[Ca2+]i signaling in pregnant human myometrium.
The purpose of the present study was to determine the changes in intracellular ionized calcium concentration ([Ca2+]i) or [Ca2+]i sensitivity accompanying spontaneous and agonist-induced contraction of human myometrium at term pregnancy, as well as to quantify the response to three prototypical agonists: 1) oxytocin, 2) vasopressin, and 3) phenylephrine. Uterine biopsies were obtained at the time of cesarean section from patients who delivered at or near full-term gestation. These preparations were used to measure isometric force development and [Ca2+]i levels with the luminescent calcium indicator aequorin. Concentration-response relationships were determined with respect to isometric force development in the presence of the agonist. [Ca2+]i-force relationships were determined with respect to spontaneous phasic contractions, as well as agonist-induced phasic and tonic contractions. The results provide evidence that the phasic nature of term human myometrium is due to 1) the resting [Ca2+]i level being less than the calcium threshold for contractions and 2) the inability of the tissue to maintain high [Ca2+]i levels for prolonged periods of time. In addition, calcium-independent mechanisms of regulation were suggested by the relatively minor calcium sensitizing action of oxytocin and the observation that relaxation of tonic contractions preceded the fall in [Ca2+]i levels.
Szal
S E
SE
Department of Medicine, Brighman and Women's Hospital, Boston 02115.
Repke
J T
JT
Seely
E W
EW
Graves
S W
SW
Parker
C A
CA
Morgan
K G
KG
D002118:Calcium / Q000378:metabolism*; D036861:Delivery, Obstetric; D004594:Electrophysiology; D005260:Female; D006801:Humans; D007425:Intracellular Membranes / Q000378:metabolism*; D009215:Myometrium / Q000378:metabolism*; D010121:Oxytocin / Q000494:pharmacology; D010656:Phenylephrine / Q000494:pharmacology; D011189:Potassium Chloride / Q000494:pharmacology; D011247:Pregnancy / Q000378:metabolism*; D015398:Signal Transduction; D014590:Uterine Contraction; D014599:Uterus / Q000187:drug effects / Q000502:physiology; D014667:Vasopressins / Q000494:pharmacology
D014667:Vasopressins; D010656:Phenylephrine; D010121:Oxytocin; D011189:Potassium Chloride; D002118:Calcium