Abstract
The early distal tubule (eDT) and the proximal tubule (PT) were dissected as tissue samples from the Triturus kidney. The oxygen consumption (QO2) of these tubules was measured and the effects on QO2 by transport inhibitors and metabolic substrates were studied. In eDT, complete Cl- replacement with NO3- or an addition of furosemide (2×10-5M) reduced QO2 from 8.4±1.7 to 4.4±0.8 or from 8.3±1.6 to4.4±0.6 nl•min-1•mg-1 (dry weight), respectively. Also Na+ replacement with choline or with an addition to ouabain (1×10-3M) reduced QO2 from 5.9±0.8 to 3.4±0.4 or from 13.2±1.8 to 4.7±0.3nl•min-1•mg-1 (dry weight), respectively. In PT, complete Cl- replacement with NO3- or the addition of furosemide did not affect QO2 significantly, but Na+ replacement with choline or the addition of ouabain reduced it from 8.1±1.0 to 5.4±0.7 or from 10.8±0.9 to 7.4±0.8nl•min-1•mg-1 (dry weight), respectively. The data indicate that about a half of the QO2 in eDT is linked to active Cl- transport, in PT, Cl- is not transported actively and is not affected by furosemide. Effects on QO2 by various metabolic substrates, including TCA-cycle intermediates and metabolizable amino acids and carboxylic acids were tested. Among them, succinate, L-glutamate, L-aspartate, citrate, and acetate were found to effectively increase the QO2 in eDT, while lactate, pyruvate and fumarate were ineffective on QO2. The substrate-dependencies of QO2 in eDT were very similar to those in PT, in kinds of effective substrates and in the extent of increase. These findings suggest that, in eDT and PT, the uptake mechanisms for substrates and their coupling with aerobic metabolism are very similar.
