Gbetagamma that interacts with adenylyl cyclase in opioid tolerance originates from a Gs protein

J Neurobiol. 2006 Oct;66(12):1302-10. doi: 10.1002/neu.20286.


We previously demonstrated that chronic morphine induces a change in G protein coupling by the mu opioid receptor (MOR) from Gi/o to Gs, concurrent with the instatement of an interaction between Gbetagamma and adenylyl cyclase types II and IV. These two signaling changes confer excitatory effects on the cell in place of the typical inhibition by opioids and are associated with morphine tolerance and dependence. Both signaling changes and these behavioral manifestations of chronic morphine are attenuated by cotreatment with ultra-low-dose naloxone. In the present work, using striatum from chronic morphine-treated rats, we isotyped the Gbeta within Gs and Go heterotrimers that coupled to MOR and compared these to the Gbeta isotype of the Gbetagamma that interacted with adenylyl cyclase II or IV after chronic morphine treatment. Isotyping results show that chronic morphine causes a Gs heterotrimer associated with MOR to release its Gbetagamma to interact with adenylyl cyclase. These data suggest that the switch to Gs coupling by MOR in response to chronic morphine, which is attenuated by ultra-low-dose opioid antagonist cotreatment, leads to a two-pronged stimulation of adenylyl cyclase utilizing both Galpha and Gbetagamma subunits of the Gs protein novel to this receptor.

Publication types

  • Comparative Study

MeSH terms

  • Adenylyl Cyclases / metabolism*
  • Analgesics, Opioid / pharmacology
  • Animals
  • Corpus Striatum / drug effects
  • Corpus Striatum / metabolism
  • Dose-Response Relationship, Drug
  • Drug Tolerance / physiology
  • GTP-Binding Protein alpha Subunits / metabolism
  • GTP-Binding Protein alpha Subunits, Gs / drug effects
  • GTP-Binding Protein alpha Subunits, Gs / metabolism*
  • GTP-Binding Protein beta Subunits / metabolism*
  • GTP-Binding Protein gamma Subunits / metabolism*
  • Male
  • Morphine / pharmacology*
  • Narcotic Antagonists / pharmacology
  • Protein Isoforms / drug effects
  • Protein Isoforms / metabolism
  • Rats
  • Rats, Sprague-Dawley
  • Receptors, Opioid, mu / drug effects*
  • Receptors, Opioid, mu / metabolism
  • Signal Transduction / drug effects
  • Signal Transduction / physiology


  • Analgesics, Opioid
  • GTP-Binding Protein alpha Subunits
  • GTP-Binding Protein beta Subunits
  • GTP-Binding Protein gamma Subunits
  • Narcotic Antagonists
  • Protein Isoforms
  • Receptors, Opioid, mu
  • Morphine
  • GTP-Binding Protein alpha Subunits, Gs
  • Adenylyl Cyclases
  • adenylyl cyclase 2
  • adenylyl cyclase 4