EPITHELIAL P2X PURINERGIC RECEPTOR CHANNELS

囊性纤维化(CF)的气道上皮细胞有许多缺陷，包括氯离子(Cl-)和液体转运的丧失，粘液纤毛清除的丧失，顶端自分泌和旁分泌的ATP信号的丧失，以及Na+转运的增加。外源性核苷酸激动剂恢复细胞外APT信号并刺激囊性纤维化(CF)气道上皮细胞的氯离子和液体运输。因此，雾化核苷酸激动剂疗法已被提出用于治疗慢性阻塞性肺疾病。为了了解核苷酸激动剂如何调节CF和非CF的气道上皮功能，需要对质膜嘌呤能受体有完整的了解。我们实验室的初步数据显示，一类新的嘌呤能受体--P2X受体通道(P2XRs)由呼吸道上皮细胞表达。P2XR在上皮细胞中的表达和功能的细胞和分子生理学研究尚未见报道。P2XRs是一种配体门控通道，它在胞外区域与ATP结合，在质膜上形成内源性的钙离子通道，具有非选择性。ATP门控的P2XRs可能通过调节细胞外钙内流或触发钙依赖的蛋白激酶信号来影响上皮细胞的功能。因此，我们将检验这一中心假设：P2X嘌呤能受体通道由呼吸道上皮细胞表达，并作为ATP门控的钙离子内流通道，调节氯离子、钠离子和液体通过呼吸道上皮细胞的运输。由于对呼吸道上皮细胞中的P2XRs知之甚少，我们预计将会发现新的和令人兴奋的结果。由于我们的初步数据显示，在CF和非CF的呼吸道上皮细胞中，P2XR的表达相似，而且信标酶P2XR激动剂在体外和体内都能刺激CF和非CF的小鼠和人的呼吸道上皮分泌Cl-，因此，激活P2XR可能提供一种新的途径，通过它来恢复正常的CI-、Na+和液体通过CF呼吸道的运输，并改善CF肺的粘液纤毛清除。

Cystic fibrosis (CF) airway epithelia have many defects including a loss in chloride (Cl-) and fluid transport, a loss in mucociliary clearance, a loss in apical autocrine and paracrine ATP signaling, and a gain in Na+ transport. Exogenous nucleotide agonists restore extracellular APT signaling and stimulate Cl- and fluid transport in cystic fibrosis (CF) airway epithelia. As such, aerosolized nucleotide agonist therapy has been proposed to treat CF airways. To understand how nucleotide agonists regulate CF and non-CF airway epithelial function, a complete understanding of plasma membrane purinergic receptors is required. Preliminary data from our laboratory reveal that a new class of purinergic receptor, the P2X receptor channels (P2XRs), are expressed by airway epithelia. The cellular and molecular physiology of P2XR expression and function has not been studied in epithelia. P2XRs are ligand-gated channels that bind ATP in an extracellular domain and form intrinsic calcium (Ca2+)- permeable, non-selective cation channels in the plasma membrane. ATP-gated P2XRs may affect epithelial cell function by mediating influx of Ca2+ from extracellular stores or by triggering Ca2+- dependent protein kinase signaling. Therefore, we will test the central hypothesis that: P2X purinergic receptor channels are expressed by airway epithelia and function as ATP-gated Ca2+ influx channels to regulate Cl-, Na+, and fluid transport across airway epithelia. Because little is known about P2XRs in airway epithelia, we anticipate that new and exciting results will be found. Because our preliminary data demonstrate that P2XR expression is similar in CF versus non-CF airway epithelia and beacuase P2XR agonists stimulate Cl- secretion across both CF and non-CF mouse and human airway epithelium in vitro and in vivo, activation of P2XRs may provide a novel approach with which to restore normal Cl-, Na+, and fluid transport across CF airways and improve mucociliary clearance from CF lungs.