Effect of furosemide on GABAA-induced 36Cl transport and Cl--ATPase activity in synaptic membranes of carp brain (Cyprinus carpio L.)

Abstract

We studied the effect of furosemide on GABAA-induced 36Cl transport and GABAA-induced Cl--ATPase activity in synaptic membranes of fish brain. At physiological pH 7.4, GABA (0.1–100 µM) stimulated 36Cl influx in synaptoneurosomes and Cl--ATPase activity in synaptic membranes. Furosemide (0.1–0.5 mM) removed the activating effect of the mediator on chloride transport and enzyme activity (I50 equaled 0.16 and 0.12 mM, respectively). In the absence of the mediator, picrotoxin (50 µM) activated the basal 36Cl influx in synaptoneurosomes and the basal Mg2+-ATPase activity of synaptic membranes. Furosemide (1 mM) removed the activating effect of picrotoxin on both biochemical processes. The obtained data demonstrated similar sensitivities of GABAA-induced transport of 36Cl in synaptoneurosomes and of GABAA-induced Cl--ATPase activity in the synaptic membranes to furosemide and indicated the involvement of the ATPase in GABAA-induced processes. The soluble ATPase, recovered by sodium deoxycholate solubilization of the membranes, remained sensitive to GABAA-ergic ligands, which suggested proximity of their binding sites with ATP hydrolysis sites in the protein molecule and their structural coupling.