Leonhard-Marek S, Martens H
Department of Physiology, School of Veterinary Medicine, Hannover, Germany.
Am J Physiol. 1996 Dec;271(6 Pt 1):G1034-8. doi: 10.1152/ajpgi.1996.271.6.G1034.
Increasing ruminal K concentration impairs active Mg transport across the forestomach epithelium of ruminants. We used Ussing chamber and microelectrode techniques to test the hypothesis that high mucosal K decreases the driving force for Mg2+ uptake by depolarizing the apical membrane. Serosal Ba enhanced net 42K secretion. Under open-circuit conditions, rumen epithelial cells showed an apical membrane potential (Va) of -67.3 +/- 1.5 mV. An increase in mucosal K concentration depolarized Va and decreased mucosal-to-serosal 28 Mg flux (Jm-->sMg). An increase in the transepithelial potential difference (Vt) depolarized Va, greatly decreased Jm-->sMg, and slightly increased Mg serosal-to-mucosal flux (Js-->mMg). Jm-->sMg exhibited an electrogenic and an electroneutral component. Mucosal verapamil depolarized Va and reduced Jm-->sMg, without affecting Js-->mMg. The study shows that rumen epithelial cells exhibit apical and basolateral K conductances and that transcellular Mg absorption has a distinct electrogenic component. This supports the assumption that a change in Va represents the link between increased ruminal K concentration and decreased Mg absorption. The results are discussed with regard to the development of hypomagnesemia in ruminants.
瘤胃钾浓度升高会损害反刍动物前胃上皮细胞对镁的主动转运。我们使用尤斯灌流小室和微电极技术来验证以下假设：高黏膜钾通过使顶端膜去极化来降低镁离子摄取的驱动力。浆膜侧的钡增强了42K的净分泌。在开路条件下，瘤胃上皮细胞的顶端膜电位（Va）为-67.3±1.5 mV。黏膜钾浓度升高会使Va去极化，并降低黏膜到浆膜的28Mg通量（Jm→sMg）。跨上皮电位差（Vt）增加会使Va去极化，大幅降低Jm→sMg，并略微增加镁从浆膜到黏膜的通量（Js→mMg）。Jm→sMg表现出一个电生性成分和一个电中性成分。黏膜维拉帕米使Va去极化并降低Jm→sMg，但不影响Js→mMg。该研究表明，瘤胃上皮细胞具有顶端和基底外侧的钾电导，并且跨细胞镁吸收具有明显的电生性成分。这支持了Va的变化代表瘤胃钾浓度升高与镁吸收减少之间联系的假设。针对反刍动物低镁血症的发生情况对结果进行了讨论。
