ClC-3 chloride channel regulation of synaptic transmission

长时程增强（Long-term potentiation，LTP）及其对NMDA受体介导的Ca[2+]内流的依赖性作为学习记忆的潜在机制已被广泛研究。许多蛋白质参与了LTP表达的诱导、维持和调节。这一提议增加了一个新的贡献者，Ca[2+]/钙调蛋白激酶II（CaMKII）门控Cl[-]通道ClC-3，以调节LTP，这是独特的能力，以调节突触反应和LTP的活动和发育依赖性的方式。尽管ClC-3在整个大脑中广泛表达，但ClC-3敲除小鼠显示海马体的完全的、选择性的出生后神经变性。事实上，多个品系的ClC-3敲除小鼠表现出类似的海马变性，表明该通道在维持正常脑功能中的新作用。最近的初步研究表明，ClC-3基因敲除小鼠中存在类似神经元的活性;尚未研究Cl[-]通道（特别是ClC-3）在调节成年大脑兴奋性中的作用。先前的工作已经证明ClC-3在空间上和功能上与NMDA受体连接：NMDA受体依赖性Ca[2+]进入、CaMKII的激活以及随后的CaMKII对ClC-3的磷酸化/门控通过Ca[2+]介导的反馈环连接两个通道。由于发育过程中Cl[-]梯度的变化，我们假设当Cl[-]的平衡电位为去极化时，ClC-3促进发育早期的兴奋和Ca[2+]内流;相反，ClC-3门控抑制兴奋和Ca[2+]内流，从而抑制成年期Cl[-]通量超极化时LTP的表达。因此，ClC-3非常适合于作为Ca[2+]内流和内部[Cl[-]]的函数来差异地影响突触可塑性。本申请的目的是表征ClC-3门控对NMDA受体电流和LTP表达的影响，作为发育调节的Cl[-]梯度的函数。ClC-3敲除模型使我们能够探索神经元发育，可塑性，兴奋-抑制平衡和长期生存之间的微妙相互作用-一种可能适用于氯离子通道以外的多种环境的统一机制。

Long-term potentiation (LTP) and its dependence upon NMDA receptor-mediated Ca[2+] entry has been widely studied as the presumptive mechanism underlying learning and memory. Numerous proteins have been implicated in the induction, maintenance, and modulation of LTP expression. This proposal adds a novel contributor, the Ca[2+]/calmodulin kinase II (CaMKII) gated Cl[-] channel ClC-3, to the regulation of LTP that is unique in its ability to modulate synaptic responses and LTP in an activity- and developmentally-dependent manner. Although ClC-3 is broadly expressed throughout the brain, the ClC-3 knockout mouse shows complete, selective postnatal neurodegeneration of the hippocampus. In fact, multiple lines of ClC-3 knockout mice exhibit similar hippocampal degeneration, suggesting a novel role of this channel in maintaining normal brain function. In support, recent preliminary studies show seizure-like activity in ClC-3 knockout mice; a role for Cl[-] channels, specifically ClC-3, in regulating excitability in the adult brain has not been studied. Prior work has demonstrated that ClC-3 is spatially and functionally linked to the NMDA receptor: NMDA receptordependent Ca[2+] entry, activation of CaMKII, and subsequent phosphorylation/gating of ClC-3 by CaMKII links the two channels via a Ca[2+]-mediated feedback loop. As a result of the shift in the Cl[-] gradient during development, we hypothesize that ClC-3 facilitates excitation and Ca[2+] influx early in development when the equilibrium potential for Cl[-] is depolarizing; conversely, ClC-3 gating suppresses excitation and Ca[2+] influx, thereby restraining the expression of LTP in adulthood when Cl[-] flux is hyperpolarizing. Thus ClC-3 is ideally suited to differentially influence synaptic plasticity as a function of Ca[2+] influx and internal [Cl[-]]. The goal of this application is to characterize the impact of ClC-3 gating on NMDA receptor currents and expression of LTP as a function of the developmentally-regulated Cl[-] gradient. The ClC-3 knockout model allows us to explore the delicate interaction between neuronal development, plasticity, excitation-inhibition balance, and long-term survival ¿ a unifying mechanism likely to be applicable in multiple contexts beyond chloride channels.