Na+-coupled sugar transport: membrane potential-dependent Km and Ki for Na+.
Na+-coupled sugar transport: membrane potential-dependent Km and Ki for Na+.
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Na 偶联糖转运：Na 的膜电位依赖性 Km 和 Ki 。
DOI：
10.1152/ajpcell.1988.255.4.c486
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发表时间：
1988
期刊：
影响因子：
--
通讯作者：
Randles,J
中科院分区：
文献类型：
--
作者：
Kimmich,GA;Randles,J
根皮苷结合特性和Na+、糖的动力学分析，以及α-甲基葡萄糖苷（α-MG）流入分离的禽类肠细胞的潜在依赖性，指出了两种可供选择的转运机制模型（D. Restrepo和G. A. Kimmich，J. 89：269-280，1986）。这些模型之一设想了一个潜在的依赖性Na+结合事件（Na+井概念）的分子机制的一部分。这里报道的数据表明，Na+的糖运输的表观Km是急剧依赖于膜电位的大小。当细胞内Na+不存在时，糖内流达到的最大速度（Vmax）在有或没有电势的情况下是相同的，尽管当施加电势时在较低的Na+浓度下获得Vmax（内部负）。细胞内Na+在没有电位的情况下严重抑制糖的流入，但当电位存在时，这种作用在很大程度上被克服。当细胞内Na+存在时获得的Vmax是电位的函数。这些结果是一致的运输模型，其中Na+结合到Na+依赖性糖载体在细胞外表面的膜和脱结合在膜的内表面都是潜在的依赖性事件。
Kinetic analysis of the characteristics of phlorizin binding and of the Na+, sugar, and potential dependence of alpha-methylglucoside (alpha-MG) influx into isolated avian intestinal cells has pointed toward two alternative models for the transport mechanism (D. Restrepo and G. A. Kimmich, J. Membr. Biol. 89: 269-280, 1986). One of these models envisions a potential-dependent Na+ binding event (Na+ well concept) as a part of the molecular mechanism. The data reported here show that the apparent Km for Na+ for sugar transport is sharply dependent on the magnitude of the membrane potential. When intracellular Na+ is absent, the maximal velocity (Vmax) achieved for sugar influx is the same with or without a potential, although Vmax is obtained at a lower Na+ concentration when a potential is imposed (interior negative). Intracellular Na+ severely inhibits the influx of sugar in the absence of a potential, but this effect is largely overcome when a potential is present. The Vmax obtained when intracellular Na+ is present is a function of the potential. These results are consistent with a transport model in which Na+ binding to the Na+-dependent sugar carrier at the extracellular surface of the membrane and debinding at the inner surface of the membrane are both potential-dependent events.