The role of sulphydryl groups in efflux of taurine and GABA from cerebral cortical cells.

1. Effluxes of taurine and GABA from pre-loaded cells in slices of rat cerebral cortex in isosmotic media is enhanced by the -SH reagent p-chloromercuriphenylsulphonic acid (pCMPS) (100 microM) accompanied by moderate swelling. Those effects were more pronounced with GABA than with taurine. N-ethylmaleimide (NEM) (100 microM) had only slight affects on these variables. 2. The acceleration of effluxes that occurs when medium osmolality is reduced from 315 to 265 mosmol/kg is blocked by NEM and by pCMPS, with pronounced cell swelling. 3. The inhibitory effects of these reagents on efflux is abolished when cell swelling is prevented by the addition of 25 mM sucrose to hyposmotic incubation media (with equimolar reduction in NaCl concentration). 4. Pre-exposure of slices to dithiothreitol (DTT) (100 microM) blocks the effects of NEM and pCMPS on GABA efflux in hyposmotic media, but has no effect on taurine efflux. 5. The cell membrane and cytoskeletal responses which may underlie these effects are briefly discussed.