Sodium-dependent nucleoside transport in the human intestinal brush-border membrane.
Sodium-dependent nucleoside transport in the human intestinal brush-border membrane.
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人肠刷状缘膜中钠依赖性核苷转运。
DOI：
10.1152/ajpgi.1997.272.6.g1314
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发表时间：
1997
期刊：
影响因子：
--
通讯作者：
Unadkat,JD
中科院分区：
文献类型：
--
作者：
Patil,SD;Unadkat,JD
该研究的目的是确定人类空肠刷状缘膜中存在的核苷转运蛋白的身份和动力学特征。通过使用刷状缘膜囊泡，[3H]尿苷的摄取被向内定向的Na+梯度刺激两到三倍，并且被100μM胸苷和100μM鸟苷核苷抑制，它们分别作为嘌呤（N1，cif）和嘧啶（N2，cit）转运蛋白的模型底物。 [3H]胸苷和[3H]鸟苷转运仅在Na+梯度存在时表现出过冲现象。 Na(+)-胸苷摄取可被 100 µM 胞苷或胸苷抑制，但不会被鸟苷、肌苷、福霉素 B 或次黄嘌呤抑制。 100 µM 肌苷、鸟苷或福霉素 B 抑制 [3H]鸟苷摄取，但胸苷或胞苷不抑制。腺苷和尿苷都以相似的程度抑制[3H]胸苷和[3H]鸟苷的摄取，表明N1、cif和N2、cit Na(+)-核苷转运蛋白在人空肠中表达。 K+ 和缬氨霉素产生的内部负电势差增强了对 Na(+)-胸苷的吸收，这证明核苷转运是流变性的，涉及正电荷的净转移。所有三种底物的希尔系数均一致，表明 Na(+)-核苷偶联化学计量为 1:1。在饱和 Na+ 浓度 (150 mM) 下，尿苷、胸苷和鸟苷摄取的动力学参数 (n = 3-4) 米氏常数和最大速度分别为 4.15 +/- 1.79、2.74 +/- 0.58、12.02 +/- 1.34 microM 和 25.93 +/- 7.38、16.10分别为+/- 3.64、63.92 +/- 10.23 pmol.mg-1.10 s-1。这些结果表明，与表达 N4 核苷转运蛋白的人肾脏相反，人空肠表达 N1 和 N2 Na(+)-核苷转运蛋白。
The objective of the study was to determine the identity and kinetic characteristics of nucleoside transporters present in the brush-border membrane of the human jejunum. With use of brush-border membrane vesicles, uptake of [3H]uridine was stimulated two- to threefold by an inwardly directed Na+ gradient and was inhibited by both 100 microM thymidine and 100 microM guanosine nucleosides, which serve as model substrates for purine (N1, cif) and pyrimidine (N2, cit) transporters, respectively. [3H]thymidine and [3H]guanosine transport exhibited an overshoot phenomenon only in the presence of a Na+ gradient. Na(+)-thymidine uptake was inhibited by 100 microM cytidine or thymidine but not by guanosine, inosine, formycin B, or hypoxanthine. [3H]guanosine uptake was inhibited by 100 microM inosine, guanosine, or formycin B but not by thymidine or cytidine. Both adenosine and uridine inhibited uptake of [3H]thymidine and [3H]guanosine to a similar extent, indicating that both N1, cif and N2, cit Na(+)-nucleoside transporters are expressed in human jejunum. Enhanced uptake of Na(+)-thymidine by an inside-negative potential difference generated by K+ and valinomycin provides evidence that nucleoside transport is rheogenic, involving net transfer of a positive charge. The Hill coefficient was unity for all three substrates, indicating a Na(+)-nucleoside coupling stoichiometry of 1:1. At saturating Na+ concentration (150 mM) the kinetic parameters (n = 3-4) Michaelis-Menten constant and maximum velocity for uridine, thymidine, and guanosine uptake were 4.15 +/- 1.79, 2.74 +/- 0.58, 12.02 +/- 1.34 microM and 25.93 +/- 7.38, 16.10 +/- 3.64, 63.92 +/- 10.23 pmol.mg-1.10 s-1, respectively. These results suggest that, in contrast to the human kidney that expresses the N4 nucleoside transporter, the human jejunum expresses both N1 and N2 Na(+)-nucleoside transporters.