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排序方式: 共有283条查询结果,搜索用时 93 毫秒
81.
82.
Beneficial effect of fluorocarbon emulsion media on the function of neuromuscular preparations in vitro
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The effects of liquid fluorocarbons as bathing media were determined by use of in vitro neuromuscular preparations. Rat hemidiaphragms were bathed in either oxygenated fluorocarbon (FC) emulsion or standard oxygenated Krebs solution. Contractile force in response to simple supramaximal nerve stimuli as well as to high frequency stimulation was greater, while twitch:tetanus ratio was smaller in FC emulsion. With such medium, post-tetanic potentiation of contraction was also more consistently observed. Indirectly stimulated diaphragms survived longer in FC emulsion. After cessation of oxygenation, oxygen tension (ρO(2)) of the medium declined more rapidly with Krebs than with FC emulsion; ρO(2) directly correlated with force of contraction. Similarly, in the chick biventer cervicis preparation, FC emulsion enhanced nerve-stimulated force of contraction; returning the preparation to standard Krebs solution reversed this phenomenon. Dose-resonse curves of muscle contraction in response to acetycholine and KCl administration were shifted upward during FC emulsion superfusion. Frequency of miniature endplate potentials was lower in FC emulsion than that observed in Krebs solution, measured from the same cell of the rat diaphragm. Resting membrane potentials were also greater in muscle cells sampled from FC emulsion-bathed preparations. These data suggest that FC emulsion is superior to standard Krebs solution as a bathing medium for in vitro neuromuscular preparations by virtue of the high solubility of oxygen in it. 相似文献
83.
A theory is presented to describe the behavior of micro-organisms, bacteria and protozoa. Individual cells are regarded as particles having internal state variables. The change of each variable with time depends on the environmental condition. The velocity and the frequency of direction change of swimming cells are determined by the values of these variables. With this framework, the theory gives a method to connect the behaviour in a spatial gradient of the environment and the behaviour upon a change of the environment with time. Observed behaviors of bacteria and protozoa are understandable on the basis of simple rate equations for internal state variables and the product expressions for the velocity and the frequency of direction change as functions of these variables. Experimental data on the thermotaxis of paramecium are shown for comparison with the theoretical results. 相似文献
84.
Total correction was performed in a child with l-transposition of the great arteries, severe subpulmonic stenosis, and a ventricular septal defect. The subpulmonic obstruction was bypassed with an extra-cardiac valved conduit. This alternate method of relieving ventricular outflow obstruction should be considered when conventional techniques cannot be employed because of complex intracardiac anatomy. Proper placement of the pulmonary ventriculotomy is important in order to avoid injury to coronary arteries on the upper and lower ventricular wall and to papillary muscles in the mid-portion of the ventricle. 相似文献
85.
Martin Nemer Irith Ginzburg Saul Surrey Samuel Litwin 《Genesis (New York, N.Y. : 2000)》1979,1(2):151-165
The relationship between heterogeneous nuclear RNA (hnRNA) and messenger RNA (mRNA) synthesis has been studied as a function of the development of the sea urchin embryo through the use of methyl incorporation. Several parameters in the metabolism of capped hnRNA and mRNA of early blastula and late gastrula stages have been investigated by measuring the kinetics of transfer of methyl groups from S-adenosylmethionine to the 5′ cap structures in nuclear and cytoplasmic RNA:
- 1 The rate constants for the decay of hnRNA caps and the synthesis of mRNA caps are equal to within experimental error. This equality indicates a flux of precursor hnRNA caps to mRNA caps with a very high degree of conservation of the hnRNA caps. This conservation holds for each embryonic stage.
- 2 From literature data on the labeling kinetics of GTP and mRNA, we have calculated the decay constant of a putative mRNA precursor component of hnRNA. The value of this constant is very close to that for the decay constant of hnRNA caps. Hence, all hnRNA caps and some portion of their associated hnRNA sequences behave kinetically as the pre-mRNA fraction. This kinetically ascribed pre-mRNA comprises approximately 30% of the hnRNA mass.
- 3 The part of the hnRNA which does not serve as precursor to mRNA turns over at least twice as rapidly as the pre-mRNA fraction.
- 4 During development from early blastula to late gastrula, the rate of hnRNA cap synthesis drops from 2 × 103 molecules/min/cell to half of this value. This decline is parallel to the decline in total hnRNA synthesis and thereby confirms the constant degree of capping of hnRNA, as previously reported. We infer that the pre-mRNA fraction of hnRNA remains nearly constant during this developmental period.
86.
Ultrastructural demonstration of endogenous peroxidatic activity in mammalian arterial wall 总被引:1,自引:0,他引:1
J. A. Litwin 《Histochemistry and cell biology》1981,72(3):459-466
Summary Endogenous peroxidatic activity has been demonstrated at the ultrastructural level in large arteries of rabbit and rat using diaminobenzidine. The reaction was positive in endothelial cells of both species and also in the smooth muscle cells of rat arteries. The reaction product was localized in the nuclear envelope and endoplasmic reticulum of the reactive cells. Since the enzymatic activity was extremely sensitive to fixation, best visualization was obtained in unfixed, directly incubated tissues in which additional mitochondrial staining occurred due to the activity of endogenous cytochrome c/cytochrome oxidase system. The peroxidatic activity was partially sensitive to cyanide and could be completely abolished by azide and aminotriazole. It has been suggested that the observed endogenous peroxidatic activity of the arterial wall components reflects the activity of prostaglandin endoperoxide synthetase and, indirectly, production of prostacyclin (PGI2).Preliminary results were presented at the VIth International Histochemistry and Cytochemistry Congress in Brighton, England, 17–22 August 1980 相似文献
87.
Gajda M Litwin JA Adriaensen D Timmermans JP Cichocki T 《Folia histochemica et cytobiologica / Polish Academy of Sciences, Polish Histochemical and Cytochemical Society》2004,42(2):95-99
Previous reports have demonstrated very rich innervation pattern in the periosteum. Most of the periosteal fibers were found to be sensory in nature. The aim of this study was to identify the primary sensory neurons that innervate the tibial periosteum in the adult rat and to describe the morphometric features of their perikarya. To this end, an axonal fluorescent carbocyanine tracer, DiI, was injected into the periosteum on the medial surface of the tibia. The perikarya of the sensory fibers were traced back in the dorsal root ganglia (DRG) L1-L6 by means of fluorescent microscopy on cryosections. DiI-containing neurons were counted in each section and their segmental distribution was determined. Using PC-assisted image analysis system, the size and shape of the traced perikarya were analyzed. DiI-labeled sensory neurons innervating the periosteum of the tibia were located in the DRG ipsilateral to the injection site, with the highest distribution in L3 and L4 (57% and 23%, respectively). The majority of the traced neurons were of small size (area < 850 microm2), which is consistent with the size distribution of CGRP- and SP-containing cells, regarded as primary sensory neurons responsible for perception of pain and temperature. A small proportion of labeled cells had large perikarya and probably supplied corpuscular sense receptors observed in the periosteum. No differences were found in the shape distribution of neurons belonging to different size classes. 相似文献
88.
89.
Bob?JA?Schijvenaars Barend?Mons Marc?Weeber Martijn?J?Schuemie Erik?M?van Mulligen Hester?M?Wain Jan?A?KorsEmail author 《BMC bioinformatics》2005,6(1):149
Background
Massive text mining of the biological literature holds great promise of relating disparate information and discovering new knowledge. However, disambiguation of gene symbols is a major bottleneck. 相似文献90.
Miguel L Soares Seiki Haraguchi Maria-Elena Torres-Padilla Tibor Kalmar Lee Carpenter Graham Bell Alastair Morrison Christopher JA Ring Neil J Clarke David M Glover Magdalena Zernicka-Goetz 《BMC developmental biology》2005,5(1):1-11