Effects of SITS on urate transport by isolated, perfused snake renal tubules

Effects of an inhibitor of membrane anion-exchange transport processes, 4-acetamido-4′-isothiocyano-2,2′-disulfonic stilbene (SITS), on urate transport by isolated, perfused snake (Thamnophis spp.) proximal renal tubules were studied. SITS (10⁻⁴ mol/l) in the luminal perfusate had absolutely no effect on net urate secretion (J(Formula presented.)) or on net fluid absorption (J_v). This observation is compatible with other data that give no support to the concept of a mediated transport step for urate from the cells to the lumen. SITS (10⁻⁴ mol/l) in the bathing medium reversibly inhibited J(Formula presented.) without affecting J_v. At the time of maximum inhibition of J(Formula presented.), the concentration of urate in the cell water was increased and the apparent permeability of the luminal membrane to urate was decreased, but the urate efflux across the peritubular membrane and the apparent permeability of the peritubular membrane to urate were unchanged. There was no evidence of significant intracellular binding or trapping of urate. Although an increase in the initial rate of urate transport into the cells across the peritubular membrane could not be demonstrated conclusively in nonperfused tubules, the results still suggest that SITS in the bathing medium may inhibit J(Formula presented.) by inhibiting urate movement from the cells to the lumen while actually enhancing transport from the bathing medium into the cells.