Abstracts

Rationale: Voltage-gated Kv1.1 potassium channel α-subunits, encoded by the Kcna1 gene, have traditionally been considered limited to neurons, where they dampen excitability and control action potential firing properties. Global Kcna1 knockout (KO) mice are widely used as a model of epilepsy and sudden unexpected death in epilepsy (SUDEP) since they exhibit spontaneous seizures, cardiac dysfunction, and sudden death. The cardiac abnormalities and premature death in Kcna1 KOs have traditionally been considered as neurogenic in origin. However, recent studies have revealed unexpected Kv1.1 expression in mouse and human heart, where the channels contribute to cardiac repolarization. The expression of Kv1.1 channels in both the brain and the heart makes it unclear whether cardiac dysfunction and SUDEP in Kcna1-null mice is mediated by neural or cardiac mechanisms or a combination of both. Thus, the aim of this research was to generate neuron-specific Kcna1 conditional knockout (cKO) mice to test the hypothesis that neuron-specific Kv1.1 deficiency is sufficient to cause cardiac dysfunction and death. Methods: Mice were engineered to carry a new floxed allele of Kcna1 and then crossed with Synapsin1-Cre (Syn-Cre) mice to generate neuron-specific Kcna1 cKOs. Western blots were performed (n=3/genotype) to verify the absence of Kv1.1 protein in various brain regions. SUDEP rates were measured in cKO mice (n≥10) using Kaplan-Meier survival curves. Simultaneous video electroencephalography (EEG) – electrocardiography (ECG) recordings were performed for a continuous 18-24 hour period in cKO mice (n≥4) and controls (n≥4) with varying allelic combinations to identify neurocardiac abnormalities, which were then quantified. Results: Immunoblots confirmed that brain Kv1.1 protein is almost completely abolished in cKO mice, with slight residual expression likely due to the presence of Kv1.1 in glial cells. Survival studies showed that neuron-specific cKOs have reduced lifespans with about 20% dying prematurely by 35 days old. Simultaneous video EEG – ECG recordings in cKO mice revealed frequent spontaneous electrographic and behavioral seizures. Although heart rate appeared unchanged in cKOs, they did exhibit increases in the frequency of skipped heart beats (i.e., atrioventricular conduction blocks) and in heart rate variability, suggesting abnormally high parasympathetic tone. Conclusions: The neurocardiac phenotypes of cKO mice appear qualitatively similar to global Kcna1 KO mice, demonstrating that neuron-specific Kv1.1 deficiency is sufficient to cause cardiac dysfunction and SUDEP. Future studies will evaluate the effects of cardiac-specific Kv1.1 deficiency on cardiac dysfunction and risk of premature death. The floxed Kcna1 mice generated herein represent a valuable new research tool for the investigation of neurological and cardiac disorders such as epilepsy and atrial fibrillation. Funding: This works was supported by grants from the National Institutes of Health (R00HL107641, R01NS099188) and a Louisiana State University Malcolm Feist Postdoctoral Fellowship.