Zicha Stephen, Fernández-Velasco María, Lonardo Giuseppe, L'Heureux Nathalie, Nattel Stanley
Department of Medicine and Research Center, Montreal Heart Institute and University of Montreal, Quebec, Canada.
Cardiovasc Res. 2005 Jun 1;66(3):472-81. doi: 10.1016/j.cardiores.2005.02.011. Epub 2005 Mar 21.
The hyperpolarization-activated cation current I(f) contributes significantly to sinoatrial node pacemaker function and possibly to ectopic arrhythmogenesis. Little is known about the expression of corresponding hyperpolarization-activated cyclic nucleotide-gated (HCN) channel subunits in normal hearts and HCN remodeling by diseases, like congestive heart failure (CHF), associated with disturbances of cardiac rhythm.
We assessed expression of HCN1, 2 and 4 in normal mongrel dogs and dogs subjected to 2-week ventricular tachypacing-induced CHF. Competitive RT-PCR, Western blot and immunohistochemistry were used to quantify HCN subunit mRNA and protein expression in the right atrium (RA) and sinoatrial node. CHF approximately doubled sinus node recovery time, indicating suppressed sinus node pacemaker function. HCN expression under control conditions was HCN4 > HCN2 >> HCN1. HCN2 and HCN4 expression was greater at both protein and mRNA levels in sinoatrial node than RA. CHF significantly decreased sinus node HCN expression at both mRNA and protein levels (HCN2 by 78% and 82%; HCN4 by 42% and 77%, respectively). RA HCN2 expression was unaltered by CHF, but HCN4 was significantly upregulated (by 209%).
HCN4 is the dominant subunit in canine sinoatrial node and RA; strong sinus node HCN expression likely contributes to its pacemaker function; downregulation of HCN4 and HCN2 expression contribute to CHF-induced sinus node dysfunction; and upregulation of atrial HCN4 may help to promote atrial arrhythmia formation. These findings provide novel information about the molecular basis of normal and disease-related impairments of cardiac impulse formation.
超极化激活的阳离子电流I(f)对窦房结起搏功能有重要作用，可能也与异位心律失常的发生有关。关于正常心脏中相应的超极化激活环核苷酸门控（HCN）通道亚基的表达以及诸如充血性心力衰竭（CHF）等与心律紊乱相关疾病对HCN的重塑作用，目前所知甚少。
我们评估了正常杂种犬以及经2周心室快速起搏诱导CHF的犬的HCN1、2和4的表达。采用竞争性逆转录聚合酶链反应（RT-PCR）、蛋白质印迹法和免疫组织化学方法对右心房（RA）和窦房结中HCN亚基的mRNA和蛋白质表达进行定量分析。CHF使窦房结恢复时间增加了约一倍，表明窦房结起搏功能受到抑制。在对照条件下，HCN的表达为HCN4 > HCN2 >> HCN1。窦房结中HCN2和HCN4在蛋白质和mRNA水平上的表达均高于RA。CHF使窦房结中HCN的mRNA和蛋白质水平均显著降低（HCN2分别降低78%和82%；HCN4分别降低42%和77%）。CHF对RA中HCN2的表达无影响，但HCN4显著上调（上调209%）。
HCN4是犬窦房结和RA中的主要亚基；窦房结中HCN的高表达可能有助于其起搏功能；HCN4和HCN2表达的下调导致CHF引起的窦房结功能障碍；心房HCN4的上调可能有助于促进房性心律失常的形成。这些发现为正常和疾病相关的心脏冲动形成障碍的分子基础提供了新的信息。
