Expression and functional features of NaCT, a sodium-coupled citrate transporter, in human and rat livers and cell lines
Expression and functional features of NaCT, a sodium-coupled citrate transporter, in human and rat livers and cell lines
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DOI：
10.1152/ajpgi.00371.2006
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发表时间：
2007-01-01
影响因子：
4.5
通讯作者：
Ganapathy, Vadivel
中科院分区：
文献类型：
--
作者：
Gopal, Elangovan;Miyauchi, Seiji;Ganapathy, Vadivel
在这篇文章中，我们报告的表达和功能的Na+-偶联转运柠檬酸盐，NaCT，在人类和大鼠肝细胞系和原代肝细胞从大鼠肝脏。我们还描述了这种转运蛋白在人类和大鼠肝脏中的极化表达。人肝细胞系HepG 2和Huh-7中的柠檬酸摄取强制性依赖于Na+。摄取系统显示出柠檬酸盐的偏好超过柠檬酸循环的其他中间体，并表现出类似于6 mM的柠檬酸盐的米氏常数。运输活性被Li+刺激，并且活化与底物亲和力的显著增加相关。大鼠肝细胞系MH 1C 1中的柠檬酸盐摄取也具有Na+依赖性，并显示出对柠檬酸盐的偏好。柠檬酸盐的米氏常数与10 μ M相似。Li+对该酶的转运活性有抑制作用。大鼠肝脏的原代肝细胞也显示出对Na+偶联柠檬酸盐摄取的稳健活性，其功能特征与大鼠肝细胞系中描述的功能特征相似。用特异性抗NaCT抗体进行的免疫标记显示，在人和大鼠肝脏中，转运蛋白在肝细胞的窦状膜中独家表达。这是首次报道NaCT在肝细胞中的表达和功能。
In this article, we report on the expression and function of a Na+-coupled transporter for citrate, NaCT, in human and rat liver cell lines and in primary hepatocytes from the rat liver. We also describe the polarized expression of this transporter in human and rat livers. Citrate uptake in human liver cell lines HepG2 and Huh-7 was obligatorily dependent on Na+. The uptake system showed a preference for citrate over other intermediates of the citric acid cycle and exhibited a Michaelis constant of similar to 6 mM for citrate. The transport activity was stimulated by Li+, and the activation was associated with a marked increase in substrate affinity. Citrate uptake in rat liver cell line MH1C1 was also Na+ dependent and showed a preference for citrate. The Michaelis constant for citrate was similar to 10 mu M. The transport activity was inhibited by Li+. Primary hepatocytes from the rat liver also showed robust activity for Na+-coupled citrate uptake, with functional features similar to those described in the rat liver cell line. Immunolabeling with a specific anti-NaCT antibody showed exclusive expression of the transporter in the sinusoidal membrane of hepatocytes in human and rat livers. This constitutes the first report on the expression and function of NaCT in liver cells.