RT Journal Article
SR Electronic
T1 Multiple Modes of Ryanodine Receptor 2 Inhibition by Flecainide
JF Molecular Pharmacology
JO Mol Pharmacol
FD American Society for Pharmacology and Experimental Therapeutics
SP 696
OP 706
DO 10.1124/mol.114.094623
VO 86
IS 6
A1 D. Mehra
A1 M. S. Imtiaz
A1 D. F. van Helden
A1 B. C. Knollmann
A1 D. R. Laver
YR 2014
UL http://molpharm.aspetjournals.org/content/86/6/696.abstract
AB Catecholaminergic polymorphic ventricular tachycardia (CPVT) causes sudden cardiac death due to mutations in cardiac ryanodine receptors (RyR2), calsequestrin, or calmodulin. Flecainide, a class I antiarrhythmic drug, inhibits Na+ and RyR2 channels and prevents CPVT. The purpose of this study is to identify inhibitory mechanisms of flecainide on RyR2. RyR2 were isolated from sheep heart, incorporated into lipid bilayers, and investigated by single-channel recording under various activating conditions, including the presence of cytoplasmic ATP (2 mM) and a range of cytoplasmic [Ca2+], [Mg2+], pH, and [caffeine]. Flecainide applied to either the cytoplasmic or luminal sides of the membrane inhibited RyR2 by two distinct modes: 1) a fast block consisting of brief substate and closed events with a mean duration of ∼1 ms, and 2) a slow block consisting of closed events with a mean duration of ∼1 second. Both inhibition modes were alleviated by increasing cytoplasmic pH from 7.4 to 9.5 but were unaffected by luminal pH. The slow block was potentiated in RyR2 channels that had relatively low open probability, whereas the fast block was unaffected by RyR2 activation. These results show that these two modes are independent mechanisms for RyR2 inhibition, both having a cytoplasmic site of action. The slow mode is a closed-channel block, whereas the fast mode blocks RyR2 in the open state. At diastolic cytoplasmic [Ca2+] (100 nM), flecainide possesses an additional inhibitory mechanism that reduces RyR2 burst duration. Hence, multiple modes of action underlie RyR2 inhibition by flecainide.