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91.
92.
Akihiro Ohira Eugene de Juan Jr Yasuo Tano Charles A. Wilson 《The Histochemical journal》1996,28(9):607-611
Summary It has been proposed that basic fibroblast growth factor (basic FGF) mediates the neovascular response in a variety of conditions,
including diabetic retinopathy and branch retinal vein occlusion. To test the hypothesis that basic FGF was released from
retinal stores as a result of retinal ischaemia, transient retinal ischaemia was induced, followed by 48 h of reperfusion,
in the rat by combined central retinal vasculature and optic nerve ligation. The immunolocalization of basic FGF was studied
in the retina. We found that basic FGF in the normal retina is present around the deeper retinal vessels and in the neuronal
tissue of the outer plexiform layer. In the eyes that had ischaemia followed by reperfusion, there was moderate cellular oedema
with retinal swelling, and mitoses in the inner nuclear and plexiform layers. There were no changes evident at the immunohistochemical
level either in the intensity or distribution of stores of basic FGF. We conclude from these data that stores of basic FGF
are not altered dramatically under the conditions of transient experimental ischaemia and reperfusion in the rat, despite
the presence of cellular proliferation. 相似文献
93.
Patricia A. Lampe Ellen B. Cornbrooks Anna Juhasz Eugene M. Johnson James L. Franklin 《Developmental neurobiology》1995,26(2):205-212
Rat sympathetic neurons undergo programmed cell death (PCD) in vitro and in vivo when they are deprived of nerve growth factor (NGF). Chronic depolarization of these neurons in cell culture with elevated concentrations of extracellular potassium ([K+]o) prevents this death. The effect of prolonged depolarization on neuronal survival is thought to be mediated by a rise of intracellular calcium concentration ([Ca2+]i) caused by Ca2+ influx through voltage-gated channels. In this report we investigate the effects of chronic treatment of rat sympathetic neurons with thapsigargin, an inhibitor of intracellular Ca2+ sequestration. In medium containing a normal concentration of extracellular Ca2+ ([Ca2+]o), thapsigargin caused a sustained rise of intracellular Ca2+ concentration and partially blocked death of NGF-deprived cells. Elevating [Ca2+]o in the presence of thapsigargin further increased [Ca2+]i, suggesting that the sustained rise of [Ca2+]i was caused by a thapsigargin-induced Ca2+ influx. This treatment potentiated the effect of thapsigargin on survival. The dihydropyridine Ca2+ channel antagonist, nifedipine, blocked both a sustained elevation of [Ca2+]i and enhanced survival caused by depolarization with elevated [K+]o, suggesting that these effects are mediated by Ca2+ influx through L-type channels. Nifedipine did not block the sustained rise of [Ca2+]i or enhanced survival caused by thapsigargin treatment, indicating that these effects were not mediated by influx of Ca2+ through L-type channels. These results provide additional evidence that increased [Ca2+]i can suppress neuronal PCD and identify a novel method for chronically raising neuronal [Ca2+]i for investigation of this and other Ca2+-dependent phenomena. © 1995 John Wiley & Sons, Inc. 相似文献
94.
Eugene N. Kozloff 《Acta zoologica》1994,75(3):191-199
Abstract Adult orthonectids develop from germinal cells within a cytoplasmic matrix called a plasmodium. This is generally assumed to be formed by the parasite. In the case of Rhopalura ophiocomae, which lives in the brittle star Amphipholis squamata, the plasmodia occupying the perivisceral coelom are closely associated with the walls of the genital bursae or the gut, and they are covered by peritoneum. They have been reported to contain scattered small nuclei distinct from those within germinal cells, embryos, and adults, but the results of the present study indicate that such nuclei probably do not exist. Furthermore, electron micrographs show that some plasmodia are in continuity with the cytoplasm of contractile cells that lie beneath the peritoneum of a genital bursa or the gut of the host. The matrix of a plasmodium of R. ophiocomaeappears, therefore, to consist of cytoplasm of a contractile cell. It is proposed that after a contractile cell has been entered by an infective cell of the parasite, it hypertrophies, bulging progressively farther into the perivisceral coelom and lifting up the peritoneum, which remains in intimate contact with it. 相似文献
95.
Eugene S. Stevens 《Biopolymers》1994,34(10):1395-1401
The optical rotation of methyl 3-O -(α-D -mannopyranosyl)-α-D -mannopyranoside is calculated semiempirically as a function of the linkage dihedral angles ? (H1-C1-O1-C3′) and ψ (C1-O1-C3′-H3′). Comparison with the observed optical rotation in aqueous solution indicates the existence of at least two conformers in solution, which implies a degree of linkage flexibility. The result is in agreement with some, but not all, calculated potential energy surfaces, and with recently published nmr data. © 1994 John Wiley & Sons, Inc. 相似文献
96.
Eugene S. Stevens 《Biopolymers》1994,34(10):1403-1407
The optical rotation of methyl 2-O -(α-D -mannopyranosyl)-α-D -mannopyranoside is calculated semiempirically as a function of the linkage dihedral angles ? (H1-C1-O1-C2′) and ψ (C1-O1-C2′-H2′). Although the rotation calculated for the global energy minimum conformation found in several rigid-residue modeling calculations (?,ψ = ?40°,?20°) is in good agreement with the observed solution rotation, the observed rotation is also compatible with the limited flexibility inferred from more recent relaxed residue modeling calculations on a structurally related rhamnose disaccharide © 1994 John Wiley & Sons, Inc. 相似文献
97.
Carbon dioxide consumption during soil development 总被引:5,自引:1,他引:4
Oliver A. Chadwick Eugene F. Kelly Dorothy M. Merritts Ronald G. Amundson 《Biogeochemistry》1994,24(3):115-127
Carbon is sequestered in soils by accumulation of recalcitrant organic matter and by bicarbonate weathering of silicate minerals. Carbon fixation by ecosystems helps drive weathering processes in soils and that in turn diverts carbon from annual photosynthesis-soil respiration cycling into the long-term geological carbon cycle. To quantify rates of carbon transfer during soil development in moist temperate grassland and desert scrubland ecosystems, we measured organic and inorganic residues derived from the interaction of soil biota and silicate mineral weathering for twenty-two soil profiles in arkosic sediments of differing ages. In moist temperate grasslands, net annual removal of carbon from the atmosphere by organic carbon accumulation and silicate weathering ranges from about 8.5 g m–2 yr–1 for young soils to 0.7 g M–2 yr–1 for old soils. In desert scrublands, net annual carbon removal is about 0.2 g m–2 yr–1 for young soils and 0.01 g m–2 yr–1 for old soils. In soils of both ecosystems, organic carbon accumulation exceeds CO2 removal by weathering, however, as soils age, rates of CO2 consumption by weathering accounts for greater amounts of carbon sequestration, increasing from 2% to 8% in the grassland soils and from 2% to 40% in the scrubland soils. In soils of desert scrublands, carbonate accumulation far outstrips organic carbon accumulation, but about 90% of this mass is derived from aerosolic sources that do not contribute to long-term sequestration of atmospheric carbon dioxide. 相似文献
98.
99.
M. J. Bennett D. Eisenberg 《Protein science : a publication of the Protein Society》1994,3(9):1464-1475
The structure of toxic monomeric diphtheria toxin (DT) was determined at 2.3 A resolution by molecular replacement based on the domain structures in dimeric DT and refined to an R factor of 20.7%. The model consists of 2 monomers in the asymmetric unit (1,046 amino acid residues), including 2 bound adenylyl 3'-5' uridine 3' monophosphate molecules and 396 water molecules. The structures of the 3 domains are virtually identical in monomeric and dimeric DT; however, monomeric DT is compact and globular as compared to the "open" monomer within dimeric DT (Bennett MJ, Choe S, Eisenberg D, 1994b, Protein Sci 3:0000-0000). Detailed differences between monomeric and dimeric DT are described, particularly (1) changes in main-chain conformations of 8 residues acting as a hinge to "open" or "close" the receptor-binding (R) domain, and (2) a possible receptor-docking site, a beta-hairpin loop protruding from the R domain containing residues that bind the cell-surface DT receptor. Based on the monomeric and dimeric DT crystal structures we have determined and the solution studies of others, we present a 5-step structure-based mechanism of intoxication: (1) proteolysis of a disulfide-linked surface loop (residues 186-201) between the catalytic (C) and transmembrane (T) domains; (2) binding of a beta-hairpin loop protruding from the R domain to the DT receptor, leading to receptor-mediated endocytosis; (3) low pH-triggered open monomer formation and exposure of apolar surfaces in the T domain, which insert into the endosomal membrane; (4) translocation of the C domain into the cytosol; and (5) catalysis by the C domain of ADP-ribosylation of elongation factor 2. 相似文献
100.