Abstract
Binding of (-)-[3H]dihydroalprenolol, a potent competitive beta adrenergic antagonist, to sites in frog erythrocyte membranes has previously been demonstrated to possess the essential properties expected of binding to adenylate cyclase-coupled beta adrenergic receptors. The present studies were designed to test the effects of a variety of membrane lipid-perturbing agents on both beta adrenergic receptor binding and catecholamine-responsive adenylate cyclase in frog erythrocyte membranes. Digestion of membranes with phospholipases A, C, and D causes a dose-dependent decline in receptor binding capacity without altering receptor affinity. Amphotericin B, a nondegradative membrane lipid perturbant, also causes a dose-dependent decrease in (-)-[3H]dihydroalprenolol binding. Decrements in catecholamine-stimulated adenylate cyclase activity caused by these agents are always greater than decreases in basal and fluoride-sensitive enzyme activities. Decreases in (-)-[3H]dihydroalprenolol binding parallel the disproportionate reduction in catecholamine responsiveness of adenylate cyclase. By contrast, the polyene antibiotic Filipin appears to "uncouple" receptor binding and enzyme activation, since a marked reduction in isoproterenol-stimulated adenylate cyclase is not accompanied by a decrease in specific (-)-[3H]dihydroalprenolol binding.
ACKNOWLEDGMENTS The electron microscopic studies in consultation were performed by Dr. J. R. Sommer, Director, Veterans Administration EM Laboratory, Veterans Administration Hospital, Durham, N. C. The authors thank Dr. Mary Ellen Switzer for fibrinogen degradation studies and Dr. Patrick McKee for helpful discussion. The authors also acknowledge Mr. Michael Coverstone for technical assistance.
- Copyright © 1976 by Academic Press, Inc.
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