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排序方式: 共有194条查询结果,搜索用时 15 毫秒
1.
Patchiness and composition of coral reef demersal zooplankton 总被引:1,自引:0,他引:1
Zooplankton samples were collected weekly for a full year withdemersal traps on a coral reef off the west coast of Barbados.There was a marked temporal variability in weekly catches bothin terms of abundance and biomass. Patchiness occurred at allsampling frequencies from 2 to 26 weeks, but spectral analysisindicated a variance shift at a frequency of 810 weeksAggregations of the two most abundant taxa, the copepoditesand the microzooplankton, occurred at 812 week intervalsand significant differences in abundance and biomass were foundbetween mean bimonthly zooplankton catches Lagged cross-correlationsat 7 and 11 weeks between chlorophyll and microzooplankton andcopepodites suggest that aggregations are connected to cyclesof primary production. There was a negative correlation betweenzooplankton abundance and surface water salinity in 8 of 16taxa Copepods were the most abundant taxon overall. Microzooplanktonand copepodites comprised 96% of the abundance and 66% of thebiomass Decreases in taxonomic richness and in diversity wereassociated with patchiness of small-sized copepodites and microzooplankton,suggesting that composition was altered and stability temporarilylessened during peaks of abundance 相似文献
2.
Activity and secretion of sialyltransferase in primary monolayer cultures of rat hepatocytes cultured with and without dexamethasone 总被引:1,自引:0,他引:1
W van Dijk W Boers M Sala A M Lasthuis S Mookerjea 《Biochimie et biologie cellulaire》1986,64(2):79-84
Monolayers of hepatocytes attached on collagen-coated dishes were cultured for 20-24 h and were found suitable to study the activity and secretion of CMP-N-acetylneuraminate:asialo-alpha 1-acid glycoprotein sialyltransferase. A progressive increase of sialyltransferase activity in the culture medium was observed during incubation of the hepatocytes. After 24 h 34-48% of the total sialyltransferase activity of the hepatocyte incubation system was present in the medium. The enzyme activity present in the medium was soluble in nature and could not be stimulated by Triton X-100. The secretion of the enzyme was stimulated about twofold by dexamethasone. The activity of sialyltransferase in the hepatocytes was also increased by dexamethasone. The Km of either hepatocyte or medium sialyltransferase for CMP-sialic acid was only slightly changed by dexamethasone, whereas the Vmax was increased about twofold. The secretion of sialyltransferase could be inhibited partially by the anti-microtubular agent colchicine. The dexamethasone-induced increase of the sialyltransferase activity in cells and media could be eliminated by inclusion of alpha-amanitin in the culture media at 0 h. The inhibiting effect of alpha-amanitin was only partially expressed when the drug was added 4 h after the addition of dexamethasone to the media. The results suggest that isolated rat hepatocytes actively secrete sialyltransferase and that the increase in the sialyltransferase activity in cells and media owing to the synthetic glucocorticosteroid dexamethasone results from increased synthesis of the enzyme molecule. It is supposed that in the intact rat the increased levels of the enzyme activity in serum observed in inflammation may originate from an induction of the synthesis of sialyltransferase in the hepatocytes of rat liver by the increased levels of circulating corticosteroids. 相似文献
3.
A new technique to reduce internal phosphorus loading by in-lake phosphate fixation in shallow lakes 总被引:3,自引:0,他引:3
A new, flexible, fast, robust and economic technique was developed to treat sediment in shallow lakes with phosphate binding chemicals. The upper 0.15 m of the sediment is thoroughly mixed with ferric chloride using a water-jet manifold coupled to a dosing pump and a navigation control system. Its logistics were tried out in a small, shallow and hypertrophic peat lake, Lake Groot Vogelenzang. 相似文献
4.
J. R. Cruysberg G. H. Boers J. M. Trijbels A. F. Deutman 《BMJ (Clinical research ed.)》1996,313(7064):1037-1040
OBJECTIVE: To assess the causes for delay in the diagnosis of homocystinuria. DESIGN: Clinical and laboratory data were collected from patients diagnosed as having homocystinuria due to cystathionine synthase deficiency, with special reference to the ages at which the patients had their first major signs of the disease, ectopia lentis was established, and homocystinuria was diagnosed. SETTING: University hospital in the Netherlands. SUBJECTS: 34 patients (18 males) in whom homocystinuria due to cystathionine synthase deficiency was diagnosed in the period 1970-94. RESULTS: Among 34 consecutively detected homocystinuria patients the mean age at diagnosis of homocystinuria was 24 (range 1-61) years. Despite frequent ocular manifestations, serious complications in the vascular, skeletal, and central nervous systems, and repeated examinations performed in these patients by clinicians of various disciplines, there was a mean delay of 11 (0-43) years between the first major signs of the disease (at mean age 13 (1-40) years) and the ultimate diagnosis of homocystinuria. Even when ectopia lentis was diagnosed (in 26 (76%) patients, mean age 18 (1-50) years), this did not lead to adequate biochemical analysis for homocystinuria at the time of detection, causing a mean diagnostic delay of 8 (0-24) years in these patients. CONCLUSIONS: Three factors should have precipitated the diagnosis of homocystinuria: early recognition that unusual myopia (high, very high, abnormal progressive, or at young age) was caused by subluxation of the ocular lenses; awareness that the occurrence of myopia combined with systemic complications ("myopia plus") might be due to homocystinuria; and appropriate biochemical investigations carried out in patients with ectopia lentis and in their siblings. 相似文献
5.
6.
The changes in germination, peroxidase activity and isoperoxidase spectrum have been studied in apple embryos at 5°C (stratification) and at 20°C in the presence or absence of seed coats. The embryo dormancy is progressively released at 5°C, but not at 20°C. The peroxidase activity in embryos covered with seed coats is very low at 5°C as well as at 20°C which corresponds to a restricted number of isoenzymes. In isolated embryos the peroxidase activity increases significantly. This is due to an increase in both the number and the activity of the isoperoxidases and it is more pronounced at 20°C than at 5°C. The obtained results suggest that the soluble peroxidases are not involved in the process of the release of embryo dormancy. The variations observed are attributed to the growth process following germination, which can occur even at low temperature. 相似文献
7.
AB Kane RP Stanton EG Raymond ME Dobson ME Knafelc JL Farber 《The Journal of cell biology》1980,87(3):643-651
The relationship between intracellular lysosomal rupture and cell death caused by silica was studied in P388d(1) macrophages. After 3 h of exposure to 150 μg silica in medium containing 1.8 mM Ca(2+), 60 percent of the cells were unable to exclude trypan blue. In the absence of extracellular Ca(2+), however, all of the cells remained viable. Phagocytosis of silica particles occurred to the same extent in the presence or absence of Ca(2+). The percentage of P388D(1) cells killed by silica depended on the dose and the concentration of Ca(2+) in the medium. Intracellular lyosomal rupture after exposure to silica was measured by acridine orange fluorescence or histochemical assay of horseradish peroxidase. With either assay, 60 percent of the cells exposed to 150 μg silica for 3 h in the presence of Ca(2+) showed intracellular lysosomal rupture, was not associated with measureable degradation of total DNA, RNA, protein, or phospholipids or accelerated turnover of exogenous horseradish peroxidase. Pretreatment with promethazine (20 μg/ml) protected 80 percent of P388D(1) macrophages against silica toxicity although lysosomal rupture occurred in 60-70 percent of the cells. Intracellular lysosomal rupture was prevented in 80 percent of the cells by pretreatment with indomethacin (5 x 10(-5)M), yet 40-50 percent of the cells died after 3 h of exposure to 150 μg silica in 1.8 mM extracellular Ca(2+). The calcium ionophore A23187 also caused intracellular lysosomal rupture in 90-98 percent of the cells treated for 1 h in either the presence or absence of extracellular Ca(2+). With the addition of 1.8 mM Ca(2+), 80 percent of the cells was killed after 3 h, whereas all of the cells remained viable in the absence of Ca(2+). These experiments suggest that intracellular lysosomal rupture is not causally related to the cell death cause by silica or . Cell death is dependent on extracellular Ca(2+) and may be mediated by an influx of these ions across the plasma membrane permeability barrier damaged directly by exposure to these toxins. A23187相似文献
8.
A covalently bound photoisomerizable agonist. Comparison with reversibly bound agonists at electrophorus electroplaques 总被引:2,自引:2,他引:0
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HA Lester ME Krouse MM Nass NH Wassermann BF Erlanger 《The Journal of general physiology》1980,75(2):207-232
After disulphide bonds are reduced with dithiothreitol, trans-3- (α-bromomethyl)-3’-[α- (trimethylammonium)methyl]azobenzene (trans-QBr) alkylates a sulfhydryl group on receptors. The membrane conductance induced by this “tethered agonist” shares many properties with that induced by reversible agonists. Equilibrium conductance increases as the membrane potential is made more negative; the voltage sensitivity resembles that seen with 50 [mu]M carbachol. Voltage- jump relaxations follow an exponential time-course; the rate constants are about twice as large as those seen with 50 μM carbachol and have the same voltage and temperature sensitivity. With reversible agonists, the rate of channel opening increases with the frequency of agonist-receptor collisions: with tethered trans-Qbr, this rate depends only on intramolecular events. In comparison to the conductance induced by reversible agonists, the QBr-induced conductance is at least 10-fold less sensitive to competitive blockade by tubocurarine and roughly as sensitive to “open-channel blockade” bu QX-222. Light-flash experiments with tethered QBr resemble those with the reversible photoisomerizable agonist, 3,3’,bis-[α-(trimethylammonium)methyl]azobenzene (Bis-Q): the conductance is increased by cis {arrow} trans photoisomerizations and decreased by trans {arrow} cis photoisomerizations. As with Bis-Q, ligh-flash relaxations have the same rate constant as voltage-jump relaxations. Receptors with tethered trans isomer. By comparing the agonist-induced conductance with the cis/tans ratio, we conclude that each channel’s activation is determined by the configuration of a single tethered QBr molecule. The QBr-induced conductance shows slow decreases (time constant, several hundred milliseconds), which can be partially reversed by flashes. The similarities suggest that the same rate-limiting step governs the opening and closing of channels for both reversible and tethered agonists. Therefore, this step is probably not the initial encounter between agonist and receptor molecules. 相似文献
9.
Owing to its lipophilic property, carbon tetrachloride (CCl4) is rapidly absorbed by both the liver and brain. We investigated the protective effects of crocin against brain damage caused by CCl4. Fifty rats were divided into five groups of ten: control, corn oil, crocin, CCl4 and CCl4 + crocin. CCl4 administration decreased glutathione (GSH) and total antioxidant status (TAS) levels, and catalase (CAT) activity, while significant increases were observed in malondialdehyde (MDA) and total oxidant status (TOS) levels and superoxide dismutase (SOD) activity. The cerebral cortex nuclear lamina developed a spongy appearance, neuronal degeneration was observed in the hippocampus, and heterochromatic and pyknotic neurons with increased cytoplasmic eosinophilia were observed in the hippocampus after CCl4 treatment. Because crocin exhibits strong antioxidant properties, crocin treatment increased GSH and TAS levels and CAT activities, and decreased MDA and TOS levels and SOD activity; significant improvements also were observed in histologic architecture. We found that crocin administration nearly eliminated CCl4 induced brain damage by preventing oxidative stress. 相似文献
10.
Danilo ML Prado Fabiana B Benatti Ana L de Sá-Pinto Ana P Hayashi Bruno Gualano Rosa MR Pereira Adriana ME Sallum Eloisa Bonfá Clovis A Silva Hamilton Roschel 《Arthritis research & therapy》2013,15(2):R46