Redox control of K+ channel remodeling in rat ventricle

Electrical remodeling of the diseased heart contributes to contractile dysfunction and arrhythmias, and is characterized by down-regulation of K+ channels that control action potential morphology. We have recently shown that remodeling of K+ channels underlying the transient outward current (Ito) involves a shift in cell redox balance that is reflected by a depletion of the endogenous redox buffer, glutathione (GSH). This study used a pharmacological model to further examine the role of redox-mediated mechanisms in regulating cardiac K+ currents. Inhibition of major redox pathways was elicited in normal rats by daily injections of 1,3-bis-(2-chloroethyl)-1-nitrosourea (BCNU), an inhibitor of thioredoxin and glutathione reductases, and buthionine sulfoximine (BSO), a blocker of GSH synthesis. Fluorescence microscopy studies showed that [GSH] in isolated ventricular myocytes was decreased ~50% from control after 3 days of BCNU/BSO treatment (P < 0.05), consistent with a shift in cell redox state. In voltage-clamp experiments, maximum Ito density was decreased 33% from control in left ventricular myocytes from BCNU/BSO-treated rats (P < 0.05), while the inward rectifier and steady state outward currents were not significantly altered. Decreased Ito density correlated with significant decreases in Kv4.2 mRNA and proteins levels of Kv4.2 and Kv1.4. Down-regulation of Ito in myocytes from BCNU/BSO rats was reversed in vitro by exogenous GSH or N-acetylcysteine, a GSH precursor and antioxidant. Ito density and [GSH] were also up-regulated by receptor tyrosine kinase activation with insulin or a tyrosine phosphatase inhibitor. The effect of these activators on Ito was blocked by inhibitors of PI 3-kinase, MEK and p38 MAP kinases. These data suggest that expression of cardiac Ito channels is regulated by endogenous oxidoreductase systems and that receptor tyrosine kinase signaling functionally impacts K+ channel remodeling through its control of cell redox state.