Research report
Effects of nitroprusside and redox reagents on NMDA receptors expressed in Xenopus oocytes

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Abstract

We have examined the effects of oxidizing and reducing agents and sodium nitroprusside (SNP) on currents evoked by NMDA (N-methyl-d-aspartate) using the Xenopus oocyte expression system. Oocytes were injected with RNA prepared from either whole rat brain or from the NMDAR1 clone recently isolated from rat brain. Bath application of 1–1000 μM SNP, which releases nitric oxide and ferrocyanide, caused a rapid inhibition of NMDA-evoked current in both preparations. The inhibitory effect reversed spontaneously within 15 min. Kainate responses were not affected by SNP. Exposure to the reducing agent, dithiothreitol (DTT), enhanced NMDA currents; the oxidant, 5,5-dithio-bis-2-nitrobenzoic acid (DTNB), inhibited NMDA responses, as has been observed in other preparations. The site of action of SNP appeared to be different than the DTT/DTNB redox site for several reasons: SNP and DTNB inhibitions were additive at high doses, DTT did not rapidly reverse SNP effects, and SNP and DTT treatments did not show the same susceptibility to block by the NMDA antagonist, aminophosphonovaleric acid (APV). The results demonstrate that modulation of NDMA receptors by SNP is a property of homomeric channels and is retained when the NMDAR1 subunit is expressed in oocytes.

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Cited by (25)

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    In contrast, the lack of inhibitory effect of FeSO4 in the present study and others (Manzoni et al., 1992) could possibly be attributed to its positive charge once in solution (Neijt et al., 2001). Also, effects of SNP on expressed NMDA receptors into oocytes do not show any interaction with the NMDA receptor redox site (Omerovic et al., 1994). In summary, the inhibitory effects of SNP on NMDA-induced excitation has been reproduced by co-applications of NMDA with either K3–(FeCN)6 or inactivated-SNP, but not with FeSO4, revealing that inhibitory effects of SNP on activated NMDA receptors were mainly due to ferricyanide ions rather than cyanide or NO.

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