Na+/K+-ATPASE INHIBITION BY OUABAIN INDUCES CaMKII-DEPENDENT APOPTOSIS IN ADULT RAT CARDIAC MYOCYTES

LUCIANA SAPIA; ALICIA MATTIAZZI; MARTIN G. VILA PETROFF

Buenos Aires

Simposio; XVII Meeting ISHR Latin American Section; 2009

Seccion Latino Americana de la ISHR

Na+/K+-ATPASE INHIBITION BY OUABAIN INDUCES CaMKII-DEPENDENT APOPTOSIS IN ADULT RAT CARDIAC MYOCYTES Sapia L, Mattiazzi A, Vila Petroff M. Centro Invest. Cardiovasculares. La Plata. Argentina.   The positive inotropic effect produced by Na+/K+ ATPase inhibition with digitalis has been used for the treatment of heart failure for over 200 years. Recently, administration of toxic doses of ouabain has been shown to induce cardiac myocyte apoptosis. We investigated whether prolonged administration of non toxic doses of ouabain can also promote cardiac myocyte apoptosis and the underlying mechanisms involved.  Cardiac myocytes from rat and cat, two species with different sensitivity to digitalis, were cultured for 24 hrs in the presence or absence of 2 µM (rat) and 2 µM-25 nm ouabain (cat). Ouabain produced, in the rat, a 43 ± 5% decrease in cell viability at least in part due to apoptosis (enhanced caspase-3 activity and increased Bax/Bcl-2 ratio). Similar results were obtained with 25 nM ouabain in the cat. Ouabain-induced reduction in cell viability was prevented by the NCX inhibitor KB-R7943 and rescued by the CaMKII inhibitors, KN93 and AIP. KN93 did not affect ouabain-induced inotropy and CaMKII overexpression exacerbated ouabain-induced cell mortality. In addition, cell death was enhanced by PI3K inhibition and not affected by ERK½ inhibition. We conclude that low doses of ouabain induce CaMKII-dependent apoptosis and activate an antiapoptotic cascade involving PI3K/AKT. Results also suggest the use of CaMKII inhibitors as an adjunct to digitalis treatment.