PDF(Pubmed)
Abstract：
At chemical synapses, voltage-gated Ca2+ channels (VGCCs) translate electrical signals into a trigger for synaptic vesicle (SV) fusion. VGCCs and the Ca2+ microdomains they elicit must be located precisely to primed SVs to evoke rapid transmitter release. Localization is mediated by Rab3-interacting molecule (RIM) and RIM-binding proteins, which interact and bind to the C terminus of the CaV2 VGCC α-subunit. We studied this machinery at the mixed cholinergic/GABAergic neuromuscular junction of Caenorhabditis elegans hermaphrodites. rimb-1 mutants had mild synaptic defects, through loosening the anchoring of UNC-2/CaV2 and delaying the onset of SV fusion. UNC-10/RIM deletion much more severely affected transmission. Although postsynaptic depolarization was reduced, rimb-1 mutants had increased cholinergic (but reduced GABAergic) transmission, to compensate for the delayed release. This did not occur when the excitation-inhibition (E-I) balance was altered by removing GABA transmission. Further analyses of GABA defective mutants and GABAA or GABAB receptor deletions, as well as cholinergic rescue of RIMB-1, emphasized that GABA neurons may be more affected than cholinergic neurons. Thus, RIMB-1 function differentially affects excitation-inhibition balance in the different motor neurons, and RIMB-1 thus may differentially regulate transmission within circuits. Untethering the UNC-2/CaV2 channel by removing its C-terminal PDZ ligand exacerbated the rimb-1 defects, and similar phenotypes resulted from acute degradation of the CaV2 β-subunit CCB-1. Therefore, untethering of the CaV2 complex is as severe as its elimination, yet it does not abolish transmission, likely due to compensation by CaV1. Thus, robustness and flexibility of synaptic transmission emerge from VGCC regulation.
摘要：
在化学突触上，电压门控Ca2+-通道（VGCC）将电信号转化为突触小泡（SV）融合的触发器。VGCC及其引出的Ca2微域必须精确定位到引发的SV，唤起快速发射器释放。定位由Rab3相互作用分子（RIM）和RIM结合蛋白（RIM-BP）介导，与CaV2VGCCα亚基的C端相互作用并结合。我们在秀丽隐杆线虫雌雄同体的混合胆碱能/GABA能神经肌肉接头（NMJ）研究了这种机制。rimb1突变体有轻度的突触缺陷,通过松开UNC-2/CaV2的锚定和延迟SV融合的开始。UNC-10/RIM删除更严重地影响传输。即使突触后去极化减少，rimb1突变体具有增加的胆碱能（但减少的GABA能）传递，以补偿延迟释放。当通过消除GABA传递来改变激发-抑制平衡时，不会发生这种情况。GABA缺陷突变体和GABAA或GABAB受体缺失的进一步分析，以及RIMB-1的胆碱能拯救，强调GABA神经元可能比胆碱能神经元受到更大的影响。因此，RIMB-1功能差异影响不同运动神经元的兴奋/抑制平衡，和RIMB-1因此可以差分地调节混合电路中的传输。通过去除其C端PDZ配体来解除UNC-2/CaV2通道的束缚加剧了rimb-1缺陷，和相似的表型是由CaV2β亚基CCB-1的急性降解引起的。因此,解除CaV2复合物的束缚与消除它一样严重，但并没有废除传播，可能是由于CaV1的赔偿。因此，突触传递的鲁棒性和灵活性来自VGCC调控。重要性陈述化学突触传递的机制以精确的空间排列进行组织，以便通过CaV2P/Q型电压门控的Ca2通道，使动作电位与Ca2浓度的升高有效且时间准确地耦合。这触发了突触小泡与质膜的融合和递质的释放。这里,我们分析了活性区支架的蛋白质的分子和功能相互作用，RIM和RIM结合蛋白（RIMB-1），秀丽隐杆线虫神经肌肉接头的CaV2通道，具有胆碱能和GABA能神经元输入的三方突触。我们的工作表明胆碱能与RIMB-1的不同需求GABA能神经元，影响电路激励-抑制平衡的调节，细胞和超微结构水平。
