title: Influence of ammonia on sodium absorption in rat proximal colon.
abstract: The influence of ammonia on sodium and chloride fluxes in rat proximal colon was studied in Ussing chamber experiments. Under short-circuit conditions, the proximal colon absorbed sodium and secreted chloride. The presence of ammonia (30 mmol 1(-1) mucosal) diminished Na+ absorption, but had hardly any influence on Cl- fluxes. Blocking the apical Na+/H+ exchanger isoform NHE2 by amiloride or HOE642 diminished absorptive Na+ and Cl- fluxes. In contrast, the NHE3-specific antagonist S3226 was ineffective. Amiloride and HOE642 also inhibited the effect of ammonia on net sodium absorption. In bicarbonate-free buffer solution, ammonia failed to alter the absorptive fluxes of sodium and chloride, but increased the secretory fluxes of Na+ and Cl-. The latter effect was blocked by HOE642. These results suggest that basal NaCl absorption in rat proximal colon depends to a large extent on NHE2. Mucosal ammonium decreases Na+ absorption and this effect can be antagonized by blocking NHE2. This observation suggests that ammonium interacts with the apical Na+/H+ exchanger, thereby diminishing sodium absorption.
authors.affiliation: Institut für Veterinär-Physiologie, Universität Zürich, Switzerland. cermak@vetphys.unizh.ch
authors.forename: R
authors.initials: R
authors.lastname: Cermak
authors.forename: C
authors.initials: C
authors.lastname: Lawnitzak
authors.forename: E
authors.initials: E
authors.lastname: Scharrer
mesh_terms: D000584:Amiloride / Q000494:pharmacology; D000641:Ammonia / Q000494:pharmacology*; D000818:Animals; D002712:Chlorides / Q000378:metabolism; D003106:Colon / Q000378:metabolism*; D006146:Guanidines / Q000494:pharmacology; D007408:Intestinal Absorption / Q000187:drug effects*; D008297:Male; D008689:Methacrylates / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012964:Sodium / Q000378:metabolism*; D017923:Sodium-Hydrogen Exchangers / Q000037:antagonists & inhibitors; D013450:Sulfones / Q000494:pharmacology
chemical_list: C118956:3-(2-(3-guanidino-2-methyl-3-oxo-propenyl)-5-methylphenyl)-N-isopropylidene-2-methyl-acrylamide dihydrochloride; D002712:Chlorides; D006146:Guanidines; D008689:Methacrylates; D017923:Sodium-Hydrogen Exchangers; D013450:Sulfones; D000641:Ammonia; D000584:Amiloride; C093373:cariporide; D012964:Sodium