[Uterotonic effect of oxytocin and transport of Ca2+ through the myometrial sarcolemma].

Effect of oxytocin on contractile activity, passive and Mg2+, ATP-dependent Ca2+ transport through myocyte plasmic membrane was studied in the experiments carried out on intact samples of the uterus smooth muscle and fraction of myometrium sarcolemma vesicules. It was shown that at short-term (30 s) application of oxytocin (2.10(-7) M) powerful prolonged contractile reaction of myometrium bands was observed. After the chelating of Ca2+ in the washing medium by means of EGTA (2mM) or while introducing into it blockers of electrically controlled calcium channels the bands responded to oxytocin application with a single physical contraction. High concentrations of peptide hormone (10(-6) M) introduced into the preincubation medium of the smooth muscle bands before the isolation of the membrane fraction or directly into the incubation medium produced no effect on passive liberation of Ca2+ vesicules from the sarcolemma vesicules. At the same time preincubation of the bands in the solution containing smaller concentration of octapeptide (10(-7) M) decreased the initial velocity of Mg2+, ATP-dependent Ca2+ transport in the vesicules by 30% on the average. Possible mechanisms of oxytocin effects on intracellular homeostasis of Ca2+ in the myometrium, on the contractile activity of the uterus are discussed.