Regulation of excitability in sinoatrial myocytes

这一项目的长期目标是了解人类免疫缺陷的分子和生物物理机制 生理范围内窦房结肌细胞心脏起搏的调节 条件。SAMS通过激发自发动作电位(AP)发挥心脏起搏细胞的作用。如中所示 其他兴奋性细胞中，窦房结的精确形状反映了复合活动的独特性 质膜上离子通道和转运体的补充。AP波形不是静态的；它们 根据生理环境中的短期和长期变化而变化。原则上，AP中的差异 波形应该有助于洞察构成细胞电生理基础的离子电流的变化 回应。然而，我们破译离子流和AP形状之间因果关系的能力 在所有可兴奋的细胞中仍然是一个难以捉摸的目标。这种理解上的鸿沟是由于缺乏信息造成的。 关于不同生理环境中的AP波形和电流以及研究的固有困难 使用传统研究方法的相互关联的系统。本提案涉及这些一般性问题 通过集中在衰老减缓心脏起搏的机制上提出问题。建议的实验 根据之前资金时期的工作和新的初步数据显示，老龄化减缓了 部分是通过降低SAM的自发AP发放率，并与有限的 AP波形参数和可笑电流(IF)和电压门控钙电流的减少(ICA，L和 ICA，T)。他们还解决了先前的观察结果，即起搏器活动的年龄相关性减少，如果在 SAMS可被高浓度的外源性cAMP通过cAMP模拟机制逆转。 拟议的实验将使用在当前资助期(1)内开发的新研究工具来确定 AP不同时相激活电流的相对贡献随年龄的变化 SAMS，(2)测试不同电流单独或联合作用对AP表型的转化能力 年轻的和老年的SAM，以及(3)测试假设，在一个新的IF调节性的年龄依赖减少 蛋白质是电压依赖的超极化转变和导致AP放电频率减慢的原因 在SAM和小鼠的心率中。这些研究的结果将首次在实验上定义因果关系 在SAM中单个离子电流与AP波形参数之间的联系，这是导致心脏 并将揭示这些机制在正常衰老过程中是如何改变的。

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.