Signal Transduction in Intrapulmonary Chemoreceptors

描述(申请人提供)：在呼吸空气的脊椎动物的不同位置发现了对二氧化碳敏感的呼吸化学感受器，包括脑干、颈动脉和主动脉体以及肺中的多个位置，证实了它们在生理pH/pCO2动态平衡中的功能重要性。长期以来，我们一直对一种异常灵敏的二氧化碳传感器--鸟类肺内化学感受器(IPC)进行二氧化碳信号转导感兴趣。过去的IPC研究表明，它们(像大多数呼吸化学感受器一样)可能直接感知H+，而不是二氧化碳。在IPC中，CO2诱导的酸中毒抑制动作电位放电率，使IPC成为许多具有这一特征的哺乳动物中枢和呼吸道化学感受器的优秀模型，并且与许多其他由CO2刺激的哺乳动物呼吸化学感受器形成了良好的对比。这项提议的第一个目的是使用电离度和膜通透性不同的弱酸和强酸和碱来检验细胞内pH感应假说。与强酸碱相比，弱酸碱应具有更好的细胞内通道，并对IPC放电和二氧化碳敏感性有更大的影响。第二个目标是研究我们最近在IPC中发现的类似Trek的串联孔域泄漏通道。由于Trek通道是由细胞内酸化开放的，它们可能是细胞内酸化/CO2抑制IPC的长期寻找的分子靶点。这将使用Trek激动剂或拮抗剂进行测试，包括利鲁唑、多不饱和脂肪酸、花生四烯酸、环丙烷、一氧化二氮、氙气和渗透压挑战。第三个目标将测试IPC的峰值放电速率和IPC峰频率适应的大小(即神经编码的属性)是否与身体大小成比例。这种比例将使IPC传入放电的信息传递与动物的呼吸频率相匹配，呼吸频率也是M-1/4。为了测试这一点，我们将量化非常小的动物(~12g体重)和非常大的动物(~10万g体重)的IPC放电对标准化CO2阶跃刺激的动态反应。这项研究将从总体上加强对呼吸化学感受器的了解，并可能发现有助于治疗呼吸衰竭期间二氧化碳不敏感的药物。这项研究调查了检测体内二氧化碳水平并向大脑发送最终控制呼吸的神经信号的基本神经过程。这对人类健康很重要，因为了解二氧化碳化学转导的基础可能有助于开发更有效的治疗方法和药物，以消除二氧化碳化学敏感性的丧失，这种敏感性往往会使严重心肺疾病患者的生存复杂化。

DESCRIPTION (provided by applicant): CO2-sensing respiratory chemoreceptors are found in diverse locations in air-breathing vertebrates, including multiple sites within the brainstem, carotid and aortic bodies, and lungs, affirming their functional importance in physiological pH/PCO2 homeostasis. We have a long-standing interest in CO2 signal transduction by an unusually responsive type of CO2 sensor -the avian intrapulmonary chemoreceptor (IPC). Past IPC research indicates they (like most respiratory chemoreceptors) probably sense H+ rather than CO2 directly. In IPC, CO2-induced acidosis inhibits action potential discharge rate, making IPC an excellent model for many mammalian central and airway chemoreceptors that share this characteristic, and a good contrast to many other mammalian respiratory chemoreceptors that are excited by CO2. The first aim of this proposal will test the intracellular pH sensing hypothesis using weak and strong acids and bases that vary in their degree of ionization and membrane permeability. Weak acids and bases should have better intracellular access and greater effects on IPC discharge and CO2 sensitivity than strong acids and bases. The second aim investigates TREK-like tandem pore domain leak channels that we recently discovered in IPC. Because TREK channels are opened by intracellular acidosis, they could be the long-sought molecular target for inhibition of IPC by intracellular acidosis/CO2. This will be tested using TREK agonists or antagonists including riluzole, polyunsaturated fatty acids, arachidonic acid, cyclopropane, nitrous oxide, xenon, and osmotic challenges. The third aim will test whether peak IPC discharge rate and the magnitude of IPC spike frequency adaptation (i.e. attributes of neural coding) scale with body size in proportion to M-1/4. Such scaling would match information delivery by IPC afferent discharge to the breathing frequency of the animals, which also scales to M-1/4. To test this, dynamic IPC discharge responses to standardized CO2 step stimuli will be quantified in very small animals (~12 g body mass) and in the very large animals (~100,000 g body mass). This research will enhance understanding of respiratory chemoreceptors in general and may reveal drugs useful for treating CO2 insensitivity during respiratory failure. This research investigates fundamental neural processes that detect CO2 levels in the body and send a neural signal to the brain that ultimately controls breathing. This is important for human health, because understanding the basis of CO2 chemotransduction may help develop more effective treatments and drugs for the loss of CO2 chemosensitivity that often complicates patient survival in serious cardiopulmonary disease.