Direct characterization of beta-adrenoceptors in membranes of immature red blood cells from rats.
By means of the radioactive antagonist ligand (3H)(-) dihydroalprenolol (DHAP) specific binding sites were identified in membrane preparations from red blood cells from rats. These specific sites were characterized as beta-adrenoceptors because of the following reasons: Specific binding of DHAP (in contrast to unspecific binding) was dependent on temperature and time of incubation. Furthermore, specific binding of DHAP showed saturability, temperature-dependent reversibility and high affinity (KD-value of DHAP = 6.51 nM). Specific binding of DHAP was competitively inhibited by beta-adrenergic antagonists (pindolol greater than alprenolol greater than or equal to propranolol greater than practolol) and agonists (isoprenaline greater than adrenaline). The (-) enantiomers of pindolol and isoprenaline showed pronounced higher affinities for the receptor sites than the respective (+) enantiomers. The receptor density in the membrane preparations (pmoles/mg protein) was strongly dependent on the degree of reticulocytosis: The Bmax-values increased more than 4 to 5 fold without alteration of the respective KD-values when reticulocyte counts were enhanced from 3 to 80% treatment of the animals with increasing doses of acetyl phenylhydrazine.
D000526:Alprenolol / Q000494:pharmacology; D000818:Animals; D001665:Binding Sites; D004837:Epinephrine / Q000494:pharmacology; D004906:Erythrocyte Count; D004910:Erythrocyte Membrane / Q000032:analysis* / Q000187:drug effects; D004912:Erythrocytes / Q000032:analysis*; D007545:Isoproterenol / Q000494:pharmacology; D008297:Male; D010869:Pindolol / Q000494:pharmacology; D011217:Practolol / Q000494:pharmacology; D011433:Propranolol / Q000494:pharmacology; D051381:Rats; D011941:Receptors, Adrenergic / Q000032:analysis*; D011943:Receptors, Adrenergic, beta / Q000032:analysis*; D012156:Reticulocytes; D013696:Temperature; D013997:Time Factors
D011941:Receptors, Adrenergic; D011943:Receptors, Adrenergic, beta; D000526:Alprenolol; D011433:Propranolol; D010869:Pindolol; D007545:Isoproterenol; D011217:Practolol; D004837:Epinephrine