Effects of oxytocin, prostaglandin F2 alpha and prostaglandin E2 on intracellular free calcium concentrations of longitudinal muscle cells isolated from term pregnant rat myometrium.

The effects of oxytocin, PGF2 alpha and PGE2 on [Ca2+]i of isolated longitudinal muscle cells of term pregnant rats were investigated using Fura-2. Oxytocin, PGF2 alpha and PGE2 induced an initial rapid increase followed by a secondary gradual increase in [Ca2+]i in the presence of 1.5 mM Ca2+. The initial maximum increases in [Ca2+]i were obtained at 6 s for oxytocin, 20 s for PGF2 alpha and 30 s for PGE2 after addition of the stimulants. The EC50 values obtained from the curves were 2.0 nM for oxytocin, 250 nM for PGF2 alpha and 2,200 nM for PGE2. On the other hand, the increases in [Ca2+]i induced by the stimulants were nearly abolished by removal of the extracellular Ca2+. The stimulants induced biphasic increases in [Ca2+]i which were highly extracellular Ca(2+)-dependent processes, and the order of potencies for the stimulants was oxytocin > > PGF2 alpha > PGE2 in terms of affinity as well as magnitude. These results might indicate differences in the weight of the physiological role of the stimulants for regulating uterine contractility.