FUROSEMIDE-SENSITIVE K-LIVER EPITHELIAL-CELLS - REGULATION BY PROTEIN-KINASE-C AND INVOLVEMENT IN CELL-GROWTH( TRANSPORT IN TRANSFORMED ANDNONTRANSFORMED RAT)

Using Rb+ as a K+ tracer and atomic absorption spectrophotometry for m easuring the Rb+ stable isotope, we studied K+ transport systems and t heir regulation by protein kinase C in nontransformed and spontaneousl y transformed rat liver epithelial cells. Ouabain-sensitive Na+/K+-ATP ase and the furosemide-sensitive Na+/K+/Cl- cotransport had comparable activity ratios in both cell types (0.92 and 1 in nontransformed and transformed rat liver epithelial cells, respectively). The protein kin ase C activators, dioctanoylglycerol and phorbol myristate acetate, pa rtly inhibited the Na+/K+/Cl- cotransport in both cell types but their effect was stronger in nontransformed cells, suggesting that, in tran sformed cells, the Na+/K+/Cl- cotransport had partly lost the ability to be inhibited by protein kinase C. In both cell types, phorbol myris tate acetate had little and dioctanoylglycerol had no inhibitory effec t on Na+/K+-ATPase. Furosemide (1 mM) partly inhibited the [H-3]thymid ine incorporation in both cell types, suggesting an involvement of the Na+/K+/Cl- cotransport in rat liver epithelial cell growth.