Radioligand Binding Assay for the Simultaneous Determination of β1- and β2-Adrenergic Receptors in Human Blood Cells

In this study, we propose a method for the separate determination of both types of adrenergic receptors based on radioligand binding analysis using 125I-iodocyanopindolol, comprising three measurements: (1) without competing ligands, (2) in the presence of selective ligand ICI 118,551 (0.25 μM), and (3) in the presence of two selective ligands, ICI 118,551 and CGP 20712 (0.25 μM each). The technique was tested on a model system of two transgenic cell lines ADL-7A and A2R9 with the expression of recombinant β1- and β2-adrenergic receptors. If the ratio of the number of β1-adrenergic receptors to β2-adrenergic receptors is 1 : 10, the measurement error is about 15%. Analysis of nine cell lines representing different types of blood cells showed the presence of β2-adrenergic receptors in Daudi, Raji, Dami, K-562, HL-60, U-937, and THP-1 cells and their absence in Jurkat and MOLT-4 cells. β1-Adrenergic receptors are reliably recorded only in THP-1 cells of monocytic origin. In other cell lines, with the exception of Dami, the number of β1-adrenergic receptors was found below the detection limit, estimated as 250 molecules per cell. Measurements performed on the peripheral blood mononuclear cells of seven healthy donors showed the presence of β2-adrenergic receptors in the range from 1000 to 2500 molecules per cell, while the content of β1-adrenergic receptors in all cases appeared to be on the border or beyond the detection limit.