Fluprostenol activates phospholipase C and Ca2+ mobilization in human myometrial cells

The objective of this study was to investigate the mechanism of action of PGF(2 alpha) in cultured human myometrial cells. We measured the effects of PGF(2 alpha) and fluprostenol, a selective PGF(2 alpha) receptor (FP receptor) agonist, on phospholipase C (PLC) activation, on changes in the intracellular free calcium concentration ([Ca2+](i)), and on protein tyrosine phosphorylation. PGF(2 alpha) and fluprostenol activated PLC (determined by measuring the formation of inositol phosphates) and increased [Ca2+](i) in a concentration-dependent manner. The apparent affinity of the FP receptor for fluprostenol was higher than that for PGF(2 alpha) when measuring PLC activation, but the receptor displayed similar affinities for both agonists when measuring increases in [Ca2+](i). These effects were not altered by treating the cells with pertussis toxin (PT), suggesting that the FP receptor is linked to PLC activation by a G protein of the G(q) family. By contrast, the effect of oxytocin on PLC activation involved both PT-resistant and PT-sensitive pathways. Human myometrial cells responded to pervanadate and epidermal growth factor with increased PLC activity and increased tyrosine phosphorylation, demonstrating a functional PLC-gamma tyrosine kinase pathway. However, neither fluprostenol nor oxytocin stimulated tyrosine phosphorylation, but the effects of both agonists were inhibited after protein kinase C stimulation. These data suggest that fluprostenol and oxytocin activate PLC-beta rather than PLC-gamma isoforms. The effect of fluprostenol is Ca2+ dependent, but is unlikely to involve a direct effect of Ca2+ on PLC activity.