Energy requirements for metabolic and excretory activities of perfused rat kidney.

A ratio 34.5 NA+/O2, or 5.8 Na+/ATP is obtained for the ouabain sensitive sodium pump, which accounts for 50% of sodium transport in the perfused kidney. Na-K-ATP'ase activity accounts for 15% of renal O2 uptake and sodium transport may account for only 30% of renal oxygen uptake. 2. Hydrogen ion secretion requires little extra energy. An increase in respiration produced by increasing the filtered load of potassium was not prevented by ouabain and active potassium secretion produced no detectable increases in oxygen consumption. 3. In general, the rate of oxidation substrates presented individually does not correlate well with the theoretical energy requirement for sodium transport. Exceptions were the low rate of oxidation of glutamine, which is consistent with limited sodium transport, and glucose, where the expected and observed rates of glucose oxidation are in close agreement. 4. The difference between substrates cannot be explained by activity of pyruvate kinase, by pyruvate dehydrogenase activation, by futile cycling between PFK/FDP'ase, or by involvement of the malate-aspartate shuttle.