The sodium/potassium ATPase (NKA) is essential for establishing the normal intracellular [Na+] and [K+] and transmembrane gradients that are essential for many cellular functions, including cardiac electrophysiology and contractility. Different NKA isoforms exhibit differential expression levels, cellular localization, and function in different tissues and species. Prior work has indicated that the NKA-α1 isoform is quantitatively predominant in cardiac myocytes, but that the α2 isoform is preferentially concentrated in the transverse tubules (TT), possibly at junctions with the sarcoplasmic reticulum (SR) where α2 may preferentially modulate cardiac contractility. Here we measured subcellular localization of NKA-α1 and α2 using super-resolution microscopy (STED and STORM) and isoform-selective antibodies in mouse ventricular myocytes. We confirm the preferential localization of NKA-α2 in TT vs. surface sarcolemma, but also show that α2 is relatively excluded from longitudinal TT elements. In contrast NKA-α1 is relatively uniformly expressed in all three sarcolemmal regions. We also tested the hypothesis that NKA-α2 (vs. α1) is preferentially concentrated at SR junctional sites near ryanodine receptors (RyR2). The results refute this hypothesis, in that NKA-α1 and α2 were equally close to RyR2 at the TT, with no preferential NKA isoform localization near RyR2. We conclude that in contrast to relatively uniform NKA-α1 distribution, NKA-α2 is preferentially concentrated in the truly transverse (and not longitudinal) TT elements. However, NKA-α2 does not preferentially cluster at RyR2 junctions, so the TT NKA-α2 concentration may suffice for preferential effects of NKA-α2 inhibition on cardiac contractility.

中文翻译：

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Na / K-ATPase同工型在心室肌细胞中的亚细胞定位。

钠/钾ATPase（NKA）对于建立正常的细胞内[Na +]和[K +]和跨膜梯度是必不可少的，而梯度对于许多细胞功能（包括心脏电生理和收缩力）都是必不可少的。不同的NKA同工型在不同的组织和物种中表现出不同的表达水平，细胞定位和功能。先前的研究表明，NKA-α1亚型在心肌细胞中占主导地位，但α2亚型优先集中在横管（TT）中，可能在与肌浆网（SR）的交界处，其中α2可能优先调节心脏收缩力。在这里，我们使用超高分辨率显微镜（STED和STORM）和同种型选择性抗体在小鼠心室肌细胞中测量了NKA-α1和α2的亚细胞定位。我们确认了NKA-α2在TT相对于表面肉瘤的优先定位，但也表明α2被纵向TT元素相对排除。相反，NKA-α1在所有三个肌膜区域相对均匀地表达。我们还测试了NKA-α2（相对于α1）优先集中在ryanodine受体（RyR2）附近的SR连接位的假设。结果驳斥了这一假设，因为NKA-α1和α2在TT处均与RyR2接近，而在RyR2附近没有优先的NKA亚型定位。我们得出的结论是，与相对均匀的NKA-α1分布相反，NKA-α2优先集中在真正的横向（而非纵向）TT元素中。但是，NKA-α2不会优先聚集在RyR2交界处，