Slowing the pace: Cellular and Molecular Mechanisms of Bradycardia in the Anoxic Turtle (Trachemys scripta)

绝大多数脊椎动物没有氧气就无法生存。由于器官（如心脏）的衰竭，缺氧很快就会导致死亡。心脏需要持续的氧气供应来产生维持其持续功能所必需的代谢能量。然而，与“正常”脊椎动物形成鲜明对比的是，一些脊椎动物物种进化出了在完全缺氧（称为缺氧）的情况下长时间生存的非凡能力。这项研究的重点是阐明缺氧生存的脊椎动物冠军之一红耳滑龟（Trachemys scripta）的心脏如何在缺氧时继续有节奏地跳动，尽管速度较慢。先前的研究表明，海龟的内在心跳速度会因缺氧而大大减慢。然而，在缺氧时抑制内在心率的机制尚不清楚。在脊椎动物的心脏中，内在心率是由位于一个称为心脏起搏器的特殊区域的细胞决定的。起搏器细胞通过产生称为起搏器动作电位的电脉冲来启动心脏收缩，其速率决定了内在心率。本研究将采用多层次、多学科的方法探讨缺氧和低温调节心脏起搏器速率的生理机制。最终，通过探索脊椎动物的心脏如何在缺氧的情况下继续跳动，这项研究将对氧、代谢和电兴奋之间的联系有更深入的了解，这是基本心脏生物学的一个重要方面。此外，研究活动与UAA学生以及更广泛的阿拉斯加社区学生在当代生理学和细胞生物学方面的培训、教育和指导机会密切相关，将为STEM学科中代表性不足的个人扩大接触范围，并增加科学研究的机会。值得注意的是，红耳滑龟（Trachemys scripta）的心脏在缺氧时可以继续有节奏地跳动，尽管速度较慢。先前的研究表明，内在起搏器的戏剧性和快速重置有助于缺氧海龟表现出的心动过缓。然而，缺氧调节心脏起搏器速率的机制尚不清楚。本研究的主要目的是利用海龟心脏作为模型来阐明心脏起搏器调节的生理和细胞机制。本研究将采用多层次和多学科的方法，系统地研究器官（分离心室的收缩特性；起搏器动作电位的体外记录）和细胞（分离心肌细胞离子电流的电生理测量）中心脏起搏器的改变，这些改变是缺氧重置内在心率的基础。该研究将为低氧低温条件下心脏起搏的分子机制提供重要的见解。两者都与基本的心脏生物学和人类病理学有关，而缺氧龟提供了一个显著的模型，说明这些过程是如何在大量压力条件下持续存在的。

The vast majority of vertebrate species are unable to survive without access to oxygen. Death quickly ensues from oxygen lack due to the failure of organs, such as the heart, which require a constant supply of oxygen to create the metabolic energy necessary to support their continued function. However, in stark contrast to "normal" vertebrates, a few vertebrate species have evolved the remarkable ability to survive for prolonged periods in the complete absence of oxygen (termed anoxia). This research focuses on elucidating how the heart of one of the vertebrate champions of anoxia survival, the red-eared slider turtle (Trachemys scripta), can continue to beat rhythmically during anoxia, albeit more slowly. Previous research has revealed that the intrinsic rate at which the turtle heart beats is vastly slowed by anoxia exposure. However, the mechanisms that act to suppress the intrinsic heart rate during anoxia remain unknown. In the vertebrate heart, intrinsic heart rate is determined by cells located in a specialized region, termed the cardiac pacemaker. The pacemaker cells initiate cardiac contraction by producing electrical impulses, called pacemaker action potentials, the rate of which sets intrinsic heart rate. This research will utilize a multi-tiered and multidisciplinary approach to investigate the physiological mechanisms by which anoxia and low temperature modulates pacemaker rate. Ultimately, by probing how a vertebrate heart can continue to beat in the absence of oxygen, this research will develop a deeper understanding of the connections between oxygen, metabolism and electrical excitation, which are a crucial aspect of basic cardiac biology. In addition, the intimate intertwining of research activities with training, education and mentoring opportunities in contemporary physiology and cell biology for students at UAA as well as those of the broader Alaskan community will broaden exposure and enhance opportunity in scientific research for individuals that are underrepresented in STEM disciplines.Remarkably, the heart of one of the vertebrate champions of anoxia survival, the red-eared slider turtle (Trachemys scripta) can continue to beat rhythmically during anoxia, albeit more slowly. Previous research has revealed that a dramatic and rapid resetting of the intrinsic pacemaker contributes to the bradycardia displayed by the anoxic turtle. However, the mechanism by which anoxia modulates pacemaker rate remains unknown. The overarching objective of this research is to exploit the turtle heart as a model to elucidate the physiological and cellular mechanisms of cardiac pacemaker regulation. This research will utilize a multi-tiered and multidisciplinary approach to systematically investigate in the organ (contractile properties of isolated heart chambers; in vitro recordings of pacemaker action potentials) and cell (electrophysiological measures of ionic currents in isolated cardiomyocytes) the alterations of the cardiac pacemaker that underlies the resetting of intrinsic heart rate by anoxia. The proposed research will provide important insights into the molecular mechanisms of cardiac pacemaking in conditions of low oxygen and temperature. Both have pertinence to basic cardiac biology as well as human pathology, and the anoxic turtle provides a remarkable model of how these processes persist in conditions of substantial stress.