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

Laboratoire de Physiologie materno-foetale, Département des Sciences Biologiques, Université du Québec à Montréal, C.P. 8888, Succursale "Centre-Ville", Montreal, Quebec, Canada H3C 3P8.
Biochimica et Biophysica Acta (Impact Factor: 4.66). 09/2002; 1564(2):325-32. DOI: 10.1016/S0005-2736(02)00466-2
Source: PubMed

ABSTRACT Placental transfer of maternal calcium (Ca(2+)) 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 Ca(2+) entry, the first step in transplacental transfer. We have investigated the basal Ca(2+) uptake by primary culture of human term placenta syncytiotrophoblast. Kinetic studies revealed an active extracellular Ca(2+) 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 Ca(2+) channels is voltage-independent, and is not sensitive to L-type Ca(2+) channels agonist and antagonist. Interestingly, modulation of membrane potential by extracellular high potassium concentration and valinomycin had no effect on the basal Ca(2+) uptake of human syncytiotrophoblast. Moreover, the addition of L-type Ca(2+) channel modulators (Bay K 8644 and nitrendipine) to the incubation medium had also no effect on the basal Ca(2+) uptake, suggesting that the process is mainly voltage-independent and does not involved L-type Ca(2+) channels. On the other hand, we observed that two known blockers of CaT-mediated Ca(2+) transport, namely extracellular magnesium (Mg(2+)) and ruthenium red, dose-dependently inhibited Ca(2+) uptake by cultured human syncytiotrophoblast. Therefore, our results suggest that basal Ca(2+) uptake of human syncytiotrophoblast may be assured by CaT1 and CaT2.

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Available from: Robert Moreau, Mar 13, 2014
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    • "The main functions of syncytiotrophoblasts are absorption, exchanges and specific hormonal secretion (Malassine, 2001). Syncytiotrophoblasts are the primary site of fetal Ca 2+ homeostasis regulation which includes mechanisms characterized by Ca 2+ entry, cytosolic diffusion and extrusion (Moreau et al., 2002; Belkacemi et al., 2005; Lafond and Simoneau, 2006). "
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    • "In the kidney, TRPV6 is expressed in the convoluted tubules, connecting tubules, and cortical and medullary collecting ducts of the nephron, where it helps resorb Ca 2ϩ (Nijenhuis et al., 2003). In the placental trophoblast, TRPV6 contributes to the transfer of Ca 2ϩ from mother to fetus (Moreau et al., 2002; Suzuki et al., 2008) and may contribute to the reduced litter size of TRPV6(Ϫ/Ϫ) mice (Bianco et al., 2007). "
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    • "However, Wissenbach et al. did not detect the expression of TRPV6 in duodenum and kidney (Wissenbach et al. 2001). TRPV5 and TRPV6 mRNA were both detected in syncytiotrophoblasts (Moreau et al. 2002a). This suggests that TRPV5 and/or TRPV6 mediate basal Ca 2+ influx in placenta as these cells mediate Ca 2+ transfer to the fetus. "
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