Distinct differences between morphine- and [D-Ala2,N-MePhe4,Gly-ol5]-enkephalin-mu-opioid receptor complexes demonstrated by cyclic AMP-dependent protein kinase phosphorylation

J Neurochem. 1998 Jul;71(1):231-9. doi: 10.1046/j.1471-4159.1998.71010231.x.


The present study demonstrates a conditional, agonist-dependent phosphorylation of the mu-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 (EC50 approximately 40 nM) 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 microM morphine and 6 nM PKA. Although morphine and related alkaloids as well as some peptide agonists (PLO17 and beta-endorphin) stimulated phosphorylation of MOR-1 by PKA, the potent mu-opioid-selective peptide [D-Ala2,N-MePhe4,Gly-ol5]-enkephalin (DAMGO) or other enkephalin analogues such as [D-Ala2]-Met5-enkephalinamide (DALA), [D-Ala2,D-Leu5]-enkephalin (DADLE), and Met5-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.

Publication types

  • Comparative Study
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Analgesics, Opioid / pharmacology*
  • Antibody Specificity
  • Carbazoles*
  • Cyclic AMP / metabolism
  • Cyclic AMP-Dependent Protein Kinases / metabolism*
  • Enkephalin, Ala(2)-MePhe(4)-Gly(5)-
  • Enkephalin, Leucine-2-Alanine / pharmacology
  • Enkephalin, Methionine / analogs & derivatives
  • Enkephalin, Methionine / pharmacology
  • Enkephalins / pharmacology*
  • Enzyme Inhibitors / pharmacology
  • Indoles / pharmacology
  • Morphine / pharmacology*
  • Neuroblastoma
  • Neurons / chemistry
  • Neurons / drug effects
  • Neurons / enzymology
  • Phosphorylation
  • Precipitin Tests
  • Pyrroles / pharmacology
  • Receptors, Opioid, mu / agonists
  • Receptors, Opioid, mu / immunology
  • Receptors, Opioid, mu / metabolism*
  • Tumor Cells, Cultured / chemistry
  • Tumor Cells, Cultured / drug effects
  • Tumor Cells, Cultured / enzymology


  • Analgesics, Opioid
  • Carbazoles
  • Enkephalins
  • Enzyme Inhibitors
  • Indoles
  • Pyrroles
  • Receptors, Opioid, mu
  • Enkephalin, Ala(2)-MePhe(4)-Gly(5)-
  • Enkephalin, Methionine
  • KT 5720
  • enkephalinamide-Met, Ala(2)-
  • Enkephalin, Leucine-2-Alanine
  • Morphine
  • Cyclic AMP
  • Cyclic AMP-Dependent Protein Kinases