REGULATION OF INTRACELLULAR PH BY IMMORTALIZED HUMAN INTRAHEPATIC BILIARY EPITHELIAL-CELL LINES

We have produced continuous cell lines using retroviral transduction of SV40 large T antigen into human intrahepatic biliary epithelial (IBE) cells from three different normal individuals. These IBE cell Lines grow in a hormone-supplemented medium in the presence of NIH/3T3 fibroblast coculture. These cells maintain their epithelial appearance and are positive for the biliary-specific markers cytokeratins 7 and 19 and gamma-glutamyl transpeptidase while being negative for the hepatocyte markers albumin and asialoglycoprotein receptor. To evaluate ion transport pathways in IBE cell lines, we utilized intracellular pH (pH(i)) measurements obtained using the intracellular fluorescent indicator 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein. In the absence of HCO3--CO2, an amiloride-sensitive Na+-H+ exchanger participated in the regulation of basal pH(i). In the presence of HCO3-CO2, a 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS)-sensitive, Na-, Cl-, and HCO3--dependent acid extrusion mechanism accounted for similar to 60% of pH(i) recovery from acidic pH(i); this mechanism is most consistent with the presence of a Na-dependent Cl--HCO3- exchanger (Na+HCO3-Cl-H+). Under basal conditions, Cl- depletion revealed a DIDS-sensitive alkalinization consistent with a Na-independent Cl--HCO3- exchanger. These model systems will allow the opportunity to study the normal mechanisms of IBE function and to study the pathobiology of IBE processes in disease states.