Abstract 17878: Calmodulin Mutation (CALM-F90L) Associated With Familial Idiopathic Ventricular Fibrillation Disrupts L-type Ca Channel Inactivation and Activates Sarcoplasmic Reticulum Ca Release in Ventricular Myocytes

Abstract

Introduction: The F90L mutation in calmodulin (CaM) has been associated with a familial form of autosomal-dominant idiopathic ventricular fibrillation (IVF) with features of exercise-induced QT prolongation, but the underlying arrhythmia mechanism is unknown. We previously found that CaM mutations that cause sudden death due to catecholaminergic polymorphic ventricular tachycardia (CPVT) activate ryanodine receptor (RyR2) Ca release channels; whereas CaM mutations associated with long QT syndrome (LQTS) have no effects on RyR2 channels but prolong the cardiac action potential by impairing L-type Ca current inactivation. Objective: To determine the effect of F90L mutant CaM on Ca binding affinity, L-type Ca currents and Ca handling and compare them to CaM mutants associated with CPVT (CPVT-CaM) and LQTS (LQTS-CaM). Methods and Results: We prepared recombinant wild-type (WT) and mutant CaM proteins associated with CPVT (N54I), LQTS (D96V, D130G, F142L) and IVF (F90L). Similar to LQTS CaMs, the F90L IVF mutation drastically reduced Ca binding affinity of CaM C-lobe (7-fold reduction compared to WT-CaM), whereas CPVT N54I has no effect. In voltage-clamped mouse ventricular myocytes dialyzed either with WT or mutant CaM, IVF-CaM F90L significantly impaired L-type Ca channel inactivation, similar to the effect of LQTS-CaMs, whereas CPVT-CaM had no effect (Fig. A, **p<0.01 vs WT). Next, mutant CaMs effects on sarcoplasmic reticulum Ca release were tested in permeabilized ventricular myocytes. At physiological free CaM [100 nM] and Ca [120 nM], IVF-CaM F90L increased spontaneous Ca wave activity analogous to CPVT-CaM N54I, but of significantly smaller effect size (Fig. B). In contrast, LQTS-CaMs had either no effect or reduced Ca waves (Fig. B). Conclusion: The F90L CaM mutation shares characteristics with both CPVT and LQTS CaMs, which may help explain clinical features of modest exercise-induced QT prolongation and sudden arrhythmic death in patient carriers.