Gallagher K, Mauskopf J, Walker J T, Lack L
J Lipid Res. 1976 Nov;17(6):572-7.
Taurocholate transport by everted ileal gut sacs was studied in physiological media containing graded amounts of sodium ions. Significant uphill transport of taurocholate was observed when the bulk of NaCl was replaced by osmotic equivalents of mannitol or choline chloride. Seventy-seven percent of control transport activity was observed when 36 milliequivalents per liter of Na+ were present in the incubation medium with mannitol acting as the isosmotic replacement, and 74% of the control transport was retained when 31 milliequivalents per liter of Na+ were present in the incubation medium with choline chloride acting as the osmotic replacement. Lowering the Na+ concentration to 19 milliequivalents per liter (i.e., 84% replacement of Na+) still allowed for 69% of the uphill transport observed in the control incubations. Taurodehydrocholate transport by ileal everted sacs was more sensitive to decreased Na+ concentrations; 29% of control transport was observed at 31 milliequivalents per liter of Na+. A kinetic analysis comparing the transport of taurocholate with taurodehydrocholate, the triketo analogue, at different concentrations of Na+ indicated that the apparent affinity of the transport system for Na+ is greater in the presence of taurocholate than in the presence of taurodehydrocholate. The ability of taurodehydrocholate to depress taurocholate transport is less in media of low Na+ concentration. Finally, in vivo intestinal perfusion studies demonstrated that the depression of taurocholate absorption, following Na+ removal, is reversible. These results are in agreement with the idea that Na+ has a physiological role in intestinal bile salt transport, and that the affinities of the anionic bile salt and the sodium cation for the transport system appear to be cooperative in that one enhances the binding of the other.
在含有不同梯度钠离子的生理介质中，研究了外翻回肠肠囊对牛磺胆酸盐的转运。当大部分氯化钠被等渗的甘露醇或氯化胆碱替代时，观察到牛磺胆酸盐有显著的逆浓度梯度转运。当孵育介质中存在每升36毫当量的Na⁺，并用甘露醇作为等渗替代物时，观察到对照转运活性的77%；当孵育介质中存在每升31毫当量的Na⁺，并用氯化胆碱作为渗透替代物时，保留了对照转运的74%。将Na⁺浓度降低至每升19毫当量（即84%的Na⁺被替代）时，仍能观察到对照孵育中69%的逆浓度梯度转运。回肠外翻囊对牛磺去氢胆酸盐的转运对降低的Na⁺浓度更敏感；在每升31毫当量的Na⁺浓度下，观察到对照转运的29%。一项动力学分析比较了在不同Na⁺浓度下牛磺胆酸盐与三酮类似物牛磺去氢胆酸盐的转运，结果表明，在牛磺胆酸盐存在下，转运系统对Na⁺的表观亲和力大于牛磺去氢胆酸盐存在时。在低Na⁺浓度介质中，牛磺去氢胆酸盐抑制牛磺胆酸盐转运的能力较小。最后，体内肠道灌注研究表明，去除Na⁺后牛磺胆酸盐吸收的降低是可逆的。这些结果与以下观点一致，即Na⁺在肠道胆汁盐转运中具有生理作用，并且阴离子胆汁盐和钠离子对转运系统的亲和力似乎具有协同作用，因为一种离子会增强另一种离子的结合。
