Conversion of big-endothelin-1 elicits an endothelin ETA receptor-mediated response in endothelial cells

Functional conversion of big-endothelin-1 to endothelin-1 and characterization of endothelin receptor subtype were investigated in cultured rat aortic endothelial cells. Exogenous endothelin-1 and big-endothelin-1 both increased arachidonic acid release and inositol phosphate production dose dependently. Endothelin-1 was more potent than big-endothelin-1 as indicated by EC50 values: 0.5 +/- 0.1 nM and 10.0 +/- 2.0 nM for endothelin-1-induced arachidonic acid release and inositol phosphate 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 endothelin-1 actions were inhibited by phosphoramidon. Comparative studies of endothelin receptor agonists and antagonists showed that endothelin-3 but not sarafotoxin S6c stimulated arachidonic acid release and inositol phosphate formation. The responses to big-endothelin-1 and endothelin-1 were specifically inhibited by the selective endothelin ETA receptor antagonist, [cyclo-D-Trp-D-Asp-Pro-D-Val-Leu] (BQ-123) but not by the selective endothelin ETB receptor antagonist [N-cis-2,6-dimethylpiperidinocarbonyl-L-gamma- methyl-Leu-D-Trp-(COMe)-D-NLeu-ONa] (BQ-788). [125I]Endothelin-1 binding was inhibited by endothelin-1, endothelin-3 and BQ-123 but not by BQ-788. These results indicate that the pharmacological responses to big-endothelin-1 in aortic endothelial cells are due to the extracellular phosphoramidon-sensitive conversion to endothelin-1. Endothelin effects are mediated through endothelin ETA receptors in these cells.