SURFACE-MEMBRANE NUCLEOSIDE TRIPHOSPHATASE-ACTIVITY AND TUMORIGENICITY OF CULTURED LIVER EPITHELIAL-CELLS

Abstract

A cell surface-located nucleoside triphosphatase activity can be assayed in liver epithelial cultures in situ with the incubation of intact cells in a medium containing [.gamma.-32P] ATP and correlated with the tumorigenicity of these cells in neonatal Wistar rats. The ectoenzyme activity of normal diploid cell lines is minimal, whereas high activity was found in all tumorigenic cell lines tested. The optimum condition for ATPase activity is physiological with regard to osmolarity, ionic composition, pH and substrate concentration in the medium. The enzyme is significantly stimulated by Ca2+, and its activation is controlled by Mg2+. Histochemical examinations indicate that glutaraldehyde fixed cells of tumorigenic lines have Ca2+-stimilated ATPase activity on the external surface. The isotopic assay of ATP hydrolysis by intact cells may provide a rapid method for screening oncogenesis in vitro of liver epithelial cells.