UNSATURATED FREE FATTY-ACIDS INCREASE BENZODIAZEPINE RECEPTOR AGONISTBINDING DEPENDING ON THE SUBUNIT COMPOSITION OF THE GABA(A) RECEPTOR COMPLEX

It has been shown previously that unsaturated free fatty acids (FFAs) strongly enhance the binding of agonist benzodiazepine receptor ligand s and GABAA receptor ligands in the CNS in vitro. To investigate the s electivity of this effect, recombinant human GABA(A)/benzodiazepine re ceptor complexes formed by different subunit compositions (alpha(x) be ta(y) gamma(2) X = 1, 2, 3, and 5; y = 1, 2, and 3) were expressed usi ng the baculovirus-transfected Sf9 insect cell system. At 10(-4) M, un saturated FFAs, particularly arachidonic (20:4) and docosahexaenoic (2 2:6) acids, strongly stimulated (>200% of control values) the binding of [H-3]flunitrazepam ([H-3] FNM) to the alpha(3) beta(2) gamma(2) rec eptor combination in whole cell preparations. No effect or small incre ases in levels of unsaturated FFAs on [H-3] FNM binding to alpha(1) be ta(x) gamma(2) and alpha(2) beta(x) gamma(2) receptor combinations wer e observed, and weak effects (130% of control values) were detected us ing the alpha(5) beta(x) gamma(2) receptor combination. The saturated FFAs, stearic and palmitic acids, were without effect on [H-3]FNM bind ing to any combination of receptor complexes. The hydroxylated unsatur ated FFAs, ricinoleic and ricinelaidic acids, were shown to decrease t he binding of [H-3] FNM Only if an alpha(1) beta(2) gamma(2) receptor combination was used. Given the heterogeneity of the GABA(A)/ benzodia zepine receptor subunit distribution in the CNS, the effects of FFAs o n the benzodiazepine receptor can be assumed to vary at both cellular and regional levels.