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61.
Åke Berg 《Oecologia》1996,107(3):343-346
Predation rates on artificial wader nests, solitary curlew (Numenius arquata) and lapwing (Vanellus vanellus) nests and lapwing nests in colonies were studied on a farmland site in central Sweden. Predation rates were highest on artificial wader nests, intermediate on solitary curlew and lapwing nests and lowest on lapwing nests in colonies, probably because of active defence of adults at real nests and/or because of selection of nest sites with lower predation risk by breeding birds. A comparison of nests close to (50 m) and far away from (200 m) forest edges revealed no increased predation risk close to edges for any of the studied nest types. Predation risk changed during the season for artificial nests (highest in the middle of May), while predation rates on lapwing and curlew nests were more stable. Artificial nests seem to be inappropriate for measuring actual predation rates and temporal differences in predation rates on real nests, but they might be suitable for use as an index of spatial differences. 相似文献
62.
Zhao Rongrui Wang Wenze Wu Bowei Hoebeke Johan Hjalmarson Åke Fu Michael L. X. 《Molecular and cellular biochemistry》1996,163(1):185-193
The effects of anti-peptide antibodies against the second extracellular loop of human M2 muscarinic receptor on transmembrane potentials and currents in guinea pig single ventricular cells were analyzed using whole-cell patch clamp technique. These effects were compared with those of the muscarinic receptor agonists carbachol and acetylcholine. The antibodies shortened the action potential duration in a dose-dependent manner. By using a ramp or step rectangular pulse protocol, it was found that the antibodies increased the outward K+ current and decreased the inward basal I Ca significantly. The reversal potential of both carbachol-and antibody-induced extra currents were close to –80 mV, being in proximity to the calculated Ek of –90 mV. A -adrenergic receptor agonist, isoprenaline, prolonged the action potential and increased the overshoot which could be inhibited by both antibody and carbachol. Isoprenaline increased inward Ica and outward Ik simultaneously. Both antibody and carbachol could significantly reduce the isoprenaline-stimulated ICa but not the isoprenaline-stimulated Ik. The antibody- or carbachol-induced outward K+ current and the depressant effects of antibody and carbachol on isoprenaline-stimulated Ica were partially antagonized by atropine. These results suggest that the anti-M2 muscarinic receptor antibodies display a stimulatory activity similar to muscarinic receptor agonist on the receptor-mediated electrophysiological events. 相似文献
63.
Margareta Lirvall Pia Ljungqvist-Höddelius Åke Wasteson Karl-Eric Magnùsson 《Bioscience reports》1996,16(3):227-238
Growth factor receptors transmit biological signals for the stimulation of cell growth in vitro and in vivo and their autocrine stimulation may be involved in tumorigenesis. It is therefore, of great value to understand receptor reactions in response to ultraviolet (UV) light which certain normal human cells are invaribly exposed to during their growth cycle. UV irradiation has recently been shown to deplete antioxidant enzymes in human skin. The aims of the present study were a) to compare the lateral mobility of epidermal growth factor receptors (EGF-R) in cultured human keratinocytes and human foreskin fibroblasts, b) to investigate effects of ultraviolet B radiation on the mobility of EGF-R in these cells, and c) study the response of EGF-R on addition of antioxidant enzymes. The epidermal growth factor receptors were labeled with rhodaminated EGF, the lateral diffusion was determined and the fraction of mobile EGF-R assessed with the fluorescence recovery after photobleaching (FRAP). We found that human keratinocytes display a higher basal level of EGF-R mobility than human skin fibroblasts, viz. with diffusion coefficients (D ± standard error of the mean, SEM) of 4.2±0.2 × 10–10 cm2/s, and 1.8±0.2 × 10–10 cm2/s, respectively. UVB-irradiated fibroblasts showed an almost four-fold increase in the diffusion coefficient; D was 6.3±0.3 × 10–10 cm2/s. The keratinocytes, however, displayed no significant increase in receptor diffusion after irradiation; D was 5.1±0.8 × 10–10 cm2/s. In both cell types the percentage of EGF-R fluorescence recovery after photobleaching, i.e. the fraction of mobile receptors, was significantly increased after irradiation. In keratinocytes it increased from 69% before irradiation to 78% after irradiation. Analogous figures for fibroblasts were 61% and 73%. The effect of UVB on fibroblast receptors was abolished by prior addition of superoxide dismutase (SOD) and catalase (CAT). It is concluded that UVB radiation of fibroblasts and keratinocytes can affect their biophysical properties of EGF-R. The finding that addition of antioxidant enzymes prevented the UVB effect in fibroblasts may indicate the involvement of reactive oxygen metabolites.Abbreviations CAT
Catalase
- D
Lateral diffusion coefficient
- EDTA
Ethylenediaminetetraacetic acid
- EGF
Epidermal growth factor
- E-MEM
Eagle's minimum essential medium
- FCS
Fetal calf serum
- FRAP
Fluorescence recovery after photobleaching
- KRG
Krebs-Ringer phosphate buffer
- PBS
Phosphate-buffered saline
- R
Mobile fraction
- ROS
Reactive oxygen species
- SEM
Standard error of the mean
- SOD
Superoxide dismutase
- UVA
Ultraviolet light-A (315-400 nm)
- UVB
Ultraviolet light-B (280-315 nm) 相似文献
64.
65.
A mannose-specific adherence mechanism in Lactobacillus plantarum conferring binding to the human colonic cell line HT-29. 总被引:6,自引:0,他引:6
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I Adlerberth S Ahrne M L Johansson G Molin L A Hanson A E Wold 《Applied microbiology》1996,62(7):2244-2251
Two Lactobacillus plantarum strains of human intestinal origin, strains 299 (= DSM 6595) and 299v (= DSM 9843), have proved to be efficient colonizers of the human intestine under experimental conditions. These strains and 17 other L. plantarum strains were tested for the ability to adhere to cells of the human colonic cell line HT-29.L.plantarum 299 and 299v and nine other L. plantarum strains, including all six strains that belong to the same genetic subgroup as L. plantarum 299 and 299v, adhered to HT-29 cells in a manner that could be inhibited by methyl-alpha-D-mannoside. The ability to adhere to HT-29 cells correlated with an ability to agglutinate cells of Saccharomyces cerevisiae and erythrocytes in a mannose-sensitive manner and with adherence to D-mannose-coated agarose beads. L. plantarum 299 and 299v adhered to freshly isolated human colonic and ileal enterocytes, but the binding was not significantly inhibited by methyl-alpha-D-mannoside. Periodate treatment of HT-29 cells abolished mannose-sensitive adherence, confirming that the cell-bound receptor was of carbohydrate nature. Proteinase K treatment of the bacteria also abolished adherence, indicating that the binding involved protein structures on the bacterial cell surface. Thus, a mannose-specific adhesin has been identified in L. plantarum; this adhesin could be involved in the ability to colonize the intestine. 相似文献
66.
Susann Teneberg Timothy R. Hirst Jonas Ångström Karl-Anders Karlsson 《Glycoconjugate journal》1994,11(6):533-540
The binding specificities of cholera toxin andEscherichia coli heat-labile enterotoxin were investigated by binding of125I-labelled toxins to reference glycosphingolipids separated on thin-layer chromatograms and coated in microtitre wells. The binding of cholera toxin was restricted to the GM1 ganglioside. The heat-labile toxin showed the highest affinity for GM1 but also bound, though less strongly, to the GM2, GD2 and GD1b gangliosides and to the non-acid glycosphingolipids gangliotetraosylceramide and lactoneotetraosylceramide. The infant rabbit small intestine, a model system for diarrhoea induced by the toxins, was shown to contain two receptor-active glycosphingolipids for the heat-labile toxin, GM1 ganglioside and lactoneotetraosylceramide, whereas only the GM1 ganglioside was receptor-active for cholera toxin. Preliminary evidence was obtained, indicating that epithelial cells of human small intestine also contain lactoneotetraosylceramide and similar sequences. By computer-based molecular modelling, lactoneotetraosylceramide was docked into the active site of the heat-labile toxin, using the known crystal structure of the toxin in complex with lactose. Interactions which may explain the relatively high toxin affinity for this receptor were found.Abbreviations CT
cholera toxin
- CT-B
B-subunits of cholera toxin
- LT
Escherichia coli heat-labile enterotoxin
- hLT
humanEscherichia coli heat-labile enterotoxin
- pLT
porcineEscherichia coli heat-labile enterotoxin
- EI
electron ionization 相似文献
67.
Target-specific arrest of mRNA translation by antisense 2'-O-alkyloligoribonucleotides. 总被引:2,自引:1,他引:1
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We describe a novel experimental approach to investigate mRNA translation. Antisense 2'-O-allyl oligoribonucleotides (oligos) efficiently arrest translation of targeted mRNAs in rabbit reticulocyte lysate and wheat germ extract while displaying minimal non-specific effects on translation. Oligo/mRNA-hybrids positioned anywhere within the 5' UTR or the first approximately 20 nucleotides of the open reading frame block cap-dependent translation initiation with high specificity. The thermodynamic stability of hybrids between 2'-O-alkyl oligos and RNA permits translational inhibition with oligos as short as 10 nucleotides. This inhibition is independent of RNase H cleavage or modifications which render the mRNA untranslatable. We show that 2'-O-alkyl oligos can also be employed to interfere with cap-independent internal initiation of translation and to arrest translation elongation. The latter is accomplished by UV-crosslinking of psoralen-tagged 2'-O-methyloligoribonucleotides to the mRNA within the open reading frame. The utility of 2'-O-alkyloligoribonucleotides to arrest translation from defined positions within an mRNA provides new approaches to investigate mRNA translation. 相似文献
68.
Tetrasomy 15q: two marker chromosomes with no detectable alpha-satellite DNA. 总被引:8,自引:3,他引:5
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E. Blennow H. Telenius D. de Vos C. Larsson P. Henriksson O. Johansson N. P. Carter M. Nordenskjld 《American journal of human genetics》1994,54(5):877-883
Two patients with specific and similar phenotypes were both found to have an unusual marker chromosome present in 70%-80% of their lymphocytes at routine cytogenetic examination. The marker chromosomes were isolated by flow sorting and were amplified by degenerate oligonucleotide-primed PCR. These libraries and a cosmid probe located at 15q26 were used to characterize the marker chromosomes by FISH. Both marker chromosomes were found to consist of duplicated chromosome material from the distal part of chromosome 15q and were identified as inv dup(15) (qter-->q23::q23-->qter) and inv dup(15) (qter-->q24::q24-->qter), respectively. Hence, the markers did not include any known centromere region, and no alpha-satellite DNA could be detected at the site of the primary constriction. Tetrasomy 15q may be a new syndrome, associated with a specific type of marker chromosome. In addition, further analyses of this type of marker chromosome might give new insight into the structure and function of the mammalian centromere. 相似文献
69.
A Primary Linkage Map of the Porcine Genome Reveals a Low Rate of Genetic Recombination 总被引:12,自引:0,他引:12
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H. Ellegren B. P. Chowdhary M. Johansson L. Marklund M. Fredholm I. Gustavsson L. Andersson 《Genetics》1994,137(4):1089-1100
A comprehensive genetic linkage map of the porcine genome has been developed by typing 128 genetic markers in a cross between the European Wild Boar and a domestic breed (Large White). The marker set includes 68 polymerase chain reaction-formatted microsatellites, 60 anchored reference markers informative for comparative mapping and 47 markers which have been physically assigned by in situ hybridization. Novel multipoint assignments are provided for 54 of the markers. The map covers about 1800 cM, and the average spacing between markers is 11 cM. We used the map data to estimate the genome size in pigs, thereby addressing the total recombination distance in a third mammalian species. A sex-average genome length of 1873 +/- 139 cM was obtained by comparing the recombinational and physical distances in defined regions of the genome. This is strikingly different from the length of the human genome (3800-4000 cM) and is more similar to the mouse estimate (1600 cM). The recombination rate in females was significantly higher than in males. 相似文献
70.
Ulf Dittmer Wolfgang Lüke Christiane Stahl-Hennig Cheick Coulibaly Harald Petry Walter Bodemer Gerhard Hunsmann Gerald Voss 《Journal of medical primatology》1994,23(5):298-303
Both naive and vaccinated macaques acquired a virus-specific proliferative helper T-cell reactivity in response to infection with the nonpathogenic human immunodeficiency virus type 2 (HIV-2). In contrast, macaques infected with the pathogenic simian immunodeficiency virus of the macaque strain (SIVmac) did not develop a helper T-cell response. Furthermore, a vaccine-induced preexisting T-cell reactivity was abrogated after SIVmac infection in vaccine failures. These differences may reflect the different pathogenicity of the two closely related viruses. 相似文献