DISCOVERY OF A POTENT ATRIAL-NATRIURETIC-PEPTIDE ANTAGONIST FOR ANPA RECEPTORS IN THE HUMAN NEUROBLASTOMA NB-OK-1 CELL-LINE

The effects of seven competitive atrial natriuretic peptide (ANP) receptor antagonists were compared on cultured human neuroblastoma NB-OK-1 cells expressing exclusively ANP(A) receptors, by evaluating their capacity to inhibit [I-125]ANP binding and to suppress ANP-stimulated cyclic GMP elevation. In ANP analogues with a shortened CyS7-Cys18 bridge, Asp13 and a hydrophobic Tic residue at position 16 expressed antagonistic activity, while Ala16 provoked lower antagonistic potency and Phe16 induced receptor activation. The binding affinity of A71915 ([Arg6,Cha8]ANP-(6-15)-D-Tic-Arg-Cys-NH2), the most potent antagonist (with a pK(i) of 9.18 and a pA2 of 9.48) was only 22 times less lower than that of the agonist ANP-(1-28).