Anandamide receptors

Abstract

Anandamide (N -arachidonoyl-ethanolamine, AEA) was the first endogenous ligand of cannabinoid receptors to be discovered. Yet, since early studies, AEA appeared to exhibit also some effects that were not mediated by cannabinoid CB1 or CB2 receptors. Indeed, AEA exerts some behavioral actions also in mice with genetically disrupted CB1 receptors, whereas in vitro it is usually a partial agonist at these receptors and a weak activator of CB2 receptors. Nevertheless, several pharmacological effects of AEA are mediated by CB1 receptors, which, by being coupled to G-proteins, can be seen as AEA ‘metabotropic’ receptors. Furthermore, at least two different, and as yet uncharacterized, G-protein-coupled AEA receptors have been suggested to exist in the brain and vascular endothelium, respectively. AEA is also capable of directly inhibiting ion currents mediated by L-type Ca2+ channels and TASK-1 K+ channels. However, to date the only reasonably well characterized, non-cannabinoid site of action for AEA is the vanilloid receptor type 1 (VR1), a non-selective cation channel gated also by capsaicin, protons and heat. VR1 might be considered as an AEA ‘ionotropic’ receptor and, under certain conditions, mediates effects ranging from vasodilation, broncho-constriction, smooth muscle tone modulation and nociception to stimulation of hippocampal pair-pulse depression, inhibition of tumor cell growth and induction of apoptosis.