Molecular basis for activation of cardiovascular sensory afferents

几十年来，对压力感受器活动的研究一直依赖于对单个纤维或整个神经的动作电位的测量。 我们对启动去极化和触发动作电位的机电转换器的分子组成没有深入的了解。 事实上，机械刺激的传导是脊椎动物感觉中最不为人所知的。我们的目标是确定动脉和心脏机械激活的分子基础， 感觉传入 在早期的研究中，我们确定了培养的主动脉压力感受器神经元（BRN）的特征。 这些通道是阳离子选择性的，非电压门控的，并被阿米洛利或钆阻断。然而，它们的分子身份仍然未知。 退化蛋白/上皮Na+通道（DEG/ENaC）是一个进化上保守的离子通道家族。优雅在过去的4年中，我们取得了重要的发现，以推进我们的假设，DEG/ENaC通道作为机械电转换器在哺乳动物的机械感受器：1）DEG/ENaC亚基表达在机械感受神经元和它们的感觉末梢。2)BRN在体内和体外的功能都被DEG/ENaC通道的抑制剂降低。3)最重要的是，定向破坏DEG/ENaC亚基 我们认为哺乳动物机械敏感通道可能是多种DEG/ENaC蛋白的异源多聚体复合物，沿着相关的细胞内和细胞外“拴系”蛋白。 因此，我们的第一个假设的目的是确定亚单位的DEG/ENaC家庭和相关的蛋白质，形成的机械敏感性复合物的BRN。 此外，我们有证据表明，DEG/ENaC通道在心脏感觉神经元中也起着重要作用，不仅作为机械传感器，而且在心肌缺血的情况下作为H+传感器。因此，这些通道可能是心脏交感神经传入激活的介质，导致心力衰竭状态下交感神经流出的明显反射增加。 因此，我们的第二个假设的目的是定义质子和机械敏感DEG/ENaC通道的背根神经节（交感神经传入）和结状神经节（迷走神经传入）的心脏感觉传入，并确定其功能正常的生理和心肌缺血和心力衰竭。

For decades, studies ofbaroreceptor activity have depended on measurements of action potentials in single fibers or whole nerve. We had no insight into the molecular components of the mechanoelectrical transducers that initiate depolarization and trigger action potentials. In fact, transduction of mechanical stimuli is one of the least understood of the vertebrate senses. Our goal has been to define the molecular basis for mechanical activation of arterial and cardiac sensory afferents. In earlier studies we defined the characteristics of aortic baroreceptor neurons (BRNs) in culture. These channels are cation-selective, non voltage-gated, and blocked by amiloride or gadolinium. However, their molecular identity remains unknown. A candidate family of evolutionary-conserved ion channels, the degenerin/epithelial Na+-channels (DEG/ENaC), was discovered in a genetic screen for mechanosensitive genes in C. elegans. During the past 4 years we made important discoveries to advance our hypothesis that DEG/ENaC channels function as the mechanoelectrical transducer in mammalian meehanoreceptors: 1) DEG/ENaC subunits are expressed in mechanoreceptive neurons and in their sensory terminals. 2) The functions of BRNs, both in vivo and in vitro are reduced by inhibitors of DEG/ENaC channels. 3) Most important, targeted disruption of a DEG/ENaC subunit in mice reduced mechanosensation in aortic BRNs and in cutaneous mechanoreceptors but did not abolish it. We believe the mammalian mechanosensitive channels may be a heteromultimeric complex of multiple DEG/ENaC proteins, along with associated intra and extracellular "tethering" proteins. Thus, our first hypothesis is aimed at defining the subunits of the DEG/ENaC family and associated proteins that form the mechanosensitive complex in BRNs. Additionally, we have evidence that DEG/ENaC channels also play an important role in cardiac sensory neurons, not only as mechanosensors, but also as H+-sensors in the setting of myocardial ischemia. Thus, these channels could be the mediators of activation of cardiac sympathetic afferents, causing the pronounced reflex increase in sympathetic outflow in heart failure states. Therefore, our second hypothesis is aimed at defining the proton- and mechano-sensitive DEG/ENaC channels of cardiac sensory afferents in dorsal root ganglia (sympathetic afferents) and nodose ganglia (vagal afferents) and determining their function under normal physiological and in myocardial ischemia and heart failure.