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21.
The role of polyamines (PA) synthesis in NMDA receptor-mediated45Ca2+ fluxes and norepinephrine release was studied in rat hippocampal synaptosomes. NMDA (50M) caused a sharp (>2-fold) transient increase in PA synthesis regulating enzyme, ornithine decarboxylase (ODC) activity with concomitant elevation in PA levels in the order putrescine>spermidine>spermine. ODC inhibitor, -difluoromethylornithine (DFMO), and NMDA antagonist, 2-amino-5-phosphonovaleric acid (D-AP5), both blocked increases in ODC activity and PA levels. Activation of NMDA receptors induced a sharp (3 to 4-fold) and quick (15 seconds) increase in45Ca2+ uptake by synaptosomes within 15 seconds of exposure at 37°C. The efflux of45Ca2+ and3H-norepinephrine (NE) release at 22°C from pre-loaded synaptosomes was also significantly (2 to 4-fold) enhanced by NMDA within 15 seconds. These NMDA receptor-mediated effects on calcium fluxes and NE release were blocked by NMDA receptor-antagonists (DAP-5 and MK-801) and PA synthesis inhibitor, DFMO and the DFMO inhibition nullified by exogenous putrescine. These observations establish that ODC/PA cascade play an important role in transduction of excitatory amino acid mediated signals at NMDA receptors.Special issue dedicated to Dr. Sidney Ochs. 相似文献
22.
The uptake of lead by two contrasting plant species, radish and red fescue, grown in soils contaminated by mine spoil was investigated. Uptake was found to be poorly correlated either with pH or total Pb concentration in the soils. By contrast, a good correlation was obtained, particularly for red fescue, between Pb uptake and Pb concentration in the solution of equilibrated soil suspensions over a wide range of soil pH, total soil Pb and soil solution Pb concentration.Calculations suggested a similar order of magnitude in the total amounts of Pb taken up by the plants and Pb in the soil solution of the root zone, justifying the latter as a good index of Pb-availability. ei]Section editor: A C Borstlap 相似文献
23.
P. E. O'Sullivan 《Hydrobiologia》1993,251(1-3):351-361
In the period since 1945, Slapton Ley, a small, coastal lake in Southwest England, has been eutrophccated by nutrient inputs generated both by the intensification of agriculture, and the discharge of sewage effluent. Two simple models have been used to identify the main sources of catchment outputs, and to evaluate historical changes in land use, and their likely effect on lake trophic status.Restoration strategies may also be evaluated using the same models. They suggest that in order to reduce loads upon the Ley to within OECD permissible limits, not only will all sewage and phosphate detergent inputs need to be prevented, but also losses from agricultural land must be reduced. This could take the form of the zoning of the catchment so that riparian zones are used, not as at present, for the grazing of livestock, but are converted to woodland, and more particularly eg to buffer strips sensu Mander (1985, 1992).This policy, if implemented comprehensively, would reduce external phosphorus loads to within permissible limits. Eventually, however, some kind of internal control, such as manipulation of the fish populations, may also have to be attempted, in order to remove the memory of five decades of eutrophication. 相似文献
24.
Growth of cells in a new defined protein-free medium 总被引:1,自引:0,他引:1
Kjell Bertheussen 《Cytotechnology》1993,11(3):219-231
The development of a new stable synthetic serum replacement (SSR) is described, which allows the cultivation of mammalian cells in a defined, protein-free medium containing only dialyzable components. With a low concentration of insulin (RPMI-SR2 medium), growth rates of the transformed cell lines L929, HELA S3, and the hybridoma 1E6 were comparable to growth rates obtained with a serum-containing medium. The same medium also supported long-term cultivation of non-dividing mouse macrophages. The main principle of SSR is a metal ion buffer containing a balanced mixture of iron and trace metals. Stability against precipitation of important metals is achieved by the combined use of EDTA and citric acid as chelating agents. Efficient iron supply is mediated through the inclusion of the compound Aurintricarboxylic acid as a synthetic replacement for transferrin. SSR also contains a growth-promoting surfactant, Pluronic F68. Thus SSR provides a general foundation for growth and differentiation normally provided by serum.Limitations of other serum-free medium designs are discussed here: 1) the inability of transferrin to chelate all metals in the medium; and 2) the use of inorganic iron salts or iron citrate as an iron supplement leads to rapid precipitation of iron hydroxide in the medium. Both these problems are solved in the design of SSR. 相似文献
25.
1 引言 传统的植物光合生理生态研究中,多用照度计来测定光照指标,它以人眼对光亮度的响应特性为基础,与植物叶片对光照的响应曲线差异很大;而太阳光谱中只有400—700nm的波段才是光合有效辐射 相似文献
26.
高维非自治系统的周期解 总被引:1,自引:0,他引:1
本文通过建立并利用齐次线性方程解的估计公式,获得了周期系统(1)的周期解的存在性、唯一性定理,对周期系统(2)给出了一个平稳振荡定理,最后给出了实例。 相似文献
27.
一类三维非线性系统空间周期解的存在性及唯一性 总被引:1,自引:1,他引:0
本文研究了一类描述天然林内红松林种群变化的三维非线性教学模型 相似文献
28.
Spring wheat plants were grown in a 137Cs labelled nutrient solution, either in the presence or absence of NH4 as a secondary N source. Between 11 and 64 days after sowing (DAS), plants were harvested on nine occasions. The plants supplied with NH4 and NO3 had lower root 137Cs Activity Concentrations (AC) than those supplied with NO3 only. Shoot AC were equal in both nutrition treatments. Shoot and root 137Cs AC (dry weight basis) showed the same trends with plant age in both nutrition treatments. Shoot AC almost doubled between 11 and 28 DAS after which they gradually decreased concomitant with a similar decrease in K concentrations. Root AC were always higher than shoot AC and increased to a maximum at 35 DAS after which they fluctuated. Expressed on a tissue water basis, the 137Cs AC varied less during plant age than did dry weight based AC. Furthermore, root and shoot AC expressed on a tissue water basis were almost equal. It is shown that the initial increase in 137Cs AC in both root and shoot can largely be explained by the initial dilution of absorbed 137Cs in the unlabelled seedling tissues. No correlation was found between K and 137Cs distribution among ears, leaves, stems and roots in 64 old wheat plants. NH4 as a secondary N source in a nitrate nutrient solution marginally affected 137Cs distribution.Abbreviations AC
activity concentrations
- DAS
days after sowing
FAX no corresponding author: +3216321997 相似文献
29.
A 500-MHz 1H-NMR study on the single-stranded DNA undecamer (11-mer) 5d AAGTGTGATAT is presented. Using a combination of one-dimensional pre-steady-state nuclear Overhauser enhancement (NOE) measurements and two-dimensional homonuclear J-correlated spectroscopy, virtually complete resonance assignments are obtained. The relative magnitudes of the intra- and internucleotide NOEs indicate that the overall structure of the single-stranded 11-mer is a right-handed B-type helix with extensive base stacking. Within this overall structure there is quite a large degree of variability, as exemplified by variations in glycosidic bond and sugar pucker conformations, most likely determined by base sequence.Abbreviations NOE
nuclear Overhauser effect
- COSY
twodimensional homonuclear J-correlated spectroscopy
- 11-mer
undecamer
- EDTA
sodium ethylenediamine tetraacetate
- HPLC
nigh-pressure liquid chromatography
- DSS
4,4-dimethylsilapentane-1-sulfonate 相似文献
30.
F Zeytin C Mougin P Brazeau N Ling 《Biochemical and biophysical research communications》1984,120(2):540-547
The effects of forskolin and cholera toxin on the regulation of cAMP release were studied in a neurotensin-secreting rat C-cell line. The interaction of these agents with norepinephrine, a potent neurotensin secretagogue, was also investigated. Forskolin stimulated cAMP release 10(2)-10(3) fold while it increased neurotensin release 2-3 fold. Cholera toxin caused a 10(2)-10(3) fold increase in cAMP release and had no effect on neurotensin release. We conclude that the 44-2 C-cells provide a new model for studying the regulation of the concomitant (via forskolin) or independent (via cholera toxin) secretion of cyclic AMP and/or neurotensin. 相似文献