Department of Regenerative Medicine and Cell Biology, Medical University of South Carolina, Charleston, South Carolina 29425, USA.
Am J Physiol Heart Circ Physiol. 2012 Apr 15;302(8):H1712-25. doi: 10.1152/ajpheart.00621.2011. Epub 2012 Feb 3.
How chronic pressure overload affects the Purkinje fibers of the ventricular peripheral conduction system (PCS) is not known. Here, we used a connexin (Cx)40 knockout/enhanced green fluorescent protein knockin transgenic mouse model to specifically label the PCS. We hypothesized that the subendocardially located PCS would remodel after chronic pressure overload and therefore analyzed cell size, markers of hypertrophy, and PCS-specific Cx and ion channel expression patterns. Left ventricular hypertrophy with preserved systolic function was induced by 30 days of surgical transaortic constriction. After transaortic constriction, we observed that PCS cardiomyocytes hypertrophied by 23% (P < 0.05) and that microdissected PCS tissue exhibited upregulated markers of hypertrophy. PCS cardiomyocytes showed a 98% increase in the number of Cx40-positive gap junction particles, with an associated twofold increase in gene expression (P < 0.05). We also identified a 50% reduction in Cx43 gap junction particles located at the interface between PCS cardiomyocytes and the working cardiomyocyte. In addition, we measured a fourfold increase of an ion channel, hyperpolarization-activated cyclic nucleotide-gated channel (HCN)4, throughout the PCS (P < 0.05). As a direct consequence of PCS remodeling, we found that pressure-overloaded hearts exhibited marked changes in ventricular activation patterns during normal sinus rhythm. These novel findings characterize PCS cardiomyocyte remodeling after chronic pressure overload. We identified significant hypertrophic growth accompanied by modified expression of Cx40, Cx43, and HCN4 within PCS cardiomyocytes. We found that a functional outcome of these changes is a failure of the PCS to activate the ventricular myocardium normally. Our findings provide a proof of concept that pressure overload induces specific cellular changes, not just within the working myocardium but also within the specialized PCS.
慢性压力超负荷如何影响心室周边传导系统（PCS）的浦肯野纤维尚不清楚。在这里，我们使用连接蛋白（Cx）40 敲除/增强型绿色荧光蛋白敲入转基因小鼠模型来特异性标记 PCS。我们假设心内膜下定位的 PCS 在慢性压力超负荷后会发生重塑，因此分析了细胞大小、肥大标志物以及 PCS 特异性 Cx 和离子通道表达模式。通过 30 天的主动脉缩窄手术诱导左心室肥厚伴收缩功能保留。主动脉缩窄后，我们观察到 PCS 心肌细胞肥大了 23%（P < 0.05），并且微分离的 PCS 组织显示出上调的肥大标志物。PCS 心肌细胞的 Cx40 阳性间隙连接颗粒数增加了 98%，基因表达增加了两倍（P < 0.05）。我们还发现 Cx43 间隙连接颗粒在 PCS 心肌细胞和工作心肌细胞之间的界面处减少了 50%。此外，我们测量到整个 PCS 中的超极化激活环核苷酸门控通道（HCN）4 增加了四倍（P < 0.05）。作为 PCS 重塑的直接后果，我们发现压力超负荷的心脏在正常窦性节律期间表现出心室激活模式的明显变化。这些新发现描述了慢性压力超负荷后 PCS 心肌细胞的重塑。我们发现，伴随着 PCS 心肌细胞中 Cx40、Cx43 和 HCN4 表达的改变，存在明显的肥大生长。我们发现这些变化的功能后果是 PCS 无法正常激活心室心肌。我们的研究结果提供了一个概念验证，即压力超负荷不仅在工作心肌内，而且在特化的 PCS 内诱导特定的细胞变化。
