HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) All Versions of this Article: 296/5/G1098    most recent 90442.2008v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Web of Science (1) Citing Articles via Google Scholar Google Scholar Articles by Aschenbach, J. R. Articles by Gäbel, G. Search for Related Content PubMed PubMed Citation Articles by Aschenbach, J. R. Articles by Gäbel, G.

MUCOSAL BIOLOGY

Bicarbonate-dependent and bicarbonate-independent mechanisms contribute to nondiffusive uptake of acetate in the ruminal epithelium of sheep

¹Institute for Veterinary Physiology, University of Leipzig, Leipzig, Germany; ²Institute for Veterinary Physiology, Free University of Berlin, Berlin, Germany

Submitted 18 July 2008 ; accepted in final form 13 February 2009

The present study investigated the significance of apical transport proteins for ruminal acetate absorption and their interaction with different anions. In anion competition experiments in the washed reticulorumen, chloride disappearance rate (initial concentration, 28 mM) was inhibited by the presence of a short-chain fatty acid mixture (15 or 30 mM of each acetate, propionate, and butyrate). Disappearance rates of acetate and propionate, but not butyrate (initial concentration, 25 mM each) were diminished by 40 or 80 mM chloride. In isolated ovine ruminal epithelia mounted in Ussing chambers, an increase in chloride concentration from 4.5 to 90 mM led to a decrease of apical acetate uptake at a concentration of 0.5 mM. Mucosal nitrate inhibited acetate uptake most potently whereas sulfate had no effect. Decreasing mucosal pH from 7.4 to 6.1 approximately doubled uptake of acetate both at 0.5 and 10 mM, but this doubling was almost abolished when HCO₃^– was absent. The stimulated uptake at mucosal pH 6.1 consisted of a bicarbonate-dependent, nitrate-inhibitable part (K_m = 54 mM) and a bicarbonate-independent component (K_m = 12 mM) that was also sensitive to nitrate inhibition. Maximal uptake was three times larger for bicarbonate-dependent vs. bicarbonate-independent uptake. Mucosal addition of 200 µM DIDS, 400 µM p-chloromercuribenzene sulfonic acid, 800 µM p-hydroxymercuribenzoic acid, or 100 µM phloretin had no effects on acetate uptake although the latter two inhibited L-lactate uptake. Our data conclusively show a dominant involvement of proteins in apical acetate uptake. Previously described pH effects on acetate absorption originate mainly from modulation of acetate/bicarbonate exchange. Additionally, there is bicarbonate-independent uptake of acetate anions that is protein coupled but not via monocarboxylate cotransporter.

anion exchanger; bicarbonate transport; forestomach; monocarboxylate cotransporter; short-chain fatty acids

This article has been cited by other articles:

				G. B. Penner, J. R. Aschenbach, G. Gabel, R. Rackwitz, and M. Oba Epithelial Capacity for Apical Uptake of Short Chain Fatty Acids Is a Key Determinant for Intraruminal pH and the Susceptibility to Subacute Ruminal Acidosis in Sheep J. Nutr., September 1, 2009; 139(9): 1714 - 1720. [Abstract] [Full Text] [PDF]