Anandamide, an endogenous cannabinoid, inhibits calcium currents as a partial agonist in N18 neuroblastoma cells.
Anandamide (arachidonyl ethanolamide) has been identified as an endogenous ligand of cannabinoid receptors on the basis of its ability to displace 3H-labeled synthetic cannabinoid in a binding assay. One well characterized cellular action of cannabinoids is inhibition of hormonally stimulated adenylyl cyclase. Another action of synthetic cannabinoids is potent, stereospecific, and reversible inhibition of N-type calcium currents (ICa) in the NG108-15 neuroblastoma-glioma cell line via a pertussis toxin (PTX)-sensitive pathway, independently of cAMP metabolism. Here we used the N18 neuroblastoma cell line and the whole-cell voltage-clamp technique to show that anandamide also potently inhibits N-type ICa in a PTX-sensitive fashion. As with the cannabinomimetic aminoalkylindole WIN 55,212-2, inhibition by anandamide was voltage dependent and N-ethylmaleimide sensitive. However, anandamide was less efficacious than either WIN 55,212-2 or the nonclassical cannabinoid CP 55,940. Indeed, anandamide appears to act as a partial agonist at the cannabinoid receptor. Application of WIN 55,212-2 always caused further inhibition of ICa in cells exposed to a maximally effective concentration of anandamide, and application of anandamide always caused a partial recovery of ICa in cells exposed to a maximally effective concentration of WIN 55,212-2. This partial agonist property of anandamide suggests that, although anandamide inhibits N-type ICa via a PTX-sensitive G protein, its action as a neuromodulator in the intact animal may be more complex than would be inferred by extrapolating the results of in vivo studies with (-)-delta 9-tetra-hydrocannabinol or synthetic cannabinoids.
Department of Physiology, University of Washington School of Medicine, Seattle 98195.
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Mackie
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D037361:Adenylate Cyclase Toxin; D000577:Amides / Q000494:pharmacology*; D001095:Arachidonic Acids; D048588:Benzoxazines; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D063388:Endocannabinoids; D005231:Fatty Acids, Unsaturated / Q000494:pharmacology*; D019204:GTP-Binding Proteins / Q000187:drug effects; D015640:Ion Channel Gating; D008564:Membrane Potentials / Q000187:drug effects; D009025:Morpholines / Q000494:pharmacology; D009281:Naphthalenes / Q000494:pharmacology; D009447:Neuroblastoma; D009474:Neurons / Q000187:drug effects*; D037342:Pertussis Toxin; D053284:Polyunsaturated Alkamides; D043882:Receptors, Cannabinoid; D011955:Receptors, Drug / Q000187:drug effects*; D014407:Tumor Cells, Cultured; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D037361:Adenylate Cyclase Toxin; D000577:Amides; D001095:Arachidonic Acids; D048588:Benzoxazines; D002121:Calcium Channel Blockers; D063388:Endocannabinoids; D005231:Fatty Acids, Unsaturated; D009025:Morpholines; D009281:Naphthalenes; D053284:Polyunsaturated Alkamides; D043882:Receptors, Cannabinoid; D011955:Receptors, Drug; D010566:Virulence Factors, Bordetella; C070417:(3R)-((2,3-dihydro-5-methyl-3-((4-morpholinyl)methyl)pyrrolo-(1,2,3-de)-1,4-benzoxazin-6-yl)(1-naphthalenyl))methanone; D037342:Pertussis Toxin; D019204:GTP-Binding Proteins; C078814:anandamide