Elevated local [Ca2+] and CaMKII promote spontaneous Ca2+ release in ankyrin-B-deficient hearts

Cardiovasc Res. 2016 Aug 1;111(3):287-94. doi: 10.1093/cvr/cvw093. Epub 2016 Apr 30.

Abstract

Aims: Loss-of-function mutations in the cytoskeletal protein ankyrin-B (AnkB) cause ventricular tachyarrhythmias in humans. Previously, we found that a larger fraction of the sarcoplasmic reticulum (SR) Ca(2+) leak occurs through Ca(2+) sparks in AnkB-deficient (AnkB(+/-)) mice, which may contribute to arrhythmogenicity via Ca(2+) waves. Here, we investigated the mechanisms responsible for increased Ca(2+) spark frequency in AnkB(+/-) hearts.

Methods and results: Using immunoblots and phospho-specific antibodies, we found that phosphorylation of ryanodine receptors (RyRs) by CaMKII is enhanced in AnkB(+/-) hearts. In contrast, the PKA-mediated RyR phosphorylation was comparable in AnkB(+/-) and wild-type (WT) mice. CaMKII inhibition greatly reduced Ca(2+) spark frequency in myocytes from AnkB(+/-) mice but had little effect in the WT. Global activities of the major phosphatases PP1 and PP2A were similar in AnkB(+/-) and WT hearts, while CaMKII autophosphorylation, a marker of CaMKII activation, was increased in AnkB(+/-) hearts. Thus, CaMKII-dependent RyR hyperphosphorylation in AnkB(+/-) hearts is caused by augmented CaMKII activity. Intriguingly, CaMKII activation is limited to the sarcolemma-SR junctions since non-junctional CaMKII targets (phospholamban, HDAC4) are not hyperphosphorylated in AnkB(+/-) myocytes. This local CaMKII activation may be the consequence of elevated [Ca(2+)] in the junctional cleft caused by reduced Na(+)/Ca(2+) exchange activity. Indeed, using the RyR-targeted Ca(2+) sensor GCaMP2.2-FBKP12.6, we found that local junctional [Ca(2+)] is significantly elevated in AnkB(+/-) myocytes.

Conclusions: The increased incidence of pro-arrhythmogenic Ca(2+) sparks and waves in AnkB(+/-) hearts is due to enhanced CaMKII-mediated RyR phosphorylation, which is caused by higher junctional [Ca(2+)] and consequent local CaMKII activation.

Keywords: Ankyrin-B; Ca2+ sparks; CaMKII; Junctions; Local Ca2+ concentration.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Ankyrins / deficiency*
  • Ankyrins / genetics
  • Arrhythmias, Cardiac / enzymology
  • Arrhythmias, Cardiac / genetics
  • Arrhythmias, Cardiac / physiopathology
  • Biosensing Techniques
  • Calcium / metabolism*
  • Calcium Signaling*
  • Calcium-Calmodulin-Dependent Protein Kinase Type 2 / metabolism*
  • Enzyme Activation
  • Genotype
  • Intercellular Junctions / enzymology
  • Membrane Potentials
  • Mice, Knockout
  • Myocytes, Cardiac / enzymology*
  • Phenotype
  • Phosphorylation
  • Ryanodine Receptor Calcium Release Channel / metabolism
  • Sarcoplasmic Reticulum / enzymology
  • Time Factors
  • Up-Regulation

Substances

  • Ank2 protein, mouse
  • Ankyrins
  • Ryanodine Receptor Calcium Release Channel
  • Calcium-Calmodulin-Dependent Protein Kinase Type 2
  • Calcium