The "cage" convulsant [(35)S]t-butylbicyclophosphorothionate ([(35)S]TBPS) binds with high affinity to specific sites "at" or "near" a ?-amino-butyric acid (GABA)-gated chloride channel according to current hypothesis. We now report that pretreatment of membranes with 2,3-butanedione, an arginine-specific reagent, causes a dose- and time-dependent decrease in the number of [(35)S]TBPS binding sites. No decrease occurs when membranes are pretreated with 2,3-butanedione in the presence of picrotoxinin. Binding of [(35)S]TBPS to the remaining sites occurs with the same characteristics as binding to the untreated receptor population.