NICOTINIC RECEPTORS IN MAMMALIAN INTRACARDIAC NEURONS

哺乳动物的副交感神经心内神经节调节心脏的自主神经。心脏的所有副交感和部分交感输入以及传入输出都是由心脏神经节内的神经元提供的。以前的研究揭示了心脏神经节的形态和神经化学的复杂性，这表明心脏神经节可能起着一种综合功能，促进局部反馈和自我调节。乙酰胆碱(ACh)是介导神经节内源性和外源性神经支配的主要神经递质，快速兴奋性传递由烟碱型ACh受体通道(AChRs)提供。最近的实验表明，单个大鼠心内神经元表达多种亚型的AChRs，其中大多数表达alpha7亚单位基因。已知α7-AChRs能结合α-银环蛇毒素(α-BGT)，对钙离子有很强的通透性，具有多种生理功能。初步结果首次显示大鼠心内神经元对αBGT敏感的ACh反应，并首次证明哺乳动物外周神经元存在α7-AChR介导的电流。令人惊讶的是，大鼠心内神经元α7-AChRs缓慢脱敏，并从α-银环蛇毒素阻断中迅速恢复，其特性与其他神经元中该AChR亚型的报道显著不同。通过描述神经节突触传递的关键成分--α7-AChRs，将获得对心脏神经节回路的深入了解。为了实现这一主要目标，本建议旨在：1.鉴定分离的大鼠心内神经细胞中α7-AChRs的独特药理和电学特性，如钙通透性。2.研究与其他AChR亚基的共组装和细胞内第二信使的调节等机制，这些机制可能是Alpha7-AChRs独特特性的基础。3.确定α7-AChRs在心脏神经节细胞-细胞信号转导中的生理作用，包括升高细胞内钙离子的能力和对动作电位放电的影响。4.研究改变AChRs特性的神经肽对α7-AChRs的调节作用。将使用涉及膜片钳电生理学、免疫组织化学和分子生物学的多方面方法。α7-AChRs可能在心内神经节的细胞-细胞信号转导中发挥重要作用，从而调节心率、心脏收缩能力和/或冠脉血管张力。了解受体的特性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.