Transepithelial urate transport by avian renal proximal tubule epithelium in primary culture

摘要

Birds are uricotelic, and because they excrete urate by renal tubular secretion, they provide a convenient model for examination of this process. Primary monolayer cultures of the isolated renal proximal tubule epithelium from the domestic chicken, Gallus gallus L., were mounted in Ussing chambers where several substrates/inhibitors of renal organic anion transporters were tested for the sidedness and specificity of their effects on transepithelial urate transport. Transepithelial electrical resistance, electrical potential and sodium-dependent glucose current were monitored to detect nonspecific effects. Under control short-circuited conditions the ratio of unidirectional fluxes of [C-14]urate was found to be 3:1. Active net secretion was specifically inhibited by 1 mmol l(-1) probenecid and 10 mmol 17, paraaminohippuric acid (PAH). Bromocresol Green, cimetidine, nocodozole, cytochalasin D and ouabain also inhibited secretion but were toxic. Interstitial-side lithium (5 mmol l(-1)) and glutarate (1 mmol l(-1)) specifically blocked transport, but 10-100 mu mol l(-1) glutarate had no effect. Interstitial estrone sulfate (ES) stimulated urate secretion at 10 mu mol l(-1) but was inhibitory at 500 mu mol l(-1). Active PAH secretion (5:1 flux ratio) was inhibited 34% by 330 mu mol l(-1) urate. ES (500 mu mol l(-1)) blocked the remainder. From the lumen side, glucose-free, Cl--free and high K+ (30 mmol l(-1)) solutions, or an alkaline pH of 7.7 had no effect, on urate transport and neither did several compounds known to be uricosuric. Lumen-side methotrexate (500 mu mol l(-1)) and MK571 (20 mu mol l(-1)) strongly inhibited urate secretion. MK571 had no effect from the interstitial side. RT-PCR revealed mRNA for OAT1-, OAT3-, NIRP2- and MRP4-like organic anion transporters in chicken proximal epithelium.