Abstract 18157: Presence of Calmodulin Potentiates Block of Ryanodine Receptor Calcium Release Channels by Dantrolene and Flecainide
Introduction: Dantrolene and flecainide have been used to suppress ventricular arrhythmias caused by spontaneous Ca release from the sarcroplasmic reticulum in animal models and humans. Since both agents exhibit much lower potency against single RyR2 Ca release channels in vitro, whether RyR2 block contributes to their antiarrhythmic mechanism of action has remained controversial.
Hypothesis: Loss of Calmodulin (CaM), a physiological binding partner of RyR2, is responsible for the discrepancy of in vivo and in vitro results.
Methods and Results: Using single channels isolated from sheep hearts and incorporated into lipid bilayers, we constructed concentration-response curves of dantrolene and flecainide in the presence and absence of physiological concentrations (100nM) of CaM. Without CaM, dantrolene (up to 100 μM) had no effect on single channel open probability (Po). In presence of CaM, dantrolene inhibited single RyR2 channels with an IC50 of 0.2 μM, and a maximum inhibitory effect (Emax) of 50%. Likewise, CaM also potentiated the action of flecainide on single RyR2 channels, with 3-fold increase in potency (i.e. lower IC50, Figure) and a modest increase in Emax (Figure). We next tested dantrolene and flecainide in permeabilized ventricular myocytes isolated from calsequestrin knockout mice, an established genetic model of Ca-release triggered ventricular arrhythmia. Addition of 100 nM CaM significantly increased the potency of dantrolene for suppressing spontaneous Ca wave activity (IC50: Dantrolene = 20 μM; dantrolene+CaM = 6 μM, n= 80 myocytes per group), whereas Emax was unchanged (75% inhibition). CaM doubled both the potency (IC50 increased from 3 μM to 1.4 μM) and efficacy (Emax increased from 40% to 80% inhibition) of Ca wave suppression by flecainide.
Conclusions: Calmodulin is critical for drug block of RyR2 channels by dantrolene and flecainide.
- Arrhythmias, treatment of
- Ventricular tachycardia
- Excitation-contraction coupling (ECC)
- Ion channels
Author Disclosures: N. Gomez-Hurtado: None. Y. Oo: None. D. Laver: None. B. Knollmann: None.
This research has received full or partial funding support from the American Heart Association.
- © 2014 by American Heart Association, Inc.