BK Channel B4 Subunit in the Dentate Gyrus and Seizures

描述（由申请人提供）：钾通道具有降低兴奋性的作用，在控制癫痫发作中起关键作用。大电导钙激活钾通道（BK型通道）具有调节细胞膜兴奋性的特殊作用，这种作用与钙内流一致。以前，发现孔形成α亚基与新的β 4辅助亚基的异源共表达产生具有所谓的神经元“II型BK通道”性质的BK电流。4亚基赋予对伊比利亚毒素阻断的抗性、缓慢的门控动力学和降低的开放概率。此外，pKA 4亚基可能赋予神经元对pKA依赖性磷酸化的敏感性。 我们已经产生了约4个基因敲除小鼠。我们的初步数据提供了直接的证据，BK通道组装与<$4亚基的基础II型BK通道。在齿状回（DG）中，敲除细胞更易兴奋并支持高频放电。最后，EEG记录表明，4敲除小鼠表现出非惊厥性部分性癫痫发作。 4基因敲除小鼠可能是第一个非惊厥性颞叶癫痫的遗传模型。 对这些小鼠的研究将使我们有独特的机会对可能导致这类癫痫的离子通道特性的变化进行生物物理学理解。 我们的兴趣是了解α 4亚基BK通道如何调节DG细胞的输入/输出特性，从而有助于抵抗同步癫痫样活动，这是DG的一个特性。 我们的工作假设是，β 4亚基下调BK通道，导致增加钙内流和减少兴奋性的SK通道的招聘。 我们有三个目标。1)利用DG细胞的膜片钳/切片记录，了解导致敲除小鼠AP放电增加的膜特性变化。2)确定如何（4亚基调节BK通道对DG中pKA依赖性磷酸化的敏感性，从而调节代谢型谷氨酸受体的兴奋性3）利用免疫组织化学和电生理记录技术来确定4亚基在神经末梢中的亚细胞定位及其对苔藓纤维末梢中神经传递的贡献。这些研究将提供一个相对不典型的BK通道亚型的第一次了解，并进一步了解这种通道的功能的背景下，一种新的遗传模型癫痫。

DESCRIPTION (provided by applicant): Potassium channels have the role of reducing excitability and are pivotal in controlling seizures. The large conductance calcium-activated potassium channels (BK-type channels) have the specialized role of regulating membrane excitability that is coincident with calcium influx. Previously, heterologous co- expression of the pore-forming a subunit with the novel ¿4 accessory subunit was found to produce BK currents with properties of so called neuronal "type II BK channels". The ¿4 subunit confers resistance to iberiotoxin block, slow gating kinetics, and a reduced open probability. In addition, the ¿4 subunit may confer sensitivity to pKA dependent phosphorylation in neurons. We have generated ¿4 gene knockout mice. Our preliminary data provides direct evidence that BK channel assembly with the ¿4 subunit underlies type II BK channels. In the dentate gyrus (DG), knockout cells are more excitable and support high frequency firing. Finally, EEG recording demonstrate that the ¿4 knockout mice exhibit non-convulsive partial seizures. The ¿4 knockout mice may be the first genetic model for non-convulsive temporal lobe epilepsy. Investigation of these mice will allow us the unique opportunity to have a biophysical understanding of the changes in ion channel properties that may underlie this class of epilepsy. Our interest is to understand how a/¿4 subunit BK channels regulate the input/output properties of DG cells, and thereby contribute to resistance of synchronized epileptiform activity that is a property of the DG. Our working hypothesis is that beta4 subunits down-regulates BK channels, resulting in increased calcium influx and reduced excitability by recruitment of SK channels. We have 3 aims. 1) Utilizing patch clamp/slice recordings from DG cells, understand the change in membrane properties that result in increased AP firing in the knockout mice. 2) Determine how the (¿4 subunit modulates sensitivity of BK channels to pKA dependent phosphorylation in the DG, and thereby regulates excitability by metabotropic glutamate receptors 3) Utilize immunohistochemistry and electrophysiological recording techniques to determine the subcellular localization of the ¿4 subunit in nerve terminals and its' contribution to neurotransmission in the mossy fiber terminals. These studies will provide the first understanding of a relatively uncharacterized BK channel subtype and further our understanding of this channels' function in the context of a novel genetic model for epilepsy.