title: Divergent regulation of ryanodine receptor 2 calcium release channels by arrhythmogenic human calmodulin missense mutants.
abstract: BACKGROUND
  Calmodulin (CaM) mutations are associated with an autosomal dominant syndrome of ventricular arrhythmia and sudden death that can present with divergent clinical features of catecholaminergic polymorphic ventricular tachycardia (CPVT) or long QT syndrome (LQTS). CaM binds to and inhibits ryanodine receptor (RyR2) Ca release channels in the heart, but whether arrhythmogenic CaM mutants alter RyR2 function is not known.
  
  
  OBJECTIVE
  To gain mechanistic insight into how human CaM mutations affect RyR2 Ca channels.
  
  
  RESULTS
  We studied recombinant CaM mutants associated with CPVT (N54I and N98S) or LQTS (D96V, D130G, and F142L). As a group, all LQTS-associated CaM mutants (LQTS-CaMs) exhibited reduced Ca affinity, whereas CPVT-associated CaM mutants (CPVT-CaMs) had either normal or modestly lower Ca affinity. In permeabilized ventricular myocytes, CPVT-CaMs at a physiological intracellular concentration (100 nmol/L) promoted significantly higher spontaneous Ca wave and spark activity, a typical cellular phenotype of CPVT. Compared with wild-type CaM, CPVT-CaMs caused greater RyR2 single-channel open probability and showed enhanced binding affinity to RyR2. Even a 1:8 mixture of CPVT-CaM:wild-type-CaM activated Ca waves, demonstrating functional dominance. In contrast, LQTS-CaMs did not promote Ca waves and exhibited either normal regulation of RyR2 single channels (D96V) or lower RyR2-binding affinity (D130G and F142L). None of the CaM mutants altered Ca/CaM binding to CaM-kinase II.
  
  
  CONCLUSIONS
  A small proportion of CPVT-CaM is sufficient to evoke arrhythmogenic Ca disturbances, whereas LQTS-CaMs do not. Our findings explain the clinical presentation and autosomal dominant inheritance of CPVT-CaM mutations and suggest that RyR2 interactions are unlikely to explain arrhythmogenicity of LQTS-CaM mutations.
authors.affiliation: From the Departments of Medicine (H.S.H., M.F., A.L.G., B.C.K.), Biochemistry (C.N.J., W.J.C.), Chemistry (W.J.C.), and Pharmacology (A.L.G., B.C.K.), Vanderbilt University, Nashville, TN; Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis (F.R.N., R.L.C.); Department of Pharmacology, University of California, Davis (Y.Y., L.P., D.M.B.); and Department of School of Biomedical Sciences and Pharmacy, University of Newcastle, New South Wales, Australia (K.W., D.L.).
authors.forename: Hyun Seok
authors.initials: HS
authors.lastname: Hwang
authors.forename: Florentin R
authors.initials: FR
authors.lastname: Nitu
authors.forename: Yi
authors.initials: Y
authors.lastname: Yang
authors.forename: Kafa
authors.initials: K
authors.lastname: Walweel
authors.forename: Laetitia
authors.initials: L
authors.lastname: Pereira
authors.forename: Christopher N
authors.initials: CN
authors.lastname: Johnson
authors.forename: Michela
authors.initials: M
authors.lastname: Faggioni
authors.forename: Walter J
authors.initials: WJ
authors.lastname: Chazin
authors.forename: Derek
authors.initials: D
authors.lastname: Laver
authors.forename: Alfred L
authors.initials: AL
authors.lastname: George
authors.forename: Razvan L
authors.initials: RL
authors.lastname: Cornea
authors.forename: Donald M
authors.initials: DM
authors.lastname: Bers
authors.forename: Björn C
authors.initials: BC
authors.lastname: Knollmann
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling; D002147:Calmodulin / Q000235:genetics / Q000378:metabolism*; D006352:Heart Ventricles / Q000166:cytology / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D020125:Mutation, Missense; D032383:Myocytes, Cardiac / Q000378:metabolism*; D011485:Protein Binding; D019837:Ryanodine Receptor Calcium Release Channel / Q000235:genetics / Q000378:metabolism*
chemical_list: D002147:Calmodulin; D019837:Ryanodine Receptor Calcium Release Channel; D002118:Calcium
keywords: calcium; catecholaminergic polymorphic ventricular tachycardia; long QT syndrome; ryanodine receptor calcium release channel; sarcoplasmic reticulum