[125I]EXP985: a highly potent and specific nonpeptide radioligand antagonist for the AT1 angiotensin receptor.
[125I]EXP985 is the first nonpeptide radioligand with high specific activity for the AT1 angiotensin receptor. The biochemical and pharmacological profiles of this ligand were determined using either ligand-receptor binding techniques in rat adrenal cortical microsomes or cellular Ca2+ mobilization in rat smooth muscle cells. Specific binding with 0.1 nM [125I]EXP985 increased slowly with time reaching an equilibrium at 60 min of incubation (22 degrees C). Scatchard analysis of the inhibition/binding data revealed a single class of binding sites having a Kd of 1.49 +/- 0.06 nM and a Bmax of 3.6 +/- 0.1 pmol/mg protein. These sites were saturable and the ligand-receptor complex dissociated with a t1/2 of 58 min. The binding was inhibited by Ang peptides with the following order of potency and IC50 (nM): Ang II (3.7) > Ang III (69) > Ang I (3650), and by the nonpeptide AT1 receptor antagonist, losartan, with an IC50 of 3.2 nM. PD123177, an AT2 selective antagonist, showed minimal inhibitory effect. Specific binding of [125I]EXP985 was found on rat aortic smooth cells. Ang II-induced Ca2+ mobilization in these cells was blocked by EXP985 in a noncompetitive manner. These data show that [125I]EXP985 (or its unlabeled) is a potent and highly specific radioligand or noncompetitive antagonist which represents a novel tool to further our understanding of the biochemistry of AT1 receptors.
Chiu
A T
AT
Du Pont Merck Pharmaceutical Company, Wilmington, DE 19880-0400.
McCall
D E
DE
Roscoe
W A
WA
D000302:Adrenal Cortex / Q000378:metabolism; D000803:Angiotensin I / Q000378:metabolism*; D000804:Angiotensin II / Q000378:metabolism; D057911:Angiotensin Receptor Antagonists; D000818:Animals; D001011:Aorta / Q000378:metabolism; D001713:Biphenyl Compounds / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D007093:Imidazoles / Q000494:pharmacology*; D007457:Iodine Radioisotopes; D008024:Ligands; D019808:Losartan; D008861:Microsomes / Q000378:metabolism; D009131:Muscle, Smooth, Vascular / Q000378:metabolism; D051381:Rats; D013777:Tetrazoles / Q000494:pharmacology*
D057911:Angiotensin Receptor Antagonists; D001713:Biphenyl Compounds; D007093:Imidazoles; D007457:Iodine Radioisotopes; D008024:Ligands; D013777:Tetrazoles; D000804:Angiotensin II; C078212:EXP 985; D000803:Angiotensin I; D019808:Losartan