Classification of beta-adrenergic subtypes in immature rabbit bone marrow erythroblasts

• Published in: Biochemical pharmacology Vol. 35; no. 21; p. 3679
• Main Authors: Setchenska, M S, Bonanou-Tzedaki, S A, Arnstein, H R
• Format: Journal Article
• Language: English
• Published: England 01.11.1986
• Subjects: Adenylyl Cyclases - metabolism; Adrenergic beta-Antagonists - pharmacology; Animals; Binding Sites - drug effects; Bone Marrow - metabolism; Epinephrine - pharmacology; Erythroblasts - classification; Erythroblasts - drug effects; Erythroblasts - metabolism; Iodocyanopindolol; Isoproterenol - pharmacology; Kinetics; Male; Pindolol - analogs & derivatives; Pindolol - metabolism; Propranolol - pharmacology; Rabbits; Receptors, Adrenergic, beta - drug effects; Receptors, Adrenergic, beta - metabolism; Stereoisomerism
• ISSN: 0006-2952
• DOI: 10.1016/0006-2952(86)90651-9

The beta-adrenergic receptors of immature rabbit bone marrow erythroid cells (proerythroblasts and basophilic erythroblasts) were identified. [125I]iodocyanopindolol bound to membrane preparations derived from these erythroblasts in a rapid, reversible and saturable manner. Scatchard analysis of binding data revealed a single class of binding sites (Hill coefficient of 0.954) with an apparent equilibrium dissociation constant (Kd) of 8 pM, and a density of binding sites (Bmax) of 1.53 pM/10(6) cells, corresponding to 920 receptors per cell. The binding of [125I]iodocyanopindolol was inhibited stereospecifically by concentrations of (-)-propranolol 2 orders of magnitude lower than by the (+)-isomer. Only L-isoprenaline and L-adrenaline activated the adenylate cyclase of immature rabbit erythroblasts, while L-noradrenaline, a beta 1-adrenergic agonist, was inactive. The order of potency of different agonists for displacement of bound [125I]iodocyanopindolol was: isoprenaline greater than adrenaline greater than noradrenaline with respective EC50 (concentration required for half maximal inhibition of binding) of 7.9 X 10(-7) M, 1.5 X 10(-5) M and 7.9 X 10(-5) M. This agonist potency series did not change with differentiation of rabbit bone marrow erythroblasts. The inhibition of specific [125I]iodocyanopindolol binding to immature cells by beta 1- and beta 2-selective drugs (noradrenaline, practolol, procaterol and butoxamine) resulted in linear Hofstee plots. The inhibition curves obtained with procaterol and butoxamine, with apparent Kd values of 3.1 X 10(-9) M and 4.9 X 10(-9) M, further evidence that the high-affinity binding sites correspond to a homogeneous beta 2-receptor subtype.