Further characterization of the sodium-dependent nucleoside transporter (N3) in choroid plexus from rabbit.
Further characterization of the sodium-dependent nucleoside transporter (N3) in choroid plexus from rabbit.
复制标题
兔脉络丛中钠依赖性核苷转运蛋白 (N3) 的进一步表征。
DOI：
10.1016/0005-2736(94)90248-8
复制
发表时间：
1994
期刊：
影响因子：
--
通讯作者：
Giacomini,KM
中科院分区：
文献类型：
--
作者：
Wu,X;Gutierrez,MM;Giacomini,KM
兔脉络丛中的Na+/核苷协同转运蛋白在底物选择性和化学计量方面不同于其他组织中的Na+/核苷协同转运蛋白。本研究的总体目标是进一步表征该系统（N3）的动力学。从兔脑获得的脉络丛组织切片耗尽ATP，并用缬氨霉素和K+处理。Na+/胸苷摄取在30秒内的负电位差的存在下，显着大于在没有电位差。Na+/胸苷摄取没有显着影响取代氯硫氰酸盐或硫酸盐。在25、50和100 mM Na+梯度存在下，Na+/鸟苷摄取的Km分别为149、85.2和30.5 μM，而Vmax不受影响，表明Na+首先与协同转运蛋白结合，然后与核苷结合。治疗相关的碱基修饰核苷类似物5-氟尿苷、2-氯腺苷和5-碘脱氧尿苷显著抑制Na+/胸苷摄取，IC 50值（平均值±SE）分别为12.0±2.3、21.3±2.2和24.4±2.1 μ M，而在核糖环上结构修饰的核苷类似物3′-叠氮胸苷、双脱氧肌苷和双脱氧胞苷（100 μM）则没有。这些研究表明，脉络丛中的Na+/核苷共转运是产电的，并且不依赖于氯。这种协同转运蛋白存在于脉络丛中，但不存在于兔肾刷状缘膜囊泡中，可能在临床相关的碱基修饰的核苷类似物进出脑的处置中发挥作用。
The Na+/nucleoside cotransporter in rabbit choroid plexus differs from Na+/nucleoside cotransporters in other tissues in terms of substrate selectivity and stoichiometry. The overall goal of this study was to further characterize the kinetics of this system (N3). Choroid plexus tissue slices obtained from rabbit brain were depleted of ATP and treated with valinomycin and K+. Na+/thymidine uptake at 30 s in the presence of an inside negative potential difference was significantly greater than in the absence of a potential difference. Na+/thymidine uptake was not significantly affected by replacing chloride with either thiocyanate or sulfate. The K m of Na+/guanosine uptake was 149, 85.2 and 30.5 μM in the presence of a 25, 50 and 100 mM Na+ gradient, respectively, whereas the V max was unaffected, suggesting that Na+ binds first to the cotransporter, then, the nucleoside. Therapeutically relevant base-modified nucleoside analogs, 5-fluorouridine, 2-chloroadenosine and 5-iododeoxyuridine, significantly inhibited Na+/thymidine uptake with IC 50 values (mean±SE) of 12.0±2.3, 21.3±2.2 and 24.4±2.1 μ M, respectively, whereas nucleoside analogs structurally modified on the ribose ring, 3′-azidothymidine, dideoxyinosine and dideoxycytidine (100 μM) did not. These studies suggest that Na+/nucleoside cotransport in the choroid plexus is electrogenic and is not dependent on chloride. This cotransporter, which is present in choroid plexus but not in renal brush-border membrane vesicles from rabbit, may play a role in the disposition of clinically relevant base-modified nucleoside analogs into and out of the brain.