Calcium-calmodulin kinase II mediates digitalis-induced arrhythmias.

101. GONANO LA, SEPÚLVEDA M, RICO Y, KAETZEL M, VALVERDE CA, DEDMAN J, MATTIAZZI A, VILA PETROFF M.

CIRCULATION-ARRHYTHMIA AND ELECTROPHYSIOLOGY

LIPPINCOTT WILLIAMS & WILKINS

Lugar: Baltimore; Año: 2011 vol. 4 p. 947 - 957

1941-3149

Background—Digitalis-induced Na+ accumulation results in an increase in Ca2+i via the Na+/Ca2+ exchanger, leading to enhanced sarcoplasmic reticulum (SR) Ca2+ load, responsible for the positive inotropic and toxic arrhythmogenic effects of glycosides. A digitalis-induced increase in Ca2+i could also activate calcium-calmodulin kinase II (CaMKII), which has been shown to have proarrhythmic effects. Here, we investigate whether CaMKII underlies digitalis-induced arrhythmias and the subcellular mechanisms involved. Methods and Results—In paced rat ventricular myocytes (0.5 Hz), 50umol/L ouabain increased contraction amplitude by 160±5%. In the absence of electric stimulation, ouabain promoted spontaneous contractile activity and Ca2+ waves. Ouabain activated CaMKII (p-CaMKII), which phosphorylated its downstream targets, phospholamban (PLN) (Thr17) and ryanodine receptor (RyR) (Ser2814). Ouabain-induced spontaneous activity was prevented by inhibiting CaMKII with 2.5umol/L KN93 but not by 2.5umol/L of the inactive analog, KN92. Similar results were obtained using the CaMKII inhibitor, autocamtide-2 related inhibitory peptide (AIP) (1 to 2.5umol/L), and in myocytes from transgenic mice expressing SR-targeted AIP. Consistently, CaMKII overexpression exacerbated ouabain-induced spontaneous contractile activity. Ouabain 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 Ca2+ content. Similar results were obtained with digoxin. In vivo, ouabain-induced arrhythmias were prevented by KN93 and absent in SR-AIP mice. Conclusions—These results show for the first time that CaMKII mediates ouabain-induced arrhythmic/toxic effects. We suggest that CaMKII-dependent phosphorylation of the RyR, resulting in Ca2+ leak from the SR, is the underlying mechanism involved.