Effect of HCO3(-) 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 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(-)/ HCO(3)(-) ratio of 5:1 (Cl(-), HCO(3)(-)-ATPase). Specific inhibitors of P-type transport ATPases (N-ethylmaleimide, o-vanadate, and oligomycin) suppressed Cl(-), HCO(3)(-)-ATPase, while the Cl(-)- and HCO(3)(-)-ATPase activities were low sensitive to these ligands. Bicuculline abolished the activating effect of Cl(-) and HCO(3)(-) ions on the enzyme. 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 HCO(3)(-) ions to the incubation medium caused the reversion of Cl(-) transport (ion efflux from liposomes). Our results suggest that HCO(3)(-) ions play an important role in the modification of properties of the ATP-dependent GABA(A) receptor-coupled Cl(-) channel and GABA(A) receptor-induced Cl(-)/ HCO(3)(-) exchange. These ions are probably involved in GABA(A) receptor-induced Cl(-)/ HCO(3)(-) exchange in neuronal membranes.