[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.
|Number of pages||9|
|Journal||Biochemical and biophysical research communications|
|Publication status||Published - Nov 14 1979|
ASJC Scopus subject areas
- Molecular Biology
- Cell Biology