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HERO ID
7107798
Reference Type
Journal Article
Title
Mechanisms of cellular uptake of long chain free fatty acids
Author(s)
Berk, PD; Stump, DD; ,
Year
1999
Publisher
KLUWER ACADEMIC PUBL
Location
DORDRECHT
Page Numbers
17-31
PMID
10331655
Web of Science Id
WOS:000079889000004
Abstract
Cells take up long chain free fatty acids (FFA) in vivo from the non-protein bound ligand pools in extracellular fluid and plasma, which contain similar to 100 and 600 mu M albumin, respectively. The physiologic range of unbound FFA concentrations in such fluids has traditionally been calculated at < 1 mu M. Studies of I:[H-3]-oleate uptake by hepatocytes, adipocytes, cardiac myocytes and other cell types demonstrate that FFA uptake within this range is saturable, and exhibits many other kinetic properties indicative of facilitated transport. Within this range, the uptake kinetics of the acidic (pKa = 0.5) FFA analog alpha(2)beta(2)omega(3)-heptafluorostearate are similar to those of stearate. Thus, uptake of physiologic concentrations of FFA involves facilitated transport of the FFA anion (FA(-)). Over a much wider range of unbound FFA concentrations hepatocellular [H-3] -oleate uptake exhibits both saturable and non-saturable components. Oleate binding to liver plasma membranes (LPM) also demonstrates such components. Comparing the two components of FFA uptake to the corresponding components of binding permits estimates of trans-membrane transport rates. T-1/2 for saturable uptake (similar to 1 sec) is less than for non-saturable uptake (similar to 14 sec). Others have determined the flip-flop rates of protonated FFA (FAH) across small and large unilamellar vesicles (SUV, LUV) and across cellular plasma membranes. These reported flip-flop rates, measured by the decrease in pH resulting from the accompanying proton flux, exhibit a highly significant inverse correlation with cell and vesicle diameter (r = 0.99). Although T-1/2's in vesicles are in the msec range, those in cells are > 10 sec, and thus comparable to the rates of non-saturable uptake we determined. Thus, under physiologic conditions, the predominant mechanism of cellular FFA uptake is facilitated transport of FA(-); at much higher, non-physiologic FFA concentrations, passive flip-flop of FAH predominates. Several plasma membrane proteins have been identified as potential mediators of facilitated FFA transport. Studies in animal models of obesity and non-insulin dependent diabetes mellitus demonstrate that tissue-specific regulation of facilitated FFA transport has important pathophysiologic consequences.
Conference Name
3rd International Conference on Lipid-Binding Proteins
Conference Location
MINNEAPOLIS, MINNESOTA
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