CHARACTERIZATION AND REGULATION OF ATRIAL-NATRIURETIC-PEPTIDE (ANP)-R1 RECEPTORS IN THE HUMAN NEUROBLASTOMA CELL-LINE NB-OK-1

We characterized in membranes from the human neuroblastoma cell line NB-OK-1, an ANP-R1 receptor (Mr 130 kDa) for the atrial natriuretic peptide (ANP). This receptor recognized biologically active forms of ANP with high affinity but showed no affinity for truncated ANP forms. It was functional in that binding correlated with guanylate cyclase activation (a 2-fold increase in V(max)) with the following rank order of potency: rat ANP-(99-126) > human ANP-(99-126) > human ANP-(102-126) > porcine BNP (brain natriuretic peptide). The enzyme required free Mn2+ in addition to the Mn-GTP substrate (K(m) of about 0.3 mM for both basal and ANP-stimulated activity). In the presence of dithiothreitol, the dose-response curve of guanylate cyclase activation was shifted rightward by a factor of 30. ANP-R1 receptors were upregulated through protein synthesis in cells exposed to 1 mM carbamylcholine or 1 mM dibutyryl cyclic AMP for 8-24 h (ANP was ineffective).