Agonist-specific alterations in receptor binding affinity associated with solubilization of turkey erythrocyte membrane beta adrenergic receptors

The beta adrenergic receptor binding sites of turkey erythrocyte membranes, identified by (-)-[³H]dihydroalprenolol binding, were solubilized with digitonin. The binding sites in particulate and soluble preparations displayed appropriate characteristics of beta₁ adrenergic specificity, stereospecificity, high affinity and saturability. The affinity of all agonists tested was significantly (2-50-fold) greater in the soluble than in the particulate preparations. The affinities of antagonists, however, were identical in the soluble and particulate preparations. Agonist-specific alterations in receptor binding affinity were also found to be mediated by assay temperature. Thus agonist but not antagonist affinities increased as the temperature was lowered from 37° to 4°. Possible molecular mechanisms responsible for the observed shifts are discussed.