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Opioid peptide receptor studies. 12. Buprenorphine is a potent and selective μ/κ antagonist in the [ 35 S]‐GTP‐γ‐S functional binding assay
Author(s) -
Romero Dana V.,
Partilla John S.,
Zheng QaioXi,
Heyliger Simone O.,
Ni Qing,
Rice Kenner C.,
Lai Josephine,
Rothman Richard B.
Publication year - 1999
Publication title -
synapse
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.809
H-Index - 106
eISSN - 1098-2396
pISSN - 0887-4476
DOI - 10.1002/(sici)1098-2396(199911)34:2<83::aid-syn1>3.0.co;2-s
Subject(s) - damgo , agonist , chemistry , etorphine , μ opioid receptor , buprenorphine , antagonist , receptor , pharmacology , opioid , κ opioid receptor , gtp' , (+) naloxone , diprenorphine , opioid receptor , biochemistry , medicine , enzyme
We utilized the [ 35 S]‐GTP‐γ‐S functional binding assay to determine the selectivity of opioid receptor agonists in guinea pig caudate membranes. The study focused on two opioid agonists used for treating opioid‐dependent patients: methadone and buprenorphine. Selective antagonists were used to generate agonist‐selective conditions: TIPP + nor‐BNI to measure μ receptors, CTAP + nor‐BNI to measure γ receptors and TIPP + CTAP to measure κ receptors. The assay was first validated with opioid agonists of known subtype specificity (DAMGO for μ, SNC80 for δ, and U69,593 for κ receptors). Methadone‐stimulated [ 35 S]‐GTP‐γ‐S binding was μ‐specific and less potent and efficacious than etorphine (K d = 1,537 nM vs. K d = 7.8 nM). Buprenorphine failed to stimulate [ 35 S]‐GTP‐γ‐S binding but inhibited agonist‐stimulated [ 35 S]‐GTP‐γ‐S binding. The antagonist‐K i values (nM) of buprenorphine at μ, δ, and κ receptors were 0.088 nM, 1.15 nM, and 0.072 nM, respectively. The antagonist‐K i values (nM) of naloxone at μ, δ, and κ receptors were 1.39 nM, 25.0 nM, and 11.4 nM, respectively. Autoradiographic studies showed that buprenorphine failed to stimulate [ 35 S]‐GTP‐γ‐S binding in caudate‐level rat brain sections but blocked DAMGO‐stimulated [ 35 S]‐GTP‐γ‐S binding. In cells expressing the cloned rat μ receptor, buprenorphine was a partial agonist and potent μ antagonist. Administration of buprenorphine to rats produced a long‐lasting (>24 h) decrease in μ and κ2 receptor binding and attenuated μ‐stimulated [ 35 S]‐GTP‐γ‐S binding. Viewed collectively, these data indicate that, in this assay system, buprenorphine is a potent μ and γ receptor antagonist. The clinical implications remain to be elucidated. Synapse 34:83–94, 1999. Published 1999 Wiley‐Liss, Inc.