BACKGROUND AND PURPOSE:

The cannabinoid receptor type 1 (CB₁ ) has an allosteric binding site. The drugs ORG27569 and PSNCBAM-1 have been extensively characterised with regard to their effects on signalling of the orthosteric ligand CP55,940 and studies have suggested that these allosteric modulators increase binding affinity but act as non-competitive antagonists in functional assays. To gain a deeper understanding of allosteric modulation of CB₁ , we examined real-time signalling and trafficking responses of the receptor in the presence of allosteric modulators.

EXPERIMENTAL APPROACH:

Studies of CB₁ signalling were carried out in HEK 293 and AtT20 cells expressing HA-tagged human and rat CB₁ . We measured real-time accumulation of cAMP, activation and desensitization of potassium channel-mediated cellular hyperpolarisation and CB₁ internalisation.

KEY RESULTS:

ORG27569 and PSNCBAM-1 produce a complex, concentration and time-dependent modulation of agonist-mediated regulation of cAMP levels, as well as an increased rate of desensitisation of CB₁ -mediated cellular hyperpolarisation and a delay in agonist-induced receptor internalisation.

CONCLUSIONS AND IMPLICATIONS:

Contrary to previous studies characterising allosteric modulators at CB_1, this study suggests that the mechanism of action is not non-competitive antagonism of signalling, but rather that enhanced binding results in an increased rate of receptor desensitisation and delayed internalisation which results in time dependent modulation of cAMP signalling. The observed effect of the allosteric modulators is therefore dependent on the time frame over which the signalling response occurs. This finding may have important consequences for the potential therapeutic application of these compounds.
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PMID:

 

23937487

 

[PubMed – as supplied by publisher]