@article {MINNEMAN1, author = {KENNETH P. MINNEMAN and GREGORY A. WEILAND and PERRY B. MOLINOFF}, title = {A Comparison of the Beta-Adrenergic Receptor of the Turkey Erythrocyte with Mammalian Beta1 and Beta2 Receptors}, volume = {17}, number = {1}, pages = {1--7}, year = {1980}, publisher = {American Society for Pharmacology and Experimental Therapeutics}, abstract = {The kinetic and pharmacological properties of β-adrenergic receptors in turkey erythrocyte membranes have been characterized by measuring adenylate cyclase activity and specific binding of 125I-iodohythoxybenzylpindolol (IHYP). Receptor properties have been compared to those of β1, and β2 receptors in a number of mammalian tissues. The affinity (KD) of IHYP for the turkey erythrocyte β-adrenergic receptor (42 pM) was similar to the KD for IHYP binding to either β1 or β2 receptors. However, the rates of both association (k1) and dissociation (k-1) of IHYP were 6-10 times faster when measured with β-adrenergic receptors on turkey erythrocytes than were observed for either β1 or β2 receptors in various mammalian tissues. Thermodynamic analysis of the k1 for IHYP binding in the turkey erythrocyte and rat heart showed similar enthalpies of activation (ΔH{\textdaggerdbl}), suggesting that the different k1 values arise mainly from different entropies of activation (ΔH{\textdaggerdbl}) in the two tissues. The order of potency of drugs for activation or inhibition of adenylate cyclase activity correlated well with that for inhibition of IHYP binding in the turkey erythrocyte. However, both the Ki and Kact values for adenylate cyclase were generally two to three times higher than the corresponding KD value determined from studies of the inhibition of IHYP binding. The pharmacological effects of a variety of drugs with similar or different affinities for β1- and β2-adrenergic receptors were determined on membranes prepared from turkey erythrocytes. The KD values for nonselective drugs in the turkey erythrocyte were identical to their KD values for β1, and β2 receptors, suggesting that this receptor should be classified as a β-adrenergic receptor. However, the KD values in the turkey erythrocyte for selective drugs did not correlate with the KD values for these drugs at either β1 or β2 receptors. Furthermore, the efficacies of partial agonists at turkey erythrocyte β-adrenergic receptors did not correlate with their efficacies for either β1 or β2 receptors. The results demonstrate that the β-adrenergic receptor in the turkey erythrocyte has kinetic and pharmacological properties distinct from either mammalian β1 or β2 receptors. ACKNOWLEDGMENTS We thank Beth Goens for excellent technical assistance and Candace Plesha for preparing the manuscript.}, issn = {0026-895X}, URL = {https://molpharm.aspetjournals.org/content/17/1/1}, eprint = {https://molpharm.aspetjournals.org/content/17/1/1.full.pdf}, journal = {Molecular Pharmacology} }