Characterization of Angiotensin II Receptors

Angiotensin II (Ang II) is the primary mediator of the renin angiotensin system and acts primarily as a circulating hormone, but may also act as a paracrine or autocrine factor. Ang II binds specifically to G protein-coupled receptors and triggers a number of characteristic cellular responses, including vascular smooth muscle contraction and adrenal cellular aldosterone secretion. There are multiple receptor subtypes for Ang II; however, the distinction between binding sites versus receptors with their associated functional manifestations has been controversial. There are two principal human receptor subtypes, designated AT1 and AT2, that are distinguished by the selective affinity of the nonpeptide antagonists losartan and PD123177. In rodents, additional isoforms of the Ang II receptor have been cloned (e.g., AT1A and AT1B), although their functional distinctions are undetermined. The focus of this unit is the identification of Ang II binding sites and receptor subtypes. Radioligand competition binding assays are provided for determining the affinity of Ang II for receptors on adrenal cortical microsomes, whole adrenal membranes, or CHO cells transfected with the AT1A receptor.