KV4.3 PROTECTS AGAINST OXIDATIVE CAMKII ACTIVATION IN HEART FAILURE

Abstract

Objective: Oxidative stress causes excessive CaMKII activation in heart failure which exacerbates cardiac dysfunction. We determined whether restoration of down-regulated membrane Kv4.3 expression in ventricular myocytes can block oxidative CaMKII activation in heart failure. Design and method: Heart failure was induced in mice by severe thoracic aortic banding. Transjugular injection of AAV-Kv4.3 was performed in mice 1 week after banding. Fluorescence spectra were measured using F-4600 spectrophotometer (Hitachi). The slit width and excitation wavelength were set to 5 mm and 270 nm, respectively. Emission spectra were increased from 280 nm to 400 nm (step = 1nm). The spectra of purified proteins were examined, including CaMKII, CaMKII and Ca2+/CaM, CaMKII and Kv4.3, CaMKII, Kv4.3, and Ca2+/CaM. Results: Dissociation of Kv4.3 from Kv4.3-CaMKII molecular complex or down-regulation of Kv4.3 in mouse ventricular myocytes enhanced H2O2-induced CaMKII oxidation and autophosphorylation. Only non-oxidized and unphosphorylated forms of CaMKII have been detected from the Kv4.3 immunoprecipitates in ventricular myocytes with H2O2 Incubation. Fluorescence spectra assay showed that Kv4.3 prevented the transformational change of inactive CaMKII to its active conformation in the presence of Ca2+/CaM and H2O2. In vivo transfection with AAV9-Kv4.3 had no impact on reactive oxygen species in heart failure myocardium but effectively suppressed CaMKII oxidation and activation. Conclusions: Kv4.3 is a potent native suppressor for oxidative CaMKII activation by binding to the regulatory domain and preventing the opening of inhibitory domain in response to Ca2+/CaM and H2O2.