Middleton H M
Gastrointestinal Research Laboratory, Veterans Affairs Medical Center, Augusta, GA.
J Nutr. 1990 Jun;120(6):588-93. doi: 10.1093/jn/120.6.588.
The uptake of riboflavin was studied in everted sacs of rat intestine using [14C]riboflavin and [3H]polyethylene glycol to define the mechanism of mucosal membrane transport. Three-minute incubations were used throughout. Initial studies indicated the presence of saturable uptake in duodenum, jejunum and ileum. Studies in jejunum at low riboflavin concentrations demonstrated saturable uptake [Km = 0.154-0.177 mumol/L, Vmax = 19.6-25.8 pmol/(100 mg dry tissue.min)]. In contrast, uptake was linear with respect to higher concentrations of vitamin (10-50 mumol/L). Uptake at low (0.1 mumol/L) but not high (20 mumol/L) riboflavin concentrations was inhibited by 50 mumol/L lumiflavin, anoxia, 5 mmol/L indoacetamide, Na(+)-free buffer and low temperature (Q10 = 1.64). Conclusions are as follows: 1) Saturable uptake of riboflavin occurs throughout the rat small intestine; 2) uptake by the jejunal mucosa is competitively inhibited and is consistent with a transport carrier located in the brush border membrane; 3) saturable uptake is energy-dependent and may be directly or indirectly driven by a Na+ gradient; and 4) riboflavin is also taken up by rat intestinal mucosa by a nonsaturable, energy-independent mechanism consistent with simple, passive diffusion.
利用[14C]核黄素和[3H]聚乙二醇，在大鼠肠外翻囊模型中研究核黄素的摄取情况，以确定黏膜膜转运机制。整个实验过程均采用三分钟孵育。初步研究表明，十二指肠、空肠和回肠均存在可饱和摄取现象。在低核黄素浓度下对空肠进行的研究显示存在可饱和摄取[Km = 0.154 - 0.177 μmol/L，Vmax = 19.6 - 25.8 pmol/(100 mg干组织·分钟)]。相比之下，较高浓度维生素（10 - 50 μmol/L）时摄取呈线性关系。50 μmol/L的光黄素、缺氧、5 mmol/L的吲哚乙酸胺、无钠缓冲液和低温（Q10 = 1.64）可抑制低浓度（0.1 μmol/L）而非高浓度（20 μmol/L）核黄素的摄取。结论如下：1）大鼠小肠各段均存在核黄素的可饱和摄取；2）空肠黏膜摄取具有竞争性抑制，这与位于刷状缘膜的转运载体一致；3）可饱和摄取依赖能量，可能直接或间接由Na+梯度驱动；4）大鼠肠黏膜也通过与简单被动扩散一致的非饱和、能量非依赖机制摄取核黄素。
