Carbon-14 Tracer Studies in the Metabolism of Isolated Rat-Liver Parenchymal Cells under Conditions of Gluconeogenesis from Lactate and Pyruvate

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Abstract
In rat liver perfusion experiments under conditions of gluconeogenesis from lactate and pyruvate 14C-labeling patterns of metabolites with (1-14C)-labeled and (2-14C)-labeled lactate or pyruvate, [14C]bicarbonate and [1-14C]octanoate as tracers, have been obtained, which do not agree with generally assumed reaction schemes. The experiments have been repeated with incubations of isolated rat-liver parenchymal cells. The results demonstrate that the discrepancies between expected and analysed 14C-labeling patterns of metabolites were still existent. From this observation it may be concluded, that 14C-labeling patterns of metabolites are indicative for the existence of still unknown metabolic relationships in liver parenchymal cells. Furthermore the results of our experiments prove that conclusions based on the exclusive analysis of metabolite levels are of limited value for studying intracellular events, because of uncharacterized compartmentations, which become evident in 14C-tracer studies. It cannot be answered by our studies, whether the apparent existence of differently labeled species of citrate, oxoglutarate or acetyl-CoA, represent intracellular compartmentation or whether it is the result of metabolic heterogeneity of liver parenchymal cells.

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