Signal transduction in human myometrial cells.

Calcium plays a pivotal role in the contraction-relaxation cycle of uterine smooth muscle. We investigated the effects of three uterine agonists; prostaglandin F2 alpha (PGF2 alpha), oxytocin and platelet activating factor (PAF) on intracellular levels of Ca ([Ca2+]i) in intact human myometrial cells and 45Ca2+ efflux from permeabilized myocytes. We observed that, whereas oxytocin and PAF activated the phosphoinositide cycle, generating inositol triphosphate to mobilize intracellular Ca2+, PGF2 alpha acted mainly to enhance Ca2+ influx. Oxytocin-, but not PGF2 alpha-elicited responses were suppressed by pertussis toxin. It is concluded that all three agonists act by regulating [Ca2+]i in myometrial cells, but the signal transduction mechanism of PGF2 alpha differs from that of oxytocin and PAF.