Transport of urate and p-aminohippurate in rabbit renal brush-border membranes

The mechanisms involved in urate and p-aminohippurate (PAH) transport in the rabbit renal brush-border membrane were investigated through study of membrane vesicles. Transport of [14C]urate and [3H]PAH was measured by a rapid filtration method. As previously reported by others, no OH(-)-PAH exchanger could be demonstrated by imposing an outwardly directed OH- gradient (pHin 7.4, pHout 6). In contrast, an OH(-)-lactate exchanger (or H(+)-lactate cotransport) was demonstrated. In the presence of valinomycin and an inwardly directed K+ gradient, both [14C]urate and [3H]PAH vesicle uptake were stimulated, demonstrating a potential-driven transport of these two anions. Probenecid, PAH, or cold urate decreased potential-driven urate uptake, suggesting that this transport was facilitated by a specific transport mechanism. The potential-driven urate transport described here may play a role in the second step of urate secretion in rabbits, because rate (or PAH) is transported across the brush-border membrane from the negative interior of the cell to the more positive omen.