AJP - Gastrointestinal and Liver Physiology, Vol 270, Issue 1 203-G212, Copyright © 1996 by American Physiological Society
Chylomicron remnant uptake by enterocytes is receptor dependent
M. Soued and C. M. Mansbach 2nd
Department of Medicine, University of Tennessee, Memphis 38163, USA.
During glyceryl trioleate absorption in the rat, mucosal triacylglycerol
(TG) fatty acids have been shown to consist of only 71% exogenous oleate.
Chylomicron remnants are enriched with endogenous TG fatty acids, compared
with their parent chylomicrons, which consist primarily of exogenous TG
fatty acids. Because enterocytes have the apolipoprotein B-100/E receptor,
this study was directed at determining whether the cells can take up and
metabolize chylomicron remnants and, if so, whether this was receptor
mediated. Isolated enterocytes were incubated with purified 3H-labeled
chylomicron remnants. The remnants were shown to be taken up by the
basolateral membrane, not the apical membrane. Remnant uptake was
proportional to time and number of enterocytes, and saturation kinetics
were observed. Nonradiolabeled remnants, human low-density lipoprotein
(LDL), anti-LDL receptor antibody, and receptor-associated protein, an
LDL-related receptor inhibitor, were all shown to compete for or reduce
3H-remnant uptake. Remnants taken up by the enterocytes could not be
removed on incubation with excess human LDL. Uptake was shown to be
greatest in the villus tips of the proximal intestine. These studies
suggest that enterocytes take up chylomicron remnants by a
receptor-mediated process from their basolateral membranes and that the
remnants could provide a source of endogenous TG fatty acids for the
enterocytes.
