Vol. 281, Issue 3, 1059-1064, 1997

-Ketoglutarate Transport in Rat Renal Brush-Border and Basolateral Membrane Vesicles

Richard M. Edwards, Elwood Stack and Walter Trizna

Department of Renal Pharmacology, SmithKline Beecham Pharmaceuticals, King of Prussia, Pennsylvania

The dicarboxylate, -ketoglutarate (KG), has been identified as the most likely physiological anion involved in renal proximal tubule basolateral membrane (BLM) dicarboxylate/organic anion exchange. In the present study, we characterized the uptake of KG in BLM and brush-border membrane (BBM) vesicles isolated from rat kidney. In both membrane preparations, KG uptake was Na⁺-dependent, saturable, electrogenic and inhibited by Li⁺. The initial rate of KG (5 µM) uptake in BLM vesicles was twice that in BBM vesicles (258 ± 8.2 vs. 126 ± 3.9 pmol/mg/5 sec). The BLM transporter had a high affinity for KG (apparent K_m = 15.2 µM), but a relatively low transport capacity (V_max = 386 pmol/mg/5 sec). In contrast, the BBM transporter had characteristics of a low-affinity (K_m = 158 µM), high-capacity (V_max = 1106 pmol/mg/5 sec) system. Other dicarboxylates such as succinate, malate, fumarate and glutarate at a concentration of 1 mM inhibited KG uptake into BLM and BBM vesicles to the same extent (>90%). The tricarboxylate, citrate, also inhibited KG uptake (70-80%). However, of these Krebs' cycle intermediates, only KG and glutarate were able to affect p-aminohippurate (PAH) uptake into BLM vesicles. These results lend further support for a BLM PAH/KG exchanger. Furthermore, if extracellular KG plays a role in the operation of the PAH/KG exchanger, the high-affinity Na⁺-dependent KG transporter located in the BLM is the likely source of the organic anion.