Abstract 641: Reactive Oxygen Species-Induced p90 Ribosomal S6 Kinase Activation Leads to Prolongation of Cardiac Repolarization via Inhibiting Voltage-Gated Outward K+ Currents
Prolongation of cardiac repolarization and cardiac arrhythmias are often seen in cardiac ischemia/reperfusion (I/R) and diabetic cardiomyopathy. The underlying mechanisms are largely unknown. p90 ribosomal S6 kinase (p90RSK) is activated in multiple heart diseases. In the present study, we determined the functional role of p90RSK activation in cardiac electrical remodeling. Transgenic mice (8–12 weeks old) with cardiac-specific overexpression of p90RSK (p90RSK-Tg) had significant prolongation of QT interval and frequent premature atrial or atrial-ventricular nodal contractions, and /or paroxysmal supraventricular tachycardia. Action potential durations (APDs) of ventricular myocytes from p90RSK-Tg mice were significantly prolonged. Whole cell voltage-clamp recordings revealed that ventricular fast transient outward current (Ito,f) and slow delayed outward current (IK,slow) were reduced in p90RSK-Tg, compared with nontransgenic littermates. Quantitative real time RT-PCR assays revealed that mRNA levels of Kv4.3, Kv4.2, Kv1.5, Kv2.1, Kv1.4 and KChIP2 from ventricles between p90RSK-Tg and wild type mice were not significantly different, indicating the possible contribution of p90RSK-mediated post-transcriptional modification of voltage-gated K+ channels. In fact, point-mutation and in vitro kinase analysis showed that Kv4.3 (main component of Ito,f) was covalently phosphorylated by p90RSK at two conserved sites, S516 amd S550. Expression of p90RSK significantly inhibited Kv4.3, and Kv4.3 and KChIP2-encoded channel activity in HEK 293 cells while p90RSK’s effects were largely blocked by amino acid mutations in phosphorylation sites. Hydrogen peroxide (H2O2), a well-known mediator of I/R and diabetic cardiomyopathy induced p90RSK activation, had effects similar to those of p90RSK on Kv4.3-encoded currents. Dominant negative form of p90RSK and two structually different p90RSK specific inhibiors, fluoromethylketone (fmk) and BI-D1879, reversed effects of H2O2 on Kv4.3 channel activity. These data suggest that p90RSK activation is critical for ROS-mediated inhibition of Kv4.3 channel activity and subsequent QT-interval prolongation, and possible involvement of p90RSK activation in arrhythmia induced by I/R.