Studies on brain-cortex slices: Differences in the oxidation of 14C-labelled glucose and pyruvate revealed by the action of triethyltin and other toxic agents

1. The rate of appearance of ¹⁴CO₂ from 6-¹⁴C]glucose and 3-¹⁴C]pyruvate was measured. Pyruvate is oxidized to carbon dioxide twice as fast as glucose, although the oxygen uptake is almost the same with each substrate. 2. The presence of 30μm-2,4-dinitrophenol increases the output of ¹⁴CO₂ from 6-¹⁴C]glucose sixfold whereas the oxygen uptake is not quite doubled. Similar results are obtained with 0·1m-potassium chloride. The stimulating action of these two agents on the output of ¹⁴CO₂ from 3-¹⁴C]pyruvate is much less than on that from 6-¹⁴C]glucose. 3. The effects of oligomycin, ouabain and triethyltin on the respiration of control and stimulated brain-cortex slices were studied. Triethyltin (1·3μm) inhibited the oxidation of 6-¹⁴C]glucose more than 70%, but did not inhibit the oxidation of3-¹⁴C]pyruvate. 3-¹⁴C]pyruvate. 4. The production of lactic acid by brain-cortex slices incubated with glucose is twice as great as that with pyruvate. Lactic acid increases two and a half times in the presence of either triethyltin or oligomycin when the substrate is glucose, but is no different from the control when the substrate is pyruvate. 5. With kidney slices the production of lactic acid from glucose is very low. It is increased by oligomycin but not by triethyltin. 6. The results are discussed in terms of the oxidation of the extramitochondrial NADH₂ produced during glycolysis.