Effect of ${\text{HCO}}_3^{-}$ Ions on the ATP-Dependent GABA_A Receptor-Coupled Cl^– Channel in Rat Brain Plasma Membranes

We studied the effect of Cl⁻ (10–75 mM) and ${\text{HCO}}_3^{-}$ ions (10–25 mM) on the ATP-dependent GABA_A receptor-coupled Cl⁻ channel (Cl⁻-ATPase) in rat brain plasma membranes. The total enzyme activity was detected in the presence of both anions at a Cl⁻/${\text{HCO}}_3^{-}$ ratio of 5:1 (Cl⁻, ${\text{HCO}}_3^{-}$-ATPase). Specific inhibitors of P-type transport ATPases (N-ethylmaleimide, ovanadate, and oligomycin) suppressed Cl⁻, ${\text{HCO}}_3^{-}$-ATPase, while the Cl⁻- and ${\text{HCO}}_3^{-}$-ATPase activities were low sensitive to these ligands. Bicuculline abolished the activating effect of Cl⁻ and ${\text{HCO}}_3^{-}$ ions on the enzyme. ${\text{HCO}}_3^{-}$ ions had no effect on the ATP-dependent Cl⁻ transport into proteoliposomes (with the involvement of reconstituted ATPase). In experiment with Cl⁻-preloaded liposomes, addition of ${\text{HCO}}_3^{-}$ ions to the incubation medium caused the reversion of Cl⁻ transport (ion efflux from liposomes). Our results suggest that ${\text{HCO}}_3^{-}$ ions play an important role in the modification of properties of the ATP-dependent GABA_A receptor-coupled Cl⁻ channel and GABAA receptor-induced Cl⁻/${\text{HCO}}_3^{-}$ exchange. These ions are probably involved in GABAA receptor-induced Cl⁻/${\text{HCO}}_3^{-}$ exchange in neuronal membranes.