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摘要
The present study investigated the segmental discrepancy 4 the rat distal colonic anion transport induced by luminal forskolin and the possible underlying mechanisms using short-circuit current recording technique and comparative quantity real-time PCR analysis. Forskolin-induced I-sc in the segment next to lymph node (DC1) and the segment 4 cm away from lymph node (DC4) were 4.09 +/- 0.66 mu A/cm(2) and 18.84 +/- 3.18 mu A/cm(2) (n=13), respectively, which were blocked by luminal Cl- channel blocker, glybenclamide (1 mM) (n=5, p<0.01), as well as removal of extracellular Cl- and HCO3- in both DC1 and DC4 (n=5, p<0.001). Furthermore luminal pretreatment with K+ blockers, TEA (5 mM) and glybenclamide (100 mu M) didn't affect forskolin and bumetanide-enhanced I-SC. Reducing serosal Cl- concentration increased forskolin-induced I-SC by 90% in DC1 but decreased forskolin-induced I-SC in DC4 by 50%. Furthermore, pretreatment with serosal bumetanide, an inhibitor of Na+-K+-2Cl(-) cotransporter, enhanced forskolin-induced I-SC by 87% in DC1, from 4.09 +/- 0.66 mu A/cm(2) to 7.65 +/- 0.53 mu A/cm(2) (n=6, p<0.01), but inhibited forskolin-induced I-SC by 50% in DC4, from 29.19 +/- 4.51 mu A/cm(2) to 15.06 +/- 4.10 mu A/cm(2) (n=6, p<0.05). Pretreatment with luminal amiloride (10 mu M), an inhibitor of ENaC, and serosal 4,4'-diisothioevanatostilbene-2,2'-disulphonic acid (DIDS) (200 mu m), an inhibitor of NBC, significantly inhibited the forskolin-induced I-SC in DC1 (n=6, p<0.05), but not in DC4. Real-time PCR analysis did not show the significant differences between the two segments in the expression amounts of CFTR and NKCC mRNAs, however the expression of NBC mRNA in DC4 was significantly higher than that in DC1. In conclusion, the rat distal colon manifests a segmental discrepancy in anion transport stimulated by luminal forskolin. HCO3- might be predominantly involved in the forskolin-induced anion secretion in DC1, but Cl- might be the main component of the anion secretion in DC4.
