Characteristics of urate transport by isolated perfused snake proximal renal tubules.

DANTZLER, WILLIAM H. Churacteristics of urate transport by isolated pcrjused snake proximal renal tubules. Am. J. Physiol. 224(2) : 445-453. 1973.-Urate transport was studied in isolated, perfused snake ( Thamnophis spp. ) p roximal renal tubules in vitro. Secretion of urate from bath to tubule lumen occurred against a concentration gradient at flow rates varying from 0.08 to 7 nl/min. Urate tubular fluid-to-bath (TF /B) concentration ratio varied inversely with flow rate but averaged 2.0 at all flow rates with 2 X lop5 M urate in bath. During secretion in perfused tubules, cell urate concentraticn was greater than that of tubule fluid or bath. This is compatible with active transport into cells on peritubular membrane and subsequent diffusion into lumen. Net secretion varied with flop rate through tubule, suggesting that backdiffusion was significant. This was confirmed in efflux studies and it is suggested that significant backflux may occur between cells. In tubules incubated without perfusion, cell urate concentration was only onethird of that in perfused tubules, suggesting that active transport into cells may depend, in part, on perfusion. Transepithelial and luminal membrane permeabilities were calculated and the results are discussed in relation to the proposed transport model.