Hormonal Regulation of Phosphoenolpyruvate Carboxykinase in Primary Cultures of Adult‐Rat Liver Parenchymal Cells

Abstract

Adult rat liver parenchymal cells, maintained in primary monolayer culture on floating collagen gels, were used for studies on the hormonal regulation of phosphoenolyruvate carboxykinse. In cells maintained in a defined, serum‐free medium containing insulin but no other hormones, phosphoenolpyruvate carboxykinse activity expressed on the basis of cell DNA content decreased over 3 days in culture with a half‐life of 9–10 h. Treatment of cells with glucagon or N6, O2′‐dibutyryladenosine 3′:5′ monophosphate (Bt2‐cAMP) caused an increase in enxyme activity up to 4‐fold higher than in untreated cells. There was little or no response during the first 24 h of culture but addition of either glucagon or Bt2‐cAMP after this period resulted in significant enzyme induction within 3 h. When cells were maintained for 2–3 days after attachment directly to palstic culture dishes rather than to collagen gels, similar inductive responses to glucagon or Bt2‐cAMP were observed. Induction by glucagon was shown to be dose‐dependent; a significant response was evident at 0.1 nM gucagon.Addition of epinephrine to cultured cells at concentration between 10 nM to 0.1 mM was without effect on phosphoenolpyruvate carboxykinase. Induction by Bt2‐cAMP was completely prevented by the simultaneous addition of actinomycin D (0.2 μg/ml) or cordycepin (10 μg/ml) suggesting that the nucletide acts or transcription to increase phosphoenolpyruvate carboxykinase synthesis.