ANGIOTENSIN-II RECEPTORS IN THE RAT LUNG ARE OF THE AII-1 SUBTYPE

In the rat lung [H-3]angiotensin II ([H-3]AII) recognizes a single class of binding sites with an equilibrium constant (K(D)) of 2.8 +/- 0.9 nM. The corresponding receptor density (B(max)) was 704 +/- 60 fmol/mg protein. Equilibrium of [H-3]AII binding was reached after 60 min. The dissociation of the radioligand was strongly influenced by mono- and divalent cations and the non-hydrolyzable GTP analog 5'-guanylyl-imido-diphosphate (Gpp[NH]p), indicating the interaction with a G protein. Specific binding of [H-3]AII to rat lung preparations was inhibited by different agonists and antagonists and sensitive to DuP 753 (2-n-butyl-4-chloro-5-hydroxymethyl-1-[(2'-(1H-tetrazol-5-yl)biphenyl-4-yl)methyl]imidazol, potassium salt) but insensitive to PD 123177 (1-(4-amino-3-methyl-benzyl)-5-diphenylacetyl-4,5,6,7-tetrahydro-imidazo[4,5-c]pyridine-6-carboxylic acid) two non-peptide AII antagonists selective for either the AII-1 or AII-2 subtype. Furthermore, specific [H-3]AII binding was inhibited by dithiothreitol. It is concluded that in the rat lung [H-3]AII binds to receptors of the AII-1 subtype which are coupled to a G protein. These receptors may be involved in the regulation of pulmonary perfusion and resistance.