MEASUREMENT OF METABOLIC FLUXES THROUGH PYRUVATE-KINASE, PHOSPHOENOLPYRUVATE CARBOXYKINASE, PYRUVATE-DEHYDROGENASE, AND PYRUVATE-CARBOXYLASE IN HEPATOCYTES OF DIFFERENT ACINAR ORIGIN

Isolated hepatocytes were prepared from the periportal and perivenous regions of the liver of 18-h-starved rats, These showed characteristic enzyme patterns and an enhanced rate of ureagenesis in the periportal cells; however, total cellular ATP content was unchanged in the two c ell types, Measurements of pyruvate kinase flux showed no significant difference in the overall rate in the two cell types; however, the flu x through phosphoenolpyruvate (PEP) carboxykinase was significantly hi gher in the periportal cells, such that the percentage of PEP being me tabolized by pyruvate kinase was enhanced in the perivenous cells, The increase in partitioning of PEP through pyruvate kinase could account for only a small percentage of the difference in gluconeogenic flux i n the two cell types, suggesting that the rate of provision of PEP was the principal limiting factor for glucose synthesis, The flux through pyruvate dehydrogenase showed no significant metabolic zonation, wher eas pyruvate carboxylase flux was enhanced in the periportal zone, The partitioning of pyruvate between pyruvate carboxylase and pyruvate de hydrogenase was increased 2.8-fold in the periportal cells compared to that in the perivenous cells and it is suggested that this, together with possible alterations in phosphoenolpyruvate carboxykinase, is pri marily responsible for the different gluconeogenic rates in the two zo nes of the liver. (C) 1996 Academic Press, Inc.