CONVERSION OF BIG-ENDOTHELIN-1 ELICITS AN ENDOTHELIN ET(A) RECEPTOR-MEDIATED RESPONSE IN ENDOTHELIAL-CELLS

Functional conversion of big-endothelin-1 to endothelin-1 and characte rization of endothelin receptor subtype were investigated in cultured rat aortic endothelial cells. Exogenous endothelin-1 and big-endotheli n-1 both increased arachidonic acid release and inositol phosphate pro duction dose dependently. Endothelin-1 was more potent than big-endoth elin-1 as indicated by EC(50) values: 0.5 +/- 0.1 nM and 10.0 +/- 2.0 nM for endothelin-1-induced arachidonic acid release and inositol phos phate formation, respectively, versus 1.0 +/- 0.4 nM and 35.0 +/- 6.0 nM for big-endothelin-1-induced responses. Big-endothelin-1, but not e ndothelin-1 actions were inhibited by phosphoramidon. Comparative stud ies of endothelin receptor agonists and antagonists showed that endoth elin-3 but not sarafotoxin S6c stimulated arachidonic acid release and inositol phosphate formation. The responses to big-endothelin-1 and e ndothelin-1 were specifically inhibited by the selective endothelin ET (A) receptor antagonist, [cyclo-D-Trp-D-Asp-Pro-D-Val-Leu] (BQ-123) bu t not by the selective endothelin ET(B) receptor antagonist rbonyl-L-g amma-methyl-Leu-D-Trp-(COMe)-D-NLeu-ONa] (BQ-788). [I-125]Endothelin-1 binding was inhibited by endothelin-1, endothelin-3 and BQ-123 but no t by BQ-788. These results indicate that the pharmacological responses to big-endothelin-1 in aortic endothelial cells are due to the extrac ellular phosphoramidon-sensitive conversion to endothelin-1. Endotheli n effects are mediated through endothelin ET(A) receptors in these cel ls.