CARRIER-MEDIATED CONCENTRATIVE URATE TRANSPORT IN RAT RENAL MEMBRANE-VESICLES

[2-14C]Urate uptake and efflux were studied in brush border and basolateral membrane vesicles of rat renal cortex that were exposed to 20 .mu.M copper chloride. In the presence of inwardly directed NaCl gradients urate uptake as maintained at levels in excess of chemical equilibrium. Comparison of glucose and Cl uptakes revealed that equilibrium glucose uptake was not affected by Cu, but Ca failed to reach equilibrium in Cu-exposed vesicles. Apparently, the persistence of an electrolyte gradient could provide a driving force to raise the concentration of free intravesicular urate above that in the media. Preincubation of vesicles with unlabeled urate failed to diminish uptake of added urate; rather, urate uptake was trans-stimulated. Uptake of labeled urate was also significantly accelerated when an outward gradient for unlabeled urate was created. Pyrazinoic and oxonic acids also trans-stimulated urate uptake. The demonstration of accelerated homeo- and heteroexchange diffusion indicates that transport is carrier mediated in both brush borders and basolateral vesicles. Outwardly directed hydroxyl gradients failed to influence urate uptake in either the presence or absence of Cu or NaCl. This carrier, which is active only in the presence of trace amounts of Cu, is distinct from a urate/anion exchanger.