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Distinct Differences Between Morphine‐ and [ d ‐Ala 2 , N ‐MePhe 4 ,Gly‐ol 5 ]‐Enkephalin‐ μ‐Opioid Receptor Complexes Demonstrated by Cyclic AMP‐Dependent Protein Kinase Phosphorylation
Author(s) -
Chakrabarti Sumita,
Law PingYee,
Loh Horace H.
Publication year - 1998
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1046/j.1471-4159.1998.71010231.x
Subject(s) - enkephalin , chemistry , stereochemistry , opioid , μ opioid receptor , receptor , morphine , biochemistry , biology , pharmacology
The present study demonstrates a conditional, agonist‐dependent phosphorylation of the μ‐opioid receptor (MOR‐1) by cyclic AMP‐dependent protein kinase (PKA) in membrane preparations of MOR‐1‐transfected neuroblastoma Neuro2A cells. Opioid agonist‐dependent phosphorylation occurs in a time‐ and concentration‐dependent manner (EC 50 ∼40 n M ) and can be abolished by the receptor antagonist naloxone. Stoichiometric analysis indicates incorporation of a maximum of 6 mol of phosphate/mol of receptor in the presence of 1 µ M morphine and 6 n M PKA. Although morphine and related alkaloids as well as some peptide agonists (PLO17 and β‐endorphin) stimulated phosphorylation of MOR‐1 by PKA, the potent μ‐opioid‐selective peptide [ d ‐Ala 2 , N ‐MePhe 4 ,Gly‐ol 5 ]‐enkephalin (DAMGO) or other enkephalin analogues such as [ d ‐Ala 2 ]‐Met 5 ‐enkephalinamide (DALA), [ d ‐Ala 2 , d ‐Leu 5 ]‐enkephalin (DADLE), and Met 5 ‐enkephalin had no effect. The lack of the effect of DAMGO on MOR‐1 phosphorylation state was evident also after chronic pretreatment. These results suggest the existence of different agonist‐dependent conformations of MOR‐1. Furthermore, phosphorylation may be a useful parameter with which to identify different agonist‐receptor conformations.