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β‐Adrenergic receptor desensitization of wild‐type but not cyc lymphoma cells unmasked by submillimolar Mg 2+
Author(s) -
Clark Richard B.,
Friedman Jacqueline,
Johnson John A.,
Kunkel Mark W.
Publication year - 1987
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.1.4.2820824
Subject(s) - desensitization (medicine) , receptor , chemistry , adrenergic receptor , adrenergic , endocrinology , pharmacology , medicine , biochemistry , biology
Treatment with low physiological concentrations of epinephrine (5‐50 nM) rapidly desensitizes β‐adrenergic stimulation of cAMP formation in S49 wild‐type (WT) lymphoma cells. Previous attempts to detect this early phase of desensitization in cell‐free assays of adenylate cyclase (EC 4.6.1.1) after intact cell treatment were unsuccessful. We have now found that reducing the Mg 2+ concentrations in the adenylate cyclase assays to <1.0 m m unmasked this rapid phase of desensitization of the WT cells, and that high Mg 2+ concentrations (5‐10 m m ) largely obscured the desensitization. Submillimolar Mg 2+ conditions also revealed a two‐ to threefold decrease in the affinity of epinephrine binding to the β‐adrenergic receptor after desensitization with 20 n m epinephrine. Detection of 4β‐phorbol 12‐myristate 13‐acetate (PMA) desensitization of the WT β‐adrencrgic receptor was also dependent on low Mg 2+ as measured either by the decrease in epinephrine stimulation of adenylate cyclase or by the reduction in the affinity of epinephrine binding. Unexpectedly, when cyc − cells were pretreated with 50 n m epinephrine, the β‐adrenergic stimulation of reconstituted adenylate cyclase was not desensitized. The characteristics of the Mg 2+ effect on epinephrine‐ and PMA‐induced desensitizations suggest a similar mechanism of action with the most likely events being phosphorylations of the β‐adrenergic receptors. Our data indicate that cAMP‐dependent protein kinase (EC 2.7.1.37) may play a role in the desensitization caused by low epinephrine concentrations inasmuch as this phase of desensitization did not occur in the cyc − . For the PMA‐induced desensitization, the phosphorylation may be mediated by protein kinase C (EC 2.7.1.37).—C lark , R. B.; F riedman , J.; J ohnson , J. A.; K unkel , M. W. β‐Adrenergic receptor desensitization of wild‐type but not cyc lymphoma cells unmasked by submillimolar Mg 2+ . FASEB J. 1: 289‐297; 1987.