Late INa increases diastolic SR-Ca2+-leak in atrial myocardium by activating PKA and CaMKII

Cardiovasc Res. 2015 Jul 1;107(1):184-96. doi: 10.1093/cvr/cvv153. Epub 2015 May 18.


Aims: Enhanced cardiac late Na current (late INa) and increased sarcoplasmic reticulum (SR)-Ca(2+)-leak are both highly arrhythmogenic. This study seeks to identify signalling pathways interconnecting late INa and SR-Ca(2+)-leak in atrial cardiomyocytes (CMs).

Methods and results: In murine atrial CMs, SR-Ca(2+)-leak was increased by the late INa enhancer Anemonia sulcata toxin II (ATX-II). An inhibition of Ca(2+)/calmodulin-dependent protein kinase II (Autocamide-2-related inhibitory peptide), protein kinase A (H89), or late INa (Ranolazine or Tetrodotoxin) all prevented ATX-II-dependent SR-Ca(2+)-leak. The SR-Ca(2+)-leak induction by ATX-II was not detected when either the Na(+)/Ca(2+) exchanger was inhibited (KBR) or in CaMKIIδc-knockout mice. FRET measurements revealed increased cAMP levels upon ATX-II stimulation, which could be prevented by inhibition of adenylyl cyclases (ACs) 5 and 6 (NKY 80) but not by inhibition of phosphodiesterases (IBMX), suggesting PKA activation via an AC-dependent increase of cAMP levels. Western blots showed late INa-dependent hyperphosphorylation of CaMKII as well as PKA target sites at ryanodine receptor type-2 (-S2814 and -S2808) and phospholamban (-Thr17, -S16). Enhancement of late INa did not alter Ca(2+)-transient amplitude or SR-Ca(2+)-load. However, upon late INa activation and simultaneous CaMKII inhibition, Ca(2+)-transient amplitude and SR-Ca(2+)-load were increased, whereas PKA inhibition reduced Ca(2+)-transient amplitude and load and additionally slowed Ca(2+) elimination. In atrial CMs from patients with atrial fibrillation, inhibition of late INa, CaMKII, or PKA reduced the SR-Ca(2+)-leak.

Conclusion: Late INa exerts distinct effects on Ca(2+) homeostasis in atrial myocardium through activation of CaMKII and PKA. Inhibition of late INa represents a potential approach to attenuate CaMKII activation and decreases SR-Ca(2+)-leak in atrial rhythm disorders. The interconnection with the cAMP/PKA system further increases the antiarrhythmic potential of late INa inhibition.

Keywords: Antiarrhythmic drugs; Atrial fibrillation; Late Na current; Protein kinases; SR-Ca2+-leak.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Atrial Fibrillation / etiology
  • Calcium / metabolism*
  • Calcium-Calmodulin-Dependent Protein Kinase Type 2 / metabolism*
  • Cyclic AMP / analysis
  • Cyclic AMP-Dependent Protein Kinases / antagonists & inhibitors
  • Cyclic AMP-Dependent Protein Kinases / physiology*
  • Diastole / physiology*
  • Enzyme Activation
  • Heart Atria / metabolism*
  • Humans
  • Mice
  • Phosphorylation
  • Sarcoplasmic Reticulum / metabolism*
  • Sodium Channels / physiology*


  • Sodium Channels
  • Cyclic AMP
  • Cyclic AMP-Dependent Protein Kinases
  • Calcium-Calmodulin-Dependent Protein Kinase Type 2
  • Calcium