A 13C 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 [2-13C] and [3-13C]pyruvate. The perchloric acid extracts of the cell pellets were examined by 13C 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 13C 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 mM 13C-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.