Loss of Ca-mediated ion transport during colitis correlates with reduced ion transport responses to a Ca-activated K channel opener.
OBJECTIVE
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.


METHODS
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.


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
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.
Hirota
Christina L
CL
Intestinal Disease Research Programme, Department of Pathology and Molecular Medicine, McMaster University, 3330 Hospital Drive Northwest, Calgary, Alberta, Canada. chirota@ucalgary.ca
McKay
Derek M
DM
D000818:Animals; D018723:Bethanechol / Q000494:pharmacology; D001693:Biological Transport, Active; D002118:Calcium / Q000502:physiology*; D002712:Chlorides / Q000378:metabolism; D003092:Colitis / Q000139:chemically induced / Q000378:metabolism*; D003106:Colon / Q000187:drug effects / Q000378:metabolism; D016264:Dextran Sulfate; D004789:Enzyme Activation; D007413:Intestinal Mucosa / Q000187:drug effects / Q000378:metabolism; D015640:Ion Channel Gating; D017136:Ion Transport; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D024681:Potassium Channels, Calcium-Activated / Q000819:agonists / Q000502:physiology*; D011493:Protein Kinase C / Q000378:metabolism; D021122:Protein Subunits / Q000096:biosynthesis / Q000235:genetics; D012333:RNA, Messenger / Q000096:biosynthesis; D043587:Receptor, Muscarinic M3 / Q000819:agonists / Q000096:biosynthesis / Q000235:genetics; D000254:Sodium-Potassium-Exchanging ATPase / Q000096:biosynthesis / Q000235:genetics; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D002712:Chlorides; D024681:Potassium Channels, Calcium-Activated; D021122:Protein Subunits; D012333:RNA, Messenger; D043587:Receptor, Muscarinic M3; D018723:Bethanechol; D016264:Dextran Sulfate; D011493:Protein Kinase C; C497344:Atp1a1 protein, mouse; D000254:Sodium-Potassium-Exchanging ATPase; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium