Horm Metab Res 1981; 13(3): 150-155
DOI: 10.1055/s-2007-1019203
ORIGINALS

© Georg Thieme Verlag, Stuttgart · New York

Characterization of β-Adrenergic Receptors by (3H) Isoproterenol in Adipocytes of Humans and Rats

Beate Pfeifle, R. Pfeifle, J. D. Faulhaber, H. Ditschuneit
  • Zentrum für Innere Medizin der Universität Ulm, Abteilung für Innere Medizin II, Ulm, Germany
Further Information

Publication History

1979

1980

Publication Date:
14 March 2008 (online)

Summary

The specific binding of (3H) isoproterenol to isolated fat cells of human and rat was characterized. Binding of (3H) isoproterenol to isolated fat cells of rat was saturable with 420 pmol of (3H) isoproterenol bound/100 mg of lipid. Halfmaximal saturation occurred at 5 μM providing an estimate of the equilibrium dissociation constant, KD, for the interaction of (3H) isoproterenol with its binding sites. Kinetic analysis of (3H) isoproterenol binding provided a value of 2.01 × 104 min-1-M-1 for the forward bimolecular rate constant, k1. Dissociation of (3H) isoproterenol was a first order reaction with a rate constant, k2, of 0.62 × 10-1. The ratio k2/k1 = 3.07 μM provides an independent measurement of the KD for the interaction of (3H) isoproterenol with its binding sites which is in agreement with the values obtained by steady state analysis (3 to 5 μM). The apparent equilibrium dissociation constant, KD for the interaction of (3H) isoproterenol with its receptor in human fat cells obtained by steady state analysis was 1 to 0.9 μM. Scatchard- and Hill-analysis suggest the possibility of different negatively cooperative interactions among the binding sites in human and rat. β-Adrenergic agonists competed for the binding sites. The order of potency was isoproterenol > epinephrine > norepinephrine. Compounds such as DOPA, dopamine and (m-Hydroxyphenyl)2-methyl-aminoethanol which are structurally related to catecholamines had little or no affinity for (3H) isoproterenol binding sites.

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