Effect of TongXie-YaoFang on Cl− and HCO3− Transport in Diarrhea-Predominant Irritable Bowel Syndrome Rats

TongXie-YaoFang (TXYF) can effectively alleviate the symptoms of diarrhea-predominant irritable bowel syndrome (D-IBS) patients. However, the curative mechanism has not been fully clarified. The study was designed to investigate the effect of TXYF on the colonic ion transport induced by serotonin (5-HT) in D-IBS rats. A method of multiple stress (neonatal maternal separation (NMS) combined with restraint stress (RS)) was used to induce the D-IBS model. The model rats were randomly divided into two groups: NMS + RS group and TXYF-formula group, and the normal control (no handling) rats were classified as NH group. In the NMS + RS group, the change of short-circuit current (ΔI sc) induced by 5-HT was lower than that in the NH and TXYF-formula groups. After removing of the extracellular Cl(-) or HCO3 (-) or basolateral Na(+) or blocking the cystic fibrosis transmembrane conductance regulator (CFTR), Na(+)-K(+)-2Cl(-) cotransporter (NKCC), Na(+)-HCO3 (-) cotransporter, Cl(-)/HCO3 (-) exchanger, K(+) channel, or Na(+)/K(+)-ATPase, respectively, there was no difference in 5-HT-induced ΔI sc among the three groups. These data suggest that TXYF can regulate 5-HT-induced Cl(-) and HCO3 (-) secretion, possibly mediated by the combined action of CFTR, NKCC, Na(+)-HCO3 (-) cotransporter, Cl(-)/HCO3 (-) exchanger, K(+) channel, and Na(+)/K(+)-ATPase.