Functional modulation of human recombinant gamma-aminobutyric acid type A receptor by docosahexaenoic acid

Human gamma-aminobutyric acid type A (GABAA) receptors were expressed in the baculovirus/Sf-9 insect cell expression system using recombinant cDNA of alpha1beta2gamma2s subunits. The effect of unsaturated fatty acids on GABAA receptor complexes was investigated electrophysiologically using conventional whole cell recording under voltage clamp. Three distinct effects of docosahexaenoic acid (DHA) on the GABA responses were observed. First, DHA, at a concentration of 10(-7) M or greater, accelerated the desensitization after the peak of the GABA-induced current. Second, DHA (10(-6) M) potentiated the peak amplitude of GABA response. This potentiation by DHA was inhibited in the presence of Zn2+ (10(-5) M); Cu2+ and Ni2+ mimicked the action of Zn2+. Zn2+ (10(-5) M) did not block the GABA response on alpha1beta2gamma2s receptor complexes. Third, DHA, at a concentration of 3 x 10(-6) M or higher, gradually suppressed the peak amplitude of GABA response. A protein kinase A inhibitor, a protein kinase C inhibitor, and a Ca2+ chelator did not modify the effects of DHA on GABA-induced chloride ion current. Six unsaturated fatty acids other than DHA were examined. Arachidonic acid mimicked the effect of DHA while e.g. oleic acid had no effect. The inhibition of the GABA response in the presence of DHA was also observed in cells expressing GABAA receptors of alpha1 and beta2 subunit combinations. The data show that the gamma subunit is essential for DHA and arachidonic acid to potentiate the GABA-induced Cl- channel activity and to affect the desensitization kinetics of the GABAA receptor.