GROWTH AND DIFFERENTIATION OF ADULT-RAT HEPATOCYTES REGULATED BY THE INTERACTION BETWEEN PARENCHYMAL AND NONPARENCHYMAL LIVER-CELLS

We have devised a medium which supports the continuous growth of hepat ocytes without losing their replicative potential and differentiation capacity for a longer period. The medium HCGM, contains four key subst ances in addition to foetal bovine serum. They are epidermal growth fa ctor, nicotinamide, ascorbic acid 2-phosphate and dimethylsulphoxide. When a non-parenchymal cell fraction containing small hepatocytes and non-parenchymal cells was cultured in HCGM, small hepatocytes grew clo nally and differentiated into cells expressing either mature hepatocyt e marker proteins or biliary cell marker proteins. Thus, for the first time, we showed the presence of a small compartment of bipotent and h ighly replicative clonogenic hepatocytes in the rat adult liver. HCGM also supported the growth of stellate cells (Ito cells) which were in the original preparation, suggesting the important role of stellate ce lls for the successful cultivation of hepatocytes. Together, these res ults suggest that a microenvironment is produced as a result of cooper ative interactions between hepatocytes and stellate cells: one which s timulates the growth and differentiation of clonogenic hepatocytes.