Adrenergic agonists do not compete with the antagonist (-)3-[125I]iodocyanopindolol for binding to rat pleural or peritoneal mast cell adrenergic receptor.

(-)3-[125I]iodocyanopindolol (ICYP), a high selective, high specific beta antagonist is employed to characterize beta-adrenoceptors on rat pleural and peritoneal mast cell populations. Results show that non specific binding is low, and that pleural mast cells exhibit greater number of receptors per cell (140,000) than peritoneal cells (90,000). Dissociation constants (Kd) are 0.37 +/- 0.01 and 0.55 +/- 0.02 nM for pleural and peritoneal cells, respectively. Competition experiments show that isoproterenol do not displaces ICYP neither in pleural nor in peritoneal cells. Low concentrations of propranolol displace ICYP from its binding sites, but atenolol does not. Results point to the existence in mast cells of mainly atypical. beta 2-receptors, since the agonist isoproterenol does not compete with the antagonist ICYP.