Dextran Sulfate Sodium-Induced Chronic Colitis Attenuates Ca2+ -Activated Cl- Secretion In Murine Colon By Downregulating Tmem16a

Attenuated Ca2+ -activated C1(-) secretion has previously been observed in the model of dextran sulfate sodium (DSS)-induced colitis. Prior studies have implicated dysfunctional muscarinic signaling from basolateral membranes as Ihe potential perpetrator leading to decreased Ca2+-activated Cl- secretion. However, in our chronic model of DSS-colitis, cholinergic receptor muscarinic 3 (ChrniS) transcript (1.028 +/- 0.12 vs. 1.029 +/- 0.27, P > 0.05) and CHRM3 protein expression (1.021 +/- 0.24 vs. 0.928 +/- 0.09, P > 0.05) were unchanged. Therefore, we hypothesized that decreased carbachol (CCH)-stimulated Cl- secretion in DSS-induced colitis could be attributed to a loss of Ca2+ -activated C1(-)-channels (CaCC) in apical membranes of colonic epithelium. To establish this chemically-induced colitis, Balb/C mice were exposed to 4% DSS for five alternating weeks to stimulate a more moderate, chronic colitis. Upon completion of the protocol, whole thickness sections of colon were mounted in an Ussing chamber under voltage-damp conditions. DSS-induced colitis demonstrated a complete inhibition of basolateral administration of CCH-stimulated C1(-) secretion that actually displayed a reversal in polarity (15.40 +/- 2.22 mu A/cm(2) vs. 2.47 +/- 0.25 mu A/cm(2)). Western blotting of potential CaCCs, quantified by densitometric analysis, demonstrated no change in bestrophin-2 and cystic fibrosis transmembrane regulator, whereas anoctamin-1 [ANOl, transmembrane protein 16A (TMEM16A)] was significantly downregulated (1.001 +/- 0.13 vs. 0.510 +/- 0.12, P < 0.05). Our findings indicate that decreased expression of TMEM16A in DSS-induced colitis contributes to the decreased Ca2+ -activated Cl- secretion in murine colon.