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 [1,3,21,22]. 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 [H-3]D-aspartate and (86)rubidium (Rb-86) release from astrocytes. Treatment of astrocytes (5 min) in isotonic buffer with the hydrophobic reagent NEM (10 mu M) caused a marked increase in Rb-86 release but had no effect on [H-3]D-aspartate release. Neither IA-, nor MMTS-treatment (both at 10 mu M) induced increase in [H-3]D-aspartate or Rb-86 release in isotonic buffer. In hypotonic condition (-50 mM Na+), astrocytes were most sensitive to MC exposure (5 mu M), exhibiting an increase in both [H-3]D-aspartate and Rb-86 efflux. The hydrophobic compounds MMTS and NEM, and the hydrophilic -SH modifying reagent, IA, attenuated the hypotonic-induced efflux of [H-3]D-aspartate, in the absence of an effect on Rb-86 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.