－甲硫基类化合物的合成

合成９种３－苯基－４－芳酰基－１，２，４－三唑－５－巯基乙酸Ⅱ１－９和９种３－苯基－４－芳酰基－５－甲硫基－１，２，４－三唑Ⅲ１－９类化合物．１８种新化合物的结构经ＩＲ，１Ｈ－ＮＭＲ和ＭＳ鉴定．     

Vpx relieves inhibition of HIV-1 infection of macrophages mediated by the SAMHD1 protein

Macrophages and dendritic cells have key roles in viral infections, providing virus reservoirs that frequently resist antiviral therapies and linking innate virus detection to antiviral adaptive immune responses. Human immunodeficiency virus 1 (HIV-1) fails to transduce dendritic cells and has a reduced ability to transduce macrophages, due to an as yet uncharacterized mechanism that inhibits infection by interfering with efficient synthesis of viral complementary DNA. In contrast, HIV-2 and related simian immunodeficiency viruses (SIVsm/mac) transduce myeloid cells efficiently owing to their virion-associated Vpx accessory proteins, which counteract the restrictive mechanism. Here we show that the inhibition of HIV-1 infection in macrophages involves the cellular SAM domain HD domain-containing protein 1 (SAMHD1). Vpx relieves the inhibition of lentivirus infection in macrophages by loading SAMHD1 onto the CRL4(DCAF1) E3 ubiquitin ligase, leading to highly efficient proteasome-dependent degradation of the protein. Mutations in SAMHD1 cause Aicardi-Goutières syndrome, a disease that produces a phenotype that mimics the effects of a congenital viral infection. Failure to dispose of endogenous nucleic acid debris in Aicardi-Goutières syndrome results in inappropriate triggering of innate immune responses via cytosolic nucleic acids sensors. Thus, our findings show that macrophages are defended from HIV-1 infection by a mechanism that prevents an unwanted interferon response triggered by self nucleic acids, and uncover an intricate relationship between innate immune mechanisms that control response to self and to retroviral pathogens.     

关于图C4h+1⊙K1的(Gr1,Gr2,…,Gr4h+2)-冠的优美性

给出了图C4h+1⊙K1的(Gr1,Gr2,…,Gr4h+2)-冠的定义,讨论了图C4h+1⊙K1的(Gr1,Gr2,…,Gr4h+2)-冠的优美性,用构造性的方法给出了一些特殊的图C4h+1⊙K1的(Gr2,Gr2,…,Gr4h+2)-冠的优美标号.     

离子色谱法测定饮用水中钠、镁、钙

本文研究了离子色谱法测定饮用水及源水中钠、镁、钙离子的方法.实验表明,该方法灵敏度高,重现性好,操作简便,分析快速.在本方法实验条件下,钠、镁、钙方法检出限,分别为0.013mg/L;0.013mg/L;0.025mg/L.相对标准偏差分布在0.07-0.76%,加标回收率分布在99-102%.     

2,3,4,5-四氢-5-甲基-1H-吡啶并[4,3-b]吲哚-1-酮的合成研究

探索了以丙二酸单乙酯、3-氨基丙酸乙酯盐酸盐为原料合成2,4-哌啶二酮,再与N-甲基-2-苯肼反应生成目标分子2,3,4,5-四氢-5-甲基-1H-吡啶并[4,3-b]吲哚-1-酮和盐酸阿洛司琼的合成方法,总收率为30.2%.此方法反应速率快、产率高、适用于大规模生产.     

Developmental acquisition of Ca2+-sensitivity by K+ channels in spinal neurones

A developmental change in the ionic basis of the inward current of action potentials has been observed in many excitable cells. In cultured spinal neurones of Xenopus, the timing of the development of the action parallels that seen in vivo. In vitro, as in vivo, neurones initially produce action potentials of long duration which are principally Ca-dependent; after 1 day of development the impulse is brief and primarily Na-dependent. At both ages, however, both inward components are present and the mechanism underlying shortening of the action potential is unknown. One possibility is that the outward currents change during development. Using the patch-clamp technique, we have recorded single K+-channel currents in membrane patches isolated from the cell bodies of cultured embryonic neurones. The unitary conductance of one class of K+ channels was approximately 155 pS and depolarization increased the probability of a channel being open. Neither conductance nor voltage dependence seemed to change with time in culture; in contrast, the Ca2+-sensitivity of this K+ channel increased. In younger neurones, Ca2+-sensitivity was greatly reduced or absent, whereas in more mature neurones, the activity of this channel was Ca-dependent. Such a change could account for the shortening of the action potential duration by increasing the relative contribution of outward currents.     

2-羧基-5-烃基-1,3,4-噁二唑的合成

本文用酰肼与三氯乙酸乙酯,在吡啶存在下,以无水乙醇为溶剂进行反应,合成2-羧基-5-烃基-1,3,心二唑类化合物.     

桑德迈尔反应合成7-取代-1,3-二氢-5-苯基-2H-1,4-苯并二氮杂-2-酮

文章叙述了由7-氨基-1,3-二氢-5-苯基-2H-1,4-苯并二氮杂(艹卓)-2-酮通过桑德迈尔反应合成7位氯、溴、碘和氰基取代的相应化合物。其中7位氰基取代化合物是一个未见报导的新化合物。