Abstract 16628: Perturbations in IK1 and Calcium Handling Underlie CPVT-like Phenotype in a Cardiac-specific R67Q-KCNJ2 Mutant Mouse
Introduction: KCNJ2 mutations are implicated in catecholaminergic polymorphic ventricular tachycardia (CPVT3). We previously reported KCNJ2 mutation R67Q, associated with adrenergic-induced polymorphic ventricular tachycardia (PMVT) and bidirectional ventricular ectopy. Underlying cellular arrhythmia mechanisms that result in a CPVT phenotype related to R67Q KCNJ2 remain elusive. A cardiac-specific R67Q “knock-in” mouse was generated to determine the cellular mechanism and in vivo phenotype.
Methods: Isolated ventricular myocytes (VM) from wild type (WT) and heterozygous R67Q mice were used for calcium transient (CaT) measurements and whole cell patch clamp, at baseline, and following isoproterenol (Iso) treatment. Intact heart simultaneous voltage and calcium optical mapping was performed, at baseline, and following Iso. Western blot using whole heart lysates from WT and R67Q mice was performed using standard protocols.
Results: In vivo ECG studies on R67Q mice demonstrated adrenergic-induced paroxysms of bi-directional VT, and PMVT. Whole cell IK1, recorded from isolated VMs, showed a lack of augmented outward current following Iso treatment in R67Q mice. Western blot revealed no significant difference in Kir2.1 protein expression between WT and R67Q mice. VMs from WT and R67Q mice demonstrated 1:1 CaTs as a result of electrical field stimulation at 1Hz and 2Hz. Following Iso administration, CaT duration at 1Hz and 2Hz was significantly decreased in R67Q cardiomyocytes compared to WT. R67Q cardiomyocytes also showed increased spontaneous calcium release events (sparks and waves) following Iso. Optical mapping revealed similar differences in CaT duration between WT and R67Q mice. In addition, analysis of ventricular conduction velocity (CV) showed a significantly slower CV in R67Q mice compared to WT. Together with a higher pacing threshold in R67Q, it may indicate a depolarized resting potential which may facilitate spontaneous calcium events to develop arrhythmogenic afterdepolarizations and promote ventricular arrhythmias.
Conclusions: These data suggest that the CPVT phenotype is caused by failure of IK1 to increase following isoproterenol, lack of a stable resting membrane potential resulting in altered calcium handling.
Author Disclosures: L. Reilly: None. D. Lang: None. R. Vaidyanathan: None. S. Abozeid: None. C. Spellman: None. H. Van Ert: None. S. Esch: None. J. Warden: None. J.C. Makielski: None. A.V. Glukhov: None. L.L. Eckhardt: None.
- © 2016 by American Heart Association, Inc.