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， 调节窦房结肌细胞（SAM）的心脏起搏， 条件SAM通过激发自发动作电位（AP）发挥心脏起搏细胞的功能。如在 与其他可兴奋细胞相比，窦房AP的精确形状反映了独特的 质膜上离子通道和转运蛋白的补充。AP波形不是静态的;它们 在生理环境中的短期和长期变化而变化。原则上，AP的差异 波形应该有助于深入了解细胞电生理学基础的离子电流的变化 应答然而，我们解码离子电流和AP形状之间因果关系的能力， 仍然是所有可兴奋细胞难以实现的目标。这种理解上的差距是由于缺乏信息造成的 关于AP波形和电流在不同的生理环境和固有的困难的研究， 使用传统的研究方法相互关联的系统。本建议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解决问题。拟议实验 根据先前资助期的工作和新的初步数据， 部分通过降低SAM的自发AP放电率与有限子集的变化相关， AP波形参数和有趣电流（If）和电压门控Ca 2+电流（伊卡，L和 伊卡，T）。他们还讨论了先前的观察结果，即年龄依赖性的起搏器活动减少，如果在 SAM可以通过cAMP模拟机制被高浓度的外源性cAMP逆转。 拟议的实验将使用在当前资助期内开发的新研究工具（1）来定义 年龄依赖性的变化，在相对贡献的电流活动在不同阶段的AP， SAM，（2）测试不同电流单独和组合转化AP表型的能力， 年轻和老年SAM，和（3）测试的假设，年龄依赖性减少，在一个新的如果调节 蛋白质负责电压依赖性的超极化转变，并导致AP放电速率减慢 和小鼠的心率。这些研究的结果将首次通过实验确定因果关系 SAM中单个离子电流和AP波形参数之间的联系， 并将揭示这些机制在正常衰老过程中是如何变化的。

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.