Role of gamma-glutamyl transpeptidase in redox regulation of K+ channel remodeling in postmyocardial infarction rat hearts.
gamma-Glutamyl transpeptidase (gamma-GT) is a key enzyme in GSH metabolism that regulates intracellular GSH levels in response to extracellular GSH (GSH(o)). 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 6-8 wk. 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 downregulation of transient outward K(+) current (I(to)) was reversed after 4-5 h by 10 mmol/l GSH(o) or N-acetylcysteine (NAC(o)), and that the effect of GSH(o) but not NAC(o) was blocked by the gamma-GT inhibitors, acivicin or S-hexyl-GSH. Inhibition of gamma-glutamylcysteine synthetase by buthionine sulfoximine did not prevent upregulation of I(to) by GSH(o), suggesting that intracellular synthesis of GSH was not directly involved. However, pretreatment of post-MI myocytes with an SOD mimetic [manganese (III) tetrapyridylporphyrin] and catalase completely blocked recovery of I(to) by GSH(o). Confocal microscopy using the fluorogenic dye 2',7'-dichlorodihydrofluorescein diacetate confirmed that GSH(o) increased reactive oxygen species (ROS) generation by post-MI myocytes and to a lesser extent in myocytes from sham hearts. Furthermore, GSH(o)-mediated upregulation of I(to) was blocked by inhibitors of tyrosine kinase (genistein, lavendustin A, and AG1024) and thioredoxin reductase (auranofin and 13-cis-retinoic acid). These data suggest that GSH(o) elicits gamma-GT- and ROS-dependent transactivation of tyrosine kinase signaling that upregulates K(+) channel activity or expression via redox-mediated mechanisms. The signaling events stimulated by gamma-GT catalysis of GSH(o) may be a therapeutic target to reverse pathogenic electrical remodeling of the failing heart.
Zheng
Ming-Qi
MQ
Department of Cellular and Integrative Physiology, University of Nebraska Medical Center, Omaha, NE 68198-5850, USA.
Tang
Kang
K
Zimmerman
Matthew C
MC
Liu
Liping
L
Xie
Bin
B
Rozanski
George J
GJ
D000818:Animals; D019328:Buthionine Sulfoximine / Q000378:metabolism; D002478:Cells, Cultured; D004791:Enzyme Inhibitors / Q000378:metabolism; D005978:Glutathione / Q000378:metabolism; D006352:Heart Ventricles / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology; D006861:Hydrogen Peroxide / Q000378:metabolism; D008297:Male; D009203:Myocardial Infarction / Q000473:pathology / Q000503:physiopathology*; D032383:Myocytes, Cardiac / Q000166:cytology / Q000378:metabolism; D016877:Oxidants / Q000378:metabolism; D010084:Oxidation-Reduction; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction / Q000502:physiology; D013880:Thioredoxin-Disulfide Reductase / Q000378:metabolism*; D013879:Thioredoxins / Q000378:metabolism; D020257:Ventricular Remodeling / Q000502:physiology*; D005723:gamma-Glutamyltransferase / Q000235:genetics / Q000378:metabolism*
D004791:Enzyme Inhibitors; D016877:Oxidants; D015221:Potassium Channels; D019328:Buthionine Sulfoximine; D013879:Thioredoxins; D006861:Hydrogen Peroxide; D013880:Thioredoxin-Disulfide Reductase; D005723:gamma-Glutamyltransferase; D005978:Glutathione