Molecular characterization of angiotensin II type II receptors in rat pheochromocytoma cells

Abstract

The binding sites and biochemical effects of angiotensin (A) II were investigated in rat pheochromocytoma (PC12W) cells. Sarcosine 1, [ 125I]-tyrosine 4, isoleucine 8-AII ([ 125I]-SI-AII) bound to a saturable population of sites on membranes with an equilibrium dissociation constant ( K d ) of 0.4 nM and a binding site maximum of 254 fmol/mg protein. Competitive displacement of [ 125I]-SI-AII by agonists and antagonists elucidated a rank order of potency of AIII ≥ AII > PD 123177 > AI > [des-Phe]AII [AII(1–7)] ⪢ DuP 753 . The stable guanine nucleotide analog 5′-guanylyl imidodiphosphate did not alter the binding affinity or slope of the inhibition curves for AI, AII, AIII, or AII(1–7). Treatment of PC12W cells with AII or AIII did not affect the free intracellular calcium concentration, phosphoinositide metabolism, arachidonate release, cyclic GMP, or cyclic AMP concentrations. [ 125I]-AII binding sites remained on the cell surface and were not internalized after 2 h at 37°C. Angiotensin II did not stimulate tyrosine, serine, or threonine phosphorylation. Northern analysis of PC12W mRNA with an AT 1 receptor gene probe failed to produce an RNA:DNA hybrid at low stringency. These data indicate that PC12W cells express a homogeneous population of AT 2 binding sites which differ significantly from AT 1 receptors in signal transduction and molecular structure. AT 2 sites may act via potentially novel, biochemical pathways or, alternatively, be vestigial receptors.