Electrophysiology of peripheral nerve sodium channels

描述(由申请人提供)：研究表明，大约30%的美国人每年遭受慢性疼痛的困扰，导致与医疗保健相关的成本高达1000亿美元。目前用于治疗剧烈疼痛的处方麻醉药具有显著的副作用，并容易发生身体上瘾。此外，这些药物在治疗神经系统病变或功能障碍引起的神经病理性疼痛方面无效。周围神经的无髓鞘C纤维将痛觉(伤害性感觉)从位于组织中的感觉神经末梢传递到中枢神经系统。这些缓慢传导的神经纤维是伤害性感受通路的初始环节，因此是疼痛治疗的重要靶点。伤害性感受器表达配体和电压门控离子通道的组合，使这些神经元能够对周围组织损伤和神经损伤做出反应。伤害性感受器的细胞体位于背根神经节(DRG)，表达一种独特的钠电流，该电流对钠通道的典型抑制剂河豚毒素(TTX)具有抵抗力。这种抗TTX的钠电流一直是密集研究的焦点，因为它被认为在慢性和神经病理性疼痛综合征中发挥作用。从周围神经中克隆了两个钠通道(Nav1.7和Nav1.8)，它们的特性类似于DRG伤害性感受器中表达的TTX敏感和TTX抵抗电流。拟议的研究将表征在哺乳动物细胞系中异源表达的Nav1.7和Nav1.8通道的生物物理特性。在体内，这些钠通道与一个或多个辅助β亚基相关，这些辅助β亚基调节通道的表达和电压依赖的门控。这项拟议的研究将使用单细胞RT-PCR来确定在DRG的痛觉伤害性感受器中表达的β亚基。已确定的β亚基对异源表达的外周神经钠通道(Nav1.7，Nav1.8)的动力学和电压依赖门控的影响将被研究。总体而言，我们提出的研究将为调控伤害性神经元电兴奋性的钠通道和调节亚单位提供新的见解。

DESCRIPTION (provided by applicant): Studies indicate that approximately 30% of Americans suffer from chronic pain conditions annually resulting in >100 billion dollars in health-care related costs. Currently prescribed narcotics used to treat severe pain have significant side effects and are prone to physical addiction. In addition, these drugs are ineffective in treating neuropathic pain resulting from lesion or dysfunction of the nervous system. The unmyelinated C fibers of peripheral nerve transmit painful sensation (nociception) from the sensory nerve terminals located in tissues to the central nervous system. These slowly conducting nerve fibers are the initial link in the nociception pathway and are therefore important targets of pain therapy. Nociceptors express a combination of ligand- and voltage-gated ion channels that enable these neurons to respond to peripheral tissue damage and nerve injury. The cell bodies of nociceptors are located in the dorsal root ganglion (DRG) and express a unique Na current that is resistant to tetrodotoxin (TTX), a prototypical inhibitor of sodium channels. This TTX-resistant Na current has been the focus of intense research because of its purported role in chronic and neuropathic pain syndromes. Two Na channels (Nav1.7, Nav1.8) have been cloned from peripheral nerve that display properties similar to the TTX-sensitive and TTX-resistant currents expressed in DRG nociceptors. The proposed studies will characterize the biophysical properties of the Nav1.7 and Nav1.8 channels heterologously expressed in a mammalian cell line. In vivo, these Na channels are associated with one or more accessory beta subunits that regulate the expression and voltage-dependent gating of the channels. The proposed studies will use single-cell RT-PCR to identify the beta subunits that are expressed in the pain-sensing nociceptors of the DRG. The effects of the identified beta subunits on the kinetics and voltage-dependent gating of heterologously expressed peripheral nerve Na channels (Nav1.7, Nav1.8) will be investigated. Overall, our proposed studies will provide new insights into the Na channels and regulatory subunits that govern the electrical excitability of nociceptive neurons.