León-Del-Río A, Hol-Soto-Borja D, Velázquez A
Unidad de Genética de la Nutrición, Instituto de Investigaciones Biomédicas UNAM, D.F.
Arch Med Res. 1993 Summer;24(2):143-6.
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.
多项关于仓鼠生物素肠道转运的研究已表明存在一种生物素特异性载体，但关于它是通过主动转运、易化扩散进行转运以及其对钠离子的依赖性，存在相互矛盾的报道。我们首次使用刷状缘膜囊泡（BBMV）对其进行研究，生物素浓度处于更接近生理水平（纳摩尔级），并发现了一个超调成分，证明存在载体介导的主动过程，能驱使该维生素逆浓度梯度转运。用钾替代钠时，摄取量大幅降低。当用胰蛋白酶处理囊泡时，钠离子依赖性摄取显著降低，超调现象消失，为载体介导的转运提供了额外证据。钾离子梯度下的摄取量被认为是由于被动扩散，约为钠离子梯度下摄取量的30%。在用胰蛋白酶处理的囊泡于后一种梯度中孵育时，也观察到了类似的摄取量。我们的结果表明，在仓鼠刷状缘肠上皮中，钠离子依赖性主动转运是纳摩尔浓度下生物素肠道摄取的最重要组成部分。
