Phospholamban knockout breaks arrhythmogenic Ca2+ waves and suppresses catecholaminergic polymorphic ventricular tachycardia in mice

Abstract

RATIONALE:: Phospholamban (PLN) is an inhibitor of cardiac sarco(endo)plasmic reticulum Ca ATPase. PLN knockout (PLN-KO) enhances sarcoplasmic reticulum Ca load and Ca leak. Conversely, PLN-KO accelerates Ca sequestration and aborts arrhythmogenic spontaneous Ca waves (SCWs). An important question is whether these seemingly paradoxical effects of PLN-KO exacerbate or protect against Ca-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 VT. METHODS AND RESULTS:: We generated a PLN-deficient, RyR2-mutant mouse model (PLN/RyR2-R4496C) by crossbreeding PLN-KO mice with catecholaminergic polymorphic VT-associated RyR2-R4496C mutant mice. Ca imaging and patch-clamp recording revealed cell-wide propagating SCWs and triggered activities in RyR2-R4496C ventricular myocytes during sarcoplasmic reticulum Ca overload. PLN-KO fragmented these cell-wide SCWs into mini-waves and Ca sparks and suppressed the triggered activities evoked by sarcoplasmic reticulum Ca overload. Importantly, these effects of PLN-KO were reverted by partially inhibiting sarco(endo)plasmic reticulum Ca ATPase with 2,5-di-tert- butylhydroquinone. 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 sarcoplasmic reticulum Ca leak, PLN-KO suppresses triggered activities and stress-induced VTs in a mouse model of catecholaminergic polymorphic VT. These data suggest that breaking up cell-wide propagating SCWs by enhancing Ca sequestration represents an effective approach for suppressing Ca-triggered arrhythmias. © 2013 American Heart Association, Inc.