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

Abstract

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 H₂O₂ significantly increased CaMKII oxidation and autophosphorylation in permeabilized rabbit cardiomyocytes. Without free [Ca]_i (5 mmol/L BAPTA/1 mmol/L Br₂-BAPTA) or after SR depletion (caffeine 10 mmol/L, thapsigargin 5 μmol/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 CaMKIIδ^−/− myocytes. H₂O₂-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 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 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.