Barbiturate and picrotoxin-sensitive chloride efflux in rat cerebral cortical synaptoneurosomes

The effects of various barbiturates and picrotoxin in modifying the efflux of chloride (³⁶Cl^-) was studied in a novel subcellular preparation from rat cerebral cortex, the 'synaptoneurosome'. Dilution of synaptoneurosomes pre-loaded with ³⁶Cl^- resulted in rapid efflux of ³⁶Cl^- that could be measured as early as 10 s following dilution. In the presence of barbiturates such as pentobarbital and hexobarbital there was a significant increase in ³⁶Cl^- efflux which was not observed with the pharmacologically-inactive barbiturate, barbital. The effect of barbiturates in enhancing ³⁶Cl^- efflux was also stereospecific [(-)-DMBB > (+)-DMBB] and reversed by picrotoxin. By contrast, picrotoxin alone significantly inhibited ³⁶Cl^- efflux. These data demonstrate pharmacologically relevant Cl^- transport for the first time in a subcellular brain preparation.