Phospholamban Knockout Breaks Arrhythmogenic Ca2+ Waves and Suppresses Catecholaminergic Polymorphic Ventricular Tachycardia in Mice
Rationale: Phospholamban (PLN) is an inhibitor of cardiac sarco(endo)plasmic reticulum Ca2+ ATPase (SERCA2a). PLN knockout (PLN-KO) enhances sarcoplasmic reticulum (SR) Ca2+ load and Ca2+ leak. Conversely, PLN-KO accelerates Ca2+ sequestration and aborts arrhythmogenic spontaneous Ca2+ waves (SCWs). An important question is whether these seemingly paradoxical effects of PLN-KO exacerbate or protect against Ca2+-triggered arrhythmias.
Objective: We investigate the impact of PLN-KO on SCWs, triggered activities, and stress-induced ventricular tachyarrhythmias (VTs) in a mouse model of cardiac ryanodine receptor (RyR2)-linked catecholaminergic polymorphic ventricular tachycardia (CPVT).
Methods and Results:We generated a PLN-deficient, RyR2 mutant mouse model (PLN-/-/RyR2-R4496C+/-) by crossbreeding PLN-KO mice with CPVT-associated RyR2-R4496C mutant mice. Ca2+ imaging and patch-clamp recording revealed cell-wide propagating SCWs and triggered activities in RyR2-R4496C+/- ventricular myocytes during SR Ca2+ overload. PLN-KO fragmented these cell-wide SCWs into mini-waves and Ca2+ sparks, and suppressed triggered activities evoked by SR Ca2+ overload. Importantly, these effects of PLN-KO were reverted by partially inhibiting SERCA2a with 2,5-Di-tert-butylhydroquinone (tBHQ). However, Bay K, caffeine, or Li+ failed to convert mini-waves to cell-wide SCWs in PLN-/-/RyR2-R4496C+/- ventricular myocytes. Furthermore, ECG analysis showed that PLN-KO mice are not susceptible to stress-induced VTs. On the contrary, PLN-KO protected RyR2-R4496C mutant mice from stress-induced VTs.
Conclusions: Our results demonstrate that despite severe SR Ca2+ leak, PLN-KO suppresses triggered activities and stress-induced VTs in a mouse model of CPVT. These data suggest that breaking up cell-wide propagating SCWs by enhancing Ca2+ sequestration represents an effective approach for suppressing Ca2+-triggered arrhythmias.
- Calcium waves
- Calcium leak
- Calcium-triggered Arrhythmias
- sarcoplasmic reticulum
- sarcoplasmic reticulum Ca2+-ATPase
- ryanodine receptor
- calcium sparks
- Received April 25, 2013.
- Revision received July 10, 2013.
- Accepted July 15, 2013.