Effect of phospholipase A2 on temperature-induced high-affinity [3H]tryptamine binding sites in rat brain

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 KD value of the high affinity sites, and this was accompanied by a decrement of the Bmax 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.