title: Studies on the mechanism of biotin uptake by brush-border membrane vesicles of hamster enterocytes.
abstract: Several studies on biotin intestinal transport in the hamster have shown a biotin-specific carrier, but there are conflicting reports on whether it is transported actively, or by facilitated diffusion and on its Na+ dependence. We have studied it for the first time using brush-border membrane vesicles (BBMV), with concentrations in a more physiological (nanomolar) range and found an overshoot component, evidencing a carrier-mediated active process, driving the vitamin against a concentration gradient. Uptake was substantially reduced when potassium substituted for sodium. When the vesicles were treated with trypsin, Na(+)-dependent uptake was markedly reduced and the overshoot phenomenon was abolished, providing additional evidence for the carrier-mediated transport. The amount of uptake in a K+ gradient was considered due to passive diffusion and was about 30% of that observed in a Na+ gradient. A similar amount was observed when trypsinized vesicles were incubated in this latter gradient. Our results indicate that in the hamster's brush border intestinal epithelium, Na(+)-dependent active transport is the most important component in the intestinal uptake of biotin at nanomolar concentrations.
authors.affiliation: Unidad de Genética de la Nutrición, Instituto de Investigaciones Biomédicas UNAM, D.F.
authors.forename: A
authors.initials: A
authors.lastname: León-Del-Río
authors.forename: D
authors.initials: D
authors.lastname: Hol-Soto-Borja
authors.forename: A
authors.initials: A
authors.lastname: Velázquez
mesh_terms: D000818:Animals; D001693:Biological Transport, Active; D001710:Biotin / Q000378:metabolism*; D006224:Cricetinae; D066298:In Vitro Techniques; D007421:Intestine, Small / Q000378:metabolism*; D007700:Kinetics; D008647:Mesocricetus; D008871:Microvilli / Q000378:metabolism
chemical_list: D001710:Biotin