At present, little is directly known about what factors influence bile ductular epithelial cell proliferation, differentiation, and transformation In Vivo and in culture. Furthermore, there is virtually nothing known of the capability of the bile ductular epithelial cell to metabolize and activate chemical procarcinogens, nor has there been evidence to date which uniquivocally demonstrates the role the bile ductular cell may play as a "faculative stem cell" during chemical hepatocarcinogenesis. In this regard, this current continuation proposal deals with the further development and characterization of novel primary and secondary cultures of well differentiated bile ductular epithelial cells isolated from noncarcinogen-treated rat livers. Important factors to be evaluated for the development of these cultures include those of substratum and specific growth regulatory substances. In addition, efforts will be made to assess the neoplastic transformation of these cells following their exposures in culture to a selected direct-acting carcinogen, as well as to some that require metabolic activation. Properties of the chemically-transformed cells will then be compared with those transformed following transfection with the H-ras oncogene. An extrahepatic transplantation model will be further developed to investigate the effects of various treatments on the growth and differentiation of both hyperplastic and neoplastic bile ductular cells. In this regard, it is anticipated that these studies will result in the development of a new in culture/in vivo cell model applicable to the characterization of patterns of cellular differentiation, proliferation, and carcinogenesis exhibited by a unique epithelial cell type.