Abstract 2809: Knockout of Ca/Calmodulin Kinase IIδ Protects Against ROS-induced Injury
Expression and activity of Ca/calmodulin kinase II (CaMKII) are enhanced in heart failure (HF) and linked to disease progression involving increased late Na current (INa). Reactive oxygen species (ROS) generated in HF can increase late INa leading to cytosolic Na and Ca overload, arrhythmias and cell death. We tested whether ROS-activated CaMKIIδ is involved, since it is known that ROS directly activate CaMKII via oxidation at methionine residues. We exposed ventricular myocytes isolated from CaMKIIδ-knockout mice (CKO, wildtype (WT) as control) to ROS generated via 200 μM H2O2. The H2O2-induced increase of late INa was almost completely abolished in myocytes lacking CaMKIIδ (fig 1A⇓). Moreover, in CKO-myocytes the blunted H2O2-induced Na influx via late INa resulted in a significantly slower increase of [Na]i compared to WT (fig 1B⇓, 10 μM SBFI-AM, ANOVA, *P<0.05 vs. WT). Consequently, H2O2-induced Ca entry via Na/Ca exchange (NCX) was significantly reduced in CKO myocytes vs. WT (fig 1C⇓, 10 μM Indo-1-AM, ANOVA, *P<0.05 vs. CKO). In WT, the H2O2-induced increase of [Ca]i was reduced in the presence of the NCX-inhibitor KB-R7943 (5 μM, fig 1C⇓, †P<0.05 vs. KB-R7943). Myocytes were monitored for H2O2-induced cellular arrhythmias using a score system. The propensity for arrhythmias was significantly lower in CKO myocytes and the cellular survival was significantly increased (fig 1D+E⇓). In conclusion, activation of CaMKIIδ is a prerequisite for ROS-induced increase of late INa, [Na]i and [Ca]i accumulation. Moreover, myocytes lacking CaMKIIδ are protected from severe arrhythmias and cell death. Therefore, strategies targeted at CaMKII may be promising for the treatment of HF.