Activity Dependent Modulation of SK2 Channels

描述(由申请人提供)：Schaffer侧枝突触的突触强度(LTP)的长期增强在很大程度上归因于a-氨基-3-羟基-5-甲基异恶唑-4-丙酸受体(AmPAR)的数量和生物物理性质的变化。小电导钙激活的K+通道(SK2通道)与N-甲基-D-天冬氨酸受体(NMDAR)在功能上偶联，从而调节兴奋性突触后电位(EPSP)的形态，提高LTP的诱导阈值。阻断SK2通道促进海马区CA1神经元可塑性并促进动物 获得海马区依赖学习任务。此外，在转基因小鼠的CA1神经元中过度表达SK2通道会损害突触可塑性的诱导和海马区依赖的记忆编码。因此，SK2通道调控突触可塑性的诱导。我的初步数据显示，SK2频道对LTP有额外的贡献。在Schaffer侧支突触上诱导LTP可取消增强突触中SK2通道的活动。这种效应是由突触后密度(PSD)进入脊髓的SK2通道内化所致。阻断PKA或用代表SK2 C-末端结构域的多肽透析的细胞可阻断LTP诱导后SK2通道的内化。因此，AMPAR的增加和SK2通道的减少共同产生了LTP下的EPSP增加。SK2通道可塑性对LTP的贡献率约为14%。虽然这是一个重要的贡献，但对EPSP的Ampar贡献增加是兴奋性增加的主要原因。然而，SK2通道内吞在LTP诱导过程中的功能后果可能对随后的突触活动产生更显著的影响。CA1神经元脊椎中的SK2通道提供负反馈，减弱通过NMDAR的钙离子内流。在随后的突触活动中，SK2通道介导的复极化效应的丧失将显著增加NMDAR(至少40%)进入NMDAR的钙离子的数量。这将有效地促进塑性的诱导。因此，一旦SK2通道从增强的脊椎中移除，以及相关的PKA信号机制，确定它们的命运是很重要的。这一建议旨在研究突触可塑性和记忆形成的基本机制，并将有助于我们对可塑性和学习过程的基础知识。

DESCRIPTION (provided by applicant): Long term potentiation of synaptic strength (LTP) at Schaffer collateral synapses has largely been attributed to changes in the number and biophysical properties of a-amino-3-hydroxy-5-methylisoxazole-4- propionic acid receptors (AMPAr). Small conductance Ca2+ activated K+ channels (SK2 channels) are functionally coupled with N-methyl-D-aspartate receptors (NMDAr) in CA1 spines such that their activity modulates the shape of excitatory postsynaptic potentials (EPSPs) and increases the threshold for induction of LTP. Blocking SK2 channels facilitates CA1 neuron plasticity in hippocampus and promotes animal acquisition of hippocampal dependent learning tasks. Moreover, overexpressing SK2 channels in CA1 neurons in transgenic mice impairs the induction of synaptic plasticity and hippocampal-dependent memory encoding. Therefore, SK2 channels modulate the induction of synaptic plasticity. My preliminary data show that SK2 channels additionally contribute to LTP. The induction of LTP at Schaffer collateral synapses abolishes SK2 channel activity in the potentiated synapses. This effect is due to SK2 channel intemalization from the postsynaptic density (PSD) into the spine. Blocking PKA or cell dialyzed with a peptide representing the C-terminal domain of SK2 that contains three known PKA phosphorylation sites blocks the intemalization of SK2 channels following LTP induction. Thus the increase in AMPAr and the decrease in SK2 channel combine to produce the increased EPSP underlying LTP. SK2 channel plasticity contributes ~14% to LTP. While this is a significant contribution, the increased AMPAr contribution to the EPSP accounts for the majority of the increased excitability. However, the functional consequence of SK2 channel endocytosis upon the induction of LTP may be more significant for the effect on subsequent synaptic activity. SK2 channels in the spines of CA1 neurons provide a negative feedback that attenuates the Ca2+ influx through NMDAr. The lost repolarizing effect mediated by the SK2 channels will profoundly increase the amount of Ca2+ entering through NMDAr (at least 40%) upon subsequent synaptic activity. This will effectively facilitate the induction of plasticity. Therefore, it is important to determine the fates of the SK2 channels once they are removed from potentiated spines and the PKA signaling mechanisms involved. This proposal is targeted to study the basic mechanisms of synaptic plasticity and memory formation, and will contribute to our fundamental knowledge in plasticity and learning process.