Nies A T, Kinne R K, Kinne-Saffran E, Grieshaber M K
Universität Düsseldorf, Institut für Tierphysiologie, Germany.
Am J Physiol. 1995 Aug;269(2 Pt 2):R339-49. doi: 10.1152/ajpregu.1995.269.2.R339.
[2-14C]urate uptake was studied in hepatopancreatic basolateral membrane vesicles and in R cell suspensions of the American lobster by Millipore filtration techniques. Unspecific binding of urate to the vesicular membrane was 25.5 +/- 3.0% of equilibrium. Vesicular uptake showed a diffusional and a saturable component (Km) 0.37 +/- 0.04 mM and maximal velocity (Vmax) 16.5 +/- 1.2 pmol urate.mg protein-1.s-1). [2-14C]urate uptake was significantly trans-stimulated by urate. Purine analogues, probenecid, p-aminohippuric acid, pyrazinoic, and oxonic acid cis-inhibited urate transport. Urate uptake was not affected by Na+ or K+ transmembrane gradients but stimulated by 1 mM 2-oxoglutarate at the cis-side in Na(+)-containing media. Cellular urate uptake was inhibited by pyrazinoic acid. Uptake was saturable (Km 0.53 +/- 0.11 mM and Vmax 3.7 +/- 0.4 pmol urate.mg protein-1.s-1) and Na(+)-independent. However, 2-oxoglutarate stimulated uptake in Na(+)-containing media. These results suggest that urate uptake across the basolateral membrane occurs via a specific, Na(+)-independent transport system that may operate in the exchange mode accepting 2-oxoglutarate as countertransported substrate. In vivo, urate uptake thereby would be a tertiary active system driven by a 2-oxoglutarate gradient established across the cell membrane by the operation of a Na(+)-2-oxoglutarate cotransport system.
采用密理博过滤技术，研究了美洲龙虾肝胰腺基底外侧膜囊泡和R细胞悬液中[2-¹⁴C]尿酸盐的摄取情况。尿酸盐与囊泡膜的非特异性结合为平衡状态的25.5±3.0%。囊泡摄取表现出扩散和饱和成分（Km为0.37±0.04 mM，最大速度（Vmax）为16.5±1.2 pmol尿酸盐·mg蛋白⁻¹·s⁻¹）。尿酸盐显著地反刺激[2-¹⁴C]尿酸盐的摄取。嘌呤类似物、丙磺舒、对氨基马尿酸、吡嗪酸和氧嗪酸顺式抑制尿酸盐转运。尿酸盐摄取不受Na⁺或K⁺跨膜梯度的影响，但在含Na⁺的培养基中，顺侧1 mM的2-氧代戊二酸可刺激其摄取。细胞尿酸盐摄取受吡嗪酸抑制。摄取是可饱和的（Km为0.53±0.11 mM，Vmax为3.7±0.4 pmol尿酸盐·mg蛋白⁻¹·s⁻¹）且不依赖Na⁺。然而，2-氧代戊二酸在含Na⁺的培养基中刺激摄取。这些结果表明，尿酸盐跨基底外侧膜的摄取是通过一种特异性的、不依赖Na⁺的转运系统进行的，该系统可能以交换模式运作，接受2-氧代戊二酸作为反向转运底物。在体内，尿酸盐摄取因此将是一个三级主动转运系统，由Na⁺-2-氧代戊二酸共转运系统的运作在细胞膜上建立的2-氧代戊二酸梯度驱动。
