Calcium influx in human uterine epithelial RL95-2 cells triggers adhesiveness for trophoblast-like cells. Model studies on signalling events during embryo implantation

RL95-2 is a human uterine epithelial cell line that exhibits adhesion competence on its apical surface for trophoblast-like JAR cells. Using confocal microscopy and an adhesion assay we have found that changes in intracellular free calcium ([Ca(2+)](i)) in RL95-2 cells are involved in binding of JAR spheroids. Impact of spheroids upon, and movement of spheroids across, monolayers of RL95-2 cells produced a transient increase in [Ca(2+)](i). Pretreatment of RL95-2 cells with the Ca(2+) channel inhibitor, diltiazem, reduced the [Ca(2+)](i) increase. Interestingly, resting of JAR spheroids on RL95-2 cells caused no detectable alterations in [Ca(2+)](i) although cell-cell bonds were formed during prolonged contact. However, separation of established bonds did produce an increase in [Ca(2+)](i) which could be reduced by the Ca(2+) channel blocker, SKF-96365, but not by diltiazem. SKF-96365 also reduced adhesion of JAR spheroids to RL95-2 cells. In all experiments, the increase in [Ca(2+)](i) was due to influx from the external medium, as it could be blocked both by removing extracellular Ca(2+) and by nickel. These results suggest that the plasma membrane of uterine RL95-2 cells contains two types of Ca(2+) channels that are involved in trophoblast adhesion, i.e. diltiazem-sensitive channels contributing to initiation of JAR cell binding and SKF-96365-sensitive channels participating in a feedback loop that controls the balance of bonds.