Coupling of metabolic CO2 production to ion transport in isolated rat thick ascending limbs and collecting tubules.

Metabolic CO2 production from appropriate [U-14C]-labelled substrates (either L-lactate or D-glucose) was measured in single pieces of tubule as previously described (Le Bouffant et al. 1984). Changing the incubate osmotic pressure by mannitol addition resulted in an increase in oxidative metabolism which was more marked in outer-medullary segment MAL and MCT) than in cortical segments (CAL and CCT). Availability of metabolic substrate was not rate limiting under these conditions because FCCP addition (1 mumol X l-1) produced a marked rise in CO2 production in these structures. Ouabain (1 mmol X l-1) decreased by more than 50% the CO2 production by CAL, MAL, CCT and MCT samples, indicating that the larger part of oxidative metabolism was coupled to active Na transport. Furosemide addition (10(-5) mol X l-1) to CAL and MAL samples, or amiloride addition (10(-4) mol X l-1) to CCT and MCT samples reduced the rate of CO2 production to an extent almost similar to that obtained with ouabain, an observation suggesting that apical entry of Na+ was present in these non-perfused tubules. Finally, the effects of changing the concentration of either K+ or Cl- was tested in CAL samples. K+ suppression greatly depressed the rate of CO2 production. Replacement of chloride with sulfate also decreased this rate to an extent similar to that observed with furosemide.(ABSTRACT TRUNCATED AT 250 WORDS)