CENTRO DE INVESTIGACIONES CARDIOVASCULARES "DR. HORACIO EUGENIO CINGOLANI"
Unidad Ejecutora - UE
congresos y reuniones científicas
CaMKII mediates Cardiac glycoside Toxicity
LUIS GONANO, YANINA RICO, ALICIA MATTIAZZI, MARTÍN VILA PETROFF
Congreso; Annual meeting of Biophysical society; 2011
The positive inotropic effect produced by inhibition of Na+/K+ ATPase (NKA) with digitalis has been used for the treatment of heart failure (HF) for over 200 years. However, digitalis toxicity-related death in HF patients undermines the beneficial effect of digitalis treatment. Digitalis-induced Na+ accumulation results in an increase in Ca2+i via the reverse mode of the Na+/Ca2+ exchanger (NCX) leading to enhanced SR Ca2+ load. The resulting increase in SR Ca2+ load would then be responsible for the positive inotropic effect and the toxic arrhythmogenic effects of glycosides. Digitalis-induced increase in Ca2+i could also activate CaMKII which has been shown to have proarrhythmic effects. Here we investigate whether CaMKII underlies glycoside arrhythmic effects and if so, which are the subcellular mechanisms involved. In electrically paced rat ventricular myocytes (0.5 Hz), 50 µM ouabain increased contraction amplitude by 160 ± 5%. Continued exposure to ouabain resulted in spontaneous contractile activity and Ca2+ waves which persisted even in the absence of electrical stimulation. Ouabain treatment was associated with activation of CaMKII (P-CaMKII) and phosphorilation of CaMKII downstream targets, site Tr17 of phospholamban and site Tr 2815 of the ryanodine receptor (RyR). Ouabain-induced spontaneous activity was prevented by inhibition of CaMKII with 1 µM KN93 but not by 1 µM of the inactive analogue KN92. Similar results were obtained using the structurally different CaMKII inhibitor, AIP (1-2.5µM). Ouabain treatment was associated with an increase in SR Ca2+ content and Ca2+ spark frequency, indicative of enhanced SR Ca2+ leak. KN93 suppressed the ouabain-induced increase in Ca2+ spark frequency without affecting SR content. These results suggest that CaMKII mediates ouabain-induced arrhythmic/toxic effects probably by phophorylating its SR targets. We speculate that CaMKII mediated phosphorylation of the RyR resulting Ca2+ leak from the SR could be the underlying mechanism involved.