Bicarbonate Secretion of Mouse Cholangiocytes Involves Na+-HCO3- Cotransport in Addition to Na+-Independent Cl-/HCO3- Exchange
Bicarbonate Secretion of Mouse Cholangiocytes Involves Na+-HCO3- Cotransport in Addition to Na+-Independent Cl-/HCO3- Exchange
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DOI：
10.1002/hep.23403
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发表时间：
2010-03-01
期刊：
影响因子：
13.5
通讯作者：
Medina, Juan F.
中科院分区：
文献类型：
--
作者：
Uriarte, Iker;Banales, Jesus M.;Medina, Juan F.
胆管细胞的胆汁分泌是沿着胆道适当调节初级小管胆汁所必需的。在人和大鼠胆管细胞中，碳酸氢盐分泌由阴离子交换剂（A-E）2介导，阴离子交换剂（A-E）2是一种电中性Na+非依赖性Cl-/HCO 3- AE，也参与细胞内pH（pH（i））调节。在Ae 2（a，B）缺陷小鼠中，淋巴细胞和成纤维细胞中的pH（i）升高，而胆管细胞中的pH（i）令人惊讶地正常。在这里，我们分析了培养的Ae 2（a，B）（+/+）和Ae 2（a，B）（-/-）小鼠胆管细胞的HCO 3-分泌的机制，通过建立灌注操作后的pH（i）变化的微荧光测量。基于羟乙基磺酸盐的灌注的Cl-撤回显示Ae 2（a，B）（+/+）而不是Ae 2（a，B）（-/-）小鼠胆管细胞可以显示Cl-/HCO 3-交换，因此其完全由Ae 2介导。然而，同时撤出的Cl-和Na+显示，小鼠胆管细胞具有额外的运输活动，在对照大鼠胆管细胞中没有观察到的HCO 3-分泌。丙酸盐为基础的演习表明，这种补充Na+驱动的HCO 3-分泌活动是Cl-独立的，与Na+-HCO 3- cotransport（NBC）一致。Ae 2（a，B）（-/-）中的NBC活性大于Ae 2（a，B）（+/+）小鼠胆管细胞，并且膜去极化实验表明其是产电的。与Slc 4a 4/Nbc 1作为相关转运蛋白的潜在作用一致，Ae 2（a，B）（-/-）小鼠胆管细胞表现出这种产电NBC载体的上调表达。Ae 2（a，B）（+/+）小鼠胆管细胞中Ae 2介导的Cl-/HCO 3-交换受环磷酸腺苷（cAMP）和乙酰胆碱刺激，而Ae 2（a，B）（-/-）小鼠胆管细胞中的NBC活性受cAMP和三磷酸腺苷（ATP）下调。极化的Ae 2（a，B）（-/-）小鼠胆管细胞置于Ussing室中显示cAMP依赖性Cl-电流减少（但未消除）和ATP依赖性/Ca 2+激活的Cl-分泌增加，这与囊性纤维化跨膜电导调节因子信使RNA表达减少和细胞内Ca 2+水平增加平行。结论：在小鼠胆管细胞中，Biclidine的分泌涉及两种不同的调节活动：Ae 2介导的Cl-/HCO 3-交换和Na+-HCO 3-共转运。（《肝脏病学》2010年;51：891-902）
Bicarbonate secretion from cholangiocytes is required for appropriate adjustment of primary canalicular bile along the biliary tract. In human and rat cholangiocytes, bicarbonate secretion is mediated by anion exchanger (A-E) 2, an electroneutral Na+-independent Cl-/HCO3- AE also involved in intracellular pH (pH(i)) regulation. In Ae2(a,b)-deficient mice, pH(i) is increased in lymphocytes and fibroblasts, whereas it is surprisingly normal in cholangiocytes. Here, we analyze the mechanisms for HCO3- secretion in cultured Ae2(a,b)(+/+) and Ae2(a,b)(-/-) mouse cholangiocytes by microfluorimetric measurement of pH(i) changes upon established perfusion maneuvers. Cl- withdrawal by isethionate-based perfusions showed that Ae2(a,b)(+/+) but not Ae2(a,b)(-/-) mouse cholangiocytes can display Cl-/HCO3- exchange, which is therefore entirely mediated by Ae2. Nevertheless, simultaneous withdrawal of Cl- and Na+ revealed that mouse cholangiocytes possess an additional transport activity for HCO3- secretion not observed in control rat cholangiocytes. Propionate-based maneuvers indicated that this supplemental Na+-driven HCO3--secreting activity is Cl--independent, consistent with a Na+-HCO3- cotransport (NBC). NBC activity is greater in Ae2(a,b)(-/-) than Ae2(a,b)(+/+) mouse cholangiocytes, and membrane-depolarization experiments showed that it is electrogenic. Consistent with the potential role of Slc4a4/Nbc1 as the involved transporter, Ae2(a,b)(-/-) mouse cholangiocytes exhibit up-regulated expression of this electrogenic NBC carrier. Whereas Ae2-mediated Cl-/HCO3- exchange in Ae2(a,b)(+/+) mouse cholangiocytes is stimulated by cyclic adenosine monophosphate (cAMP) and acetylcholine, the NBC activity is down-regulated by cAMP and adenosine triphosphate (ATP) in Ae2(a,b)(-/-) mouse cholangiocytes. Polarized Ae2(a,b)(-/-) mouse cholangiocytes placed in Ussing chambers show decreased (but not abolished) cAMP-dependent Cl- current and increased ATP-dependent/Ca2+-activated Cl- secretion, which run in parallel with decreased cystic fibrosis transmembrane conductance regulator messenger RNA expression and increased intracellular Ca2+ levels. Conclusion: Bicarbonate secretion in mouse cholangiocytes involves two differentially regulated activities: Ae2-mediated Cl-/HCO3- exchange and Na+-HCO3- cotransport. (HEPATOLOGY 2010;51:891-902.)