SPECIES-DEPENDENT FUNCTIONAL-PROPERTIES OF NON-NMDA RECEPTORS EXPRESSED IN XENOPUS-LAEVIS OOCYTES INJECTED WITH MAMMALIAN AND AVIAN BRAIN MESSENGER-RNA

1 Species-dependent variation in the functional properties of non-NMDA receptors was investigated by intracellular recording in Xenopus laev is oocytes injected with rat, chick acid calf brain mRNA. 2 In all mRN A-injected oocytes, kainic acid (KA), domoic acid (Dom) and 5-bromowil lardiine (BrW) evoked large, maintained membrane currents, in contrast to the smaller, desensitizing responses elicited by lpha-amino-3-hydr oxy-5-methyl-4-isoxazolepropionic acid (AMPA), quisqualic acid (QA) an d L-glutamic acid (L-Glu). Dose-response curves for KA in oocytes inje cted with calf EC(50) = 96.4 +/- 12.3 mu M; mean +/- s.e.mean), chick (87.0 +/- 8.9 mu M) or rat (88.7 +/- 4.3 mu M) brain mRNA were similar . 3 Current-voltage (I-V relationships determined with KA inwardly rec tified in oocytes injected with calf or chick mRNA; whereas, outward r ectification was observed in oocytes injected with rat brain mRNA. 4 I n oocytes injected with rat brain mRNA, AMPA antagonized responses evo ked by KA in a competitive manner. The absolute amplitudes of KA and A MPA responses in the same oocytes were significantly correlated, which is consistent with both agonists acting on the same receptor-ionophor e complex. 5 In contrast, in oocytes injected with calf or chick brain mRNA, AMPA (QA and L-Glu) antagonized the response evoked by KA in a non-competitive manner. The response amplitudes of KA compared to AMPA , QA or L-Glu in the same oocytes were not correlated suggesting discr ete receptor-ionophores. 6 This study favours the existence of distinc t non-NMDA receptor subtypes that are equi-sensitive to KA. The expres sed receptors from different species of mRNA may be distinguished by t heir voltage-sensitivities and the type of antagonism exerted by AMPA on KA-activated responses. Our observations may reflect further hetero geneity of non-NMDA receptors in the central nervous system of differe nt vertebrate species.