Effect of free fatty acids on GABAA receptor ligand binding

Phospholipase A2 (PLA2) treatment of synaptosomal membranes, which causes the release of fatty acids, particularly unsaturated fatty acids, inhibits the flux of chloride ions through the gamma-aminobutyric acid (GABA) benzodiazepine receptor ion channel in response to activation by agonists. PLA2 treatment has also been shown to affect ligand binding to the receptor. In the present study, we have investigated the effect of unsaturated free fatty acids, arachidonic acid and oleic acid and saturated free fatty acids, arachidic acid and stearic acid on various characteristics of GABAA receptor ligand binding. Only the unsaturated fatty acids showed any effect: arachidonic acid and oleic acid enhanced flunitrazepam binding and muscimol binding but inhibited tert-butylbicyclophosphorothionate (TBPS) binding in a dose-dependent manner. The effects on muscimol and TBPS binding were shown to be due to changes in receptor density by saturation analysis. Oleic acid and arachidonic acid also decreased the enhancement of flunitrazepam and muscimol binding by cartazolate and pentobarbital but did not affect GABA enhancement of flunitrazepam binding. These data indicate that unsaturated free fatty acids can mimic the effects of PLA2 treatment and underline the importance of the lipid microenvironment on ligand binding to the GABAA receptor.