Inverse agonism at adrenergic and opioid receptors: studies with wild type and constitutively active mutant receptors

Recept Channels. 1997;5(3-4):209-13.

Abstract

Ligands which display inverse agonism at G protein-coupled receptors do so by decreasing the intrinsic ability of a receptor to active the cellular G protein population in the absence of an agonist ligand. Expression of the murine delta opioid receptor in Rat-1 fibroblasts resulted in the inverse agonist ICI174864 being able to cause inhibition of basal high affinity GTPase activity and of the binding of [35S]GTP gamma S in membranes of a clone (D2) of these cells which expresses high levels of the receptor. These effects were blocked by co-addition of the neutral antagonist TIPP[psi], demonstrating a requirement for the delta opioid receptor, and by pertussis toxin pretreatment of the cells, showing them to be produced via a Gi-like G protein. The inverse agonist properties of ICI174864 could also be demonstrated in whole cells. Stimulation of forskolin-amplified adenylyl cyclase activity was produced by ICI174864 following [3H]adenine prelabelling of the cells. Constitutively activated mutants of receptors should provide a convenient means to detect inverse agonists. Incubation of cells either transiently or stably transfected with a constitutively activated mutant of the human beta 2-adrenoceptor with the beta 2-inverse agonists betaxolol or sotalol, which are both able to inhibit CAM beta 2-adrenoceptor-mediated basal adenylyl cyclase activity, resulted in a strong upregulation of levels of the receptor. In the stable cells lines this effect was prevented by co-incubation with neutral antagonists but could not be reproduced by an adenylyl cyclase P-site ligand which also inhibited basal adenylyl cyclase levels.

Publication types

  • Research Support, Non-U.S. Gov't
  • Review

MeSH terms

  • Adrenergic beta-Antagonists / metabolism*
  • Animals
  • Betaxolol / metabolism*
  • Enkephalin, Leucine / analogs & derivatives*
  • Enkephalin, Leucine / metabolism
  • Humans
  • Mice
  • Receptors, Opioid, delta / antagonists & inhibitors*
  • Receptors, Opioid, delta / genetics
  • Sotalol / metabolism*

Substances

  • Adrenergic beta-Antagonists
  • Receptors, Opioid, delta
  • Enkephalin, Leucine
  • N,N-diallyl-tyrosyl-alpha-aminoisobutyric acid-phenylalanyl-leucine
  • Sotalol
  • Betaxolol