A 13 C NMR study on fluxes into the krebs cycle of rabbit renal proximal tubular cells

Suspensions of rabbit renal proximal tubular (PCT) cells were incubated with [2‐ 13 C] and [3‐ 13 C]pyruvate. The perchloric acid extracts of the cell pellets were examined by 13 C NMR. All experiments showed that enriched lactate, alanine, glutamate, and glutamine were the main metabolic intermediates, and that enrichment to a minor extent was found in the glutamate residue of glutathione (GSH). From these experiments, it could be deduced that PCT cells show a highly glycolytic activity, whereas enrichment of glucose exhibits gluconeogenesis. The estimation by 13 C NMR of the ratio of the flux into the Krebs cycle via pyruvate carboxylase to the flux via pyruvate dehydrogenase is discussed. From incubations with 10 m M 13 C‐labelled pyruvate, we calculated from the relative enrichments of the glutamate carbon atoms that the ratio of pyruvate carboxylase to pyruvate dehydrogenase is 1.44 ± 0.04 in rabbit renal proximal tubules.