title: Biotin uptake mechanisms in brush-border and basolateral membrane vesicles isolated from rabbit kidney cortex.
abstract: Biotin transport was studied using brush-border and basolateral membrane vesicles isolated from rabbit kidney cortex. An inwardly directed Na+ gradient stimulated biotin uptake into brush-border membrane vesicles and a transient accumulation of the anion against its concentration gradient was observed. In contrast, uptake of biotin by basolateral membrane vesicles was found to be Na+-gradient insensitive. Generation of a negative intravesicular potential by valinomycin-induced K+ diffusion potentials or by the presence of Na+ salts of anions of different permeabilities enhanced biotin uptake by brush-border membrane vesicles, suggesting an electrogenic mechanism. The Na+ gradient-dependent uptake of biotin into brush-border membrane vesicles was saturable with an apparent Km of 28 microM. The Na+-dependent uptake of tracer biotin was significantly inhibited by 50 microM biotin, and thioctic acid but not by 50 microM L-lactate, D-glucose, or succinate. Finally, the existence in both types of membrane vesicles of a H+/biotin- cotransport system could not be demonstrated. These results are consistent with a model for biotin reabsorption in which the Na+/biotin- cotransporter in luminal membranes provides the driving force for uphill transport of this vitamin.
mesh_terms: D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D001710:Biotin / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D005947:Glucose / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007672:Kidney Cortex / Q000378:metabolism*; D008564:Membrane Potentials; D008871:Microvilli / Q000378:metabolism; D009997:Osmotic Pressure; D011189:Potassium Chloride / Q000494:pharmacology; D011817:Rabbits; D012964:Sodium / Q000378:metabolism / Q000494:pharmacology; D014634:Valinomycin / Q000494:pharmacology
chemical_list: D014634:Valinomycin; D011189:Potassium Chloride; D001710:Biotin; D012964:Sodium; D005947:Glucose