Karbach U, Schmitt A, Saner F H
Medizinische Klinik, Klinikum Innenstadt, University of Munich, Germany.
Dig Dis Sci. 1991 Nov;36(11):1611-8. doi: 10.1007/BF01296406.
Concentration and voltage dependence of Mg transport across the rat duodenum was measured in an Ussing chamber. Mucosa (m) to serosa (s) Mg flux exhibits a cellular fraction comparable to that found for Ca. Mg sm flux is purely diffusive and probably restricted to the paracellular pathway. At all concentrations between 0.5 and 5 mmol/liter, Mg is secreted. Diffuse sm Mg flux is 3.5 times higher than the diffusive component of ms Mg transport. This prevalence of diffusive sm Mg flux over that from mucosa to serosa, which may be explained by an "anomalous solvent drag effect," is responsible for the Mg secretion observed. Mg 5 mmol/liter decreases ms Ca flux and abolishes Ca absorption. The voltage clamp experiments reveal that Mg has no effect on the cellular transport but only decreases diffusive ms Ca flux. 1 alpha,25-dihydroxyvitamin D3 has only a small effect on cellular Mg transport but remarkably stimulates ms Ca flux and increases Ca absorption by about 85%. Dexamethasone increases ms Mg flux but decreases ms Ca transport and hereby abolished Mg secretion or Ca absorption. In conclusion, Mg is secreted across the short-circuited duodenum whereas Ca is absorbed. There is evidence that both earth alkalines are transported by distinct cellular mechanisms. The data also demonstrate that diffusive movement across the paracellular pathway plays an important role on net Mg transport.
在尤斯灌流小室中测量了镁跨大鼠十二指肠转运的浓度和电压依赖性。从黏膜（m）到浆膜（s）的镁通量显示出与钙相似的细胞部分。镁的浆膜到黏膜通量纯粹是扩散性的，可能局限于细胞旁途径。在0.5至5毫摩尔/升的所有浓度下，镁都是分泌的。扩散性的浆膜到黏膜镁通量比黏膜到浆膜镁转运的扩散成分高3.5倍。这种浆膜到黏膜的扩散性镁通量高于从黏膜到浆膜的通量，这可能由“异常溶剂拖曳效应”来解释，它导致了观察到的镁分泌。5毫摩尔/升的镁会降低黏膜到浆膜的钙通量并消除钙吸收。电压钳实验表明，镁对细胞转运没有影响，只是降低了扩散性的黏膜到浆膜钙通量。1α,25 - 二羟维生素D3对细胞镁转运只有很小的影响，但显著刺激黏膜到浆膜的钙通量并使钙吸收增加约85%。地塞米松增加黏膜到浆膜的镁通量，但降低黏膜到浆膜的钙转运，从而消除镁分泌或钙吸收。总之，镁通过短路的十二指肠分泌，而钙被吸收。有证据表明这两种碱土金属通过不同的细胞机制进行转运。数据还表明，跨细胞旁途径的扩散运动在镁的净转运中起重要作用。
