Taurine allosterically inhibits binding of [S]-t-Butylbicyclophosphorothionate (TBPS) to rat brain synaptic membranes

The modulatory effects of taurine on [³⁵S]-t-Butylbicyclophosphorothionate (TBPS) binding to rat brain synaptic membranes were evaluated and compared with that of GABA. Taurine allosterically inhibited TBPS binding by interacting with a bicuculline-sensitive site, similar to GABA. Taurine was as effective as GABA but less potent. The potency of taurine inhibition of TBPS binding varied among brain regions with cerebellum > olfactory bulb > cortex, similar to that of GABA. Inhibition of TBPS binding to cortical membranes measured under nonequilibrium conditions yielded a dynamic biphasic inhibition curve that was similarly shaped for GABA and taurine. The effect of taurine on TBPS binding was pharmacologically specific in that β-alanine and guanadinoethanesulfonate were as effective as taurine, while hypotaurine and -aminoethylhydrogen sulfate were only partially effective at high concentrations, and isethionic acid was without effect. Taurine, similar to GABA enhanced the effects of pentobarbital on TBPS binding when present at concentrations that were otherwise ineffective on their own. The results of these studies support the notion that taurine interacts with the GABA recognition site of the GABA_A receptor complex.