[3H]CGP-12177, a beta-adrenergic ligand suitable for measuring cell surface receptors.

[3H]CGP-12177, in contrast to lipophilic ligands like [3H]Dihydroalprenolol, shows very little non-specific binding to intact cells. It also differs from lipophilic ligands in that it can be completely displaced from the receptors on intact cells by isoproterenol. Furthermore, binding sites for this ligand disappear rapidly upon exposure of cells to agonists. These binding sites reappear rapidly upon removal of the agonist, if any possible interaction with residual traces of the agonist are prevented. These results indicate that [3H]CGP-12177 binds only to cell surface receptors and that agonist causes a rapid and reversible shift of receptors from the cell surface to the interior of the cell.