Metabolic coupling of glutathione between mouse and quail cardiac myocytes and its protective role against oxidative stress

Abstract

Cultured quail myocytes were much more resistant to H2O2 toxicity than cultured mouse myocytes. The intracellular concentration of glutathione ([GSH](i)) and the activity of γ-glutamylcysteine synthetase (γ-GCS) in quail heart cells were about five and three times higher, respectively, than in mouse heart cells, although catalase and glutathione peroxidase (GSH(px)) activity was similar in both. Preloading of γ-glutamylcysteine monoethyl ester (γ-GCE), a membrane-permeating GSH precursor, increased the H2O2 resistance of cultured mouse myocytes. These observations suggest that the high [GSH](i) and the high activity of γ-GCS in quail myocytes are responsible for their high resistance to H2O2. Both H2O2 sensitivity and [GSH](i) of mosaic sheets composed of equal amounts of mouse and quail myocytes approximated those of sheets composed entirely of quail myocytes. From these observations, it is hypothesized that GSH was transferred from quail myocytes to mouse myocytes, probably through gap junctions between them, and that quail myocytes resynthesized GSH by a feedback mechanism, thus maintaining their intracellular GSH levels. When the fluorescent dye lucifer yellow was injected into a beating quail myocyte in a mosaic sheet, it spread to neighboring mouse myocytes but not to neighboring L cells (a cell line derived from mouse connective tissue). These observations indicate the existence of gap junctions in the region of cell contact between mouse and quail myocytes but not between quail myocytes and L cells. When quail myocytes preloaded with [3H]γ-GCE were cocultured with mouse myocytes and L cells, the radioactivity was transmitted to neighboring mouse myocytes but not L cells. These observations show that GSH and/or its precursors can be transmitted from quail myocytes to mouse myocytes through gap junctions and that this can protect mouse myocytes from H2O2 toxicity. Mouse myocyte sheets composed of 104 cells or more showed higher resistance to H2O2 toxicity than single isolated mouse myocytes. Metabolic coupling of GSH between myocytes may contribute at least in part to this high resistance of the cell sheets.