AJP - Renal Physiology, Vol 249, Issue 6 789-F798, Copyright © 1985 by American Physiological Society
Urate transport in the proximal tubule: in vivo and vesicle studies
A. M. Kahn and E. J. Weinman
The transport of urate in the mammalian nephron is largely confined to the
proximal tubule. Depending on the species, net reabsorption or net
secretion is observed. The rat, like the human and the mongrel dog,
demonstrates net reabsorption of urate and has been the most extensively
studied species. The unidirectional reabsorption and secretion of urate in
the rat proximal tubule occur via a passive and presumably paracellular
route and by a mediated transcellular route. The reabsorption of urate, and
possibly its secretion, can occur against an electrochemical gradient. A
variety of drugs and other compounds affect the reabsorption and secretion
of urate. The effects of these agents depend on their site of application
(luminal or blood), concentration, and occasionally their participation in
transport processes that do not have affinity for urate. Recent studies
with renal brush border and basolateral membrane vesicles from the rat and
brush border vesicles from the dog have determined the mechanisms for urate
transport across the luminal and antiluminal membranes of the proximal
tubule cell. Brush border membrane vesicles contain an anion exchanger with
affinity for urate, hydroxyl ion, bicarbonate, chloride, lactate,
p-aminohippurate (PAH), and a variety of other organic anions. Basolateral
membrane vesicles contain an anion exchanger with affinity for urate and
chloride but not for PAH. Both membrane vesicle preparations also permit
urate translocation by simple diffusion. A model for the transcellular
reabsorption and secretion of urate in the rat proximal tubule is proposed.
This model is based on the vesicle studies, and it can potentially explain
the majority of urate transport data obtained with in vivo techniques.
