Endogenous cannabinoid anandamide directly inhibits voltage-dependent Ca(2+) fluxes in rabbit T-tubule membranes.
The effect of the endogenous cannabinoid, anandamide on Ca(2+) flux responses mediated by voltage-dependent Ca(2+) channels was studied in transverse tubule membrane vesicles from rabbit skeletal muscle. Vesicles were loaded with 45Ca(2+) and membrane potentials were generated by establishing K(+) gradients across the vesicle using the ionophore, valinomycin. Anandamide, in the range of 1-100 microM, inhibited depolarization-induced efflux responses. Anandamide also functionally modulated the effects of nifedipine (1-10 microM) and Bay K 8644 (1 microM) on Ca(2+) flux responses. Pretreatment with the specific cannabinoid receptor antagonist, SR141716A (1 microM), pertussis toxin (5 microg/ml), the amidohydrolase inhibitor, phenylmethylsulfonyl fluoride (0.2 mM) or the cyclooxygenase inhibitor, indomethacin (5 microM) did not alter the inhibition of efflux responses by anandamide. Arachidonic acid (10-100 microM) also effectively inhibited 45Ca(2+) efflux from membrane vesicles. In radioligand binding studies, it was found that both anandamide and arachidonic acid inhibited the specific binding of [3H]PN 200-110 to transverse tubule membranes with IC(50) values of 4.4+/-0. 7 and 13.4+/-3.5 microM, respectively. These results indicate that anandamide, independent of cannabinoid receptor activation, directly inhibits the function of voltage-dependent calcium channels and modulates the specific binding of calcium channel ligands of the dihydropyridine class.
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Loeb Research Institute, Neuroscience, 725 Parkdale Ave., Ottawa Hospital, Civic Campus, K1Y 4K9, Ottawa, Ontario, Canada.
Tchugunova
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YB
Dunn
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SM
D000704:Analysis of Variance; D000818:Animals; D001095:Arachidonic Acids / Q000494:pharmacology*; D001667:Binding, Competitive; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism*; D002186:Cannabinoids / Q000494:pharmacology*; D063388:Endocannabinoids; D066298:In Vitro Techniques; D017275:Isradipine / Q000494:pharmacology; D018482:Muscle, Skeletal / Q000187:drug effects* / Q000378:metabolism; D053284:Polyunsaturated Alkamides; D011817:Rabbits; D014316:Tritium
D001095:Arachidonic Acids; D002121:Calcium Channel Blockers; D015220:Calcium Channels; D002186:Cannabinoids; D063388:Endocannabinoids; D053284:Polyunsaturated Alkamides; D014316:Tritium; D002118:Calcium; C078814:anandamide; D017275:Isradipine