Enhancement of t‐[35S]Butylbicyclophosphorothionate and [3H]Strychnine Binding by Monovalent Anions Reveals Similarities Between γ‐Aminobutyric Acid‐ and Glycine‐Gated Chloride Channels

Abstract

The characteristics of [3H]strychnine and t-[32S]-butylbicyclophosphorothionate ([35S]TBPS) binding to sites associated with glycine- and .gamma.-aminobutyric acid (GABA)-gated chloride channels were compared in the presence of a series of anions with known permeabilities through these channels. Good correlations were found between the potencies (EC50) of these anions to stimulate radioligand binding and their permeabilities relative to chloride: the affinities (KD) of these radioligands in the presence of fixed concentrations of these anions and their relative permeabilities: the potencies (EC50) of these anions to stimulate [35S]TBPS and [3H]strychnine binding; and the affinities (KD) of [3H]strychnine and [35S]TBPS measured at a fixed concentration of these anons. The studies support electrophysiological and biochemical observations demonstrating similarities between glycine- and GABA-gated chloride channels, and suggest that anions enhance [3H]strychnine and [35S]BTS binding through specific anion binding sites located at the channels.