Characterization of the Human Lymphocyte β-Adrenergic Receptor by Photoaffinity Labeling: Alterations with Desensitization

Desensitization of the leukocyte β-receptor system has been associated with a functional uncoupling of the components of the β-receptor complex. In order to determine whether desensitization and uncoupling of the leukocyte β-receptor is associated with any structural alterations in the β-receptor, we studied labeling of lymphocytes using the photoactive /S-adrenergic antagonist p-azido-m-[I]iodobenzylcarazolol. Labeled peptides were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and detected using autoradiographic techniques. In broken cell preparations, specific labeling was demonstrated in two major peptide bandsmol wt =68,000 and mol wt =55,000. Inhibition of photolabeling was stereospecific and demonstrated an order of potency for agonists consistent with labeling of aʼ β2-receptor. Preincubation of cells with the β-agonist, isoproterenol, resulted in a reduction in β-adrenergic-mediated adenylate cyclase activity to 60% of control, but no change in total binding sites as determined by [I]iodocyanopindolol binding. In photolabeling studies, desensitization was associated with a reduction in proportional labeling of the 55,000 mol wt band as compared to the 68,000 mol wt band to 58 ± 3% of control and a reduction in mobility of the upper band. These studies suggest that structural alterations in the human lymphocyte β-receptors occur with desensitization, analogous to changes in several other β-receptor model systems. Also, since the techniques described can identify alterations in human β-receptor structure, these methods may be exploited to determine whether structural alterations in lymphocyte β-receptors may occur in human disease states.