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: 289/4/G768    most recent 00451.2004v1 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 ISI Web of Science (2) Citing Articles via Google Scholar Google Scholar Articles by Worrell, R. T. Articles by Matthews, J. B. Search for Related Content PubMed PubMed Citation Articles by Worrell, R. T. Articles by Matthews, J. B.

MUCOSAL BIOLOGY

Apical ammonium inhibition of cAMP-stimulated secretion in T84 cells is bicarbonate dependent

¹Epithelial Pathobiology Group, Department of Surgery, ²Department of Molecular and Cellular Physiology, ³Department of Medicine, and ⁴Veterans Affairs Medical Center, University of Cincinnati, Cincinnati, Ohio

Submitted 1 October 2004 ; accepted in final form 25 June 2005

Normal human colonic luminal (NH₄⁺) concentration ([NH₄⁺]) ranges from 10 to 100 mM. However, the nature of the effects of NH₄⁺ on transport, as well as NH₄⁺ transport itself, in colonic epithelium is poorly understood. We elucidate here the effects of apical NH₄⁺ on cAMP-stimulated Cl^– secretion in colonic T84 cells. In HEPES-buffered solutions, 10 mM apical NH₄⁺ had no significant effect on cAMP-stimulated current. In contrast, 10 mM apical NH₄⁺ reduced current within 5 min to 61 ± 4% in the presence of 25 mM HCO₃^–. Current inhibition was not simply due to an increase in extracellular K⁺-like cations, in that the current magnitude was 95 ± 5% with 10 mM apical K⁺ and 46 ± 3% with 10 mM apical NH₄⁺ relative to that with 5 mM apical K⁺. We previously demonstrated that inhibition of Cl^– secretion by basolateral NH₄⁺ occurs in HCO₃^–-free conditions and exhibits anomalous mole fraction behavior. In contrast, apical NH₄⁺ inhibition of current in HCO₃^– buffer did not show anomalous mole fraction behavior and followed the absolute [NH₄⁺] in K⁺-NH₄⁺ mixtures, where K⁺ concentration + [NH₄⁺] = 10 mM. The apical NH₄⁺ inhibitory effect was not prevented by 100 µM methazolamide, suggesting no role for apical carbonic anhydrase. However, apical NH₄⁺ inhibition of current was prevented by 10 min of pretreatment of the apical surface with 500 µM DIDS, 100 µM 4,4'-dinitrostilbene-2,2'-disulfonic acid (DNDS), or 25 µM niflumic acid, suggesting a role for NH₄⁺ action through an apical anion exchanger. mRNA and protein for the apical anion exchangers SLC26A3 [downregulated in adenoma (DRA)] and SLC26A6 [putative anion transporter (PAT1)] were detected in T84 cells by RT-PCR and Northern and Western blots. DRA and PAT1 appear to associate with CFTR in the apical membrane. We conclude that the HCO₃^– dependence of apical NH₄⁺ inhibition of secretion is due to the action of NH₄⁺ on an apical anion exchanger.

CFTR; SLC26A3; SLC26A6; downregulated in adenoma; putative anion transporter 1

This article has been cited by other articles:

				R. T. Worrell, L. Merk, and J. B. Matthews Ammonium transport in the colonic crypt cell line, T84: role for Rhesus glycoproteins and NKCC1 Am J Physiol Gastrointest Liver Physiol, February 1, 2008; 294(2): G429 - G440. [Abstract] [Full Text] [PDF]