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

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.

International Union of Basic and Clinical Pharmacology. LXXVI. Current Progress in the Mammalian TRP Ion Channel Family

“…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).…”

K+channel inhibition modulates the biochemical and morphological differentiation of human placental cytotrophoblast cells in vitro

“…Several studies have shown that hCG release from normal-term placental villous tissue is modulated by extracellular Ca 2ϩ (35), consistent with hCG secretion by excitation-secretion coupling. It has been suggested that L-type voltage-gated Ca 2ϩ channels (VGCC), which are expressed by placenta (38), permit Ca 2ϩ entry into trophoblast cells, thereby regulating intracellular Ca 2ϩ concentration ([Ca 2ϩ ] i ) and exocytosis. Thus, raising extracellular K ϩ , to depolarize the cell membrane, stimulated hCG secretion in a nifedipine-sensitive manner (37).…”

The Human TRPV6 Channel Protein Is Associated with Cyclophilin B in Human Placenta

“…TRPV5 and TRPV6, which belong to the vanilloid receptor-like TRP subfamily, are highly selective calcium channels (PCa 2ϩ / PNa ϩ Ͼ 100) (7), and both genes are expressed in the trophoblast layer of the placenta (6, 8 -11). Reduced calcium uptake in cultured trophoblast cells was detected in the presence of magnesium or Ruthenium Red, which are known to block TRPV5 and TRPV6 channel activity (10). Apparently TRPV5 and/or TRPV6 are involved in the calcium transport mechanism in these cells.…”