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 0.5Hz/τ 3Hz=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 language||English (US)|
|Number of pages||10|
|State||Published - Feb 2006|
- Excitation-contraction coupling
- Sarcoplasmic reticulum
ASJC Scopus subject areas
- Cardiology and Cardiovascular Medicine