Inhibition of late sodium current prevents pathological hyperactivation of calcium/calmodulin‐dependent protein kinase IIδ in a murine model of acute doxorubicin‐related cardiotoxicity

Background and Purpose Doxorubicin (DOX) is a highly effective anthracycline, whose clinical application for cancer is limited by cardiotoxicity. The mechanisms underlying doxorubicin‐induced toxic cardiomyopathy (DICM) involve electrophysiological remodelling with intracellular Na + overload because of increased late I Na and hyperactivation of CaMKII δ . Increased [Na + ] i contributes to CaMKII δ activation through Na‐dependent Ca 2+ overload, and CaMKII δ can further amplify late I Na . Experimental Approach We tested whether pharmacological inhibition of the late I Na by either ranolazine (RAN, 10 μmol·L −1 ) or empagliflozin (EMPA, 1 μmol·L −1 ) is sufficient to attenuate DOX‐mediated hyperactivation of CaMKII δ in isolated wildtype (WT) ventricular cardiomyocytes. The contribution of reciprocal CaMKII‐dependent stimulation of late I Na was tested in transgenic S571A cardiomyocytes lacking the CaMKII‐specific phosphorylation site S571A on Na V 1.5. Functional readouts were obtained using patch‐clamp technique, as well as confocal and epifluorescence microscopy. Key Results DOX acutely increased late I Na in WT cardiomyocytes by twofold, which was associated with redox‐ and phospho‐dependent activation of CaMKII δ . Hyperactivated CaMKII δ led to acutely impaired Ca 2+ handling because of diastolic Ca 2+ loss from the sarcoplasmic reticulum (SR) mediated by phosphorylation of the RyR2 at the CaMKII‐specific phosphorylation site serine‐2814. Pharmacological inhibition of late I Na by EMPA or RAN, and genetic deletion of the CaMKII‐specific phosphorylation‐site serine‐571 at Na V 1.5 prevented DOX‐related stimulation of the late I Na and subsequent CaMKII δ hyperactivation, which functionally preserved intracellular Ca handling. Conclusion and Implications Inhibition of late I Na protects cardiomyocytes from pathologic CaMKII δ hyperactivation and impaired Ca 2+ handling in the setting of acute DOX cardiotoxicity.