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: 294/2/G429    most recent 00251.2006v1 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 Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Web of Science (1) 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

Ammonium transport in the colonic crypt cell line, T84: role for Rhesus glycoproteins and NKCC1

Departments of ¹Surgery and ²Molecular and Cellular Physiology, University of Cincinnati, Cincinnati, Ohio; ³Department of Surgery, University of Chicago, Chicago, Illinois

Submitted 8 June 2006 ; accepted in final form 15 November 2007

Although colonic lumen NH₄⁺ levels are high, 15–44 mM normal range in humans, relatively few studies have addressed the transport mechanisms for NH₄⁺. More extensive studies have elucidated the transport of NH₄⁺ in the kidney collecting duct, which involves a number of transporter processes also present in the distal colon. Similar to NH₄⁺ secretion in the renal collecting duct, we show that the distal colon secretory model, T84 cell line, has the capacity to secrete NH₄⁺ and maintain an apical-to-basolateral NH₄⁺ gradient. NH₄⁺ transport in the secretory direction was supported by basolateral NH₄⁺ loading on NKCC1, Na⁺-K⁺-ATPase, and the NH₄⁺ transporter, RhBG. NH₄⁺ was transported on NKCC1 in T84 cells nearly as well as K⁺ as determined by bumetanide-sensitive ⁸⁶Rb-uptake. ⁸⁶Rb-uptake and ouabain-sensitive current measurement indicated that NH₄⁺ is transported by Na⁺-K⁺-ATPase in these cells to an equal extent as K⁺. T84 cells expressed mRNA for the basolateral NH₄⁺ transporter RhBG and the apical NH₄⁺ transporter RhCG. Net NH₄⁺ transport in the secretory direction determined by ¹⁴C-methylammonium (MA) uptake and flux occurred in T84 cells suggesting functional RhG protein activity. The occurrence of NH₄⁺ transport in the secretory direction within a colonic crypt cell model likely serves to minimize net absorption of NH₄⁺ because of surface cell NH₄⁺ absorption. These findings suggest that we rethink the present limited understanding of NH₄⁺ handling by the distal colon as being due solely to passive absorption.

RhBG; RhCG; colon; hyperammonemia