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排序方式: 共有406条查询结果,搜索用时 15 毫秒
1.
2.
High concentrations of exogenous arachidonate inhibit calcium mobilization in platelets by stimulation of adenylate cyclase. 总被引:1,自引:1,他引:0
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1. Exposure of platelets to exogenous arachidonic acid results in aggregation and secretion, which are inhibited at high arachidonate concentrations. The mechanisms for this have not been elucidated fully. In our studies in platelet suspensions, peak aggregation and secretion occurred at 2-5 microM-sodium arachidonate, with complete inhibition around 25 microM. 2. In platelets loaded with quin2 or fura-2, the cytoplasmic Ca2+ concentration, [Ca2+]i, rose in the presence of 1 mM-CaCl2 from 60-80 nM to 300-500 nM at 2-5 microM-arachidonate, followed by inhibition to basal values at 25-50 microM. Thromboxane production was not inhibited at 25 microM-arachidonate. Cyclic AMP increased in the presence of theophylline, from 3.5 pmol/10(8) platelets in unexposed platelets to 8 pmol/10(8) platelets at 50 microM-arachidonate; all platelet responses were inhibited with doubling of cyclic AMP contents. 3. The adenylate cyclase inhibitor 2',5'-dideoxyadenosine attenuated the inhibitory effect of arachidonate, suggesting that it is mediated by increased platelet cyclic AMP and that it is unlikely to be due to irreversible damage to platelets. 4. Aspirin or the combined lipoxygenase/cyclo-oxygenase inhibitor BW 755C did not prevent the inhibition by arachidonate of either [Ca2+]i signals or aggregation induced by U46619. 5. Thus high arachidonate concentrations inhibit Ca2+ mobilization in platelets, and this is mediated by stimulation of adenylate cyclase. High arachidonate concentrations influence platelet responses by modulating intracellular concentrations of two key messenger molecules, cyclic AMP and Ca2+. 相似文献
3.
Chromosome studies have been conducted on the long-term callus cultures of threeAllium species:A. porrum (2n=32),A. tuberosum (2n=32) andA. fistulosum (2n=16). In cultures ofA. fistulosum several interesting cytological abnormalities were observed. They included direct elimination of chromatin from nuclei, multiple chromosome fusions and formation of polycentric and megachromosomes. The rate of abnormalities increased with the time of culture.
Allium fistulosum may provide an excellent model system to analyse cytogenetic and molecular aspects of callus-induced genomic changes and, thus, somaclonal variation. 相似文献
4.
Przybyłowski J Kowalski D Widłak H Kowalska K Maślany P 《Polski tygodnik lekarski (Warsaw, Poland : 1960)》1995,50(1-35):794-796
In 66 patients with peptic ulcer (11 with gastric ulcer, 55 with duodenal ulcer, 19 women, 47 men) the serum concentrations of prolactin, dehydrocholic acid and gastrin were determined. The studies were repeated after treatment with ranitidine: in 50 patients after three weeks and in 40 patients after another 30 days. During the first period ranitidine 2 x 150 mg was administered, while during the second period the dose was 1 x 150 mg. The results were compared with those obtained from 120 healthy subjects. Before starting the treatment prolactin levels were significantly higher than those in the control group. During the treatment a significant decrease of the levels was observed. Similar changes of prolactin concentrations were found in the group of 39 men with duodenal ulcer isolated from the studied patients, who were compared with a group of 50 healthy men. It was not found that the development of peptic ulcer and the treatment with ranitidine exerted and effect on the changes of gastrin and dehydrocholic acid concentrations. 相似文献
5.
M Koter M A Kowalska W Leyko M Waterman 《International journal of radiation biology and related studies in physics, chemistry, and medicine》1977,32(4):369-374
The dependence of the yield of free radicals in gamma-irradiated, freeze-dried erythrocyte membranes on their haemoglobin content was studied. A non-monotonous relationship was found--different from that observed in mixtures of freeze-dried membranes and haemoglobin, which suggests the existence of radiation-energy transfer between the membranes and bound haemoglobin. 相似文献
6.
The effect of neurotensin on submaximally-stimulated hepatobiliary and pancreatic secretion was studied in 6 healthy subjects. An intravenous infusion of neurotensin 1.4 ± 0.3 pmol/kg/min, designed to reproduce plasma neurotensin immunoreactivity levels within the physiological range, produced a significant increase in pancreatic bicarbonate output. Plasma concentrations of pancreatic polypeptide rose by 83 ± 16 pmol/l and were associated with a small reduction in trypsin, but no significant change in bilirubin outputs. 相似文献
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Wei Su Sergey V. Slepenkov Michael K. Slevin Shawn M. Lyons Marcin Ziemniak Joanna Kowalska Edward Darzynkiewicz Jacek Jemielity William F. Marzluff Robert E. Rhoads 《RNA (New York, N.Y.)》2013,19(1):1-16
Metazoan replication-dependent histone mRNAs are only present in S-phase, due partly to changes in their stability. These mRNAs end in a unique stem–loop (SL) that is required for both translation and cell-cycle regulation. Previous studies showed that histone mRNA degradation occurs through both 5′→3′ and 3′→5′ processes, but the relative contributions are not known. The 3′ end of histone mRNA is oligouridylated during its degradation, although it is not known whether this is an essential step. We introduced firefly luciferase reporter mRNAs containing the histone 3′ UTR SL (Luc-SL) and either a normal or hDcp2-resistant cap into S-phase HeLa cells. Both mRNAs were translated, and translation initially protected the mRNAs from degradation, but there was a lag of ∼40 min with the uncleavable cap compared to ∼8 min for the normal cap before rapid decay. Knockdown of hDcp2 resulted in a similar longer lag for Luc-SL containing a normal cap, indicating that 5′→3′ decay is important in this system. Inhibition of DNA replication with hydroxyurea accelerated the degradation of Luc-SL. Knockdown of terminal uridyltransferase (TUTase) 4 but not TUTase 3 slowed the decay process, but TUTase 4 knockdown had no effect on destabilization of the mRNA by hydroxyurea. Both Luc-SL and its 5′ decay intermediates were oligouridylated. Preventing oligouridylation by 3′-deoxyadenosine (cordycepin) addition to the mRNA slowed degradation, in the presence or absence of hydroxyurea, suggesting oligouridylation initiates degradation. The spectrum of oligouridylated fragments suggests the 3′→5′ degradation machinery stalls during initial degradation, whereupon reuridylation occurs. 相似文献
9.
10.
AB Zarafi AM Emechebe AD Akpa O Alabi 《Archives Of Phytopathology And Plant Protection》2013,46(4):261-268
Pearl millet downy mildew (DM) incidence, severity and yield losses of two pearl millet varieties (local and improved) due to the disease were determined in the field. Significant differences in the disease incidence and severity were recorded in the plots sown with metalaxyl-treated seeds and those sown with non-treated seeds, indicating the efficacy of the fungicide on the fungus. Yield losses due to non-treatment of seeds with metalaxyl was 40.88 and 45.39% in a local variety and 43.00 and 18.60% in an improved variety in the 2000 and 2001 cropping seasons respectively. Significant differences between plots sown with metalaxyl-treated and those sown with non-treated seeds were obtained for other yield components such as 1000-grains weight, panicle length and weight. 相似文献