title: Na+-dependent SR Ca2+ overload induces arrhythmogenic events in mouse cardiomyocytes with a human CPVT mutation.
abstract: OBJECTIVE
  Mutations in the cardiac ryanodine receptor Ca(2+) release channel, RyR2, underlie catecholaminergic polymorphic ventricular tachycardia (CPVT), an inherited life-threatening arrhythmia. CPVT is triggered by spontaneous RyR2-mediated sarcoplasmic reticulum (SR) Ca(2+) release in response to SR Ca(2+) overload during beta-adrenergic stimulation. However, whether elevated SR Ca(2+) content--in the absence of protein kinase A activation--affects RyR2 function and arrhythmogenesis in CPVT remains elusive.
  
  
  RESULTS
  Isolated murine ventricular myocytes harbouring a human RyR2 mutation (RyR2(R4496C+/-)) associated with CPVT were investigated in the absence and presence of 1 micromol/L JTV-519 (RyR2 stabilizer) followed by 100 micromol/L ouabain intervention to increase cytosolic [Na(+)] and SR Ca(2+) load. Changes in membrane potential and intracellular [Ca(2+)] were monitored with whole-cell patch-clamping and confocal Ca(2+) imaging, respectively. At baseline, action potentials (APs), Ca(2+) transients, fractional SR Ca(2+) release, and SR Ca(2+) load were comparable in wild-type (WT) and RyR2(R4496C+/-) myocytes. Ouabain evoked significant increases in diastolic [Ca(2+)], peak systolic [Ca(2+)], fractional SR Ca(2+) release, and SR Ca(2+) content that were quantitatively similar in WT and RyR2(R4496C+/-) myocytes. Ouabain also induced arrhythmogenic events, i.e. spontaneous Ca(2+) waves, delayed afterdepolarizations and spontaneous APs, in both groups. However, the ouabain-induced increase in the frequency of arrhythmogenic events was dramatically larger in RyR2(R4496C+/-) when compared with WT myocytes. JTV-519 greatly reduced the frequency of ouabain-induced arrhythmogenic events.
  
  
  CONCLUSIONS
  The elevation of SR Ca(2+) load--in the absence of beta-adrenergic stimulation--is sufficient to increase the propensity for triggered arrhythmias in RyR2(R4496C+/-) cardiomyocytes. Stabilization of RyR2 by JTV-519 effectively reduces these triggered arrhythmias.
authors.affiliation: Division of Cardiology, Medical University of Graz, Auenbruggerplatz 15, Graz A-8036, Austria.
authors.forename: Simon
authors.initials: S
authors.lastname: Sedej
authors.forename: Frank R
authors.initials: FR
authors.lastname: Heinzel
authors.forename: Stefanie
authors.initials: S
authors.lastname: Walther
authors.forename: Nataliya
authors.initials: N
authors.lastname: Dybkova
authors.forename: Paulina
authors.initials: P
authors.lastname: Wakula
authors.forename: Jan
authors.initials: J
authors.lastname: Groborz
authors.forename: Phillip
authors.initials: P
authors.lastname: Gronau
authors.forename: Lars S
authors.initials: LS
authors.lastname: Maier
authors.forename: Marc A
authors.initials: MA
authors.lastname: Vos
authors.forename: F Anthony
authors.initials: FA
authors.lastname: Lai
authors.forename: Carlo
authors.initials: C
authors.lastname: Napolitano
authors.forename: Silvia G
authors.initials: SG
authors.lastname: Priori
authors.forename: Jens
authors.initials: J
authors.lastname: Kockskämper
authors.forename: Burkert
authors.initials: B
authors.lastname: Pieske
mesh_terms: D000200:Action Potentials; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling; D002395:Catecholamines / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D055879:Gene Knock-In Techniques; D006801:Humans; D008297:Male; D051379:Mice; D008822:Mice, Transgenic; D018613:Microscopy, Confocal; D009154:Mutation; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000378:metabolism*; D010042:Ouabain / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D010766:Phosphorylation; D019837:Ryanodine Receptor Calcium Release Channel / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors / Q000378:metabolism; D017180:Tachycardia, Ventricular / Q000235:genetics / Q000378:metabolism* / Q000517:prevention & control; D013841:Thiazepines / Q000494:pharmacology; D013997:Time Factors
chemical_list: D002395:Catecholamines; D004791:Enzyme Inhibitors; D019837:Ryanodine Receptor Calcium Release Channel; D013841:Thiazepines; C109183:K201 compound; D010042:Ouabain; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D002118:Calcium