Characterization of alpha-1 adrenergic receptors in the heart using [sup 3H]WB4101: Effect of 6-hydroxydopamine treatment

S. Yamada, H. I. Yamamura, W. R. Roeske

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125 Scopus citations

Abstract

To identify and characterize the cardiac alpha-adrenoceptors, a radioreceptor binding assay using the potent alpha adrenergic antagonist, [3H]WB4101 was performed in rat hearts. Specific [3H]WB4101 binding to rat left ventricular homogenates was saturable, reversible and of high affinity (Kd = 0.18 nM) with a B(max) of 2.57 fmol/mg of tissue (27.7 fmol/mg of protein). Adrenergic agonists competed for specific [3H]WB4101 binding in the order: (-)-epinephrine > (-)-norepinephrine >> (-)-isoproterenol. Stereospecificity of the [3H]WB4101 binding sites was also demonstrated with (-)-epinephrine, (Ki = 90) nM being 270 times as potent as (+)-epinephrine, (K1 = 24 μM). Adrenergic antagonists competed for the binding in the order: WB4101 = prazosin >> yohimbine > (-)-propranolol. WB4101 and prazosin exhibited a markedly greater (2000 times) affinity for [3H]WB4101 binding sites than yohimbine. The affinities (pKi) of alpha agonists and antagonists for [3H]WB4101 binding sites in the rat heart closely correlated with their pharmacological potencies in the heart. Scatchard analysis for [3H]WB4101 binding, performed in five regions from control and 6-hydroxydopamine-treated rat hearts, revealed specific [3H]WB4101 binding (Bmax) significantly greater in the ventricles and intraventricular septae than in atria. At 1 week after 6-hydroxydopamine treatment, there was a significant increase (40%) in the Bmax for [3H]WB4101 binding to ventricles and intraventricular septae without a change in Kd. We conclude: 1) [3H]WB4101 selectively labels postsynaptic alpha-1 adrenoceptors in the rat heart; 2) there is a definite regional variation for cardiac alpha-1 adrenoceptors; and 3) 6-hydroxydopamine treatment caused a significant increase in the density of alpha-1 adrenoceptors in ventricles and intraventricular septae, compatible with a postsynaptic localization of the [3H]WB4101 binding site.

Original languageEnglish (US)
Pages (from-to)176-185
Number of pages10
JournalJournal of Pharmacology and Experimental Therapeutics
Volume215
Issue number1
StatePublished - 1980
Externally publishedYes

ASJC Scopus subject areas

  • Molecular Medicine
  • Pharmacology

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