Abstract 627: CaMKII Activation is Involved in Angiotensin II-Mediated Cell Death
Angiotensin II (Ang II) is involved in the excitation contraction coupling through its modulation of Ca2+i homeostasis via PKC. Moreover, Ang II-induced myocyte apoptosis has been described in the late 1990s. Furthermore, Ca2+-calmodulin-dependent protein kinase II (CaMKII), although typically activated by Ca2+ and calmodulin binding, has been described to be also activated by Ca2+-independent pathways that involve oxidative stress and PKC. It is also known that CaMKII initiates an apoptotic pathway in cardiac cells. Interestingly, a link between Ang II and CaMKII has never been examined. Therefore the present study was conducted to establish this nexus. To this purpose we cultivated adult cat cardiac myocytes in control conditions, treated 24 h with 1 μM Ang II and with 1μM Ang II plus 1μM KN-93, a specific CaMKII inhibitor. We evaluated cell viability and CaMKII activation by western blot of P-CaMKII and P-Thr17 of phospholamban, a specific substrate of active CaMKII. Additionally, in situ DNA nick end labelling (TUNEL) assay was used to determine apoptosis. Ang II treatment induced cell death in 64.6±3.6% versus 29.4±3.3% (control). The mortality induced by Ang II was abolished by concomitant treatment of the myocytes with the CaMKII inhibitor. The apoptotic assay followed the same pattern, being the TUNEL positive cells significantly greater in Ang II treated cells than in the group treated with Ang II and KN-93. The Ang II-induced cell death was associated with 32.6±5.6% increase in P-CaMKII and a concomitant increase in P-Thr17 was also detected (Figure⇓). These results indicate a previously unrecognized pathway of cardiac cell death triggered by Ang II mediated by CaMKII.