Complex structure of quisqualate-sensitive glutamate receptors in rat cortex

1 Responses to kainate (KA), willardiine and a-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) were recorded from rat brain mRNA-injected Xenopus laevis oocytes by use of a two-electrode voltage clamp.2 Thiocyanate (SCN-; 50jM-4mM) ions reversibly and selectively inhibited the membrane current responses to AMPA in a non-competitive manner without affecting KA or willardiine-induced responses.3 The inhibition of AMPA-induced responses by SCN-was dependent on the SCN-concentration with an estimated IC50 of 1 mm. The antagonism was not dependent on the AMPA concentration. 4 The response to a high concentration of AMPA (100-200I1M) exhibited a peak inward current which declined to a steady-state. SCN-inhibited the steady-state current more than the peak response. The inhibition was unaffected by prior incubation with concanavalin-A (Con-A; 10#M). 5 Responses to KA were antagonized by AMPA in a competitive manner, suggesting that both agonists may activate a common receptor-channel complex. This interaction between two non-NMDA agonists was not affected by the SCN-induced inhibition of the AMPA response. 6 AMPA-induced responses recorded from large cultured cerebellar neurones by whole-cell recording were also inhibited by SCN-in a non-competitive manner. The AMPA-induced peak current was less affected than the steady-state response. 7 We conclude that SCN-can inhibit the response to AMPA in expressed non-NMDA receptors in Xenopus oocytes and also in native receptors in cultured cerebellar neurones. One possible mechanism of action for SCN-inhibition of responses to AMPA may involve a Con-A-insensitive, non-NMDA receptor-mediated desensitization.

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 98%

Thiocyanate ions selectively antagonize AMPA‐evoked responses in Xenopus laevis oocytes microinjected with rat brain mRNA

Bowie

Smart

1993

“…In this study we have described the binding of the radiolabelled form of (S)-5-fluorowillardiine. (Honore & Nielsen, 1985 (Honore & Drejer, 1988;Nielsen et al, 1990). Evidence to date suggests that KSCN increases the affinity of [3H]-AMPA binding, although the exact mechanism by which this is effected is unknown.…”

Section: Discussionmentioning

confidence: 99%

Characterization of the pharmacology and regional distribution of (S)‐[³H]‐5‐fluorowillardiine binding in rat brain

Hawkins

Beaver

Jane

et al. 1995

“…[1,2-3H]-CPP (20 Ci mmol-1; Tocris Neuramin) Murphy et al, 1987) and [2-3H]-glycine (43.5Cimmol-t; Dupont-New England Nuclear) (Bristow et al, 1986;Kessler et al, 1989) (Foster et alt, 1981;Honore & Nielsen, 1985;Lehmann et al, 1988). Assays (and radioligands) used were as follows: quisqualate (AMPA), kainate (kainate), GABAA (muscimol), benzodiazepine (flunitrazepam), GABAB (CGP 27492), adenosine (cyclohexyladenosine), muscarinic cholinoceptor (diozalane and QNB), xl-adrenoceptor (prazosin), a2-adrenoceptor (clonidine), f0-adrenoceptor (dihydroalprenolol), 5-HT1 (5-HT), 5-HT2 (ketanserin), histamine H1 (doxepine), histamine H2 (thiotidine), substance P (substance P) and neurotensin (neurotensin).…”

Section: Methodsmentioning

confidence: 99%

CGP 37849 and CGP 39551: novel and potent competitive N‐methyl‐d‐aspartate receptor antagonists with oral activity

Fagg

Olpe²,

Pozza³

et al. 1990

189

1 The pharmacological properties of CGP 37849 (DL-(E)-2-amino-4-methyl-5-phosphono-3-pentenoic acid; 4-methyl-APPA) and its carboxyethylester, CGP 39551, novel unsaturated analogues of the Nmethyl-D-aspartate (NMDA) receptor antagonist, 2-amino-5-phosphonopentanoate (AP5), were evaluated in rodent brain in vitro and in vivo. 2 Radioligand binding experiments demonstrated that CGP 37849 potently (K1 220 nM) and competitively inhibited NMDA-sensitive L-[3H]-glutamate binding to postsynaptic density (PSD) fractions from rat brain. It inhibited the binding of the selective NMDA receptor antagonist, [3H]-( ±)-342-carboxypiperazin-4-yl)propyl-1-phosphonate (CPP), with a Ki of 35 nm, and was 4, 5 and 7 fold more potent than the antagonists ((±)-cis-4-phosphonomethylpiperidine-2-carboxylic acid) (CGS 19755), CPP and D-AP5, respectively. Inhibitory activity was associated exclusively with the trans configuration of the APPA molecule and with the D-stereoisomer. CGP 39551 showed weaker activity at NMDA receptor recognition sites and both compounds were weak or inactive at 18 other receptor binding sites. 3 CGP 37849 and CGP 39551 were inactive as inhibitors of L-[3H]-glutamate uptake into rat brain synaptosomes and had no effect on the release of endogenous glutamate from rat hippocampal slices evoked by electrical field stimulation. 4 In the hippocampal slice in vitro, CGP 37849 selectively and reversibly antagonized NMDA-evoked increases in CAI pyramidal cell firing rate. In slices bathed in medium containing low Mg2+ levels, concentrations of CGP 37849 up to 10pM suppressed burst firing evoked in CAl neurones by stimulation of Schaffer collateral-commissural fibres without affecting the magnitude of the initial population spike; CGP 39551 exerted the same effect but was weaker. In vivo, oral administration to rats of either CGP 37849 or CGP 39551 selectively blocked firing in hippocampal neurones induced by ionophoreticallyapplied NMDA, without affecting the responses to quisqualate or kainate. al., 1988). Many studies have demonstrated that activation of the NMDA receptor is involved in the generation of epileptiform activity and in hypoxic-ischaemic neuronal damage, and conversely that NMDA receptor antagonists are anticonvulsant and cerebroprotective in animal models of epilepsy and stroke (see reviews by Meldrum, 1985;Rothman & Olney, 1986;Choi, 1988;Patel et al., 1988;Iversen et al., 1989;Albers et al., 1989 (Meldrum, 1985;Rothman & Olney, 1986;Albers et al., 1989;.Antagonism of NMDA receptor mechanisms potentially may be achieved by a number of different approaches. In addition to the transmitter recognition site, the NMDA receptor complex comprises an allosteric regulatory site and a channel binding domain (Foster & Fagg, 1987b), and possibly also sites defined by the actions of Zn2", polyamines, tricyclic antidepressants, ifenprodil and CGP 31358 (see Lodge, 1989;Baud et al., 1989). At present, however, the two most well characterized sites are (1) the transmitter recognition site, at which substances such as ...