The role of diacylglycerol lipase in constitutive and angiotensin AT1 receptor-stimulated cannabinoid CB1 receptor activity

The cannabinoid CB1 receptor (CB1R) is,a G protein-coupled receptor, which couples to the G(i/o) family of heterotrimeric G proteins. The receptor displays both basal and agonist-induced signaling and internalization. Although basal activity of CBIRs is attributed to constitutive (agonist-independent) receptor activity, studies in neurons suggested a role of postsynaptic endocannabinoid (eCB) release in the persistent activity of presynaptic CB1Rs. To elucidate the role of eCBs in basal CB1R activity, we have investigated the role of diacylglycerol lipase (DAGL) in this process in Chinese hamster ovary (CHO) cells, which are not targeted specifically with I Agonist-induced G protein activation was determined by detecting dissociation G protein subunits expressed in CHO cells with bioluminescence resonance energy transfer (BRET), after labeling the alpha and beta subunits with Renilla luciferase and enhanced yellow fluorescent protein (EYFP), respectively. Pre-incubation of the cells with tetrahydrolipstatin (THL), a known inhibitor of DAGLs, caused inhibition of the basal activity of CBIR. Moreover, preincubation of CHO and cultured hippocampal neurons with THL increased the number of CBIRs on the cell membrane, which reflects its inhibitory action on CB1R internalization in non-simulated cells. In CHO cells co-expressing CB1R and angiotensin AT(1) receptors, angiotensin II-induced Go protein activation that was blocked by both a CBIR antagonist and THL. These data indicate that cell-derived I mediators have a general role in the basal activity of CB1Rs in non-neural cells and neurons, and that this mechanism can be stimulated by AT(1) receptor activation.