[Effect of chloride and bicarbonate ions on Mg2+ -ATPase of plasma membranes of bream (Abramis brama L.) brain sensitive to GABAA-ergic compounds].

Effect of Cl and HCO3- ions on the Mg2+ -ATPase activity of the plasma membrane of bream brain was investigated. Cl- (5 or 10 mM) and HCO3- (1-5 mM) individually have low effect on the "basal" Mg2+ -ATPase. Simultaneous presence of Cl- and HCO3- in the incubation medium significantly increased the enzyme activity. Maximum effect of anions on the enzyme is observed in the presence of Cl- (approximately 7 mM) and HCO3- (approximately 3 mM). Br- can replace Cl- under joint effect with HCO3-, while I- has half maximum activity compared with Cl-. Bicuculline (7 microM) inhibits completely the joint effect of Cl- and HCO3- on the enzyme, while it has no effect on the "basal" Mg2+ -ATPase activity. SH-reagents (5, 5-dithiobis-2-nitrobenzoic acid, N-ethylmaleimide), oligomycine and orthovanadate inhibited the Cl-, HCO3- -activated Mg2+ -ATPase. The obtained results demonstrated that Mg2+ -ATPase of the bream brain sensitive to GABAergic ligands at a fixed concentrations of Cl- and HCO3- ions in the incubation medium is Cl-, HCO3- -activated by Mg2+ -ATPase, whose activity meets a number of requirements to the system which may be involved by GABAA receptors in the Cl-/HCO3- -exchange processes.