Chloride homeostasis and DRG neuron excitability

初级传入神经元的感觉反应大多是在兴奋和阳离子流入的背景下研究的，伴随着膜去极化的诱导和随后的动作电位的产生/传播。然而，很少有人注意到氯化物通量的作用，它可以抑制或调节这些兴奋性反应。在中枢神经系统（CNS）中，氯离子作为抑制信号的重要性已经得到了很好的确立，与之相反，在初级传入神经元中，氯离子的稳态和抑制信号还没有得到很好的理解。在目前的研究计划中，我们将集中研究背根神经节（DRG）神经元的氯离子稳态，氧化应激对其的调节，以及它对感觉功能的贡献。我们的团队使用猪和小鼠DRG神经元的初步发现表明，这些神经元中氯离子稳态的控制比以前认为的要复杂得多。利用药理学工具和转基因动物，我们观察到Na-K-Cl共转运蛋白（NKCC1）和囊性纤维化跨膜传导调节剂（CFTR）共同作用于细胞内氯离子水平。缺乏CFTR导致DRG神经元细胞内氯离子水平升高，这表明该通道将氯离子从细胞中挤出，而NKCC1参与了摄取。缺乏CFTR功能的DRG神经元兴奋性较低，兴奋反应受损，表明这些转运体的联合作用是正常感觉功能所必需的。因此，作为短期目标，我们计划进一步研究NKCC1和CFTR在DRG神经元生理中的作用，并评估K-Cl共转运体KCC2和KCC3可能参与的作用。我们将集中理解如何信号调节兴奋性（如氧化应激），也可能影响氯化物稳态。我们特别感兴趣的是了解氯离子水平和离子通道功能之间的关系，以及氯离子转运体和神经元兴奋性信号通路之间可能的相互作用。作为长期目标，我们计划将我们的研究扩展到感官知觉。将我们的发现放在细胞水平上，我们将在活体动物的感觉功能中测试它们的相关性。因此，我们的研究有可能对疼痛的生理和病理知识做出贡献。

Sensory responses in primary afferent neurons have mostly been studied in the context of excitation and the influx of cations, with the induction of membrane depolarization and subsequent action potential generation/propagation. Much less attention, however, has been given to the role of chloride fluxes, which can inhibit or modulate those excitatory responses. In contrast to neurons in the central nervous system (CNS), where the importance of chloride as an inhibitory signal is already well established, in primary afferent neurons chloride homeostasis and inhibitory signals are not well understood. In the current research program, we will concentrate on chloride homeostasis in dorsal root ganglion (DRG) neurons, its modulation by oxidative stress, and its contribution to sensory function. Preliminary findings from our team using swine and mouse DRG neurons suggest that the control of chloride homeostasis in these neurons is more complex than previously thought. Using pharmacological tools and transgenic animals, we observed that the Na-K-Cl cotransporter (NKCC1) and the cystic fibrosis transmembrane conductance regulator (CFTR) act in combination to set the intracellular chloride levels. Lack of CFTR lead to increase intracellular chloride levels in DRG neurons, suggesting that this channel extrudes chloride from the cell, while NKCC1 is involved it the uptake. DRG neurons lacking CFTR function were less excitable and had impaired excitatory responses, suggesting that the combined action of these transporter is required for normal sensory function. Therefore, as short-term objectives we plan on further study the involvement of NKCC1 and CFTR in DRG neuron physiology, as well as to evaluate the possible involvement of the K-Cl cotransporters KCC2 and KCC3. We will concentrate on understanding how signals that modulate excitability (such as oxidative stress), may also affect chloride homeostasis. We are particularly interested in understanding the relationship between chloride levels and ion channel function, as well as the possible interaction between chloride transporters and signalling pathways involved in neuronal excitability. As longer-term objectives, we plan to extend our study into sensory perception. Taking our findings at the cellular level, we will test their relevance in sensory function in live animals. Thus, our research has the potential to contribute to the knowledge on the physiology and pathology of pain.