Glial chemosensitivity: pH sensing and interactions with neuronal chemoreceptors

描述（由申请人提供）：中枢化学感受器是位于脑干的专门的CO2/pH传感器（即化学感受器）根据组织pH变化调节呼吸的机制。该机制对正常呼吸很重要，特别是在睡眠期间，化学感受器的中断被认为会导致几种病理状态，包括中枢性睡眠呼吸暂停、周期性呼吸和中枢性低通气综合征。尽管深入研究，中枢化学接受的细胞和分子机制仍然知之甚少。最近的证据表明，位于后梯形核（RTN）的ph敏感神经元是重要的化学感受器。也有证据表明，CO2/H+在RTN中引起的ATP释放有助于RTN和呼吸驱动的综合输出。我们假设ph敏感的RTN神经胶质细胞是这种嘌呤能驱动呼吸的来源。我们提出，RTN胶质细胞通过抑制异聚体Kir4.1-Kir5.1通道来感知H+，并通过激活P2受体释放ATP来激活ph敏感神经元。我们还提出，在RTN中释放的一部分H+诱导的ATP将被水解成腺苷，并通过启动血管舒张来缓冲组织pH，从而限制化学受体的活性。我们提出的研究将结合电生理学、免疫组织化学和遗传学方法来确定pH敏感RTN胶质细胞的细胞特性、它们感知pH的分子机制，以及它们与pH敏感神经元和局部脉管系统的相互作用。该项目的四个具体目标是：1)确定pH敏感的RTN胶质细胞的细胞身份，2)确定RTN胶质细胞感知pH变化的分子机制，3)确定pH敏感胶质细胞与pH敏感神经元之间的相互作用，4)确定RTN中的pH敏感胶质细胞是否调节局部微循环。这是我们的希望，确定这些机制将导致新的治疗途径的条件下，由抑制呼吸驱动的管理。

DESCRIPTION (provided by applicant): Central chemoreception is the mechanism by which specialized CO2/pH sensors (i.e., chemoreceptors) located in the brainstem regulates breathing in response to changes in tissue pH. This mechanism is important for normal breathing, especially during sleep, and disruption of chemoreception is thought to contribute to several pathological states including central sleep apnea, periodic breathing and central hypoventilation syndrome. Despite intensive investigation, cellular and molecular mechanisms underlying central chemoreception remain poorly understood. Recent evidence indicates that pH-sensitive neurons located in the retrotrapezoid nucleus (RTN) are important chemoreceptors. Evidence also indicates that CO2/H+-evoked ATP release in the RTN contributes to integrated output of the RTN and respiratory drive. We hypothesize that pH-sensitive RTN glial cells are the source of this purinergic drive to breathe. We propose that a discreet population of RTN glia sense H+ by inhibition of heteromeric Kir4.1-Kir5.1 channels, and release ATP to activate pH-sensitive neurons by activation of P2 receptors. We also propose that a portion of H+-evoked ATP released in the RTN will be hydrolyzed to adenosine and serve to limit chemoreceptor activity by initiating vasodilation to buffer tissue pH. The proposed research will use a combination of electrophysiological, immunohistochemical and genetic approaches to determine the cellular identity of pH-sensitive RTN glia, the molecular mechanism by which they sense pH, and their interactions with pH-sensitive neurons and local vasculature. The four specific aims of this project are: 1) determine the cellular identity of pH-sensitive RTN glia, 2) determine the molecular mechanism by which RTN glia sense changes in pH, 3) identify interactions between pH-sensitive glia and pH-sensitive neurons, 4) determine if pH-sensitive glia in the RTN modulate local microcirculation. It is our hope that determining these mechanisms will lead to new therapeutic avenues for the management of conditions resulting from suppressed respiratory drive. PUBLIC HEALTH RELEVANCE: The results of these studies will identity two novel mechanisms by which glial cells contribute to the mechanism by of chemoreception. Specifically, we will establish that a population of glial cells sense H+ by inhibition of Kir4.1-Kir5.1 channels and can provide an excitatory purinergic drive to the neural network that controls depth and frequency of breathing. We also determine that these pH-sensitive glia regulate vascular tone to help buffer tissue pH and limit chemoreceptor activity. Determining these basic cellular mechanisms will help guide new pharmacological approaches for the treatment of respiratory control disorders.