Reactive Oxygen Species–Activated Ca/Calmodulin Kinase IIδ Is Required for Late INa Augmentation Leading to Cellular Na and Ca OverloadNovelty and Significance

Rationale: 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. Methods and 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.