Effects of potassium on magnesium transport across rumen
epithelium.
Leonhard-Marek, Sabine, and Holger Martens.
Department of Physiology, School of Veterinary Medicine, Hannover,
and Department of Veterinary Physiology, Free University of
Berlin,Germany
APStracts 3:0138G, 1996.
Increasing ruminal potassium concentration impairs active magnesium
transport across the forestomach epithelium of ruminants. We used
Ussing chamber and microelectrode techniques to test for the
hypothesis that high mucosal potassium decreases the driving force
for Mg2+ uptake by depolarizing the apical membrane. Serosal barium
enhanced net 42K secretion. Under open circuit conditions rumen
epithelial cells showed an apical membrane potential (Va) of -67.3+/
-1.5 mV. Increasing mucosal [K] depolarized Va and decreased mucosal
to serosal (ms) 28Mg flux. Increasing the transepithelial potential
difference (Vt) depolarized Va, greatly decreased Mg ms-flux and
slightly increased Mg serosal to mucosal (sm) flux. Mg ms-flux
exhibited an electrogenic and an electroneutral component. Mucosal
verapamil depolarized Va and reduced Mg ms-flux, without affecting Mg
sm-flux. 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.
Received 29 April 1996; accepted in final form 12 July 1996.
APS Manuscript Number G166-6.
Article publication pending Am. J. Physiol. (Gastrointest. Liver
Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 25 July 1996