Brain regional heterogeneity of pH effects on GABAA receptor-associated [35S]TBPS binding

We have utilized quantitative autoradiography with the GABA(A) receptor chloride channel blocker [S-35] t-butylbicyclophosphorothionate ([S-35] TBPS) in rodent brain sections to investigate if differential proton modulation of various GABAA receptor subtypes expressed in various brain regions are differentially sensitive to pH alternations. Acidic and basic pHs decreased the binding, the mean values at pH 5.4 and pH 9.4 being 17% and 76% of the binding at pH 7.4, respectively. The regional profiles of the pH effects could be divided into two types. In regions with high basal binding at pH 7.4, the pH profile was usually 'bell-shaped,' with maximal binding at pH 7.4 ( type 1). In regions with low basal binding at pH 7.4, the pH profile ( type 2) revealed very low binding at pH 5.4, lower sensitivity to high pH, and usually maximal binding at pH 8.4. In brain regions with type 1 pH modulation alpha1 and beta2 subunits are abundantly expressed, whereas alpha2 and beta3 subunits are abundant in type 2 regions. Therefore the alpha1beta2gamma2 and alpha2beta3gamma2 receptor subtypes are suggested to be preferentially responsible for brain regional heterogeneity of the pH modulation of [S-35] TBPS binding.