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Sigma selective antagonists potentiate G‐protein coupled receptor signaling without altering receptor occupancy
Author(s) -
Kim Felix J,
Kovalyshyn Ivanka,
Nielan Claire,
Pasternak Gavril W
Publication year - 2007
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.21.5.a425
Subject(s) - gtpgammas , μ opioid receptor , damgo , sigma 1 receptor , opioid receptor , sigma receptor , δ opioid receptor , pharmacology , enkephalin , receptor , chemistry , opioid , enzyme linked receptor , microbiology and biotechnology , biology , g protein , agonist , biochemistry
Sigma receptors have been linked to numerous, diverse biological phenomena. However, current knowledge of sigma biology remains largely descriptive, with no established molecular mechanisms of action. Previous work from our laboratory showed that sigma ligands could modulate opioid analgesia in vivo. Using human neuroblastoma cells (BE2C), which possess intrinsic opioid receptor activity, and Chinese hamster ovary (CHO) and human embryonic kidney cells (HEK), stably transfected with mu (MOR) or delta (DOR) opioid receptor cDNA, we determined that sigma1 binding sites physically associated with opioid receptors, as shown by co‐immunoprecipitation with MOR and DOR expressed in HEK cells. In BE2C cells, as low as 10 nM sigma selective antagonist BD1047, significantly potentiated DAMGO (mu selective) and DPDPE (delta selective) induction of [35S]GTPgammaS binding. The sigma selective antagonists shifted the opioid EC50 5 to 10‐fold to the left without significantly influencing maximal stimulation, an indication of efficacy. Alone, six prototypic sigma ligands, including agonists and antagonists, did not significantly stimulate [35S] GTPgammaS binding. Despite its ability to influence the stimulation of [35S] GTPgammaS binding, BD1047 alone did not affect either the Kd or Bmax of [3H]DAMGO binding. Thus, sigma receptors can modulate opioid transduction without influencing opioid receptor binding. Moreover, using mouse brain membrane preparations we found that a sigma selective antagonist could potentiate both opioid receptor and muscarinic acetylcholine receptor mediated stimulation of [35S] GTPgammaS binding, suggesting a broader role for sigma binding sites in modulating G‐protein coupled receptor signaling.