Binding of beta-adrenergic antagonists 3H-DHA and 3H-CGP 12177 to intact rainbow trout (Salmo gairdneri) and carp (Cyprinus carpio) red blood cells.

beta-Adrenergic ligand binding to trout (Salmo gairdneri) and carp (Cyprinus carpio) red cells using a hydrophobic (3H-DHA) and a hydrophilic (3H-CGP) ligand was studied. Conditions which lead to the appearance (in vivo and in vitro hypoxia in carp cells) or disappearance ("winter" acclimation history in trout red cells) of beta-adrenergic responses were associated with either an appearance or marked increase of isoproterenol-displaceable binding (carp), or a disappearance of isoproterenol-displaceable binding (trout), respectively. The apparent number of binding sites was markedly greater for the hydrophobic than for the hydrophilic ligand, suggesting that binding of the hydrophobic ligand to internalized receptors and to nonreceptor sites may affect the results obtained with intact cells.