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  • 1
    Book
    Book
    Berlin [u.a.] : Springer
    Type of Medium: Book
    Pages: XV, 376 S. , graph. Darst. , 235 mm x 155 mm
    ISBN: 3540330852 , 9783540330851
    RVK:
    RVK:
    Language: English
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    The journal of membrane biology 98 (1987), S. 79-87 
    ISSN: 1432-1424
    Keywords: Na+−K+ pump ; Na+−K+ cotransport ; Na+/Li+ exchange ; Ca depletion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary To study the possible role of intracellular Ca (Ca i ) in controlling the activities of the Na+−K+ pump, the Na+−K+ cotransport and the Na+/Li+ exchange system of human erythrocytes, a method was developed to measure the amount of Ca embodied within the red cell. For complete removal of Ca associated with the outer aspect of the membrane, it proved to be essential to wash the cells in buffers containing less than 20nm Ca. Ca was extracted by HClO4 in Teflon® vessels boiled in acid to avoid Ca contaminations and quantitated by flameless atomic absorption. Ca i of fresh human erythrocytes of apparently healthy donors ranged between 0.9 and 2.8 μmol/liter cells. The mean value found in females was significantly higher than in males. The interindividual different Ca contents remained constant over periods of more than one year. Sixty to 90% of Ca i could be removed by incubation of the cells with A23187 and EGTA. The activities of the Na+−K+ pump, of Na+−K+ cotransport and Na+/Li+ exchange and the mean cellular hemoglobin content fell with rising Ca i ; the red cell Na+ and K+ contents rose with Ca i . Ca depletion by A23187 plus EGTA as well as chelation of intracellular Ca2+ by quin-2 did not significantly enhance the transport rates. It is concluded that the large scatter of the values of Ca i of normal human erythrocytes reported in the literature mainly results from a widely differing removal of Ca associated with the outer aspect of the membrane.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    The journal of membrane biology 122 (1991), S. 231-238 
    ISSN: 1432-1424
    Keywords: transport ; membrane ; lipid-protein interactions ; essential hypertension ; inner and outer monolayer
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The effects of cholesterol loading and depletion and of a 10% replacement of native phosphatidylcholine by dipalmitoyl phosphatidylcholine (di 16:0-PC) on kinetic properties of human red cell Na−Li exchange have been studied. Compared to control erythrocytes (cholesterol/phospholipid ratio (C/P=0.8–0.9)),V max of phloretin-sensitive Li uptake and of Li efflux stimulated by extracellular Na (Na o ) were reduced by 15–30% in cholesterol-loaded red cells (C/P=1.05–1.33). The apparentK m values for external Li (Li o ) and for internal Li (Li i ) were decreased by about one-third in these cells. Cholesterol depletion (C/P=0.7) exerted opposite effects on the kinetics of Na o -dependent Li efflux. On augmentingC/P from 0.66 to 1.0,V max of Na o -dependent Li efflux was reduced by about 30%; increasingC/P above 1.0 caused no further lowering ofV max. Li leakage rates monotonically decreased over the whole range ofC/P ratios examined (0.66–1.3). This indicates that Na−Li exchange and Li leak are differentially affected by cholesterol. Incorporation of di 16:0-PC (replacement of 3% of total red cell phospholipids) caused similar kinetic alterations of Na−Li exchange as a rise in membrane cholesterol by 20–50%. Notably, selective incorporation of di 16:0-PC into the outer monolayer increased both intra- and extracellular Li binding affinities of Na−Li exchange and lowered its maximum velocity. Thus, both di 16:0-PC enrichment and cholesterol loading exerted an uncompetitive type of transport inhibition. The results are in agreement with the hypothesis that the kinetic alterations of red cell Na−Li exchange seen in a subgroup of essential hypertensive patients could be due to subtle changes in the molecular species composition of individual phospholipids.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    The journal of membrane biology 133 (1993), S. 99-106 
    ISSN: 1432-1424
    Keywords: red blood cells ; Na+-Li+ countertransport ; diacyl-phosphatidylcholine ; diacyl-phosphatidylethanolamine ; alkenylacyl-phosphatidylethanolamine ; phosphatidylcholine-specific transfer-protein
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Previous studies indicate a particular sensitivity of red blood cell Na+-Li+ countertransport activity to small variations in the fatty acid composition of membrane phospholipids. To assess whether the interindividual variability of Na+-Li+ countertransport is related to differences in the species pattern of erythrocyte phosphatidylcholine (PC) and phosphatidylethanolamine (PE) in vivo, the molecular species composition of PC and PE as well as the kinetics of Na+-Li+ countertransport were analyzed in parallel in normo- and hyperlipidemic donors. Both in diacyl PC and in diacyl-PE the species 16∶0/20∶4 and 16∶0/18∶2 were, respectively, positively and negatively related to the apparent maximal velocity of Na+-Li+ countertransport. The sum of all species with 20∶4 at sn2 of diacyl-PE exhibited a strong positive (r = 0.82, 2p 〈 0.001), and those containing 18∶2 a negative correlation (r = −0.63, 2p 〈 0.01) to the transport activity. Essentially similar connections were observed between these species and the apparent affinity of the transport system for intracellular Na+. To evaluate whether the associations between molecular species of membrane phospholipids and Na+-Li+ countertransport activity were indicative of a causal relationship, the species 16∶0/20∶4-PC and 16∶0/18∶2-PC were selectively introduced into the erythrocyte membrane by means of the PC-specific transfer protein. Replacement of 11% of native PC by 16∶0/18∶2-PC inhibited the transport rate by about 25%. Exchange of 6 and 9% of PC with 16∶0/20∶4-PC, in contrast, accelerated the transport rate by 30 and 60%, respectively. The accordance between the in vivo relations and the results of the in vitro modification strongly suggests that elevations and reductions in the arachidonic acid and linoleic acid content of membrane PC and PE contribute to the interindividual variability of red blood cell Na+-Li+ counter-transport activity and its acceleration in hyperlipidemias.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Pflügers Archiv 421 (1992), S. 497-502 
    ISSN: 1432-2013
    Keywords: Reversed Na+/Ca2+ exchange ; 22Na+ efflux ; Quin-2-loaded cells
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract To examine the functional significance of epidermal growth factor (EGF) binding sites present on the human erythrocyte membrane [Engelmann et al. (1992) Am J Hematol 39:239–241], the effect of EGF on 45Ca2+ uptake and on 22Na+ efflux from these cells has been studied. In all cases media contained 1.25 mM Ca2+, whereas Na+ and K+ were varied. In 140 mM Na+/5 mM K+ medium EGF (250 ng/ml) stimulated 45Ca2+ uptake by 50%–90% in quin-2-loaded cells, and by up to threefold in untreated cells. Increasing extracellular K+ up to 75 mM at the expense of extracellular Na2+ stimulated the EGF-induced 45Ca2+ uptake by about twofold compared to 145 mM Na+ medium both in quin-2-loaded and in untreated cells. In 145 mM K+ medium, however, no EGF-induced 45Ca2+ uptake was detectable in quin-2-loaded cells, while in untreated cells Ca2+ entry was stimulated twofold by EGF. After increasing intracellular Na+ from 6 mmol/l cells to 18 mmol/l cells in untreated cells suspended in 145 mM K+ medium, 45Ca2+ uptake induced by EGF gradually increased. In contrast, in 140 mM Na+/5 mM K+ as well as in 70 mM Na+/75 mM K+ medium, 45Ca2+ uptake accelerated by EGF was largely unaffected by a modified red cell Na+ content. When 22Na-loaded untreated red cells were suspended in 145 mM K+ medium EGF stimulated red cell 22Na+ efflux by more than threefold. In 140 mM Na+/5 mM K+ as well as in 70 mM Na+/75 mM K+ medium, no 22Na+ efflux induced by the growth factor was evident. The results are consistent with the idea that EGF stimulates (at least) two components of 45Ca2+ uptake in human erythrocytes. One of the two is unmasked in 145 mM K+ medium, inhibited by quin-2 loading, accelerated by intracellular Na+ and appears to involve reversed Na+/Ca2+ exchange.
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Cell Biochemistry and Function 11 (1993), S. 225-230 
    ISSN: 0263-6484
    Keywords: Electrophoresis ; endothelia ; glycoproteins ; lectins ; smooth muscle cells ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Endothelial and smooth muscle cells were isolated from porcine aorta and kept in short-term culture. To determine the terminal carbohydate composition of the plasma membranes from both cell populations, the cells were incubated with a panel of fluorescein-labelled lectins. Both cell populations shared a number of terminal carbohydrates, but the N-galactosamine specific lectin Wistaria floribunda agglutinin labelled only the endothelial cells. A lectin which selectively labelled smooth muscle cells was not found. Western blot analysis of isolated endothelial cell membrane glycoproteins indicated that most membrane glycoproteins are labelled by Wistaria floribunda agglutinin.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 143 (1990), S. 357-363 
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The uptake of chlortetracycline (CTC) and the nature of the fluorescence of CTC was studied in intact human erythrocytes from apparently healthy donors. The uptake of CTC at 22°C proceeded with a t½ of about 3 min, and after 15 min a stable equilibrium was achieved with an intracellular accumulation by a factor of 5-6 relative to the medium concentration. The accumulation did not change in the range of CTC concentrations tested (20-500 μM). The Ca specificity of the CTC fluorescence spectrum was confirmed by Ca depletion of red cells using A23187 in the presence of EGTA and 0.2 mM Mg. This procedure decreased the total intracellular calcium content by about 70% and reduced the fluorescence intensity to one-fourth. Fluorescence microscopy of red cells incubated with 100 μM CTC at 22°C showed that the fluorescence originated mainly from the red cell membrane. In addition, in about 15% of erythrocytes one or more fluorescent dots (diameter 〉0.2 〈1μm) were detected. The fluorescence of the dots and membranes was related to calcium, as evidenced by the reduction of their intensity in Ca depleted cells. The number of erythrocytes with fluorescent dots and the frequency of the dots per cell was largely unaffected by lowering the incubation temperature to 0°C, indicating that the dots most probably do not represent endocytotic artifacts induced by CTC. The number of dots was increased in erythrocytes preincubated with primaquine, demonstrating that CTC fluorescence can be applied to monitor the appearance of intracellular Ca storing vesicles. It is concluded that in (at least) 15% of erythrocytes obtained from apparently healthy donors intracellular vesicles containing Ca can be detected by CTC fluorescence microscopy.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 157 (1993), S. 403-407 
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The blood group antigen H (blood group O) and fucose-specific lectin Ulex europaeus agglutinin I (UEA1) (10 μg/ml) was found to increase the rate constant of CL- efflux into 100mM Na+ oxalate media by about 40% in erythrocytes taken from antigen H donors. In 100 mMK + oxalate, 150 mM Na+ pyruvate and in 150 mM Na+ acetate media the lectin elevated the rate constant of CL- efflux by 20-50%. The acceleration of Cl- efflux by UEA1 was completely blocked by 10 μM 4,4′-dllsothiocyanato-stilbene-2,2′-disulfonic acid (DIDS) indicating that the effect of the lectin is mediated by the anion exchanger of human erythrocytes (band 3 protein). In antigen A1 erythrocytes no significant stimulation of anion exchange by UEA1 was seen. The activation of Cl- efflux was completely prevented by addition of 1 mM fucose to the medium. These results suggest that the effect of UEA1 is mediated through interaction with the fucose residues of H antigens. Increasing extracellular Ca++ from 0.5 to 5 mM in Na + pyruvate or Na+ acetate media slightly reduced the acceleration of anion exchange by the lectin. On the other hand, replacing part of extracellular chloride by bicarbonate did not considerably alter the (previously reported) stimulatory effect of UEA1 on red blood cell Ca++ uptake. This suggests that the acceleration of anion exchange and of Ca++ uptake by UEA1, respectively, are mediated by different mechanisms. It is concluded that UEA1 activates anion exchange of human erythrocytes most probably by a direct interaction with H antigens present on extracellular domains of the band 3 protein. © 1993 Wiley-Liss, Inc.
    Additional Material: 4 Ill.
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  • 9
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    Unknown
    Frankfurt a. M.: Deutsche Bundesbank
    Publication Date: 2020-04-08
    Description: Assessing the discriminative power of rating systems is an important question to banks and to regulators. In this article we analyze the Cumulative Accuracy Profile (CAP) and the Receiver Operating Characteristic (ROC) which are both commonly used in practice. We give a test-theoretic interpretation for the concavity of the CAP and the ROC curve and demonstrate how this observation can be used for more efficiently exploiting the informational contents of accounting ratios. Furthermore, we show that two popular summary statistics of these concepts, namely the Accuracy Ratio and the area under the ROC curve, contain the same information and we analyse the statistical properties of these measures. We show in detail how to identify accounting ratios with high discriminative power, how to calculate confidence intervals for the area below the ROC curve, and how to test if two rating models validated on the same data set are different. All concepts are illustrated by applications to real data.
    Keywords: G10 ; C52 ; ddc:330 ; Validation ; Rating Models ; Credit Analysis ; Kreditwürdigkeit ; Bilanzanalyse ; Diskriminanzanalyse ; Statistischer Test ; Kreditrisiko ; Validität
    Language: English
    Type: doc-type:workingPaper
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