Activation of phospholipase D by metabotropic glutamate receptor agonists in rat cerebrocortical synaptosomes

1 The pharmacological profile of metabotropic glutamate receptor (mGluR) ac tivation of phospholipase D (PLD), and the associated signalling pathways, were examined in rat cerebrocortical synaptosomes. The assay was conducted using a transphosphatidylation reaction in synaptosomes which were pre-labe lled with either [H-3]-arachidonic acid or [P-32]-orthophosphate. 2 The mGluR agonists (1S,3R)1-aminocyclopentane-1,3-dicarboxylic acid (1S,3 R-ACPD) and (RS)-3,5-dihydroxyphenylglycine (DHPG), both activated PLD, whi le phorbol 12,13-dibutyrate (PDBu) treatment caused receptor-independent ac tivation of PLD and had an additive effect on 1S,3R-ACPD induced PLD activi ty. 3 A protein kinase C (PKC) inhibitor, GF109203X, failed to antagonize mGluR receptor-coupled PLD activity. We could not detect any increase in the pro ducts of PI (phosphoinositide)-specific phospholipase C (PI-PLC), inositol( 1,4,5)trisphosphate or diacylglycerol, by 1S, 3R-ACPD at 15 s. However, dia cylglycerol increased monophasically in response to mGluR agonists and rema ined elevated for at least 15 min. Phosphatidic acid phosphohydrolase (PAP) activity, which converts PA to DAG, was present in the synaptosomes. 4 These data suggest that, in rat cerebrocortical synaptosomes, the 1S,3R-A CPD-sensitive mGluR is coupled to PLD through a mechanism that is independe nt of both PKC and PI-PLC.