Epifluorescence microscopy and intact S2 segments of rabbit proximal tubules were used to study peritubular organic anion transport Preloading tubules with 100 μM α-ketoglutarate (αKG) in HEPES buffer increased initial rates of 1 μM fluorescein (FL) uptake 4.3-fold. Incubating tubules in HCO3-buffered media, however, increased basal FL transport to the same level achieved in αKG-preloaded, HEPES-buffered tubules Preloading tubules with 100 μM αKG in HCO3 buffer also stimulated FL uptake, but only by two-fold. Inhibition of transaminase activity by 1 mM aminooxyacetate stimulated FL uptake into tubules incubated in HEPES-buffer, suggesting that elevated cytosolic αKG concentrations were the basis for the higher rate of transport noted in HCO3-buffered media. Mimicking the in situ condition, steady-state exposure of tubules to 10 μM αKG in a HCO3-buffer increased FL transport by 40% Inhibiting peritubular Na-dicarboxylate cotransporter with 2 mM Li under these conditions immediately reduced transport by 20%. Inhibiting the Na-dicarboxylate cotransporter in the absence of αKG (but the presence of HCO3) using either 2 mM Li or 1 mM methylsuccinate, also inhibited FL transport by 20% Thus, dicarboxylate transport increases organic anion transport by a direct coupling effect and by increasing cytosolic concentrations of αKG We conclude that 60% of the exchangeable dicarboxylate that drives organic anion uptake across the peritubular membrane of proximal tubules is supplied from endogenous sources. Activity of the Na-dicarboxylate cotransporter supplies approximately 50% to 60% of the exchangeable dicarboxylate by providing exogenous αKG and "recycling" endogenous dicarboxylate.
|Original language||English (US)|
|State||Published - Dec 1 1997|
ASJC Scopus subject areas
- Molecular Biology