Relative affinity of angiotensin peptides and novel ligands at AT1 and AT2 receptors

The angiotensin type-1 receptor (AT1R) and the angiotensin type-2 receptor (AT2R) are well known to be involved in the complex cardiovascular actions of angiotensin II (Ang II). However, shorter peptide fragments of the Ang II are thought to have biological activity in their own right and elicit effects that oppose those mediated by Ang II. In this study we have used HEK-293 cells stably transfected with either the AT1R or the AT2R to perform a systematic analysis of binding affinities of all the major Ang peptides. Additionally, we tested the novel AT2R agonist, Compound 21, as well as the MasR agonist and antagonist, AVE0991 and A779 respectively, for their ability to bind to the AT1R or the AT2R. Candesartan, CGP42214 and PD123319 were used as reference compounds. Binding studies using [125I]-Sar1Ile8Ang II on the AT1R transfected HEK-293 cells revealed only Ang II, Ang III and candesartan to have high affinity for the AT1R. In the AT2R transfected HEK-293 cells, competition for [125I]-Sar1Ile8Ang II binding was observed for all ligands except candesartan, AVE0991 and A-779, the latter 2 compounds having negligible affinity at either AT1R or AT2R. The rank order of affinity of ligands at AT2R was CGP42112 <Ang II >/= Ang III <Compound 21 >/= PD123319