Glutathione and K+ channel remodeling in postinfarction rat heart

Electrical remodeling of the diseased ventricle is characterized by downregulation of K+ channels that control action potential repolarization. Recent studies suggest that this shift in electrophysiological phenotype involves oxidative stress and changes in intracellular glutathione (GSH), a key regulator of redox-sensitive cell functions. This study examined the role of GSH in regulating K+ currents in ventricular myocytes from rat hearts 8 wk after myocardial infarction (MI). Colorimetric analysis of tissue extracts showed that endogenous GSH levels were significantly less in post-MI hearts compared with controls, which is indicative of oxidative stress. This change in GSH status correlated with significant decreases in activities of glutathione reductase and gamma-glutamylcysteine synthetase. Voltage-clamp studies of isolated myocytes from post-MI hearts demonstrated that downregulation of the transient outward K+ current (I-to) could be reversed by pretreatment with exogenous GSH or N-acetylcysteine, a precursor of GSH. Upregulation of I-to was also elicited by dichloroacetate, which increases glycolytic flux through the GSH-related pentose pathway. This metabolic effect was blocked by inhibitors of glutathione reductase and the pentose pathway. These data indicate that oxidative stress-induced alteration in the GSH redox state plays an important role in I-to channel remodeling and that GSH homeostasis is influenced by pathways of glucose metabolism.