In Vitro and In Vivo Characterization of Conantokin-R, a Selective Nmda Receptor Antagonist Isolated from the Venom of the Fish-Hunting Snail Conus radiatus1
- H. Steve White1,
- R. Tyler McCabe2,
- Heather Armstrong1,
- Sean D. Donevan1,
- Lourdes J. Cruz3,4,
- Fe C. Abogadie3,
- Josep Torres5,
- Jean E. Rivier5,
- Ingo Paarmann6,
- Michael Hollmann6 and
- Baldomero M. Olivera3
- 1Department of Pharmacology and Toxicology, University of Utah, Salt Lake City, Utah (H.S.W., H.A., S.D.D.); 2Cognetix Inc., Salt Lake City, Utah (R.T.M.); 3Department of Biology, University of Utah, Salt Lake City, Utah (L.J.C., F.C.A., B.M.O.); 4Marine Science Institute, University of the Philippines, Diliman, Philippines (L.J.C.); 5The Salk Institute, La Jolla, California (J.T., J.E.R.); and 6Max-Planck Institute for Experimental Medicine, Gottingen, Germany (I.P., M.H.)
Abstract
The purification, characterization, and synthesis of conantokin-R (Con-R), an N-methyl-d-aspartate (NMDA) receptor peptide antagonist from the venom of Conus radiatus, are described. With the use of well defined animal seizure models, Con-R was found to possess an anticonvulsant profile superior to that of ifenprodil and dizocilpine (MK-801). With voltage-clamp recording of Xenopus oocytes expressing heteromeric NMDA receptors from cloned NR1 and NR2 subunit RNAs, Con-R exhibited the following order of preference for NR2 subunits: NR2B ≈ NR2A > NR2C ≫ NR2D. Con-R was without effect on oocytes expressing the α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptor subunit GluR1 or the kainate receptor subunit GluR6. In mouse cortical neurons voltage-clamped at −60 mV, Con-R application produced a slowly developing block of inward currents evoked by 10 μM NMDA and 1 μM glycine (IC50 = 350 nM). At 3 μM, Con-R did not affect γ-aminobutyric acid- or kainate-evoked currents. Con-R prevented sound-induced tonic extension seizures in the Frings audiogenic seizure-susceptible mice at i.c.v. doses below toxic levels. It was also effective at nontoxic doses in CF#1 mice against tonic extension seizures induced by threshold (15 mA) and maximal (50 mA) stimulation, and it partially blocked clonic seizures induced by s.c. pentylenetetrazol. In contrast, MK-801 and ifenprodil were effective only at doses approaching (audiogenic seizures) or exceeding (electrical and pentylenetetrazol seizures) those required to produce significant behavioral impairment. These results indicate that the subtype selectivity and other properties of Con-R afford a distinct advantage over the noncompetitive NMDA antagonists MK-801 and ifenprodil. Con-R is a useful new pharmacological agent for differentiation between the anticonvulsant and toxic effects of NMDA antagonists.
Footnotes
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Send reprint requests to: Dr. Baldomero M. Olivera, University of Utah, Department of Biology, 257 South 1400 East, Room 201, Salt Lake City, UT 84112-0840.
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1 This work was supported by Phase I SBIR Grant IR33 NS36507-01 from the NINDS (H.S.W., R.T.M.), Grant GM48677 from the National Institute of General Medical Sciences (B.M.O.), DFG Sonderforschungsbereich 406 (M.H.), and the Graduiertenkolleg “Organization and Dynamics of Neural Networks” at Göttingen University (I.P.).
- Abbreviations:
- AMPA
- α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid
- Con-R
- conantokin-R
- Con-G
- conantokin-G
- MK-801
- dizocilpine
- NMDA
- N-methyl-d-aspartate
- CNS
- central nervous system
- RT
- room temperature
- GluR
- glutamate receptor
- Gla
- γ-carboxyglutamate
- i.c.v.
- intracerebroventricular
- TPE
- time to peak effect
- TFA
- trifluoroacetic acid
- PI
- protective index
- MES
- maximal electroshock
- TTE
- threshold tonic extension
- PTZ
- pentylenetetrazol
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- Received July 2, 1999.
- Accepted September 16, 1999.
- The American Society for Pharmacology and Experimental Therapeutics
