Urate uptake in membrane vesicles of rat renal cortex: effect of copper

Abstract

[2-14C]Urate uptake was studied in brush border and basolateral membrane vesicles of rat renal cortex. In the absence of copper, urate equilibrated without metabolism of transported urate. Exposure of the vesicles to copper significantly stimulated uptake, and in these vesicles uptake was also stimulated by NaCl or KCl gradients. Allantoin accumulated in these vesicles due to oxidation of transported urate. This oxidation is ascribed to a copper-stimulated, membrane-associated uricase since purified uricase and the membranes had similar Km values, both were inhibited by oxonic acid, and extramembranal uricase was not detected. Oxonic acid and pyrazinoic acid inhibited both uptake and enzyme activity. These findings suggest that urate uptake is carrier mediated and that uricase may play some role in transport. In addition, it appears that a significant loss of copper occurs during isolation of membrane vesicles that profoundly affects the characteristics of urate uptake. Those properties of the membrane that influence urate uptake, however, can be restored by exposure of the membranes to copper.