Characterisation of the rat cerebella CB1 receptor using SR141716A, a central cannabinoid receptor antagonist

We describe the use of SR141716A, a central cannabinoid antagonist, in radioligand binding and adenylyl cyclase (AC) inhibition studies in rat cerebella membranes. The binding of [3H]SR141716A was dose-dependent and saturable, with Kd and Bmax of 0.61 +/- 0.12 nM and 1752 +/- 294 fmol/mg protein, respectively. Kinetic analysis of [3H]SR141716A binding afforded a Kd of 0.72 nM. In addition [3H]SR141716A was displaced dose-dependently by unlabelled SR141716A yielding a pKi of 8.37 +/- 0.07. Cannabinoid receptor agonists displaced [3H]SR141716A in a dose-dependent manner, (pKi) nabilone (8.29 +/- 0.08), WIN 55,212-2 (7.75 +/- 0.15), delta 9-tetrahydrocannabinol (7.29 +/- 0.21), delta 8-tetrahydrocannabinol (6.53 +/- 0.09) and anandamide (5.92 +/- 0.04). The affinity of anandamide was increased (6.26 +/- 0.13) by co-incubation with a serine protease inhibitor. A range of 13 commonly used non-cannabinoid ligands included at 100 microM were unable to displace [3H]SR141716A. WIN 55,212-2 inhibited basal cAMP formation dose-dependently with a pIC50 of 7.61 +/- 0.12 (24.3 nM) in an SR141716A (1 microM) reversible manner.