Assays for enhanced activity of low efficacy partial agonists at the D(2) dopamine receptor

Br J Pharmacol. 2006 Oct;149(3):291-9. doi: 10.1038/sj.bjp.0706866. Epub 2006 Aug 21.


Background and purpose: Low efficacy partial agonists at the D2 dopamine receptor may be useful for treating schizophrenia. In this report we describe a method for assessing the efficacy of these compounds based on stimulation of [35S]GTPgammaS binding.

Experimental approach: Agonist efficacy was assessed from [(35)S]GTPgammaS binding to membranes of CHO cells expressing D2 dopamine receptors in buffers with and without Na+. Effects of Na+ on receptor/G protein coupling were assessed using agonist/[3H]spiperone competition binding assays.

Key results: When [35S]GTPgammaS binding assays were performed in buffers containing Na+, some agonists (aripiprazole, AJ-76, UH-232) exhibited very low efficacy whereas other agonists exhibited measurable efficacy. When Na+ was substituted by N-methyl D-glucamine, the efficacy of all agonists increased (relative to that of dopamine) but particularly for aripiprazole, aplindore, AJ-76, (-)-3-PPP and UH-232. In ligand binding assays, substitution of Na+ by N-methyl D-glucamine increased receptor/G protein coupling for some agonists -. aplindore, dopamine and (-)-3-PPP - but for aripiprazole, AJ-76 and UH-232 there was little effect on receptor/G protein coupling.

Conclusions and implications: Substitution of Na+ by NMDG increases sensitivity in [(35)S]GTPgammaS binding assays so that very low efficacy agonists were detected clearly. For some agonists the effect seems to be mediated via enhanced receptor/G protein coupling whereas for others the effect is mediated at another point in the G protein activation cycle. AJ-76, aripiprazole and UH-232 seem particularly sensitive to this change in assay conditions. This work provides a new method to discover these very low efficacy agonists.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • 8-Hydroxy-2-(di-n-propylamino)tetralin / analogs & derivatives
  • 8-Hydroxy-2-(di-n-propylamino)tetralin / metabolism
  • Animals
  • CHO Cells
  • Cricetinae
  • Dopamine Agonists / pharmacology*
  • Guanosine 5'-O-(3-Thiotriphosphate) / metabolism
  • Guanosine Triphosphate / pharmacology
  • Meglumine / pharmacology
  • Receptors, Dopamine D2 / agonists*
  • Sodium / pharmacology


  • Dopamine Agonists
  • Receptors, Dopamine D2
  • Guanosine 5'-O-(3-Thiotriphosphate)
  • Meglumine
  • 8-Hydroxy-2-(di-n-propylamino)tetralin
  • Guanosine Triphosphate
  • UH 232
  • Sodium