Yada Hirotaka, Murata Mitsushige, Shimoda Kouji, Yuasa Shinsuke, Kawaguchi Haruko, Ieda Masaki, Adachi Takeshi, Murata Mitsuru, Ogawa Satoshi, Fukuda Keiichi
Cardiopulmonary Division, Keio University, 35 Shinanomachi, Shinjuku-ku, Tokyo 160-8582, Japan.
Circ Res. 2007 Jul 6;101(1):69-77. doi: 10.1161/CIRCRESAHA.106.146399. Epub 2007 May 24.
Disorders of L-type Ca2+ channels can cause severe cardiac arrhythmias. A subclass of small GTP-binding proteins, the RGK family, regulates L-type Ca2+ current (I(Ca,L)) in heterologous expression systems. Among these proteins, Rad (Ras associated with diabetes) is highly expressed in the heart, although its role in the heart remains unknown. Here we show that overexpression of dominant negative mutant Rad (S105N) led to an increase in I(Ca,L) and action potential prolongation via upregulation of L-type Ca2+ channel expression in the plasma membrane of guinea pig ventricular cardiomyocytes. To verify the in vivo physiological role of Rad in the heart, a mouse model of cardiac-specific Rad suppression was created by overexpressing S105N Rad, using the alpha-myosin heavy chain promoter. Microelectrode studies revealed that action potential duration was significantly prolonged with visible identification of a small plateau phase in S105N Rad transgenic mice, when compared with wild-type littermate mice. Telemetric electrocardiograms on unrestrained mice revealed that S105N Rad transgenic mice had significant QT prolongation and diverse arrhythmias such as sinus node dysfunction, atrioventricular block, and ventricular extrasystoles, whereas no arrhythmias were observed in wild-type mice. Furthermore, administration of epinephrine induced frequent ventricular extrasystoles and ventricular tachycardia in S105N Rad transgenic mice. This study provides novel evidence that the suppression of Rad activity in the heart can induce ventricular tachycardia, suggesting that the Rad-associated signaling pathway may play a role in arrhythmogenesis in diverse cardiac diseases.
L型钙离子通道紊乱可导致严重的心律失常。小GTP结合蛋白的一个亚类，即RGK家族，在异源表达系统中调节L型钙电流（I(Ca,L)）。在这些蛋白中，Rad（与糖尿病相关的Ras）在心脏中高度表达，但其在心脏中的作用尚不清楚。在这里，我们表明，显性负性突变体Rad（S105N）的过表达通过上调豚鼠心室心肌细胞质膜上L型钙离子通道的表达，导致I(Ca,L)增加和动作电位延长。为了验证Rad在心脏中的体内生理作用，利用α-肌球蛋白重链启动子过表达S105N Rad，创建了心脏特异性Rad抑制的小鼠模型。微电极研究表明，与野生型同窝小鼠相比，S105N Rad转基因小鼠的动作电位时程显著延长，可见一个小的平台期。对不受约束的小鼠进行遥测心电图显示，S105N Rad转基因小鼠有明显的QT间期延长和多种心律失常，如窦房结功能障碍、房室传导阻滞和室性早搏，而野生型小鼠未观察到心律失常。此外，给予肾上腺素可诱发S105N Rad转基因小鼠频繁的室性早搏和室性心动过速。这项研究提供了新的证据，即心脏中Rad活性的抑制可诱发室性心动过速，表明Rad相关信号通路可能在多种心脏疾病的心律失常发生中起作用。
