Characterization and distribution of a cloned rat μ-opioid receptor

James R. Bunzow, Ge Zhang, Claudia Bouvier, Carmen Saez, Oline K. Ronnekleiv, Martin J. Kelly, David K. Grandy

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75 Scopus citations


We have cloned and expressed a rat brain cDNA, TS11, that encodes a μ- opioid receptor based on pharmacological, physiological, and anatomical criteria. Membranes were prepared from COS-7 cells transiently expressing TS11 bound [3H] diprenorphine with high affinity (K(D) = 0.23 ± 0.04 nM). The rank order potency of drugs competing with [3H] diprenorphine was as follows: levorphanol (K(i) = 0.6 ± 0.2 nM) ≃ β-endorphin (K(i) = 0.7 ± 0.5 nM) ≃ morphine (K(i) = 0.8 ± 0.5 nM) ≃ [D-Ala2, N-Me- Phe4,Gly-ol5]-enkephalin (DAMGO; K(i) = 1.6 ± 0.5 nM) >>> U50,488 (K(i) = 910 ± 0.78 nM) > [D-Pen2,5]-enkephalin (K(i) = 3,170 ± 98 nM) > dextrorphan (K(i) = 4,100 ± 68 nM). The rank order potencies of these ligands, the stereospecificity of levorphanol, and morphine's subnanomolar K(i) are consistent with a μ-opioid binding site. Two additional experiments provided evidence that this opioid-binding site is functionally coupled to G proteins: (a) In COS-7 cells 50 μM 5'- guanylylimi-dodiphosphate shifted a fraction of receptors with high affinity for DAMGO (IC50 = 3.4 ± 0.5 nM) to a lower-affinity state (IC50 = 89.0 ± 19.0 nM), and (b) exposure of Chinese hamster ovary cells stably expressing the cloned μ-opioid receptor to DAMGO resulted in a dose-dependent, naloxone-sensitive inhibition of forskolin-stimulated cyclic AMP production. The distribution of mRNA corresponding to the μ- opioid receptor encoded by TS11 was determined by in situ hybridization to brain sections prepared from adult female rats. The highest levels of μ- receptor mRNA were detected in the thalamus, medial habenula, and the caudate putamen; however, significant hybridization was also observed in many other brain regions, including the hypothalamus.

Original languageEnglish (US)
Pages (from-to)14-24
Number of pages11
JournalJournal of neurochemistry
Issue number1
StatePublished - Jan 1995


  • Cyclic AMP
  • G protein coupling
  • In situ hybridization
  • Receptor binding
  • μ-Opioid receptors

ASJC Scopus subject areas

  • Cellular and Molecular Neuroscience
  • Biochemistry


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