Selective labeling of IRAP by the tritiated AT(4) receptor ligand [3H]Angiotensin IV and its stable analog [3H]AL-11.
'AT(4) receptors' through which Angiotensin IV (Ang IV) improves memory acquisition, were recently identified as insulin regulated aminopeptidase (IRAP). Radioligand binding studies have hitherto been performed with iodinated Ang IV in the presence of divalent cation chelators EDTA and 1,10-phenanthrolin. Hence, they referred to the apo-form of IRAP. Presently, binding of [(3)H]Ang IV and [(3)H]AL-11, a stable Ang IV analog, was compared on Chinese hamster ovary (CHO-K1) and mouse hippocampal (P40H1) cell membranes. With chelators, their high affinity sites showed the same pharmacological profile as for [(125)I]Ang IV binding. Without chelators, only high affinity binding was perceived for [(3)H]AL-11. The same pharmacological profile was recorded in both membrane preparations; it was different from the one in the presence of chelators and corresponded to catalytically active IRAP (despite the concurrent presence of aminopeptidase N (APN) in P40H1 cell membranes). This confirms that the active and apo-forms of IRAP have a distinct pharmacological profile.
Demaegdt
Heidi
H
Research Group of Experimental Pharmacology, Department of Molecular and Biochemical Pharmacology, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium. hdemaegd@vub.ac.be
Lukaszuk
Aneta
A
De Buyser
Evi
E
De Backer
Jean-Paul
JP
Szemenyei
Erzsébet
E
Tóth
Géza
G
Chakravarthy
Sridhara
S
Panicker
Mitradas
M
Michotte
Yvette
Y
Tourwé
Dirk
D
Vauquelin
Georges
G
D000804:Angiotensin II / Q000031:analogs & derivatives* / Q000378:metabolism; D000818:Animals; D001667:Binding, Competitive; D001681:Biological Assay; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D010122:Cystinyl Aminopeptidase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D008024:Ligands; D051379:Mice; D011945:Receptors, Angiotensin / Q000378:metabolism*; D013194:Staining and Labeling; D014316:Tritium
C090830:AT4 receptor; D008024:Ligands; D011945:Receptors, Angiotensin; D014316:Tritium; D000804:Angiotensin II; C012877:angiotensin II, des-Asp(1)-des-Arg(2)-Ile(5)-; D010122:Cystinyl Aminopeptidase; C105964:leucyl-cystinyl aminopeptidase