AUTOSOMAL-DOMINANT POLYCYSTIC KIDNEY-DISEASE DECREASES ANION-EXCHANGER ACTIVITY

Liver cysts, the most common extrarenal manifestation of autosomal dom inant polycystic kidney disease (ADPKD), derive fl om the intrahepatic biliary epithelium (IBE) and are found in 60-75% of ADPKD patients on dialysis. Secretin-induced secretion by the normal IBE is rich in HCO 3- whereas intact ADPKD liver cysts secrete primarily Cl- in response to secretin. To evaluate the mechanisms of decreased HCO3- secretion b y ADPKD liver cysts, we utilized SV40 large T antigen-immortalized nor mal IBE and ADPKD liver cyst-derived epithelial (LCDE) cell lines that we created. These cell Lines express biliary but not hepatocyte marke rs. Anion exchanger (AE) function was assessed by the response of intr acellular pH (pH(i)) to acute Cl- removal. '-Bis(carboxyethyl)-5(6)-ca rboxyfluorescein-loaded monolayers were continuously perfused with phy siological HCO3- buffer containing Cl- or gluconate. In IBE cell line H75 (n = 6), acute Cl- removal alkalinized pH(i) at a rate of 0.04 +/- 0.01 min(-1). AE function was significantly decreased in LCDE cell Li ne CL3 (n = 6) to a rate of 0.01 +/- 0.01 min(-1) after Cl- removal. N orthern blot analysis demonstrated equivalent levels of AE2 mRNA in bo th cell Lines. AE1 mRNA was undetectable. Immunoblot analysis demonstr ated the AE2 polypeptide in both cell lines, but the level of mature g lycosylated AE2 polypeptide was reduced in LCDE cells. Immunofluoresce nce microscopy demonstrated decreased membrane-localized AE2 in LCDE c ells. These findings suggest that decreased plasmalemmal AE2 may accou nt for decreased AE function in LCDE cells and suggest a possible expl anation for decreased secretion of HCO3- by ADPKD liver cysts.