title: KCNJ2 mutation causes an adrenergic-dependent rectification abnormality with calcium sensitivity and ventricular arrhythmia.
abstract: BACKGROUND
  KCNJ2 mutations are associated with a variety of inherited arrhythmia syndromes including catecholaminergic polymorphic ventricular tachycardia 3.
  
  
  OBJECTIVE
  To characterize the detailed cellular mechanisms of the clinically recognized KCNJ2 mutation R67Q.
  
  
  METHODS
  Kir2.1 current density was measured from COS-1 cells transiently transfected with wild-type human Kir-2.1 (WT-Kir2.1) and/or a heterozygous missense mutation in KCNJ2 (R67Q-Kir2.1) by using the whole-cell voltage clamp technique. Catecholamine activity was simulated with protein kinase A-stimulating cocktail exposure. Phosphorylation-deficient mutants, S425N-Kir2.1 and S425N-Kir2.1/R67Q-S425N-Kir2.1, were used in a separate set of experiments. HA- or Myc-Tag-WT-Kir2.1 and HA-Tag-R67Q-Kir2.1 were used for confocal imaging.
  
  
  RESULTS
  A 33-year-old woman presented with a catecholaminergic polymorphic ventricular tachycardia-like clinical phenotype and was found to have KCNJ2 missense mutation R67Q. Treatment with nadolol and flecainide resulted in the complete suppression of arrhythmias and symptom resolution. Under baseline conditions, R67Q-Kir2.1 expressed alone did not produce inward rectifier current while cells coexpressing WT-Kir2.1 and R67Q-Kir2.1 demonstrated the rectification index (RI) similar to that of WT-Kir2.1. After PKA stimulation, R67Q-Kir2.1/WT-Kir2.1 failed to increase peak outward current density; WT-Kir2.1 increased by 46% (n = 5), while R67Q-Kir2.1/WT-Kir2.1 decreased by 6% (n = 6) (P = .002). Rectification properties in R67Q-Kir2.1/WT-Kir2.1 demonstrated sensitivity to calcium with a decreased RI in the high-calcium pipette solution (RI 20.3% ± 4.1%) than in the low-calcium pipette solution (RI 36.5% ± 5.7%) (P < .05). Immunostaining of WT-Kir2.1 and R67Q-Kir2.1 individually and together showed a normal membrane expression pattern and colocalization by using the Pearson correlation coefficient.
  
  
  CONCLUSIONS
  R67Q-Kir2.1 is associated with an adrenergic-dependent clinical and cellular phenotype with rectification abnormality enhanced by increased calcium. These findings are a significant advancement of our knowledge and understanding of the phenotype-genotype relationship of arrhythmia syndromes related to KCNJ2 mutations.
authors.affiliation: Cellular and Molecular Arrhythmia Research Program, University of Wisconsin-Madison, Wisonsin.
authors.forename: Matthew M
authors.initials: MM
authors.lastname: Kalscheur
authors.affiliation: Cellular and Molecular Arrhythmia Research Program, University of Wisconsin-Madison, Wisonsin.
authors.forename: Ravi
authors.initials: R
authors.lastname: Vaidyanathan
authors.affiliation: University of Wisconsin-Madison Inherited Arrhythmia Clinic, Division of Cardiovascular Medicine, Department of Medicine, University of Wisconsin-Madison, Wisconsin.
authors.forename: Kate M
authors.initials: KM
authors.lastname: Orland
authors.affiliation: Cellular and Molecular Arrhythmia Research Program, University of Wisconsin-Madison, Wisonsin.
authors.forename: Sara
authors.initials: S
authors.lastname: Abozeid
authors.affiliation: Cellular and Molecular Arrhythmia Research Program, University of Wisconsin-Madison, Wisonsin.
authors.forename: Nicholas
authors.initials: N
authors.lastname: Fabry
authors.affiliation: University of Wisconsin-Madison Inherited Arrhythmia Clinic, Division of Cardiovascular Medicine, Department of Medicine, University of Wisconsin-Madison, Wisconsin.
authors.forename: Kathleen R
authors.initials: KR
authors.lastname: Maginot
authors.affiliation: Cellular and Molecular Arrhythmia Research Program, University of Wisconsin-Madison, Wisonsin; University of Wisconsin-Madison Inherited Arrhythmia Clinic, Division of Cardiovascular Medicine, Department of Medicine, University of Wisconsin-Madison, Wisconsin.
authors.forename: Craig T
authors.initials: CT
authors.lastname: January
authors.affiliation: Cellular and Molecular Arrhythmia Research Program, University of Wisconsin-Madison, Wisonsin.
authors.forename: Jonathan C
authors.initials: JC
authors.lastname: Makielski
authors.affiliation: Cellular and Molecular Arrhythmia Research Program, University of Wisconsin-Madison, Wisonsin; University of Wisconsin-Madison Inherited Arrhythmia Clinic, Division of Cardiovascular Medicine, Department of Medicine, University of Wisconsin-Madison, Wisconsin. Electronic address: lle@medicine.wisc.edu.
authors.forename: Lee L
authors.initials: LL
authors.lastname: Eckhardt
mesh_terms: D000328:Adult; D002118:Calcium / Q000378:metabolism; D004247:DNA / Q000235:genetics*; D004252:DNA Mutational Analysis; D005260:Female; D020022:Genetic Predisposition to Disease; D006579:Heterozygote; D006801:Humans; D020125:Mutation, Missense; D018408:Patch-Clamp Techniques; D024661:Potassium Channels, Inwardly Rectifying / Q000235:genetics* / Q000378:metabolism; D017180:Tachycardia, Ventricular / Q000235:genetics* / Q000378:metabolism / Q000503:physiopathology; D000098850:Polymorphic Catecholaminergic Ventricular Tachycardia
chemical_list: C489461:Kir2.1 channel; D024661:Potassium Channels, Inwardly Rectifying; D004247:DNA; D002118:Calcium
keywords: Arrhythmia syndrome; CPVT3; Inherited arrhythmia; KCNJ2; Kir2.1; Potassium inward-rectifier channel; Ventricular arrhythmia