The mechanism of Na-K interaction on Na,K-ATPase.
The mechanism of Na-K interaction on Na,K-ATPase.
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Na,K-ATP酶上Na-K相互作用的机制。
DOI：
10.1111/j.1749-6632.2003.tb07174.x
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发表时间：
2003
影响因子：
5.2
通讯作者：
Sweadner,KathleenJ
中科院分区：
文献类型：
--
作者：
Donnet,Claudia;Sweadner,KathleenJ
已有大量证据表明，高浓度的K+通过改变Na，K-ATP酶对Na+（KNa）的表观亲和力而抑制Na，K-ATP酶活性。由于细胞质K+通常很高，这对于理解生理条件下的泵特性很重要。对K+敏感性的差异导致了表观Na+亲和力的组织特异性（和异构体独立性）差异1以及γ亚基对Na，K-ATP酶性质的影响。2，3许多先前的证据表明KNa和[K+]之间的线性关系，与Na+-K+竞争的简单动力学模型一致。然而，在研究γ在NRK-52 E细胞中的作用时，我们观察到KNa与[K+]之间不存在线性关系，无论有无γ。与文献相比，配体浓度的差异是差异的可能原因。用纯化的大鼠肾Na，K-ATP酶进行了研究，在不同浓度的K+存在下，测定了Na，K-ATP酶活性随Na+浓度的变化。当规定时，通过添加胆碱来保持离子强度恒定。重复实验，改变游离Mg 2+和ATp的浓度以及所用缓冲液的种类。与以前的报道一致，在所有条件下，K+升高都会降低KNa。仅在4 mM Mg 2+、1 mM ATp和1 mM游离Mg 2+的条件下，数据接近KNa和[K+]之间的线性关系，但在3 mM Mg 2+、3 mM ATp和< 0.5 mM游离Mg 2+的条件下，数据不接近KNa和[K+]之间的线性关系。此外，我们观察到[K+]对Vmax和Na+的协同性程度的影响。这些结果表明，K+对Na+激活的影响不是一个纯粹的竞争效应。模型生产作为Na+和K+浓度的函数的活性表达式拟合到整个数据集使用双变量回归，也不支持简单的竞争。见图1结果表明：（1）添加胆碱以保持离子强度不变，对KNa值有影响，但仍产生非线性曲线
There is much prior evidence that K+ in high concentrations acts as an inhibitor of Na, K-ATpase activity through a shift in the apparent affinity of Na, K-ATpase for Na+(KNa). Because cytoplasmic K+ is generally high, this is important for understanding pump properties in physiological conditions. Differences in sensitivity to K+ contribute to tissue-specific (and isoform-independent) differences in apparent Na+ affinity1 and to the effect of the γ subunit on Na, K-ATpase properties. 2, 3 Much prior evidence shows a linear relationship between KNa and [K+], consistent with a simple kinetic model for Na+-K+ competition. While investigating the roles of γ in NRK-52E cells, however, we observed that KNa did not relate linearly to [K+], with or without γ. Differences in ligand concentrations compared to the literature were a possible reason for the discrepancy. This was investigated with purified rat kidney Na, K-ATpase.Na, K-ATpase activity was measured as a function of Na+ concentration in the presence of different concentrations of K+. Ionic strength was kept constant by addition of choline when specified. The experiments were repeated, varying the concentrations of free Mg2+ and ATp and the kind of buffer used. Confirming previous reports, elevated K+ decreased KNa in all conditions. The data approximated a linear relationship between KNa and [K+] only in conditions of 4 mM Mg2+, 1 mM ATp with 1 mM free Mg2+, but not with 3 mM Mg2+, 3 mM ATp with< 0.5 mM free Mg2+. Furthermore, we observed effects of [K+] on Vmax and on the degree of cooperativity for Na+. These observations suggest that the K+ effect on Na+ activation is not a pure competitive effect. Models producing expressions for activity as a function of Na+ and K+ concentration were fitted to the whole set of data using twovariable regression, also not supporting simple competition. See FIGURE 1. The following conclusions can be drawn:(a) Addition of choline to keep constant ionic strength affected the values of KNa, but still produced nonlinear plots of KNa