共查询到20条相似文献,搜索用时 15 毫秒
1.
Compartmentalization of cyclic AMP during phagocytosis by human neutrophilic granulocytes 总被引:4,自引:0,他引:4
K B Pryzwansky A L Steiner J K Spitznagel C L Kapoor 《Science (New York, N.Y.)》1981,211(4480):407-410
Immunocytochemistry shows that early during phagocytosis of zymosan, adenosine 3',5'-monophosphate (cyclic AMP) appears on the cell surface before the phagosome is internalized. The appearance of cyclic AMP on the cell surface is coincident with that of granule products and regulatory subunit of type I cyclic AMP-dependent protein kinase. Guanosine 3',5'-monophosphate is not associated with the initiation site of phagocytosis, but is observed throughout the granular cytoplasmic region. This sharply localized accumulation of cyclic AMP may serve as a signal for the initiation of phagocytosis. 相似文献
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Vasoactive intestinal peptide alters membrane potential and cyclic nucleotide levels in retinal horizontal cells 总被引:1,自引:0,他引:1
Vasoactive intestinal peptide stimulated the synthesis of adenosine 3',5'-monophosphate in fractions of isolated carp horizontal cells. When applied extracellularly to isolated and cultured horizontal cells, the peptide also induced a slow depolarization (30 to 40 millivolts) accompanied by a decrease in membrane resistance. However, analogs of adenosine 3',5'-monophosphate applied extracellularly or intracellularly, and forscolin applied extracellularly, had no effect on the membrane potential of cultured horizontal cells, indicating that the induced depolarization was not related to the accumulation of adenosine 3',5'-monophosphate in these cells. 相似文献
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Leukemia virus activation during homograft rejection 总被引:4,自引:0,他引:4
Activation of murine leukemia viruses, as detected by the mixed culture cytopathogenicity (XC) assay, followed the transplantation of A/J skin onto immunosuppressed BALB/c mice. Virus was found in most of the mice receiving both skin grafts and antilymphocyte serum, but not in animals receiving either the serum alone, skin graft alone, or no treatment. 相似文献
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Jardine AP Dworski S Fouquet P Alexandrowicz G Riley DJ Lee GY Ellis J Allison W 《Science (New York, N.Y.)》2004,304(5678):1790-1793
We demonstrate two approaches that use the recently developed helium spin-echo technique to measure surface potential energy landscapes. For helium-lithium fluoride (100), we use the selective adsorption phenomenon to obtain the complete experimental band structure of atoms in a corrugated surface potential. For carbon monoxide-copper (001), we measure the diffusion-induced energy broadening in the scattered helium beam and extract properties of the adsorbate-substrate potential. The measurements are made possible by the resolution of our new spectrometer, which improves on existing resolution by three orders of magnitude. We show that it is possible to produce benchmark energy landscapes to assist evaluation and development of first-principles theory in the problematic van der Waals/weak chemisorption regime. 相似文献
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横向滑坡过程中管道的内力和变形计算 总被引:3,自引:0,他引:3
将滑坡体中的管道简化成大挠度的梁,将滑坡体外管道看作半无限长的梁或杆,考虑管梁的几何非线性、滑坡体外土壤的纵向抗力的物理非线性以及管道的内压和温差作用,基于滑坡体内外管道内力和变形的连续性,推导得出了在当量轴向力为拉力或压力两种情况下管道的内力和位移的有关计算式,提出了当量轴力为拉力或压力的判别式。横向滑坡中埋地管道的位移和内力计算最终归结于两个非线性方程的求解,可用牛顿迭代法或作图法解之。提供了 相似文献
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Lysosomal stability during phagocytosis of Aspergillus flavus spores by alveolar macrophages of cortisone-treated mice 总被引:8,自引:0,他引:8
Control mice and those treated with cortisone were exposed to aerosols of viable spores of Aspergillus flavus. Fifteen to 20 minutes later, animals were killed, and alveolar macrophages were obtained by tracheobronchial lavage. Electron-microscopic examination of these cells revealed that, whereas the lysosomes of control macrophages showed extensive attraction and fusion with the phagocytic membranes surrounding spores, the lysosomes of macrophages from animals treated with cortisone revealed little, if any, interaction. This diminished lysosomal response in forming phagocytic vacuoles may be important in the subsequent development of hyphal bronchopneumonia which frequently, occurs in cortisonetreated mice exposed to spores of A. flavus. 相似文献
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运用响应面法优化芦苇基生物炭活化工艺 总被引:1,自引:1,他引:0
为优化芦苇基生物炭制备工艺,在单因素试验考察热解温度、氨水质量分数和浸渍比(生物质原料与氨水质量之比)等3种参数对芦苇基生物炭吸附性能影响的基础上,利用Box-Benhnken中心组合设计实验,运用响应面法对其活化工艺参数进行优化。结果表明,3个因素均对生物质炭的比表面积产生影响,其影响显著性大小为热解温度氨水质量分数浸渍比。通过模型优化确定了最佳活化工艺参数为热解温度620℃、氨水质量分数8%、浸渍比1∶5;该工艺条件下制备的生物炭比表面积和碘吸附值分别为334.49 m~2/g、585.52 mg/g,均优于未进行优化改性的样品。该值与理论值(335.2 m~2/g、582.288 mg/g)基本相符,表明响应面模型与实际情况拟合良好,验证了模型的有效可行性。 相似文献
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1种螺旋榨油机榨膛内表面温度预估方法 总被引:1,自引:0,他引:1
【目的】预估榨油机榨膛内表面的温度.【方法】运用有限元分析技术对榨油机榨膛结构进行了热学分析;通过构造榨膛外表面温度分布的目标函数,提出了1种根据榨膛外表面温度反求榨膛内表面温度的计算方法.【结果和结论】算例验证了该预估方法的有效性.此方法可为榨油机榨膛结构的研发提供理论依据,为高性能榨油机设计提供参考. 相似文献
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Increased Wnt signaling during aging alters muscle stem cell fate and increases fibrosis 总被引:1,自引:0,他引:1
Brack AS Conboy MJ Roy S Lee M Kuo CJ Keller C Rando TA 《Science (New York, N.Y.)》2007,317(5839):807-810
The regenerative potential of skeletal muscle declines with age, and this impairment is associated with an increase in tissue fibrosis. We show that muscle stem cells (satellite cells) from aged mice tend to convert from a myogenic to a fibrogenic lineage as they begin to proliferate and that this conversion is mediated by factors in the systemic environment of the old animals. We also show that this lineage conversion is associated with an activation of the canonical Wnt signaling pathway in aged myogenic progenitors and can be suppressed by Wnt inhibitors. Furthermore, components of serum from aged mice that bind to the Frizzled family of proteins, which are Wnt receptors, may account for the elevated Wnt signaling in aged cells. These results indicate that the Wnt signaling pathway may play a critical role in tissue-specific stem cell aging and an increase in tissue fibrosis with age. 相似文献
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Membrane potential changes during chemokinesis in Paramecium 总被引:1,自引:0,他引:1
J Van Houten 《Science (New York, N.Y.)》1979,204(4397):1100-1103
Intracellular recordings show that (i) paramecia hyperpolarize slightly in attractants and depolarize in repellents that depend on the avoiding reaction (an abrupt change of swimming direction), and (ii) paramecia more strongly hyperpolarize in repellents and more strongly depolarize in attractants that depend on changes of swimming velocity. These membrane potential changes are in agreement with a hypothesis of membrane potential control of chemokinesis in Paramecium. 相似文献
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Although ion channels have been detected in mitochondria, scientists have not been able to record ion transport in mitochondria of intact cells. A variation of the patch clamp technique was used to record ion channel activity from intracellular organelles in the presynaptic terminal of the squid. Electron microscopy indicated that mitochondria are numerous in this terminal and are the only organelles compatible with the tips of the pipettes. Before synaptic stimulation, channel activity was infrequent and its conductance was small, although large conductances ( approximately 0.5 to 2.5 nanosiemens) could be detected occasionally. During a train of action potentials, the conductance of the mitochondrial membrane increased up to 60-fold. The conductance increased after a delay of several hundred milliseconds and continued to increase after stimulation had stopped. Recovery occurred over tens of seconds. 相似文献
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Krupa DJ Wiest MC Shuler MG Laubach M Nicolelis MA 《Science (New York, N.Y.)》2004,304(5679):1989-1992
Ensemble neuronal activity was recorded in each layer of the whisker area of the primary somatosensory cortex (SI) while rats performed a whisker-dependent tactile discrimination task. Comparison of this activity with SI activity evoked by similar passive whisker stimulation revealed fundamental differences in tactile signal processing during active and passive stimulation. Moreover, significant layer-specific functional differences in SI activity were observed during active discrimination. These differences could not be explained solely by variations in ascending thalamocortical input to SI. Instead, these results suggest that top-down influences during active discrimination may alter the overall functional nature of SI as well as layer-specific mechanisms of tactile processing. 相似文献
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《山东省农业管理干部学院学报》2016,(10):154-155
试验研究了白砂糖添加量、面火温度、底火温度和焙烤时间对面包褐变的影响,其中面火温度对面包表面褐变影响最大。正交试验结果表明:面火温度180℃、底火温度210℃、白砂糖添加量18%、焙烤时间16min时,面包的色泽最佳。 相似文献
15.
Malik FI Hartman JJ Elias KA Morgan BP Rodriguez H Brejc K Anderson RL Sueoka SH Lee KH Finer JT Sakowicz R Baliga R Cox DR Garard M Godinez G Kawas R Kraynack E Lenzi D Lu PP Muci A Niu C Qian X Pierce DW Pokrovskii M Suehiro I Sylvester S Tochimoto T Valdez C Wang W Katori T Kass DA Shen YT Vatner SF Morgans DJ 《Science (New York, N.Y.)》2011,331(6023):1439-1443
Decreased cardiac contractility is a central feature of systolic heart failure. Existing drugs increase cardiac contractility indirectly through signaling cascades but are limited by their mechanism-related adverse effects. To avoid these limitations, we previously developed omecamtiv mecarbil, a small-molecule, direct activator of cardiac myosin. Here, we show that it binds to the myosin catalytic domain and operates by an allosteric mechanism to increase the transition rate of myosin into the strongly actin-bound force-generating state. Paradoxically, it inhibits adenosine 5'-triphosphate turnover in the absence of actin, which suggests that it stabilizes an actin-bound conformation of myosin. In animal models, omecamtiv mecarbil increases cardiac function by increasing the duration of ejection without changing the rates of contraction. Cardiac myosin activation may provide a new therapeutic approach for systolic heart failure. 相似文献
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Hageman factor: alterations in physical properties during activation 总被引:10,自引:0,他引:10
Highly purified preparations of Hageman factor, a potent clotpromoting agent in normal mammalian plasma, had a sedimentation coefficient of approximately 5S before activation. After activation, the Hageman factor behaved as a much less soluble or larger molecule during ultracentrifugation and gel filtration. No significant change in sedimentation behavior was noted when the Hageman factor in plasma deficient in plasma thromboplastin antecedent was activated. The altered sedimentation behavior of purified activated Hageman factor probably reflects its decreased solubility in aqueous media. 相似文献
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Flätgen G Krischer K Pettinger B Doblhofer K Junkes H Ertl G 《Science (New York, N.Y.)》1995,269(5224):668-671
The potential dependence of resonance conditions for the excitation of surface plasmons was exploited to obtain two-dimensional images of the potential distribution of an electrode with high temporal resolution. This method allows the study of spatiotemporal patterns in electrochemical systems. Potential waves traveling across the electrode with a speed on the order of meters per second were observed in the bistable regime of an oscillatory electrochemical reaction. This velocity is close to that of excitation waves in nerve fibers and is far greater than the velocity of reaction-diffusion waves observed in other chemical systems. 相似文献
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Makarov EM Makarova OV Urlaub H Gentzel M Will CL Wilm M Lührmann R 《Science (New York, N.Y.)》2002,298(5601):2205-2208
Major structural changes occur in the spliceosome during its activation just before catalyzing the splicing of pre-messenger RNAs (pre-mRNAs). Whereas changes in small nuclear RNA (snRNA) conformation are well documented, little is known about remodeling of small nuclear ribonucleoprotein (snRNP) structures during spliceosome activation. Here, human 45S activated spliceosomes and a previously unknown 35S U5 snRNP were isolated by immunoaffinity selection and were characterized by mass spectrometry. Comparison of their protein components with those of other snRNP and spliceosomal complexes revealed a major change in protein composition during spliceosome activation. Our data also suggest that the U5 snRNP is dramatically remodeled at this stage, with the Prp19 complex and other factors tightly associating, possibly in exchange for other U5 proteins, and suggest that after catalysis the remodeled U5 is eventually released from the postsplicing complex as a 35S snRNP particle. 相似文献
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Seismic potential revealed by surface folding: 1983 coalinga, california, earthquake 总被引:2,自引:0,他引:2
The 2 May 1983 Coalinga, California, earthquake (magnitude 6.5) failed to rupture through surface deposits and, instead, elastically folded the top few kilometers of the crust. The subsurface rate of fault slip and the earthquake repeat time are estimated from seismic, geodetic, and geologic data. Three larger earthquakes (up to magnitude 7.5) during the past 20 years are also shown to have struck on reverse faults concealed beneath active folds. 相似文献