Inhibition of Voltage‐Sensitive Sodium Channels by the Cannabinoid 1 Receptor Antagonist AM 251 in Mammalian Brain

Inhibition of Voltage‐Sensitive Sodium Channels by the Cannabinoid 1 Receptor Antagonist AM 251... Abstract: The cannabinoid 1 receptor antagonist AM 251 is known to block the inhibitory effects of endocannabinoids and synthetic cannabinoid agonists on transmitter release through an action at presynaptic cannabinoid 1 receptors in brain. We examined the ability of AM 251 to inhibit sodium channel‐dependent functions and the binding of (3H)batrachotoxinin A 20‐α‐benzoate to sodium channels in mouse brain synaptic preparations. Depolarization of synaptoneurosomes by the sodium channel site 2‐specific neurotoxin veratridine, which is abolished by tetrodotoxin, was found to be inhibited in a concentration‐dependent fashion by AM 251 (IC50=8.9 μM). Veratridine‐dependent (tetrodotoxin suppressible) release, of L‐glutamic acid and GABA from synaptosomes was also reduced by AM 251 (IC50s=8.5 μM (L‐glutamic acid), 9.2 μM (GABA)). The binding of the radioligand (3H)batrachotoxinin A 20‐α‐benzoate to site 2 on sodium channels was displaced by AM 251 (IC50=11.2 μM). Scatchard analysis of binding showed that at its IC50, AM 251 increased (by 2.3 times) the KD of radioligand without altering Bmax, suggesting a competitive mechanism of inhibition by AM 251. Kinetic experiments indicated that AM 251 inhibits equilibrium binding by allosterically accelerating the dissociation of the (3H)‐batrachotoxinin A 20‐α‐benzoate:sodium channel complex. Our data suggest that micromolar concentrations of AM 251 are capable of reducing neuronal excitability and inhibiting release of excitatory and inhibitory transmitters through blockade of voltage‐sensitive sodium channels in brain. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Basic and Clinical Pharmacology & Toxicology Wiley

Inhibition of Voltage‐Sensitive Sodium Channels by the Cannabinoid 1 Receptor Antagonist AM 251 in Mammalian Brain

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Publisher
Wiley
Copyright
Copyright © 2004 Wiley Subscription Services, Inc., A Wiley Company
ISSN
1742-7835
eISSN
1742-7843
DOI
10.1111/j.1742-7843.2004.pto940204.x
Publisher site
See Article on Publisher Site

Abstract

Abstract: The cannabinoid 1 receptor antagonist AM 251 is known to block the inhibitory effects of endocannabinoids and synthetic cannabinoid agonists on transmitter release through an action at presynaptic cannabinoid 1 receptors in brain. We examined the ability of AM 251 to inhibit sodium channel‐dependent functions and the binding of (3H)batrachotoxinin A 20‐α‐benzoate to sodium channels in mouse brain synaptic preparations. Depolarization of synaptoneurosomes by the sodium channel site 2‐specific neurotoxin veratridine, which is abolished by tetrodotoxin, was found to be inhibited in a concentration‐dependent fashion by AM 251 (IC50=8.9 μM). Veratridine‐dependent (tetrodotoxin suppressible) release, of L‐glutamic acid and GABA from synaptosomes was also reduced by AM 251 (IC50s=8.5 μM (L‐glutamic acid), 9.2 μM (GABA)). The binding of the radioligand (3H)batrachotoxinin A 20‐α‐benzoate to site 2 on sodium channels was displaced by AM 251 (IC50=11.2 μM). Scatchard analysis of binding showed that at its IC50, AM 251 increased (by 2.3 times) the KD of radioligand without altering Bmax, suggesting a competitive mechanism of inhibition by AM 251. Kinetic experiments indicated that AM 251 inhibits equilibrium binding by allosterically accelerating the dissociation of the (3H)‐batrachotoxinin A 20‐α‐benzoate:sodium channel complex. Our data suggest that micromolar concentrations of AM 251 are capable of reducing neuronal excitability and inhibiting release of excitatory and inhibitory transmitters through blockade of voltage‐sensitive sodium channels in brain.

Journal

Basic and Clinical Pharmacology & ToxicologyWiley

Published: Feb 1, 2004

References

  • Neurotoxins that act of voltage‐sensitive sodium channels in excitable membranes
    Catterall, Catterall

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