Abstract
Many of the pharmacological effects of Δ9-tetrahydrocannabinol are mediated through CB1 and CB2 cannabinoid receptors. However, with the discovery of endogenous cannabinoids, some discrepancies have arisen. Furthermore, unlike the CB1 receptor, the sequences of the mouse and human CB2 receptor are divergent, raising the possibility of species specificity. The gene for the rat CB2 receptor was cloned, expressed, and its properties compared with those of mouse and human CB2 receptors. Sequence analysis of the coding region of the rat CB2genomic clone indicates 90% nucleic acid identity (93% amino acid identity) between rat and mouse and 81% nucleic acid identity (81% amino acid identity) between rat and human. The rat CB2receptor was stably expressed in human embryonic kidney-293 cells to examine its pharmacology. The rat CB2 showed low affinity for anandamide, an endogenous ligand shown to act at the CB1 receptor. In contrast, high-affinity binding for SR144528 (CB2-selective antagonist) as well as several cannabinoid receptor agonists was observed. Coupling to adenylate cyclase was observed. Aspects of the pharmacology of palmitoylethanolamide were also examined. It bound to CB1and CB2 receptors with low affinity and stimulated GTPγS binding in the cerebellum and CB2-expressing cell lines with low potency. The data in this study suggest that the discrepancies in affinities between rat and human may represent species differences. The rat CB2 receptor genomic clone will be a useful tool for studying the function and regulation of CB2 in rats.
Footnotes
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Send reprint requests to: Dr. Mary Abood, Forbes Norris ALS Research Center, California Pacific Medical Center, 2351 Clay St., #418, San Francisco, CA 94115. E-mail: mabood{at}cooper.cpmc.org
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↵1 This work was supported in part by National Institute on Drug Abuse Grants DA-09978, DA-05274, and DA-09789 and the Council for Tobacco Research Grant CTR-4482.
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↵2 Current address: Forbes Norris ALS Research Center, 2351 Clay St., Suite #416, California Pacific Medical Center, San Francisco, CA 94115.
- Abbreviations:
- THC
- (–)-Δ9-tetrahydrocannabinol
- CB1 and CB2
- cannabinoid receptors
- PCR
- polymerase chain reaction
- CP-55,940
- (−)-3-[2-hydroxyl-4-(1,1-dimethylheptyl)-phenyl]-4-[3-hydroxyl propyl] cyclohexan-1-ol
- SR141716A
- [N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamidehydrochloride]
- G418
- geneticin
- WIN-55212-2
- (R)-(+)-[2,3-dihydro-5-methyl-3-[(4-morpholinyl)methyl]pyrolo[1,2,3-de]-1,4-benzoxazin-6-yl](1-naphthalenyl)methanone
- CHO
- Chinese hamster ovary
- HEK
- human embryonic kidney
- PMSF
- phenylmethylsulfonyl fluoride
- PEA
- palmitoylethylanolamide
- GCR
- G-protein-coupled receptor
- Received June 8, 1999.
- Accepted November 5, 1999.
- The American Society for Pharmacology and Experimental Therapeutics
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