Direct evidence of intercellular sharing of glutathione via metabolic cooperation

Intracellular glutathione (GSH) content and cell density are known to be two important determinants of cell sensitivity to free radicals and radiation. We have investigated intercellular sharing of GSH via metabolic cooperation (MC) by measuring the GSH content of Chinese hamster V79 cells under conditions that varied MC among cells. GSH was measured by flow cytometry with monochlorobimane, which becomes fluorescent after conjugation to GSH by GSH-S-transferase. High-performance liquid chromatography was used to confirm the accuracy of GSH measurements by flow cytometry. Several lines of evidence indicate sharing of GSH or its precursor gamma-glutamylcysteine via MC. These include a cell density-dependent heterogeneity in GSH content, reconstitution of GSH in GSH-depleted cells by coculture with nondepleted cells (except when the depleted cells were MC deficient), and decreased equilibration of GSH among GSH-depleted cells and nondepleted cells when an inhibitor of MC (phorbol myristate acetate) was present. The equilibration of GSH among GSH-depleted cells and nondepleted cells in coculture was not inhibitable by acivicin, suggesting that this form of intercellular sharing of GSH does not rely on gamma-glutamyltransferase-mediated extracellular transport of GSH.