Effects of K⁺ and Na⁺ on urate transport by isolated perfused snake renal tubules

Effects of potassium and sodium on urate transport by isolated perfused snake (Thamnophis spp.) proximal renal tubules were studied. Removal of potassium from bath led to significant depression of net urate transfer from bath to lumen in 20 min and to maximal depression in 60 min. In absence of potassium, cell water urate concentration was lower than that in bath but greater than that in lumen, suggesting that active uptake into cells was blocked and movement from bath to lumen was by passive diffusion. In absence of potassium, unidirectional urate permeability from bath to lumen (19.5 x 10^-6 cm sec^-1) was not significantly different from unidirectional permeability from lumen to bath in the presence of potassium, suggesting that removal of potassium does not affect transepithelial permeability. When potassium was restored to bath, net urate transfer from bath to lumen increased significantly within 40 min and was restored to control levels in 60 min. Increasing potassium in bath to 40 mM slightly depressed net urate transfer. Replacing sodium in bath or perfusion fluid with choline had no significant effect on net urate transfer over periods as long as 4 hr.