The role of -SH groups in methylmercuric chloride-induced d-aspartate and rubidium release from rat primary astrocyte cultures

Methylmercuric chloride (MeHgCl) was shown to increase d-aspartate and rubidium (Rb; a marker for potassium) release from preloaded astrocytes in a dose- and time-dependent fashion. Two sulfhydryl (-SH) protecting agents: a cell membrane non-penetrating compound, reduced glutathione (GSH), and the membrane permeable dithiothreitol (DTT), were found to inhibit the stimulatory action of MeHgCl on the efflux of radiolabeled d-aspartate as well as Rb. MeHgCl-induced d-aspartate and Rb release was completely inhibited by the addition of 1 mM DTT or GSH during the actual 5 min perfusion period with MeHgCl (10 μM). However, when added after MeHgCl treatment, this inhibition could not be fully sustained by GSH, while DTT fully inhibited the MeHgCl-induced release of d-aspartate. Neither DTT or GSH alone had any effect on the rate of astrocytic d-aspartate release. Accordingly, it is postulated that the stimulatory effect exerted by MeHgCl on astrocytic d-aspartate release is associated with vulnerable -SH groups located within, but not on the surface of the cell membrane. Omission of Na⁺ from the perfusion solution did not accelerate MeHgCl-induced d-aspartate release, suggesting that reversal of the d-aspartate carrier cannot be invoked to explain MeHgCl-induced d-aspartate release. Omission of Ca²⁺ from the perfusion solution increased the time-dependent MeHgCl-induced d-aspartate release.