Characteristics of the binding of high-density lipoprotein 3 by intact cells and membrane preparations of rat intestinal mucosa

Abstract

We have investigated the binding of high-density lipoprotein (HDL 3, d = 1.12−1.21 g/ml), and apolipoprotein E-deficient human and rat HDL, obtained by heparin-Sepharose affinity chromatography, to intact cells and membrane preparations of rat intestinal mucosal cells. Binding of 125I-labeled HDL 3 to the basolateral plasma membranes was characterised by a saturable, specific process ( K d = 21 μg of HDL 3 protein/ml, B max = 660 ng HDL 3 protein/mg membrane protein) and E-deficient human HDL demonstrated a similar affinity for the binding site. The basolateral plasma membranes isolated from proximal and distal portion of rat small intestine showed similar binding affinities for HDL 3, whereas the interaction of HDL with brush-border membranes was characterised by mainly nonspecific and nonsaturable binding. The binding of 125I-labeled HDL, to basolateral plasma membranes was competitively inhibited by unlabeled HDL 3 but less efficiently by unlabeled human LDL. The putative HDL receptor was not dependent on the presence of divalent cations but was markedly influenced by temperature and sensitive to pronase treatment. We have also demonstrated, using whole intestinal mucosal cells, that lysine and arginine-modified HDL, inhibited binding of normal 125I-labeled HDL 3 to the same extent as normal excess HDL 3. These data suggest that basolateral plasma membranes of rat intestinal mucosal cells possess a specific receptor for HDL, which contains mainly apolipoprotein A-I and A-II, and the mechanisms of recognition of HDL, differ from those involved in binding to the B/E receptor.