The Rolf Luft Research Center for Diabetes and Endocrinology, Karolinska Institutet, Stockholm, Sweden.
Proc Natl Acad Sci U S A. 2012 Jul 24;109(30):12183-8. doi: 10.1073/pnas.1115070109. Epub 2012 Jul 9.
Inositol hexakisphosphate (InsP(6)) levels rise and fall with neuronal excitation and silence, respectively, in the hippocampus, suggesting potential signaling functions of this inositol polyphosphate in hippocampal neurons. We now demonstrate that intracellular application of InsP(6) caused a concentration-dependent inhibition of autaptic excitatory postsynaptic currents (EPSCs) in cultured hippocampal neurons. The treatment did not alter the size and replenishment rate of the readily releasable pool in autaptic neurons. Intracellular exposure to InsP(6) did not affect spontaneous EPSCs or excitatory amino acid-activated currents in neurons lacking autapses. The InsP(6)-induced inhibition of autaptic EPSCs was effectively abolished by coapplication of an antibody to synaptotagmin-1 C2B domain. Importantly, preabsorption of the antibody with a GST-WT synaptotagmin-1 C2B domain fragment but not with a GST-mutant synaptotagmin-1 C2B domain fragment that poorly reacted with the antibody impaired the activity of the antibody on the InsP(6)-induced inhibition of autaptic EPSCs. Furthermore, K(+) depolarization significantly elevated endogenous levels of InsP(6) and occluded the inhibition of autaptic EPSCs by exogenous InsP(6). These data reveal that InsP(6) suppresses excitatory neurotransmission via inhibition of the presynaptic synaptotagmin-1 C2B domain-mediated fusion via an interaction with the synaptotagmin Ca(2+)-binding sites rather than via interference with presynaptic Ca(2+) levels, synaptic vesicle trafficking, or inactivation of postsynaptic ionotropic glutamate receptors. Therefore, elevated InsP(6) in activated neurons serves as a unique negative feedback signal to control hippocampal excitatory neurotransmission.
肌醇六磷酸（InsP(6)) 水平在海马体中分别随着神经元兴奋和沉默而升高和降低，这表明这种肌醇多磷酸在海马神经元中具有潜在的信号传递功能。我们现在证明，细胞内应用 InsP(6) 导致培养的海马神经元的自突触兴奋性突触后电流（EPSC）浓度依赖性抑制。该处理不会改变自突触神经元中易释放池的大小和补充率。细胞内暴露于 InsP(6) 不会影响缺乏自突触的神经元中的自发性 EPSC 或兴奋性氨基酸激活的电流。用突触结合蛋白-1 C2B 结构域的抗体共处理可有效消除 InsP(6) 诱导的自突触 EPSC 抑制。重要的是，用 GST-WT 突触结合蛋白-1 C2B 结构域片段而不是与抗体反应不佳的 GST-突变突触结合蛋白-1 C2B 结构域片段预先吸收抗体，可削弱抗体对 InsP(6) 诱导的自突触 EPSC 抑制的活性。此外，K(+) 去极化显著增加内源性 InsP(6) 水平，并阻断外源性 InsP(6) 对自突触 EPSC 的抑制。这些数据表明，InsP(6) 通过抑制突触结合蛋白-1 C2B 结构域介导的融合来抑制兴奋性神经递质传递，这种融合通过与突触结合蛋白 Ca(2+) 结合位点相互作用而不是通过干扰突触前 Ca(2+) 水平、突触囊泡运输或失活 postsynaptic 离子型谷氨酸受体来实现。因此，激活神经元中升高的 InsP(6) 作为一种独特的负反馈信号来控制海马兴奋性神经传递。
