Charney Alan N, Egnor Richard W, Henner David, Rashid Haroon, Cassai Nicholas, Sidhu Gurdip S
Nephrology Section, VA Medical Center, 423 East 23rd St., New York, NY 10010, USA.
Am J Physiol Cell Physiol. 2004 May;286(5):C1062-70. doi: 10.1152/ajpcell.00454.2003. Epub 2003 Dec 24.
In rat ileum and colon, apical membrane Cl(-)/HCO(3)(-) exchange and net Cl(-) absorption are stimulated by increases in Pco(2) or [HCO(3)(-)]. Because changes in Pco(2) stimulate colonic Na(+) absorption, in part, by modulating vesicular trafficking of the Na(+)/H(+) exchanger type 3 isoform to and from the apical membrane, we examined whether changes in Pco(2) affect net Cl(-) absorption by modulating vesicular trafficking of the Cl(-)/HCO(3)(-) exchanger anion exchanger (AE)1. Cl(-) transport across rat distal ileum and colon was measured in the Ussing chamber, and apical membrane protein biotinylation of these segments and Western blots of recovered proteins were performed. In colonic epithelial apical membranes, AE1 protein content was greater at Pco(2) 70 mmHg than at Pco(2) 21 mmHg but was not affected by pH changes in the absence of CO(2). AE1 was internalized when Pco(2) was reduced and exocytosed when Pco(2) was increased, and both mucosal wortmannin and methazolamide inhibited exocytosis. Wortmannin also inhibited the increase in colonic Cl(-) absorption caused by an increase in Pco(2). Increases in Pco(2) stimulated ileal Cl(-) absorption, but wortmannin was without effect. Ileal epithelial apical membrane AE1 content was not affected by Pco(2). We conclude that CO(2) modulation of colonic, but not ileal, Cl(-) absorption involves effects on vesicular trafficking of AE1.
在大鼠回肠和结肠中，顶膜Cl⁻/HCO₃⁻交换和净Cl⁻吸收会因Pco₂或[HCO₃⁻]升高而受到刺激。由于Pco₂的变化部分通过调节3型钠/氢交换体往返顶膜的囊泡运输来刺激结肠钠吸收，我们研究了Pco₂的变化是否通过调节Cl⁻/HCO₃⁻交换体阴离子交换蛋白（AE）1的囊泡运输来影响净Cl⁻吸收。在尤斯灌流小室中测量Cl⁻跨大鼠远端回肠和结肠的转运，并对这些节段的顶膜蛋白进行生物素化以及对回收的蛋白进行蛋白质免疫印迹分析。在结肠上皮顶膜中，Pco₂为70 mmHg时AE1蛋白含量高于Pco₂为21 mmHg时，但在无CO₂时不受pH变化影响。当Pco₂降低时AE1被内化，当Pco₂升高时则被胞吐，并且黏膜侧的渥曼青霉素和甲唑酰胺均抑制胞吐作用。渥曼青霉素还抑制了因Pco₂升高引起的结肠Cl⁻吸收增加。Pco₂升高刺激回肠Cl⁻吸收，但渥曼青霉素无作用。回肠上皮顶膜AE1含量不受Pco₂影响。我们得出结论，CO₂对结肠而非回肠Cl⁻吸收的调节涉及对AE1囊泡运输的影响。
