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Acute gouty arthritis occurs when crystals of monosodium urate form and deposit in joints and connective tissue. These crystals then provoke the characteristic acute inflammatory response of gout (Seegmiller, 1965), and may accumulate chronically forming gouty tophi.Although To determine the urate solubility of each solution, three ml of the solution to be tested was added to a 16 ml glass test tube containing a small magnetic stirring bar. The test tubes were placed on a magnetic stirrer and maintained at the desired temperature. After 16 hours the solutions were centrifuged at 12,000g in a 6 ml glass centrifuge tube and the supernatant was removed. The centrifugation was repeated until no precipitate was visible. Two centrifugations were usually sufficient. The final supernatant was then assayed for urate. Using this procedure, urate crystals could not be detected in the final supernatant by light microscopy. Care was taken to maintain the desired temperature closely during all steps of the procedure including centrifugation. URATE SOLUBILITY IN BUFFER SOLUTIONSThe effect of sodium on urate solubility was determined in 0-01 mol/l. potassium phosphate buffer, pH 7 40, containing appropriate amounts of sodium chloride. The desired pH was obtained by titrating solutions of monobasic and dibasic potassium phosphate.The effect of pH on urate solubility was determined in 0-01 mol/l. sodium phosphate buffer containing 015 mol/l. sodium chloride and adjusted to the desired pH by titrating solutions of monobasic and tribasic sodium phosphate. The effect of albumin on urate solubility was determined by adding the appropriate amount of albumin to 3 ml 0 01 mol/l. sodium phosphate buffer, pH 7*40, containing 0-15 mol/l. sodium chloride and 100 mg/100 ml sodium urate. The albumin was dissolved by gentle mixing.All buffers were boiled before use. Excess sodium urate (approximately 100 mg/100 ml) was added to solutions before titration to prevent pH changes due to the urate itself. URATE SOLUBILITY IN BIOLOGICAL FLUIDSAll blood and urine samples were obtained from normal volunteers. Blood was drawn in heparinized vacutainers, separated by centrifugation for 10 minutes at 3500 r.p.m. and the plasma frozen at -20°C until the time of assay (not

Uptake studies employing renal brush border membranes were used to examine the structural specificity of the TCA cycle intermediate transport system. The kinetics of reciprocal inhibition between succinate and citrate revealed these compounds to be transported by a common mechanism. The Michaelis constant for succinate (0.11 mM) was significantly lower than that of citrate (0.28 mM), indicating that the system has a higher affinity for succinate than for citrate. The specificity of the transport system was determined from the relative inhibitory constants of 40 organic acids on the transport of succinate. The results established that the system is highly specific for 4-carbon, terminal dicarboxylic acids in the trans-configuration, including the major intermediates of the TCA cycle. The system is comparatively insensitive to monocarboxylates. Substitution of one of several polar, non-charged residues on the alpha-carbon of succinate permitted interaction of the substrate with the transport system, but substitutions on both the alpha and beta-carbons did not. The structural specificity of the system is fundamentally different from that of the dicarboxylate and tricarboxylate exchange systems of mitochondria. The role of this transport system in the reabsorption of TCA cycle intermediates from the proximal tubule is discussed.

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 (K; = 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 a-ketoglutarate in synaptosomes suggests a possible target for lithium in the central nervous system.Since 1949 lithium has been used successfully in the therapy of manic-depressive illness. However, there are few clues as to the site and mode of action of this psychoactive agent. One of the most striking immediate effects of Li' is on the renal excretion of Krebs cycle intermediates in both man and experimental animals (1, 2). Within minutes, Li+ at therapeutic doses increases renal excretion of a-ketoglutarate and succinate by 1-2 orders ofmagnitude. Jenner's group (3-5) speculated that Li+ increased excretion by inhibiting the active reuptake of the dicarboxylic acids by the renal tubule.Recently we (6-10) established the presence of an avid Na cotransport system for dicarboxylic acids in the brush border membrane of the renal cortex and this led us to examine the interactions of Li+ with this system. We find that Li' is a potent specific inhibitor of dicarboxylic transport, and this has important implications in both lithium therapy and the kinetics of a Na-dependent transport process. METHODSTransport experiments were carried out on rabbit renal brush border membrane vesicles as described in detail elsewhere (9,10). For most experiments the vesicles were loaded with 100 mM KC1, 5 mM Tris Hepes at pH 7.5, and sufficient mannitol to give a final osmolarity of 300-955 mosM. Rates of transport [Js mol/(mg protein x min)] were obtained from 1-to 10-sec uptakes by using radioactive isotopes obtained from New England Nuclear and a rapid filtration procedure. The final composition ofthe uptake medium was 0-450 mM in chloride salts, 100 mM KC1, 5 mM Tris Hepes at pH 7.5, and sufficient mannitol to make the solution iso-osmotic with the loading buffer. Unless otherwise noted, the electrical potential (PD) across the membrane of the vesicle was clamped at 0 mV by the addition of the ionophores valinomycin (25 pg/ml) and p-trifluoromethoxyphenylhydrazone (75 AM) (FCCP) to the loading and uptake buffers. Note that Ki = Ko and pHi = pH0, and in the presence of these ionophores the K and H conductance is high enough to shunt the PD (unpublished data).Data reduction and kinetic analysis of transport ...