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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