title: Endogenous cannabinoid receptor binding activity released from rat brain slices by depolarization.
abstract: As previously reported by this laboratory, an endogenous factor capable of inhibiting the specific binding of the radiolabeled cannabinoid agonist [3H]CP-55940 to its receptor can be released from nerve terminals in response to an influx of Ca++ induced by an ionophore (Evans et al., 1992). In the present report, we provide evidence that the endogenous ligand for the cannabinoid receptor can be released in response to a depolarizing stimulus (75 mM K+) in the presence of extracellular Ca++. K(+)-evoked release was not observed in the absence of extra-cellular Ca++ and was reduced by the specific calcium channel blockers verapamil and omega-conotoxin. The efflux of cannabinoid receptor binding activity is greatest within 2 min of stimulation with the Ca++ ionophore A23187. Within this period of time, the cannabinoid receptor binding activity was enhanced by the presence of a cocktail of peptidase inhibitors. Examination of the contribution of individual inhibitors for enhancing high K(+)-released material revealed a selectivity for captopril and thiorphan. The specificity of the released factor for the cannabinoid receptor was corroborated by its ability to compete with the aminoalkylindole radioligand [3H]WIN-55212 for binding to this receptor. Fractions from a semi-purified sample of the effluent demonstrated binding to the cannabinoid receptor and behaved as agonists in that these fractions could inhibit adenylate cyclase activity in neuroblastoma membrane preparations.
authors.affiliation: Department of Pharmacological and Physiological Science, Saint Louis University School of Medicine, Missouri.
authors.forename: D M
authors.initials: DM
authors.lastname: Evans
authors.forename: J T
authors.initials: JT
authors.lastname: Lake
authors.forename: M R
authors.initials: MR
authors.lastname: Johnson
authors.forename: A C
authors.initials: AC
authors.lastname: Howlett
mesh_terms: D000818:Animals; D048588:Benzoxazines; D001665:Binding Sites; D001921:Brain / Q000378:metabolism*; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D003511:Cyclohexanols / Q000378:metabolism; D004336:Drug Antagonism; D066298:In Vitro Techniques; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D009025:Morpholines / Q000378:metabolism; D009281:Naphthalenes / Q000378:metabolism; D011188:Potassium / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D043882:Receptors, Cannabinoid; D011955:Receptors, Drug / Q000378:metabolism*
chemical_list: D048588:Benzoxazines; D002121:Calcium Channel Blockers; D003511:Cyclohexanols; D009025:Morpholines; D009281:Naphthalenes; D043882:Receptors, Cannabinoid; D011955:Receptors, Drug; D000001:Calcimycin; C070417:(3R)-((2,3-dihydro-5-methyl-3-((4-morpholinyl)methyl)pyrrolo-(1,2,3-de)-1,4-benzoxazin-6-yl)(1-naphthalenyl))methanone; C054649:3-(2-hydroxy-4-(1,1-dimethylheptyl)phenyl)-4-(3-hydroxypropyl)cyclohexanol; D011188:Potassium; D002118:Calcium