Hoyumpa A M, Nichols S, Schenker S, Wilson F A
Biochim Biophys Acta. 1976 Jun 17;436(2):438-47. doi: 10.1016/0005-2736(76)90206-6.
As part of a systematic study of alcoholism and thiamine absorption, the effect of diet-induced thiamine deficiency and the role of the unstirred water layer on the thiamine transport were investigated. Using 3H-labeled dextran as a marker of adherent mucosal volume, jejunal uptake of 14C-labeled thiamine hydrochloride was measured, in vitro, in thiamine-deficient rats and pair-fed controls. Uptake of low thiamine concentrations (0.2 and 0.5 muM) was greater in the thiamine-deficient rats than in the controls. In contrast, uptake rates for high thiamine concentrations (20 and 50 muM) were similar in both groups. While Jmax was unaltered, Km was decreased in thiamine deficiency, suggesting a decrease in unstirred water layer thickness. Accordingly, the thickness of the water layer was measured in both groups of animals and correlated with Jmax and Km under unstirred and stirred conditions. Without stirring, there was no difference in Jmax between the two groups. In contrast, both Km and the water layer were reduced in the thiamine-deficient rats. With stirring, Jmax was not affected, but both Km and the water layer thickness were reduced to similar values in both groups. Reversal of thiamine deficiency resulted in the return of thiamine uptake and the unstirred water layer thickness to control values. These data support the concept of a dual system of thiamine transport and emphasize the role of the unstirred water layer as an important determinant of transport kinetics not only under physiologic situations but also in diet-induced rat thiamine deficiency, a model for a clinical patholigical state. The decrease in the unstirred water layer thickness in thiamine deficiency may be also viewed as a possible adaptive mechanism to facilitate absorption of meager supplies of thiamine.
作为对酒精中毒和硫胺素吸收的系统研究的一部分，研究了饮食诱导的硫胺素缺乏的影响以及静止水层在硫胺素转运中的作用。以3H标记的右旋糖酐作为黏附黏膜体积的标志物，在体外测量硫胺素缺乏大鼠和配对喂养对照大鼠空肠对14C标记的盐酸硫胺素的摄取。硫胺素缺乏大鼠对低硫胺素浓度（0.2和0.5μM）的摄取高于对照组。相比之下，两组对高硫胺素浓度（20和50μM）的摄取率相似。虽然最大转运速率（Jmax）未改变，但硫胺素缺乏时米氏常数（Km）降低，提示静止水层厚度减小。因此，测量了两组动物的水层厚度，并将其与静止和搅拌条件下的Jmax和Km相关联。不搅拌时，两组之间的Jmax没有差异。相比之下，硫胺素缺乏大鼠的Km和水层均减少。搅拌时，Jmax不受影响，但两组的Km和水层厚度均降低至相似值。硫胺素缺乏的逆转导致硫胺素摄取和静止水层厚度恢复到对照值。这些数据支持硫胺素转运双重系统的概念，并强调静止水层不仅在生理情况下，而且在饮食诱导的大鼠硫胺素缺乏（一种临床病理状态模型）中作为转运动力学重要决定因素的作用。硫胺素缺乏时静止水层厚度的减小也可被视为促进少量硫胺素吸收的一种可能的适应性机制。
