Abstract
Conantokin G (Con G) is a 17-amino-acid peptide antagonist ofN-methyl-d-aspartate (NMDA) receptors isolated from the venom of the marine cone snail, Conus geographus. The mechanism of action of Con G has not been well defined; both competitive and noncompetitive interactions with the NMDA-binding site have been proposed. In this study the mechanism of action and subunit selectivity of Con G was examined in whole-cell voltage-clamp recordings from cultured neurons and in two electrode voltage-clamp recordings from Xenopus oocytes expressing recombinant NMDA receptors. Con G was a potent and selective antagonist of NMDA-evoked currents in murine cortical neurons (IC50 = 480 nM). The slow onset of Con G block could be prevented by coapplication with high concentrations of NMDA or of the competitive antagonist (RS)-3-(2-carboxypiperazine-4-yl)-propyl-1-phosphonic acid. Furthermore, in oocytes expressing NR1a/NR2B receptors, Con G produced a rightward shift in the concentration-response curve for NMDA, providing support for a competitive interaction with the NMDA-binding site. Con G produced an apparent noncompetitive shift in the concentration-response curve for spermine potentiation of NMDA responses, but this was due to spermine-induced enhancement of Con G block. Spermine produced a similar enhancement ofdl-2-amino-S-phosphopentanoic acid block. Finally, Con G selectively blocked NMDA receptors containing the NR2B subunit. These results demonstrate that Con G is a subunit-specific competitive antagonist of NMDA receptors. The unique subunit selectivity profile of Con G may explain its favorable in vivo profile compared with nonselective NMDA antagonists.
Footnotes
- Received November 10, 1999.
- Accepted May 25, 2000.
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Send reprint requests to: Sean D. Donevan, Ph.D., Parke-Davis Research, 2800 Plymouth Rd., Ann Arbor, MI 84105. E-mail:sean.donevan{at}wl.com
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↵1 Current address: Parke-Davis Research, Ann Arbor, MI 48105.
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This study was supported by a sponsored research project with Cognetix, Inc., Salt Lake City, UT 84114.
- The American Society for Pharmacology and Experimental Therapeutics
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