Matamoros Marcos, Pérez-Hernández Marta, Guerrero-Serna Guadalupe, Amorós Irene, Barana Adriana, Núñez Mercedes, Ponce-Balbuena Daniela, Sacristán Sandra, Gómez Ricardo, Tamargo Juan, Caballero Ricardo, Jalife José, Delpón Eva
Department of Pharmacology, School of Medicine, Universidad Complutense, Madrid 28040, Spain Instituto de Investigación Sanitaria Gregorio Marañón, School of Medicine, Universidad Complutense, Madrid 28040, Spain.
Department of Internal Medicine, Center for Arrhythmia Research, University of Michigan, Ann Arbor, MI 48109, USA Department of Molecular and Integrative Physiology, Center for Arrhythmia Research, University of Michigan, Ann Arbor, MI 48109, USA.
Cardiovasc Res. 2016 May 15;110(2):279-90. doi: 10.1093/cvr/cvw009. Epub 2016 Jan 19.
Cardiac excitability and refractoriness are largely determined by the function and number of inward rectifier K⁺ channels (Kir2.1-2.3), which are differentially expressed in the atria and ventricles, and Nav1.5 channels. We have focused on how Nav1.5 and Kir2.x function within a macromolecular complex by elucidating the molecular determinants that govern Nav1.5/Kir2.x reciprocal modulation.
The results demonstrate that there is an unexpected 'internal' PDZ-like binding domain located at the N-terminus of the Nav1.5 channel that mediates its binding to α1-syntrophin. Nav1.5 N-terminal domain, by itself (the 132 aa peptide) (Nter), exerts a 'chaperone-like' effect that increases sodium (I(Na)) and inward rectifier potassium (I(K1)) currents by enhancing the expression of Nav1.5, Kir2.1, and Kir2.2 channels as demonstrated in Chinese hamster ovary (CHO) cells and in rat cardiomyocytes. Site-directed mutagenesis analysis demonstrates that the Nter chaperone-like effect is determined by Serine 20. Nav1.5-Kir2.x reciprocal positive interactions depend on a specific C-terminal PDZ-binding domain sequence (SEI), which is present in Kir2.1 and Kir2.2 channels but not in Kir2.3. Therefore, in human atrial myocytes, the presence of Kir2.3 isoforms precludes reciprocal I(K1)-INa density modulation. Moreover, results in rat and human atrial myocytes demonstrate that binding to α1-syntrophin is necessary for the Nav1.5-Kir2.x-positive reciprocal modulation.
The results demonstrate the critical role of the N-terminal domain of Nav1.5 channels in Nav1.5-Kir2.x-reciprocal interactions and suggest that the molecular mechanisms controlling atrial and ventricular cellular excitability may be different.
心脏的兴奋性和不应期很大程度上由内向整流钾通道（Kir2.1 - 2.3）的功能和数量以及Nav1.5通道决定，这些通道在心房和心室中差异表达。我们通过阐明调控Nav1.5/Kir2.x相互调节的分子决定因素，重点研究了Nav1.5和Kir2.x在大分子复合物中的功能。
结果表明，在Nav1.5通道的N端存在一个意想不到的“内部”类PDZ结合结构域，介导其与α1 - 肌营养不良素结合。Nav1.5的N端结构域自身（132个氨基酸的肽段）（Nter）发挥“伴侣样”作用，通过增强Nav1.5、Kir2.1和Kir2.2通道的表达来增加钠电流（I(Na)）和内向整流钾电流（I(K1)），这在中国仓鼠卵巢（CHO）细胞和大鼠心肌细胞中得到了证实。定点诱变分析表明，Nter的伴侣样作用由丝氨酸20决定。Nav1.5 - Kir2.x的相互正向作用依赖于特定的C端PDZ结合结构域序列（SEI），该序列存在于Kir2.1和Kir2.2通道中，但不存在于Kir2.3中。因此，在人心房肌细胞中，Kir2.3亚型的存在排除了I(K1)-INa密度的相互调节。此外，在大鼠和人心房肌细胞中的结果表明，与α1 - 肌营养不良素的结合对于Nav1.5 - Kir2.x的正向相互调节是必要的。
结果证明了Nav1.5通道N端结构域在Nav1.5 - Kir2.x相互作用中的关键作用，并表明控制心房和心室细胞兴奋性的分子机制可能不同。
