title: Differential Cl- and HCO3- mediated anion secretion by different colonic cell types in response to tetromethylpyrazine.
abstract: OBJECTIVE
  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.
  
  
  METHODS
  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.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Epithelial Cell Biology Research Center, Department of Physiology, Faculty of Medicine, The Chinese University of Hong Kong, Shatin, NT, Hong Kong, China.
authors.forename: Jin-Xia
authors.initials: JX
authors.lastname: Zhu
authors.forename: Ning
authors.initials: N
authors.lastname: Yang
authors.forename: Qiong
authors.initials: Q
authors.lastname: He
authors.forename: Lai-Ling
authors.initials: LL
authors.lastname: Tsang
authors.forename: Wen-Chao
authors.initials: WC
authors.lastname: Zhao
authors.forename: Yiu-Wa
authors.initials: YW
authors.lastname: Chung
authors.forename: Hsiao-Chang
authors.initials: HC
authors.lastname: Chan
mesh_terms: D000818:Animals; D000838:Anions / Q000378:metabolism; D001639:Bicarbonates / Q000378:metabolism*; D018938:Caco-2 Cells; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D002712:Chlorides / Q000378:metabolism*; D015870:Gene Expression; D006801:Humans; D007413:Intestinal Mucosa / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D008297:Male; D011719:Pyrazines / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D020133:Reverse Transcriptase Polymerase Chain Reaction; D027982:Sodium-Bicarbonate Symporters / Q000235:genetics / Q000378:metabolism
chemical_list: D000838:Anions; D001639:Bicarbonates; D002121:Calcium Channel Blockers; D002712:Chlorides; D011719:Pyrazines; D027982:Sodium-Bicarbonate Symporters; C017953:tetramethylpyrazine