Localization of atrial natriuretic peptide receptors in the rat tongue and hard palate

Abstract

Atrial natriuretic peptide (ANP) receptors were characterized in rat oral mucosa using quantitative in vitro autoradiography and activation of particulate guanylyl cyclase (GC) by natriuretic peptides. Competition-binding analysis performed by quantitative in vitro autoradiography demonstrated specific [ 125I]rANP (1–28) binding sites in the tongue and hard palate. The precise location of this binding was revealed on the basal and parabasal cells of the epithelia by microautoradiography. The dissociation constant ( K d ) and maximal binding capacity ( B max) of these sites were 3.34±1.35 nM and 2.71±2.21 fmol/mm 2 on the epithelium of the tongue, and 4.09±1.52 nM and 3.45±3.01 fmol/mm 2 on the epithelium of the hard palate, respectively. Receptor subtypes were characterized by competition with des [Gln 18, Ser 19, Gly 20, Leu 21, Gly 22] ANP (4–23) (C-ANP), a specific ligand for the clearance receptor (NPR-C). These binding sites were displaced by C-ANP with inhibition constant ( K i ) of 8.96±3.18 nM and B max of 2.89±2.45 fmol/mm 2 on the epithelium of the tongue, and K i of 9.12±2.71 nM and B max of 3.08±2.94 fmol/mm 2 on the epithelium of the hard palate, respectively. Production of cyclic GMP by particulate GC in the epithelial membranes of the tongue and hard palate was stimulated by rANP (1–28), porcine brain natriuretic peptide (BNP) (1–26), and C-type natriuretic peptide (CNP) (1–22) in a dose-dependent manner. These results indicate that ANP-binding sites in the epithelium of the tongue and hard palate are mainly clearance receptors (NPR-C) but biological receptors (NPR-A and/or NPR-B) with GC activity are also present, and suggest that ANP may have a role in the proliferation of the oral epithelial cells, especially in the tongue and hard palate.