ENDOTHELIN-STIMULATED SECRETION OF NATRIURETIC PEPTIDES BY RAT ATRIAL MYOCYTES IS MEDIATED BY ENDOTHELIN-A RECEPTORS

Endothelin (ET), a potent vasoconstrictor peptide, is known to enhance the secretion of atrial natriuretic factor (ANF) by the heart. In the present study, we investigated the potency of ET isopeptides to stimulate ANF and brain natriuretic peptide (BNP) secretion in primary cultures of neonatal atrial myocytes, and we characterized the receptor mediating these effects. All ET isopeptides caused a twofold increase of ANF and BNP secretion with the following order of potency: ET-1 approximate to ET-2>sarafotoxin 6b>>ET-3. Secretion of the natriuretic peptides was blocked by BQ-123, an ET(A)-receptor antagonist, but was not affected by either IRL-1620 or [Ala(1,3,11,15)]ET-1, two ET(B)-receptor agonists. ET receptors were localized by autoradiography on the surface of atrial myocytes, indicating that contaminating cells were not responsible for I-125-ET-1 binding. Competition binding analyses were then used to assess the ET-receptor subtype on atrial myocyte membrane preparations. A high-affinity (100 pmol/L) binding site with high density (approximate to 1500 fmol/mg) was found to preferentially bind the ET isopeptides in the following order: ET-1 greater than or equal to ET-2 greater than or equal to sarafotoxin 6b>ET-3. Binding was totally displaced by BQ-123 but not by IRL-1620. The ET binding site therefore had the characteristics of an ET(B)-like receptor. Analysis by cross-linking and sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed that it possessed a molecular mass of approximate to 50 kD. Northern blot analysis of both ET(A)- and ET(B)-receptor mRNAs allowed only the detection of the former, indicating that the ET(B) receptor may be expressed in very small amounts. These results demonstrate that ANF and BNP secretion by atrial myocytes is enhanced by ET(A)-like receptor (Circ Res. 1994;74:460-470.)