Department of Biomedical Engineering, Washington Univ. in St. Louis, St. Louis, MO 63130, USA.
Am J Physiol Heart Circ Physiol. 2010 Aug;299(2):H482-91. doi: 10.1152/ajpheart.00756.2009. Epub 2010 Jun 4.
The mouse is widely used as a genetic platform to investigate the molecular mechanisms of sinoatrial node (SAN) pacemaking. Recently, it has been shown that isolated SAN cells from the ankyrin-B (AnkB)-deficient mice display severe pacemaking dysfunction similar to individuals harboring ankyrin 2 allele variants. However, these results have been limited to isolated SAN cells only and thus did not evaluate the functional anatomy of the widely distributed atrial pacemaker complex (e.g., the dynamic interaction of primary and subsidiary pacemakers). We studied pacemaker function in an intact mouse atrial preparation, which included the SAN, atrioventricular junction (AVJ), and both atria, excluding most of the septum. Optical mapping with a voltage-sensitive dye and CMOS camera ULTIMA-L was used to map spontaneous pacemaker activity with or without autonomic modulation in wild-type (WT) mice (n = 7) and in the AnkB heterozygous (AnkB(+/-); n = 9) mouse model of human SAN disease. In WT mice, isoproterenol accelerated the SAN rate (for 10 microM: from 325 + or - 19 to 510 + or - 33 beat/min, P < 0.01) and shifted the leading pacemaker site superiorly by 0.77 + or - 0.11 mm within the SAN. ACh decreased the SAN rate (from 333 + or - 26 to 96 + or - 22 beats/min, P < 0.01) and shifted the leading pacemaker either inferiorly within the SAN or abruptly toward the AVJ. After isoproterenol, AnkB(+/-) mice exhibited a larger beat-to-beat variability (SD of a cycle length: 13.4 + or - 3.6 vs. 2.5 + or - 0.8 ms, P < 0.01 vs. WT mice), disorganized shift of the leading pacemaker (2.04 + or - 0.37 mm, P < 0.05 vs. WT mice), and competing multiple pacemakers, resulting in beat-to-beat changes of the leading pacemaker location site between the SAN and AVJ regions. Notably, AnkB(+/-) mice also displayed a reduced sensitivity to ACh (rate slowing by 32 + or - 12% vs. 67 + or - 4%, P < 0.05, AnkB(+/-) vs. WT mice, respectively). In conclusion, AnkB dysfunction results in SAN abnormalities in an isolated mouse atria preparation. While AnkB dysfunction dramatically alters single SAN cell function, the mechanisms underlying cardiac automaticity are clearly complex, and phenotypes may be partially compensated by the dynamic interaction of cells within the pacemaker complex. These new findings highlight the importance of the functional anatomy of the entire atrial distributed pacemaker complex, including the SAN and AVJ, and clearly demonstrate the role of AnkB in cardiac automaticity.
鼠标被广泛用作研究窦房结（SAN）起搏的分子机制的遗传平台。最近，已经表明，从锚蛋白-B（AnkB）缺陷小鼠中分离出的 SAN 细胞表现出严重的起搏功能障碍，类似于携带锚蛋白 2 等位基因变异的个体。然而，这些结果仅限于分离的 SAN 细胞，因此并未评估广泛分布的心房起搏复合体的功能解剖结构（例如，主要和辅助起搏点的动态相互作用）。我们在完整的小鼠心房准备中研究了起搏功能，其中包括 SAN、房室结（AVJ）和两个心房，不包括大部分间隔。使用带电压敏感染料的光学映射和 CMOS 相机 ULTIMA-L，在野生型（WT）小鼠（n=7）和人类 SAN 疾病的 AnkB 杂合子（AnkB(+/-)；n=9）小鼠模型中，在有或没有自主调节的情况下，对自发起搏活动进行映射。在 WT 小鼠中，异丙肾上腺素加速了 SAN 率（对于 10 μM：从 325 +或-19 增加到 510 +或-33 次/分钟，P<0.01），并将主导起搏点向上移动了 0.77 +或-0.11 毫米。ACh 降低了 SAN 率（从 333 +或-26 减少到 96 +或-22 次/分钟，P<0.01），并将主导起搏点向下移至 SAN 内或突然移向 AVJ。在异丙肾上腺素之后，AnkB(+/-)小鼠表现出更大的心动周期变异性（心动周期长度标准差：13.4 +或-3.6 与 2.5 +或-0.8 毫秒，P<0.01 与 WT 小鼠相比），主导起搏点的移位变得混乱（2.04 +或-0.37 毫米，P<0.05 与 WT 小鼠相比），并出现多个竞争起搏点，导致 SAN 和 AVJ 区域之间主导起搏点位置的跳动变化。值得注意的是，AnkB(+/-)小鼠对 ACh 的敏感性也降低（速率减慢 32 +或-12%与 67 +或-4%，P<0.05，AnkB(+/-)与 WT 小鼠相比）。总之，AnkB 功能障碍导致分离的小鼠心房制备中出现 SAN 异常。虽然 AnkB 功能障碍显著改变了单个 SAN 细胞的功能，但心脏自动性的潜在机制显然很复杂，表型可能部分由起搏复合体中细胞的动态相互作用补偿。这些新发现强调了整个心房分布起搏复合体（包括 SAN 和 AVJ）的功能解剖结构的重要性，并清楚地表明了 AnkB 在心脏自动性中的作用。
