High throughput quantitation of cAMP production mediated by activation of seven transmembrane domain receptors

Impairment of G protein-coupled seven-transmembrane (7 TM) receptor function has been implicated in a variety of different pathologic conditions, suggesting that the discovery of specific antagonists may lead to the development of successful therapeutic agents. The effect of different agents on receptor-ligand interaction is often measured directly in a receptor binding assay; however, this assay format can be time consuming and does not detect agents that interact at sites distal to the native ligand binding site. Cyclic adenosine monophospate (cAMP) represents a ubiquitous second messenger generated in response to ligand binding to many 7 TM receptors. The present study describes the practical adaptation of scintillation proximity methodology, using FlashPlate(TM) (NEN Life Sciences, Boston, MA) technology to evaluate cAMP production. The bioassay is based on competition between endogenously produced cAMP and exogenously added radiolabeled [I-125]-CAMp. Cyclic AMP capture is mediated through an anti-cAMP antibody onto a microplate well surface. Removal of unbound radioligand is not necessary because only ligand within less than or equal to 20 mu m of the plate surface is detected due to the proximity effect. The data indicate that the use of scintillation proximity technology allows accurate and specific evaluation of G protein-coupled receptor function as measured by cAMP production and is suitable for high throughput screening.