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-γ-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.