Mercapturic acids are N -acetyl-l-cysteine S -conjugates that are formed from a range of endogenous and exogenous chemicals. Although the kidney is a major site for elimination of mercapturic acids, the transport mechanisms involved have not been identified. The present study examined whether mercapturic acids are substrates for the renal basolateral organic anion transporter-1 (Oat1) from rat kidney. This carrier mediates uptake of organic anions from the bloodstream in exchange for intracellular α-ketoglutarate. Uptake of [3H] p -aminohippuric acid (PAH) in Oat1-expressing Xenopus laevis oocytes was strongly inhibited by S -(2,4-dinitrophenyl)- N -acetyl-l-cysteine (DNP-NAC) and by all other mercapturic acids tested, including the endogenous mercapturic acid N -acetyl-leukotriene E4. Inhibition by the mercapturic acids was competitive, which is consistent with the hypothesis that these compounds are substrates for Oat1. This conclusion was supported by the direct demonstration of saturable [35S]DNP-NAC uptake in Oat1-expressing oocytes. [35S]DNP-NAC uptake was inhibited by PAH and other mercapturic acids and was stimulated in oocytes preloaded with glutarate. The apparent K m value for DNP-NAC uptake was only 2 μM, indicating that this mercapturic acid is a high affinity substrate for Oat1. Together, these data indicate that clearance of endogenous mercapturic acids is an important function of the renal organic anion transporter.
巯基酸是由一系列内源性和外源性
化学物质形成的 N -乙酰-半胱
氨酸 S -共轭物。虽然肾脏是消除巯基酸的主要场所,但相关的转运机制尚未确定。本研究考察了巯基酸是否是大鼠肾脏基底侧有机阴离子转运体-1(Oat1)的底物。这种载体介导从血液中摄取有机阴离子以交换细胞内的α-酮
戊二酸。S -(2,4-
二硝基苯基)- N -乙酰-l-半胱
氨酸(DNP-
NAC)和所有其他经测试的巯基酸(包括内源性巯基酸 N -乙酰-
白三烯 E4)都能强烈抑制表达 Oat1 的爪蟾卵母细胞对[3H] p -
氨基海马酸(PAH)的摄取。巯基酸的抑制作用是竞争性的,这与这些化合物是 Oat1 底物的假设是一致的。在表达 Oat1 的卵母细胞中,[35S]DNP-
NAC 的饱和吸收直接证明了这一结论。PAH 和其他巯基酸抑制了 [35S]DNP-
NAC 的摄取,而预载
戊二酸的卵母细胞则刺激了这种摄取。DNP-
NAC 摄取的表观 K m 值仅为 2 μM,表明这种巯基酸是 Oat1 的高亲和力底物。这些数据共同表明,清除内源性巯基酸是肾脏有机阴离子转运体的一项重要功能。