Bijvelds M J, Kolar Z I, Wendelaar Bonga S E, Flik G
Department of Animal Physiology, Faculty of Science, University of Nijmegen, Toernooiveld, 6525 ED Nijmegen, The Netherlands.
J Membr Biol. 1996 Dec;154(3):217-25. doi: 10.1007/s002329900146.
In tilapia (Oreochromis mossambicus) intestine, Mg2+ transport across the epithelium involves a transcellular, Na+- and Na+/K+-ATPase dependent pathway. In our search for the Mg2+ extrusion mechanism of the basolateral compartment of the enterocyte, we could exclude Na+/Mg2+ antiport or ATP-driven transport. Evidence is provided, however, that Mg2+ movement across the membrane is coupled to anion transport. In basolateral plasma membrane vesicles, an inwardly directed Cl- gradient stimulated Mg2+ uptake (as followed with the radionuclide 27Mg) twofold. As Cl--stimulated uptake was inhibited by the detergent saponin and by the ionophore A23187, Mg2+ may be accumulated intravesicularly above chemical equilibrium. Valinomycin did not affect uptake, suggesting that electroneutral symport activity occurred. The involvement of anion coupled transport was further indicated by the inhibition of Mg2+ uptake by the stilbene derivative, 4,4'-diisothiocyanato-stilbene-2,2'-disulfonic acid. Kinetic analyses of the Cl--stimulated Mg2+ uptake yielded a Km (Mg2+) of 6.08 +/- 1.29 mmol . l-1 and a Km (Cl-) of 26.5 +/- 6.5 mmol . l-1, compatible with transport activity at intracellular Mg2+- and Cl--levels. We propose that Mg2+ absorption in the tilapia intestine involves an electrically neutral anion symport mechanism.
在罗非鱼（莫桑比克罗非鱼）肠道中，镁离子跨上皮细胞转运涉及一条跨细胞、依赖钠离子和钠钾ATP酶的途径。在我们探寻肠上皮细胞基底外侧区室镁离子外排机制的过程中，我们排除了钠镁反向转运或ATP驱动转运的可能性。然而，有证据表明镁离子跨膜移动与阴离子转运相关联。在基底外侧质膜囊泡中，内向的氯离子梯度使镁离子摄取（用放射性核素27Mg追踪）增加了两倍。由于氯离子刺激的摄取被去污剂皂角苷和离子载体A23187抑制，镁离子可能在囊泡内积累至化学平衡以上。缬氨霉素不影响摄取，这表明发生了电中性同向转运活性。二苯乙烯衍生物4,4'-二异硫氰基二苯乙烯-2,2'-二磺酸对镁离子摄取的抑制进一步表明了阴离子偶联转运的参与。对氯离子刺激的镁离子摄取进行动力学分析，得出镁离子的米氏常数（Km）为6.08±1.29 mmol·l-1，氯离子的米氏常数为26.5±6.5 mmol·l-1，这与细胞内镁离子和氯离子水平下的转运活性相符。我们提出罗非鱼肠道中的镁离子吸收涉及一种电中性阴离子同向转运机制。
