Defective regulation of cholangiocyte Cl-/HCO3(-) and Na+/H+ exchanger activities in primary biliary cirrhosis.
Primary biliary cirrhosis (PBC) is a disorder of unknown origin with autoimmune features. Recently, impaired biliary secretion of bicarbonate has been shown in patients with PBC. Here we have investigated whether bile duct epithelial cells isolated from PBC patients exhibit defects in transepithelial bicarbonate transport by analyzing the activities of 2 ion exchangers, Cl(-)/HCO3(-) anion exchanger 2 (AE2) and Na(+)/H(+) exchanger (NHE) in isolated cholangiocytes. AE2 and NHE activities were studied in basal conditions and after stimulation with cyclic adenosine monophosphate (cAMP) and extracellular adenosine triphosphate (ATP), respectively. Cholangiocytes were grown from needle liver biopsies from 12 PBC patients, 8 normal controls, and 9 patients with other liver diseases. Also, intrahepatic cholangiocytes were cultured after immunomagnetic isolation from normal liver tissue (n = 6), and from recipients undergoing liver transplantation for end-stage PBC (n = 9) and other forms of liver disease (n = 8). In needle-biopsy cholangiocytes, basal AE2 activity was significantly decreased in PBC as compared with normal livers and disease controls. In addition, we observed that though cAMP increased AE2 activity in cholangiocytes from both normal and non-PBC livers, this effect was absent in PBC cholangiocytes. Similarly, though in cholangiocytes from normal and disease control livers extracellular ATP induced a marked enhancement of NHE activity, cholangiocytes from PBC patients failed to respond to purinergic stimulation. In conclusion, our findings provide functional evidence that PBC cholangiocytes exhibit a widespread failure in the regulation of carriers involved in transepithelial H(+)/HCO3(-) transport, thus, providing a molecular basis for the impaired bicarbonate secretion in this cholestatic syndrome.
Melero
Saida
S
Division of Hepatology and Gene Therapy, University of Navarra, Pamplona, Spain.
Spirlì
Carlo
C
Zsembery
Akos
A
Medina
Juan F
JF
Joplin
Ruth E
RE
Duner
Elena
E
Zuin
Massimo
M
Neuberger
James M
JM
Prieto
Jesús
J
Strazzabosco
Mario
M
D000136:Acid-Base Equilibrium; D000255:Adenosine Triphosphate / Q000378:metabolism; D027321:Anion Transport Proteins; D017920:Antiporters; D001652:Bile Ducts / Q000166:cytology / Q000378:metabolism*; D001707:Biopsy, Needle; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000378:metabolism; D004847:Epithelial Cells / Q000378:metabolism; D015870:Gene Expression; D006801:Humans; D008099:Liver / Q000166:cytology / Q000378:metabolism; D008105:Liver Cirrhosis, Biliary / Q000378:metabolism* / Q000503:physiopathology; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000032:analysis; D064606:SLC4A Proteins; D017923:Sodium-Hydrogen Exchangers / Q000235:genetics / Q000378:metabolism*
D027321:Anion Transport Proteins; D017920:Antiporters; D008565:Membrane Proteins; D012333:RNA, Messenger; D064606:SLC4A Proteins; D017923:Sodium-Hydrogen Exchangers; D000255:Adenosine Triphosphate; D000242:Cyclic AMP