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21.
Résumé Chez les rats on a observé l'augmentation de la diurèse provoquée par l'injection de la dopamine et de la noradrénaline dans les ventricules latéraux du cerveau. La pimozide, administré dans le péritoine, inhibe l'action de la dopamine. L'action diurétique de la noradrénaline est enrayée après injection intraventriculaire de phentolamine. 相似文献
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Sauvage E Kerff F Fonzé E Herman R Schoot B Marquette JP Taburet Y Prevost D Dumas J Leonard G Stefanic P Coyette J Charlier P 《Cellular and molecular life sciences : CMLS》2002,59(7):1223-1232
Penicillin-binding proteins (PBPs) are membrane proteins involved in the final stages of peptidoglycan synthesis and represent the targets of beta-lactam antibiotics. Enterococci are naturally resistant to these antibiotics because they produce a PBP, named PBP5fm in Enterococcus faecium, with low-level affinity for beta-lactams. We report here the crystal structure of the acyl-enzyme complex of PBP5fm with benzylpenicillin at a resolution of 2.4 A. A characteristic of the active site, which distinguishes PBP5fm from other PBPs of known structure, is the topology of the loop 451-465 defining the left edge of the cavity. The residue Arg464, involved in a salt bridge with the residue Asp481, confers a greater rigidity to the PBP5fm active site. In addition, the presence of the Val465 residue, which points into the active site, reducing its accessibility, could account for the low affinity of PBP5fm for beta-lactam. This loop is common to PBPs of low affinity, such as PBP2a from Staphylococcus aureus and PBP3 from Bacillus subtilis. Moreover, the insertion of a serine after residue 466 in the most resistant strains underlines even more the determining role of this loop in the recognition of the substrates. 相似文献
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Neural networks are fitted to real exchange rates of several industrialized countries. The size and topology of the networks is found through the use of multiple correlation coefficients, principal component analysis of residuals and graphical analysis of network output per hidden layer cell and input layer cell. These pruned neural networks are good approximations to varying non‐linear trends in real exchange rates. Non‐linear dynamic analysis shows that the long‐term equilibrium values of several European currencies correspond to the actual values within the European Monetary System. Based on its long‐term equilibrium value, the Euro appears to be undervalued vis‐à‐vis the US dollar at the introduction of the Euro on 1 January 1999. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
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When many ligands bind to cell-surface receptors, ligand-receptor complexes are internalized via clathrin coated pits by a process called receptor-mediated endocytosis. The cytoplasmic fate of ligands internalized within endocytic vesicles or endosomes is variable. For example, maternal immunoglobulins are transported through the cytoplasm of neonatal intestinal epithelial cells and are exocytosed at the basolateral surface. However, other ligands are degraded as a result of their delivery to the lysosomal compartment of cells. Although the translocation of endosomes to the Golgi region in the cell centre seems to be a general phenomenon presumably coupled to ligand degradation by lysosomes and endosomes and lysosomes undergo saltatory movements within the cytoplasm, the spatial control of interaction between the two structures is not understood. To address this problem we have begun to examine the spatial and temporal intracellular distribution of endosomes and lysosomes. Utilizing a new fluorescent microscopic approach, we have now been able simultaneously to visualize endosome and lysosome populations in living cells. Our results suggest that a specific relocation of lysosomes is rapidly induced upon binding of different types of ligands to the cell surface; this migration of lysosomes to the Golgi region of the cell precedes the translocation of endosomes into the same area. 相似文献
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Blebbing, free Ca2+ and mitochondrial membrane potential preceding cell death in hepatocytes 总被引:1,自引:0,他引:1
Cell surface 'blebbing' is an early consequence of hypoxic and toxic injury to cells. A rise in cytosolic free Ca2+ has been suggested as the stimulus for bleb formation and the final common pathway to irreversible cell injury. Here, using digitized low-light video microscopy, we examine blebbing, cytosolic free Ca2+, mitochondrial membrane potential and loss of cell viability in individual cultured hepatocytes. Unexpectedly, we found that after 'chemical hypoxia' with cyanide and iodoacetate, cytosolic free Ca2+ does not change during bleb formation or before loss of cellular viability. Cell death was precipitated by a sudden breakdown of the plasma membrane permeability barrier, possibly caused by rupture of a cell surface bleb. 相似文献
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