title: Increased Ca2+ sensitivity of the ryanodine receptor mutant RyR2R4496C underlies catecholaminergic polymorphic ventricular tachycardia.
abstract: Cardiac ryanodine receptor (RyR2) mutations are associated with autosomal dominant catecholaminergic polymorphic ventricular tachycardia, suggesting that alterations in Ca(2+) handling underlie this disease. Here we analyze the underlying Ca(2+) release defect that leads to arrhythmia in cardiomyocytes isolated from heterozygous knock-in mice carrying the RyR2(R4496C) mutation. RyR2(R4496C-/-) littermates (wild type) were used as controls. [Ca(2+)](i) transients were obtained by field stimulation in fluo-3-loaded cardiomyocytes and viewed using confocal microscopy. In our basal recording conditions (2-Hz stimulation rate), [Ca(2+)](i) transients and sarcoplasmic reticulum Ca(2+) load were similar in wild-type and RyR2(R4496C) cells. However, paced RyR2(R4496C) ventricular myocytes presented abnormal Ca(2+) release during the diastolic period, viewed as Ca(2+) waves, consistent with the occurrence of delayed afterdepolarizations. The occurrence of this abnormal Ca(2+) release was enhanced at faster stimulation rates and by beta-adrenergic stimulation, which also induced triggered activity. Spontaneous Ca(2+) sparks were more frequent in RyR2(R4496C) myocytes, indicating increased RyR2(R4496C) activity. When permeabilized cells were exposed to different cytosolic [Ca(2+)](i), RyR2(R4496C) showed a dramatic increase in Ca(2+) sensitivity. Isoproterenol increased [Ca(2+)](i) transient amplitude and Ca(2+) spark frequency to the same extent in wild-type and RyR2(R4496C) cells, indicating that the beta-adrenergic sensitivity of RyR2(R4496C) cells remained unaltered. This effect was independent of protein expression variations because no difference was found in the total or phosphorylated RyR2 expression levels. In conclusion, the arrhythmogenic potential of the RyR2(R4496C) mutation is attributable to the increased Ca(2+) sensitivity of RyR2(R4496C), which induces diastolic Ca(2+) release and lowers the threshold for triggered activity.
authors.affiliation: Institut National de la Santé et de la Recherche Médicale, U637, Université de Montpellier, Montpellier, France.
authors.forename: María
authors.initials: M
authors.lastname: Fernández-Velasco
authors.forename: Angélica
authors.initials: A
authors.lastname: Rueda
authors.forename: Nicoletta
authors.initials: N
authors.lastname: Rizzi
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Benitah
authors.forename: Barbara
authors.initials: B
authors.lastname: Colombi
authors.forename: Carlo
authors.initials: C
authors.lastname: Napolitano
authors.forename: Silvia G
authors.initials: SG
authors.lastname: Priori
authors.forename: Sylvain
authors.initials: S
authors.lastname: Richard
authors.forename: Ana María
authors.initials: AM
authors.lastname: Gómez
mesh_terms: D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D020013:Calcium Signaling / Q000187:drug effects; D002304:Cardiac Pacing, Artificial; D002395:Catecholamines / Q000378:metabolism*; D005260:Female; D007545:Isoproterenol / Q000494:pharmacology; D008297:Male; D008564:Membrane Potentials; D051379:Mice; D008822:Mice, Transgenic; D018613:Microscopy, Confocal; D009154:Mutation; D009200:Myocardial Contraction / Q000187:drug effects; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000378:metabolism*; D010766:Phosphorylation; D019837:Ryanodine Receptor Calcium Release Channel / Q000235:genetics / Q000378:metabolism*; D012519:Sarcoplasmic Reticulum / Q000378:metabolism; D017180:Tachycardia, Ventricular / Q000235:genetics / Q000378:metabolism* / Q000503:physiopathology; D013997:Time Factors
chemical_list: D000318:Adrenergic beta-Agonists; D002395:Catecholamines; D019837:Ryanodine Receptor Calcium Release Channel; D002110:Caffeine; D007545:Isoproterenol