Effects of potassium on magnesium transport across rumen epithelium.
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.
Leonhard-Marek
S
S
Department of Physiology, School of Veterinary Medicine, Hannover, Germany.
Martens
H
H
D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D004848:Epithelium / Q000378:metabolism; D008274:Magnesium / Q000378:metabolism*; D008564:Membrane Potentials; D011188:Potassium / Q000378:metabolism*; D012417:Rumen / Q000378:metabolism*; D012756:Sheep
D008274:Magnesium; D011188:Potassium