Differential regulation of muscarinic M1 receptors by orthosteric and allosteric ligands
Activation of muscarinic M1 receptors is mediated via interaction of orthosteric agonists with the acetylcholine binding site or via interaction of allosteric agonists with different site(s) on the receptor. The focus of the present study was to determine if M1 receptors activated by allosteric agonists undergo the same regulatory fate as M1 receptors activated by orthosteric agonists.
Results: The orthosteric agonists carbachol, oxotremorine-M and pilocarpine were compared to the allosteric agonists AC-42, AC-260584, N-desmethylclozapine and xanomeline.
All ligands activated M1 receptors and stimulated interaction of the receptors with beta-arrestin-1. All ligands reduced cell surface binding and induced the loss of total receptor binding.
Receptor internalization was blocked by treatment with hypertonic sucrose indicating that all ligands induced formation of clathrin coated vesicles. However, internalized receptors recycled to the cell surface following removal of orthosteric but not allosteric agonists.
Whereas, all ligands induced loss of cell surface receptor binding, no intracellular vesicles could be observed after treatment with AC-260584 or xanomeline. Brief stimulation of M1 receptors with AC-260584 or xanomeline resulted in persistent activation of M1 receptors, suggesting that continual receptor signaling might impede or delay receptor endocytosis into intracellular vesicles.
Conclusion: These results indicate that allosteric agonists differ from orthosteric ligands and among each other in their ability to induce different regulatory pathways.
Thus, signaling and regulatory pathways induced by different allosteric ligands are ligand specific.
Author: Christopher DavisStefania Risso BradleyHans SchifferMikael FribergKristian KochBo-Ragnar TolfDouglas BonhausJelveh Lameh
Credits/Source: BMC Pharmacology 2009, 9:14
Published on: 2009-12-02
Copyright by the authors listed above - made available via BioMedCentral (Open Access). Please
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