Beta-adrenoceptors of human lymphocytes: decrease in affinity of agonist for (-)3h-dihydroalprenolol binding sites by cytoplasmic fractions

The beta-adrenoceptors of intact human lymphocytes were investigated by binding assays with a radiolabeled β-adrenergic antagonists, (?)³H-dihydroalprenolol (DHA). Results shown are 1.48 ± 0.57 × 10⁴ binding sites for the ligand per cell. Binding of (?)³H-DHA to the membrane fractions of human lymphocytes was studied for comparison. The affinity of (?)³H-DHA for membrane was similar to that for whole lymphocytes, but the binding to the membranes was inhibited more strongly by β-adrenergic agonist. Moreover, the cytoplasmic fraction of human lymphocytes decreased the inhibition by (?)-isoproterenol of (?)³H-DHA binding to the membrane fraction. The results imply that the cytoplasmic fraction of human lymphocytes lowered the affinity of (?)-isoproterenol to (?)³H-DHA binding sites and left no effect on the binding of the β-adrenergic antagonist to the sites.