Differential CI^-and HCO_3^- mediated anion secretion by different colonic cell types in response to tetromethylpyrazine

AIM: Colonic epithelium is known to secrete both CI- and HCO3, but the secretory mechanisms of different colonic cell types are not fully understood. The present study aimed to investigate the differential activation of Cl-and HCO3 secretion by tetramethylpyrazine (TMP) in human crypt-like cell line, T84, and villus-like cell line, Caco-2, in comparison to the TMP-induced secretory response in freshly isolated rat colonic mucosa. METHODS: Colonic epithelial anion secretion was studied by using the short circuit current (Isc) technique. RT-PCR was used to examine the expression of Na^+-HCO3-cotranspoter in different epithelial cell types. RESULTS: TMP produced a concentration-dependent Isc which was increase in both T84 and Caco-2 cells. When extracellular CI was removed, TMP-induced Isc was abolished by 76.6% in T84 cells, but not in Caco-2 cells. However, after both CI and HCO3- were removed, TMP-induced Isc in Caco-2 cells was reduced to 10%. Bumetanide, an inhibitor of Na^+-K^+-Cl-cotranspoter, inhibited the TMP-induced Isc by 96.7% in T84 cells, but only 47.9% in Caco-2 cells. In the presence of bumetanide and 4, 4'-diisothiocyanostilbene-2, 2'-disulfonic acid, an inhibitor of Na^+-HCO3- cotransporter, inhibited the TMP-induced current in Caco-2 cells by 93.3% .In freshly isolated rat colonic mucosa, TMP stimulated distinct Isc responses similar to that observed in T84 and Caco-2 cells depending on the concentration used. RT-PCR revealed that the expression of Na^+-HCO3- cotransporter in Caco-2 cells was 4-fold more greater than that in T84 cells. CONCLUSION: TMP exerts concentration-dependent differential effects on different colonic cell types with stimulation of predominant Cl- secretion by crypt cells at a lower concentration, but predominant HCO3- secretion by villus cells at a higher concentration, suggesting different roles of these cells in colonic Cl and HCO3 secretion.

Effect of tetramethylpyrazine on exocrine pancreatic and bile secretion

AIM: To investigate the effect of tetramethylpyrazine (ligustrazine, TMP) on the secretion of exocrine pancreas (and biliary).METHODS: In in vivo study, we investigated the effect of TMP on the secretion of pancreatic-bile juice (PBJ) in rats.Using human pancreatic duct cell line, CAPAN-1, combined with the short-circuit current (ISC) technique we further studied the effect of TMP on the pancreatic anion secretion.RESULTS: Administration of TMP (80 mg/kg, ip) significantly increased the secretion of PBJ (P<0.05), but the pH of PBJ and the secretion of pancreatic protein were not significantly affected. Basolateral addition of TMP produced a dosedependent increase in ISC(EC50=1.56 mmol/L), which contained a fast transient ISC response followed by a slow decay. Apical application of Cl- channel blockers, DPC (1 mmol/L),decreased the response by about 67.1% (P<0.001), whereas amiloride (100 μmol/L), a epithelial sodium channel blockers,had no effect. Removal of extracellular HCO3- abolished TMP-induced increase in ISC by about 74.4 % (P<0.001),but the removal of external Cl- did not. Pretreatment with phosphodiesterase inhibitor, TBMX(0.5 mmol/L), decreased the TMP-induced ISC by 91% (P<0.001).CONCLUSION: TMP could stimulate the secretion of PBJ,especially pancreatic ductal HCO3- secretion via cAvlp or cGMP-dependent pathway. It need further study to investigate the roles of cAMP or cGMP in the effect of TMP on the secretion of exocrine pancreas.