Interactions of Phospholipids and Free Fatty Acids with Antidepressant Recognition Binding Sites in Rat Brain

Abstract

The lipid microenvironment of cell membranes has been shown to regulate both neurotransmitter and hormone receptors. Preincubation of cortical synaptosomal membranes of rat brain with phospholipase A₂ (PLA₂) increases the number of [³H]imipramine ([³H]IMI) high affinity binding sites without altering K_d(B_max control: 2.53± 0.28 pmol/mg protein vs B_max PLA₂: 3.66± 0.26 pmol/mg protein). The displacement curves of [³H]IMI binding in synaptosomal membranes with other tricyclic antidepressants are not affected by the presence of PLA₂. The effect of PLA₂ was prevented by incubation with EGTA (2x10) or bovine serum albumin (BSA; 1:1). In addition, end products of catalytic activity of PLA₂ such as unsaturated fatty acids (arachidonic or oleic acids) mimicked the effect of PLA₂. These effects were entirely prevented by preincubation with BSA. The in vitroaddition of the acidic phospholipid phosphatidylserine isolated from bovine brain (BC-PS) produced a similar increase in B_max. This action was also blocked by addition of BSA. On the other hand, palmitic acid, a saturated fatty acid, and lysophosphatidylserine (lysoPS) or lysophosphatidylethanolamine (lysoPE) failed to modify [³H]IMI binding sites. The chronic administration of tricyclic antidepressant (AD) resulted in a 25% decrease in [³H]IMI binding sites in synaptosomal membranes. Preincubation of these AD-treated membranes with PLA₂ did not alter [³H]IMI binding, whereas the addition of unsaturated free fatty acids (FFA) produced a greater increase in the density of [³H]IMI binding sites in comparison with control membranes. Taken together, these findings suggest that unsaturated free fatty acids could play an important role in the regulation of the number of [³H]IMI high affinity binding sites in the mammalian brain.