Center for Neuroscience, Aging and Stem Cell Research, Sanford-Burnham Medical Research Institute, La Jolla, California 92037, USA.
J Cardiovasc Electrophysiol. 2012 Mar;23(3):309-18. doi: 10.1111/j.1540-8167.2011.02191.x. Epub 2011 Oct 10.
Understanding sinoatrial node (SAN) development could help in developing therapies for SAN dysfunction. However, electrophysiological investigation of SAN development remains difficult because mutant mice with SAN dysfunctions are frequently embryonically lethal. Most research on SAN development is therefore limited to immunocytochemical observations without comparable functional studies.
We applied a multielectrode array (MEA) recording system to study SAN development in mouse hearts acutely isolated at embryonic ages (E) 8.5-12.5 days. Physiological heart rates were routinely restored, enabling accurate functional assessment of SAN development. We found that dominant pacemaking activity originated from the left inflow tract (LIFT) region at E8.5, but switched to the right SAN by E12.5. Combining MEA recordings and pharmacological agents, we show that intracellular calcium (Ca(2+))-mediated automaticity develops early and is the major mechanism of pulse generation in the LIFT of E8.5 hearts. Later in development at E12.5, sarcolemmal ion channels develop in the SAN at a time when pacemaker channels are down-regulated in the LIFT, leading to a switch in the dominant pacemaker location. Additionally, low micromolar concentrations of tetrodotoxin (TTX), a sodium channel blocker, minimally affect pacemaker rhythm at E8.5-E12.5, but suppress atrial activation and reveal a TTX-resistant SAN-atrioventricular node (internodal) pathway that mediates internodal conduction in E12.5 hearts.
Using a physiological mapping method, we demonstrate that differential mechanistic development of automaticity between the left and right inflow tract regions confers the pacemaker location switch. Moreover, a TTX-resistant pathway mediates preferential internodal conduction in E12.5 mouse hearts.
了解窦房结（SAN）的发育有助于开发治疗 SAN 功能障碍的方法。然而，由于 SAN 功能障碍的突变小鼠通常在胚胎期致死，因此对 SAN 发育的电生理学研究仍然很困难。因此，大多数关于 SAN 发育的研究仅限于免疫细胞化学观察，而没有可比的功能研究。
我们应用多电极阵列（MEA）记录系统在胚胎期（E）8.5-12.5 天急性分离的小鼠心脏中研究 SAN 的发育。常规恢复生理心率，从而能够准确评估 SAN 的发育。我们发现，主导起搏活动源自左流入道（LIFT）区域在 E8.5 时，但在 E12.5 时切换到右 SAN。结合 MEA 记录和药理学试剂，我们表明，细胞内钙（Ca（2+））介导的自动性很早就发展起来，是 E8.5 心脏 LIFT 脉冲产生的主要机制。在发育后期，在 E12.5 时，在 LIFT 中起搏通道下调的同时，肌膜离子通道在 SAN 中发育，导致主导起搏位置发生切换。此外，低微摩尔浓度的河豚毒素（TTX），一种钠通道阻滞剂，在 E8.5-E12.5 时对起搏节律的影响最小，但抑制了心房激活并揭示了一种 TTX 抵抗的 SAN-房室结（结间）途径，该途径介导 E12.5 心脏中的结间传导。
使用生理映射方法，我们证明了左、右流入道区域自动性的差异发育赋予了起搏位置的切换。此外，TTX 抵抗的途径介导了 E12.5 小鼠心脏中优先的结间传导。
