EXTRACELLULAR ACCESS TO THE NA,K PUMP - PATHWAY SIMILAR TO ION CHANNEL
EXTRACELLULAR ACCESS TO THE NA,K PUMP - PATHWAY SIMILAR TO ION CHANNEL
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DOI：
10.1126/science.7682009
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发表时间：
1993-04-02
期刊：
影响因子：
56.9
通讯作者：
DEWEER, P
中科院分区：
文献类型：
--
作者：
GADSBY, DC;RAKOWSKI, RF;DEWEER, P
在每个正常的Na，K泵循环中，首先输送三个钠离子，然后输送两个钾离子;在这两种情况下，离子暂时封闭在泵构象中，将它们与内部和外部溶液隔离。一个主要的电荷运动发生在钠易位和伴随着钠离子的释放或释放到细胞外部，或两者兼而有之。通过测量由Na（i）-Na（o）交换（Na（i）和Na（o）是内部和外部钠离子）介导的电压钳位、内部透析的鱿鱼巨轴突中的单向钠-22流出来检查电荷运动的性质;以这种方式，泵活性被限制在钠转运途径。虽然Na（i）-Na（o）交换是电中性的，但它对电压敏感：随着负电位的增加，它的速率沿着一条饱和的S形曲线增加。这种电压依赖性表明，外部钠的释放和重新结合是主要的电荷移动（因此，电压敏感）步骤，这表明细胞外钠离子必须通过高场通道到达泵分子深处的结合位点。这意味着泵分子的一部分在功能上类似于离子通道。
In each normal Na,K pump cycle, first three sodium and then two potassium ions are transported; in both cases, the ions become temporarily occluded in pump conformations that isolate them from internal and external solutions. A major charge movement occurs during sodium translocation and accompanies the deocclusion of sodium ions or their release to the cell exterior, or both. The nature of the charge movement was examined by measurement of the unidirectional sodium-22 efflux mediated by Na(i)-Na(o) exchange (Na(i) and Na(o) are internal and external sodium ions) in voltage-clamped, internally dialyzed squid giant axons in the absence of potassium; in this way the pump activity was restricted to the sodium-translocation pathway. Although electroneutral, the Na(i)-Na(o) exchange was nevertheless voltage-sensitive: increasingly negative potentials enhanced its rate along a saturating sigmoid curve. Such voltage dependence demonstrates that the release and rebinding of external sodium is the predominant charge-moving (hence, voltage-sensitive) step, suggesting that extracellular sodium ions must reach their binding sites deep in the pump molecule through a high-field access channel. This implies that part of the pump molecule is functionally analogous to an ion channel.