Increased sarcoplasmic reticulum calcium leak but unaltered contractility by acute CaMKII overexpression in isolated rabbit cardiac myocytes

Michael Kohlhaas, Tong Zhang, Tim Seidler, Darya Zibrova, Nataliya Dybkova, Astrid Steen, Stefan Wagner, Lu Chen, Joan Heller Brown, Donald M Bers, Lars S. Maier

Research output: Contribution to journalArticlepeer-review

160 Scopus citations


The predominant cardiac Ca 2+/calmodulin-dependent protein kinase (CaMK) is CaMKIIδ. Here we acutely overexpress CaMKIIδ C using adenovirus-mediated gene transfer in adult rabbit ventricular myocytes. This circumvents confounding adaptive effects in CaMKIIδ C transgenic mice. CaMKIIδ C protein expression and activation state (autophosphorylation) were increased 5- to 6-fold. Basal twitch contraction amplitude and kinetics (1 Hz) were not changed in CaMKIIδ C versus LacZ expressing myocytes. However, the contraction-frequency relationship was more negative, frequency-dependent acceleration of relaxation was enhanced (τ 0.5Hz3Hz=2.14±0.10 versus 1.87±0.10), and peak Ca 2+ current (I Ca) was increased by 31% (-7.1±0.5 versus -5.4±0.5 pA/pF, P<0.05). Ca 2+ transient amplitude was not significantly reduced (-27%, P=0.22), despite dramatically reduced sarcoplasmic reticulum (SR) Ca 2+ content (41%; P<0.05). Thus fractional SR Ca 2+ release was increased by 60% (P<0.05). Diastolic SR Ca 2+ leak assessed by Ca 2+ spark frequency (normalized to SR Ca 2+ load) was increased by 88% in CaMKIIδ C versus LacZ myocytes (P<0.05; in an multiplicity-of-infection-dependent manner), an effect blocked by CaMKII inhibitors KN-93 and autocamtide-2-related inhibitory peptide. This enhanced SR Ca 2+ leak may explain reduced SR Ca 2+ content, despite measured levels of SR Ca 2+-ATPaSe and Na +/Ca 2+ exchange expression and function being unaltered. Ryanodine receptor (RyR) phosphorylation in CaMKIIδ C myocytes was increased at both Ser2809 and Ser2815, but FKBP12.6 coimmunoprecipitation with RyR was unaltered. This shows for the first time that acute CaMKIIδ C overexpression alters RyR function, leading to enhanced R Ca 2+ leak and reduced SR Ca 2+ content but without reducing twitch contraction and Ca 2+ transients. We conclude that this is attributable to concomitant enhancement of fractional SR Ca 2+ release in CaMKIIδ C myocytes (ie, CaMKII-dependent enhancement of RyR Ca 2+ sensitivity during diastole and systole) and increased I Ca.

Original languageEnglish (US)
Pages (from-to)235-244
Number of pages10
JournalCirculation Research
Issue number2
StatePublished - Feb 2006
Externally publishedYes


  • Calcium
  • CaMKII
  • Excitation-contraction coupling
  • Sarcoplasmic reticulum

ASJC Scopus subject areas

  • Physiology
  • Cardiology and Cardiovascular Medicine


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