Contractile activity, membrane potential, and cytoplasmic calcium in human uterine smooth muscle in the third trimester of pregnancy and during labor

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OBJECTIVE: This study was undertaken to investigate in human tissue samples the mechanisms underlying spontaneous and prostaglandin F(2α)- induced contractions during the final trimester of pregnancy and labor. STUDY DESIGN: Membrane potential and cytoplasmic calcium were recorded simultaneously with contraction in uterine strips obtained from the lower segment during cesarean delivery. RESULTS: Between week 28 of gestation and term there was a progressive increase in the frequency of spontaneous contractions and a decrease in the negative potential of the membrane. The response to prostaglandin F(2α) was biphasic. The initial excitatory component remained stable toward term. A later inhibitory component, which was underpinned by increased activity of the sodium-potassium adenosine triphosphatase pump, decreased at the time of labor. CONCLUSIONS: There is a gradual increase in excitability in uterine muscle throughout the third trimester of human pregnancy. The initial component of the prostaglandin response is a large contraction that is kept brief by a subsequent inhibitory component of the response, which ensures that full relaxation occurs between contractions.

Original languageEnglish
Pages (from-to)1445-1451
Number of pages7
JournalAmerican Journal of Obstetrics and Gynecology
Issue number6
Publication statusPublished - 1 Jan 1999


  • Cytoplasmic calcium
  • Intracellular microelectrodes
  • Prostaglandins
  • Smooth muscle
  • Sodium-potassium adenosine triphosphatase

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