Differential effects of endogenous and synthetic cannabinoids on alpha7-nicotinic acetylcholine receptor-mediated responses in Xenopus Oocytes.
The effects of endogenous and synthetic cannabinoid receptor agonists, including 2-arachidonoylglycerol (2-AG), R-methanandamide, WIN55,212-2 [4,5-dihydro-2-methyl-4(4-morpholinylmethyl)-1-(1-naphthalenylcarbonyl)-6H-pyrrolo[3,2,1ij]quinolin-6-one], and CP 55,940 [1alpha,2beta-(R)-5alpha]-(-)-5-(1,1-dimethyl)-2-[5-hydroxy-2-(3-hydroxypropyl) cyclohexyl-phenol], and the psychoactive constituent of marijuana, Delta9-tetrahydrocannabinol (Delta9-THC), on the function of homomeric alpha7-nicotinic acetylcholine (nACh) receptors expressed in Xenopus oocytes was investigated using the two-electrode voltage-clamp technique. The endogenous cannabinoid receptor ligands 2-AG and the metabolically stable analog of anandamide (arachidonylethanolamide), R-methanandamide, reversibly inhibited currents evoked with ACh (100 microM) in a concentration-dependent manner (IC50 values of 168 and 183 nM, respectively). In contrast, the synthetic cannabinoid receptor agonists CP 55,940, WIN55,212-2, and the phytochemical Delta9-THC did not alter alpha7-nACh receptor function. The inhibition of alpha7-mediated currents by 2-AG was found to be non-competitive and voltage-independent. Additional experiments using endocannabinoid metabolites suggested that arachidonic acid, but not ethanolamine or glycerol, could also inhibit the alpha7-nACh receptor function. Whereas the effects of arachidonic acid were also noncompetitive and voltage-independent, its potency was much lower than 2-AG and anandamide. Results of studies with chimeric alpha7-nACh-5-hydroxytryptamine (5-HT)3 receptors comprised of the amino-terminal domain of the alpha7-nACh receptor and the transmembrane and carboxyl-terminal domains of 5-HT3 receptors indicated that the site of interaction of the endocannabinoids with the alpha7-nAChR was not located on the N-terminal region of the receptor. These data indicate that cannabinoid receptor ligands that are produced in situ potently inhibit alpha7-nACh receptor function, whereas the synthetic cannabinoid ligands, and Delta9-THC, are without effect, or are relatively ineffective at inhibiting these receptors.
Oz
Murat
M
National Institute on Drug Abuse/Intramural Research Program, Cellular Neurobiology Branch, 5500 Nathan Shock Dr., Baltimore, MD 21224, USA. moz@intra.nida.nih.gov
Zhang
Li
L
Ravindran
Arippa
A
Morales
Marisela
M
Lupica
Carl R
CR
D018712:Analgesics, Non-Narcotic / Q000494:pharmacology; D000818:Animals; D063385:Cannabinoid Receptor Modulators / Q000494:pharmacology*; D002186:Cannabinoids / Q000138:chemical synthesis / Q000494:pharmacology*; D013759:Dronabinol / Q000494:pharmacology; D009865:Oocytes / Q000187:drug effects* / Q000502:physiology; D043882:Receptors, Cannabinoid / Q000378:metabolism; D011978:Receptors, Nicotinic / Q000378:metabolism* / Q000502:physiology; D015398:Signal Transduction / Q000187:drug effects* / Q000502:physiology; D014982:Xenopus laevis; D064569:alpha7 Nicotinic Acetylcholine Receptor
D018712:Analgesics, Non-Narcotic; D063385:Cannabinoid Receptor Modulators; D002186:Cannabinoids; D043882:Receptors, Cannabinoid; D011978:Receptors, Nicotinic; D064569:alpha7 Nicotinic Acetylcholine Receptor; D013759:Dronabinol