ISSN:
1471-4159
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Medicine
Notes:
Abstract: The identities of heterotrimeric G proteins that can interact with the μ-opioid receptor were investigated by α-azidoanilido[32P]GTP labeling of α subunits in the presence of opioid agonists in Chinese hamster ovary (CHO)-MORIVA3 cells, a CHO clone that stably expressed μ-opioid receptor cDNA (MOR-1). This clone expressed 1.01 × 106μ-opioid receptors per cell and had higher binding affinity and potency to inhibit adenylyl cyclase for the μ-opioid-selective ligands [d-Ala2,N-MePhe4,Gly-ol]-enkephalin and [N-MePhe3,d-Pro4]-morphiceptin, relative to the δ-selective opioid agonist [d-Pen2,d-Pen5]-enkephalin or the κ-selective opioid agonist U-50,488H. μ-Opioid ligands induced an increase in α-azidoanilido[32P]GTP photoaffinity labeling of four Gα subunits in this clone, three of which were identified as Gi3α, Gi2α, and Go2α. The same pattern of simultaneous interaction of the μ-opioid receptor with multiple Gα subunits was also observed in two other clones, one expressing about three times more and the other 10-fold fewer receptors as those expressed in CHO-MORIVA3 cells. The opioid-induced increase of labeling of these G proteins was agonist specific, concentration dependent, and blocked by naloxone and by pretreatment of these cells with pertussis toxin. A greater agonist-induced increase of α-azidoanilido[32P]GTP incorporation into Gi2α (160–280%) and Go2α (110–220%) than for an unknown Gα (G?α) (60%) or Gi3α (40%) was produced by three different μ-opioid ligands tested. In addition, slight differences were also found between the ability of various μ-opioid agonists to produce half-maximal labeling (ED50) of any given Gα subunit, with a rank order of Gi3α 〉 Go2α 〉 Gi2α = G?α. In any case, these results suggest that the activated μ-opioid receptor couples to four distinct G protein α subunits simultaneously.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1046/j.1471-4159.1995.64062534.x
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