Zheng MQ, Tang K, Zimmerman MC, Liu L, Xie B, Rozanski GJ
Role of {gamma}-Glutamyl Transpeptidase in Redox Regulation of K+ Channel Remodeling in Post-Myocardial Infarction Rat Hearts. [JOURNAL ARTICLE]
Am J Physiol Cell Physiol 2009 May 6.
gamma-Glutamyl transpeptidase (gamma-GT) is a key enzyme in GSH metabolism that regulates intracellular GSH levels in response to extracellular GSH (GSHo). The objective of this study was to identify the role of gamma-GT in reversing pathogenic K(+) channel remodeling in the diseased heart. Chronic ventricular dysfunction was induced in rats by myocardial infarction (MI) and studies were done after 6-8wks. Biochemical assays of tissue extracts from post-MI hearts revealed significant increases in gamma-GT activity in left ventricle (47%) and septum (28%) compared with sham hearts, which paralleled increases in protein abundance and mRNA. Voltage-clamp studies of isolated left ventricular myocytes from post-MI hearts showed that down-regulation of transient outward K(+) current (Ito) was reversed after 4-5 h by 10 mmol/l GSHo or N-acetylcysteine (NACo), and that the effect of GSHo but not NACo was blocked by the gamma-GT inhibitors, acivicin or S-hexyl-GSH. Inhibition of gamma-glutamylcysteine synthetase by buthionine sulfoximine did not prevent up-regulation of Ito by GSHo, suggesting that intracellular synthesis of GSH was not directly involved. However, pre-treatment of post-MI myocytes with an SOD mimetic (MnTPyP) and catalase completely blocked recovery of Ito by GSHo. Confocal microscopy using the fluorogenic dye 2', 7' -dichlorodihydrofluorescein diacetate confirmed that GSHo increased reactive oxygen species (ROS) generation by post-MI myocytes and to a lesser extent in myocytes from sham hearts. Furthermore, GSHo-mediated up-regulation of Ito was blocked by inhibitors of tyrosine kinase (genistein, lavendustin A, AG1024) and thioredoxin reductase (auranofin, 13-cis-retinoic acid). These data suggest that GSHo elicits gamma-GT- and ROS-dependent transactivation of tyrosine kinase signaling that up-regulates K(+) channel activity or expression via redox-mediated mechanisms. The signaling events stimulated by gamma-GT catalysis of GSHo may be a therapeutic target to reverse pathogenic electrical remodeling of the failing heart. Key words: Glutathione, Kv channel, Thioredoxin, gamma-glutamyl transpeptidase.
More from this journal |
