Appearance of segmental discrepancy of anion transport in rat distal colon.
The present study investigated the segmental discrepancy of 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 (DC(1)) and the segment 4 cm away from lymph node (DC(4)) were 4.09+/-0.66 muA/cm(2) and 18.84+/-3.18 muA/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 HCO(3)(-) in both DC(1) and DC(4) (n=5, p<0.001). Furthermore luminal pretreatment with K(+) blockers, TEA (5 mM) and glybenclamide (100 muM) didn't affect forskolin and bumetanide-enhanced I(SC). Reducing serosal Cl(-) concentration increased forskolin-induced I(SC) by 90% in DC(1) but decreased forskolin-induced I(SC) in DC(4) by 50%. Furthermore, pretreatment with serosal bumetanide, an inhibitor of Na(+)-K(+)-2Cl(-) cotransporter, enhanced forskolin-induced I(SC) by 87% in DC(1), from 4.09+/-0.66 muA/cm(2) to 7.65+/-0.53 muA/cm(2) (n=6, p<0.01), but inhibited forskolin-induced I(SC) by 50% in DC(4), from 29.19+/-4.51 muA/cm(2) to 15.06+/-4.10 muA/cm(2) (n=6, p<0.05). Pretreatment with luminal amiloride (10 muM), an inhibitor of ENaC, and serosal 4,4'-diisothiocyanatostilbene-2,2'-disulphonic acid (DIDS) (200 muM), an inhibitor of NBC, significantly inhibited the forskolin-induced I(SC) in DC(1) (n=6, p<0.05), but not in DC(4). 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 DC(4) was significantly higher than that in DC(1). In conclusion, the rat distal colon manifests a segmental discrepancy in anion transport stimulated by luminal forskolin. HCO(3)(-) might be predominantly involved in the forskolin-induced anion secretion in DC(1), but Cl(-) might be the main component of the anion secretion in DC(4).
Xue
Hong
H
Department of Physiology, Basic Medical College, Capital Medical University, Beijing 100069, China.
Tian
Yue Min
YM
Yan
Ming
M
Yang
Ning
N
Chen
Xin
X
Xing
Ying
Y
Zhu
Jin Xia
JX
D000262:Adenylyl Cyclases / Q000378:metabolism; D000818:Animals; D000838:Anions / Q000378:metabolism; D001693:Biological Transport, Active / Q000502:physiology; D005576:Colforsin / Q000494:pharmacology; D003106:Colon / Q000378:metabolism*; D000242:Cyclic AMP / Q000502:physiology; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000096:biosynthesis / Q000235:genetics; D020536:Enzyme Activators / Q000494:pharmacology; D015870:Gene Expression / Q000502:physiology; D005905:Glyburide / Q000494:pharmacology; D008297:Male; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D051381:Rats; D017207:Rats, Sprague-Dawley; D020133:Reverse Transcriptase Polymerase Chain Reaction; D028021:Sodium-Potassium-Chloride Symporters / Q000096:biosynthesis / Q000235:genetics; D064506:Solute Carrier Family 12, Member 2
D000838:Anions; D020536:Enzyme Activators; D012333:RNA, Messenger; C578879:Slc12a2 protein, rat; D028021:Sodium-Potassium-Chloride Symporters; D064506:Solute Carrier Family 12, Member 2; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D005576:Colforsin; D000242:Cyclic AMP; D000262:Adenylyl Cyclases; D005905:Glyburide