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首页> 外文期刊>Proceedings of the National Academy of Sciences of the United States of America >Altered Na~+ transport after an intracellular α-subunit deletion reveals strict external sequential release of Na~+ from the Na/K pump
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Altered Na~+ transport after an intracellular α-subunit deletion reveals strict external sequential release of Na~+ from the Na/K pump

机译：细胞内α-亚基缺失后改变的Na〜+转运揭示了Na〜+从Na / K泵的外部严格顺序释放

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摘要

The Na/K pump actively exports 3 Na~+ in exchange for 2 K~+ across the plasmalemma of animal cells. As in other P-type ATPases, pump function is more effective when the relative affinity for transported ions is altered as the ion binding sites alternate between opposite sides of the membrane. Deletion of the five C-terminal residues from the α-subunit diminishes internal Na~+ (Na_i~+) affinity 25-fold [Morth et al. (2007) Nature 450:1043-1049]. Because external Na~+ (Na_o~+) binding is voltage-dependent, we studied the reactions involving this process by using two-electrode and inside-out patch voltage clamp in normal and truncated (ΔKESYY) Xeno-pus-α1 pumps expressed in oocytes. We observed that ΔKESYY (i) decreased both Na_o~+ and Na_i~+ apparent affinities in the absence of K_o~+, and (ii) did not affect apparent Na_o~+ affinity at high K_o~+. These results support a model of strict sequential external release of Na~+ ions, where the Na~+-exclusive site releases Na~+ before the sites shared with K~+ and the ΔKESYY deletion only reduces Na~+ affinity at the shared sites. Moreover, at nonsaturating K_o~+, ΔKESYY induced an inward flow of Na~+ through Na/K pumps at negative potentials. Guanidinium~+ can also permeate truncated pumps, whereas N-methyl-D-glucamine cannot. Because guanidiniumo can also traverse normal Na/K pumps in the absence of both Na_o~+ and K_o~+ and can also inhibit Na/K pump currents in a Na~+-like voltage-dependent manner, we conclude that the normal pathway transited by the first externally released Na~+ is large enough to accommodate guanidinium~+.
机译：Na / K泵通过动物细胞质膜主动输出3 Na〜+来交换2 K〜+。与其他P型ATP酶一样，当转运离子的相对亲和力随着离子结合位点在膜的相对两侧之间交替变化而改变时，泵功能更有效。从α-亚基中删除五个C-末端残基使内部Na +（Na_i +）亲和力降低了25倍[Morth et al。 （2007）Nature 450：1043-1049]。因为外部Na〜+（Na_o〜+）绑定是电压依赖性的，所以我们在正常和截断（ΔKESYY）Xeno-pus-α1泵中使用两电极和由内而外的贴片电压钳研究了涉及此过程的反应卵母细胞。我们观察到，ΔKESYY（i）在不存在K_o〜+的情况下降低了Na_o〜+和Na_i〜+的表观亲和力，并且（ii）在高K_o〜+时不影响表观的Na_o〜+亲和力。这些结果支持了Na〜+离子严格顺序外部释放的模型，其中Na〜+独有的位点在与K〜+共享的位点之前释放Na〜+，而ΔKESYY缺失仅降低了共享位点的Na〜+亲和力。 。此外，在非饱和K_o〜+处，ΔKESYY诱导Na〜+通过Na / K泵以负电势向内流动。胍盐+也可渗透截短的泵，而N-甲基-D-葡萄糖胺则不能。由于胍盐也可以在不存在Na_o〜+和K_o〜+的情况下穿越正常的Na / K泵浦，并且还可以以类似Na〜+的电压依赖性方式抑制Na / K泵浦电流，因此我们得出结论，正常途径已经过渡第一次对外释放的Na〜+足以容纳胍盐〜+。

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