Bicarbonate and thiocyanate ions affect the gating of γ-aminobutyric acidA receptors in cultured rat cortical cells

The ionophore function of gamma -aminobutyric acid(A) (GABA(A)) receptors was studied by whole-cell patch clamp electrophysiology in primary cultures of rat cerebral cortex. Chloride ions were replaced for SCN- (thiocyanate) and HCO3(bicarbonate) ions. The EC50 values of the GABA(A) agonist muscimol (HCO3- > Cl- > SCN-) varied parallel with the free energies of dehydration of the anions, while the inhibition constants of the GABA(A) antagonist bicuculline methiodide were not affected. These findings might be relevant in the interpretation of the contribution of HCO3- versus Cl- currents to the pharmacological differences between depolarizing and hyperpolarizing GAB(A) responses. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.