Inhibition of angiotensin II-induced inositol phosphate production by triacid nonpeptide antagonists in CHO cells expressing human AT1 receptors.
OBJECTIVE
The aim of the present work is to describe the inhibitory properties of LY301875 and LY303336, two polysubstituted 4-aminoimidazole AT1 receptor antagonists, on CHO cells expressing human recombinant AT1 receptors.


METHODS
The binding of [3H]-angiotensin II to intact cells as well as to angiotensin II induced inositol phosphate accumulation is measured.


RESULTS
Both antagonists inhibit specific [3H]-angiotensin II binding to AT1 receptors in these cells, with IC50 values of 5.9 and 5.2 nM, respectively. Preincubation of the cells with LY301875 results in a decline of up to 80% of the maximal angiotensin II-stimulated inositol phosphate (IP) production. A near complete decline of the maximal response is observed for LY303336. This insurmountable inhibition is attenuated for both antagonists when losartan is included during the preincubation of the cells.


CONCLUSIONS
Functional recovery experiments, in which antagonist-preincubated cells are washed and exposed to fresh media, suggest that the insurmountable inhibition by LY301875 and LY303336 is related to their relatively slow dissociation from the AT1 receptors. As already described for losartan and the derived insurmountable AT1 antagonists candesartan. EXP3174, and irbesartan, coincubation experiments reveal that LY301875 and LY303336 interact with the AT1 receptor in a manner that is competitive with angiotensin II.
Vanderheyden
P M
PM
Department of Molecular and Biochemical Pharmacology, Institute of Molecular Biology and Biotechnology, Free University of Brussels, Sint-Genesius Rode, Belgium. pvandhey@vub.ac.be
Verheijen
I
I
Fierens
F L
FL
DeBacker
J P
JP
Vauquelin
G
G
D000804:Angiotensin II / Q000037:antagonists & inhibitors* / Q000378:metabolism / Q000494:pharmacology; D047228:Angiotensin II Type 1 Receptor Blockers; D057912:Angiotensin II Type 2 Receptor Blockers; D057911:Angiotensin Receptor Antagonists; D000818:Animals; D001667:Binding, Competitive / Q000187:drug effects; D016466:CHO Cells; D003001:Cloning, Molecular; D006224:Cricetinae; D006801:Humans; D007295:Inositol Phosphates / Q000096:biosynthesis*; D044140:Receptor, Angiotensin, Type 1; D044139:Receptor, Angiotensin, Type 2; D011945:Receptors, Angiotensin / Q000096:biosynthesis*
D047228:Angiotensin II Type 1 Receptor Blockers; D057912:Angiotensin II Type 2 Receptor Blockers; D057911:Angiotensin Receptor Antagonists; D007295:Inositol Phosphates; D044140:Receptor, Angiotensin, Type 1; D044139:Receptor, Angiotensin, Type 2; D011945:Receptors, Angiotensin; D000804:Angiotensin II