title: Uptake of vitamin B12 by isolated ileal enterocytes.
abstract: Isolated ileal enterocytes incubated with intrinsic factor-[57Co]vitamin B12 (IF-B12) at 37 degrees C took up 25 times more B12 than jejunal enterocytes. Uptake of B12 by ileal cells was dependent upon IF and Ca2+. B12 taken up by ileal enterocytes could be separated into two components: 1) B12 which was retained (E component) and 2) released (R-E component) by chelation of divalent cations. The E component could be removed from ileal cells by treatment with Triton X-100. Incubation of ileal enterocytes at 22 degrees C or with 2,4-dinitrophenol reduced incorporation of B12 into the E, but not the R-E, component. Ileal enterocytes were incubated with IF-[57Co]B12 washed and reincubated with unlabeled IF-B12. Reincubation resulted in a decrease in the amount of [57Co]B12 in the R-E component and a concomitant increase of that in the E component indicating that B12 was transferred from the R-E to the E component. Dinitrophenol reduced transfer from R-E to E components. These results suggest that, using isolated enterocytes, two sequential steps in ileal absorption of B12 can be identified: 1) energy-independent binding of IF-B12 to its receptor on the brush border followed by 2) an energy-dependent event which probably represents transfer of B12 from its receptor into the cell.
mesh_terms: D019297:2,4-Dinitrophenol; D000818:Animals; D002118:Calcium / Q000378:metabolism; D006224:Cricetinae; D004140:Dinitrophenols / Q000494:pharmacology; D004492:Edetic Acid / Q000494:pharmacology; D005260:Female; D005947:Glucose / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007082:Ileum / Q000378:metabolism*; D066298:In Vitro Techniques; D007408:Intestinal Absorption / Q000187:drug effects; D007437:Intrinsic Factor / Q000378:metabolism; D007583:Jejunum / Q000378:metabolism; D008871:Microvilli / Q000378:metabolism; D017830:Octoxynol; D010042:Ouabain / Q000494:pharmacology; D011092:Polyethylene Glycols / Q000494:pharmacology; D014805:Vitamin B 12 / Q000378:metabolism*
chemical_list: D004140:Dinitrophenols; D011092:Polyethylene Glycols; D010042:Ouabain; D017830:Octoxynol; D007437:Intrinsic Factor; D004492:Edetic Acid; D005947:Glucose; D014805:Vitamin B 12; D019297:2,4-Dinitrophenol; D002118:Calcium