Chan Fu-Chi, Cheng Chiao-Pei, Wu Kuo-Ho, Chen Yao-Chang, Hsu Chih-Hsiung, Gustafson-Wagner Elisabeth A, Lin Jenny Li-Chun, Wang Qinchuan, Lin Jim Jung-Ching, Lin Cheng-I
Institute of Physiology, National Defense Medical Center, Taipei, Taiwan, ROC.
Front Biosci (Elite Ed). 2011 Jun 1;3(4):1425-42. doi: 10.2741/e344.
Mouse Xin-alpha (mXin-alpha) encodes a Xin repeat-containing, actin-binding protein localized to the intercalated disc (ICD). Ablation of mXin-alpha progressively leads to disrupted ICD structure, cardiac hypertrophy and cardiomyopathy with conduction defects during adulthood. Such conduction defects could be due to ICD structural defects and/or cell electrophysiological property changes. Here, we showed that despite the normal ICD structure, juvenile mXina-null cardiomyocytes (from 3~4-week-old mice) exhibited a significant reduction in the transient outward K+ current (ITO), similar to adult mutant cells. Juvenile but not adult mutant cardiomyocytes also had a significant reduction in the delayed rectifier K+ current. In contrast, the mutant adult ventricular myocytes had a significant reduction in the inward rectifier K+ current (IK1) on hyperpolarization. These together could account for the prolongation of action potential duration (APD) and the ease of developing early afterdepolarization observed in juvenile mXin-alpha-null cells. Interestingly, juvenile mXin-alpha-null cardiomyocytes had a notable decrease in the amplitude of intracellular Ca2+ transient and no change in the L-type Ca2+ current, suggesting that the prolonged APD did not promote an increase in intracellular Ca2+ for cardiac hypertrophy. Juvenile mXin-alpha-null ventricles had reduced levels of membrane-associated Kv channel interacting protein 2, an auxiliary subunit of ITO, and filamin, an actin cross-linking protein. We further showed that mXin-alpha interacted with both proteins, providing a novel mechanism for ITO surface expression.
小鼠Xin-α（mXin-α）编码一种含有Xin重复序列的肌动蛋白结合蛋白，定位于闰盘（ICD）。成年期mXin-α的缺失会逐渐导致ICD结构破坏、心脏肥大和伴有传导缺陷的心肌病。这种传导缺陷可能是由于ICD结构缺陷和/或细胞电生理特性改变所致。在这里，我们发现，尽管ICD结构正常，但幼年mXin-α基因敲除的心肌细胞（来自3至4周龄小鼠）的瞬时外向钾电流（ITO）显著降低，这与成年突变细胞相似。幼年而非成年突变心肌细胞的延迟整流钾电流也显著降低。相比之下，突变的成年心室肌细胞在超极化时内向整流钾电流（IK1）显著降低。这些共同作用可以解释幼年mXin-α基因敲除细胞中动作电位时程（APD）的延长以及早期后去极化的易发性。有趣的是，幼年mXin-α基因敲除的心肌细胞细胞内钙瞬变幅度显著降低，L型钙电流无变化，这表明延长的APD并未促进细胞内钙增加以导致心脏肥大。幼年mXin-α基因敲除的心室中，膜相关的Kv通道相互作用蛋白2（ITO的一个辅助亚基）和细丝蛋白（一种肌动蛋白交联蛋白）水平降低。我们进一步表明，mXin-α与这两种蛋白相互作用，为ITO的表面表达提供了一种新机制。
