Cannabinoids inhibit N- and P/Q-type calcium channels in cultured rat hippocampal neurons.
Cannabinoids and their analogues have been found to inhibit N- and P/Q-type Ca2+ currents in cell lines and sympathetic neurons transfected with cannabinoid CB1 receptor. However, the effects of cannabinoids on Ca2+ currents in the CNS are largely unexplored. In this study we investigated whether these compounds inhibit Ca2+ channels in cultured rat hippocampal neurons. With the use of antibodies directed against the amino-terminus of the CB1 receptor, we found that in 5-day cultures pyramidally shaped neurons expressed somatic CB1 receptors, whereas in 4-wk cultures the receptor was predominately located on neurites. In early cultures, the cannabimimetic WIN 55,212-2 reversibly inhibited whole cell Ba2+ current in a concentration-dependent (K(1/2) = 21 nM) and pertussis-toxin-sensitive fashion. Inhibition was reduced by the CB1 antagonist SR141716. The current was unaffected by the nonpsychoactive enantiomer WIN 55,212-3. Maximal inhibition by the nonclassical cannabinoid agonist CP 55,940 and by an endogenous cannabinoid, anandamide, were similar to that seen with maximal concentrations of WIN 55,212-2. The Ba2+ current modulated by cannabinoids was carried by N-type (omega-conotoxin-GVIA-sensitive) and P/Q-type (omega-conotoxin-MVIIC-sensitive) channels. These results demonstrate cannabinoid-receptor-mediated inhibition of distinct Ca2+ channels in central neurons. Because the channels that underlie these currents are chiefly located presynaptically, and are required for evoked neurotransmitter release, our results suggest a major role for cannabinoids (endogenous and exogenous) in the modulation of synaptic transmission at CNS synapses.
Twitchell
W
W
Department of Anesthesiology, School of Medicine, University of Washington, Seattle 98195, USA.
Brown
S
S
Mackie
K
K
D000818:Animals; D001095:Arachidonic Acids / Q000494:pharmacology; D048588:Benzoxazines; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D002186:Cannabinoids / Q000494:pharmacology*; D002478:Cells, Cultured; D003511:Cyclohexanols / Q000494:pharmacology; D063388:Endocannabinoids; D006624:Hippocampus / Q000166:cytology / Q000187:drug effects*; D008564:Membrane Potentials / Q000187:drug effects; D009025:Morpholines / Q000494:pharmacology; D009281:Naphthalenes / Q000494:pharmacology; D009474:Neurons / Q000187:drug effects* / Q000378:metabolism; D010852:Picrotoxin / Q000494:pharmacology; D053284:Polyunsaturated Alkamides; D051381:Rats
D001095:Arachidonic Acids; D048588:Benzoxazines; D002121:Calcium Channel Blockers; D002186:Cannabinoids; D003511:Cyclohexanols; D063388:Endocannabinoids; D009025:Morpholines; D009281:Naphthalenes; D010852:Picrotoxin; D053284:Polyunsaturated Alkamides; 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; C078814:anandamide