Abbott Geoffrey W
Bioelectricity Laboratory, Department of Pharmacology and Department of Physiology and Biophysics, School of Medicine, University of California, Irvine Irvine, CA, USA.
Front Physiol. 2017 Feb 8;8:66. doi: 10.3389/fphys.2017.00066. eCollection 2017.
The human ventricular cardiomyocyte transient outward K current () mediates the initial phase of myocyte repolarization and its disruption is implicated in Brugada Syndrome and heart failure (HF). Human cardiac is generated primarily by two Kv4.3 splice variants (Kv4.3L and Kv4.3S, diverging only by a C-terminal, S6-proximal, 19-residue stretch unique to Kv4.3L), which are differentially remodeled in HF, but considered functionally alike at baseline. Kv4.3 is regulated in human heart by β subunits including KChIP2b and KCNEs, but their effects were previously assumed to be Kv4.3 isoform-independent. Here, this assumption was tested experimentally using two-electrode voltage-clamp analysis of human subunits co-expressed in oocytes. Unexpectedly, Kv4.3L-KChIP2b channels exhibited up to 8-fold lower current augmentation, 40% slower inactivation, and 5 mV-shifted steady-state inactivation compared to Kv4.3S-KChIP2b. A synthetic peptide mimicking the 19-residue stretch diminished these differences, reinforcing the importance of this segment in mediating Kv4.3 regulation by KChIP2b. KCNE subunits induced further functional divergence, including a 7-fold increase in Kv4.3S-KCNE4-KChIP2b current compared to Kv4.3L-KCNE4-KChIP2b. The discovery of β-subunit-dependent functional divergence in human Kv4.3 splice variants suggests a C-terminal signaling hub is crucial to governing β-subunit effects upon Kv4.3, and demonstrates the potential significance of differential Kv4.3 gene-splicing and β subunit expression in myocyte physiology and pathobiology.
人类心室心肌细胞瞬时外向钾电流（）介导心肌复极化的初始阶段，其功能紊乱与Brugada综合征和心力衰竭（HF）有关。人类心脏的主要由两种Kv4.3剪接变体（Kv4.3L和Kv4.3S，仅在C末端、S6近端有19个残基的延伸区域不同，该区域是Kv4.3L特有的）产生，它们在HF中发生不同程度的重塑，但在基线时被认为功能相似。Kv4.3在人类心脏中受包括KChIP2b和KCNEs在内的β亚基调节，但之前认为它们的作用与Kv4.3亚型无关。在此，通过对在卵母细胞中共表达的人类亚基进行双电极电压钳分析，对这一假设进行了实验验证。出乎意料的是，与Kv4.3S-KChIP2b相比，Kv4.3L-KChIP2b通道的电流增强降低了8倍，失活速度慢40%，稳态失活偏移了5 mV。一种模拟19个残基延伸区域的合成肽减少了这些差异，强化了该片段在介导KChIP2b对Kv4.3调节中的重要性。KCNE亚基导致了进一步的功能差异，包括与Kv4.3L-KCNE4-KChIP2b相比，Kv4.3S-KCNE4-KChIP2b电流增加了7倍。人类Kv4.3剪接变体中β亚基依赖性功能差异的发现表明，C末端信号枢纽对于控制β亚基对Kv4.3的作用至关重要，并证明了Kv4.3基因剪接差异和β亚基表达在心肌细胞生理学和病理生物学中的潜在意义。
