REGULATION OF INTRACELLULAR FREE CALCIUM IN HUMAN MYOMETRIAL CELLS BY PROSTAGLANDIN-F2-ALPHA - COMPARISON WITH OXYTOCIN

The effects of prostaglandin F2α (PGF2α) on intracellular Ca2+ concentration ([Ca2+]i) and inositol phosphate (IP) generation in human myometrial cells were evaluated and compared to the effects of oxytocin. Basal [Ca2+]i levels were 146 and 153 nM in the absence and presence of 1 mm extracellular Ca, respectively. In Ca-containing medium, both PGF2α and oxytocin significantly (P < 0.01) increased [Ca2+]i over control values, eliciting half-maximal stimulation (ED50) at 4 and 1 nm, respectively. In Ca-free medium the potency of PGF2α to raise [Ca2+]i was drastically reduced (ED50, 2 nm), whereas that of oxytocin remained the same, although maximal responses were markedly decreased. PGF2α had no effect on total IP production in the concentration range that significantly raised [Ca2+]i. However, at a 100 times higher concentration (10 μ m), PGF2α produced a maximum 48% increase in total IP, with a rapid (15–30 s) rise in IP3 and IP2, followed by IP1. A similar increase in IP production was obtained when [Ca2+]i levels were raised by A23187 to the same level as that obtained with 10–50 μ m PGF2α. The effect of PGF2α was dependent on extracellular Ca and could be suppressed by verapamil, but not by pertussis toxin, or phorbol ester. In contrast, the potencies of oxytocin to raise IP and [Ca2+]i were similar and independent of extracellular Ca2+, and could be suppressed by pertussis toxin and phorbol ester, but not by verapamil. These data provide evidence that in isolated human myometrial cells, PGF2α and oxytocin trigger an increase in [Ca2+]i by different mechanisms. The action of PGF2α depends on extracellular Ca2+, whereas oxytocin activates the G-protein-dependent phospholipase-C-IP3-Ca2+ signal-transducing pathway, complemented by the influx of extracellular Ca2+. © 1990 by The Endocrine Society.