Affinity labelling of α-adrenoceptors in intact liver cells by [3H]phenoxybenzamine

Wai Ho Kan, C. Farsang, Harold G. Preiksaitis, George Kunos

Research output: Contribution to journalArticle

7 Citations (Scopus)

Abstract

[3H]phenoxybenzamine of high specific activity (5.3 Ci/mmol) was synthesized and its binding to isolated, viable rat liver cells was studied. Phentolamine suppressible binding of [3H]phenoxybenzamine was irreversible and saturable (EC50: 10 nM, bmax: 200 fmol/mg wet cell weight). Competition-inhibition studies showed structural and stereoselectivity compatible with α-receptors. The IC50 of unlabelled phenoxybenzamine to reduce specific binding (9 nM) or to block adrenaline-induced phosphorylase activation in the same cells (2 nM) was similar, whereas the IC50 of agonists to suppress binding was higher than their EC50's for phosphorylase activation. The results represent the first example of labelling α-adrenoceptors in intact liver cells. The sites labelled by [3H]phenoxybenzamine mediate the block of phosphorylase activation by α-adrenoceptor antagonists. However, the relationship of these sites to receptors that mediate responses to physiological, low concentrations of catecholamines remains to be clarified.

Original languageEnglish
Pages (from-to)303-311
Number of pages9
JournalBiochemical and Biophysical Research Communications
Volume91
Issue number1
DOIs
Publication statusPublished - Nov 14 1979

Fingerprint

Phenoxybenzamine
Liver
Phosphorylases
Adrenergic Receptors
Labeling
Chemical activation
Inhibitory Concentration 50
Stereoselectivity
Phentolamine
Epinephrine
Catecholamines
Rats
Weights and Measures

ASJC Scopus subject areas

  • Biochemistry
  • Biophysics
  • Molecular Biology

Cite this

Affinity labelling of α-adrenoceptors in intact liver cells by [3H]phenoxybenzamine. / Kan, Wai Ho; Farsang, C.; Preiksaitis, Harold G.; Kunos, George.

In: Biochemical and Biophysical Research Communications, Vol. 91, No. 1, 14.11.1979, p. 303-311.

Research output: Contribution to journalArticle

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N2 - [3H]phenoxybenzamine of high specific activity (5.3 Ci/mmol) was synthesized and its binding to isolated, viable rat liver cells was studied. Phentolamine suppressible binding of [3H]phenoxybenzamine was irreversible and saturable (EC50: 10 nM, bmax: 200 fmol/mg wet cell weight). Competition-inhibition studies showed structural and stereoselectivity compatible with α-receptors. The IC50 of unlabelled phenoxybenzamine to reduce specific binding (9 nM) or to block adrenaline-induced phosphorylase activation in the same cells (2 nM) was similar, whereas the IC50 of agonists to suppress binding was higher than their EC50's for phosphorylase activation. The results represent the first example of labelling α-adrenoceptors in intact liver cells. The sites labelled by [3H]phenoxybenzamine mediate the block of phosphorylase activation by α-adrenoceptor antagonists. However, the relationship of these sites to receptors that mediate responses to physiological, low concentrations of catecholamines remains to be clarified.

AB - [3H]phenoxybenzamine of high specific activity (5.3 Ci/mmol) was synthesized and its binding to isolated, viable rat liver cells was studied. Phentolamine suppressible binding of [3H]phenoxybenzamine was irreversible and saturable (EC50: 10 nM, bmax: 200 fmol/mg wet cell weight). Competition-inhibition studies showed structural and stereoselectivity compatible with α-receptors. The IC50 of unlabelled phenoxybenzamine to reduce specific binding (9 nM) or to block adrenaline-induced phosphorylase activation in the same cells (2 nM) was similar, whereas the IC50 of agonists to suppress binding was higher than their EC50's for phosphorylase activation. The results represent the first example of labelling α-adrenoceptors in intact liver cells. The sites labelled by [3H]phenoxybenzamine mediate the block of phosphorylase activation by α-adrenoceptor antagonists. However, the relationship of these sites to receptors that mediate responses to physiological, low concentrations of catecholamines remains to be clarified.

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