Glutathione levels in primary glial cultures: monochlorobimane provides evidence of cell type-specific distribution

Abstract

Because glutathione (GSH) levels in glia play an important role in cellular defense against oxidative and nitrosative stress, the present study was designed to study GSH levels in the primary glial cell cultures. Here we used fluorescence microscopy and spectroscopy with monochlorobimane for measurement of intracellular glutathione content. Monochlorobimane showed high specificity for GSH with very little binding to protein sulphydryls as ascertained from the low fluorescence intensity of the protein fraction of the cells as well as from the low fluorescence of the GSH-depleted cells. The formation of the monochlorobimane-glutathione conjugate was observed to be enzymatically catalyzed as seen from its higher rate of formation in the presence of cell homogenate. A monochlorobimane concentration of 60 microM was used for conjugation of cellular GSH; at higher mBCl concentrations there was no appreciable increase in fluorescence. Therefore, cultures were treated with 60 microM mBCl for an incubation time of 20 min (beyond this time, export of the bimane-glutathione adduct was significantly large) and examined by fluorescence microscopy. This adduct could be fixed with a mixture of paraformaldehyde and glutaraldehyde, and excellent fixation was observed with 4% paraformaldehyde and 0.2% glutaraldehyde. Analysis of the fluorescence images revealed differences in fluorescence intensity between astro- and microglial cells, which were identified by glial fibrilliary acidic protein and OX42 staining, respectively. Microglial cells isolated from primary glial cultures were found to have higher GSH content than astrocytes. Biochemical determination of GSH levels in microglia isolated from primary glial cultures corroborated this fact. From our findings it seems that owing to the greater intracellular concentration of reactive oxygen and nitrogen species to which microglia are subjected, especially under conditions of inflammation, this cell type is fortified with higher GSH levels as a means to combat oxidative and nitrosative stress.