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  • 1
    ISSN: 1573-4919
    Keywords: endotoxins ; cytochrome b5 ; cytochrome P450 ; hepatocyte cultures ; detoxification
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract Cytotoxic lesions, induced by Gram-negative lipopolysaccharides (LPS), occur mainly in liver where the microsomal compartment of hepatocytes is involved in the detoxification mechanisms as well as in the biosynthesis of different active metabolites. The alterations induced by LPS from E. coli 0111: 134 on cytochrome b5 and its correlation with cytochrome P450, have been studied using an in vivo reversible endotoxic shock model and 24 h non-replicative hepatocyte monolayers. Results show that cytochrome b5 is directly affected by LPS that induces also a membrane damage with an active release of lactate dehydrogenase (LDH). The increase of cytochrome b5 levels may enhance the efficiency of the electron transport, thus facilitating the cytochrome P450-associate oxidations and reactions involved in the repair mechanisms of membranes.
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  • 2
    ISSN: 1573-4919
    Keywords: ethanol ; plasma membranes ; phospholipid (rat liver) ; miocroviscosity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Summary Male Wistar rats were maintained for 35–40 days on a liquid diet containing 36% of calories as ethanol. Ethanol was replaced by carbohydrates in the isocaloric diet fed to control animals. The effect of ethanol consumption has been studied on the fluorescence polarization of rat liver plasma membranes and artificial lipid vesicles and on the lipid composition of the membranes. Fluorescence polarization in both membranes and vesicles was determined using DPH and TMA-DPH as fluorescence markers; from these data, the polarization term (ro/r−1)−1 and flow activation energy (ΔE) were calculated. The ethanol consumption induces a more fluid environment within the membrane core of liver plasma membranes; the ethanol-fed rat membranes are more resistant to the in vitro effect of ethanol disordering the membrane structure. Vesicles obtained with lipids from either control membranes or ethanol-fed rat membranes were treated with ethanol and the changes in polarization paralleled to those exhibited by the membranes. The absence of phase transitions and of ΔE changes was also shown in temperature-dependence studies. The lower cholesterol content found in ethanol-fed rat plasma membranes might be responsible for observed variations in the microviscosity.
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  • 3
    ISSN: 1573-4919
    Keywords: adenylate cyclase regulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Summary The regulatory properties of saturated and unsaturated fatty acids on membrane-bound preparations of adenylate cyclase from Ceratitis capitata brains have been investigated. Saturated long-chain fatty acids do not exhibit any significant modification of the enzyme activity of the enzyme preparations but the presence of one, two or three double bonds in the 18C chain provokes an inhibitory effect. Binding of oleate and linoleate to the membrane enzyme preparation is non-specific and simply stochiometric in the range of concentrations examined. Studies of cis and trans isomers of the double-bond isomers, 18:1 (n−9) and 18:1(n−11), reveal the higher inhibitory effect of the cis isomers on membrane-bound adenylate cyclase of the insect brain. The inhibitory effect of cis-vaccenate in the basal conditions of the enzyme assay is identical to the effects obtained in the presence of GTP and octopamine. Insect membrane preparations were labeled with 1,6-diphenyl-1,3,5-hexatriene as fluorescent probe and treated with cis and trans 18:1(n−9) and 18:1 (n−11). The fluorescence polarization parameter was measured, from which the microviscosity of the preparations was calculated; microviscosity of the membranes treated with both cis isomers decreased in a clear extent whereas it is not influenced by the trans isomers.
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  • 4
    ISSN: 1573-4919
    Keywords: endotoxic shock ; lipopolysaccharide ; pneumocytes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Summary The interaction between lipopolysaccharide from E. coli0111:B4 and rat alveolar type II pneumocytes and its influence on the functional properties of the cells and their membranes were studied. Type II cells were isolated by a novel procedure involving digestion of the lung connective tissue with elastase and Percoll-gradient centrifugation. Binding of (14C)lipopolysaccharide to type II cells resulted in a partially reversible, non-specific, high affinity process. (l4C)Choline incorporation into phosphatidylcholine by type II cells was stimulated by lipopolysaccharide, the maximum effect being observed at 10–20 μg/ml. 45Ca2+ uptake by type II cells was also increased by lipopolysaccharide. Using plasma membranes from lung homogenates an increase of membrane microviscosity versus the amount of lipopolysaccharide was shown. These results indicate that E. coli lipopolysaccharide interacts with alveolar type 11 cells by binding reversibly to particular ingredients of the membrane bilayer and induces a modification of ion permeability and fluidity of the membrane.
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  • 5
    ISSN: 1573-4919
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Summary Number and affinity constant of low affinity binding sites of insulin and glucagon to isolated hepatocytes decreased when the cells were incubated with Escherichia coli 0111:B4 lipopolysaccharide. This effect agrees with a non-specific binding of lipopolysaccharide to hepatocytes, similar to the well-recognized non-specific binding of albumin. Also, binding of different lectins to their glycoprotein receptors did not affect the [14C]lipopolysaccharide interaction with the cell membrane surface. Endotoxin depresses gluconeogenesis from lactate when the precursor was incubated with the cells for short time intervals. The longer the preincubation interval with lipopolysaccharide, the higher the inhibition of gluconeogenesis in the absence and in the presence of glucagon. The effect of endotoxin was also studied on the glucagon-induced synthesis of cyclic AMP and the glucagon binding. Levels of cyclic AMP and hormone binding decreased with increasing both endotoxin concentrations and preincubation intervals at which cells were in contact with endotoxin.
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  • 6
    ISSN: 1573-4919
    Keywords: endotoxic shock ; lipopolysaccharide ; type II cells ; phosphatidylcholine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Summary Alterations in pulmonary surfactant are partly responsible for the respiratory insufficiency seen under septic shock process. We have used an experimental model of LPS-induced shock in rats to examine the cells responsible for the pulmonary surfactant synthesis and its relationship to lung injury. (14C)Choline incorporation into phosphatidylcholine was significantly reduced in lung homogenates or type II cells obtained from LPS-treated animals. Addition of LPS in vitro fails to increase (14C)choline incorporation in type II cells obtained from LPS-treated animals. We suggest that this depression of pulmonary phosphatidylcholine synthesis may partly explain the occurrence of respiratory failure with septic shock.
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  • 7
    ISSN: 0263-6484
    Keywords: Lung ; phosphatidylcholine ; lysolecithin acyltansferase ; membrane fluidity ; hyperoxemia ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Phosphatidylcholine metabolism and membrane fluidity were studied in microsomes isolated from rabbit lung, which had been exposed to high oxygen tension for 30 min.In these microsomes the incorporation of [3H]-palmitate into phosphatidylcholine increased whereas the incorporation of [14C]-glycerol and [14C]-choline from CDP-[methyl-14C]-choline remained unchanged in comparison to the control microsomes. The enhanced [3H]-palmitate incorporation may be explained by an increase of the specific activity of acyl-CoA:lysophosphatidylcholine acyltransferase which was measured in microsomes from hyperoxic lung.Although microsomal parameters influencing membrane fluidity, such as the cholesterol/phospholipid molar ratio, unsaturation degree of phospholipid acyl chains and lipid/protein ratio, are altered after oxygen treatment in vivo, no change of fluorescence polarization (PDPH) and lipid structural order parameter (SDPH) could be measured. Probably, the membrane maintains its fluidity by counteracting effects on different factors on which the fluidity depends.
    Additional Material: 4 Tab.
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  • 8
    ISSN: 0263-6484
    Keywords: Endotoxins ; membranes ; hepatocytes ; hepatocyte cultures ; microviscosity ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The fluorescence probe 1,6-diphenylhexa-1,3,5-triene (DPH) was used for monitoring structural perturbations induced by lipopolysaccharide (LPS) of Escherichia coli (0111 : B4) in plasma membranes of rat liver. Changes in microviscosity were observed in plasma membrane preparations from control rats after treatment with LPS and in plasma membrane preparations from liver perfused with LPS. In both systems fluorescence polarization was measured from which microviscosity was calculated. This parameter increases with LPS treatment. From temperature dependence studies was inferred that LPS interaction with plasma membrane preparations induces an increase of both the polarization term (r0/r-1)-1 and flow activation energy (ΔE). Addition of LPS to hepatocyte suspensions also induces an increase on microviscosity and a delay in the fall of microviscosity induced by a temperature rise in hepatocyte monolayers grown on microcover slides.These data suggest that LPS interaction can be attributed to its binding to membrane hydrophobic regions in a non-specific manner.
    Additional Material: 4 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Trends in Biochemical Sciences 4 (1979), S. N202-N203 
    ISSN: 0968-0004
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 0005-2736
    Keywords: (Rabbit) ; Glycerolipid ; Lysophosphatidylcholine ; Membrane fluidity ; Microsome ; Respiratory distress
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology , Medicine , Physics
    Type of Medium: Electronic Resource
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