Fast Action of Estrogen on Intracellular Calcium in Dormant Mouse Blastocyst and Its Possible Mechanism

Objective: To study the fast action of estrogen on intracellular calcium of dormant mouse blastocysts and the possible mechanism.

Design: Controlled, prospective study.

Setting: Academic research unit.

Animal(s): Forty adult Kun-ming mice.

Intervention(s): A laser scanning confocal microscope was used to detect the dynamic change of intracellular calcium labeled by Fluo-3/AM, a fluorescent probe of calcium, which was caused by 17-beta-estradiol (17beta-E(2)) in dormant mouse blastocysts. A fluorescent microscope was used to check out the alteration of [Ca(2+)](i) induced by E(2)-BSA, a large molecule of estrogen coupling with bovine serum albumin; by 17beta-E(2) with Ca(2+)-free M2 medium; by 17beta-E(2) with tamoxifen, a blocking agent of traditional estrogen receptor (ER); and by 17beta-E(2) with U73122, a specific inhibitor of phospholipase C. Immunocytochemistry was used to detect the change of intracellular phosphorylated phospholipase C (p-PLC) induced by 17beta-E(2).

Main Outcome Measure(s): Intracellular calcium and intracellular p-PLC in dormant mouse blastocysts.

Result(s): Both 17beta-E(2) and E(2)-BSA could increase the intracellular calcium concentration ([Ca(2+)](i)) of blastocysts rapidly, and this increase of [Ca(2+)](i) was independent of either estrogen getting into the cells or the extracellular calcium in the incubation medium. However, this action was possibly blocked by a specific inhibitor of phospholipase C but not by the traditional blocking agent of ER. Moreover, the intracellular p-PLC increased after estrogen acting on blastocysts.

Conclusion(s): Estrogen may induce the increase of intracellular calcium in dormant mouse blastocysts by its action on the composition of the cell membrane to cause the release of Ca(2+) from the endoplasmic reticulum through the transmembrane signal transduction mediated by PLC.