Abstracts

Rationale: Voltage-gated Kv1.1 potassium channel α-subunits, encoded by the Kcna1 gene, exhibit widespread expression throughout the central and peripheral nervous systems and their dysfunction leads to human neurological diseases including epilepsy and episodic ataxia type 1. Mutations in Kcna1 have also been linked to sudden unexpected death in epilepsy (SUDEP) in mice and one human patient. Kv1.1 channels have traditionally been regarded as predominantly neural-specific with no known expression or function in the heart. However, recent data from mice and humans reveal that Kv1.1 channels are expressed in cardiomyocytes with 10-fold higher expression in atria than in ventricles. Kv1.1 knockout (KO) mice exhibit seizure-associated bradycardia, atrioventricular conduction blocks, and increased susceptibility to atrial arrhythmias. However, the functional effects of Kv1.1 deficiency at the cellular level in cardiac tissue have not yet been investigated. Methods: Atrial cardiomyocytes were isolated enzymatically from Kcna1-null (KO) mice and wild type (WT) siblings (ages 6-8 weeks) using Langendorff perfusion with Liberase TH. Whole-cell patch clamp recordings were performed at 37 °C. Action potentials (APs) were recorded using current clamp method and were evoked by electrical stimulation with 2 nA current pulses of 1 ms duration. Outward K+ currents were recorded using voltage clamp configuration. Dendrotoxin-K (DTX-K; 10 nM), a specific inhibitor of Kv1.1 subunits, was used to identify Kv1.1 currents in cardiomyocytes. Quantitative real-time PCR (qPCR) was used to measure atrial ion channel mRNA expression. Results: Patch clamp recordings of isolated atrial cardiomyocytes showed that action potential durations (APDs) are significantly prolonged in KO mice (APD90; P P demonstrating a substantial contribution by Kv1.1 channels to atrial repolarization currents. However, total outward potassium currents were not significantly reduced in KO cells, suggesting compensatory remodeling of other cardiac potassium currents. Atrial qPCR revealed that KO mice exhibit alterations in Kcna5, Kcnh2, Kcnj2, and Scn5a gene expression (P=0.042, 0.026, 0.013, and 0.007, respectively) suggesting transcriptional level ion channel remodeling contributes to electrophysiological abnormalities in atria of KO mice. Conclusions: In summary, the DTX-K sensitive currents in WT atrial cells suggest that Kv1.1 channels are important for normal atrial function. Action potential prolongation and transcriptional ion channel remodeling in the atria of Kcna1 KO mice, in addition to the known increased atrial arrhythmia susceptibility, suggest that Kv1.1 deficiency leads to impaired cardiac repolarization and alterations in other major cardiac currents, further contributing to cardiac dysfunction. We speculate that the lack of Kv1.1 channel subunits in cardiomyocytes could render the heart a more vulnerable substrate for potentially deleterious brain-driven cardiac arrhythmias, thereby increasing risk of SUDEP in this model. Funding: This work was supported by grants from the National Institutes of Health (R00HL107641, R01NS099188) and a Louisiana State University Malcolm Feist Postdoctoral Fellowship.