Inhibition of voltage-sensitive sodium channels by the cannabinoid 1 receptor antagonist AM 251 in mammalian brain.
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-alpha-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 microM). Veratridine-dependent (tetrodotoxin suppressible) release, of L-glutamic acid and GABA from synaptosomes was also reduced by AM 251 [IC50s=8.5 microM (L-glutamic acid), 9.2 microM (GABA)]. The binding of the radioligand [3H]batrachotoxinin A 20-alpha-benzoate to site 2 on sodium channels was displaced by AM 251 (IC50=11.2 microM). 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-alpha-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.
Liao
Chengyong
C
Department of Biological Sciences, Simon Fraser University, 8888 University Drive, Burnaby, BC, V5A 1S6, Canada.
Zheng
Jian
J
David
Laurence S
LS
Nicholson
Russell A
RA
D000818:Animals; D001496:Batrachotoxins / Q000378:metabolism; D001921:Brain / Q000187:drug effects*; D063387:Cannabinoid Receptor Antagonists; D004347:Drug Interactions; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D051379:Mice; D010880:Piperidines / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D011720:Pyrazoles / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D015222:Sodium Channels / Q000187:drug effects* / Q000378:metabolism; D013574:Synaptosomes / Q000187:drug effects* / Q000378:metabolism; D014701:Veratridine / Q000494:pharmacology
D001496:Batrachotoxins; D063387:Cannabinoid Receptor Antagonists; D010880:Piperidines; D011720:Pyrazoles; D015222:Sodium Channels; C103505:AM 251; D014701:Veratridine; C031775:batrachotoxinin A 20-alpha-benzoate