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  • Title: Studies on the mechanism of biotin uptake by brush-border membrane vesicles of hamster enterocytes.
    Author: León-Del-Río A, Hol-Soto-Borja D, Velázquez A.
    Journal: Arch Med Res; 1993; 24(2):143-6. PubMed ID: 8274840.
    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.
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