Rationale: Angiotensin (Ang) II–induced apoptosis was reported to be mediated by different signaling molecules. Whether these molecules are either interconnected in 1 single pathway or constitute different and alternative cascades by which Ang II exerts its apoptotic action, is not known.

Objective: To investigate in cultured myocytes from adult cat and rat, 2 species in which Ang II has opposite inotropic effects, the signaling cascade involved in Ang II–induced apoptosis.

Methods and Results: Ang II (1 μmol/L) reduced cat/rat myocytes viability by 40%, in part, because of apoptosis (TUNEL/caspase-3 activity). In both species, apoptosis was associated with reactive oxygen species (ROS) production, Ca²⁺/calmodulin–dependent protein kinase (CaMK)II, and p38 mitogen-activated protein kinase (p38MAPK) activation and was prevented by the ROS scavenger MPG (2-mercaptopropionylglycine) or the NADPH oxidase inhibitor DPI (diphenyleneiodonium) by CaMKII inhibitors (KN-93 and AIP [aryl hydrocarbon receptor–interacting protein]) or in transgenic mice expressing a CaMKII inhibitory peptide and by the p38MAPK inhibitor, SB202190. Furthermore, p38MAPK overexpression exacerbated Ang II–induced cell mortality. Moreover, although KN-93 did not affect Ang II–induced ROS production, it prevented p38MAPK activation. Results further show that CaMKII can be activated by Ang II or H₂O₂, even in the presence of the Ca²⁺ chelator BAPTA-AM, in myocytes and in EGTA-Ca²⁺–free solutions in the presence of the calmodulin inhibitor W-7 in in vitro experiments.

Conclusions: (1) The Ang II–induced apoptotic cascade converges in both species, in a common pathway mediated by ROS-dependent CaMKII activation which results in p38MAPK activation and apoptosis. (2) In the presence of Ang II or ROS, CaMKII may be activated at subdiastolic Ca²⁺ concentrations, suggesting a new mechanism by which ROS reset the Ca²⁺ dependence of CaMKII to extremely low Ca²⁺ levels.