In situ confocal imaging in intact heart reveals stress-induced Ca(2+) release variability in a murine catecholaminergic polymorphic ventricular tachycardia model of type 2 ryanodine receptor(R4496C+/-) mutation.
BACKGROUND
Catecholaminergic polymorphic ventricular tachycardia is directly linked to mutations in proteins (eg, type 2 ryanodine receptor [RyR2](R4496C)) responsible for intracellular Ca(2+) homeostasis in the heart. However, the mechanism of Ca(2+) release dysfunction underlying catecholaminergic polymorphic ventricular tachycardia has only been investigated in isolated cells but not in the in situ undisrupted myocardium.


RESULTS
We investigated in situ myocyte Ca(2+) dynamics in intact Langendorff-perfused hearts (ex vivo) from wild-type and RyR2(R4496C+/-) mice using laser scanning confocal microscopy. We found that myocytes from both wild-type and RyR2(R4496C+/-) hearts displayed uniform, synchronized Ca(2+) transients. Ca(2+) transients from beat to beat were comparable in amplitude with identical activation and decay kinetics in wild-type and RyR2(R4496C+/-) hearts, suggesting that excitation-contraction coupling between the sarcolemmal Ca(2+) channels and mutated RyR2(R4496C+/-) channels remains intact under baseline resting conditions. On adrenergic stimulation, RyR2(R4496C+/-) hearts exhibited a high degree of Ca(2+) release variability. The varied pattern of Ca(2+) release was absent in single isolated myocytes, independent of cell cycle length, synchronized among neighboring myocytes, and correlated with catecholaminergic polymorphic ventricular tachycardia. A similar pattern of action potential variability, which was synchronized among neighboring myocytes, was also revealed under adrenergic stress in intact hearts but not in isolated myocytes.


CONCLUSIONS
Our studies using an in situ confocal imaging approach suggest that mutated RyR2s are functionally normal at rest but display a high degree of Ca(2+) release variability on intense adrenergic stimulation. Ca(2+) release variability is a Ca(2+) release abnormality, resulting from electric defects rather than the failure of the Ca(2+) release response to action potentials in mutated ventricular myocytes. Our data provide important insights into Ca(2+) release and electric dysfunction in an established model of catecholaminergic polymorphic ventricular tachycardia.
Division of Cardiovascular Medicine, Department of Internal Medicine, University of Iowa Carver College of Medicine, Iowa City, IA 52242, USA.
Biyi
B
Chen
Ang
A
Guo
Zhan
Z
Gao
Sheng
S
Wei
Yu-Ping
YP
Xie
S R Wayne
SR
Chen
Mark E
ME
Anderson
Long-Sheng
LS
Song
D000200:Action Potentials; D000322:Adrenergic Agonists / Q000494:pharmacology; D000818:Animals; D020013:Calcium Signaling / Q000187:drug effects; D004195:Disease Models, Animal; D004562:Electrocardiography; D004837:Epinephrine / Q000494:pharmacology; D056966:Excitation Contraction Coupling; D020022:Genetic Predisposition to Disease; D066298:In Vitro Techniques; D007700:Kinetics; D051379:Mice; D008817:Mice, Mutant Strains; D018613:Microscopy, Confocal; D009154:Mutation; D009200:Myocardial Contraction; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000378:metabolism*; D010477:Perfusion; D010641:Phenotype; D019837:Ryanodine Receptor Calcium Release Channel / Q000235:genetics*; D017180:Tachycardia, Ventricular / Q000235:genetics / Q000378:metabolism* / Q000503:physiopathology; D000098850:Polymorphic Catecholaminergic Ventricular Tachycardia
D000322:Adrenergic Agonists; D019837:Ryanodine Receptor Calcium Release Channel; D004837:Epinephrine