Downregulation of dendritic HCN channel gating in epilepsy is mediated by altered phosphorylation signaling.
Downregulation of dendritic HCN channel gating in epilepsy is mediated by altered phosphorylation signaling.
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DOI：
10.1523/jneurosci.1290-10.2010
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发表时间：
2010-05-12
期刊：
影响因子：
--
通讯作者：
Poolos NP
中科院分区：
文献类型：
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作者：
Jung S;Bullis JB;Lau IH;Jones TD;Warner LN;Poolos NP
匹罗卡品癫痫模型的自发性发作引起CA1区锥体神经元树突超极化激活的环核苷酸门控(HCN)通道介导电流(Ih)的超极化漂移，导致神经元的过度兴奋性，并可能导致癫痫的发生。然而，自发性癫痫发作导致HCN通道门控下调的具体机制尚不清楚。我们询问，癫痫依赖的HCN通道门控下调是由于磷酸酶钙调神经磷酸酶(CaN)或p38丝裂原活化蛋白激酶(P38MAPK)介导的磷酸化信号改变所致。我们首次发现，在正常条件下，CaN可上调HCN通道门控，降低神经元兴奋性，表明CaN是HCN通道的强调制子。然后，我们发现，一个癫痫的体外模型(在35-37℃，0μ+和50 mM荷包牡丹碱中1小时)重现了在体内看到的HCN通道门控变化。药物抑制CaN或激活p38MAPK可部分逆转体外惊厥引起的HCN通道门控超极化漂移，而CaN抑制和p38MAPK激活联合应用可完全逆转这一漂移。然后，我们在体内展示了慢性癫痫动物CA1海马区CaN活性的增强和p38MAPK活性的降低。这些磷酸化改变的药物逆转使癫痫组织中HCN通道门控下调和神经元过度兴奋恢复到对照水平。综上所述，这些结果提示癫痫中两种不同的磷酸化途径的改变有助于下调HCN通道门控，从而产生神经元的过度兴奋性，从而可能成为新的抗癫痫治疗的靶点。
The onset of spontaneous seizures in the pilocarpine model of epilepsy causes a hyperpolarized shift in the voltage-dependent activation of hyperpolarization-activated cyclic nucleotide-gated (HCN) channel-mediated current (Ih) in CA1 hippocampal pyramidal neuron dendrites, contributing to neuronal hyperexcitability and possibly to epileptogenesis. However, the specific mechanisms by which spontaneous seizures cause downregulation of HCN channel gating are yet unknown. We asked whether the seizure-dependent downregulation of HCN channel gating was due to altered phosphorylation signalling mediated by the phosphatase calcineurin (CaN) or the kinase p38 mitogen-activated protein kinase (p38 MAPK). We first found that CaN inhibition upregulated HCN channel gating and reduced neuronal excitability under normal conditions, showing that CaN is a strong modulator of HCN channels. We then found that an in vitro model of seizures (one hour in 0 Mg2+ and 50 μM bicuculline at 35 – 37 °C) reproduced the HCN channel gating change seen in vivo. Pharmacological inhibition of CaN or activation of p38 MAPK partially reversed the in vitro seizure-induced hyperpolarized shift in HCN channel gating, and the shift was fully reversed by the combination of CaN inhibition and p38 MAPK activation. We then demonstrated enhanced CaN activity as well as reduced p38 MAPK activity in vivo in the CA1 hippocampal area of chronically epileptic animals. Pharmacological reversal of these phosphorylation changes restored HCN channel gating downregulation and neuronal hyperexcitability in epileptic tissue to control levels. Together, these results suggest that alteration of two different phosphorylation pathways in epilepsy contributes to the downregulation of HCN channel gating, which consequently produces neuronal hyperexcitability and thus may be a target for novel antiepileptic therapies.