Electrophysiology of peripheral nerve sodium channels

描述（由申请人提供）：研究表明，大约30%的美国人患有慢性疼痛疾病，每年导致1000亿美元的医疗保健相关费用。目前用于治疗剧烈疼痛的处方麻醉药有明显的副作用，而且容易使人身体上瘾。此外，这些药物对由神经系统病变或功能障碍引起的神经性疼痛无效。周围神经的无髓鞘C纤维将疼痛感觉（痛觉）从组织中的感觉神经末梢传递到中枢神经系统。这些传导缓慢的神经纤维是痛觉通路的初始环节，因此是疼痛治疗的重要目标。痛觉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外周组织损伤和神经损伤作出反应。伤害感受器的细胞体位于背根神经节（DRG），并表达一种独特的Na电流，该电流对河豚毒素（TTX）具有抗性，TTX是一种典型的钠通道抑制剂。由于其在慢性和神经性疼痛综合征中的作用，这种耐ttx钠电流已成为激烈研究的焦点。从周围神经中克隆出两个Na通道（Nav1.7和Nav1.8），显示出与DRG伤害感受器中表达的ttx敏感和ttx抗性电流相似的特性。本研究将对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进行表征。在体内，这些Na通道与一个或多个辅助β亚基相关，这些亚基调节通道的表达和电压依赖性门控。拟议的研究将使用单细胞RT-PCR来鉴定在DRG的痛觉伤害感受器中表达的β亚基。鉴定的β亚基对异源表达的周围神经Na通道（Nav1.7, Nav1.8）的动力学和电压依赖性门控的影响将被研究。总的来说，我们提出的研究将为控制伤害神经元电兴奋性的Na通道和调节亚基提供新的见解。

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.