Reactive oxygen species-activated Ca/calmodulin kinase IIδ is required for late I(Na) augmentation leading to cellular Na and Ca overload.
BACKGROUND
In heart failure Ca/calmodulin kinase (CaMK)II expression and reactive oxygen species (ROS) are increased. Both ROS and CaMKII can increase late I(Na) leading to intracellular Na accumulation and arrhythmias. It has been shown that ROS can activate CaMKII via oxidation.


OBJECTIVE
We tested whether CaMKIIδ is required for ROS-dependent late I(Na) regulation and whether ROS-induced Ca released from the sarcoplasmic reticulum (SR) is involved.


RESULTS
40 μmol/L H(2)O(2) significantly increased CaMKII oxidation and autophosphorylation in permeabilized rabbit cardiomyocytes. Without free [Ca](i) (5 mmol/L BAPTA/1 mmol/L Br(2)-BAPTA) or after SR depletion (caffeine 10 mmol/L, thapsigargin 5 μmol/L), the H(2)O(2)-dependent CaMKII oxidation and autophosphorylation was abolished. H(2)O(2) significantly increased SR Ca spark frequency (confocal microscopy) but reduced SR Ca load. In wild-type (WT) mouse myocytes, H(2)O(2) increased late I(Na) (whole cell patch-clamp). This increase was abolished in CaMKIIδ(-/-) myocytes. H(2)O(2)-induced [Na](i) and [Ca](i) accumulation (SBFI [sodium-binding benzofuran isophthalate] and Indo-1 epifluorescence) was significantly slowed in CaMKIIδ(-/-) myocytes (versus WT). CaMKIIδ(-/-) myocytes developed significantly less H(2)O(2)-induced arrhythmias and were more resistant to hypercontracture. Opposite results (increased late I(Na), [Na](i) and [Ca](i) accumulation) were obtained by overexpression of CaMKIIδ in rabbit myocytes (adenoviral gene transfer) reversible with CaMKII inhibition (10 μmol/L KN93 or 0.1 μmol/L AIP [autocamtide 2-related inhibitory peptide]).


CONCLUSIONS
Free [Ca](i) and a functional SR are required for ROS activation of CaMKII. ROS-activated CaMKIIδ enhances late I(Na), which may lead to cellular Na and Ca overload. This may be of relevance in hear failure, where enhanced ROS production meets increased CaMKII expression.
Department of Cardiology and Pneumology, Georg-August-University, Robert-Koch-Strasse 40, 37075 Göttingen, Germany.
Stefan
S
Wagner
Hanna M
HM
Ruff
Sarah L
SL
Weber
Sarah
S
Bellmann
Thomas
T
Sowa
Timo
T
Schulte
Mark E
ME
Anderson
Eleonora
E
Grandi
Donald M
DM
Bers
Johannes
J
Backs
Luiz
L
Belardinelli
Lars S
LS
Maier
D000818:Animals; D001145:Arrhythmias, Cardiac / Q000378:metabolism / Q000473:pathology; D002118:Calcium / Q000378:metabolism*; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2 / Q000235:genetics / Q000378:metabolism*; D002478:Cells, Cultured; D006861:Hydrogen Peroxide / Q000494:pharmacology; D051379:Mice; D018345:Mice, Knockout; D023421:Models, Animal; D032383:Myocytes, Cardiac / Q000166:cytology / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D011817:Rabbits; D017382:Reactive Oxygen Species / Q000378:metabolism*; D019837:Ryanodine Receptor Calcium Release Channel / Q000378:metabolism; D012519:Sarcoplasmic Reticulum / Q000378:metabolism; D012964:Sodium / Q000378:metabolism*; D015222:Sodium Channels / Q000378:metabolism*
D017382:Reactive Oxygen Species; D019837:Ryanodine Receptor Calcium Release Channel; D015222:Sodium Channels; D012964:Sodium; D006861:Hydrogen Peroxide; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D002118:Calcium
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