title: Intestinal alkaline phosphatase: selective endocytosis from the enterocyte brush border during fat absorption.
abstract: Absorption of dietary fat in the small intestine is accompanied by a rise of intestinal alkaline phosphatase (IAP) in the serum and of secretion of IAP-containing surfactant-like particles from the enterocytes. In the present work, fat absorption was studied in organ cultured mouse intestinal explants. By immunofluorescence microscopy, fat absorption caused a translocation of IAP from the enterocyte brush border to the interior of the cell, whereas other brush-border enzymes were unaffected. By electron microscopy, the translocation occurred by a rapid (5 min) induction of endocytosis via clathrin-coated pits. By 60 min, IAP was seen in subapical endosomes and along membranes surrounding fat droplets. IAP is a well-known lipid raft-associated protein, and fat absorption was accompanied by a marked change in the density and morphology of the detergent-resistant membranes harboring IAP. A lipid analysis revealed that fat absorption caused a marked increase in the microvillar membrane contents of free fatty acids. In conclusion, fat absorption rapidly induces a transient clathrin-dependent endocytosis via coated pits from the enterocyte brush border. The process selectively internalizes IAP and may contribute to the appearance of the enzyme in serum and surfactant-like particles.
authors.affiliation: Dept. of Cellular and Molecular Medicine, The Panum Institute University of Copenhagen, Bldg. 6.4, Blegdamsvej 3, DK-2200 Copenhagen N, Denmark. midan@imbg.ku.dk
authors.forename: Gert H
authors.initials: GH
authors.lastname: Hansen
authors.forename: Lise-Lotte
authors.initials: LL
authors.lastname: Niels-Christiansen
authors.forename: Lissi
authors.initials: L
authors.lastname: Immerdal
authors.forename: Birthe T
authors.initials: BT
authors.lastname: Nystrøm
authors.forename: E Michael
authors.initials: EM
authors.lastname: Danielsen
mesh_terms: D000469:Alkaline Phosphatase / Q000378:metabolism*; D000818:Animals; D002478:Cells, Cultured; D004041:Dietary Fats / Q000493:pharmacokinetics*; D004705:Endocytosis / Q000502:physiology*; D020895:Enterocytes / Q000378:metabolism*; D007421:Intestine, Small / Q000502:physiology* / Q000648:ultrastructure*; D051379:Mice; D008871:Microvilli / Q000378:metabolism
chemical_list: D004041:Dietary Fats; D000469:Alkaline Phosphatase