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排序方式: 共有210条查询结果,搜索用时 31 毫秒
51.
We assessed effects of groundwater pumping to elevate lake levels on lake water chemistry and fish population metrics at seven
Florida lakes. Following groundwater pumping, lake level fluctuation was reduced and lake water samples increased in mean
pH, total alkalinity, total phosphorus, chloride and Secchi depth compared to historical means, indicating a close resemblance
to the chemistry of aquifer water in the region. Fish community metrics from the augmented lakes were compared to 36 non-augmented
lakes in Florida. The mean values for catch per unit effort, species richness and biomass of harvestable fishes, determined
by electrofishing, were lower in augmented lakes compared to non-augmented lakes. Canonical correspondence analysis (CCA)
indicated a high probability of a low abundance of individual species in augmented lakes compared to a majority of non-augmented
lakes. The augmented lake with the lowest pumping rate exhibited less of a shift in limnological variables from historical
values, and had fish population characteristics more closely resembling those of non-augmented lakes. Thus, reduced volumes
of groundwater introduction could lower impacts to limnological and fish population characteristics. Augmentation allows for
lakes to be utilized for recreational activities, and without augmentation some lakes in central Florida would likely go dry
due to groundwater withdrawals for water supply. Therefore, allowing more natural water level fluctuations and possible reductions
in total pumpage are recommended to reduce impacts to limnological and fish population characteristics, while still allowing
sufficient groundwater pumping to preserve lake habitats. 相似文献
52.
Jun Pu Anthony F. Kreft Suzan H. Aschmies Kevin P. Atchison Joshua Berkowitz Thomas J. Caggiano Micheal Chlenov George Diamantidis Boyd L. Harrison Yun Hu Donna Huryn J. Steven Jacobsen Mei Jin Kerri Lipinski Peimin Lu Robert L. Martone Koi Morris June Sonnenberg-Reines Dave R. Riddell Joan Sabalski Lynn Resnick 《Bioorganic & medicinal chemistry》2009,17(13):4708-4717
γ-Secretase inhibitors have been shown to reduce the production of β-amyloid, a component of the plaques that are found in brains of patients with Alzheimer’s disease. A novel series of heterocyclic sulfonamide γ-secretase inhibitors that reduce β-amyloid levels in cells is reported. Several examples of compounds within this series demonstrate a higher propensity to inhibit the processing of amyloid precursor protein compared to Notch, an alternative γ-secretase substrate. 相似文献
53.
An inbred 129SvEv GFPCre transgenic mouse that deletes loxP-flanked genes in all tissues 总被引:3,自引:0,他引:3
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Scheel JR Garrett LJ Allen DM Carter TA Randolph-Moore L Gambello MJ Gage FH Wynshaw-Boris A Barlow C 《Nucleic acids research》2003,31(10):e57
A common method for generating mice with subtle genetic manipulations uses homologous recombination (HR) in embryonic stem (ES) cells to replace a wild-type gene with a slightly modified one. Generally, a drug resistance gene is inserted with the modified gene to select correctly targeted clones. Often, however, the presence of this drug resistance gene interferes with the normal locus and creates a null or hypomorphic allele. Flanking of the selectable marker by loxP sites followed by Cre-mediated deletion after drug selection can overcome this problem. The simplest method used to remove a loxP-flanked selectable marker is to breed an animal carrying a loxP-flanked drug resistance gene to an animal that expresses Cre recombinase in the germline. To date only outbred transgenic mice are available for this purpose. This can be problematic for phenotypic analysis in many organ systems, including the brain, and for the analysis of behavior. While attempting to make 129S6/SvEvTac inbred background (isogenic to our ES cells) mice that express Cre under the control of several tissue-specific promoters, we serendipitously generated a line that excises loxP-flanked drug resistance genes in all tissues, including the germline. This reagent allows deletion of loxP-flanked sequences while maintaining the mutation on an inbred background. 相似文献
54.
55.
Cardiomyocyte-specific endothelin A receptor knockout mice have normal cardiac function and an unaltered hypertrophic response to angiotensin II and isoproterenol
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Kedzierski RM Grayburn PA Kisanuki YY Williams CS Hammer RE Richardson JA Schneider MD Yanagisawa M 《Molecular and cellular biology》2003,23(22):8226-8232
Even though endothelin is recognized as an important vasoregulatory molecule, the roles of endothelin receptors in specific cell types are not yet fully understood. Mice with a null mutation in endothelin A receptor gene (ET(A)) or in the gene of its ligand (endothelin 1) die neonatally due to craniofacial and cardiac abnormalities. This early lethality has in the past hindered studies on the role of endothelin in cardiovascular physiology and pathophysiology. To overcome this obstacle, we utilized the cre/loxP technology to generate mice in which the ET(A) gene could be deleted specifically in cardiomyocytes. The cre recombinase transgene driven by the alpha-myosin heavy-chain promoter deleted the floxed ET(A) allele specifically in the hearts of these mice, resulting in a 78% reduction in cardiac ET(A) mRNA level compared to wild-type controls. Cardiomyocyte-specific ET(A) knockout animals are viable and exhibit normal growth, cardiac anatomy, and cardiac contractility, as assessed by echocardiography. In addition, these animals exhibit hypertrophic and contractile responses to 10-day infusion of angiotensin II or isoproterenol similar to those observed in control animals. These results indicate that in adult mice cardiac ET(A) receptors are not necessary for either baseline cardiac function or stress-induced response to angiotensin II or isoproterenol. 相似文献
56.
Zhang W Loughran MG Kanna S Yano K Ikebukuro K Yokobayashi Y Kuroda R Karube I 《Proteins》2003,53(2):193-200
A genetic algorithm (GA)-based strategy to dissect the determinants of peptide folding into alpha-helix was developed. The structural information of helical peptides was obtained with respect to patterns of sequence variability. In many previously reported studies the intrinsic alpha-helical propensities of amino acids although sequence-dependent are apparently independent of the amino acid position. In this research, monomeric helical peptides selected from possible sequences produced by a GA-chemical synthesis were analyzed to identify possible influential structural features. These hexadeca-peptides were obtained after four successive generations. A total of 128 synthetic peptides were evaluated via circular dichroism (CD) measurements in aqueous solution, while the mean ellipticity at 222 nm confirmed the monomeric state of the peptides. The results presented here show that our GA-based strategy may be useful in the design of proteins with increased alpha-helix content. 相似文献
57.
Gaul MD Guo Y Affleck K Cockerill GS Gilmer TM Griffin RJ Guntrip S Keith BR Knight WB Mullin RJ Murray DM Rusnak DW Smith K Tadepalli S Wood ER Lackey K 《Bioorganic & medicinal chemistry letters》2003,13(4):637-640
We have identified a novel class of 6-thiazolylquinazolines as potent and selective inhibitors of both ErbB-2 and EGFR tyrosine kinase activity, with IC(50) values in the nanomolar range. These compounds inhibited the growth of both EGFR (HN5) and ErbB-2 (BT474) over-expressing human tumor cell lines in vitro. Using xenograft models of the same cell lines, we found that the compounds given orally inhibited in vivo tumor growth significantly compared with control animals. 相似文献
58.
Lee HG Zhu X Ghanbari HA Ogawa O Raina AK O'Neill MJ Perry G Smith MA 《Neuro-Signals》2002,11(5):282-292
Selective neurodegeneration is a prominent feature in Alzheimer's disease; however, the mechanism of neuronal death is still unclear. Nonetheless, the topographical distribution of different types of receptors is thought to contribute to the regional selective nature of neuronal degeneration. Specifically, since glutamatergic transmission is severely altered by the early degeneration of cortico-cortical connections and hippocampal projections in Alzheimer's disease, we suspect that glutamate receptors may play a new role in the pathophysiology of disease. Here we review the salient aspects of glutamate receptor expression in Alzheimer's disease and how their differential regulation can contribute to the selective neurodegeneration seen in the disease. Additionally, we assess the potential therapeutic value of glutamate receptors as a target for drug intervention in Alzheimer's disease. 相似文献
59.
活细胞染色体切割(光刀)和光捕捉(光钳)的研究 总被引:1,自引:0,他引:1
本文报道了光捕捉活细胞染色体的最新实验结果。对PTK_2有丝分裂细胞的染色体先围激光刀切割,再用光钳捕捉使该切割的染色体片断的行为发生改变。光捕捉中期切割的染色体片断有可能使它们整合到同一个子细胞中或丢失在分裂沟中。光捕捉后期切割的染色体可使该切割片断或掺入相反的细胞中或丢失在分裂沟中或回到原有的相应子细胞中。光捕捉操纵染色体去水螈肺上支子细胞中不仅同样有效,还可以在纺缍体的边缘,即纺缍体和间丝笼之间的细胞质清澈区域内用光钳操纵染色体片断移动,旋转。根据细胞和染色体形态和行为,对700-840nm波长范围内的各种波长的光捕捉进行了比较,结果表明,700nm或800-820nm波长操纵的细胞,出现最少的异常细胞百分率,760nm则诱发百分之百的异常细胞率。根据各方面的综合比较,700nm为最佳波长,共次为1060和800nm。760nm损伤细胞最严重,应避免使用。文中并讨论了光捕捉染色体的应用前景。 相似文献
60.
Phil Skolnick Kathleen Boje Rachel Miller Micheal Pennington Maria-Luisa Maccecchini 《Journal of neurochemistry》1992,59(4):1516-1521
Conantokins T and G are polypeptide toxins present in snails of the genus Conus. These substances were recently reported to act as N-methyl-D-aspartate (NMDA) antagonists. In the present study, we examined the possible mechanisms producing this antagonism. Conantokin-G inhibited spermine- and spermidine-stimulated [3H]MK-801 binding to extensively washed rat forebrain membranes in a noncompetitive manner with IC50 values of approximately 507 and approximately 946 nM, respectively. In contrast, glutamate-enhanced [3H]MK-801 binding was unaffected by conantokin-G concentrations of less than or equal to 20 microM. At concentrations greater than or equal to 5 microM, conantokin-G effected a modest, noncompetitive inhibition of glycine-stimulated [3H]MK-801 binding and also produced a small enhancement of basal [3H]MK-801 binding. Conantokin-G reduced (IC50 approximately 1.08 microM) the NMDA-stimulated accumulation of cyclic GMP in cerebellar granule cell cultures to basal values, but did not affect kainate-mediated increases in cyclic GMP. These findings indicate that conantokin-G acts as a noncompetitive NMDA antagonist through an allosteric inhibition of polyamine responses. The neurochemical profile of this polypeptide is distinct from previously described noncompetitive NMDA antagonists. 相似文献