Molecular Pharmacology, Vol 18, 370-378, Copyright © 1980 by the American Society for Pharmacology and Experimental Therapeutics

Loss and Restoration of Sensitivity to Epinephrine in Cultured BHK Cells: Effect of Inhibitors of RNA and Protein Synthesis

¹ Department of Pharmacology, University of Texas Medical School, Houston, Texas 77025

Cultured baby hamster kidney fibroblasts were used to study the phenomenon of receptor-mediated tachyphylaxis. Exposure to epinephrine or other -adrenergic agonists causes the adenylyl cyclase of these cells to become less responsive to stimulation by catecholamines without affecting the response to PGE₁ or NaF. Conversely, preincubation with PGE₁ leads to a selective loss of the response to PGE₁ but not to catecholamines. The loss of responsiveness to epinephrine is concentration dependent, can be prevented by propranolol, occurs rapidly (detectable within 2 min), requires approximately 2 h to reach maximum, and is not secondary to increased levels of cyclic AMP. Recovery from tachyphylaxis (resensitization) is ordinarily a slower process but may occur rapidly in certain circumstances. When tachyphylaxis is allowed to develop fully, as after exposure to epinephrine for 2 h, the cells remain poorly responsive for many hours and may require 24 h for complete resensitization. But if exposure to epinephrine is limited to 20 min or less, then recovery occurs much more rapidly (complete within 30 to 60 min). Inclusion of cycloheximide or actinomycin D during preincubation with epinephrine does not prevent tachyphylaxis but permits rapid recovery even after prolonged exposure to epinephrine. Both the development of tachyphylaxis and the recovery from it are temperature-dependent processes: Cells incubated with epinephrine at 6 instead of 30 or 37°C do not become tachyphylactic, and tachyphylactic cells incubated at low temperatures in the absence of epinephrine do not regain their sensitivity. The data suggest that the interaction of epinephrine with -receptors in these cells leads to a third effect in addition to the stimulation of adenylyl cyclase and the development of tachyphylaxis. This third effect is slower than the other two and can be inhibited by cycloheximide or actinomycin D, but the nature of the effect is obscure.

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ACKNOWLEDGMENTS The authors are grateful to Ms. Carol Laird and Ms. Barbara Couture for expert technical assistance.

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