Phospholipase A 2 Modulates Different Subtypes of Excitatory Amino Acid Receptors: Autoradiographic Evidence

Abstract

Exogenous phospholipases have been used extensively as tools to study the role of membrane lipids in receptor mechanisms. We used in vitro quantitative autoradiography to evaluate the effect of phospholipase A 2 (PLA 2 ) on N -methyl-D-aspartate (NMDA) and non-NMDA glutamate receptors in rat brain. PLA 2 pretreatment induced a significant increase in Α-[ 3 H]amino-3-hydroxy-5-methylisoxazole-4-propionate ([ 3 H]AMPA) binding in the stratum radiatum of the CA1 region of the hippocampus and in the stratum moleculare of the cerebellum. No modification of [ 3 H]AMPA binding was found in the stratum pyramidale of the hippocampus at different ligand concentrations. [ 3 H]-Glutamate binding to the metabotropic glutamate receptor and the non-NMDA-, non-kainate-, non-quisqualate-sensitive [ 3 H]glutamate binding site were also increased by PLA 2 pretreatment. [ 3 H]Kainate binding and NMDA-sensitive [ 3 H]glutamate binding were minimally affected by the enzyme pretreatment. The PLA 2 effect was reversed by EGTA, the PLA 2 inhibitor p -bromophenacyl bromide, and prolonged pretreatment with heat. Bovine serum albumin (1%) prevented the increase in metabotropic binding by PLA 2 . Arachidonic acid failed to mimic the PLA 2 effect on metabotropic binding. These results indicate that PLA 2 can selectively modulate certain subtypes of excitatory amino acid receptors. This effect is due to the enzymatic activity but is probably not correlated with the formation of arachidonic acid metabolites. Independent of their possible physiological implications, our results provide the first autoradiographic evidence that an enzymatic treatment can selectively affect the binding properties of excitatory amino acid receptors in different regions of the CNS.