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Antagonists show GTP‐sensitive high‐affinity binding to the sigma‐1 receptor
Author(s) -
Brimson JM,
Brown CA,
Safrany ST
Publication year - 2011
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.2011.01417.x
Subject(s) - receptor , radioligand , sigma receptor , gtp' , agonist , radioligand assay , binding site , enzyme linked receptor , chemistry , biochemistry , biology , pharmacology , biophysics , enzyme
BACKGROUND AND PURPOSE Sigma‐1 receptors are atypical receptors with potentially two transmembrane domains. Antagonists require doses significantly higher than their published affinities to have biological effects. We have reassessed the binding characteristics of these ligands and found antagonists bind to high‐ and low‐affinity states not distinguished by agonists. EXPERIMENTAL APPROACH The affinities of sigma‐1 receptor ligands was assessed using radioligand saturation and competition binding of [ 3 H]‐(+)‐pentazocine to permeabilized MDA‐MB‐468 cells. This was compared with the effect of ligands on metabolic activity using an MTS‐based assay and calcium signalling using cells loaded with the calcium dye, Fura‐2. KEY RESULTS Sigma‐1 receptor antagonists, but not agonists, show GTP‐ and suramin‐sensitive high‐affinity binding. Functional responses (calcium signalling and metabolic activity), while associated with sigma‐1 receptor binding, required binding to an unidentified, low‐affinity target. CONCLUSIONS AND IMPLICATIONS Sigma‐1 receptors are coupled to G proteins. This interaction is only observed when analysing antagonist binding. The identity of the G protein remains to be resolved. The concept of agonist and antagonist at the sigma‐1 receptor needs to be revisited.