The role of sulfhydryl groups in D-aspartate and rubidium release from neonatal rat primary astrocyte cultures.

We have recently demonstrated that both methylmercury (MeHg) and mercuric chloride (MC) induce D-aspartate release from neonatal rat primary astrocyte cultures maintained in isotonic conditions. In the present study, we compare several other sulfhydryl-(-SH) selective alkylating reagents [methyl methanethiosulfonate (MMTS), N-ethylmaleimide (NEM), and iodoacetamide (IA)] in isotonic, as well as hypotonic conditions to discern the functional importance of -SH groups in [3H]D-aspartate and 86rubidium (86Rb) release from astrocytes. Treatment of astrocytes (5 min) in isotonic buffer with the hydrophobic reagent NEM (10 microM) caused a marked increase in 86Rb release but had no effect on [3H]D-aspartate release. Neither IA-, nor MMTS-treatment (both at 10 microM) induced increase in [3H]D-aspartate or 86Rb release in isotonic buffer. In hypotonic condition (-50 mM Na+), astrocytes were most sensitive to MC exposure (5 microM), exhibiting an increase in both [3H]D-aspartate and 86Rb efflux. The hydrophobic compounds MMTS and NEM, and the hydrophilic -SH modifying reagent, IA, attenuated the hypotonic-induced efflux of [3H]D-aspartate, in the absence of an effect on 86Rb release. These observations are consistent with a critical role for -SH groups both in basal (i.e. isotonic) and hypotonic-induced release of D-aspartate and Rb from astrocytes. Lack of uniformity of these effects may be attributed to site-specificity, related to the physicochemical properties of these -SH alkylating reagents.