EXCITATORY AMINO-ACID RECEPTOR-STIMULATED PHOSPHOINOSITIDE TURNOVER IN PRIMARY CEREBROCORTICAL CULTURES

1 Characterization of excitatory amino acid-induced accumulation of [H -3]-phosphoinositides was carried out in primary cerebrocortical cultu res isolated from foetal rats. 2 All of the excitatory amino acid rece ptor agonists examined caused concentration-dependent enhancement of p hosphoinositide (PI) formation. The most potent excitatory amino acid receptor agonists were quisqualate, (1S,3R)-1-aminocyclopentane-1,3-di carboxylic acid ((1S,3R)-ACPD), ibotenate and glutamate with mean EC50 values of 0.9 +/- 0.4 muM, 15 +/- 5 muM, 15 +/- 3 muM and 41 +/- 8 mu M respectively. 3 The selective ionotropic receptor antagonists kynure nic acid (1 mM), dihydroxy-6-nitro-7-sulphamoyl-benzo(F)quinoxaline (N BQX, 10 muM) and (+/-)-4-(3-phosphonopropyl)-2 piperazinecarboxylic ac id (CPP, 100 muM), failed to block responses to quisqualate, (1S,3R)-A CPD or glutamate. D,L-2-Amino-3-phosphonopropionate (D,L-AP3) did not block 1S,3R-ACPD or quisqualate-induced PI turnover, but had an additi ve effect with quisqualate or (1S,3R)-ACPD. 4 Exposure of cultures to agonists in the absence of added extracellular calcium reduced the max imal quisqualate response by approximately 45%, revealing a two-compon ent concentration-response curve. Concentration-response curves to ibo tenate and glutamate became flattened by omission of extracellular cal cium, whereas (1S,3R)-ACPD-stimulated PI turnover was unaffected. 5 Pr etreatment of cultures with pertussis toxin markedly inhibited PI resp onses evoked by (1S,3R)-ACPD. 6 These results suggest that excitatory amino acid-stimulated PI turnover in cerebrocortical cultures is indep endent of ionotropic receptor activation and is mediated via specific G-protein-linked metabotropic receptors. The partial dependence of the responses to quisqualate, ibotenate and glutamate on the presence of extracellular calcium suggests that the effects of these agonists may be mediated by more than one receptor subtype.