Placental transfer of maternal calcium (Ca2 ) is carried out in vivo by the syncytiotrophoblast layer. Although this process is crucial for fetal development, it remains poorly understood. Cytotrophoblasts isolated from human term placenta undergo spontaneous syncytiotrophoblast-like morphological and biochemical differentiation in vitro and are thought to reflect in vivo syncytiotrophoblast. In the present study, we characterized the Ca2 uptake potential and the expression of several Ca2 channels by human trophoblasts during differentiation in vitro for up to 6 days. Secretion of hCG (specific differentiation marker) and uptake of Ca2 by trophoblasts increased gradually as a function of days in culture. Both hCG secretion and Ca2 uptake were maximal on Day 4 and declined on Days 5–6. Expression of the Ca2 transporter proteins CaT1 and CaT2 was revealed by reverse transcription-polymerase chain reaction in cytotrophoblasts freshly isolated from human term placenta. In addition, messengers for two L-type Ca2 channel isoforms (α1C and α1D) were also detected. Levels of CaT1, CaT2, and L-type Ca2 channel mRNA increased gradually during culture, reaching a maximum between Days 2 and 3. In contrast to CaT1 and CaT2 expression that declined thereafter to levels observed on Day 1, L-type channel expression decreased by 50% but remained above the expression level of Day 1. Our results indicate that the pattern of CaT1 and CaT2 expression correlates with the Ca2 uptake potential along the differentiation of cultured human trophoblasts isolated from term placenta. This correlation provides circumstantial evidence for a role of this family of channels in basal Ca2 uptake by the syncytiotrophoblast.
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