Iacobucci Gary J, Popescu Gabriela K
Department of Biochemistry, Jacobs School of Medicine and Biomedical Sciences, State University of New York at Buffalo, Buffalo, New York.
Biophys J. 2017 Nov 21;113(10):2236-2248. doi: 10.1016/j.bpj.2017.06.035. Epub 2017 Jul 14.
N-methyl-d-aspartate (NMDA) receptors are glutamate- and glycine-gated channels that flux Na and Ca into postsynaptic neurons during synaptic transmission. The resulting intracellular Ca transient is essential to physiological and pathological processes related to synaptic development, plasticity, and apoptosis. It also engages calmodulin (CaM) to reduce subsequent NMDA receptor activity in a process known as Ca-dependent inactivation (CDI). Here, we used whole-cell electrophysiology to measure CDI and computational modeling to dissect the sequence of events that underlies it. With these approaches, we estimate that CaM senses NMDA receptor Ca influx at ∼9 nm from the channel pore. Further, when we controlled the frequency of Ca influx through individual channels, we found that a kinetic model where apoCaM associates with channels before their activation best predicts the measured CDI. These results provide, to our knowledge, novel functional evidence for CaM preassociation to NMDA receptors in living cells. This particular mechanism for autoinhibitory feedback reveals strategies and challenges for Ca regulation in neurons during physiological synaptic activity and disease.
N-甲基-D-天冬氨酸（NMDA）受体是谷氨酸和甘氨酸门控通道，在突触传递过程中使钠离子和钙离子流入突触后神经元。由此产生的细胞内钙离子瞬变对于与突触发育、可塑性和凋亡相关的生理和病理过程至关重要。它还会结合钙调蛋白（CaM），在一个被称为钙依赖性失活（CDI）的过程中降低随后的NMDA受体活性。在这里，我们使用全细胞膜片钳电生理学来测量CDI，并通过计算建模来剖析其背后的一系列事件。通过这些方法，我们估计CaM在距离通道孔约9纳米处感知NMDA受体的钙离子内流。此外，当我们控制通过单个通道的钙离子内流频率时，我们发现一种动力学模型，即无钙CaM在通道激活之前与通道结合，能最好地预测所测量的CDI。据我们所知，这些结果为活细胞中CaM与NMDA受体的预结合提供了新的功能证据。这种自动抑制反馈的特殊机制揭示了生理突触活动和疾病期间神经元中钙离子调节的策略和挑战。
