Characteristics of Calcium Uptake by BeWo Cells, a Human Trophoblast Cell Line

Abstract

Placental transfer of maternal calcium (Ca2+) is a crucial process for fetal development although the biochemical mechanisms responsible for this transfer are largely unknown. We have investigated the characteristics of Ca2+uptake by the human placental trophoblast cell line BeWo. The kinetics studies revealed an active extracellular Ca2+uptake by BeWo cells, which was rapid in the first 2min (initial velocity (Vi) of 4.17±0.25nmol/mg/min), and showed a subsequent plateau. Uptake experiments performed at Viwith increasing concentrations of Ca2+resulted in a typical saturation curve (Kmof 0.54±0.07m m and Vmaxof 7.07±0.28nmol/mg protein/min). Lowering the pH of the incubation medium from 7.4 to 5.5 led to Ca2+uptake inhibition of 40–50 per cent. The presence of voltage-sensitive (l -type) Ca2+channels in BeWo cells was demonstrated by Western blot. Therefore, the implication of such channels in basal Ca2+uptake of BeWo cells was investigated. Cell depolarization with extracellular high potassium concentration (40m m), and hyperpolarization with extracellular high chloride concentration (60m m) or with valinomycin (10μm) did not influence the basal Ca2+uptake of BeWo cells. The L-type Ca2+channel modulators (Bay K 8644 and Nitrendipine) had no effect on the Ca2+uptake. An antagonist of receptor-mediated, store-operated and voltage-gated Ca2+channels (SKF-96365) also did not modulate the Ca2+uptake of BeWo cells. Therefore, our results indicate that the basal Ca2+uptake of BeWo cells is inhibited by lowering pH of the incubation medium, is voltage independent, and is not influenced by l -type Ca2+channel and capacitative Ca2+conductance modulators.