title: Late INa increases diastolic SR-Ca2+-leak in atrial myocardium by activating PKA and CaMKII.
abstract: OBJECTIVE
  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).
  
  
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Klinik für Kardiologie und Pneumologie/Herzzentrum, Georg-August-Universität Göttingen, Robert-Koch-Str. 40, 37075 Göttingen, Germany.
authors.forename: Thomas H
authors.initials: TH
authors.lastname: Fischer
authors.affiliation: Klinik für Kardiologie und Pneumologie/Herzzentrum, Georg-August-Universität Göttingen, Robert-Koch-Str. 40, 37075 Göttingen, Germany.
authors.forename: Jonas
authors.initials: J
authors.lastname: Herting
authors.affiliation: Klinik für Kardiologie und Pneumologie/Herzzentrum, Georg-August-Universität Göttingen, Robert-Koch-Str. 40, 37075 Göttingen, Germany.
authors.forename: Fleur E
authors.initials: FE
authors.lastname: Mason
authors.affiliation: Klinik für Kardiologie und Pneumologie/Herzzentrum, Georg-August-Universität Göttingen, Robert-Koch-Str. 40, 37075 Göttingen, Germany.
authors.forename: Nico
authors.initials: N
authors.lastname: Hartmann
authors.affiliation: Klinik für Kardiologie und Pneumologie/Herzzentrum, Georg-August-Universität Göttingen, Robert-Koch-Str. 40, 37075 Göttingen, Germany.
authors.forename: Saera
authors.initials: S
authors.lastname: Watanabe
authors.affiliation: Klinik für Kardiologie und Pneumologie/Herzzentrum, Georg-August-Universität Göttingen, Robert-Koch-Str. 40, 37075 Göttingen, Germany DZHK (German Center for Cardiovascular Research), partner site Göttingen, Göttingen, Germany.
authors.forename: Viacheslav O
authors.initials: VO
authors.lastname: Nikolaev
authors.affiliation: Klinik für Kardiologie und Pneumologie/Herzzentrum, Georg-August-Universität Göttingen, Robert-Koch-Str. 40, 37075 Göttingen, Germany.
authors.forename: Julia U
authors.initials: JU
authors.lastname: Sprenger
authors.affiliation: Department of Biology, Cardiovascular, Therapeutic Area, Gilead Sciences, Foster City, CA, USA.
authors.forename: Peidong
authors.initials: P
authors.lastname: Fan
authors.affiliation: Department of Biology, Cardiovascular, Therapeutic Area, Gilead Sciences, Foster City, CA, USA.
authors.forename: Lina
authors.initials: L
authors.lastname: Yao
authors.affiliation: Klinik für Thorax-, Herz-, Gefäßchirurgie/Herzzentrum, Georg-August-Universität Göttingen, Göttingen, Germany.
authors.forename: Aron-Frederik
authors.initials: AF
authors.lastname: Popov
authors.affiliation: Klinik für Thorax-, Herz-, Gefäßchirurgie/Herzzentrum, Georg-August-Universität Göttingen, Göttingen, Germany.
authors.forename: Bernhard C
authors.initials: BC
authors.lastname: Danner
authors.affiliation: Klinik für Thorax-, Herz-, Gefäßchirurgie/Herzzentrum, Georg-August-Universität Göttingen, Göttingen, Germany.
authors.forename: Friedrich
authors.initials: F
authors.lastname: Schöndube
authors.affiliation: Department of Biology, Cardiovascular, Therapeutic Area, Gilead Sciences, Foster City, CA, USA.
authors.forename: Luiz
authors.initials: L
authors.lastname: Belardinelli
authors.affiliation: Klinik für Kardiologie und Pneumologie/Herzzentrum, Georg-August-Universität Göttingen, Robert-Koch-Str. 40, 37075 Göttingen, Germany DZHK (German Center for Cardiovascular Research), partner site Göttingen, Göttingen, Germany.
authors.forename: Gerd
authors.initials: G
authors.lastname: Hasenfuss
authors.affiliation: Innere Medizin II - Kardiologie, Universitätsklinikum Regensburg, Regensburg, Germany.
authors.forename: Lars S
authors.initials: LS
authors.lastname: Maier
authors.affiliation: Klinik für Kardiologie und Pneumologie/Herzzentrum, Georg-August-Universität Göttingen, Robert-Koch-Str. 40, 37075 Göttingen, Germany DZHK (German Center for Cardiovascular Research), partner site Göttingen, Göttingen, Germany ssossalla@med.uni-goettingen.de.
authors.forename: Samuel
authors.initials: S
authors.lastname: Sossalla
mesh_terms: D000818:Animals; D001281:Atrial Fibrillation / Q000209:etiology; D002118:Calcium / Q000378:metabolism*; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2 / Q000378:metabolism*; D000242:Cyclic AMP / Q000032:analysis; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000502:physiology*; D003971:Diastole / Q000502:physiology*; D004789:Enzyme Activation; D006325:Heart Atria / Q000378:metabolism*; D006801:Humans; D051379:Mice; D010766:Phosphorylation; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*; D015222:Sodium Channels / Q000502:physiology*
chemical_list: D015222:Sodium Channels; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D002118:Calcium
keywords: Antiarrhythmic drugs; Atrial fibrillation; Late Na current; Protein kinases; SR-Ca2+-leak