Regulation of excitability in sinoatrial myocytes

该项目的长期目标是了解分子和生物物理机制 窦房结肌细胞（SAM）在整个生理过程中对心脏起搏的调节 条件。 SAM 通过激发自发动作电位 (AP) 发挥心脏起搏细胞的作用。如在 其他可兴奋细胞，窦房 AP 的精确形状反映了独特的复合活性 质膜上离子通道和转运蛋白的补充。 AP 波形不是静态的；他们 对生理环境的短期和长期变化的反应有所不同。原则上AP的差异 波形应该有助于深入了解细胞电生理基础的离子电流的变化 回应。然而，我们解码离子电流和 AP 形状之间因果关系的能力 在所有可兴奋细胞中仍然是一个难以捉摸的目标。这种理解上的差距是由于缺乏信息造成的 关于不同生理环境下的 AP 波形和电流以及研究固有的困难 使用传统研究方法相互关联的系统。本提案涉及这些一般性问题 通过关注衰老减缓心脏起搏的机制来提出问题。提议的实验 根据之前资助期间的工作和新的初步数据，这些数据表明老龄化减缓了 部分是通过降低 SAM 的自发 AP 发射率与有限子集的变化相关 AP 波形参数以及有趣电流 (If) 和电压门控 Ca2 电流 (ICa、L 和 ICa，T）。他们还解决了先前的观察结果，即起搏器活动与年龄相关的减少和如果 SAM 可以通过 cAMP 模拟机制被高浓度的外源 cAMP 逆转。 拟议的实验将使用当前资助期间开发的新研究工具 (1) 来定义 AP 不同阶段活跃电流的相对贡献随年龄的变化 SAM，(2) 测试不同电流（单独或组合）改变 AP 表型的能力 年轻和年长的 SAM，以及 (3) 检验以下假设：新型 If 调节中年龄依赖性减少 蛋白质导致电压依赖性超极化转变并导致 AP 放电速率减慢 SAM 和小鼠心率。这些研究的结果将首次通过实验定义因果关系 SAM 中各个离子电流和 AP 波形参数之间的联系，这些参数负责心脏 起搏的一般情况，并将揭示这些机制在正常衰老过程中如何变化。

The long term goals of this project are to understand the molecular and biophysical mechanisms for the regulation of cardiac pacemaking in sinoatrial node myocytes (SAMs) across the gamut of physiological conditions. SAMs function as cardiac pacemaker cells by firing spontaneous action potentials (APs). As in other excitable cells, the precise shape of sinoatrial APs reflects the composite activity of the unique complement of ion channels and transporters on the plasma membrane. AP waveforms are not static; they vary in response to short- and long-term changes in physiological context. In principle, differences in AP waveforms should lend insight into the changes in ionic currents that underlie cellular electrophysiological responses. However, our ability to decode the causal relationships between ionic currents and AP shape remains an elusive goal in all excitable cells. This gap in understanding is caused by a lack of information about AP waveforms and currents in different physiological contexts and by difficulties inherent to the study of interrelated systems using conventional research approaches. The present proposal addresses these general questions by focusing on the mechanisms by which aging slows cardiac pacemaking. Proposed experiments follow from work in prior funding periods and new preliminary data which show that aging slows pacemaking in part by decreasing the spontaneous AP firing rate of SAMs in association with changes in a limited subset of AP waveform parameters and reductions in the funny current (If) and voltage-gated Ca2+ currents (ICa,L and ICa,T). They also address the prior observation that age-dependent reductions in pacemaker activity and If in SAMs can be reversed by high concentrations of exogenous cAMP via a cAMP-mimetic mechanism. Proposed experiments will use new research tools developed during the current funding period (1) to define age-dependent changes in the relative contributions of currents active during different phases of the AP in SAMs, (2) to test the ability of different currents, singly and in combination, to transform the AP phenotype of young and aged SAMs, and (3) to test the hypothesis that age-dependent reduction in a novel If regulatory protein is responsible for the hyperpolarizing shift in voltage-dependence and resulting slowing of AP firing rate in SAMs and heart rate in mice. Results of these studies will experimentally define for the first time causal links between individual ionic currents and AP waveform parameters in SAMs that are responsible for cardiac pacemaking in general and will reveal how these mechanisms are changed during normal aging.