The recently cloned GB2 cannabinoid receptor subtype was stably transfected into AtT-20 and Chinese hamster ovary cells to compare the binding and signal transduction properties of this receptor with those of the CB, receptor subtype. The binding of rH] CP 55,940 to both CB1 and CB2 was of similar high affinity (2.6 and 3.7 rlM, respectively) and saturable. In competitive binding experiments,(-)-9-tetrahydrocannabinol and CP 55,940 were equipotent at the CB1 and CB2 receptors, but WIN 55212-2 and cannabinol bound with higher affinity to the CB2 than the CB1 receptor. HU 21 0 had a higher affinity for the CB1 receptor. Anandamide, a recently identified endogenous cannabinoid agonist, was essentially equipotent at both receptor subtypes. The structurally related fatty acid ethanol-amides dihomo-y-Iinolenylethanolamide and mead ethanolamide also bound with relatively equal affinity to both receptors, but adrenylethanolamide had a higher affinity for the CB1 receptor. The rank order of potency and efficacy for binding of the selected agonists to the GB1 and GB2 receptors was mim-icked in functional inhibition of cAMP accumulation experi-ments for all compounds tested. Both CB1 and CB2 receptors couple to the inhibition of cAMP accumlation that was pertussis toxin sensitive. SRi 41 71 6A, a CB1 receptor antagonist, was a poor antagonist at the CB2 receptor in both binding and func-tional inhibition of cAMP accumlation experiments. When ex-pressed in AtT-20 cells, the CB1 receptor mediated an inhibition of Q-type calcium channels and an activation of inward rectifying potassium channels. In contrast, the GB2 receptor did not modulate the activity of either channel under identical assay conditions. Similar to results obtained for CB1 receptor, the CB2 receptor did not couple to the activation of phospholipases A2, C, or D or to the mobilization of intracellular Ca2. Except for its inability to couple to the modulation of Q-type calcium channels or inwardly rectifying potassium channels, the CB1 and GB2 receptors display similar pharmacological and biochemical properties.

The cannabinoids, which include(-)-z9-THC, the active principle in marijuana, are a large and diverse group of lipophilic compounds that mediate both psychoactive and systemic physiological effects such as analgesia, anticonvulsion, immunosuppression, and the alleviation ofboth intraocular pressure and emesis(1). The cannabinoids exert their effects by binding selectively to G protein-coupled cannabinoid receptors located in the plasma membrane(2). Two subtypes of cannabinoid receptor have been cloned, CB1 (3)