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

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 CaMKII delta 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 mu mol/L H2O2 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 mu mol/L), the H2O2-dependent CaMKII oxidation and autophosphorylation was abolished. H2O2 significantly increased SR Ca spark frequency (confocal microscopy) but reduced SR Ca load. In wild-type (WT) mouse myocytes, H2O2 increased late I-Na (whole cell patch-clamp). This increase was abolished in CaMKII delta(-/-) myocytes. H2O2-induced [Na](i) and [Ca](i) accumulation (SBFI [sodium-binding benzofuran isophthalate] and Indo-1 epifluorescence) was significantly slowed in CaMKII delta(-/-) myocytes (versus WT). CaMKII delta(-/-) myocytes developed significantly less H2O2-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 CaMKII delta in rabbit myocytes (adenoviral gene transfer) reversible with CaMKII inhibition (10 mu mol/L KN93 or 0.1 mu mol/L AIP [autocamtide 2-related inhibitory peptide]). Conclusions: Free [Ca](i) and a functional SR are required for ROS activation of CaMKII. ROS-activated CaMKII delta 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. (Circ Res. 2011; 108: 555-565.)