A molecular model for the synergic interaction between γ-aminobutyric acid and general anaesthetics

Abstract

Within the context of the discussion about rational polytherapy, we determined the effects of four anaesthetics on the binding of [ 3 H ] t-butylbicycloorthobenzoate ([ 3 H ]TBOB) to the GABA A receptor complex in the presence of several concentrations of GABA (γ-aminobutyric acid), in order to build a molecular model that can describe and quantify the interactions between the compounds. The empirical isobole method revealed that GABA and the anaesthetics acted synergically in displacing [ 3 H ]TBOB. This synergy could be described by a simple molecular model in which both GABA and the anaesthetics displaced [ 3 H ]TBOB allosterically and in which GABA allosterically enhanced the binding of the anaesthetics. To get information about the interaction between GABA and anaesthetics, we used [ 3 H ]TBOB as a tracer ligand. The model indicated that GABA enhanced the affinity of thiopental 3.0-fold, propofol 5.0-fold, the neuroactive steroids Org 20599 3.5-fold and Org 20549 13-fold. Insight into the molecular mechanism and strength of these interactions can help clinicians to choose therapeutically optimal drug and dose combinations: a step towards rational polytherapy.