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Secreted intestinal surfactant‐like particles interact with cell membranes and extracellular matrix proteins in rats
Author(s) -
Mahmood Akhtar,
Engle Michael J.,
Alpers David H.
Publication year - 2002
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2002.017087
Subject(s) - fibronectin , laminin , lamina propria , extracellular matrix , chemistry , integrin , epithelial polarity , biochemistry , microbiology and biotechnology , membrane , biophysics , biology , epithelium , cell , genetics
Surfactant‐like particles (SLP) are secreted from enterocytes basolaterally into the lamina propria, and reach the apical surface through the intercellular tight junctions. Interactions of SLP with apical and basolateral membranes and with extracellular matrix proteins were measured using a solid‐phase binding assay and gel overlays. Small‐intestinal SLP bound to basolateral membranes much more than to apical membranes, and more tightly to fibronectin than to laminin (affinity constant K a = 1.23 × 10 −2 μg vs . 0.67 × 10 −2 μg; maximal number of binding sites 4.1 μg ml −1 vs . 0.32 μg ml −1 ), but did not bind to collagen types I or IV. Small‐intestinal SLP bound fibronectin more than colonic or gastric SLP. Binding to fibronectin was inhibited only partially by RGD peptide and gelatin, but not by heparin. An antibody against αv integrin also identified the fibronectin‐binding component in SLP at ∼220 kDa, which is the expected size for integrin heterodimers. SLP binding to apical microvillous membranes was weaker and was inhibited by heparin. SLP bound more strongly to heparin itself, and this binding was inhibited by glucuronic acid and chondroitin sulfate. These data are consistent with the hypothesis that the time spent by secreted SLP in the lamina propria is prolonged by strong interactions with proteins in the basolateral membranes, and in the intestinal lumen by weaker interactions with apical membrane components, including heparin. These interactions may allow SLP the time to exert their functions in each tissue compartment.