期刊
HEPATOLOGY
卷 51, 期 3, 页码 891-902出版社
WILEY-BLACKWELL
DOI: 10.1002/hep.23403
关键词
-
资金
- Spanish Ministry of Education and Science [SAF2005-02468, SAF2006-07818]
- Carlos III Institute of Health [FIS-01/0777]
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.)
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