Effect of Phospholipase A₂ on Temperature-Induced High-Affinity [³H]Tryptamine Binding Sites in Rat Brain

Abstract

To investigate a link between membrane phospholipids and tryptamine binding molecules, we examined the effects of phospholipases A₂ and D on the temperature-sensitive high-affinity [³H]tryptamine binding sites in rat brain. When the phospholipase A₂-treated membranes were exposed to 1% bovine serum albumin (BSA) before assaying for [³H]tryptamine binding, a complete dose-dependent inhibition curve was observed. At a concentration of 0.03 U, the action of phospholipase A₂ resulted in the splitting of phosphatidylserine (PS), choline phosphatides (PC) and ethanolamine phosphatides (PE) by about 32, 34 and 65%, respectively, and reduced [³H]ligand binding by about 32%. On the contrary, in the case of phospholipase D (500 U), PS and PC decreased by about 8% and 33% and PE by about 29% with no significant alteration in the binding capacity. Moreover, Scatchard analysis of the [³H]tryptamine binding showed that phospholipase A₂ drastically increased only the K_D value of the high affinity sites, and this was accompanied by a decrement of the B_max values of both the high and low affinity binding sites. From these results, it is inferred that certain lipids (PS) may be a modulator for the function of the temperature-induced high-affinity [³H]tryptamine binding molecules.