Colonic anion secretory defects and metabolic acidosis in mice lacking the NBC1Na+/HCO-3 cotransporter
Colonic anion secretory defects and metabolic acidosis in mice lacking the NBC1Na+/HCO-3 cotransporter
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DOI：
10.1074/jbc.m607041200
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发表时间：
2007-03-23
影响因子：
4.8
通讯作者：
Shull, Gary E.
中科院分区：
文献类型：
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作者：
Gawenis, Lara R.;Bradford, Emily M.;Shull, Gary E.
NBC1 Na+/HCO3- 协同转运蛋白在许多组织中表达，包括肾和肠上皮。 NBC1 突变会导致人类近端肾小管酸中毒，与其在肾脏中 HCO3- 吸收中的作用一致。在肠和结肠上皮细胞中，NBC1 定位于基底外侧膜，并被认为在阴离子分泌中发挥作用。为了检验NBC1在肠道跨上皮HCO3分泌中发挥作用的假设，通过靶向破坏其基因(Slc4a4)来制备无效突变体(NBC1(-/-))小鼠。 NBC1(-/-)小鼠表现出严重的代谢性酸中毒、生长迟缓、血浆Na+减少、醛固酮增多症、脾肿大、牙列异常、肠梗阻和断奶前死亡。在cAMP刺激的NBC1(-/-)盲肠上皮细胞中，细胞内pH值(pH;)没有改变，但在钠去除和再添加过程中pH(i)调节受到损害。 NBC1(-/-) 结肠的生物电测量显示阿米洛利敏感的 Na+ 吸收增加。在同时含有 Cl- 和 HCO3- 的林格溶液中，cAMP 刺激的阴离子分泌量在 NBC1(-/-) 远端结肠中正常，但在近端结肠中增加，这种增加在很大程度上受到基底外侧 NKCC1 Na+-K+-2Cl(-) 协同转运蛋白活性增强的支持。在阴离子替代研究中，碳酸酐酶受到抑制，跨上皮阴离子电导仅限于 HCO3-，结果显示 NBC1(-/-) 近端结肠中 cAMP 刺激的 HCO3- 分泌和 SITS 敏感电流均急剧下降。这些结果与 NBC1 在肾脏 HCO3- 吸收中的已知功能一致，并证明 NBC1 活性是近端结肠中 cAMP 刺激的阴离子分泌期间 HCO3- 吸收的基底外侧机制的组成部分。
The NBC1 Na+/HCO3- cotransporter is expressed in many tissues, including kidney and intestinal epithelia. NBC1 mutations cause proximal renal tubular acidosis in humans, consistent with its role in HCO3- absorption in the kidney. In intestinal and colonic epithelia, NBC1 localizes to basolateral membranes and is thought to function in anion secretion. To test the hypothesis that NBC1 plays a role in transepithelial HCO3- secretion in the intestinal tract, null mutant (NBC1(-/-)) mice were prepared by targeted disruption of its gene (Slc4a4). NBC1(-/-) mice exhibited severe metabolic acidosis, growth retardation, reduced plasma Na+, hyperaldosteronism, splenomegaly, abnormal dentition, intestinal obstructions, and death before weaning. Intracellular pH (pH;) was not altered in cAMP-stimulated epithelial cells of NBC1(-/-) cecum, but pH(i) regulation during sodium removal and readdition was impaired. Bioelectric measurements of NBC1(-/-) colons revealed increased amiloride-sensitive Na+ absorption. In Ringer solution containing both Cl- and HCO3-, the magnitude of cAMP-stimulated anion secretion was normal in NBC1(-/-) distal colon but increased in proximal colon, with the increase largely supported by enhanced activity of the basolateral NKCC1 Na+-K+-2Cl(-) cotransporter. Anion substitution studies in which carbonic anhydrase was inhibited and transepithelial anion conductance was limited to HCO3- revealed a sharp decrease in both cAMP-stimulated HCO3- secretion and SITS-sensitive current in NBC1(-/-) proximal colon. These results are consistent with the known function of NBC1 in HCO3- absorption in the kidney and demonstrate that NBC1 activity is a component of the basolateral mechanisms for HCO3- uptake during cAMP-stimulated anion secretion in the proximal colon.