Alpha-2 adrenoreceptors on arterial smooth muscle: Selective labeling by [3H]clonidine

R. J. Weiss, R Clinton Webb, C. B. Smith

Research output: Contribution to journalArticle

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Abstract

The specific binding of [3H]clonidine was used to characterize alpha-2 adrenoreceptors on rat tail artery smooth muscle membranes. At 24°C binding of 8 nM [3H]clonidine was rapid (T 1/2 of association = 2.1 min) and reversible (T 1/2 of dissociation = 0.7 min). The binding sites for the [3H]clonidine showed the specificity required for the alpha-2 adrenoreceptor. The rank order of potency of inhibitors of [3H]clonidine binding for agonists was clonidine > phenylephrine > methoxamine and for antagonists was yohimbine and piperoxan >> prazosin. Scatchard analysis of the binding data indicated the existence of a single population of binding sites with the maximum number of binding sites, B(max), equal to 33.5 ± 0.3 fmoles/mg of protein and the dissociation constant, K(D), equal to 7.3 ± 0.4 nM. There was no evidence for cooperativity (Hill coefficient = 0.96). The inhibition constants, K(i) values, of various adrenergic agonists and antagonists for the displacement of [3H]clonidine from tail artery membranes were well correlated with K(i) values determined for the displacement of this ligand from rat hippocampal membranes. Similar correlations were found with the potencies of these same agents in producing contractions of isolated tail artery strips. This study confirms the presence of alpha-2 adrenoreceptors on arterial smooth muscle and suggests that these receptors might be important in vascular function.

Original languageEnglish (US)
Pages (from-to)599-605
Number of pages7
JournalJournal of Pharmacology and Experimental Therapeutics
Volume225
Issue number3
StatePublished - Jan 1 1983
Externally publishedYes

Fingerprint

Clonidine
Smooth Muscle
Tail
Arteries
Binding Sites
Membranes
Piperoxan
Methoxamine
Adrenergic Agonists
Adrenergic Antagonists
Yohimbine
Prazosin
Phenylephrine
Blood Vessels
Ligands
Population
Proteins

ASJC Scopus subject areas

  • Molecular Medicine
  • Pharmacology

Cite this

Alpha-2 adrenoreceptors on arterial smooth muscle : Selective labeling by [3H]clonidine. / Weiss, R. J.; Webb, R Clinton; Smith, C. B.

In: Journal of Pharmacology and Experimental Therapeutics, Vol. 225, No. 3, 01.01.1983, p. 599-605.

Research output: Contribution to journalArticle

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