N-Methyl-D-aspartate and quisqualate/DL-alpha-amino-3-hydroxy-5- methylisoxazole-4-propionic acid receptors: differential regulation by phospholipase C treatment.

The effect of phospholipase C (PLC) treatment of rat brain membranes on the binding properties of excitatory amino acid receptors was investigated using both a phosphsphatidylcholine-hydrolyzing PLC from Clostridium perfringens and a phosphatidylinositol-specific PLC from Bacillus thuringiensis. PLC from C. perfringens produced an increased affinity of the quisqualate/DL-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptor for its ligand, whereas kainate receptor binding was not affected. Both kinetic analysis and equilibrium saturation experiments indicated that PLC treatment produced a decrease in affinity for [3H]N-(1-[thienyl]cyclohexyl)-piperidine [( 3H]TCP), a ligand for the N-methyl-D-aspartate (NMDA) receptor-associated ionic channel, when the channel was fully activated by high concentrations of glutamate and glycine but increased its binding under conditions in which the channel was presumably closed. This latter component of the binding was not due to an interaction of [3H]TCP with non-glutamate receptor sites, such as sigma opioid and histamine H3 receptors. Binding of [3H]glutamate and [3H] glycine to the NMDA receptors was not modified by PLC treatment, but there was a large decrease in the binding of the NMDA antagonist [3H]3-[(+/-)-2-carboxypiperazine-4-yl)propyl-1-phosphonic acid. Stimulation by glycine of [3H]glutamate binding was also abolished following PLC treatment. In contrast to PLC from C. perfringens, phosphatidylinositol-specific PLC treatment did not detectably modify the binding properties of the quisqualate/AMPA receptor or the NMDA receptor channel. These data indicate that alterations in the lipid microenvironment of the glutamate receptors modulate both the conformation and the function of the receptors and suggest a possible role for phospholipases in the regulation of synaptic transmission at excitatory synapses.