Effects of Cl⁻ and Ca²⁺-free solution on CQ-evoked increase in <i>I_SC</i> in rat ileum.

<p>CQ-induced increases in <i>I_SC</i> was greatly reduced in the absence of Cl<i>⁻</i>(n = 6,A). In the absence of Ca²⁺, CQ-induced increases in <i>I_SC</i> were totally abolished, whereas a decrease in basal <i>I_SC</i> was seen in this Ca²⁺-free condition(n = 5,B). A similar effect was obtained in response to pretreatment with thapsigargin(10⁻⁶M), a Ca²⁺ pump inhibitor(n = 6, C). **<i>P</i><0.01 by unpaired <i>t</i>-test.</p

A working model of CQ in intestinal epithelial cells.

<p>CQ binds to T2Rs activating a G-protein to produce phospholipase C (PLC) in the basement membrane of intestinal epithelial cells followed by Ca²⁺ release from the sarcoplasmic reticulum (SR). Local Ca²⁺ entry through store-operated Ca²⁺ release-activated Ca²⁺ channels(CRAC) drives Cl<i>⁻</i> secretion by stimulating Ca²⁺-activated Cl<i>⁻</i> channels(CaCC) in the apical membrane of intestinal epithelial cells. The intracellular-free chloride concentration is maintained by a Na⁺-K⁺-2Cl⁻ co-transporter that actively accumulates Cl⁻.</p

CQ evoked an increase in <i>I_SC</i> in rat ileum.

<p>CQ dose-dependently increased basal <i>I_SC</i> at low concentrations(≤5×10⁻⁴M), however, it markedly decreased basal <i>I_SC</i> at high concentrations (≥10⁻³ M) (n = 6, A). The serosal addition of CQ (3×10⁻⁴M) increased basal <i>I_SC</i>, whereas CQ to mucosal bathing solution had no effect on basal <i>I_SC</i> (n = 6,B)_. The CQ-induced increase in <i>I_SC</i> was not influenced by TTX(n = 4,C). *<i>P</i><0.05; **<i>P</i><0.01 compared with control or apical addition; ^#<i>P</i><0.05 compared with 100 µM group; n.s: no significance by the one-way ANOVA or unpaired <i>t</i>-test.</p

Colocalization of CaCC-TMEM16A and bitter receptor T2R in small intestinal epithelial cells.

<p>Immunohistochemistry was showing TMEM16A and bitter receptor TAS2R10 in rat ileum epithelial cell line IEC-18.</p

Effects of amiloride, CFTR(inh)-172, niflumic acid and furosemide on CQ-evoked increase in I_SC in rat ileum.

<p>The CQ-evoked increase in <i>I_SC</i> was partly inhibited by a blocker of epithelial Na⁺ channels, amiloride(10⁻⁴M)(n = 7, A and G). Cl⁻ channel inhibitor CFTR(inh)-172(10⁻⁵M) did not affect this CQ-evoked response (n = 5,B and G)_. An inhibitor of Na⁺-K⁺ -2Cl⁻ cotransporter, furosemide (10⁻⁴M) also reduced the CQ-evoked increase in <i>I_SC</i> (n = 4, C and G). Niflumic acid (10⁻⁴M), DIDS and NPPB almost completely abolished the CQ-evoked increase in Isc(n = 9, D-F and H). *<i>P</i><0.05; **<i>P</i><0.01;n.s: no significance by unpaired <i>t</i>-test.</p