Differential Cl- and HCO3- mediated anion secretion by different colonic cell types in response to...

Colonic epithelium is known to secrete both Cl(-) and HCO(3)(-), 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 HCO(3)(-) 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.

Colonic epithelial anion secretion was studied by using the short circuit current (I(SC)) technique. RT-PCR was used to examine the expression of Na(+)-HCO(3)(-)-cotranspoter in different epithelial cell types.

TMP produced a concentration-dependent I(SC) which was increase in both T84 and Caco-2 cells. When extracellular Cl(-) was removed, TMP-induced I(SC) was abolished by 76.6% in T84 cells, but not in Caco-2 cells. However, after both Cl(-) and HCO(3)(-) were removed, TMP-induced I(SC) in Caco-2 cells was reduced to 10%. Bumetanide, an inhibitor of Na(+)-K(+)-Cl(-)-cotranspoter, inhibited the TMP-induced I(SC) 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(+)-HCO(3)(-) cotransporter, inhibited the TMP-induced current in Caco-2 cells by 93.3%. In freshly isolated rat colonic mucosa, TMP stimulated distinct I(SC) responses similar to that observed in T84 and Caco-2 cells depending on the concentration used. RT-PCR revealed that the expression of Na(+)-HCO(3)(-) cotransporter in Caco-2 cells was 4-fold more greater than that in T84 cells.

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 HCO(3)(-) secretion by villus cells at a higher concentration, suggesting different roles of these cells in colonic Cl(-) and HCO(3)(-) secretion.