BK Channel B4 Subunit in the Dentate Gyrus and Seizures

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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.