GLUTAMINE INHIBITS THE LOWERING EFFECT OF GLUCOSE ON THE LEVEL OF PHOSPHOENOLPYRUVATE CARBOXYKINASE MESSENGER-RNA IN ISOLATED RAT HEPATOCYTES

The expression of phosphoenolpyruvate carboxykinase (P-pyruvate CK) wa s shown to be decreased by hypoosmolarity and increased by glutamine i n perfused liver from fed rats [Newsome, W. P, Warskulat, U., Noe, B., Wettstein, M., Stoll, B.; Gerok, W. & Haussinger, D. (1994) Biochem. J. 304, 555-560]. This work was undertaken to specify the mechanisms o f glutamine action, using isolated hepatocytes from rats that had been starved for 24 h. At low concentrations (up to 5 mM), glutamine elici ted a decrease in the level of P-pyruvate CK mRNA through cell swellin g and, at higher concentrations, an increase in the mRNA level was obs erved. Experiments with combinations of glucose and glutamine or gluco se and various amino acids demonstrated that glutamine counteracted th e inhibitory effect of glucose on P-pyruvate CK mRNA at a transcriptio nal level, and strongly suggested that the amide group of glutamine wa s involved in this effect. The metabolism of glucose was required for the reinforcement of the apparent stimulatory effect of glutamine, as demonstrated by the use of various sugars. Glucosamine, but not mannos amine, increased the level of P pyruvate CK mRNA, as did glucose plus glutamine. These results suggest that the pathway leading from glucosa mine-6-phosphate production might be responsible, at least partly, for the effect observed on P-pyruvate CK mRNA.