Role of γ-glutamyl transpeptidase in redox regulation of K + channel remodeling in postmyocardial infarction rat hearts

Ming Qi Zheng, Kang Tang, Matthew C. Zimmerman, Liping Liu, Bin Xie, George J. Rozanski

Research output: Contribution to journalArticle

19 Scopus citations

Abstract

γ-Glutamyl transpeptidase (γ-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 γ-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 γ-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 (Ito) was reversed after 4-5 h by 10 mmol/l GSHo or N-acetylcysteine (NAC o), and that the effect of GSHo but not NACo was blocked by the γ-GT inhibitors, acivicin or S-hexyl-GSH. Inhibition of γ-glutamylcysteine synthetase by buthionine sulfoximine did not prevent upregulation of Ito by GSHo, 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 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 upregulation of Ito 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 GSHo elicits γ-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 γ-GT catalysis of GSH o may be a therapeutic target to reverse pathogenic electrical remodeling of the failing heart.

Original languageEnglish (US)
Pages (from-to)C253-C262
JournalAmerican Journal of Physiology - Cell Physiology
Volume297
Issue number2
DOIs
StatePublished - Aug 1 2009

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Keywords

  • Glutathione
  • Thioredoxin
  • Transient outward current
  • Voltage-dependent K channel

ASJC Scopus subject areas

  • Physiology
  • Cell Biology

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