Abstract 2869: Angiotensin II Induces Afterdepolarizations via Reactive Oxygen Species and Calmodulin Kinase II Signaling
Background: Recent clinical evidence demonstrates that renin-angiotensin system inhibitors significantly reduce the incidence of arrhythmias suggesting angiotensin II (Ang II) is arrhythmogenic, however, its underlying mechanism (s) is not well understood. Ang II increases oxidative stress by the production of reactive oxygen species (ROS) and is associated with increased risk of multiple cardiac disorders. We tested the hypothesis that AngII induces early afterdepolarizations (EADs) and triggered activities (TAs) via the ROS-calmodulin kinase II (CaMK II) pathway.
Methods and Results: Action potentials were measured in isolated rabbit ventricular myocytes using the perforated patch-clamp technique. EADs emerged in 22 out of 35 cells 15.1±2.2 min after Ang II (1 ~ 4 microM) perfusion. Ang II-induced EADs were abolished by Ang II type1 receptor antagonist losartan (n=5), the NADPH oxidase inhibitor apocynin (n=6), or ROS scavenger trolox (n=5). CaMK II inhibitor, KN-93, prevented Ang II-induced EADs (n=6), whereas the inactive analogue KN-92 did not (n=4). Nifedipine, a blocker of L-type Ca current (ICa,L), or ranolazine, an inhibitor of late Na current (INa), effectively eliminated Ang II-induced EADs. To further investigate the ionic mechanisms, we directly examined the effects of Ang II on ICa, L and late phase of INa, the two major currents that are thought to be attributable to EAD generation. Ang II (1 microM) increased ICa.L by 48.9±5.5 %(n=19), which was significantly attenuated by losartan (21.9±3.7%, n=5), apocynin (27.1±6.6%, n=6), trolox (38.1±6.3% n=4), or KN-93 (33.9±3.4%, n=7) at the same concentrations used above. Similar results were also observed in late INa. Ang II increased late INa from 30.1±3.1 pA to 60.4±4.9 pA (n=20) at 50 ms after a voltage step from −90mV to −30mV, which was significantly decreased by apocynin, (35.9±3.7%, n=4), trolox (40.7±2.2%, n =4) or KN-93 (37.0±5.2%, n=6).
Conclusion: These findings indicate that Ang II induces EADs and TAs, which are mediated by intracellular ROS production through NAD(P)H oxidase, activation of CaMK II, and activation of ICa,L and late INa. Our results provide evidence supporting a link between renin-angiotensin system and serious cardiac arrhythmia.
This research has received full or partial funding support from the American Heart Association, National Center.