title: Arrhythmogenic calmodulin mutations impede activation of small-conductance calcium-activated potassium current.
abstract: Apamin-sensitive small-conductance calcium-activated potassium (SK) channels are gated by intracellular Ca(2+) through a constitutive interaction with calmodulin.
  
  
  
  We hypothesize that arrhythmogenic human calmodulin mutations impede activation of SK channels.
  
  
  
  We studied 5 previously published calmodulin mutations (N54I, N98S, D96V, D130G, and F90L). Plasmids encoding either wild-type or mutant calmodulin were transiently transfected into human embryonic kidney 293 cells that stably express subtype 2 of SK protein channels (SK2 cells). Whole-cell voltage-clamp recording was used to determine apamin-sensitive current densities. We also performed optical mapping studies in normal murine hearts to determine the effects of apamin in hearts with (n=7) or without (n=3) pretreatment with sea anemone toxin.
  
  
  
  SK2 cells transfected with wild-type calmodulin exhibited an apamin-sensitive current density of 33.6 pA/pF (31.4-36.5 pA/pF) (median and confidence interval 25th-75th percentile), which was significantly higher than that observed for cells transfected with N54I (17.0 pA/pF [14.0-27.7 pA/pF]; P = .016), F90L (22.6 pA/pF [20.3-24.3 pA/pF]; P = .011), D96V (13.0 pA/pF [10.9-15.8 pA/pF]; P = .003), N98S (13.7 pA/pF [8.8-20.4 pA/pF]; P = .005), and D130G (17.6 pA/pF [13.8-24.6 pA/pF]; P = .003). The decrease in SK2 current densities was not associated with a decrease in membrane protein expression or intracellular distribution of the channel protein. Apamin increased the ventricular action potential duration at 80% repolarization (from 79.6 ms [63.4-93.3 ms] to 121.8 ms [97.9-127.2 ms]; P = .010) in hearts pretreated with anemone toxin but not in control hearts.
  
  
  
  Human arrhythmogenic calmodulin mutations impede the activation of SK2 channels in human embryonic kidney 293 cells.
authors.affiliation: Krannert Institute of Cardiology and Division of Cardiology, Department of Medicine, Indiana University, Indianapolis, Indiana; Department of Internal Medicine, National Taiwan University Hospital, Taipei, Taiwan.
authors.forename: Chih-Chieh
authors.initials: CC
authors.lastname: Yu
authors.affiliation: Krannert Institute of Cardiology and Division of Cardiology, Department of Medicine, Indiana University, Indianapolis, Indiana; Division of Cardiology, Department of Internal Medicine, Wonkwang University School of Medicine and Hospital, Iksan, Korea.
authors.forename: Jum-Suk
authors.initials: JS
authors.lastname: Ko
authors.affiliation: Krannert Institute of Cardiology and Division of Cardiology, Department of Medicine, Indiana University, Indianapolis, Indiana; Department of Molecular Pathogenesis, Medical Research Institute; Department of Emergency Medicine, Tokyo Medical and Dental University, Tokyo, Japan.
authors.forename: Tomohiko
authors.initials: T
authors.lastname: Ai
authors.affiliation: Krannert Institute of Cardiology and Division of Cardiology, Department of Medicine, Indiana University, Indianapolis, Indiana; Hualien Tzu-Chi General Hospital, Hualien City, Taiwan.
authors.forename: Wen-Chin
authors.initials: WC
authors.lastname: Tsai
authors.affiliation: Krannert Institute of Cardiology and Division of Cardiology, Department of Medicine, Indiana University, Indianapolis, Indiana.
authors.forename: Zhenhui
authors.initials: Z
authors.lastname: Chen
authors.affiliation: Krannert Institute of Cardiology and Division of Cardiology, Department of Medicine, Indiana University, Indianapolis, Indiana; Department of Pediatrics, Riley Heart Research Center.
authors.forename: Michael
authors.initials: M
authors.lastname: Rubart
authors.affiliation: Krannert Institute of Cardiology and Division of Cardiology, Department of Medicine, Indiana University, Indianapolis, Indiana; Department of Medical and Molecular Genetics, Indiana University School of Medicine, Indianapolis, Indiana.
authors.forename: Matteo
authors.initials: M
authors.lastname: Vatta
authors.affiliation: Krannert Institute of Cardiology and Division of Cardiology, Department of Medicine, Indiana University, Indianapolis, Indiana.
authors.forename: Thomas H
authors.initials: TH
authors.lastname: Everett
authors.affiliation: Department of Pharmacology, Northwestern University Feinberg School of Medicine, Chicago, Illinois.
authors.forename: Alfred L
authors.initials: AL
authors.lastname: George
authors.affiliation: Krannert Institute of Cardiology and Division of Cardiology, Department of Medicine, Indiana University, Indianapolis, Indiana. Electronic address: chenpp@iu.edu.
authors.forename: Peng-Sheng
authors.initials: PS
authors.lastname: Chen
mesh_terms: D000200:Action Potentials; D000818:Animals; D001145:Arrhythmias, Cardiac; D015153:Blotting, Western; D002147:Calmodulin / Q000235:genetics* / Q000378:metabolism; D004247:DNA / Q000235:genetics*; D004252:DNA Mutational Analysis; D004195:Disease Models, Animal; D057809:HEK293 Cells; D006801:Humans; D017136:Ion Transport; D051379:Mice; D009154:Mutation; D032383:Myocytes, Cardiac / Q000378:metabolism* / Q000473:pathology; D018408:Patch-Clamp Techniques; D051640:Small-Conductance Calcium-Activated Potassium Channels / Q000235:genetics* / Q000378:metabolism; D017180:Tachycardia, Ventricular / Q000235:genetics* / Q000378:metabolism / Q000473:pathology
chemical_list: D002147:Calmodulin; D051640:Small-Conductance Calcium-Activated Potassium Channels; D004247:DNA
keywords: Arrhythmias; Catecholaminergic polymorphic ventricular tachycardia; Ion channels; Long QT syndrome; Patch clamp