Abstract 13512: Mutated Ryanodine Receptors are Not Leaky at Rest, but Exhibit High Ca2+ Release Variability under Stress in a Mouse Model of CPVT
Catecholaminergic polymorphic ventricular tachycardia (CPVT) is directly linked to mutations in proteins (e.g., RyR2R4496C) responsible for intracellular Ca2+ homeostasis in the heart. However, the potential relationship between CPVT and Ca2+ release dysfunction has only been documented in isolated cells but not in in situ undisrupted myocardium. We investigated in situ myocyte Ca2+ dynamics in intact Langendorff perfused hearts (ex vivo) of wildtype (WT) and RyR2R4496C+/- mice, using laser scanning confocal microscopy, in comparison to data from freshly isolated myocytes (in vitro). We found spontaneous Ca2+ sparks during diastolic period under sinus rhythm were 40-fold less frequent in undisrupted myocytes from intact WT hearts, comparing to that from isolated myocytes. Furthermore, spontaneous Ca2+ sparks or waves were indistinguishable in ex vivo WT and RyR2R4496C+/- hearts in the absence of adrenergic stress, suggesting physiologically-coupled myocytes carrying CPVT mutants are not leaky at rest, in shape contrast to findings from isolated myocytes. More interestingly, upon adrenergic stimulation RyR2R4496C hearts exhibited a high degree of Ca2+ release variability (CRV) under ex vivo, but not in vitro conditions. The varied pattern of Ca2+ release was independent of cell cycle length and synchronized among neighboring myocytes. Lastly, we demonstrated that CRV was correlated with CPVT occurrence documented on ECG. In conclusion, our studies using the in situ confocal imaging approach provide compelling evidence that mutated RyR2s are functionally normal at rest, but display high degree of CRV upon intense adrenergic stimulation. CRV is an integrated, tissue level response of mutated myocytes to adrenergic stress. Our data provide important insights of Ca2+ release dysfunction in an established model of CPVT.
- © 2011 by American Heart Association, Inc.