title: Arrhythmogenesis in catecholaminergic polymorphic ventricular tachycardia: insights from a RyR2 R4496C knock-in mouse model.
abstract: Catecholaminergic polymorphic ventricular tachycardia (CPVT) is an inherited disease characterized by life threatening arrhythmias and mutations in the gene encoding the ryanodine receptor (RyR2). Disagreement exists on whether (1) RyR2 mutations induce abnormal calcium transients in the absence of adrenergic stimulation; (2) decreased affinity of mutant RyR2 for FKBP12.6 causes CPVT; (3) K201 prevent arrhythmias by normalizing the FKBP12.6-RyR2 binding. We studied ventricular myocytes isolated from wild-type (WT) and knock-in mice harboring the R4496C mutation (RyR2(R4496C+/-)). Pacing protocols did not elicit delayed afterdepolarizations (DADs) (n=20) in WT but induced DADs in 21 of 33 (63%) RyR2(R4496C+/-) myocytes (P=0.001). Superfusion with isoproterenol (30 nmol/L) induced small DADs (45%) and no triggered activity in WT myocytes, whereas it elicited DADs in 87% and triggered activity in 60% of RyR2(R4496C+/-) myocytes (P=0.001). DADs and triggered activity were abolished by ryanodine (10 micromol/L) but not by K201 (1 micromol/L or 10 micromol/L). In vivo administration of K201 failed to prevent induction of polymorphic ventricular tachycardia (VT) in RyR2(R4496C+/-) mice. Measurement of the FKBP12.6/RyR2 ratio in the heavy sarcoplasmic reticulum membrane showed normal RyR2-FKBP12.6 interaction both in WT and RyR2(R4496C+/-) either before and after treatment with caffeine and epinephrine. We suggest that (1) triggered activity is the likely arrhythmogenic mechanism of CPVT; (2) K201 fails to prevent DADs in RyR2(R4496C+/-) myocytes and ventricular arrhythmias in RyR2(R4496C+/-) mice; and (3) RyR2-FKBP12.6 interaction in RyR2(R4496C+/-) is identical to that of WT both before and after epinephrine and caffeine, thus suggesting that it is unlikely that the R4496C mutation interferes with the RyR2/FKBP12.6 complex.
authors.affiliation: Molecular Cardiology, IRCCS Fondazione Salvatore Maugeri, Pavia, Italy.
authors.forename: Nian
authors.initials: N
authors.lastname: Liu
authors.forename: Barbara
authors.initials: B
authors.lastname: Colombi
authors.forename: Mirella
authors.initials: M
authors.lastname: Memmi
authors.forename: Spyros
authors.initials: S
authors.lastname: Zissimopoulos
authors.forename: Nicoletta
authors.initials: N
authors.lastname: Rizzi
authors.forename: Sara
authors.initials: S
authors.lastname: Negri
authors.forename: Marcello
authors.initials: M
authors.lastname: Imbriani
authors.forename: Carlo
authors.initials: C
authors.lastname: Napolitano
authors.forename: F Anthony
authors.initials: FA
authors.lastname: Lai
authors.forename: Silvia G
authors.initials: SG
authors.lastname: Priori
mesh_terms: D000818:Animals; D001145:Arrhythmias, Cardiac / Q000209:etiology*; D002110:Caffeine / Q000494:pharmacology; D002478:Cells, Cultured; D004837:Epinephrine / Q000494:pharmacology; D008564:Membrane Potentials; D051379:Mice; D008817:Mice, Mutant Strains; D020125:Mutation, Missense; D032383:Myocytes, Cardiac / Q000502:physiology; D011485:Protein Binding; D012433:Ryanodine / Q000494:pharmacology; D019837:Ryanodine Receptor Calcium Release Channel / Q000235:genetics* / Q000378:metabolism; D017180:Tachycardia, Ventricular / Q000209:etiology*; D022021:Tacrolimus Binding Proteins / Q000378:metabolism; D013841:Thiazepines / Q000494:pharmacology
chemical_list: D002110:Caffeine; D004837:Epinephrine; D012433:Ryanodine; D019837:Ryanodine Receptor Calcium Release Channel; D022021:Tacrolimus Binding Proteins; D013841:Thiazepines; C509259:FKBP1B protein, mouse; C109183:K201 compound