Depolarization-induced rapid generation of 2-arachidonoylglycerol, an endogenous cannabinoid receptor ligand, in rat brain synaptosomes.
2-arachidonoylglycerol (2-AG) is an endogenous ligand for the cannabinoid receptors with a variety of potent biological activities. In this study, we first examined the effects of potassium-induced depolarization on the level of 2-AG in rat brain synaptosomes. We found that a significant amount of 2-AG was generated in the synaptosomes following depolarization. Notably, depolarization did not affect the levels of other molecular species of monoacylglycerols. Furthermore, the level of anandamide was very low and did not change markedly following depolarization. It thus appeared that the depolarization-induced accelerated generation is a unique feature of 2-AG. We obtained evidence that phospholipase C is involved in the generation of 2-AG in depolarized synaptosomes: U73122, a phospholipase C inhibitor, markedly reduced the depolarization-induced generation of 2-AG, and the level of diacylglycerol was rapidly elevated following depolarization. A significant amount of 2-AG was released from synaptosomes upon depolarization. Interestingly, treatment of the synaptosomes with SR141716A, a CB1 receptor antagonist, augmented the release of glutamate from depolarized synaptosomes. These results strongly suggest that the endogenous ligand for the cannabinoid receptors, i.e. 2-AG, generated through increased phospholipid metabolism upon depolarization, plays an important role in attenuating glutamate release from the synaptic terminals by acting on the CB1 receptor.
Oka
Saori
S
Faculty of Pharmaceutical Sciences, Teikyo University, Sagamihara, Kanagawa 199-0195 Japan.
Arai
Shunsuke
S
Waku
Keizo
K
Tokumura
Akira
A
Sugiura
Takayuki
T
D000818:Animals; D001095:Arachidonic Acids / Q000096:biosynthesis* / Q000378:metabolism; D001921:Brain / Q000166:cytology / Q000187:drug effects*; D000001:Calcimycin / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D001892:Camphanes / Q000494:pharmacology; D004075:Diglycerides / Q000378:metabolism; D063388:Endocannabinoids; D004963:Estrenes / Q000494:pharmacology; D005227:Fatty Acids / Q000378:metabolism; D005989:Glycerides / Q000096:biosynthesis* / Q000378:metabolism; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D009467:Neuromuscular Depolarizing Agents / Q000494:pharmacology; D010880:Piperidines / Q000494:pharmacology; D053284:Polyunsaturated Alkamides / Q000378:metabolism; D011720:Pyrazoles / Q000494:pharmacology; D011760:Pyrrolidinones / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D043882:Receptors, Cannabinoid / Q000187:drug effects / Q000378:metabolism*; D000077285:Rimonabant; D013574:Synaptosomes / Q000187:drug effects*
D001095:Arachidonic Acids; D002121:Calcium Channel Blockers; D001892:Camphanes; D004075:Diglycerides; D063388:Endocannabinoids; D004963:Estrenes; D005227:Fatty Acids; D005989:Glycerides; D009467:Neuromuscular Depolarizing Agents; D010880:Piperidines; D053284:Polyunsaturated Alkamides; D011720:Pyrazoles; D011760:Pyrrolidinones; D043882:Receptors, Cannabinoid; C110630:SR 144528; C060229:1-(6-((3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl)-1H-pyrrole-2,5-dione; D000001:Calcimycin; C094503:glyceryl 2-arachidonate; D000077285:Rimonabant; C078814:anandamide