Phospholipase A2 down-regulates the affinity of [3H]AMPA binding to rat cortical membranes.

The effects of exogenous phospholipase A 2 on the binding of α-[ 3 H]amino-3-hydroxy-5-methylisoxazole-4-propionate ([ 3 H]AMPA) to rat cortical membranes in the presence of the chaotrope potassium thiocyanate were assessed. Pretreatment of membranes with secretory phospholipase A 2 (sPLA 2 ) elicited a concentration-dependent decrease in specific [ 3 H]AMPA binding due mainly to a decrease in affinity (K D ). This observation, together with protease inhibitor and western blot evidence, suggest that the SPLA 2 effect is not due to proteolysis. The sPLA 2 -evoked decrease was temperature and calcium dependent. Inclusion of the specific inhibitor oleoyloxyethyl phosphocholine or preincubation of the enzyme with reducing agents to degrade its secondary structure significantly reduced the SPLA 2 inhibition. These results suggest that the effects of sPLA 2 arise from an enzymatic action rather than a competitive interaction at the AMPA binding site. However, arachidonic acid, a major metabolite of sPLA 2 action, did not cause a similar decrease in the affinity of [ 3 H]AMPA binding. In contrast to the effects on [ 3 H]AMPA binding, sPLA 2 caused an increase in [ 3 H]CNQX binding, which is in accordance with the functionality of the AMPA receptor complex. These results suggest that sPLA 2 may play a role in the physiological and pathophysiological regulation of AMPA receptors.