Cytochemical and ultrastructural alterations associated with confluent growth in cell cultures of epithelial like cells from rat liver

The purpose of this study was to determine whether epithelial like cell cultures from rat liver in the confluent state were functionally more active than in the preconfluent state. Studies of the cytochemical activities of 13 enzymes and the ultrastructure of the cells were performed on cells in preconfluent, confluent, and postconfluent cultures. The activities of 5 of the 12 enzymes possessed by the cells were greater in confluent cultures. The ultrastructure of confluent cells differed from that of preconfluent cells by displaying a large increase on cytoplasmic 75 Å fibrils. In postconfluent cultures the amount of free polyribosomes was reduced and in some cells microbodies were more numerous. In the preconfluent and newly confluent state, the growth fraction was 1.0. Only when cultures were maintained postconfluency did the growth fraction decrease. It is concluded that phenotypic modulation occurs in confluent cultures before a decrease in the growth fraction, but that further modulation occurs when the degree of cell proliferation is reduced.