Abstract

γ-Aminobutyric acid (GABA) and a few monovalent anions enhance benzodiazepine (BZ) binding to its receptor in rat brain by virtue of an increase in affinity. The effects of 4,4'-diisothiocyano-2,2'-disulfonic acid stilbene (DIDS) and 4-acetamido-4'-isothiocyano-2,2'-disulfonic acid stilbene (SITS), which are blockers of the anion channel in eyrthrocyte membranes, have been evaluated in this system. DIDS inhibits the increase in affinity of benzodiazepine receptors that is produced by maximal concentrations of GABA and iodide. DIDS also exerts a slight effect on control binding, due to a decrease in the number of sites without substantial change in apparent affinity. When membranes were pretreated with DIDS and then extensively washed, the effect of DIDS was reversible at 0° but irreversible at 37°. Dose-response studies of GABA and iodide using DIDS-pretreated membranes indicate that DIDS reduces the maximal response for GABA and decreases the sensitivity (increases the ED₅₀) for iodide. DIDS is more potent than SITS, which has weaker chloride channel-blocking properties. Four other amino-reactive reagents without anion channel-blocking properties failed to alter selectively BZ binding. These studies indicate that DIDS and related compounds may serve as useful probes of the interaction between the benzodiazepine receptor and the GABA receptor and further support the concept that these receptors are coupled to a mutually shared chloride channel.