Abstract
Intracellular calcium concentration ([Ca2+]i) plays a major role in neuronal excitability, especially that triggered by the N-methyl-d-aspartate (NMDA)-sensitive glutamatergic receptor. We have previously shown that σ1 receptor agonists potentiate NMDA receptor-mediated neuronal activity in the hippocampus and recruit Ca2+-dependent second messenger cascades (e.g., protein kinase C; PKC) in brainstem motor structures. The present study therefore assessed whether the potentiating action of σ1 agonists on the NMDA response observed in the hippocampus involves the regulation of [Ca2+]i and PKC. For this purpose, [Ca2+]i changes after NMDA receptor activation were monitored in primary cultures of embryonic rat hippocampal pyramidal neurons using microspectrofluorometry of the Ca2+-sensitive indicator Fura-2/acetoxymethyl ester in the presence of σ1 agonists and PKC inhibitors. We show that successive activations of the σ1 receptor by 1-min pulses of (+)-benzomorphans or (+)-N-cyclopropylmethyl-N-methyl-1,4-diphenyl-1-ethyl-but-3-en-1-ylamine hydrochloride (JO-1784) concommitantly with glutamate time dependently potentiated before inconstantly inhibiting the NMDA receptor-mediated increase of [Ca2+]i, whereas 1,3-di-o-tolyl-guanidine, a mixed σ1/σ2 agonist, did not significantly modify the glutamate response. Both potentiation and inhibition were prevented by the selective σ1 antagonist N,N-dipropyl-2-[4-methoxy-3-(211phenylethoxy) phenyl]-ethylamine monohydrochloride (NE-100). Furthermore, only (+)-benzomorphans could induce [Ca2+]i influx by themselves after a brief pulse of glutamate. A pretreatment with the conventional PKC inhibitor 12-(2-cyanoethyl)-6,7,12,13-tetrahydro-13-methyl-5-oxo-5H-indolo [2,3-a] pyrrolo [3,4-c] carbazole (Gö-6976) prevented the potentiating effect of (+)-benzomorphans on the glutamate response. Our results provide further support for a general mechanism for the intracellular σ1 receptor to regulate Ca2+-dependent signal transduction and protein phosphorylation.
Footnotes
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DOI: 10.1124/jpet.103.053447.
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ABBREVIATIONS: DTG, 1,3-di-o-tolyl-guanidine; NMDA, N-methyl-d-aspartate; PKC, protein kinase C; [Ca2+]i, intracellular calcium concentration; AM, acetoxymethyl ester; Glu, glutamate; (+)-SKF-10047, (+)-N-allylnormetazocine; (+)-PTZ, (+)-pentazocine; JO-1784, (+)N-cyclopropylmethyl-N-methyl-1,4-diphenyl-1-ethyl-but-3-en-1-ylamine hydrochloride; NE-100, N,N-dipropyl-2-[4-methoxy-3-(211phenylethoxy) phenyl]-ethylamine monohydrochloride; MK-801, dizocilpine; Gö-6976, 12-(2-cyanoethyl)-6,7,12,13-tetrahydro-13-methyl-5-oxo-5H-indolo [2,3-a] pyrrolo [3,4-c] carbazole; cPKC, conventional protein kinase C; PCP, phencyclidine; BD-737, (+)-cis-N-methyl-N-[2-(3,4-dichlorophenyl)ethyl]-2-(1-pyrrolidinyl)cyclohexylamine; BD-1047, N-[2-3,4-dichlorophenyl)-ethyl]-N-methyl-2-(dimethylamino)ethylamine; (+)3-PPP, (+)3-hydroxyphenyl-N-(1-propyl)-piperidine.
- Received April 24, 2003.
- Accepted August 6, 2003.
- The American Society for Pharmacology and Experimental Therapeutics
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