Interactions between lithium and renal transport of Krebs cycle intermediates

The effect of lithium on the renal transport of Krebs cycle intermediates was studied in brush border membrane vesicles isolated from the rabbit renal cortex. The di- and tricarboxylic acids are avidly transported across renal brush border membranes by a sodium cotransport system. Lithium acted as a potent, specific, competitive inhibitor (Ki = 1.2 mM) of succinate/sodium cotransport when added to the uptake medium. Similar effects were observed for citrate but not D-glucose, L-phenylalanine, L-proline, L-alanine, or L-lactate transport. Intravesicular lithium behaved as a noncompetitive inhibitor of succinate transport in the absence of sodium. These results account for the observation that therapeutic doses of lithium increase the renal excretion of Krebs cycle intermediates. The existence of a transport system for alpha-ketoglutarate in synaptosomes suggests a possible target for lithium in the central nervous system.