Epinephrine desensitization of adenylate cyclase from cyc- and S49 cultured lymphoma cells

Abstract

The characteristics of the specific beta-adrenergic desensitization of adenylate cyclase from the adenylate cyclase deficient lymphoma cell line (cyc-) and the wild type S49 (WT) are presented in detail in this report. We have previously shown that the cyc- adenylate cyclase desensitized with 1-3 hr pretreatment of the cells with the beta-adrenergic agonist epinephrine. Adenylate cyclase of cyc- was measured after reconstitution with cholate extracts of the coupling proteins (G/F) from WT. We have now demonstrated that: (i) the initial epinephrine-induced desensitization of adenylate cyclase from either cyc- or WT was similar and occurred rapidly, with a half-life of approximately 2 min, although WT desensitized to a greater extent with prolonged hormone treatment (18 hr pretreatment of cyc- or WT with 0.1 mM terbutaline resulted in a 92% desensitization of the WT adenylate cyclase and only a 48% desensitization of cyc-); (ii) the 60 min epinephrine desensitization of cyc- was reversed after addition of propranolol and continued (40-60 min) incubation, while that of WT was only partially reversed; (iii) similar concentrations of epinephrine (0.2-0.4 muM) were required for half-maximal desensitization of both cell lines; and (iv) the Kact for epinephrine stimulation of reconstituted adenylate cyclase from cyc- or WT was increased after a 1 hr desensitization with 10 muM epinephrine. Kact was approximately 5-fold less than the half-maximal concentration required for desensitization. The data support the conclusion that the mechanisms of the rapid, reversible specific beta-adrenergic desensitization of adenylate cyclase in cyc- and WT cells are similar and occur independently of the G/F proteins of the adenylate cyclase complex, whereas the slower, apparently irreversible phase of desensitization occurs only in WT.