LOCALIZATION AND ANALYSIS OF NATRIURETIC PEPTIDE RECEPTORS IN THE GILLS OF THE TOADFISH, OPSANUS-BETA (TELEOSTEI)

The distribution and nature of natriuretic peptide binding sites was determined in the gills of the toadfish, Opsanus beta. Specific I-125-labeled rat atrial natriuretic peptide (rANP) and I-125-labeled porcine C-type natriuretic peptide (pCNP) binding sites were observed on the afferent and efferent filamental arteries and lamellar arterioles, and on the marginal channels of the secondary lamellae. In both section autoradiography and competition assays, the binding of both ligands was completely displaced by 1 mu M rANP and 1 mu M pCNP, but residual binding was observed with 1 mu M of the type C natriuretic peptide receptor (NPR-C)-specific ligand C-ANF. Electrophoresis of gill membranes crosslinked with I-125-rANP showed a major band at 75 kDa and a fainter band at 140 kDa. Both rANP and pCNP significantly stimulated the production of cGMP above basal levels; C-ANF had no stimulatory effect. These data show that the intrafilamental gill vasculature of toadfish contains a major population of natriuretic peptide receptors very similar to mammalian clearance receptors and a smaller population of receptors that are linked to a membrane-bound guanylate cyclase.