QUICK SEARCH:   [advanced] Author: Keyword(s):
Home     Help     Feedback     Subscriptions     Archive     Search     Table of Contents

First published online July 31, 2009
Journal of Experimental Biology 212, 2645-2655 (2009)
Published by The Company of Biologists 2009
doi: 10.1242/jeb.028928

This Article Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted 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 Google Scholar Articles by Bartolo, R. C. Articles by Butt, A. G. PubMed PubMed Citation Articles by Bartolo, R. C. Articles by Butt, A. G. Social Bookmarking                         What's this?

Secretagogues stimulate electrogenic HCO₃^– secretion in the ileum of the brushtail possum, Trichosurus vulpecula: evidence for the role of a Na⁺/HCO₃^– cotransporter

Ray C. Bartolo^1,2, Natalie Harfoot¹, Mike Gill¹, Bernie J. McLeod² and A. Grant Butt^1,*

¹ Department of Physiology, School of Medical Sciences, University of Otago, PO Box 913, Dunedin 9054, New Zealand
² AgResearch, Invermay Agricultural Centre, Private Bag 50034, Mosgiel 9024, New Zealand

^* Author for correspondence (e-mail: grant.butt{at}otago.ac.nz)

Accepted 13 May 2009

Fluid secretion is essential for intestinal function and, in eutherian mammals, is driven by electrogenic Cl^– transport, which is dependent upon a bumetanide-sensitive, basolateral Na⁺/K⁺/2 Cl^– cotransporter, NKCC1. However, ileal secretion in the brushtail possum, a marsupial, involves a fundamentally different process, since NKCC1 expression is low in this tissue and the secretagogue-induced short circuit current (I_sc) is insensitive to bumetanide. In view of these differences we have investigated the basis of the secretory response of the possum ileum. In the Ussing chamber the secretory I_sc is independent of Cl^– but dependent upon Na⁺ and serosal HCO₃^–/CO₂, suggesting that secretagogues stimulate electrogenic HCO₃^– secretion. In agreement with this, serosal DIDS (4,4'-diisothiocyano-stilbene-2,2'-disulfonate; 1 mmol l^–1) inhibited the secretory response. However, acetazolamide (1 mmol l^–1) and serosal amiloride (1 mmol l^–1) had little effect, indicating that HCO₃^– secretion is driven by HCO₃^– transport from the serosal solution into the cell, rather than hydration of CO₂ by carbonic anhydrase. Consistent with this the pancreatic variant of the electrogenic Na⁺/HCO₃^– cotransporter (pNBC) is highly expressed in the ileal epithelium and is located in the basolateral membrane of the epithelial cells, predominantly in the mid region of the villi, with lower levels of expression in the crypts and no expression in the villous tips. We conclude that the secretory response of the possum ileum involves electrogenic HCO₃^– secretion driven by a basolateral pNBC and that the ileal HCO₃^– secretion is associated with a specialised function of the possum ileum, most probably related to hindgut fermentation.

Key words: brushtail possum, Trichosurus vulpecula, marsupial, ileum, bicarbonate secretion, NaHCO₃ cotransport

CiteULike    Complore    Connotea    Del.icio.us    Digg    Reddit    Technorati    Twitter    What's this?