| Title | Loss of Ca-mediated ion transport during colitis correlates with reduced ion transport responses to a Ca-activated K channel opener. | | Author(s) | Hirota CL, McKay DM | | Institution | Intestinal Disease Research Programme, Department of Pathology and Molecular Medicine, McMaster University, 3330 Hospital Drive Northwest, Calgary, Alberta, Canada. chirota@ucalgary.ca | | Source | Br J Pharmacol 2009 Apr; 156(7):1085-97. | | MeSH | Animals
Bethanechol
Biological Transport, Active
Calcium
Chlorides
Colitis
Colon
Dextran Sulfate
Enzyme Activation
Intestinal Mucosa
Ion Channel Gating
Ion Transport
Male
Mice
Mice, Inbred BALB C
Potassium Channels, Calcium-Activated
Protein Kinase C
Protein Subunits
RNA, Messenger
Receptor, Muscarinic M3
Sodium-Potassium-Exchanging ATPase
Tetradecanoylphorbol Acetate
| | Abstract | BACKGROUND AND PURPOSE: Epithelial surface hydration is critical for proper gut function. However, colonic tissues from individuals with inflammatory bowel disease or animals with colitis are hyporesponsive to Cl(-) secretagogues. The Cl(-) secretory responses to the muscarinic receptor agonist bethanechol are virtually absent in colons of mice with dextran sodium sulphate (DSS)-induced colitis. Our aim was to define the mechanism underlying this cholinergic hyporesponsiveness. EXPERIMENTAL APPROACH: Colitis was induced by 4% DSS water, given orally. Epithelial ion transport was measured in Ussing chambers. Colonic crypts were isolated and processed for mRNA expression via RT-PCR and protein expression via immunoblotting and immunolocalization. KEY
RESULTS: Expression of muscarinic M(3) receptors in colonic epithelium was not decreased during colitis. Short-circuit current (I(SC)) responses to other Ca(2+)-dependent secretagogues (histamine, thapsigargin, cyclopiazonic acid and calcium ionophore) were either absent or severely attenuated in colonic tissue from DSS-treated mice. mRNA levels of several ion transport molecules (a Ca(2+)-regulated Cl(-) channel, the intermediate-conductance Ca(2+)-activated K(+) channel, the cystic fibrosis transmembrane conductance regulator, the Na(+)/K(+)-ATPase pump or the Na(+)/K(+)/2Cl(-) co-transporter) were not reduced in colonic crypts from DSS-treated mice. However, protein expression of Na(+)/K(+)-ATPase alpha1 subunits was decreased twofold during colitis. Activation of Ca(2+)-activated K(+) channels increased I(SC) significantly less in DSS colons compared with control, as did the protein kinase C activator, phorbol 12-myristate 13-acetate.
CONCLUSIONS AND
IMPLICATIONS: Decreased Na(+)/K(+)-ATPase expression probably contributes to overall epithelial hyporesponsiveness during colitis, while dysfunctional K(+) channels may account, at least partially, for lack of epithelial secretory responses to Ca(2+)-mediated secretagogues. | | Language | eng | | Pub Type(s) | Journal Article
Research Support, Non-U.S. Gov't
| | PubMed ID | 19298254 |
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