Ultrastructural and cytochemical studies on hyperbasophilic foci with special reference to the demonstration of cell surface alterations in hepatocarcinogenesis.

Following the formation of hyperplastic nodules at a late stage of azo dye hepatocarcinogenesis, some areas of parenchyma show an intense RNA staining, and such hyperbasophilic foci apparently develop hepatomas. Radioautographic analyses with [3H]thymidine labeling indicate the foci to be areas of continued cell proliferation, and the hepatocytes are morphologically distinguishable from the surrounding tissue. The increase of basophilia occurs simultaneously with histochemically demonstrable decreases in bound cations and concomitant increases in pyroantimonate-precipitable free cations. Thus, the phenomenon of hyperbasophilia and the ensuing alteration of cell cycle appears to be associated with changes in intracellular homeostasis. Ultrahistochemical localizations of adenosine triphosphatase and alkaline phosphatase suggest topographic alterations of membrane enzyme activities in the foci and the persistence of altered patterns during tumor progression. The developmental feature of surface adenosine triphosphatase activity has been further studied with subcultures of epithelial cells, which were derived from normal and precancerous livers. The enzyme activity of nontumorigenic cells is minimal, while a considerably high activity is detectable in situ at the outer surface of plasma membranes of tumorigenic cells. A Ca2+- Mg2+-dependent adenosine triphosphatase is identified at the cell surface, and the ectoenzyme would be a useful marker for detection of malignant liver epithelial cells.