HIGH-AFFINITY BINDING-SITES FOR I-125 LABELED PANCREATIC SECRETORY PHOSPHOLIPASE A(2) IN RAT-BRAIN

Porcine pancreatic secretory phospholipase A(2) (ppsPLA(2)) has been s hown to modulate agonist and antagonist binding to alpha-amino-3-hydro xy-5-methylisoxazolepropionate (AMPA) receptors and to effect neurotra nsmission in the central nervous system (CNS). To further elucidate th e mechanism of action of ppsPLA(2) in the CNS. the binding profile of I-125-labelled ppsPLA(2) to rat whole-brain membranes was assessed. Tw o classes of calcium-dependent binding sites were detected using unlab elled ppsPLA(2) as a displacer with IC50 values of 3 and 217 nM. Simil ar values were obtained for [I-125]ppsPLA(2) binding to membranes prep ared from isolated cortical and hippocampal rat brain regions. [I-125] ppsPLA(2) binding displayed bell-shaped concentration-dependence curve s to Ca2+, Zn2+ and pH. Binding was not inhibited by AMPA, the false s ubstrate, oleoyloxyethyl phosphocholine (OOPC), or by BSA-galactose or wheat germ agglutinin. [I-125]ppsPLA(2) binding was reduced by treatm ent of the rat brain membranes with mercaptoethanol and proteinase K t reatment or by their pre-incubation at 95 degrees C. These results sho w a different binding profile to the previously characterised snake ve nom sPLA(2) N-type receptors and suggest the existence of novel class of sPLA(2) N-type binding sites. (C) 1997 Elsevier Science B.V.