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  • 1
    Electronic Resource
    Electronic Resource
    Molecular species of membrane phospholipids containing arachidonic acid and linoleic acid contribute to the interindividual variability of red blood cell Na+-Li+ countertransport: In vivo and in vitro evidence (1993)
    Springer
    The journal of membrane biology 133 (1993), S. 99-106 
    Details
    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
    URL: http://dx.doi.org/10.1007/BF00233791
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  • 2
    Electronic Resource
    Electronic Resource
    Effect of cholesterol and dipalmitoyl phosphatidylcholine enrichment on the kinetics of Na−Li exchange of human erythrocytes (1991)
    Springer
    The journal of membrane biology 122 (1991), S. 231-238 
    Details
    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
    URL: http://dx.doi.org/10.1007/BF01871423
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