[Treatment of intact myometrial cells with oxytocin inhibits Mg2+, ATP-dependent accumulation of Ca2+ in endoplasmic reticulum].

Uterotonic peptide hormone oxytocin has been studied for its effect on ATP-dependent accumulation of Ca2+ nonsensitive to the effect of ruthenium red (10 microM) that is potentiated by Ca2+-precipitating anion - oxalate. That was studied in experiments made on the suspension of myometrium cells from estrogenized rats processed by digitonin (0.1 mg/ml) with the aim permeabilization of plasmatic membrane. The preliminary processing of intact myocytes by oxytocin solution (final concentration 100 mM) to permeabilization of plasmatic membrane causes partial inhibition (stimulated by oxalate by 25-30% (0-10 mM) of Mg2+, ATP-dependent accumulation of Ca2+ in nonmitochondrion intracellular calcium depot of perforates smooth-muscled cells. The value of the component of power-dependent accumulation of Ca2+, that is inhibited by oxytocin, increased with both the incubation time and oxalate concentration. Thapsigargin and cyclopiasonium acid, selective inhibitors of calcium pump of endo(sarco)plasmatic reticulum, when used in saturation concentration (50 mM and 10 mM, respectively), completely inhibit the component of Mg2+, ATP-dependent accumulation of Ca2+ in nonmitochondrial intracellular calcium depot that is stimulated with oxalate (< 10 mM) and inhibited with oxytocin (100 mM). It is concluded that oxytocin partially inhibits Mg2+, ATP-dependent calcium pump of myometrium cell endoplasmic reticulum.