ISSN:
1432-2013
Keywords:
Single nephron segments
;
Oxidative metabolism
;
Furosemide, Amiloride, FCCP, Nystatin
;
Cl− concentration
;
Osmotic pressure
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Abstract Metabolic CO2 production from appropriate [U-14C]-labelled substrates (eitherl-lactate ord-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 outermedullary segments (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 μmol·l−1) produced a marked rise in CO2 production in these structures. Ouabain (1 mmol·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·l−1) to CAL and MAL samples, or amiloride addition (10−4 mol·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. The CO2 production increased in a sigmoid way (apparentK a=41 mmol·l−1, Hill coefficient=2.12) as a function of [Cl−] in the incubate, suggesting that oxidative metabolism was coupled to bath chloride via the Cl−-requiring Na entry along the 1 Na+−1K+−2Cl− luminal contrasport system.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00652628
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