Prostacyclin synthesis elicited by endothelin-1 in rat aorta is mediated by an ETA receptor via influx of calcium and is independent of protein kinase C.
The purpose of this study was to characterize the receptor(s) and second messenger systems involved in prostacyclin (prostaglandin [PG] I2) synthesis elicited by endothelin (ET)-1 in the rat aorta. PGI2 synthesis, measured as immunoreactive 6-keto-PGF1 alpha, was assessed in aortic rings exposed to endothelin receptor agonists in the presence and absence of selective ETA and ETB receptor antagonists. ET-1, which has equal affinity for both endothelin receptor subtypes, and ET-3, a preferential ETB receptor agonist, enhanced 6-keto-PGF1 alpha synthesis in a time- and concentration-dependent manner. ET-1 was more potent than ET-3 in increasing 6-keto-PGF1 alpha synthesis. Moreover, the selective ETB receptor agonists IRL-1620 and sarafotoxin S6c did not significantly increase 6-keto-PGF1 alpha synthesis. Furthermore, ET-1-induced 6-keto-PGF1 alpha synthesis was attenuated by an ETA receptor antagonist, BQ-123, in a dose-dependent manner but not by an ETB receptor antagonist, BQ-788. Depletion of extracellular Ca2+ or addition of Ca2+ channel blockers (nifedipine, verapamil, SK&F 96365) attenuated ET-1-mediated 6-keto-PGF1 alpha synthesis, while a Ca2+ 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-PGF1 alpha synthesis. These data suggest that PGI2 synthesis elicited by ET-1 in the rat aorta is mediated primarily through influx of extracellular Ca2+ via activation of an ETA receptor and is independent of protein kinase C.