Good news for CB1 receptors: endogenous agonists are in the right place.
Endocannabinoids are endogenous ligands of brain-type (CB1) and spleen-type (CB2) cannabinoid receptors. N-Arachidonoylethanolamine (anandamide, AEA) and 2-arachidonoylglycerol (2-AG) are prototype members of the fatty acid amides and the monoacylglycerols, two groups of endocannabinoids. Unlike CB1, CB2 receptors do not reside within 'caveolae', specialized membrane microdomains that are well-known modulators of the activity of a number of G protein-coupled receptors. In this issue of the British Journal of Pharmacology, Rimmerman and coworkers demonstrate that 2-AG is entirely localized in the caveolae of dorsal root ganglion cells, where also part of AEA (approximately 30%) can be detected. However, most of AEA (approximately 70%) was detected in non-caveolae fractions, that is where CB2 receptors are localized. The different interaction of AEA and 2-AG with membrane microdomains might have significant implications for endocannabinoid-dependent autocrine and/or retrograde-paracrine signalling pathways. It also raises an important question about the structural determinants responsible for a different localization of two apparently similar endocannabinoids within lipid bilayers.
Maccarrone
M
M
Department of Biomedical Sciences, University of Teramo, Teramo, Italy. mmaccarrone@unite.it
D000818:Animals; D063385:Cannabinoid Receptor Modulators / Q000737:chemistry / Q000502:physiology*; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D006801:Humans; D021962:Membrane Microdomains / Q000235:genetics / Q000502:physiology; D043884:Receptor, Cannabinoid, CB1 / Q000819:agonists* / Q000737:chemistry / Q000502:physiology*
D063385:Cannabinoid Receptor Modulators; D043884:Receptor, Cannabinoid, CB1