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This Article Full Text (PDF) All Versions of this Article: ajpgi.00157.2009v2    most recent ajpgi.00157.2009v1 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 Yu, H. Articles by Bachmann, O. PubMed PubMed Citation Articles by Yu, H. Articles by Bachmann, O.

Research Article

Secretagogue stimulation enhances NBCe1 (electrogenic Na⁺/HCO₃^- cotransporter) surface expression in murine colonic crypts

¹Hannover Medical School, Hannover, Germany ²Hannover Medical School ³Case Western Reserve University ⁴University of Cincinnati College of Medicine ⁵Medizinische Hochschule Hannover

Submitted 27 April 2009 ; revision received 25 August 2009 ; accepted in final form 17 September 2009

ABSTRACT

A Na⁺/HCO₃^- cotransporter (NBC) is located in the basolateral membrane of the gastrointestinal epithelium, where it imports HCO₃^- during stimulated anion secretion. Having previously demonstrated secretagogue activation of NBC in murine colonic crypts, we now asked whether vesicle traffic and exocytosis are involved in this process. Electrogenic NBCe1-B was expressed at significantly higher levels than electroneutral NBCn1 in colonic crypts as determined by QRT-PCR. In cell surface biotinylation experiments, a time-dependent increase in biotinylated NBCe1 was observed, which occured with a peak of +54.8 % after 20 minutes with forskolin (p<0.05), and more rapidly with a peak of +59.8 % after 10 minutes with carbachol (p<0.05), and which corresponded well with the time course of secretagogue-stimulated colonic bicarbonate secretion in Ussing chamber experiments. Accordingly, in isolated colonic crypts pre-treated with forskolin and carbachol for 10 minutes, respectively, and subjected to immunohistochemistry, the NBCe1 signal showed a markedly stronger colocalization with the E-cadherin signal which was used as a membrane marker, as compared with the untreated control. Cytochalasin D did not change the observed increase in membrane abundance, while colchicine alone enhanced NBCe1 membrane expression without an additional increase after carbachol or forskolin, and LY294002 had a marked inhibitory effect. Taken together, our results demonstrate a secretagogue-induced increase of NBCe1 membrane expression. Vesicle traffic and exocytosis might thus represent a novel mechanism of intestinal NBC activation by secretagogues.

Na+/HCO3- cotransport; Colon; Membrane expression