title: Multiple modes of ryanodine receptor 2 inhibition by flecainide.
abstract: 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 [Ca(2+)], [Mg(2+)], 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 [Ca(2+)] (100 nM), flecainide possesses an additional inhibitory mechanism that reduces RyR2 burst duration. Hence, multiple modes of action underlie RyR2 inhibition by flecainide.
authors.affiliation: School of Biomedical Sciences and Pharmacy, University of Newcastle and Hunter Medical Research Institute, Callaghan, New South Wales, Australia (D.M., M.S.I., D.F.v.H., D.R.L.); and Division of Clinical Pharmacology, Department of Medicine, Vanderbilt University School of Medicine, Nashville, Tennessee (B.C.K.).
authors.forename: D
authors.initials: D
authors.lastname: Mehra
authors.affiliation: School of Biomedical Sciences and Pharmacy, University of Newcastle and Hunter Medical Research Institute, Callaghan, New South Wales, Australia (D.M., M.S.I., D.F.v.H., D.R.L.); and Division of Clinical Pharmacology, Department of Medicine, Vanderbilt University School of Medicine, Nashville, Tennessee (B.C.K.).
authors.forename: M S
authors.initials: MS
authors.lastname: Imtiaz
authors.affiliation: School of Biomedical Sciences and Pharmacy, University of Newcastle and Hunter Medical Research Institute, Callaghan, New South Wales, Australia (D.M., M.S.I., D.F.v.H., D.R.L.); and Division of Clinical Pharmacology, Department of Medicine, Vanderbilt University School of Medicine, Nashville, Tennessee (B.C.K.).
authors.forename: D F
authors.initials: DF
authors.lastname: van Helden
authors.affiliation: School of Biomedical Sciences and Pharmacy, University of Newcastle and Hunter Medical Research Institute, Callaghan, New South Wales, Australia (D.M., M.S.I., D.F.v.H., D.R.L.); and Division of Clinical Pharmacology, Department of Medicine, Vanderbilt University School of Medicine, Nashville, Tennessee (B.C.K.).
authors.forename: B C
authors.initials: BC
authors.lastname: Knollmann
authors.affiliation: School of Biomedical Sciences and Pharmacy, University of Newcastle and Hunter Medical Research Institute, Callaghan, New South Wales, Australia (D.M., M.S.I., D.F.v.H., D.R.L.); and Division of Clinical Pharmacology, Department of Medicine, Vanderbilt University School of Medicine, Nashville, Tennessee (B.C.K.) Derek.Laver@newcastle.edu.au.
authors.forename: D R
authors.initials: DR
authors.lastname: Laver
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D005424:Flecainide / Q000494:pharmacology*; D006863:Hydrogen-Ion Concentration; D008274:Magnesium / Q000378:metabolism; D019837:Ryanodine Receptor Calcium Release Channel / Q000187:drug effects*; D012756:Sheep
chemical_list: D002121:Calcium Channel Blockers; D019837:Ryanodine Receptor Calcium Release Channel; D008274:Magnesium; D005424:Flecainide; D002118:Calcium