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961.
Chronic ethanol causes heterologous desensitization of receptors by reducing alpha s messenger RNA 总被引:7,自引:0,他引:7
One of the biochemical results of ethanol exposure is a change in the amount of the intracellular second messenger cyclic AMP (cAMP) produced in response to receptor stimulation. In general, acute ethanol exposure increases the amount of cAMP produced on stimulation of receptors coupled to the enzyme adenylyl cyclase via the GTP-binding protein Gs, whereas chronic ethanol exposure has the opposite effect (results for receptors coupled via Gi have been more variable). We previously reported that adaptation to continuous ethanol exposure reduces receptor-stimulated cAMP production by 25-35% in a neuroblastoma cell line (NG108-15), and an even greater reduction of 75% was observed in lymphocytes taken from actively-drinking alcoholics. This reduction in receptor-stimulated cAMP levels was recently confirmed in platelets from alcoholics. None of these studies, however, determined whether more than one receptor coupled to adenylyl cyclase activity was affected in the same cell. Here we report that chronic ethanol exposure causes desensitization of heterologous receptors coupled to Gs as cAMP production mediated by prostaglandin E1 as well as by adenosine is reduced by approximately 30% in NG108-15 cells. We show that, after chronic ethanol exposure, the activity of the alpha subunit of Gs is decreased by 29%, the amount of alpha s protein is decreased by 38.5%, and alpha s messenger RNA is decreased by 30%. Thus, cellular adaptation to ethanol involves a reduction in alpha s mRNA and, as a consequence, reduced cAMP production by heterologous receptors coupled to Gs. Such changes in cAMP production may account for the tolerance and physical dependence on ethanol in alcoholism. 相似文献
962.
用最小二乘拟合法,将稀土区的能谱实验数据,拟合不同的能谱公式,从而证明E=a〔(1+bI(I+1))~(1/2)-1〕是符合得较好的,本文还推导了与上述能谱相应的两类转动惯量,并以此与实验计算值进行比较,结果仍很满意. 相似文献
963.
本文主要为了改善苎麻纱和麻棉纱的弹性,对苎麻纱、麻棉纱和棉纱进行了碱处理。并根据前人所做的工作,即有张力状态下碱处理和松弛状态下碱处理,其纱线性能存在较大差异,因而本文着重考虑在不同张力状态下进行碱处理,研究结果表明,采用低张力进行碱处理。其苎麻纱和麻棉纱的最大变形能力即断裂伸长显著增加,初始弹性模量显著下降,纱线变形恢复能力显著提高。 相似文献
964.
J. v. Schönfeld M. Rünzi H. Goebell M. K. Müller 《Cellular and molecular life sciences : CMLS》1995,51(6):556-560
It is well known that oral administration of camostate induces hyperplasia and hypertrophy of the rat pancreas. It is not clear, however, whether pancreatic hormone and enzyme secretion are affected by camostate treatment.In rats, daily administration of 200 mg camostate/kg b. wt for 14 days significantly increased pancreatic weight and pancreatic content of DNA, protein, amylase, lipase, trypsin and chymotrypsin, as well as the amount of insulin, glucagon and somatostatin. In the intact animal, blood glucose levels and serum concentrations of insulin and glucagon in response to an oral glucose load were not impaired after camostate treatment. In the isolated perfused pancreas, however, insulin and glucagon secretions were reduced, whereas somatostatin release was not affected. The volume of pancreatic juice produced by the unstimulated isolated perfused organ, as well as protein and enzyme secretion, were increased after camostate treatment. Likewise, the isolated perfused pancreas from camostate-treated rats secreted a larger volume of pancreatic juice and more protein in response to cholecystokinin (CCK), while enzyme secretion was affected in a non-parallel manner: amylase release was markedly reduced, lipase release was unchanged, and release of trypsin and chymotrypsin was increased. 相似文献
965.
This paper examines the information on future exchange rate movements provided by the doctrine of purchasing power parity (PPP). Previous research has studied this issue by analyzing the time-series properties of period-by-period levels of, or changes in, exchange rates. In contrast, the present study focuses on the durations of periods in which exchange rates deviate from their PPP levels. If PPP provides information about future exchange rate movements, these durations should exhibit positive duration dependence. That is, the probability of returning to PPP levels should increase as the period of deviation increases. Parametric hazard functions estimated using data from eighteen countries provide no evidence of positive duration dependence. These results are robust to alternative definitions of PPP and to alternative functional specifications. While exchange rates take prolonged swings away from their PPP levels and then eventually return, these movements apparently constitute Monte Carlo cycles in which, at any point in time, the probability of moving back toward PPP is the same as the probability of moving farther away. Thus, PPP provides no useful information on future exchange rate changes, a result consistent with market efficiency. 相似文献
966.
龙门山中段茂汶─汶川韧性剪切带中可见到绿片岩相到角闪岩相的古生界。该地的巴罗型中压变质相相当于松潘—甘孜褶皱带中地壳的绿泥石带,构成了北东—南西向的茂汶—汶川变质带。雪隆包花岗岩体正位于该变质带的中心部位。三次韧性变形作用(D1~D3)造就了印支褶皱带,并在三叠纪末末形成了松潘—甘孜褶皱带。D1变形作用为北东—南西向的挤压作用和冲断作用,形成了大型的等斜褶皱,使古生界缩短和加厚。在持续的D2北京—南西向挤压作用下,松潘—甘孜褶皱带和稳定的扬子克拉通之间的差异应变由茂汶—汶川剪切带中非同轴左旋剪切作用所容纳。雪隆包花岗岩体是在D2变形作用的晚期侵入到剪切带的。产生蓝晶石的变质条件也是在D2或D2变形作用后出现的。D3变形作用为北西—南东向挤压,在局部地方形成糜棱岩状的道冲剪切带。这些特征与绿泥石退变质作用有关,揭示出在D3变形期间茂汶—汶川变质带有较大幅度的隆升。尽管雪隆包岩体在空间上与茂汶—汶川变质带有关,但作者认为其变质作用是岩层加厚引起的热作用重新达到平衡的产物,而不是由侵入作用引起的热接触变质作用。然而,与岩浆作用伴生的高温和活动性流体仍是产生D3局部变形和雪隆包岩体隆升的原因,这也是局部出现角闪告相 相似文献
967.
贵州植物园珍稀濒危蕨类植物 总被引:1,自引:0,他引:1
本文介绍引种自贵州各地及我国华中、华东和华东的贵州植物园内的珍稀濒危蕨类植物。除列表表示来源、现状等情况外,还对桫椤Alsphila spinulosa (Hook)Tryon,扇蕨Neocheiropteris plamatopedata (Bak.)Chsist,宽叶水韭Isoetes japonica A.Br.,中华水韭I.sinensis Palmer和截基盾蕨Neolepisorus 相似文献
968.
灰色理论在化学研究中用作建模与预测新的方法 总被引:1,自引:0,他引:1
研究了灰色理论作为一种有用的化学计量学多元建模与定量预测新方法的可行性,将其应用于某些不确定关系如电泳迁移率,色谱保留值和农药需求量等建模,定量预测结果良好。 相似文献
969.
本文使用SEM、EDS、EAS、XRD和电阻率测量技术,研究了工艺参数和加入(Co,Fe2O3)对PTC(V1-x,Crx)2O3陶瓷的显微结构和电性能的影响。实验结果表明,为了制造优良性能、高可靠的热敏电阻器,必须精确控制陶瓷组份和工艺。引人象C。这样的添加物是重要的,它主要以金属形式分布在基体中,同时发现添加物对试样致密度和电性能的影响也是有益的。 相似文献
970.
Cloning of decay-accelerating factor suggests novel use of splicing to generate two proteins 总被引:9,自引:0,他引:9
Decay-accelerating factor (DAF), a glycoprotein that is anchored to the cell membrane by phosphatidylinositol, binds activated complement fragments C3b and C4b, thereby inhibiting amplification of the complement cascade on host cell membranes. Here, we report the molecular cloning of human DAF from HeLa cells. Analysis of DAF complementary DNAs revealed two classes of DAF messenger RNA, one apparently derived from the other by a splicing event that causes a coding frameshift near the C terminus. The apparent 'intron' sequence contains an Alu family member and encodes contiguous protein sequence. Two DAF proteins are therefore possible, having divergent C-terminal domains which differ in their hydrophobicity. Both mRNAs are found on polysomes, suggesting that both are translated. We propose that the major (90%) spliced DAF mRNA encodes membrane-bound DAF whereas the minor (10%) unspliced DAF mRNA may encode secreted DAF and we present expression data supporting this. The deduced DAF sequence contains four repeating units homologous to a consensus repeat found in a recently described family of complement proteins. 相似文献