Magnesium sulfate inhibits oxytocin-induced calcium mobilization in human puerperal myometrial cells: possible involvement of intracellular free magnesium concentration.
OBJECTIVE
Our purpose was to elucidate the mechanisms of the tocolytic action of Mg2+ on the human myometrium.


METHODS
The effects of extracellular Mg2+ on oxytocin-induced increases in the intracellular free Ca2+ concentration in human puerperal myometrial cells were examined by means of indo-1-AM. The changes in the intracellular free Mg2+ concentration under various conditions were also measured with Mg(2+)-fura-2-AM.


RESULTS
The increase in intracellular free Ca2+ concentration induced by oxytocin was reduced to 26% of that in the normal solution 20 minutes after replacement of the normal solution with an extracellular Mg2+ solution, 10 mmol/L. When extracellular Ca2+ was removed, the increase in intracellular free Ca2+ concentration was not suppressed even 20 minutes after the replacement. A solution of extracellular Mg2+ concentration, 10 mmol/L, raised the intracellular free Mg2+ concentration gradually, by approximately 150% in 20 minutes, concomitant with the suppression of the response to oxytocin in the intracellular free Ca2+ concentration.


CONCLUSIONS
High intracellular free Mg2+ concentration, caused by high extracellular Mg2+, is essential for suppression of oxytocin-induced Ca2+ influx across the cell membrane; this presumably results in inhibition of uterine contractions.
Mizuki
J
J
Department of Obstetrics and Gynecology, Osaka University Medical School, Japan.
Tasaka
K
K
Masumoto
N
N
Kasahara
K
K
Miyake
A
A
Tanizawa
O
O
D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D005260:Female; D006801:Humans; D007700:Kinetics; D008274:Magnesium / Q000378:metabolism*; D008278:Magnesium Sulfate / Q000494:pharmacology*; D009215:Myometrium / Q000187:drug effects / Q000378:metabolism*; D010121:Oxytocin / Q000494:pharmacology*; D049590:Postpartum Period; D012996:Solutions
D012996:Solutions; D010121:Oxytocin; D008278:Magnesium Sulfate; D008274:Magnesium; D002118:Calcium