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Species‐dependent functional properties of non‐NMDA receptors expressed in Xenopus laevis oocytes injected with mammalian and avian brain mRNA
Author(s) -
Bowie Derek,
Smart Trevor G.
Publication year - 1994
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1994.tb14809.x
Subject(s) - ampa receptor , xenopus , kainic acid , biology , nmda receptor , glutamate receptor , receptor , kainate receptor , medicine , tetrodotoxin , endocrinology , messenger rna , biochemistry , gene
1 Species‐dependent variation in the functional properties of non‐NMDA receptors was investigated by intracellular recording in Xenopus laevis oocytes injected with rat, chick and calf brain mRNA. 2 In all mRNA‐injected oocytes, kainic acid (KA), domoic acid (Dom) and 5‐bromowillardiine (BrW) evoked large, maintained membrane currents, in contrast to the smaller, desensitizing responses elicited by α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionic acid (AMPA), quisqualic acid (QA) and l ‐glutamic acid ( l ‐Glu). Dose‐response curves for KA in oocytes injected with calf (EC 50 = 96.4 ± 12.3 μ m ; mean ± s.e.mean), chick (87.0 ± 8.9 μ m ) or rat (88.7 ± 4.3 μ m ) brain mRNA were similar. 3 Current‐voltage ( I–V ) relationships determined with KA inwardly rectified in oocytes injected with calf or chick mRNA; whereas, outward rectification was observed in oocytes injected with rat brain mRNA. 4 In oocytes injected with rat brain mRNA, AMPA antagonized responses evoked by KA in a competitive manner. The absolute amplitudes of KA and AMPA responses in the same oocytes were significantly correlated, which is consistent with both agonists acting on the same receptor‐ionophore 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 discrete receptor‐ionophores. 6 This study favours the existence of distinct non‐NMDA receptor subtypes that are equi‐sensitive to KA. The expressed receptors from different species of mRNA may be distinguished by their voltage‐sensitivities and the type of antagonism exerted by AMPA on KA‐activated responses. Our observations may reflect further heterogeneity of non‐NMDA receptors in the central nervous system of different vertebrate species.