Résumé
The ryanodine receptor / Ca2+ release channel (RyR2) is one of the main actors of the excitation-contraction coupling in the heart. Single-point mutations on RyR2 have been associated with catecholaminergic polymorphic ventricular tachycardia (CPVT) and arrhythmogenic right ventricular dysplasia (ARVD) and sudden cardiac death.
In this study, we characterized a novel heterozygous RyR2 mutation found in a 31-year-old female and her mother with syncope at rest and recurrent short-coupled premature ventricular contractions (PVCs) initiating polymorphic ventricular tachycardia (PMVT). Using site-directed mutagenesis, we expressed human RyR2-H29D mutant channels with its stabilizing protein calstabin2 (FKBP12.6). Single channel measurements of RyR2-H29D channels revealed significantly higher open probability (Po) and opening frequency (Fo) at diastolic levels of cytosolic Ca2+ when compared with RyR2-WT channels under non-stress conditions (i.e. in absence of PKA phosphorylation). This leaky phenotype at rest in RyR2-H29D channels was associated with a modest but significant depletion of calstabin2 binding from the RyR2 macromolecular complex when compared to RyR2-WT channels. Interestingly, under stress conditions, RyR2-H29D channels also exhibited a significant higher Po and Fo at diastolic concentrations of Ca2+ while no significant depletion of calstabin2 was observed.
In conclusion, the RyR2-H29D mutation is associated with a clinical phenotype of short-coupled PMVT at rest. In contrast to CPVT-associated RyR2 mutations, RyR2-H29D causes a leaky channel at diastolic levels of Ca2+ under non-stress conditions. Leaky RyR2 may be an under-recognized mechanism for idiopathic PMVT at rest.