CaMKII Mediates rapid pacing induced apoptosis in rat ventricular myocytes.

MARISA SEPULVEDA; LUIS GONANO; MARTÍN VILA PETROFF

New London

Congreso; Gordon Research Conferences, Cardiac Regulatory Mechanism, New London, USA. Junio 2012.; 2012

Gordon Conferences

CaMKII Mediates Rapid Pacing-Induced Apoptosis in Adult Rat Cardiac Myocytes.  , Marisa Sepúlveda Luis Gonano and Martin Vila Petroff. Centro de Investigaciones Cardiovasculares CCT-CONICET. Facultad de Cs. Médicas, UNLP. 60 y 120 La Plata, Argentina.,   Ventricular tachycardia promotes cell death and cardiac remodeling leading to congestive heart failure.  Myocyte loss by apoptosis is recognized as a critical factor in the progression to heart failure and simulation of tachycardia by rapid pacing has been shown to activate distinct, potentially proapoptotic molecules including CaMKII, p38MAPK and reactive oxygen species (ROS). However, whether these molecules mediate tachycardia- or rapid pacing-induced cell death has not as yet been determined. The aim of this study was to examine the subcellular mechanisms underlying rapid pacing-induced apoptosis.  For this purpose rat ventricular myocytes were maintained quiescent or paced at 0.5, 5 and 8 Hz for 1 hr. Rapid pacing (5 and 8 Hz) decreased myocytes viability by 25 ± 3% and 45 ± 6%  compared to cells maintained at 0.5 Hz and increased caspase-3 activity and Bax/Bcl-2 ratio, indicative of apoptosis. Rapid pacing-induced cell death and apoptosis were prevented when pacing protocols were conducted either in the presence of the ROS scavenger, MPG or the CaMKII inhibitor, KN93.  Consistently, myocytes from transgenic mice expressing a CaMKII inhibitory peptide (AC3-I) were protected against rapid pacing-induced cell death.  Interestingly, PI3K and NO sintase inhibition with wortmannin and L-Name, respectively, increased CaMKII activity and exacerbated pacing-induced myocyte death whereas rapid pacing-induced cell mortality was prevented by p38MAPK.  We conclude that rapid pacing triggers an apoptotic cascade that involves ROS-dependent CaMKII activation and p38MAPK as a downstream effector. Rapid pacing simultaneously activates a protective cascade that modulates CaMKII through PI3K/AKT/NO signaling. These results suggest a novel mechanism by which NO regulates CaMKII activity in cardiac muscle.