Abstract 3503: Hydrogen Peroxide-Induced Afterdepolarizations are Dependent on Calmodulin Kinase II Signaling
Background: In the heart, hydrogen peroxide (H2O2) has been shown to cause early afterdepolarizations (EADs) and triggered activity by impairing Na current (INa) inactivation. Since H2O2 has been recently shown to activate Ca2+/calmodulin kinase II (CaMKII), and since CaMKII activation has also been reported to impair INa inactivation and predispose to EADs, we hypothesized that CaMKII activation by H2O2 may be an important factor in the genesis of EADs induced by oxidative stress.
Methods and Results: Patch-clamped Fluo-4 AM-loaded rabbit ventricular myocytes were exposed to H2O2 (0.1–1mM), which induced spontaneous EADs after 5–15 min. Both the INa blocker tetrodoxtin (TTX, 10 μM) and the ICa,L blocker nifedipine shortened AP duration (APD) and suppressed EADs. H2O2 increased both peak and steady-state ICa,L under square-pulse voltage clamp, and enhanced ICa,L to a greater extent during the AP plateau than during the AP upstroke under AP clamp conditions. In addition, by prolonging the AP plateau and increasing Ca influx via maintained ICa,L, H2O2-induced EADs frequently caused DADs delayed afterdepolarizations (DADs) due to spontaneous SR Ca release waves after repolarization. KN-93(1 μM), a CaMKII inhibitor, prevented H2O2 -induced EADs (n=4), whereas the inactive analogue KN-92 did not (n=5).
Conclusion: These findings indicate that H2O2-induced EADs depend on both impaired INa inactivation to reduce repolarization reserve and enhanced ICa,L to reverse repolarization. Intact CaMKII signaling is necessary for EAD generation in this setting, presumably via its actions on INa and ICa,L, although direct redox effects on other ion channels/transporters may also be important. Our observations support a link between increased oxidative stress, CaMKII activation and afterdepolarizations as triggers of lethal ventricular arrhythmias in diseased heart.
This research has received full or partial funding support from the American Heart Association, AHA National Center.