Incubation of human mononuclear leukocytes (MLN) with isoproterenol rapidly desensitizes β-adrenergic receptors, i.e. isoproterenol-stimulated cAMP accumulation decreases. This desensitization is accompanied by a redistribution of the receptor into a cellular environment to which hydrophilic compounds have limited access. We found that the total number of β-receptors [defined as binding of [3H]dihydroalprenolol (DHA) inhibited by 1 μM propranolol] was unchanged in the desensitized MNL. In control MNL, virtually all DHA binding was inhibited by 1 μM CGP-12177, suggesting that all of these receptors are on the cell surface, whereas in desensitized cells, only 33 ± 2% (mean ± SEM) of the DHA binding was inhibited by CGP-12177. We quantitated the sequestered receptors by subtracting the number of surface receptors from the total number of receptors. The sequestered receptors were homogeneous, with an affinity for DHA identical to that of surface receptors (K(d), 0.66 ± 0.12 vs. 0.62 ± 0.08 nM). The time courses of desensitization and sequestration were identical. The functional status of the sequestered receptors was assessed using the agonist zinterol, which (unlike catecholamines) is quite hydrophobic. Zinterol compted for DHA binding to both sequestered and surface receptors, whereas isoproterenol only competed for binding to the surface receptors. However, cAMP accumulation in desensitized MNL was reduced to the same extent regardless of whether isoproterenol or zinterol was used as the agonist. These results demonstrate that desensitization of intact cells to β-agonists cannot be attributed to limited accessibility of the sequestered receptors to catecholamines, but, rather, that the sequestered receptors are not functionally coupled to adenylate cyclase.
|Number of pages||8|
|Journal||Journal of Clinical Endocrinology and Metabolism|
|Publication status||Published - 1985|
ASJC Scopus subject areas
- Endocrinology, Diabetes and Metabolism