Direct Determination of Ligand Interactions with Beta-Adrenergic Receptors on Intact Turkey Erythrocytes: Correlation of Binding with Biological Activity*

Publisher Website
Google Scholar
Abstract
Previous studies on the interaction of labeled .beta.-adrenergic blockers with .beta.-adrenergic receptors employed broken cell or membrane preparations. Direct binding analysis was carried out on intact turkey erythrocytes employing the potent, high specific activity blocker [125I]-hydroxybenzylpindolol (HYP). [125I]HYP binds to a single class of receptor sites with a K of 5.3 .times. 1010M-1 and a binding capacity of 400-500 sites/cell. These results and the kinetics of association and dissociation and lack of evidence for negative cooperativity all agree well with studies reported earlier on membrane preparations from the same cells. True dissociation constants (Kd) for agonists and antagonists determined by inhibition of binding of [125I]HYP are in good agreement with results in membrane preparations. These Kd were compared directly with activation or inhibition constants for effects on adenylate cyclase using generation of [14C]c[cyclic]AMP from [14C]adenine in intact cells. The close correlation between effects on binding and adenylate cyclase activity in whole cells are similar to results obtained in membrane preparations in the presence of guanine nucleotides, suggesting the presence of an analogous regulatory substance in vivo. [Response to catecholamines is discussed.].