Urate transport in brush-border membrane of human kidney.

Mechanisms of urate transport were investigated in human renal brush-border membrane vesicles. The imposition of an outwardly directed Cl- gradient, in voltage-clamp and pH-clamp conditions, stimulated [14C]urate uptake. Organic anions, including pyrazinoate (PZA), probenecid, lactate, ketone bodies, succinate, and alpha-ketoglutarate in their monovalent forms, cis-inhibited [14C]urate uptake. The affinity order was PZA > urate > probenecid > other anions. Vesicle preloading with these anions trans-stimulated urate uptake. These observations demonstrate the presence of a urate/anion exchanger. p-Aminohippurate and OH- were not substrates for this exchanger. In the presence of an inwardly directed K+ gradient and valinomycin (intravesicular positive potential) [14C]urate uptake was stimulated. Voltage-sensitive [14C]urate uptake was cis-inhibited by organic anions in the following affinity order: urate > probenecid > PZA. The differences in affinity orders for the urate exchanger and the urate voltage-sensitive transport suggest different pathways for apical transport. The anion exchanger might be the main mechanism involved in urate tubular reabsorption in humans.