Inhibition of Elevated Ca2+/Calmodulin-Dependent Protein Kinase II Improves Contractility in Human Failing Myocardium

Rationale: Heart failure (HF) is known to be associated with increased Ca2+/calmodulin-dependent protein kinase (CaMK)II expression and activity. There is still controversial discussion about the functional role of CaMKII in HF. Moreover, CaMKII inhibition has never been investigated in human myocardium. Objective: We sought to investigate detailed CaMKII delta expression in end-stage failing human hearts (dilated and ischemic cardiomyopathy) and the functional effects of CaMKII inhibition on contractility. Methods and Results: Expression analysis revealed that CaMKII delta, both cytosolic delta(C) and nuclear delta(B) splice variants, were significantly increased in both right and left ventricles from patients with dilated or ischemic cardiomyopathy versus nonfailing. Experiments with isometrically twitching trabeculae revealed significantly improved force frequency relationships in the presence of CaMKII inhibitors (KN-93 and AIP). Increased postrest twitches after CaMKII inhibition indicated an improved sarcoplasmic reticulum (SR) Ca2+ loading. This was confirmed in isolated myocytes by a reduced SR Ca2+ spark frequency and hence SR Ca2+ leak, resulting in increased SR Ca2+ load when inhibiting CaMKII. Ryanodine receptor type 2 phosphorylation at Ser2815, which is known to be phosphorylated by CaMKII thereby contributing to SR Ca2+ leak, was found to be markedly reduced in KN-93-treated trabeculae. Interestingly, CaMKII inhibition did not influence contractility in nonfailing sheep trabeculae. Conclusions: The present study shows for the first time that CaMKII inhibition acutely improves contractility in human HF where CaMKII delta expression is increased. The mechanism proposed consists of a reduced SR Ca2+ leak and consequently increased SR Ca2+ load. Thus, CaMKII inhibition appears to be a possible therapeutic option for patients with HF and merits further investigation. (Circ Res. 2010;107:1150-1161.)