High affinity L-aspartate transport in chick small intestine.
High affinity L-aspartate transport in chick small intestine.
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L-天冬氨酸在鸡小肠中的高亲和力转运。
DOI：
10.1152/ajpcell.1987.252.1.c105
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发表时间：
1987
期刊：
影响因子：
--
通讯作者：
Kimmich,GA
中科院分区：
文献类型：
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作者：
Wingrove,TG;Kimmich,GA
利用从鸡小肠分离的上皮细胞来研究L-天冬氨酸转运机制。观察到两种动力学上不同的高亲和力 (Km' = 16 microM) 和低亲和力 (Km'' = 2.7 mM) 的摄取系统。本文研究了高亲和力系统的阳离子依赖性和膜电位敏感性。单向流入研究表明细胞外 Na+ 是转运功能的绝对必要条件。当细胞内存在 K+ 时，通量是最佳的，但 Na+ 依赖性 L-天冬氨酸吸收不需要该阳离子。在缺乏 K+ 的情况下，当细胞内 pH 值呈酸性时，会观察到通量增强。相反，酸性细胞内 pH 在用 K+ 预平衡的细胞中具有抑制作用。钠（[Na+]o 大于 [Na+]i 梯度）和钾（[K+]o 小于 [K+]i）或质子（[H+]o 小于 [H+]i）梯度可以独立地激发 L-天冬氨酸的 Na+ 依赖性积累高于平衡水平，表明 Na+ 和 L-天冬氨酸共转运伴随着 K+ 或 H+ 逆向转运发生。L-天冬氨酸流入对膜电位变化不敏感在存在或不存在细胞内 K+ 的情况下，通过向内定向的阴离子梯度创建一个模型，该模型与具有低特异性离子反转运位点的电中性 Na+ 偶联转移一致。
Epithelial cells isolated from chick small intestine were used to study the mechanism of L-aspartate transport. Two kinetically distinct uptake systems of high (Km' = 16 microM) and low (Km'' = 2.7 mM) affinity are observed. This paper examines the cation dependence and membrane potential sensitivity of the high affinity system. Unidirectional influx studies indicate that extracellular Na+ is an absolute requirement for transport function. Flux is optimal when K+ is present intracellularly, however this cation is not required for Na+-dependent L-aspartate uptake. In the absence of K+, flux enhancement is observed when the intracellular pH is acidic. In contrast, acidic intracellular pH is inhibitory in cells that are preequilibrated with K+. Sodium ([Na+]o greater than [Na+]i gradients, and potassium ([K+]o less than [K+]i) or proton ([H+]o less than [H+]i) gradients can independently energize the Na+-dependent accumulation of L-aspartate above equilibrium levels, suggesting that Na+ and L-aspartate cotransport occurs with concomitant K+ or H+ antiport. L-Aspartate influx is insensitive to membrane potential changes created by inwardly directed anion gradients in the presence or absence of intracellular K+. A model is presented that is consistent with electroneutral Na+-coupled transfer with an ion antiport site of low specificity.