Identification and characterization of a homogeneous population of beta 2-adrenergic receptors on human alveolar macrophages.

Human alveolar macrophages obtained by bronchoalveolar lavage were studied with the high specific activity beta-adrenergic ligand [125I]pindolol and found to possess a moderate density of beta-adrenergic receptors. Using macrophage membranes, the receptor density (Bmax) was 42 +/- 9 fmol/mg protein with an apparent equilibrium dissociation constant (Kd) of 44 +/- 9 pM (mean +/- SEM). With intact macrophages, the Bmax = 5,643 +/- 942 sites/cell with Kd = 29 +/- 9 pM. Competition binding studies with subtype-specific antagonists revealed an exclusive population of beta 2-adrenergic receptors. Incubation of intact macrophages with the beta-adrenergic agonist isoproterenol caused a 6-fold increase in intracellular cyclic AMP (cAMP). Prostaglandin E1 and forskolin, which activate adenylate cyclase via different mechanisms, afforded typical marked increases in macrophage cAMP. Saturation binding, competition binding, and cAMP accumulation studies may all be performed from a single sample of about 2 x 10(7) cells, which can be obtained by bronchoalveolar lavage. This should facilitate studies of in vivo regulation of human alveolar macrophage beta-adrenergic receptors with regard to immune function and mediator release, and as a possible reflection of lung parenchymal receptors.