Abstracts

Rationale: Kv4.2 contributes to the A-type current (I_A) in hippocampus, and reduction of it leads to increased dendritic excitability. Kv4.2 channels and I_A are regulated by various signaling pathways. Alterations in Kv4.2 expression and kinase regulation have been demonstrated in chronic epilepsy. The present study evaluated Kv4.2 expression and localization acutely following status epilepticus (SE). We also investigated whether ERK and CaMKII pathway modulation during SE contributes to alterations in Kv4.2 during SE.Methods: We administered kainate (15 mg/kg IP) or vehicle to adult rats to induce SE. After 1 hour of SE, animals were sacrificed and hippocampal homogenates, membranes and synaptosomes prepared. Whole brains were prepared for immunohistochemistry. In parallel experiments, cultured hippocampal neurons were treated with high-K ⁺, 0 Mg ²⁺, to induce continuous seizure-like activity in vitro. Neuronal cultures were processed for biochemistry after 3 hr of treatment. Surface biotinylation and Kv4.2 immunoprecipitation were performed in both models. Immunohistochemistry and western blotting were performed with antibodies against activated ERK and CaMKII and phosphorylated Kv4.2. Results: Kv4.2 surface biotinylation was reduced following kainate induced SE in vivo and in neuronal cultures treated with high-K ⁺, 0 Mg ²⁺ (p<0.05). During SE, Kv4.2 expression in synaptosomal preparations was decreased in hippocampus (p<0.05). Immunolabeling of Kv4.2 was increased in the cell body region and decreased in the dendritic fields in hippocampal neurons from both preparations. We examined phosphorylation of Kv4.2 by ERK in the SE model in vivo and found increased ERK activation (p<0.01) and ERK-phosphorylated Kv4.2 (p<0.05). In addition, we found CaMKII inhibition and decreased CaMKII phosphorylation of Kv4.2 (p<0.01) following SE. Parallel studies are underway in the culture system.Conclusions: Our results reveal reduced surface expression and synaptosomal Kv4.2 following SE in the whole animal and hyperexcitability in neuronal cultures, findings that are anticipated to contribute to an increase in postsynaptic excitability and potentially seizure activity in these models. Furthermore, we demonstrate that there are alterations in ERK and CaMKII phosphorylation of Kv4.2 following SE. It is possible that post-translational modifications contribute to alterations in Kv4.2 expression and localization during SE. Future experiments will be aimed at this possibility. Supported by: NIH/NINDS, Epilepsy Foundation.