The phosphorylation of μ-opioid receptors (MOPRs) by G protein-coupled receptor kinases (GRKs), followed by arrestin binding, is thought to be a key pathway leading to desensitization and internalization. The present study used the combination of intracellular and whole-cell recordings from rats and mice, as well as live cell imaging of Flag-tagged MOPRs from mouse locus ceruleus neurons, to examine the role of protein kinases in acute desensitization and receptor trafficking. Inhibition of GRKs by using heparin or GRK2-mutant mice did not block desensitization or alter the rate of recovery from desensitization. The nonselective kinase inhibitor staurosporine did not reduce the extent of [Met5]enkephalin (ME)-induced desensitization but increased the rate of recovery from desensitization. In the presence of staurosporine, ME-activated FlagMOPRs were internalized but did not traffic away from the plasma membrane. The increased rate of recovery from desensitization correlated with the enhancement in the recycling of receptors to the plasma membrane. ME-induced MOPR desensitization persisted and the trafficking of receptors was modified after inhibition of protein kinases. The results suggest that desensitization of MOPRs may be an early step after agonist binding that is modulated by but is not dependent on kinase activity.
This work was supported by National Institutes of Health National Institute of Drug Abuse [Grants DA08163, DA026617].
Article, publication date, and citation information can be found at http://molpharm.aspetjournals.org.
- μ-opioid receptor
- G protein-coupled receptor
- G protein-coupled receptor kinase
- locus ceruleus
- arrestin 3-knockout
- artificial cerebrospinal fluid
- Flag-tagged μ-opioid receptor
- analysis of variance
- 1,2-bis(2-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid
- mitogen-activated protein kinase
- α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid
- dizocilpine maleate
- Received October 4, 2011.
- Accepted November 23, 2011.
- Copyright © 2012 The American Society for Pharmacology and Experimental Therapeutics