title: The endocytosis of transferrin by rat intestinal epithelial cells.
abstract: OBJECTIVE
  The transferrin receptor is a prominent protein on the basal and lateral membranes of intestinal epithelial cells, yet little is known of the function of the receptor in the intestine. The aim of the present study was to determine whether intestinal transferrin receptors were capable of facilitating transferrin internalization.
  
  
  METHODS
  Using the rat as an experimental model, the uptake of radiolabeled transferrin by cells isolated from different regions along the crypt-villus axis of the proximal small intestine was studied.
  
  
  RESULTS
  An intestinal epithelial cell fraction highly enriched in crypt cells bound most radiolabeled transferrin. Cells in this fraction were able to internalize transferrin and recycle it back to the cell surface. A high affinity, saturable pathway of transferrin uptake by these cells predominated at transferrin concentrations below 0.3 mumol/L, whereas at higher concentrations, most uptake was via a nonsaturable process. Intravenously injected radiolabeled transferrin could be detected within intestinal crypt cells, indicating that these cells are able to internalize transferrin in vivo.
  
  
  CONCLUSIONS
  These data suggest that intestinal crypt cells have an active transferrin/transferrin receptor system. Transferrin may play an important role in iron delivery to and/or as a growth factor for the rapidly proliferating intestinal epithelium.
authors.affiliation: Liver Unit, Queensland Institute of Medical Research, Brisbane, Australia.
authors.forename: G J
authors.initials: GJ
authors.lastname: Anderson
authors.forename: L W
authors.initials: LW
authors.lastname: Powell
authors.forename: J W
authors.initials: JW
authors.lastname: Halliday
mesh_terms: D000818:Animals; D002469:Cell Separation; D004705:Endocytosis; D004848:Epithelium / Q000378:metabolism; D007421:Intestine, Small / Q000378:metabolism*; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D011990:Receptors, Transferrin / Q000378:metabolism*; D014168:Transferrin / Q000008:administration & dosage / Q000378:metabolism*
chemical_list: D011990:Receptors, Transferrin; D014168:Transferrin