EFFECTS OF OXYTOCIN, PROSTAGLANDIN-F2-ALPHA AND PROSTAGLANDIN E-2 ON INTRACELLULAR FREE CALCIUM CONCENTRATIONS OF LONGITUDINAL MUSCLE-CELLSISOLATED FROM TERM PREGNANT RAT MYOMETRIUM

The effects of oxytocin, PGF(2 alpha) and PGE(2) on [Ca2+](i) of isola ted longitudinal muscle cells of term pregnant rats were investigated using Fura-2. Oxytocin, PGF(2 alpha) and PGE(2) induced an initial rap id increase followed by a secondary gradual increase in [Ca2+](i) in t he presence of 1.5 mM Ca2+. The initial maximum increases in [Ca2+](i) were obtained at 6 s for oxytocin, 20 s for PGF(2 alpha) and 30 s for PGE(2) after addition of the stimulants. The EC50 values obtained fro m the curves were 2.0 nM for oxytocin, 250 nM for PGF(2 alpha) and 2,2 00 nM for PGE(2). On the other hand, the increases in [Ca2+](i) induce d by the stimulants were nearly abolished by removal of the extracellu lar Ca2+. The stimulants induced biphasic increases in [Ca2+](i) which were highly extracellular Ca2+-dependent processes, and the order of potencies for the stimulants was oxytocin much greater than PGF(2 alph a) > PGE(2) in terms of affinity as well as magnitude. These results m ight indicate differences in the weight of the physiological role of t he stimulants for regulating uterine contractility.