BINDING OF BRAIN AND ATRIAL NATRIURETIC PEPTIDES TO CULTURED MOUSE ASTROCYTES AND EFFECT ON CYCLIC-GMP

I-125-Porcine brain natriuretic peptide (I-125-pBNP) bound to mouse astrocytes in primary culture in a time-dependent manner (t1/2 = 4.5 min), similar to I-125-human atrial natriuretic peptide (I-125-hANP) (t1/2) = 5 min). Binding was saturable and reached equilibrium after 90 min at 22-degrees-C for both radioligands. Scatchard analysis suggested a single class of binding sites for pBNP with a binding affinity and capacity (K(D) = 0.08 nM; B(max) = 78.3 fmol/mg of protein) similar to those of hANP1-28 (K(D) = 0.1 nM; B(max) = 90.3 fmol/mg of protein). In competition binding studies, pBNP or human/rat atrial natriuretic peptide (ANP) analogues [hANP1-28, rat ANP1-28 (rANP1-28), and rANP5-28] displaced I-125-hANP, I-125-pBNP, and I-125-rANP1-28 completely, all with IC50 values of < 1 nM (0.14-0.83 nM). All four peptides maximally stimulated cyclic GMP (cGMP) production by 10 min at 22-degrees-C at concentrations of 1-mu-M with EC50 values ranging from 50 to 100 nM. However, maximal cGMP induction by brain natriuretic peptide (BNP) (25.9 +/- 2.1 pmol/mg of protein) was significantly greater than that by hANP1-28 (11.5 +/- 2.2 pmol/mg of protein), rANP1-28 (16.5 +/- 2.0 pmol/mg of protein), and rANP5-28 (15.8 +/- 2.2 pmol/mg of protein). These studies indicate that BNP and ANPs act on the same binding sites and with similar affinities in cultured mouse astrocytes. BNP, however, exerts a greater effect on cGMP production. The difference in both affinity and selectivity between binding and cGMP production may indicate the existence of receptor subtypes that respond differentially to natriuretic peptides despite similar binding characteristics.