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-ketoglutarate on organic anion transport in
single rabbit renal proximal tubules
Department of Physiology, College of Medicine, University of Arizona, Tucson, Arizona 85724
The effect of
exogenous 
-ketoglutarate (KG) and the peritubular
Na+-dicarboxylate (Na-DC)
cotransporter on organic anion/dicarboxylate (OA/DC)
exchange in S2 segments of single, nonperfused rabbit proximal tubules
was measured using 1 µM fluorescein (FL), a model OA, and
epifluorescence microscopy. The effect of different transmembrane distributions of 10 µM KG on peritubular FL uptake was measured at
37°C using bicarbonate-buffered, nutrient-containing buffers, which
are conditions similar to those found in vivo. Compared with FL uptake
in the absence of exogenous KG, preloading tubules with KG
(trans-configuration) or acute
exposure to KG (cis-configuration) increased FL uptake 62% and 54%, respectively, whereas a
cis-trans-configuration of KG
increased FL uptake by 76%. The
cis-stimulation of FL uptake by KG
was rapid, within 5-7 s. This stimulation was blocked 96% by
simultaneous exposure to 2 mM Li+,
indicating that stimulation of transport was secondary to the uptake of
exogenous KG. In the absence of exogenous KG, selective inhibition of Na-DC cotransport using 2 mM
Li+ or 1 mM methylsuccinate
decreased FL uptake by 25% (effects that were reversible but not
additive), suggesting that the Na-DC cotransporter recycles endogenous
KG that has left the cell in exchange for FL and that this activity
supports ~25% of baseline activity of the OA/DC exchanger. With
recycling of KG accounting for ~25% of FL uptake and with
accumulation of exogenous KG accounting for another ~75% increase
in FL uptake, Na-DC cotransport appears to directly support (25% + 75%)/175%, or ~57%, of total FL transport.
kidney; metabolic intermediates; fluorescein; cotransport; epifluorescence microscopy
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