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51.
Vessel diameters and branching angles are measured from a large number of arterial bifurcations in the retina of a normal human subject and in that of a rhesus monkey. The results are compared with each other and with theoretical results on this subject. 相似文献
52.
JW Mills ADC MacKnight JA Jarrell JM Dayer DA Ausiello 《The Journal of cell biology》1981,88(3):637-643
To determine the specificity and efficacy of [(3)H]ouabain binding as a quantitative measure of the Na(+) pump (Na(+), K(+)-ATPase) and as a marker for the localization of pumps involved in transepithelial Na(+)-transport, we analyzed the interaction of [(3)H]ouabain with its receptor in pig kidney epithelial (LLC-PK(1)) cells. When these epithelial cells are depleted of Na(+) and exposed to 2 muM [(3)H]ouabain in a Na(+)-free medium, binding is reduced by 90 percent. When depleted of K(+) and incubated in a K(+)- free medium, the ouabain binding rate is increase compared with that measured at 5 mM. This increase is only demonstable when Na(+) is present. The increased rate could be attributed to the predominance of the Na(+)-stimulated phosphorylated form of the pump, as K(+) is not readily available to stimulate dephosphorylation. However, some binding in the K(+)-free medium is attributable to pump turnover (and therefore, recycling of K(+)), because analysis of K(+)-washout kinetics demonstrated that addition of 2 muM ouabain to K(+)-depleted cells increased the rate of K(+) loss. These results indicate that in intact epithelial cells, unlike isolated membrane preparations, the most favorable condition for supporting ouabain binding occurs when the Na(+), K(+)-ATPase is operating in the Na(+)-pump mode or is phosphorylated in the presence of Na(+). When LLC-PK(1) cells were exposed to ouabain at 4 degrees C, binding was reduced by 97 percent. Upon rewarming, the rate of binding was greater than that obtained on cells kept at a constant 37 degrees C. However, even at this accelerated rate, the time to reach equilibrium was beyond what is required for cells, swollen by exposure to cold, to recover normal volume. Thus, results from studies that have attempted to use ouabain to eliminate the contribution of the conventional Na(+) pump to volume recovery must be reevaluated if the exposure to ouabain was done in the cold or under conditions in which the Na(+) pump is not operating. 相似文献
53.
Studies on the mechanism for entry of vesicular stomatitis virus glycoprotein g mRNA into membrane-bound polyribosome complexes 下载免费PDF全文
Glycoprotein mRNA (G mRNA) of vesicular stomatitis virus is synthesized in the cytosol fraction of infected HeLa cells. Shortly after synthesis, this mRNA associates with 40S ribosomal subunits and subsequently forms 80S monosomes in the cytosol fraction. The bulk of labeled G mRNA is then found in polysomes associated with the membrane, without first appearing in the subunit or monomer pool of the membrane-bound fraction. Inhibition of the initiation of protein synthesis by pactamycin or muconomycin A blocks entry of newly synthesized G m RNA into membrane-bound polysomes. Under these circumstances, labeled G mRNA accumulates into the cytosol. Inhibition of the elongation of protein synthesis by cucloheximide, however, allows entry of 60 percent of newly synthesized G mRNA into membrane-bound polysomes. Furthermore, prelabeled G mRNA associated with membrane-bound polysomes is released from the membrane fraction in vivo by pactamycin or mucomycon A and in vitro by 1mM puromycin - 0.5 M KCI. This release is not due to nonspecific effects of the drugs. These results demonstrate that association of G mRNA with membrane-bound polysomes is dependent upon polysome formation and initiation of protein synthesis. Therefore, direct association of the 3' end of G mRNA with the membrane does not appear to be the initial event in the formation of membrane-bound polysomes. 相似文献
54.
Background
Irreversible airflow obstruction in Chronic Obstructive Pulmonary Disease (COPD) is thought to result from airway remodelling associated with aberrant inflammation. Patients who experience frequent episodes of acute deterioration in symptoms and lung function, termed exacerbations, experience a faster decline in their lung function, and thus over time greater disease severity However the mechanisms by which these episodes may contribute to decreased lung function are poorly understood.This study has prospectively examined changes in sputum levels of inflammatory cells, MMP-9 and TIMP-1 during exacerbations comparing with paired samples taken prior to exacerbation.Methods
Nineteen COPD patients ((median, [IQR]) age 69 [63 to 74], forced expiratory volume in one second (FEV1) 1.0 [0.9 to1.2], FEV1% predicted 37.6 [27.3 to 46.2]) provided sputa at exacerbation. Of these, 12 were paired with a samples collected when the patient was stable, a median 4 months [2 to 8 months] beforehand.Results
MMP-9 levels increased from 10.5 μg/g [1.2 to 21.1] prior to exacerbation to 17.1 μg/g [9.3 to 48.7] during exacerbation (P < 0.01). TIMP-1 levels decreased from 3.5 μg/g [0.6 to 7.8] to 1.5 μg/g [0.3 to 4.9] (P = 0.16). MMP-9/TIMP-1 Molar ratio significantly increased from 0.6 [0.2 to 1.1] to 3.6 [2.0 to 25.3] (P < 0.05). Neutrophil, eosinophil and lymphocyte counts all showed significant increase during exacerbation compared to before (P < 0.05). Macrophage numbers remained level. MMP-9 levels during exacerbation showed highly significant correlation with both neutrophil and lymphocyte counts (Rho = 0.7, P < 0.01).Conclusion
During exacerbation, increased inflammatory burden coincides with an imbalance of the proteinase MMP-9 and its cognate inhibitor TIMP-1. This may suggest a pathway connecting frequent exacerbations with lung function decline. 相似文献55.
Zawadowska B Majerczak J Semik D Karasinski J Kolodziejski L Kilarski WM Duda K Zoladz JA 《Folia histochemica et cytobiologica / Polish Academy of Sciences, Polish Histochemical and Cytochemical Society》2004,42(3):181-190
Twenty-four male volunteers (mean +/- SD: age 25.4+/-5.8 years, height 178.6+/-5.5 cm, body mass 72.1+/-7.7 kg) of different training background were investigated and classified into three groups according to their physical activity and sport discipline: untrained students (group A), national and sub-national level endurance athletes (group B, 7.8+/-2.9 years of specialised training) and sprint-power athletes (group C, 12.8+/-8.7 years of specialised training). Muscle biopsies of vastus lateralis were analysed histochemically for mATPase and SDH activities, immunohistochemically for fast and slow myosin, and electrophoretically followed by Western immunoblotting for myosin heavy chain (MyHC) composition. Significant differences (P<0.05) regarding composition of muscle fibre types and myosin heavy chains were found only between groups A (41.7+/-1.6% of MyHCI, 40.8+/-4.0% of MyHCIIA and 17.5+/-4.0% of MyHCIIX) and B (64.3+/-0.8% of MyHCI, 34.0+/-1.4% of MyHCIIA and 1.7+/-1.4% of MyHCIIX) and groups A and C (59.6+/-1.6% of MyHCI, 37.2+/-1.3% of MyHCIIA and 3.2+/-1.3% of MyHCIIX). Unexpectedly, endurance athletes (group B) such as long-distance runners, cyclists and cross country skiers, did not differ from the athletes representing short term, high power output sports (group C) such as ice hockey, karate, ski-jumping, volleyball, soccer and modern dance. Furthermore, the relative amount of the fastest MyHCIIX isoform in vastus lateralis muscle was significantly lower in the athletes from group C than in students (group A). We conclude that the myosin profile in the athletes belonging to group C was unfavourable for their sport disciplines. This could be the reason why those athletes did not reach international level despite of several years of training. 相似文献
56.
Many electric fish species modulate their electric organ discharges (EODs) to produce transient social signals that vary in number and structure. In Apteronotus leptorhynchus, males modulate their EOD more often than females, whereas in Apteronotus albifrons, males and females produce similar numbers of modulations. Sex differences in the number of EOD modulations in A. leptorhynchus are associated with sex differences in substance P in the diencephalic nucleus that controls transient EOD modulations, the CP/PPn. These sex differences in substance P have been hypothesized to regulate sex differences in the production of EOD modulations. To comparatively test this hypothesis, we examined substance P immunoreactivity in the CP/PPn of male and female A. leptorhynchus and A. albifrons. Because the number of EOD modulations is sexually monomorphic in A. albifrons, we predicted no sex difference in substance P in the CP/PPn of this species. Contrary to this prediction, male A. albifrons had significantly more substance P in the CP/PPn than females. This suggests that sex differences in substance P are not sufficient for controlling sex differences in the number of EOD modulations. Modulation structure (frequency excursion and/or duration), however, is also sexually dimorphic in A. leptorhynchus and is another possible behavioral correlate of the sexually dimorphic distribution of substance P. The present study found pronounced sex differences in the structure of EOD modulations in A. albifrons similar to those in A. leptorhynchus. Thus, sex differences in substance P may influence sex differences in the structure, rather than the number, of EOD modulations. 相似文献
57.
TE Willnow C Antignac AW Br?ndli EI Christensen RD Cox D Davidson JA Davies O Devuyst G Eichele ND Hastie PJ Verroust A Schedl IC Meij 《Organogenesis》2005,2(2):42-47
Rapid progress in genome research creates a wealth of information on the functional annotation of mammalian genome sequences. However, as we accumulate large amounts of scientific information we are facing problems of how to integrate and relate the data produced by various genomic approaches. Here, we propose the novel concept of an organ atlas where diverse data from expression maps to histological findings to mutant phenotypes can be queried, compared and visualized in the context of a three-dimensional reconstruction of the organ. We will seek proof of concept for the organ atlas by elucidating genetic pathways involved in development and pathophysiology of the kidney. Such a kidney atlas may provide a paradigm for a new systems-biology approach in functional genome research aimed at understanding the genetic bases of organ development, physiology and disease.Key Words: EuReGene, kidney, genome, development, pathophysiology, genetics 相似文献
58.
In order to reconstruct phylogenetic trees from extremely dissimilar
sequences it is necessary to estimate accurately the extent of sequence
divergence. In this paper a new method of sequence analysis, Markov triple
analysis, is developed for determining the relative frequencies of
nucleotide substitutions within the three branches of a three-taxon
dendrogram. Assuming that nucleotide sites are independently and
identically distributed and assuming a Markov model for nucleotide (or
protein) evolution, it is shown that the unique Markov matrices can be
reconstructed given only the joint probability distribution relating three
taxa. (In the much simpler case involving only two taxa and two character
states, Markov matrices can also be reconstructed, provided symmetry
assumptions are placed on the elements of the matrices.) The method is
illustrated using sequence data from the combined first and second codon
positions derived from complete human, mouse, and cow mitochondrial
sequences.
相似文献
59.
DNA hybridization evidence for the principal lineages of hummingbirds (Aves:Trochilidae) 总被引:3,自引:0,他引:3
The spectacular evolutionary radiation of hummingbirds (Trochilidae) has
served as a model system for many biological studies. To begin to provide a
historical context for these investigations, we generated a complete matrix
of DNA hybridization distances among 26 hummingbirds and an outgroup swift
(Chaetura pelagica) to determine the principal hummingbird lineages. FITCH
topologies estimated from symmetrized delta TmH-C values and subjected to
various validation methods (bootstrapping, weighted jackknifing, branch
length significance) indicated a fundamental split between hermit
(Eutoxeres aquila, Threnetes ruckeri; Phaethornithinae) and nonhermit
(Trochilinae) hummingbirds, and provided strong support for six principal
nonhermit clades with the following branching order: (1) a predominantly
lowland group comprising caribs (Eulampis holosericeus) and relatives
(Androdon aequatorialis and Heliothryx barroti) with violet-ears (Colibri
coruscans) and relatives (Doryfera ludovicae); (2) an Andean-associated
clade of highly polytypic taxa (Eriocnemis, Heliodoxa, and Coeligena); (3)
a second endemic Andean clade (Oreotrochilus chimborazo, Aglaiocercus
coelestis, and Lesbia victoriae) paired with thorntails (Popelairia
conversii); (4) emeralds and relatives (Chlorostilbon mellisugus, Amazilia
tzacatl, Thalurania colombica, Orthorhyncus cristatus and Campylopterus
villaviscensio); (5) mountain-gems (Lampornis clemenciae and Eugenes
fulgens); and (6) tiny bee-like forms (Archilochus colubris, Myrtis fanny,
Acestrura mulsant, and Philodice mitchellii). Corresponding analyses on a
matrix of unsymmetrized delta values gave similar support for these
relationships except that the branching order of the two Andean clades (2,
3 above) was unresolved. In general, subsidiary relationships were
consistent and well supported by both matrices, sometimes revealing
surprising associations between forms that differ dramatically in plumage
and bill morphology. Our results also reveal some basic aspects of
hummingbird ecologic and morphologic evolution. For example, most of the
diverse endemic Andean assemblage apparently comprises two genetically
divergent clades, whereas the majority of North American hummingbirds
belong a single third clade. Genetic distances separating some
morphologically distinct genera (Oreotrochilus, Aglaiocercus, Lesbia;
Myrtis, Acestrura, Philodice) were no greater than among congeneric
(Coeligena) species, indicating that, in hummingbirds, morphological
divergence does not necessarily reflect level of genetic divergence.
相似文献
60.