Membrane potential difference and intracellular cation concentrations in human placental trophoblast cells in culture.

Abstract

1. The electrochemical gradients for Na+ and K+ were assessed in a cell culture model of trophoblast differentiation. 7. The Nae equilibrium potential (ENa) was positive in the trophoblast cells and the difference between ENa and Em was 122, 100 and 100 mV in JAr, mono-and multinucleate cytotrophoblast cells, respectively.8. These results suggest that the electrochemical gradient for K' is affected by the stage of trophoblast cell differentiation. In contrast, the electrochemical gradient for Na+ is similar in mono-and multinucleate cytotrophoblast cells.The transporting epithelium of the human placenta, the syncytiotrophoblast, plays an essential role in fetal growth and development. It is in direct contact with maternal blood and forms a continuous multinucleated cell layer which mediates materno-fetal exchange. Several ion transporters and conductances have been identified in its maternalfacing microvillous plasma membrane (e.g.Na+-H+ and Cl--HC03-exchangers; sodium-amino acid cotransporter; Cl-and K+ conductances) and fetal-facing basal plasma membrane (e.g. Na+-K+-ATPase and Ca2+-ATPase:reviewed by Shennan & Boyd, 1987;Sibley & Boyd, 1988;Shennan, 1992). However, it is unclear how these transport systems function in the intact syncytium to effect transplacental transfer and/or syncytiotrophoblast homeostasis.It is also unclear how their function changes during placental development and differentiation. The syncytiotrophoblast is formed throughout gestation by the fusion and differentiation of underlying cytotrophoblast cells (Boyd & Hamilton, 1970

Placental nutrient supply and fetal growth

“…Na + -linked co-transport). With the use of microelectrodes, a fetal-side negative potential difference has been shown to exist across the human syncytiotrophoblast/cytotrophoblast layer (Greenwood et al, 1993a;Greenwood et al, 1996). The microvillous membrane potential (E m ) is significantly more negative (hyperpolarized) in first trimester villi compared to term (Birdsey et al, 1997).…”

“…2F). The Na + pump actively extrudes sodium from the cell in exchange for K + using energy in the form of ATP (Clarson et al, 1996). This generates an inwardly directed Na + gradient which in turn facilitates the Na + entry mechanisms.…”

ATP-stimulated Ca2+-activated K+ efflux pathway and differentiation of human placental cytotrophoblast cells

“…Cytotrophoblast cells were isolated using an adaptation of the method of Kliman et al (30) as previously described in detail (7,18). Briefly, human placentas were collected within 30 min of delivery, and the villous tissue was removed, roughly minced, and washed thoroughly with saline.…”

“…All cells were maintained at 37°C in a humidified incubator gassed with 5% CO 2-95% air for up to 3 days of culture. We have previously shown that during this time cytotrophoblast cells isolated from human term placenta undergo both morphological and biochemical differentiation to form multinuclear syncytiotrophoblast-like cells (7,18). Cells were studied at two time points in culture: after 18 h, when the majority of cells are mononuclear, and after 66 h, when the majority of cells are multinucleate syncytiotrophoblast-like cells.…”

“…This process, which is ongoing throughout gestation, can be reproduced in vitro using cytotrophoblast cells isolated from human term placenta (7,18). Ion exchange across the syncytiotrophoblast is essential for normal fetal homeostasis; however, little is known about the expression and function of ion conductances in the syncytiotrophoblast or during its formation by differentiation, or how these conductances may be regulated by agonists.…”