Prostacyclin Synthesis Elicited by Endothelin-1 in Rat Aorta Is Mediated by an ET A Receptor via Influx of Calcium and Is Independent of Protein Kinase C

Abstract

Abstract The purpose of this study was to characterize the receptor(s) and second messenger systems involved in prostacyclin (prostaglandin [PG] I 2 ) synthesis elicited by endothelin (ET)-1 in the rat aorta. PGI 2 synthesis, measured as immunoreactive 6-keto-PGF 1α , was assessed in aortic rings exposed to endothelin receptor agonists in the presence and absence of selective ET A and ET B receptor antagonists. ET-1, which has equal affinity for both endothelin receptor subtypes, and ET-3, a preferential ET B receptor agonist, enhanced 6-keto-PGF 1α synthesis in a time- and concentration-dependent manner. ET-1 was more potent than ET-3 in increasing 6-keto-PGF 1α synthesis. Moreover, the selective ET B receptor agonists IRL-1620 and sarafotoxin S6c did not significantly increase 6-keto-PGF 1α synthesis. Furthermore, ET-1–induced 6-keto-PGF 1α synthesis was attenuated by an ET A receptor antagonist, BQ-123, in a dose-dependent manner but not by an ET B receptor antagonist, BQ-788. Depletion of extracellular Ca 2+ or addition of Ca 2+ channel blockers (nifedipine, verapamil, SK&F 96365) attenuated ET-1–mediated 6-keto-PGF 1α synthesis, while a Ca 2+ channel agonist, S (−)-Bay K 8644, potentiated this effect of ET-1. Selective protein kinase C inhibitors (bisindolylmaleimide I, calphostin C) did not alter ET-1–induced 6-keto-PGF 1α synthesis. These data suggest that PGI 2 synthesis elicited by ET-1 in the rat aorta is mediated primarily through influx of extracellular Ca 2+ via activation of an ET A receptor and is independent of protein kinase C.