title: Phospholamban knockout breaks arrhythmogenic Ca²⁺ waves and suppresses catecholaminergic polymorphic ventricular tachycardia in mice.
abstract: BACKGROUND
  Phospholamban (PLN) is an inhibitor of cardiac sarco(endo)plasmic reticulum Ca²⁺ ATPase. PLN knockout (PLN-KO) enhances sarcoplasmic reticulum 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 VT.
  
  
  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. Ca²⁺ imaging and patch-clamp recording revealed cell-wide propagating SCWs and triggered activities in RyR2-R4496C+/- ventricular myocytes during sarcoplasmic reticulum Ca²⁺ overload. PLN-KO fragmented these cell-wide SCWs into mini-waves and Ca²⁺ sparks and suppressed the triggered activities evoked by sarcoplasmic reticulum Ca²⁺ overload. Importantly, these effects of PLN-KO were reverted by partially inhibiting sarco(endo)plasmic reticulum Ca²⁺ 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 Ca²⁺ 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 Ca²⁺ sequestration represents an effective approach for suppressing Ca²⁺-triggered arrhythmias.
authors.affiliation: Department of Physiology and Pharmacology, Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, Alberta, Canada.
authors.forename: Yunlong
authors.initials: Y
authors.lastname: Bai
authors.forename: Peter P
authors.initials: PP
authors.lastname: Jones
authors.forename: Jiqing
authors.initials: J
authors.lastname: Guo
authors.forename: Xiaowei
authors.initials: X
authors.lastname: Zhong
authors.forename: Robert B
authors.initials: RB
authors.lastname: Clark
authors.forename: Qiang
authors.initials: Q
authors.lastname: Zhou
authors.forename: Ruiwu
authors.initials: R
authors.lastname: Wang
authors.forename: Alexander
authors.initials: A
authors.lastname: Vallmitjana
authors.forename: Raul
authors.initials: R
authors.lastname: Benitez
authors.forename: Leif
authors.initials: L
authors.lastname: Hove-Madsen
authors.forename: Lisa
authors.initials: L
authors.lastname: Semeniuk
authors.forename: Ang
authors.initials: A
authors.lastname: Guo
authors.forename: Long-Sheng
authors.initials: LS
authors.lastname: Song
authors.forename: Henry J
authors.initials: HJ
authors.lastname: Duff
authors.forename: S R Wayne
authors.initials: SR
authors.lastname: Chen
mesh_terms: D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D002135:Calcium-Binding Proteins / Q000172:deficiency* / Q000235:genetics / Q000502:physiology; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D002478:Cells, Cultured / Q000187:drug effects / Q000502:physiology; D004195:Disease Models, Animal; D004562:Electrocardiography; D006873:Hydroquinones / Q000494:pharmacology; D007545:Isoproterenol / Q000494:pharmacology; D018021:Lithium Chloride / Q000494:pharmacology; D051379:Mice; D018345:Mice, Knockout; D020125:Mutation, Missense; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000201:enzymology / Q000502:physiology; D018408:Patch-Clamp Techniques; D019837:Ryanodine Receptor Calcium Release Channel / Q000172:deficiency / Q000235:genetics / Q000502:physiology; D012519:Sarcoplasmic Reticulum / Q000201:enzymology / Q000502:physiology; D017180:Tachycardia, Ventricular / Q000000981:diagnostic imaging / Q000503:physiopathology / Q000517:prevention & control*; D014463:Ultrasonography; D000099211:Phospholamban
chemical_list: D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D002110:Caffeine; D002135:Calcium-Binding Proteins; D000252:Calcium-Transporting ATPases; D006873:Hydroquinones; D007545:Isoproterenol; D018021:Lithium Chloride; D019837:Ryanodine Receptor Calcium Release Channel; D000099211:Phospholamban; C019359:2,5-di-tert-butylhydroquinone
keywords: Ca2+ leak; Ca2+ waves; Ca2+-triggered arrhythmias; phospholamban; ryanodine receptor calcium release channel; sarcoplasmic reticulum