Mechanism of oxygen sensing by chemoreceptor cells

描述(申请人提供)：颈动脉小体中的化学感受器细胞(CB细胞)，响应低氧，启动稳态机制来调节呼吸和自主神经系统活动。CB细胞感知O2的一个被广泛接受的模型是，低氧抑制K+电流，从而导致去极化，电压依赖性钙通道的开放，以及[Ca+]i的升高。当[Ca+]i上升时，CB细胞分泌作用于 感觉神经末梢诱发到达脑干心肺中心的动作电位。在CB细胞中，低氧被认为是导致兴奋的多个K+通道的靶点。低氧抑制的K+通道之一是TASK(TASK-1和TASK-3)，它在CB细胞中高表达，并活跃于Em的整个生理范围。低氧抑制作业的机制尚不清楚。最近，我们在大鼠CB细胞上发现了一种可被低氧激活的Na+通透通道(低氧激活通道或HA通道)。因此，我们推测K+电流的抑制和Na+电流的激活都参与了低氧诱导的CB细胞去极化。最近的研究表明，硫化氢是在低氧过程中产生的，并介导了低氧引起的颈动脉窦神经活动和通气量的增加。然而，H_2S在低氧诱导的CB细胞兴奋中的作用尚不清楚。因此，我们提出了三个特定的目标来确定低氧诱导的TASK和HA通道的调节机制，以及HA通道在低氧诱导的CB细胞兴奋中的作用。目的1验证低氧通过产生硫化氢抑制任务的假说，并探讨这种抑制的机制。我们还研究了血红素加氧酶-2在这一过程中的作用，因为一氧化碳调节产生硫化氢的胱硫醚裂解酶的活性。初步数据表明，HA通道是一种钙激活的单价阳离子通道。因此，目的2验证了一种假设，即透明质酸通道是一个对钙离子敏感的色氨酸离子通道，而硫化氢在低氧诱导的透明质酸通道激活中起信号作用。目的3测试HA通道作为正反馈机制的一部分在中度到重度缺氧时对CB细胞的兴奋作用。还测试了HA通道在BK激活中的作用，作为限制过度兴奋的负反馈机制的一部分。S使用透明质酸通道的抑制剂和缺乏色氨酸离子通道的小鼠研究了透明质酸通道对CB细胞激发的贡献。这些实验的结果将建立HA通道作为低氧的新靶点，并有助于确定硫化氢作为低氧产生的信号调节任务和HA通道的作用。这些研究应该会填补我们对颈动脉小体化学感受器氧气感知机制的一个重要知识空白。 公共卫生相关性：我们研究的目标是提高对位于颈动脉的特殊细胞(颈动脉体细胞)如何感知血液中氧气水平的下降(缺氧)并引发调节呼吸的代偿机制的理解。更好地了解这一机制对于改善因颈动脉小体功能障碍而出现的各种异常呼吸系统状况具有重要意义。

DESCRIPTION (provided by applicant): Chemoreceptor cells in the carotid body (CB cells), in response to hypoxia, initiate homeostatic mechanisms to regulate breathing and autonomic nerve system activity. A widely accepted model for O2 sensing by CB cells is that hypoxia inhibits K+ current and thereby causes depolarization, opening of voltage-dependent Ca2+ channels, and elevation of [Ca2+]i. Upon rise of [Ca2+]i, CB cells secrete transmitters that act on sensory nerve terminals to elicit action potentials that reach the brainstem cardio-respiratory centers. In CB cells, hypoxia is believed to target a number of K+ channels to cause excitation. One of the K+ channels inhibited by hypoxia is TASK (TASK-1 and TASK-3) that is highly expressed in CB cells and active across the physiological range of Em. The mechanism of inhibition of TASK by hypoxia is not yet known. Recently, we discovered a Na+ permeable channel that is activated by hypoxia (hypoxia-activated or HA channel) in rat CB cells. Therefore, we hypothesize that inhibition of K+ current and activation of Na+ current both contribute to hypoxia-induced depolarization of CB cells. Recent studies suggest that hydrogen sulfide (H2S) is generated during hypoxia and mediates the hypoxia-induced increase in carotid sinus nerve activity and ventilation. However, the role of H2S in hypoxia-induced excitation of CB cells remains undefined. Therefore, we propose three specific aims to identify the mechanisms of hypoxia-induced modulation of TASK and the HA channel, and the role of the HA channel in hypoxia-induced excitation in CB cells. Aim 1 tests the hypothesis that hypoxia inhibits TASK via generation of H2S, and investigates the mechanism of this inhibition. The role of hemeoxygenase-2 in this process is also studied, as carbon monoxide regulates the activity of cystathionine-?-lyase that generates H2S. Preliminary data show that the HA channel is a Ca2+-activated monovalent cation channel. Aim 2 therefore tests the hypothesis that the HA channel is a Ca2+-sensitive TRP ion channel, and that H2S serves as a signal in hypoxia-induced activation of the HA channel. Aim 3 tests the role of the HA channel as part of a positive feedback mechanism involved in the excitation of CB cells during moderate to severe hypoxia. The role of the HA channel in the activation of BK, as part of the negative feed-back mechanism to limit over- excitation is also tested. The contribution of the HA channel to CB cell excitation s studied using an inhibitor of the HA channel and mice lacking the TRP ion channel. The outcome of these experiments should establish the HA channel as a new target of hypoxia, and also help to define the role of H2S as a hypoxia-generated signal that modulates both TASK and the HA channel. These studies should fill an important knowledge gap in our understanding of the O2 sensing mechanisms by carotid body chemoreceptors. PUBLIC HEALTH RELEVANCE: The goal of our research is to improve the understanding of how the specialized cells located at the carotid artery (carotid body cells) sense the decrease in oxygen level (hypoxia) in the blood and elicits a compensatory mechanism to regulate breathing. Better understanding of this mechanism is important for improving various abnormal respiratory conditions that arise due to the dysfunction of the carotid body.