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

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 (Kd) and maximal binding capacity (Bmax) of these sites were 3.34±1.35 nM and 2.71±2.21 fmol/mm2 on the epithelium of the tongue, and 4.09±1.52 nM and 3.45±3.01 fmol/mm2 on the epithelium of the hard palate, respectively. Receptor subtypes were characterized by competition with des [Gln18, Ser19, Gly20, Leu21, Gly22] 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 (Ki) of 8.96±3.18 nM and Bmax of 2.89±2.45 fmol/mm2 on the epithelium of the tongue, and Ki of 9.12±2.71 nM and Bmax of 3.08±2.94 fmol/mm2 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.