Abstract

Cannabinoid receptors couple to both G_s and G_iproteins and can consequently stimulate or inhibit the formation of cAMP. To test whether there is specificity among cannabinoid receptor agonists in activating G_s- or G_i-coupled pathways, the potency and intrinsic activity of various cannabinoid receptor ligands in stimulating or inhibiting cAMP accumulation were quantified. The rank order of potencies of cannabinoid receptor agonists in increasing or inhibiting forskolin-stimulated cAMP accumulation, in CHO cells expressing hCB₁ receptors, was identical (HU-210 > CP-55,940 > THC > WIN-55212–2 > anandamide). However, the activities of these agonists were different in the two assays with anandamide and CP-55,940 being markedly less efficacious in stimulating the accumulation of cAMP than in inhibiting its formation. Studies examining the effects of forskolin on cannabinoid receptor mediated stimulation of adenyly cyclase also revealed differences among agonists in as much as forskolin enhanced the potency of HU-210 and CP-55,940 by ∼100-fold but, by contrast, had no effect on the potency of WIN-55212–2 or anandamide. Taken together these findings demonstrate marked differences among cannabinoid receptor agonists in their activation of intracellular transduction pathways. This provides support for the emerging concept of agonist-specific trafficking of cellular responses and further suggests strategies for developing receptor agonists with increased therapeutic utility.