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- Title
Agonist efficacy at the α<sub>2A</sub>-adrenoceptor:G<sub>α</sub><sub>15</sub> fusion protein: an analysis based on Ca<sup>2+</sup> responses.
- Authors
Pauwels, P.J.; Finana, F.; Tardif, S.; Colpaert, F.C.; Wurch, T.
- Abstract
A fusion protein was constructed between the recombinant human α2A-adrenoceptor and a mouse Gα15 protein to measure the efficacy of agonist-induced Ca2+ responses at a receptor:Gα15 protein stoichiometry of 1. Activation of this fusion protein in CHO-K1 cells by (-)-adrenaline induced a time- and concentration-dependent (pEC50: 7.28±0.04) increase in the intracellular Ca2+ concentration. The magnitude of the Ca2+ response was related to the amount of the fusion protein and the number of surface α2A-adrenoceptor binding sites as estimated by [3H]RX 821002 binding. Whereas UK 14304 was as efficacious as (-)-adrenaline, the following ligands displayed partial agonist properties [Emax in percentage vs. (-)-adrenaline: d-medetomidine (76±3) > BHT 920 (53±3) > clonidine (39±4) >> oxymetazoline (10±1)]. This ligand activation profile was not affected over a 30-fold range of expression of the fusion protein in contrast to the observed enhancement of the partial agonists' maximal responses by co-expression of the α2A-adrenoceptor with increasing amounts of the Gα15 protein. In conclusion, the fusion protein approach opens perspectives to quantify intrinsic activities of ligands under controlled experimental conditions of a fixed receptor:Gα15 protein ratio of 1.
- Subjects
ADRENERGIC receptors; PROTEINS; LABORATORY rats; LIGANDS (Biochemistry); ADRENALINE; CATECHOLAMINES
- Publication
Naunyn-Schmiedeberg's Archives of Pharmacology, 2000, Vol 361, Issue 6, p672
- ISSN
0028-1298
- Publication type
Article
- DOI
10.1007/s002100000250