Dissociation of gluconeogenesis from fluid and phosphate reabsorption in isolated rabbit proximal tubules

Dissociation of gluconeogenesis from fluid and phosphate reabsorption in isolated rabbit proximal tubules. Gluconeogenesis in the kidney is a metabolic function characteristic of proximal tubules. Recent studies suggest that renal gluconeogenesis (GNG) may in some way be coupled to fluid and phosphate reabsorption in the proximal tubule. Therefore, the present studies examined more directly the relationship between GNG and transport of fluid and phosphate using isolated proximal straight tubules of rabbit kidney. Glucose production rates were determined in isolated tubules with a glucose microassay while both phosphate (Jp) and net fluid fluxes (Jv) were measured by the in vitro isolated tubule perfusion technique. Glucose production rates from individual substrates, including pyruvate, lactate, glutamate and α-ketoglutarate, differed significantly, but neither Jv nor Jp was altered when different substrates in the bath medium were used. Inhibition of GNG by 3-mercaptopicolinate did not alter the Jv or Jp. Acid pH (7.0) stimulated GNG and suppressed both Jv and Jp. The addition of 3-mercaptopicolinate at acid pH abolished the stimulatory effect of acid pH on GNG but had no effect on Jv or Jp. These data thus indicate that, in the isolated rabbit renal proximal tubule, GNG rates can be dissociated from both the Jv and Jp and suggest that renal GNG may not directly regulate the fluid and phosphate transport rates in the proximal straight tubule. Dissociation entre la glucogenese et la reabsorption de fluides et de phosphates dans des tubules proximaux isoles de lapins. La gluconeogenese dans le rein est une fonction metabolique caracteristique des tubules proximaux. Des etudes recentes suggerent que la gluconeogenese renale (GNG) pourrait d'une facon ou d'une autre etre complee a la reabsorption de fluides et de phosphates dans le tubule proximal. C'est pourquoi ces travaux ont examine plus directement la relation entre la GNG et le transport de phosphates et de fluides en utilisant des tubules proximaux droits isoles de rein de lapin. Les taux de production de glucose ont ete determines dans les tubules isoles avec un microdosage du glucose tandis que les flux nets de liquide (Jv) et de phosphates (Jp) etaient mesures par la technique de perfusion in vitro de tubules isoles. Les taux de production de glucose a partir de substrats individuels, notamment pyruvate, lactate, glutamate et α-cetoglutarate, differaient significativement, mais ni Jv ni Jp n'etaient alteres lorsque ces differents substrats etaient utilises dans le bain d'incubation. L'inhibition de GNG par du 3-mercaptopicolinate n'a pas altere Jv ou Jp. Un pH acide (7,0) a stimule GNG, et supprime Jv et Jp. L'addition de 3-mercaptopicolinate a un pH acide a abolit l'effet stimulateur du pH acide sur GNG, mais n'a pas eu d'effet sur Jv ou Jp. Ces donnees indiquent donc que dans le tubule proximal isole de rein de lapin, les taux de GNG peuvent etre dissocies de Jv et de Jp et suggerent que la GNG renale pourrait ne pas reguler directement les vitesses de transport de fluides et de phosphates dans le tubule droit proximal.