Cellular CO2 Transduction In Avian Intrapulmonary Chemoreceptors

禽类肺内化学感受器中的细胞 CO2 转导

• 批准号: 0217815
• 负责人: Steve Hempleman
• 金额: $ 31.55万
• 依托单位: Northern Arizona University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2002
• 资助国家: 美国
• 起止时间: 2002-08-01 至 2006-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0217815&HistoricalAwards=false
• 关键词: Cellular; CO2; Transduction; Avian; Intrapulmonary

Carbon dioxide is a major waste product of cellular metabolism and an important determinant of body fluid pH in all air-breathing vertebrates. Body CO2 levels are detected by CO2 sensitive neurons (respiratory chemoreceptors) that provide critical feedback control of CO2 elimination by the lungs. Failure of CO2 regulation causes metabolic impairment or death, and is, unfortunately, a common complication of severe cardiopulmonary disease or neurological injury. Because the problem of CO2 sensing and regulation is fundamental for active air-breathing vertebrates, animals have evolved a variety of CO2-sensing neurons (respiratory chemoreceptors) in diverse locations including the brainstem, systemic arterial system, and lung airways. We are studying CO2-sensitive intrapulmonary chemoreceptors (IPC) in avian lungs to understand the fundamental steps of cellular CO2 transduction (i.e. mechanisms that alter IPC action potential discharge rate when CO2 levels change, thereby encoding neural information about lung CO2). Avian IPC are a powerful cellular model of respiratory chemoreception because they are extremely CO2 sensitive, their axons are easily accessible for measuring action potentials, the CO2 around their sensory endings can be precisely controlled in the laboratory, and they have a unique inverse response to CO2 (i.e. low PCO2 excites IPC, high PCO2 inhibits). Here we test the following novel hypotheses about IPC CO2 transduction: that IPC sense CO2 through changes in intracellular pH; and that at a given CO2 level the intracellular pH of IPC is uniquely determined by a dynamic kinetic balance between the rate of intracellular CO2 hydration catalyzed by carbonic anhydrase, the rate of intracellular H+ buffering, and the rates of transmembrane H+ and HCO3- extrusion by pumping mechanisms and antiports. We also hypothesize that IPC membrane excitability and action potential generation are coupled to changes in intracellular pH. Specific aims for this study include: (1) development of a mathematical model of CO2 chemotransduction to test the kinetic transduction hypothesis, (2) histochemical identification of IPC sensory endings in the lung and cell bodies in the nodose ganglia, (3) use of molecular antagonists, agonists and neurotoxins targeting specific ion channels, antiports and neurotransmitters to determine their role in CO2 transduction, and (4) altering intracellular pH buffering to test its role in CO2 transduction. Northern Arizona University emphasizes laboratory-based undergraduate biology education. Accordingly, this project is an efficient vehicle for introducing students to neurobiological research (so far ten students have been significantly involved, half of whom have been minority students--including two Navajo Native Americans). This remains a priority for the continuing grant cycle.

二氧化碳是细胞代谢的主要废物，也是所有呼吸空气的脊椎动物体液pH的重要决定因素。人体的二氧化碳水平是由对二氧化碳敏感的神经元(呼吸化学感受器)检测的，这些神经元提供了对肺部二氧化碳排出的关键反馈控制。二氧化碳调节失败会导致代谢障碍或死亡，不幸的是，这是严重心肺疾病或神经损伤的常见并发症。由于二氧化碳的感知和调节问题是呼吸空气的活跃脊椎动物的基础，动物在不同的位置进化出了各种二氧化碳感知神经元(呼吸化学受体)，包括脑干、全身动脉系统和肺气道。我们正在研究鸟类肺中对二氧化碳敏感的肺内化学感受器(IPC)，以了解细胞CO2转导的基本步骤(即当CO2水平改变时改变IPC动作电位放电率的机制，从而编码关于肺CO2的神经信息)。鸟类IPC是一种强大的呼吸化学感受细胞模型，因为它们对CO2极其敏感，它们的轴突很容易测量动作电位，它们感觉末梢周围的CO2可以在实验室中精确控制，并且它们对CO2有独特的反向反应(即低二氧化碳刺激IPC，高二氧化碳抑制IPC)。在这里，我们测试了以下关于IPC二氧化碳转导的新假说：IPC通过改变细胞内的pH来感知CO2；在给定的CO2水平下，IPC的细胞内pH唯一地由碳酸酐酶催化的细胞内CO2水合速率、细胞内H+缓冲速率以及通过泵送机制和反转运机制的跨膜H+和HCO3-排出速率之间的动态平衡决定。我们还假设IPC膜的兴奋性和动作电位的产生与细胞内pH的变化有关。本研究的具体目的包括：(1)建立二氧化碳化学转导的数学模型以验证动力学转导假说；(2)对肺和结状神经节中的IPC感觉末梢进行组织化学鉴定；(3)使用针对特定离子通道、拮抗剂和神经递质的分子拮抗剂、激动剂和神经毒素来确定它们在二氧化碳转导中的作用；以及(4)改变细胞内的pH缓冲以测试其在二氧化碳转导中的作用。北亚利桑那大学强调以实验室为基础的本科生生物学教育。因此，该项目是向学生介绍神经生物学研究的有效工具(到目前为止，已有10名学生参与其中，其中一半是少数族裔学生--包括两名纳瓦霍印第安人)。这仍然是持续赠款周期的优先事项。