Oxidative-stress-induced afterdepolarizations and calmodulin kinase II signaling.
In the heart, oxidative stress caused by exogenous H(2)O(2) has been shown to induce early afterdepolarizations (EADs) and triggered activity by impairing Na current (I(Na)) inactivation. Because H(2)O(2) activates Ca(2+)/calmodulin kinase (CaMK)II, which also impairs I(Na) inactivation and promotes EADs, we hypothesized that CaMKII activation may be an important factor in EADs caused by oxidative stress. Using the patch-clamp and intracellular Ca (Ca(i)) imaging in Fluo-4 AM-loaded rabbit ventricular myocytes, we found that exposure to H(2)O(2) (0.2 to 1 mmol/L) for 5 to 15 minutes consistently induced EADs that were suppressed by the I(Na) blocker tetrodotoxin (10 micromol/L), as well as the I(Ca,L) blocker nifedipine. H(2)O(2) enhanced both peak and late I(Ca,L), consistent with CaMKII-mediated facilitation. By prolonging the action potential plateau and increasing Ca influx via I(Ca,L), H(2)O(2)-induced EADs were also frequently followed by DADs in response to spontaneous (ie, non-I(Ca,L)-gated) sarcoplasmic reticulum Ca release after repolarization. The CaMKII inhibitor KN-93 (1 micromol/L; n=4), but not its inactive analog KN-92 (1 micromol/L, n=5), prevented H(2)O(2)-induced EADs and DADs, and the selective CaMKII peptide inhibitor AIP (autocamtide-2-related inhibitory peptide) (2 micromol/L) significantly delayed their onset. In conclusion, H(2)O(2)-induced afterdepolarizations depend on both impaired I(Na) inactivation to reduce repolarization reserve and enhancement of I(Ca,L) to reverse repolarization, which are both facilitated by CaMKII activation. Our observations support a link between increased oxidative stress, CaMKII activation, and afterdepolarizations as triggers of lethal ventricular arrhythmias in diseased hearts.
Xie
Lai-Hua
LH
Department of Cell Biology and Molecular Medicine, University of Medicine and Dentistry, New Jersey-New Jersey Medical School, Newark, USA.
Chen
Fuhua
F
Karagueuzian
Hrayr S
HS
Weiss
James N
JN
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020746:Calcium Channels, L-Type / Q000187:drug effects / Q000502:physiology; D020013:Calcium Signaling / Q000187:drug effects; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2 / Q000037:antagonists & inhibitors / Q000502:physiology*; D003064:Cnidarian Venoms / Q000494:pharmacology; D006352:Heart Ventricles / Q000166:cytology; D006861:Hydrogen Peroxide / Q000494:pharmacology; D066298:In Vitro Techniques; D032383:Myocytes, Cardiac / Q000201:enzymology / Q000502:physiology*; D009543:Nifedipine / Q000494:pharmacology; D018384:Oxidative Stress / Q000502:physiology*; D018408:Patch-Clamp Techniques; D010455:Peptides / Q000494:pharmacology; D011817:Rabbits; D026941:Sodium Channel Blockers / Q000494:pharmacology; D013779:Tetrodotoxin / Q000494:pharmacology
D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type; D003064:Cnidarian Venoms; D010455:Peptides; D026941:Sodium Channel Blockers; C514527:autocamptide-2-related inhibitory peptide II; D013779:Tetrodotoxin; C028800:toxin II (Anemonia sulcata); D006861:Hydrogen Peroxide; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D009543:Nifedipine; D002118:Calcium