CHARACTERIZATION OF THE FUNCTIONAL ANGIOTENSIN-II RECEPTOR COMPLEX ISOFORM IN RAT-LIVER PLASMA-MEMBRANE

In rat liver plasma membrane a single angiotensin II (Ang II) binding site (K-d of 3.71 +/- 0.33 nM and B-max of 1143.7 +/- 83.9 fmol/mg pro tein) was identified using radioligand binding assay. Pharmacologicall y, this receptor match with the AT(1) receptor subtypes in term of aff inity for the selective antagonist Losartan, and probably with the AT( 1A) receptor form in term of insensitivity for the antagonist PD123319 . Nevertheless, using polyacrylamide gel isoelectric focusing, two I-1 25-Ang II binding sites migrating to pI 6.8 and 6.5 were found in thes e membrane preparations. Monophasic displacement of I-125-Ang II bound to isoform migrating at pI 6.8 clearly indicate that this isoform rep resents a functional Ang II-receptor complex. In contrast, the high co ncentrations of agonist and peptidic derivates of Ang necessary to dis place I-125-Ang II bound to isoform migrating at pI 6.5 indicate that this atypical I-125-Ang II binding site represents a biologically nonf unctional Ang II binding molecule, presumably a nonspecific I-125-Ang II binding site.