Calcium uptake and calcium transporter expression by trophoblast cells from human term placenta

AbstractPlacental transfer of maternal calcium (Ca2+) is a crucial step for fetal development although the biochemical mechanisms responsible for this process are largely unknown. This process is carried out in vivo by the placental syncytiotrophoblast layer. The aim of this study was to define the membrane gates responsible for the syncytiotrophoblast Ca2+ entry, the first step in transplacental transfer. We have investigated the basal Ca2+ uptake by primary culture of human term placenta syncytiotrophoblast. Kinetic studies revealed an active extracellular Ca2+ uptake by cultured human syncytiotrophoblast. We demonstrated by Northern blot the presence of transcript for calcium transporter type 1 (CaT1) in cultured human syncytiotrophoblast and CaT1 expression was further confirmed by reverse transcription polymerase chain reaction (RT-PCR). In addition, the expression of calcium transporter type 2 (CaT2) was revealed by RT-PCR in cultured human syncytiotrophoblast. It has been reported that the activity of this family of Ca2+ channels is voltage-independent, and is not sensitive to L-type Ca2+ channels agonist and antagonist. Interestingly, modulation of membrane potential by extracellular high potassium concentration and valinomycin had no effect on the basal Ca2+ uptake of human syncytiotrophoblast. Moreover, the addition of L-type Ca2+ channel modulators (Bay K 8644 and nitrendipine) to the incubation medium had also no effect on the basal Ca2+ uptake, suggesting that the process is mainly voltage-independent and does not involved L-type Ca2+ channels. On the other hand, we observed that two known blockers of CaT-mediated Ca2+ transport, namely extracellular magnesium (Mg2+) and ruthenium red, dose-dependently inhibited Ca2+ uptake by cultured human syncytiotrophoblast. Therefore, our results suggest that basal Ca2+ uptake of human syncytiotrophoblast may be assured by CaT1 and CaT2