Molecular basis for activation of cardiovascular sensory afferents

几十年来，对压力感受器活性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换能器的分子成分一无所知。事实上，机械刺激的传导是脊椎动物中最不被理解的感觉之一。我们的目标是确定机械激活动脉和心脏的分子基础 感官传入。在早期的研究中，我们定义了培养的主动脉压力感受器神经元(Brns)的特性。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Gd阻断。然而，它们的分子身份仍不清楚。在线虫机械敏感基因的遗传筛选中，发现了一个进化保守的离子通道候选家族，即退行性/上皮性钠通道(DEG/ENaC)。在过去的四年中，我们取得了一些重要的发现来支持我们的假设，即DEG/ENaC通道在哺乳动物的机械感受器中起着机械电转导的作用：1)DEG/ENaC亚单位在机械感受性神经元及其感觉终末中表达。2)DEG/ENaC通道的抑制剂降低了Brns在体内和体外的功能。3)最重要的是，有针对性地干扰DEG/ENaC亚单位 在小鼠中，降低了主动脉Brns和皮肤机械感受器的机械感觉，但没有消除它。我们认为哺乳动物的机械敏感通道可能是由多个DEG/ENaC蛋白以及相关的细胞内和细胞外“系留”蛋白组成的异多聚体复合体。因此，我们的第一个假设旨在定义DEG/ENaC家族的亚单位以及形成Brns机械敏感复合体的相关蛋白质。此外，我们有证据表明，DEG/ENaC通道在心脏感觉神经元中也扮演着重要的角色，不仅是作为机械传感器，而且在心肌缺血的环境中也是H传感器。因此，这些通道可能是激活心脏交感神经传入的媒介，导致心力衰竭状态下交感神经流出显著增加。因此，我们的第二个假设旨在明确心脏感觉传入的质子和机械敏感的DEG/ENaC通道在背根神经节(交感传入)和结状神经节(迷走神经传入)中的作用，并确定它们在正常生理条件下以及在心肌缺血和心力衰竭中的功能。

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.