NICOTINIC RECEPTORS IN MAMMALIAN INTRACARDIAC NEURONS

哺乳动物心内副交感神经节介导心脏的自主调节。心脏的所有副交感神经和一些交感神经输入以及传入输出都是由心脏神经节内的神经元提供的。先前的研究揭示了一种形态学和神经化学的复杂性，这表明心脏神经节可能具有整合功能，促进局部反馈和自动调节。乙酰胆碱（Acetylcholine，ACh）是介导神经节内、外神经支配的主要神经递质，其快速兴奋性传递由烟碱型ACh受体通道（aceticinicACh receptor-channels，AChRs）提供。最近的实验表明，多个亚型的AChRs表达的个别大鼠心内神经元，和大多数表达的α 7亚基基因。已知α 7-AChR结合α-银环蛇毒素（α Bgt），对Ca 2+具有高度渗透性，并发挥多种生理功能。初步结果首次显示了大鼠心内神经元中的α Bgt敏感性ACh反应，并首次证明了哺乳动物外周神经元中的α 7-AChR介导的电流。令人惊讶的是，大鼠心内神经元α 7-AChR缓慢脱敏并从α-银环蛇毒素阻断中迅速恢复，其性质与其他神经元中报道的这种AChR亚型的性质显著不同.深入了解心脏神经节的电路将通过表征神经节突触传递的关键元素，α 7-乙酰胆碱受体。 为了实现这一主要目标，本提案旨在：1.确定独特的药理学和电学特性，如钙离子渗透性，α 7-乙酰胆碱受体在离体大鼠心内神经元。2.研究机制，如与其他AChR亚基的共组装和细胞内第二信使的调节，这可能是alpha 7-AChRs独特特性的基础。3.确定alpha 7-AChRs在心神经节细胞间信号传导中的生理作用，包括提高细胞内Ca 2+的能力和对动作电位放电的影响。4. 研究神经肽对alpha 7-AChRs的调节作用，这些神经肽可改变AChRs的特性。 一个多方面的方法，包括膜片钳电生理学，免疫组织化学和分子生物学将被使用。α 7-AChR可能在心内神经节的细胞-细胞信号传导中起主要作用，因此在心率、心肌收缩力和/或冠状血管张力的调节中起主要作用。了解受体的性质和生理作用对于理解心脏的神经控制是必要的。

The mammalian parasympathetic intracardiac ganglia mediate autonomic regulation of the heart. All parasympathetic and some sympathetic input to the heart, as well as afferent output, is provided by neurons within cardiac ganglia. Previous studies have revealed a morphological and neurochemical complexity which suggests that the cardiac ganglia may serve an integrative function, facilitating local feedback and autoregulation. Acetylcholine (ACh) is the primary neurotransmitter mediating intrinsic and extrinsic innervation of the ganglia, and fast excitatory transmission is provided by nicotinic ACh receptors- channels (AChRs). Recent experiments indicate that multiple subtypes of AChRs are expressed by individual rat intracardiac neuron, and the majority express the alpha7 subunit gene. Alpha7- AChRs are known to bind alpha-bungarotoxin (alpha Bgt), are highly permeable to Ca2+, and serve a variety of physiological functions. Preliminary results have shown for the first time alpha Bgt-sensitive ACh responses in rat intracardiac neurons and the first evidence for alpha7-AChR-mediated currents in mammalian peripheral neurons. Surprisingly, rat intracardiac neuron alpha7- AChRs slowly desensitize and rapidly recover from alpha- bungarotoxin blockade, properties significantly different from those reported for this AChR subtype in other neurons. Insight into the circuitry of the cardiac ganglia will be gained by characterizing a key element of ganglionic synaptic transmission, alpha7-AChRs. To achieve this primary objective, this proposal aims to: 1. Identify the distinctive pharmacological and electrical properties, such as Ca2+ permeability, of alpha7-AChRs in isolated rat intracardiac neurons. 2. Investigate mechanisms, such as co-assembly with other AChR subunits and regulation by intracellular second messengers, that may underlie the distinct properties of alpha7-AChRs. 3. Determine the physiological role of alpha7-AChRs in cell-cell signaling in the cardiac ganglion, including ability to elevate intracellular Ca2+ and effects on action potential firing. 4. Investigate the modulation of alpha7-AChRs by neuropeptides shown to alter the properties of AChRs. A multifaceted approach involving patch-clamp electrophysiology, immunohistochemistry, and molecular biology will be used. alpha7-AChRs are likely to play a major role in cell-cell signaling in intracardiac ganglia and therefore in the regulation of heart rate, cardiac contractility, and/or coronary vascular tone. An understanding of the properties and physiological role of the receptors is necessary to comprehend neural control of the heart.