Abstracts

Rationale: Voltage-gated Kv1.1 K+ channel alpha subunits, which are encoded by the Kcna1 gene, are expressed in mouse and human atria and ventricles where they mediate outward K+ currents that influence arrhythmia susceptibility and cardiac action potential repolarization. Mice lacking Kv1.1 exhibit frequent spontaneous generalized tonic-clonic seizures that lead to cardiorespiratory dysregulation and death, making them an extensively used model of sudden unexpected death in epilepsy (SUDEP). In this research, we seek to define the electrophysiological consequences of lacking Kv1.1 channels in the sinoatrial node (SAN) of the heart which controls cardiac pacemaking. Previous studies have detected significant levels of Kcna1 mRNA in mouse SAN, suggesting Kv1.1 may contribute to SAN physiological function. Therefore, in this study, we test the hypothesis that Kv1.1 channels are required for normal physiological function of the SAN and that lacking Kv1.1 channels leads to intrinsic cardiac pacemaking defects. Several neurocardiac genes, such as Kcna1, that have been implicated in sudden unexpected death in epilepsy (SUDEP) also demonstrate dysfunction in the SAN, suggesting that SAN functional deficits could be a risk factor for SUDEP.

Methods: Langendorff isolated heart recordings, multielectrode array (MEA) recordings, and perforated patch clamp recordings were employed to study intrinsic cardiac activity of SAN tissue and cells from Kcna1 knockout (KO) mice and wildtype (WT) controls of both sexes between the ages of 1-6 months old. Administration of 4-AP and DTX-K was used to inhibit Kv1.1 channels, whereas acetylcholine and isoproterenol were used as selective parasympathetic and sympathetic agonists, respectively.

Results: Although KO mice have heart rates that are similar to WT when measured by in vivo ECG recordings, in isolated heart recordings without neural influences, KO hearts (n=10) exhibited significantly slower heart rates (P < 0.05) that were reduced by 27% compared to WT (n=11), suggesting a role in regulation of heart rate. In MEA recordings of ex vivo sinoatrial tissue, KO hearts also showed significantly reduced spontaneous firing rates (P < 0.01; n=13) further confirming the presence of pacemaking defects due to Kv1.1 deficiency. In current clamp studies, DTX-K significantly decreased spontaneous action potential firing rate in WT isolated SAN cells by about 16% (P < 0.001; n=7), suggesting a contribution by Kv1.1 channels. DTX-K had no effect in KO SAN cells (P=0.36; n=6) demonstrating specificity for Kv1.1 channels. DTX-K application significantly increased cycle length of spontaneous action potentials in WT SAN cells by about 21% (n=7) but had no effect in KO SAN cells. Cycle length was significantly prolonged in KO SAN cells by about 72% (n=7) compared to WT (n=7).