Abstract 12302: Na V 1.6 Dysregulation by Mutant Calmodulin Enhances Late Sodium Current in Human iPSC Cardiomyocytes and Promotes Arrhythmias in D96V Calmodulin-Expressing Transgenic Mice

Abstract

Calmodulin (CaM) mutants are associated with severe arrhythmias (calmodulinopathy). While dysregulation of Ca 2+ handling proteins (RyR2, Ca V 1.2) are known mediators of calmodulinopathy, the role of Na + channels (Na V s) remains unclear. Interestingly, effects on Ca V 1.2 do not fully explain action potential (AP) prolongation by the long QT syndrome CaM mutant D96V. We investigated Na V dysregulation by D96V-CaM and its arrhythmogenic impact. In wild-type (WT) murine cardiomyocytes (CM) dialysis of D96V-CaM (6.5 μM) via a patch pipette prolonged AP, induced early and delayed afterdepolarizations (EADs and DADs) and increased Ca 2+ waves compared to WT-CaM. The effects of D96V-CaM were abrogated by a Na V 1.6 blocker, 4,9-anhydrotetrodotoxin (4,9ahTTX, 300 nM; Fig. 1A ). Dialysis of D96V-CaM dysregulated inactivation of 4,9ahTTX-sensitive Na + current (I Na ) promoting late I Na in WT murine CM ( Fig. 1B ) and in Chinese Hamster Ovary (CHO) cells expressing Na V 1.6 but not Na V 1.5. D96V-CaM, but not WT-CaM, also promoted late I Na in human induced pluripotent stem cell (iPSC) - derived ventricular myocytes, underscoring translational relevance ( Fig. 1C ). To examine the arrhythmia potential of Na V 1.6 dysregulation by D96V-CaM, we generated mice with cardiac-specific expression of D96V-CaM (cD96V; tgD96V-CaM x β-MHC-Cre). cD96V mice exhibited increased late I Na and Ca 2+ waves resembling those in D96V-CaM-dialyzed WT CMs. In vivo cD96V mice evidenced prolonged QTc intervals and ventricular tachycardia (VT) during bradycardia (carbachol 0.5 mg/kg intraperitoneal). Cardiac-specific Na V 1.6 knockout protected cD96V mice from impaired I Na inactivation and arrhythmogenic Ca 2+ waves on cellular level as well as long QT and VT in vivo ( Fig. 1D, E ). In summary, D96V-CaM promotes arrhythmias by dysregulating Na V 1.6 and thereby, facilitating aberrant Ca 2+ release. Importantly, Na V 1.6 may be a therapeutic target for management of CaM-related arrhythmias.