Conantokin G is an NR2B-selective competitive antagonist of N-methyl-D-aspartate receptors.
Conantokin G (Con G) is a 17-amino-acid peptide antagonist of N-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 (IC(50) = 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 of DL-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.
Donevan
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Department of Neurology, University of Utah, USA. sean.donevan@wl.com
McCabe
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D000818:Animals; D001667:Binding, Competitive / Q000187:drug effects; D002478:Cells, Cultured; D020916:Conotoxins / Q000494:pharmacology*; D004347:Drug Interactions; D004594:Electrophysiology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology*; D051379:Mice; D009474:Neurons / Q000187:drug effects* / Q000378:metabolism; D011073:Polyamines / Q000494:pharmacology; D016194:Receptors, N-Methyl-D-Aspartate / Q000037:antagonists & inhibitors*; D014162:Transfection; D014982:Xenopus laevis
D020916:Conotoxins; D018691:Excitatory Amino Acid Antagonists; C121001:NR2B NMDA receptor; D011073:Polyamines; D016194:Receptors, N-Methyl-D-Aspartate; C055407:conotoxin GV