Paradoxical effect of increased diastolic Ca(2+) release and decreased sinoatrial node activity in a mouse model of catecholaminergic polymorphic ventricular tachycardia.
BACKGROUND
Catecholaminergic polymorphic ventricular tachycardia is characterized by stress-triggered syncope and sudden death. Patients with catecholaminergic polymorphic ventricular tachycardia manifest sinoatrial node (SAN) dysfunction, the mechanisms of which remain unexplored.


RESULTS
We investigated SAN [Ca(2+)](i) handling in mice carrying the catecholaminergic polymorphic ventricular tachycardia-linked mutation of ryanodine receptor (RyR2(R4496C)) and their wild-type (WT) littermates. In vivo telemetric recordings showed impaired SAN automaticity in RyR2(R4496C) mice after isoproterenol injection, analogous to what was observed in catecholaminergic polymorphic ventricular tachycardia patients after exercise. Pacemaker activity was explored by measuring spontaneous [Ca(2+)](i) transients in SAN cells within the intact SAN by confocal microscopy. RyR2(R4496C) SAN presented significantly slower pacemaker activity and impaired chronotropic response under β-adrenergic stimulation, accompanied by the appearance of pauses (in spontaneous [Ca(2+)](i) transients and action potentials) in 75% of the cases. Ca(2+) spark frequency was increased by 2-fold in RyR2(R4496C) SAN. Whole-cell patch-clamp experiments performed on isolated RyR2(R4496C) SAN cells showed that L-type Ca(2+) current (I(Ca,L)) density was reduced by ≈50%, an effect blunted by internal Ca(2+) buffering. Isoproterenol dramatically increased the frequency of Ca(2+) sparks and waves by ≈5 and ≈10-fold, respectively. Interestingly, the sarcoplasmic reticulum Ca(2+) content was significantly reduced in RyR2(R4496C) SAN cells in the presence of isoproterenol, which may contribute to stopping the "Ca(2+) clock" rhythm generation, originating SAN pauses.


CONCLUSIONS
The increased activity of RyR2(R4496C) in SAN leads to an unanticipated decrease in SAN automaticity by a Ca(2+)-dependent decrease of I(Ca,L) and sarcoplasmic reticulum Ca(2+) depletion during diastole, identifying subcellular pathophysiological alterations contributing to the SAN dysfunction in catecholaminergic polymorphic ventricular tachycardia patients.
INSERM U-769, Faculté de Pharmacie, Université de Paris Sud, 92296 Châtenay-Malabry, France.
Patricia
P
Neco
Angelo G
AG
Torrente
Pietro
P
Mesirca
Esther
E
Zorio
Nian
N
Liu
Silvia G
SG
Priori
Carlo
C
Napolitano
Sylvain
S
Richard
Jean-Pierre
JP
Benitah
Matteo E
ME
Mangoni
Ana María
AM
Gómez
D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000328:Adult; D000368:Aged; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects; D004195:Disease Models, Animal; D015444:Exercise; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008817:Mice, Mutant Strains; D008875:Middle Aged; D009154:Mutation / Q000235:genetics*; D018408:Patch-Clamp Techniques; D019837:Ryanodine Receptor Calcium Release Channel / Q000235:genetics* / Q000378:metabolism; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism*; D012849:Sinoatrial Node / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology*; D017180:Tachycardia, Ventricular / Q000235:genetics / Q000378:metabolism* / Q000503:physiopathology*; D000098850:Polymorphic Catecholaminergic Ventricular Tachycardia
D000318:Adrenergic beta-Agonists; D019837:Ryanodine Receptor Calcium Release Channel; D007545:Isoproterenol; D002118:Calcium