A non-radioactive method for angiotensin II receptor binding studies using the rat liver.
BACKGROUND
A new non-radioactive method based on competitive ELISA has been developed for binding studies on angiotensin II (Ang II) receptors.


METHODS
Rat liver membrane was used as the source of angiotensin receptors and FITC-angiotensin II (FITC-Ang II) was used as the labeled ligand with an affinity similar to unlabeled Ang II. The effects of different concentrations of Ang II, losartan, CGP-42112A and saralasin were studied on FITC-Ang II binding.


RESULTS
The Ki values for Ang II, losartan and CGP-42112A were calculated as 0.52+/-0.22 nM, 6+/-3 nM and 0.15+/-0.07 nM, respectively. Saralasin inhibited the binding of labeled ligand biphasically, revealing two different populations of Ang receptor with different affinities for saralasin. About 74% of the binding sites were more sensitive to saralasin with a Ki value of 0.32+/-0.04 nM while saralasin showed a Ki value of 2.7+/-0.8 nM for the remaining binding sites.


CONCLUSIONS
The competitive ELISA method developed in this work yields Ki values for angiotensin antagonists similar to those obtained by others using radiolabeled ligands. The simplicity of this method makes it a suitable alternative to radioligand studies for routine analysis of interaction of drugs with angiotensin receptors.
Akhavan
Maziar Mohammad
MM
Razi Institute for Drug Research, Iran University for Medical Sciences, Shaheed Hemmat Expressway, Tehran 14551, Iran.
Ebrahimi
Soltan Ahmed
SA
Mahmoudian
Massoud
M
D000804:Angiotensin II / Q000031:analogs & derivatives / Q000037:antagonists & inhibitors* / Q000378:metabolism / Q000494:pharmacology; D057911:Angiotensin Receptor Antagonists; D000818:Animals; D001665:Binding Sites / Q000187:drug effects; D001667:Binding, Competitive; D001681:Biological Assay; D002462:Cell Membrane / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D004797:Enzyme-Linked Immunosorbent Assay; D016650:Fluorescein-5-isothiocyanate / Q000378:metabolism; D019084:Fluorescent Antibody Technique, Indirect; D005456:Fluorescent Dyes / Q000378:metabolism; D066298:In Vitro Techniques; D007700:Kinetics; D008024:Ligands; D008099:Liver / Q000166:cytology / Q000187:drug effects*; D019808:Losartan / Q000494:pharmacology; D008297:Male; D018448:Models, Immunological; D009842:Oligopeptides / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D011945:Receptors, Angiotensin / Q000378:metabolism*; D012504:Saralasin / Q000494:pharmacology; D014662:Vasoconstrictor Agents / Q000494:pharmacology; D014665:Vasodilator Agents / Q000494:pharmacology
D057911:Angiotensin Receptor Antagonists; D005456:Fluorescent Dyes; D008024:Ligands; D009842:Oligopeptides; D011945:Receptors, Angiotensin; D014662:Vasoconstrictor Agents; D014665:Vasodilator Agents; D000804:Angiotensin II; C060894:CGP 42112A; D012504:Saralasin; D016650:Fluorescein-5-isothiocyanate; D019808:Losartan