Differential coupling of the human cannabinoid receptors hCB1R and hCB2R to the G-protein Gαi2β1γ2

Human cannabinoid receptors 1 (hCB 1 R) and 2 (hCB 2 R) are expressed in the CNS and couple to G i /G o -proteins. The aim of this study was to compare coupling of hCB 1 R and hCB 2 R to Gα i2 β 1 γ 2 in Sf9 insect cells. High-affinity agonist binding at hCB 1 R, but not at hCB 2 R, was resistant to guanine nucleotides. hCB 1 R activated Gα i2 β 1 γ 2 much more rapidly than hCB 2 R in the [ 35 S]guanosine 5′-[γ-thio]triphosphate ([ 35 S]GTPγS) binding assay. Moreover, hCB 1 R exhibited a higher constitutive activity than hCB 2 R as assessed by the relative inhibitory effects of inverse agonists on [ 35 S]GTPγS binding and steady-state high-affinity GTPase activity compared to the stimulatory effects of the hCB 1/2 R agonist CP 55,940 [(-)- cis -3-[2-hydroxy-4-(1,1-dimethylheptyl)phenyl]- trans -4-(3-hydroxypropyl)cyclohexanol]. Gα i2 β 1 γ 2 coupled to hCB 2 R exhibited higher GDP- and GTPγS-affinities than Gα i2 β 1 γ 2 coupled to hCB 1 R. NaCl effectively reduced constitutive activity of hCB 1 R but not of hCB 2 R. Collectively, hCB 1 R and hCB 2 R couple differentially to Gα i2 β 1 γ 2 . Moreover, hCB 1 R exhibits higher constitutive activity than hCB 2 R. These differences point to distinct functions of hCB 1 R and hCB 2 R in the CNS.